The ripple noise comes from the FP resonator structure formed in the joint between discrete optics according to the theoretical analysis for the presence of it in the modulation and demodulation system. According to the analysis of the fiber FP cavity characteristics, transmittance function of the FP cavity is obtained. Its resonance characteristics were simulated and the resonance characteristic curves were obtained under different facets with different reflectivity. The relationship between the reflectivity and the finesse, and the influence of the reflectivity on the characteristics of the resonant are obtained. The two methods to suppress the ripple noise are proposed, the facet reflection method and the phase modulation suppression method. The result of the experiment shows that both methods suppress the ripple noise in the system effectively, improve the signal-to-noise ratio of the resonant signal, and lay the foundation to obtain the demodulated signal and track the optical micro-cavity resonance point.