Compact, Broadband and Low-Loss Polarization Beam Splitter on Lithium-Niobate-On-Insulator Using a Silicon Nanowire Assisted Waveguide

We propose a compact, broadband, and low-loss polarization beam splitter (PBS) based on an asymmetrical directional coupler on the lithium-niobate-on-insulator platform, consisting of an amorphous silicon (a-Si) assisted waveguide, and a normal waveguide. With proper design of the a-Si nanowire, and lithium niobate waveguides, the phase-matching condition is satisfied for TE polarization, while significant mismatching exists for TM polarization. A 16-mu m-long PBS (including the s-bend region) with a 200 nm gap is achieved. Numerical simulations show that the PBS exhibits a 140-nm bandwidth for extinction ratios lager than 10 dB. Moreover, the device has an ultra-low insertion loss (IL similar to 0.05 dB), and maintaining ILs < 0.5 dB over a 170 nm wavelength range.