A Photon-Counting Optical Time-Domain Reflectometry Based Optical Fiber Temperature Sensor System

A photon-counting optical time-domain reflectometry (PC-OTDR) based optical fiber temperature sensor system is proposed and demonstrated experimentally in this work. In the system, a high speed photon-counting module is developed for fast measurement and a cascade SMF (single- mode fiber)-COF (capillary optical fiber)-SMF fiber structure is designed for the temperature sensing. Thanks to the newly developed active quench and reset integrated circuits, the photon-counting module achieves a maximum counting rate of nearly 35 Mcounts/s that allows the PC-OTDR based optical fiber sensor system achieving the OTDR trace of a 20 m fiber-under-test (FUT) within 0.2 ms and a 6 km FUT within 20 s. The spatial resolution measured is about 3.8 cm and 60 cm for the FUT of 20 m and 6 km respectively. To test the system's optical sensing usefulness, a SMF-COF-SMF is developed and connected to the FUT of the system to form a temperature sensor. The COF is filled by UV glue whose refractive index is sensitive to the temperature. Experimental results show that this system is capable of measuring the temperature in the range from 20 °C (room temperature) to 220 °C, which can also locate the sensing position accurately.