Automatic carrier signal track algorithm in all-digital PGC demodulation scheme for optical interferometric sensors

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Abstract
An optimal all-digital phase generated carrier (PGC) demodulation scheme for optical interferometric sensors is presented in order to reduce the effect of frequency and phase difference between the carrier and reference signals. First, the influence on the signal from the PGC demodulation scheme is discussed when the frequency and phase of the carrier signal are inconsistent with the reference signal. It reveals that the different frequencies and phases will cause modulation and fading phenomena in the output signal of the scheme. Second, a carrier signal track algorithm is proposed to lock the frequency and phase of the carrier signal in real time to reduce these influences on the scheme. The frequency and phase of the carrier signal can be tracked by frequency analysis, desampling, and curve fitting. After that, the measurement signal can be demodulated accurately by the scheme from the signal detected by the photodiode in real time. The accuracy and effectiveness of this algorithm is verified by experimental results.