Instability Mechanism of Intensity-Noise-Induced Phase Noise in PGC Detection System and Suppression Thereof

The phase noise induced by the intensity noise fluctuates in some sensing systems, which could affect the assessment of system performance. In this paper, the phase noise induced by the intensity noise in the phase generated carrier (PGC) detection system is modeled. It manifests that the phase noise level has a trigonometric relation with the initial phase of the interference fringes, namely workpoint-related fluctuation. Besides, the shape of the fluctuation to the workpoint is also a function of the modulation depth. As a result, the measurement for phase noise should iterate over many workpoint sets at a special modulation depth. Whereas the workpoint iteration is not always actually viable, a modified PGC detection scheme that combined the 3x3 coupler multi-phase method is proposed. To average out the three demodulated outputs, the phase noise is theoretically independent of the workpoint, which is also smaller than the traditional value. The tested results show good accordance with the theory. The theoretical model and method in this paper can be used as a guidance of the noise assessment in large-scale multiplexed sensing networks.