Fiber grating sensing interrogation system based on a modulated grating Y-branch tunable laser for core-and-cladding-integrated fiber Bragg grating temperature measurement.

Numerous studies have addressed various methods to interrogate fiber Bragg gratings (FBGs). However, conventional methods are ineffective for multipeak FBG demodulation. A core-and-cladding-integrated fiber Bragg grating (FBG) temperature-interrogation system, based on a modulated grating Y-branch (MG-Y) tunable laser and home-built FBG, is proposed in this study. The sensing system comprises an MG-Y tunable laser interrogation system, a 3-dB optical fiber coupler, a core-and-cladding-integrated FBG, a heating platform, and a personal computer. The core-and-cladding-integrated FBG with two reflection peaks is sampled by the designed MG-Y laser. The FBG has a period of 534 nm and a grating length of 2000 µm. It is fabricated in a single-mode fiber by femtosecond-laser writing through the fiber coating. The interrogator is suitable for temperature measurement via the core-and-cladding-integrated FBG. In tests of the temperature-interrogation system, a temperature change from 30 to 100 °C generates spectral shifts toward longer wavelengths for both the core and cladding reflection peaks. For the core and cladding, temperature sensing sensitivities of 111 and 113 pm/°C with linearities of 0.993 and 0.99, respectively, during heating and 117 and 120 pm/°C with linearity coefficients of 0.994 and 0.99, respectively, during cooling are achieved.