TM Mode Bending Waveguide Based on x-Cut Thin-Film Lithium Niobate (Invited)

Due to the anisotropy of the x-cut thin-film lithium niobate optical integration platform, the transverse magnetic ( TM) mode of the optical waveguide is prone to mode hybridization and coupling to other modes during bending, posing a challenge to the bending of the TM mode. This article takes a 400 nm thick, semi-etched lithium niobate waveguide as an example to analyze the mode hybridization phenomenon of TM0 mode under different waveguide widths and transmission directions, and simulates its 90 degrees bending transmission performance. The findings indicate that within a certain waveguide width range (approximately 1. 7 mu m to 2. 15 mu m), no mode hybridization occurs when bending the TM0 mode. However, for waveguide width lower than 1. 7 mu m or higher than 2. 15 mu m, coupling between the TM0 and TE1 (or TE2) mode occurs. Experimental demonstrations further corroborate this conclusion. This study offers a design methodology for achieving TM mode bending in thin-film lithium niobate waveguides, with potential applications in polarization-control-related optical integrated devices on this platform.