Ultra‐Compact, Broadband Polarization Beam Splitters on Etchless Thin‐Film Lithium Niobate Platform

ABSTRACT Thin‐film lithium niobate (TFLN) has emerged as a promising platform for high‐performance photonic integrated circuits (PICs) due to its excellent electro‐optic (EO) properties, wide transparency window, and efficient optical nonlinearity. However, most of the optical components based on the TFLN platform are effective for only one single polarization, therefore, polarization management is very important for polarization‐insensitive TFLN‐PICs. Polarization beam splitters (PBSs) are one of the key polarization management components for separating and combining orthogonal polarizations—transverse electric (TE) and transverse magnetic (TM) polarizations. In this work, two ultra‐compact, broadband PBSs using metamaterial structures formed by subwavelength grating (SWG) are demonstrated on the etchless TFLN platform by introducing a silicon nitride thin film layer on top of the TFLN wafer as the loading material. These metamaterial structures constructed by SWG can flexibly control the refractive index while reducing radiation loss. The footprints of the proposed PBSs are reduced to 2.45 × 78.0 µm 2 and 4.20 × 53.2 µm 2 , respectively. This work offers a promising approach for achieving compact, high‐speed, and large data capacity lithium niobate PICs in the future.