OFDR based distributed temperature sensor using the three-channel simultaneous radio-frequency lock-in technique

Abstract

Weak signal detection for single-mode fiber-optic distributed temperature sensor (DTS) is a key technology to achieve better performance. A hybrid technique combining the incoherent optical frequency domain reflectometry (IOFDR) and the three-channel simultaneous radio-frequency (RF) lock-in amplifier (LIA) is presented to improve the signal-to-noise ratio (SNR) of the measured spontaneous Raman backscattered light. The field programmable gate array (FPGA) based RF-LIA is designed with a novel and simple structure. The measurement frequency range is achieved from 1 kHz to 100 MHz. Experimental results show that the backscattered light signal of picowatt level can be detected with high SNR. With a 2.5 km single-mode fiber, a 1064 nm laser source, and the measurement time of 500 s, this sensing system can reach a spatial resolution of 0.93 m and a temperature resolution of about 0.2℃.

A Fiber Optic Probe for Tumor Laser Ablation With Integrated Temperature Measurement Capability

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“…A home-made lock-in amplifier was used to extract the second-harmonic (2 f ) PA signal. The detailed information of the lock-in amplifier could be found in this work . The output lights were collimated by the fiber-optic collimator and incident into the O-shaped LHCF.…”

“…The detailed information of the lock-in amplifier could be found in this work. 25 The output lights were collimated by the fiber-optic collimator and incident into the O-shaped LHCF. The thinner end of the LHCF and the fiber-optic collimator was put inside a 3D-printed buffer chamber.…”

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“…As a result, the generated PA pressure signal was periodic and certainly with high-order harmonic signals. More detailed information of the lock-in amplifier could be found in this work . The sine modulation frequency (1 f ) and the modulation depth could be adjusted through the LabVIEW-based computer program.…”

“…More detailed information of the lock-in amplifier could be found in this work. 31 The sine modulation frequency (1f) and the modulation depth could be adjusted through the LabVIEWbased computer program. The second-harmonic (2f) signal was detected and extracted by the MEMS microphone and the lock-in amplifier.…”