Whispering gallery mode microcavities: from fabrication to applications

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Madugani, Ramgopal
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University College Cork
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Trapping and cooling macroscopic objects using light has attracted great interest recently as it may enable us to see quantum mechanical features in large systems. A microsphere pendulum is one such system to put it to test. This thesis work is devoted to solving many of the steps necessary for future trapping and cooling works of a microsphere pendulum using a whispering gallery mode (WGM) cavity-based photonic molecule scheme. In the course of implementing this scheme, microcavity devices, such as microspheres and microbubbles were studied for topics as diverse as optomechanics, photonics, laser tuning and spectroscopy. The WGMs in the microsphere pendulum sense its mechanical mode through fibre taper coupling of light. Its properties in the evanescent light fields and its optomechanical transduction characteristics were investigated. This system is highly dissipative - a feature which could prove to be very useful for cavity cooling applications. Owing to its pressure tuning capability, a microbubble cavity can be used as a means of finding co-resonances as needed to achieve a photonic molecule and mode splitting. By locking a laser to a WGM of a microbubble resonator, linear tuning and stability characteristics of the WGM via pressure were studied. A fast method of sensing and estimation of dissipation and dispersion individually in an optomechanical system with minimal invasion was required. In this regard, cavity-ringup spectroscopy (CRUS) was investigated by simply measuring the peak height of the CRUS signal, enabling ultrafast sensing applications. Finally, a coupled, two cavity system, known as a photonic molecule, was studied for its optomechanical transduction properties in CMIT, ATS and their intermediate regimes making way for understanding the trapping capabilities of such a system. The range of studies in this thesis also illustrate the versatility of WGM-based resonators in optics measurements extending from fundamental optomechanics to applied photonics.
Whispering gallery modes , Microcavities , Microresonators , Micropendulum , Microbubble cavity
Madugani, R. 2017. Whispering gallery mode microcavities: from fabrication to applications. PhD Thesis, University College Cork.