Directional amplifiers in a hybrid optomechanical system

Abstract

The unidirectional amplification of signals is of great importance in signal processing and communication. We propose a hybrid optomechanical system to achieve directional amplification between light fields with different frequencies, where three cavities are coupled to a common mechanical resonator. Two cavities function as an input cavity and an output cavity, respectively, while the third cavity is introduced to facilitate the unidirectional transfer between the input and output cavities. In our scheme, three tones are required to realize the directional amplifier without requiring any gain medium or additional mechanical driving. We find that under certain conditions, the amplifier can reach a large photon number gain with the quantum-limited added noise, with no limitation on the gain–bandwidth product. Furthermore, the directional amplification behavior is controllable by modulating the phase differences between the effective optomechanical couplings.