Compact Variable ${\rm TE}$-${\rm TM}$ Polarization Splitter Based on Simplified Coherent Coupling in Lithium Niobate

A compact-sized electrically tunable TE-TM mode splitter composed of a mode converter and an asymmetric Y-branch structure is presented. The asymmetric Y-branch consists of a straight and a bent waveguides to split two polarization modes based on the mode-sorting effect. To shorten the device length, a simplified coherently coupled-bending structure is utilized for the bent waveguide. Experimental results show that the device length is reduced about 52%, extinction ratios of both TE and TM modes are higher than 25 dB, yet the applied voltage is not significantly increased.