Multimode Opto-Electro-Mechanical Transducer for Non-Reciprocal Conversion of Radio-Frequency and Optical Signals

An opto-electro-mechanical system formed by a nano-membrane capacitively coupled to an LC resonator and to an optical interferometer has recently been proposed and employed for the highly sensitive optical readout of radio-frequency signals [1]. We propose and experimentally demonstrate how the bandwidth of such a transducer can be increased by controlling the interference between two electromechanical interaction pathways of a two-mode mechanical system. We have realized a device based on a SiN nanomembrane coated with a 30 nm-thick Nb film which is coupled to an LC resonator and optically readout by an interferometer [2]. Operating this proof-of-principle device at room temperature, we achieve a sensitivity of 300 nV/√Hz over a bandwidth of 15 kHz in the presence of radio-frequency noise, and an optimal shot-noise-limited sensitivity of 10 nV/√Hz over a bandwidth of 5 kHz. The performance of the device can be improved by controlling the frequency mismatch of the two mechanical modes and the electrode distance and, for the same given sensitivity, a mechanical multimode transducer can achieve a bandwidth significantly larger than that for a single-mode one by creating constructive interference between the two opto-electro-mechanical interaction pathways [3]. The nature of the interference can be controlled by choosing proper electrode configurations with respect to the membrane vibrational modes involved. We show that such an interference allows to create nonreciprocal transmission between optical and radio-frequency signals. One can for example isolate the optical output from radiofrequency noise or viceversa depending upon the electrode configuration.