Study Of FBG Fiber Grating Thin Film Sensors

Based on optical fiber Bragg grating (FBG) sensors, a theoretical model is established for FBG thin film sensors. Fiber grating was treated as a multiple thin-film stack. For the difference of thermal expansion factor between thin-film stack and substrate, thin-film stack will deform under the action of stress and result in drift of the reflective wavelength when the temperature increases. A film temperature sensor based on the reflective wavelength of thin-film stack that monotonously depends on temperature is introduced.Based on the investigation of relevant literatures, the principle of optical fiber Bragg grating thermometer is discussed in the paper. Because the limitations in manufacture of fiber Bragg grating, we present that optical thin films could instead of grating in sensing. An advantage of the method is that reflective wavelength of visible light monotonously depends on temperature. The design of thin-film stack depends on vector analysis.TiO₂ thin films were prepared as high refractive index material by DC reactive magnetron sputtering. The effect of each factor during production on the structure and optical properties of TiO₂ thin films was investigated.SiO₂/TiO₂ composite thin films were prepared by RF magnetron co-sputtering. The ratio of SiO₂ to TiO₂ can be adjusted by controlling the sputtering current of TiO₂. Increasing of the sputtering current, the refractive index of the composite thin film is correspondingly decreased and approximately linearly dependent on it. The temperature properties of TiO₂/SiO₂ band pass filters are characterized. The temperature coefficient is 0.017nm/℃. Finally, it proved that the film temperature mentioned in this paper is feasible in theory.