Mechanical Exceptional-Point-Enhanced Second-Order Sideband Generation

Realizing the enhancement and control of the optomechanical induced second-order sideband generation is of great significance in making a low-power optomechaical amplifier and highly sensitive sensor. Here we analyze theoretically light transmission obtained from a hybrid optomechanical system composed of an optical cavity and a pair of directly coupled PT-symmetric mechanical resonators, and in which the cavity is coherently driven by a bichromatic input field consisting of a strong control field and a weak probe field and that works within the perturbative regime. Using experimentally achievable parameters, we show that the transmission of the probe field changes from single to double transparency window via the transition from a broken mechanical PT-symmetric phase to an unbroken mechanical PT-symmetric phase, correspondingly, the second-order sideband generation can be also split from one frequency center into two frequency centers. Especially, when the assisted mechanical PT-symmetric systems reach the vicinity of the exceptional point, the efficiency of second-order generation can be significantly enhanced, compared to the conventional optomechanical system, what can be improved about four orders of magnitude, which is a manifestation of the unique property of mechanical PT-symmetric systems. The proposed mechanism of reaching new levels of second-order sideband generation for optomechanical systems, offers a promising route towards achieving the multimode higher-order sidebands generation and controlling optical frequency combs with an integrable structure.