Rongguang Liang

Interests

Research

Optical engineering and biomedical imaging

Teaching

Geometric opticsOptical DesignBiomedical imagingLens design

Courses

Scholarly Contributions

Journals/Publications

• Galvez, D., Hong, Z., Rocha, A. D., Heusinkveld, J. M., Ye, P., Liang, R., & Barton, J. K. (2023). Characterizing close-focus lenses for microendoscopy. Journal of optical microsystems, 3(1).
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  Microendoscopes are commonly used in small lumens in the body, for which a focus near to the distal tip and ability to operate in an aqueous environment are paramount for navigation and disease detection. Commercially available distal optic systems below 1mm in diameter are severely limited, and custom micro lenses are generally very expensive. Gradient index of refraction (GRIN) singlets are available in small diameters but have limited optical performance adjustability. Three-dimensional (3D) printed monolithic optical systems are an emerging option that may be suitable for enabling high performance, close-focus imaging. In this manuscript, we compared the optical performance of three custom distal optic systems; a custom-pitch GRIN singlet, 3D-printed monolithic doublet, and 3D-printed monolithic triplet, with a nominal working distance (WD) of 1.5mm, 0.5mm and 0.4mm in 0.9% saline. These short WDs are ideal for microendoscopy in collapsed or flushed lumens such as pancreatic duct or fallopian tube. The GRIN singlet had performance limited only by the fiber bundle relay over 0.9mm to 1.6 mm depth of field (DOF). The 3D printed doublet was able to achieve a comparable DOF of 0.71mm, while the 3D printed triplet suffered the most limited DOF of 0.55mm. 3D printing enables flexible design of monolithic multi-element systems with aspheric surfaces of very short WDs and relative ease of integration.
• Gurushanth, K., Mukhia, N., Sunny, S. P., Song, B., Raghavan, S. A., Gurudath, S., Mendonca, P., Li, S., Patrick, S., Imchen, T., Leivon, S. T., Shruti, T., Kolur, T., Shetty, V., Bhushan R, V., Ramesh, R. M., Pillai, V., S, K. O., Smith, P. W., , Suresh, A., et al. (2023). Inter-observer agreement among specialists in the diagnosis of Oral Potentially Malignant Disorders and Oral Cancer using Store-and-Forward technology. Research square.
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  Oral Cancer is one of the most common causes of morbidity and mortality. Screening and mobile Health (mHealth) based approach facilitates remote early detection of Oral cancer in a resource-constrained settings. The emerging eHealth technology has aided specialist reach to rural areas enabling remote monitoring and triaging to downstage Oral cancer. Though the diagnostic accuracy of the remote specialist has been evaluated, there are no studies evaluating the consistency among the remote specialists, to the best of our knowledge. The purpose of the study was to evaluate the interobserver agreement between the specialists through telemedicine systems in real-world settings using store and forward technology. Two remote specialists independently diagnosed the clinical images from image repositories, and the diagnostic accuracy was compared with onsite specialist and histopathological diagnosis when available. Moderate agreement (k = 0.682) between two remote specialists and (k = 0.629) between the onsite specialist and two remote specialists in diagnosing oral lesions. The sensitivity and specificity of remote specialist 1 were 92.7% and 83.3%, whereas remote specialist 2 was 95.8% and 60%, respectively, compared to histopathology. The store and forward technology and telecare can be effective tools in triaging and surveillance of patients.
• Hong, Z., Sun, Y., Ye, P., Loy, D. A., & Liang, R. (2023). Bio-inspired Compact, High-resolution Snapshot Hyperspectral Imaging System with 3D Printed Glass Lightguide Array. Advanced optical materials, 11(9).
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  To address the major challenges to obtain high spatial resolution in snapshot hyperspectral imaging, 3D printed glass lightguide array has been developed to sample the intermediate image in high spatial resolution and redistribute the pixels in the output end to achieve high spectral resolution. Curved 3D printed lightguide array can significantly simplify the snapshot hyperspectral imaging system, achieve better imaging performance, and reduce the system complexity and cost. We have developed two-photon polymerization process to print glass lightguide array, and demonstrated the system performance with biological samples. This new snapshot technology will catalyze new hyperspectral imaging system development and open doors for new applications from UV to IR.
• Keerthi, G., Mukhia, N., Sunny, S. P., Song, B., Raghavan, S. A., Gurudath, S., Mendonca, P., Li, S., Patrick, S., Imchen, T., Leivon, S. T., Shruti, T., Kolur, T., Shetty, V., Vidya Bhushan, R., Ramesh, R. M., Pillai, V., Kathryn, O. S., Smith, P. W., , Suresh, A., et al. (2023). Inter-observer agreement among specialists in the diagnosis of oral potentially malignant disorders and oral cancer using store-and-forward technology. Clinical oral investigations, 27(12), 7575-7581.
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  Oral cancer is a leading cause of morbidity and mortality. Screening and mobile Health (mHealth)-based approach facilitates early detection remotely in a resource-limited settings. Recent advances in eHealth technology have enabled remote monitoring and triage to detect oral cancer in its early stages. Although studies have been conducted to evaluate the diagnostic efficacy of remote specialists, to our knowledge, no studies have been conducted to evaluate the consistency of remote specialists. The aim of this study was to evaluate interobserver agreement between specialists through telemedicine systems in real-world settings using store-and-forward technology.
• Khan, S., Song, B., Mallidi, S., Li, S., Liu, H., Bilal Hussain, M. A., Siddiqui, S., Khan, A. P., Akhtar, K., Siddiqui, S. A., Hasan, S. A., Hopper, C., Bown, S. G., Liang, R., Hasan, T., & Celli, J. P. (2023). Clinical assessment of a low-cost, hand-held, smartphone-attached intraoral imaging probe for 5-aminolevulinic acid photodynamic therapy monitoring and guidance. Journal of biomedical optics, 28(8), 082809.
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  India has one of the highest rates of oral squamous cell carcinoma (OSCC) in the world, with an incidence of 15 per 100,000 and more than 70,000 deaths per year. The problem is exacerbated by a lack of medical infrastructure and routine screening, especially in rural areas. New technologies for oral cancer detection and timely treatment at the point of care are urgently needed.
• Liang, R. (2023). Fiber-Fed 3D Printing of Germanate Glass Optics. Photonics. doi:https://doi.org/10.3390/photonics10040378
• Liang, R. (2023). Two-step phase-shifting algorithms with background removal and no background removal. Optics and Lasers in Engineering. doi:https://doi.org/10.1016/j.optlaseng.2022.107327
• Liang, R. (2023). Performance of Automated Oral Cancer Screening Algorithm in Tobacco Users vs. Non-Tobacco Users. Applied Sciences. doi:https://doi.org/10.3390/app13053370
• Nguyen, J., Takesh, T., Parsangi, N., Song, B., Liang, R., & Wilder-Smith, P. (2023). Compliance with Specialist Referral for Increased Cancer Risk in Low-Resource Settings: In-Person vs. Telehealth Options. Cancers, 15(10).
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  Efforts are underway to improve the accuracy of non-specialist screening for oral cancer (OC) risk, yet better screening will only translate into improved outcomes if at-risk individuals comply with specialist referral. Most individuals from low-resource, minority, and underserved (LRMU) populations fail to complete a specialist referral for OC risk. The goal was to evaluate the impact of a novel approach on specialist referral compliance in individuals with a positive OC risk screening outcome. A total of 60 LRMU subjects who had screened positive for increased OC risk were recruited and given the choice of referral for an in-person (20 subjects) or a telehealth (40 subjects) specialist visit. Referral compliance was tracked weekly over 6 months. Compliance was 30% in the in-person group, and 83% in the telehealth group. Approximately 83-85% of subjects from both groups who had complied with the first specialist referral complied with a second follow-up in-person specialist visit. Overall, 72.5% of subjects who had chosen a remote first specialist visit had entered into the continuum of care by the study end, vs. 25% of individuals in the in-person specialist group. A two-step approach that uses telehealth to overcome barriers may improve specialist referral compliance in LRMU individuals with increased OC risk.
• Peterson, T., Mann, S., Sun, B. L., Peng, L., Cai, H., & Liang, R. (2023). Motionless volumetric structured light sheet microscopy. Biomedical optics express, 14(5), 2209-2224.
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  To meet the increasing need for low-cost, compact imaging technology with cellular resolution, we have developed a microLED-based structured light sheet microscope for three-dimensional and imaging of biological tissue in multiple modalities. All the illumination structure is generated directly at the microLED panel-which serves as the source-so light sheet scanning and modulation is completely digital, yielding a system that is simpler and less prone to error than previously reported methods. Volumetric images with optical sectioning are thus achieved in an inexpensive, compact form factor without any moving parts. We demonstrate the unique properties and general applicability of our technique by imaging of porcine and murine tissue from the gastrointestinal tract, kidney, and brain.
• Song, B., Zhang, C., Sunny, S., Kc, D. R., Li, S., Gurushanth, K., Mendonca, P., Mukhia, N., Patrick, S., Gurudath, S., Raghavan, S., Tsusennaro, I., Leivon, S. T., Kolur, T., Shetty, V., Bushan, V., Ramesh, R., Pillai, V., Wilder-Smith, P., , Suresh, A., et al. (2023). Interpretable and Reliable Oral Cancer Classifier with Attention Mechanism and Expert Knowledge Embedding via Attention Map. Cancers, 15(5).
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  Convolutional neural networks have demonstrated excellent performance in oral cancer detection and classification. However, the end-to-end learning strategy makes CNNs hard to interpret, and it can be challenging to fully understand the decision-making procedure. Additionally, reliability is also a significant challenge for CNN based approaches. In this study, we proposed a neural network called the attention branch network (ABN), which combines the visual explanation and attention mechanisms to improve the recognition performance and interpret the decision-making simultaneously. We also embedded expert knowledge into the network by having human experts manually edit the attention maps for the attention mechanism. Our experiments have shown that ABN performs better than the original baseline network. By introducing the Squeeze-and-Excitation (SE) blocks to the network, the cross-validation accuracy increased further. Furthermore, we observed that some previously misclassified cases were correctly recognized after updating by manually editing the attention maps. The cross-validation accuracy increased from 0.846 to 0.875 with the ABN (Resnet18 as baseline), 0.877 with SE-ABN, and 0.903 after embedding expert knowledge. The proposed method provides an accurate, interpretable, and reliable oral cancer computer-aided diagnosis system through visual explanation, attention mechanisms, and expert knowledge embedding.
• Ye, P., Hong, Z., Loy, D. A., & Liang, R. (2023). UV-curable thiol-ene system for broadband infrared transparent objects. Nature communications, 14(1), 8385.
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  Conventional infrared transparent materials, including inorganic ceramic, glass, and sulfur-rich organic materials, are usually processed through thermal or mechanical progress. Here, we report a photo-curable liquid material based on a specially designed thiol-ene strategy, where the multithiols and divinyl oligomers were designed to contain only C, H, and S atoms. This approach ensures transparency in a wide range spectrum from visible light to mid-wave infrared (MWIR), and to long-wave infrared (LWIR). The refractive index, thermal properties, and mechanical properties of samples prepared by this thiol-ene resin were characterized. Objects transparent to LWIR and MWIR were fabricated by molding and two-photon 3D printing techniques. We demonstrated the potential of our material in a range of applications, including the fabrication of IR optics with high imaging resolution and the construction of micro-reactors for temperature monitoring. This UV-curable thiol-ene system provides a fast and convenient alternative for the fabrication of thin IR transparent objects.
• Zhu, S., Wang, D., Kang, W., & Liang, R. (2023). On-axis deflectometric system for freeform surface measurement. Optics letters, 48(8), 1986-1989.
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  We propose an on-axis deflectometric system for the accurate measurement of freeform surfaces with large slope ranges. A miniature plane mirror is attached on the illumination screen to fold the optical path and achieve the on-axis deflectometric testing. Due to the existence of the miniature folding mirror, the deep-learning method is applied to recover the missing surface data in a single measurement. Low sensitivity to the calibration error of system geometry and high testing accuracy can be achieved with the proposed system. The feasibility and accuracy of the proposed system have been validated. The system is low in cost and simple in configuration, and it provides a feasible way for the flexible and general testing of freeform surfaces, with a significant potential of the application in on-machine testing.
• Birur N, P., Song, B., Sunny, S. P., G, K., Mendonca, P., Mukhia, N., Li, S., Patrick, S., G, S., A R, S., Imchen, T., Leivon, S. T., Kolur, T., Shetty, V., R, V. B., Vaibhavi, D., Rajeev, S., Pednekar, S., Banik, A. D., , Ramesh, R. M., et al. (2022). Field validation of deep learning based Point-of-Care device for early detection of oral malignant and potentially malignant disorders. Scientific reports, 12(1), 14283.
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  Early detection of oral cancer in low-resource settings necessitates a Point-of-Care screening tool that empowers Frontline-Health-Workers (FHW). This study was conducted to validate the accuracy of Convolutional-Neural-Network (CNN) enabled m(mobile)-Health device deployed with FHWs for delineation of suspicious oral lesions (malignant/potentially-malignant disorders). The effectiveness of the device was tested in tertiary-care hospitals and low-resource settings in India. The subjects were screened independently, either by FHWs alone or along with specialists. All the subjects were also remotely evaluated by oral cancer specialist/s. The program screened 5025 subjects (Images: 32,128) with 95% (n = 4728) having telediagnosis. Among the 16% (n = 752) assessed by onsite specialists, 20% (n = 102) underwent biopsy. Simple and complex CNN were integrated into the mobile phone and cloud respectively. The onsite specialist diagnosis showed a high sensitivity (94%), when compared to histology, while telediagnosis showed high accuracy in comparison with onsite specialists (sensitivity: 95%; specificity: 84%). FHWs, however, when compared with telediagnosis, identified suspicious lesions with less sensitivity (60%). Phone integrated, CNN (MobileNet) accurately delineated lesions (n = 1416; sensitivity: 82%) and Cloud-based CNN (VGG19) had higher accuracy (sensitivity: 87%) with tele-diagnosis as reference standard. The results of the study suggest that an automated mHealth-enabled, dual-image system is a useful triaging tool and empowers FHWs for oral cancer screening in low-resource settings.
• Dou, J., Wang, D., Yu, Q., Kong, M., Liu, L., Xu, X., & Liang, R. (2022). Deep-learning-based deflectometry for freeform surface measurement. Optics letters, 47(1), 78-81.
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  We propose a deep-learning based deflectometric method for freeform surface measurement, in which a deep neural network is devised for freeform surface reconstruction. Full-scale skip connections are adopted in the network architecture to extract and incorporate multi-scale feature maps from different layers, enabling the accuracy and robustness of the testing system to be greatly enhanced. The feasibility of the proposed method is numerically and experimentally validated, and its excellent performance in terms of accuracy and robustness is also demonstrated. The proposed method provides a feasible way to achieve the general measurement of freeform surfaces while minimizing the measurement errors due to noise and system geometry calibration.
• Figueroa, K. C., Song, B., Sunny, S., Li, S., Gurushanth, K., Mendonca, P., Mukhia, N., Patrick, S., Gurudath, S., Raghavan, S., Imchen, T., Leivon, S. T., Kolur, T., Shetty, V., Bushan, V., Ramesh, R., Pillai, V., Wilder-Smith, P., Sigamani, A., , Suresh, A., et al. (2022). Interpretable deep learning approach for oral cancer classification using guided attention inference network. Journal of biomedical optics, 27(1).
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  Convolutional neural networks (CNNs) show the potential for automated classification of different cancer lesions. However, their lack of interpretability and explainability makes CNNs less than understandable. Furthermore, CNNs may incorrectly concentrate on other areas surrounding the salient object, rather than the network's attention focusing directly on the object to be recognized, as the network has no incentive to focus solely on the correct subjects to be detected. This inhibits the reliability of CNNs, especially for biomedical applications.
• Gu, Z., Wang, D., Ruan, Y., Kong, M., Xu, X., & Liang, R. (2022). Design and error calibration of an on-axis deflectometric microscope system. Applied optics, 61(10), 2856-2863.
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  An on-axis deflectometric microscope system (ODMS) is proposed for the microscopic surface measurement with high accuracy and a large slope dynamic range. To reduce the geometry sensitivity, a beam splitter is employed to build the coaxial configuration among the illumination screen, camera, and tested sample, which facilitates the calibration of system geometrical parameters. Due to the small working distance, the system model miscalibration in the model-ray-tracing-based "null" testing could cause obvious geometrical aberrations. In this paper, the geometrical aberrations due to the system model miscalibration are analyzed, and the corresponding calibration method based on computer-aided reverse optimization is applied to achieve accurate measurement. In addition, the systematic error introduced by the system components in the ODMS are also discussed. Both the simulation and experiment have been carried out to demonstrate the feasibility and high accuracy of the proposed measurement method. The proposed system is compact in structure, large in measurable slope range, and high in spatial resolution, providing a viable metrological tool for the microscopic testing of various freeform surfaces, microstructural elements, and micro-devices.
• Hong, Z., Ye, P., Loy, D. A., & Liang, R. (2022). High-Precision Printing of Complex Glass Imaging Optics with Precondensed Liquid Silica Resin. Advanced science (Weinheim, Baden-Wurttemberg, Germany), 9(18), e2105595.
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  3D printing of optics has gained significant attention in optical industry, but most of the research has been focused on organic polymers. In spite of recent progress in 3D printing glass, 3D printing of precision glass optics for imaging applications still faces challenges from shrinkage during printing and thermal processing, and from inadequate surface shape and quality to meet the requirements for imaging applications. This paper reports a new liquid silica resin (LSR) with higher curing speed, better mechanical properties, lower sintering temperature, and reduced shrinkage, as well as the printing process for high-precision glass optics for imaging applications. It is demonstrated that the proposed material and printing process can print almost all types of optical surfaces, including flat, spherical, aspherical, freeform, and discontinuous surfaces, with accurate surface shape and high surface quality for imaging applications. It is also demonstrated that the proposed method can print complex optical systems with multiple optical elements, completely removing the time-consuming and error-prone alignment process. Most importantly, the proposed printing method is able to print optical systems with active moving elements, significantly improving system flexibility and functionality. The printing method will enable the much-needed transformational manufacturing of complex freeform glass optics that are currently inaccessible with conventional processes.
• Kang, W., Seigo, M., Xiao, H., Wang, D., & Liang, R. (2022). Experimental Studies on Fabricating Lenslet Array with Slow Tool Servo. Micromachines, 13(10).
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  On the demand of low-cost, lightweight, miniaturized, and integrated optical systems, precision lenslet arrays are widely used. Diamond turning is often used to fabricate lenslet arrays directly or molds that are used to mold lenslet arrays. In this paper, mainly by real-time monitoring position following error for slow tool servo, different fabrication parameters are quantitatively studied and optimized for actual fabrication, then by actual fabrication validation, uniform and high-fidelity surface topography across the actual whole lenslet array is achieved. The evaluated fabrication parameters include sampling strategy, inverse time feed, arc-length, etc. The study provides a quick, effective, and detailed reference for both convex and concave lenslet array cutting parameter selection. At the end, a smooth zonal machining strategy toolpath is demonstrated for fabricating concave lenslet arrays.
• Liang, J., Sun, Y., Ren, L., & Liang, R. (2022). Short-wave infrared polarimetric image reconstruction using a deep convolutional neural network based on a high-frequency correlation. Applied optics, 61(24), 7163-7172.
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  Imaging in visible and short-wave infrared (SWIR) wavebands is essential in most remote sensing applications. However, compared to visible imaging cameras, SWIR cameras typically have lower spatial resolution, which limits the detailed information shown in SWIR images. We propose a method to reconstruct high-resolution polarization SWIR images with the help of color images using the deep learning method. The training dataset is constructed from color images, and the trained model is well suited for SWIR image reconstruction. The experimental results show the effectiveness of the proposed method in enhancing the quality of the polarized SWIR images with much better spatial resolution. Some buried spatial and polarized information may be recovered in the reconstructed SWIR images.
• Song, B., Li, S., Sunny, S., Gurushanth, K., Mendonca, P., Mukhia, N., Patrick, S., Peterson, T., Gurudath, S., Raghavan, S., Tsusennaro, I., Leivon, S., Kolur, T., Shetty, V., Bushan, V., Ramesh, R., Pillai, V., Wilder-Smith, P., Suresh, A., , Kuriakose, M. A., et al. (2022). Exploring uncertainty measures in convolutional neural network for semantic segmentation of oral cancer images. Journal of biomedical optics, 27(11).
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  Oral cancer is one of the most prevalent cancers, especially in middle- and low-income countries such as India. Automatic segmentation of oral cancer images can improve the diagnostic workflow, which is a significant task in oral cancer image analysis. Despite the remarkable success of deep-learning networks in medical segmentation, they rarely provide uncertainty quantification for their output.
• Sun, Y., Zhang, J., & Liang, R. (2022). pHSCNN: CNN-based hyperspectral recovery from a pair of RGB images. Optics express, 30(14), 24862-24873.
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  To increase the fidelity of hyperspectral recovery from RGB images, we propose a pairwise-image-based hyperspectral convolutional neural network (pHSCNN) to recover hyperspectral images from a pair of RGB images, obtained by the same color sensor with and without an optical filter in front of the imaging lens. The proposed method avoids the pitfall of requiring multiple color sensors to obtain different RGB images and achieves higher accuracy than recovery from single RGB image. Besides, pHSCNN can also optimize the optical filter to further improve the performance. To experiment on real data, we built a dual-camera hyperspectral imaging system and created a real-captured hyperspectral-RGB dataset. Experimental results demonstrate the superiority of pHSCNN with the highest accuracy of the recovered hyperspectral signature perceptually and numerically.
• Xiao, H., Yin, S., Wu, H., Wang, H., & Liang, R. (2022). Theoretical model and digital extraction of subsurface damage in ground fused silica. Optics express, 30(11), 17999-18017.
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  Based on the fracture mechanics and grinding kinematics, a theoretical model is developed to determine various subsurface damage (SSD) parameters and roughness Rz of the ground brittle material with consideration of the material removal mode and spring back. Based on the image processing, a digital method is proposed to extract various SSD parameters from the cross-section micrograph of the ground sample. To verify the model and method, many fused silica samples are ground under different processing parameters, and their SSD depth and roughness Rz are measured. The research results show the average SSD depth (SSD) can be expressed as SSD = χRz + χRz (χ and χ are coefficients). The SSD is closer to half of the maximum SSD depth (SSD) as the wheel speed decreases or the grinding depth, feed speed, or abrasive diameter increases. The SSD length or density basically increases linearly with the increase of the SSD. The digital method is reliable with a largest relative error of 6.65% in SSD depth, extraction speed of about 1.63s per micrograph, and good robustness to the micrograph size and small-scale residue interference. The research will contribute to the evaluation of SSDs and the optimization of the grinding process of fused silica.
• Zheng, W., LaCourse, S. M., Song, B., Singh, D. K., Khanna, M., Olivo, J., Stern, J., Escudero, J. N., Vergara, C., Zhang, F., Li, S., Wang, S., Cranmer, L. M., Huang, Z., Bojanowski, C. M., Bao, D., Njuguna, I., Xiao, Y., Wamalwa, D. C., , Nguyen, D. T., et al. (2022). Diagnosis of paediatric tuberculosis by optically detecting two virulence factors on extracellular vesicles in blood samples. Nature biomedical engineering, 6(8), 979-991.
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  Sensitive and specific blood-based assays for the detection of pulmonary and extrapulmonary tuberculosis would reduce mortality associated with missed diagnoses, particularly in children. Here we report a nanoparticle-enhanced immunoassay read by dark-field microscopy that detects two Mycobacterium tuberculosis virulence factors (the glycolipid lipoarabinomannan and its carrier protein) on the surface of circulating extracellular vesicles. In a cohort study of 147 hospitalized and severely immunosuppressed children living with HIV, the assay detected 58 of the 78 (74%) cases of paediatric tuberculosis, 48 of the 66 (73%) cases that were missed by microbiological assays, and 8 out of 10 (80%) cases undiagnosed during the study. It also distinguished tuberculosis from latent-tuberculosis infections in non-human primates. We adapted the assay to make it portable and operable by a smartphone. With further development, the assay may facilitate the detection of tuberculosis at the point of care, particularly in resource-limited settings.
• Cheng, W., Pieterse, J. W., & Liang, R. (2021). Damage Inside Borosilicate Glass by a Single Picosecond Laser Pulse. Micromachines, 12(5).
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  We investigate damage inside the bulk of borosilicate glass by a single shot of IR picosecond laser pulse both experimentally and numerically. In our experiments, bulk damage of borosilicate glass with aspect ratio of about 1:10 is generated. The shape and size of the damage site are shown to correspond to an electron cloud with density of about 1020 cm-3. The underlying mechanism of electron generation by multiphoton ionization and avalanche ionization is numerically investigated. The multiphoton ionization rate and avalanche ionization rate are determined by fitting experimental results. The relative role of multiphoton ionization and avalanche ionization are numerically studied and the percentage of electron contribution from each ionization channel is determined.
• Gu, H., Wang, D., Gu, Z., Kong, M., Liu, L., Lei, L., & Liang, R. (2021). High-accuracy deflectometric microscope system with a large slope range. Optics letters, 46(9), 2011-2014.
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  We propose an off-axis deflectometric microscope system for microscopic surface testing with both high measurement accuracy and a large slope dynamic range. A high-luminance liquid crystal display directly illuminates the tested sample with coded fringes, and then the reflected fringes passing through a microscope objective are captured by a pinhole camera, from which the deflectometric microscopic testing with a large slope range can be achieved. The accuracy of the proposed system is validated numerically and experimentally, and a large measurable slope dynamic range is also demonstrated. The proposed system provides a feasible way with the slope range in the order of sub-radians and sag resolution better than 0.05 nm.
• Hong, Z., Ye, P., Loy, D. A., & Liang, R. (2021). Three-dimensional printing of glass micro-optics. Optica, 8(6), 904--910.
• Kang, W., Hong, Z., & Liang, R. (2021). 3D printing optics with hybrid material. Applied optics, 60(7), 1809-1813.
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  Three-dimensional (3D) printing technology has evolved tremendously in recent years, but due to stringent requirements on surface finish and limited material selection for optical performance purposes, 3D printing optics is still lagging behind. This paper reports on a quantitative study on the printing process of optical lenses using acrylic and cationic combined commercial hybrid material. By utilizing its unique curing property with digital light process technology, we demonstrate the concept of continuous printing in the top-down light projection setup. Also, an equal thickness and equal arc combo method has been proposed and evaluated to further help smooth the surface finish. Millimeter-level spherical lenses have been successfully fabricated, and their optical performance has also been discussed.
• Khreishi, M., Ohl, R. G., Howard, J. M., Papa, J. C., Mcclelland, R., Hovis, C., Hadjimichael, T., Thompson, P., Ranson, K., Liang, R., & others, . (2021). Enabling precision coordinate metrology for universal optical testing and alignment applications. Optical Engineering, 60(3), 035106.
• Khreishi, M., Ohl, R. G., McClelland, R. S., Shiri, R. S., Hewagama, T., Aslam, S., Ulmer, M. P., Canavan, E. R., & Liang, R. (2021). Measuring large amplitude surface figure error using coordinate metrology. Optical Engineering, 60(8), 084103.
• Li, S., Song, B., Peterson, T., Hsu, J., & Liang, R. (2021). MicroLED chromatic confocal microscope. Optics letters, 46(11), 2722-2725.
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  In this Letter, a microLED-based chromatic confocal microscope with a virtual confocal slit is proposed and demonstrated for three-dimensional (3D) profiling without any mechanical scanning or external light source. In the proposed method, a micro-scale light-emitting diode (microLED) panel works as a point source array to achieve lateral scanning. Axial scanning is realized through the chromatic aberration of an aspherical objective. A virtual pinhole technique is utilized to improve the contrast and precision of depth reconstruction. The system performance has been demonstrated with a diamond-turned copper sample and onion epidermis. The experimental results show that the microLED panel could be a potential solution for portable 3D confocal microscopy. Several considerations and prospects are proposed for future microLED requirements in confocal imaging.
• Liang, J., Ren, L., & Liang, R. (2021). Low-pass filtering based polarimetric dehazing method for dense haze removal. Optics express, 29(18), 28178-28189.
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  Polarimetric dehazing method is very promising in enhancing the quality of images captured in the scattering media. However, it is found that the dehazing results calculated by hazy images are very sensitive to the noise, which may cause the method unstable or even invalid. To overcome this drawback and enhance the capability and stability of the polarimetric dehazing method, digital image processing algorithms or bias parameters need to be added into the method, however, they will make the algorithm complex and time consuming. In this paper, using low pass filter to suppress the noise of the hazy images, a novel polarimetric dehazing method is proposed to enhance the visibility of hazy images, especially for dense haze removal. Experimental results demonstrate that this method is totally automatic and very effective in dense haze processing. This method may have great potential usage in many applications, such as optical surveillance, underwater imaging, and bio-tissue imaging, etc.
• Liu, Z., Gray, B. D., Barber, C., Wan, L., Furenlid, L. R., Liang, R., Li, Z., Woolfenden, J. M., Pak, K. Y., & Martin, D. R. (2021). PEGylated and Non-PEGylated TCP-1 Probes for Imaging of Colorectal Cancer. Molecular imaging and biology.
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  Previous studies indicate that Tc- and fluorescent-labeled c[Cys-Thr-Pro-Ser-Pro-Phe-Ser-His-Cys]OH (TCP-1) peptides were able to detect colorectal cancer (CRC) and tumor-associated vasculature. This study was designed to characterize the targeting properties of PEGylated and non-PEGylated TCP-1 peptides for CRC imaging.
• Song, B., Li, S., Sunny, S., Gurushanth, K., Mendonca, P., Mukhia, N., Patrick, S., Gurudath, S., Raghavan, S., Tsusennaro, I., Leivon, S. T., Kolur, T., Shetty, V., Bushan, V., Ramesh, R., Peterson, T., Pillai, V., Wilder-Smith, P., Sigamani, A., , Suresh, A., et al. (2021). Classification of imbalanced oral cancer image data from high-risk population. Journal of biomedical optics, 26(10).
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  Early detection of oral cancer is vital for high-risk patients, and machine learning-based automatic classification is ideal for disease screening. However, current datasets collected from high-risk populations are unbalanced and often have detrimental effects on the performance of classification.
• Song, B., Sunny, S., Li, S., Gurushanth, K., Mendonca, P., Mukhia, N., Patrick, S., Gurudath, S., Raghavan, S., Imchen, T., Leivon, S., Kolur, T., Shetty, V., Bushan, V., Ramesh, R., Lima, N., Pillai, V., Wilder-Smith, P., Sigamani, A., , Suresh, A., et al. (2021). Mobile-based oral cancer classification for point-of-care screening. Journal of biomedical optics, 26(6).
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  Oral cancer is among the most common cancers globally, especially in low- and middle-income countries. Early detection is the most effective way to reduce the mortality rate. Deep learning-based cancer image classification models usually need to be hosted on a computing server. However, internet connection is unreliable for screening in low-resource settings.
• Song, B., Sunny, S., Li, S., Gurushanth, K., Mendonca, P., Mukhia, N., Patrick, S., Gurudath, S., Raghavan, S., Tsusennaro, I., Leivon, S. T., Kolur, T., Shetty, V., Bushan, V. R., Ramesh, R., Peterson, T., Pillai, V., Wilder-Smith, P., Sigamani, A., , Suresh, A., et al. (2021). Bayesian deep learning for reliable oral cancer image classification. Biomedical optics express, 12(10), 6422-6430.
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  In medical imaging, deep learning-based solutions have achieved state-of-the-art performance. However, reliability restricts the integration of deep learning into practical medical workflows since conventional deep learning frameworks cannot quantitatively assess model uncertainty. In this work, we propose to address this shortcoming by utilizing a Bayesian deep network capable of estimating uncertainty to assess oral cancer image classification reliability. We evaluate the model using a large intraoral cheek mucosa image dataset captured using our customized device from high-risk population to show that meaningful uncertainty information can be produced. In addition, our experiments show improved accuracy by uncertainty-informed referral. The accuracy of retained data reaches roughly 90% when referring either 10% of all cases or referring cases whose uncertainty value is greater than 0.3. The performance can be further improved by referring more patients. The experiments show the model is capable of identifying difficult cases needing further inspection.
• Sun, Y., Zhang, J., & Liang, R. (2021). Color polarization demosaicking by a convolutional neural network. Optics letters, 46(17), 4338-4341.
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  To address color polarization demosaicking problems in polarization imaging with a color polarization camera, we propose a color polarization demosaicking convolutional neural network (CPDCNN), which has a two-branch structure to ensure the fidelity of polarization signatures and enhance image resolution. To train the network, we built a unique dual-camera system and captured a pairwise color polarization image dataset. Experimental results show that CPDCNN outperformances other methods by a large margin in contrast and resolution.
• Wang, D., Yin, Y., Dou, J., Kong, M., Xu, X., Lei, L., & Liang, R. (2021). Calibration of geometrical aberration in transmitted wavefront testing of refractive optics with deflectometry. Applied optics, 60(7), 1973-1981.
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  Deflectometry, with its noticeable advantages such as simple structure, large dynamic range, and high accuracy comparable to interferometry, has been one of the powerful metrological techniques for optical surfaces in recent years. In the "null" deflectometric transmitted wavefront testing of refractive optics, ray tracing of the test system model is required, in which both the miscalibration of system geometrical parameters and optical tolerances on tested optics could introduce significant geometrical aberrations in the testing results. In this paper, the geometrical aberration introduced by a system modeling error in the transmitted wavefront testing is discussed. Besides, a calibration method based on polynomial optimization of geometrical aberration is presented for the geometrical aberration calibration. Both simulation and experiment have been performed to validate the feasibility of the proposed calibration method. The proposed method can calibrate the optical tolerances on tested optics effectively, and it is feasible even with a large geometric error, providing a viable way to address the uncertainty in system modeling in transmitted wavefront testing of freeform refractive optics with large dynamic range.
• Xiao, H., Yin, S., Wang, H., Liu, Y., Wu, H., Liang, R., & Cao, H. (2021). Models of grinding-induced surface and subsurface damages in fused silica considering strain rate and micro shape/geometry of abrasive. Ceramics International, 47(17), 24924--24941.
• Yin, S., Xiao, H., Kang, W., Wu, H., & Liang, R. (2021). Shoulder Damage Model and Its Application for Single Point Diamond Machining of ZnSe Crystal. Materials (Basel, Switzerland), 15(1).
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  The damaging of ZnSe crystal has a significant impact on its service performance and life. Based on the specific cutting energies for brittle and ductile mode machining, a model is proposed to evaluate the damage depth in the shoulder region of ZnSe crystal during single point diamond machining. The model considers the brittle-ductile transition and spring back of ZnSe crystal. To verify the model, the elastic modulus, hardness, spring back, and friction coefficient of ZnSe crystal are measured by nanoindentation and nanoscratch tests, and its critical undeformed chip thickness is obtained by spiral scratching. Meanwhile, orthogonal cutting experiments are conducted to obtain the different shoulder regions and cutting surfaces. The shoulder damage depth is analyzed, indicating that the effect of the feed on the damage depth at a high cutting depth is stronger than that at a low one. The model is verified to be effective with an average relative error of less than 7%. Then, the model is used to calculate the critical processing parameters and achieve a smooth ZnSe surface with a roughness Sa = 1.0 nm. The model is also extended to efficiently predict the bound of the subsurface damage depth of a cutting surface. The research would be useful for the evaluation of surface and subsurface damages during the ultra-precision machining of ZnSe crystal.
• Zhang, J., Zhao, D., Chen, J., Sun, Y., Yang, D., & Liang, R. (2021). Unsupervised learning for hyperspectral recovery based on a single RGB image. Optics letters, 46(16), 3977-3980.
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  Hyperspectral imagery often suffers from the degradation of spatial, spectral, or temporal resolution due to the limitations of hyperspectral imaging devices. To address this problem, hyperspectral recovery from a single red-green-blue (RGB) image has recently achieved significant progress via deep learning. However, current deep learning-based methods are all learned in a supervised way under the availability of RGB and correspondingly hyperspectral images, which is unrealistic for practical applications. Hence, we propose to recover hyperspectral images from a single RGB image in an unsupervised way. Moreover, based on the statistical property of hyperspectral images, a customized loss function is proposed to boost the performance. Extensive experiments on the BGU iCVL Hyperspectral Image Dataset demonstrate the effectiveness of the proposed method.
• Gannon, C., & Liang, R. (2020). Evolving expertise for automated lens optimization. Applied optics, 59(22), G129-G136.
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  We present a process to locate the desired local optimum of high-dimensional design problems such as the optimization of freeform mirror systems. By encoding active design variables into a binary vector imitating DNA sequences, we are able to perform a genetic optimization of the optimization process itself. The end result is an optimization route that is effectively able to sidestep local minima by warping the variable space around them in a way that mimics the expertise of veteran designers. The generality of the approach is validated through the automated generation of high-performance designs for off-axis three- and four-mirror free-form systems.
• Li, S., & Liang, R. (2020). DMD-based three-dimensional chromatic confocal microscopy. Applied optics, 59(14), 4349-4356.
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  In this paper, a digital mirror device (DMD)-based chromatic confocal microscopy is proposed and demonstrated for three-dimensional (3D) surface profiling without any mechanical scanning. In this method, the DMD works as the multipoint source and multi-pinhole at the same time to achieve the lateral scanning. Moreover, axial scanning is realized through the chromatic aberration of the confocal optics. Since the micromirror array of the DMD is not perpendicular to the confocal imaging axis, a corresponding calibration is needed to eliminate the tilt effects and perform accurate 3D imaging. The measurement range with the current optical system is 45 µm over 505-650 nm working spectrum and can be increased by using a custom objective with large chromatic aberration. The system performance has been demonstrated with a multistep sample.
• Li, Z., Li, X., & Liang, R. (2020). Random two-frame interferometry based on deep learning. Optics express, 28(17), 24747-24760.
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  A two-frame phase-shifting interferometric wavefront reconstruction method based on deep learning is proposed. By learning from a large number of simulation data based on a physical model, the wrapped phase can be calculated accurately from two interferograms with an unknown phase step. The phase step can be any value excluding the integral multiples of π and the size of interferograms can be flexible. This method does not need a pre-filtering to subtract the direct-current term, but only needs a simple normalization. Comparing with other two-frame methods in both simulations and experiments, the proposed method can achieve better performance.
• Liang, J., Ju, H., Ren, L., Yang, L., & Liang, R. (2020). Generalized Polarimetric Dehazing Method Based on Low-Pass Filtering in Frequency Domain. Sensors (Basel, Switzerland), 20(6).
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  Polarimetric dehazing methods can significantly enhance the quality of hazy images. However, current methods are not robust enough under different imaging conditions. In this paper, we propose a generalized polarimetric dehazing method based on low-pass filtering in the frequency domain. This method can accurately estimate the polarized state of the scattering light automatically without adjusting bias parameters. Experimental results show the effectiveness and robustness of our proposed method in different hazy weather and scattering underwater environments with different densities. Furthermore, computational efficiency is enhanced more than 70% compared to the polarimetric dehazing method we proposed previously.
• Liang, J., Zhang, J., Shao, J., Song, B., Yao, B., & Liang, R. (2020). Deep Convolutional Neural Network Phase Unwrapping for Fringe Projection 3D Imaging. Sensors (Basel, Switzerland), 20(13).
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  Phase unwrapping is a very important step in fringe projection 3D imaging. In this paper, we propose a new neural network for accurate phase unwrapping to address the special needs in fringe projection 3D imaging. Instead of labeling the wrapped phase with integers directly, a two-step training process with the same network configuration is proposed. In the first step, the network (network I) is trained to label only four key features in the wrapped phase. In the second step, another network with same configuration (network II) is trained to label the wrapped phase segments. The advantages are that the dimension of the wrapped phase can be much larger from that of the training data, and the phase with serious Gaussian noise can be correctly unwrapped. We demonstrate the performance and key features of the neural network trained with the simulation data for the experimental data.
• Park, J., Feng, X., Liang, R., & Gao, L. (2020). Snapshot multidimensional photography through active optical mapping. Nature communications, 11(1), 5602.
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  Multidimensional photography can capture optical fields beyond the capability of conventional image sensors that measure only two-dimensional (2D) spatial distribution of light. By mapping a high-dimensional datacube of incident light onto a 2D image sensor, multidimensional photography resolves the scene along with other information dimensions, such as wavelength and time. However, the application of current multidimensional imagers is fundamentally restricted by their static optical architectures and measurement schemes-the mapping relation between the light datacube voxels and image sensor pixels is fixed. To overcome this limitation, we propose tunable multidimensional photography through active optical mapping. A high-resolution spatial light modulator, referred to as an active optical mapper, permutes and maps the light datacube voxels onto sensor pixels in an arbitrary and programmed manner. The resultant system can readily adapt the acquisition scheme to the scene, thereby maximising the measurement flexibility. Through active optical mapping, we demonstrate our approach in two niche implementations: hyperspectral imaging and ultrafast imaging.
• Tian, X., & Liang, R. (2020). Snapshot phase-shifting diffraction phase microscope. Optics letters, 45(12), 3208-3211.
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  We propose a novel and simple snapshot phase-shifting diffraction phase microscope with a polarization grating and spatial phase-shifting technology. Polarization grating separates the incident beam into left and right circular polarization beams, one of which is used as the reference beam after passing through a pinhole. Four phase-shifted interferograms can be captured simultaneously from the polarization camera to reconstruct the high spatial resolution phase map. The principle is presented in this Letter, and the performance of the proposed system is demonstrated experimentally. Due to the near-common-path configuration and snapshot feature, the proposed system provides a feasible way for real-time quantitative phase measurement with minimal sensitivity to vibration and thermal disturbance.
• Uthoff, R., Song, B., Maarouf, M., Shi, V., & Liang, R. (2020). Point-of-care, multispectral, smartphone-based dermascopes for dermal lesion screening and erythema monitoring. Journal of biomedical optics, 25(6), 1-21.
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  The rates of melanoma and nonmelanoma skin cancer are rising across the globe. Due to a shortage of board-certified dermatologists, the burden of dermal lesion screening and erythema monitoring has fallen to primary care physicians (PCPs). An adjunctive device for lesion screening and erythema monitoring would be beneficial because PCPs are not typically extensively trained in dermatological care.
• Zhang, J., Shao, J., Chen, J., Yang, D., Liang, B., & Liang, R. (2020). PFNet: an unsupervised deep network for polarization image fusion. Optics letters, 45(6), 1507-1510.
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  Image fusion is the key step to improve the performance of object detection in polarization images. We propose an unsupervised deep network to address the polarization image fusion issue. The network learns end-to-end mapping for fused images from intensity and degree of linear polarization images, without the ground truth of fused images. Customized architecture and loss function are designed to boost performance. Experimental results show that our proposed network outperforms other state-of-the-art methods in terms of visual quality and quantitative measurement.
• Zhang, J., Sun, Y., Chen, J., Yang, D., & Liang, R. (2020). Deep-learning-based hyperspectral recovery from a single RGB image. Optics letters, 45(20), 5676-5679.
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  Commercial hyperspectral imaging devices are expensive and tend to suffer from the degradation of spatial, spectral, or temporal resolution. To address these problems, we propose a deep-learning-based method to recover hyperspectral images from a single RGB image. The proposed method learns an end-to-end mapping between an RGB image and corresponding hyperspectral images. Moreover, a customized loss function is proposed to boost the performance. Experimental results on a variety of hyperspectral datasets demonstrate that our proposed method outperforms several state-of-the-art methods in terms of both quantitative measurements and perceptual quality.
• Zhang, Y., Liang, R., Spires, O. J., Yin, S., Yi, A., & Milster, T. D. (2020). Precision glass molding of diffractive optical elements with high surface quality. Optics letters, 45(23), 6438-6441.
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  Diffractive optical surfaces have attractive properties for use in optical systems, like reducing weight and correcting for chromatic aberrations, but fabrication of high-quality glass diffractive optics is challenging, preventing it from being widely adopted in commercial applications. In this Letter, we report on a fabrication method to address molding challenges for high-surface-quality diffractive glass optics at molding temperatures up to 550°C, including selection of mold material, mold fabrication, precision glass molding, durability, and stability of the mold. To enable optimal mold machining and easy mold release, nickel phosphorous (NiP) is chosen as the plating material for its cutting performance and anti-adhesion properties, and copper-nickel C71500 (CuNi) is selected as the mold substrate because its coefficient of thermal expansion (CTE) is close to NiP. By the proposed method, diffractive glass optics with 2 nm Sa surface roughness is demonstrated.
• Zhang, Y., Yin, S., Liang, R., Luo, H., Xiao, H., & Yuan, N. (2020). New testing and calculation method for determination viscoelasticity of optical glass. Optics express, 28(1), 626-640.
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  Viscoelastic properties of glass within molding temperatures, such as shear relaxation modulus and bulk relaxation modulus, are key factors to build successful numerical model, predict forming process, and determine optimal process parameters for precision glass molding. However, traditional uniaxial compression creep tests with large strains are very limited in obtaining high-accuracy viscoelastic data of glass, due to the declining compressive stress caused by the increasing cross-sectional area of specimen in testing process. Besides, existing calculation method has limitation in transforming creep data to viscoelasticity data, especially when Poisson's ratio is unknown at molding temperature, which further induces a block to characterize viscoelastic parameter. This study proposes a systematic acquisition method for high-precision viscoelastic data, including creep testing, viscoelasticity calculation, and finite element verification. A minimal uniaxial creep testing (MUCT) method based on thermo-mechanical analysis (TMA) instrument is first built to obtain ideal and accurate creep data, by keeping compressive stress as a constant. A new calculation method on viscoelasticity determination is then proposed to derive shear relaxation modulus without the need of knowing bulk modulus or Poisson's ratio, which, compared with traditional method, extends the application range of viscoelasticity calculation. After determination, the obtained viscoelastic data are further incorporated into a numerical simulation model of MUCT to verify the accuracy of the determined viscoelasticity. Base on the great consistence between simulated and measured results (uniaxial creep displacement), the proposed systematic acquisition method can be used as a high accuracy viscoelasticity determination method.
• Cui, Q., & Liang, R. (2019). Chromatic confocal microscopy using liquid crystal display panels. Applied optics, 58(8), 2085-2090.
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  A chromatic confocal microscopy system in combination with two liquid crystal display (LCD) panels is proposed and demonstrated for surface profiling. The major advantage of this system is no mechanical translation is needed for three-dimensional (3D) imaging. Axial scanning is realized thanks to the chromatic aberration in the objective, whereas lateral scanning is achieved by turning on different pixels on LCDs. Chromatic aberration of the objective lens is used to provide wavelength-to-depth coding, and decoding is realized by using a dispersion prism. System performance is validated with a 50 μm step standard and the capability of 3D imaging is demonstrated with an onion epidermis.
• Huang, C., Geng, J., Luo, T., Han, J., Wang, Q., Liang, R., Fan, S., & Jiang, S. (2019). Rare Earth Doped Optical Fibers with Multi-section Core. iScience, 22, 423-429.
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  The gain bandwidth of a single-mode fiber is limited by the atomic transitions of one rare earth gain element. Here we overcome this long-standing challenge by designing a new single-mode fiber with multi-section core, where each section is doped with different gain element. We theoretically propose and experimentally demonstrate that this configuration provides a gain bandwidth well beyond the capability of conventional design, whereas the inclusion of multiple sections does not compromise single-mode operation or the quality of the transverse modal profile. This new fiber will be beneficial in realizing all fiber laser systems with few-cycle pulse duration or octave tunability.
• Liang, J., Ju, H., Ren, L., Zhang, W., Yang, L., Bai, Z., & Liang, R. (2019). High-resolution reconstruction of shortwave infrared polarimetric images using the intensity information of visible images. Applied optics, 58(18), 4866-4870.
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  Shortwave infrared (SWIR) polarimetric imaging has been found very effective in various applications. However, the low resolution of the SWIR camera severely limits the capacity of this technique. Image reconstruction methods have been developed to improve the spatial resolution, but these methods typically do not consider the polarized information that the images may contain. In this paper, we propose a high-resolution reconstruction method for SWIR images based on the spatial information of visible images without losing polarized information in the SWIR image. Experimental results demonstrate that this method is feasible to reconstruct high-resolution polarized SWIR images. We have also demonstrated its potential application in image fusion.
• Liang, J., Tian, X., Ju, H., Wang, D., Wu, H., Ren, L., & Liang, R. (2019). Reconfigurable snapshot polarimetric imaging technique through spectral-polarization filtering. Optics letters, 44(18), 4574-4577.
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  In this Letter, we propose a simple, low-cost, reconfigurable snapshot polarimetric imaging technique for a color camera to measure polarization properties with spectral-polarization filters. Experimental results demonstrate the unique capabilities, such as obtaining circular or elliptical polarized information in a snapshot, that are not available from commercial polarization cameras and other polarization imaging techniques.
• Mu, T., Han, F., Bao, D., Zhang, C., & Liang, R. (2019). Compact snapshot optically replicating and remapping imaging spectrometer (ORRIS) using a focal plane continuous variable filter. Optics letters, 44(5), 1281-1284.
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  In this Letter, a novel snapshot spectral imaging technique, optically replicating and remapping imaging spectrometer, is presented. It is based on the combination of shifting subimages by a specially designed lenslet array (LA) and filtering subimages by a focal plane continuous variable filter (CVF). The 3D datacube is recovered by just using a simple image remapping process. The use of the LA and the focal plane CVF makes the system compact and low in cost. A handheld proof-of-principle prototype has been built and demonstrated; it covers a wavelength range of 380-860 nm with 80 spectral channels with a spatial resolution of 400×400  pixels.
• Shao, J., Zhang, J., Huang, X., Liang, R., & Barnard, K. (2019). Fiber bundle image restoration using deep learning. Optics letters, 44(5), 1080-1083.
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  We propose a deep learning-based restoration method to remove honeycomb patterns and improve resolution for fiber bundle (FB) images. By building and calibrating a dual-sensor imaging system, we capture FB images and corresponding ground truth data to train the network. Images without fiber bundle fixed patterns are restored from raw FB images as direct inputs, and spatial resolution is significantly enhanced for the trained sample type. We also construct the brightness mapping between the two image types for the effective use of all data, providing the ability to output images of the expected brightness. We evaluate our framework with data obtained from lens tissues and human histological specimens using both objective and subjective measures.
• Shao, J., Zhang, J., Liang, R., & Barnard, K. (2019). Fiber bundle imaging resolution enhancement using deep learning. Optics express, 27(11), 15880-15890.
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  We propose a deep learning based method to estimate high-resolution images from multiple fiber bundle images. Our approach first aligns raw fiber bundle image sequences with a motion estimation neural network and then applies a 3D convolution neural network to learn a mapping from aligned fiber bundle image sequences to their ground truth images. Evaluations on lens tissue samples and a 1951 USAF resolution target suggest that our proposed method can significantly improve spatial resolution for fiber bundle imaging systems.
• Tian, X., Tu, X., Della Croce, K., Yao, G., Cai, H., Brock, N., Pau, S., & Liang, R. (2019). Multi-wavelength quantitative polarization and phase microscope. Biomedical optics express, 10(4), 1638-1648.
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  We introduce a snapshot multi-wavelength quantitative polarization and phase microscope (MQPPM) for measuring spectral dependent quantitative polarization and phase information. The system uniquely integrates a polarized light microscope and a snap-shot quantitative phase microscope in a single system, utilizing a novel full-Stokes camera operating in the red, green, and blue (RGB) spectrum. The linear retardance and fast axis orientation of a birefringent sample can be measured simultaneously in the visible spectra. Both theoretical analysis and experiments have been performed to demonstrate the capability of the proposed microscope. Data from liquid crystal and different biological samples are presented. We believe that MQPPM will be a useful tool in measuring quantitative polarization and phase information of live cells.
• Uthoff, R. D., Song, B., Sunny, S., Patrick, S., Suresh, A., Kolur, T., Gurushanth, K., Wooten, K., Gupta, V., Platek, M. E., Singh, A. K., Wilder-Smith, P., Kuriakose, M. A., Birur, P., & Liang, R. (2019). Small form factor, flexible, dual-modality handheld probe for smartphone-based, point-of-care oral and oropharyngeal cancer screening. Journal of biomedical optics, 24(10), 1-8.
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  Oral cancer is a growing health issue in low- and middle-income countries due to betel quid, tobacco, and alcohol use and in younger populations of middle- and high-income communities due to the prevalence of human papillomavirus. The described point-of-care, smartphone-based intraoral probe enables autofluorescence imaging and polarized white light imaging in a compact geometry through the use of a USB-connected camera module. The small size and flexible imaging head improves on previous intraoral probe designs and allows imaging the cheek pockets, tonsils, and base of tongue, the areas of greatest risk for both causes of oral cancer. Cloud-based remote specialist and convolutional neural network clinical diagnosis allow for both remote community and home use. The device is characterized and preliminary field-testing data are shared.
• Wang, D., Tian, X., Xu, P., Liang, J., Wu, H., Spires, O., & Liang, R. (2019). Compact snapshot multiwavelength interferometer. Optics letters, 44(18), 4463-4466.
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  We propose a snapshot and compact multiwavelength interferometer for real-time testing of optical surfaces with large slopes. A color camera with a micropolarizer array simultaneously captures the phase-shifted interferograms of multiple wavelengths, from which four interferograms with π/2 phase shift at each wavelength are extracted for multiwavelength phase-shifting interferometric measurement. The accuracy of the proposed system is validated experimentally, and the testing of freeform surface with large slopes is also demonstrated. The proposed system provides a feasible way to obtain the instantaneous online measurement of freeform surfaces while minimizing environmental disturbance.
• Xiao, H., Liang, R., Spires, O., Wang, H., Wu, H., & Zhang, Y. (2019). Evaluation of surface and subsurface damages for diamond turning of ZnSe crystal. Optics express, 27(20), 28364-28382.
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  With single-point diamond turning (SPDT), a series of samples are processed under different cutting parameters. The brittle-ductile transition depth of ZnSe crystal is obtained, and the damages of the samples are measured from surface and subsurface damage depths as well as damage density. The effects of cutting parameters on the damages are investigated quantitatively. The results show the cutting depth has a minor while the feed has a major effects on the damages. Also, the interaction effect between feed and cutting depth is very small for surface damage depth or damage density, while it is large for subsurface damage depth. Based on the indentation mechanics and the kinetic characteristics of SPDT, a model is proposed to evaluate the surface and subsurface damage depths of ZnSe crystal by cutting parameters. The model has an average relative error less than 15.0%, which could be further used to obtain the depth and the removal characteristics of cracks in shoulder region.
• Yan, Y., Tian, X., Liang, R., & Sasian, J. (2019). Optical performance evaluation and chromatic aberration correction of a focus tunable lens used for 3D microscopy. Biomedical optics express, 10(12), 6029-6042.
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  Recently, the development of motion-free 3D microscopy utilizing focus tunable lenses (FTL) has been rapid. However, the downgrade of optical performance due to FTL and its gravity effect are rarely discussed in detail. Also, color dispersion is usually maintained purely depending on the FTL material without further correction. In this manuscript, we provide a quantitative evaluation of the impact of FTL on the optical performance of the microscope. The evaluation is based on both optical ray tracing simulations and lab experiments. In addition, we derive the first order conditions to correct axial color aberration of FTL through its entire power tuning range. Secondary spectrum correction is also possible and an apochromatic motion-free 3D microscope with 2 additional doublets is demonstrated. This study will serve a guidance in utilizing FTL as a motion-free element for 3D microscopy.
• Zhang, J., Tian, X., Shao, J., Luo, H., & Liang, R. (2019). Phase unwrapping in optical metrology via denoised and convolutional segmentation networks. Optics express, 27(10), 14903-14912.
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  The interferometry technique is commonly used to obtain the phase information of an object in optical metrology. The obtained wrapped phase is subject to a 2π ambiguity. To remove the ambiguity and obtain the correct phase, phase unwrapping is essential. Conventional phase unwrapping approaches are time-consuming and noise sensitive. To address those issues, we propose a new approach, where we transfer the task of phase unwrapping into a multi-class classification problem and introduce an efficient segmentation network to identify classes. Moreover, a noise-to-noise denoised network is integrated to preprocess noisy wrapped phase. We have demonstrated the proposed method with simulated data and in a real interferometric system.
• Zhang, Y., Tian, X., & Liang, R. (2019). Accurate and fast two-step phase shifting algorithm based on principle component analysis and Lissajous ellipse fitting with random phase shift and no pre-filtering. Optics express, 27(14), 20047-20063.
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  To achieve high measurement accuracy with less computational time-in-phase shifting interferometry, a random phase-shifting algorithm based on principal component analysis and Lissajous ellipse fitting (PCA&LEF) is proposed. It doesn't need pre-filtering and can obtain relatively accurate phase distribution with only two phase shifted interferograms and less computational time and is suitable for different background intensity, modulation amplitude distributions and noises. Moreover, it can obtain absolutely accurate result when the background intensity and modulation amplitude are perfect and can partly suppress the effect of imperfect background intensity and modulation amplitude. Last but not least, it removes the restriction that PCA needs more than three interferograms with well-distributed phase shifts to subtract relatively accurate mean. The simulations and experiments verify the correctness and feasibility of PCA&LEF.
• Zhang, Y., Tian, X., & Liang, R. (2019). Two-step random phase retrieval approach based on Gram-Schmidt orthonormalization and Lissajous ellipse fitting method. Optics express, 27(3), 2575-2588.
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  To overcome the phase shift error in phase shifting interferometry, a two-step random phase retrieval approach based on Gram-Schmidt (GS) orthonormalization and Lissajous ellipse fitting (LEF) method (GS&LEF) is proposed. It doesn't need pre-filtering, and can obtain relatively accurate phase distribution with only two phase shifted interferograms and less computational time. It is suitable for different background intensity, modulation amplitude distributions and noises. Last but not least, this method is effective for circular, straight or complex fringes. The simulations and experiments verify the correctness and feasibility of GS&LEF.
• Aftab, M., Choi, H., Liang, R., & Kim, D. W. (2018). Adaptive Shack-Hartmann wavefront sensor accommodating large wavefront variations. Optics express, 26(26), 34428-34441.
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  Shack-Hartmann wavefront sensors (SHWFSs) usually have fixed subaperture areas on the detector, in order to fix the minimum and maximum amounts of wavefront departure, or the dynamic range of measurement. We introduce an active approach, named Adaptive Shack Hartmann Wavefront Sensor (A-SHWFS). A-SHWFS is used to reconfigure detection subaperture areas by either blocking or unblocking desired lenslets by using an electronically modulated mask. This mask either increases or decreases the measurable aberration magnitude by placing a liquid crystal display (LCD) panel in front of the lenslet array. Depending on which control signal that is sent to the LCD, the variable, application-dependent blocking pattern (horizontal, vertical, diagonal, uneven) makes this an adaptive and efficient sensor with a variable dynamic range of measurement. This scheme is also useful for regional blocking, which occurs when the wavefront is severely aberrated in a limited region.
• Barnard, J. J., Shao, J., & Liang, R. (2018). Resolution enhancement for fiber bundle imaging using maximum a posteriori estimation. Optics Letters.
• Gannon, C., & Liang, R. (2018). Using spherical harmonics to describe large-angle freeform lenses. Applied optics, 57(28), 8143-8147.
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  We propose the use of spherical harmonics for large-angle freeform lenses as a dramatic improvement over polynomials set on the disk and plane, such as Zernike and - polynomials. This new representation enables fitting of surfaces designed in spherical coordinates, such as freeform illumination lenses that would be impossible to describe with respect to a plane. The proposed representation is validated through an extremely compact, high-performance design.
• Garcia, M., Edmiston, C., York, T., Marinov, R., Mondal, S., Zhu, N., Sudlow, G. P., Akers, W. J., Margenthaler, J., Achilefu, S., Liang, R., Zayed, M. A., Pepino, M. Y., & Gruev, V. (2018). Bio-inspired imager improves sensitivity in near-infrared fluorescence image-guided surgery. Optica, 5(4), 413-422.
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  Image-guided surgery can enhance cancer treatment by decreasing, and ideally eliminating, positive tumor margins and iatrogenic damage to healthy tissue. Current state-of-the-art near-infrared fluorescence imaging systems are bulky and costly, lack sensitivity under surgical illumination, and lack co-registration accuracy between multimodal images. As a result, an overwhelming majority of physicians still rely on their unaided eyes and palpation as the primary sensing modalities for distinguishing cancerous from healthy tissue. Here we introduce an innovative design, comprising an artificial multispectral sensor inspired by the butterfly's compound eye, which can significantly improve image-guided surgery. By monolithically integrating spectral tapetal filters with photodetectors, we have realized a single-chip multispectral imager with 1000 × higher sensitivity and 7 × better spatial co-registration accuracy compared to clinical imaging systems in current use. Preclinical and clinical data demonstrate that this technology seamlessly integrates into the surgical workflow while providing surgeons with real-time information on the location of cancerous tissue and sentinel lymph nodes. Due to its low manufacturing cost, our bio-inspired sensor will provide resource-limited hospitals with much-needed technology to enable more accurate value-based health care.
• Liao, C., Wang, P. u., Huang, C. Y., Lin, P., Eakins, G., Bentley, R. T., Liang, R., & Cheng, J. (2018). In Vivo and in Situ Spectroscopic Imaging by a Handheld Stimulated Raman Scattering Microscope. ACS PHOTONICS, 5(3), 947-954.
• Shao, J., Liao, W. C., Liang, R., & Barnard, J. J. (2018). Resolution enhancement for fiber bundle imaging using maximum a posteriori estimation. Optics Letters, 43, 1906-1909.
• Shao, J., Liao, W. C., Liang, R., & Barnard, K. (2018). Resolution enhancement for fiber bundle imaging using maximum a posteriori estimation. Optics letters, 43(8), 1906-1909.
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  We propose a new framework to jointly improve spatial resolution and remove fixed structural patterns for coherent fiber bundle imaging systems, based on inverting a principled forward model. The forward model maps a high-resolution representation to multiple images modeling random probe motions. We then apply a point spread function to simulate low-resolution figure bundle image capture. Our forward model also uses a smoothing prior. We compute a maximum a posteriori (MAP) estimate of the high-resolution image from one or more low-resolution images using conjugate gradient descent. Unique aspects of our approach include (1) supporting a variety of possible applicable transformations; (2) applying principled forward modeling and MAP estimation to this domain. We test our method on data synthesized from the USAF target, data captured from a transmissive USAF target, and data from lens tissue. In the case of the USAF target and 16 low-resolution captures, spatial resolution is enhanced by a factor of 2.8.
• Song, B., Sunny, S., Uthoff, R. D., Patrick, S., Suresh, A., Kolur, T., Keerthi, G., Anbarani, A., Wilder-Smith, P., Kuriakose, M. A., Birur, P., Rodriguez, J. J., & Liang, R. (2018). Automatic classification of dual-modalilty, smartphone-based oral dysplasia and malignancy images using deep learning. Biomedical optics express, 9(11), 5318-5329.
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  With the goal to screen high-risk populations for oral cancer in low- and middle-income countries (LMICs), we have developed a low-cost, portable, easy to use smartphone-based intraoral dual-modality imaging platform. In this paper we present an image classification approach based on autofluorescence and white light images using deep learning methods. The information from the autofluorescence and white light image pair is extracted, calculated, and fused to feed the deep learning neural networks. We have investigated and compared the performance of different convolutional neural networks, transfer learning, and several regularization techniques for oral cancer classification. Our experimental results demonstrate the effectiveness of deep learning methods in classifying dual-modal images for oral cancer detection.
• Tian, X., Tu, X., Zhang, J., Spires, O., Brock, N., Pau, S., & Liang, R. (2018). Snapshot multi-wavelength interference microscope. Optics express, 26(14), 18279-18291.
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  A snapshot multi-wavelength interference microscope is proposed for high-speed measurement of large vertical range discontinuous microstructures and surface roughness. A polarization CMOS camera with a linear micro-polarizer array and Bayer filter accomplishes snapshot multi-wavelength phase-shifting measurement. Four interferograms with 𝜋/2 phase shift are captured at each wavelength for phase measurement, the 2𝜋 ambiguities are removed by using two or three wavelengths.
• Tu, X., Spires, O. J., Tian, X., Brock, N., Liang, R., & Pau, S. (2018). Division of amplitude RGB full-Stokes camera using micro-polarizer arrays: erratum. Optics express, 26(4), 4192-4193.
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  We correct two figures showing the micro-polarizer arrangement on the RGB full-Stokes camera.
• Uthoff, R. D., Song, B., Sunny, S., Patrick, S., Suresh, A., Kolur, T., Keerthi, G., Spires, O., Anbarani, A., Wilder-Smith, P., Kuriakose, M. A., Birur, P., & Liang, R. (2018). Point-of-care, smartphone-based, dual-modality, dual-view, oral cancer screening device with neural network classification for low-resource communities. PloS one, 13(12), e0207493.
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  Oral cancer is a growing health issue in a number of low- and middle-income countries (LMIC), particularly in South and Southeast Asia. The described dual-modality, dual-view, point-of-care oral cancer screening device, developed for high-risk populations in remote regions with limited infrastructure, implements autofluorescence imaging (AFI) and white light imaging (WLI) on a smartphone platform, enabling early detection of pre-cancerous and cancerous lesions in the oral cavity with the potential to reduce morbidity, mortality, and overall healthcare costs. Using a custom Android application, this device synchronizes external light-emitting diode (LED) illumination and image capture for AFI and WLI. Data is uploaded to a cloud server for diagnosis by a remote specialist through a web app, with the ability to transmit triage instructions back to the device and patient. Finally, with the on-site specialist's diagnosis as the gold-standard, the remote specialist and a convolutional neural network (CNN) were able to classify 170 image pairs into 'suspicious' and 'not suspicious' with sensitivities, specificities, positive predictive values, and negative predictive values ranging from 81.25% to 94.94%.
• Wang, D., Gong, Z., Xu, P., Wang, C., Liang, R., Kong, M., & Zhao, J. (2018). Accurate calibration of geometrical error in reflective surface testing based on reverse Hartmann test. Optics express, 26(7), 8113-8124.
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  The deflectometry provides a powerful metrological technique enabling the high-precision testing of reflective surfaces with high dynamic range, such as aspheric and freeform surfaces. In the fringe-illumination deflectometry based on reverse-Hartmann-test configuration, the calibration of system geometry is required to achieve "null" testing. However, the system miscalibration can introduce a significant systematic error in the testing results. A general double-step calibration method, which is based on the low-order Zernike aberration optimization and high-order aberration separation, is proposed to separate and eliminate the geometrical error due to system miscalibration. Both the numerical simulation and experiments have been performed to validate the feasibility of the proposed calibration method. The proposed method provides a general way for the accurate calibration of system geometrical error, avoids the over-correction and is feasible for the testing of various complex freeform surfaces.
• Zhang, J., Luo, H., Liang, R., Ahmed, A., Zhang, X., Hui, B., & Chang, Z. (2018). Sparse representation-based demosaicing method for microgrid polarimeter imagery. Optics letters, 43(14), 3265-3268.
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  To address the key image interpolation issue in microgrid polarimeters, we propose a machine learning model based on sparse representation. The sparsity and non-local self-similarity priors are used as regularization terms to enhance the stability of an interpolation model. Moreover, to make the best of the correlation among different polarization orientations, patches of different polarization channels are joined to learn adaptive sub-dictionary. Synthetic and real images are used to evaluate the interpolated performance. The experimental results demonstrate that our proposed method achieves state-of-the-art results in terms of quantitative measures and visual quality.
• Zhang, J., Shao, J., Luo, H., Zhang, X., Hui, B., Chang, Z., & Liang, R. (2018). Learning a convolutional demosaicing network for microgrid polarimeter imagery. Optics letters, 43(18), 4534-4537.
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  We propose a polarization demosaicing convolutional neural network to address the image demosaicing issue, the last unsolved issue in microgrid polarimeters. This network learns an end-to-end mapping between the mosaic images and full-resolution ones. Skip connections and customized loss function are used to boost the performance. Experimental results show that our proposed network outperforms other state-of-the-art methods by a large margin in terms of quantitative measures and visual quality.
• Zhang, Y., Tian, X., & Liang, R. (2018). Random two-step phase shifting interferometry based on Lissajous ellipse fitting and least squares technologies. Optics express, 26(12), 15059-15071.
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  To accurately obtain the phase distribution of an optical surface under test, the accurate phase extraction algorithm is essential. To overcome the phase shift error, a random two-step phase shifting algorithm, which can be used in the fluctuating and non-uniform background intensity and modulation amplitude, Lissajous ellipse fitting, and least squares iterative phase shifting algorithm (LEF&LSI PSA), is proposed; pre-filtering interferograms are not necessary, but they can get relatively accurate phase distribution and unknown phase shift value. The simulation and experiment verify the correctness and feasibility of the LEF & LSI PSA.
• Zhang, Y., Tian, X., & Liang, R. (2018). Three-step random phase retrieval approach based on difference map normalization and diamond diagonal vector normalization. Optics express, 26(22), 29170-29182.
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  To overcome the phase shift error in phase shifting interferometry, a three-step random phase retrieval approach based on difference map normalization and diamond diagonal vector normalization (DN&DDVN) is proposed. It does not need pre-filtering for the interferograms and can obtain relatively accurate phase distribution with a simple process and less computational time. This simulation and experiment verify the correctness and feasibility of DN&DDVN.
• Zhu, Z., Ma, D., Hu, Q., Tang, Y., & Liang, R. (2018). Catadioptric freeform optical system design for LED off-axis road illumination applications. Optics express, 26(2), A54-A65.
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  The aim of this paper is to develop a new composite structure of catadioptric optical system containing both freeform refractive surface and freeform total internal reflective (TIR) surface for LED road illumination applications. The role of freeform refractive part is to generate the shifted general rectangular illumination pattern to optimally match the shape of the road surface. The application of TIR mechanism is aimed to control the stray light in the sidewalk direction of the road luminaire and maximize the efficient energy efficiency. In this paper, we use the "double pole" ray mapping technique to design the refractive optical surface and the θ-φ coordinate ray mapping technique to derive the freeform TIR surface. The simulation shows that the novel catadioptric design has relatively high collection efficiency, thus high average illuminance level inside the effective illumination area. This lens also has good control of stray light on the backside of the road luminaire.
• Feng, Z., Froese, B. D., Liang, R., Cheng, D., & Wang, Y. (2017). Simplified freeform optics design for complicated laser beam shaping. APPLIED OPTICS, 56(33), 9308-9314.
• Gannon, C., & Liang, R. (2017). Ray mapping with surface information for freeform illumination design. OPTICS EXPRESS, 25(8), 9426-9434.
• He, Y., Hou, X. i., Wu, F., Ma, X., & Liang, R. (2017). Analysis of spurious diffraction orders of computer-generated hologram in symmetric aspheric metrology. OPTICS EXPRESS, 25(17), 20556-20572.
• He, Y., Huang, L., Hou, X. i., Fan, W. u., & Liang, R. (2017). Modeling near-null testing method of a freeform surface with a deformable mirror compensator. APPLIED OPTICS, 56(33), 9132-9138.
• Hong, Z., & Liang, R. (2017). IR-laser assisted additive freeform optics manufacturing. SCIENTIFIC REPORTS, 7.
• Hong, Z., & Liang, R. (2017). IR-laser assisted additive freeform optics manufacturing. Scientific reports, 7(1), 7145.
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  Computer-controlled additive manufacturing (AM) processes, also known as three-dimensional (3D) printing, create 3D objects by the successive adding of a material or materials. While there have been tremendous developments in AM, the 3D printing of optics is lagging due to the limits in materials and tight requirements for optical applicaitons. We propose a new precision additive freeform optics manufacturing (AFOM) method using an pulsed infrared (IR) laser. Compared to ultraviolet (UV) curable materials, thermally curable optical silicones have a number of advantages, such as strong UV stability, non-yellowing, and high transmission, making it particularly suitable for optical applications. Pulsed IR laser radiation offers a distinct advantage in processing optical silicones, as the high peak intensity achieved in the focal region allows for curing the material quickly, while the brief duration of the laser-material interaction creates a negligible heat-affected zone.
• Huang, C., & Liang, R. (2017). Modeling of surface topography on diamond-turned spherical and freeform surfaces. APPLIED OPTICS, 56(15), 4466-4473.
• Luo, Y., Huang, X., Bai, J., & Liang, R. (2017). Compact polarization-based dual-view panoramic lens. APPLIED OPTICS, 56(22), 6283-6287.
• Mondal, S. B., Gao, S., Zhu, N., Habimana-Griffin, L., Akers, W. J., Liang, R., Gruev, V., Margenthaler, J., & Achilefu, S. (2017). Optical See-Through Cancer Vision Goggles Enable Direct Patient Visualization and Real-Time Fluorescence-Guided Oncologic Surgery. ANNALS OF SURGICAL ONCOLOGY, 24(7), 1897-1903.
• Mu, T., Pacheco, S., Chen, Z., Zhang, C., & Liang, R. (2017). Snapshot linear-Stokes imaging spectropolarimeter using division-of-focal-plane polarimetry and integral field spectroscopy. SCIENTIFIC REPORTS, 7.
• Pacheco, S., Wang, C., Chawla, M. K., Nguyen, M., Baggett, B. K., Utzinger, U., Barnes, C. A., & Liang, R. (2017). High resolution, high speed, long working distance, large field of view confocal fluorescence microscope. SCIENTIFIC REPORTS, 7.
• Pacheco, S., Wang, C., Chawla, M. K., Nguyen, M., Baggett, B. K., Utzinger, U., Barnes, C. A., & Liang, R. (2017). High resolution, high speed, long working distance, large field of view confocal fluorescence microscope. Scientific reports, 7(1), 13349.
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  Confocal fluorescence microscopy is often used in brain imaging experiments, however conventional confocal microscopes are limited in their field of view, working distance, and speed for high resolution imaging. We report here the development of a novel high resolution, high speed, long working distance, and large field of view confocal fluorescence microscope (HL-CFM) with the capability of multi-region and multifocal imaging. To demonstrate the concept, a 0.5 numerical aperture (NA) confocal fluorescence microscope is prototyped with a 3 mm × 3 mm field of view and 12 mm working distance, an array of 9 beams is scanned over the field of view in 9 different regions to speed up the acquisition time by a factor of 9. We test this custom designed confocal fluorescence microscope for future use with brain clarification methods to image large volumes of the brain at subcellular resolution. This multi-region and multi-spot imaging method can be used in other imaging modalities, such as multiphoton microscopes, and the field of view can be extended well beyond 12 mm × 12 mm.
• Salahieh, B., Rodriguez, J. J., Stetson, S., & Liang, R. (2017). Single-image full-focus reconstruction using depth-based deconvolution. OPTICAL ENGINEERING, 56(4).
• Wang, D., Wang, Z., Liang, R., Kong, M., Zhao, J., Zhao, J., Mo, L., & Li, W. (2017). Fast searching measurement of absolute displacement based on submicron-aperture fiber point-diffraction interferometer. OPTICAL MEASUREMENT SYSTEMS FOR INDUSTRIAL INSPECTION X, 10329.
• Wang, Z., Wang, D., Gong, Z., Xu, P., Liang, R., Zhao, J., & Li, W. (2017). Measurement of absolute displacement based on dual-path submicron-aperture fiber point-diffraction interferometer. OPTIK, 140, 802-811.
• Wu, R., Sasian, J., & Liang, R. (2017). Algorithm for designing free-form imaging optics with nonrational B-spline surfaces. APPLIED OPTICS, 56(9), 2517-2522.
• Zhang, J., Luo, H., Liang, R., Zhou, W., Hui, B., & Chang, Z. (2017). PCA-based denoising method for division of focal plane polarimeters. OPTICS EXPRESS, 25(3), 2391-2400.
• Zhang, Y. u., Cheng, H., Wu, R., & Liang, R. (2017). Data processing for point-based in situ metrology of freeform optical surface. OPTICS EXPRESS, 25(12), 13414-13424.
• Zhang, Y. u., Tian, X., & Liang, R. (2017). Fringe-print-through error analysis and correction in snapshot phase-shifting interference microscope. OPTICS EXPRESS, 25(22), 26554-26566.
• Zhu, Z., Yuan, X., Liang, R., & Ma, D. (2017). Free-form surface generation in a double pole coordinate system for off-axis illumination application. APPLIED OPTICS, 56(4), 771-776.
• Feng, Z., Froese, B. D., & Liang, R. (2016). Freeform illumination optics construction following an optimal transport map. APPLIED OPTICS, 55(16), 4301-4306.
• Gao, S., Garcia, M., Edmiston, C., York, T., Marinov, R., Mondal, S. B., Zhu, N., Sudlow, G. P., Akers, W. J., Margenthaler, J. A., Liang, R., Pepino, M., Achilefu, S., & Gruev, V. (2016). A compact bio-inspired visible/NIR imager for image-guided surgery (Conference Presentation). MOLECULAR-GUIDED SURGERY: MOLECULES, DEVICES, AND APPLICATIONS II, 9696.
• Liu, Z., Gray, B. D., Barber, C., Bernas, M., Cai, M., Furenlid, L. R., Rouse, A., Patel, C., Banerjee, B., Liang, R., Gmitro, A. F., Witte, M. H., Pak, K. Y., & Woolfenden, J. M. (2016). Characterization of TCP-1 probes for molecular imaging of colon cancer. JOURNAL OF CONTROLLED RELEASE, 239, 223-230.
• Mu, T., Chen, Z., Pacheco, S., Wu, R., Zhang, C., & Liang, R. (2016). Generation of a controllable multifocal array from a modulated azimuthally polarized beam. OPTICS LETTERS, 41(2), 261-264.
• Mu, T., Chen, Z., Zhang, C., & Liang, R. (2016). Optimal configurations of full-Stokes polarimeter with immunity to both Poisson and Gaussian noise. JOURNAL OF OPTICS, 18(5).
• Mu, T., Chen, Z., Zhang, C., & Liang, R. (2016). Optimal design and performance metric of broadband full-Stokes polarimeters with immunity to Poisson and Gaussian noise. OPTICS EXPRESS, 24(26), 29692-29705.
• Pacheco, S., Zheng, G., & Liang, R. (2016). Reflective Fourier ptychography. JOURNAL OF BIOMEDICAL OPTICS, 21(2).
• Salahieh, B., Rodriguez, J. J., Stetson, S., & Liang, R. (2016). Single-Image Full-Focus Reconstruction Using Depth-Based Deconvolution. Optical Engineering, 56(4), 041302.01-10. doi:10.1117/1.OE.56.4.041302
• Wang, D., & Liang, R. (2016). Simultaneous polarization Mirau interferometer based on pixelated polarization camera. OPTICS LETTERS, 41(1), 41-44.
• Wang, D., Xu, Y., Liang, R., Kong, M., Zhao, J., Zhang, B., & Li, W. (2016). High-precision method for submicron-aperture fiber point-diffraction wavefront measurement. OPTICS EXPRESS, 24(7), 7079-7090.
• Wang, D., Zhang, S., Wu, R., Huang, C. Y., Cheng, H., & Liang, R. (2016). Computer-aided high-accuracy testing of reflective surface with reverse Hartmann test. OPTICS EXPRESS, 24(17), 19671-19681.
• Woolfenden, J. M., Pak, K. Y., Witte, M. H., Gmitro, A. F., Liang, R., Banerjee, B., Patel, C., Rouse, A. R., Furenlid, L. R., Bernas, M., Cai, M., Barber, C., Gray, B. D., & Liu, Z. (2016). Characterization of TCP-1 molecular imaging probes in mouse models with xenografted human colon cancer.. J Control Release, 239, 223-230.
• Wu, R., Hua, H., Benitez, P., Minano, J. C., & Liang, R. (2016). Design of compact and ultra efficient aspherical lenses for extended Lambertian sources in two-dimensional geometry. OPTICS EXPRESS, 24(5), 5078-5086.
• Wu, R., Huang, C. Y., Zhu, X., Cheng, H., & Liang, R. (2016). Direct three-dimensional design of compact and ultra-efficient freeform lenses for extended light sources. OPTICA, 3(8), 840-843.
• Chen, Z., Wang, X., & Liang, R. (2015). RGB-NIR multispectral camera. OPTICS EXPRESS, 22(5), 4985-4994.
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  A multispectral imaging technique with a new CMOS camera is proposed. With a four channel Bayer patterns, the camera can acquire four spectral images simultaneously. We have developed a color correction process to obtain accurate color information, and we have also demonstrated its applications on portrait enhancement, shadow removal, and vein enhancement. (C)2014 Optical Society of America
• Chen, Z., Wang, X., & Liang, R. (2015). Snapshot phase shift fringe projection 3D surface measurement. OPTICS EXPRESS, 23(2), 667-673.
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  We propose a novel snapshot phase shift fringe projection three-dimensional (3D) surface measurement method using polarization-coded light illumination and polarization camera. The light from the light source is split into two beams, one is left circularly polarized and the other is right circularly polarized, to illuminate the object simultaneously. A four-channel division of focal plane (DoFP) polarization camera is employed to capture the light reflected from the object surface. Four images with a phase shift of pi/2 are extracted from the snapshot image and then analyzed to reconstruct a 3D object surface. The proposed method is the first snapshot phase shift fringe projection approach for 3D surface imaging. It is insensitive to motion and has the potential for ultrafast 3D surface imaging. (C) 2015 Optical Society of America
• Feng, Z., Froese, B. D., & Liang, R. (2015). Composite method for precise freeform optical beam shaping. APPLIED OPTICS, 54(31), 9364-9369.
• Feng, Z., Froese, B. D., Huang, C., Ma, D., & Liang, R. (2015). Creating unconventional geometric beams with large depth of field using double freeform-surface optics. APPLIED OPTICS, 54(20), 6277-6281.
• Gao, S., Modal, S., Zhu, N., Liang, R., Achilefu, S., & Gruev, V. (2015). Live Demonstration: A Compact NIR Fluorescence Imaging System Design with Goggle Display for Intraoperative Guidance. 2015 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS), 1910-1910.
• Gao, S., Mondal, S. B., Zhu, N., Liang, R., Achilefu, S., & Gruev, V. (2015). Image overlay solution based on threshold detection for a compact near infrared fluorescence goggle system. JOURNAL OF BIOMEDICAL OPTICS, 20(1).
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  Near infrared (NIR) fluorescence imaging has shown great potential for various clinical procedures, including intraoperative image guidance. However, existing NIR fluorescence imaging systems either have a large footprint or are handheld, which limits their usage in intraoperative applications. We present a compact NIR fluorescence imaging system (NFIS) with an image overlay solution based on threshold detection, which can be easily integrated with a goggle display system for intraoperative guidance. The proposed NFIS achieves compactness, light weight, hands-free operation, high-precision superimposition, and a real-time frame rate. In addition, the miniature and ultra-lightweight light-emitting diode tracking pod is easy to incorporate with NIR fluorescence imaging. Based on experimental evaluation, the proposed NFIS solution has a lower detection limit of 25 nM of indocyanine green at 27 fps and realizes a highly precise image overlay of NIR and visible images of mice in vivo. The overlay error is limited within a 2-mm scale at a 65-cm working distance, which is highly reliable for clinical study and surgical use. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE).
• Gao, S., Mondal, S., Zhu, N., Liang, R., Achilefu, S., & Gruev, V. (2015). A Compact NIR Fluorescence Imaging System with Goggle Display for Intraoperative Guidance. 2015 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS), 1622-1625.
• Huang, C., & Liang, R. (2015). Modeling of surface topography in single-point diamond turning machine. APPLIED OPTICS, 54(23), 6979-6985.
• Katkam, R., Banerjee, B., Huang, C. Y., Zhu, X., Ocampo, L., Kincade, J., & Liang, R. (2015). Compact dual-view endoscope without field obscuration. JOURNAL OF BIOMEDICAL OPTICS, 20(7).
• Liang, R. (2015). Short wavelength and polarized phase shifting fringe projection imaging of translucent objects. OPTICAL ENGINEERING, 53(1).
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  Measuring surface topography of translucent objects with phase shifting fringe projection method is a challenge because of the reduced fringe contrast due to the scattering inside the object. The internal structure also has an impact to the measurement. We present a new phase shifting fringe project imaging method to measure three-dimensional surface shapes of translucent objects. This method employs polarized short wavelength to increase the fringe contrast by reducing the internal scattered light from reaching the camera. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
• Ma, D., Feng, Z., & Liang, R. (2015). Tailoring freeform illumination optics in a double-pole coordinate system. APPLIED OPTICS, 54(9), 2395-2399.
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  We have developed a new method to design freeform illumination optics by introducing a double-pole coordinate system in ray mapping. This method establishes a much more accurate ray mapping by moving the two poles of the spherical coordinate system to the southernmost point of the sphere and overlapping them together. It can reduce surface error and improve illumination uniformity significantly. The residual surface error (RSE) of the freeform lens designed in the double-pole coordinate system is one magnitude smaller than that of the lens designed in the (theta,phi) coordinate system and is only 1/3 of that of the freeform surface designed in the (u, v) coordinate system. (c) 2015 Optical Society of America
• Ma, D., Feng, Z., Wang, C., & Liang, R. (2015). Hybrid freeform TIR optics construction in Cartesian coordinate system: a new composite ray mapping method. FOURTEENTH INTERNATIONAL CONFERENCE ON SOLID STATE LIGHTING AND LED-BASED ILLUMINATION SYSTEMS, 9571.
• Ma, D., Pacheco, S., Feng, Z., & Liang, R. (2015). Non-uniformly sampled grids in double pole coordinate system for freeform reflector construction. NONIMAGING OPTICS: EFFICIENT DESIGN FOR ILLUMINATION AND SOLAR CONCENTRATION XII, 9572.
• Ma, D., Pacheco, S., Wang, C., & Liang, R. (2015). Freeform optics construction with nonuniformly sampled grids in modified double-pole coordinate system. OPTICAL ENGINEERING, 54(12).
• Mondal, S. B., Gao, S., Zhu, N., Sudlow, G. P., Liang, K., Som, A., Akers, W. J., Fields, R. C., Margenthaler, J., Liang, R., Gruev, V., & Achilefu, S. (2015). Binocular Goggle Augmented Imaging and Navigation System provides real-time fluorescence image guidance for tumor resection and sentinel lymph node mapping. SCIENTIFIC REPORTS, 5.
• Mu, T., Zhang, C., & Liang, R. (2015). Demonstration of a snapshot full-Stokes division-of-aperture imaging polarimeter using Wollaston prism array. JOURNAL OF OPTICS, 17(12).
• Mu, T., Zhang, C., Li, Q., & Liang, R. (2015). Achromatization of waveplate for broadband polarimetric system. OPTICS LETTERS, 40(11), 2485-2488.
• Ocampo, L. H., Zhu, X., Kincade, J., Brooling, J., Kisso, B., Lin, M. T., Liang, R., & Banerjee, B. (2015). A Novel Dual-View Probe That Produces a Single Image and Improves Polyp Detection. GASTROENTEROLOGY, 148(4), S583-S583.
• Pacheco, S., Brand, J. F., Zaverton, M., Milster, T., & Liang, R. (2015). Sensitivity analysis and optimization method for the fabrication of one-dimensional beam-splitting phase gratings. OPTICS EXPRESS, 23(9), 11771-11782.
• Pacheco, S., Milster, T., & Liang, R. (2015). Analysis of grating doublets for achromatic beam-splitting. OPTICS EXPRESS, 23(17), 22939-22952.
• Pacheco, S., Salahieh, B., Milster, T. D., Rodriguez, J. J., & Liang, R. (2015). Transfer Function Analysis in Epi-Illumination Fourier Ptychography. Optics Letters, 40(22), 5343-5346.
• Pacheco, S., Salahieh, B., Milster, T., Rodriguez, J. J., & Liang, R. (2015). Transfer function analysis in epi-illumination Fourier ptychography. OPTICS LETTERS, 40(22), 5343-5346.
• Salahieh, B., Rodriguez, J. J., & Liang, R. (2015). Direct superresolution for realistic image reconstruction. OPTICS EXPRESS, 23(20), 26124-26138.
• Salahieh, B., Rodriguez, J. J., Liang, R., Salahieh, B., Rodriguez, J. J., & Liang, R. (2015). Direct Superresolution for Realistic Image Reconstruction. Optics Express, 23(20), 26124-26138. doi:10.1364/OE.23.026124
• Zhu, N., Huang, C., Mondal, S., Gao, S., Huang, C., Gruev, V., Achilefu, S., & Liang, R. (2015). Compact wearable dual-mode imaging system for real-time fluorescence image-guided surgery. JOURNAL OF BIOMEDICAL OPTICS, 20(9).
• Zhu, N., Mondal, S., Gao, S., Achilefua, S., Gruev, V., & Liang, R. (2015). Dual-mode optical imaging system for fluorescence image-guided surgery. OPTICS LETTERS, 39(13), 3830-3832.
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  In this Letter, we present a novel imaging concept that a single imaging system can image different spectral bands with different aperture sizes. It is achieved by using a filter with different transmitted spectral bands in different annular rings as the aperture stop. This concept will enable more efficient system configurations and practical clinical applications. We have demonstrated this concept with a dual-mode near-infrared fluorescence image guided surgical system. (C) 2014 Optical Society of America
• Chatrath, H., Liang, R., Chen, Z., & Banerjee, B. (2014). Polarized Light Imaging for Detection of Aberrant Cryptic Foci (ACF). GASTROENTEROLOGY, 146(5), S523-S523.
• Chen, Z., Wang, X., & Liang, R. (2014). Calibration method of microgrid polarimeters with image interpolation. APPLIED OPTICS, 54(5), 995-1001.
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  Microgrid polarimeters have large advantages over conventional polarimeters because of the snapshot nature and because they have no moving parts. However, they also suffer from several error sources, such as fixed pattern noise (FPN), photon response nonuniformity (PRNU), pixel cross talk, and instantaneous field-of-view (IFOV) error. A characterization method is proposed to improve the measurement accuracy in visible waveband. We first calibrate the camera with uniform illumination so that the response of the sensor is uniform over the entire field of view without IFOV error. Then a spline interpolation method is implemented to minimize IFOV error. Experimental results show the proposed method can effectively minimize the FPN and PRNU. (C) 2015 Optical Society of America
• Chen, Z., Wang, X., Pacheco, S., & Liang, R. (2014). Impact of CCD camera SNR on polarimetric accuracy. APPLIED OPTICS, 53(32), 7649-7656.
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  A comprehensive charge-coupled device (CCD) camera noise model is employed to study the impact of CCD camera signal-to-noise ratio (SNR) on polarimetric accuracy. The study shows that the standard deviations of the measured degree of linear polarization (DoLP) and angle of linear polarization (AoLP) are mainly dependent on the camera SNR. With increase in the camera SNR, both the measurement errors and the standard deviations caused by the CCD camera noise decrease. When the DoLP of the incident light is smaller than 0.1, the camera SNR should be at least 75 to achieve a measurement error of less than 0.01. When the input DoLP is larger than 0.5, a SNR of 15 is sufficient to achieve the same measurement accuracy. An experiment is carried out to verify the simulation results. (C) 2014 Optical Society of America
• Chen, Z., Zhu, N., Pacheco, S., Wang, X., & Liang, R. (2014). Single camera imaging system for color and near-infrared fluorescence image guided surgery. BIOMEDICAL OPTICS EXPRESS, 5(8), 2791-2797.
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  Near-infrared (NIR) fluorescence imaging systems have been developed for image guided surgery in recent years. However, current systems are typically bulky and work only when surgical light in the operating room (OR) is off. We propose a single camera imaging system that is capable of capturing NIR fluorescence and color images under normal surgical lighting illumination. Using a new RGB-NIR sensor and synchronized NIR excitation illumination, we have demonstrated that the system can acquire both color information and fluorescence signal with high sensitivity under normal surgical lighting illumination. The experimental results show that ICG sample with concentration of 0.13 mu M can be detected when the excitation irradiance is 3.92 mW/cm(2) at an exposure time of 10 ms. (C) 2014 Optical Society of America
• Huang, C., Youngworth, R., & Liang, R. (2014). Tolerancing sub-aperture regions of optical surfaces using circular and elliptical Zernike polynomials. OPTICAL SYSTEM ALIGNMENT, TOLERANCING, AND VERIFICATION VIII, 9195.
• Ma, D., Feng, Z., & Liang, R. (2014). Deconvolution method in designing freeform lens array for structured light illumination. APPLIED OPTICS, 54(5), 1114-1117.
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  We have developed a deconvolution freeform lens array design approach to generate high-contrast structured light illumination patterns. This method constructs the freeform lens array according to the point response obtained by deconvoluting the prescribed illumination pattern with the blur response of the extended light source. This design method is more effective in designing a freeform lens array to achieve accurate structured light patterns. For a sinusoidal fringe pattern, the contrast ratio can be as high as 97%, compared to 62% achieved by the conventional ray mapping method. (C) 2015 Optical Society of America
• Ma, D., Feng, Z., & Liang, R. (2014). Freeform illumination lens design using composite ray mapping. APPLIED OPTICS, 54(3), 498-503.
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  We develop a new ray mapping approach to address the surface error and hot spot issues in designing a freeform total internal reflection (TIR) lens for nonrotational uniform illumination. Our proposed ray mapping approach partitions the source intensity distribution in the peripheral regions using the traditional spherical coordinate system to design the freeform TIR surfaces and in the central regions using the modified spherical coordinate system to design the freeform refractive surface. This new design method will reduce the surface error in the current ray mapping methods, therefore improving the illumination uniformity significantly. In addition, the freeform lens designed with this approach is much more robust than the lenses designed using other ray mapping methods. (C) 2015 Optical Society of America
• Salahieh, B., Rodriguez, J. J., & Liang, R. (2014). Multi-Polarization Fringe Projection Imaging for High Dynamic Range Objects. Optics Express, 22(8), 10064-10071. doi:10.1364/OE.22.010064
• Zhao, M., Zhang, H., Li, Y., Ashok, A., Liang, R., Zhou, W., & Peng, L. (2014). Cellular imaging of deep organ using two-photon Bessel light-sheet nonlinear structured illumination microscopy. BIOMEDICAL OPTICS EXPRESS, 5(5), 1296-1308.
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  In vivo fluorescent cellular imaging of deep internal organs is highly challenging, because the excitation needs to penetrate through strong scattering tissue and the emission signal is degraded significantly by photon diffusion induced by tissue-scattering. We report that by combining two-photon Bessel light-sheet microscopy with nonlinear structured illumination microscopy (SIM), live samples up to 600 microns wide can be imaged by light-sheet microscopy with 500 microns penetration depth, and diffused background in deep tissue light-sheet imaging can be reduced to obtain clear images at cellular resolution in depth beyond 200 microns. We demonstrate in vivo two-color imaging of pronephric glomeruli and vasculature of zebrafish kidney, whose cellular structures located at the center of the fish body are revealed in high clarity by two-color two-photon Bessel light-sheet SIM. (C) 2014 Optical Society of America
• Zhu, N., Mondal, S., Gao, S., Achilefu, S., Gruev, V., & Liang, R. (2014). Engineering light-emitting diode surgical light for near-infrared fluorescence image-guided surgical systems. JOURNAL OF BIOMEDICAL OPTICS, 19(7).
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  The near-infrared (NIR) fluorescence signal in the 700 to 900 nm from molecular probes used in fluorescence image-guided surgery (FIGS) is usually weak compared to the NIR component from white light-emitting diode surgical light, which is typically switched off during FIGS to enhance the molecular fluorescence contrast of the image. We propose a simple solution to this critical issue in FIGS by removing NIR light from surgical light with a low cost commercial 3M cool mirror film 330. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
• Guoqiang, L. i., & Liang, R. (2013). Introduction to the BODA 2013 feature issue. Biomedical Optics Express, 4(11), 2507-.
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  Abstract: The guest editors introduce a feature issue containing papers based on research presented at the BODA 2013 meeting. © 2013 Optical Society of America.
• Loock, H., Liang, R., & Pedrini, G. (2013). Applied industrial optics. Applied Optics, 52(4), AIO1.
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  Abstract: The annual symposium of Applied Industrial Optics has since its inception in 2010 attracted a large number of industrial researchers, as well as academic researchers who are considering commercialization of their work. To make their work more accessible, the past participants of the symposium were invited to contribute to this special issue of Applied Optics. This current issue therefore focuses on optical techniques and measurements that are either already applied in an industrial setting, have the strong potential to be commercially viable, or have been developed by industrial researchers to address their specific problems. © 2013 Optical Society of America.
• Salahieh, B., Chen, Z., Rodriguez, J. J., & Liang, R. (2013). Multi-polarization fringe projection imaging for high dynamic range objects. OPTICS EXPRESS, 22(8), 10064-10071.
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  Traditional fringe-projection three-dimensional (3D) imaging techniques struggle to estimate the shape of high dynamic range (HDR) objects where detected fringes are of limited visibility. Moreover, saturated regions of specular reflections can completely block any fringe patterns, leading to lost depth information. We propose a multi-polarization fringe projection (MPFP) imaging technique that eliminates saturated points and enhances the fringe contrast by selecting the proper polarized channel measurements. The developed technique can be easily extended to include measurements captured under different exposure times to obtain more accurate shape rendering for very HDR objects. (C) 2014 Optical Society of America
• Liang, R., Wong, V., & McLaughlin, P. (2008). Optical design of a multimodal imaging system. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 6849.
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  Abstract: A multimodal imaging system has been developed for tooth tissue imaging. This imaging system is designed to obtain one or more two-dimensional images of the tooth tissue, and those two-dimensional images are rendered with advanced algorithms to provide a high-contrast image. This system combines polarized reflectance imaging, fluorescence imaging, and optical coherence tomography (OCT) imaging. The imaging system design, as well as some experimental results, will be discussed in the presentation.
• Liang, R., Wong, V., Marcus, M., Burns, P., & McLaughlin, P. (2007). Multimodal imaging system for dental caries detection. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 6425.
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  Abstract: Dental caries is a disease in which minerals of the tooth are dissolved by surrounding bacterial plaques. A caries process present for some time may result in a caries lesion. However, if it is detected early enough, the dentist and dental professionals can implement measures to reverse and control caries. Several optical, nonionized methods have been investigated and used to detect dental caries in early stages. However, there is not a method that can singly detect the caries process with both high sensitivity and high specificity. In this paper, we present a multimodal imaging system that combines visible reflectance, fluorescence, and Optical Coherence Tomography (OCT) imaging. This imaging system is designed to obtain one or more two-dimensional images of the tooth (reflectance and fluorescence images) and a three-dimensional OCT image providing depth and size information of the caries. The combination of two- and three-dimensional images of the tooth has the potential for highly sensitive and specific detection of dental caries.
• Mu, T., Zhang, C., Li, Q., & Liang, R. (2007). Error analysis of single-snapshot full-Stokes division-of-aperture imaging polarimeters. OPTICS EXPRESS, 23(8), 10822-10835.
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  Single-snapshot full-Stokes imaging polarimetry is a powerful tool for the acquisition of the spatial polarization information in real time. According to the general linear model of a polarimeter, to recover full Stokes parameters at least four polarimetric intensities should be measured. In this paper, four types of single-snapshot full-Stokes division-of-aperture imaging polarimeter with four subapertures are presented and compared, with maximum spatial resolution for each polarimetric image on a single area-array detector. By using the error propagation theories for different incident states of polarization, the performance of four polarimeters are evaluated for several main sources of error, including retardance error, alignment error of retarders, and noise perturbation. The results show that the configuration of four 132 degrees retarders with angular positions of (+/- 51.7 degrees, +/- 15.1 degrees) is an optimal choice for the configuration of four subaperture single-snapshot full-Stokes imaging polarimeter. The tolerance and uncertainty of this configuration are analyzed. (C)2015 Optical Society of America
• Pacheco, S., & Liang, R. (2007). Snapshot, reconfigurable multispectral and multi-polarization telecentric imaging system. OPTICS EXPRESS, 22(13), 16377-16385.
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  A reconfigurable telecentric imaging system that can simultaneously capture multispectral and multi-polarization information in a single snapshot is demonstrated. The proposed design utilizes a telecentric imaging objective and a light pipe for image multiplexing. An array of filters is used to filter each of the multiplexed images at an intermediate image plane. In this paper, we will discuss the system configuration and present the experimental results. (C)2014 Optical Society of America
• Rongguang, L. (2007). High numerical aperture line scanning system. Proceedings of SPIE - The International Society for Optical Engineering, 6668.
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  Abstract: In order to scan a line, the scanning optics usually employs either NSG's SELFOC lens or a 1:1 lenslet array. Each of these two methods has its limitation. The SELFOC lens' numerical aperture (NA) is low, which limits its light-collection efficiency. A 1:1 lenslet array can have a high NA, but its resolution along the scanning direction is low, which means it is not suitable for 2-D scanning. In this paper, line scan optics with a high NA will be discussed. Unlike the above-mentioned methods, this method has the same high resolution in both line and scan directions. It has a 1:-1 (preferred 1:

Proceedings Publications

• Liang, R., Wong, V., McLaughlin, P., Raghavachari, R., & Liang, R. (2015). Optical design of a multimodal imaging system. In DESIGN AND QUALITY FOR BIOMEDICAL TECHNOLOGIES, 6849, U42-U50.
  More info

  A multimodal imaging system has been developed for tooth tissue imaging. This imaging system is designed to obtain one or more two-dimensional images of the tooth tissue, and those two-dimensional images are rendered with advanced algorithms to provide a high-contrast image. This system combines polarized reflectance imaging, fluorescence imaging, and optical coherence tomography (OCT) imaging. The imaging system design, as well as some experimental results, will be discussed in the presentation.
• Mondal, S. B., Gao, S., Zhu, N., Liu, Y., Sudlow, G. P., Akers, W. J., Liang, R., Gruev, V., Achilefu, S., Raghavachari, R., & Liang, R. (2015). Intraoperative imaging and fluorescence image guidance in oncologic surgery using a wearable fluorescence goggle system. In DESIGN AND QUALITY FOR BIOMEDICAL TECHNOLOGIES VII, 8936.
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  We have developed a wearable, fluorescence goggle based system for intraoperative imaging of tumors and image guidance in oncologic surgery. Our system can detect fluorescence from cancer selective near infra-red (NIR) contrast agent, facilitating intraoperative visualization of surgical margins and tumors otherwise not apparent to the surgeon. The fluorescence information is displayed directly to the head mounted display (HMD) of the surgeon in real time, allowing unhindered surgical procedure under image guidance. This system has the potential of improving surgical outcomes in oncologic surgery and reduce the chances of cancer recurrence.
• Salahieh, B., Rodriguez, J. J., Liang, R., Salahieh, B., Rodriguez, J. J., & Liang, R. (2015, June 7-11). Computational Depth-Variant Deconvolution Technique for Full-Focus Imaging. In Imaging and Applied Optics 2015: Computational Optical Sensing and Imaging, CT3F.5.1-3.
• Salahieh, B., Rodriguez, J. J., Liang, R., Salahieh, B., Rodriguez, J. J., & Liang, R. (2015, June 7-11). Direct Superresolution Technique for Solving a Miniature Multi-Shift Imaging System. In Imaging and Applied Optics 2015: Computational Optical Sensing and Imaging, JW3A.5.1-3.
• Liang, R., Koshel, R., & Gregory, G. (2014). High numerical aperture line scanning system - art. no. 66680I. In NOVEL OPTICAL SYSTEMS DESIGN AND OPTIMIZATION X, 6668, I6680-I6680.
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  In order to scan a line, the scanning optics usually employs either NSG's SELFOC lens or a 1: 1 lenslet array. Each of these two methods has its limitation. The SELFOC lens' numerical aperture (NA) is low, which limits its light-collection efficiency. A 1: 1 lenslet array can have a high NA, but its resolution along the scanning direction is low, which means it is not suitable for 2-D scanning. In this paper, line scan optics with a high NA will be discussed. Unlike the above-mentioned methods, this method has the same high resolution in both line and scan directions. It has a 1:-1 (preferred 1:
• Liang, R., Wong, V., Marcus, M., Burns, P., McLaughlin, P., Rechmann, P., & Fried, D. (2014). Multimodal imaging system for dental caries detection - art. no. 642502. In Lasers in Dentistry XIII, 6425, 42502-42502.
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  Dental caries is a disease in which minerals of the tooth are dissolved by surrounding bacterial plaques. A caries process present for some time may result in a caries lesion. However, if it is detected early enough, the dentist and dental professionals can implement measures to reverse and control caries. Several optical, nonionized methods have been investigated and used to detect dental caries In early stages. However, there is not a method that can singly detect the caries process with both high sensitivity and high specificity. In this paper, we present a multimodal imaging system that combines visible reflectance, fluorescence, and Optical Coherence Tomography (OCT) imaging. This imaging system is designed to obtain one or more two-dimensional images of the tooth (reflectance and fluorescence images) and a three-dimensional OCT image providing depth and size information of the caries. The combination of two- and three-dimensional images of the tooth has the potential for highly sensitive and specific detection of dental caries.
• Pacheco, S., Liang, R., Raghavachari, R., & Liang, R. (2014). Multifocal Confocal Spectral Microscope. In Design and Quality for Biomedical Technologies VIII, 9315.
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  The concept and design for a multifocal confocal spectral microscope is discussed. The multifocal confocal spectral microscope utilizes an array of focal beams to capture to the spectrum of multiple points simultaneously. Experimental results from a 3x3 multifocal confocal spectral microscope with spectral resolution less than 2 nm are shown.
• Pacheco, S., Milster, T., Zhou, J., Liang, R., Raghavachari, R., & Liang, R. (2008). System Design and Evaluation of the Array Confocal Fluorescence Microscope. In DESIGN AND QUALITY FOR BIOMEDICAL TECHNOLOGIES VII, 8936.
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  The scanning speed for conventional confocal fluorescence imaging systems is limited due to several factors. To improve the speed of scanning, we develop an array confocal fluorescence microscope (ACFM) that can image large 3D volumes faster than conventional confocal microscopes over a large field of view (FOV). This paper will discuss the design and evaluation of the array confocal fluorescence microscope.

Reviews

• Mondal, S. B., Gao, S., Zhu, N., Liang, R., Gruev, V., Achilefu, S., Pomper, M., & Fisher, P. (2014. Real-Time Fluorescence Image-Guided Oncologic Surgery(pp 171-211).
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  Medical imaging plays a critical role in cancer diagnosis and planning. Many of these patients rely on surgical intervention for curative outcomes. This requires a careful identification of the primary and microscopic tumors, and the complete removal of cancer. Although there have been efforts to adapt traditional-imaging modalities for intraoperative image guidance, they suffer from several constraints such as large hardware footprint, high-operation cost, and disruption of the surgical workflow. Because of the ease of image acquisition, relatively low-cost devices and intuitive operation, optical imaging methods have received tremendous interests for use in real-time image-guided surgery. To improve imaging depth under low interference by tissue autofluorescence, many of these applications utilize light in the near-infrared (NIR) wavelengths, which is invisible to human eyes. With the availability of a wide selection of tumor-avid contrast agents, advancements in imaging sensors, electronic and optical designs, surgeons are able to combine different attributes of NIR optical imaging techniques to improve treatment outcomes. The emergence of diverse commercial and experimental image guidance systems, which are in various stages of clinical translation, attests to the potential high impact of intraoperative optical imaging methods to improve speed of oncologic surgery with high accuracy and minimal margin positivity.

Others

• Erdmann, A., Liang, R., Sezginer, A., & Smith, B. (2014, DEC 1). Advances in lithography: introduction to the feature. APPLIED OPTICS.
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  Optical projection lithography has been the key technology for the ongoing miniaturization in semiconductor devices over the past 40 years. This issue features original research covering mask and image modeling methods and computational techniques for various inverse problems in advanced lithography, including source and mask optimization, wavefront retrieval, and design of Fresnel lenses. (C) 2014 Optical Society of America
• Erdmann, A., Liang, R., Sezginer, A., & Smith, B. (2014, DEC). Advances in lithography: introduction to the feature. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION.
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  Optical projection lithography has been the key technology for the ongoing miniaturization in semiconductor devices over the past 40 years. This issue features original research covering mask and image modeling methods and computational techniques for various inverse problems in advanced lithography, including source and mask optimization, wavefront retrieval, and design of Fresnel lenses. (C) 2014 Optical Society of America
• Li, G., & Liang, R. (2014, NOV 1). Introduction to the BODA 2013 feature issue. BIOMEDICAL OPTICS EXPRESS.
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  The guest editors introduce a feature issue containing papers based on research presented at the BODA 2013 meeting. (C) 2013 Optical Society of America
• Zhang, S., Liang, R., & Yang, L. (2014, NOV). High-Speed 3-D Optical Metrology and Applications. OPTICAL ENGINEERING.