Fiber-based polarization-sensitive optical coherence tomography

Polarization-sensitive optical coherence tomography (PS-OCT) is an interferometric technique capable of non-invasive depth-resolved imaging of the polarization properties of biological tissue that has shown great promise for a wide variety of clinical applications. Furthering these applications almost necessitate fiber-based implementation; however, optical fiber can induce an unknown birefringence that complicates determination of sample polarization properties. In principle, cumulative sample polarization properties can be determined by comparison of the polarization states reflected from the surface of the sample to those reflected from some depth within the sample for two unique incident polarization states optimally separated by 90° in a Poincare sphere representation.; Three different solutions capable of determining sample polarization properties using a fiber-based PS-OCT system with the unrestricted use of optical fiber and non-diattenuating fiber components are presented. First, a simple Stokes vector-based method assuming no sample diattenuation is discussed, and applied to an in vivo animal study demonstrating a correlation between histological burn depth and PS-OCT derived measurements. This computationally-efficient method has been used in a number of clinical studies to date. Second, a vector-based method that additionally determines sample diattenuation in a separate step is presented. Third, a Jones matrix-based analysis that simultaneously determines the amounts and common optic axis for sample birefringence and diattenuation is described, as are fundamental ambiguities in optic axis determination. The latter two methods were experimentally verified by comparison with independent measurements, and demonstrate the relative importance of diattenuation versus birefringence to the angular displacement of Stokes vectors in a Poincare sphere representation.; Practical implementation of PS-OCT in a clinical setting also demands high acquisition speed and real-time display. Two fiber-based systems capable of high acquisition speeds and real-time display of simultaneous tissue structure, birefringence, and flow images are presented. The first system, based on traditional time-domain technology, has been used in a number of clinical studies to date, and even been adapted for endoscopic applications.; Finally, fundamental limitations on the accuracy of phase determination as functions of signal-to-noise ratio and lateral scan speed are described and their relative contributions are compared. The consequences of phase accuracy are discussed for PS-OCT measurements.