Polarization beam splitter on lithium niobate on insulator using a silicon nitride assisted waveguide

A polarization beam splitter (PBS) is proposed based on an asymmetric directional coupler consisting of a silicon nitride assisted waveguide and two ridge waveguides on a lithium niobate on insulator. Due to the silicon nitride buffer layer, the phase-matching condition is satisfied for TE polarization, whereas TM polarization has a significant phase mismatch by choosing reasonable widths of three waveguides. A 112.2-μm-long PBS is designed, and the gap width is chosen to be 300 nm to make it easy to fabricate. Numerical simulations show that the designed PBS has a broad bandwidth (>80 nm) for an extinction ratio of >15 dB and an ultralow insertion loss (<0.35 dB).