Passive on-chip isolators based on the thin-film lithium niobate platform

Optical isolators, the photonic analogs of electronic diodes, are essential for ensuring the unidirectional flow of light in optical systems, thereby mitigating the destabilizing effects of back reflections. Thin-film lithium niobate (TFLN), hailed as "the silicon of photonics," has emerged as a pivotal material in the realm of chip-scale nonlinear optics, propelling the demand for compact optical isolators. We report a breakthrough in the development of a fully passive, integrated optical isolator on the TFLN platform, leveraging the Kerr effect to achieve an impressive 10.3 dB of isolation with a minimal insertion loss of 1.87 dB. Further theoretical simulations have demonstrated that our design, when applied to a microring resonator with a Q factor of 5 x 106, can achieve 20 dB of isolation with an input power of merely 8 mW. This advancement underscores the immense potential of lithium niobate-based Kerr-effect isolators in propelling the integration and application of high-performance on-chip lasers, heralding a new era in integrated photonics.