Solid Insulation Partial Discharge Detection of Fiber Laser Based on Polarized Light Feedback Demodulation System

Distributed feedback fiber lasers (DFBs) demonstrate significant potential for partial discharge detection due to their high precision, narrow linewidth, and single-longitudinal-mode characteristics. However, their sensing performance is severely constrained by phase noise in complex industrial environments. This study addresses the phase noise issue in DFB fiber-optic ultrasonic sensing systems and the limitations of conventional external optical feedback methods by proposing an improved polarization optical feedback scheme. Experimental validation was conducted using a 220 kV actual cable model. Results indicate that the system not only effectively detects partial discharge signals in solid insulation but also enhances phase noise suppression capability by approximately 15 dB (under conditions of 30 m delay fiber and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{0}^{\circ}$</tex> polarization angle difference). The detection range reaches <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1 0}$</tex> cm, with time-domain signal characteristics conforming to typical partial discharge attenuation patterns and frequencydomain concentration in the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$10-30 \text{kHz}$</tex> range. This research provides novel demodulation insights for DFB sensors and holds substantial significance for the industrial application of DFB technology.