Automatic amplitude control for phasemeter of spaceborne laser interferometry

Laser interferometry of the space gravitational wave antenna needs to demodulate the gravitational wave signal by a phasemeter with high phase readout precision. A phasemeter in digital phase locking loop structure was proved to be sensitive to the amplitude fluctuation of the input signal experimentally in previous studies. In this work, we have carried out theoretical analysis on the influence of amplitude fluctuation on phase readout precision. The results show that amplitude noise belongs to multiplicative noise, which cannot be eliminated by differential measurement. We used the automatic gain control (AGC) circuit to suppress the fluctuation of amplitude. Contrast experiments were performed to verify that the AGC circuit could promote the performance of the phasemeter system for gravitational wave detection.