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31 January 2014 Microstrip-antenna-coupled distributed feedback terahertz quantum-cascade lasers
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Abstract
By introducing coupled microstrip antennas on THz Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), the radiation efficiency of each feedback aperture is greatly enhanced. Single mode emission ~3 THz from a 31-period antenna-coupled third-order DFB laser yields ~4 times improvement in output power comparing with a corrugated thirdorder device fabricated on the same gain medium. This 31-period device has ~15×25° beam divergence and 4 mW pulsed power (4%) at 10 K with maximum lasing temperature (Tmax) at 134 K (pulsed). When phase matching condition is met, emissions from 81 apertures (4-mm long) are coherently combined to form a narrow beam with 12.5° divergence. Further experiment demonstrated the new device at 4 THz (25-period, ~18 μm×1-mm long. The 4 THz device reaches >8 mW pulsed power (10%) at 12 K with Tmax 109 K (pulsed) and >77 K (cw). The slope efficiency is 450 mW/A with 0.57% wall-plug. It is worth pointing out although the antennas would be excited differently, similar enhancement in out-coupling efficiency can also be observed in second-order surface-emitting THz DFB lasers. Begin the abstract two lines below author names and addresses.
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Tsung-Yu Kao, Xiaowei Cai, Qing Hu, and John L. Reno "Microstrip-antenna-coupled distributed feedback terahertz quantum-cascade lasers", Proc. SPIE 8993, Quantum Sensing and Nanophotonic Devices XI, 89930E (31 January 2014); https://doi.org/10.1117/12.2036604
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