Polarization-constrained ring-illumination microscopy for label-free relative 3D surface reconstruction

We present a label-free relative 3D surface reconstruction method via polarization-constrained ring illumination. A programmable 12-sector ring LED sequentially illuminates the transparent sample to generate direction-sensitive intensity responses, while a division-of-focal-plane polarization sensor records linear polarization components without mechanical rotation. The ring-illumination responses are used to estimate initial surface-gradient cues, and polarization features, including the degree and angle of linear polarization, are incorporated into a height-field optimization model to suppress unstable reconstruction in weak-texture and low-contrast regions. We validate the method on 20 µm standard microspheres and living yeast cells. The microsphere-calibrated model reduces full-region height RMSE from 2.16 µm to 0.45 µm. For a budding yeast cell, single-sector and overlapping paired-sector 12-direction encodings yield consistent relative-height maps (r = 0.970; NRMSE = 6.03%), while polarization-weighted regularization reduces weak-interior high-frequency RMS by 10.8%.