Dissipation and coherent control in nano-optomechanical systems

This thesis presents experimental realization and theoretical investigation of nanooptomechanical systems on integrated silicon photonic platform with emphasis on noise and dissipation characteristics subject to different operating conditions and environments. First, an ultra-high quality factor nanostring resonators integrated in silicon nitride nanophotonic platform is demonstrated. Because of the high quality factor of the resonator, its frequency noise can be detected and studied with high precision. In such a weakly dissipative system, a sizable frequency fluctuation far above the thermomechanical noise limit has been observed. The observed kTB/ f frequency noise is attributed as the signature of two-level systems in the defect states inside the material. The device is further applied to realize an optically tunable photonic directional coupler.;Next, the fluidic damping of a micro-wheel optomechanical resonator operated in liquid environment is studied. With the highly sensitive cavity-enhanced optical readout, we are able to observe the thermomechanical noise with large signal-tobackground ratio even in the highly dissipative water- environment. A theoretical model is developed to describe the hydrodynamics of the resonator-fluid interaction. The hydrodynamic loading predicted by our model agrees with the experimental results. This device is further integrated with microfluidics to develop a fully integrated platform for optomechanical sensing in atmospheric or liquid environment.;To apply optomechanical oscillator for sensing applications, understanding of its phase noise characteristics is very- important. For this we present an in-depth theoretical study on the phase noise of a self-sustained optomechanical oscillator. Contributions from thermomechanical noise, cavity vacuum fluctuations and low-frequency technical laser noise are considered. This study addresses the question about the fundamental limit of the phase noise that can be achieved in such a system. Lastly, a hybrid opto-electro-mechanical system combining an optomechanical resonator with microwave piezoelectric actuation is developed. This integration of optomechanics with microwaves provides an extra degree of freedom for coherent control of the system. Enabled by this strong piezoelectric actuation, nonlinear operation of optomechanical system which manifests as multi-phonon scattering is demonstrated. Our demonstration shows that the strong coherent microwave drive can be a useful tool for studying the nonlinear dynamics of optomechanical systems driven in large amplitude. Examining the noise characteristic in this regime will be an interesting topic for further study.