Improved PGC-Arctan demodulation algorithm based on real-time feedback control

Abstract

The phase generated carrier (PGC) demodulation algorithm has the characteristics of high accuracy, good linearity, and large dynamic range, which makes it widely used in interferometric fiber optic sensors. However, due to the influence of carrier phase delay (CPD), phase modulation depth (C), and light intensity disturbance, the system introduces nonlinear distortions. To address this problem, we proposed a highly stable PGC demodulation algorithm that combines CPD compensation and C self-calibration. Multitone mixing is used in the CPD compensation and C self-calibration. The CPD compensation algorithm calculates CPD using the harmonic components and their differential components obtained from two orthogonal carrier signals and uses CPD to set the initial phase of the reference carrier to obtain the harmonic components that eliminate the influence of CPD. The C self-calibration algorithm calculates the real-time C by the ratio of the two harmonic components and introduces proportional-integral-derivative control to stabilize C at the optimal value by controlling the output voltage. The experimental results show that the standard deviation of the CPD calculated by the CPD compensation algorithm is 0.0012 rad. The real-time modulation depth of the system can quickly reach the optimal value and maintain it for a long time. The average phase modulation depth is 2.63 rad with a standard deviation of 0.00735 rad. Compared with the traditional PGC-Arctan demodulation algorithm, our algorithm yields higher SINADs and lower THDs under different CPDs; the average SINAD is 62.68 dB, and the THD is 0.075%.