Research On The Functionalization Of Optical Microfibers

Microfibers are a kind of micro-/nano- optical waveguides and building blocks of micro-/nano- photonic devices. Benefitted from the small footprints, high fractional evanescent fields, and tailorable dispersion, microfibers have been adopted in many applications, such as microfiber sensors, microfiber lasers and nonlinear optics. However, applications of microfibers are limited by the material and structure. A functionalization of microfibers would provide more opportunities for microfibers.Material functionalization and structural functionalization, including directly doping, surface decoration, functional assembly and micro/nano fabrication, are the typical approaches to the functionalization of microfibers. Functionalized by these approaches, microfibers can be used for many active and passive micro-/nano- photonic devices and provide excellent platforms for the fundamental researches, ranging from surface plasmon optics to nonlinear optics.In this thesis, we functionalized silica microfibers with surface coatings via a modified dip-coating method. The mode guiding properties,mode field distribution and dispersion of functionalized silica microfiber was investigated theoretically, and then we performed functionalization experimentally in the following three ways:(1) Dispersion tailoring of silica microfibers. Since the dispersion of microfibers depend on the diameters, we were able to in-situ finely tailor the dispersion of silica microfiber by changing the thickness of coatings. The zero-dispersion-wavelength could be shifted by more than 30 nm. Numerical simulations demonstrated that fine dispersion tailoring of microfibers could be applied in nonlinear optics such as four-wave mixing and supercontinuum generation.(2) Gain functionalization of microfibers. We coated silica microfibers by Er/Yb co-doped sol-gel. The pumped Er/Yb co-doped coatings were able to provide gain for the silica microfibers in the C-band. Because of the low propagation loss and coupling loss of silica microfibers, we were able to obtain a net gain of 0.8 dB in the functionalized microfibers.(3) Fabrication of microfiber long period gratings. Ultraviolet exposure was used to fabricate the microfiber long period gratings on the PMMA coated silica microfibers. The microfiber long period gratings showed a stress sensitivity of-1.93 pm/???and a temperature sensitivity of-12.75 pm/°C. Because of the the diameters, microfiber long period gratings also have a high sensitivity of axial force. A further reduction of the size of focused spot would promise finer micro-/nano- structures on silica microfibers.