Micro/nanofiber For Integrated Photonic Device Coupling And Applications

Photonic integrated chips(PICs),compared with integrated electric circuit,have attracted extensive attention in information fields due to the advantages of low energy consumption,high-speed,and large bandwidth,among which integrated photonic waveguide and optical microcavity are the most important components in PICs.The integrated photonic waveguide is generally used for connecting different devices in a single PIC,and fiber connection is utilized when the light is coupled into the PIC via the long distance transmission and the interconnection between different PICs.Therefore,the coupling between fiber and integrated photonic waveguide is essential to PICs.The high coupling efficiency between fiber and integrated photonic waveguide is difficult to achieve due to the mode field mismatch between them.Benifitting from the controllable diameter,small footprint,light weight,low loss,strong optical confinement,and strong evanescent field of micro/nanofiber(MNF),the coupling problem of the integrated photonic waveguide can be solved.Meanwhile,the MNF is pulled by standard single-mode fiber,and have the characteristics of seamless connection with standard fiber.Combined with the above advantages,the MNF brings new opportunities for improving optical coupling efficiency and increasing device integration.By optimizing the structural parameters of the optical components,the thesis analyzed how to effectively couple the light to an integrated photonic waveguide and whispering gallery mode(WGM)microcavity.Meanwhile,the implementation of MNF coupled WGM microcavity for optical sensing and nonlinear optics are discussed.The main contents of the thesis are as follows:In the first part of the thesis,fabrication of the high-quality MNF was investigated.With a flame-brush method,diameter-controlled(<3 nm)short-waist MNF and high transmittance(99.4%)ultra-long waist(>10 cm)MNF were successfully fabricated,greatly enhanced the coupling efficiency between MNF and integrated photonic devices.In addition,we studied the influence of the MNF surface roughness on transmittance.The transmittance loss of the MNF was described by the overlap of the fundamental mode with fiber surface,which provided a theoretical guidance for the fabrication of high transmission MNF.In part two,the applications of the MNF coupled WGM microcavity in optical sensing and nonlinear optics were investigated.With the characteristics of adjustable diameter and strong evanescent field of the MNF,the high coupling efficiency between the MNF and WGM microcavity was achieved.The application of the MNF coupled polymer WGM microcavity in optical sensing was investigated.Based on the quasi-phase matching method of the single microcavity and the strongly coupled splitting of the two microcavities to compensate the dispersion,the applications of the MNF coupled lithium niobate thin film WGM microcavity in nonlinear sources were discussed.The observed nonlinear frequency conversion efficiency by this two phase matching methods were the highest value reported so far,which laid a foundation for realizing the efficient nonlinear frequency conversion of the microcavity.In part three,the coupling mechanism between the MNF and the lithium niobate waveguide was investigated.With the benifits of controllable diameter and strong optical confinement of the MNF,a new idea about the MNF coupled reverse-proton-exchanged periodically poled lithium niobate waveguide was proposed.Meanwhile,in order to prevent the pollution of the MNF and improve the integration of the device,the MNF was encapsulated by a microcapillary tube with low refractive index adhesive.Utilizing the encapsulated MNF coupled reverse-proton-exchanged lithium niobate waveguide,the coupling efficiency between them is up to 93%.The single photon detection efficiency and noise of silion-based single photon detector to the communication band are 40%and 200 cps,respectively,by applying MNF coupling with reverse-proton-exchanged waveguide.The application of the MNF coupled single photon detector in quantum key distribution was also explored.Furthermore,the edge-to-edge coupling of the MNF was applied to the lithium niobate thin film waveguide,experimentally measured coupling efficiency of transverse electric(TE)and transverse magnetic(TM)mode are 73.7%and 64.8%,respectively,which is the highest coupling efficiency of lithium niobate thin film waveguide reported so far.It is a key step for the industrial applications of lithium niobate integrated photonics.