Design and Numerical Verification of Four States Polarization-independent Grating Coupler Using a Double-Layer Approach for a Single-photon Source based on HPW

Abstract

In this paper, a double-layer approach is proposed to design a compact four states polarization-independent grating coupler (GC). The proposed polarization-independent GC is designed to couple a 700 nm polarized light propagated in a 150 nm Gallium Phosphide (GaP) waveguide to a polarization-maintaining fiber (PMF). The double-layer approach is based on the deposition of GaP gratings designed to couple the transverse magnetic (TM) light over the GaP gratings designed to couple the transverse electric (TE) light. The two layers are separated by a Hydrogen silsesquioxane (HSQ) with an optimum thickness of 20 nm. The proposed method resulted in relatively high coupling efficiencies (CEs) of 39.2%, 31.1%, and 23.3% for the TE, TM, and 45º/-45º linearly polarized light, respectively. The polarization-dependent loss (PDL) is 1 dB, 1.26 dB, and 2.26 dB corresponds to TE-TM, TM-45º/-45º, and TE-45º/-45º, respectively. The performance of the double-layer approach is numerically verified by the two-dimensional (2D) finite element algorithm (FEM) using COMSOL software. The proposed method suggests a novel and simple approach to design a compact four states polarization-independent GC that could be used in integrated (on-chip) photonic communication circuits.