PATENT DOCUMENT

Publication Number: US-12032146-B2
Application Number: US-201917278251-A
Country: US
Kind Code: B2

Title: Camera lens system

Abstract:
A folded optical system that comprises two prisms with refractive power and in which at least one surface of at least one of the prisms is not rotationally symmetric. The materials and surfaces of the prisms in the folded optical system may be selected to provide a low F-number (e.g., &lt;=2.4), full field of view (FOV) of 30 degrees or less. The folded optical system may be implemented in a small package size while still capturing sharp, high-resolution images, making embodiments of a camera including the folded optical system suitable for use in small and/or mobile multipurpose devices.

Claims:
What is claimed is: 
     
       1. A folded optical system, comprising:
 a first prism; and 
 a second prism; 
 wherein the first prism has refractive power and has only one reflecting surface for internally reflecting light and is configured to redirect the light received from an object field, toward the second prism; 
 wherein the second prism has only one reflecting surface for internally reflecting the light and is configured to redirect the light to form an image of the object field at an image plane; 
 wherein for the first prism or the second prism, the respective reflecting surface is flat/plano; and 
 wherein at least one surface of at least one of the prisms is rotationally asymmetric and the at least one surface provides refractive power to the light that passes through the at least one surface. 
 
     
     
       2. The folded optical system as recited in  claim 1 , further comprising an aperture stop located at a first surface of the first prism. 
     
     
       3. The folded optical system as recited in  claim 1 , wherein F-number of the folded optical system is &lt;=2.4, and wherein full field of view (FOV) of the folded optical system is &lt;=30 degrees. 
     
     
       4. The folded optical system as recited in  claim 1 , wherein each prism has a respective first surface S 1 , a respective second surface S 2 , and a respective third surface S 3  on an optical axis of the folded optical system, wherein optical characteristics of the surfaces are defined along two axes of symmetry x and a y relative to the optical axis at the surfaces, wherein the x axis at the surfaces are parallel to each other and perpendicular to the optical axis, and wherein the y axis at each surface is rotated around the x axis to conform to the surface. 
     
     
       5. The folded optical system as recited in  claim 4 , wherein the folded optical system satisfies the following condition:
     f   x   =f   y   =f   sys , 
 where f x  is focal length through the folded optical system on the x axis, f y  is focal length through the folded optical system on the y axis, and f sys  is effective focal length of the folded optical system. 
 
     
     
       6. The folded optical system as recited in  claim 4 , wherein, for each prism, focal lengths along the x axis at the prism are different than focal lengths along the y axis at the prism. 
     
     
       7. The folded optical system as recited in  claim 4 , wherein refractive power of the first prism along the x axis is stronger than refractive power of the first prism along the y axis. 
     
     
       8. The folded optical system as recited in  claim 7 , wherein the first prism satisfies the following conditions:
   0.55&lt; f   P1y   /f   sys &lt;0.85, 
   0.5&lt; f   P1x   /f   sys &lt;0.8, 
 where f P1y  is focal length of the first prism along the y axis, f P1x  is focal length of the first prism along the x axis, and f sys  is effective focal length of the folded optical system. 
 
     
     
       9. The folded optical system as recited in  claim 4 , wherein surface S 1  of the first prism is convex in a paraxial region and satisfies the following conditions:
   1.2&lt; f   P1S1y   /f   P1y , 
     f   P1S1x   /f   P1x &lt;2.8, 
 where f P1S1y  and f P1S1x  are focal lengths of surface S 1  of the first prism on the y and x axes, respectively. 
 
     
     
       10. The folded optical system as recited in  claim 4 , wherein surface S 3  of the first prism is convex in a paraxial region and satisfies the following conditions:
   1&lt; f   P1S3x   /f   P1x &lt;3, 
   4&lt; f   P1S3y   /f   P1y &lt;5, 
 where f P1S3y  and f P1S3x  are focal lengths of surface S 3  of the first prism on the y and x axes, respectively. 
 
     
     
       11. The folded optical system as recited in  claim 4 , wherein refractive power of the second prism along the x axis is stronger than refractive power of the second prism along the y axis. 
     
     
       12. The folded optical system as recited in  claim 11 , wherein the second prism satisfies the following conditions:
   −1&lt; f   P2y   /f   sys &lt;−0.4,
 
   −1&lt; f   P2x   /f   sys &lt;−0.7,
 
 where f P2y  is focal length of the second prism along the y axis, f P2x  is focal length of the second prism along the x axis, and f sys  is the effective focal length of the folded optical system. 
 
     
     
       13. The folded optical system as recited in  claim 4 , wherein surface S 1  of the second prism is concave in the paraxial region, and satisfies the following conditions:
   1&lt; f   P2S1y   /f   P2y , 
     f   P2S1x   /f   P2x &lt;3, 
 where f P2S1y  and f P2S1x  are focal lengths of surface S 1  of the second prism on the y and x axes, respectively. 
 
     
     
       14. The folded optical system as recited in  claim 4 , wherein surface S 3  of the second prism is concave in a paraxial region and satisfies the following conditions:
   3&lt; f   P2S3x   /f   P2y &lt;7, 
   1&lt; f   P2S3y   /f   P2y &lt;3, 
 where f P2S3y  and f P2S3x  are focal lengths of surface S 3  of the second prism on the y and x axes, respectively. 
 
     
     
       15. The folded optical system as recited in  claim 4 ,
 wherein surface S 2  of the first prism reflects light from a first axis to a second axis; 
 wherein surface S 2  of the second prism reflects light from the second axis to a third axis; and 
 wherein at least one of the surfaces S 2  is rotationally asymmetric. 
 
     
     
       16. The folded optical system as recited in  claim 4 , wherein the first prism satisfies the following condition:
   70 degrees&lt;Alpha 1&lt;110 degrees, 
 where Alpha 1 is the angle between a tangent line to surface S 1  of the first prism and a tangent line to surface S 3  of the first prism. 
 
     
     
       17. The folded optical system as recited in  claim 4 , wherein the second prism satisfies the following condition:
   70 degrees&lt;Alpha 2&lt;110 degrees, 
 where Alpha 2 is the angle between a tangent line to surface S 1  of the second prism and a tangent line to surface S 3  of the second prism. 
 
     
     
       18. The folded optical system as recited in  claim 1 , wherein the first prism is formed of an optical material with an Abbe number vd1 that satisfies the condition vd1&gt;50, and wherein the second prism is formed of an optical material with an Abbe number vd2 that satisfies the condition vd2&lt;30. 
     
     
       19. The folded optical system as recited in  claim 1 , wherein the folded optical system is a component of a camera comprising a photosensor configured to capture light projected onto a surface of the photosensor, wherein the second prism redirects the light to form the image of the object field at the image plane at the surface of the photosensor. 
     
     
       20. The folded optical system as recited in  claim 19 , wherein the camera is a component of a device comprising:
 one or more processors; and 
 a memory comprising program instructions executable by at least one of the one or more processors to control operations of the camera.

Description:
This application is a 371 of PCT Application No. PCT/US2019/052244, filed Sep. 20, 2019, which claims benefit of priority to U.S. Provisional Patent Application No. 62/736,394, filed Sep. 25, 2018. The above applications are incorporated herein by reference. To the extent that any material in the incorporated application conflicts with material expressly set forth herein, the material expressly set forth herein controls. 
    
    
     BACKGROUND 
     Technical Field 
     This disclosure relates generally to camera systems, and more specifically to small form factor camera and lens systems. 
     Description of the Related Art 
     The advent of small, mobile multipurpose devices such as smartphones and tablet or pad devices has resulted in a need for high-resolution, small form factor cameras that are lightweight, compact, and capable of capturing high resolution, high quality images at low F-numbers for integration in the devices. However, due to limitations of conventional camera technology, conventional small cameras used in such devices tend to capture images at lower resolutions and/or with lower image quality than can be achieved with larger, higher quality cameras. Achieving higher resolution with small package size cameras generally requires use of a photosensor with small pixel size and a good, compact imaging lens system. Advances in technology have achieved reduction of the pixel size in photosensors. However, as photosensors become more compact and powerful, demand for compact imaging lens systems with improved imaging quality performance has increased. In addition, there are increasing expectations for small form factor cameras to be equipped with higher pixel count and/or larger pixel size image sensors (one or both of which may require larger image sensors) while still maintaining a module height that is compact enough to fit into portable electronic devices. Thus, a challenge from an optical system design point of view is to provide an imaging lens system that is capable of capturing high brightness, high resolution images under the physical constraints imposed by small form factor cameras. 
     SUMMARY OF EMBODIMENTS 
     Embodiments of the present disclosure may provide a folded optical system that may, for example, be used as a camera lens in small form factor cameras. Embodiments of a folded optical system are described that include two prisms with refractive power that together form the optical system. At least one surface of at least one of the prisms is a “freeform” surface, and thus the prism(s) may be referred to as freeform prisms. A freeform prism may be broadly defined as a prism with at least one surface that provides refractive power and that is asymmetric (not rotationally symmetric) (i.e., is a “freeform” surface). The prisms provide a “folded” optical axis for the camera, for example to reduce the Z-height of the camera. A first prism (P 1 ) redirects light from an object field from a first axis to a second axis. A second prism (P 2 ) receives the light on the second axis and redirects the light onto a third axis on which a photosensor of the camera is disposed. The redirected light forms an image at an image plane at or near the surface of a photosensor. 
     Each of the two prisms includes three surfaces that affect light passing through the prism. A first surface (S 1 ) receives the light from an object side of the prism; a second surface (S 2 ) reflects or redirects the light received through the first surface to a third surface (S 3 ); the light then passes through or is refracted by the third surface to the next prism or to the photosensor. For each prism, a given surface may be flat/plano with no refractive power; symmetrically concave, convex, or aspherical with refractive power; or freeform (asymmetrically concave, convex, or aspherical with refractive power). As noted above, in some embodiments, at least one surface of at least one of the prisms is a freeform surface. In some embodiments, at least two of the six surfaces of the prisms in the optical system are freeform surfaces. In some embodiments, the first and third surfaces in both prisms are freeform surfaces, while the second surfaces in both prisms are flat/plano. However, in some embodiments, one or both of the second surfaces may be freeform surfaces with refractive power or symmetrical surfaces with refractive power. 
     The materials and surfaces of the prisms in the optical system may be selected to capture high resolution, high quality images. Parameters and relationships of the prisms, including but not limited to the materials and surface shapes may be selected at least in part to reduce, compensate, or correct for optical aberrations and artifacts and effects across the field of view. In some embodiments, the materials and surfaces of the prisms in the optical system may be selected to provide a low F-number (e.g., &lt;=2.4), full field of view (FOV) of 30 degrees or less, and high brightness, high resolution images with high image quality. 
     In some embodiments, an aperture stop is located in the optical system at the first (object side) surface of the first prism. In some embodiments, the aperture stop may be elliptical; however, circular or other shapes may be used for the aperture in some embodiments. In some embodiments, the folded camera may include an infrared (IR) filter to reduce or eliminate interference of environmental noise on the photosensor. The IR filter may, for example, be located between the second prism and the photosensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a conventional folded lens system that includes a lens stack positioned between two prisms. 
         FIG.  2    illustrates a folded optical system that consists of two freeform prisms, according to some embodiments. 
         FIGS.  3 A,  3 B, and  3 C  are diagrams illustrating orientation of the x and y axes at the surfaces of the freeform prisms as shown in  FIG.  2   , according to some embodiments. 
         FIG.  4    is a 3D cross-sectional illustration of a folded optical system that includes two freeform prisms, according to some embodiments. 
         FIG.  5    is a cross-sectional illustration of a folded optical system that includes two freeform prisms, according to some embodiments. 
         FIG.  6    is a cross-sectional illustration of a folded optical system that includes two freeform prisms and shows the angles between the surfaces of the freeform prisms, according to some embodiments. 
         FIG.  7    is a flowchart of a method for capturing images using embodiments of a folded optical system as illustrated in  FIGS.  2  through  6   , according to some embodiments. 
         FIG.  8    illustrates an example computer system that may be used in embodiments. 
     
    
    
     This specification includes references to “one embodiment” or “an embodiment.” The appearances of the phrases “in one embodiment” or “in an embodiment” do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure. 
     “Comprising.” This term is open-ended. As used in the appended claims, this term does not foreclose additional structure or steps. Consider a claim that recites: “An apparatus comprising one or more processor units . . . ”. Such a claim does not foreclose the apparatus from including additional components (e.g., a network interface unit, graphics circuitry, etc.). 
     “Configured To.” Various units, circuits, or other components may be described or claimed as “configured to” perform a task or tasks. In such contexts, “configured to” is used to connote structure by indicating that the units/circuits/components include structure (e.g., circuitry) that performs those task or tasks during operation. As such, the unit/circuit/component can be said to be configured to perform the task even when the specified unit/circuit/component is not currently operational (e.g., is not on). The units/circuits/components used with the “configured to” language include hardware—for example, circuits, memory storing program instructions executable to implement the operation, etc. Reciting that a unit/circuit/component is “configured to” perform one or more tasks is expressly intended not to invoke 35 U.S.C. § 112, sixth paragraph, for that unit/circuit/component. Additionally, “configured to” can include generic structure (e.g., generic circuitry) that is manipulated by software and/or firmware (e.g., an FPGA or a general-purpose processor executing software) to operate in manner that is capable of performing the task(s) at issue. “Configure to” may also include adapting a manufacturing process (e.g., a semiconductor fabrication facility) to fabricate devices (e.g., integrated circuits) that are adapted to implement or perform one or more tasks. 
     “First,” “Second,” etc. As used herein, these terms are used as labels for nouns that they precede, and do not imply any type of ordering (e.g., spatial, temporal, logical, etc.). For example, a buffer circuit may be described herein as performing write operations for “first” and “second” values. The terms “first” and “second” do not necessarily imply that the first value must be written before the second value. 
     “Based On.” As used herein, this term is used to describe one or more factors that affect a determination. This term does not foreclose additional factors that may affect a determination. That is, a determination may be solely based on those factors or based, at least in part, on those factors. Consider the phrase “determine A based on B.” While in this case, B is a factor that affects the determination of A, such a phrase does not foreclose the determination of A from also being based on C. In other instances, A may be determined based solely on B. 
     DETAILED DESCRIPTION 
     Embodiments of a folded optical system are described that include two prisms with refractive power that together form the optical system. At least one surface of at least one of the prisms is a “freeform” surface, and thus the prism(s) may be referred to as freeform prisms. A freeform prism may be broadly defined as a prism with at least one surface that provides refractive power and that is asymmetric (not rotationally symmetric) (i.e., is a “freeform” surface). 
     Embodiments of the folded optical system as described herein may be implemented in a small package size while still capturing sharp, high-resolution images, making embodiments of a camera including the optical system suitable for use in small and/or mobile multipurpose devices such as cell phones, smartphones, pad or tablet computing devices, laptop, netbook, notebook, subnotebook, and ultrabook computers, and so on.  FIG.  8    illustrates an example device that may include one or more small form factor cameras that use embodiments of the folded optical system as described herein. However, note that aspects of the camera (e.g., the optical system and photosensor) may be scaled up or down to provide cameras with larger or smaller package sizes. In addition, embodiments of the camera may be implemented as stand-alone digital cameras. In addition to still (single frame capture) camera applications, embodiments of the camera may be adapted for use in video camera applications. 
       FIG.  1    illustrates a conventional folded camera  100  that includes a lens stack positioned between two prisms, according to some embodiments. The prisms  141  and  142  provide a “folded” optical axis for the camera  100 , for example to reduce the Z-height of the camera  100  when compared to conventional straight camera lenses. A lens stack  114  including one or more refractive lens elements is located between prisms  141  and  142 . A first prism  141  redirects light from an object field from a first axis to the lens stack  114  on a second axis. The lens element(s) in the lens stack  114  refract the light to a second prism  142  that redirects the light onto a third axis on which a photosensor  120  of the camera  100  is disposed. The redirected light forms an image at an image plane  121  at or near the surface of the photosensor  120 . 
       FIG.  2    illustrates a camera  200  that includes a folded optical system that consists of two freeform prisms  241  and  242  with refractive power, according to some embodiments. The prisms  241  and  242  provide a “folded” optical axis for the camera  200 , for example to reduce the Z-height of the camera. For example, a camera  100  with a conventional folded lens system as illustrated in  FIG.  1    may have a Z-axis height of &gt;6 mm, for example 6.4 mm, while a camera  200  with a folded optical system as illustrated in  FIG.  2    may have a Z-axis height of &lt;6 mm, for example 5.4 mm, while providing similar performance to the camera  100  of  FIG.  1   . In addition, the freeform prisms  241  and  242  in the folded optical system of camera  200  may eliminate the need for a lens stack between the prisms as shown in the camera  100  of  FIG.  1   , which may reduce the length of the long axis of the camera  200  when compared to the camera  100  of  FIG.  1   . Further, the folded optical system of  FIG.  2    requires fewer optical elements (two freeform prism) when compared to the folded lens system of  FIG.  1    (two prisms and at least one refractive lens element in the lens stack). Having fewer optical elements may, for example, simplify packaging and alignment of the optical system during manufacture when compared to the lens system of  FIG.  1   . 
     In the folded optical system of  FIG.  2   , a first freeform prism  241  (P 1 ) receives light from an object field through an aperture stop  230  and refracts and redirects the light from a first axis to a second axis. Prism  241  includes three surfaces that affect light passing through the prism  241 . A first surface (P 1 S 1 ) refracts light received from an object field through aperture stop  230 ; a second surface (P 1 S 2 ) reflects or redirects the light to a third surface (P 1 S 3 ); the light is refracted by the third surface to the second prism  242 . 
     A second freeform prism  242  (P 2 ) receives the light on the second axis and refracts and redirects the light onto a third axis on which a photosensor  220  of the camera is disposed. The refracted and redirected light forms an image at an image plane  221  at or near the surface of the photosensor  220 . Prism  242  includes three surfaces that affect light passing through the prism  242 . A first surface (P 2 S 1 ) refracts light received from the first prism  241 ; a second surface (P 2 S 2 ) reflects or redirects the light to a third surface (P 2 S 3 ); the light is refracted by the third surface to form an image at an image plane  221  at or near the surface of the photosensor  220 . In some embodiments, an infrared (IR) filter  250  may be located between the second prism  242  and the photosensor  220 . 
     For each prism in the folded optical system, a given surface may be flat/plano with no refractive power; symmetrically concave, convex, or aspherical with refractive power; or freeform (asymmetrically concave, convex, or aspherical with refractive power). As noted above, in some embodiments, at least one surface of at least one of the prisms is a freeform surface. In some embodiments, at least two of the six surfaces of the prisms in the optical system are freeform surfaces. In some embodiments, the first and third surfaces in both prisms are freeform surfaces, while the second surfaces in both prisms are flat/plano. However, in some embodiments, one or both of the second surfaces may be freeform surfaces with refractive power or symmetrical surfaces with refractive power. 
     In the example embodiment illustrated in  FIG.  2   , P 1 S 1  is a freeform convex surface with positive refractive power, P 1 S 2  is a flat/plano surface, P 1 S 3  is a freeform convex surface with positive refractive power, P 2 S 1  is a freeform concave surface with negative refractive power, P 2 S 2  is a flat/plano surface, and P 2 S 3  is a freeform concave surface with negative refractive power. In some embodiments, P 1 S 2  and P 2 S 2  may be coated with a reflective material to redirect light. However, in some embodiments, at least one of P 1 S 2  and P 2 S 2  may reflect light via total internal reflection (TIR). Further, in some embodiments, one or both of P 1 S 2  and P 2 S 2  may be freeform surfaces with refractive power or symmetrical surfaces with refractive power. 
     The materials and surfaces of prisms  241  and  242  may be selected to capture high resolution, high quality images. Parameters and relationships of the prisms  241  and  242 , including but not limited to the materials and surface shapes may be selected at least in part to reduce, compensate, or correct for optical aberrations and artifacts and effects across the field of view. In some embodiments, the materials and surfaces of the prisms in the optical system may be selected to provide a low F-number (e.g., &lt;=2.4), full field of view (FOV) of 30 degrees or less, and high brightness, high resolution images with high image quality. 
     In some embodiments, an aperture stop  230  is located in the folded optical system at the first (object side) surface of the first prism  241 . In some embodiments, the aperture stop  230  may be elliptical; however, circular or other shapes may be used for the aperture in some embodiments. In some embodiments, the camera  200  may include an infrared (IR) filter  250  to reduce or eliminate interference of environmental noise on the photosensor  220 . The IR filter  250  may, for example, be located between the second prism  242  and the photosensor  220 . 
       FIGS.  3 A,  3 B, and  3 C  are diagrams illustrating orientation of the x and y axes at the surfaces of the freeform prisms as shown in  FIG.  2   , according to some embodiments.  FIG.  3 A  is s cross-sectional illustration of a folded optical system, according to some embodiments. Referring to  FIG.  3 A , optical characteristics of the freeform surfaces of the prisms in an optical system as illustrated in  FIG.  2    may be defined for a paraxial region of the surfaces along two axes of symmetry (x and y) relative to the optical axis at the surfaces of the prisms  241  and  242 . As shown in  FIG.  3 A , the optical axis is a line that passes through surface P 1 S 1  at a center point of aperture stop  230  and perpendicular to a tangent plane at that point of surface P 1 S 1 . A light ray on the optical axis passes through the folded optical system to strike at or near the center of photosensor  220  and perpendicular to the surface plane of photosensor  220 . At the photosensor, the x axis corresponds to a horizontal axis of the photosensor  220  that intersects the optical axis, and the y axis corresponds to a vertical axis of the photosensor  220  that intersects the optical axis. The y axis and the optical axis are on the plane of the cross-section, and the x axis is perpendicular to the plane of the cross-section. At each surface of prisms  241  and  242 , the x axis is on a tangent plane at the intersection of the optical axis with the surface and is parallel to the x axis at the photosensor  220  and perpendicular to the optical axis. However, at each surface of prisms  241  and  242 , the y axis rotates around the x axis to conform to the tangent plane, and thus is not necessarily parallel to the y axis at the photosensor  220 .  FIG.  3 C  graphically illustrates the x, y, and optical axes on a 3D model of a prism. As shown in  FIG.  3 C , the x axes at S 1 , S 2 , and S 3  are parallel to each other and perpendicular to the optical axis. However, the y axis at each surface rotates around the x axis to conform to the tangent plane at the respective surface. 
     As noted above, the optical characteristics of the freeform surfaces of the prisms in an optical system as illustrated in  FIG.  2    may be defined for a paraxial region around the optical axis along two axes of symmetry (x and y).  FIG.  3 B  graphically illustrates the effective aperture and paraxial region of a surface of a prism as illustrated in  FIG.  3 A . At P 1 S 1 , the aperture is defined by aperture stop  230 . At each successive surface (P 1 S 2 , P 1 S 3 , P 2 S 1 , P 2 S 2 , and P 2 S 3 ), the aperture may be defined by the light that the surface receives from the preceding surface. As previously noted, in some embodiments, the aperture stop  230  may be elliptical; however, circular or other shapes may be used for the aperture in some embodiments.  FIG.  3 C  shows the x and y axes at the aperture as previously defined at the surface. The paraxial region is a region around the optical axis that extends 10% or less of the width of the aperture in each direction from the optical axis on the x and y axes. 
       FIG.  4    is a 3D cross-sectional illustration of an example folded optical system that includes two freeform prisms, according to some embodiments. A telephoto camera  400  may include a folded optical system that consists of two freeform prisms  441  and  442 . An aperture stop may be located at a first (object side) surface of the first prism  441 . The aperture stop may be elliptical or circular. The camera  400  also includes a photosensor  420 . In some embodiments, an infrared filter may be located between the second prism  442  and the photosensor. In some embodiments, the folded optical system may be configured to provide a low F-number (e.g., &lt;=2.4), full field of view (FOV) of 30 degrees or less, and high brightness, high resolution images with high image quality. 
     The folded optical system consists of two freeform prisms  441  (P 1 ) and  442  (P 2 ). Each of the two prisms  441  and  442  includes three surfaces that affect light passing through the prism. A first surface (S 1 ) receives the light from an object side of the prism; a second surface (S 2 ) reflects or redirects the light received through the first surface to a third surface (S 3 ); the light then passes through or is refracted by the third surface to the next prism or to the photosensor  420 . Each of the prisms includes at least one freeform surface in the imaging path that is not rotationally symmetric. 
     At prism  441 , incoming light through aperture stop  430  is converged by P 1 S 1 , reflected by P 1 S 2 , and converged by P 1 S 3  to exit prism  441 . At prism  442 , the light from prism  441  is diverged by P 2 S 1 , reflected by P 2 S 2 , diverged by P 2 S 3 , and exits prism  442  to form an image at an image plane at or near the surface of photosensor  420 . The folding surfaces (surfaces P 1 S 2  and P 2 S 2 ) may reflect light either through total internal reflection (TIR) or via a mirror coating. 
     In some embodiments, the aperture stop  430  of the folded optical system is at or near the object side surface (P 1 S 1 ) of prism  441 . In some embodiments, the aperture stop  430  is at or near (within 0.3 mm) surface P 1 S 1  for imaging purposes. 
     In some embodiments, the folded optical system has same focal lengths along the x axis and along the y axis. The folded optical system satisfies the following condition:
 
 f   x   =f   y   =f   sys ,
 
where f x  is the focal length through the folded optical system on the x axis, f y  is the focal length through the folded optical system on they axis, and f sys  is the effective focal length of the folded optical system.
 
     For each of the prisms  441  and  442 , focal lengths along the x axis (f P1X , f P2X ) are different than focal lengths along the y axis (f P1Y , f P2Y ), respectively, which defines both prisms  441  and  442  as freeform prisms:
 
 f   P1X   ≠f   P1Y   ,f   P2X   ≠f   P2Y .
 
     In some embodiments, an optional infrared cutoff filter (IRCF) is positioned in front of the photosensor  420  to remove unwanted infrared light and thus improve the signal-to-noise ratio (SNR). 
       FIG.  5    is a cross-sectional illustration of an example folded optical system as illustrated in  FIG.  4    that includes two freeform prisms  441  and  442 , according to some embodiments. On the optical axis, prism  441  includes three surfaces with power. The refractive power of prism  441  along the x axis is stronger than the refractive power along the y axis. Prism  441  satisfies the following conditions:
 
0.55&lt; f   P1y   /f   sys &lt;0.85
 
0.5&lt; f   P1x   /f   sys &lt;0.8
 
where f P1y  is the focal length of prism  441  along the y axis, f P1x  is the focal length of prism  441  along the x axis, and f sys  is the effective focal length of the freeform folded optical system.
 
     Prism  441  has three surfaces along the optical axis from an object side to an image side: P 1 S 1 , P 1 S 2 , and P 1 S 3 . P 1 S 1  is convex in the paraxial region, and satisfies the following conditions:
 
1.2&lt; f   P1S1y   /f   P1y  
 
 f   P1S1x   /f   P1x &lt;2.8
 
where f P1S1y  and f P1S1x  are focal lengths of surface P 1 S 1  on they and x axes, respectively.
 
     P 1 S 2  is reflective coated to reflect visible light and fold the optical axis. 
     P 1 S 3  is convex in the paraxial region, and satisfies the following conditions:
 
1&lt; f   P1S3x   /f   P1x &lt;3
 
4&lt; f   P1S3y   /f   P1y &lt;5
 
where f P1S3y  and f P1S3x  are focal lengths of surface P 1 S 3  on they and x axes, respectively.
 
     In some embodiments, prism  441  may be formed of an optical plastic material. In some embodiments, prism  441  is formed of an optical material with an Abbe number vd1 that satisfies the following condition:
 
 vd 1&gt;50.
 
     On the optical axis, prism  442  includes three surfaces with power. The refractive power of prism  442  along x axis is stronger than that along the y axis. Prism  442  satisfies the following conditions:
 
−1&lt; f   P2y   /f   sys &lt;−0.4
 
−1&lt; f   P2x   /f   sys &lt;−0.7
 
where f P2y  is the focal length of prism  442  along the y axis, f P2x  is the focal length of prism  442  along the x axis, and f sys  is the effective focal length of the freeform folded optical system.
 
     Prism  442  has three surfaces along the optical axis from an object side to an image side: P 2 S 1 , P 2 S 2 , and P 2 S 3 . P 2 S 1  is concave in the paraxial region, and satisfies the following conditions:
 
1&lt; f   P2S1y   /f   P2y  
 
 f   P2S1x   /f   P2x &lt;3
 
where f P2S1y  and f P2S1x  are focal lengths of surface P 2 S 1  on they and x axes, respectively.
 
     P 2 S 2  is reflective coated to reflect visible light and fold the optical axis. 
     P 2 S 3  is concave in the paraxial region, and satisfies the following conditions:
 
3&lt; f   P2S3x   /f   P2y &lt;7
 
1&lt; f   P2S3y   /f   P2y &lt;3
 
where f P2S3y  and f P2S3x  are focal lengths of surface P 2 S 3  on the y and x axes, respectively.
 
     In some embodiments, prism  442  may be formed of an optical plastic material. In some embodiments, prism  442  is formed of an optical material with an Abbe number vd2 that satisfies the following condition:
 
 vd 2&lt;30
 
       FIG.  6    is a cross-sectional illustration of an example folded optical system that includes two freeform prisms and shows the angles between surfaces of the freeform prisms, according to some embodiments. The angle between the tangent line of P 1 S 1  and the tangent line of P 1 S 3  is Alpha 1. In some embodiments, Alpha 1 satisfies the following condition:
 
70 degrees&lt;Alpha 1&lt;110 degrees
 
     The angle between the tangent line of P 2 S 1  and the tangent line of P 2 S 3  is Alpha 2. In some embodiments, Alpha 2 satisfies the following condition:
 
70 degrees&lt;Alpha 2&lt;110 degrees
 
Example Flowchart
 
       FIG.  7    is a flowchart of a method for capturing images using embodiments of a camera as illustrated in  FIGS.  2  through  6   , according to some embodiments. As indicated at  1900 , light from an object field in front of the camera is received through an aperture stop at a first surface of a first freeform prism on a first axis. As indicated at  1910 , the light is refracted and redirected by the first freeform prism to a second axis. As indicated at  1920 , the light is received at a first surface of a second freeform prism. As indicated at  1930 , the light is refracted and redirected by the second freeform prism to a third axis. As indicated at  1940 , the light forms an image at an image plane at or near the surface of a photosensor or sensor module on the third axis. As indicated at  1950 , the image is captured by the photosensor. 
     While not shown in  FIG.  7   , in some embodiments, the light may pass through an infrared filter that may for example be located between the second freeform prism and the photosensor. 
     In some embodiments, the components of the folded optical system referred to in  FIG.  7    may be configured as illustrated in any of  FIG.  2 ,  3 ,  4 ,  5   , or  6 . However, note that variations on the examples given in the Figures are possible while achieving similar optical results. 
     Example Computing Device 
       FIG.  8    illustrates an example computing device, referred to as computer system  2000 , that may include or host embodiments of a camera with a folded optical system as illustrated in  FIGS.  2  through  7   . In addition, computer system  2000  may implement methods for controlling operations of the camera and/or for performing image processing of images captured with the camera. In different embodiments, computer system  2000  may be any of various types of devices, including, but not limited to, a personal computer system, desktop computer, laptop, notebook, tablet or pad device, slate, or netbook computer, mainframe computer system, handheld computer, workstation, network computer, a camera, a set top box, a mobile device, a wireless phone, a smartphone, a consumer device, video game console, handheld video game device, application server, storage device, a television, a video recording device, a peripheral device such as a switch, modem, router, or in general any type of computing or electronic device. 
     In the illustrated embodiment, computer system  2000  includes one or more processors  2010  coupled to a system memory  2020  via an input/output (I/O) interface  2030 . Computer system  2000  further includes a network interface  2040  coupled to I/O interface  2030 , and one or more input/output devices  2050 , such as cursor control device  2060 , keyboard  2070 , and display(s)  2080 . Computer system  2000  may also include one or more cameras  2090 , for example one or more cameras as described above with respect to  FIGS.  2  through  7   , which may also be coupled to I/O interface  2030 , or one or more cameras as described above with respect to  FIGS.  2  through  7    along with one or more other cameras such as conventional wide-field cameras. 
     In various embodiments, computer system  2000  may be a uniprocessor system including one processor  2010 , or a multiprocessor system including several processors  2010  (e.g., two, four, eight, or another suitable number). Processors  2010  may be any suitable processor capable of executing instructions. For example, in various embodiments processors  2010  may be general-purpose or embedded processors implementing any of a variety of instruction set architectures (ISAs), such as the x86, PowerPC, SPARC, or MIPS ISAs, or any other suitable ISA. In multiprocessor systems, each of processors  2010  may commonly, but not necessarily, implement the same ISA. 
     System memory  2020  may be configured to store program instructions  2022  and/or data  2032  accessible by processor  2010 . In various embodiments, system memory  2020  may be implemented using any suitable memory technology, such as static random access memory (SRAM), synchronous dynamic RAM (SDRAM), nonvolatile/Flash-type memory, or any other type of memory. In the illustrated embodiment, program instructions  2022  may be configured to implement various interfaces, methods and/or data for controlling operations of camera  2090  and for capturing and processing images with integrated camera  2090  or other methods or data, for example interfaces and methods for capturing, displaying, processing, and storing images captured with camera  2090 . In some embodiments, program instructions and/or data may be received, sent or stored upon different types of computer-accessible media or on similar media separate from system memory  2020  or computer system  2000 . 
     In one embodiment, I/O interface  2030  may be configured to coordinate I/O traffic between processor  2010 , system memory  2020 , and any peripheral devices in the device, including network interface  2040  or other peripheral interfaces, such as input/output devices  2050 . In some embodiments, I/O interface  2030  may perform any necessary protocol, timing or other data transformations to convert data signals from one component (e.g., system memory  2020 ) into a format suitable for use by another component (e.g., processor  2010 ). In some embodiments, I/O interface  2030  may include support for devices attached through various types of peripheral buses, such as a variant of the Peripheral Component Interconnect (PCI) bus standard or the Universal Serial Bus (USB) standard, for example. In some embodiments, the function of I/O interface  2030  may be split into two or more separate components, such as a north bridge and a south bridge, for example. Also, in some embodiments some or all of the functionality of I/O interface  2030 , such as an interface to system memory  2020 , may be incorporated directly into processor  2010 . 
     Network interface  2040  may be configured to allow data to be exchanged between computer system  2000  and other devices attached to a network  2085  (e.g., carrier or agent devices) or between nodes of computer system  2000 . Network  2085  may in various embodiments include one or more networks including but not limited to Local Area Networks (LANs) (e.g., an Ethernet or corporate network), Wide Area Networks (WANs) (e.g., the Internet), wireless data networks, some other electronic data network, or some combination thereof. In various embodiments, network interface  2040  may support communication via wired or wireless general data networks, such as any suitable type of Ethernet network, for example; via telecommunications/telephony networks such as analog voice networks or digital fiber communications networks; via storage area networks such as Fibre Channel SANs, or via any other suitable type of network and/or protocol. 
     Input/output devices  2050  may, in some embodiments, include one or more display terminals, keyboards, keypads, touchpads, scanning devices, voice or optical recognition devices, or any other devices suitable for entering or accessing data by computer system  2000 . Multiple input/output devices  2050  may be present in computer system  2000  or may be distributed on various nodes of computer system  2000 . In some embodiments, similar input/output devices may be separate from computer system  2000  and may interact with one or more nodes of computer system  2000  through a wired or wireless connection, such as over network interface  2040 . 
     As shown in  FIG.  8   , memory  2020  may include program instructions  2022 , which may be processor-executable to implement any element or action to support integrated camera  2090 , including but not limited to image processing software and interface software for controlling camera  2090 . In some embodiments, images captured by camera  2090  may be stored to memory  2020 . In addition, metadata for images captured by camera  2090  may be stored to memory  2020 . 
     Those skilled in the art will appreciate that computer system  2000  is merely illustrative and is not intended to limit the scope of embodiments. In particular, the computer system and devices may include any combination of hardware or software that can perform the indicated functions, including computers, network devices, Internet appliances, PDAs, wireless phones, pagers, video or still cameras, etc. Computer system  2000  may also be connected to other devices that are not illustrated, or instead may operate as a stand-alone system. In addition, the functionality provided by the illustrated components may in some embodiments be combined in fewer components or distributed in additional components. Similarly, in some embodiments, the functionality of some of the illustrated components may not be provided and/or other additional functionality may be available. 
     Those skilled in the art will also appreciate that, while various items are illustrated as being stored in memory or on storage while being used, these items or portions of them may be transferred between memory and other storage devices for purposes of memory management and data integrity. Alternatively, in other embodiments some or all of the software components may execute in memory on another device and communicate with the illustrated computer system  2000  via inter-computer communication. Some or all of the system components or data structures may also be stored (e.g., as instructions or structured data) on a computer-accessible medium or a portable article to be read by an appropriate drive, various examples of which are described above. 
     In some embodiments, instructions stored on a computer-accessible medium separate from computer system  2000  may be transmitted to computer system  2000  via transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as a network and/or a wireless link. Various embodiments may further include receiving, sending or storing instructions and/or data implemented in accordance with the foregoing description upon a computer-accessible medium. Generally speaking, a computer-accessible medium may include a non-transitory, computer-readable storage medium or memory medium such as magnetic or optical media, e.g., disk or DVD/CD-ROM, volatile or non-volatile media such as RAM (e.g. SDRAM, DDR, RDRAM, SRAM, etc.), ROM, etc. In some embodiments, a computer-accessible medium may include transmission media or signals such as electrical, electromagnetic, or digital signals, conveyed via a communication medium such as network and/or a wireless link. 
     The methods described herein may be implemented in software, hardware, or a combination thereof, in different embodiments. In addition, the order of the blocks of the methods may be changed, and various elements may be added, reordered, combined, omitted, modified, etc. Various modifications and changes may be made as would be obvious to a person skilled in the art having the benefit of this disclosure. The various embodiments described herein are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of claims that follow. Finally, structures and functionality presented as discrete components in the example configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of embodiments as defined in the claims that follow.

Metadata:
Filing Date: 20190920
Publication Date: 20240709
Grant Date: 20240709
Priority Date: 20180925
Inventors: YAO, YUHONG
SCEPANOVIC, MIODRAG
SHINOHARA, YOSHIKAZU
Assignee: APPLE INC
CPC Classifications: [{"code": "G02B13/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B5/04", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B17/0856", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B17/0856", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02B17/0856", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B13/007", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B13/007", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02B13/007", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B17/0856", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 68136567