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Proceedings Paper

Surface-emitting quantum cascade lasers with 2nd-order metal/semiconductor gratings for high continuous-wave performance
Author(s): J. H. Ryu; C. Sigler; C. Boyle; J. D. Kirch; D. Lindberg; T. Earles; D. Botez; L. J. Mawst
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Paper Abstract

Grating-coupled, surface-emitting (GCSE) quantum-cascade lasers (QCLs) offer a pathway towards realizing watt-range, surface-emitted output powers in the mid-infrared spectral region with high beam quality. Previously we have reported wide-ridge GCSE QCLs which employed metal/semiconductor, 2nd-order distributed feedback (DFB) gratings with distributed Bragg reflector (DBR) terminations. We report here on the lasing characteristics of narrow-ridge (~7 μm-wide) GCSE devices, which employ the STA-RE-type active-region design, for obtaining single-spatial-mode both laterally and longitudinally. The QCL structure was grown using Metalorganic Chemical Vapor Deposition (MOCVD) and the grating was defined using a combination of e-beam lithography patterning and wet-chemical etching, and the ridge (~7 μm) was dry-etched. The total length of the DFB + DBR regions is 5.1 mm, and was electrically isolated in the DBR regions by employing AlOx. Due to resonant coupling of the guided light to the antisymmetric surface-plasmon modes of the 2nd-order grating, the antisymmetric (A) modes are strongly absorbed; thus, allowing for the symmetric (S) mode to be favored to lase. Initial devices have demonstrated maximum pulse output power from the surface of ~150 mW at 4.88 μm, with only ~10% power emitted from the edge facets. An anti-reflective (AR) coating of a quarter-wavelength Y2O3 layer was applied on the emission window, drastically improving the far-field beam pattern, that resulting in a central, near-diffraction-limited single-lobe beam pattern. COMSOL simulations were performed to further optimize the SE-base design for high CW performance. Parameter sweeps of cladding-layer thickness, grating height, and grating duty cycle were performed, which identified design tradeoffs for the various structural parameters.

Paper Details

Date Published: 24 February 2020
PDF: 11 pages
Proc. SPIE 11301, Novel In-Plane Semiconductor Lasers XIX, 113011P (24 February 2020); doi: 10.1117/12.2543595
Show Author Affiliations
J. H. Ryu, Univ. of Wisconsin-Madison (United States)
C. Sigler, Univ. of Wisconsin-Madison (United States)
C. Boyle, Univ. of Wisconsin-Madison (United States)
J. D. Kirch, Univ. of Wisconsin-Madison (United States)
D. Lindberg, Intraband, LLC (United States)
T. Earles, Intraband, LLC (United States)
D. Botez, Univ. of Wisconsin-Madison (United States)
L. J. Mawst, Univ. of Wisconsin-Madison (United States)

Published in SPIE Proceedings Vol. 11301:
Novel In-Plane Semiconductor Lasers XIX
Alexey A. Belyanin; Peter M. Smowton, Editor(s)

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