An optical fiber sensor based on carboxymethyl cellulose/carbon nanotubes composite film for simultaneous measurement of relative humidity and temperature

In this paper, a carboxymethyl cellulose (CMC)/carbon nanotubes (CNTs) composite film was manufactured and used as a good humidity sensitive material to design a humidity and temperature simultaneous measurement sensor with simple structure, high sensitivity and fast response time. The sensor is constructed by a fiber Bragg grating (FBG) and then connected a hollow-core fiber (HCF) on the end face of which coated a CMC/CNTs hydrogel composite film. Through contrast experimental tests, the results show that the humidity sensitivity of the sensor with CMC film is 170.55 pm/%RH, while the sensitivity of the sensor with CMC/CNTs composite film is 230.95 pm/%RH. The humidity-insensitive FBG can be used to obtain accurate temperature information, and the temperature sensitivity is 26.35 pm/°C. This paper not only proves that CMC is an excellent humidity sensitive material for optical fiber sensors but also proves that carbon nanotubes can increase the humidity sensitivity of the hydrogel film effectively. This temperature and humidity simultaneous measurement sensor has a good application prospect.