Abstract

We report the design and theoretical analysis of optical waveguides of the InP-based quantum cascade laser (QCL) operating at λ~ 9.5 μm. The effective refractive index, optical confinement and absorption coefficient are calculated by using the finite element method (FEM). From FEM simulations, the effect of the number of active/injector stages (N_s) on the optical confinement and waveguide loss of QCLs was investigated. As the N_s in QCLs increased from N_s = 30 to N_s = 70 for the 19 μm wide QCLs structure, the optical confinement was improved from 73.6 % to 90.6 % and the absorption coefficient was reduced from 3.91 cm⁻¹ to 1.47 cm⁻¹. However, the N_s should be optimized considering the heat generated within the active region because the increase in N_s causes a large voltage rise. The influence of ridge width on the optical confinement and absorption coefficient in QCLs with SiO₂ and Si₃N₄ insulation layers was also studied.

© 2009 OSA, IEEE Photonics Society, SPIE, COS, CIC