Research On Coupling And Transmission Properties And Application Of Optical Whispering Gallery Mode Microcavity

With the development of optical inforrmation science,the requirement for perception,propagation,and control of optical information is becoming more and more important.As the traditional photonic device cannot meet this requirement,an increasing interest has been focused on novel photonic integrated devices that can transmit and engineer optical information.Among them,whispering gallery mode(WGM)resonators strongly enhance light-matter interaction owing to their ultrahigh quality factor(Q factor)and extremely small mode volume(V),offering an ideal platform for fundamental physics and applied photonics,which have found important applications in optical communication,sensing,microwave photonics,and quantum computing.Based on WGM resonator platform,we can generate,transmit,and engineer light,and with the development of microfabrication and packaging technique,the platform will become a miniature and compact one.In this dissertation,based on quasi-cylindrical microresonator and microsphere,we study the basic principle,properties,and fabrication methods of microcavity,and carry out experiment on narrow bandwidth filtering,nanoparticle detection,electromagnetically induced transparency,and group delay devices.The details are summarized as follows:(1)Development of WGM resonator coupling platform.The dissertation details the fabrication processes of microsphere,quasi-cylindrical resonator,crystalline resonator,and tapered fiber.Specifically,we build a optical-mechanical-electrical integrative facility with function of rough grinding,rough polishing,and fine polishing processes for crystalline microcavity.In addition,we build the coupling platform,and characterize the coupling properties of different microcavities.Finally,we compare the features of three different types of microresonators,which establish the foundation for future experiments.(2)Research on tunable ultranarrow linewidth filters based on a quasi-cylindrical microresonator coupling platform.We propose and realize a novel surface nanoscale varied quasi-cylindrical microresonator,and build a stable controlled coupling platform.By adding a probing fiber,we realize a tunable ultranarrow linewidth filter based on a quasi-cylindrical microresonator(QCMR)coupling platform successfully.The QCMR developed in our lab exhibits clean and regular spectra,ultrahigh quality factors(3.1×107),and a small axial free spectral range(FSR-0.03 nm),reducing the difficulties of full tunability.Its mode volume is relatively large,which makes it easier to access,control,and steer themode fields.Moreover,we construct the physical model of the QCMR coupling system theoretically and numerically,and the field distribution,transmission spectra,mode volume,and frequency spacing are obtained.We realize a stable and controlled coupling as well as selective excitation of axial modes.In addition,by adding a probing fiber,we demonstrate selective excitation and probing of WGMs,and therefore realize a tunable and robust add-drop filter device.(3)Research on electromagnetically induce transparency(EIT)and Fano resonances in a single quasi-cylindrical microresonator.We realize controlled EIT and Fano resonances in a single quasi-cylindrical microresonator,and demonstrate that they can convert into each other.By constructing a theoretical model,we explain the mechanisms of EIT and Fano phenomena generation as well as their conversion.The experiment shows that,by vertically moving the QCMR,the lineshapes of EIT and Fano resonances change due to the variation of coupling strength,and they can convert into each other;The horizontal translating brings about an interesting periodic asymmetric Fano lineshape.More important,the above two mechanisms can work on the same mode simultaneously,which can be observed and engineered in our platform.The developed approach here,provides a stable and fine platform for observation,tuning,and steering of EIT and Fano resonances.(4)First experimental demonstration of distributed nanoparticle detection in the large particle-flux regime.We measured the distributed nanoparticle induced mode splitting which comes from a burning candle.The experiment shows that the total linewidth broadening is proportional to the number of adsorbed particles,which is in good agreement with the theoretical model.The signal is insensitive to the angular positions of particles as well as the thermal fluctuations.In addition,the mode splitting mechanism works equally well even when the splitting is unresolvable.This result paves the way for concentration detection of nanoparticles in combustion,traffic exhaust and ambient atmosphere.(5)Revealing dispersion control properties of the triple-layer-coated microsphere,propose and demonstrate a multi-vertically coupled resonator(multi-VCR)for dispersion compensation and tunable,larger delay.We propose to control the group velocity dispersion(GVD)of a microsphere by three layers coating of high,low,and high refractive indices(RIs).We theoretically demonstrate that,the GVD is controllable over a broad range in both the normal and anomalous dispersion regimes,and the zero dispersion wavelength(ZDW)can be tuned from the visible to the near-infra red window through changing the coating thickness,the gap between the two high-RI layers,or the coating materials of the two high-RI layers,In particular,it has been showrn for what we believe the first time that the ZDW in such a structure depends approximately linearly on the refractive index of the two high-RI layers.On the other hand,we describe a multi-VCR system that exhibits nearly zero-GVD,tunable,and large delay,and theoretically demonstrate that,the GVD compensation property makes it a more flexible optical group delay lines.