Patent Publication Number: US-2022221691-A1

Title: Aspect ratio modifying imaging systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and benefit of U.S. Provisional Patent Application No. 62/841,161 filed Apr. 30, 2019 and entitled “ASPECT RATIO MODIFYING IMAGING SYSTEMS AND METHODS,” which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     One or more embodiments relate generally to optical components for imaging and more particularly, for example, to aspect ratio modifying imaging systems and methods. 
     BACKGROUND 
     Imaging systems may include an array of detectors, with each detector functioning as a pixel to produce a portion of a two-dimensional image. In some cases, imaging systems may include one or more optical elements (e.g., lenses, mirrors) to facilitate imaging applications, such as by directing light to the array of detectors. There are a wide variety of image detectors, such as visible-light image detectors, infrared image detectors, or other types of image detectors that may be provided in an image detector array for capturing an image. As an example, a plurality of sensors may be provided in an image detector array to detect electromagnetic (EM) radiation at desired wavelengths. In some cases, such as for infrared imaging, readout of image data captured by the detectors may be performed in a time-multiplexed manner by a readout integrated circuit (ROIC). The image data that is read out may be communicated to other circuitry, such as for processing, storage, and/or display. In some cases, a combination of a detector array and an ROIC may be referred to as a focal plane array (FPA). Advances in process technology for FPAs and image processing have led to increased capabilities and sophistication of resulting imaging systems. 
     SUMMARY 
     In one or more embodiments, an infrared imaging device includes at least one lens element configured to transmit electromagnetic radiation associated with a portion of a scene. The portion has a first aspect ratio. The electromagnetic radiation includes mid-wave and/or long-wave infrared light. The at least one lens element has a freeform surface having no translational symmetry and no rotational symmetry. The infrared imaging device further includes a detector array configured to receive image data associated with the electromagnetic radiation from the at least one lens element and generate, based on the image data, an image. The image data has a second aspect ratio different from the first aspect ratio. Each of the first and second aspect ratios is a ratio of a size along a first direction and a size along a second direction orthogonal to the first direction. 
     In one or more embodiments, a method includes transmitting, by at least one lens element, electromagnetic radiation associated with a portion of a scene. The portion of the scene has a first aspect ratio. The electromagnetic radiation includes mid-wave infrared light and/or long-wave infrared light. The method further includes receiving, by a detector array, image data associated with the electromagnetic radiation. The image data has a second aspect ratio different from the first aspect ratio. Each of the first aspect ratio and the second aspect ratio is a ratio of a size along a first direction and a size of a second direction orthogonal to the first direction. The method further includes generating, by the detector array, an image based on the image data. 
     The scope of the invention is defined by the claims, which are incorporated into this section by reference. A more complete understanding of embodiments of the invention will be afforded to those skilled in the art, as well as a realization of additional advantages thereof, by a consideration of the following detailed description of one or more embodiments. Reference will be made to the appended sheets of drawings that will first be described briefly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a block diagram of an infrared imaging device in accordance with one or more embodiments of the disclosure. 
         FIG. 2A  illustrates a perspective view of an infrared imaging device in accordance with one or more embodiments of the disclosure. 
         FIG. 2B  illustrates a cross-sectional view of the infrared imaging device of  FIG. 2A  in accordance with one or more embodiments of the disclosure. 
         FIG. 3  illustrates a perspective view of an optical system in accordance with one or more embodiments of the disclosure. 
         FIGS. 4A and 4B  illustrate a cross-section view of the optical system of  FIG. 3  in the XZ plane and the YZ plane, respectively. 
         FIG. 5  illustrates another perspective view of the optical system of  FIG. 3  along with examples of sags associated with various optical surfaces of lens elements of the optical system in accordance with one or more embodiments of the present disclosure. 
         FIGS. 6-11  each illustrate an example of a lens element in accordance with one or more embodiments of the disclosure. 
         FIGS. 12A and 12B  illustrate perspective views of an imaging device in accordance with one or more embodiments of the disclosure. 
         FIGS. 13A and 13B  illustrate perspective views of an optical system and trajectories of ray bundles through the optical system in accordance with one or more embodiments of the disclosure. 
         FIGS. 14A and 14B  illustrate perspective views of an imaging device and trajectories of ray bundles through the imaging device in accordance with one or more embodiments of the disclosure. 
         FIG. 15  illustrates a flow diagram of an example process for manufacturing an infrared imaging device in accordance with one or more embodiments of the disclosure. 
         FIG. 16  illustrates a flow diagram of an example process for using an infrared imaging device in accordance with one or more embodiments of the disclosure. 
     
    
    
     Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It is noted that sizes of various components and distances between these components may not be drawn to scale in the figures. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures. 
     DETAILED DESCRIPTION 
     The detailed description set forth below is intended as a description of various configurations of the subject technology and is not intended to represent the only configurations in which the subject technology can be practiced. The appended drawings are incorporated herein and constitute a part of the detailed description. The detailed description includes specific details for the purpose of providing a thorough understanding of the subject technology. However, it will be clear and apparent to those skilled in the art that the subject technology is not limited to the specific details set forth herein and may be practiced using one or more embodiments. In one or more instances, structures and components are shown in block diagram form in order to avoid obscuring the concepts of the subject technology. One or more embodiments of the subject disclosure are illustrated by and/or described in connection with one or more figures and are set forth in the claims. 
     In one or more embodiments, aspect ratio modifying imaging systems and methods are provided. In some aspects, such imaging systems and methods are utilized for infrared imaging, such as thermal infrared imaging. In one embodiment, an imaging device includes a detector array and at least one lens element. The detector array may receive image data (e.g., electromagnetic radiation) having an aspect ratio projected (e.g., directed, transmitted) by the lens element(s) of the detector array onto the imaging device. The detector array may generate an image based on the image the received image data. In an aspect, a scene may be referred to as an object, a target scene, or a target object. The lens element(s) of the imaging device may be transmissive of electromagnetic radiation within a waveband dependent on a desired application. In an aspect, the imaging device may be an infrared imaging device for facilitating capture of a waveband encompassing at least a portion of the thermal infrared spectrum, such as a mid-wave infrared spectrum and/or a long-wave infrared spectrum. In infrared imaging applications, the detector array may include an array of microbolometers and/or an array of other types of infrared detectors. By way of non-limiting examples, a lens element may include silicon, germanium, chalcogenide glass, and/or germanium arsenide selenium (GeAsSe). Lens material used to manufacture lens elements is generally based on a desired application (e.g., a desired transmission waveband of the lens elements). 
     In an embodiment, an aspect ratio of the image data is a ratio of a size of the image data along a first direction and a size of the image along a second direction. In some cases, the first direction is orthogonal to the second direction. For explanatory purposes, the Cartesian coordinate system is generally used in the present disclosure, in which the first direction may be an x-direction and the second direction may be a y-direction, or vice versa. A third direction may be denoted as a z-direction and is orthogonal to the x-direction and y-direction. Other coordinate systems may be utilized dependent on application. 
     For a given lens element of the imaging device, the lens element may receive EM radiation associated with a portion of a scene and may transmit the EM radiation. The lens element may be characterized by a focal length or focal lengths appropriate to capture a certain aspect ratio. In this regard, the portion of the scene captured by the lens element is of the certain aspect ratio. The focal length may be indicative of a field of view of the lens element. In an embodiment, an aspect ratio of the portion of the scene is a ratio of a size of the portion along the first direction and a size of the portion along the second direction. The lens element may have a different focal length in different directions. For example, the lens element may have a focal length f x  in the x-direction and a focal length f y  in the y-direction. The focal lengths f x  and f y  may correspond to a horizontal field of view (FOV) and a vertical FOV, respectively, of the lens element. 
     In a case the imaging device includes a single lens element, the single lens element may receive EM radiation from the portion of the scene and transmit (e.g., direct, project) the EM radiation to the detector array. In some applications, the single lens element may be or may include a refractive element that refracts the EM radiation onto the detector array. In a case the imaging device includes a series of lens elements, each lens element may receive and direct EM radiation to a next lens element of the series, with a last lens element receiving and directing EM radiation to the detector array. In some applications, at least one of the lens elements in the series refracts EM radiation. 
     The imaging device may include a lens barrel (e.g., also referred to as a lens housing) to hold (e.g., receive, secure, align) one or more lens elements. The imaging device may include a housing coupled to the lens barrel. The housing may include (e.g., enclose) the detector array. In some cases, the housing may include a processor to process image data from the detector array, memory to store raw image data and/or processed image data, a battery, and/or other components to facilitate operation of the imaging device. 
     In some embodiments, each lens element may include at least one mating feature (e.g., also referred to as a mounting feature). The lens barrel may have a corresponding mating feature(s) that couples to a mating feature(s) of the lens element(s) to receive and secure the lens element(s). In this regard, each mating feature of a lens element may couple to a corresponding mating feature of the lens barrel to couple the lens element to the lens barrel. In one example, a mating feature of a lens element may include a first surface and a second surface at an angle (e.g., 90° angle, obtuse angle, or acute angle) relative to the first surface, and a mating feature of a lens barrel may have corresponding surfaces to couple to the first and second surfaces. In another example, a mating feature of a lens element may include a pin portion, and a mating feature of a lens barrel may include a slot portion to receive the pin portion, and/or vice versa. More generally, a mating feature(s) of a lens element and a corresponding mating feature(s) of a lens barrel may be any structure (e.g., indentation, hole, pin, or other structure) that facilitates coupling of the lens element to the lens barrel. In some aspects, a mating feature may be defined as part of a freeform surface. 
     In some cases, a mating feature of a lens element may be appropriate to facilitate rotation and/or other movement of the lens element. In some cases, a mating feature may be utilized to facilitate alignment of a lens element, such as via pattern recognition during molding, machining, and/or assembling. For example, one or more mating features on a surface of a lens element can be located (e.g., using pattern recognition to scan the surface) to facilitate machining of a different surface of the lens element according to a desired design (e.g., freeform surface design). As another example, a mating feature(s) of a surface(s) of a first lens element and/or a mating feature(s) of a surface(s) of a second lens element may be utilized to facilitate alignment of the first lens element relative to the second lens element. 
     In various embodiments, the aspect ratio of the portion of the scene is different from the aspect ratio of image data received by the detector array. In one example embodiment, the aspect ratio of the portion of the scene may be 3:1 (e.g., or other highly asymmetrical aspect ratio) whereas the aspect ratio of the image data received by the detector array may be 4:3, 5:4, or 16:9 by way of non-limiting examples. In some embodiments, the lens element(s) may have freeform surfaces to facilitate such aspect ratio modification from the aspect ratio of the portion of the scene to the aspect ratio of the image data. A freeform surface has no translational symmetry and no rotational symmetry. A lens element having at least one freeform surface may be referred to as a freeform lens. In an aspect, at least one of the lens element(s) (or surface thereof) is a refractive element and at least one of the lens element(s) (or surface thereof) is a diffractive element. The diffractive element may be utilized to correct chromatic aberrations. In one case, the diffractive element may be formed by a freeform surface. In some aspects, lens elements formed with freeform surfaces generally have less weight and are of smaller sizes relative to conventional anamorphic lenses that rely on cylindrical and rotationally symmetric elements. As such, lens elements formed with freeform surfaces may be of appropriate compactness for integration into a camera module (e.g., of a mobile phone). 
     In one example embodiment, aspect ratio modifying imaging systems and methods may be utilized in automotive imaging applications. In automotive imaging applications, an imaging device having a panoramic field of view may be desired. For example, the imaging device may include a front looking camera. In some cases, the front looking camera may be utilized to capture long-wave infrared light and/or mid-wave infrared light. As an example, a panoramic field of view having around a 3:1 aspect ratio may be desired. A 3:1 aspect ratio sensor may not be readily available in the market and designing, prototyping, and manufacturing of a 3:1 format detector array (e.g., microbolometer array) may be cost ineffective and/or associated with a long lead time exercise. In this example, using various embodiments, the 3:1 aspect ratio scene may be captured using standard 4:3 or 5:4 imaging aspect ratio sensors by disposing a lens element(s) between the scene and the detector array to allow directing of EM radiation to the detector array via the lens element(s). In an aspect, at least one of the lens element(s) (or surface thereof) is a refractive element and at least one of the lens element(s) (or surface thereof) is a diffractive element. In one case, the diffractive element may be formed by a freeform surface. 
       FIG. 1  illustrates a block diagram of an infrared imaging device  100  in accordance with one or more embodiments of the disclosure. The infrared imaging device  100  may be used to capture and process image frames. The infrared imaging device  100  includes optical components  105 , an image capture component  110 , and an image capture interface component  115 . 
     The optical components  105  may receive EM radiation through an aperture  120  of the infrared imaging device  100  and pass the EM radiation to the image capture component  110 . For example, the optical components  105  may direct and/or focus EM radiation on the image capture component  110 . The optical components  105  may include one or more windows, lenses, mirrors, beamsplitters, beam couplers, and/or other components. In an embodiment, the optical components  105  may include one or more chalcogenide lenses, such as lenses made of As 40 Se 60 , that allow for imaging in a wide infrared spectrum. Other materials, such as silicon, germanium, and GeAsSe, may be utilized depending on desired transmission characteristics, such as desired transmission wavelengths and/or ray transfer matrix characteristics. 
     The image capture component  110  includes, in one embodiment, one or more sensors (e.g., visible-light sensor, infrared sensor, or other type of detector) for capturing image signals representative of an image of a scene  125 . The image capture component  110  may capture (e.g., detect, sense) infrared radiation with wavelengths in the range from around 700 nm to around 1 mm, or portion thereof. For example, in some aspects, the image capture component  110  may include one or more sensors sensitive to (e.g., better detect) thermal infrared wavelengths, including mid-wave infrared (MWIR) radiation (e.g., EM radiation with wavelength of 2-7 μm) and/or long-wave infrared (LWIR) radiation (e.g., electromagnetic radiation with wavelength of 7-15 μm). In one embodiment, the sensor(s) of the image capture component  110  may represent (e.g., convert) or facilitate representation of a captured thermal image signal of the scene  125  as digital data (e.g., via an analog-to-digital converter). 
     The image capture interface component  115  may receive image data captured at the image capture component  110  and may communicate the captured image data to other components or devices, such as via wired and/or wireless communication. In various embodiments, the infrared imaging device  100  may capture image frames, for example, of the scene  125 . 
     In some embodiments, the optical components  105 , image capture component  110 , and image capture interface component  115  may be housed in a protective enclosure. In one case, the protective enclosure may include a lens barrel (e.g., also referred to as a lens housing) that houses the optical components  105  and a housing that houses the image capture component  110  and/or the image capture interface component  115 . In this case, the lens barrel may be coupled to the housing. In an aspect, the protective enclosure may be represented by the solid-line box in  FIG. 1  having the aperture  120 . For example, the aperture  120  may be an opening defined in the protective enclosure that allows electromagnetic radiation to reach the optical components  105 . In some cases, the aperture  120  may be a limiting aperture of the infrared imaging device  100 . 
     The infrared imaging device  100  may represent any type of camera system which, for example, detects electromagnetic radiation (e.g., thermal radiation) and provides representative data (e.g., one or more still image frames or video image frames). For example, the infrared imaging device  100  may be configured to detect visible light and/or infrared radiation and provide associated image data. 
       FIG. 2A  illustrates a perspective view of an infrared imaging device  200  in accordance with one or more embodiments of the disclosure. As one example, the infrared imaging device  200  may be an LWIR thermal camera (e.g., for capturing electromagnetic radiation with wavelengths of 7-14 15). In other cases, the infrared imaging device  200  may be utilized to capture electromagnetic radiation within other wavelength ranges. 
     The infrared imaging device  200  may include a lens barrel  205  configured to accommodate lens elements  210 A and  210 B. The infrared imaging device  200  also may include an image capture portion  215  including an image capture component configured to capture images viewed through the lens barrel  205 . The image capture portion  215  may include arrays of microbolometers configured to detect EM radiation. As one example, the arrays of microbolometers may be configured to detect long-wave infrared light of wavelengths between 7.5 μm and 13.5 μm. In an embodiment, the infrared imaging device  200  may be the infrared imaging device  100  of  FIG. 1 . In this embodiment, the optical components  105  of  FIG. 1  may include the lens elements  210 A and  210 B, and the image capture component  110  of  FIG. 1  may include the image capture portion  215 . 
       FIG. 2B  illustrates a cross-sectional view of the infrared imaging device  200  of  FIG. 2A  in accordance with one or more embodiments of the disclosure. As shown in  FIG. 2B , the lens elements  210 A and  210 B are lenses accommodated in the lens barrel  205 . In one embodiment, one or both of the lens elements  210 A and  210 B may be lenses configured to transmit a wide spectrum of infrared light, such as chalcogenide lenses. Each of the lens elements  210 A and  210 B (e.g., and other optical components not labeled or shown in  FIGS. 2A and 2B ) may have specific optical characteristics, such as a specific effective focal length (EFL) and modulation transfer function (MTF). The lens elements  210 A and  210 B may coordinate to direct and focus infrared light onto the image capture portion  215 . A limiting aperture associated with a lens system including the lens elements  210 A and  210 B defines an amount of light that is transmitted into the infrared imaging device  200 . The limiting aperture may have spatial dimensions comparable to spatial dimensions of a front optical surface of the lens element  210 A. In  FIG. 2B , the limiting aperture is positioned in front of the lens element  210 A and defined by physical properties (e.g., shape, size, material) of the lens element  210 A and physical properties of a structure that holds (e.g., fixedly secures, movably secures) the lens element  210 A. The structure includes holding structure  220 A and  220 B. As shown in  FIG. 2B , a portion of the holding structures  220 A and  220 B conforms in shape to a portion of the lens element  210 A. The structure may be formed of metal or generally any material appropriate to hold/secure the lens element  210 A. 
       FIG. 3  illustrates a perspective view of an optical system  300  in accordance with one or more embodiments of the disclosure. The optical system  300  is oriented along three orthogonal directions, denoted as X, Y, and Z. The X-direction and the Y-direction may be referred to as the horizontal direction and the vertical direction, respectively.  FIGS. 4A and 4B  illustrate a cross-section view of the optical system  300  in the XZ plane and the YZ plane, respectively. The optical system  300  includes a lens element  305 , a lens element  310 , and a detector array  315 . In an aspect, the lens element  305  and/or  310  has one or more freeform surfaces that differentiates effective focal lengths between two orthogonal directions. A limiting aperture  405  is provided in front of the lens element  305 . The limiting aperture  405  may have spatial dimensions comparable to spatial dimensions of a front surface of the lens element  305 . The lens element  305  and/or  310  may be made of chalcogenide glass (e.g., IG6 chalcogenide glass). In this embodiment, the optical components  105  of  FIG. 1  may include the lens elements  305  and  310 , and the image capture component  110  of  FIG. 1  may include the detector array  315 . 
     The limiting aperture  405  defines an amount of light that is transmitted into the optical system  300 . The limiting aperture  405  may have spatial dimensions comparable to spatial dimensions of a front optical surface of the lens element  305 . In some cases, the limiting aperture  405  may be the same or substantially the same in size and shape as a clear aperture of the lens element  305 . The limiting aperture  405  may be defined by physical properties of the lens element  305 , such as a size, shape, and material of the front surface of the lens element  305 , and physical properties of a structure that holds the lens element  305 . For instance, the structure may be a part of a lens barrel. In one case, the structure may be a metal structure at least partially in front of the lens element  305 . As one example, the structure may be a metal structure that has a shape that conforms to the front surface of the lens element  305 . 
     The lens element  305  receives EM radiation of a scene  320 . The scene  320  may be referred to as an object, a target scene, or a target object. The lens element  305  can be utilized to capture EM radiation associated with an aspect ratio of a to b (e.g., also denoted as a:b), where the aspect ratio is a ratio between a first dimension/direction (e.g., an scene width) and a second dimension/direction (e.g., a scene height). The lens element  305  directs the received EM radiation to the lens element  310 . The lens element  310  directs the EM radiation received from the lens element  305  to the detector array  315 . As such, the lens elements  305  and  310  collectively projects the scene  320  onto the detector array  315 . The lens elements  305  and  310  may collectively convert the scene  320  of the aspect ratio a:b to image data having an aspect ratio c:d. In this regard, the lens elements  305  and  310  may be referred to as imaging an a:b aspect ratio scene/object onto a c:d aspect ratio sensor.  FIG. 3  illustrates the scene  320  of the aspect ratio a:b ray tracked through the lens elements  305  and  310  to result in the image  325  of the aspect ratio c:d. The detector array  315  receives the image data and generates the image  325  based on the image data. The lens elements  305  and  310  may be appropriately designed to effectuate conversion from the aspect ratio of a:b to the aspect ratio of c:d. The aspect ratio of c:d may be a ratio that corresponds to a size (e.g., number of rows and columns of detector elements) of the detector array  315 . In  FIG. 3 , slanted black bars shown in the image  325  represent distortion (e.g., in the form of squeezing along the X and Y directions). In an aspect, the image  325  is processed using processing circuitry downstream of the detector array  315  to correct the distortion (e.g., dewarp the image  325 ) to obtain a processed image. In some cases, such compression/distortion can be determined (e.g., as part of calibration) and appropriate processing performed to compensate for the compression/distortion. 
     As an example, the aspect ratio a:b may be 3:1 and the aspect ratio c:d may be 4:3. In this example, the detector array  315  may have a size of 320×256 sensors (e.g., 320×256 array of microbolometers) and receives image data having the 4:3 aspect ratio. An effective focal length (collectively provided by the lens elements  305  and  310 ) in an X-direction and a Y-direction is 4.790 mm and 10.902 mm, respectively, which corresponds to a 50° horizontal FOV and a 16° FOV. Other aspect ratios a:b and c:d may be utilized dependent on application. 
     In an embodiment, to facilitate alignment of the horizontal FOV with the horizontal direction of the detector array  315  and the vertical FOV with the vertical direction of the detector array  315 , one or both of the lens elements  305  and  310  can be moved relative to the detector array  315 . In some aspects, the lens elements  305  and/or  310  may be moved via sliding motion (e.g., translational motion) to facilitate focusing, such as by using one or more actuators coupled to the lens elements  305  and/or  310 . In one case, the sliding motion may be along the Z-axis (e.g., the direction perpendicular to the focal plane) while preserving a fixed angular orientation. In these aspects, a focusing mechanism of the lens elements  305  and/or  310  may include components (e.g., actuators) for moving the lens elements  305  and/or  310 . In one case, a rotation about the Z-axis may be constrained within an alignment tolerance between the major FOV associated with the lens elements  305  and  310  and the corresponding major dimension (e.g., X-dimension) of the detector array  315  and/or constrained within an alignment tolerance between the minor FOV associated with the lens elements  305  and  310  and the minor dimension (e.g., Y-dimension) of the detector array  315 . 
     In other aspects, one or more lenses may be focused by rotating the lens(es) inside a threaded housing. 
       FIG. 5  illustrates another perspective view of the optical system  300  along with examples of sags associated with various optical surfaces of the lens elements  305  and  310  in accordance with one or more embodiments of the present disclosure. The lens element  305  has a surface  505  and a surface  510  opposite the surface  505 . The lens element  310  has a surface  515  and a surface  520  opposite the surface  515 . The surface  505  of the lens element  305  faces the scene  320 . The surface  510  of the lens element  305  faces the surface  515  of the lens element  310 . The surface  520  of the lens element  310  faces the detector array  315 . Graph  525 ,  530 ,  535 , and  540  provide example sags of the surfaces  505 ,  510 ,  515 , and  520 , respectively. It is noted that the sags provided in the graphs  525 ,  530 ,  535 , and  540  are by way of non-limiting examples. The surfaces  505  and/or  510  of the lens element  305  and/or the surfaces  515  and/or  515  of the lens element  310  may have different sags from those shown in the graphs  525 ,  530 ,  535 , and  540 . 
     In some embodiments, the surfaces  505 ,  510 ,  515 , and  520  are each associated with a freeform lens prescription. In some aspects, each prescription may be expressed via coefficients of Chebyshev orthogonal polynomials according to the following: 
     
       
         
           
             
               
                 
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     where c(i, j) are normalized coefficients. 
     Table 1 illustrates example values of various parameters of the optical system  300 . 
                                            Lens Element 305   Lens Element 310                                 Surface   Surface 505   Surface 510   Surface 515   Surface 520                                 Element Central   5.548   5.661       Thickness [mm]       Material   IG6   IG6                     Air gap between two   6.856       elements [mm]                                 Clear Aperture   7.378   9.113   10.759   11.338       Normalization Z   5.000   5.000   12.000   12.000       Length [mm]       Normalization Y   5.000   5.000   10.000   10.000       Length [mm]       c(2, 0) [mm −1 ]   −4.82E−02    −3.57E−02   2.83E−03   −2.79E−04       c(4, 0) [mm −3 ]   6.19E−03    1.09E−03   −3.40E−03     2.10E−03       c(6, 0) [mm −5 ]   1.09E−03    2.47E−04   −8.82E−04     1.87E−04       c(0, 2) [mm −1 ]   −4.02E−03    −1.64E−02   −3.48E−03    −1.27E−02       c(2, 2) [mm −1 ]   9.04E−03    3.80E−03   1.59E−03    2.71E−03       c(4, 2) [mm −3 ]   1.99E−03    1.19E−03   4.59E−04   −2.54E−03       c(6, 2) [mm −5 ]   −1.04E−03     2.30E−04   7.00E−04   −2.29E−04       c(0, 4) [mm −3 ]   1.07E−03   −1.32E−03   1.26E−03    7.81E−04       c(2, 4) [mm −3 ]   2.72E−03   −1.46E−03   −3.49E−03    −7.30E−04       c(4, 4) [mm −3 ]   −4.59E−04    −6.50E−04   −9.49E−04     9.00E−04       c(6, 4) [mm −5 ]   −7.43E−04    −1.01E−04   1.86E−04   −2.56E−04       c(0, 6) [mm −5 ]   4.15E−04   −2.18E−04   5.09E−04    4.63E−04       c(2, 6) [mm −5 ]   2.60E−04   −2.81E−04   1.30E−03    1.35E−03       c(4, 6) [mm −5 ]   −5.63E−04    −4.15E−05   −1.90E−03    −7.25E−05       c(6, 6) [mm −5 ]   −3.41E−04     5.59E−05   −7.27E−05    −1.29E−04                    
Although the foregoing prescriptions are expressed via coefficients of Chebyshev orthogonal polynomials, other manners by which to express the prescriptions may be utilized. In addition, while the surfaces  505 ,  510 ,  515 , and  520  are freeform surfaces, in other cases a lens element may have one freeform surface or no freeform surfaces.
 
       FIGS. 6-8  each illustrates an example of a lens element in accordance with one or more embodiments of the disclosure. In particular,  FIGS. 6, 7, and 8  illustrate a lens element  600 ,  700 , and  800 , respectively. The lens elements  600 ,  700 , and  800  extend along three directions (e.g., three orthogonal directions) X, Y, and Z. A limiting aperture of the lens element  600 ,  700 , or  800  may be based on physical characteristics (e.g., shape, size) of a front surface  605 ,  705 , or  805 , respectively, of the lens elements  600 ,  700 , and  800 , respectively. One of more surfaces of the lens elements  600 ,  700 , and/or  800  may be freeform surfaces. The lens elements  600 ,  700 , and  800  may have physical characteristics/features, such as slopes (e.g., chamfers), indentations, etc., of various sizes and shapes at various locations as appropriate to direct light for an imaging application. 
     The lens element  700  has chamfers  710  and  715  and a mating feature  720 . The lens element  800  includes a mating feature  810 . The mating feature  810  has a first surface  815  and a second surface  820  at an angle relative to the first surface  815 . For example, the first surface  815  may be orthogonal to or substantially orthogonal to the second surface  820 . More generally, the mating features  720  and  810  may be of any appropriate shape, size, and/or other physical characteristic to facilitate mating of the lens element  700  and  800  to a lens housing, such as a lens barrel. For example, although the first surface  815  and the second surface  820  are depicted as being flat surfaces that are orthogonal to or substantially orthogonal to each other, in some cases the first surface  815  and the second surface  820  may be of any shape and at any angle to each other as appropriate to mate the lens element  800  to a lens housing. 
       FIGS. 9-11  each illustrates an example of a lens element in accordance with one or more embodiments of the disclosure. In particular,  FIGS. 9, 10, and 11  illustrate a lens element  900 ,  1000 , and  1100 , respectively. The lens elements  900 ,  1000 , and  1100  extend along three directions X, Y, and Z. One of more surfaces of the lens elements  900 ,  1000 , and/or  1100  may be freeform surfaces. The lens elements  900 ,  1000 , and  1100  may have physical characteristics/features (e.g., shapes, sizes) appropriate for a desired imaging application. The lens element  1000  has chamfers  1010  and  1015  and a mating feature  1020 . 
     The lens element  1100  includes chamfers  1105  and  1110  and a mating feature  1115 . The mating feature  1115  has a first surface  1120  and a second surface  1125  at an angle relative to the first surface  1120 . Generally, the mating features  1020  and  1115  may be of an appropriate shape, size, and/or other physical characteristic to facilitate mating of the lens element  1000  and  1100  to a lens housing (e.g., lens barrel). In some embodiments, the optical components  105  of  FIG. 1  may include the lens element  600 ,  700 , or  800  as a front lens of the optical components  105  (e.g., lens element closer to the scene  125 ), and the lens element  900 ,  1000 , or  1100  as a rear lens of the optical components  105  (e.g., lens element closer to the image capture component  110 ). 
     In some embodiments, formation of surfaces, such as freeform surfaces, to obtain the lens elements may be an iterative process. In some aspects, one or more surfaces of a lens element may be associated with a freeform lens prescription. For example, each prescription may be expressed via coefficients of Chebyshev orthogonal polynomials. Various parameters, such as those shown in Table 1, may be utilized to characterize a lens element. In some cases, trajectories of ray bundles may be analyzed, such as by determining associated ray transfer matrices, and appropriate adjustment to a remaining portion of a lens material may be performed. For example, the remaining portion of the lens material may be truncated based on analyzing the trajectories. In some cases, portions of the lens material that are truncated may include portions of the lens material through which no light passes. Such portions of the lens material may add bulk (e.g., and thus take up space) without performing imaging, and may be considered as serving no optical purpose. In some cases, such truncated portions may appear as chamfers in the lens elements. For example, with reference to  FIG. 7 , a lens material may be truncated to form the lens element  700  having the chamfers  710  and  715 . 
       FIGS. 12A and 12B  illustrate perspective views of an imaging device  1200  that includes a lens housing  1205  (e.g., a lens barrel) and lens elements  1210  and  1215  coupled to the lens housing  1205 , in accordance with one or more embodiments of the disclosure. The imaging device  1200  and components thereof are oriented along three directions X, Y, and Z. The perspective view of  FIG. 12A  is rotated to obtain the perspective view of  FIG. 12B . The lens housing  1205  includes mating features  1220  and  1225 . The lens housing  1205  provides a limiting aperture  1230  in front of a front surface  1235  of the lens element  1210 . The lens element  1210  includes chamfers  1240  and  1245  and a mating feature  1250 . The mating feature  1250  couples to the mating feature  1220  of the lens housing  1205 . The lens element  1215  includes chamfers  1255  and  1260  and a mating feature  1265 . The mating feature  1265  couples to the mating feature  1220  of the lens housing  1205 . As an example, in an embodiment, the lens element  1210  may be the lens element  700  of  FIG. 7 , and/or the lens element  1215  may be the lens element  1100  of  FIG. 11 . In this example, the chamfers  710  and  715  may be the chamfers  1240  and  1245 , respectively, and the mating feature  1250  may be the mating feature  720 . The chamfers  1105  and  1110  may be the chamfers  1255  and  1260 , respectively, and the mating feature  1115  may be the mating feature  1265 . 
       FIGS. 13A and 13B  illustrate perspective views of an optical system  1300  and trajectories of ray bundles through the optical system  1300  in accordance with one or more embodiments of the disclosure. The optical system  1300  is oriented along three directions X, Y, and Z. The perspective view of  FIG. 13A  is rotated to obtain the perspective view of FIG.  13 B. The optical system  1300  includes a lens element  1305  having a mating feature  1315  and a lens element  1310  having a mating feature  1320 . The mating feature  1315  and  1320  may couple the lens element  1305  and  1310 , respectively, to a lens housing (e.g., lens barrel). As an example, in an embodiment, the lens element  1305  may be the lens element  800  of  FIG. 8 , and/or the lens element  1310  may be the lens element  1100  of  FIG. 11 . In this example, the mating features  1315  and  1320  may be the mating features  810  and  1115 , respectively. 
     In the optical system  1300 , the lens elements  1305  and  1310  are arranged such that the mating feature  1315  and the mating feature  1320  are orthogonal or substantially orthogonal to each other. In other cases, mating features of two lens elements are not orthogonal or substantially orthogonal to each other. For example, the mating features of two lens elements may be parallel to each other or otherwise at any angle appropriate for a desired alignment of the lens elements. In this regard, an arrangement/orientation of the mating feature  1315  relative to that of the mating feature  1320  (and, more generally, an arrangement/orientation of various surfaces of the lens element  1305  to those of the lens element  1310 ) may be dependent, by way of non-limiting examples, on dimensional aspects of the lens elements  1305  and  1310  in relation to dimensional aspects of a lens housing configured to hold (e.g., receive, secure) the lens elements  1305  and  1310  and desired light propagation characteristics through the lens elements  1305  and  1310  (e.g., to direct light through the lens elements  1305  and  1310  to a detector array). 
       FIGS. 14A and 14B  illustrate perspective views of an imaging device  1400  and trajectories of ray bundles through the imaging device  1400  in accordance with one or more embodiments of the disclosure. The imaging device  1400  includes a lens housing  1405  (e.g., a lens barrel) and the lens elements  1305  and  1310  coupled to the lens housing  1405 . The imaging device  1400  and components thereof are oriented along three directions X, Y, and Z. The lens housing  1405  includes a mating feature  1410  that couples to the mating feature  1315  of the lens element  1305  and a mating feature  1415  that couples to the mating feature  1320  of the lens element  1310 . A limiting aperture  1420  of the imaging device  1400  is provided by an aperture of the lens housing  1405  in front of a front surface of the lens element  1305 . The limiting aperture may have spatial dimensions comparable to spatial dimensions of the front surface of the lens element  1305 . As shown in the ray bundles, light propagates through the limiting aperture  1420 , the lens element  1305 , and the lens element  1310 . Light can be directed by the lens element  1310  to a detector array (e.g., infrared detector array). 
     It is noted that while the foregoing mating features are primarily depicted as flat or substantially flat surfaces for mating with corresponding mating features of a lens housing, a mating feature of a lens element or a lens housing may be of any appropriate shape for coupling the lens element to the lens housing such that the lens element is appropriately positioned, secured, aligned, etc. to facilitate a desired imaging application. For example, a mating feature may be a structure, such as a protruding pin, that can be received by a corresponding mating feature of a lens housing. In some cases, a mating feature of a lens element may facilitate rotation and/or other movement of the lens element. 
       FIG. 15  illustrates a flow diagram of an example process  1500  for manufacturing an infrared imaging device in accordance with one or more embodiments of the disclosure. For explanatory purposes, the example process  1500  is primarily described herein with reference to components of  FIGS. 1-3  and associated arrangement of these components. However, the example process  1500  is not limited to the components of  FIGS. 1-3 . 
     At block  1505 , the image capture component  110  is provided. At block  1510 , the optical components  105  are formed. The optical components  105  may include one or more lens elements. At block  1515 , the lens element(s) are at least partially disposed within a lens barrel (e.g.,  205  of  FIGS. 2A-2B ). In some aspects, the lens element(s) may have mating features to couple to corresponding mating features of the lens barrel. The image capture component  110  may be disposed within a housing of the infrared imaging device  100 . The lens barrel may be coupled to the housing. For infrared applications, the lens elements may be formed from material that is transmissive in the 2-7 μm and/or 7-15 μm wavebands. In some aspects, the lens elements may include the lens elements  305  and  310  of  FIG. 3 . In some cases, at least one surface of the lens elements may be a freeform surface. In such cases, one or more freeform surfaces may be formed from lens material, such that portions of the lens material are removed to define the desired freeform surface(s). 
     Formation of surfaces, such as freeform surfaces, to obtain the lens elements may be an iterative process. Trajectories of ray bundles may be analyzed, such as by determining associated ray transfer matrices, and appropriate adjustment to a remaining portion of the lens material may be performed. For example, the remaining portion of the lens material may be truncated based on analyzing the trajectories. In some cases, portions of the lens material that are truncated may include portions of the lens material through which no light passes. Such portions of the lens material may add bulk (e.g., and thus take up space) without performing imaging. 
     In one case, the lens elements  305  and  310 , may be produced using wafer-level techniques. In such cases, transmissive crystalline material, such as germanium or silicon by way of non-limiting examples, may first be prepared in a wafer form. An array of lens elements (e.g., identical lens elements) may be diamond turned on one or two sides of the wafer. Machining of the array of lens elements may be on one or two sides of a wafer. In some cases, one or more mating features on a surface of a lens element can be located (e.g., using pattern recognition to scan the surface) to facilitate machining of a different surface of the lens element according to a desired design (e.g., freeform surface design). Lens elements formed as part of a wafer-level procedure may then be singulated to obtain individual lens elements that can be disposed in imaging devices. In a case that the lens elements  305  and  310  are different, the lens elements  305  and  310  may be formed as part of one wafer-level procedure (e.g., a wafer-level procedure that can be used to obtain differently shaped and/or sized lens elements) or two separate wafer-level procedures. 
     In one case, the lens elements  305  and  310  may be made of amorphous material. Examples of the material may include As 40 Se 60  and GeAsSe glass. In some cases, the lens elements  305  and  310  may be diamond turned from disk-like preforms, diamond turned from near to shape ground preforms, molded from spherical performs, or molded from disk-like preforms using precision glass molding (PGM) technique. In some cases, an array of lenses can be molded simultaneously on a disk of glass. 
       FIG. 16  illustrates a flow diagram of an example process  1600  for using an infrared imaging device in accordance with one or more embodiments of the disclosure. For explanatory purposes, the example process  1600  is primarily described herein with reference to components of  FIGS. 1-3  and associated arrangement of these components. However, the example process  1600  is not limited to the components of  FIGS. 1-3 . At block  1605 , the lens elements  305  and  310  transmits EM radiation associated with the scene  320  having a first aspect ratio. At block  1610 , the detector array  315  receives image data having a second aspect ratio different from the first aspect ratio. At block  1615 , the detector array generates the image  325  based on the received image data. In some cases, the image  325  generated by the detector array  315  may be provided for processing, storage, and/or display. For example, the image  325  may be provided to a processor for processing to remove distortion in the image  325 , and the processed image may then be provided for storage, display, and/or further processing. 
     Although the foregoing provides a two lens system, one lens element or more than two lens elements may be utilized. In some cases, each additional lens element provided in the system allows more degrees of freedom with regard to characteristics (e.g., shape such as curvature, size) defined for each of the lens elements to achieve a desired performance. Fewer number of lens elements is generally associated with a smaller size associated with the optical system. For instance, manufacturing limitations may constrain a maximum curvature that can be manufactured for a given lens element. 
     It is noted that dimensional aspects provided above are examples and that other values for the dimensions can be utilized in accordance with one or more implementations. Furthermore, the dimensional aspects provided above are generally nominal values. As would be appreciated by a person skilled in the art, each dimensional aspect has a tolerance associated with the dimensional aspect. Similarly, aspects related to distances between features also have associated tolerances. 
     Terms such as “top”, “bottom”, “front”, “rear”, “side”, “horizontal”, “vertical”, and the like refer to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, such a term may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference. 
     Where applicable, various embodiments provided by the present disclosure can be implemented using hardware, software, or combinations of hardware and software. Also where applicable, the various hardware components and/or software components set forth herein can be combined into composite components comprising software, hardware, and/or both without departing from the spirit of the present disclosure. Where applicable, the various hardware components and/or software components set forth herein can be separated into sub-components comprising software, hardware, or both without departing from the spirit of the present disclosure. In addition, where applicable, it is contemplated that software components can be implemented as hardware components, and vice-versa. 
     Software in accordance with the present disclosure, such as program code and/or data, can be stored on one or more computer readable mediums. It is also contemplated that software identified herein can be implemented using one or more general purpose or specific purpose computers and/or computer systems, networked and/or otherwise. Where applicable, the ordering of various steps described herein can be changed, combined into composite steps, and/or separated into sub-steps to provide features described herein. 
     Embodiments described above illustrate but do not limit the invention. It should also be understood that numerous modifications and variations are possible in accordance with the principles of the present invention. Accordingly, the scope of the invention is defined only by the following claims.