Polarization-Insensitive Electrooptic Modulation on Anisotropic Thin-Film Lithium Niobate

Abstract

Lithium niobate (LN) is an ideal material for electrooptic (EO) modulation due to its strong EO effect. However, significant differences exist in the EO modulation efficiencies for different polarizations, given the anisotropy of LN. Here, we propose an innovative approach to mitigate the modulation polarization dependence of thin-film LN. We convert one of the orthogonal polarizations of the incident light to the higher-order mode of the other polarization and utilize mode-compatible components to achieve mode-independent signal processing, thereby converting the polarization issue into a mode issue and achieving polarization-independent signal processing. We also demonstrated a polarization-insensitive EO switch to validate this approach. The fabricated device demonstrates a low polarization-dependent loss of 0−2.4 dB across a 30 nm range (1260−1290 nm) and achieves the same modulation efficiency of 2.7 V•cm for TE and TM polarizations. The approach provides a robust solution to the EO modulation polarization dependence problem caused by the anisotropy in LN and other similar materials.