Real-Time Temperature Sensor Based on In-Fiber Fabry–Perot Interferometer Embedded in a Resin

A simple to fabricate, cost-effective, robust, and highly accurate fiber optic temperature sensor is proposed and experimentally demonstrated. The sensor head consists of an in-fiber Fabry-Perot interferometer (FFPI) embedded in a mold made of a polyester resin. FFPI, which in general present good strain sensitivity and low-temperature sensitivity, was assembled by splicing a microsegment of capillary fiber of 14.66 μm between two single-mode fibers. The reflected spectrum of the FFPI exhibited a single interference dip within a span of 80 nm. The dimensions of the resin mold can be modified by changing the ambient temperature, which in turn changes the length of the FFPI air-cavity. The dip of the reflected spectrum is shifted toward shorter (larger) wavelengths when external temperature is decreased (increased). The large free spectral range (FSR) allowed to monitor the temperature changes by either a wavelength or an intensity interrogation scheme. Using a laser and an optical power meter it was possible to demonstrate a real-time temperature sensor with a sensitivity of -60.79 nW/°C and a resolution of 0.5 °C, in the range of 10-30 °C. We believe that the practicality of this real-time sensor can be very attractive for environmental sensing application.