Integrated TM-through/TE-converted polarization beam splitter based on z-cut lithium niobate-on-insulator platform

Abstract

Lithium niobate-on-insulator (LNOI) platform has been regarded as the new driving force to push the developments of integrated photonics, where efficient polarization management and mode conversion are the fundamental issues to be solved. In this work, we propose a triple waveguide-based TM-through/TE-converted polarization beam splitter (PBS) integrated on the z-cut LNOI platform, where the device works on the phase matching of optical mode. To improve the device performance and shorten the device size, we have added two cutting angles on both ends of the intermediate waveguide and optimized the length overlap between two evanescent coupling regions. From results, polarization extinction ratio 26.15 dB, insertion loss 0.47 dB for input TM0 mode, and mode conversion efficiency 99.6%, crosstalk − 22.82 dB, insertion loss 0.12 dB for input TE0 to output TE1 mode have been obtained, respectively. So, efficient polarization separation and mode conversion have been achieved simultaneously on-chip. Further, the proposed device scheme can be extended to output other higher-order TE modes via adding the width of the cross output waveguide. We hope such device scheme can make for the compact integration and capacity improvement of on-chip optical interconnects through multiplexing transmissions on the LNOI platform.