DISTRIBUTED TEMPERATURE SENSOR USING HOLMIUM-DOPED OPTICAL-FIBER AND SPREAD-SPECTRUM TECHNIQUES

This paper describes the feasibility analysis of using Holmium-doped s ingle-mode fiber and spread-spectrum techniques to monitor a temperatu re distribution in the cryogenic range. An optimized holmium-doped fib er was realized and thermally characterized. For probing the sensitive fiber we realized an optical time domain reflectometer using pseudora ndom sequences to improve the dynamic range at the operating wavelengt h and to obtain both rapid response time and high spatial resolution. The system, tested over a fiber length of 240 m, provides temperature dependent fiber attenuation measurements in good agreement with the tr ansmission results. With a 10 MHz pseudorandom binary sequence the sys tem detects changes of 24 degrees C with a spatial resolution of 30 m. (C) 1995 American Institute of Physics.