Polarization-sensitive optical tomography of scattering media using low coherent light

Abstract

PS-OCT(Polarization-Sensitive Optical Coherence Tomography) is adapted to aquire microscopic tomography of light polarization change inside scattering media. PS-OCT can extract depth-resolved polarization change by combining photon selection ability based on low coherence of source and interferometric ellipsometry. In order to improve PS-OCT technology, firstly, statistics of PS-OCT signals is identified. The amplitude of the detected signal is found to faithfully follow the Rayleigh distribution predicted by the scattering theory of electromagnetic waves in random media. The probability density function of the phase difference between the two orthogonal signal components of PS-OCT is explicitly derived and then verified in comparison with the experimental data measured from in-vitro tissues. Secondly, to describe PS-OCT signals for various scattering media, a Monte Carlo model for polarized light propagation in a multiple layered birefringent scattering medium based on the Jones formalism and Mie scattering theroy is developed. The simulation makes it possible to derive the depth-resolved Stokes vector, which provides a complete characterization of the optical polarization state change of a scattering media. The experimental PS-OCT system is utilized to expand PS-OCT applications for engineering materials and tissues. Nondestructive testing of translucent glass-epoxy composites was performed to map the inside stresses distribution by means of the PS-OCT. Cross-section image of Stokes vectors successfully visualize internal stress distribution and microscopic damage inside composite. The developed system is also exploited to classify types of connective tissue. Sample tissues corresponding to typical connective tissue types were extracted from human tongue, bovine cartilage and rodent skin, and PS-OCT images for each tissue are compared with morphological characteristics of tissues including collagen fiber types and its orientation.