Over the last years, LiNbO₃ on insulator (LNOI) has emerged as one of the most important platforms for integrated photonic applications because of its large refractive index contrast, outstanding electro-optical and nonlinear optical properties. Rib-loaded waveguide technology is an efficient approach to avoid high surface and sidewall roughness and to relax the difficulty in construction of sub-wavelength structures with steep sidewalls in case of dry-etched LNOI on-chip nanowires. The main issue for the development of rib-loaded LNOI waveguides is the intrinsic TM loss which is caused by the mode conversion between different polarizations at rib boundaries. In this work we show that the intrinsic TM loss can be eliminated by precise control of the waveguide cross section, and a silicon rib-loaded LNOI polarization beam splitter (PBS) is proposed theoretically based on a symmetric directional coupler design. The PBS is designed with a compact size of 42-$\mathrm{\mu }$m coupling length and relatively large bandwidth of $\sim$90 nm for extinction ratio above 15 dB. It is, to the best of our knowledge, the first PBS proposed on rib-loaded LNOI waveguide. We believe this work paves the way for exploration of functional integrated devices based on rib-loaded LNOI waveguides.

近年来，LiNbO ₃绝缘体上（LNOI）由于其大的折射率对比度、出色的电光和非线性光学特性，已成为集成光子应用最重要的平台之一。肋加载波导技术是一种有效的方法，可以避免高表面和侧壁粗糙度，并在干法蚀刻 LNOI 片上纳米线的情况下缓解构建具有陡峭侧壁的亚波长结构的难度。肋加载 LNOI 波导开发的主要问题是固有 TM 损耗，这是由肋边界处不同极化之间的模式转换引起的。在这项工作中，我们表明可以通过精确控制波导截面来消除固有的 TM 损耗，基于对称定向耦合器设计，理论上提出了一种硅肋负载LNOI偏振分束器（PBS）。PBS 设计紧凑，尺寸为 42-$\mathrm{\mu }$m 耦合长度和相对较大的带宽 $～$90 nm 用于消光比高于 15 dB。据我们所知，这是第一个在肋加载 LNOI 波导上提出的 PBS。我们相信这项工作为探索基于肋加载 LNOI 波导的功能集成设备铺平了道路。