Abstract
A Swept Source Polarization-Sensitive Optical Coherence Tomography (SS-PS-OCT) instrument has been designed, constructed, and verified to provide high sensitivity depth-resolved birefringence and phase retardation measurements of the retinal nerve fiber layer. The swept-source laser had a center wavelength of 1059 nm, a full-width-half-max spectral bandwidth of 58 nm and an A-line scan rate of 34 KHz. Power incident on the cornea was 440 µW and measured axial resolution was 17 µm in air. A multiple polarization state nonlinear fitting algorithm was used to measure retinal birefringence with low uncertainty. Maps of RNFL phase retardation in a subject measured with SS-PS-OCT compare well with those generated using a commercial scanning laser polarimetry instrument. Peak-to-valley variation of RNFL birefringence given here is less than values previously reported at 840nm.
Highlights
Optical Coherence Tomography (OCT) was first introduced as a time domain (TD) technique in 1991 [1] with frequency domain (FD) techniques introduced in 1995 [2,3]
Frequency domain techniques increased in use after 2003 when FD-OCT was shown to provide an advantage over TD-OCT in terms of signal-to-noise ratio and acquisition speed [3,4,5]
Park et al measured single pass phase retardation δ = 24.76° +/ 0.62° for the same birefringent film in 80 μm thickness, which corresponds to single pass phase retardation per unit depth (SPPR/UD) of 30.95°/100 μm or Δn = 7.14 10 4 at 840 nm [47]
Summary
Optical Coherence Tomography (OCT) was first introduced as a time domain (TD) technique in 1991 [1] with frequency domain (FD) techniques introduced in 1995 [2,3]. Frequency domain techniques increased in use after 2003 when FD-OCT was shown to provide an advantage over TD-OCT in terms of signal-to-noise ratio and acquisition speed [3,4,5]. PS-OCT provides additional contrast to standard OCT by making use of interference fringe intensity and relative phase of two detected orthogonal polarization states. PS-OCT systems utilized bulk optics [8,9,10], but later, fiber-based systems were developed and demonstrated [11,12,13]. Fiber-based systems are smaller in size and more convenient to align compared to free space systems. Free space systems‘ polarization state at the reference and sample paths is easier to control and reference to a fixed laboratory frame. Controlling the polarization state of light in single mode fiber-based systems is more difficult because of uncontrolled polarization changes that can occur in single mode optical fiber [14]
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