Low-Cost-By-Design Mid-Wave Infrared Semiconductor Surface Emitting Lasers


OBJECTIVE: Develop high-power, surface-emitting semiconductor lasers or beam-combined surface-emitting laser arrays emitting at ~4.5 um range. DESCRIPTION: Monolithic surface-emitting (SE) semiconductor lasers hold promise for significant advantages over edge-emitting lasers in terms of both reliable operation and manufacturing cost. Device-failure modes of edge-emitting lasers that are triggered by high facet optical-power densities and/or temperatures, which, in turn, generally limit the reliable output power of edge-emitting lasers, are thus eliminated. Due to these advantages of the surface emitting designs, near-infrared vertical cavity surface emitting lasers (VCSELs) has been very successfully commercialized and VCSELs have been ultra low-cost sources in the market. The substantial cost reduction of the surface emitting laser diodes is primarily achieved via the elimination of a few high-cost, low-yield, labor intensive fabrication and packaging steps such as wafer lapping, cleaving, dicing, facet-coatings, and chip bonding, etc., which amount to 60 to 75% of the total cost of manufacturing the edge-emitting laser diodes. Using the similar design and manufacturing paradigm in the near-infrared surface emitting laser diodes, one can envision that SE mid-wave infrared (MWIR) lasers or beam-combined laser arrays can significantly improve the affordability of these semiconductor lasers because of the ability to perform full wafer-scale device array fabricating and testing, without the need to separate and package the individual chips prior to testing. Extension of the VCSEL technology to the mid-infrared region by employing interband-transition laser structures has proven challenging due to its unique emission polarization caused by the intersubband transitions that is not compatible with VCSEL"s distributed Bragg reflectors (DBRs). As an alternate technology path to VCSEL based on DBRs, grating-coupled (GC) surface emitters have been demonstrated with single-spatial-mode, single-frequency continuous wave (CW) operation, with the added advantage that higher single-mode CW output powers can potentially be achieved. In particular, SE laser with distributed feedback (DFB) out-coupling gratings that enables both stable-beam as well as frequency-stabilized operation has been demonstrated with output power as high as 73 Watt (W) in the near-infrared regime (<1 m). However, MWIR GC-SE-DFB lasers employing intersubband transitions and emitting through the substrate have been demonstrated as well, but with emission wavelengths longer than 5.0 m and also without spatial-mode stabilization. Last but not the least, GC surface emitting ring quantum cascade lasers (QCL) has also been demonstrated with reasonably high output power but with an asymmetric and non-Gaussian circular far-field beam pattern. It is therefore the goal of this program to seek an innovative low-cost-by-design, power-scalable, chip-based platform solution that enables high-power surface emission from a single aperture with outstanding beam quality from either a single SE QCL or monolithic coherently or spectrally beam-combined SE QCL array at ~ 4.5 m range. The device development in this program should enable innovative wafer-level fabrication and testing for the mid-infrared semiconductor lasers to substantially reduce the cost of manufacturing and hence the affordability of the lasers. PHASE I: Develop a design for a single SE QCL or monolithic beam-combined SE QCL array in the 4.5 m wavelength region. The device should be capable of emitting an output power of over 15 W CW through a single aperture and with an outstanding output beam quality (M2<1.2). PHASE II: Fabricate and demonstrate a prototype single SE QCL or monolithic beam-combined QCL array with output emission out of a single aperture with output power>15 W CW and with outstanding beam quality (M2<1.2) operating in the 4.5 m wavelength region. Demonstrate a path forward to power-scale the SE QCL or SE QCL array monolithically at the wafer level without external optics to power levels exceeding 100 W CW while maintaining M2<1.2. PHASE III: Develop low cost manufacturing process and transition the high-power QCL or beam-combined QCL array for DoD application in the areas of DIRCM, advanced chemical sensors, and LIDAR. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The commercial sector can significantly benefit from this technology development in the areas of detection of toxic industrial gases, environmental monitoring, and non-invasive medical health monitoring and sensing. REFERENCES: 1. Arafin, S., Bachmann, A., & Aman, M.C. (2011). Transverse-mode characteristics of GaSb-based VCSELs with buried-tunnel junctions. IEEE Journal of Selected Topics in Quantum Electronics, 17(6), 1576-1583. doi:10.1109/JSTQE.2011.2107571 2. Bai, Y., Tsao, S., Bandyopadhyay, N., Slivken, S., Lu, Q.Y., Caffey, D., Pushkarsky, M., Day, T., & Razeghi, M. (2011). High power, continuous wave, quantum cascade ring laser. Applied Physics Letters, 99(26), 261104. doi:10.1063/1.3672049 3. Lyakh, A., Zory, P., D"Souza, M., Botez, D., & Bour, D. (2007). Substrate-emitting, distributed feedback quantum cascade lasers. Applied Physics Letters, 91(18). doi:10.1063/1.2803851 4. Kanskar, M., Cai, J., Kedlaya, D., Olson, D., Xiao, Y., Klos, T., Martin, M., Galstad, C., & Macomber, S.H. (2010). High-brightness surface-emitting distributed feedback laser and arrays. Proceedings of SPIE, Laser Technology for Defense and Security VI, 7686. doi:10.1117/12.853037

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