Reflective SFT-FBG Hybrid Micro-Probe for Simultaneous Measurement of Relative Humidity and Temperature

An optical fiber probe composed of a fiber Bragg grating (FBG) and a reflective S fiber taper (SFT) with graphene oxide (GO) film, for simultaneous relative humidity (RH) and temperature measurement, was proposed and experimentally demonstrated in this paper. The SFT is made into reflection type by depositing silver mirror at the fiber end face, which is highly sensitive to surrounding refractive index (RI). The GO nanosheets, as a two-dimensional hydrophilic nano material, is coated on the fiber surface, acting as a RH-to-RI converter. The simultaneous RH and temperature measurements are realized by monitoring the characteristic wavelength shifts of the SFT and FBG in the reflection spectrum. Experimental results show that the RH sensitivity of the probe is 161.1 pm/%RH during the range of 30%RH∼90%RH, and the temperature sensitivity is 14.1 pm/°C during the range of 10 °C∼50 °C. The proposed probe is compact, flexible, and easy to be fabricated, which has potential application for precise localized measurement in medical and biochemical fields.