Physics-Guided Neural Phase Demodulation for Non-Contact Laser-Ultrasound Sensing of Corneal Phantom Deformation

Non-contact detection of weak, transient acoustic signals is essential for photoacoustic and laser-ultrasound (LUS) bioimaging, including the assessment of corneal deformation and thickness variation. Passive 3 × 3 fiber-coupler interferometers provide phase-diverse sensing without external modulation; however, conventional ellipse-based calibration becomes unreliable when the measured phase excursion covers only a small fraction of the characteristic ellipse, as in nanometer-scale corneal responses. This study presents a physics-guided temporal convolutional network (PG-TCN) that directly maps two nonideal interferometric outputs to a continuous dynamic phase signal without ellipse fitting or separate phase unwrapping during inference. The model combines dilated one-dimensional convolutions with interferometric-consistency and temporal-regularization losses. Tests using PZT-modulated calibration signals acquired under several static chamber pressures of 10, 15, 20, and 25 kPa showed lower mean absolute error, higher normalized cross-correlation, and lower displacement RMSE than a CNN-LSTM baseline. In corneal-phantom LUS measurements, the first detected echo shifted from 4.632 to 4.488 µs between 10 and 20 kPa, corresponding to a relative thickness reduction of approximately 7.8 µm/kPa. The PG-TCN required 210 ± 18 µs per sequence while using approximately half the trainable parameters of the CNN-LSTM baseline. These results demonstrate a fast physics-guided optical detection framework for non-contact sensing of weak acoustic responses, supporting the use of 3 × 3 optical interferometry as a biosensing approach for LUS and photoacoustic applications.