Laser frequency noise correction in LFM-based interferometric fiber-optic hydrophone array.

In this paper, we propose a novel time-division multiplexed (TDM) array for a large-scale interferometric fiber-optic hydrophone system, in which we introduce a power-optimized reference probe and effectively reduce the additional white noise while correcting for light source frequency noise. Laser frequency noise usually introduces appreciable phase noise during demodulation of interferometric fiber-optic hydrophones. In the previous means, one would introduce an additional probe isolated from the environment in sensor array, and use it as a reference to calibrate the demodulation results of the other actual sensors. However, while correcting, the reference probe also introduces a large white noise. In our array, the echo of the reference probe is higher than the other sensors, thus solving this problem. The novel array design is applied to our previously proposed fiber-optic hydrophone based on a linear frequency modulated (LFM) light source. Experiments show that the deterioration of phase noise floor caused by additional white noise is improved from at least 3 dB originally to within 1 dB. This paper analyzes the factors that need to be concerned for the successful implementation of correction algorithms in hydrophone systems based on LFM sources. Particular focus is given to the impact of the power optimization of reference probe on the white noise and the corrected phase noise. Our proposal allows a significant relaxation of the demanding linewidth requirement for interferometric hydrophone. It is shown that laser with linewidth of 338.06 MHz can replace that with 1.417 kHz in our new system, while achieves the same demodulation noise floor.