Fiber optic Raman distributed temperature sensor based on an ultrashort pulse mode-locked fiber laser

摘要

Nowadays fiber optic Raman distributed temperature sensors (RDTS) are broadly used for e.g. fire detection, gas leaksdetection in pipelines and aircraft icing monitoring. The most common sources of probe pulses for RDTS are CW laserswith external intensity modulation or Q-switched lasers with a pulse duration of several tens of nanoseconds which limitsthe RDTS effective spatial resolution to a few meters. In this paper we have developed an Er-doped ultrashort pulse(USP) mode-locked fiber laser and implemented it to Raman distributed temperature sensor.This feature allow us toachieve high spatial resolution (down to several centimeters) and high signal-to-noise ratio in the receiving system. Anall-fiber erbium-doped laser of 180 fs pulse duration and an average output power of 30 mW was used as a source ofprobing pulses. We have studied limiting factors of fiber sensor effective length such as high pulse repetition rate of 12.2MHz and intensity noise of the USP laser (relative intensity noise RIN ～ 6.3 ∙ 10-4). Furthermore, the peak power of theUSP laser has to be at kW level to get high signal-to-noise ratio in the receiving system and pulse duration < 100 ps atfull-width-half-maximum for desirable spatial resolution of ～2 cm. Moreover, we have developed an experimental prototypeof RDTS with the spatial resolution of ～ 0.1 m limited by the receiving system according to the detector bandwidthof 2 GHz, the effective sensor length of 3 m and ±1.5 °C temperature measurement error. As a result, a list of requirementsfor a new laser source for distributed temperature sensor was formulated.