| Simplified band-gap photonic crystal fiber(PCF), a new type of hollow-core PCF, has retained attention owing to guiding light over broad transmission band with relative low loss and large air-core. Besides, it has been demonstrated that this new fiber exhibit “inhibited interaction”, which means the coupling between the core modes and the surface modes, cladding modes are effectively inhibited. Based on these unique characters, two kinds of modal interferometer were fabricated. Besides, a novel optical fiber sensor for minor chemical vapor content detecting, based on Rayleigh scattering effect, was proposed in this paper. We also designed a new technique to manufacture the taper in simplified band-gap PCF by CO2 laser. The main contents are shown as following:1. We proposed and experimentally demonstrated two kinds of modal interferometer based on the simplified band-gap PCF in this paper. At first, the simplified band-gap PCF is spliced to single mode fiber(SMF). The high order core modes were excited through a collapse fusion splicing method. In order to decrease the transmission loss, a modal interferometer based on a simplified band-gap PCF, which diffused with volatile organic compounds(VOCs) in the air holes, was designed. Compared with the former one, the transmission loss is much reduced under simple procedures. A full-vector finite element method(FEM) was used to analyze the propagating modes in the used simplified band-gap PCF. The theoretical results were found in good accordance with the experimental ones.2. We proposed and experimentally demonstrated a novel optical fiber sensor for minor chemical vapor content detecting, based on Rayleigh scattering in the simplified band-gap PCF. Both the ends of the simplified band-gap PCF were aligned with SMFs without splicing, allowing the VOC molecules diffusing. It’s easy for molecules coming into the air holes when the VOC’s concentration increases, exciting Rayleigh scattering and resulting in an intensity loss of transmission light. The change of VOC concentration can be detected by monitoring the output transmission intensity. The simplified band-gap PCF in the experiment is 51 mm, and the ethanol concentration sensitivity is 0.022 d B/ppm.3. We proposed a novel fused taper system by CO2 laser, and a high-sensitivity curvature sensor based on two cascading abrupt-tapers modal interferometer in SMF was experimentally demonstrated. The experimental results show that the optimum visibility of interference fringe can be got only when the two abrupt-tapers are at different sizes. The curvature sensitivit y is as high as-25.946 nm/m-1 in the measurement ranges of 6.38 m-1 to 7.98 m-1, and the angle sensitivity is 601.8 nm/ o ranging from 0.02o to 0.0375o. This sensor is low sensitive to either the external refractive index or temperature. The sensitivities are 0.09 nm/℃ and 36.3 nm/RIU in the range of 20-110℃ and 1.3394-1.422, respectively, indicating it can be employed in a relatively stable environment.On this basis, a modal interferometer with two cascading abrupt-tapers was manufactured in simplified band-gap PCF by this system. The sensing characteristic was also discussed. |
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