Environmental Noise Cancellation Technique for the Compensation Interferometer in Fiber-Optic PMDI-Based Sensor Arrays

A path matched differential interferometry (PMDI) is one of the most common architectures for fiber-optic sensor arrays. It allows to interrogate many fiber-optic sensors time-multiplexed at a single fiber by using an auxiliary compensation interferometer (CIF). The CIF is typically based on an unbalanced Michelson or Mach-Zehnder interferometer. Therefore, it may be affected by different acoustic and vibration environmental noises. Any vibroacoustic impacts on the CIF might produce undesirable noises in the sensor signals and the noise performance of the measuring system will degrade. An environmental noise cancellation technique for the CIF in fiber-optic PMDI-based sensor arrays is presented in this paper. The proposed approach is based on the separate interrogation of the CIF by the additional fiber laser together with using polarization-division multiplexing. The noise cancellation is performing by the subtraction of the independent CIF's signal from measured signals from the sensors array. In this paper, the main parameters of the noise cancellation system, which are critical for its performance, are discussed in detail. The experimental efficiency estimation of the proposed technique was performed in situ under open water conditions. It was shown, that for the measured signal with the standard deviation of 0.059 rad and the environmental impact on the CIF with the standard deviation of 0.61 rad the noise cancellation efficiency was -24.9 dB. The proposed technique might be easily integrated to large-scale PMDI-based fiber-optic sensors arrays and it's compatible with PMDI-based Fiber Bragg Grating arrays in combination with the wavelength division multiplexing.