Lithium Niobate Thin Film Polarization Beam Splitter Based on Asymmetric Directional Coupling

Polarization devices on lithium niobate thin film (LNTF) are vital components for photonic integrated circuits (PICs) on the novel platform. Because both linear and nonlinear devices on the anisotropic platform are intrinsically polarization-dependent. Here, we demonstrate compact polarization beam splitters (PBS) on LNTF based on two asymmetric directional couplers with an effective length of only 180 μm. The PBS is fabricated via a single-step electron beam lithography (EBL) and inductively coupled plasma (ICP) etching process. Our device shows efficient PBS operation at the telecom bands with an extinction ratio over 26 dB and 13 dB for fundamental TE and TM modes, respectively. The device holds promise for efficient on-chip polarization division multiplexing and polarization manipulation, which would become an indispensable component in future LNTF PICs.