Integrated cavity opto-electromechanics: electrical tuning and control of optomechanical systems

An optomechanical system is formed when the resonance frequency of an optical cavity is linked to the position of a mechanical resonator. The study of optomechanical systems has exploded over the last few decades, with many geometries and applications arising from this coupling of light and mechanical motion. Among these, applications in optical and mechanical control have opened new avenues of study in the development of technologies, for example photonic circuit signal routing and creating networks of sensors, as well as fundamental studies such as mechanical many-body dynamics.In this thesis, we introduce an additional feature to the canonical optomechanical system, namely an electrical means to actuate the mechanical element, in the form of metal electrodes integrated directly on to the device. These electrodes generate a capacitive force upon the application of a voltage bias, which is used to control the device properties. We present in this work two geometries of such opto-electromechanical devices in silica, namely microtoroids and double-disks. In the microtoroidal geometry we demonstrate the use of capacitive actuation as a control knob to tune the optical resonances of the device by over 20 linewidths and a rate of 80 kHz, and to lock its mechanical motion over a range of 71 kHz.In comparison to microtoroidal structures, double-disks present a much less studied platform. Double-disks possess strong optomechanical coupling due to a hybridisation of optical modes between the stacked disk. Therefore we are able to demonstrate optical tuning over more than three free spectral ranges in this geometry, which allows the device to be set on resonance with any desired frequency in the material transparency window. Furthermore, the tuning mechanism requires a low power consumption of ∼400 pW to achieve and maintain tuning, while preserving the quality of the cavity across the entire tuning range. This promises many exciting applications, including wide-band operation of multi-frequency photonic circuits and on-chip spectrometry. We further investigate the inclusion of an active medium to a double-disk cavity and show photoluminescence in the telecommunications (∼1550 nm) and green (∼530 nm) optical bands. Incorporating this active optomechanics into the opto-electromechanical system, we propose its use as an on-chip tunable source of coherent light as an important step towards developing fully on-chip optical experiments.We lastly discuss utilising the electrical element of the system not simply as a forcing mechanism, but as a cavity similar to the optical whispering gallery modes, but for microwave light. In this system, the mechanical resonator is coupled to both the optical and microwave cavities, and can be used to transduce signals between the two regimes. In the quantum regime this would allow, for example, transportation of quantum states generated by superconducting qubits through room temperature, an important goal for the quantum computing community. We theoretically analyse the potential of our proposed system, based on a double-disk optomechanical geometry, and present progress towards its experimental implementation.