Design and Optimization of a Compact Ultra-Broadband Polarization Beam Splitter for the SCL-Band Based on a Thick Silicon Nitride Platform

Abstract

The polarization beam splitter is an essential photonic integrated circuit in applications where a high-performing on-chip polarization diversity scheme is required. The lower refractive index contrast of the silicon nitride material platform compared to silicon-on-insulator constitutes the separation of polarized light states a challenging task since for this purpose a large difference between the effective refractive indices of the fundamental TE and TM modes is highly desirable. In this paper, we present the design and optimization analysis of an ultra-broadband polarization beam splitter based on a thick silicon nitride platform through extensive 3D-FDTD simulations. The proposed device exploits two different Si3N4 thicknesses that enable the discrimination of the two polarizations at the proximity of an 800 nm thick slot and a 470 nm thick strip waveguide via directional coupling. The proposed two-stage PBS achieves higher than 30.6 dB polarization extinction ratio (PER) for both TE and TM polarizations across a 130 nm span at the SCL-band. The dimensions of the PBS are 94 × 14 μm2 and the insertion losses are calculated to be lower than 0.8 dB for both polarizations. The fabrication tolerance of the device is also discussed.