Highly efficient and tunable polarization rotator based on lithium niobate on an insulator

The lithium niobate on an insulator (LNOI) platform has greatly advanced the development of integrated photonics recently, where efficient polarization management components are indispensable. In this work, we propose a highly efficient and tunable polarization rotator based on the LNOI platform and the low-loss optical phase change material antimony triselenide (S b ₂ S e ₃). The key polarization rotation region is formed by a LNOI waveguide with a cross section of the double trapezoidal shape and a S b ₂ S e ₃ layer deposited atop the LNOI waveguide in an asymmetrical way, where an isolating layer of silicon dioxide is sandwiched between them to reduce the material absorption loss. Based on such a structure, we have achieved the efficient polarization rotation in a length of only 17.7 µm, where the polarization conversion efficiency and insertion loss are 99.6% (99.2%) and 0.38 dB (0.4 dB) for the trans-electric (TE)-to-trans-magnetic (TM) rotation. If we further change the phase state of the S b ₂ S e ₃ layer, other polarization rotation angles besides 90° can also be obtained for the same device, revealing a tunable function. We believe that the proposed device and design scheme could offer an efficient method for realizing the polarization management on the LNOI platform.