In Situ Optomechanical Mode Tuning Engineered using an Integrated MEMS Varactor for Enhancing Efficiency of Microwave-to-Optical Quantum Transduction

Piezoelectric optomechanical platforms have provided a reliable route towards efficient microwave-to-optical signal transduction. In these approaches, the wavelength mismatch between the microwave (≈ cm) and the optical
$(\approx\mu \mathrm{m})$
signals is circumvented by converting the microwave signal to an acoustic wave (wavelength ≈ few
$\mu\mathrm{m}$
at GHz frequencies), using a piezoelectric resonator, thus providing a large overlap (coupling) between the interacting fields [1], [2]. The transduction efficiency of these devices can be significantly enhanced by hybridising the modes of the piezoelectric resonator and the optomechanical cavity to form a mechanical supermode [2], [3]. However, such hybridisation requires both the frequency and impedance matching between the piezoelectric resonator and the optomechanical cavity, which is restricted by the fabrication lithography. In this study, we propose to achieve the in situ impedance and frequency matching using an LC network containing a MEMS varactor. A piezoelectric resonator can be represented using Butterworth-Van Dyke (BVD) model consisting of four element RLC network, which can be tuned when connected to a varactor in the network, and a MEMS capacitor can be integrated within the same device and is highly power efficient.