Field distribution in waveguide of mid-infrared strain-compensated InAlAs/InGaAs/InP quantum cascade laser

In this paper we present calculated mode distributions in double-trench mesa waveguide of a quantum cascade laser (QCL) and far-field distributions of the QCL beam—both calculated and experimental. We have computed electric field distribution in the waveguide, confinement factor and mode absorption for different transversal modes and far-field distributions based on them. The parameters of the modes were calculated for various sizes: width and length, of the QCL waveguide. The maximal mesa width for single-transverse-mode operation was determined to be about 0.7 times wavelength. This value and the mode discrimination depend only slightly on the resonator length. To verify experimentally the results of the simulations we have measured power distribution in the far field by using goniometric profiler. The measured distribution agrees well with the results of the numerical calculations.