研究目的
To propose and demonstrate a cascaded tilted fiber Bragg grating for enhanced refractive index sensing with an enlarged measurement range and higher accuracy.
研究成果
The cascaded TFBG provides an enlarged SRI sensing range of 1.30–1.45 and higher accuracy due to reduced wavelength separation, with sensitivities of 510.48 nm/RIU and 494.12 nm/RIU in different regions. It also allows for temperature self-calibration with a core mode temperature coefficient of 11.83 pm/°C, making it suitable for biochemical and environmental sensing applications.
研究不足
The study is limited to refractive indices in the range of 1.30–1.45 and temperatures up to 80°C. The fabrication process requires precise control of splicing and UV inscription parameters, which may affect reproducibility. The use of specific fiber types (SMF and RD-SMF) and equipment may constrain broader applicability.
1：Experimental Design and Method Selection:
The study involves designing a cascaded TFBG structure inscribed in series in SMF and RD-SMF with the same tilt angle to excite superposed cladding modes for refractive index sensing. The principle is based on phase-matching conditions and spectral analysis of cladding modes.
2：Sample Selection and Data Sources:
A segment of RD-SMF (core/cladding diameter approximately 3.8/80 μm) is spliced between standard SMFs. Refractive index matching liquids in the range of 1.300–1.450 are used to change the surrounding refractive index.
3：8/80 μm) is spliced between standard SMFs. Refractive index matching liquids in the range of 300–450 are used to change the surrounding refractive index.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes a fiber arc fusion splicer, frequency doubled continuous wave Ar+ laser (244 nm wavelength) for UV inscription, supercontinuum light source (superK), optical spectrum analyzer (OSA), temperature-controllable heating chamber, and calibrated temperature probe. Materials include hydrogen-loaded SMF and RD-SMF, phase mask with grating period of 543.8 nm, and refractive index matching liquids.
4：8 nm, and refractive index matching liquids.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Fabrication involves splicing RD-SMF between SMFs, hydrogen loading for 72 hours, UV inscription using scanning phase-mask technique with tilt angle of 6.5°, annealing at 80°C for 48 hours. Characterization uses broadband light from superK source transmitted into the TFBG, with transmission spectrum monitored by OSA. SRI response is tested by injecting liquids into a sample cell, and temperature response is tested by heating from 0°C to 80°C.
5：5°, annealing at 80°C for 48 hours. Characterization uses broadband light from superK source transmitted into the TFBG, with transmission spectrum monitored by OSA. SRI response is tested by injecting liquids into a sample cell, and temperature response is tested by heating from 0°C to 80°C.
Data Analysis Methods:
5. Data Analysis Methods: Spectral evolution is analyzed to extract wavelengths of core and cutoff modes. Linear fitting is applied to determine sensitivities (nm/RIU and pm/°C), and separations between adjacent resonances are tracked to assess accuracy.
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