Opto-thermal Study And Applications Based On Whispering-gallery Microcavities

The whispering-gallery microcavity has been widely studied due to its excellent properties,such as ultra-high quality factors,ultra-low mode volumes,strong non-linear effects,etc.The fabrications are compatible with standard semiconductor techniques,which makes the WGM microcavity easy to be integrated and expanded on the chip.Therefore,it is of great value to investigate the properties of micro-nano photonic microcavities for the fundamental study and applications in both cavity quantum electrodynamics and all-optical integrated optics.This thesis is mainly focused on the research and applications of the nonlinear optical effects based on the whispering-gallery cavity.We study the opto-thermal effect and its applications theoretically and experimentally using the whispering-gallery mode optical micro-cavity.The main work are as follows(1)Raman lasing and Fano lineshapes in the packaged fiber-coupled whispering-gallery mode microresonators.In order to solve the issues of tapered fiber couplers in practical and in-field applications,we cooperated with Prof.Lan Yang in the University of Washington in St.Louis,and proposed the overall packaging method for the first time by using a low refractive index polymer.The coupling can be adjusted to maintain the quality factor of the packaged optical mode in a higher value of up to 2 × 107.We achieved a high success rate in packaging.By adjusting the temperature,all-optical Electromagnetically Induced Transparency(EIT)and Fano lineshape were observed.Besides,Raman lasing were obtained in both single-and multimode lasing of our packaged microresonator.(2)Rapid and high precision measurement of opto-thermal relaxation with pump-probe method.We propose a pump-probe method(PPM)to optically measure the thermal relaxation using whispering gallery mode(WGM)microcavities.In experiments,we used the thermal locking method to lock the signal light near on-resonance.When the pump laser shines on a microcavity,the materials absorb the input power resonantly and heat up.Then the heat dissipates from the cavities to the surroundings.The opto-thermal effect induces a refractive index change reflected in the signal light transmission spectra.By analyzing the curve character of the transmission spectra of the signal response in the spontaneous relaxation process,the thermal relaxation time can be rapidly measured with high precision.The PPM method is novel and simple.The small rate of refractive index changes(10-8)can be discerned with an input pump power as low as 11.816?W.Our method is very robust to various factors like laser parameters or coupling conditions.(3)Thermally induced dynamical non-reciprocity in optical microcavity.We use a silica microtoroid and a PDMS microcavity simultaneously coupled to a tapered fiber waveguide.PDMS and silica have opposite thermal effect properties.Within certain frequency detuning ranges,the optothermal broadening transmission spectra of the PDMS microcavity would be cut by silica microtoroid's absorbing input power in the backward direction.Experimentally,we achieved a non-reciprocal transmission ratio up to 22 d B with the input power as low as 179.42?W,and a waveguide insertion loss of less than 0.1 d B.Our method is simple and easy to integrate in practice.(4)Optothermal control of the Raman gain enhanced ringing in microresonators.We report a novel method–the combination of optothermal scanning method and Raman gain to achieve and control the ringing effect in a silica optical microsphere.We build dynamic models that can fit well with the experimental results and show how these two methods affect the ringing strength theoretically.Comparing to the usual method requiring laser sweeping,our method does not require the sweeping of probe laser,which makes it easier and more stable in applications.The optothermal control method is robust to external fluctuations,which can enhance the performance and stability of the transient microcavity sensors.