Study On Photosensivity Of Germanosilicate Fiber

The study of fiber photosensitivity is proposed because of the rapid development of FBG and its great influence on optical communication and optical sensing, room temperature high pressure hydrogen loading technique has been recognized as an efficient means of achieving ultrahigh photosensitivity. Although a lot of study on fiber photosensitivity is established, the mechanism of germanosilicate fiber and the dependence of photosensitivity on hydrogen loading condition is not studied systematically, the photosensitivity data through experimental measurement is used in this paper. Thus it is a urgent problem to understand exactly the effects of hydrogen-loaded condition on fiber photosensitivity and improve the performance of FBG.This paper explains in detail the mechanism of UV photosensitivity, experiment and experimental analysis and discussion, and the method calculating the UV-induced changes and presents the factors of photosensitivity. The results provide guidance for the fabrication of FBG. Moreover, based on the study of germanosilicate fiber, the multi-mode fiber grating was fabricated and its sensing properties were studied experimentally and theoretically.Much work has been done in this paper:1. The photosensitivity experiment of non-hydrogen-loaded and hydrogen-loaded germanosilicate fiber was done; the mechanism of non-hydrogen-loaded fiber was compared with that of hydrogen-loaded fiber; the process of FBG formation was simulated. The results show: the mechanism is color-center model in the non-hydrogen-loaded fiber; the mechanism is structural model.2. The pressure- and time-dependent fiber photosensitivity was studied in this paper and the UV-induced index changes were measured. The results show: while hydrogen pressure was increased, the photosensitivity gradually increases; while hydrogen-loading time prolongs, the change of photosensitivity is consistent with the evolution of hydrogen concentration. The results provide guidance for optimizing the H2-loading technique.3. The FBG was fabricated and the relation between H2-loading condition and performancesof FBG was discussed; the effects of annealing on FBG were studied. The results provide guidance for FBG writing technique.4. The methods calculating the UV-induced index changes were evaluated by the analysis and comparison of experimental and theoretical data.5. The sensing properties of multimode fiber gratings was investigated experimentally and theoretically in this paper. Experimental results show that the Bragg wavelength of grating in multimode graded-index fiber is linearly dependent on its temperature and axial strain and its repeatability is good. The characteristics are similar to that of a conventional Bragg grating in single-mode fiber.