The excimer laser was used to perform precise machining of optic fiber to form FBG for fiber optic sensing. The influence of various H2-loading conditions to the photosensitivity of fiber and performance of FBG have been studied, and the temperature sensing properties of the FBG have been investigated. The results show that the photosensitivity of the fiber is determined by hydrogen concentration and the refractive index changes of fiber increases dramatically with the increase of treatment times and finally become saturated. Therefore, the grating reflectivity of the fiber can be controlled by adjusting hydrogen-loading pressure and H2-loading times. The results also show that when the FBG was used for temperature sensing, the Bragg wavelength of the grating is linearly dependent on the environment temperature and the repeatability is good, which indicate that this kind of FBG are appropriate elements to fabricate fiber optic temperature sensors and their systems.
Micromachining of optic fiber is one of the key technologies in the field of fiber optic sensing. In this paper, the progress of optic fiber machining has been discussed and our study in this field has been described. Because the main component of fiber optic materials is SiO2 and the optic fibers are thin, small, hard and crisp, the results of micromachining of optic fiber are poor by using traditional methods. It is impossible to do the partial precise modification for optic fibers or make holes on them and therefore it is difficult to meet the needs of practical use. The newly deep ultraviolet light micromachining technology is the effective technology for the micromachining of optic fiber. By using excimer laser, the three-dimensional micromachining of fiber materials has been studied, and the results show that with the increase of the pulse laser energy, the etching width of the fiber grooves will increase and then keep unchanged after the pulse laser energy reaches a certain value. For the two-dimensional micromachining of fiber materials, it was found that the etching was related to the focused spot quality such as energy uniformity, scanning velocity and repetition frequency, which provides theoretical and technical preliminary for the direct micromachining of optic fiber using excimer laser. Fiber Bragg Grating (FBG) sensors are new sensors which developed in recently years and have important application in many fields. FBG is the key sensing element and can be prepared by the precise micro modification of fiber optic materials. In this paper, the study on the micromachining to change precisely the local refractive ratio of optic fiber materials with excimer laser has performed and FBG can be formed in this way. Various kinds of FBG including single mode, multimode, chirp and long period fiber grating have been prepared, and the FBG sensors for the detection of stress/strain, pressure, temperature, vibration have been manufactured and used in many fields such as bridges, petroleum chemistry, industry and civil construction, navigation.