A new phase generated carrier demodulation method based on fixed phase delay

Abstract

Phase Generated Carrier (PGC) with directly Frequency Modulation (FM) is one of the most important demodulation methods for optical fiber interferometric sensor system. Previous research has confirmed that system performance using Orthogonal Demodulation Type PGC (ODT-PGC) method is determined by many parameters, such as signal phase delay, FM depth, laser intensity accompanying modulation. This article proposes a new PGC demodulation method based on Fixed Phase Delay (FPD-PGC) by 3x2 directional coupler, using second-harmonic components of two interferometric signals to demodulate. The demodulation principle of the new method is described in detail and its performances have been studied. Theoretical analysis and experimental results show that the new method combines main advantages of directional coupler method and ODT-PGC method, and eliminates, to a great extent, the impacts of FM depth, signal phase delay, intensity modulation. Signal-to-total-Harmonic Ratio (SHR) of new method increases more than 30dB compare with ODT-PGC method under the condition of intensity modulation coefficient is 0.4. Besides that, Signal to Noise Ratio (SNR) also improves significantly.