Efficient Common-Mode Noise Suppression for Fiber-Optic Interferometric Sensor Using Heterodyne Demodulation

Common-mode noises (CMNs) are frequently encountered in all types of fiber sensor systems. Through involving a reference interferometer, here we report the application of a differential delay heterodyne scheme to suppress CMNs in fiber-optic interferometric sensor systems. The contributions of CMNs are shared by both sensing and reference interferometers and are further suppressed by heterodyne demodulation. For the first time, we develop the full theoretical model describing this method, and experimental results are also presented to confirm the theory. Theoretical analysis shows that the CMN suppression effect (SE, defined as the ratio of the noise floor of the sensing interferometer after and before suppression) is sensitive to several key parameters, including the mean phase difference, the ratio of the visibility, and ac amplitude between the two interferometers. Experimental results show that the proposed method can suppress CMNs by ~24 dB within the frequency range of 20 Hz to 1 kHz. The measured CMN SE agrees well with the theory. The CMN suppression method and the theory reported here can also be extended to other interferometric systems.