Polarization Maintaining And Microstructured Optical Fiber Gratings And Their Sensing Applications

The optical fiber gratings are one of the most rapid developing passive fiber components in recent years and have a widely applicative prospect in sensing area. In this thesis, fiber Bragg gratings (FBGs) are inscribed in polarization maintaining and microstructured optical fibers by use of phase mask method, and sensing characterizations of the gratings are investigated. The details are described as following:1. FBGs are inscribed in two types of grapefruit microstructured optical fiber using phase mask method. The effect of air expansion in the holes on temperature response of large-air-hole grapefruit microstructured fiber grating is investigated via placing grating under sealed and unsealed air holes condition, respectively. Then the pressure sensitivities of large-and small-air-hole microstructured optical fiber are demonstrated in comparison of a single-mode fiber. The pressure coefficient is triple and twice higher than that of standard FBG. The air holes enhance the pressure response.2. FBGs are written in three types of polarization maintaining fibers (PMFs),the birefringence of PMFs gratings is experimentally compared when ultraviolet (UV) light exposes along the fast axis and slow axis, respectively. The results demonstrate that PandaPMF has a different birefringence while. bow-tie and elliptical core PMFs almost have no difference. Then we investigate the temperature and strain responses of FBGs in PMFs. Fast axis of panda and bow-tie PMFs is more sensitive to temperature than slow axis, while slow axis has higher sensitivity to strain than fast axis. Both axes of elliptical core PMF exhibit the same responses to temperature and strain. Moreover, the birefringence thermal stability of PMFs has been obtained by monitoring the grating resonance wavelength. Panda and bow-tie PMFs have a nonlinear behavior while a quadratic decrease in elliptical core PMF.3. FBGs are photowritten in pure-silica polarization maintaining photonic crystal fiber. The responses of these gratings to temperature, strain and hydrostatic pressure are investigated. The two resonance wavelengths corresponding to the two polarization axes show the same responses to strain and temperature but different response to pressure. The pressure dependence of the peak separation is independent of temperature. In addition, the thermal stability of birefringence in the fiber is investigated in detail. Birefringence of PM PCF presents a flat trend to temperature with only a small decrease of-1.2%, which benefits for the high-temperature fiber sensing applications.