System and method for polarization-sensitive optical coherence tomography

Abstract

A system for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the system including: an OCT apparatus including a sample arm and a reference arm; a polarization altering element disposed in a round-trip portion of the sample arm of the OCT apparatus, the polarization altering element configured to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample, and the polarization altering element configured to vary its polarization alteration during imaging; and a processor configured to: acquire a plurality of cross-sectional images of the sample with different polarization alterations based on the variation of the polarization altering element, and generate an image of the sample based on the plurality of cross-sectional images of the sample.

Description

MGH 2025-182-02Quarles 125141.04956SYSTEM AND METHOD FOR POLARIZATION-SENSITIVE OPTICAL COHERENCE TOMOGRAPHY CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is based on and claims priority from U.S. Patent Application Ser. No. 63 / 748,636, filed on January 23, 2025, the entire disclosure of which is incorporated herein by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under grant number P41EB015903, R01EB033321 awarded by NIH. The government has certain rights in the invention.BACKGROUND

[0003] Polarization-sensitive optical coherence tomography (PS-OCT) extends OCT by analyzing the polarization states of backscattered light to quantify tissue birefringence. However, conventional implementations require polarization-diverse detection and are therefore incompatible with typical commercial OCT systems. As a result, PS-OCT has largely remained restricted to specialized research groups, limiting its broader scientific and clinical use.SUMM ARY OF THE INVENTION

[0004] Accordingly, new apparatus, systems, and methods for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus are desirable.

[0005] Disclosed herein are embodiments of a device that enables existing OCT instruments to acquire polarimetric sample measurements. Embodiments of the device include a module including polarization altering element (e.g., a retarding element such as a waveplate) that may be inserted into the accessible round-trip portion of the system’s sample arm to alter the polarization state of the illuminating and of the backscattered light. The waveplate may be configured to dynamically vary its retardance and / or optic axis orientation during imaging.Acquiring a series of repeated cross-sectional images (B-scans) through the evolving retarder allows the use of a single detector / spectrometer for measuring how the sample modifies the 1QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956polarization of the probing light. Existing methods for such polarization-sensitive OCT employ polarization-diverse detection and / or multiple input states, which makes them incompatible with conventional OCT instruments and requires major modifications that are difficult to revert. One possible implementation includes a waveplate that is continuously rotating at a defined speed. Alternative implementations may use a voltage-controlled retarder or a retarder with other control mechanisms. The module can be configured to be inserted into the free-space portion of the sample beam or, for a fiber-based system, may also be fiber-based. For a free-space system, the module can readily be removed, leaving the original instrument unchanged.

[0006] The embodiments also include methods and algorithms to compensate for phase drift between the sample and reference arm of the interferometer, where such drift is common, e.g., in ophthalmic imaging of the retina. Retinal imaging is further complicated by the presence of retardance in the anterior portion of the eye, which prevents trivial phase stabilization strategies used in Doppler-OCT and angiographic imaging.

[0007] The measurement strategy and reconstruction algorithm in accordance with the invention may rely on a fundamental reciprocity-induced symmetry constraint manifesting when measuring back- scattered light through identical illumination and detection optics, as typically used in OCT. Algebraically, this constraint manifests as a transpose-symmetry of the Jones matrix describing the round-trip transmission through the sample as a function of pathlength at each measurement location. This symmetry reduces the number of unknown parameters from eight to six, considering that a Jones matrix is a complex-valued two by two matrix. Each (complex-valued) measurement defines two unknown parameters, requiring at least three measurements to fully determine the underlying Jones matrix.

[0008] In the presence of phase drift, which adds an unknown phase offset to each tomogram column (A-line), it is possible to acquire additional repeat measurements and compensate for the phase drift by maximizing the agreement among the multiple measurements. From the sequential cross-sectional measurements, it is then possible to reconstruct the full Jones matrix, from which tissue polarization properties such as retardance, fast axis orientation, and diattenuation can be determined. The round-trip Jones matrix can further serve to reconstruct local, depth-resolved polarization properties, as from Jones matrix measurements performed with conventional polarization-sensitive OCT systems.2QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956

[0009] Various embodiments feature a detachable waveplate module and advanced image reconstruction methods. The module may be inserted into the accessible round-trip portion of the system’s sample arm to alter the polarization state of the illuminating and of the backscattered light, enabling existing clinical OCT instruments to perform polarimetric measurements without modification of their hardware. It offers an efficient and cost-effective solution to overcome the barriers hindering the clinical exploration of polarimetric OCT.

[0010] In one embodiment, a system for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the system including: an OCT apparatus including a sample arm and a reference arm; a polarization altering element disposed in a round-trip portion of the sample arm of the OCT apparatus, the polarization altering element configured to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample, and the polarization altering element configured to vary its polarization alteration during imaging; and a processor configured to: acquire a plurality of cross-sectional images of the sample with different polarization alterations based on rotation of the polarization altering element, and generate an image of the sample based on the plurality of cross-sectional images of the sample.

[0011] In another embodiment, an actuator for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the actuator including: a polarization altering element configured to be disposed in a round-trip portion of a sample arm of an OCT apparatus, the polarization altering element configured to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample, and the polarization altering element configured to vary its polarization alteration during imaging.

[0012] In yet another embodiment, a method for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the method including: disposing a polarization altering element in a round-trip portion of a sample arm of the OCT apparatus; varying the polarization altering element during imaging to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample; acquiring a plurality of cross-sectional images of the sample at different polarization alterations based on variation of the polarization altering element; and generating an image of the3QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956sample based on the plurality of cross-sectional images of the sample.

[0013] In still another embodiment, a method for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the method including: disposing a polarization altering element in a round-trip portion of a sample arm of the OCT apparatus; varying the polarization altering element during imaging to alter the polarization state of illuminating light directed toward an OCT sample and of backscattered light returning from the OCT sample; and acquiring a plurality of cross-sectional images of the OCT sample at different polarization alterations of the polarization altering element.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Various objects, features, and advantages of the disclosed subject matter can be more fully appreciated with reference to the following detailed description of the disclosed subject matter when considered in connection with the following drawings.

[0015] FIG. 1 illustrates a construction of a system including polarization module to convert an OCT system to perform polarization-sensitive measurements.

[0016] FIG. 2 illustrates a conventional OCT system.

[0017] FIG. 3 illustrates a construction of the polarization module in the sample arm of an OCT apparatus for ophthalmic imaging.

[0018] FIG. 4 illustrates a construction of the polarization module in the sample arm of an OCT apparatus for imaging of biological tissues.

[0019] FIG. 5 illustrates a construction of the polarization module in the fibered portion of the sample arm of an OCT apparatus.

[0020] FIG. 6 shows a diagram of a spectrometer-based OCT system for ophthalmic imaging with the polarization module.

[0021] FIG. 7 illustrates a construction of a polarization module configured as a rotating waveplate module.

[0022] FIG. 8 illustrates a construction of the polarization modulator implemented on a commercial optical coherence tomography (OCT) system.

[0023] FIG 9 shows results of imaging of a birefringence phantom. (FIG. 9 A) SLO image; (FIG. 9B) Structural B-scan; (FIG. 9C) Phase difference map before correction; (FIG. 9D) Phase difference map after correction; (FIG. 9E) Cumulative retardance and (FIG. 9F) optic 4QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956axis orientation reconstructed from corrected tomograms; (FIG. 9G) Cumulative retardance and (FIG. 9H) optic axis orientation after surface retardance compensation.

[0024] FIG 10 shows a polarimetric reconstruction of healthy human retina. (FIG. 10A) Scanning laser ophthalmoscopy (SLO) image with the scan region centered on the ONH. (FIG.10B) En face, surface retardance, (FIG. 10C) surface optic axis orientation, and (FIG. 10D) cumulative retardance maps after surface retardance compensation, with vessel regions excluded.

[0025] FIG 11 shows a polarimetric reconstruction of healthy human retina. (FIG. 11A) SLO image with the scan region centered on the fovea (FIG. 1 IB) B-scan cumulative retardance and (FIG. 11C) optic axis orientation after surface retardance compensation corresponding to the white line in the SLO image. (FIG. 1 ID) En face retardance map reconstructed from the region indicated by the dashed box. (FIG. 1 IE) En face optic-axis orientation map from the same region, revealing a radially organized orientation pattern characteristic of healthy retinal tissue.

[0026] FIG. 12 shows a schematic of a particular construction (referred to herein as RevoPol) of the system of FIG. 1. A rotating waveplate, placed in the sample arm, modulates the polarization state of the probing light and enables extraction of tissue polarization properties on a standard spectral -domain OCT platform. In this example, the light source is a broadband light source, the retarding element is a rotating waveplate, the sample is an eye (e.g., the retina), and the detector is a spectrometer.

[0027] FIG. 13 shows a RevoPol module for the Spectralis HRA+OCT instrument. (FIG.13 A) The module includes an achromatic half-wave plate driven by a belt-coupled DC motor. A motor controller, programmed via a micro-USB connection, allows the user to select rotation speeds using a dial on the module. The unit is powered by rechargeable batteries that can be recharged, eliminating the need for a wall outlet. The module operates independently and does not require synchronization with the OCT instrument. The tilt adjuster lowers the internal reflection from the waveplate. (FIG. 13B) A physical gap between the scan head and the objective lens facilitates integration of the module, which can be easily attached to and detached from the scan head.

[0028] FIG. 14 shows simulations of imaging and polarimetric reconstruction using the RevoPol framework, (panel A) Intensity of sequential tomographic measurements acquired during waveplate rotation (rotation step: 7t / l 2 per B-scan) with speckle and phase noise applied.5QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956Three birefringent bars and surface cumulative retardance were included in the simulation, (panel B) Phase differences between the first and subsequent measurements, (panel C) Phase differences after zero-phase correction, (panel D) Two candidate solutions of optic axis orientation (0) and retardance (5) obtained from retarder-constrained phase optimization, compared with the ground-truth retarder (red dashed line). The blue curve corresponds to the solution with smaller residual errors, while the green curve represents the rejected candidate, (panel E) Phase offsets (q>) generated from the estimated retarder corresponding to the blue curve in (panel D). (panel F) Final corrected phase differences obtained by applying the phase offsets from (panel E) to (panel C). (panel G) Cumulative retardance and optic axis orientation reconstructed from tomograms with corrected phases, compared with polarimetric reconstruction from noise-free signals.

[0029] FIG. 15 shows simulation of rotation speed error on polarimetric reconstruction. Estimated rotation speeds (co) are 15° / B-scan (top) and 18° / B-scan (bottom). Rotation speed error is defined as (coactuai -(Destimated) / coestimatedx100%. (panel A) Retardance error and (panel B) optic axis orientation error as a function of known optic axis orientation, (panel C) Reconstruction of a constant optic axis orientation along the B-scan direction without compensation for continuous rotation. With an estimated speed of 15° / B-scan, the orientation remains constant when the rotation speed is correct (Rotation speed error = 0%) and exhibits progressive variation in the presence of speed error. In contrast, an estimated speed of 18° / B-scan produces high-frequency fluctuations in the reconstructed orientations, regardless of speed accuracy.

[0030] FIG. 16 shows imaging of a birefringence phantom using the RevoPol framework, (panel A) Structural B-scan. (panel B) Phase difference map before correction, (panel C) Optic axis orientation (0) and retardance (d) estimated using retarder-constrained phase optimization, (panel D) Phase difference map after correction, (panel E) Cumulative retardance and optic axis orientation reconstructed from corrected tomograms, (panel F) Cumulative retardance and optic axis orientation after surface retardance compensation, (panel G) Surface retardance maps acquired using different waveplate rotation speeds. All scale bars: 200 pm.

[0031] FIG. 17 shows a calibration of waveplate rotation speed, (panel A) During waveplate rotation, the fixed retarder placed along the light path induced periodic intensity6QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956modulation in the phantom. After coherence filtering, the normalized intensity across repeated B-scans (blue) shows a periodicity of 3 B-scans, corresponding to a waveplate rotation speed of 7t / 12 (-15°) per B-scan. The intensity inconsistency between B-scans (green arrows) indicates inter-B-scan time, (panel B) In a C-scan, the reconstructed surface optic axis orientation shows drifts (top) due to small deviations in the estimated rotation speed. Precise calibration of the waveplate rotation speed eliminates these drifts (bottom).

[0032] FIG. 18 shows an effect of coherency filtering on tomograms, (panel A) Original tomogram, (panel B) Tomogram after registration and coherency filtering, shown without phase correction, (panel C) Q metric derived from the coherency matrix, used to enhance boundary contrast, (panel D) Phase difference between the first tomogram and a repeated measurement for the original, registered, and coherency-filtered data, masked by Q > 0.4. Registration reduces phase noise, and coherency filtering further suppresses speckle and phase fluctuations while preserving structural boundaries. Scale bar: 200 pm.

[0033] FIG. 19 shows a polarimetric reconstruction of healthy human retina using RevoPol (panel A) Left'. Scanning laser ophthalmoscopy (SLO) image with the scan region centered on the ONH (red box). Right. En face, surface retardance (<5, 48.5°±5.4°), surface optic axis orientation (ff), and cumulative retardance maps after surface retardance compensation, with vessel regions excluded, (panel B) Left: SLO image with the scan region centered on the fovea (red box). Right: B-scan cumulative retardance and optic axis orientation after surface retardance compensation corresponding to the green line in the SLO image. En face images from the whitebox region show reduced retardance and a radial optic-axis orientation pattern. All scale bars: 200 pm.DETAILED DESCRIPTION

[0034] In accordance with some embodiments of the disclosed subject matter, mechanisms (which can include apparatus, systems, and methods) for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus are provided.

[0035] Presented herein are embodiments of a modular polarization-sensitive OCT (PS-OCT) framework that integrates with a standard OCT platform (e.g., spectral domain or swept-source OCT, to name a few), for example through a detachable polarization altering element disposed in the sample arm. This polarization altering element modulates both incident and 7QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956reflected polarization states. Three or more repeated measurements at distinct polarization altering element configurations enable reconstruction of the sample’s round-trip Jones matrix and the corresponding polarization properties. To mitigate random phase variations between repeated measurements, we introduce a retarder-constrained phase optimization strategy. We validate the framework with imaging of birefringent phantoms and the human retina in vivo, demonstrating reliable reconstruction of retardance and optic axis orientation. This approach requires only minimal hardware modification and is readily deployable on standard / mainstream OCT systems. Lowering technical barriers paves the way for rapid and widespread deployment of PS-OCT across diverse biomedical applications in both research and clinical environments.

[0036] Optical coherence tomography (OCT) is a non-invasive imaging technique that generates cross-sectional images of biological tissues at micrometer resolution. Since its introduction, OCT has become an indispensable tool in biomedical imaging, with applications ranging from ophthalmology to cardiology, gastrointestinal and pulmonary imaging, and dermatology. PS-OCT extends OCT by analyzing the polarization states of backscattered light, enabling tomographic reconstruction of tissue polarization properties such as birefringence and optic axis orientation. These polarimetric measurements offer insights into tissue microstructure beyond conventional OCT resolution, revealing information about tissue integrity, composition, and biomechanical factors. PS-OCT has been used to investigate a variety of tissues, including skin and skin-related conditions such as burns and scars, coronary arteries, pulmonary airways, and ocular tissues in studies of glaucoma, age-related macular degeneration, and myopia. Despite these advances, PS-OCT has remained largely confined to research settings. Current implementations rely on custom-built systems with multiple polarization states for illumination and / or polarization-diverse detection channels. While prior PS-OCT systems use pairs of detectors to detect polarization signals, e.g., horizontally and vertically polarized components of the output signal, the present device only requires a single detector.

[0037] The conventional PS-OCT frameworks are fundamentally incompatible with the widely deployed OCT platforms used in clinical and translational research. This incompatibility has hindered the development of commercially viable, clinically adaptable PS-OCT solutions, slowing progress across multiple fields of medicine. To enable broad adoption, PS-OCT requires a technical transition paradigm that integrates seamlessly with existing OCT systems while8QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956providing advanced polarization contrast. In this study, we introduce RevoPol, a novel PS-OCT framework that enables commercial spectral-domain OCT instruments to perform seamless polarimetric measurements through modular hardware modifications. By expanding PS-OCT capabilities to standard OCT platforms, RevoPol facilitates rapid deployment across diverse biomedical applications, from ophthalmology to other tissue imaging domains, accelerating both research and clinical translation.

[0038] In various embodiments, systems and methods for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus are disclosed herein. In some embodiments, the system relies on inserting a polarization altering element (e.g., a rotating waveplate) into the sample arm of a spectral-domain OCT instrument. In various embodiments, employing an achromatic half-wave plate preserves the linearity of the source polarization state upon transmission while rotating it by twice the angle between the incident state and the waveplate's fast axis.

[0039] OCT systems are sensitive to polarization due to their coherent measurement scheme, where only the portion of the backscattered light that matches the polarization of the reference light contributes to the interference signal. With an achromatic half-wave plate, scatterers in non-birefringent tissues keep identical interference signals for all waveplate orientations, whereas the interference signals change in birefringent tissues depending on waveplate orientations. The disclosed procedures capture a sequence of images (generally at least three repeated cross-sectional images) at the same sample location through the varied polarization alterations (for example due to a revolving waveplate), enabling reconstruction of the tissue's polarization properties.

[0040] Various embodiments include a module including an achromatic half-wave plate driven by a belt-coupled DC motor, where the rotation speed is controlled by a motor controller. The module may be tailored for integration with a clinical OCT instrument by insertion into the free-space section of the sample arm. In one embodiment, the OCT instrument combines a spectrometer-based OCT system operating at 85 kHz A-line rate with a source centered on 870 nm, along with a confocal scanning laser ophthalmoscope providing active eye tracking, although other frequencies and wavelengths are also possible. Furthermore, while certain examples are presented in the context of a rotating retarding element such as a waveplate, other9QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956mechanisms for polarization altering or modulation (e.g., which do not involve rotation of a halfwave plate or other element) are also possible, as discussed further below.

[0041] Embodiments of the disclosed procedures perform repeated measurements through a rotating waveplate placed in the sample arm, each using a single input and detection state. Measurements through distinct waveplate orientations effectively correspond to different polarization states incident on the sample, and the collected back-scattered light interferes with the reference light. Only the portion of the scattered light matching the polarization of the reference contributes to the interference signal, serving as a form of polarization detection.

[0042] When the sensing matrix is constructed using only a rotating waveplate with fixed retardance, its maximum column rank is three, regardless of the number of waveplate orientations. The intrinsic round-trip symmetry of OCT further imposes that the Jones matrix equals its transpose, and accordingly the off-diagonal elements are equal. Thus, instead of four independent elements, each vectorized Jones matrix reduces to three independent complexvalued scalars. At least three tomographic measurements acquired with different waveplate orientations are utilized to enable unambiguous reconstruction of the sample's Jones matrix.

[0043] Pathlength drift between the sample and reference arms introduces phase variations between repeated measurements of the complex -valued tomograms. In various embodiments, the strategy for estimating these phase shifts is to perform phase optimization by minimizing the disagreement among repeated measurements obtained from more than three waveplate orientations.

[0044] First, phase differences at the sample surface across repeated A-line measurements are compensated. This procedure, referred to as zero-phase correction, eliminates random phase noise but also the meaningful phase offsets arising from tissue retardance along the light path, such as the cornea in retinal imaging. Second, retarder-induced, meaningful phase offsets are recovered through optimization, referred to as retarder-constrained phase optimization.

[0045] To further constrain the solution, the phase offset is modeled as a linear retarder at the sample surface, where 8 and 0 represent the retardance and optic axis orientation, respectively. The optimization exhibits two local minima corresponding to similar retardance values, but optic axis orientations separated by x. To resolve this ambiguity, optic axis10QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956consistency across neighboring A-lines and B-scans is enforced and the solution is selected by comparing the residual errors at the minima.

[0046] Coherency filtering aims to retain the spatial coherence properties of the OCT signal while suppressing noise and incoherent artifacts. A stack of measurements acquired at different waveplate orientations at each pixel can be described as a complex vector. The local coherency matrix is computed as the outer product, which is a rank-1 Hermitian matrix.

[0047] To suppress uncorrelated noise, the coherency matrices are spatially filtered. The filtered coherency matrix is then decomposed by singular value decomposition. Only the dominant coherent mode is retained, and a denoised measurement vector is reconstructed from the leading singular vector and its singular value. A metric is defined as the normalized ratio of the dominant singular value to the total energy, which delineates tissue signal with a high value from noise-dominated or dynamically changing areas featuring a low value.

[0048] The waveplate rotation speed may be set to approximately 7i / 12 radians between each repeated B-scan. For a B-scan pattern including 1024 A-lines at an A-line rate of 85 kHz, this corresponds to a rotation speed of approximately 3 revolutions per second. While the waveplate is rotating, six tomograms may be acquired at the same location using the system's OCTA mode to enable reconstruction of the Jones matrices for a cross-sectional image, in various embodiments, any rotation speed achieving a total waveplate evolution of at least 60° across the six tomograms provides measurements suitable for further analysis, although faster rotation speeds may introduce more phase noise.

[0049] Image registration is performed to align repeated A-line measurements, reducing motion artifacts and ensuring signal consistency for accurate phase analysis. Coherency filtering, surface segmentation, and zero-phase correction are subsequently applied to the registered tomograms.

[0050] The estimated phase offsets are applied to the filtered tomograms, followed by reconstruction of the complex-valued Jones matrix representing the polarization response of the sample. The Jones matrix is then decomposed into a unitary rotation matrix, from which the cumulative retardance and optic axis orientation are extracted. The optic axis orientations are compensated for the waveplate rotation, determined by the rotation speed, the inter-B-scan time interval, and the B-scan timestamps.11QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956

[0051] Surface retardance, originating from birefringent tissues along the imaging path such as the cornea, is extracted as rotation vectors. The square root of these vectors is converted into Jones matrices and applied symmetrically to the measured Jones matrices, thereby removing the cumulative retardance contribution along the imaging path.

[0052] The detachable module may include a tilt adjuster for adjusting the orientation of the waveplate to avoid detecting the reflected portions of the light. The module may be powered by batteries to enable operation without a wall outlet. The motor controller may be programmed via micro-USB and enables the selection of multiple rotation speeds through a dial on the module. The module may be inserted between the scan head and the objective lens of a clinical OCT instrument by clamping it to the scan head and may be easily detachable to return the system to its initial state.

[0053] Accordingly, FIG. 1 illustrates an embodiment of a system including a polarization module 5 which can be used to convert a conventional OCT system to perform polarization-sensitive measurements. The OCT apparatus includes a light source 1 directed to a beamsplitter 9, which divides the light into a reference beam 4 and a sample beam 7, also referred to as illumination light. The reference beam 4 propagates along a reference arm and is reflected by a reference mirror 3, returning toward the beamsplitter 9. The illumination light 7 passes through the polarization module 5 and propagates along a sample arm toward a sample 6. Light backscattered or reflected from the sample 6 forms backscattered light 8, which propagates back toward the beamsplitter 9. The polarization module 5 modifies the polarization state of the illumination light 7 and the backscattered light 8. At the beamsplitter 9, the backscattered light 8 interferes with the reflected reference beam 4, thereby generating an interference signal. The interference signal is recorded by a detector 10 (e.g., a spectrometer) and processed to reconstruct tomograms, as common for OCT. The modification of the polarization state imparted by the module 5 on the transmitted beams varies between the recording of the interference signals. In one embodiment, the modification achieved by the polarization module is actively synchronized with the OCT data acquisition. In other embodiments, the polarization module 5 operates passively, varying the modification of the modulation in a pre-defined way without active synchronization.

[0054] FIG. 2 illustrates an example of a conventional OCT system without a12QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956polarization module. The OCT apparatus includes a light source 1 directed to a beamsplitter 8, which divides the light into a reference beam 4 and a sample beam 6, also referred to as illumination light. The reference beam 4 propagates along a reference arm and is reflected by a reference mirror 3, returning toward the beamsplitter 8. Light backscattered or reflected from the sample 7 forms backscattered light, which propagates back toward the beamsplitter 8. At the beamsplitter 8, the backscattered light 7 interferes with the reflected reference beam 4, thereby generating an interference signal. The interference signal is recorded by a detector 9 and processed to reconstruct tomograms for OCT.

[0055] FIG. 3 illustrates an embodiment of the polarization module 2 placed in the sample arm of an OCT apparatus for ophthalmic imaging. The polarization module 2 is placed after an intermediate image plane 1. The scanned image beam is relayed by a lens 3 and focused by the lens of the eye 4 onto the retina, from where backscattered light returns through the lens 3 and the polarization module 2.

[0056] FIG. 4 illustrates an embodiment of the polarization module 3 placed in the sample arm of an OCT apparatus for imaging of biological tissues. Light is delivered through a fiber 1 and collimated by a lens 2. The polarization module 3 is placed before a beam scanner 4, which in concert with the sample objective lens 5 scans the beam across the sample plane 6. A portion of the backscattered light is collected by the objective lens 5, de-scanned and coupled back into the sample arm fiber I with the collimation lens 2.

[0057] FIG. 5 illustrates an embodiment of the polarization module 4 placed in the fibered portion of the sample arm of an OCT apparatus. Light from the source delivered through a fiber 1 is split into a sample arm 3 and a reference arm 5 by a fiber coupler 2. The polarization module 4 is placed in the sample fiber. Backscattered light returning from the sample through the sample arm fiber 3 is recombined by the fiber coupler 2.

[0058] FIG. 6 shows a diagram of a spectrometer-based OCT system for ophthalmic imaging with the polarization module. The system includes a polarization module 8 to convert a conventional OCT system to perform polarization-sensitive measurements. The OCT apparatus includes a light source 2 directed to a beamsplitter 7, which divides the light into a reference beam 6 and a sample beam 9, also referred to as illumination light. The reference beam 6 propagates along a reference arm and is reflected by a reference mirror 4, returning toward the13QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956beamsplitter 7. The illumination light 9 passes through the polarization module 8 and propagates along a sample arm toward a sample 11 (e.g., a cornea). Light backscattered or reflected from the sample 11 forms backscattered light 10, which propagates back toward the beamsplitter 7. The polarization module 8 modifies the polarization state of the illumination light 9 and the backscattered light 10. At the beamsplitter 7, the backscattered light 10 interferes with the reflected reference beam, thereby generating an interference signal. The interference signal is recorded by a detector 5 (e.g., a spectrometer) and processed to reconstruct tomograms for OCT. In one embodiment, the polarization module 8 is actively synchronized with the OCT data acquisition. In other embodiments, the polarization module 8 operates passively, without active synchronization.FIG. 7 illustrates an embodiment of a polarization module configured as a rotating waveplate module 14 which can be attached to an existing OCT device. The rotating waveplate module 14 includes a waveplate 15, which in one embodiment is a half-wave plate, mounted for rotational motion about an optical axis. Rotation of the waveplate 15 modulates the polarization state of light propagating through the polarization modulator 8. Other retarding waveplates or diattenuating elements that, in combination with the polarization state of the source, result in varying transmitted polarization states may serve in a similar way to record tomograms encoding the sample’s polarization effects.

[0059] In the illustrated embodiment, the waveplate 15 is mechanically coupled to one or more timing belt pulleys 16, which are driven by an electric motor 17 to provide controlled rotational motion of the waveplate 15. The rotating waveplate module 14 may further include an on / off button 18 and a speed selector 19 configured to control activation and rotational speed of the electric motor 17. A microcontroller 20 is configured to control motor operation, including rotational speed and timing, and may further provide communication or synchronization signals to external components. In one embodiment, the rotating waveplate module 14 is powered by a battery 21, enabling self-contained operation.

[0060] Although FIG. 7 illustrates a mechanically rotating waveplate implementation, the polarization modulator / polarization altering element (e.g., element 8 of FIG. 6) is not limited to this configuration. In other embodiments, the polarization modulator may include an electrooptic modulator (EOM), a liquid-crystal retarder, a piezo-actuated birefringent element, or other14QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956polarization-modifying devices configured to alter optical retardance, optic axis orientation, or both, either statically or dynamically. Such alternative implementations may operate with or without synchronization to OCT data acquisition.

[0061] FIG. 8 illustrates an embodiment of the polarization modulator 14 implemented on a commercial optical coherence tomography (OCT) system 22. The commercial OCT system 22 includes a clinically deployed imaging platform, such as a retinal OCT instrument, configured for in vivo imaging.

[0062] FIG 9 shows results of imaging of a birefringence phantom. (FIG. 9A) SLO image; (FIG. 9B) Structural B-scan; (FIG. 9C) Phase difference map before correction; (FIG. 9D) Phase difference map after correction; (FIG. 9E) Cumulative retardance and (FIG. 9F) optic axis orientation reconstructed from corrected tomograms; (FIG. 9G) Cumulative retardance and (FIG. 9H) optic axis orientation after surface retardance compensation.

[0063] FIG 10 shows a polarimetric reconstruction of healthy human retina. (FIG. 10A) Scanning laser ophthalmoscopy (SLO) image with the scan region centered on the ONH. (FIG.10B) En face, surface retardance, (FIG. 10C) surface optic axis orientation, and (FIG. 10D) cumulative retardance maps after surface retardance compensation, with vessel regions excluded.

[0064] FIG 11 shows a polarimetric reconstruction of healthy human retina. (FIG. 11A) SLO image with the scan region centered on the fovea (FIG. 1 IB) B-scan cumulative retardance and (FIG. 11C) optic axis orientation after surface retardance compensation corresponding to the white line in the SLO image. (FIG. 1 ID) En face retardance map reconstructed from the region indicated by the dashed box. (FIG. 1 IE) En face optic-axis orientation map from the same region, revealing a radially organized orientation pattern characteristic of healthy retinal tissue.

[0065] Thus, the present procedures do not require a polarizer or ‘polarization determining device’ in the sample arm. Instead, the device uses, e g., a rotating waveplate or another device that alters the polarization state of the transmitted light in the round-trip part of the OCT system, however it does not include any element that ‘determines’ the polarization state (i.e., polarizer). This makes the implementation into an existing OCT system simpler.Furthermore, the procedures measure the full cumulative Jones matrix, including both retardance and diattenuation / dichroism, explicitly relying on the important insight that this Jones matrix is transpose symmetric. Additionally, the procedures specifically address and manage phase drift15QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956occurring between the sequential measurements, even in the complicating presence of anterior segment retardance, which leads to a change of the polarization state effectively incident on, and detected from the retina (because we do not measure any reflection from before the anterior segment, determining the Jones matrix of this element is more challenging).

[0066] In various embodiments, the procedures include a detachable module which can convert a ‘conventional’ OCT system, for example based on a Michelson or Mach-Zehnder interferometer with non-polarizing beam splitter(s), into a polarization-sensitive OCT system. In contrast, other OCT systems utilize a polarizing beam splitter as the basis for an interferometer and thus, as a result, the interferometer in other systems requires a polarizer in the detection arm, because the recombined sample and reference beams are orthogonally polarized and need to become co-polarized to interfere. Furthermore, while the disclosed system measures the full cumulative Jones matrix, including both retardance and diattenuation / dichroism, explicitly relying on the important insight that this Jones matrix is transpose symmetric, and addresses phase drift between sequential measurements to use the complex-valued tomogram, other systems only use the intensity of the signal, which fails to make use of valuable phase information.

[0067] Embodiments of the present system use multiple sequential measurements through a varying retarding element to deduce the pathlength-resolved sample Jones matrix and use interferometric detection to resolve the pathlength of the light scattered by the sample to perform OCT. The presently-disclosed procedures do not use a detection system in which a sensor is configured to detect polarization components, e.g., a polarizing beam splitter, to detect multiple polarization components simultaneously in parallel. Instead, the procedures detect the sample light along a single polarization state defined through the reference arm polarization state. Other systems are focused on physically compensating the polarization effects of the system and the anterior segment of the eye for a single input state and a single wavelength through use of waveplates, without performing OCT or resolving the signal from individual layers, and with the goal to determine the fixation status of the eye by leveraging its intrinsic, characteristic retardance pattern.

[0068] Certain embodiments of the present apparatus can be used to modify an existing OCT system simply by adding a polarization varying element into the sample arm, without16QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956altering the reference arm of the detection system, and collecting sequential measurements through different configurations of the polarization varying element. In contrast, other systems achieve polarization-sensitive imaging by inserting a static polarization-delay unit into the sample arm, for instance through the use of polarization-maintaining fiber. This can result in multiple (by default three) pathlength-multiplexed tomogram copies, encoding distinct combinations of illumination and detection polarization states that enable recovering the sample Jones matrix. These multiple signals are detected simultaneously, not sequentially. This, however, requires either a detection system with a higher imaging range, or else causes a reduction of the available imaging range. Hence, these other approaches are incompatible with spectrometer-based OCT systems, which already have a limited imaging range. Furthermore, in certain systems the delay unit in the sample arm must be paired with an extension of the pathlength in the reference arm. Accordingly, this may be a significantly more invasive modification of the original OCT system than the ones disclosed herein.

[0069] As noted above, the present procedures build upon the fundamental insight that the sample Jones matrix is transpose symmetric, a feature that has not been leveraged by others. This symmetry makes it mathematically feasible to resolve the full sample Jones matrix from a set of measurements through a monotonically varying retarding element (i.e., a rotating waveplate, where the optic axis linearly evolves with time, or a waveplate with a fixed optic axis orientation yet changing retardance). In some embodiments, three sequential measurements through distinct waveplate configurations are sufficient for performing these calculations, although additional measurements help to suppress noise and manage phase drift. Without this symmetry constraint, measuring a general Jones matrix would require at least four independent measurements, with polarization states that cannot be generated through a single varying waveplate. Our measurement system has been designed to meet the minimum requirement to obtain a full characterization of the underlying sample Jones matrix with the simplest possible hardware modification. Depending on the mathematical convention used to describe the electromagnetic field between the illumination and detection light, the symmetry in the Jones matrix may manifest in different, interchangeable ways.

[0070] Thus, various embodiments of the present disclosure include a general polarization module that alters the polarization state of the source in the sample arm of a17QBM25141.049561100549193.1MGH 2025-182-02Quarles 125141.04956‘conventional’ OCT system, i.e., an OCT system that does not have multiple channels for polarization-diverse detection, and which can therefore be adapted to perform polarizationsensitive OCT (PS-OCT). The module sequentially alters the transmitted polarization state, both on the illumination and on the detection path. From a sequence of measurements through distinct module configurations, the sample round-trip Jones matrix is recovered, which in general includes both retardance and diattenuation / dichroism.

[0071] In various embodiments, the polarization module is compatible with both spectrometer-based and wavelength- swept frequency-domain implementations of OCT.However, polarization-diverse detection is more ‘expensive’ for spectrometer-based systems, owing to the need to duplicate a spectrometer, whereas in frequency domain systems fiber-based polarization-diverse detection is more readily available.

[0072] In certain embodiments, the polarization module can be configured in free space, which may be more desirable for direct integration into existing OCT systems (e.g., ophthalmic OCT systems), where the sample arm is physically accessible. It could also be inserted in the portion of the sample arm before the scanner or in the fiber portion (if present) of the sample arm.

[0073] Various embodiments of the polarization module include elements that modify the polarization state of the transmitted light with nominal loss, i.e., it is a retarder or waveplate, as opposed to a polarizer. In one embodiment the polarization module includes a rotating waveplate as described herein. In other embodiments the polarization module may include one or more of electro-optic, ferro-electric, or liquid-crystal polarization modulators. Mathematically, three measurements through distinct module configurations are needed. It is sufficient to vary only the optic axis orientation, or only the retardance, although a combination of both parameters is also suitable, although more difficult to achieve in practice with a single, common modulation device. A change in the optic axis orientation may be achieved through mechanical rotation of a waveplate. A change in retardance may be obtained with an electrically tunable waveplate. A combined change in axis orientation and retardance requires two controllable or rotatable waveplates in series.

[0074] EXAMPLE

[0075] The following is a non-limiting example according to embodiments of the18QBM25141.049561100549193.1MGH 2025-182-02Quarles 125141.04956disclosure.

[0076] Imaging Framework and Setup

[0077] The novel PS-OCT framework, RevoPol, relies on inserting a rotating waveplate into the sample arm of a spectral-domain OCT instrument (FIG. 12). Specifically, employing an achromatic half-wave plate preserves the linearity of the source polarization state upon transmission while rotating it by twice the angle between the incident state and the waveplate’s fast axis. During repeated cross-sectional imaging, the changing waveplate orientation modulates the polarization state of the illuminating and backscattered light to and from the sample. Every OCT system is natively sensitive to polarization due to its coherent measurement scheme. Only the portion of the backscattered light that matches the polarization of the reference light contributes to the interference signal. In the RevoPol framework, scatterers in non-birefringent tissues keep identical interference signals for all waveplate orientations, while the interference signals change in birefringent tissues depending on waveplate orientations. This framework captures a sequence of at least three repeated cross-sectional images at the same location through the revolving waveplate, enabling reconstruction of the tissue’s polarization properties.

[0078] To implement the rotating waveplate function in the RevoPol framework, we developed a module consisting of an achromatic half-wave plate (Edmund Optics, USA) driven by a belt-coupled DC motor, with rotation speed controlled by a motor controller (FIG. 13 A). The module was tailored for integration with the Spectralis HRA+OCT instrument (Heidelberg Engineering, Germany) by insertion into the free-space section of the sample arm (FIG. 13B). The Spectralis combines a spectrometer-based OCT system — operating at 85 kHz A-line rate with a source centered on 870 nm — with a confocal scanning laser ophthalmoscope (SLO) providing a 30° field-of-view and 30-Hz active eye tracking. Simultaneous SLO imaging enables real-time eye motion tracking, which stabilizes OCT imaging by dynamically correcting scan locations. This capability also supports OCT angiography (OCTA) acquisition, which uses repeated scans at each sampling location. Leveraging this OCTA mode, RevoPol reconstructs tissue polarization properties by acquiring at least three repeated cross-sectional images at the same location, each corresponding to a different waveplate orientation. The Spectralis evaluates the quality of each set of repeated measurements immediately after acquisition. If a set fails to meet quality control — for example, due to motion artifacts or signal dropout — it is discarded and19QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956reacquired. With authorized software access from Heidelberg Engineering, raw OCT fringe data and B-scan timestamps can be exported for offline analysis. The associated signal formalism and processing workflow are described in the following sections.

[0079] Terminology

[0080] A-line: A depth-resolved signal profile at a single lateral position.

[0081] B-scan: A cross-sectional image acquired by sequentially acquiring A-lines while scanning laterally along the fast axis.

[0082] Repeated measurements: Multiple acquisitions at the same B-scan position, typically performed in OCTA mode while the waveplate rotates. A set of repeated measurements is used to reconstruct a polarization-resolved cross-sectional image.

[0083] C-scan: A three-dimensional dataset formed by acquiring multiple sets of repeated measurements along the slow axis. The index of the reconstructed cross-sectional images is denoted as the slow-axis number (slow-axis #).

[0084] Surface retardance: The cumulative retardance measured at the sample surface, introduced by birefringent tissues along the imaging path (e.g., cornea in retinal imaging).

[0085] Jones Matrix Reconstruction

[0086] The RevoPol framework performs repeated measurements through a rotating waveplate placed in the sample arm, each using a single input and detection state. Measurements through distinct waveplate orientations effectively correspond to different polarization states incident on the sample, and the collected back- scattered light interferes with the reference light. Only the portion of the scattered light matching the polarization of the reference contributes to the interference signal, serving as a form of polarization detection. Algebraically, the recovered complex-valued tomogram can be expressed as

[0087] m(z, ri)

[0088] where Q(a+ / ?Aa) describes the transmission through the rotating half-wave plate at an initial angle a increasing by Aa between the sequential measurements, indexed by n. e is the complex Jones vector of the source polarization state, and f is the corresponding reference state, e'n and f „ denote the polarization states of the illumination and reference beams, respectively, after (reverse) transmission through the waveplate at the nth measurements. Js(^)20QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956represents the 2><2 round-trip Jones matrix of the tissue at depth z. Without loss of generality, the OCT system’s free-space interferometer is linearly polarized and identical to the source polarization state (i.e., e = f).

[0089] Invoking the Kronecker product rule, each individual tomogram can be described as a linear projection of the unknown, vectorized Jones matrix Js(z) onto the known 4x 1 sensing vector g^, such that

[0090] m(z, n) = e,nT®f,nt■ Js(z). (2)

[0091] Here, the sensing vectorencodes the illumination and detection polarization states at a specific waveplate orientation.

[0092] A sequence of tomographic measurements m forms a linear system that relates the unknown, vectorized Jones matrix J$(z) to the known sensing matrix G:

[0094] It is important to note that when the sensing matrix is constructed using only a rotating waveplate with fixed retardance, its maximum column rank is three, regardless of the number of waveplate orientations. The intrinsic round-trip symmetry of OCT further imposes that Js(z) = JsT(z), and accordingly jn = ju. Thus, instead of four independent elements, each vectorized Jones matrix reduces to three independent complex-valued scalars. This reduction can be expressed using a modified sensing matrix G' with only three columns:

[0096] When the column rank of the modified sensing matrix is three — i.e., when G'^ ■ G'is invertible — the vectorized Jones matrix of the sample can be calculated using the pseudoinverse as21QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956

[0098] To achieve this condition, at least three tomographic measurements acquired with different waveplate orientations are required to enable unambiguous reconstruction of the sample’s Jones matrix.

[0099] Phase Correction

[0100] Pathlength drift between the sample and reference arms introduces phase variations between repeated measurements of the complex -valued tomograms. Our strategy for estimating these phase shifts is to perform phase optimization by minimizing the disagreement among repeated measurements obtained from more than three waveplate orientations.

[0101] Each acquired A-line measurement deviates from the ideal signal by an unknown, depth-independent phase shift combined with random noise. This effect can be modeled as

[0102] m = diag(e-t<p) ■ m -I- T| = diag(«I>) ■ m -I- T|, (7)

[0103] where (p is a vector of unknown phase offsets (one per A-line measurement), and 'll is a noise matrix that perturbs the ideal measurements. Without loss of generality, the first element of q> is set to zero to define the global phase reference.

[0104] First, we compensate for phase differences <p at the sample surface across repeated A-line measurements

[0105] in0= diag(e'*P) ■ m. (8)

[0106] We refer to this procedure as zero-phase correction, which eliminates random phase noise but also the meaningful phase offsets arising from tissue retardance along the light path, such as the cornea in retinal imaging.

[0107] Second, we recover these retarder-induced, meaningful phase offsets through optimization. We refer to this procedure as retarder-constrained phase optimization. From Eqs. (5) and (8), the sample’s Jones matrix can be recovered as

[0108] s = (G'+■ GT1■ G'+ ■ diag(Oo) ’ m0, (9)

[0109] where <I»0represents an estimate of the phase offsets arising from tissue birefringence along the light path. Any phase estimation vector results in a plausible Jones matrix. The most suitable phase compensation is obtained by minimizing the reconstruction error of the corresponding Jones matrix

[0110] $ = argmin |<22QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956[OHl] This phase estimation can be further simplified as

[0112] $ = argmin||U ■ diag(4>0) - mollz

[0113] = argmin<>

[0114] diag(m0)t■ U+■ U ■ diag(m0). The matrix W is determined jointly by the tomographic measurements and the waveplate orientations, owing to diag(«t»0) ■ m0= diag(m0) ■ <0. Because W is non-coherent, it can be averaged along depth or across multiple A-lines.

[0115] To further constrain the solution, <P0is modeled as a linear retarder at the sample surface, denoted Jsurf (3, 6), where 3 and Q represent the retardance and optic axis orientation, respectively.>

[0117] This restriction ensures that the estimated phase offsets correspond to a physically plausible transformation.

[0118] Empirically, the optimization exhibits two local minima corresponding to similar retardance values, but optic axis orientations separated by 7t. To resolve this ambiguity, we enforce optic axis consistency across neighboring A-lines and B-scans and select the solution by comparing the residual errors at the minima. The chosen axis orientation then determines the corresponding phase offsets used for correction.

[0119] Coherency Filtering

[0120] Coherency filtering aims to retain the spatial coherence properties of the OCT signal while suppressing noise and incoherent artifacts. A stack of RevoPol measurements acquired at different waveplate orientations at each pixel can be described as a complex vector m. The local coherency matrix is computed as the outer product

[0121] H = mm1(14)

[0122] which is a rank-1 Hermitian matrix. To suppress uncorrelated noise, the coherency matrices are spatially filtered, where the matrix Hfiit does not remain rank-1. The filtered coherency matrix is then decomposed by singular value decomposition,

[0123] Hfilt= VSV+. (15)

[0124] Only the dominant coherent mode is retained, and a denoised measurement vector23QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956is reconstructed as

[0125] mfiit= Vs^Vi. (16)

[0126] where vi is the leading singular vector and si is its singular value, which encodes the coherent signal power. This corresponds to the least squares approximation of Hfiit with a rank-1 matrix.

[0127] We define a metric as the normalized ratio of the dominant singular value to the total energy,

[0129] which delineates tissue signal with a high Q from noise-dominated or dynamically changing areas featuring a low Q. Thresholds applied to this metric enable surface segmentation and filter out shadowing from blood vessels (e.g., large retinal vessels).

[0130] Imaging Workflow

[0131] This study involved simulations, imaging of birefringence phantoms, and retinal imaging in healthy human eyes. Simulations were conducted to validate the RevoPol framework, while phantom experiments were used to calibrate the waveplate’s rotation speed and confirm ex vivo robustness. The phantoms were fabricated from polycarbonate embedded in an epoxy matrix, as previously described

[0026] , and an additional, static waveplate was inserted into the imaging path to simulate corneal birefringence. To demonstrate in vivo applicability, retinal imaging was performed in a healthy volunteer. The pilot human study adhered to the tenets of the Declaration of Helsinki and was approved by the Mass General Brigham Institutional Review Board (IRB). Written informed consent was obtained from all participants prior to enrollment. The following section details the procedures used to extract tissue polarization properties with the RevoPol framework.

[0132] Step 1 : Image acquisition. The waveplate rotation speed was set to approximately 7t / 12 radians between each repeated B-scan. For a B-scan pattern comprising 1024 A-lines (20° field-of-view) at an A-line rate of 85 kHz, this corresponded to a rotation speed of approximately 3 revolutions per second. The actual rotation speed was calibrated by imaging a birefringent phantom and analyzing the periodicity of the resulting signal together with the uniformity of the reconstructed optic axis orientation. While the waveplate was rotating, six tomograms were acquired at the same location using the system’s OCTA mode to enable reconstruction of the 24QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956Jones matrices for a cross-sectional image.

[0133] Step 2: Image pre-processing. Image registration was performed to align repeated A-line measurements, reducing motion artifacts and ensuring signal consistency for accurate phase analysis. For axial registration, correlation signals were computed along laterally filtered A-lines using the chirped z-transform to obtain an oversampled correlation plot within a limited range. The correlation peak was identified and refined by fitting a third-order polynomial, weighted by the effective correlation values. The frame with the highest overall correlation was selected as the reference. For lateral registration, tomograms were divided into smaller, 50% overlapping windows, and the same procedure was applied to each subwindow. This yielded an interpolated, continuous lateral shift function. Correlation was performed only between directly adjacent scans, and the resulting shifts were summed to obtain cumulative displacement.Coherency filtering, surface segmentation, and zero-phase correction were subsequently applied to the registered tomograms.

[0134] Step 3: Phase offset estimation. The W matrix from (11) was constructed by averaging signals along depth over several pixels, guided by surface segmentation. A retarder-constrained phase optimization was then applied to estimate candidate optic axis orientations and retardance values. Each A-line yields two possible optic axis orientations; these were separated into two groups along the B-scan or C-scan. The group with the smaller overall residual error was selected, and the corresponding optic axis orientation and retardance were used to determine the phase offset. This step can be skipped if no birefringent material is present along the imaging path.

[0135] Step 4: Polarimetric reconstruction. The estimated phase offsets were applied to the filtered tomograms, followed by reconstruction of the complex-valued Jones matrix representing the polarization response of the sample. The Jones matrix was then decomposed into a unitary rotation matrix, from which the cumulative retardance and optic axis orientation were extracted. The optic axis orientations were compensated for the waveplate rotation, determined by the rotation speed, the inter-B-scan time interval, and the B-scan timestamps.

[0136] Step 5: Surface retardance compensation. Surface retardance, originating from birefringent tissues along the imaging path (e.g., the cornea), was extracted as rotation vectors. The square root of these vectors was converted into Jones matrices and applied symmetrically to25QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956the measured Jones matrices, thereby removing the cumulative retardance contribution along the imaging path.

[0137] Results

[0138] Simulation

[0139] We used numerical simulations to assess the ability of the RevoPol framework to reconstruct polarization properties. The simulated dataset included speckle and phase noise, as well as known birefringent structures consisting of three embedded bars and significant cumulative surface retardance. Sequential tomographic measurements were generated during waveplate rotation, and phase differences were computed relative to the initial acquisition (FIG.14A-14B). With the waveplate increment of K / 12 radians between repeated B-scans, the first-fourth, second-fifth, and third-sixth measurements exhibited matching intensities but showed distinct phase differences. Zero-phase correction effectively removed random phase noise (FIG.14C). Retarder-constrained phase optimization then produced two candidate solutions for optic axis orientation and retardance (FIG. 14D). Comparison with the ground-truth retarder confirmed that the solution with smaller residual errors was the correct one. Using this validated solution, we extracted the phase offsets (FIG. 14E). Applying the recovered phase offsets enables accurate reconstruction of cumulative retardance and optic axis orientation (FIG. 14F-14G). We evaluated the effect of rotation speed estimation on polarimetric reconstruction. We found that an estimated speed of 18° (K / IO) per B-scan was the most robust against errors in reconstructed retardance and optic axis orientation (FIG. 15A-15B). In comparison, at 15° (TI / 12) per B-scan the reconstructed orientation remained largely stable along the slow-axis scan, showing only minor drifts in a C-scan under estimation error when continuous rotation was not compensated (FIG. 15C).

[0140] Phantom Imaging

[0141] We applied the RevoPol framework to a birefringent phantom with a retarder placed in the imaging path to experimentally validate the reconstruction workflow, using a waveplate rotation speed of 7t / 12 (-15°) per B-scan (FIG. 16A-16F). Phase shifts were uniform along each A-line but varied randomly between successive A-lines (FIG. 16B). Using retarder-constrained phase optimization, we obtained optic axis orientation and retardance at the surface, where the apparent optic axis orientation varied with waveplate rotation while the retardance26QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956remained constant (FIG. 16C). Using the correct solution, consistent phase offsets were recovered, which enabled reconstruction of cumulative retardance and optic axis orientation across the phantom (FIG. 16D-16E). Polarization properties were further corrected through surface retardance compensation, ensuring that the reconstructed properties originated from the phantom itself (FIG. 16F). We measured cumulative retardance at the surface using different waveplate rotation speeds (FIG. 16G). Both measurements exhibited consistent patterns, demonstrating that the polarimetric reconstruction was independent of the waveplate speed.

[0142] We used a non-birefringent phantom with a retarder placed in the imaging path (between the lens and the phantom) to calibrate the waveplate rotation increment per B-scan (FIG. 17). For a rough estimation, we analyzed the signal intensity modulated by a fixed retarder along the imaging path (FIG. 17A). After applying coherence filtering, the normalized intensity across repeated B-scans exhibited a periodicity of three B-scans. The intensity varies as>

[0144] where i / i is the half-waveplate fast-axis angle, i.e., the angular period of the waveplate is one-eighth of the observed intensity period. This yielded a waveplate rotation speed of 7i / 12 (-15°) per B-scan. For accurate calibration, the reconstructed surface optic axis orientations in a C-scan are highly sensitive to rotation speed (FIG. 17B), making uniform orientation across the scan a reliable metric for precise waveplate calibration.

[0145] Retinal Imaging

[0146] In retinal imaging, the original tomogram exhibited strong speckle fluctuations (FIG. 18A). After registration and coherency filtering, speckle noise was substantially suppressed while structural boundaries were preserved (FIG. 18B). The Q metric further highlights retinal boundaries and effectively excludes regions shadowed by blood flow (FIG. 18C). The corresponding phase-difference maps (FIG. 18D) show that the original data contain significant phase noise within A-lines. Registration reduces this noise, and coherency filtering further suppresses high-frequency fluctuations while retaining phase-difference features, i.e., the phase variations along each A-line. It is worth noting that these A-line phase fluctuations are more pronounced in retinal data than in phantom experiments, primarily due to eye motion in vivo compared with the stationary phantom. Then, we demonstrated the feasibility of RevoPol reconstruction in healthy human retina (FIG. 19). At the ONH-centered scan, the surface27QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956retardance and optic axis orientation appeared spatially uniform (FIG. 19A), suggesting that corneal birefringence along the light path can be effectively modeled as a well-aligned retarder. After compensating for this surface contribution, the cumulative retardance exhibited a circumpapillary annular pattern consistent with birefringence distributions reported in previous studies using conventional PS-OCT. In the fovea-centered scan (FIG. 19B), we observed reduced retardance near the foveal center and the characteristic radial optic-axis orientation of photoreceptor axons extending outward from the fovea. These birefringence features are in close agreement with established descriptions of Henle’s fiber layer. The clear visualization of retinal birefringence and organization highlights the ability of RevoPol to recover physiologically relevant polarization signatures in vivo with minimal hardware modification to the clinical OCT platform.

[0147] Discussion

[0148] In this study, we presented RevoPol, a new PS-OCT framework that enables full Jones matrix reconstruction using a single-detector OCT system. As a practical implementation, we developed a detachable rotating waveplate module that can be integrated into a commercial OCT platform. Using this setup, we demonstrated reconstruction of retardance and optic axis orientation in both birefringent phantoms and the healthy human retina. These results confirm that RevoPol achieves effective reconstruction of known polarization signatures in vivo through a simple add-on module compatible with existing OCT hardware. Although demonstrated here with spectral-domain OCT, the RevoPol framework should be compatible with swept-source systems, as the optic axis shift of the waveplate within a single A-line is negligible.

[0149] Compared with existing PS-OCT methods, RevoPol offers distinct advantages. A previous study employed a linear polarizer followed by an LCD-based addressable wave plate set to 45°, 90°, and 135°. This configuration required longer imaging times and lacked phase correction, which prevented its use for in vivo imaging. Conventional PS-OCT with a single circular input state is limited to reporting cumulative retardance or assuming a uniform optic axis orientation with depth. This limitation arises from an intrinsic degeneracy in the polarization measurement: whenever the detected polarization state coincides with the mirror state of the input — that is, the same state with flipped helicity reflected across the horizontal QU-plane on the Poincare sphere — the reconstruction becomes indeterminate. For example, with a perfectly28QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956circular input state and an observed circular state of opposite handedness, the measured retardance is n, yet the optic axis orientation cannot be determined. In contrast, RevoPol enables full Jones matrix reconstruction, allowing calculation of both depth-resolved birefringence and optic axis orientation. While multi-input PS-OCT offers robust polarimetric reconstruction, its implementation typically relies on depth-multiplexing or electro-optic polarization modulators in combination with polarization-diverse detection. These requirements substantially increase system complexity and have limited widespread translational and clinical adoption. In contrast, RevoPol employs sequential polarization modulation with a rotating waveplate, combined with a sensing matrix and retarder-constrained phase optimization, to recover tissue polarization properties using standard OCT hardware. This framework preserves the integrity of the underlying OCT system, and its modular design favors clinical translation, particularly in multisite studies where hardware standardization is important. We acknowledge that the RevoPol framework requires additional computational effort, and achieving real-time processing will be important for clinical implementation. Note that the goal of RevoPol is not to replace conventional PS-OCT but to provide an accessible approach for polarimetric imaging in both clinical and research settings.

[0150] The choice of waveplate rotation speed plays an important role in the accuracy and practicality of RevoPol reconstruction. Ideally, any rotation speed would be sufficient for polarimetric reconstruction within the RevoPol framework. In practice, however, the selected speed affects reconstruction stability and quality control. From simulations with six repeated measurements, we found that a TI / 10 rotation step provides the greatest robustness against reconstruction errors when the estimated speed deviates from the actual speed. For retinal imaging, however, we implemented six repeated measurements with a TT / 12 rotation step. Under this configuration, the reconstructed optic axis orientations are expected to remain approximately constant along the slow-axis direction in a C scan, which facilitates estimation of the actual rotation speed, particularly in cases where imaging timestamps are inaccurate or unavailable. In addition, the first-fourth, second-fifth, and third-sixth measurements should exhibit matching intensities because they correspond to orthogonal polarization states. This feature may provide a convenient quality-control metric for active eye-tracking. The current, unsynchronized setup simplifies implementation but introduces two limitations: (i) because only an averaged rotation29QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956speed is estimated, intra-volume speed fluctuations may be missed, potentially introducing residual phase errors; and (ii) the initial optic axis orientation of the rotating waveplate is unknown, complicating cross-dataset comparisons, though retardance estimates remain unaffected.

[0151] Phase correction is important for accurate polarimetric reconstruction in the RevoPol framework. Phase drift in OCT measurements follows an approximate 1 / f behavior. Variations are minimal over short timescales but can accumulate substantially over longer acquisitions. RevoPol acquires repeated B-scans over longer timescales (-10-2 s), making the reconstruction more susceptible to phase drift and motion artifacts. When no birefringent material is present along the light path, zero-phase correction informed by the surface signal can be applied, uniformly resetting the phase across all A-lines. In retinal imaging, however, corneal birefringence introduces cumulative retardance at the sample surface, invalidating this simple approach. In such cases, phase offset estimation is required. Unconstrained phase optimization (Eq. 10) introduces unknown phase terms that grow with the number of repeated measurements, producing multiple local minimum and ambiguity. By modeling the cornea as a pure retarder, the number of unknown parameters is reduced to two. Retarder-constrained phase optimization, therefore, provides a robust strategy for estimating the phase offsets induced by the anterior segment. Moreover, this approach allows spatial filtering of the estimated retarder before conversion into phase offsets, suppressing local noise and discontinuities and thereby improving the stability of the reconstructed optic axis orientation. Since the cornea is considered a highly ordered birefringent tissue and the surface retardance corresponds to a very small region, it is reasonable that we observed a uniform collagen structure with nearly constant retardance.

[0152] Both surface retardance compensation and accurate phase correction rely on reliable surface segmentation. In retinal imaging, however, surface detection is often challenged by speckle noise, low signal contrast at certain boundaries, and local signal dropout caused by vessels or eye motion. Conventional segmentation methods frequently fail to provide smooth and continuous delineation under these conditions, which in turn compromises the stability of the reconstructed polarimetric parameters. These limitations are not unique to RevoPol. To address this, we developed a Q metric (Eq. 17) based on the ratio of the dominant singular value to the total energy of the coherency matrix. This metric, analogous to the degree of polarization,30QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956enhances surface contrast by suppressing speckle fluctuations while preserving structural boundaries, thereby improving the robustness of surface segmentation.

[0153] In summary, we demonstrated that RevoPol enables reliable reconstruction of retardance and optic axis orientation in both phantoms and human retina, requiring only minimal hardware modification to a commercial OCT platform. This framework extends the applicability of PS-OCT beyond retinal imaging and is suitable for both ex vivo and in vivo studies across diverse research and clinical settings. By lowering technical barriers, RevoPol facilitates broader adoption of polarization-sensitive OCT for diverse diagnostic, translational, and research applications.

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[0194] Thus, while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto.35QB\125141.04956\100549193.1

Claims

1. MGH 2025-182-02Quarles 125141.04956CLAIMSWhat is claimed is:

1. A system for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the system comprising:an OCT apparatus comprising a sample arm and a reference arm;a polarization altering element disposed in a round-trip portion of the sample arm of the OCT apparatus,the polarization altering element configured to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample, andthe polarization altering element configured to vary its polarization alteration during imaging; anda processor configured to:acquire a plurality of cross-sectional images of the sample with different polarization alterations based on the variation of the polarization altering element, and generate an image of the sample based on the plurality of cross-sectional images of the sample.

2. The system of claim 1, wherein the polarization altering element varies at least one of an eigen-polarization state, a retardance, or a diattenuation to achieve distinct alterations of the polarization of the illuminating light and the backscattered light.

3. The system of claim 1, wherein the OCT apparatus does not include a polarizer in the sample arm.

4. The system of claim 1, further comprising an actuator coupled to the polarization altering element, wherein the actuator is configured to rotate the polarization altering element during imaging.36QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.049565. The system of claim 4, wherein the polarization altering element comprises a retarder or a waveplate.

6. The system of claim 4, wherein the polarization altering element comprises an achromatic half-wave plate.

7. The system of claim 4, wherein the actuator is further configured to continuously rotate the polarization altering element at a defined rotation speed during imaging.

8. The system of claim 7, wherein the actuator comprises a motor coupled to the polarization altering element via a drive belt.

9. The system of claim 1, wherein the polarization altering element is configured to rotationally advance by a predetermined angular difference between each of the plurality of cross-sectional images acquired by the OCT apparatus.

10. The system of claim 9, wherein the predetermined angular difference is 30 degrees.

11. The system of claim 1, further comprising a detachable module configured to be inserted into the round-trip portion of the sample arm of the OCT apparatus, wherein the detachable module comprises the polarization altering element.

12. The system of claim 11, wherein the detachable module is configured to be inserted between a scan head and an objective lens of the OCT apparatus.

13. The system of claim 11, wherein the detachable module further comprises a controller programmable to select from a plurality of variations of the polarization alteration.37QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.0495614. The system of claim 1, wherein the processor, when acquiring the plurality of cross-sectional images of the sample at different polarization alterations, is further configured to:acquire at least three cross-sectional images of the sample at different polarization alterations, andwherein the processor, when generating the image of the sample, is further configured to:reconstruct a round-trip Jones matrix of the sample based on the at least three cross-sectional images of the sample.

15. The system of claim 14, wherein the processor, when reconstructing the round-trip Jones matrix of the sample, is further configured to:reconstruct the round-trip Jones matrix of the sample by exploiting a transposesymmetry constraint arising from round-trip transmission through the sample based on identical illumination and detection optical paths.

16. The system of claim 15, wherein the processor, when reconstructing the round-trip Jones matrix of the sample, is further configured to determine at least one of retardance, fast axis orientation, diattenuation, or diattenuation axis orientation from the reconstructed round-trip Jones matrix.

17. The system of claim 15, wherein the transpose-symmetry constraint reduces a number of unknown parameters of the Jones matrix, including global phase and scaling, from eight to six.

18. The system of claim 14, wherein the processor, when generating the image of the sample, is further configured to:calculate at least one of depth-resolved birefringence and depth-resolved optic axis orientation of the sample based on reconstructing the round-trip Jones matrix of the sample.

19. The system of claim 1, wherein the processor is further configured to compensate for phase drift between the sample arm and the reference arm of the OCT apparatus by:38QB\125141.049561100549193.1MGH 2025-182-02Quarles 125141.04956acquiring redundant measurements, andadjusting unknown phase offsets to maximize agreement among the redundant measurements.

20. The system of claim 19, wherein the processor is further configured to determine a phase offset from the sample using retarder-constrained phase optimization based on an estimate of phase offsets arising from retardance in the sample at shorter pathlengths than those resolved in the measurements.

21. The system of claim 1, wherein the OCT system comprises a single detector.

22. The system of claim 21, wherein the single detector comprises a spectrometer.

23. An actuator for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the actuator comprising:a polarization altering element configured to be disposed in a round-trip portion of a sample arm of an OCT apparatus,the polarization altering element configured to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample, andthe polarization altering element configured to vary its polarization alteration during imaging.

24. The actuator of claim 23, wherein the actuator comprises a motor coupled to the polarization altering element via a drive belt.

25. The actuator of claim 24, wherein the actuator is further configured to continuously rotate the polarization altering element at a defined rotation speed during imaging.39QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.0495626. The actuator of claim 24, wherein the polarization altering element comprises a retarder or a waveplate.

27. The actuator of claim 24, wherein the polarization altering element comprises an achromatic half-wave plate.

28. The actuator of claim 23, wherein the polarization altering element varies at least one of an eigen-polarization state, a retardance, or a diattenuation to achieve distinct alterations of the polarization of the illuminating light and the backscattered light.

29. The actuator of claim 23, wherein the polarization altering element is configured to rotationally advance by a predetermined angular difference between each of a plurality of cross-sectional images acquired by the OCT apparatus.

30. The actuator of claim 29, wherein the predetermined angular difference is 30 degrees.

31. The actuator of claim 23, wherein the actuator is housed within a detachable module, wherein the detachable module is configured to be inserted into the round-trip portion of the sample arm of the OCT apparatus.

32. The actuator of claim 31, wherein the detachable module is configured to be inserted between a scan head and an objective lens of the OCT apparatus.

33. The actuator of claim 23, further comprising a controller programmable to select from a plurality of variations of the polarization alteration.

34. A method for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the method comprising:disposing a polarization altering element in a round-trip portion of a sample arm of the OCT apparatus;40QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956varying the polarization altering element during imaging to alter the polarization state of illuminating light directed toward a sample and of backscattered light returning from the sample;acquiring a plurality of cross-sectional images of the sample at different polarization alterations based on variation of the polarization altering element; andgenerating an image of the sample based on the plurality of cross-sectional images of the sample.

35. The method of claim 34, wherein the polarization altering element varies at least one of an eigen-polarization state, a retardance, or a diattenuation to achieve distinct alterations of the polarization of the illuminating light and the backscattered light.

36. The method of claim 34, wherein the sample arm of the OCT apparatus does not include a polarizer.

37. The method of claim 34, wherein varying the polarization altering element comprises actuating an actuator coupled to the polarization altering element.

38. The method of claim 34, wherein the polarization altering element comprises a retarder or a waveplate.

39. The method of claim 34, wherein the polarization altering element comprises an achromatic half-wave plate.

40. The method of claim 37, wherein actuating the actuator comprises continuously rotating the polarization altering element at a defined rotation speed during imaging.

41. The method of claim 40, wherein the actuator comprises a motor coupled to the polarization altering element via a drive belt.41QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.0495642. The method of claim 34, wherein rotating the polarization altering element comprises rotationally advancing the polarization altering element by a predetermined angular difference between each of the plurality of cross-sectional images acquired by the OCT apparatus.

43. The method of claim 42, wherein the predetermined angular difference is 30 degrees.

44. The method of claim 34, further comprising inserting a detachable module into the roundtrip portion of the sample arm of the OCT apparatus, wherein the detachable module comprises the polarization altering element.

45. The method of claim 44, wherein inserting the detachable module comprises inserting the detachable module between a scan head and an objective lens of the OCT apparatus.

46. The method of claim 44, further comprising programming a controller of the detachable module to select from a plurality of variations of the polarization alteration.

47. The method of claim 34, wherein acquiring the plurality of cross-sectional images comprises:acquiring at least three cross-sectional images of the sample at different polarization alterations, andwherein generating the image of the sample comprises:reconstructing a round-trip Jones matrix of the sample based on the at least three cross-sectional images of the sample.

48. The method of claim 47, wherein reconstructing the round-trip Jones matrix of the sample comprises:exploiting a transpose-symmetry constraint arising from round-trip transmission through the sample based on identical illumination and detection optical paths.42QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.0495649. The method of claim 48, further comprising determining at least one of retardance, fast axis orientation, diattenuation, or diattenuation axis orientation from the reconstructed round-trip Jones matrix.

50. The method of claim 48, wherein the transpose-symmetry constraint reduces a number of unknown parameters of the Jones matrix, including global phase and scaling, from eight to six.

51. The method of claim 47, wherein generating the image of the sample comprises:calculating at least one of depth-resolved birefringence and depth-resolved optic axis orientation of the sample based on reconstructing the round-trip Jones matrix of the sample.

52. The method of claim 34, further comprising compensating for phase drift between the sample arm and a reference arm of the OCT apparatus by:acquiring redundant measurements; andadjusting unknown phase offsets to maximize agreement among the redundant measurements.

53. The method of claim 52, further comprising determining a phase offset from the sample using retarder-constrained phase optimization based on an estimate of phase offsets arising from retardance in the sample at shorter pathlengths than those resolved in the measurements.

54. The method of claim 34, wherein the OCT apparatus comprises a single detector.

55. The method of claim 54, wherein the single detector comprises a spectrometer.

56. A method for acquiring polarimetric sample measurements using an optical coherence tomography (OCT) apparatus, the method comprising:disposing a polarization altering element in a round-trip portion of a sample arm of the OCT apparatus;43QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.04956varying the polarization altering element during imaging to alter the polarization state of illuminating light directed toward an OCT sample and of backscattered light returning from the OCT sample; andacquiring a plurality of cross-sectional images of the OCT sample at different polarization alterations of the polarization altering element.

57. The method of claim 56, wherein varying the polarization altering element comprises actuating a motor coupled to rotate the polarization altering element via a drive belt.

58. The method of claim 57, wherein actuating the motor comprises continuously rotating the polarization altering element at a defined rotation speed during imaging.

59. The method of claim 57, wherein the polarization altering element comprises a retarder or a waveplate.

60. The method of claim 57, wherein the polarization altering element comprises an achromatic half-wave plate.

61. The method of claim 56, wherein rotating the polarization altering element varies at least one of an eigen-polarization state, a retardance, or a diattenuation to achieve distinct alterations of polarization of the illuminating light and the backscattered light.

62. The method of claim 56, wherein rotating the polarization altering element comprises rotationally advancing the polarization altering element by a predetermined angular difference between each of the plurality of cross-sectional images acquired by the OCT apparatus.

63. The method of claim 62, wherein the predetermined angular difference is 30 degrees.44QB\125141.04956\100549193.1MGH 2025-182-02Quarles 125141.0495664. The method of claim 56, further comprising housing the polarization altering element within a detachable module, wherein the detachable module is configured to be inserted into the round-trip portion of the sample arm of the OCT apparatus.

65. The method of claim 64, wherein inserting the detachable module comprises inserting the detachable module between a scan head and an objective lens of the OCT apparatus.

66. The method of claim 56, further comprising programming a controller to select from a plurality of variations of the polarization alteration.45QB\125141.04956\100549193.1

Images