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Theoretical analysis of free carrier absorption in the cavity of a quantum cascade laser
Author(s) -
Bogdanov Andrey,
Suris Robert
Publication year - 2012
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201100126
Subject(s) - cladding (metalworking) , lasing threshold , terahertz radiation , materials science , quantum cascade laser , optics , waveguide , cascade , dielectric , laser , physics , optoelectronics , chemistry , chromatography , metallurgy
In this work we analyze free carrier absorption (FCA) and polarization ratio (transversality degree) for eigenmodes of a quantum cascade laser (QCL) waveguide. We consider the dielectric function and conductivity of the waveguide core and cladding layers within the Drude–Lorentz approximation. We show that the entire spectrum of a QCL cavity consists of three kinds of eigenmodes: volume, surface, and Langmuir modes. We perform an analytical analysis and numerical calculations of FCA and polarization ratio for each type of the eigenmodes within a wide frequency range from the microwave up to the ultraviolet spectrum. We make a comparative analysis of FCA in the cladding layers and waveguide core. We specify frequency intervals where absorption in the core or in the cladding layers is dominant. Identification of the most favorable modes for lasing is carried out for each part of the spectrum. So, we identify that the main Langmuir mode is the most favorable mode for the lasing at the long‐wave edge of the terahertz (THz) region: (i) it has no frequency cutoff and can be excited at arbitrarily low frequency, (ii) it is nearly transversal that is very favorable for the QCL operation, and (iii) it is almost totally confined within the waveguide core. The model analyzed is directly related to one‐dimensional photonic crystals and metamaterials consisting of alternating anisotropic layers.