Constrained polarization evolution simplifies depth-resolved retardation measurements with polarization-sensitive optical coherence tomography.

Qiaozhou Xiong,Xinyu Liu,Martin Villiger,Cilwyn S Braganza,Nanshuo Wang,Si Chen,Linbo Liu,Brett E Bouma

doi:10.1364/boe.10.005207

Abstract

We observed that the polarization state of light after round-trip propagation through a birefringent medium frequently aligns with the employed input polarization state 'mirrored' by the horizontal plane of the Poincaré sphere. We explored the predisposition for this mirror state and evidence that it constrains the evolution of polarization states as a function of the round-trip depth into weakly scattering birefringent samples, as measured with polarization-sensitive optical coherence tomography (PS-OCT). Combined with spectral variations in the polarization state transmitted through system components, we demonstrate how this constraint enables measurement of depth-resolved birefringence using only a single input polarization state, which offers a critical simplification compared to conventional PS-OCT employing two input states.

Highlights

Polarization offers access to unique, distinguishing signatures of samples for diverse applications from remote sensing [1,2] to biomedical optics [3,4,5]
Repeated with different launching polarization states s, which were measured by reflecting the light to the detector before entering the fiber, we identified the state m = D · s, where D = diag(1, 1, −1), as the input state mirrored by the horizontal QU-plane, and designated it as the polarization mirror state
This study reports how the evolution of the polarization state after round-trip propagation through a medium with changing retardation is constrained to pass through the polarization mirror state

Summary

Introduction

Polarization offers access to unique, distinguishing signatures of samples for diverse applications from remote sensing [1,2] to biomedical optics [3,4,5]. Observing the depth-dependence of the polarization state backscattered from a sample illuminated with a single input state provides the cumulative round-trip retardation from the tissue surface to a given depth in the tissue [9,10]. Because the rate of polarization change depends on the alignment of the polarization state with the local optic axis in the sample, it is in general very difficult to interpret cumulative retardation. Multiple input polarization states are employed [11] in addition to polarization-diverse detection to fully characterize the polarization properties of a sample and compute local retardation, i.e. depth-resolved tissue birefringence [12,13,14,15,16]. Alleviating the demanding hardware requirements for local retardation imaging would enable more widespread exploration of this compelling contrast mechanism

Methods

Discussion

Conclusion