Coupled Structures Based On-chip High-Q Silica Microcavities And Their Optical Properties

Thanks to its ultrahigh quality factor and small mode volume,whispering gallery mode optical microcavities have been used in many fields such as microsensors,microlasers,optomechanics,cavity QED in recently years.Double-cavity coupled system,due to its similarity to atomic systems in spectral properties and energy band structures,has been named as photonic molecule(PM)and been used to study fundamental applications such as many modes lasers,analog to electromagnetically induced transparency,slow light,and explore fundamental theory like parity time symmetry,exceptional points,coherent perfect absorber,etc.Other researchers have fabricated three-cavity configurations in several platforms,but the structures are with limited tunability in the coupling strengths and individual resonant frequencies.The thesis includes main contents as following:1,Controllable double-cavity PM(DCPM)and realization of PT symmetry.Firstly linewidth evolution of DCPM;by introducing an active microcavity,we systemically studied parity time symmetry unbroken to broken process in active-passive DCPM;by using gain saturation of the active cavity,optical isolation is realized.2,An experimental realization of a coupled triple-cavity photonic molecule(TCPM)composed of three independently-selectable ultrahigh quality microtoroids with multiple degrees of freedom controllable.By tuning the inter-cavity coupling strengths(via distances)and the resonant frequencies(via fine temperature control),as well as coupling the tapered optical fiber onto either the side or middle cavity,evolutions of the TCPM,s supermodes are fully mapped and analyzed.Interesting phenomena,such as dark state and double anti-crossing,emerge in this TCPM system.3,Study on analog to electromagnetically-induced absorption(EIT)related phenomena.After we select the quality factors of the cavities for TCPM properly,four level atomic system is simulated,and,transition from double EIT to double ELA(electro-magnetically-induced absorption phenomena)happens.What's more,analogy to intracavity EIT is realized with proper conditions.4,Hamiltonian eigensolutions analysis on multiple-cavity photonic molecules.Based on coupled mode theory,we introduce Hamiltonian matrix approach into coupled mode theory and by solving the eigensolutions,we analyze the relations between supermode splitting and coherent parameters,linewidths and energy distributions.In DCPM and TCPM,we fully developed understanding on mode splitting,phase transition points and dark states.5,Exploration on optical devices.(1)Based on mode splitting and three microcavity coupling system,we realized a high-order optical filter,of which the stop band is 159 MHz and depth is up to 99%,the minimum of the stop band is 90%.(2)Using gain saturation nonlinearity in Er3+ doped silica microtoroid,we studied optical nonreciprocity.The isolation ratio was realized to be more than 15 dB in a wide range of signal power(20 nW to 4 ?W)with very low insertion loss of less than 3 dB.(3)based on nonreciprocity,we demonstrated an optical pseudo-circulator,with directivity to be(7.3 dB,9.6 dB).