Theory And Sensing Application Research On Tilted Fiber Bragg Grating

Fiber gratings, as novel passive devices, have been widely used in the field of optical fiber communication and fiber sensing field since appeared for the advantages such as light weight, immunity to electromagnetic, be able to multiplexing, and in-fiber. Tilted fiber Bragg gratings(TFBGs), as emerging member of fiber gratings’ family, have attracted considerable attention for the special structure, which has a certain angle between the fiber axis and wave vector of grating.In this thesis, the current domestic and international research status of fiber Bragg grating sensors and tilted fiber Bragg gratings are described firstly, then study on the mode couplings, transmission spectrum and sensing characteristics of TFBG with different tilted angle in theory analysis, computer simulation and experiment research are developed. Finally, a novel fiber sensing structure based on the semiconductor optical amplifier(SOA) and laser resonance amplification is proposed, the main contents of this thesis are as follows:1. On the basis of TFBGs’ special structure, the different patterns of mode couplings in TFBGs with different tilted angle are discussed, and the mode coupling equations and phase matching conditions are derived in theory by using mode coupling method. What’ more, computer simulations are carried on to investigate the transmission spectral characteristics and spectral responses on the key impact parameters, such as tilted angle, grating period, grating length and refractive index modulation amplitude of weakly tilted fiber Bragg gratings.2. Sensing principle of temperature, longitudinal strain and surrounding refractive index(SRI) about weakly or excessively tilted fiber Bragg gratings are studied, and the sensing equations are derived. Furthermore, the different responses of core mode and cladding mode are presented in the temperature, longitudinal strain and SRI sensing simulations of weakly TFBGs.3. Temperature, longitudinal strain, transverse load and SRI sensing experiments of 81 o TFBG are carried on, which show that cladding modes with different order and polarization exhibit distinctive behaviours, provide a meaningful reference for the specific sensing applications.4. A novel fiber sensing structure based on the semiconductor optical amplifier(SOA) and laser resonance amplification, woks on the self-oscillation threshold of the resonator is proposed. It is modeled theoretically, simulated by computer and validated experimentally. And it is found that sensing parameters can be enlarged to 10200 times by the proposed structure, which has high sensitivity, can effectively solve the low sensitive problem of grating sensors. In addition to the performance of the sensing structure, further studies confirm that the structure has good repeatability and no hysteresis. With more characteristics such as small bulk, easy to be integrated and demodulated, this sensing structureis anticipated to be widely applied in the future for high sensitivity.