Mahmoud Fallahi

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Journals/Publications

• Gottesman, N., Slocum, M., Sevison, G., Wolf, M., Lukowski, M., Hessenius, C., Fallahi, M., & Bedford, R. (2024). Infrared Vertical External Cavity Surface Emitting Laser Threshold Magnetometer. Applied Physics Letters, 124, 091110-1 -9091110-5. doi:Doi.org/10.1063/5.0174282
• Gottesman, N., Lukowski, M., Meyer, J., Hessenius, C., Wright, E., & Fallahi, M. (2022). Intra-Cavity Astigmatic Mode Converting VECSEL. IEEE PHOTONICS JOURNAL, 14(4), 1538906.
• Meyer, J. T., Lukowski, M., Hessenius, C., Wright, E. M., & Fallahi, M. (2021). All-intracavity fourth harmonic generation in a passively mode locked VECSEL for ultrafast UV emission. Optics Communications, 499, 127255. doi:doi.org/10.1016/j.optcom.2021.127255
• Meyer, J., Lukowski, M., Hessenius, C., Wright, E., & Fallahi, M. (2020). High peak power, sub-ps green emission in a passively mode locked W-cavity VECSEL. Optics Express, 28(4), 5794-5800.
• Lukowski, M., Meyer, J., Hessenius, C., Wright, E., & Fallahi, M. (2019). High-Power High Order Hermite-Gaussian and Laguerre-Gaussian Beams from Vertical External Cavity Surface Emitting Lasers. IEEE Journal of Selected Topics in Quantum Electronics, 5, 1500406.
• Lukowski, M. L., Hessenius, C., Meyer, J. T., Wright, E. M., & Fallahi, M. (2018). High power two-color orbital angular momentum beam generation using vertical external cavity surface emitting lasers. APPLIED PHYSICS LETTERS, 112(4).
• Lukowski, M. L., Meyer, J. T., Hessenius, C., Wright, E. M., & Fallahi, M. (2017). Generation of high-power spatially structured beams using vertical external cavity surface emitting lasers. OPTICS EXPRESS, 25(21), 25504-25514.
• Lukowski, M., Hessenius, C., Meyer, J., Wright, E., & Fallahi, M. (2017). Generation of high-power spatially structured beams using vertical external cavity surface emitting lasers. Optics Express, 25(21), 25504-25514.
• Lukowski, M., Hessenius, C., Bedford, R., & Fallahi, M. (2015). Tunable type II intracavity difference frequency generation at 5.4 mu m in a two chip vertical external cavity surface emitting laser. OPTICS LETTERS, 40(17), 4174-4177.
• Fallahi, M., Hessenius, C., & Lukowski, M. (2013). Recent developments in high-power two-wavelength vertical external-cavity surface-emitting lasers. Proceedings of SPIE - The International Society for Optical Engineering, 8631.
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  Abstract: Two-color, high-power, tunable lasers are highly beneficial for the generation of new wavelengths through various nonlinear methods. Vertical external cavity surface emitting lasers (VECSEL) are particularly flexible for intracavity wavelength control. We report a novel VECSEL cavity capable of generation high-power, tunable, two-color generation. The laser employs overlapping VECSEL cavities in a two-chip T-shape cavity configuration which uses a polarizing beam splitter/combiner to fold one cavity and thus allows for two-color orthogonally polarized high power outputs. The tunable collinear, orthogonally polarized two-color is ideal for type II nonlinear conversion. A continuous wave (CW) output power in excess of 13 W for the two-color emissions was demonstrated to be the sum of the output from each of the overlapped cavities. In a high Q cavity, birefringent filters were used to facilitate tunability, and wavelength separation was varied from 35 nm to 52 nm. In a modified T-Cavity configuration, high power intracavity type-II sum frequency generation resulted in tunable blue-green emission with more than 750 mW output. By selecting identical or different chips in the cavity, the wavelength separation and tuning can cover a wide range from zero to several hundreds of nm opening doors for broad mid- to far-infrared applications. © 2013 SPIE.
• Hessenius, C., Lukowski, M., & Fallahi, M. (2013). Tunable type II intracavity sum-frequency generation in a two chip collinear vertical external cavity surface emitting laser. Optics Letters, 38(5), 640-642.
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  PMID: 23455250;Abstract: We report on the generation and experimental demonstration of intracavity type II sum-frequency generation (SFG) in a two chip InGaAs/GaAs vertical external cavity surface emitting laser cavity. The demonstrated two-chip cavity generates two orthogonally polarized, independently tunable, high-intensity intracavity lasing modes at different colors. Using a lithium triborate nonlinear crystal in the common collinear folded cavity region, high output power in the blue-green band is generated. Wavelength tuning with CW output powers in excess of 750 mW is demonstrated. By independent wavelength tuning of each fundamental color, tunable SFG output around 490 nm is reported. © 2013 Optical Society of America.
• Hessenius, C., Lukowski, M., & Fallahi, M. (2012). High-power tunable two-wavelength generation in a two chip co-linear T-cavity vertical external-cavity surface-emitting laser. Applied Physics Letters, 101(12).
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  Abstract: We report the design and experimental results of a two chip co-linear T-cavity vertical external cavity surface emitting laser (VECSEL) capable of generating two continuously tunable orthogonally polarized lasing wavelengths. A polarizing beamsplitter is used to overlap two VECSEL cavities thus generating high-power intra-cavity two-wavelength generation ideal for type-II nonlinear frequency conversion. Nearly equal power at each wavelength with a combined dual-wavelength CW output power in excess of 13 W was observed. In a high Q cavity, the wavelength separation was tuned from 35 nm to 52 nm by using birefringent filters in regions where each wavelength lases independently of the other. © 2012 American Institute of Physics.
• Borgentun, C., Hessenius, C., Bengtsson, J., Fallahi, M., & Larsson, A. (2011). Widely tunable high-power semiconductor disk laser with nonresonant AR-assisted gain element on diamond heat spreader. IEEE Photonics Journal, 3(5), 946-953.
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  Abstract: We report on an optically pumped semiconductor disk laser with a wide wavelength tuning range and a high peak output power. This was achieved using a combination of efficient thermal management and a broadband gain element (GE) with carefully engineered spectral gain characteristics. For heat removal, a flip-chip bonding scheme on diamond was used. To provide high active mirror reflectance over a large wavelength region, the layered structure of the GE formed a nonresonant subcavity assisted by an antireflective structure. A peak output power of more than 7.5 W and a tuning range of 32 nm around the center wavelength of 995 nm were obtained. © 2009 IEEE.
• Greenlee, C., Luo, J., Leedy, K., Bayraktaroglu, B., Norwood, R. A., Fallahi, M., Jen, A. K., & Peyghambarian, N. (2011). Electro-optic polymer spatial light modulator based on a Fabry-Perot interferometer configuration. Optics Express, 19(13), 12750-12758.
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  PMID: 21716517;Abstract: A spatial light modulator (SLM) based on a Fabry-Perot interferometer configuration has been fabricated and tested. The Fabry-Perot spacer layer is a thin film of the SEO100 electro-optic polymer which serves as the nonlinear medium. Measurement results demonstrate the modulation of multiple pixels operating simultaneously at frequencies ranging from 300 kHz to 800 kHz which is significantly faster than SLMs based on liquid crystal and digital micromirror device technology. An average modulation contrast of 50% for all pixels is achieved with a drive voltage of 70 Vrms at 100 kHz. Microwave speeds and CMOS compatibility are feasible with improved transmission line and cavity design. © 2011 Optical Society of America.
• Greenlee, C., Guilmo, A., Opadeyi, A., Himmelhuber, R., Norwood, R. A., Fallahi, M., Luo, J., Huang, S., Zhou, X., Jen, A. K., & Peyghambarian, N. (2010). Mach-Zehnder interferometry method for decoupling electro-optic and piezoelectric effects in poled polymer films. Applied Physics Letters, 97(4).
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  Abstract: A Mach-Zehnder interferometer (MZI) is utilized to decouple the electro-optic and piezoelectric tensor effects occurring in a poled polymer film. This method has significant advantages over the commonly used Teng-Man reflection ellipsometry technique by allowing for the independent determination of the Pockel's coefficients r13 and r33 and the piezoelectric coefficient d33. The r33 value of a guest host polymer that consists of AJLZ53 amorphous polycarbonate was found to be 122.69 pm/V and 123.03 pm/V using the MZI and reflection ellipsometry method, respectively. The r33 data fits well to the dispersion of the second order susceptibility tensor based on the two-level model approximation. © 2010 American Institute of Physics.
• Greenlee, C., Guilmo, A., Opadeyi, A., Himmelhuber, R., Norwood, R. A., Fallahi, M., Luo, J., Huang, S., Zhou, X., Jen, A. K., & Peyghambarian, N. (2010). Mach-Zehnder interferometry method for decoupling electro-optic and piezoelectric tensor components in poled polymer films. Proceedings of SPIE - The International Society for Optical Engineering, 7774.
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  Abstract: A Mach-Zehnder interferometer (MZI) is used to decouple the electro-optic (EO) and piezoelectric tensor components for a poled polymer film. In the past those using the MZI method failed to take into account the piezoelectric contribution in the polymer which can lead to erroneous EO coefficient data. The typical poled sample of polymer sandwiched between ITO glass and gold that was developed for the popular Teng-Man reflection ellipsometry method is used, providing for easy comparison with that method. The sample serves as a mirror in one arm of the interferometer with the gold side facing the beam for measuring the piezoelectric modulation and the glass side facing the beam to measure the coupled piezoelectric and EO modulation. Optical biasing in the reference arm allows for the baseline and modulated contrast of the system to be measured from which the tensor components are calculated. This method has the advantage over the reflection ellipsometry method of allowing for the independent determination of the Pockel's coefficients r13 and r33 and the piezoelectric coefficient d33. The r33 value of a guest host polymer that consists of AJLZ53/amorphous polycarbonate (APC) was found to be 122.7 pm/V and 123.0 pm/V for the MZI and reflection ellipsometry method respectively. The r33 data fits well to the dispersion of the second order susceptibility tensor χ333(2) based on the two-level model approximation. Measurements were done from 100 Hz to 100 kHz with the results showing that at higher frequencies the mechanical effects in the sample are negligible and modulation is almost entirely due to the EO effect, as expected. © 2010 SPIE.
• Zhang, H., Fallahi, M., Pau, S., Norwood, R. A., & Peyghambarian, N. (2010). Solar powered wireless sensor systems for border security. Proceedings of SPIE - The International Society for Optical Engineering, 7666.
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  Abstract: A secure border necessitates the development of new technology for remote sensing and surveillance. We investigate and develop wireless sensor network systems consisting of spatially distributed sensor nodes that can monitor various environmental parameters including temperature, humidity, motion, and vibration, etc. The sensors, nodes and transceivers have low-power consumption and are powered by solar energy so that the systems can work over long time periods with minimal human intervention and maintenance. This paper presents the technology development, wireless sensor integration, power management, and communication architecture, as well as a demonstration of environmental monitoring. © 2010 Copyright SPIE - The International Society for Optical Engineering.
• Gan, H., Greenlee, C., Sheng, C., Norwood, R. A., Fallahi, M., Wang, S., Lin, W., Yamamoto, M., Mohanalingam, K., & Peyghambarian, N. (2008). Near-resonance electro-optic activity enhancement and improved modulation performance for polymer based Fabry-Ṕrot interferometers. Applied Physics Letters, 92(20).
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  Abstract: Fabry-Ṕrot interferometers (FPIs) are designed to work near and off the absorption resonance of an electro-optic (EO) polymer. The near-resonance EO activity (EO coefficient r13 ∼25.4 pmV at ∼1086 nm) is enhanced over that off resonance (r13 ∼9.0 pmV at ∼1526 nm). The full width at half maximum of the FPI transmission band is ∼16 nm near resonance compared to ∼22 nm off resonance. The modulation performance can, therefore, be improved with a modulation ratio increased to ∼78% near resonance (at 1064 nm) from ∼19% off resonance (at 1520 nm). The modulation speed is approximately megahertz and can be increased to greater than gigahertz with improved circuit design. © 2008 American Institute of Physics.
• Fallahi, M. (2007). Hybrid organic-inorganic for low-cost photonics integration. Proceedings of 2007 9th International Conference on Transparent Optical Networks, ICTON 2007, 1, 234-235.
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  Abstract: Hybrid organic-inorganic sol-gel materials are attractive for their process simplicity, optical properties. In this talk the recent developments in hybrid sol-gel integrated optics and electro-optical components including, splitters, tunable filters and modulators will be presented. © 2007 IEEE.
• Gan, H., Zhang, H., DeRose, C. T., Norwood, R. A., Fallahi, M., Luo, J., Jen, A. K., Liu, B., Ho, S., & Peyghambarian, N. (2007). Optical modulation from an electro-optic polymer based hybrid Fabry-Pérot étalon using transparent conducting oxides. Proceedings of SPIE - The International Society for Optical Engineering, 6470.
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  Abstract: Fabry-Pérot étalons using electro-optic (EO) organic materials can be used for devices such as tunable filters and spatial light modulators (SLM's) for wavelength division multiplexing (WDM) communication systems1-5 and ultrafast imaging systems. For these applications the SLM's need to have: (i) low insertion loss, (ii) high speed operation, and (iii) large modulation depth with low drive voltage. Recently, there have been three developments which together can enhance the SLM performance to a higher level. First, low loss distributed Bragg reflector (DBR) mirrors are now used in SLM's to replace thin metal mirrors, resulting in reduced transmission loss, high reflectivity (>99%) and high finesse. Second, EO polymer materials have shown excellent properties for wide bandwidth optical modulation for information technology due to their fabrication flexibility, compatibility with high speed operation, and large EO coefficients at telecommunication wavelengths. For instance, the EO polymer AJL8/APC (AJL8: nonlinear optical chromophore, and APC: amorphous polycarbonate has recently been incorporated into waveguide modulators and achieved good performance for optical modulation. Finally, very low loss transparent conducting oxide (TCO) electrodes have drawn increasing attention for applications in optoelectronic devices. Here we will address how the low loss indium oxide (In2O3) electrodes with an absorption coefficient ∼1000/cm and conductivity ∼204 S/cm can help improve the modulation performance of EO polymer Fabry-Pérot étalons using the advanced electro-optic (EO) polymer material (AJL8/APC). A hybrid etalon structure with one highly conductive indium tin oxide (ITO) electrode outside the etalon cavity and one low-absorption In 2O3 electrode inside etalon cavity has been demonstrated. High finesse (∼234), improved effective applied voltage ratio (∼0.25), and low insertion loss (∼4 dB) have been obtained. A 10 dB isolation ratio and ∼10% modulation depth at 200 kHz with only 5 V applied voltage have been achieved. These results indicate that such etalons are very promising candidates for ultrafast spatial light modulation in information technology.
• Norwood, R. A., Derose, C., Enami, Y., Gan, H., Greenlee, C., Himmelhuber, R., Kropachev, O., Loychik, C., Mathine, D., Merzylak, Y., Fallahi, M., & Peyghambarian, N. (2007). Hybrid sol-gel electro-optic polymer modulators: Beating the drive voltage/loss tradeoff. Journal of Nonlinear Optical Physics and Materials, 16(2), 217-230.
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  Abstract: There has been great progress in the development of electro-optic (EO) polymers with exceptionally high r 33 coefficients, with values ranging from 100-400 pm/V now being reported for single layer electro-optic polymer films. While this enables the fabrication of EO modulators with sub-volt operation, it is also necessary to make devices with acceptably low insertion loss (
• DeRose, C. T., Enami, Y., Loychik, C., Norwood, R. A., Mathine, D., Fallahi, M., Peyghambarian, N., Luo, J. D., Jen, A. K., Kathaperumal, M., & Yamamoto, M. (2006). Pockel's coefficient enhancement of poled electro-optic polymers with a hybrid organic-inorganic sol-gel cladding layer. Applied Physics Letters, 89(13).
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  Abstract: Ultraefficient poling of electro-optic polymers is reported using an organically modified sol-gel cladding layer. This poling technique has resulted in a Pockel's coefficient enhancement of up to a factor of 2.5, going from 26 pm/V when poled without a sol-gel cladding to 65 pm/V when optimally poled with a sol-gel cladding. The poling process directly applies to a previously reported hybrid electro-optic polymer/sol-gel waveguide modulator and may have applications in other poled polymer based devices. © 2006 American Institute of Physics.
• Fallahi, M., Gan, H., Derose, C., Norwood, R., Peyghambarian, N., Luo, J., Chen, B., & Jen, A. (2006). Tunable Fabry-Perot filters using electro-optic hybrid sol-gel. 2006 European Conference on Optical Communications Proceedings, ECOC 2006.
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  Abstract: We report on the development of a tunable Fabry-Perot filter using an electro-optic hybrid organic-inorganic incorporated in highly reflective distributed Bragg reflector (DBR) mirrors. Large tunability (>0.7 nm/V) and high finesse (> 200) have been obtained.
• Gan, H., Zhang, H., Derose, C. T., Norwood, R. A., Fallahi, M., Luo, J., Jen, A. K., Liu, B., Ho, S., & Peyghambarian, N. (2006). Hybrid Fabry-Ṕrot ́talon using an electro-optic polymer for optical modulation. Applied Physics Letters, 89(14).
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  Abstract: The authors present a Fabry-Ṕrot ́talon using an electro-optic (EO) polymer material as the nonlinear medium. The two electrodes used to apply voltage across the EO polymer include an indium tin oxide electrode outside the ́talon cavity and a low-absorption indium oxide electrode inside the ́talon cavity. High finesse (∼234) and a low insertion loss (∼4 dB) have been obtained. An isolation ratio of 10 dB and ∼10% modulation depth at 200 kHz with 5 V applied voltage have been achieved. These results indicate that EO polymer ́talons are promising as spatial light modulators for information technology. © 2006 American Institute of Physics.
• Gan, H., Zhang, H., Derose, C. T., Norwood, R. A., Peyghambarian, N., Fallahi, M., Luo, J., Chen, B., & Jen, A. K. (2006). Low drive voltage Fabry-Pérot étalon device tunable filters using poled hybrid sol-gel materials. Applied Physics Letters, 89(4).
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  Abstract: Nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Pérot étalon devices (ED's) using highly reflective distributed Bragg reflector mirrors. Étalon structures with indium tin oxide electrodes outside the ED cavity have been applied to reduce absorptive loss. Large tunability (∼0.75 nm/V), high finesse (∼235), and wide tunable range (>50 nm) have been obtained. A transmitted light intensity isolation ratio of ∼35 dB at ∼1550 nm has been achieved at a low drive voltage of 10 V. The electro-optic effect and inverse piezoelectric effect are discussed. The results indicate that such hybrid sol-gel ED's are promising candidates for tunable filters in wavelength division multiplexing communication systems. © 2006 American Institute of Physics.
• Zhang, H., Dong, L. u., & Fallahi, M. (2006). Nonlinear optical and electro-optic properties of hybrid sol-gels doped with organic chromophores. Optical Materials, 28(8-9), 992-999.
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  Abstract: This paper reports a systematic investigation on the nonlinear and electro-optic properties of hybrid sol-gel doped with azo-type chromophores. The host is based on photosensitive sol-gel prepared from 3-(methacryloxy)propyl trimethoxysilane-zirconium (or aluminum) oxide (MAPTMS-Zr(Al)) hybrid system. The chromophores are incorporated into the hybrid sol-gel as both guest and side-chain. Second harmonic generation experiment is conducted to optimize the poling parameters for the active sol-gel films. The stability of the second-order nonlinear optical coefficients is investigated by temporal decay test and heat-cool cycling experiment at elevated temperature. Electro-optic channel waveguides have been fabricated by direct ultra-violet exposure, direct blue laser writing, and reverse-mesa methods. Electro-optic effect of the waveguides is measured at 1550 nm and optical intensity modulation has been demonstrated. All the results show that the hybrid sol-gels are promising media for electro-optic devices for integrated optics in both performance and fabrication flexibility. © 2005 Elsevier B.V. All rights reserved.
• Dong, L. u., Zhang, H., & Fallahi, M. (2005). Electro-optic modulation in hybrid solgel doped with Disperse Red chromophore. Optics Letters, 30(3), 278-280.
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  PMID: 15751884;Abstract: An electro-optically active hybrid solgel doped with Disperse Red 13 has been developed by use of a simple solvent-assisted method. It permits a high loading concentration and has low optical loss at 1550 nm. A channel waveguide amplitude modulator has been fabricated by use of active and passive hybrid solgel materials. The device shows an electro-optic coefficient of 14 pm/V at 1550 nm and stable operation. © 2005 Optical Society of America.
• Fallahi, M., & Zhang, H. (2005). Passive and active sol-gel integrated optics. Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2005, 679-680.
• Kosterin, A., Temyanko, V., Fallahi, M., & Mansuripur, M. (2005). Tapered fiber bundles for high power applications. Conference on Optical Fiber Communication, Technical Digest Series, 2, 177-179.
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  Abstract: A method of brightness enhancement for fiber combiners is discussed. The enabling condition is low launched-mode fraction of the input fiber modal capacity. Fiber bundle preparation methods for end-pumping as well as cladding-pumping are described. ©2005 Optical Society of America.
• Mishechkin, O. V., Davis, R. L., Fan, L., Dong, L. u., & Fallahi, M. (2005). Passivation of organic-inorganic hybrid sol-gel. Journal of Sol-Gel Science and Technology, 34(1), 47-51.
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  Abstract: A passivation method for improving long-term stability of organic-inorganic sol-gel material is reported. The effect is observed in experiments with two different passivation materials: Teflon AF and SiO2. A regime of material curing prior to the passivation is found to strongly affect the optical loss. The degradation of waveguide loss with time due to moisture adsorption from the atmosphere is drastically suppressed by coating the material with a thin silica film. The results indicate a long-term optical loss below 0.3 dB/cm in coated waveguides, significantly smaller than that in uncoated waveguides. The mechanism of the loss reduction is described and experimentally confirmed. © Springer Science + Business Media, Inc. 2005.
• Zhang, H. X., Dong, L. u., Peyghambarian, N., Fallahi, M., Luo, J. D., Chen, B. Q., & Jen, A. K. (2005). Electro-optic properties of hybrid solgel doped with a nonlinear chromophore with large hyperpolarizability. Optics Letters, 30(2), 117-119.
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  PMID: 15675685;Abstract: We report the electro-optic properties of hybrid silica solgel doped with a nonlinear chromophore with large hyperpolarizability. Electro-optic coefficients of higher than 30 pm/V have been obtained. Moreover, the electro-optic coefficients have good temporal stability and show promise for the development of high-speed electro-optic devices. © 2005 Optical Society of America.
• Zhang, H., & Fallahi, M. (2005). Electro-optic waveguide based on hybrid sol-gel doped with organic chromophore. Optics Communications, 248(4-6), 415-418.
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  Abstract: Electro-optic waveguides were fabricated from organic chromophore doped hybrid sol-gel through an all-wet process. The waveguide has good optical confinement at 1550 nm and shows stable electro-optic performance. The results indicate that the hybrid sol-gel is promising medium for the electro-optic devices and components with low cost, easy processing, and fabrication flexibility. © 2004 Elsevier B.V. All rights reserved.
• Zhang, H., Gan, H., Dong, L. u., & Fallahi, M. (2005). Nonlinear optical and electro-optic properties of organic-inorganic hybrid sol-gels doped with chromophores. Proceedings of SPIE - The International Society for Optical Engineering, 5935, 1-9.
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  Abstract: We report a systematic investigation on organic-inorganic hybrid sol-gels doped with nonlinear optical chromophores. The host is based on photosensitive sol-gels prepared from precursor of 3-(methacryloxy)propyl trimethoxysilanezirconium (or aluminum) oxide (MAPTMS-Zr(Al)) hybrid system. The chromophores are incorporated into the hybrid sol-gels as both guest and side-chain. Second harmonic generation experiment has been conducted to optimize the poling parameters for the active sol-gel films and examine the stability of the second-order nonlinear optical coefficients. Electro-optic channel waveguides have been fabricated by direct ultra-violet (UV) exposure, direct blue laser writing, and reverse-mesa methods. Electro-optic effect of the waveguides is measured at 1550 nm. All the results show that the hybrid sol-gels are promising media for electro-optic devices for integrated optics in both performance and fabrication flexibility.
• Bedford, R., & Fallahi, M. (2004). Analysis of high-reflectivity metal-dielectric mirrors for edge-emitting lasers. Optics Letters, 29(9), 1010-1012.
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  PMID: 15143657;Abstract: A metal-dielectric mirror is shown as a simple solution for high-reflectivity coatings on cleaved-facet edge-emitting lasers, as well as a means to provide wavelength stabilization and spectral filtering. We show, through the use of a simple SiO2/Ti/Au coating, reflectivities better than 90% and a 25% reduction in the 30-dB linewidth of the output spectrum. Wavelength filtering and varying reflectivities are described as the result of multiple reflections and a coupled-cavity effect. © 2004 Optical Society of America.
• Davis, R. L., Long Jr., W., Wang, C., Lam, T., Ho, J. G., Nachman, P. M., Poylio, J., Mishechkin, O. V., & Fallahi, M. (2004). Distributed Bragg Deflectors Fabricated in Sol-Gel Based Waveguides. IEEE Photonics Technology Letters, 16(2), 464-466.
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  Abstract: We report the fabrication and first demonstration of a grating-coupled waveguide device called a distributed Bragg deflector (DBD). The device consists of a grating imprinted on a channel waveguide, which is in turn, embedded in a planar guide. Light propagating in the channel waveguide is coupled to a well-collimated, planar waveguide-propagating beam at nominally a right angle to the channel. The precise angle of the planar waveguide beam (the diffracted beam) is determined by the Bragg condition for the incident wavelength. The diffracted beams complex amplitude profile can be controlled by adjusting properties of the grating. Our devices were designed for operation at around 1.55 μm. In accordance with theory, the DBDs diffraction efficiency exhibits a strong polarization dependence. Both 1- and 4-cm-long grating devices have been evaluated.
• Fallahi, M. (2004). Passive and active sol-gel integrated optics for heterogeneous integration. Proceedings of SPIE - The International Society for Optical Engineering, 5451, 164-172.
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  Abstract: The advantage of hybrid organic-inorganic sol-gel as a simple, low-cost method for the fabrication of optoelectronic integration is described. High performance integrated optics using multi-layer photo-patternable hybrid sol-gel on high-index InP compound semiconductor is achieved. An MMI based 1 × 12 beam splitter with low polarization sensitivity and high uniformity is demonstrated. The development of EO and NLO active sol-gels are described and the fabrication of active waveguides are presented. The chromophore doped active sol-gels demonstrate high stability which makes them attractive material for integrated optoelectronics. The results show the great potential of the hybrid sol-gel for heterogeneous integration with semiconductor lasers and optoelectronic components.
• Fallahi, M. (2004). Semiconductor lasers and sol-gel photonic components. Proceedings of SPIE - The International Society for Optical Engineering, 4087, 237-240.
• Kosterin, A., Erwin, J. K., Fallahi, M., & Mansuripur, M. (2004). Heat and temperature distribution in a cladding-pumped, Er: Yb co-doped phosphate fiber. Review of Scientific Instruments, 75(12), 5166-5172.
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  Abstract: High-gain-per-unit-length, Er: Yb co-doped, phosphate glass fibers are a new class of active photonic materials. Due to their high concentration of active ions (typically 2-6 × 10 20 cm -3), the generation of heat in these materials is rather severe. To facilitate the design of cladding-pumped, high-power lasers and amplifiers using these materials, we introduce two diagnostic techniques for measuring the total heat and the profile of temperature distribution along the length of an active fiber. Thermal experiments on a 6.0-cm-long piece of cladding-pumped phosphate fiber with Er: Yb doping (3:16 wt %) are conducted, and the results are compared with indirect estimates of total heat by scattered light measurements using a power-balance argument. The difference between the two methods is about 8.0%. Even at low pump powers, the temperature of the core (without heat-sinking) is found to be a large fraction of the glass transition temperature. The temperature distribution along the length of the fiber is found to be relatively flat compared with the absorption profile. Our thermal diagnostic tools yield valuable information that can be used to optimize the design of fiber lasers and amplifiers. © 2004 American Institute of Physics.
• Kosterin, A., Temyanko, V., Fallahi, M., & Mansuripur, M. (2004). Tapered fiber bundles for combining high-power diode lasers. Applied Optics, 43(19), 3893-3900.
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  PMID: 15250555;Abstract: Tapered fiber bundles are often used to combine the output power of several semiconductor lasers into a multimode optical fiber for the purpose of pumping fiber lasers and amplifiers. It is generally recognized that the brightness of such combiners does not exceed the brightness of the individual input fibers. We report that the brightness of the tapered fibers (and fiber bundles) depends on both the taper ratio and the mode-filling properties of the beams launched into the individual fibers. Brightness, therefore, can be increased by selection of sources that fill a small fraction of the input fiber's modal capacity. As proof of concept, we present the results of measurements on tapered fiber-bundle combiners having a low-output étendue. Under low mode-filling conditions per input multimode fiber (i.e., fraction of filled modes ≤ 0.29), we report brightness enhancements of 8.0 dB for 19 × 1 bundles, 6.7 dB for 7 × 1 bundles, and 4.0 dB for 3 × 1 combiners. Our measured coupling efficiency variations of ∼1%-2% among the various fibers in a given bundle confirm the uniformity and quality of the fabricated devices. © 2004 Optical Society of America.
• Lu, D., Zhang, H., Gordon, J. A., & Fallahi, M. (2004). Enhanced second-order nonlinearity by photoassisted poling of active hybrid sol-gel. Electronics Letters, 40(16), 1013-1014.
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  Abstract: Second-harmonic generation in chromophore doped hybrid sol-gel is investigated. Blue light assisted corona poling is applied to hybrid sol-gel doped with Disperse Red 13 around the glass transition temperature. As a result a threefold enhancement in second-order nonlinear optical coefficient has been achieved.
• Mishechkin, O. V., & Fallahi, M. (2004). Sol-gel-derived 4 × 4 multimode interference coupler: Optimization and fabrication. Optical Engineering, 43(3), 662-666.
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  Abstract: The design and fabrication of a 4 × 4 multimode interference (MMI) coupler is reported. A photopatternable organic-inorganic sol-gel on silica-on-silicon is adopted for the device fabrication. Optimization of waveguide parameters led to the coupler excess loss below 1 dB and power imbalance below 0.2 dB. An optical 90-deg hybrid based on the coupler is realized and tested. The experimental data are in very good agreement with predicted simulation results, demonstrating the simplicity and exactness of the sol-gel method as an advantageous fabrication route in integrated optics. © 2004 Society of Photo-Optical Instrumentation Engineers.
• Zhang, H. X., Dong, L. u., Liu, T., Mansuripur, M., & Fallahi, M. (2004). Direct laser writing of electro-optic waveguide in chromophore-doped hybrid sol-gel. Applied Physics Letters, 85(19), 4275-4277.
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  Abstract: To overcome the influence of chromophore absorption and degradation in the ultraviolet spectral range for direct photopatterning of electro-optic devices, a blue laser writing technique operating at 405 nm has been used to fabricate electro-optic waveguides from side-chain disperse red-1 doped photosensitive hybrid sol-gel films. The waveguide has good optical confinement and shows an electro-optic coefficient of about 9.0±0.4 pm/V and high temporal stability. The results indicate that the hybrid sol-gel a promising matrix for chromophores, and this technique can find applications in direct patterning of electro-optic devices from nonlinear chromophores-doped photosensitive materials including sol-gels and polymers. © 2004 American Institute of Physics.
• Zhang, H. X., Dong, L. u., Peyghambarian, N., Fallahi, M., Luo, J. D., Chen, B. Q., & Jen, A. K. (2004). Electro-optic properties of hybrid sol-gel doped with nonlinear chromophore. Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 1, 138-139.
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  Abstract: This paper reports the electro-optic properties of hybrid silica sol-gel doped with a chromophore of high nonlinearity. High electro-optic coefficient and temporal stability have been demonstrated, showing the promise of the material for the development of high-speed electro-optic devices.
• Zhang, H., Dong, L. u., & Fallahi, M. (2004). Active organic-inorganic sol gel with high thermal stability for nonlinear optical applications. Applied Physics Letters, 84(7), 1064-1066.
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  Abstract: The second-harmonic generation and thermal stability of hybrid photosensitive sol-gel films doped with a side-chain electro-optic chromophore were studied. Ultraviolet exposure was applied during poling to obtain photopolymerization at the same time as thermal densification. The nonlinear optic coefficient was derived for the cross-linked and noncross-linked sol-gel films. The results indicate that the film could withstand the long-term stability requirement for optical components.
• Bedford, R., & Fallahi, M. (2003). Metal/dielectric high-reflectivity facet coating for semiconductor lasers. Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 1, 206-207.
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  Abstract: A simple solution to achieve high-reflectivity coatings on edge-emitting lasers by using metal/dielectric mirrors is presented. This results in improved threshold, DQE, thermal characteristics, and wavelength stabilized operation.
• Bedford, R., Fan, L., & Fallahi, M. (2003). Semiconductor unstable resonators with laterally finite mirrors. Proceedings of SPIE - The International Society for Optical Engineering, 4993, 28-36.
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  Abstract: Tapered unstable resonator lasers incorporating laterally finite mirrors are reported. By reducing the lateral extent of mirrors, cavity losses may be shifted from internal losses (contributing to scattering and absorption) to mirror losses (contributing to output power). Design of these cavities will be discussed and evaluated. Experimental data substantiates theoretical analysis, showing an increase in slope efficiency of 40% over conventional infinite aperture tapered lasers.
• Bedford, R., Schillgalies, M., & Fallahi, M. (2003). Demonstration of finite-aperture tapered unstable resonator lasers. Applied Physics Letters, 83(5), 822-824.
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  Abstract: A finite-aperture tapered unstable resonator laser was investigated. The finite-aperture tapered unstable resonator laser was compared to the conventional infinite-aperture tapered laser. Results showed that the differential quantum efficiency was increased by 40%.
• Mishechkin, O. V., Dong, L. u., & Fallahi, M. (2003). Reliability improvement of hybrid organic-inorganic waveguides by dielectric passivation. Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2, 674-675.
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  Abstract: A simple passivation method based on a dielectric coating above the fabricated waveguides was reported. The results indicated that a significant reduction in waveguide loss and improved reliability of the waveguides. This paper presents long-term propagation loss stabilized below 0.3 db/cm at 1550 nm of a silica passivated sol-gel slab waveguide.
• Bedford, R., & Fallahi, M. (2002). Semiconductor unstable resonators with laterally finite mirrors. IEEE Journal of Quantum Electronics, 38(7), 716-723.
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  Abstract: The design of semiconductor-based unstable resonators with laterally finite mirrors is investigated. A time-independent model used for tapered cavity semiconductor lasers is implemented to analyze this cavity design. Initial investigations show a significant improvement in external quantum efficiency, as well as a decrease in threshold current density as compared to the traditional tapered lasers with laterally infinite mirrors. The advantages and disadvantages of the proposed design will be discussed.
• Fallahi, M., Bedford, R., & Dong, L. u. (2002). Photopatternable sol-gel for compound semiconductor processing. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 20(6), 2942-2945.
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  Abstract: An overview is given of several features of hybrid inorganic-organic sol-gel for compound semiconductor processing. Hybrid sol-gel films, with dual organic-inorganic properties, can be easily spin-coated and photopatterned on semiconductor substrates and used as the dielectric masking layer for dry etching of semiconductor compounds such as GaAs and InP. Planarization capabilities of the hybrid sol-gels on deep mesas are also demonstrated.
• Fardad, M. A., Mishechkin, O. V., & Fallahi, M. (2001). Hybrid sol-gel materials for integration of optoelectronic components. Journal of Lightwave Technology, 19(1), 84-91.
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  Abstract: In this paper, we report on the integration of the Bragg filters with 1 × 8 multimode interference (MMI) power splitters on silicon substrate, and the demonstration of 1 × 8 external cavity distributed Bragg reflector (DBR) lasers. Hybrid organic-inorganic material is developed based on the sol-gel synthesis of an organically modified silicon alkoxide. The sol-gel material is spin coated on grated SiO2/Si wafers, and the designed components (splitters and filters) are UV imprinted and developed using solvent assisted photolithography. The Bragg reflectors show filtering up to 98% with a bandwidth of about 0.8 nm consistent with their theoretical prediction. Integrated reflectors and MMI splitters are then used as feedback resonators for DBR lasers. Single-mode lasing with sidemode suppressions of up to 40 dB and a linewidth of about 400 kHz is observed. At 1550- nm wavelength, the loss and power uniformity in the MMI splitters, designed on the basis of lowest loss, are, respectively, 0.13 dB and 0.03 dB poorer than their theoretical calculations.
• Bedford, R., Luo, H., & Fallahi, M. (2000). Bow-tie surface-emitting lasers. IEEE Photonics Technology Letters, 12(8), 948-950.
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  Abstract: In this letter we report a new design for surface emitting semiconductor lasers operating at 940 nm, incorporating a double-flare cavity, and distributed Bragg reflector (DBR) mirrors also providing surface emission. This design can take advantage of the modal behavior of the unstable resonator, and has shown very good mode control, with coherent emission from two facets in the same direction. We report preliminary performance results showing very promising characteristics including single-mode diffraction limited operation, and spectral behavior with 42 dB side-mode suppression. This design has exhibited promising results for increasing the current range between the lasing threshold and the filament threshold.
• Kristjansson, S., Eriksson, N., Larsson, A., Penner, R., & Fallahi, M. (2000). Observation of stable cylindrical modes in electrically pumped circular grating-coupled surface-emitting lasers. Doktorsavhandlingar vid Chalmers Tekniska Hogskola, 1946-1953.
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  Abstract: We present the results of a comprehensive experimental study of the modal behavior of electrically pumped circular grating-coupled surface-emitting lasers with resonant second-order gratings. Our results show stable cylindrical mode operation with azimuthal orders m = 1 and m = 52. We have found that, when a passive, unpumped 0.7-μm-deep indentation is included at the center of the circular resonator contact, the modal behavior becomes more stable with respect to increasing current. This result manifests itself in the lasing of two orthogonal m = 1 modes along with one higher-order mode from threshold to 2.2 times threshold or more. The spatial coherence of the cylindrical modes over the area of the resonator leads to better beam quality. Lasers without passive central indentations exhibit mode hopping between quasi-linear modes and higher-order cylindrical modes as the current is increased.
• Kristjánsson, S., Eriksson, N., Larsson, A., Penner, R. S., & Fallahi, M. (2000). Observation of stable cylindrical modes in electrically pumped circular grating-coupled surface-emitting lasers. Applied Optics, 39(12), 1946-1953.
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  PMID: 18345092;Abstract: We present the results of a comprehensive experimental study of the modal behavior of electrically pumped circular grating-coupled surface-emitting lasers with resonant second-order gratings. Our results show stable cylindrical mode operation with azimuthal orders m = 1 and m = 52. We have found that, when a passive, unpumped 0.7-μm-deep indentation is included at the center of the circular resonator contact, the modal behavior becomes more stable with respect to increasing current. This result manifests itself in the lasing of two orthogonal m = 1 modes along with one higher-order mode from threshold to 2.2 times threshold or more. The spatial coherence of the cylindrical modes over the area of the resonator leads to better beam quality. Lasers without passive central indentations exhibit mode hopping between quasi-linear modes and higher-order cylindrical modes as the current is increased. © 2000 Optical Society of America.
• Penner, R. S., Bedford, R., Luo, H., Mendes, S., & Fallahi, M. (2000). High-power wavelength-tunable circular-grating surface-emitting distributed Bragg deflector lasers. Applied Physics Letters, 76(11), 1359-1361.
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  Abstract: We present a promising approach to achieve wavelength tuning in high-power circular-grating surface-emitting lasers. A transparent electrode of indium tin oxide (ITO) was used to inject carriers into the second-order grating section of the device. Powers in excess of 225 mW and slope efficiencies of better than 0.40 mW/mA are reported. A continuous tuning range of 0.5 nm was achieved, while an overall wavelength shift of 1 nm was obtained for an ITO injection current of 30 mA. © 2000 American Institute of Physics.
• Beregovski, Y., Fardad, A., Luo, H., & Fallahi, M. (1999). Single-mode operation of the external cavity DBR laser with sol-gel waveguide Bragg grating. Optics Communications, 164(1), 57-61.
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  Abstract: A sol-gel-based external cavity DBR laser with narrow linewidth is described. The sol-gel waveguide grating is formed on the SiO2-coated silicon substrate with a loss of about 0.2 dB/cm. The threshold current is 32 mA at the lasing wavelength of about 1530 nm and T = 20°C. The side-mode suppression is close to 30 dB at 43 mA. The laser linewidth is less than 500 kHz.
• Fallahi, M. (1999). Grating-coupled surface emitting quantum well semiconductor lasers. Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 3, 634-635.
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  Abstract: Circular-grating surface emitting distributed Bragg reflector lasers and unstable resonators surface emitting distributed reflector Bragg lasers are attractive candidates for high power, low divergence surface emission. Quantum wells and strained quantum wells are widely used as active structure. In order to simplify the fabrication process, it is desirable to use the same layer structure for both the active and passive grating section. The absorption in a passive quantum well can be significantly reduced by red shifting the lasing wavelength with respect to the gain peak, combined with absorption coefficient saturation at relatively low power. In this paper, the design and operation of the grating coupled surface emitting lasers with strained quantum wells for the active and the grating sections are described.
• Fardad, M. A., & Fallahi, M. (1999). Demonstration of sol-gel based distributed Bragg reflector lasers. Optics Communications, 163(1), 33-37.
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  Abstract: We report on the development of a new composition of organoaluminosilicate sol-gel material and on the design and fabrication of Bragg reflectors and demonstration of external cavity distributed Bragg reflector (DBR) laser. The material is found very attractive for the fabrication of high quality channel waveguides, which in this study exhibit a total loss of approximately 0.2 dB/cm at 1550 nm. The Bragg reflectors are studied by a tunable laser, almost 96% filtering around the designed wavelength (1530 nm) and a full width half maximum (FWHM) of approximately 7.5 angstroms are observed. Both filtering and bandwidth are found in good agreement with their theoretical calculations. Reflectors are then employed as feedback resonators and single mode DBR lasers with side mode suppressions better than 28 dB are demonstrated.
• Fardad, M. A., & Fallahi, M. (1999). Sol-gel multimode interference power splitters. IEEE Photonics Technology Letters, 11(6), 697-699.
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  Abstract: We report on the design and fabrication of 1 × 32 MMI power splitters through the sol-gel process. The MMI splitter is designed for 1.55-μm wavelength and characterized in terms of tolerance, wavelength response, and polarization sensitivity. The splitter is then UV-imprinted in aluminosilicate material coated on SiO2. It is found that the responses of fabricated and designed splitter are in good agreement, with an excess loss of approx. 0.75 dB and power uniformity of approx. 0.95 dB.
• Fardad, M. A., Luo, H., Beregovski, Y., & Fallahi, M. (1999). Solgel grating waveguides for distributed Bragg reflector lasers. Optics Letters, 24(7), 460-462.
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  PMID: 18071539;Abstract: External-cavity distributed Bragg reflector (DBR) lasers based on solgel Bragg grating waveguides as feedback elements have been fabricated. The single-mode waveguide and the Bragg reflectors are made out of a new composition of aluminosilicate material. The solgel process of integrated optics provides low cost, low loss, processing flexibility and simplicity. Single-mode lasing with a sidemode suppression of better than 25 dB is demonstrated.
• Hennig, O., Mendes, S., Fallahi, M., & Peyghambarian, N. (1999). Chemical sensors based on the modification of a resonator cavity. Proceedings of SPIE - The International Society for Optical Engineering, 3537, 336-341.
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  Abstract: An optical resonator is modified by changing the optical path length of the resonant cavity to enhance the sensitivity of the device. The resonator-based sensors provide an attractive alternative for existing chemical sensors using a change of refractive index inside a sensitive region to detect the species in question, by promising high resolution at low cost.
• Luo, H., Bedford, R., Penner, S., & Fallahi, M. (1999). High-power grating coupled surface emitting flared laser. Electronics Letters, 35(14), 1165-1166.
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  Abstract: A high-power surface emitting flared laser with curved feedback grating is reported. Low threshold, low divergence out-coupling is achieved. Single longitudinal mode operation with surface emitting power in excess of 110mW and sidemode suppression of > 40dB is demonstrated.
• Luo, H., Bedford, R., Penner, S., & Fallahi, M. (1999). Tunable grating coupled surface-emitting tapered laser. IEEE Photonics Technology Letters, 11(9), 1102-1104.
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  Abstract: We report on the design and fabrication of a wavelength-tunable grating coupled surface-emitting laser. A curved second-order grating is used at the end of a tapered gain section to provide feedback as well as collimated surface out-coupling. Wavelength tuning is achieved by current injection into the grating section through a film of indium-tin oxide deposited on the grating surface. Low-divergence single-frequency surface emission with approximately 1-nm wavelength tuning is demonstrated.
• Penner, S., Latipov, R., Luo, H., & Fallahi, M. (1999). Circular grating surface emitting lasers for free-space optical interconnects. Proceedings of SPIE - The International Society for Optical Engineering, 3632, 346-353.
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  Abstract: Circular grating surface emitting distributed Bragg reflector lasers exhibit extremely small divergence angles and moderately high output power levels which makes them an attractive candidate for free-space interconnects. Computational simulations are used to model the observed results and assist in the design of new functionality such as focusing and beam shaping. Numerical analysis of the coupled mode equations for DBR lasers and free-space propagation of the emitted field have been performed. Surface emission is realized through grating outcoupling provided by a second order grating while feedback is accomplished with an inner annulus consisting of either a first order or second order grating. These gratings are written using electron beam lithography (EBL) and subsequently etched using ECR-RIE. The flexibility of the EBL process enables a variety of different grating designs to be created on a single sample and subsequently compared during device testing.
• Rantala, J. T., Penner, R. S., Honkanen, S., Vähäkangas, J., Fallahi, M., & Peyghambarian, N. (1999). Negative tone hybrid sol-gel material for electron-beam lithography. Thin Solid Films, 345(2), 185-187.
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  Abstract: A novel high-resolution sol-gel material for electron-beam lithography and direct writing of micro-optical elements is reported. A negative tone hybrid sol-gel material was synthesized and used for fabrication of submicrometer grating structures by electron-beam lithography. Doses from 10 to 100 μC/cm2 were able to crosslink the material and convert it into hybrid sol-gel glass. The sensitivity and the contrast of the material were found to be good with a linewidth of 0.5 μm.
• Yeh, W., Mansuripur, M., Fallahi, M., & Penner, R. S. (1999). Talbot imaging with increased spatial frequency: A technique for replicating truncated self-imaging objects. Optics Communications, 170(4), 207-212.
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  Abstract: The Talbot effect in the presence of a convergent beam of coherent light yields a demagnified image of a self-imaging object. In fact, the object does not even have to fulfill the self-imaging condition; the object with truncated self-imaging feature is sufficient to yield an image that is sufficiently accurate for many practical purposes. We have taken this approach to fabricating circular gratings with a reduced period compared to the period of the mask. Using a simple experimental setup and a concentric circular grating mask, we have created images whose periods are either one-half or one-third of the mask's period. Demagnified Talbot imaging of fully or truncated self-imaging objects provides an attractive approach to photolithographic fabrication of structures whose periods are somewhat greater than the wavelength of the light source.
• Beregovski, Y., Hennig, O., Fallahi, M., Guzman, F., Clemens, R., Mendes, S., & Peyghambarian, N. (1998). Design and characteristics of DBR-laser-based environmental sensors. Sensors and Actuators, B: Chemical, 53(1-2), 116-124.
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  Abstract: This paper reports on the development of a new laser-based chemical sensor. The optical sensor is based on the modification of the resonant cavity of a distributed-Bragg-reflector (DBR) laser. Part of the cavity (phase section and/or DBR grating) is covered by a sensitive layer that changes its refractive index as a result of interaction with a given chemical. This produces the change of optical cavity length, resulting in the lasing frequency shift. The results of modeling and preliminary experiments proving the concept of chemical sensing are presented. © 1998 Elsevier Science S.A. All rights reserved.
• Fallahi, M., Kasunic, K. J., Penner, S., Nordman, O., & Peyghambarian, N. (1998). Design and fabrication of circular grating coupled distributed Bragg reflector lasers. Optical Engineering, 37(4), 1169-1174.
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  Abstract: The design and fabrication of circular grating surface emitting lasers are presented. The influence of device parameters on the mode selection is described. The fabrication of an InGaAs/GaAs circular grating distributed Bragg reflector (DBR) laser is presented. Significant improvement is obtained by using a quantum-well structure with a multistack and an etch-stop layer. A threshold current as low as 15 mA and an output power in excess of 170 mW without saturation are obtained. The potential of circular grating DBR laser arrays for multiwavelength operation is demonstrated. © 1998 Society of Photo-Optical Instrumentation Engineers.
• Fallahi, M., Linden, K. J., & Wang, S. C. (1998). Erratum: (Fabrication, Testing and Reliability of Semiconductor Lasers III (29-30 January 1998)). Proceedings of SPIE - The International Society for Optical Engineering, 3285, 229-.
• Fardad, M. A., & Fallahi, M. (1998). Organic-inorganic materials for integrated optoelectronics. Electronics Letters, 34(20), 1940-1941.
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  Abstract: A new composition of organic-inorganic photosensitive materials is grown using the sol-gel process. The material, organoaluminosilicate, is spin coated onto Si wafers and channel waveguides are photoinscribed and developed using solvent assisted photolithographic process. The process is simple, reproducible, low cost and low loss.
• Hennig, O., Beregovskii, Y., Clemens, R., Mendes, S., Fallahi, M., & Peyghambarian, N. (1998). Distributed Bragg reflector laser-based sensor for chemical detection. Optics Communications, 156(4-6), 311-315.
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  Abstract: In this paper we present a novel sensor based on the modification of a distributed Bragg reflector (DBR) laser: the optical path length of a resonant cavity is changed thus changing the resonant frequency. The external cavity of the DBR laser, with a sensitive element within is used to detect chemical species and temperature. We will show the expected resolution as well as preliminary experimental results. © 1998 Published by Elsevier Science B.V. All rights reserved.
• Mendes, S. B., Honkanen, S., Fallahi, M., & Peyghambarian, N. (1998). New optical detection techniques for chemical sensors. Proceedings of SPIE - The International Society for Optical Engineering, 3270, 42-49.
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  Abstract: In this work we present three novel optical approaches towards the implementation of bio- and chemical sensors. First we describe an absorbance spectroscopic technique developed on a waveguide platform that features a sensitivity enhancement of 4 orders of magnitude compared to the conventional transmission measurements of ultra-thin films. Next we show a waveguide Zeeman interferometric technique, which is based on the relative phase change between the TE and TM waveguide modes, applied as a sensor platform. Finally an external-cavity laser, a semiconductor laser combined with a single mode optical fiber and a Bragg grating reflector, was built to work as an active sensor where the analyte species were incorporated inside the resonant cavity to increase sensitivity.
• Penner, S., Fallahi, M., & Nordman, O. (1998). Electron cyclotron resonance reactive ion etching of GaAs in chlorine-methane. Microelectronic Engineering, 41-42, 383-386.
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  Abstract: Highly anisotropic ECR etching of sub-half-micron features in GaAs and AlGaAs using a Cl2-CH4 mixture is reported. Etch depths greater than 1 μm with aspect ratios nearing 5:1 were achieved while maintaining vertical sidewalls, sharp transitions and smooth etched surface.
• Sarid, D., Yao, X., Workman, R. K., Peterson, C. A., & Fallahi, M. (1998). Observation of interface band bending on GaAs/AlAs heterostructures by scanning tunneling microscopy. Proceedings of SPIE - The International Society for Optical Engineering, 3285, 51-58.
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  Abstract: The electronic structure at the interface of GaAs/AlAs multilayers grown by molecular beam epitaxy is investigated on the (110) surface using scanning tunneling microscopy. The valence band bending, which is produced by an interface dipole layer, is observed from cross-sectional profiles exhibiting spike structures. It is found that the transition region of the AlAs/GaAs interface (3.0-4.0 nm) is smaller than that of the GaAs/AlAs interface (4.0-5.0 nm). Similar spike structures showing a transition region of 3.5-4.5 nm are also observed at the GaAs/Al0.6Ga0.4As interface.
• Schülzgen, A., Spiegelberg, C., Morrell, M. M., Mendes, S. B., Allemand, P. M., Kawabe, Y., Kuwata-Gonokami, M., Honkanen, S., Fallahi, M., Kippelen, B., & Peyghambarian, N. (1998). Semiconducting conjugated polymers - Light amplification and lasing. Proceedings of SPIE - The International Society for Optical Engineering, 3281, 192-201.
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  Abstract: We study the emission properties of various laser cavities under pulsed optical excitation of the active semiconducting conjugated polymer material. Physical origin, magnitude, and dynamics of optical gain in these novel active laser materials are discussed leading to a selection of suitable cavity configurations for laser applications. We demonstrate laser action for various planar and ring resonator configurations that can be achieved in the regimes of transient inversion and quasi stationary excitation of the polymer material pumping with femtosecond and nanosecond pulses, respectively.
• Schülzgen, A., Spiegelberg, C., Morrell, M. M., Mendes, S. B., Allemand, P., Kawabe, Y., Kuwata-Gonokami, M., Honkanen, S., Fallahi, M., Kippelen, B., & Peyghambarian, N. (1998). Light amplification and laser emission in conjugated polymers. Optical Engineering, 37(4), 1149-1156.
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  Abstract: We study optical gain and laser emission from semiconducting conjugated polymers after strong optical excitation with femtosecond laser pulses. Stimulated emission from few-hundred-nanometer thin films results in a sharp increase in emission intensity and emission line narrowing. Very large optical gain due to the stimulated emission is measured directly by pump-probe spectroscopy. Using the large light amplification in these conjugated polymers, we demonstrated planar and ring lasers of very small sizes that are suitable for applications in integrated optics. Vertical cavity surface emitting lasers, distributed feedback through surface relief grating, and whispering-gallery mode emission from ring resonators are demonstrated. © 1998 Society of Photo-optical Instrumentation Engineers.
• Beregovski, Y., Ten, S. Y., Mendes, S. B., Honkanen, S., Fallahi, M., Peyghambarian, N., Grace, K. M., & Swanson, B. I. (1997). In-situ chemical detection based on photonic devices. Proceedings of SPIE - The International Society for Optical Engineering, 3082, 76-82.
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  Abstract: A novel scheme of a laser-based chemical sensor has been examined. The scheme is based on the lasing frequency shift of a DBR laser as a result of refractive index change of the sensitive coating in the presence of chemicals in question. The applicability and advantages of different schemes are discussed. The results of preliminary experiments related to the construction and stability of an external cavity DBR laser and interferometric measurements of refractive index change are presented. ©2004 Copyright SPIE - The International Society for Optical Engineering.
• Fallahi, M., Mathine, D., Penner, S., & Peyghambarian, N. (1997). Circular-grating surface-emitting DBR laser array with high performance. Pacific Rim Conference on Lasers and Electro-Optics, CLEO - Technical Digest, 7-.
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  Abstract: Low threshold current, high power operation of circular-grating surface-emitting distributed Bragg-reflector (CG-SE-DBR) lasers are presented as well as 2×2 multiwavelengths laser array operation. The lasers are fabricated in a strained multi-quantum well InGaAs/GaAs GRINSCH structure. The 2×2 array of the two lasers were made with the same grating periodicity, while the other two had slightly different periodicity. A threshold current as low as 18 mA was measured under pulsed and continuous wave operation. The lasers with the same periodicity in the array have the same wavelength, and the wavelength shift between different periodicity is 1.5 nm. The far field divergence of the lasers was 2° at full width at half maximum (FWHM).
• Kasunic, K. J., & Fallahi, M. (1997). Gain and index saturation in circular-grating distributed-feedback semiconductor lasers. Proceedings of SPIE - The International Society for Optical Engineering, 2994, 205-214.
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  Abstract: We report numerical results for the above-threshold spectral properties of circular-grating distributed-feedback semiconductor lasers. Our model includes a radially-varying gain and index saturation, as well as a uniformly- distributed grating loss, in the solution of the coupled- mode equations. Our results show a multi-mode spectrum for large coupling strengths, a consequence of mode competition induced by the spatially-varying gain distribution associated with the grating losses. We also find that a single-mode spectrum is possible over a limited power range.
• Kasunic, K. J., & Fallahi, M. (1997). Gain saturation in circular-grating distributed-feedback semiconductor lasers. Journal of the Optical Society of America B: Optical Physics, 14(8), 2147-2152.
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  Abstract: We report numerical results for gain saturation in circular-grating distributed-feedback semiconductor lasers. Our model includes a radially varying nonlinear gain and a uniformly distributed grating loss in the solution of the coupled-mode equations. Our results show that lossy, high-power operation results in an optimum coupling strength for efficient conversion of pump power into useful output power. Our results also show a multimode spectrum for large-coupling strengths, a consequence of mode competition induced by a spatially varying gain distribution. Single-mode selection entails operating at approximately the optimum coupling coefficient determined for efficient pumping. © 1997 Optical Society of America.
• Dagenais, M., Lu, C. -., Tabatabaei, S. A., Stone, D., Chen, Y. J., Temkin, H., Fallahi, M., & Peyghambarian, N. (1996). Methodology for testing WDM laser arrays. Proceedings of SPIE - The International Society for Optical Engineering, 2690, 263-274.
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  Abstract: The coming of age of wavelength-division-multiplexed (WDM) laser arrays is bringing new challenges in the testing of semiconductor lasers. Because of stringent requirements on the laser linewidths and their frequency stability and because of electrical, optical, and thermal crosstalk problems, a new methodology is required for evaluating the performance of WDM laser arrays. This paper describes techniques that will be used to test WDM laser arrays both cw and under pulsed conditions. The laser arrays for these studies will be procured under a new program called `The WDM Alliance' sponsored by BMDO/AFOSR. Preliminary data on monolithic WDM laser arrays are also presented in this paper.
• Fallahi, M., & Peyghambarian, N. (1996). Integration issues in transmitter and receiver modules for WDM. Proceedings of SPIE - The International Society for Optical Engineering, 2690, 163-169.
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  Abstract: The research activity on WDM transmitter and receiver modules is presented. The integration of laser array and optical combiner as well as demultiplexer and detector array is discussed. The challenges and potential approaches for integrated modules are presented.
• Fallahi, M., Peyghambarian, N., Kasunic, K., Dion, M., & Wasilewski, Z. (1996). Circular-grating surface-emitting DBR laser array for free-space applications. Electronics Letters, 32(17), 1583-1585.
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  Abstract: The operation of a 2 × 2 circular-grating surface-emitting distributed Bragg reflector laser array is demonstrated. An InGaAs/GaAs multiquantum well structure with an etch-stop layer is used. A threshold current of ∼20mA is measured for each laser in the array. High power output with accurate wavelength control was obtained.
• Ten, S. Y., Fallahi, M., & Peyghambarian, N. (1996). Design of a novel semiconductor laser-based chemical sensor. Proceedings of SPIE - The International Society for Optical Engineering, 2763, 64-69.
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  Abstract: We present concept and design considerations of a novel optical sensor based on the distributed Bragg reflector (DBR) laser. The operation of this sensor relies on the shift of the lasing wavelength upon exposure of the chemically sensitive element to the gas species to be detected. We discuss physics of the proposed device, show the compromises in its design, and estimate potential sensitivity. Compactness and simplicity of this DBR laser- based optical sensor may play a crucial role in its mass production for various applications.
• Charbonneau, S., Poole, P. J., Piva, P. G., Aers, G. C., Koteles, E. S., Fallahi, M., He, J. -., McCaffrey, J. P., Buchanan, M., Dion, M., Goldberg, R. D., & Mitchell, I. V. (1995). Quantum-well intermixing for optoelectronic integration using high energy ion implantation. Journal of Applied Physics, 78(6), 3697-3705.
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  Abstract: It is shown that the high energy ion-implantation-induced quantum well (QW) intermixing technique can be used to modify the band gap of InGaAs graded-index separate confinement heterostructure QW laser structures. The spatial selectivity inherent in this technique makes it useful for the monolithic integration of optoelectronic devices having different functionalities. This process offers a simple and potentially low-cost route for fabricating photonic integrated circuits. The major differences between earlier results, using low energy ion implantation, and those presented are related to the introduction of vacancies and defects directly in the vicinity of an active region of a few microns below the surface without relying on poorly controlled mechanisms such as channeling. Further advantages are discussed.
• Dion, M. M., Fallahi, M., Chatenoud, F., Templeton, I. M., Delage, A., & Barber, R. A. (1995). Effect of temperature on the threshold current and wavelength of MQW InGaAs/GaAs circular-grating, surface-emitting, distributed Bragg reflector (CG-SE-DBR) diode lasers. Proceedings of SPIE - The International Society for Optical Engineering, 2398, 5-9.
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  Abstract: Results will be presented on the variation of threshold current and emission wavelength with temperature of MQW InGaAs/GaAs circular-grating, surface-emitting, distributed Bragg reflector (CG-SE-DBR) lasers, in the range 10 - 90°C. The structures were grown by one-step MBE and the circular gratings were defined by electron-beam lithography. Measurements were made pulsed and CW. The characteristic temperature ranged between 18 - 48 K. A wavelength variation with temperature of around 0.1 nm/°C was obtained. The results are compared with those of linear, GaAs- based DBR lasers.
• Fallahi, M., Chatenoud, F., Dion, M., Templeton, I., Barber, R., & Thompson, J. (1995). Circular-grating surface-emitting distributed Bragg reflector lasers on an InGaAs-GaAs structure for 0.98-μm applications. IEEE Journal on Selected Topics in Quantum Electronics, 1(2), 382-386.
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  Abstract: In this paper, we report on the design and fabrication of electrically-pumped circular-grating surface-emitting DBR lasers for operation in the 0.98-μm wavelength range. The layer structure with InGaAs-GaAs-AlGaAs strained multiquantum-wells was obtained by one-step epitaxial growth. Circular gratings are defined by electron-beam lithography around circular gain sections of different diameters. Low threshold CW operation as low as 26 mA for a 60-μm diameter gain section, and high-power pulsed operation of over 120 mW for a 100-μm diameter gain region are demonstrated. A quasi-circular far-field pattern with a divergence of about 1° is obtained.
• Fallahi, M., Chatenoud, F., Templeton, I. M., Dion, M. M., Wasilewski, Z. R., Buchanan, M., & Barber, R. A. (1995). Recent developments on InGaAs/GaAs circular-grating distributed Bragg reflector lasers. Proceedings of SPIE - The International Society for Optical Engineering, 2398, 135-141.
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  Abstract: In this paper, we report on the design and fabrication of electrically-pumped circular-grating surface-emitting DBR lasers for operation in 0.98 μm wavelength range. The layer structure consists of InGaAs/GaAs/AlGaAs strained multi-quantum-wells grown by one step epitaxial growth. Circular gratings are defined by electron-beam lithography around the circular gain sections. The effect of various parameters are discussed and the most recent results are presented.
• Fallahi, M., Dion, M., Wasilewski, Z., Buchanan, M., Nournia, M., Stapledon, J., & Barber, R. (1995). Performance improvement of circular-grating surface-emitting DBR lasers using an MQW structure with etch-stop layer. Electronics Letters, 31(18), 1581-1582.
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  Abstract: The authors demonstrate low threshold current high efficiency operation of circular-grating surface-emitting distributed Bragg reflector (CG-SE-DBR) lasers. A strained InGaAsIGaAs triple quantum well with an etch-stop layer was grown by MBE. Circular gratings are defined by electron beam lithography. A threshold current as low as 17mA and a pulsed output power > 170mW at approx.980nm wavelength are obtained.
• Fallahi, M., Koteles, E. S., Delage, A., Chatenoud, F., Templeton, I. M., Champion, G., He, J. J., Wang, W., Dion, M., & Barber, R. A. (1995). WDM module research within the Canadian Solid State Optoelectronics Consortium. Proceedings of SPIE - The International Society for Optical Engineering, 2449, 54-61.
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  Abstract: We report on the design, growth, fabrication, and characterization of monolithic wavelength division multiplexed (WDM) modules produced within the Canadian Solid State Optoelectronics Consortium. The transmitter module includes multiple, discrete wavelength, distributed Bragg reflector (DBR) laser diodes monolithically integrated with waveguide combiners fabricated using an InGaAs/GaAs heterostructure. The wavelength demultiplexer unit is based on a Rowland circle grating spectrometer monolithically integrated with a metal- semiconductor-metal (MSM) detector array fabricated on an InGaAs/AlGaAs/GaAs heterostructure. The epitaxial layer wafers for both transmitter and receiver modules were grown in single molecular beam epitaxy (MBE) runs.
• Templeton, I. M., Fallahi, M., Erickson, L. E., Chatenoud, F., Koteles, E. S., Champion, H. G., He, J. J., & Barber, R. (1995). Focused ion beam lithography of multiperiod gratings for a wavelength-division-multiplexed transmitter laser array. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures, 13(6), 2722-2724.
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  Abstract: This paper demonstrates the design, construction, and performance of a monolithically integrated wavelength-division-multiplexed transmitter module having ten distributed-Bragg-reflector (DBR) laser diodes operating at predefined frequencies in the 0.98μm to 1.0μm range with a frequency separation of about 2nm. The DBR gratings are written by focused ion beam lithography with manual stepping of the x-deflection gain to produce the required variation of period.
• Chunmeng, W. u., Makino, T., Fallahi, M., Craig, R. G., Knight, G., Templeton, I., & Blaauw, C. (1994). Novel circular grating surface-emitting laser with emission from center. Japanese Journal of Applied Physics, Part 2: Letters, 33(3 B), L427-L429.
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  Abstract: In this letter, we propose a new circular grating surface-emitting laser that is featured by a central emission area. Pulsed room temperature operation has been demonstrated.
• Fallahi, M. (1994). Design and fabrication of a compact wavelength demultiplexer integrated with fast MSM detector suitable for optoelectronic integrated circuits. Proceedings of SPIE - The International Society for Optical Engineering, 2145, 112-118.
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  Abstract: In this paper, we report on the design and fabrication of a wavelength demultiplexer integrated with photodetector array in InGaAs/AlGaAs/GaAs structure. The demultiplexer is based on the Rowland circle grating. InGaAs MSM detectors grown on the top of an GaAs/AlGaAs waveguide structure are used for light detection. Only one step epitaxial growth is used. The cross-talk between adjacent channels measured from the detectors response is about -11 dB. The device can provide 38 output channels operating in the 1-μm wavelength region. The structure has the potential to be integrated with GaAs transistors without any complication in the fabrication.
• Fallahi, M., Chatenoud, F., Dion, M., Templeton, I. M., Barber, R., & Thompson, J. (1994). Circular-grating surface-emitting distributed Bragg reflector lasers on an InGaAs/GaAs structure for 0.98 μm applications. Conference Digest - IEEE International Semiconductor Laser Conference, 141-142.
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  Abstract: InGaAs/GaAs circular-grating surface-emission DBR lasers with a pulsed external efficiency over 11% (power > 100 mW) and a divergence of 1° are obtained. We also demonstrate the first CW operation near room temperature.
• Fallahi, M., Dion, M., Chatenoud, F., Templeton, I. M., & Barber, R. (1994). High temperature operation of circular-grating surface-emitting DBR lasers fabricated on an InGaAs/GaAs structure. IEEE Photonics Technology Letters, 6(3), 326-329.
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  Abstract: We demonstrate high temperature operation of circular-grating surface-emitting distributed Bragg reflector lasers. The structure is a strained InGaAs/GaAs double quantum well. Circular gratings are defined by electron beam lithography. No epitaxial regrowth is used. A surface emission power of over 40 mW under pulsed operation at temperatures of up to 80 °C is obtained without saturation. A fixed single mode operation was achieved over a temperature range of 60 degrees.
• Fallahi, M., Dion, M., Chatenoud, F., Templeton, I. M., Barber, R., & Sedivy, J. (1994). Low threshold CW operation of circular-grating surface-emitting DBR lasers using MQW and a self-aligned process. IEEE Photonics Technology Letters, 6(11), 1280-1282.
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  Abstract: In this letter, we present the first room temperature continuous wave operation of circular-grating surface-emitting DBR lasers. The structure is an InGaAs/GaAs strained multi-quantum-well. A modified fabrication process with a better control on the steps is used. A CW threshold current as low as 26 mA at a lasing wavelength of about 977 nm are reported. This is the first demonstration of CW operation for these lasers in any material system.
• Janz, C. F., Keyworth, B. P., Allegretto, W., MacDonald, R. I., Fallahi, M., Hillier, G., & Rolland, C. (1994). Mach-Zehnder switch employing an ultra-compact directional coupler. Conference on Lasers and Electro-Optics Europe - Technical Digest, 346-347.
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  Abstract: Multimode waveguide couplers using widely spaced access waveguides have showed good performance, but carries the penalty of increased device length. This can be detrimental to deeply etched, strongly confining rib waveguides. A theoretical and experimental study on ultra-compact couplers were conducted by implementing in these structures small separations and large branching angles of the access waveguides. A computer model is utilized to examine the effects of employing large branching angles of the access guides and to describe mode fields which were effectively x-y separable. The results of an experimental study on quantum well Mach Zehnder directional switch showed good correlation with the model predictions.
• Janz, C. F., Keyworth, B. P., Allegretto, W., MacDonald, R. I., Fallahi, M., Hillier, G., & Rolland, C. (1994). Mach-Zehnder switch using an ultra-compact directional coupler in a strongly-confining rib structure. IEEE Photonics Technology Letters, 6(8), 981-983.
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  Abstract: A quantum well Mach-Zehnder switch operating at 1.55 μm, fabricated in a strongly-confining rib waveguide structure, and employing a multi-mode 3-dB output coupler only 40 μm long, is described. The device yields almost 10 dB of contrast between outputs at 3 V bias, with 4.3 dB of excess coupler loss. The total cleaved device length is only 1.5 mm, and high bandwidth (15 GHz) operability is anticipated. A simple computer model of the coupler is in good agreement with the measured results, and predicts enhanced performance with a small increase in the coupler length.
• Najafi, S., & Fallahi, M. (1994). Circular grating surface emitting lasers. Proceedings of SPIE - The International Society for Optical Engineering, 2213, 178-186.
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  Abstract: In this paper, we discuss circular grating surface emitting lasers and review the progress in this field. The theoretical approach to analyze these lasers is mentioned. The fabrication technology to make them is explained. Recent achievements are presented.
• Najafi, S., Fallahi, M., Lefebvre, P., Francois, V., & Templeton, I. M. (1994). Integrated optical tap-power-divider. Proceedings of SPIE - The International Society for Optical Engineering, 2213, 133-136.
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  Abstract: A new integrated optical 1:N tap-power-divider is proposed and demonstrated. It is compact, and can tap and divide light at any ratio in an integrated optical system.
• Chunmeng, W. u., Makino, T., Najafi, S., Maciejko, R., Svilans, M., Glinski, J., & Fallahi, M. (1993). Threshold gain and threshold current analysis of circular grating DFB and DBR lasers. IEEE Journal of Quantum Electronics, 29(10), 2596-2606.
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  Abstract: A TE-cylindrical wave threshold gain and threshold current analysis is presented for circular grating distributed feedback (CG-DFB) and circular grating distributed-Bragg-reflector (CG-DBR) lasers. Mode properties of CG-DFB/DBR lasers are discussed. It is found that the threshold gain, threshold current density and threshold current of CG-DBR lasers can be much lower than those of CG-DFB lasers.
• Fallahi, M., Dion, M., Chatenoud, F., Templeton, I. M., & Barber, R. (1993). High power emission from strained DQW circular-grating surface-emitting DBR lasers. Electronics Letters, 29(24), 2117-2118.
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  Abstract: High power operation of circular-grating surface-emitting distributed Bragg reflector lasers is demonstrated. The structure is a strained InGaAs/GaAs double quantum well grown by one step MBE. Circular gratings are defined by electron beam lithography. A surface emission power over 100 mW is obtained.
• Fallahi, M., Dion, M., Chatenoud, F., Templeton, I. M., McGreer, K. A., Champion, G., & Barber, R. (1993). Low divergence electrically pumped circular-grating surface-emitting DBR laser on an InGaAs/GaAs structure. Electronics Letters, 29(16), 1412-1414.
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  Abstract: The Letter reports the fabrication and low divergence operation of an electrically pumped circular grating surface emitting DBR laser on an InGaAs/GaAs SQW structure. A threshold current below 85 mA, output power of more than 20 mW and a divergence of less than 1° FWHM were obtained.
• Najafi, S. I., Fallahi, M., Lefebvre, P., Wu, C., & Templeton, I. (1993). Integrated optical circular grating tap power divider. Electronics Letters, 29(16), 1417-1418.
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  Abstract: A new compact integrated optical tap and multiport power divider is provided. A four-port device is made in a glass substrate and is tested at 514 nm wavelength.
• Pakulski, G., Moore, R., Maritan, C., Shepherd, F., Fallahi, M., Templeton, I., & Champion, G. (1993). Fused silica masks for printing uniform and phase adjusted gratings for distributed feedback lasers. Applied Physics Letters, 62(3), 222-224.
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  Abstract: A method for producing durable fused silica self-interference grating photomasks is described. These masks allow repeated printing of both uniform and phase adjusted gratings. Periods as fine as 200 nm have been demonstrated. The fabrication of these masks via holographic and focused ion beam lithography and their use as a lithography tool are explained. Distributed feedback lasers, with gratings made by this technique, were produced. These lasers operated in a single longitudinal mode at a wavelength of either 1.55 or 1.3 μm.
• Fallahi, M., Chatenoud, F., Templeton, I. M., Dion, M., Wu, C. M., Delage, A., & Barber, R. (1992). Electrically pumped circular-grating surface-emitting DBR laser on InGaAs strained single-quantum-well structure. IEEE Photonics Technology Letters, 4(10), 1087-1089.
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  Abstract: The authors demonstrate the fabrication and room temperature operation of an electrically pumped circular-grating surface-emitting distributed-Bragg-reflector laser. An InGaAs/GaAs single quantum well (SQW) graded-index separate confinement heterostructure (GRINSCH) structure was grown by one-step molecular beam epitaxy (MBE). Circular gratings were defined by focused ion beam lithography. The lasing wavelength was 942 nm, and the threshold current was 280 mA. This is the first demonstration of these lasers with no epitaxial regrowth.
• Fallahi, M., McGreer, K. A., Delage, A., Normandin, R., Templeton, L. M., Barber, R., Chatnoud, F., & Champion, G. (1992). Demonstration of grating demultiplexer in GaAs/AlGaAs suitable for integration. Electronics Letters, 28(24), 2217-2218.
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  Abstract: Based on Rowland circle construction, a grating spectrometer integrated with 90°C curved output waveguides was designed and fabricated in a GaAs/AlGaAs waveguide structure. By incorporating curved waveguides, a larger separation between output facets was obtained.
• Taylor, R. P., Fortin, S., Sachrajda, A. S., Adams, J. A., Fallahi, M., Davies, M., Coleridge, P. T., & Zawadzki, P. (1992). Low-frequency noise in multiple-quantum-point-contact systems. Physical Review B, 45(16), 9149-9152.
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  Abstract: Electrical-transport measurements were performed on a system consisting of two quantum point contacts (QPCs) in series, where one of the point contacts exhibited low-frequency telegraph noise due to single-impurity effects. We show this system to be ideal for the study of equilibration between the edge states that form at high magnetic fields. We investigate both the adiabatic and nonadiabatic regimes and show that in the transitional magnetic-field range the conductance is compatible with a complete equilibration but between a limited number of edge states only. We also discuss the equivalent experiment at zero field, where one can study the effect of the potential fluctuations on the collimation of the ballistic electrons. In addition, we confirm the observation of 4e2/h quantization in the conductance of a wide QPC. © 1992 The American Physical Society.
• Wu, C. M., Svilans, M., Fallahi, M., Templeton, I., Makino, T., Glinski, J., Maciejko, R., Najafi, S. I., Blaauw, C., Maritan, C., & Knight, D. G. (1992). Electrically pumped circular-grating distributed-Bragg-reflector lasers. IEEE Photonics Technology Letters, 4(9), 960-963.
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  Abstract: The design, fabrication, and lasing characteristics of electrically pumped circular-grating distributed-Bragg-reflector (CG-DBR) surface-emitting lasers, were studied. Surface-emitted lasing action was achieved at room temperature under pulsed condition. Although the measured threshold current is still higher than theoretical calculations, CW operation should be possible by improving the fabrication and the device structure.
• Wu, C., Svilans, M., Fallahi, M., Templeton, I., Makino, T., Glinski, J., Maciejko, R., Najafi, S. I., Maritan, C., Blaauw, C., & Knight, G. (1992). Room temperature operation of electrically pumped surface-emitting circular grating DBR laser. Electronics Letters, 28(11), 1037-1039.
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  Abstract: The first 1.3 μm electrically-pumped surface-emitting circular grating DBR laser operating at room temperature in a GaInAsP/InP heterostructure is reported. The threshold current was 170mA. The surface-emitted output power was 10mW.
• Fallahi, M., Templeton, I. M., & Normandin, R. (1991). Fabrication of circular gratings by FIB damage on GaAs. Institute of Physics Conference Series, 120, 505-509.
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  Abstract: The authors demonstrate a simple technique for the fabrication of circular gratings using direct focused ion beams and selective etching. This technique allows one to fabricate high quality circular gratings and also to control the tooth height and pitch.
• Wu, C., Svilans, M., Fallahi, M., Makino, T., Glinski, J., Maritan, C., & Blaauw, C. (1991). Optically pumped surface-emitting DFB GaInAsP/InP lasers with circular grating. Electronics Letters, 27(20), 1819-1821.
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  Abstract: The lasing action in surface-emitting DFB lasers with circular grating (SE-CG DFB) is reported for the first time. 1.283 μm laser oscillation is demonstrated by optical pumping.
• Filippozzi, J. L., Therez, F., Estève, D., Fallahi, M., Kendil, D., Silva, M. D., Barbe, M., & Cohen-Solal, G. (1990). Integration of a CdTe interdigitated photoconductor with AlGaAs field-effect transistor. Journal of Crystal Growth, 101(1-4), 1013-1017.
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  Abstract: A device associating a GaAs/GaAlAs heterojunction FET with a CdTe photoconductor is presented. FET optimization criteria yielding maximum transconductance have been determined and the Cgs/Gm ratio has been evaluated. The successive technological steps highlight the thermal compatibility of the method of fabrication. The dimensions of our transistor are as follows: 5 μm X 350 μm gate length and width respectively. The photoconductor with an area of 100 μm X 100 μm has three sets of interdigitated ohmic contacts with 10 μm spacing between the fingers. FET transconductance values over 25 mS/mm have been achieved. The integrated circuit presents a responsivity Iout/Popt as high as 30 A/W while that of the photoconductor is 2 A/W at 4 V gate bias. The Hall measurement of the CdTe layer gives a mobility of 270 cm2/V·s at room temperature and a resistivity of 100 Ω cm. © 1989.
• Fallahi, M., Therez, F., Esteve, D., Kendil, D., Barbe, M., & Cohen-Solal, G. (1988). Compatibility in heterogeneous integration of a CdTe interdigitated field-effect transistor. Electronics Letters, 24(19), 1245-1246.
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  Abstract: A CdTe PC-AlGaAs/GaAs FET OEIC has been fabricated for the first time. The compatibility of such an integration is shown. Such an integration permits the use of high-quality optical compounds with performance electronic materials. A responsibility of 30 A/W at 0.77 μm has been obtained for integrated circuits. This integration opens a new perspective in heterostructure infra-red OEICs.
• Therez, F., Belaroussi, M. T., Fallahi, M., & Kendil, D. (1987). DESIGN AND REALIZATION OF A GaAs FET INTEGRATED WITH A HETEROJUNCTION PHOTODIODE.. Le Vide, les couches minces, 42(239), 479-484.
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  Abstract: Integrated receivers associating an amplifier with a photodiode increases the detector sensitivity. During this work, we have designed and characterized the FET amplifier. The field-effect transistor JFET has been fabricated on a GaAs semi-insulating substrate using liquid phase epitaxy. The structure involved two epitaxial layers of n-GaAs for the channel and GaAlAs for the gate. The design, the technology process and the current-voltage characteristics are described. A transconductance values over 10 mA/V has been achieved and the transistor have shown a threshold voltage of 4. 6 V. The previous results will be applied to two kinds of structures: FET devices without the detector and for the amplifier integrating the photodiode. The various devices have been characterized and analysed.

Proceedings Publications

• Gottesman, N., Slocum, M., Sevison, G., Wolf, M., Lukowski, M., Hessenius, C., Fallahi, M., & Bedford, R. (2024, February). Infrared vertical external cavity surface emitting laser threshold quantum magnetometer. In Photonics West 2024 Proceeding.
• Meyer, J. T., Lukowski, M., Hessenius, C., Wright, E. M., & Fallahi, M. (2021, May). Passively Mode Locked 265 nm VECSEL Utilizing All-Intracavity Harmonic Generation. In CLEO 2021.
• Yakshin, M., Prasad, C., Hessenius, C., & Fallahi, M. (2017, May). A Compact, Efficient Deep UV Optically Pumped VECSEL. In CLEO 2017.
• Fallahi, M., Lukowski, M., Hessenius, C., & Meyer, J. (2016, spring). Over 10 Watt, collinear blue and green vertical external cavity surface emitting laser. In Photonics West, Proc. SPIE 9734.

Presentations

• Bedford, R., Gottesman, N., Sevison, G., Fallahi, M., Wolf, M., & Slocum, M. (2023, Fall). Intracavity Laser Absorption-based Vector Magnetic Field Sensing . Frontiers in Optics + Laser Science Conference, Presentation ID: JTu5A.38 ; 09 - 12 October 2023.
• Fallahi, M. (2019, February). Watt- Level, Two- Color Tunable Semiconductor Lasers. ARIZONA PHOTONICS DAYS 2019. Tucson, AZ.
• Yakshin, M., Prasad, C., Hessenius, C., & Fallahi, M. (2019, March). A Compact, Efficient, Optically Pumped Deep UV Laser. GOMACTech 2019. Albuquerque, NM.
• Fallahi, M. (2017, April). 2D Materials for Photonic Devices: An NSF Perspective (keynote talk). Conference on Micro- and Nanotechnology Sensors, Systems, and Applications IX, SPIE Defense and Security. Anaheim: SPIE.
• Fallahi, M. (2017, January). Advances in Vertical External Cavity Surface Emitting Lasers (VECSEL) for New Wavelengths Generation (Keynote talk). Conference on Quantum Sensing and Nano Electronics and Photonics XVSPIE Photonics West 2017. San Francisco.
• Fallahi, M. (2016, Fall). High-Power, High-Brightness Tunable Two Color Vertical External Cavity Surface Emitting Lasers (VECSELs). Optics-2016. Atlanta, GA..
• Fallahi, M. (2016, June). Latest Developments in High-Power Vertical External Cavity Surface Emitting Lasers (Invited). Seventh International Conference on Optical, Optoelectronic and Photonic Materials and Applications 2016 (ICOOPMA 2016), June 2016, Montreal, Canada. Montreal, Canada: IEEE.