Squeezing-induced nonreciprocal transparency and the slow-to-fast-light switch

We propose a theoretical method to realize nonreciprocal light transmission in an optomechanical device assisted by directional quantum squeezing. Specifically, we consider the device consisting of an optomechanical resonator and a nonlinear optical resonator with directional pumping. We find that optical squeezing occurs along the pump direction when the nonlinear resonator is directionally pumped, enabling nonreciprocal light transmission as well as nonreciprocal group delay (slow light) or advancement (fast light). Furthermore, we find that the efficiency of the second-order sidebands can be enhanced in one direction compared with the opposite direction. Our work provides a promising design for the application of directionally squeezed optomechanical devices in nonreciprocal optical communication and signal processing.