Broadband dynamic nonreciprocity based on a nonlinear Mach-Zehnder interferometer

Nonreciprocal optical devices play a pivotal role in modern optical systems and advanced quantum technologies. Nonreciprocal devices based on optical nonlinearity have garnered significant attention due to their compatibility with on-chip photonics fabrication techniques. However, when the opposite-propagating continuous waves are incident to such nonlinear nonreciprocal devices simultaneously, achieving dynamic nonreciprocity has remained a formidable challenge. In addition, the devices relying on nonlinear resonators suffer from limited bandwidths. In this paper, we theoretically propose a method for achieving an on-chip isolator and quasicirculator by employing a nonlinear Mach-Zehnder interferometer. Harnessing the chirality between self- and cross-Kerr nonlinearities in the nonlinear arm of the interferometer, our device achieves remarkable dynamic nonreciprocity. We obtain an isolation contrast of $\ensuremath{\geqslant}0.9$ for the optical isolator and fidelity of $\ensuremath{\geqslant}0.97$ for the optical quasicirculator, and a broad bandwidth of $20\phantom{\rule{3.33333pt}{0ex}}\text{nm}$ for both. Our protocol paves a way to realize a broadband on-chip nonlinear nonreciprocal device.