Compact polarization splitter-rotator based on lithium niobate-on-insulator platform

We propose a compact mode-coupled polarization splitter-rotator (PSR) based on the lithium niobate-on-insulator platform. The PSR is composed of an asymmetric directional coupler, a taper, and an S-bend. Cross-polarization mode coupling is achieved using a ridge waveguide and air cladding to break the symmetry of the waveguide cross section with a length of only 61 mu m. Simulation results show that the insertion losses of this device in the 1500-1600 nm range are less than 1.85 and 0.31 dB for TM0 and TE0 modes, respectively, and the extinction ratios are more than 22.5 and 22.7 dB, respectively. In addition, the PSR exhibits a polarization conversion efficiency of 99.97% at 1550 nm. The proposed PSR has great potential for applications in polarization-division multiplexing transmitters and on-chip polarization controllers.