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Keywords:

  • buried heterostructures;
  • InGaAs/InAlAs superlattices;
  • quantum cascade lasers;
  • waveguide structures

Abstract

Optical waveguide structures of InP-based quantum cascade lasers (QCLs) are theoretically analyzed and designed using the finite element method. The optical confinement factor (Γ) and absorption coefficient (α) of the waveguide structures for λ ∼ 4.6, 6, 8.8, and 9.5 µm QCLs with different numbers of active/injector stages (Ns) are calculated. As Ns is decreased at longer wavelength, Γ is gradually decreased and α is increased. For double-channel (DC) ridge waveguide structures of QCLs operating at λ ∼ 9.5 µm, a relatively high optical loss is caused by the lossy insulation layer. To improve the performance, the buried heterostructure (BH) by InP regrowth is used for waveguide design in terms of Ns and waveguide width. For a narrow BH width of ∼10 µm, a low α value of 3.92 cm−1 is obtained compared to 12.32 cm−1 in the DC ridge waveguide structure. With the calculated optical properties of waveguide structures, the device characteristics of QCLs operating at λ ∼ 4.6 and 9.5 µm are theoretically investigated in comparison with the experimental results.