| With the development of the grating sensing technology, tilted fiber gratings(TFGs) have attracted large amount of attention because of their novel structure and variety of functions. It has exhibited a series of merits e.g., compactness, high flexibility,light weight, strong anti-jamming capability etc. However, the existing reported mainly focused on small-angle TFG. The research on wide-angle TFG is quite few. Based on TFG coupled-mode theory, the theoretical of 81°-TFG sensing mechanism and spectral characteristics were simulated. The experiments about 81°-TFG including temperature,refractive index, bending and vibration sensing were studied. The main content of this thesis can be divided into the following three parts:(1) Based on the coupled mode equation, a theoretical model of the 81°-TFG transmission was constructed. The effective refractive index of core mode, each order cladding mode and the spectral characteristics of TFG were numerically simulated.Simultaneously, we constructed the theoretical model for 81°-TFG sensing based on this model, the output spectral characteristics under different external conditions e.g.,temperature, refractive index, etc, were simulated, and the optimum operating parameters of the sensor were obtained.(2) Based on the photosensitive characteristics of the fiber, 45° and 81°-TFG were inscrived by using a phase mask technology in the single-mode fiber, the influences of exposure time, annealing time, the wavelength of the laser light source, pulse parameters on the TFG quality during the fabrication processes were analyzed. The tilt angle of the gratings was mainly determined by the positions of the relationship between the mask and the engraved fiber, and we obtained a set of grating writing parameters to optimize the system about TFG.(3) Experimental research on 81°-TFG fiber sensor was performed. Firstly, 45°and 81°-TFG polarization characteristics were studied experimentally and analyzed.The results show that 45°-TFG having high polarization dependent loss(PDL) of 22 dB.Then, the fiber sensor based on 45° and 81°-TFG fiber gratings was constructed, it includes temperature, refractive index, bending and vibration sensing. The system includes a broad spectrum light source, and the transmission spectrum was recorded by using the optical spectrometer. The experimental results show that the temperaturesensitivity of TM and TE modes were 7.8 pm/°C and 7.6 pm/°C, respectively, and the temperature does not affect the coupling mode of transmission light in the TFG. For the refractive index(SRI) sensing. The SRI sensitivities of TM modes at 1570 nm of81°-TFG were measured at 196.23 nm/RIU(0.001 refractive index change), and the TE modes at 1576 nm of 81°-TFG were measured at 191.31 nm/RIU. The change of SRI also affects the strength of the coupling cladding mode each order. For the bend sensing,no matter how change the TFG bending direction or extent would influence the TFG transmission spectra. In the bending radius of curvature of 6.6~16.26 m-1 range, the sensitivity can be reached at 0.0135 mW/m-1. For vibration sensing, a good vibration sensitivity of 81°-TFG were proved from 80 to 500 Hz. The vibration sensitivity can be reached at 0.1520 mW/kHz. |
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