Integrated Broadband and Low-Loss TM Mode Magneto-Optical Circulator Based on Lithium Niobate on Insulator

In photonic integrated circuits (PICs), optical isolators and circulators are utilized to protect active devices from backscattering and to reroute the optical signal. An optical circulator based on the LNOI platform is required to possess wide bandwidth and high isolation ratio simultaneously. A 4-port broadband optical circulator for TM mode with high isolation ratio on the lithium niobate on insulator (LNOI) platform is proposed. The circulator, based on the Mach–Zehnder Interferometer (MZI), consists of two 2 × 2 multimode interferometers (MMIs), and a non-reciprocal and reciprocal waveguide. The circulator we designed based on the magneto-optical effect achieved an ultra-wide 30 dB isolation bandwidth of 84 nm. We optimized the configuration of the Ce:YIG/LiNbO3 composite waveguide and 3 dB power splitter/combiner, achieving low-loss and compact non-reciprocal waveguides and MMIs. The total insertion loss is 1.04 dB. The wide bandwidth and low-loss characteristics give our device significant potential for application in high-density photonic integrated circuits.