N13A-T006 TITLE: Low-Cost-By-Design Mid-Wave Infrared Semiconductor Surface Emitting Lasers

TECHNOLOGY AREAS: Air Platform, Sensors, Electronics

ACQUISITION PROGRAM: PMA 272

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