Low-loss and compact TE-pass polarizer based on hybrid plasmonic waveguide on LNOI platform

On-chip polarization management is a critical challenge for high-performance photonic integrated circuits on the lithium-niobate-on-insulator (LNOI) platform. Here, we propose and theoretically demonstrate an ultra-compact TE-pass polarizer based on a hybrid plasmonic LNOI waveguide that overcomes the traditional trade-off between device footprint and insertion loss. The device leverages mode coupling between a surface plasmon polariton and the fundamental TE and TM waveguide modes. By strategically introducing a low-index SiO₂ spacer layer, the TM mode is strongly confined within the high-loss metal-dielectric interface and is effectively extinguished. Conversely, the TE mode remains almost unaltered within the LN waveguide, experiencing minimal perturbation. The device demonstrates strong polarization-dependent attenuation with an extinction ratio of 40 dB and an insertion loss below 0.02 dB for the TE mode at the central wavelength of 1550 nm, all within an ultra-compact device length of just 13 μm. Furthermore, the device exhibits a broad operation bandwidth of 100 nm (1500-1600 nm), maintaining an extinction ratio above 20 dB and an insertion loss below 0.02 dB. The design also shows strong tolerance to key fabrication variations and is fully compatible with standard LNOI processing, offering a practical and high-performance solution for next-generation polarization-diverse photonic systems.