Broadband thin-film lithium niobate-based polarization rotator-splitter with symmetrical Y-junction and adiabatic coupler

A broadband thin-film lithium niobate-based polarization rotator-splitter (PRS) fabricated via standard photolithography is demonstrated. The fully shallow-etched device exhibits polarization extinction ratios exceeding 20.2 dB (TM 0 input) and 18 dB (TE 0 input) in the C-band, with insertion losses of 0.22 dB and 1.57 dB, respectively. This design innovatively incorporates a Y-junction and a 3-dB adiabatic coupler, which eliminates the need for the filter used in conventional PRSs and results in a shorter device length compared to a full coupler. Additionally, it features a simple fabrication process and cost efficiency, coupled with the system-level advantage of mitigated back-reflection.