Comparison of cross-section profile designs for integrated polarization mode controllers

Many laser applications in quantum technology require circularly polarized light at wavelengths accessible only through the GaAs-AlGaAs material system. Two proven designs of polarization mode convertor (PMC) were compared through simulation for a modified commercial 830 nm GaAs-AlGaAs structure. Structure type 1 used a deep-etched ridge waveguide, with a shallow-etched slot placed asymmetrically within the ridge. Structure type 2 also used a deep-etched ridge, but with sides of the ridge etched to different depths. Both structures support zero-order TE and TM modes, with the effective index difference between the modes determining the length of the PMC device. Although a range of dimensions and compositions was investigated, it was found the geometry of the waveguides did not significantly affect the effective index difference. The refractive index of the waveguide core was swept from 3.39 to 3.43, corresponding to Al contents from 0.45 to 0.3 respectively. In both structures, a higher index leads to the mode being concentrated in the core, which may lead to lower losses. As the structures give similar results, the main decider as to which one should be chosen should be the relative simplicity of fabrication.