Weak signal detection for single-mode fiber-optic distributed temperature sensor (DTS) is\na key technology to achieve better performance. A hybrid technique combining the incoherent optical\nfrequency domain reflectometry (IOFDR) and the three-channel simultaneous radio-frequency (RF)\nlock-in amplifier (LIA) is presented to improve the signal-to-noise ratio (SNR) of the measured\nspontaneous Raman backscattered light. The field programmable gate array (FPGA) based RF-LIA is\ndesigned with a novel and simple structure. The measurement frequency range is achieved from\n1 kHz to 100 MHz. Experimental results show that the backscattered light signal of picowatt level\ncan be detected with high SNR. With a 2.5 km single-mode fiber, a 1064 nm laser source, and the\nmeasurement time of 500 s, this sensing system can reach a spatial resolution of 0.93 m and a\ntemperature resolution of about 0.2.C.
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