Design of High-precision Optical Heterodyne Interferometer Phase Demodulation System

When power equipment fails, ultrasonic and thermal signals are often generated. At present, optical diagnostic methods have become a research hotspot, among which phase-based optical detection technology based on interference structure is widely used due to its high sensitivity. In the previous research, the differential-cross multiplication (DCM) software demodulation method is used to demodulate the phase of the heterodyne interference signal. However, the current software-based phase demodulation algorithms have problems such as large amount of data and long calculation time, which are difficult to meet the needs of online monitoring. This paper proposed a hardware-based phase demodulation scheme based on dual phase detectors. The demodulation of small phase from 0.01°∼1° was achieved, and the signal-to-noise (SNR) is improved by 46% compared with the traditional DCM algorithm. Besides, it only takes 0.8 s to demodulate sensing data, which is 1125 times faster than DCM scheme and contributes to fast real-time monitoring. An optical Mach-Zehnder interferometer (MZI) ultrasonic sensing platform was built for the detection of ultrasound accompanied by partial discharge (PD). The result indicated the developed demodulation scheme was more sensitive than DCM scheme when detecting PD ultrasound signals. The developed demodulation scheme can quickly and accurately figure out the fault of the power equipment, which brought new possibility for online monitoring.