Polarization-encoded coaxial structured light for high-precision 3D surface profilometry

Traditional three-dimensional imaging techniques, such as structured light profilometry or confocal microscopy, have limitations in terms of imaging speed, system complexity, or adaptability to weak texture samples. To overcome these limitations, this paper proposes and validates what we feel is a novel coaxial three-dimensional imaging method based on the longitudinal variation of polarization state of the structured light field. The core innovation of this method lies in generating a structured illumination light field with a polarization state that changes in a predetermined pattern along the optical axis through polarization modulation. The inherent axial polarization gradient of this light field serves as the "optical ruler" for depth encoding. Combined with a polarization resolving detector, the system can decode the three-dimensional topography information of the object surface from the acquired two-dimensional polarization images with a single exposure, achieving rapid three-dimensional measurement without axial scanning. Theoretical analysis clarifies the mathematical model of encoding and reconstruction, and an experimental compact system based on polarization grating and polarization camera has been built. Quantitative tests show that the axial measurement accuracy of this method for highly reflective samples can reach the micron level. Compared with traditional schemes, this method has the advantages of a compact coaxial optical path structure, high stability, and fast single-frame imaging speed, providing a believed to be novel and promising three-dimensional imaging tool for dynamic observation in life sciences and industrial online inspection.