High Precision Phase-OFDR Scheme Based on Fading Noise Suppression

In recent years, Optical Frequency Domain Reflectometry (OFDR) has been able to realize strain measurement with high sensitivity and high spatial resolution (SR) along the sensing fiber. Compared with the conventional cross-correlation method, OFDR based on phase-measuring method has the potential to obtain strain information with better SR. However, the accuracy of this method is severely affected by coherent fading. In this paper, a method combining multi-frequency detection and nearest neighbor analysis is proposed to solve this problem. By comparing the sub-phase curves in different wavelength regions, we successfully eliminate the interference of fading noise and obtain the undistorted phase signal. Finally, in the case of an effective wavelength scanning range of 3.6 nm (corresponding to the ranging SR of 0.22 mm), we realized the deformation measurement with standard deviation of 0.015 μm and SR of 1.1 mm, as well as the strain measurement with standard deviation of 0.55 μϵ and SR of 5.6 cm. The experimental results also show that compared with the conventional multi-frequency average method, the proposed scheme can achieve similar phase measurement accuracy under less frequency division, so as to obtain better SR in the same scanning range.