Research On High Resolution FBG Interrogation System

With various advantages such as high sensitivity, reliability, stability and anti-electromagnetic interference, as well as compactness, corrosion resistance, good scalability and integration, fiber Bragg grating (FBG) sensing system has been widely used in structure monitoring, communication, aerospace and several other fields.We report a compact and high-resolution multiplexed fiber Bragg grating (FBG) wavelength interrogation system using a tunable LD. A compact tunable LD covering wavelength from 1546 nm to 1558 nm was applied as the light source to improve the simplicity, wavelength resolution and the response rate of the FBG demodulation system. A standard HCN gas-cell was incorporated as the wavelength reference. Direct modulation of the tunable semiconductor LD was realized to guarantee the quasi-continuous wavelength scanning of the LD.The demodulation process and algorithm was simulated. The quantitative relationship between the demodulation error and the sweeping step of the tunable laser was analyzed. The demodulation error would increase with the sweeping step and was slightly smaller than the sweeping step. Then it was concluded that the lpm wavelength resolution of the tunable laser would lead to the demodulation resolution of better than lpm. Then we tested the robustness of the spectral centroid algorithm under different types of noises. With multiple cycles of simulation, the stability of the algorithm is verified, which provides a solid theoretical basis for the application.Then the spectral centroid algorithm which utilizes FBG’s spectral characteristics was applied to achieve high accuracy of the FBG interrogation, as well as high stability of the demodulation. The system’s demodulation wavelength resolution of better than lpm and the precision of about 2pm were verified, achieving 0.1℃ temperature resolution around 1550nm. By changing the ambient environment from 30℃ to 120℃, the achieved linearity and the repeatability between the demodulated wavelength and the temperature were both satisfactory. Multiple FBGs were connected into the sensing network to verify the multiplex capability of the demodulation system. The demodulation cycle was about 30s. The test results showed that the demodulation system could stay stable for a long time and had various application prospects.