Investigation Of Micro-structured Fiber-optic Sensing And Application

Micro-structured optical fiber includes traditional photonic crystal fiber (PCF) and micro/nano structured fiber made on common fiber. Micro-structured optical fiber has caused extensive concern of the scientific community because it can provide various optical characteristics in need due to its flexible and diverse structure designs, which is unmatched by the common fiber. There are many kinds of micro-structured optical fiber sensors working on different principles and research in this paper is mainly based on two of them: one is based on surface plasmon polaritons, including the local and non-local field surface plasma resonance and the other based on interference, including Fabry-Parot and Michelson interference.Firstly, an all-solid photonic fiber with D-shaped structure based surface plasmonic resonance sensor is proposed and investigated. This sensor can resolve phase matching problem and simplify the production process. Simulation results show increasing shifts in resonance wavelength for the same index change, so the refractive index sensitivity of at least7300nm/RIU (refractive index unit) can be achieved and216for FOM (figure of merit). Then, we study the effect of size variation of the thicknesses of a silver coating, first layer rods, as well as polishing depth, with a view of tuning and optimizing plasmon excitation by the core-guided mode. A unique phenomenon is observed:the resonant wavelength red shifts at first and then blue shifts with the polishing depth increasing, and the FOM achieves maximum at watershed wavelength.Secondly, a novel grid nanostructure design that can be used as an effective SERS (surface enhanced Raman scattering) fiber sensor when fabricated directly on the tip of an optical fiber. With this structure, the plasmonic resonances peak have good stability and keep on working under the high efficiency of enhance. Double-Resonance Plasmon can be effectively excited, which is more than two orders of magnitude larger than the Single Resonance Plasmon under the same conditions, so strong local field enhancement can be obtained. The structure is symmetric, so the polarization effect on the resonance wavelength can be negligible.Thirdly, a compact micro multicavity Fabry-Perot (FP) optical fiber tip sensor is presented. In the end of the single-mode fiber (SMF), we drill a short air hole with femtosecond laser, which forms a multicavity together with the fiber flat face tip. The sensor has been experimentally tested for refractive index and temperature sensing by monitoring its wavelength shift. Measurement results show that the in-line FP exhibits the gas RI sensitivity of867.76nm/RIU and the temperature sensitivity of7.8pm/℃. Two independent cavities exist in the sensor, and the air cavity is used for RI sensing and the glass cavity for temperature sensing, thus, avoid the temperature and RI cross-sensitivity.Finally, a compact miniature in-line Michelson interferometers (MI) optical fiber tip sensor based on polymer-filled photonic crystal fiber (PCF) temperature measurement is proposed and demonstrated, which consists of single mode fiber, UV glue and PCF, and UV glue connecting the SMF and PCF. We offer a quite simple way to fabricate compact in-line FP at a low cost. The optical properties of the PCFs can be effectively modified by filling the air holes with polymer. Due to difference of thermal expansion and thermal optics coefficient between silica and polymer, the temperature sensitivity can be adjusted by changing the ratio of the length of the filling polymer and PCF. In the meantime, the sensor exhibits a high temperature sensitivity of-99.3pm/℃when the length ratio is1.556, and the sensitivity can be greatly improved by decreasing the ratio in theory.