Integrated circulators and isolators are important for developing on-chip optical technologies such as laser cavities, communication systems and quantum information processors. These devices seem to inherently require mirror symmetry breaking to separate backwards from forwards propagation, and thus existing implementations rely on magnetic materials or interactions driven by propagating waves. By contrast to past works, we exhibit a mirror-symmetric non-reciprocal device that comprises three coupled photonic resonators implemented in thin-film lithium niobate. Applying radiofrequency modulation, we drive conversion between the frequency eigenmodes of this system. We measure nearly 40 dB of isolation for approximately 75 mW of radiofrequency power near 1,550 nm. We simultaneously generate non-reciprocal conversion between all of the eigenmodes to demonstrate circulation. Mirror-symmetric circulation simplifies the fabrication and operation of non-reciprocal integrated devices. Finally, we consider applications of such on-chip isolators and circulators, such as full-duplex isolation within a single waveguide.

集成环行器和隔离器对于开发片上光学技术（如激光腔、通信系统和量子信息处理器）非常重要。这些设备似乎天生就需要打破镜像对称性才能将向后与向前传播分开，因此现有的实现依赖于磁性材料或由传播波驱动的相互作用。与过去的工作相比，我们展示了一种镜像对称的非互易器件，该器件包括三个在薄膜铌酸锂中实现的耦合光子谐振器。应用射频调制，我们驱动该系统的频率特征模式之间的转换。对于 1,550 nm 附近的约 75 mW 射频功率，我们测量了近 40 dB 的隔离度。我们同时在所有本征模态之间产生非互易转换以证明循环。镜像对称循环简化了非互易集成器件的制造和操作。最后，我们考虑了这种片上隔离器和环行器的应用，例如单个波导内的全双工隔离。