Raman Modulation Of Whispering Gallery Mode Microresonators And Its Application

Whispering Gallery mode(WGM)micro-resonators with high quality factor,small mode volume and good integration performance,have been applied in many various fields of modern science,such as high performance sensors,on-chip micro-lasers,nonlinear optics,optical communication devices,cavity optomechanics,quantum information and so on.To achieve better performace(e.g.higher quality factor),WGM resonators are doped with optical gain providing material such as rare earth ions,and these doped resonators are known as active resonators.However,active resonators require additional fabrication process,and are suitable only for specific pumping and working window since each type of rare earth ions has its own specific pumping and emission spectrum.So we attempt to use Raman effect,which have been realized in most of the common used materials of WGM resonators,instead of rare earth iron doping,to avoid dopant or additional fabrication complexities,eliminate doping induced cavity loss,and loosen the requirement of specific wavelength for pump and emission.This thesis is focused on Raman modulation of whispering gallery mode microresonators and my work is listed as follows:1.Highly sensitive detection of nanoparticles with whispering-gallery Raman microlaser.We cooperate with Prof.Lan Yang's research group in Washington University in St.Louis,improve paticle detection limit through Raman gain-induced loss compensation in silica WGM resonators,and detect and count single nanoparticles down to 10 nm in radius via self-referenced beatnote from mode splitting in a WGM Raman microlaser.This scheme has enabled achieving record-high polarizability sensitivity(down to 3.82 × 106?m3),and has good biological compatibility compared to rare earth doped cavity sensors.2.Raman gain induced mode evolution and on-demand coupling control in whispering-gallery-mode microcavities.We systematically investigated both theoretically and experimentally the evolution of mode splitting spectra under Raman gain in various initial coupling conditions.It is showed that Raman gain compensates losses leading to not only narrower linewidths but also transitions between various coupling regimes.Based on this we propose and experimentally demonstrate that by utilizing Raman gain one can achieve on-demand control of the coupling regime without any mechanical movement in the resonator system.This scheme has good performance in driving the system from under-coupling to over-coupling regime,which is not possible in previous similar schemes,and provide better resolvability of transmission spectra,thus provides an practical route to realize a bidirectional,on-demand all optical control of cavity resonances.3.All optical coupling control in whispering-gallery-mode microcavities.We for the first time to our knowledge study the stimulated Raman loss of silica WGM micro resonantors.On this basis we experimentally demonstrate an all optical coupling control of fiber taper coupled micro-cavity system through adjusting cavity effective loss by stimulated Raman loss.We turn the system from deep over-coupling to critical-coupling just by injecting a low power pump the pump power without moving any part of the system.On resonance transmission is driven down by 19.58 dB,which is a much higher contrast that the previous record of 9 dB in silicon micro-ring,and our control is not disturbed by two-photon absorption or free-carrier absorption.