Highly Efficient Polarization Splitter Based on a Silicon-on-Nitride Asymmetric Waveguide for Mid-IR

Abstract

Design of a silicon-based ultracompact polarization splitter (PS) with high extinction ratio (ER) is proposed for the midinfrared-operating wavelength of 4.47 μm. It is based on a directional coupler (DC) that consists of a horizontal slot waveguide (WG) and a strip WG with Si as the core material and CaF 2 as the slot and substrate material. By choosing appropriate structural parameters, we have designed the DC-PS such that only the TM polarization satisfies the phase-matching condition for coupling at the targeted wavelength of 4.47 μm; achieved ERs are 1/441.6 dB and 1/437.1 dB for the cross-coupled and the throughput ports, respectively. Corresponding estimated insertion losses (ILs) are 1/40.25 dB and 1/40.07 dB in a device length of just 1/46.6 μm. Over a broad bandwidth of 200 nm (4.37 to 4.57 μm) in the mid-IR, our designed PS exhibited ER of >37 dB (with IL of <0.5 dB) for the cross-coupled port and an ER of >17 dB (with IL of <0.1 dB) for the throughput port. Numerical estimations revealed excellent tolerance to the potential fabrication errors. © 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).