Whispering Gallery Mode Microresonators For Cavity Optomechanics

Whispering gallery mode(WGM)microresonators have ultrahigh quality factors and small mode volume,which could greatly enhance the light-matter interaction.Thus they have been widely used in highly sensitive sensors,non-linear optics,low-threshold microlasers,cavity optomechanics and quantum information processing.However,the laser-heating-induced optical bistability that occurs at extremely low optical power,especially in a vacuum and low temperature environment,hindering the use of these otherwise excellent optomechanical resonators.Besides,the geometry-deformation of the resonator itself could perturb the mechanical motion in the WGM microresonators.So it is vital to fabricate the chip-based microspheres with not only high optical and mechanical quality factors but also better thermal conductivity properties,and charaterize the geometrydeformation induced perturbation on the mechanical motion.In this thesis,we have studied the follwing issues related to the opto-thermal and opto-mechanical property of the chip-based silica microspheres:1.Opto-thermal property of chip-based silica microsphere.We have fabricated the chip-based silica microspheres with HNA solution,and demonstrated that chip-based silica microspheres can feature optical and mechanical properties that are similar to comparable fiber-stem-attached silica microspheres.The thermal coupling through a monocrystalline silicon pedestal greatly improves the thermal performance of the chip-based microspheres,avoiding or minimizing problems such as optical bistability induced by laser heating.Our work opens up avenues for experimental investigations of cavity optomechanics using microsphere-based resonators in vacuum environments.2.Asymmetric whispering-gallery mode microresonators for cavity optomechanics.We have studied the geometry-induced perturbation on the mechanical frequencies and intrinsic quality factors dominated by the clamping loss for different spheroidal modes in the WGM microresonators.The subsidence of the sphere and a more general condition with fewer symmetries and complex deformation such as an off-centered subsided microspheroid are first modeled in this paper.The symmetry breaking generated by deformation in the system induces the formation of mechanical BICs in the resonator,which reveals new mechanisms to confine radiation.Benefitting from its wider tuning range in mechanical eigenfrequency and broader BIC window width with higher mechanical quality factor,the off-centered subsided microspheroid shows importance and potential in both fundamental research and scientific applications.3.Cryostat setup for optical resonator.We have set up a new low-temperature optical system based on the Dilution Refrigerator,aiming at achieving the ground state cooling for mechanical oscillators in the WGM microcavity,and the preparation of quantum bit based on the coupled whipering-gallery mode microresonator with the color centers in NV or Silicon.We have mainly solved the following technical problems: 1)Special design and update of the commercial standard Dilution Refrigerator in studies related to the whispering-gallery mode resonators;2)The control of coupling between the tapered fiber,the optical resonators and the NV centers;3)The real-time imaging problem at room temperature and low temperature.