Temperature and refractive index measurement using an optical fiber sensor featuring PCF-FP and FBG inscribed by femtosecond laser

Abstract

The temperature and refractive index measurement using an optical fiber sensor featuring a Fabry-Perot interferometer (FPI) and fiber Bragg grating (FBG) has been proposed and realized both theoretically and experimentally. The FPI is formed by sequentially cascading a section of single-mode fiber, photonic crystal fiber (PCF), and multi-mode fiber. The FBG is inscribed using the direct point-by-point method of femtosecond laser. The reflection spectrum of the proposed sensor incorporates with both the PCF-FP and FBG characteristics, making it suitable for dual-parameter measurement. FBG peak at 1532.10 nm and PCF-FP interference dip at 1593.25 nm are chosen for following analysis. The temperature experimental results show that in the range of 30˜120℃, the temperature sensitivities are 11.46 pm/℃ for FBG peak and 8.62 pm/℃ for PCF-FP dip, respectively. The refractive index (RI) experimental results show that in the range of 1.3315˜1.3708, the RI sensitivities are 0 for FBG peak and 9.14 dB/RIU for PCF-FP dip, respectively. By analyzing wavelength shifts and parameter responses of the characterized wavelengths, the corresponding sensitivities can be determined. Such combination also avoids the cross-sensitivity problem by utilizing components with different sensing mechanisms. Therefore, the proposed sensor featuring PCF-FP and FBG structure can be efficiently used for temperature and RI measurement with promising application prospect and great research reference value.