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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 3 — Jan. 30, 2012
  • pp: 2539–2547

Ridge-width dependence of the threshold of long wavelength (λ ≈14 µm) quantum cascade lasers with sloped and vertical sidewalls

Xue Huang, Yenting Chiu, William O. Charles, and Claire Gmachl  »View Author Affiliations

Optics Express, Vol. 20, Issue 3, pp. 2539-2547 (2012)

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We investigate the ridge-width dependence of the threshold of Quantum Cascade lasers fabricated by wet and dry etching, respectively. The sloped sidewalls resulting from wet etching affect the threshold in two ways as the ridge gets narrower. First, the transverse modes are deeper in the substrate, hence reducing the optical confinement factor. Second, more important, a non-negligible field exists in the lossy SiO2 insulation layer, as a result of transverse magnetic mode coupling to the surface plamon mode at the insulator/metal surface, which increases the waveguide loss. By contrast, dry etching is anisotropic and leads to waveguides with vertical sidewalls, which avoids the shift of the modes to the substrate layer and coupling to the surface plasmons, resulting in improved threshold compared with wet-etched lasers, e.g., for narrow ridge widths below 20 µm, the threshold of a 14 µm wide λ ≈14 µm laser by dry etching is ~60% lower than that of a wet-etched laser of the same width, at 80 K.

© 2012 OSA

OCIS Codes
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(230.5590) Optical devices : Quantum-well, -wire and -dot devices

ToC Category:
Lasers and Laser Optics

Original Manuscript: December 1, 2011
Revised Manuscript: January 1, 2012
Manuscript Accepted: January 9, 2012
Published: January 19, 2012

Xue Huang, Yenting Chiu, William O. Charles, and Claire Gmachl, "Ridge-width dependence of the threshold of long wavelength (λ ≈14 µm) quantum cascade lasers with sloped and vertical sidewalls," Opt. Express 20, 2539-2547 (2012)

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