High sensitive temperature sensor based on narrow band-pass filters via optical heterodyne technique

This research aims to develop a high sensitive temperature sensor to get around challenges like cost and complexity as well as to improve sensitivity in the megahertz band. Depending on the optical heterodyne technique, a new approach is proposed to construct an optical fiber sensor for measuring temperature. Two types of the narrow band pass filters (BPF) are employed in this approach as sensing elements. Both BPFs are Fabry–Perot filters, which are made from quartz and crystron material. The thermo-optics coefficients of filters materials are approximate. In the proposed sensor, a wideband optical source is equally split and then launched to sensing elements. A 3-dB coupler combines the output of the thermo-sensitive BPFs. A combined signal from these two BPF, which centered at 1552.22 nm and 1552.187 nm, is detected by a photodiode and the beat frequency can be defined to attain a high-resolution. The temperature sensing strategy is explored to evaluate the proposed approach. The results show that the proposed sensing system has the beat frequency varied from 4 to 12.5 GHz over temperature range from 0 to 100 °C. The sensor has sensitivity of 85.9 MHz/ o C with fast response to temperature change and reducing the cost of manufacturing and measuring of the optical fiber sensors.