Aperture-metasurface and hybrid refractive-metasurface imaging system

Abstract

The invention relates to an aperture-metasurface and a mixed refractive-metasurface imaging system. Hybrid imaging systems incorporating conventional optical elements and metasurface elements and light sources and / or detectors, and methods of making and operating such optical arrangements, are provided. Systems and methods describe integrating apertures with metasurface elements and integrating refractive optics with metasurface elements in illumination sources and sensors.

Description

[0001] This application is a divisional application of the patent application for invention titled "Pore-Metasurface and Hybrid Refractive-Metasurface Imaging Systems" with the application date of July 24, 2020, application number 202080060755.4. Technical Field

[0002] The present disclosure relates to optical arrangements of metasurface elements, integrated systems having refractive optical devices, light sources, and / or detectors and such metasurface elements, and methods of manufacturing such optical arrangements and integrated systems. Background Art

[0003] Metasurface elements are diffractive optical devices in which individual waveguide elements have sub-wavelength spacing and a planar profile. Metasurface elements have recently been developed for use in the UV-IR band (300 to 10,000 nm). Compared with traditional refractive optical devices, metasurface elements abruptly introduce a phase shift into the light field. This enables the thickness of the metasurface element to be comparable to the wavelength of the light at which the metasurface element is designed to operate, while the thickness of a traditional refractive surface is 10 to 100 times (or more) greater than the wavelength of the light at which the refractive surface is designed to operate. Additionally, metasurface elements do not vary in the thickness of their constituent elements and can thus shape light without any curvature, which is required for refractive optical devices. Compared with traditional diffractive optical elements (DOEs), such as binary diffractive optical devices, metasurface elements can impart a range of phase shifts to the incident light field. At least the metasurface element can have a phase shift between 0 and 2π, where the range has at least 5 different values, while a binary DOE can only impart two different phase shift values and is typically limited to phase shifts of 0 or 1π. Compared with multi-level DOEs, metasurface elements do not require a change in the height of their constituent elements along the optical axis, and only the in-plane geometry of the metasurface element features changes. Summary of the Invention

[0004] This application relates to optical arrangements of metasurface elements, integrated systems having light sources and / or detectors and such metasurface elements, and methods of manufacturing such optical arrangements and integrated systems.

[0005] Many embodiments relate to an imaging system comprising:

[0006] at least one image sensor;

[0007] a substrate layer having a substrate thickness, disposed at a first distance above the at least one image sensor, the substrate layer being configured to be transmissive to a target wavelength of light, the substrate layer having a first surface remote from the at least one image sensor and a second surface proximate to the at least one image sensor;

[0008] A pore, which is disposed on the first surface of the substrate and has a pore opening disposed therein; and

[0009] A single layer of a plurality of identical or distinct nanostructured elements, which includes a metasurface disposed on the second surface, such that light incident on the pore opening passes through at least a portion of the metasurface, such that a specified angular deflection is thereby imposed;

[0010] wherein the distance between the pore and the layer of metasurface elements is separated by a second distance determined by the substrate thickness; and

[0011] wherein the pore and the layer of metasurface elements are configured to collect light having a specified operating bandwidth across a specified field of view and shift the incident light such that it is focused on the at least one image sensor at a chief ray angle of zero or near zero degrees.

[0012] In still many embodiments, the system further includes a glass cover disposed on top of the at least one image sensor.

[0013] In still many others, the first distance is determined by a spacer layer including one of a solid-state spacer material or an air gap.

[0014] In yet still many embodiments, the field of view is at least ±30 degrees.

[0015] In yet still many embodiments, the system further includes a narrow-band optical filter disposed between the metasurface element and the at least one image sensor.

[0016] Various embodiments relate to an imaging system, which includes:

[0017] At least one image sensor;

[0018] A substrate layer having a substrate thickness, the substrate layer being configured to be transmissive to a target wavelength of light, the substrate layer having a first surface remote from the at least one image sensor and a second surface proximate to the at least one image sensor;

[0019] A pore, which is disposed above the substrate and has a pore opening disposed therein; and

[0020] A single layer of a plurality of identical or distinct nanostructured elements, which includes a metasurface disposed on one of the first surface or the second surface, such that light incident on the pore opening passes through at least a portion of the metasurface, such that a specified angular deflection is thereby imposed;

[0021] wherein the distance between the pore and the metasurface layer is separated by a first distance; and

[0022] Wherein the pores and the metasurface layer are configured to collect light having a specified operating bandwidth across a specified field of view and shift the incident light such that it is focused on the at least one image sensor at a chief ray angle of zero or near zero degrees.

[0023] In various further embodiments, the system further includes an air gap between the second surface of the substrate and the image sensor.

[0024] In still various embodiments, a spacer layer is disposed within the air gap.

[0025] In yet various further embodiments, the metasurface layer is disposed on the first surface.

[0026] In yet various further embodiments, the system further includes a narrowband optical filter disposed on the second surface between the metasurface element and the at least one image sensor.

[0027] In yet various further embodiments, at least a portion of the pores is interconnected with the first surface.

[0028] In yet various further embodiments, the metasurface layer is disposed on the second surface.

[0029] In yet various further embodiments, the image sensor is in contact with the second surface.

[0030] In yet various further embodiments, the field of view is at least ±30 degrees.

[0031] Certain embodiments relate to an imaging system comprising:

[0032] At least one image sensor;

[0033] A substrate layer having a substrate thickness, the substrate layer being configured to be transmissive to a target wavelength of light, the substrate layer having a first surface remote from the at least one image sensor and a second surface proximate to the at least one image sensor;

[0034] At least one refractive lens disposed above the substrate and configured to focus incident light on the first surface of the substrate layer; and

[0035] A single layer of a plurality of identical or distinct nanostructured elements including a metasurface disposed on one of the first surface or the second surface such that light incident on the at least one refractive lens passes through at least a portion of the metasurface element such that an angular deflection is thereby imparted;

[0036] Wherein the distance between the at least one refractive lens and the layer of metasurface elements is separated by a first distance; and

[0037] Wherein the layers of the refractive lens and the metasurface element are configured to collect light having a specified operating bandwidth across a specified field of view and shift the incident light such that it is focused on the at least one image sensor at a chief ray angle of zero or near zero degrees.

[0038] In yet further embodiments, the system further includes an air gap between the second surface of the substrate and the image sensor.

[0039] In still further embodiments, a spacer layer is disposed within the air gap.

[0040] In still yet further embodiments, the metasurface layer is disposed on the first surface.

[0041] In still yet further embodiments, the system further includes a narrow-band optical filter disposed on the second surface between the metasurface element and the at least one image sensor.

[0042] In still yet further embodiments, at least a portion of at least one of the refractive lenses is interconnected with the first surface.

[0043] In still yet further embodiments, the metasurface layer is disposed on the second surface.

[0044] In still yet further embodiments, the image sensor is in contact with the second surface.

[0045] In still yet further embodiments, the field of view is at least ±30 degrees.

[0046] In still yet further embodiments, the at least one refractive lens is selected from the group consisting of plano-convex, convex-plano, biconvex, biconcave, plano-concave, or concave-plano.

[0047] In still yet further embodiments, the system includes at least two refractive lenses, the at least two refractive lenses including a convex-concave lens and a concave-convex lens.

[0048] In still yet further embodiments, the system includes at least three refractive lenses, the at least three refractive lenses including a convex-concave lens, a biconvex lens, and a concave-plano lens.

[0049] In various of the above embodiments, at least the imaging sensor and the metasurface have a rectangular geometry.

[0050] In yet various of the above embodiments, at least one refractive lens adjacent to the metasurface has a circular geometry.

[0051] In still various embodiments above, the image sensor is characterized by a vertical dimension v and a horizontal dimension h, and wherein the at least one refractive lens is characterized by an f-number N of the lens, the N being defined as N = f / D, where f is the focal length of the optical system and D is the diameter of the lens, and wherein the metasurface width is given by: = v + f / N, and wherein the metasurface length I is given by: l = h + f / N.

[0052] Additional embodiments and features are set forth in part in the following description, and, upon referring to this specification, the additional embodiments and features will in part become apparent to those skilled in the art or may be learned by practicing the present disclosure. A further understanding of the nature and advantages of the present disclosure may be realized by reference to the remainder of this specification and the drawings that form a part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] The description will be more fully understood with reference to the following drawings, which are presented as exemplary embodiments of the present invention and should not be construed as a complete recitation of the scope of the present invention.

[0054] Figure 1 A schematic illustration in accordance with an embodiment of the present invention is provided, which illustrates a pore-metasurface imaging system with a glass cover over an image sensor.

[0055] Figure 2 A schematic illustration in accordance with an embodiment of the present invention is provided, which illustrates a ray-tracing diagram that includes Figure 1 the chief ray angle at the image sensor plane of the pore-metasurface imaging system.

[0056] Figure 3 A schematic illustration in accordance with an embodiment of the present invention is provided, which illustrates a pore-metasurface imaging system having an air gap between the pore and the metasurface.

[0057] Figure 4 A schematic illustration in accordance with an embodiment of the present invention is provided, which illustrates a ray-tracing diagram that includes Figure 3 the chief ray angle at the image sensor plane of the pore-metasurface imaging system.

[0058] Figure 5 A schematic illustration in accordance with an embodiment of the present invention is provided, which illustrates a pore-metasurface imaging system having an air gap over the image sensor and a metasurface layer closer to the object plane.

[0059] Figure 6 A schematic illustration in accordance with an embodiment of the present invention is provided, which illustrates a pore-metasurface imaging system having an air gap over the image sensor and a metasurface layer closer to the image plane.

[0060] Figure 7Provided is a schematic diagram according to an embodiment of the present invention, which illustrates a pore-metasurface imaging system with an air gap and a spacer between pores above an image sensor and a metasurface.

[0061] Figure 8A Provided is a data graph according to an embodiment of the present invention, which shows relative illumination versus field of view for a pore-metasurface imaging system.

[0062] Figure 8B Provided is a data graph according to an embodiment of the present invention, which shows field of view versus distortion level for a pore-metasurface imaging system.

[0063] Figure 8C Provided is a data graph according to an embodiment of the present invention, which shows the modulation transfer function over a 40-degree field of view of a pore-metasurface imaging system.

[0064] Figure 8D Provided is an image of a standard test target captured using a pore-metasurface imaging system according to an embodiment of the present invention.

[0065] Figure 9 Provided is a schematic diagram according to an embodiment of the present invention, which illustrates a hybrid imaging system of a single refractive element and a metasurface.

[0066] Figure 10A and 10B Provided is a schematic diagram according to an embodiment of the present invention, which illustrates a hybrid imaging system of multiple refractive elements and a metasurface.

[0067] Figure 11A Provided is a schematic diagram of an image sensor wafer according to an embodiment of the present invention.

[0068] Figure 11B Provided is a schematic diagram of an image sensor die according to an embodiment of the present invention.

[0069] Figure 12A Provided is a schematic diagram of a spacer wafer according to an embodiment of the present invention.

[0070] Figure 12B Provided is a schematic diagram of a spacer according to an embodiment of the present invention.

[0071] Figure 13 Provided is a schematic diagram according to an embodiment of the present invention, which illustrates an integrated hybrid imaging system with refractive elements, metasurface elements, and a spacer.

[0072] Figure 14 Provided is a schematic diagram according to an embodiment of the present invention, which illustrates an integrated hybrid imaging system with a refractive element having a metasurface element.

[0073] Figure 15Provided is a schematic diagram according to an embodiment of the present invention, which illustrates a manufacturing process for a hybrid refractive element and a metasurface imaging system.

[0074] Figure 16 Provided is a schematic diagram according to an embodiment of the present invention, which illustrates an imaging system having a rectangular metasurface lens element.

[0075] Figure 17A And 17B Provided is a schematic diagram according to an embodiment of the present invention, which illustrates the imaging sensing ( Figure 17A ) and the relative sizes of the rectangular metasurface lens element ( Figure 17B ).

[0076] Figures 18A to 18D Provided is a schematic diagram according to an embodiment of the present invention, which illustrates an optical system of N pores on N rectangular lenses on a single image sensor. Detailed Description

[0077] Turning now to the figures, there is provided a hybrid imaging system having conventional optical elements and metasurface elements and a light source and / or detector, and methods of manufacturing and operating such optical arrangements. Many embodiments relate to systems and methods for integrating pores and metasurface elements in illumination sources and sensors. Various embodiments relate to systems and methods for integrating refractive optical devices and metasurface elements in illumination sources and sensors.

[0078] Many embodiments of optical imaging systems may have a single pore and a single metasurface layer that can be used to correct aberrations over a large field of view. Many embodiments of such single-pore and metasurface imaging systems are configured to be telecentric over a large field of view (e.g., having an incident angle of nearly 0 degrees at the image sensor plane), such that there is no attenuation of relative illumination over the field of view (e.g., such that the intensity of on-axis light is nearly the same as the intensity at the edge of the field of view).

[0079] In many embodiments, a hybrid refractive optical device and metasurface imaging system may include a metasurface element that is independent (i.e., not directly integrated into the system with a specific illuminator or sensor). In some embodiments, the optical system may consist of a single physical component or substrate with a metasurface element disposed on either side thereof. In some embodiments, multiple refractive optical devices may be combined with at least one metasurface element to fabricate a more complex system.

[0080] In embodiments of a hybrid pore or refractive optical device and a metasurface imaging system, the metasurface may be disposed on a surface of a support substrate facing the pore or facing the imaging system. In various embodiments, an air gap may be disposed between the pore and the metasurface structure and / or between the metasurface substrate and the imaging system. The air gap between the elements may further include a spacer structure to provide support for the elements.

[0081] In many embodiments, the metasurface elements may be standalone or may be embedded within another material. In various such embodiments, the choice of the embedding material includes a suitable choice of refractive index and absorption characteristics. In many such embodiments, the embedding material may provide mechanical stability and protection as well as additional design freedom, enabling the metasurface to perform the desired optical function.

[0082] In some embodiments, a spacer layer having a defined thickness (e.g., working distance) may be deposited on a CMOS image sensor, an LED, a VCSEL, etc. to implement an optical distance suitable for the desired camera design, illuminator design, or optimal system performance. In various such embodiments, the spacer layer material may be organic or inorganic and may have a refractive index lower than that of the dielectric elements constituting the metasurface. In some such embodiments, the thickness of the spacer layer may be modified to provide an appropriate optical spacing for a particular optical system.

[0083] Various embodiments also relate to methods of fabricating a hybrid metasurface imaging system. In some such embodiments, the method involves fabricating metasurface elements on a wafer having other devices such as a sensor or an illuminator, thereby avoiding in some embodiments expensive manufacturing processes such as mechanical assembly of small-sized elements or active alignment of optical devices and sensors. In some such embodiments, the metasurface elements may be integrated with a sensor (or illuminator) in a series of operations of semiconductor manufacturing. In many such embodiments, the sequence may include: (i) a sensor or an illuminator, (ii) an optional microlens array / collimator, an optional filter, an optional spacer layer, an optional metasurface element, an optional additional spacer layer, an optional refractive optical device or pore element, an optional anti-reflection (AR) layer, an optional protective layer. In many such embodiments, the element sequence may include: (i) a sensor or an illuminator, (ii) an optional microlens array / collimator, an optional filter, an optional spacer layer, an optional metasurface element, an optional additional spacer layer, and an optional refractive element or pore.

[0084] Embodiments for implementing a pore / metasurface imaging system

[0085] Typically, in order to form an optical system that corrects for aberrations over a selected field of view, the system must include multiple optical surfaces or multiple optical elements (e.g., two or more). This is true for both conventional refractive optical systems and metasurface optical systems. Specifically, only optical systems with two or more metasurfaces and sufficiently low aberrations over a certain field of view are shown. Various embodiments relate to imaging systems integrating pores with a single metasurface element, which allow the combined system to achieve high-quality imaging over a large field of view without attenuation of relative illumination and telecentricity over a large field of view (e.g., near 0-degree incidence at the image sensor plane).

[0086] Specifically, such systems can be used, for example, in imaging systems such as CMOS cameras (e.g., imaging systems in cellular phones, computers, tablet computers, etc., which are used to collect images of visible light scenes or scenes in the infrared for biometric verification). These CMOS imaging systems require an increased field of view (FOV), independent control of the chief ray angle (CRA) varying with field height at the CMOS image sensor, and minimal optical distortion of the scene being imaged. These terms will be understood to have their conventional meanings to those skilled in the art. For traditional imaging systems including refractive lenses, up to five or six unique lenses must be combined to perform this function. Similarly, conventional metasurface imaging systems implement multiple metasurface elements to provide sufficient degrees of freedom to adequately control these parameters (CRA, FOV, and minimizing distortion). However, various embodiments show that by combining pores with a single metasurface and combining the imaging system with a wide FOV, controllable distortion and controllable CRA can be achieved according to the embodiments.

[0087] Figures 1 to 7 Exemplary embodiments of this system are illustrated. As shown, in many such embodiments, the system (10a to 10d) generally includes a pore structure (12a to 12d) disposed at a set distance (13a to 13d) from a metasurface layer (14a to 14d), and the metasurface layer itself is at a set distance (15a to 15d) from an image sensor (16a to 16d). As will be described in more detail below, in such systems, it should be understood that the distance between the pore and the metasurface layer and the distance between the metasurface layer and the imaging system (e.g., the back focal length of the imaging system) can take the form of an air gap or an optically transmissive material (e.g., a substrate, etc.).

[0088] For the purposes of many embodiments, the pore structure (12a to 12d) includes: a first pore structure portion (18a to 18d) that is transmissive to light at the wavelength of interest; and a second pore structure portion (20a to 20d) that is at a certain distance (d ap)The internal energy is completely transmitted by light at the wavelength of interest. In various embodiments, such a pore structure does not impart an optical function (e.g., does not deflect light rays), but rather limits the lateral extent of the light beam entering the imaging system, or otherwise equivalently sets the entrance aperture of the imaging system.

[0089] For the purposes of many embodiments, the metasurface layer (14a to 14e) generally includes a plurality of nanostructures (22a to 22e) disposed on a substrate (24a to 24e) defined by a substrate thickness (t sub ), and the substrate can be formed of any material that is transmissive at the wavelength of interest. In many embodiments of the hybrid pore / metasurface imaging system, the metasurface layer is the only functional layer provided that significantly deflects the incident light to form a focused image (e.g., the metasurface layer serves as an arbitrary phase mask).

[0090] Embodiments of the nanostructures generally include the same or distinct three-dimensional elements (e.g., squares, circles, triangles, ellipses, etc.) having a characteristic size that is less than the wavelength of light within a specified operating bandwidth and configured to impose a phase shift on the illumination light in a plurality of planes separated by a macroscopic distance (a distance of 10 or more wavelengths), such that the metasurface layer performs a single optical function in a combined manner. Each individual metasurface in the optical system can be configured to have a particular 2D phase and transmission function φ(x,y) and t(x,y) that it implements. Although generally each metasurface can have a unique distribution of phase and transmission, the nanostructure elements that make up any metasurface embedded in the same material, having the same underlying composition, and at a particular wavelength are the same. In most practical single-wavelength applications, the transmittance can be configured to be maximized (close to 1) and uniform across the metasurface, while the phase can be configured to take values between 0 and 2π. Overall, according to embodiments, for a particular wavelength of interest, material system (metasurface material and embedding material), fixed thickness, and element spacing, the set of in-plane dimensions of the nanostructures that are formed can be configured such that a phase delay of 0 to 2π can be imparted on the incident light field. Thus, for different implementations of the metasurface design under fixed material and wavelength conditions, the only variable between the designs is the distribution of the appropriate nanostructure elements across the metasurface.

[0091] The metasurface layer according to some embodiments can be designed to be freestanding, i.e., the metasurface elements protrude from the end of the substrate and are separated only by an air gap, and this process is completed in this step. In other embodiments, the metasurface can be further configured to have an AR coating or mechanical protection. In some such embodiments, in order to protect the metasurface and provide improved functionality, the metasurface constituent elements and the substrate surface can be coated with some materials or material layers. In embodiments with embedded metasurface elements, the elements can be of any material having the desired optical properties and are embedded in a lower refractive index medium. The lower refractive index medium completely encapsulates the metasurface and extends a certain thickness above the metasurface elements. The lower refractive index medium acts as a protective barrier for the metasurface elements (i.e., provides mechanical stability), and provides additional design freedom for a system that allows optimization of certain properties (e.g., the total transmittance or efficiency of the metasurface).

[0092] The metasurface layer or metasurface system according to embodiments can be mass-produced using any suitable manufacturing technique, which includes, for example, lithography, machining, etching, and standard CMOS manufacturing techniques, as previously described in U.S. Patent Application No. 16 / 120,174, filed on August 31, 2018, the disclosure of which is incorporated herein by reference. The metasurface substrate can be any low refractive index material, such as, for example, polymers, SiO2, glass. The metasurface elements can also be of any material that has been optimized for a specific bandwidth, such as, for example, silicon, TiO2, alumina, metals, etc.

[0093] The imaging system can take the form of a single monolithic image sensor or a pixel array. Such image sensors and pixel arrays can take any suitable form that includes, for example, CMOS sensors.

[0094] Figure 1 Schematic illustrations of implementations of various embodiments of such hybrid pore / metasurface imaging systems are provided. As shown, in many embodiments, a substrate layer (24a) is provided that is transmissive to the wavelength of interest and has a thickness (t sub ) and has a pore structure (12a) that is not transmissive to light at the wavelength of interest and is completely transmissive to light at the wavelength of interest within a certain distance (d ap ) and is disposed on a first side away from the imager (16a); and a metasurface layer (14a) that is composed of nanostructures (22a) of the same height and is disposed on a second side close to the imager (16a). In such embodiments, the pore structure (12a) and the metasurface layer (14a) are separated by the substrate thickness (t sub)A defined first distance (13a). Additionally, in such embodiments, the pore structure (12a) and the metasurface layer (14a) may be deposited directly on the substrate (24a) or bonded via an adhesive. A distance (15a) defining a back focal length formed by an air gap (t air ) is disposed between the metasurface layer (14a) and the imager (16a). Although not required, many embodiments of such imaging systems may further include an optional glass cover or filter (26) that does not affect the imaging performance of the device but provides other functionality (e.g., optical or structural).

[0095] It should be understood that in such embodiments, the pores do not confer an optical function (do not deflect light rays), but rather only limit the lateral extent of the light beam that can enter the imaging system, or equivalently set the entrance aperture or f / # of the system. Meanwhile, the metasurface layer may include the sole functional optical layer, which in such embodiments deflects light rays significantly to form a focused image. In some such embodiments, the metasurface layer may act as an arbitrary phase mask that imparts any value of phase shift from 0 to 2π to the incident light at any radial position of the lens.

[0096] Referring to Figure 2 , there is provided according to Figure 1The ray tracing diagram of an exemplary embodiment of a system including a single pore (12a) and a single metasurface (14a) combined on a single substrate (24a) as described in. (Although not described in detail herein, it should be understood that these metasurface elements can be fabricated using methods such as those described herein or in the previously cited U.S. Patent Application No. 16 / 120,174, using suitable conformal deposition processes such as low-pressure chemical vapor deposition or atomic layer deposition.) In this exemplary embodiment, the pore and the metasurface element have been configured such that, in combination, they are capable of forming a good image across a wide FOV (in this example, ±40 degrees, however, it should be understood that this is not a limiting situation). It has been unexpectedly found that the embodiment of this single pore and single metasurface system as shown will naturally produce focused rays that are telecentric (i.e., having a 0-degree CRA) at the image plane. Simply put, while traditional refractive and metasurface designs require complex, multi-element systems to achieve such telecentric designs, according to an embodiment, only a single pore and a single metasurface element are required to achieve a similar telecentricity. This telecentricity in turn results in improved optical properties. Specifically, a low (e.g., zero or near-zero CRA) allows the bandwidth of the optical filter (26) to be narrowed for narrowband applications. In traditional refractive designs, especially for compact mobile applications, the CRA is typically about 15 degrees to 30 degrees. These larger CRAs in turn require a significant increase in the filter bandwidth, allowing more ambient light to enter the detector. In narrowband applications (e.g., near-IR VCSEL arrays), such ambient light can be a persistent source of noise. Thus, for example Figure 2 The embodiment of the combined metasurface / filter system shown in allows for better ambient light performance.

[0097] Although Figure 1 and 2 provide one arrangement of optical elements for a hybrid pore / metasurface imaging system, it should be understood that many other arrangements of the elements are possible. For example, Figure 3 provides a schematic illustration of an embodiment of an imaging system in which the positions of the air gap and the substrate have been interchanged. This structure allows for the formation of a thinner imaging system, but requires a more complex assembly process. Specifically, as Figure 3 shown in, such an embodiment of an imaging system includes a substrate (24b) that is transmissive to the wavelength of interest and has a provided thickness (t sub), the substrate has a metasurface layer (14b) composed of nanostructures (22b) of the same height disposed on a first side away from the imager (16b) and on a second side close to the imager (16b). In such embodiments, the metasurface layer (14b) and the imager (16b) can be directly joined via an adhesive or other suitable means. A distance (15b) defining the back focal length formed through the substrate thickness (t sub ) is disposed between the metasurface layer (14b) and the imager (16b). This distance serves as a free parameter to design an imaging system with optimal performance and will vary based on, for example, the desired f / # or field of view of the imaging system. In such embodiments, such an imaging system does not require the optional glass cover or filter used as the substrate (24b) in the embodiments shown in Figure 1 to provide such dual functionality. In such embodiments, a pore structure (12b) that is not transmissive to light at the wavelength of interest and is completely transmissive to light at the wavelength of interest within a certain distance (d ap ), and the metasurface layer (14b) separate a first distance (13b) defined by an air gap (t air ).

[0098] Reference Figure 4 , provides a ray tracing diagram of an exemplary embodiment of a through-system according to the embodiment illustrated in Figure 3 , the system including a single pore (12b) together with a single metasurface (14b) and an imager (16b) combined on a single substrate (24b). (Although not described in detail herein, it should be understood that these metasurface elements can be fabricated using suitable conformal deposition processes such as low-pressure chemical vapor deposition or atomic layer deposition as described herein or in the previously cited U.S. Patent Application No. 16 / 120,174.) In this exemplary embodiment, the pore and the metasurface element have been configured such that they can form a good image across a wide FOV (±40 degrees in this example, however, it should be understood that this is not a limiting condition) in a combined manner. It has been unexpectedly found that the illustrated embodiment of this single pore and single metasurface system will naturally produce focused rays that are telecentric (i.e., having a 0-degree CRA) at the image plane.

[0099] Although Figure 1 and 4 provide an arrangement of optical elements in which the elements are in direct contact with the image sensor for a hybrid pore / metasurface imaging system, it should be understood that many other arrangements of elements with a spacer disposed between the image sensor and the substrate supporting the metasurface layer are possible and can be implemented. For example, Figure 5 provides a schematic illustration of an embodiment of an imaging system in which a second air gap (28) is disposed within the imaging system.

[0100] Specifically, as shown in Figure 5 , an embodiment of such an imaging system includes a substrate (24c) that is transmissive to the wavelength of interest and has a provided thickness (t sub ), the substrate having a metasurface layer (14c) that consists of nanostructures (22c) of the same height disposed on a first side away from the imager (16c) and a second air gap (28) disposed between the second side of the metasurface layer near the imager (16c). An advantage of such an embodiment with an air gap is that, compared to an embodiment such as shown in Figure 1 , light passes through the system at a higher angle, thus allowing the total form factor of the metasurface optical system to be reduced. Additionally, the gap between the metasurface substrate and the image sensor allows other optical elements, including, for example, a microlens array or an optical color filter, to be introduced to improve the optical functionality of the imaging system.

[0101] In such embodiments, the metasurface layer (14c) and the imager (16c) can be directly deposited on the substrate (24c) or bonded via an adhesive. Such embodiments can also include a suitable spacer (30) to support the substrate (24c) and maintain the distance between the substrate and the image sensor (16c). A distance (15c) is disposed between the metasurface layer (14c) and the imager (16c), the distance defining the back focal length formed by the combination of the substrate thickness (t sub ) and the spacer height (t spacer ). The spacer (30) can be fixed to the image sensor (16c) and the substrate layer (24c), thereby creating a fixed distance for (t spacer ), or the substrate can be placed in a standard optical barrel and (t spacer ) can be adjusted after assembly. Such embodiments allow the surface (34) of the substrate (24c) near the image sensor (16c) to remain unpatterned, thereby allowing an optional optical filter to be directly integrated thereon.

[0102] Although an embodiment of a hybrid pore / metasurface configuration with an air gap above the image sensor has been described, as shown in Figure 6 , in various embodiments, the metasurface layer (14d) can also be disposed on the surface of the substrate (24d) near the image sensor (16d), the image sensor facing an air gap (32) supported by a spacer (30'). This implementation allows the metasurface elements to be protected from environmental contamination. Additionally, such embodiments allow the surface (34') of the metasurface substrate (24d) away from the image sensor (16d) to remain unpatterned, never allowing an optional optical filter to be directly integrated on the substrate. Again, in such embodiments, the spacer (30') can be fixed to the image sensor (16d) and the substrate (24d), thereby creating a fixed distance for (tspacer ) creates a fixed distance, or the substrate (24d) can be placed into a standard optical barrel and (t spacer ) can be adjusted after assembly.

[0103] Thus, Figure 5 and 6 the embodiments illustrated in show that the metasurface elements can be arranged inwardly or outwardly with respect to the air gap between the substrate and the image sensor. Figure 5 and 6 the production of the metasurface system illustrated in can follow, for example, the process described in U.S. Patent Application No. 16 / 120,174. The spacer layer can be any low refractive index material, e.g., polymer, SiO2, glass.

[0104] Although Figure 3 , 5 and 6 show embodiments of a hybrid pore / metasurface imaging system having pores and an air gap between the metasurface substrate, these embodiments would require a separate support structure to hold the pores and ensure that the pore distance (t air ) remains constant. However, the pore structure (12e) can also be directly attached to the substrate layer (24e). Figure 7 illustrates an exemplary embodiment of this imaging system. As shown, in this exemplary embodiment, the top pore (12e) has a pore body (36) that has a width d ap,top , which sets the entrance pore of the system, has a pore offset from the substrate by a certain distance (t ap ), and at a distance along the optical axis set by (t ap ) is set by the width of the metasurface layer and is tilted by a minimum angle set by half of the field of view of the imaging system with respect to the width of the pore given by (d ap,bottom ). Although Figure 7 the embodiment shown in depicts a system in which the metasurface layer (14e) is disposed on the surface of the substrate (24e) remote from the image sensor (16e), it should be understood that the metasurface layer can also be disposed on the surface (34”) of the substrate near the image sensor. Additionally, it should be understood that while the exemplary embodiment has a spacer structure (30”) and an air gap between the substrate (24e) and the image sensor (16e), the embodiment can omit this element and mount the substrate directly on top of the image sensor.

[0105] An attribute of embodiments of such telecentric designs is that the metasurface imaging system provides more uniform illumination (referred to by those skilled in the art as “relative illumination”) at the image sensor. Figure 8AA data plot is provided of the relative illumination of an exemplary system according to an embodiment, and the data plot shows that the relative illumination of the pore / supersurface imaging system is maintained at 100% across the entire field of view, which is a significant improvement compared to conventional systems that can have a difference between the center and the edge of 50% or more. Thus, embodiments of the imaging system are capable of collecting more total illumination across the full field of view. Embodiments of the supersurface system also provide additional design variations relative to traditional refractive lens systems. A typical complementary metal-oxide-semiconductor (CMOS) image sensor (CIS) requires microlenses to be associated with each pixel. Because there is a large variation in the chief ray angle (CRA) across a given sensor plane inherent to refractive optical systems, the microlens array on the CIS also requires complex CRA specifications. However, in embodiments of the supersurface system as described herein, the CRA of the microlens array can be configured to be a constant 0 degrees across the CIS, allowing for a simpler design and manufacture of the microlens array. Alternatively, in some embodiments, the microlens array can be completely removed from the CIS, eliminating a process step in CIS production. Additionally, such pore supersurface systems with 0 CRA allow for the limitation of a persistent problem in traditional imaging systems known to those skilled in the art as "pixel crosstalk". Traditional refractive systems that send light into an image sensor are prone to coupling light into adjacent pixels, which adds noise to the system.

[0106] Conventional supersurface systems can be configured with multiple supersurface layers to control the field of view (FOV) and distortion. Compared to typical systems including an equivalent number of refractive elements, introducing additional supersurface elements allows for the implementation of an arbitrary phase distribution individually, providing more degrees of freedom to control the path of light rays. In embodiments of current imaging systems using a single supersurface layer, it is not possible to control the CRA and correct grid distortion simultaneously. Therefore, a certain amount of grid distortion is inevitable. For example, Figure 8B A data plot is provided that illustrates Figure 1 the distortion varying with the field at the CMOS image sensor of the imaging system based on the embodiment shown in Figure 8C For an embodiment of the imaging system as shown in Figure 1 a plot of the modulation transfer function across the field of view is shown. Figure 8D A standard test image is provided that illustrates Figures 8A to 8C the grid distortion of the imaging system based on the embodiment shown in

[0107] Embodiments implementing a hybrid of refractive and supersurface elements

[0108] Although embodiments having pores and a single metasurface layer have been described, it is to be understood that embodiments also relate to hybrid systems of metasurface elements having refractive lens elements. Figure 9 Schematic illustrations of implementations of various embodiments of such hybrid refractive lens / metasurface imaging systems are provided. In many embodiments, the hybrid imaging surface consists of at least one of each of the following: a refractive lens having one or more curved surfaces, and a metasurface layer on a substrate, wherein all elements constituting the metasurface have the same height. More generally, a hybrid optical system can include any number of refractive elements and multiple metasurface layers. In certain embodiments, having metasurface elements on a substrate layer that is the final component before an image sensor provides a particular advantage of creating an imaging system with a so-called image space telecentric. Additionally, the substrate on which the metasurface layer is formed can have a set of deposited filter layers. As described in embodiments having filters, the metasurface layer is closer to the object plane of the imaging system, while the near-infrared filter is closer to the image sensor.

[0109] Figure 9 Illustrates exemplary embodiments of a hybrid refractive element / metasurface imaging system. In many embodiments, the system includes: at least one refractive optical device (38) disposed at a set distance from a substrate layer (40) that is transmissive of the wavelength of interest and has a thickness (t sub ), having a metasurface layer (42) formed of nanostructures (44) of the same height disposed on a first surface (45) thereof remote from an image sensor (46); an optional optical filter (48) disposed on a second side (47) of the substrate proximate the imager.

[0110] Although Figure 9 the embodiments shown illustrate a hybrid system having a single refractive optical device and a single metasurface layer, it is to be understood that embodiments can also have other arrangements of refractive optical devices. Figure 10A and 10B provide diagrams illustrating such metasurface / refractive hybrid systems. Specifically, Figure 10A illustrates a hybrid system including two refractive elements (50 and 51) and a metasurface layer (52), where the two refractive elements are convex-concave and concave-convex. Figure 10B illustrates a hybrid system including three refractive elements (54, 55, 56) and a metasurface element (58), where the three refractive elements are convex-concave, biconvex, and concave-flat, respectively.

[0111] Regarding the refractive optical elements in the hybrid system described above, i.e., the elements before the metasurface layer, it should be understood that the surface curvature of these elements can take any positive, negative, or infinite value. Thus, although specific arrangements of refractive elements are shown in the figures, the refractive elements can take any suitable form and combination for a particular application, including, for example, plano-convex, convex-plano, biconvex, biconcave, plano-concave, or concave-plano.

[0112] Embodiment of implementing an image sensor wafer

[0113] Imaging systems known in the art typically consist specifically of conventional refractive lenses (glass or plastic materials with at least one curved surface). According to an embodiment, a single metasurface layer is incorporated in combination with one or more curved refractive lenses. Unexpectedly, it has been found that including a single metasurface layer makes the optical system telecentric. Specifically, in many such embodiments, including a metasurface element as the final element before the image plane makes the system telecentric.

[0114] Embodiments of the metasurface layer can be integrated with a CMOS image sensor (CIS) as a glass cover and filter, while the refractive optical device can be assembled in a lens barrel, as is conventionally done in an optical imaging module. In certain embodiments, the glass on which the metasurface layer is fabricated can also be pre-deposited with a dielectric layer and act as a near-infrared bandpass or longpass filter in addition to being the glass cover for the CIS. Such embodiments provide a single component that functions in the optical imaging process and eliminate unwanted wavelengths from incident on the image sensor.

[0115] Although the above embodiments focus on hybrid metasurface imaging systems with a single sensor element, e.g., as Figures 1 to 10B shown, the metasurface element can also be integrated with an image sensor wafer containing multiple image sensor dies. Figure 11A The figure shows a schematic diagram illustrating an image sensor wafer. As shown, an embodiment can include an image sensor wafer (60) that includes a set of image sensor dies (62), although this is shown in a periodically spaced 2D array, it should be understood that the array need not be periodically spaced. As Figure 11B shown, each sensor die (62) in turn includes an image sensor active area (64). Although each image sensor can be the same, in many embodiments, the characteristics of each sensor are typically unique. Since each imager that makes up the array can have unique properties, an array with metasurface elements, each having uniquely designed properties, can also be advantageous.

[0116] It should be understood that only the source region (64) needs to be available for imaging. Regions outside the active region (66) of the image sensor can be used for attaching lenses or spacers. Additionally, in various embodiments, the metasurface substrate can be offset from the image array by a spacer. Figure 12A and 12B Exemplary embodiments of the spacer wafer (70) are described respectively in Figure 12A and 12B , the spacer wafer including: a plurality of spacer openings adapted to be attached to the sensor wafer; and spacer dies (72) adapted to be attached to the image sensor or lens dies. The design and thickness of the spacer layer will depend on the particular configuration, but in many embodiments, the thickness is configured to allow light from the illumination source to diverge sufficiently before interacting with the image sensor. Again, the function of each metasurface element in the array can typically be unique and can be patterned on top of each individual image sensor in the array using any suitable technique outlined, for example, in U.S. Patent Application No. 16 / 120,174. For example, the metasurface can be fabricated directly on each individual image sensor in the array, or a suitable dielectric spacer can be deposited on the image sensor and then the metasurface integrated on top of the combined dielectric layer and image sensor. In such embodiments, the metasurface can provide a specific radiation pattern for each image sensor, and the overall system (image sensor properties, geometric parameters, and metasurface-enabled radiation pattern) can be repeatedly optimized for a set of specific performance parameters.

[0117] In various other embodiments, a dielectric material having a refractive index less than that of the image sensor constituent material can be deposited and planarized such that a single metasurface can be patterned on top of the dielectric material. This is in contrast to embodiments where each image sensor in the array has a unique metasurface patterned on its facet. Again, in such embodiments, the combined system can be optimized to achieve the desired performance. Finally, in all of the above embodiments, wafer-level optical processes can be used to achieve the integration of the metasurface with the image sensor array. In such embodiments, the spacer layer can be air rather than a solid dielectric, Figure 13 and 14 and illustrations of exemplary embodiments of such devices are shown in Figure 13 and 14 .

[0118] Specifically, Figure 13Schematic diagrams showing embodiments including an image sensor die (74) and a lens die (76) separated by a spacer (78). In such embodiments, the spacer (78) controls the distance between the metasurface region (80) and the image sensor active region (82). The spacer in such embodiments may be attached to the image sensor die or the image sensor wafer, and then the lens may be attached to the spacer. Alternatively, the spacer may first be attached to the lens, and then the sensor is attached to the spacer. In such embodiments, the spacer may be attached using an adhesive (e.g., UV-cured epoxy or thermally cured epoxy), solder, or fusion bonding.

[0119] Figure 14 Describes exemplary embodiments that do not include a spacer. In such embodiments, the thickness of the lens die (84) determines the distance between the image sensor active region (86) and the metasurface region (88). The image sensor die (90) and the lens die (84) may be directly attached using an adhesive, solder, fusion bonding, bump bonding, etc. Alternatively, the image sensor wafer and the lens wafer may be directly attached at the wafer level as previously described.

[0120] As Figure 15 shown, in some embodiments, the refractive lens (91) of the hybrid system may first be assembled in a barrel (92), as is already known in the art. The metasurface element (94) may then be combined with the CMOS image sensor element (96), as described above with respect to Figure 13 and 14 described. These two sub-assemblies are then assembled together to form the final system. In such embodiments, the refractive lens may be configured to be screwed into a housing (98) such that the distance (t gap ) between the adjustable refractive element and the metasurface can be adjusted.

[0121] Embodiments implement

[0122] As is well known in the art, the image of a scene formed by a circular, radially symmetric lens or a system of circular, radially symmetric lenses will also be circular. Therefore, the geometry of the image formed is generally referred to as the image circle of the lens. However, in modern photography, the media for recording images (e.g., CMOS image sensors) typically have a rectangular shape. In camera design, the image circle of the lens is designed such that the diameter D image of the image circle is at least as large as the diagonal d of the image sensor. However, since the image sensor is rectangular, only a portion of the image circle falls on the image sensor. Therefore, most of the lens area onto which light from the scene is incident is not used for the final formation of the image from the camera system.

[0123] In a conventional injection-molded plastic refractive lens, the shape of the lens remains ideally circular. The circular shape is used because, from a manufacturing perspective, a circular shape and a radially symmetric lens are the easiest to achieve and the most reproducible in production. Additionally, the cost increase for manufacturing a circular lens with a larger area is minimal compared to a rectangular lens with a smaller area. Thus, conventional cameras use circular lenses, and only a portion of the light incident on the entire circular lens is collected by a rectangular image sensor. These portions of the circular lens where light is incident but does not contribute to light falling on the image sensor are not used in the final image formation.

[0124] For a metasurface lens according to various embodiments, the shape of the lens can be engineered such that the image it forms uniquely matches a specific image sensor size. Compared to a conventional refractive lens, in many such embodiments, the lens shape is configured to no longer be circular and the lens is configured to no longer form an image circle. In various embodiments, the metasurface lens is formed in a rectangular configuration with a specific size, and thus the scene image formed is also rectangular. In an ideal situation of this design embodiment, all the light incident on the rectangular metasurface lens falls on the image sensor. Embodiments of the metasurface with a rectangular lens break the radial symmetry, and thus the image formed by the lens is no longer circular or radially symmetric.

[0125] Thus, in many embodiments of a lens system, a metasurface lens element can be formed in a rectangular configuration. Advantages of such rectangular or non-circular lenses include: limiting the total area of the lens, eliminating portions of the lens that would otherwise be illuminated by light and then not form an image on the image sensor, and simplifying the post-processing of the lens wafer. Specific embodiments of rectangular metasurface lenses and imaging systems are described herein.

[0126] Many embodiments of a metasurface lens system with a non-circular configuration have the following in common: an entrance aperture that serves as the aperture stop of the lens system, and a metasurface lens that serves as the final active optical surface before the image sensor plane. In such embodiments, the cross-section of the entrance aperture (and the aperture stop) can be circular, as in a conventional optical system, while the metasurface lens can be patterned into a rectangular or any other shape.

[0127] Figure 16Descriptions of exemplary embodiments of a light-passing aperture metasurface are provided, where an imaging system (100) includes: a rectangular image sensor (102) offset from a single rectangular metasurface (104); and a circular entrance aperture (106) offset from the rectangular metasurface lens (104). In embodiments implementing a hybrid metasurface refraction system, the optical system includes an entrance aperture, at least one refractive lens, and a metasurface lens, and the metasurface lens is the last optical lens element before the image sensor in the system. In these embodiments of such hybrid systems, the entrance aperture and at least one refractive lens may still have a circular or radially symmetric cross-section. Thus, embodiments of such hybrid systems will include a circular aperture (106) offset from at least one circular refractive lens (not shown), and the at least one circular refractive lens is then offset from the rectangular metasurface lens (104), as Figure 16 shown therein. Similarly, in such embodiments, the metasurface lens has a rectangular size configured to match a specific image sensor. Although the examples herein describe an implementation where only the metasurface lens element has a rectangular cross-section, this need not be a restrictive condition. For example, the entrance aperture (and the aperture stop of the optical system) may also be rectangular or at least one refractive lens may be rectangular, as long as at least the metasurface lens element, which is the last lens element before the image sensor, has a rectangular cross-section.

[0128] In some cases, the size of the rectangular lens in the system can be fully characterized by the size of the image sensor in the system and the specifications of the lens. Specifically, as Figure 17A shown, the image sensor is characterized by its vertical dimension v and horizontal dimension h, respectively. The lens system is most commonly characterized by the f-number N of the lens, where N is defined as N = f / D, where f is the focal length of the optical system and D is the diameter of the lens. Thus, as Figure 17B shown, the desired width of the rectangular superlens can be shown as w = v + f / N, and the length can be shown as l = h + f / N. Such a definition of the lens size will result in an image that almost perfectly fills the sensor geometry. In practice, the image formed by the imaging system needs to be slightly larger than the image sensor size. This oversize of the image allows for greater tolerance in the final assembly of the lens system. A typical oversize range can take the nominal rectangular lens size given above and increase each dimension by 40 microns.

[0129] Although the above examples specify a single circular aperture coupled to a rectangular lens, in other embodiments, an optical system with N apertures on N rectangular lenses on a single image sensor can also be provided. For example, the circular apertures and the rectangular metasurface lenses can be arranged in a 2×2 grid on a single image sensor. Figures 18A to 18B An example of such a system is shown in Figure 18ADisclosed is a single image sensor die (110), around which a single spacer (112) can be placed as shown in Figure 18B . The spacer sets the distance between the rectangular metasurface (114) shown in Figure 18C and the image sensor (110). The final element in the assembly contains a set of circular pores (116), which are placed in association with an additional spacer layer (118) to set the distance between the rectangular metasurface and the circular pores. Figure 18D A cross-sectional view of the entire assembly is shown in

[0130] Although Figures 18A to Figure 18D an example shows a 2×2 array of circular pores on a rectangular metasurface, in general, the grid of circular pores and rectangular metasurface lenses can be arranged in any way (symmetric or asymmetric, e.g., 3×3 or 5×2). Additionally, each individual rectangular metasurface and circular pore that makes up the system has unique dimensions relative to other pore metasurface pairs in the system. For example, the diameter of each pore in the array can typically be unique, or each rectangular lens can be unique. However, the distances between the metasurface lens and the image sensor and between the metasurface lens and the circular pores are typically fixed for the entire system. Changing the mechanical parameters of each individual component of the array, such as the pore size, allows the optical properties of each camera in the array to be unique. For example, according to an embodiment, each sub-camera can have a unique f / #, field of view, resolution, etc.

[0131] Doctrine of equivalents

[0132] Accordingly, although the invention has been described in certain specific aspects, many additional modifications and variations will be apparent to those skilled in the art. Accordingly, it is to be understood that the invention may be practiced otherwise than as specifically described. Therefore, the embodiments of the invention are to be considered in all respects as illustrative and not restrictive.

Claims

1. An imaging system, comprising: at least one image sensor; a substrate layer having a substrate thickness, the substrate layer being configured to be transmissive to a target wavelength of light, the substrate layer having a first surface remote from the at least one image sensor and a second surface proximate to the at least one image sensor; a spacer layer that creates an air gap between the second surface of the substrate and the image sensor; and a metasurface comprising a single layer of a plurality of identical or distinct nanostructured elements disposed on either the first surface or the second surface such that light passes through at least a portion of the nanostructured elements, whereby angular deflection is imparted; wherein the metasurface is configured to collect light of a specified operating bandwidth across a specified field of view and shift the incident light such that it is focused on the at least one image sensor with a chief ray angle of zero or near zero degrees; wherein the image sensor and the metasurface have a rectangular geometry in plan view; and wherein the rectangular metasurface is configured to create a rectangular image of the specified field of view onto the rectangular image sensor.

2. The imaging system according to claim 1, wherein the metasurface is disposed on the first surface.

3. The imaging system according to claim 2, further comprising a narrow-band optical filter disposed on the second surface between the nanostructured elements and the at least one image sensor.

4. The imaging system according to claim 2, wherein the image sensor is in contact with the spacer layer.

5. The imaging system according to claim 1, wherein the metasurface is disposed on the second surface.

6. The imaging system according to claim 1, wherein the field of view is at least ±30 degrees.

7. An imaging system, comprising: at least one image sensor; a substrate layer having a substrate thickness, the substrate layer being configured to be transmissive to a target wavelength of light, the substrate layer having a first surface remote from the at least one image sensor and a second surface proximate to the at least one image sensor; at least one refractive lens disposed above the substrate and configured to focus the incident light onto the first surface of the substrate layer; and a single layer of a plurality of identical or distinct nanostructured elements, including a metasurface disposed on either the first surface or the second surface such that light incident on the at least one refractive lens passes through at least a portion of the nanostructured elements, whereby angular deflection is imparted; wherein the distance between the at least one refractive lens and the metasurface is spaced by a first distance; wherein the refractive lens and the metasurface are configured to collect light of a specified operating bandwidth across a specified field of view and shift the incident light such that it is focused on the at least one image sensor with a chief ray angle of zero or near zero degrees; wherein at least the image sensor and the metasurface have a rectangular geometry; wherein the image sensor is characterized by a vertical dimension v and a horizontal dimension h, and wherein the at least one refractive lens is characterized by an f-number N of the at least one refractive lens, N being defined as N = f / D, where f is the focal length of the imaging system and D is the diameter of the at least one refractive lens, and wherein the metasurface width is given by: w = v + f / N, and wherein the metasurface length l is given by: l = h + f / N.

8. The imaging system according to claim 7, wherein the at least one refractive lens is selected from the group consisting of: plano-convex, convex-plano, biconvex, biconcave, plano-concave, or concave-plano.

9. The imaging system according to claim 7, wherein at least a portion of at least one of the refractive lenses is interconnected with the first surface.

10. The imaging system according to claim 7, wherein the at least one refractive lens comprises at least two refractive lenses, the at least two refractive lenses comprising a convex-concave lens and a concave-convex lens.

11. The imaging system according to claim 7, wherein the at least one refractive lens comprises at least two refractive lenses, the at least two refractive lenses comprising a convex-concave lens, a biconvex lens, and / or a concave-plano lens.

12. The imaging system according to claim 7, wherein the at least one refractive lens has a circular geometry.

Images