[Department of Ocean Science] PhD Qualifying Examination Defense Seminar: Research and Experiment on Key Technologies of a High-Precision Swept-DFB Michelson Optical Pressure Sensing System for Shallow-Sea Observation
 

Abstract:

In shallow-sea and coastal waters, pressure measurements support observations of tides, storm-driven and long-period sea-level variations, surface and infragravity waves, and nonlinear internal-wave disturbances. Because these signals vary across space, synchronized multi-point pressure arrays are needed to resolve their propagation and spatial structure. Motivated by this need, this work develops an array-oriented reflective Michelson optical pressure sensing system combining compact passive fiber probes with centralized swept-DFB interrogation and gas-cell/MZI-referenced demodulation. The dual-arm Michelson structure helps reduce common-mode thermal effects, while reference-assisted readout reduces sweep uncertainty. In the embedded sweep-linearity calibration experiment, the MZI-assisted method reduced wavelength-linearity residuals from tens of picometres to sub-picometre levels over a 0.52 nm sweep range, with repeatable performance over 10,000 consecutive sweep periods, providing a more stable wavelength coordinate for subsequent embedded interferometric demodulation. In a preliminary laboratory pressure-loading experiment, the fabricated probe was loaded stepwise from atmospheric pressure to 2.8 MPa (approximately 280 m of seawater-equivalent hydrostatic depth), with its output recorded during each pressure hold. The resulting synchronized optical responses were processed offline using a gas-referenced MZI phase coordinate, multiscale derivative features, and local PCA–RBF regression. Using previously acquired measurements for calibration, repeated sensor pressure estimates under fixed applied pressures showed mean and worst within-pressure-level standard deviations of 0.274 and 0.694 kPa, equivalent to approximately 2.7 and 6.9 cm of seawater depth, respectively. These results indicate good within-pressure-level repeatability under stable applied pressure conditions and establish a basis for centralized fiber-optic pressure arrays for shallow-sea observations.