Novel Silica Optical Microcavities And Applications

Optical microcavities are essential optical components finding wide applications in both applied and fundamental studies for e.g., optical communication, low threshold microlasers, biosensing, cavity QED and cavity optomechanics. This thesis largely focuses on novel silica optical microcavities and their applications.In the first part, we demonstrate optical resonance from microfiber knots obtained by manipulating freestanding silica microfibers. Optical microfiber knot cavities are fabricated with Q-factors around 60 000 and finesse around 22. Free spectral range of the cavity can be easily tuned by tightening the knot structure in air. Optical resonance is well maintained when the knot is immersed in water or supported on a low-index substrate. An all-fiber add-drop filter composed of a microfiber knot (working as a resonator) and a fiber taper (working as a dropping fiber) is also presented.Applications of the microfiber knot cavities as active devices are also demonstrated.1.5μm wavelength microfiber knot lasers are fabricated by tightening a Er:Yb-doped phosphate glass microfiber into a knot in air. Single-longitudinal-mode laser emission with threshold of about 5 mW and output higher than 8μW is obtained. Microfiber knot dye laser based on evanescent-wave-coupled gain is also obtained. Laser emission around 570- and 580-nm wavelength, which is evanescently coupled back into the microfiber, is observed with a threshold of about 9.2μJ/pulse. The use of the microfiber knot cavity suggests a convenient and efficient approach to both pumping and collection of the evanescent-wave-coupled dye laser. In addition, hybrid structure laser consisting of a single or multiple zinc oxide nanowires attached to a silica microfiber knot cavity is realized. The hybrid laser provides low threshold and narrow linewidth due to the combination of high gain of semiconductor nanowires and high Q factor of microfiber knot cavities. In the second part of the thesis, we describe a double-disk microcavity consisting of a pair of silica microdisks separated by a nanoscale gap region on a silicon chip for cavity optomechanics. We show that this type of structure can provide a per-photon gradient force with a magnitude much larger than for scattering-force-based structures. Moreover, this device provides for nearly independent optimization of optical and mechanical properties. We present the processing details and optical testing of fabricated devices, showing strong dynamic backaction.