Polarization conversion in passive deep-etched GaAs/AlGaAs waveguides

Experimental results are presented to demonstrate polarization conversion in passive deep-etched gallium arsenide waveguides. The effect due to process-dependent features of waveguide cross-section geometry, in particular the asymmetry resulting from nonvertical etching, is investigated. A qualitative agreement with vector finite element method (VFEM) simulations is shown. A coupled-mode formulation is used to describe the behavior. The results are compared with an elliptical-polarization analysis, obtained from measurements of the polarization angles of the fundamental waveguide modes and the difference between their effective indices. A novel technique used to carry out effective-index-difference measurements is reported