Ultra-broadband magneto-optical isolators and circulators on a silicon nitride photonics platform

Broadband optical isolators and circulators are highly desirable for wavelength-division multiplexing, light detection, and ranging systems. However, the silicon-integrated optical isolators and circulators reported so far have a limited isolation bandwidth of only several nanometers, due to waveguide and material dispersion. In this paper, we report the development of broadband magneto-optical isolators on silicon nitride waveguides. We proposed a general method of dispersion compensation to achieve a constant phase difference between reciprocal and nonreciprocal phase shifts in a Mach–Zehnder interferometer over a wide frequency range. This method enabled a theoretical 30 dB isolation/circulation bandwidth of more than 240 nm, which covers the S, C, L, and U bands. The fabricated devices showed a maximum isolation ratio of 28 dB, crosstalk of −28dB, high 20-dB isolation bandwidth of 29 nm (3.48 THz), and a relatively low loss of 2.7 dB in the wavelength range of 1520–1610 nm. By further heating the reciprocal phase shifter based on the thermo-optic effect, the experimental 20 dB isolation bandwidth of the device increased to 90 nm (11.03 THz). This method has also been applied to the design of broadband, low-loss isolators, and O/C dual-band isolators/circulators. Our work experimentally demonstrated broadband-integrated optical isolators and circulators on silicon, paving the way for their use in optical communication, data communication, and LiDAR applications.