High-sensitivity refractive index and temperature sensor based on cascading FBGs and droplet-like fiber interferometer

Abstract

In this paper, a highly sensitive refractive index (RI) and temperature sensor based on two fiber Bragg gratings (FBGs) cascaded with a droplet-like fiber interferometer (DLFI) is proposed and experimentally demonstrated. The DLFI was fabricated by mechanically bending a section of coating-stripped single-mode fiber. As the surrounding RI changes, the transmission spectrum of the DLFI shifts, which causes the intensity difference of the two FBGs change. Whereas, the temperature change induces a Bragg wavelength shift of the FBGs. Thus, RI and temperature can be simultaneously measured by the senor through monitoring the intensity-difference change and the wavelength change. In our experiment, the proposed sensor exhibits a RI sensitivity of 385.2 dB/RIU (refractive index unit) in the range of 1.3388–1.3998, which is the highest in RI sensors based on intensity demodulation so far. Meanwhile, the temperature sensitivity is 11 pm/℃ in the range of 25–70 ℃.