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

Area of Science:

• Optical Engineering
• Acoustic Sensing
• Signal Processing

Background:

• Interferometric fiber-optic hydrophones are susceptible to phase noise caused by laser frequency noise.
• Traditional methods use a reference probe to calibrate sensor data but introduce significant white noise.
• Existing systems require lasers with very narrow linewidths, increasing costs and complexity.

Purpose of the Study:

• To propose a novel time-division multiplexed (TDM) array for large-scale fiber-optic hydrophone systems.
• To introduce a power-optimized reference probe to reduce white noise and correct for laser frequency noise.
• To relax the stringent linewidth requirements for lasers used in interferometric hydrophones.

Main Methods:

• Implementation of a TDM array with a power-optimized reference probe.
• The reference probe's echo is amplified relative to other sensors to mitigate introduced white noise.
• Application of the novel array design to a fiber-optic hydrophone utilizing a linear frequency modulated (LFM) light source.

Main Results:

• The novel array design significantly reduces the phase noise floor deterioration caused by additional white noise, improving it from at least 3 dB to within 1 dB.
• Power optimization of the reference probe effectively minimizes white noise and corrects phase noise.
• The system successfully allows the use of a laser with a 338.06 MHz linewidth, replacing the need for a 1.417 kHz linewidth laser while maintaining the same demodulation noise floor.

Conclusions:

• The proposed TDM array with a power-optimized reference probe offers a robust solution for large-scale fiber-optic hydrophone systems.
• This approach effectively mitigates white noise and laser frequency noise, enhancing system performance.
• The developed method substantially relaxes laser linewidth requirements, enabling the use of less expensive and more accessible lasers.