Compact line-field oct system with intolerance to spurious reflections

Abstract

A compact line- or full-field optical coherence tomography (OCT) system designed for high-resolution retinal imaging with reduced artifacts employs quarter wave plates in both the sample and reference arms to manipulate the polarization state of light, effectively suppressing spurious reflections and coherence repeat artifacts. A symmetrical arrangement of, for example, Plössl eyepiece and camera objective lenses minimizes optical aberrations and maintains a flat imaging field despite the retina's curvature. The scanning galvanometer mirror is positioned at the conjugate plane of the patient's eye pupil and sized to act as an aperture stop. An adjustable eyepiece compensates for individual refractive errors, enhancing image clarity across a wide range of patients.

Description

[0001] Docket: 0407-0023W01

[0002] COMPACT LINE-FIELD OCT SYSTEM WITH INTOLERANCE TO SPURIOUS REFLECTIONS

[0003] RELATED APPLICATIONS

[0004] [ o o o i ] This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63 / 723,211, filed on November 21, 2024, which is incorporated herein by reference in its entirety.

[0005] BACKGROUND OF THE INVENTION

[0006]

[0002] Designing an optical system for imaging the retina presents challenges due to the eye's anatomical and optical characteristics. One primary difficulty is accommodating the curved retinal surface while maintaining sufficient depth of field. Traditional optical systems are typically optimized for flat imaging planes, but the retina's curvature means that different regions are at varying distances from the imaging optics. This necessitates optical designs that can either match the curvature, such as employing curved detectors or specialized lens systems, or extend the depth of field without compromising resolution, which can be achieved through techniques like wavefront coding or focus stacking. Any optical designs further need to account for the fluid-filled nature of the eye.

[0007]

[0003] Light scattering and reflectivity variations of the eye and the optical elements of the optical system itself also pose significant obstacles to collecting the often-weaker scattered light signal from the retina. The cornea, lens, and vitreous humor can scatter light, reducing image contrast and introducing aberrations. Moreover, the retina consists of multiple layers with different optical properties, leading to non-uniform reflectivity. Antireflection coating on optics of the optical system can be imperfect or non-existent. These factors can degrade image quality and obscure fine retinal details essential for diagnostic purposes. To mitigate these issues, the optical system must include features that minimize scattering and carefully control the illumination pathways.

[0008]

[0004] Achieving high resolution and contrast is critical for effective retinal imaging, as clinicians need to visualize small and subtle features within the retinal tissue. High resolution requires optical systems with large numerical apertures and minimal aberrations, which can conflict with the need for a wide field of view and sufficient depth of field. Advanced optical designs may employ techniques such as diffraction-limited optics, adaptive wavefront correction, and high-sensitivity detectors to enhance image quality. Docket: 0407-0023W01

[0009] Balancing these requirements demands meticulous optical engineering to optimize the system's performance without introducing prohibitive complexity or cost.

[0010]

[0005] These challenges are particularly significant in retinal optical coherence tomography (OCT), an imaging technique that provides high-resolution cross-sectional views of the retina. The curved retinal surface presents a fundamental challenge in OCT because depth must be carefully managed by control of the length of the OCT system interferometer’s reference arm, which is confounded by this curvature.

[0011]

[0006] Individual variability in eye anatomy and refractive errors significantly impact the quality of OCT images. Variations in axial length, corneal curvature, and lens thickness alter the optical path lengths within the eye, affecting the coherence between the sample and reference beams in OCT systems. Refractive errors like myopia or hyperopia can lead to defocus and reduced resolution if not properly compensated. OCT devices often include adjustable optics or allow for the input of individual refractive measurements to correct for these differences. Some advanced systems incorporate adaptive optics to dynamically adjust for higher-order aberrations, enhancing image clarity and resolution across a wide range of patients.

[0012]

[0007] Coherence repeats are still further sources of artifacts that can impair OCT image quality and accuracy. Coherence repeats are artifacts specific to swept-source or Fourier-domain OCT systems, where the system periodically replicates structures of the optical system at defined intervals along the depth axis where the differential path length between sample and reference arm match the optical cavity length of the laser. This phenomenon occurs due to the periodicity of the source’s coherence length, resulting in multiple, ghost-like repetitions of structures at predictable depths. Careful control of the OCT system’s sweep parameters and source design is required to minimize the effects of coherence repeats.

[0013]

[0008] Achieving high resolution and contrast while minimizing artifacts is critical in OCT to detect subtle pathological changes in the retinal microstructure. However, the need for high resolution must be balanced against factors like imaging depth and signal -to-noise ratio. In OCT, axial resolution is determined by the bandwidth of the light source; broader bandwidths provide finer resolution but can also increase susceptibility to dispersion and reduce coherence length. Engineers might address this by selecting superluminescent diode Docket: 0407-0023W01 or supercontinuum sources, for example, and / or by implementing dispersion compensation techniques within the system.

[0014] SUMMARY OF THE INVENTION

[0015]

[0009] Several inventions are presented related to a compact line or full field optical coherence tomography (OCT) system designed for imaging the retina and potentially other objects of interest with enhanced image quality and reduced artifacts. The key inventions and innovations are as follows:

[0016]

[0010] The system can incorporate quarter wave plates in both the sample arm and the reference arm to manipulate the polarization state of the light. By converting linearly polarized light into circularly polarized light before it enters the eye or reflects off the reference mirror, and then back into linearly polarized light with a rotated polarization upon return, the system effectively distinguishes the desired signal from unwanted reflections. This rotation by 90 degrees suppresses spurious reflections from optical components that have not passed through the quarter wave plates twice, enhancing the signal-to-noise ratio and improving image quality. This design mitigates coherence repeat artifacts and reduces the impact of reflections from imperfect anti-reflection coatings. A polarizer at this 90 degrees angle at the camera can further suppress the DC background signal from parasitic reflections and thus increase the dynamic range of the system.

[0017]

[0011] The system can also employ a Plbssl eyepiece and a Plbssl camera objective, both constructed from pairs of identical achromatic doublet lenses arranged symmetrically. This configuration minimizes optical aberrations such as spherical aberration, coma, and astigmatism by counteracting distortions introduced in one part of the system with the other. The symmetrical design ensures a wide apparent field of view and sharp, high- contrast images across the entire field, enhancing image formation on the line field sensor and maintaining a flat field at the imaging sensor despite the curved retinal surface.

[0018]

[0012] The scanning galvanometer mirror is preferably placed at the conjugate plane of the patient's eye pupil and is designed with a limited size, functioning as an aperture stop. By restricting the range of angles over which light can enter and exit the eye, the system controls the numerical aperture and limits off-axis rays that contribute to optical aberrations. This selective acceptance of primarily paraxial rays reduces aberrations like spherical aberration, coma, and astigmatism, improving image resolution and contrast. The Docket: 0407-0023W01 mirror's positioning also ensures consistent illumination during scanning, reducing vignetting and enhancing image uniformity.

[0019]

[0013] Also possibly are alternative lens groups to replace the Plbssl lens pairs to better accommodate the curved field of view at the retina while maintaining a flat field at the imaging sensor. These alternatives include: Monocentric Lenses, Aspheric Lenses with Field-Flattening Elements, Petzval Lens Systems, Schmidt Optical Systems and Freeform Optics.

[0020]

[0014] These alternative designs aim to optimize the optical performance by effectively managing the curvature mismatch between the retina and the imaging sensor.

[0021]

[0015] The system can also include an eyepiece linear actuator that adjusts the position of the Plbssl eyepiece along the optical axis. This adjustment compensates for refractive errors in the patient's eye, such as myopia or hyperopia, ensuring that the retinal image remains in sharp focus despite individual anatomical differences.

[0022]

[0016] The system can utilize a cat's eye laser as the swept-source, tuned with an intracavity thin-film interference filter. This laser configuration produces highly linearly polarized light and offers advantages such as higher power output, lower cost, and reduced manufacturing tolerances compared to other swept-source architectures. The linear polarization is essential for the polarization manipulation techniques employed to suppress spurious reflections.

[0023]

[0017] By positioning a dichroic mirror appropriately within the optical path, the system allows for the placement of a tracking camera and a fixation target (such as a video display) without requiring extra lenses. The fixation target is located at an image plane formed by the Plbssl eyepiece, enabling the patient to view it naturally while focusing at infinity. This design simplifies the system and enhances patient comfort during imaging.

[0024]

[0018] Examples define the effective size of the scanning galvanometer mirror to achieve an optimal pupil size (e.g., 2.5 mm), which balances the need for high resolution with the minimization of optical aberrations. This optimization allows the system to approach the eye's diffraction limit without introducing significant blurring from the eye's inherent aberrations.

[0025]

[0019] In certain embodiments, a line-field or full-field swept-source OCT system for imaging a retina of a patient’s eye or other object of interest includes a swept source Docket: 0407-0023W01 configured to generate linearly polarized light over a range of wavelengths, a beam splitter configured to divide light from the swept source between a sample arm and a reference arm, and a detection arm configured to receive light returning from the sample and reference arms and to detect interference between light returning from the object of interest and light returning from a reference mirror. The sample arm comprises optics configured to direct the light toward the object of interest and a sample arm quarter- wave plate positioned in an optical path between the beam splitter and the object of interest. The reference arm comprises the reference mirror and a reference arm quarter-wave plate positioned in an optical path between the beam splitter and the reference mirror.

[0026]

[0020] In some implementations, each of the sample arm quarter-wave plate and the reference arm quarter-wave plate has a fast axis oriented at about 45 degrees to a polarization axis of the linearly polarized light from the swept source so that light undergoing a double pass through the respective quarter-wave plate is converted back to linearly polarized light with a polarization direction rotated by about 90 degrees relative to the incident light. In such embodiments, light that has undergone a double pass through the sample arm quarter- wave plate and reflection from the object of interest and light that has undergone a double pass through the reference arm quarter-wave plate and reflection from the reference mirror are both linearly polarized along a common rotated polarization direction, while spurious reflections originating at optical surfaces that do not include a double pass through one of the quarter-wave plates retain the original polarization direction and are thereby substantially prevented from producing interference at the sensor. The system may further include a polarizer or a polarizing beam splitter in the detection arm oriented to substantially transmit light having the rotated polarization direction and to attenuate light having the original polarization direction.

[0027]

[0021] In these polarization-managed systems, the swept source may have a cavity length that would produce coherence repeat or coherence revival artifacts for reflections separated in optical path by integer multiples of the cavity length in the absence of polarization manipulation. By arranging the sample arm quarter-wave plate and the reference arm quarter-wave plate as described above, reflections associated with such coherence repeats do not produce significant interference signals at the sensor, thereby reducing coherence repeat artifacts and providing intolerance to spurious reflections. In ophthalmic embodiments, the optics of the sample arm can comprise an eyepiece Docket: 0407-0023W01 configured to couple light into the patient’s eye, with the sample arm quarter-wave plate positioned between the eyepiece and a cornea of the patient’s eye. The optics of the reference arm can comprise a convex cylindrical lens positioned between the beam splitter and the reference mirror, with the reference arm quarter-wave plate positioned between the convex cylindrical lens and the reference mirror.

[0028]

[0022] In another aspect, an OCT imaging system is configured for imaging a curved retinal surface onto a flat imaging sensor. A swept source generates light over a range of wavelengths and an interferometer divides the light between a sample arm and a reference arm and recombines light returning from the sample arm and the reference arm. The sample arm comprises an eyepiece lens group disposed to receive light from the interferometer (for example from a beam splitter) and to couple the light through a cornea of a patient’s eye to form an image on a curved retinal surface. A detection arm comprises an imaging objective lens group disposed to receive light returning from the retinal surface via the interferometer and a flat line-field or area sensor located at an image plane of the imaging objective lens group. The eyepiece lens group and the imaging objective lens group together define a field-flattening optical subsystem configured to map the curved retinal surface onto the flat imaging sensor with reduced field curvature.

[0029]

[0023] In some embodiments of this aspect, at least one of the eyepiece lens group and the imaging objective lens group comprises an optical design selected from the group consisting of (i) a Plbssl lens group comprising two identical achromatic doublet lenses arranged symmetrically about a central plane; (ii) a monocentric lens group having substantially concentric spherical surfaces; (iii) an aspheric lens group including one or more aspheric elements in combination with field-flattening optical elements; (iv) a Petzval lens group configured to correct field curvature at the imaging sensor; (v) a Schmidt-type optical system including a spherical primary mirror and a Schmidt corrector configured to produce a substantially flat image at the imaging sensor; and (vi) a freeform optical element having a non-rotationally symmetric surface profile configured to correct field curvature between the retinal surface and the imaging sensor. In certain embodiments, the system further comprises a sample arm quarter-wave plate positioned in an optical path between the eyepiece lens group and the patient’s eye and a reference arm quarter-wave plate positioned in an optical path between the interferometer and a reference mirror, such that light that undergoes a double pass through each of the sample arm quarter-wave plate Docket: 0407-0023W01 and the reference arm quarter-wave plate is converted back to linearly polarized light and spurious reflections that do not include a double pass through one of the quarter-wave plates are suppressed from producing interference at the imaging sensor.

[0030]

[0024] In still another aspect, an OCT imaging system for retinal imaging comprises a swept source configured to generate light over a range of wavelengths and an interferometer configured to divide light from the swept source between a sample arm and a reference arm and to recombine light returning from the sample arm and the reference arm. The sample arm includes a scanning galvanometer mirror disposed to receive light and to direct the light toward a patient’s eye, one or more sample arm lenses configured to image the scanning galvanometer mirror onto a pupil of the patient’s eye such that the scanning galvanometer mirror is located at a plane conjugate to the pupil, and an eyepiece configured to couple the light through a cornea of the patient’s eye and to scan the light laterally across a retina in response to angular deflection of the scanning galvanometer mirror. A detection arm comprises an imaging lens group and a line-field or area sensor configured to receive and detect light returning from the retina. In such embodiments, the scanning galvanometer mirror has an effective aperture dimension selected such that the scanning galvanometer mirror functions as an aperture stop of the system, limiting a range of angles over which light entering and exiting the eye contributes to image formation at the sensor.

[0031]

[0025] The effective aperture dimension of the scanning galvanometer mirror can correspond to an effective pupil size at the patient’s eye of less than about 5 millimeters, for example less than about 3 millimeters, such as about 2.5 millimeters, thereby limiting the numerical aperture of the system. The effective aperture dimension may be defined by a physical size of a reflective surface of the mirror and / or by an aperture element disposed on or proximate to the mirror configured to block light outside the effective aperture dimension. Locating the scanning galvanometer mirror at the plane conjugate to the pupil of the patient’s eye and selecting the effective aperture dimension such that the mirror functions as an aperture stop causes primarily paraxial rays relative to an optical axis of the system to contribute to image formation at the sensor, thereby reducing aberrations such as spherical aberration, coma, astigmatism, and incorrect field curvature, as well as reducing vignetting and promoting uniform illumination across a scanned retinal field. Docket: 0407-0023W01

[0032]

[0026] In yet another aspect, a line-field or full-field swept-source OCT method includes generating linearly polarized light over a range of wavelengths using a swept source, dividing the light between a sample arm and a reference arm using an interferometer, directing the light in the sample arm toward an object of interest through a sample arm quarter- wave plate positioned in an optical path to the object of interest, providing a reference mirror in the reference arm with a reference arm quarter-wave plate positioned in an optical path to the reference mirror, and receiving light returning from the sample arm and the reference arm and detecting interference between light returning from the object of interest and light returning from the reference mirror. In some embodiments, the method further includes directing the light in the sample arm to a scanning galvanometer mirror having an effective aperture dimension, imaging the scanning galvanometer mirror onto a pupil of a patient’s eye so that the scanning galvanometer mirror is located at a plane conjugate to the pupil, coupling the light through a cornea of the patient’s eye with an eyepiece so that angular deflection of the scanning galvanometer mirror scans the light laterally across a retina, and selecting the effective aperture dimension of the scanning galvanometer mirror such that the mirror functions as an aperture stop of the system, limiting a range of angles over which light entering and exiting the eye contributes to image formation at the sensor. This control of the numerical aperture allows primarily paraxial rays to contribute to image formation, reducing optical aberrations and improving image resolution and uniformity across the retinal field.

[0033]

[0027] The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS

[0035]

[0028] In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: Docket: 0407-0023W01

[0036]

[0029] Fig. 1 shows the optical train of a line-field swept source OCT according to the invention.

[0037] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0038]

[0031] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Also, all conjunctions used are to be understood in the most inclusive sense possible. Thus, the word "or" should be understood as having the definition of a logical "or" rather than that of a logical "exclusive or" unless the context clearly necessitates otherwise. Further, the singular forms and the articles "a", "an" and "the" are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and / or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and / or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present.

[0039]

[0032] It will be understood that although terms such as “first” and “second” are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, an element discussed below could be termed a second element, and similarly, a second element may be termed a first element without departing from the teachings of the present invention.

[0040]

[0033] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the Docket: 0407-0023W01 art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0041]

[0034] Fig. 1 shows a line-field or full-field swept source OCT system 200 that has been constructed according to the principles of the present invention. The system 200 generally includes a sample arm 202, a reference arm 204, an illumination arm 206, and a detection or camera arm 208.

[0042]

[0035] A swept source 100 generates the light for interrogating the obj ect of interest, which in the illustrated example is an eye 10 of a patient, such as a human eye. Currently, the swept source is a cat’s eye laser that is tuned with an intra cavity thin film interference filter. The preferred configuration is described U.S. Pat. Pub. No. 2023 / 0299565 Al or International Pub. No. WO 2023 / 178126 Al, which are incorporated herein by this reference in their entirety. This laser uses an edge emitting gain chip and as a consequence produces highly, linearly polarized light.

[0043]

[0036] Nevertheless, other swept source architectures include tunable superluminescent light emitting diode (SLED) sources and other tunable laser sources, including other interference tuned lasers and grating tuned lasers. That said, the cat’s eye laser has some advantages including relatively higher power, relatively lower cost, and reduced manufacturing tolerances.

[0044]

[0037] The current swept source generates light in the wavelength range of about 800 to 900 nanometers. Preferably its center wavelength is around 840 nanometers, which is useful for applications such as ophthalmic imaging and other diagnostic uses because of the water window (650 to 950 nm) at these wavelengths. Another advantage of this wavelength range is that it can be detected with standard cameras with silicon-based imager chips. Specifically, the output is detected with silicon, e.g., complementary metal- oxide-semiconductor (CMOS) or charge-coupled device (CCD), imagers.

[0045]

[0038] Other material systems can be selected for the gain chip of the swept source

[0046] 100, however, enabling operation in different spectral bands. Common material systems are based on III-V semiconductor materials, including binary materials, such as GaN, GaAs, InP, GaSb, InAs, as well as ternary, quaternary, and pentenary alloys, such as InGaN, InAlGaN, InGaP, AlGaAs, InGaAs, GalnNAs, GalnNAsSb, AlInGaAs, InGaAsP, Docket: 0407-0023W01

[0047] AlGaAsSb, AlGalnAsSb, AlAsSb, InGaSb, InAsSb, and InGaAsSb. Collectively, these material systems support operating wavelengths from about 400 nanometers (nm) to 2500 nm, including longer wavelength ranges extending into multiple micrometer wavelengths. Semiconductor quantum well, quantum cascade and quantum dot gain regions are typically used to obtain especially wide gain and spectral emission bandwidths, and support operation up to 250 pm in wavelength. Quantum well layers may be purposely strained or unstrained depending on the exact materials and the desired wavelength coverage.

[0048]

[0039] When longer wavelengths lasers are used, the InGaAs imager chips would often be used.

[0049]

[0040] Wavelength tuning speed of the swept source is usually given in nm / sec, so for a 100Hz tuning speed for retinal imaging applications where a line-speed sensor is operating at an approximately 100kHz framerate giving 1000 sampled bandwidth points and 70nm tuning range, this would give 70nm / 10msec=7000nm / sec. In general, the tuning speed is often between 3,000nm / sec and 1 l,000nm / sec or higher.

[0050]

[0041] A first illumination arm achromatic doublet lens 210 in the illumination arm 206 generally collimates the linearly polarized light from the swept source 100. Then, a concave cylindrical lens 214 causes the beam to diverge in the plane of the drawing to form a line extending in the direction of the Z-axis when configured for a line-field system. An optional illumination arm fold mirror 218 changes the direction of the beam. This fold mirror is not necessary but provides a more compact system.

[0051]

[0042] The achromatic doublet lenses in this optical design are typically constructed by pairing two lens elements made from glasses or a plastic such as acrylic with different dispersion characteristics: a positive (convex) lens typically made of crown glass and a negative (concave) lens made of flint glass. Crown glass has a lower refractive index and dispersion, while flint glass has a higher refractive index and dispersion. When these two elements are cemented together, their opposite dispersion properties effectively cancel out chromatic aberration for two specific wavelengths — usually in the lower wavelength and higher wavelength regions of the wavelengths of operation of the swept source 100. This construction results in a lens that brings multiple wavelengths into the same focal point, minimizing color fringing and improving image sharpness across a range of wavelengths generated by the swept source 100. Docket: 0407-0023W01

[0052]

[0043] A second illumination arm achromatic doublet lens 222 receives the expanding beam from the concave cylindrical lens 214. This second illumination arm achromatic doublet lens 222 focuses the beam into a cube beam splitter 230. The beam splitter 230 divides the light from the swept source 100 between a sample arm 202 and a reference arm 204.

[0053]

[0044] In the sample arm 202, the light is reflected by a scanning mirror galvanometer mirror 240. This device includes a mirrored substrate on the rotor of a galvanometer such that the galvanometer rotates or tilts the mirror at different angles around the galvanometer rotor axis. This rotor axis in the illustrated design extends parallel to the z-axis.

[0054]

[0045] The light from the scanning mirror galvanometer 240 is received by a sample arm achromatic doublet lens 244. The light is subsequently reflected by a dichroic mirror 248 to pass through a pair of achromatic doublet lenses configured as a Plbssl eyepiece 252. Typically, light from the eyepiece 252 is diverging into the eye to couple the light through the patient's eye cornea to form a line on the back of the eye on the retina 12 and then collimated returning from the eye.

[0055]

[0046] Each Plbssl lens pair 252, 294 is constructed by combining two identical achromatic doublets arranged symmetrically around the eyepiece's central plane. Each achromatic doublet consists of two lens elements made from different types of optical glass. E.g., a positive (convex) lens made of crown glass and a negative (concave) lens made of flint glass. These elements are cemented together to correct for chromatic aberration by bringing different wavelengths of light across the wavelength range of the swept source 100 into the same focus. The symmetrical back-to-back arrangement of the doublets in the Plbssl design helps minimize optical aberrations such as spherical aberration, coma, and astigmatism. This configuration results in a wide apparent field of view and provides sharp, high-contrast images across the entire field, making Plbssl lens pairs efficient and cost-effective components.

[0056]

[0047] Other lens groups could replace of the Plbssl lens pairs used in the present design to achieve similar or improved optical performance. Generally, the design requires a curved field of view at the retina 12 and a flat field at imaging sensor 300.

[0057]

[0048] The following are potential alternatives include monocentric lenses, which consist of concentric spherical surfaces sharing a common center of curvature. They are well-suited for imaging curved objects like the retina because they naturally accommodate Docket: 0407-0023W01 spherical surfaces. By matching the curvature of the lens system to that of the retina, a monocentric lens can minimize field curvature and aberrations when capturing the retinal image. To project this curved image onto a flat imaging sensor, additional relay optics or field-flattening elements are incorporated to correct the curvature before the light reaches the sensor.

[0058]

[0049] Aspheric lenses are another alternative. They have surfaces designed to correct specific aberrations, including field curvature. By incorporating aspheric elements into the optical system, it is possible to correct for the retina's curvature. Coupling these lenses with field-flattening optics transforms the curved image formed by the retina into a flat image at the sensor plane. This combination allows for high-resolution imaging while effectively managing the curvature mismatch between the retina and the sensor.

[0059]

[0050] The Petzval lens design is known for its ability to correct field curvature, resulting in a flat image plane. A Petzval system typically uses a combination of positive and negative lens elements strategically placed to counteract the natural curvature of the image field. Implementing a Petzval lens group in the OCT system can help in mapping the curved retinal field onto a flat imaging sensor without significant loss of image quality.

[0060]

[0051] The Schmidt camera design includes a spherical primary mirror and a Schmidt corrector plate that compensates for spherical aberration and field curvature. Adapting a Schmidt system for retinal imaging involves using a spherical mirror to collect light from the curved retina and a specially designed corrector element to produce a flat image at the sensor. While more complex, this approach can handle large fields of view and correct for the retina's curvature.

[0061]

[0052] Freeform optical elements have surfaces without rotational symmetry, allowing for highly customized shapes that correct complex aberrations, including field curvature. Designing a custom freeform lens or mirror specifically tailored to the curvature of the retina enables precise correction of the image field. This method can directly map the curved retinal image onto a flat sensor, improving image quality.

[0062]

[0053] Using a relay lens system that includes field-flattening elements are another alternative that can effectively re-image the curved retinal field onto a flat sensor. The relay lenses capture the curved image from the retina and, through careful optical design, transform it into a flat field suitable for the imaging sensor. This approach can be Docket: 0407-0023W01 customized to correct specific amounts of field curvature and can be integrated into the existing optical pathway with minimal disruption.

[0063]

[0054] Telecentric lenses maintain constant magnification and chief ray angles across the field of view, which can help in minimizing perspective errors. By adapting a telecentric system with additional optical elements designed to correct field curvature, it is possible to image the curved retina onto a flat sensor. This combination ensures uniform imaging conditions across the field while addressing the curvature mismatch.

[0064]

[0055] In the illustrated example, a tracking camera and fixation target 250 are located behind the dichroic mirror 248 to enable the operators to view patient’s eye 10 via the tracking camera and also to provide a fixation target via a video display for the patient to fixate on during the imaging of the eye. Preferably, the video display is at an image plane, i.e., the same optical distance as image plane 205, formed by the Plbssl eyepiece 252. As a result, no extra lenses are required to allow the patient to view the video display when the patient naturally focuses at infinity.

[0065]

[0056] The position of the Plbssl eyepiece 252 along the direction of the X-axis is controlled by an eyepiece linear actuator 256 to control the focus and thereby compensate for refractive error in the patient’s eye 10.

[0066]

[0057] In the preferred embodiment, an ocular quarter wave plate 260 is located between the eyepiece 252 and the patient’s eye 10.

[0067]

[0058] In turn, the light scattered by the patient’s eye or other objective interest 10 is collected by the eyepiece 252 through the ocular wave plate 260 and returns back through the sample arm achromatic doublet lens 244 and descanned by the scanning galvanometer mirror 240 to the cube beam splitter 230.

[0068]

[0059] At the same time, the light that is transmitted through the cube beam splitter 230 passes to the reference arm 204. It is reflected by a reference arm fold mirror 270 to a reference arm achromatic doublet lens 274. The light is then collimated by a convex cylindrical lens 278 and is then reflected by a reference arm mirror 286. Preferably, a reference arm quarter wave plate 282 is located between the convex cylindrical lens 278 and the reference arm mirror 286. Docket: 0407-0023W01

[0069]

[0060] The position of the reference mirror along the direction of the X-axis is controlled by a reference arm mirror linear actuator 290 to control the delay in the reference arm to path match to the desired depth of the patient’s retina 12.

[0070]

[0061] Light reflected by the reference arm mirror 286 and the object of interest 10 is mixed in the cube beam splitter 230 and is transmitted to the sensor 300 through a Plbssl camera objective 294.

[0071]

[0062] When a line-scan sensor is used, it typically has a linear array of at least 512 pixels, and often at least 1024 or 2048 pixels or even more to detect interference signals for a line. This sensor can be one or two or several pixels wide. Pixels can also be binned along the short axis of the sensor to create larger effective pixel sizes in this direction.

[0072]

[0063] Nevertheless, on other embodiments, a full field, 2-dimensional sensor 300 is used. These typically have a two dimension array of at least 512x512 pixels, and often at least 1024 or 2048 pixels in both dimensions or even more to detect interference signals.

[0073]

[0064] The sample quarter wave plate 260 and the reference arm quarter wave plate 282 are preferably incorporated in both the sample arm 202 and the reference arm 204 to manipulate the polarization state of the light, thereby enhancing the quality of the interference signals detected by the line or full field sensor 300 by suppressing spurious reflections.

[0074]

[0065] In the sample arm 202, the light originating from the swept source is initially linearly polarized. Before the light enters the object of interest or patient's eye 10, it passes through the sample arm quarter wave plate 260 positioned between the Plbssl eyepiece 252 and the eye 10. This quarter wave plate is oriented at 45 degrees with respect to the polarization axis of the incident light.

[0075]

[0066] As the linearly polarized light passes through the sample arm quarter wave plate 260, it is converted into circularly polarized light due to the quarter wave plate introducing a phase shift of 90 degrees (K / 2 radians) between the orthogonal components of the electric field vector. When this circularly polarized light reflects off the retinal structures, it undergoes a reversal in the sense of rotation of its electric field vector (from right-handed to left-handed circular polarization, or vice versa). Upon returning through the same sample arm quarter wave plate 260, the circularly polarized light is converted back into linearly polarized light. However, because of the round-trip passage through the sample Docket: 0407-0023W01 arm quarter wave plate 260 and the reflection from the retina 12, the polarization direction of the returning light is rotated by 90 degrees relative to the original incident polarization.

[0076]

[0067] A similar process occurs in the reference arm 204. The linearly polarized light transmitted through the beam splitter 230. Before reaching the reference mirror 286, the light passes through the reference arm quarter wave plate 282, also oriented at 45 degrees to the incident polarization. The reference arm quarter wave plate 282 converts the linearly polarized light into circularly polarized light. Upon reflection from the reference mirror 286, the circular polarization reverses its handedness. Passing back through the reference arm quarter wave plate 282, the light is converted back into linearly polarized light with its polarization direction rotated by 90 degrees compared to the incident light.

[0077]

[0068] By rotating the polarization of the returning light by 90 degrees in both arms 202, 204, the system can effectively distinguish the desired signal from unwanted reflections. Spurious reflections originating from optical surfaces before the quarter wave plates — such as lenses, mirrors, or the beam splitter — do not undergo this polarization rotation because they have not passed through the quarter wave plates twice and have not reflected off the object of interest or reference mirror. These unwanted reflections maintain their original polarization state, which remains orthogonal to the polarization of the desired signal returning from the retina 12 and the reference mirror 286.

[0078]

[0069] At the beam splitter 230 and in the detection or camera arm 208 leading to the line field camera 300, only the light that has interacted with the retina and reference mirror contributes significantly to the interference pattern detected by the line field sensor or camera 300. Any returning light from a specular reflection from a poorly antireflection coated lens, for example, has an orthogonal polarization state and does not contribute to the interference signal detected by the sensor 300.

[0079]

[0070] By rejecting light that has not undergone the polarization rotation — namely, spurious reflections from intermediate optical components — the system reduces noise and enhances the contrast of the interference fringes. This polarization-based rejection improves the signal-to-noise ratio, allowing the OCT system to produce clearer and more accurate images of the retinal structures. The quarter wave plates thus play a critical role in optimizing the performance of the OCT system by manipulating the polarization states to differentiate between desired signals and unwanted reflections. Docket: 0407-0023W01

[0080]

[0071] This also obviates the need to avoid reflections that are a multiple of the laser cavity length of the swept source 100 and give rise to so-called "coherence revival" or “coherence repeat” or "zero-beat" artifacts which in particular cause the ocular lens to give spurious interference reflections on certain variable delay line settings of the reference arm mirror linear actuator 290 of the reference arm for matching the optical path length of the eye. The inclusion of the quarter waveplates negates the impact of laser’s cavity length and optical design and gives rise to much easier design constraints.

[0081]

[0072] Performance can be further improved by adding a polarizer 310 in front of the line-field sensor 300 to block light of the original polarization from the swept source. This polarizer or a polarizing beam splitter is aligned to transmit only the light polarized in the direction of the rotated returning signal while blocking or attenuating light polarized in the original incident direction. But such filtering should only lead to a negligible improvement in performance since it would be only blocking interference from spurious reflections in each arm. In a current embodiment, the polarizer is not used to reduce the system’s cost and complexity.

[0082]

[0073] The combination of the Plbssl eyepiece 252 and the Plbssl camera objective 294 enhances image formation on the sensor 300 in several ways:

[0083]

[0074] The symmetrical and matched design of the two Plbssl systems allows for the compensation of optical aberrations. Aberrations that may arise as the light travels through the eyepiece 252 are counteracted by the camera objective 294, resulting in a net reduction of distortions in the final image.

[0084]

[0075] In the preferred embodiment, the size of the scanning galvanometer mirror 240 is selected to act as an aperture that controls the angular distribution of light returning from the patient's eye that is relayed onto the sensor 300. Positioned at the conjugate plane of the patient's eye pupil, this mirror effectively serves as an aperture stop, limiting optical aberrations and enhancing image quality on the line field sensor 300. The scanning mirror size can be controlled for example by controlling the physical size of the mirror or by controlling its effective size by adding a light absorbing aperture to the mirror’s surface or other physical aperture near the mirror.

[0085]

[0076] The concept of conjugate planes in optics refers to two points where an obj ect at one plane is imaged onto another plane through the optical elements in between. By placing the scanning galvanometer mirror 240 at the plane conjugate to the patient's eye Docket: 0407-0023W01 pupil, any angular changes or movements at the mirror correspond directly to angular changes at the pupil. This alignment allows the mirror to control the entrance pupil of the system — the aperture through which light enters the eye.

[0086]

[0077] Moreover, limiting the size of the scanning galvanometer mirror restricts the range of angles over which light can enter and exit the eye and still return to the sensor 300. This restriction defines the system's numerical aperture and controls the cone of light rays contributing to image formation. By constraining the angular extent of the light, the system reduces the inclusion of off-axis light rays — those entering at larger angles relative to the optical axis — that are more likely to introduce optical aberrations such as spherical aberration, coma, astigmatism, and incorrect field curvature not matching the retina’s curvature. These aberrations become more pronounced with increasing aperture size and larger incident angles, potentially blurring the image and reducing resolution and contrast.

[0087]

[0078] By effectively narrowing the range of angles, the system allows primarily paraxial rays — those close to the optical axis — to participate in image formation. This selective acceptance of light minimizes aberrations and improves the overall image quality on the sensor 300. Additionally, positioning the scanning mirror at the pupil conjugate plane ensures that the scanning motion corresponds to angular scanning at the eye's pupil, resulting in lateral scanning across the retina. Because the mirror is at this specific plane, scanning does not introduce significant beam displacement at the eye's entrance pupil, helping to maintain consistent illumination across different scanning positions. This consistency reduces vignetting and ensures uniform intensity across the retinal image, which is essential for accurate OCT measurements.

[0088]

[0079] Furthermore, the limited size of the scanning galvanometer mirror restricts aberrated light returning from the patient's eye at larger angles. Light that would have entered or exited the eye at high angles — potentially contributing to aberrations — is effectively blocked by the mirror's limited aperture. This selective blocking prevents aberrated rays from reaching the detection system, enhancing the clarity and sharpness of the image formed on the camera.

[0089]

[0080] In the current design, 2.5 millimeters (mm) pupil size is ideal for getting to the eye's diffraction limit as going larger gives rise to blurring from the eye's optical aberrations. Thus, in embodiments, the effective size of the scanning galvanometer mirror Docket: 0407-0023W01

[0090] 240 is usually less than 8 mm in diameter and preferably less than 5 mm, such as less than 3 mm, and currently about 2.5 mm.

[0091]

[0081] Understanding this aperturing exposes nuances implicit in the optical design of the illumination arm. The illumination arm plays a role in delivering light to the patient's eye, despite the aperture limitation imposed by the scanning galvanometer mirror. This is achieved through the careful arrangement and interaction of two achromatic doublet lenses 210, 222 and a concave cylindrical lens 214, which together shape and guide the illumination beam to match the constraints of the system while ensuring sufficient light reaches the retina for high-quality imaging.

[0092]

[0082] In essence, the combination of the two achromatic doublet lenses and the concave cylindrical lens in the illumination arm 206 allows the system to tailor the illumination beam precisely. By collimating, shaping, and focusing the beam to match the scanning galvanometer mirror's aperture, the design ensures efficient light delivery to the eye despite the aperture's limitations. This approach enables the system to benefit from the aberration-reducing effects of the limited aperture — improving resolution and contrast — while still providing sufficient illumination intensity for high-quality retinal imaging.

[0093]

[0083] In other embodiments, the system 200 is configured for full-field swept-source OCT. In such embodiments the concave cylindrical lens 214 may be replaced by a spherical or other 2D focusing optic and the line-field sensor 300 may be replaced by an area camera. The polarization management using quarter-wave plates 260, 282, the pupilconjugate scanning galvanometer 240, and the Plossl ey epiece / camera objective 252, 294 remain applicable.

[0094]

[0084] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

Docket: 0407-0023W01CLAIMSWhat is claimed is:

1. A line-field or full-field swept-source optical coherence tomography (OCT) system for imaging a retina of a patient’s eye or other object of interest, comprising: a swept source configured to generate linearly polarized light over a range of wavelengths; a beam splitter configured to divide light from the swept source between a sample arm and a reference arm; the sample arm comprising optics configured to direct the light toward the object of interest and a sample arm quarter-wave plate positioned in an optical path between the beam splitter and the object of interest; the reference arm comprising a reference mirror and a reference arm quarterwave plate positioned in an optical path between the beam splitter and the reference mirror; and a detection arm comprising optics configured to receive light returning from the sample arm and the reference arm via the beam splitter and a line-field or area sensor configured to detect interference between light returning from the object of interest and light returning from the reference mirror.

2. The system of claim 1, wherein each of the sample arm quarter-wave plate and the reference arm quarter-wave plate has a fast axis oriented at about 45 degrees to a polarization axis of the linearly polarized light from the swept source so that light undergoing a double pass through the respective quarter-wave plate is converted back to linearly polarized light with a polarization direction rotated by about 90 degrees relative to the incident light.

3. The system of claim 1, further comprising a polarizer or a polarizing beam splitter in the detection arm, the polarizer or polarizing beam splitter being oriented to substantially transmit light having the rotated polarization direction and to attenuate light having the original polarization direction.

4. The system of any of claims 1-3, wherein light that has undergone a double pass through the sample arm quarter-wave plate and reflection from the object of interestDocket: 0407-0023W01 and light that has undergone a double pass through the reference arm quarter-wave plate and reflection from the reference mirror are both linearly polarized along a common rotated polarization direction, and spurious reflections originating at optical surfaces that do not include a double pass through one of the quarter-wave plates retain the original polarization direction and are thereby substantially prevented from producing interference at the sensor.

5. The system of any of claims 1-3, wherein the swept source has a cavity length that would produce coherence repeat artifacts for reflections separated in optical path by integer multiples of the cavity length in the absence of polarization manipulation, and wherein the sample arm quarter-wave plate and the reference arm quarter-wave plate are configured such that reflections associated with such coherence repeats do not produce significant interference signals at the sensor.

6. The system of any of claims 1-3, wherein the optics of the sample arm comprise an eyepiece configured to couple light into the patient’s eye, and wherein the sample arm quarter-wave plate is positioned between the eyepiece and a cornea of the patient’s eye.

7. The system of any of claims 1-3, wherein the optics of the reference arm comprise a convex cylindrical lens positioned between the beam splitter and the reference mirror, and wherein the reference arm quarter-wave plate is positioned between the convex cylindrical lens and the reference mirror.

8. The system of any of claims 1-3 configured as a line-field OCT system, further comprising a concave cylindrical lens configured to form a line beam at the object of interest and a line-field sensor configured to detect the interference along a line corresponding to the line beam.

9. The system of any of claims 1-3 configured as a full-field OCT system, wherein the system is configured to illuminate a two-dimensional field at the object of interest and the sensor is an area sensor configured to detect interference over a two-dimensional field.Docket: 0407-0023W0110. The system of any of claims 1-3, further comprising a scanning galvanometer mirror positioned at a plane conjugate to a pupil of the patient’s eye and configured to scan illumination across the retina, wherein the sample arm quarter-wave plate is positioned on a side of the scanning galvanometer mirror that is optically closer to the patient’s eye than the beam splitter.

11. A line-field or full-field swept-source optical coherence tomography (OCT) method, comprising: generating linearly polarized light over a range of wavelengths; dividing light between a sample arm and a reference arm; directing the light toward the object of interest and a sample arm quarter- wave plate positioned in an optical path to the obj ect of interest; providing a reference mirror and a reference arm quarter-wave plate positioned in an optical path to the reference mirror; and receiving light returning from the sample arm and the reference arm and detecting interference between light returning from the object of interest and light returning from the reference mirror.

12. An optical coherence tomography (OCT) imaging system for imaging a curved retinal surface onto a flat imaging sensor, comprising: a swept source configured to generate light over a range of wavelengths; an interferometer configured to divide light from the swept source between a sample arm and a reference arm and to recombine light returning from the sample arm and the reference arm; the sample arm comprising an eyepiece lens group disposed to receive light from the beam splitter and to couple the light through a cornea of a patient’s eye to form an image on a curved retinal surface; and a detection arm comprising an imaging objective lens group disposed to receive light returning from the retinal surface via the beam splitter and sensor located at an image plane of the imaging objective lens group, wherein the eyepiece lens group and the imaging objective lens group together define a field-flattening optical subsystem configured to map the curved retinal surface onto the flat imaging sensor with reduced field curvature.Docket: 0407-0023W0113. The system of claim 12, wherein at least one of the eyepiece lens group and the imaging objective lens group comprises an optical design selected from the group consisting of:(i) a Plbssl lens group comprising two identical achromatic doublet lenses arranged symmetrically about a central plane;(ii) a monocentric lens group having substantially concentric spherical surfaces;(iii) an aspheric lens group including one or more aspheric elements in combination with field-flattening optical elements;(iv) a Petzval lens group configured to correct field curvature at the imaging sensor;(v) a Schmidt-type optical system including a spherical primary mirror and aSchmidt corrector configured to produce a substantially flat image at the imaging sensor; and(vi) a freeform optical element having a non-rotationally symmetric surface profile configured to correct field curvature between the retinal surface and the imaging sensor.

14. The OCT imaging system of either of claims 12 or 13, further comprising: a sample arm quarter-wave plate positioned in an optical path between the eyepiece lens group and the patient’s eye; and a reference arm quarter-wave plate positioned in an optical path between a beam splitter and a reference mirror, wherein light that undergoes a double pass through each of the sample arm quarter-wave plate and the reference arm quarter-wave plate is converted back to linearly polarized light, thereby suppressing spurious reflections that do not include a double pass through one of the quarter-wave plates from producing interference at the imaging sensor.

15. An optical coherence tomography (OCT) imaging system for retinal imaging, comprising: a swept source configured to generate light over a range of wavelengths; an interferometer configured to divide light from the swept source between a sample arm and a reference arm and to recombine light returning from the sample arm and the reference arm;Docket: 0407-0023W01 the sample arm comprising: a scanning galvanometer mirror disposed to receive light and to direct the light toward a patient’s eye; one or more sample arm lenses configured to image the scanning galvanometer mirror onto a pupil of the patient’s eye such that the scanning galvanometer mirror is located at a plane conjugate to the pupil; and an eyepiece configured to couple the light through a cornea of the patient’s eye and to scan the light laterally across a retina in response to angular deflection of the scanning galvanometer mirror; a detection arm comprising an imaging lens group and a line-field or area sensor configured to receive and detect light returning from the retina, wherein the scanning galvanometer mirror has an effective aperture dimension selected such that the scanning galvanometer mirror functions as an aperture stop of the system, limiting a range of angles over which light entering and exiting the eye contributes to image formation at the sensor.

16. The system of claim 15 or any of claims 1-3, wherein an effective aperture dimension of the scanning galvanometer mirror corresponds to an effective pupil size at the patient’s eye of less than about 5 millimeters, preferably less than about 3 millimeters, and in some embodiments about 2.5 millimeters, thereby limiting the numerical aperture of the system.

17. The system of claim 15 or any of claims 1-3, wherein the effective aperture dimension of the scanning galvanometer mirror is defined by at least one of a physical size of a reflective surface of the mirror, and an aperture element disposed on or proximate to the mirror configured to block light outside the effective aperture dimension.

18. The system of claim 15 or any of claims 1-3, wherein locating the scanning galvanometer mirror at the plane conjugate to the pupil of the patient’s eye and selecting the effective aperture dimension such that the mirror functions as an aperture stop causes primarily paraxial rays relative to an optical axis of the systemDocket: 0407-0023W01 to contribute to image formation at the sensor, thereby reducing at least one aberration selected from spherical aberration, coma, astigmatism, and incorrect field curvature.

19. The system of claim 15 or any of claims 1-3, wherein imaging the scanning galvanometer mirror onto the pupil of the patient’s eye causes angular deflection of the scanning galvanometer mirror to correspond substantially to angular scanning at the eye’s pupil without substantial lateral displacement of a beam at the pupil, thereby reducing vignetting and promoting uniform illumination across a scanned retinal field while the effective aperture dimension limits off-axis rays.

20. A method of optical coherence tomography (OCT) retinal imaging using a pupil-conjugate scanning galvanometer mirror, comprising: generating light over a range of wavelengths using a swept source; dividing light from the swept source between a sample arm and a reference arm using an interferometer; in the sample arm: o directing the light to a scanning galvanometer mirror having an effective aperture dimension; o imaging the scanning galvanometer mirror onto a pupil of a patient’s eye with one or more sample arm lenses such that the scanning galvanometer mirror is located at a plane conjugate to the pupil; and o coupling the light through a cornea of the patient’s eye with an eyepiece so that angular deflection of the scanning galvanometer mirror scans the light laterally across a retina; in the reference arm, directing light along a reference path toward a reference reflector; recombining light returning from the retina and light returning from the reference reflector in the interferometer; in a detection arm, receiving recombined light with an imaging lens group and detecting interference at a line-field or area sensor to form OCT data representing the retina; selecting the effective aperture dimension of the scanning galvanometer mirror such that the scanning galvanometer mirror functions as an aperture stop ofDocket: 0407-0023W01 the system, limiting a range of angles over which light entering and exiting the eye contributes to image formation at the sensor; and thereby controlling a numerical aperture of the system such that primarily paraxial rays relative to an optical axis contribute to image formation, reducing optical aberrations and improving image resolution and uniformity across the retinal field.

Images