| Fiber Bragg grating(FBG) have been extensively explored and widely used in the fields of optical fiber sensors and telecommunications. There are many fiber Bragg grating of fabrication methods, such as: phase masks and two-beam interferometry. Compared with point-by-point inscription methods by femtosecond laser, femtosecond laser point-by-point inscription methods has advantages of more flexible, low cost, and high reliable, which already aroused widespread concern. In this paper, we proposed a femtosecond laser point-by-point inscription methods based on inscription novel FBG. The spectral characteristics and sensing characteristics of these novel FBGs are studied in detail, based on the research by foreign scholars, and some innovative results were achieved. The main work is summarized as follows:1. The transmission spectrum characteristics of FBG, the reflection core mode effective refractive index and wavelength is analyzed by use of coupled mode theory;introduction the advantage of femtosecond laser fabrication and the mechanism for femtosecond laser and silica material.2.An experimental system of femtosecond laser inscription FBG based on point-by-point methods was designed and build, including femtosecond laser optical system and computer-control motorized translation stages. Such a system could be used to inscribe FBGs with good reproducibility, stability and success rate by optimizing laser power, movement speed, grating length and grating position. FBG are inscribed in conventional SMF by use of this system, and investigate the spectral characteristic. Temperature response and strain response are further studied, which lay an important foundation for following study of novel FBGs.3. It is demonstrated, for the first time to our best knowledge, that parallel and integrated muti-wavelength FBG, ultra short FBG are inscribed in single mode fiber by use of femtosecond laser point-by-point inscription methods. Ultra short FBG is extremely small, and the length of three FBGs is all 800?m. The spectralcharacteristic and sensing characteristic of parallel and integrated muti-wavelength FBG are deeply studied:(1) each grating is parallel and interval in the fabrication process of parallel and integrated muti-wavelength FBG. The centre wavelength,reflectivity and 3d B-bandwidth of FBG will not change with other FBG inscriptions,and the insertion loss of parallel and integrated muti-wavelength FBG is increasing with FBG inscription.(2) The strain response of three FBGs are all 1pm/??, and the temperature response is respectively 8.9pm/?C,8.9pm/?C and 9pm/?C. It's sensitivity is same with other FBG's by other fabrication methods. The high temperature stability test of parallel and integrated muti-wavelength FBG shows that the high temperature stability is very good and the parallel and integrated muti-wavelength FBG is not degenerate when keeping more 12 hours in 500?C.4. FBG is inscribed in D-shape fiber by use of femtosecond laser point-by-point inscription methods. Conventional FBG is not sensitivity to refractive index. Specific structure of D-shape fiber is the main reason why refractive index is sensitive. Single mode fiber is polished to D-shape fiber, and the origin structure is damaged. Thus, the D-shape FBG is sensitivity to reflectivity for FBG inscription in the core of D-shape fiber. Meanwhile, D-shape FBG exhibits a maximum sensitivity of 30nm/RIU at RI range from 1.44 to 1.45, which much higher than that of conventional FBG. The limit of detection is 0.0026. The temperature sensitivity of D-shape FBG is similar with that of conventional FBG due to thermal effects of the fiber materials. |
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