We present a programmable silicon photonic integrated circuit (PIC) that can be configured to show nonlinear nonreciprocal transmission at high optical input power. Nonreciprocal transmission in PICs is of fundamental importance in various fields. Despite diverse approaches to generate nonreciprocal transmission, the research on efficient control of this effect is still scarce. The silicon PIC presented here has programmable linear and nonlinear behavior using integrated phase shifters. In the nonlinear regime (high optical power), the device can be configured to be either reciprocal or nonreciprocal between opposite propagation directions with over 30 dB extinction ratio and only 1.5 dB insertion loss. More importantly, the high/low transmission direction can be dynamically reconfigured. Furthermore, nonreciprocal transmission based on nonlinearities usually requires the optical field in both propagation directions to be high, in order to induce a large extinction ratio. For our circuit, only the forward-propagating light needs to have high power to enjoy low-loss transmission while the backward propagating light will always suffer a high rejection. Besides this nonreciprocal behavior, the circuit also offers the ability for all-optical functions, such as switching, optical compute gates, or optical flip-flops, thanks to its unique controllable nonlinear behavior. This work can trigger new research efforts in nonreciprocal photonics circuits.
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