Backscattering Control In A System Consisting Of Quantum Dots And Whispering-gallery Optical Microcavities

Whispering-gallery optical microcavities have very high quality of factors and relatively small mode volumes,and have been used to realize various detectors and optical elements,and to study nonlinear optical effects,cavity opto-mechanics et al.Quantum dots,on one hand,they can work as gain media to realize ultra-low-threshold microcavity lasers,on the other hand,they can work as quantum emitters for realizing high-quality single-photon or entangled-photon sources,working as carriers for solidstate qubits and studying cavity quantum electrodynamics.Meanwhile,Rayleigh scatterers in a microcavity will result in the backscattering coupling between two originally degenerate cavity modes,forming two new modes with mode fields redistributed in frequency and space.By macroscopically controlling the intrinsic Rayleigh scatterers in a microcavity or by actively introducing designed Rayleigh scatterers in a microcavity,cavity modes can be controlled to realize some special states in an optical microcavity,such as diabolical points in an optical molecule or exceptional points in a single microcavity.These special points indicate that backscattering is a very important property.Backscattering has expanded the research on optical cavities and has further enriched the interactions between quantum dots and a microcavity.The main research results in this thesis are classified by the parts below:1.Degenerate modes in a whispering-gallery microcavity will couple with each other due to the backscattering caused by intrinsic Rayleigh scatterers in a microcavity.Air holes introduced into a whispering-gallery optical microdisk can work as Rayleigh scatterers to modulate the backscattering coupling.This method allows smart designability,integrability and stability.The modulation of backscattering from the radius and the location of an air hole is obtained by numerical simulations,providing references for designing scatterers to modulate whispering-gallery modes.2.Multiple and randomly positioned intrinsic Rayleigh scatterers exist in active optical microcavities.The competition between two types of intrinsic Rayleigh scatterers can be macroscopically controlled and balanced by optimizing the microdisk radius in order to study the effects of symmetric backscattering coupling strength on eigenstates and eigenvalues of an optical molecule.When the backscattering coupling strengths are opposite in two microdisks,the optical molecule is at diabolical points with nonlinear relations between two microdisks.3.By designing two identical scatterers as Rayleigh scatterers into the microdisk edge,periodic control on the backscattering in a microdisk can be achieved,including periodically appeared diabolical points.Though this method sacrifices the quality factors to some degree,the quality factors are still high enough to allow the weak coupling between a single quantum dot and a microdisk.Purcell enhancement of a single quantum dot in a microcavity at a deterministic diabolical point is achieved with six times of the intensity enhancement.4.According to the conditions to achieve exceptional points in a two-mode approximation model,two air holes with different radii and distances from the microdisk center are introduced as Rayleigh scatterers into a microdisk.Numerical simulations are used to analyse and achieve exceptional points.The corresponding microdisks are fabricated by using numerical simulation parameters and the preliminary experimental progress is obtained,demonstrating the experimental feasibility of this method of controlling cavity modes.