With the increasing use of optical coherence tomography (OCT) in biomedical applications, robust yet simple methods for calibrating and benchmarking a system are needed. We present here a procedure based on a calibration object complemented with an algorithm that analyzes three-dimensional OCT datasets to retrieve key characteristics of an OCT system. The calibration object combines state-of-the-art tissue phantom material with a diamond-turned aluminum multisegment mirror. This method is capable of determining rapidly volumetric field-of-view, axial resolution, and image curvature. Moreover, as the phantom material mimics biological tissue, the system’s signal and noise levels can be evaluated in conditions close to biological experiments. We believe this method could improve OCT quantitative data analysis and help OCT data comparison for longitudinal or multicenter studies.
Stress-engineered optical elements have potential applications in snapshot polarimetry, in which a single irradiance
image is used to measure a spatially varying polarization. In this paper, we present star test polarimetry
which is a method of polarization retrieval by analyzing a single frame point spread function. A trigonally
stressed window placed at the pupil plane of an imaging system is used to produce point spread functions which
are then processed to extract the polarization state of the incoming beam under investigation. We outline several
methods which are used to recover the Stokes parameters of a beam of unknown polarization from the irradiance
distribution of its point spread function.
We describe an analytic formulation that describes the spatial behavior and propagation of a class of fully
correlated beams that span the complete Poincaré sphere. The beams can be constructed from a superposition
of a fundamental Gaussian mode and a spiral phase Laguerre-Gauss (LG) mode having orthogonal polarization.
When the orthogonal polarizations are right and left circular, the coverage extends from one pole of the sphere
to the other in such a way that concentric circles on the beam map onto parallels on the Poincaré sphere and
radial lines map onto meridians. If the beam waists match, the beam propagation corresponds to a rigid rotation
about the pole; a mismatch in beam waist size or position produces a beam in which parallels rotate at different
rates with propagation distance. We describe an experimental example of how a symmetrically stressed window
can produce these beams and show that the predicted rotation indeed occurs when moving through the focus of
a paraxial Gaussian beam. We discuss nonparaxial behavior and end with a discussion of how the idea can be
extended to include beams that not only cover the surface of the Poincaré sphere, but fill the volume within the
We explore polarization distribution in point spread functions and Stokes parameter signatures of pupil aberrations.
With the aid of stress-engineered optical elements, we explore how pupil aberrations map onto Stokes
parameters in the focal plane.
Stress-engineered optical elements show fascinating and potentially useful effects when placed at the pupil plane
of an imaging system. When illuminated by a beam of spatially uniform polarization, a snapshot (single measurement)
polarimetry method can be constructed. We expand upon this method to perform snapshot pupil
polarimetry for spatially varying pupil polarization. We present the theory for snapshot non-uniform pupil
polarization measurement using a stress-engineered optical element, as well as simulation results.
A variety of interesting polarization effects can be observed using a parallel-face window placed under symmetric
stress of order <i>m</i> = 3 and illuminated with polarized light. Such windows, when placed under sufficient stress,
can produce rings of alternating vortex and non-vortex fields. When light is brought to a focus, one component of
circular polarization forms two nearly diffraction limited focal spots with axial separation larger than the usual
depth of focus. We analyze and experimentally test these phenomena using interferometric methods as well as a
Strehl ratio model and conclude by discussing applications to optical imaging.