4-channel optical circulator based on traveling-wave electro-optic modulation

Optical circulators enable bidirectional transmission of light and play an important role in data centers, communication networks and LIDAR. The integration of optical circulators is currently one of the thorny issues limiting the full integration of optical systems, and the usual schemes require hybrid integration of magneto-optical materials to break the optical reciprocity. In this work, we propose a thin-film lithium niobate (TFLN) optical circulator consisting of a traveling-wave electrode modulator (TWEM) and micro-ring resonators (MRRs). It realizes optical non-reciprocity based on the phase accumulation asymmetry of forward and backward traveling wave modulation, and adjusts the path of light with the help of the MRRs. The circulator has four optical channels to realize the light propagation along the 1-2-3-4-1 spatial sequence. The calculated isolation of each channel is greater than 20 dB, and the channel loss is less than 3 dB. Our scheme is wavelength-tunable, scalable, and process-friendly, and provides a promising implementation route for all-optical integration.