Compact TE-pass polarizer based on lithium-niobate-on-insulator assisted by indium tin oxide and silicon nitride

An indium tin oxide (ITO) and silicon nitride (Si₃N₄) assisted compact TE-pass waveguide polarizer based on lithium-niobate-on-insulator is proposed and numerically analyzed. By properly designing the ITO and Si₃N₄ assisted structure and utilizing the epsilon-near-zero effect of ITO, the TM mode is strongly confined in the ITO layer with extremely high loss, while the TE mode is hardly affected and passes through the waveguide with low loss. The simulation results show that the polarizer has an extinction ratio of 22.5 dB and an insertion loss of 0.8 dB at the wavelength of 1.55 μm, and has an operating bandwidth of about 125 nm (from 1540 nm to 1665 nm) for an extinction ratio of > 20 dB and an insertion loss of < 0.95 dB. Moreover, the proposed device exhibits large fabrication tolerances. More notably, the device is compact, with a length of only 7.5 μm, and is appropriate for on-chip applications.