Compact fiber biocompatible temperature sensor based on a hermetically-sealed liquid-filling structure

A compact and robust fiber temperature sensor based on a hermetically-sealed liquid-filling Fabry–Perot (FP) cavity was fabricated by low-cost but efficient processes, including fusion splicing, liquid injection, and fused tapering. Owing to the high thermal optical coefficient (TOC) of the ethanol, the optical path difference (OPD) in the FP cavity varied strongly with temperature, which consequently induced a drastic wavelength shift of the reflection spectrum. Meanwhile, the low freezing point of the ethanol caused the fiber sensor to have the ability of detecting the sub–zero temperatures. As a result, a linear sensitivity as high as 429 pm/°C was achieved in the range between -5 °C and 30 °C. In addition, our fiber temperature sensor also exhibited rapid response time, good repeatability, and stability. The biocompatible structure, low fabrication cost, and high performance of such a temperature sensor can provide it potential for biological applications.