Optical Frequency Comb And Fano Resonance Based On Whispering-gallery-mode Microcavity System

In recent years,with the continuous development and mature technolo-gy of microcavities,the whispering-gallery-mode microcavity systerms have attracted much attention due to their small volumes,high quality factors and easy integration.They have been applied in various fields such as quantum electrodynamics,nonlinear optics,biological sensors,optical communication,quantum information processing,optical filter,enhanced Raman gain,optomc-chanical effect.In this thesis,based on the nonlinear optical effect and quantum interference effect in whispering-gallery-mode microcavity systerm,we mainly study the properties of these kind of systerms and their applications in precision measurement and high-precision sensors.The main work are as follows:1.Based on atom-resonator-fiber coupling system,we put forward a scheme to generate optical frequency combs at driving laser powers as low as a few nanowatts.We find that the combination of the atom and the resonator can induce a large nonlinearity which is significantly stronger than Kerr non-linearity in Kerr frequency combs.Moreover,it is found that the threshold of the optical nonlinearity is greatly reduced.Through numerical simulation and theoretical analysis,we investigate in detail the influences of different atom-ic positions and taper-resonator coupling regimes on optical-frequency-comb generation.And find that our generated frequency comb is robust against large variations of atomic position and coupling regime.In addition,the comb spac-ing can be well tuned by changing the frequency beating between the driving control and probe lasers.The proposed method is versatile and can be adopted to different types of resonators,such as microdisks,microspheres,microtoroids.Based on the above advantages,our system has the potential application in pre-cision frequency calibration,arbitrary waveform generation,multi wavelength light source,quantum information network and optical computing.2.Based on a three-mode(i.e.,a clockwise mode,a counterclock-wise mode,and a mechanical mode)coherent coupling regime of the optical whispering-gallery-mode(WGM)microresonator optomechanical system,we study the tunable multistability and Fano resonance effects.The WGM mi-croresonator is coherently driven by a strong control laser field and a relatively weak probe laser field via a tapered fiber.With the help of the Heisenberg Langevin equation and analyzing its steady-state solution,it is found that the coupling strength between the two cavity modes plays an important role in the regulation of the multistability of the mechanical displacement.By changing the coupling strength between the two cavities,the conversion between the bista-bility and the multistability can be achieved.By using the perturbation approx-imation method,we give the transmission spectrum and the back propagation reflection spectrum of the weak probe field.By choosing the appropriate sys-tem parameters,the asymmetric Fano resonance is observed.By controlling the mode coupling rate between the two counterpropagating modes,the distance between the cavity and the tapered fiber,the power of the control field,and the optomechanical coupling strength between the counterpropagating modes and mechanical mode,the Fano line can be controlled.Our obtained results in this study can be used for designing efficient all-optical switching and high-sensitivity sensor.3.Based on the active whispering-gallery-mode cavity optomechanical systerm,We theoretically study the effect of gain on whispering gallery mode cavity.It is found that with the increase of the gain coefficient,the threshold of the multistability is getting smaller and smaller.Moreover,the conversion between the bistability and multistability can be achieved by adjusting the gain coefficient.Through the numerical analysis of the transmission line,the multi Fano resonance phenomenon is found in the whispering gallery mode cavity system which is very important in the refractive index sensor.In addition,the sensitivity of the sensor can be greatly improved by choosing the appropriate gain coefficient.