An MMF–HCF Reflective SPR Sensor for Simultaneous Measurement of Temperature and Relative Humidity

In this article, a reflective surface plasmon resonance (SPR) sensor based on multimode fiber (MMF)–hollow core fiber (HCF) structure is proposed for simultaneous measurement of temperature and humidity. Along the HCF, two different films, i.e., polyvinyl alcohol (PVA) film and polydimethylsiloxane (PDMS) film are coated on the outer surface to generate two SPR resonances at different wavelengths and achieve the simultaneous measurement function. In order to get a better sensing performance, the length ratio of PVA film and PDMS film, and the PVA coating times are optimized. The experimental results show that the humidity sensitivity of the sensor is 0.6351 nm/% relative humidity (RH) in the RH range of 48%–84% RH, and the temperature sensitivity of the sensor is 1.791 nm/°C in the temperature measurement range of 25 °C–80 °C. The sensor has great potential applications in monitoring the environmental temperature and humidity changes.