Fully-distributed Fiber Optic Sensor for Strain Measurement at High Temperature

摘要

Measurement of strain distribution at high temperature is of great importance both for academic research and industrial applications. This paper presents a fully-distributed fiber optic sensor for the measurement of strain distribution in high-temperature environment based on the pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). A telecom grade single mode fiber (SMF-28e~+) was used to sense and transmit strain information. The optical fiber was placed and heated in a furnace that is instrumented and precisely monitored with a thermocouple in the middle of the furnace. The strain sensitivity of the sensor was experimentally calibrated with a precision translation stage for controllable fiber elongation over a temperature range of 22 (room temperature) to 800 °C. The precision stage was controlled with an accuracy of ±0.5 μm and an operation range of 20 mm. A quantitative calibration relationship was obtained using curve fitting technique. The accuracy and repeatability of the sensor for strain measurement were ±25 με and ±32 με, respectively, over a temperature range of 22 to 700 °C. At approximately 800 °C, the sensor remained intact but greatly lost accuracy and repeatability. It demonstrated satisfactory thermal stability for three heating-cooling cycles from 22 to 800 °C and steady heating for 32 hours.