High-resolution polarization sensitive imaging and polarization measuring device and method thereof

Abstract

A lens has an optical center and an optical axis passing through the optical center; and at least a first lens portion located at a distance from the optical center for refracting light of a predefined polarization state irradiated thereon at a right angle from the first side to an optical axis on the second side at a constant bending angle, thereby defining a focal line on the second side along the optical axis.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Patent Application No. 63 / 320,589, filed on March 16, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates generally to imaging devices, and in particular, to bijective illumination collection ellipsometry (BICE) devices and methods for high-resolution imaging and polarimetry. Background Art

[0004] Lenses have been widely used in the field of imaging. Typically, a converging lens is associated with a focal point defined along the optical axis of the lens, which determines the position of a light sensor or light detector (denoted as "focused sensor position", which defines an image plane) for capturing a focused or sharp image of an object at a specific distance (denoted as "focused object position" hereinafter). Examples of light sensors may be eyes, light-sensitive materials (e.g., camera film), photosensors, etc.

[0005] If the light sensor deviates from the focus sensor position or the object deviates from the focus object position, the captured image will be blurred. In the prior art, the depth of focus (DOF) of a lens refers to the range around the focus sensor position (which can be characterized by a corresponding range around the focus point) within which the captured image may be blurred (when the light sensor deviates from the focus sensor position), but the blur is within an acceptable range and still provides acceptable sharpness (e.g., blurred but perceived sharpness). Extended depth of focus (EDOF) allows objects to be located within an extended object range around the focus object position while still obtaining an acceptable image.

[0006] High-resolution microscopic imaging of tissue microstructure is helpful in biology and enables many clinical applications. Three-dimensional microscopic imaging enables many biological and clinical applications. However, high-resolution optical imaging preserved over relatively large depths is hampered by the rapid diffusion of tightly confined light due to diffraction.

[0007] As is known in the art, optical microscopy using tightly focused light cannot be maintained over a relatively large depth range due to the rapid diffusion of light caused by diffraction. Imaging modalities such as confocal microscopy (see reference 1) and two-photon microscopy (see reference 2) can only achieve high-resolution imaging from a narrow region around the focus. Therefore, an additional scanning mechanism is required to translate the focus axially relative to the target to achieve depth-resolved imaging (see reference 3). This hinders fast imaging, and the imaging depth is usually limited to a few hundred microns (see reference 4), which is insufficient for many applications.

[0008] Using coherence gating, optical coherence tomography (OCT) captures real-time depth-resolved images of structures several millimeters deep in scattering tissue (see Refs. 5-9). Despite the improvement in axial resolution, OCT is still challenged by competing lateral resolution and depth of focus because diffraction hinders high-resolution imaging in three dimensions over a large depth range (see Refs. 10-12).

[0009] The core issue is how the light intensity should be distributed to achieve high-resolution 3D imaging over a large depth range. Focusing light at a single depth point, widely used in existing imaging systems, yields an arbitrary primacy of that point, which is inconsistent with the goal of depth imaging. Alternatively, a more uniform distribution of light intensity along the axial direction inevitably sacrifices lateral resolution due to diffraction.

[0010] Ellipsometry is the measurement of the optical polarization-changing properties of a material or system (see Ref. 60). An optically linear material or system can be characterized by a 4×4 Miller matrix (M) with the Stokes vector S in The incident light is converted into a light with Stokes vector S out (S out =M×S in ) of light (reflected, transmitted, or scattered). If the material or system does not depolarize light, the 2×2 Jones matrix (J) can provide a complete description of the polarization-changing properties of the material or system. Determining M and J requires at least four and three measurements, respectively.

[0011] Traditionally, ellipsometry is performed by recording multiple measurements and post-processing the measurements. However, this method is slow due to the serial nature of the measurements. Real-time imaging of biological matter or tissue in vivo requires a fast method for ellipsometry. Rotational compensator ellipsometry (see Ref. 61) has been reported for fast ellipsometry, however, in principle, it is still a sequential method and involves the movement of components, which complicates the design. Summary of the invention

[0012] According to one aspect of the present disclosure, a lens is provided, comprising: an optical center and an optical axis passing through the optical center; and one or more lens portions; the one or more lens portions include at least a first lens portion for refracting light of a predefined polarization state irradiated thereon at right angles from a first side to the optical axis on a second side at a constant bending angle, thereby defining a focal line on the second side along the optical axis.

[0013] In some embodiments, at least the first lens portion is located a distance from the optical center.

[0014] In some embodiments, at least the first lens portion includes a first lens portion and a second lens portion; the centers of the first lens portion and the second lens portion are located on diagonally opposite sides of the optical center; and the first lens portion and the second lens portion are configured to allow light of orthogonal polarization states to pass therethrough.

[0015] In some embodiments, the one or more lens portions further include: at least a third lens portion for refracting light irradiated onto the third lens portion from the focal line on the second side to the first side in a direction parallel to the optical axis at a constant bending angle.

[0016] In some embodiments, at least the third lens portion includes a third lens portion and a fourth lens portion; the centers of the third lens portion and the fourth lens portion are located on diagonally opposite sides of the optical center; and the third lens portion and the fourth lens portion are configured to allow light of orthogonal polarization states to pass therethrough.

[0017] In some embodiments, for a two-dimensional (2D) coordinate system defined on the lens with its origin at the optical center, each of the one or more lens portions is located in a corresponding quadrant of the 2D coordinate system.

[0018] In some embodiments, the centers of each pair of circumferentially adjacent lens portions of one or more lens portions are at right angles to the optical center.

[0019] In some embodiments, the bend angle is 21°.

[0020] In some embodiments, each of the one or more lens portions has a circular shape.

[0021] In some embodiments, each lens portion of the one or more lens portions has a diameter of 1.1 millimeters (mm).

[0022] In some embodiments, each of the one or more lens portions includes a metasurface coupled to a substrate.

[0023] In some embodiments, each metasurface includes a plurality of nanopillars in an arc-shaped pattern, wherein the arcs are portions of a plurality of concentric circles centered at the optical center.

[0024] In some embodiments, the plurality of nanopillars have a cubic shape with a square cross-section; and the plurality of nanopillars have the same height and different widths.

[0025] In some embodiments, the plurality of nanorods have a width between 80 nanometers (nm) and 300 nm.

[0026] In some embodiments, the plurality of nanorods has a height of 750 nm.

[0027] In some embodiments, an adjacent pair of nanopillars in the plurality of nanopillars has a center-to-center distance of 370 nm.

[0028] In some embodiments, the lens further comprises an axicon having its vertex as an optical center; and the one or more lens portions are defined on the axicon.

[0029] In some embodiments, the lens is opaque except at one or more lens portions.

[0030] According to one aspect of the present disclosure, there is provided an imaging device, comprising: a polarization beam splitter for splitting light into a first polarized light and a second polarized light in orthogonal polarization states; a beam adjustment module for receiving the first polarized light and the second polarized light, and outputting the first polarized light and the second polarized light to a lens according to any one of claims 1 to 17; and an adjustment module for introducing a time delay into at least one of the first polarized light and the second polarized light and / or adjusting the frequency of at least one of the first polarized light and the second polarized light before inputting the first polarized light and the second polarized light to the beam adjustment module.

[0031] In some embodiments, the lens is the above-mentioned lens; the beam adjustment module includes: a main knife-edge prism; a first knife-edge prism for directing a first polarized light to the main knife-edge prism; and a second knife-edge prism for directing a second polarized light to the main knife-edge prism; and the main knife-edge prism is configured to: output the first polarized light and the second polarized light to the lens; receive a third light and a fourth light from the lens; direct the third light to the first knife-edge prism; and direct the fourth light to the second knife-edge prism.

[0032] According to one aspect of the present disclosure, a method for manufacturing the above-mentioned lens is provided, the method comprising: depositing an amorphous silicon (a-Si) layer on a substrate using plasma enhanced chemical vapor deposition; coating a layer of negative photoresist on the a-Si layer; generating an etching pattern on the layer of negative photoresist using electron beam lithography (EBL); and generating a-Si nanopillars using deep reactive ion etching for forming a metasurface of one or more lens portions.

[0033] In some embodiments, the etched pattern corresponds to an arc pattern.

[0034] In some embodiments, the etch pattern corresponds to a plurality of concentric circles.

[0035] In some embodiments, the method further comprises: masking the one or more unusable areas as opaque.

[0036] According to one aspect of the present disclosure, there is provided a method for using a lens according to claim 5 or any one of claims 6 to 17, the method comprising at least one of the following items: aiming a first light beam at a first lens portion; and collecting a third light beam and a fourth light beam from a third lens portion and a fourth lens portion, respectively; a cross-sectional size of the first light beam matches a size of the first lens portion.

[0037] According to one aspect of the present disclosure, a lens is provided, comprising: an optical center and an optical axis passing through the optical center; and a plurality of lens portions, the plurality of lens portions comprising: a first lens portion and a second lens portion on diagonally opposite first and second quadrants of a plane perpendicular to the optical axis, for refracting light from a first side to a second side; and a third lens portion on a third quadrant of the plane, for refracting light from the second side to the first side; the first lens portion and the second lens portion are configured to refract light incident thereon at a right angle from the first side to the optical axis on the second side at a constant bending angle, thereby defining a focal line on the second side along the optical axis, and the third lens portion is configured to refract light incident from the focal line on the second side at a constant bending angle to the first side parallel to the optical axis; or the third lens portion is configured to refract light incident thereon at a right angle from the second side to the optical axis on the first side at a constant bending angle, thereby defining a focal line on the first side along the optical axis, and the first lens portion and the second lens portion are configured to refract light incident from the focal line on the first side at a constant bending angle to the second side parallel to the optical axis.

[0038] In some embodiments, the plurality of lens portions are distal from the optical center.

[0039] In some embodiments, the centers of the first lens portion and the third lens portion or the centers of the second lens portion and the third lens portion are at right angles to the optical center.

[0040] In some embodiments, the multiple lens portions also include: a fourth lens portion on the fourth quadrant of the plane, for refracting light incident from the focal line on the second side at a constant bending angle to the first side parallel to the optical axis; or for refracting light incident thereon at a right angle from the second side to the optical axis on the first side at a constant bending angle, thereby refracting onto the focal line of the first side.

[0041] In some embodiments, the bend angle is 21°.

[0042] In some embodiments, each lens portion of the one or more lens portions has a circular shape.

[0043] In some embodiments, each lens portion of the one or more lens portions has a diameter of 1.1 mm.

[0044] In some embodiments, each of the one or more lens portions includes a metasurface coupled to a substrate.

[0045] In some embodiments, each metasurface includes a plurality of nanopillars in an arc-shaped pattern, wherein the arcs are portions of a plurality of concentric circles centered at the optical center.

[0046] In some embodiments, the plurality of nanopillars have a cubic shape with a square cross-section; and the plurality of nanopillars have the same height and different widths.

[0047] In some embodiments, the width of the plurality of nanorods is between 80 nm and 300 nm.

[0048] In some embodiments, the plurality of nanorods has a height of 750 nm.

[0049] In some embodiments, an adjacent pair of nanopillars in the plurality of nanopillars has a center-to-center distance of 370 nm.

[0050] In some embodiments, the lens includes an axicon having its vertex as an optical center; and the one or more lens portions are defined on the axicon.

[0051] In some embodiments, the lens is opaque except at one or more lens portions. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1A is a schematic plan view of a bi-directional illumination collection imaging (BICI) lens according to some embodiments of the present disclosure, wherein the BICI lens includes an illumination lens portion and a collection lens portion, and wherein the centers of the illumination lens portion and the collection lens portion of the BICI lens are at an angle of 90° relative to the optical center of the BICI lens;

[0053] Figure 1B Some embodiments of the present disclosure are shown Figure 1A Detail of the illumination lens portion of the BICI lens shown, wherein the illumination lens portion includes a metasurface;

[0054] Figure 1C yes Figure 1A Schematic diagram of the BICI lens shown, showing the patterns of the metasurface of the illumination lens portion and the collection lens portion;

[0055] FIG. 2A to FIG. 2I Shows Figure 1A The interaction of the BICI lens with the illumination and collection light is shown, where

[0056] Figure 2A yes Figure 1A A schematic perspective view of a BICI lens is shown, showing that the illumination light is incident at a right angle to the image plane at a point offset from the imaging optical axis. Figure 1A In the illumination lens portion of the BICI lens shown, the illumination lens portion bends or refracts the illumination light at a constant angle β to form a focus on the z-axis.

[0057] Figure 2B yes Figure 1A A schematic perspective view of a BICI lens is shown, showing a family of rays or a sheet of rays impinging upon Figure 1A At the position of the arc of radius r on the illumination lens portion of the BICI lens shown, the illumination lens portion bends or refracts the light sheet at a constant angle β to form a focus on the z axis,

[0058] Figure 2C yes Figure 1A A schematic perspective view of a BICI lens is shown, showing the Figure 1A The sheet of rays incident on the illumination lens portion of the BICI lens shown as being subject to the same bending paradigm constitutes the focal line along the z-axis, although for clarity the focal line is not shown in FIG. Figure 2C A finite number of focal points are shown, but the focal lines are continuous.

[0059] Figure 2D yes Figure 1A A schematic perspective view of a BICI lens is shown, showing the Figure 1A The collecting lens portion of the BICI lens shown establishes a trajectory of collected light in the ray sheet, which mirrors the image of the illumination path relative to the xz plane, thereby enabling a one-to-one correspondence (i.e., a bijective relationship) between the focal points of the illumination path and the collection path to eliminate out-of-focus signals.

[0060] Figure 2E is a bijective relation Figure 2DAn enlarged schematic perspective view of a portion A of

[0061] Figure 2F is a schematic plan view showing an illumination beam and a collection beam,

[0062] Figure 2G is shown for verification Figure 1A Schematic diagram of the experimental setup showing the optical characterization of the BICI lens.

[0063] Figure 2H Shown by the camera in Figure 2G A snapshot captured from the side of the focal line intersection shown, which illustrates the arrangement of the illumination path and the collection path, which allows the collection of only photons originating from the corresponding illumination focus, and

[0064] Fig.2I yes Figure 1A Schematic diagram of the BICI lens shown, showing the length of the focal line and the distance between the focal line and the BICI lens;

[0065] FIG. 3A to FIG. 3F A metasurface of an illumination lens portion and a collection lens portion is shown, where

[0066] Figure 3A is a schematic perspective view of the nanopillars of the metasurface.

[0067] Figure 3B yes Figure 3A Schematic side view of a nanopillar shown,

[0068] Figure 3C yes Figure 3A Schematic plan view of the nanopillar shown,

[0069] Figure 3D is a schematic plan view of nanopillars of a metasurface, showing that the nanopillars have periodically varying sizes and are in a grid pattern for forming an arc or circular pattern,

[0070] Figure 3E is a wide-field optical image of the fabricated metasurface of the illumination lens portion and the collection lens portion, each metasurface having a diameter of 1.1 millimeters (mm), and

[0071] Figure 3F The illumination lens part and the collection lens part include square amorphous silicon (a-Si)

[0072] Scanning electron micrograph of the fabricated metasurface of nanopillars;

[0073] Figure 4 Shows Figure 1AThe analytical point spread function (PSF) of the BICI lens shown shows that the BICI lens has a lateral resolution of about 3.2 micrometers (μm) and a focal line or depth of focus of about 1.25 mm;

[0074] FIG. 5A to FIG. 5C The analytical PSF using the conventional technique of common path Gaussian and Bessel beams is shown, where

[0075] Figure 5A shows that the PSF of a tightly focused Gaussian beam (about 3.2 μm full width at half maximum (FWHM)) degrades rapidly away from the focus.

[0076] Figure 5B shows the PSF of a Gaussian beam with a relatively large focal depth (about 1.25 mm) assuming a significant sacrifice in lateral resolution, and

[0077] Figure 5C The PSF of a Bessel beam with a central lobe of 3.2 μm FWHM is shown, which involves spreading the power into several side lobes that are detrimental to the imaging quality;

[0078] Figure 6 is a schematic diagram of an interferometer according to some embodiments of the present disclosure, the interferometer comprising in one of its arms Figure 1A The BICI lens shown;

[0079] 7A to 7C Shows the use of Figure 6 The interferometer test results are shown in Figure 2, where

[0080] Fig. 7A shows the intensity distribution measurement of the illumination beam of 1300nm wavelength in the xz plane,

[0081] Figure 7B shows the intensity distribution measurement of the collected beam at 1300 nm wavelength in the xy plane, and

[0082] Figure 7C The imaging PSF, which is the product of the illumination intensity profile and the collection intensity profile, is shown, demonstrating that a sharp PSF is maintained over a large axial range;

[0083] FIG. 8A to FIG. 8C The resolution and depth of focus measurements of the BICI lens shown in Figure 1 are shown, where

[0084] Fig. 8A is a schematic diagram of the measurement setup used to image a subwavelength gold wire that is scanned across the focal line at different depth points.

[0085] Figure 8B shows the imaging PSF measured at three depth points, and

[0086] Figure 8C shows the measured resolution of the BICI lens shown in FIG1 compared to the theoretical resolution obtained from a Gaussian beam with the same lateral resolution (in a common path illumination-collection scheme), thereby highlighting the ability of the BICI lens shown in FIG1 to maintain high resolution over a large depth range;

[0087] Fig. 9A is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the centers of the illumination lens portion and the collection lens portion of the BICI lens are at an angle of less than 90° relative to the optical center of the BICI lens;

[0088] Fig. 9B is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the centers of the illumination lens portion and the collection lens portion of the BICI lens are at an angle greater than 90° relative to the optical center of the BICI lens;

[0089] FIG. 10A to FIG. 10D A BICI lens according to some embodiments of the present disclosure is shown, wherein:

[0090] Fig. 10A is a schematic plan view of a BICI lens, wherein the illumination lens portion and the collection lens portion of the BICI lens are in diagonally opposite quadrants of the BICI lens,

[0091] Fig. 10B yes Fig. 10A Schematic plan view of a BICI lens showing the illumination beam and the collection beam,

[0092] Fig. 10C yes Fig. 10A A schematic perspective view of a BICI lens is shown, showing the illumination path and the collection path, and

[0093] Fig. 10D is a bijective relation Fig. 10D An enlarged schematic perspective view of a portion B of FIG.

[0094] Fig.11A is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens includes two illumination lens portions and one collection lens portion;

[0095] Fig. 11B is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens includes an illumination lens portion and two collection lens portions;

[0096] Fig.12is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens includes two illumination lens portions and two collection lens portions;

[0097] Fig.13A and Fig. 13B Shows Figure 1A The BICI lens shown (see Fig.13A )and Fig.12 The BICI lens shown (see Fig. 13B )’s resolution comparison;

[0098] Fig.14A and Fig. 14B Some embodiments of the present disclosure are shown Figure 1A The manufacturing process of the BICI lens shown;

[0099] Fig.15 is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens comprises a metasurface having a pattern of a plurality of concentric circles centered at an optical center, and wherein, in use, an illumination beam can be aimed at a first region to use it as an illumination lens portion, and a light collector can be aimed at a second region to use it as a collection lens portion;

[0100] Fig.16 is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens has a square shape;

[0101] Fig.17 is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the optical center of the BICI lens does not overlap with the geometric center of the BICI lens;

[0102] Fig.18 is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens includes four circular lens portions, each circular lens portion having a maximized size in a corresponding quadrant;

[0103] Fig.19A is a schematic perspective view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens includes an axicon;

[0104] Fig.19B yes Fig.19A A schematic plan view of the BICI lens shown;

[0105] Fig. 20A is a schematic plan view of a BICI lens according to some embodiments of the present disclosure, wherein the BICI lens includes a collecting lens portion;

[0106] Fig. 20B yes Fig. 20A A schematic perspective view of a BICI lens and a line camera for collecting light from various focal points within the focal line of the BICI lens;

[0107] Fig.21 is a schematic diagram showing a bi-illumination collection ellipsometry (BICE) lens for fast high-resolution ellipsometry according to some embodiments of the present disclosure;

[0108] Fig. 22 According to some embodiments of the present disclosure Fig.21 A schematic perspective view of a BICE lens shown, which is used to focus a pair of illumination rays toward its focal line;

[0109] Fig.23 According to some other embodiments of the present disclosure Fig.21 A schematic perspective view of a BICE lens for focusing a pair of illumination rays toward its focal line and for collecting rays from its focal line;

[0110] Fig.24 According to some other embodiments of the present disclosure Fig.21 A schematic perspective view of a BICE lens shown for focusing illumination light toward its focal line;

[0111] Fig.25 According to some other embodiments of the present disclosure Fig.21 A schematic perspective view of a BICE lens shown for focusing illumination light toward its focal line and for collecting light from its focal line;

[0112] Fig.26 According to some other embodiments of the present disclosure Fig.21 A schematic perspective view of a BICE lens shown for focusing illumination light toward its focal line;

[0113] Fig. 27 According to some other embodiments of the present disclosure Fig.21 A schematic perspective view of a BICE lens shown for focusing illumination light toward its focal line and for collecting light from its focal line;

[0114] Fig.28 It is shown that the use Fig.21 Schematic diagram of the ellipsometric system of the BICE lens shown, wherein a time delay is introduced to the light rays therein;

[0115] Fig.29 It is shown that the use Fig.21Schematic diagram of the ellipsometric system of the BICE lens shown, wherein the light is frequency-adjusted;

[0116] Fig.30 yes Fig.28 or Fig.29 A schematic perspective view of a beam adjustment module of an ellipsometric system is shown;

[0117] Fig.31A yes Fig.28 or Fig.29 A schematic perspective view of a beam conditioning module of an ellipsometric system, showing the path of illumination light; and

[0118] Fig.31B yes Fig.28 or Fig.29 A schematic perspective view of the beam conditioning module of an ellipsometric system is shown, illustrating the path of the collected light rays. DETAILED DESCRIPTION

[0119] Embodiments disclosed herein relate to a bi-beam illumination collection imaging (BICI) apparatus and method for three-dimensional high-resolution imaging over a relatively large depth range.

[0120] According to one aspect of the present disclosure, a lens is provided having a focal line defined along an optical axis of the lens. Light rays irradiated at various positions of the lens at angles parallel to the optical axis are converged by the lens to various positions within the focal line. Therefore, such a lens having a focal line provides an improved depth of focus (DOF), so that a light sensor located at any position within its improved DOF can capture a clear image (i.e., a high-resolution image). In contrast, images captured using conventional extended depth of focus (EDOF) techniques may still be blurry or have reduced resolution.

[0121] According to one aspect of the present disclosure, high-resolution imaging is achieved by a specific arrangement of illumination and collection paths that allows a one-to-one spatial correspondence (birefringence) between illumination and collection light defined along a focal line, thereby freeing optical imaging from the limitations imposed by diffraction. The impact on imaging is shown by applying BICI to overcome limitations in high-resolution optical coherence tomography (OCT).

[0122] The boundaries of lateral resolution and depth of focus are coupled via diffraction. There is a class of so-called non-diffraction solutions to the Helmholtz equation (see Refs. 18–23). However, these modes have spatially unbounded profiles in their exact mathematical form (plane waves are a simple example) and produce sidelobes that carry most of the optical power (even in a physical realization where the sidelobes are limited by a finite aperture). When used for imaging, out-of-focus scattering from the sidelobes sacrifices imaging resolution and sensitivity.

[0123] Re-examining lateral resolution and depth of focus in the context of the imaging point spread function (PSF) provides an opportunity to circumvent the limitations imposed by diffraction. The PSF at any point is the illumination (P ill ) photons and the photons collected from this point (P coll ) is the product of the probabilities: PSF = P ill ×P coll (See Refs. 24-25.) Based on this concept, lateral resolution can be decoupled from depth of focus using uniquely crafted illumination and collection paths. In this context, the illumination path refers to the path of light from a light source that hits an object, while the collection path refers to the path of light that is scattered from or originates from the object.

[0124] In some embodiments, a metasurface with the ability to impart customized phase (see references 13-17) is used to implement the illumination paths and collection paths required for BICI implementation. In some embodiments, a lateral resolution of approximately 3.2 microns (μm) remains nearly intact over an imaging depth of 1.25 mm without additional acquisition or computational burden, which produces an imaging depth of focus approximately 12 times greater than that obtained using an ideal Gaussian beam with the same lateral resolution. Porcine tracheobronchial tissue specimens were imaged, indicating that BICI has the prospect of preserving high-resolution imaging over a large depth range. The methods disclosed herein can be applied to a variety of existing imaging modalities.

[0125] Now go to Figures 1A to 1C , a BICI lens according to some embodiments of the present disclosure is shown and is generally identified using reference numeral 100. For ease of explanation, a three-dimensional (3D) coordinate system is defined as having an xy plane and a z axis on the BICI lens 100 (see Figure 2A ), the z-axis is the optical axis of the BICI lens 100 and passes through its optical center 108 (i.e., the origin of the 3D coordinate system is located at the optical center 108). In these embodiments, the optical center 108 is also the centroid or geometric center of the BICI lens 100.

[0126] like Figures 1A to 1C As shown, the BICI lens 100 includes an illumination lens portion 102 and a collection portion 104 located on the xy plane of the BICI lens 100 for allowing light to pass through. The illumination lens portion 102 and the collection lens portion 104 preferably have circular shapes of the same size.

[0127] Each of the illumination lens portion 102 and the collection lens portion 104 is located at a distance from the optical axis. More specifically, for a two-dimensional (2D) xy coordinate system, the illumination lens portion 102 and the collection lens portion 104 are located in adjacent quadrants of the xy plane and are symmetrical about an axis (e.g., the x-axis on the BICI lens 100), such that each of the illumination lens portion 102 or the collection lens portion 104 is at an angle to the x-axis relative to the center 112 of the optical center 108. In other words, the center 112 of the illumination lens portion 102 and the collection lens portion 104 is 90° relative to the optical center 108. In order to reduce noise, it is preferred that, in addition to the illumination lens portion 102 and the collection lens portion 104, other areas of the BICI lens 100 (in the Figures 1A to 1C The area 106 in FIG. 1 is opaque, so the other areas are not available.

[0128] In these embodiments, each lens portion 102, 104 comprises a metasurface formed from an array of nanoscale, sub-wavelength spaced optical elements (denoted as "nanopillars"), such as Figure 1B As shown. The two metasurfaces 102, 104 have mirror-image profiles about the x-axis (i.e., mirror-image geometry of the nanopillars). In other words, the metasurface of the collection lens portion 104 has a flipped profile of the metasurface of the illumination lens portion 102 with respect to the x-axis. More specifically, each of the metasurfaces of the lens portions 102 and 104 has a pattern of arcs 110 that are portions of a plurality of concentric circles 114 centered about the optical center 108 (see Figure 1C ).

[0129] like Figure 2A As shown, a collimated light source (not shown) emits an illumination ray 116 that strikes the illumination lens portion 102 at a right angle at a point 118 having coordinates (r, θ), where r is the radius of the point 118 (relative to the optical center 108), and θ is the angle of the point 118 relative to the y-axis. The metasurface of the illumination lens portion 102 bends or refracts the ray 116 incident at the point 118 in the rz surface toward the optical axis (i.e., the z-axis) by a constant angle β. The focus 120 can be defined as the intersection of the refracted ray 116' and the optical axis.

[0130] The light bending angle β is constant with respect to r and θ. Therefore, Figure 2B As shown, the ray family of light 122 incident on the arc 110 of radius r (denoted as a "ray sheet of radius r") passes through the focus 120 on the z-axis (i.e., is focused at the focus 120). Therefore, as Figure 2CAs shown, a light beam or set of light rays 132 impinging at right angles on the illumination metasurface 102 in an arc 110 of constant but varying radius is generally focused within a continuous focal line 134 along the optical axis.

[0131] Since the collection metasurface 104 has a flipped profile of the illumination metasurface 102 relative to the x-axis, the illumination metasurface 102 has similar optical properties to the illumination metasurface 102. Figure 2D and Figure 2E As shown, the light sheet 142 originates from the focal line 134 in the rz surface at a constant angle β relative to the optical axis and impinges on the illumination metasurface 102 in an arc 110 of constant radius and then refracts to form a light beam 142' parallel to the optical axis. Figure 2F Snapshots of the illumination and collection beams in one transverse plane intersecting the focal line 134 are shown. Obviously, with the BICI lens 100 of the above structure, the BICI lens 100 provides separate illumination paths 132-132' and collection paths 142-142' that overlap only in focus along the focal line 134.

[0132] Although light beams 132 and 142 having any suitable cross-sectional dimensions may be used, for optimal optical efficiency, light beams 132 and 142 preferably have the same dimensions as illumination lens portion 102 and collection lens portion 104. Therefore, the dimensions of illumination lens portion 102 or collection lens portion 104 are also hereinafter referred to as beam dimensions.

[0133] As an example, Figure 2G is a schematic diagram showing an experimental setup for verifying the optical properties of the BICI lens 100, wherein two light beams 132 and 142' are aimed at the illumination lens portion 102 and the collection lens portion 104 at right angles, respectively. As described above, the light beams 132 and 142' are focused by the BICI lens 100 on the focal line 134. An image sensor (e.g., a camera; not shown) located on a transverse plane 144 intersecting the focal line 134 captures an image 152 of the light sheets 132' and 142. Figure 2H As shown, light sheets 132 ′ and 142 are focused on a point or dot 154 in captured image 152 .

[0134] It is noteworthy that the BICI lens 100 produces a constant lateral resolution (determined by β) along the focal line 134. Based on wave analysis using Fresnel-Kirchhoff integrals (see Reference 26), the lateral resolution is determined only by the bending angle β (regardless of beam size). However, according to Fig.2I The simple geometry shown, the depth of focus or focal line 134 depends on both the bending angle β and the beam size, where the distance between the BICI lens 100 and the focal line 134 is approximately The length of the focal line 134 is approximately 2R / tan(β).

[0135] Thus, the desired focal depth and bending angle β (set according to the desired resolution) yields a beam size, e.g., its radius R. In some embodiments, Fig.2I The illustrated ray optics based calculations may be combined with wave analysis to obtain a more accurate interpretation of the depth of focus 134 .

[0136] The BICI lens 100 establishes a one-to-one correspondence or bijective relationship between the illumination point and the point from which light is collected, which is defined only on the focal line 134, eliminating out-of-focus signals and back-reflected signals. The separate illumination paths 132-132' and collection paths 142-142' ensure that the illumination beam used to illuminate the point on the focal line 134 and the collection beam collected from the illumination point on the focal line 134 do not overlap.

[0137] As described above, the illumination lens portion 102 and the collection lens portion 104 may include a metasurface. The distribution and geometry of the nanopillars on the metasurface are designed to realize the illumination beam and the collection beam in the BICI. Based on the generalized Snell's law (see reference 13), the phase Φ required to bend the light sheet by an angle β in the rz plane (e.g., Figure 2B that is, the family of rays illuminating the illumination lens portion 102 at the same radius r) satisfies:

[0138]

[0139] Wherein, in some embodiments, λ d = 1300 nm is the design wavelength, for example, corresponding to the center wavelength of the OCT source. FIG. 3A to FIG. 3C , which is achieved by the illumination lens portion 102, which includes a metasurface of square amorphous silicon (a-Si) nanorods 162, which produces polarization-insensitive performance. In this article, a square nanorod refers to a nanorod having a height H and a square cross-section (perpendicular to the height H; for example, along Figure 3A AA) and the base size of the nanorods refers to their cross-sectional dimensions. In these embodiments, the a-Si nanorods 162 have the same height.

[0140] For example, in some embodiments, the a-Si nanorods have the same height H = 750 nm. The a-Si nanorods can have a square cross-section with a width S (determining its base size) between 80 nm and 300 nm, which can provide a full phase range [0-2π] with high transmittance (greater than 78%) at a wavelength of 1300 nm. The a-Si nanorods are distributed in a grid pattern of P = 370 nm unit cells 166 (i.e., the center-to-center distance between adjacent a-Si nanorods is P = 370 nm).

[0141] Likewise Figure 3D As shown, square a-Si nanorods 162 are distributed in a square grid pattern on a glass (SiO2) substrate 164. By periodically changing the base size of the nanorods 162, an arc or circular pattern 110 or 114 is then formed.

[0142] Nanopillars of varying substrate size in the grid impart the desired local phase. Due to its high refractive index and low absorptivity in the near-infrared range (see Refs. 29-31), a-Si is a suitable material for realizing an efficient metasurface for this application (greater than 70% of the incident power is concentrated on the focal line 134). The metasurface can be fabricated on a glass substrate using electron beam lithography.

[0143] In particular, the metasurfaces of the illumination lens portion 102 and the collection lens portion 104 can be fabricated using top-down photolithography techniques (see references 30 and 32). Plasma-enhanced chemical vapor deposition is used to deposit an a-Si layer (e.g., a 750 nm thick a-Si layer) on a glass substrate. A negative photoresist (Microresist Technology, ma-N2403) is then coated on the a-Si layer, and electron beam lithography (EBL) is used to produce a desired pattern on the negative photoresist, e.g., Figures 1A to 1C The patterns of the illumination lens portion 102 and the collection lens portion 104 are shown. Then, deep reactive ion etching is used to generate a-Si nanorods. The BICI lens 100 having the illumination lens portion 102 and the collection lens portion 104 is then fabricated.

[0144] Figure 3E is a wide-field optical image of the fabricated metasurface of the illumination lens portion 102 and the collection lens portion 104, and Figure 3F Scanning electron micrograph of a fabricated metasurface comprising square amorphous silicon (a-Si) nanopillars is shown. The phase profile of the metasurface is achieved using an appropriate distribution of a-Si nanopillars of different substrate sizes.

[0145] Integral to high-resolution imaging, the BICI lens 100 uses uniquely crafted illumination paths 132-132' and collection paths 142-142' to reject out-of-focus signals without sacrificing depth range. Thus, the BICI lens 100 provides high lateral resolution over a large depth range. Furthermore, due to the focal line 134 created by the illumination and detection beams, the BICI lens 100 can capture images over the entire depth range.

[0146] On the other hand, in existing high-resolution imaging systems, tightly focused light is usually used to mitigate the effect of out-of-focus signals, thereby relatively increasing the signal from the focal point (using confocal geometry or nonlinear effects at the focal point). Due to the severe diffraction of tightly focused light, this approach inevitably limits the depth range.

[0147] Metasurfaces typically exhibit strong dispersion unless corrected using special techniques (see Refs. 33 to 37). Applying BICI to OCT operating over a wide wavelength range (1240 nm to 1350 nm) requires addressing dispersion-related issues. The bending angle β imparted by the metasurface to the light path (see Figure 2B ) is clearly wavelength dependent (Eq. (1)). For BICI correction to operate, the focal line 134 needs to remain on the optical axis throughout the spectrum in order to preserve the bijection between the foci. The azimuthally symmetric phase profile of the metasurface with respect to the optical axis and the infinite correction configuration of the optical system ensure that the focal points are only displaced along the optical axis (z-axis) due to dispersion. This in turn ensures the conservation of the bijection relationship between the illumination and collection light over the entire spectrum.

[0148] To demonstrate the effect on imaging, the BICI lens 100 was used in a Fourier domain OCT system in the near infrared range. The illumination / collection beam had a wavelength of λ = 1300 nanometers (nm) ± 50 nm and a Gaussian profile (350 μm 1 / e 2 Intensity falloff radius). Figure 1A The illumination lens portion 102 and the collection lens portion 104 are centered at (x, y) = (550 μm, 550 μm) and (x, y) = (550 μm, +550 μm), respectively, according to the coordinates defined in FIG. Each of the illumination lens portion 102 and the collection lens portion 104 has a metasurface with a diameter of 1.1 millimeters (mm) and a bending angle β = 21° (numerical aperture NA = 0.36).

[0149] Wave analysis was performed using Fresnel-Kirchhoff integration (see Reference 26) to design the imaging PSF required for the desired resolution and depth of focus. The design parameters were selected to achieve microscopic resolution imaging over a relatively large depth range (greater than one (1) mm), beyond which scattering becomes the dominant limitation. Given the design parameters (collimated beam size of approximately 1.1 mm; β = 21°), the wave analysis yielded a sharp PSF of 3.2 μm full width at half maximum (FWHM) and a relatively large axial range (defined as 1 / e in the axial direction) of 1.25 mm depth of focus. 2 PSF intensity decay), where the contribution of the out-of-focus signal can be neglected, such as Figure 4 shown.

[0150] Figures 5A to 5C Results of the conventional approach in terms of lateral resolution and depth of focus are presented.

[0151] Specifically, Figure 5A and Figure 5B The results for an imaging system using an ideal Gaussian beam with a conventional common path for illumination and collection are shown. As shown, the PSF of a tightly focused Gaussian beam (about 3.2 μm FWHM) degrades rapidly away from the focus ( Figure 5A ), while the PSF of a Gaussian beam with a relatively large focal depth (about 1.25 mm) shows a significant sacrifice in lateral resolution ( Figure 5B Obviously, such a conventional imaging system with a lateral resolution comparable to that of the BICI lens 100 will have a significantly shorter depth of focus of 100 μm (see Figure 5A On the other hand, a conventional imaging system with a focal depth comparable to that of the BICI lens 100 would have a significantly compromised lateral resolution of 12 μm (see Figure 5B ).

[0152] Figure 5C A Bessel beam is shown with the same central lobe FWHM (3.2 μm) as the BICI lens 100. Such a Bessel beam, while providing an extended depth of focus, suffers from side lobes that carry most of the optical power (see references 27 and 28).

[0153] Figure 6An interferometer 200 using a BICI metasurface lens 100 is shown. As shown, the interferometer 200 includes a light source 202 for emitting a light beam 204. The light beam 204 is divided into two parts, respectively leading to a first path 206 toward a light detector 212 and a second path 208 toward an illumination path through a collimating lens assembly 214. The collimating lens assembly 214 forms the second path of light 208 into an illumination beam 132 toward the illumination lens portion 102 of the BICI lens 100. As described above, the illumination lens portion 102 of the BICI lens 100 refracts the illumination beam 132 so that the refracted illumination beam 132' intersects the imaging optical axis at the focal line 134.

[0154] The target 216 (e.g., a sample) is axially positioned to overlap the focal line 134 of the reflected illumination beam 132'. The reflected light forms a collection beam 142' toward the collection lens portion 104 of the BICI lens 100. The collection lens portion 104 refracts the collection beam 142', and the refracted collection beam 142 is injected into the receiving lens assembly 218. The receiving lens assembly 218 allows the received light to pass through the receiving light path 222 and be combined with the first light path 206. The combined light 224 is injected into the light detector 212.

[0155] The intensity profiles of the illumination beam 132 and the collection beam 142 are measured. The measured illumination beam 132 / 132' (see Fig. 7A ) and the collection beam 142 / 142'( Figure 7B ) form overlapping focal lines 134 along the z-axis. Figure 7C The imaging PSF (which is the product of the illumination intensity profile and the collection intensity profile) is shown, showing that a clear PSF with a small FWHM (about 3.7 μm at z=0) is maintained over a relatively large depth range (about 1.22 mm), where the position z=0 is about 2 mm from the BICI lens 100. These measurements are consistent with Figure 4 The results of the wave analysis shown are consistent (3.2 μm FWHM; 1.25 mm focal depth), although there may be minor deviations due to nonlinear response of the camera, alignment imperfections of the optical setup, and / or manufacturing errors. Despite the dispersion of the metasurface (see Refs. 33-37), the focal lines 134 of the illumination beam 132 / 132' and the collection beam 142 / 142' remain aligned over the entire spectrum of the light source, and the imaging PSF does not change significantly.

[0156] The BICI lens 100 is characterized by lateral resolution and depth of focus by imaging a resolution target made of sub-wavelength gold wires (200 nm wide and 50 nm high) fabricated on a glass substrate. The BICI lens 100 is coupled to an internal Fourier domain OCT system. Fig. 8AAs shown, lateral resolution and depth of focus are measured by scanning a gold wire 242 on the focal line 134 (not shown) at varying target metasurface distances. Figure 8B The imaging PSFs measured at three selected depth points are shown.

[0157] Figure 8C The measured resolution of the BICI lens 100 is shown compared to the theoretical resolution obtained from a Gaussian beam with the same lateral resolution (in a common path illumination-collection scheme), highlighting the ability of the BICI lens 100 to maintain high resolution over a large depth range, where position z=0 is approximately 2 mm from the metasurface. Figure 8C The results summarized in show that high lateral resolution (about 3.28 μm) is maintained over a depth range of more than 1.25 mm, consistent with wave analysis. To demonstrate these improvements, Figure 8C Also included is the analytical imaging PSF of an ideal Gaussian beam with the same lateral resolution, which demonstrates the reduced imaging depth of focus (approximately 12 times) compared to the BICI lens 100.

[0158] There are also techniques that use free-form metasurfaces to obtain mathematically optimized phase profiles for maximum depth of focus (see references 40 to 43). Although these techniques can alleviate the problem to some extent by providing a modest increase in depth of focus (about 1.5 to 2 times), they cannot be considered strategies that completely change the limitations of maintaining high-resolution imaging over relatively large depths.

[0159] The BICI lens 100 has no additional processing (see reference 44) or acquisition (see reference 10) burden and can be implemented in a variety of wavelength ranges because its operating principle does not change with wavelength. For example, the BICI lens 100 can be implemented in broadband OCT systems operating at shorter wavelengths with improved axial resolution. The wavelength ranges described herein are selected to avoid increased scattering at shorter wavelengths that primarily limits imaging depth (see references 10, 45, and 46).

[0160] Various configurations of illumination and collection beams have been previously reported in OCT (for speckle reduction (see Refs. 47 and 48) and deep tissue imaging (see Ref. 49)), two-photon microscopy (for enhanced signal-to-background ratio (see Refs. 50 to 52)), theta confocal (see Refs. 25 and 53), 4pi (see Ref. 54) and light sheet (see Ref. 55) microscopy (for improved resolution), and dark-field microscopy (see Ref. 56) (for enhanced sensitivity). These systems are designed to capture signal from a region near a single focal point. Therefore, imaging at moderate depths requires the use of very small translations of the objective relative to the imaging system (see Refs. 47 to 49) (at the expense of lateral resolution) or physical translation (see Refs. 25 and 50 to 56) (at the expense of imaging speed).

[0161] It is apparent that an optical arrangement for depth imaging with preserved lateral resolution should 1) focus light uniformly along the depth range (on the focal line), and 2) reject out-of-focus signals originating from points outside the focal line. Unlike previous work, the optical arrangement of the BICI lens 100 satisfies both criteria, enabling imaging of a relatively large depth range along which lateral resolution is preserved.

[0162] OCT is a coherent imaging technique that includes speckle, which is both an information carrier and a noise source (see Ref. 57). Signal-attenuating speckle is primarily due to the effects of multiple backscattering, while signal-carrying speckle is a result of single backscattered components whose spatial frequency content extends to the diffraction limit of the imaging optics (see Ref. 57). Magnified in proportion to the spot size, signal-carrying speckle originates from the focal region, while signal-attenuating speckle is produced by multiply scattered out-of-focus light. The BICI lens 100 is much less affected by speckle effects due to: 1) its high lateral resolution along the depth range, resulting in significantly smaller speckle size, 2) its ability to eliminate out-of-focus signals as well as multiple scattering effects, and 3) its ability to reject backreflections from the imaging optics.

[0163] Pathological changes in the early stages of diseases such as cancer are often very subtle and can be easily overlooked. High-resolution in vivo imaging maintained over a large depth range has the potential to enable early and accurate detection and diagnosis. By using metasurfaces to achieve this, the BICI lens 100 can be feasibly miniaturized into endoscopic devices (see references 58 and 59) for in vivo high-resolution imaging of internal organs.

[0164] The emergence of high-resolution optical imaging technology has impacted basic medical research and clinical applications. However, expanding the scope of application makes it necessary to overcome the main limitations in current technologies. By collecting imaging through bi-irradiation illumination, the trade-off between lateral resolution and depth of focus caused by diffraction is avoided, and three-dimensional high-resolution imaging is achieved. Although the BICI metasurface lens 100 is applied to OCT in the present disclosure, the basic concept is universal, and the BICI metasurface lens 100 can be applied to various imaging modalities, for example, confocal and two-photon microscopy.

[0165] Those skilled in the art will appreciate that various alternative embodiments are readily available. For example, although the metasurface in the above embodiments includes square nanopillars 162, in various embodiments, the metasurface may include other suitable nanostructures, such as nanopillars with circular or elliptical cross-sections.

[0166] In the above embodiment, the arcs 110 or circles 114 are concentric (see Figure 1C ). In some embodiments, arc 110 or circle 114 may not be concentric.

[0167] Although the illumination lens portion 102 and the collection lens portion 104 in the above embodiment have circular shapes of the same size, in alternative embodiments, the illumination lens portion 102 and the collection lens portion 104 may have any suitable shape and size.

[0168] In some embodiments, region 106 of BICI lens 100 may be transparent or translucent, but the area is prohibited or not allowed to be used.

[0169] In the above embodiment, the center 112 of the illumination lens portion 102 and the collection lens portion 104 is located relative to the optical center 108. In such Fig. 9A In some of the embodiments shown, the center 112 of the illumination lens portion 102 and the collection lens portion 104 is at an angle of less than 90° relative to the optical center 108. In such Fig. 9B In some of the embodiments shown, the center 112 of the illumination lens portion 102 and the collection lens portion 104 is at an angle greater than 90° relative to the optical center 108. However, Fig. 9A and Fig. 9B The lateral resolution in the illustrated embodiment may be reduced in the vertical and horizontal directions, respectively.

[0170] In the above embodiment, the illumination lens portion 102 and the collection lens portion 104 are located in adjacent quadrants relative to the optical center 108, thereby allowing the illumination path and the collection path to extend to diagonally opposite quadrants respectively and ensuring that the illumination path and the collection path do not overlap except on the focal line 134.

[0171] In such FIG. 10A to FIG. 10D In some alternative embodiments shown, the illumination lens portion 102 and the collection lens portion 104 may be located in diagonally opposite quadrants and symmetrical about the optical center 108. However, in these embodiments, the illumination path 132' and the collection path 142 overlap outside the focal line 134, as shown in Figures 9C and 9D. Wave analysis shows that this overlap may result in a reduction in PSF due to the presence of out-of-focus signals.

[0172] Fig.11A BICI lenses 100 according to some embodiments of the present disclosure are shown. In these embodiments, the BICI lens 100 may include two illumination lens portions 102 located in diagonally opposite quadrants (or diagonally opposite sides of the optical center 108) and symmetrical about the optical center 108, and one collection portion 104 in a quadrant adjacent to the two illumination lens portions 102 and symmetrical to the illumination lens portions 102 about a corresponding axis. In other words, the centers of each pair of circumferentially adjacent lens portions 102 and / or 104 are at right angles to the optical center 108. Although the two illumination paths in these embodiments may overlap outside the focal line 134, the collection path does not overlap with the illumination path.

[0173] Fig. 11B BICI lenses 100 according to some embodiments of the present disclosure are shown. The BICI lenses 100 in these embodiments are similar to Fig.11A The lenses shown, except that two diagonally opposite lens portions are collecting lens portions 104 , and a third lens portion adjacent to the two collecting lens portions 104 is an illumination lens portion 102 .

[0174] In some embodiments, the BICI lens 100 includes three lens portions (similar to Fig.11A and Fig. 11B Any circumferentially adjacent pair of lens portions of the three lens portions may be the illumination lens portion 102 , and the other lens portion may be the collection lens portion 104 .

[0175] In some embodiments, the BICI lens 100 includes three lens portions (similar to Fig.11A and Fig. 11BAny circumferentially adjacent pair of lens portions of the three lens portions may be the collecting lens portion 104 , and the other lens portion may be the illuminating lens portion 102 .

[0176] The arrangement of the illumination and collection beams in the BICI necessitates the use of a higher bend angle (β) to achieve a resolution equal to that obtained by imaging the focal point with an ideal diffraction limited lens (NA matched to the bend angle β). However, in some embodiments, this can be corrected using a BICI lens 100 having two illumination lens sections 102 and two collection lens sections 104. Fig.12 As shown, two illumination lens sections 102 are located in two diagonally opposite quadrants, and two collection sections 104 are located in the other two diagonally opposite quadrants. The illumination lens sections 102 and the collection lens sections 104 are symmetrical about respective axes.

[0177] In these embodiments, the two illumination paths overlap outside of the focal line 134, and the two collection paths also overlap outside of the focal line 134. However, the collection paths do not overlap with the illumination paths.

[0178] The BICI lens 100 in these embodiments maintains the desired bijection relationship at a higher resolution. Fig.13A and Fig. 13B Shows Figure 1A The resolution of the BICI lens shown (see Fig.13A )and Fig.12 The resolution of the BICI lens shown (see Fig. 13B ). Obviously, Fig.12 The BICI lens shown shows a higher resolution close to the diffraction limit (about 2 μm at NA=0.36; bending angle β=21° at 1300 nm).

[0179] In some embodiments, the BICI lens 100 includes four lens portions (similar to Fig.12 Any circumferentially adjacent pair of lens portions among the four lens portions may be the illumination lens portion 102 , while the other two lens portions may be the collection lens portions 104 .

[0180] In some embodiments, the BICI lens 100 can be fabricated by manufacturing a lens 100' having a metasurface having a pattern of multiple concentric circles 114 centered at the optical center 108, such as Fig.14A Then, except for the area of ​​the illumination lens portion 102 and the collection lens portion 104, the lens 100' is masked to be opaque. Fig. 14B As shown, the BICI lens 100 is then formed.

[0181] In some embodiments, the illumination lens portion 102 and the collection lens portion 104 may be fabricated first and then embedded or otherwise coupled to the BICI lens 100 .

[0182] like Fig.15 As shown, in some embodiments, the BICI lens 100 can include a metasurface having a pattern of multiple concentric circles 114 centered at the optical center 108. In use, an illumination beam (not shown) can be aimed at the region 102 to use the region 102 of the BICI lens 100 as an illumination lens portion 102, and a light collector (not shown) can be aimed at the region 104 to use the region 104 as a collection lens portion.

[0183] In some embodiments, some illumination lens portions 102 and collection lens portions 104 may be asymmetrical.

[0184] In the above embodiments, the BICI lens 100 is shown as having a circular shape. In some embodiments, the BICI lens 100 can have any suitable shape, for example, Fig.16 Square shape shown.

[0185] In the above embodiments, the optical center 108 of the BICI lens 100 is also its center of mass. Fig.17 In the embodiment shown in the figure, the optical center 108 of the BICI lens 100 can be offset from its center of mass 302. Each of the metasurfaces of the lens portions 102 and 104 has a pattern of arcs 110 that are part of a plurality of concentric circles 114 centered at the optical center 108.

[0186] In such Fig.18 In the above-described embodiment shown, the BICI lens 100 may include a plurality of illumination lens portions 102 and collection lens portions 104 in a circular lens body 312. Each lens portion 102, 104 has a maximum size fit in a corresponding quadrant, and the BICI lens 100 has a plurality of unusable portions 106 distributed around the illumination lens portion 102 and the collection lens portion 104.

[0187] Those skilled in the art will appreciate that the illumination lens portion 102 and / or the collection lens portion 104 may be implemented using other suitable optical structures. For example, in some embodiments, the illumination lens portion 102 and / or the collection lens portion 104 and the linear phase profile in equation (1) may be implemented using an axicon, which is a lens having a conical surface.

[0188] like Fig.19A and Fig.19B As shown, the BICI lens 100 has a conical shape, wherein the optical axis (i.e., z-axis) passes through its vertex 108. The illumination lens portion 102 and the collection lens portion 104 are located at a distance from the optical axis in adjacent quadrants of the xy plane and are symmetrical about, for example, the x-axis (i.e., positioned similarly to the illumination lens portion 102 and the collection lens portion 104 described above). Preferably, each of the illumination lens portion 102 or the collection lens portion 104 is at an angle of φ=45° to the x-axis relative to the center 112 of the optical center 108. As will be appreciated by those skilled in the art, similar to the above description, the illumination lens portion 102 and the collection lens portion 104 in these embodiments can be obtained by making the rest of the first surface 322 opaque, by making the rest of the transmission surface 324 opaque, or by aligning the illumination beam and the light collector (not shown) to the position of the illumination lens portion 102 and the collection lens portion 104.

[0189] BICI lenses implemented using axicons may not offer the same advantages as BICI lenses using metasurfaces. For example, for the same lateral resolution, a BICI lens using an axicon may have a shorter depth of focus than a BICI lens using a metasurface. Because the resolution achieved by a BICI lens is primarily determined by the bend angle β, a metasurface can be used to precisely achieve the desired bend angle given a desired resolution. On the other hand, it may be more difficult to design a BICI lens using an axicon to achieve the same bend angle β and thereby achieve the same resolution. Furthermore, it may be more difficult to achieve a wide range of performance and achieve miniaturization for endoscopic applications with BICI lenses using an axicon.

[0190] In the above embodiments, the BICI lens 100 includes one or more illumination lens sections 102 and one or more collection lens sections 104 offset from the optical axis, wherein the illumination lens section 102 and the collection lens section 104 form a focal line 134 along the optical axis. In some embodiments, the illumination lens section 102 and the collection lens section 104 may be conventional lenses that do not form a focal line 134 but have sufficient depth of focus (although their lateral resolution may be reduced compared to the above illumination lens section 102 and the collection lens section 104). By utilizing spatially separated illumination paths and collection paths, the BICI lenses in these embodiments may still provide better performance than conventional lenses.

[0191] In the above embodiments, the BICI lens 100 includes one or more illumination lens portions 102 and one or more collection lens portions 104 that are offset from the optical axis. In some embodiments, the BICI lens 100 may only include one or more illumination lens portions 102 that are offset from the optical axis. In these embodiments, light collection and imaging of the sample or target object may be performed using other suitable methods.

[0192] In some embodiments, the BICI lens 100 may only include one or more collection lens portions 104 that are offset from the optical axis. In these embodiments, illumination of the sample or target object may be performed using other suitable means.

[0193] In such Fig. 20A and Fig. 20B In some embodiments shown, the BICI lens 100 is similar to Figure 1A The lenses shown, except that the BICI lens 100 in these embodiments includes a collection lens portion 104 that is distal or offset from the optical center 108 and does not include any illumination lens portion.

[0194] In these embodiments, focal points (e.g., focal points 402 to 412 along focal line 134) are mapped into arcs 422 to 432, and subsequently mapped into individual pixels 442 to 452 of a light detector 462, such as a camera having a row light sensor (i.e., a light sensor having a plurality of light detecting pixels arranged in a row). This is achieved when the phase of the collection lens portion 104 is designed to map the focal line 134 onto the pixels of the light detector 462. Such a BICI lens 100 can resolve depth information independently of OCT.

[0195] In the above-described embodiment, the illumination lens portion 102 and the collection lens portion 104 are usable areas for illumination and imaging purposes, while other areas (e.g., Figure 1A The illustrated area 106) is an unusable area (optically unusable (eg, opaque) or unusable) where use is prohibited or not permitted.

[0196] Fig.21 1 is a schematic diagram showing a BICI lens 100 for fast high-resolution ellipsometry (hereinafter referred to as a "bi-illumination collection ellipsometry (BICE)" lens). As shown in the figure, the BICE lens 100 includes two illumination lens portions 102 and two collection lens portions 104 (similar to Fig.12 100). The illumination lens portion 102 and the collection lens portion 104 preferably have a circular shape of the same size.

[0197] Each of the illumination lens portion 102 and the collection lens portion 104 is located at a distance from the optical axis. The two illumination lens portions 102 are located in two diagonally opposite quadrants (or two diagonally opposite sides of the optical center 108) and are symmetrical with respect to the optical center 108. The two collection lens portions 104 are located in the other two diagonally opposite quadrants (or the other two diagonally opposite sides of the optical center 108) and are symmetrical with respect to the optical center 108. The illumination lens portion 102 and the collection lens portion 104 are symmetrical about the corresponding axis.

[0198] The illumination lens section 102 and the collection lens section 104 are generally the same as those described above (see also reference 62). More specifically, the illumination lens section 102 and the collection lens section 104 are generally focused within a continuous focal line 134 along the optical axis (i.e., the z-axis), thereby ensuring high-resolution imaging along the entire depth range. As described above, this requires that all incident light rays whose projections on the lenses 102 or 104 are at the same distance from the optical axis be bent toward the optical axis at the same angle.

[0199] In these embodiments, the metasurfaces of the two illumination lens portions 102 are used to illuminate the substance with light of two orthogonal polarization states, and the metasurfaces of the two collection lens portions 104 are used to collect light of two orthogonal polarization states from the substance.

[0200] Each of the illumination lens portion 102 and the collection lens portion 104 includes a metasurface that allows light of a corresponding polarization state to pass therethrough. Fig.21 In the illustrated embodiment, the illumination lens portion 102 is designed to focus light of different circular polarization states onto the focal line 134. For example, Fig. 22 As shown, illumination lens portion 102A is designed to focus left circularly polarized (LCP) light 502 onto focal line 134, while illumination lens portion 102B is designed to focus right circularly polarized (RCP) light 504 onto focal line 134. In these embodiments, the metasurface of each of illumination lens portion 102 and collection lens portion 104 changes the polarization state of light 502 or 504 passing therethrough, for example, from LCP to RCP, or from RCP to LCP.

[0201] The collection lens portion 104 is designed to collect light from the LCP and RCP of the material within the focal line 134, wherein the collected light corresponds to the excitation or illumination of the light incident from the illumination lens portions 102A and 102B, respectively. Fig.23As shown, the collecting lens portion 104A is designed to collect light 512 of the LCP, while the collecting lens portion 104B is designed to collect light 512 of the RCP.

[0202] In some embodiments, the illumination rays 502 and 504 can be separated or isolated by time division multiplexing and / or frequency division multiplexing. For example, in one example, when the light 504 incident on the illumination lens 102B is delayed in time relative to the light 502 incident on the illumination lens 102A, the isolation of the illumination rays 502 and 504 is achieved by using interferometry. In another example, the incident rays 502 and 504 on the illumination lenses 102A and 102B are modulated at various frequencies to be isolated from each other, and demodulated accordingly on the receiving side.

[0203] exist Fig.24 In the example shown, a single illumination lens portion (eg, LCP illumination lens portion 102A) is used to illuminate material within focal line 134 using LCP light illumination 502. In these embodiments, lens 100 may not include RCP illumination lens portion 102B. Fig.25 Collected light rays 512 and 514 under LCP light illumination 502 are shown.

[0204] exist Fig.26 In the example shown, a single illumination lens portion (eg, RCP illumination lens portion 102B) is used to illuminate material within focal line 134 using LCP light illumination 504. In these embodiments, lens 100 may not include LCP illumination lens portion 102A. Fig. 27 Collected light rays 512 and 514 under RCP light illumination 504 are shown.

[0205] In the above embodiments, RCP and LCP polarization states are used. The use of RCP and LCP is suitable for ellipsometry of linear birefringent materials.

[0206] In other embodiments, other suitable two orthogonal polarization states may be used. For example, in some embodiments, a linear polarization state may be used, for example, for materials with significant optical activity (eg, circular birefringence).

[0207] exist Figure 22 to Figure 27 In the example shown, the collected light 512 and 514 due to LCP and / or RCP excitation can be separated by using different time delays and / or different modulation frequencies. Fig.28 is a schematic diagram illustrating an ellipsometric system 600 using the BICE lens 100 according to some embodiments of the present disclosure, wherein different time delays are used to separate the collection rays 512 and 514 .

[0208] exist Fig.28 In the illustrated ellipsometric system 600 , a light 604 emitted from a light source 602 is split into two light rays 610 and 612 by a beam splitter 608 , wherein each of the two light rays 610 and 612 includes light in two orthogonal polarization states.

[0209] The light 610 is further split into two polarized light rays 616 and 618 of different polarization states by the polarization beam splitter 614. Each of the two polarized light rays 616 and 618 passes through a corresponding quarter wave plate (QWP) 620 to obtain phase-shifted polarized light rays 622 and 632, respectively. One of the phase-shifted polarized light rays (e.g., phase-shifted polarized light 632) is then guided by, for example, a plurality of reflectors 634 and 636 through an additional propagation path to introduce a time delay. In these embodiments, the introduced additional propagation path is adjustable for adjusting the introduced time delay of the phase-shifted polarized light 632.

[0210] The phase-shifted polarized light rays 622 and 632 (wherein the light 632 is also time-delayed) are then directed to the beam conditioning module 624, which outputs the illumination light rays 502 and 504 incident into the BICE lens 100 for illuminating the material within its focal line 134. The BICE lens 100 collects the light reflected and / or refracted from the material and outputs the collected polarized light rays 512 and 514 as described above, which are directed to the beam conditioning module 624.

[0211] The beam conditioning module 624 outputs polarized light rays 628 and 638, which are phase-shifted by passing through the corresponding QWP 646. The phase-shifted polarized light rays 652 and 654 output from the QWP 646 are then directed to polarization beam combiners 656 and 658, respectively.

[0212] The light 612 output from the beam splitter 608 is further split into two polarized light rays 706 and 708 of different polarization states by the polarization beam splitter 704. Each of the two polarized light rays 706 and 708 is guided by, for example, a plurality of reflectors 714 and 716 for the polarized light 706 and a plurality of reflectors 724 and 726 for the polarized light 708 to pass through a corresponding additional propagation path to introduce a corresponding time delay. In these embodiments, the additional propagation paths of the polarized light rays 706 and 708 are adjustable to adjust the time delay introduced therein. In addition, the time delay introduced into the polarized light rays 632, 706, and 708 may be different.

[0213] Time delayed polarized light rays 706 and 708 are then directed to polarization beam combiners 656 and 658, respectively.

[0214] Polarization beam combiner 656 combines light rays 652 and 706 having the same polarization state and outputs combined light 802, which is then directed to photodetector 806 (at Fig.28 denoted as “Detector X” in FIG.

[0215] Polarization beam combiner 658 combines light rays 654 and 708 having the same polarization state (orthogonal to the polarization state of light rays 652 and 706) and outputs combined light 812, which is then directed to photodetector 816 (at Fig.28 denoted as “Detector Y” in FIG.

[0216] Fig.28 Also shown are some other optical components that may be needed (depending on the implementation), such as lenses 606, 804, and 814 for shaping light rays 604, 802, and 812, respectively, as desired, and light reflectors 630, 702, 718, 722, and 728 for redirecting the paths of light rays 618, 612, 706, and 708, respectively, as desired. Ellipsometry system 600 may also include other optical components as desired.

[0217] Fig.29 is a schematic diagram showing an ellipsometric system 600 using a BICE lens 100 according to some embodiments of the present disclosure, wherein the collected light rays 512 and 514 are separated using different frequencies. The ellipsometric system 600 in these embodiments is similar to Fig.28 The ellipsometric system is shown, except that the ellipsometric system 600 in these embodiments includes an optical modulator 822 for adjusting the frequency of the light 622 and another optical modulator 824 for adjusting the frequency of the light 632, rather than using an additional propagation path for the light 632.

[0218] Fig.30 is a schematic diagram showing a beam conditioning module 624 that uses a knife-edge prism and a reflector to separate the light and couple the illumination light and collection light from the BICE lens 100 to the rest of the system 600 . Fig.31A shows the path of the illumination light, and Fig.31B The paths of the collected rays are shown.

[0219] As indicated by arrow 840, polarized light 622 is directed to a reflector 842, such as a mirror, which reflects polarized light 622 to a knife edge prism 844. Knife edge prism 844 directs polarized light 622 to a primary knife edge prism 846, which outputs polarized light 622 as illumination light 502 for incident on BICE lens 100.

[0220] Similarly, as indicated by arrow 860, polarized light 632 is directed to reflector 852, e.g., a mirror that reflects polarized light 632 to knife edge prism 854. Knife edge prism 854 directs polarized light 632 to primary knife edge prism 846, which outputs polarized light 632 as illumination light 504 for incident on BICE lens 100.

[0221] As described above, the BICE lens 100 collects light from the focal line 134. As indicated by arrow 880, the collected light 512 is directed to the primary knife-edge prism 846 of the beam conditioning module 624, which directs the collected light 512 (renumbered as 628) to the knife-edge prism 844. The knife-edge prism 844 then directs the collected light 628 to the reflector 856, which outputs the collected light 628 from the beam conditioning module 624.

[0222] Similarly, as indicated by arrow 890, the collection light 514 is directed to the primary knife edge prism 846 of the beam conditioning module 624, which directs the collection light 514 (renumbered as 638) to the knife edge prism 854. The knife edge prism 854 then directs the collection light 638 to the reflector 858, which outputs the collection light 638 from the beam conditioning module 624.

[0223] The BICE lens 100 disclosed herein combines the principles of ellipsometry with those of a BICI lens to provide fast, high-resolution ellipsometry over a relatively large depth range.

[0224] In some embodiments, the BICE lens 100 can be readily implemented in an endoscopic setting using fiber optic components and gradient refractive index (GRIN) lenses to collimate light toward the BICE lens 100 located at the distal end of the endoscope.

[0225] Although the embodiments have been described above with reference to the accompanying drawings, those skilled in the art will appreciate that changes and modifications may be made without departing from the scope defined by the appended claims.

[0226] References:

[0227] Listed below are references cited throughout this disclosure, the contents of each reference are hereby incorporated by reference in their entirety.

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Claims

1. A lens comprising: an optical center and an optical axis passing through the optical center; as well as one or more lens portions; The one or more lens portions include at least a first lens portion for refracting light of a predefined polarization state incident thereon at right angles from a first side to the optical axis on a second side at a constant bending angle, thereby defining a focal line on the second side along the optical axis.

2. The lens according to claim 1, wherein: The at least first lens portion is located a distance from the optical center.

3. The lens according to claim 1 or 2, wherein: The at least first lens portion comprises the first lens portion and a second lens portion; wherein the centers of the first lens portion and the second lens portion are located on diagonally opposite sides of the optical center; and The first lens portion and the second lens portion are configured to allow light of orthogonal polarization states to pass therethrough.

4. The lens according to any one of claims 1 to 3, wherein: The one or more lens portions further include: At least a third lens portion for refracting light irradiated onto the third lens portion from the focal line on the second side at the constant bending angle to the first side in a direction parallel to the optical axis.

5. The lens according to claim 4, wherein: The at least third lens portion comprises the third lens portion and a fourth lens portion; wherein centers of the third lens portion and the fourth lens portion are located at diagonally opposite sides of the optical center; and The third lens portion and the fourth lens portion are configured to allow light of orthogonal polarization states to pass therethrough.

6. The lens according to claim 5, wherein: For a two-dimensional (2D) coordinate system defined on the lens with its origin at the optical center, each of the one or more lens portions is located in a corresponding quadrant of the 2D coordinate system.

7. The lens according to claim 6, wherein: The centers of each pair of circumferentially adjacent lens portions of the one or more lens portions are at right angles to the optical center.

8. The lens according to any one of claims 1 to 7, wherein: The bending angle is 21°.

9. The lens according to any one of claims 1 to 8, wherein: Each of the one or more lens portions has a circular shape.

10. The lens according to claim 9, wherein: Each of the one or more lens portions has a diameter of 1.1 millimeters (mm).

11. The lens according to any one of claims 1 to 10, wherein: Each of the one or more lens portions includes a metasurface coupled to a substrate.

12. The lens according to claim 11, wherein: Each metasurface includes a plurality of nanopillars in an arc-shaped pattern, wherein the arcs are portions of a plurality of concentric circles centered about the optical center.

13. The lens according to claim 12, wherein: The plurality of nanopillars have a cubic shape with a square cross-section; and Wherein, the plurality of nanorods have the same height and different widths.

14. The lens according to claim 13, wherein: The plurality of nanorods have a width between 80 nanometers (nm) and 300 nm.

15. The lens according to claim 14, wherein: The height of the plurality of nanorods is 750 nm.

16. The lens according to claim 14 or 15, wherein: A pair of adjacent nanopillars in the plurality of nanopillars has a center-to-center distance of 370 nm.

17. The lens according to any one of claims 1 to 16, wherein: The lens is opaque except at the one or more lens portions.

18. The lens according to any one of claims 1 to 17, further comprising: An axicon having its vertex as said optical center; Wherein, the one or more lens portions are defined on the axicon.

19. An imaging device comprising: A polarization beam splitter, used for splitting the light into a first polarized light and a second polarized light in orthogonal polarization states; a beam adjustment module, configured to receive the first polarized light and the second polarized light, and output the first polarized light and the second polarized light to the lens according to any one of claims 1 to 18; as well as An adjustment module is used to introduce a time delay into at least one of the first polarized light and the second polarized light and / or adjust the frequency of at least one of the first polarized light and the second polarized light before inputting the first polarized light and the second polarized light into the beam adjustment module.

20. The imaging device according to claim 19, wherein The lens is a lens according to claim 6 or any one of claims 6 to 18 dependent on claim 6; Wherein, the beam adjustment module comprises: Main blade prism, a first knife-edge prism for directing the first polarized light to the primary knife-edge prism, and A second knife-edge prism for directing the second polarized light to the primary knife-edge prism; and Wherein, the main blade prism is configured to: outputting the first polarized light and the second polarized light to the lens, receiving a third light ray and a fourth light ray from the lens, directing the third light to the first knife-edge prism, and The fourth light is directed to the second knife edge prism.

21. A method of manufacturing a lens according to any one of claims 1 to 18, the method comprising: depositing an amorphous silicon (a-Si) layer on the substrate using plasma enhanced chemical vapor deposition; Coating a layer of negative photoresist on the a-Si layer; generating an etch pattern on the layer of negative photoresist using electron beam lithography (EBL); as well as Deep reactive ion etching is used to generate a-Si nanopillars for forming the metasurface of the one or more lens portions.

22. A method according to claim 21 when appended to claim 12, wherein: The etching pattern corresponds to the arc pattern.

23. The method of claim 21 when appended to claim 12, wherein: The etching pattern corresponds to the plurality of concentric circles.

24. The method according to claim 23, further comprising: Mask one or more unusable areas as opaque.

25. A method of using a lens according to claim 5 or any one of claims 6 to 18, the method comprising at least one of the following: aiming a first light beam at the first lens portion; and collecting a third light beam and a fourth light beam from the third lens portion and the fourth lens portion, respectively; in, The cross-sectional size of the first light beam matches the size of the first lens portion.

26. A lens comprising: an optical center and an optical axis passing through the optical center; as well as a plurality of lens portions, the plurality of lens portions comprising: a first lens portion and a second lens portion on diagonally opposite first and second quadrants of a plane perpendicular to the optical axis, for refracting light from a first side to a second side; and a third lens portion on a third quadrant of the plane, for refracting light from the second side to the first side; wherein the first lens portion and the second lens portion are configured to refract light incident thereon at right angles from the first side to the optical axis on the second side at a constant bending angle, thereby defining a focal line on the second side along the optical axis, and the third lens portion is configured to refract light incident from the focal line on the second side at the constant bending angle to the first side parallel to the optical axis; or wherein the third lens portion is configured to refract light incident thereon at a right angle from the second side to the optical axis on the first side at the constant bending angle, thereby defining the focal line on the first side along the optical axis, and the first lens portion and the second lens portion are configured to refract light incident from the focal line on the first side at the constant bending angle to the second side parallel to the optical axis.

27. The lens according to claim 26, wherein: The plurality of lens portions are distal from the optical center.

28. The lens according to claim 26 or 27, wherein: Centers of the first lens portion and the third lens portion or centers of the second lens portion and the third lens portion are at right angles to the optical center.

29. The lens according to any one of claims 26 to 28, wherein: The plurality of lens portions further comprises: The fourth lens portion on the fourth quadrant of the plane is used to refract light incident from the focal line on the second side at the constant bending angle to the first side parallel to the optical axis; or to refract light incident thereon at a right angle from the second side to the optical axis on the first side at the constant bending angle, thereby refracting to the focal line of the first side.

30. The lens according to any one of claims 26 to 29, wherein: The bending angle is 21°.

31. The lens according to any one of claims 26 to 30, wherein: Each of the one or more lens portions has a circular shape.

32. The lens according to claim 31, wherein: Each of the one or more lens portions has a diameter of 1.1 mm.

33. The lens according to any one of claims 26 to 32, wherein: Each of the one or more lens portions includes a metasurface coupled to a substrate.

34. The lens according to claim 33, wherein: Each metasurface includes a plurality of nanopillars in an arc-shaped pattern, wherein the arcs are portions of a plurality of concentric circles centered about the optical center.

35. The lens according to claim 34, wherein: The plurality of nanopillars have a cubic shape with a square cross-section; and Wherein, the plurality of nanorods have the same height and different widths.

36. The lens according to claim 35, wherein: The width of the plurality of nanorods is between 80 nm and 300 nm.

37. The lens according to claim 36, wherein: The height of the plurality of nanorods is 750 nm.

38. The lens according to claim 36 or 37, wherein: A pair of adjacent nanopillars in the plurality of nanopillars has a center-to-center distance of 370 nm.

39. The lens according to any one of claims 26 to 38, wherein: The lens comprises an axicon having its vertex as the optical center; and Wherein, the one or more lens portions are defined on the axicon.

40. The lens according to any one of claims 26 to 39, wherein: The lens is opaque except at the one or more lens portions.

Images