Varifocal immersive display, eye-prescription-adjustable immersive display, and image stabilization cell phone camera with telecentric folded lens

Abstract

A head-mounted display (HMD) including an electronic display; a telecentric folded lens comprising a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, where the first optical lens element is closer to the electronic display than the second optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element facing the first optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, where an optical path of a chief ray entering the telecentric folded lens is parallel to the optical axis of the telecentric folded lens; and an adjustment element configured to adjust a distance between the electronic display and the telecentric folded lens.

Description

Varifocal Immersive Display, Eye-Prescription-Adjustable Immersive Display, and Image Stabilization Cell Phone Camera with Telecentric Folded LensTECHNICAL FIELD

[0001] The present disclosure is generally related to methods and apparatus for viewing or image-capturing and, in particular embodiments, to immersive displays, vision correction, or cell phone cameras.BACKGROUND

[0002] Varifocal technology may be useful in a variety of devices, including eyeglasses, immersive display devices or systems (e.g., for virtual reality (VR), augmented reality (AR), or mixed reality), and cameras. For example, in immersive display devices, a head-mounted display (HMD) may be positioned close to a user’s eyes and may present stereoscopic digital images to the user's eyes to provide a three-dimensional (3D) visual experience (e.g., with 3D objects and 3D scenes). The images may be projected through one or more lenses. Varifocal technology may be used to enable a focal distance of the images to be adjusted, such as to counteract or supplement natural focal changes in the user's eyes as the user observes the images at different perceived 3D depths or distances. In a camera, varifocal technology may be used to provide image stabilization by dynamically adjusting the focal length in the cell phone camera to counteract the movements of the cell phone camera, resulting in sharper images and more comfortable visual experience for the users. Additionally, varifocal technology may be useful in providing vision correction in immersive displays. For instance, because HMDs are typically positioned close to the user’s eyes and the form factors of some HMDs are continuing to be reduced, there may not be sufficient space for the user to fit their eye-prescription glasses (a.k.a., prescription eyeglasses) under the HMDs.SUMMARY

[0003] The disclosed aspects / embodiments of the present disclosure provide techniques, methods and devices or systems for utilizing a telecentric folded lens in a head-mounted display (HMD) and for varying a distance between a display panel and the telecentric folded lens in the HMD to provide 1) a varifocal immersive display device (e.g., for augmented reality (AR), virtual reality (VR), and / or mixed reality (MR)) or 2) an immersive display device with built-in vision (eyesight) correction. The telecentric folded lens is designed to provide a constant magnificationregardless of the image’s distance (from the user’s eye) or the location in the field of view (FOV). Accordingly, software-implemented algorithm(s) and / or additional optics that are commonly used to correct for magnification and image distortion that result from providing the varifocal property may be eliminated to provide a more efficient and compact varifocal system. The telecentric folded lens with a reverse optical architecture can be used to provide 3) image stabilization for image and / or video recording at a cell phone camera. The telecentric folded lens with the reverse optical architecture is designed to provide a constant magnification regardless of the object’s distance (from the telecentric folded lens) or the location in the FOV. Further, an adjustment mechanism can be added within the optics of the telecentric folded lens to provide a zooming capability decoupled from the focusing operations.

[0004] A first aspect of the embodiments of the present disclosure relates to a head-mounted display (HMD) comprising an electronic display configured to emit light; a telecentric folded lens configured to direct the light to an exit pupil of the HMD, the telecentric folded lens comprising a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, wherein the first optical lens element is closer to the electronic display than the second optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element facing the first optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, disposed such that an optical path of a chief ray of the light entering the telecentric folded lens is parallel to the optical axis of the telecentric folded lens, and wherein the chief ray is a ray that passes through a center of an aperture stop of the telecentric folded lens; and an adjustment element configured to adjust a focal length of the telecentric folded lens.

[0005] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the adjustment element is configured to adjust the focal length of the telecentric folded lens by adjusting a distance between the electronic display and the telecentric folded lens.

[0006] Optionally, in any of the preceding aspects, another implementation of the aspect provides that an entrance pupil of the telecentric folded lens is greater than 10 meters away from the telecentric folded lens.

[0007] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the telecentric folded lens provides a constant half field of view greater than 50 degrees for a plurality of image distances.

[0008] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the first optical lens element comprises a flint glass, which has a dispersion V-value less than 50 and a refractive index greater than 1.65 and less than 1.9 at a wavelength of 589.25 nanometers (nm) wavelength.

[0009] Optionally, in any of the preceding aspects, another implementation of the aspect provides that at least one of a first surface of the first optical lens element facing the electronic display or a second surface of the first optical lens element opposite the first surface is aspherical.

[0010] Optionally, in any of the preceding aspects, another implementation of the aspect provides that a radius of a surface of the first optical lens element facing the electronic display is between 120 millimeters (mm) and 140 mm, and a conic constant of the surface is between -5 and -6.

[0011] Optionally, in any of the preceding aspects, another implementation of the aspect provides that a radius of a surface of the first optical lens element facing the second optical lens element is between -190 millimeter (mm) and -200 mm, and a conic constant of the surface is between 7 and 8.

[0012] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the second optical lens element comprises a crown glass with a refractive index greater than 1.4 and less than 1.6 at a wavelength of 589.25 nanometers (nm) and a dispersion V- value greater than 50 and less than 90.

[0013] Optionally, in any of the preceding aspects, another implementation of the aspect provides that a radius of a second surface of the second optical lens element opposite the surface of the second optical lens element facing the first optical lens element is between -8 millimeters (mm) and -9 mm, and a conic constant of the second surface is between -6.5 x 1014and -7.5* IO14

[0014] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the surface of the second optical lens element facing the first optical lens element is flat, and a second surface of the second optical lens element opposite the surface of the second optical lens element facing the first optical lens element is aspherical.

[0015] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the telecentric folded lens further comprises a partially reflective optical element disposed on a surface of the first optical lens element facing the electronic display.

[0016] Optionally, in any of the preceding aspects, another implementation of the aspect provides that a distance between the telecentric folded lens and an eye of a user of the HMD is adjustable.

[0017] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the adjustment element is between the electronic display and the telecentric folded lens and comprises a sliding wedge system comprising a pair of wedge blocks with opposing inclined planes; and a sliding mechanism for sliding the pair of wedge blocks in opposite directions along an axis different than the optical axis of the telecentric folded lens.

[0018] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the adjustment element is coupled to the electronic display and comprises an actuator.

[0019] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the actuator comprises at least one of a voice coil motor (VCM), a step motor, or an ultrasonic motor (USM).

[0020] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the HMD is a varifocal immersive display device.

[0021] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the HMD is an eye-prescription adjustable immersive display device, wherein a prescription power of the HMD is based on at least one of a manual or automatic adjustment of the distance between the electronic display and the telecentric folded lens.

[0022] A second aspect relates to an apparatus comprising an optical imaging device comprising an image sensor configured to convert first light to an electrical signal; a telecentric folded lens configured to receive second light associated with an external object and propagate at least a portion of the second light towards the image sensor, wherein the at least the portion of the second light corresponds to the first light, and wherein the telecentric folded lens comprises a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, wherein the second optical lens element is closer to the image sensor than the first optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, disposed such that an optical path of a chief ray exiting the telecentric folded lens is parallel to the optical axis of the telecentric folded lens; and an adjustment element configured to adjust a focal length of the telecentric folded lens.

[0023] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the adjustment element is configured to adjust the focal length of the telecentric folded lens by adjusting a distance between the image sensor and the telecentric folded lens.

[0024] Optionally, in any of the preceding aspects, another implementation of the aspect provides that an exit pupil of the telecentric folded lens is greater than 10 meters away from the telecentric folded lens.

[0025] Optionally, in any of the preceding aspects, another implementation of the aspect provides that a diameter of the telecentric folded lens is between 4 millimeters (mm) to 20 mm.

[0026] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the telecentric folded lens further comprises a partially reflective optical element disposed on a surface of the first optical lens element facing an entrance aperture.

[0027] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the adjustment element comprises at least one of a sliding wedge system, or an electronically adjustable actuator comprising at least one of a voice coil motor (VCM), a step motor, or an ultrasonic motor (USM).

[0028] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the optical capturing device further comprises a second adjustment element configured to adjust a distance between the first optical lens element and the second optical lens element of the telecentric folded lens.

[0029] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the apparatus is a user equipment (UE).

[0030] A third aspect relates to a method comprising determining, by a processor of a headmounted display (HMD) comprising an electronic display and a telecentric folded lens, that is configured to place the telecentric folded lens in front of a user’s eye, a distance between the user’s eye and a virtual object plane that is farther away from the user’s eye than the electronic display; and adjusting, by the processor, based on the distance between the user’s eye and the virtual object plane, a distance between the electronic display and the telecentric folded lens while maintaining a constant distance between the telecentric folded lens and the user’s eye.

[0031] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the method further comprises tracking, by a sensing device, a gaze of the user’s eye,wherein the determining the distance between the virtual object plane and the user’s eye is based on the gaze of the user’s eye.

[0032] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the determining the distance between the virtual object plane and the user’s eye is based on an image content to be projected on to the virtual object plane.

[0033] Optionally, in any of the preceding aspects, another implementation of the aspect provides that the telecentric folded lens comprises a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, wherein the first optical lens element is closer to the electronic display than the second optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element facing the first optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, and an optical path of a chief ray entering the telecentric folded lens is parallel to the optical axis of the telecentric folded lens.

[0034] For the purpose of clarity, any one of the foregoing embodiments may be combined with any one or more of the other foregoing embodiments to create a new embodiment within the scope of the present disclosure.

[0035] These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

[0037] FIG. 1 is a schematic diagram of a side view of an example head-mounted display (HMD) arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0038] FIG. 2 illustrates an example optical path of a telecentric folded lens according to an embodiment of the present disclosure.

[0039] FIG. 3 is a schematic diagram illustrating an example adjustment arrangement for an HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0040] FIGS. 4A-4B are schematic diagrams illustrating another example adjustment arrangement for an HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0041] FIG. 5 is a schematic diagram illustrating the generation of a virtual image according to an embodiment of the present disclosure.

[0042] FIG. 6 is a schematic diagram of an example adjustment configuration for an HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0043] FIG. 7 is a schematic diagram of another example adjustment configuration for an HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0044] FIG. 8 is a schematic diagram of yet another example adjustment configuration for an HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0045] FIG. 9 is a schematic diagram of a further example adjustment configuration for an HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0046] FIG. 10 is a schematic diagram of a side view of another example HMD arrangement with a telecentric folded lens according to an embodiment of the present disclosure.

[0047] FIG. 11 is a schematic diagram of a side view of an example camera arrangement with a telecentric folded lens according to according to an embodiment of the present disclosure.

[0048] FIG. 12 is a schematic diagram of a side view of an example camera arrangement with a zoomable telecentric folded lens according to an embodiment of the present disclosure.

[0049] FIG. 13 is a flowchart of an example method for operations of an HMD with a telecentric folded lens according to an embodiment of the present disclosure.

[0050] FIG. 14 is a block diagram of an example computer apparatus according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0051] It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and / or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, andtechniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.

[0052] The following terms are defined as follows unless used in a contrary context herein. Specifically, the following definitions are intended to provide additional clarity to the present disclosure. However, terms may be described differently in different contexts. Accordingly, the following definitions should be considered as a supplement and should not be considered to limit any other definitions of descriptions provided for such terms herein.

[0053] A telecentric optical system is one in which the chief rays are parallel to the optical axis when the chief rays enter the optical system and / or when the chief rays exit the optical system. A chief ray refers to a light ray originating from an off-axis object point that passes through the center of the aperture stop of an optical system. Generally, a chief ray is a ray that passes through the center of the aperture stop of an optical system. An off-axis ray may refer to a light ray that is not aligned to the optical axis (the main or central optical axis) of a lens system. An entrance pupil of a telecentric optical system may refer to a point (an apparent or virtual point) from which light appears to enter the system. An exit pupil of a telecentric optical system may refer to a point (an apparent or virtual point) where rays of light (from the lenses) converge after passing through the system.

[0054] In immersive displays (e.g., virtual reality (VR), augmented reality (AR), and / or mixed reality (MR) head-mounted displays (HMDs)), an image distance may refer to the distance between the virtual object plane (or virtual image plane) and the viewer’s eye. The virtual object plane may refer to the apparent position where the virtual image created by the HMD is perceived by the user after passing through the optical lenses within the HMD. Stated differently, the image distance is the perceived distance at which a virtual object plane appears to be located in front of the user. Further, in immersive displays, a focal length may refer to the distance from the center of a lens (or lenses) to the focal point, where light rays that are parallel to the optical axis converge (for converging lenses) or diverge (for diverging lenses).

[0055] In optical image-capturing systems (e.g., cameras), an object distance may refer to the distance between the real object for imaging and the camera lenses. Stated differently, the object distance is the actual physical distance between the camera lens and the real object being imaged. Further, in image-capturing systems, a focal length may refer to the distance from the center of thelens (or lenses) to the focal point, where parallel light rays coming into the lens converge to form a sharp image.

[0056] As providing natural human vision in immersive systems is important, there are various immersive systems built with varifocal technology. For instance, one such immersive system provides varifocal capabilities by utilizing optical lenses (e.g., including Fourier transfer lenses) and a mechanically actuated, eye-tracked varifocal display that follows the user’s vergence point. That is, the display is moved closer or farther away from the eyes of a user to change the focal length of the lenses based on eye tracking. However, moving the display causes the system magnification and image distortion to change dynamically. To overcome the magnification and image distortion issues, the immersive system further utilizes a closed-loop proportional-integral- derivative (PID) display distortion rendering pipeline to ensure that the virtual content (e.g., VR, AR, or MR content) remains correct in perspective despite the varying display magnification. To provide such distortion correction in real-time, the amount of processing can be intense, requiring high processing power. Another immersive system provides a multifocal display by utilizing a complex tunable and programmable split-Lohmann lens system with a phase spatial light modulator. Such an immersive system may have a large size and can be heavy, and the computations can be complex, requiring high processing power. For cameras, image stabilization is typically achieved by software-implemented algorithms with heavy computations, requiring high processing power, and may require additional hardware optics. Accordingly, improvements to varifocal technologies can yield benefits.

[0057] Disclosed herein are techniques for providing efficient and compact varifocal optical systems by designing and utilizing a telecentric folded lens (or telecentric pancake lens) in the optical system. In one embodiment, the telecentric folded lens is included in an immersive display (e g., a head-mounted display (HMD)). The telecentric folded lens is designed such that the optical paths of all chief rays entering the telecentric folded lens are parallel to the optical axis of the telecentric folded lens. The HMD may further include an electronic display (e.g., a display panel) configured to emit image light towards the telecentric folded lens and an adjustment element configured to adjust the distance between the electronic display and the telecentric folded lens, which in turn adjusts the focal lengths of the telecentric folded lens. Because all the chief rays (entering the telecentric folded lens) are parallel to the optical axis of the telecentric folded lens, the telecentric folded lens may provide a constant magnification ratio and a constant field of view(FOV) regardless of the focal length (of the telecentric folded lens) or the image distance (the distance between the target virtual object plane and the viewer’s eye looking into the telecentric folded lens). In some instances, the HMD is a varifocal immersive display device. In some instances, the HMD is an eye-prescription adjustable immersive display device.

[0058] In another embodiment, the telecentric folded lens with a reverse optical architecture is included in an optical imaging device (e.g., a cellphone camera) to provide image stabilization. The optical imaging device may further include an image sensor configured to convert light into electrical signals (for digital image creation) and an adjustment element configured to adjust the distance between the image sensor and the telecentric folded lens, which in turn adjusts the focal lengths of the telecentric folded lens. With the reverse optical architecture, the optical paths of all chief rays exiting the telecentric folded lens are parallel to the optical axis of the telecentric folded lens, and thus the image magnification ratio and the FOV may be constant irrespective of the focal length (of the telecentric folded lens) or the object distance (the distance between the real object for imaging and the telecentric folded lens). Stated differently, the telecentric folded lens may provide a constant magnification ratio and a constant FOV during focusing on a near object or a far object. In a further embodiment, a further, separate adjustable mechanism is included in the telecentric folded lens for adjusting the optical lens element within the telecentric folded lens to provide a zooming capability (e.g., to vary the image magnification or the FOV). The separate adjustable mechanism for zooming allow for the tele-centricity to be maintained during zooming.

[0059] Utilizing telecentric folded lens with adjustment mechanisms between the telecentric folded lens and an electronic display (in an HMD) or an image sensor (in a camera) can provide varying focal lengths with a constant magnification and a constant FOV without having to utilize additional hardware and / or software (e.g., a PID controller) to correct the magnification and / or image distortion, and thus providing a more efficient and compact varifocal system. Focusing or varying the focal length while maintaining the magnification and / or FOV imitates the human eye (providing natural human vision), making it suitable for use in immersive displays, cell phone cameras (e.g., to provide smooth and stable video recording without heavy computations), and / or for vision correction in immersive displays. Additionally, because the telecentric folded lens has a folded optical path (that bends lights within the telecentric folded lens), the telecentric folded lens is compact in size (e.g., thin and light), again making it suitable for use in immersive displays and cell phone cameras and / or for vision correction in immersive displays. Further, using separateadjustable mechanisms to adjust the zoom ratio and the focal lengths can decouple the zoom and focus operations of optics, allowing for a compact size and a large FOV.

[0060] While the present disclosure is discussed in the context of designing and utilizing a telecentric folded lens for one eye (e.g., a left eye or a right eye) of the user, similar mechanisms can be applied for providing a telecentric folded lens and corresponding adjustment mechanism for the other one of the user’s left eye or right eye. That is, an HMD may have a first display and a first telecentric folded lens with a corresponding first adjustment mechanism for adjusting the distance between the first display and the first telecentric folded lens (e.g., for the user’s right eye), and a second display and a second telecentric folded lens with a second adjust mechanism for adjusting the distance between the first display and the first telecentric folded lens (e.g., for the user’s left eye).

[0061] The terms “folded lens” and “pancake lens” may be used interchangeably herein, such that a description referring to one of the terms shall be treated as though the description also referred to the other term.

[0062] FIG. 1 is a schematic diagram of a side view (e.g., in the y-z plane) of an example HMD arrangement 100 with a telecentric folded lens 114 according to an embodiment of the present disclosure. In one embodiment, the HMD 110 is a varifocal immersive display device (e.g., an AR and / or VR display headset). In another embodiment, the HMD 110 is an eye-prescription adjustable immersive display device (e.g., providing vision correction for presbyopia, which is a common age-related vision condition). The HMD 110 may be fitted over a user’s head and may present digital content to the user. The digital content is computer-generated information. Examples of digital content may include, but are not limited to, images, video, audio, or some combination thereof. In some instances, audio content may be presented via a separate device (e.g., speakers, headphones, and / or consoles) external to the HMD 110 that receives audio information from the HMD 110.

[0063] As shown in FIG. 1, the HMD 110 includes an electronic display 112 and the telecentric folded lens 114 spaced apart from each other by an adjustable distance 140, denoted as L. The electronic display 112 is configured to emit light 106 . Example electronic displays 112 may include, but are not limited to, a liquid crystal display (LCD) panel, an organic light-emitting diode (OLED) panel, an active-matrix OLED panel, and a micro-LED panel. The light 106 emitted from the electronic display 112 may pass through the telecentric folded lens 114. The telecentric foldedlens 1 14 may focus, shape, and direct the light 106 to an exit pupil 132 for viewing by a user’s eye (shown by the eye model 130). The final image is formed on the user’ s retina. As will be discussed more fully below with reference to FIG. 5, the telecentric folded lens 114 may focus and shape the light such that the light 106 appears to be projected from a virtual object plane 150 that is on the far left behind the electronic display 112.

[0064] As further shown in FIG. 1, the telecentric folded lens 114 includes an optical lens element 116 (e.g., a first optical lens element) and an optical lens element 118 (e.g., a second optical lens element) disposed along an optical axis 102 of the telecentric folded lens 114, where the optical lens element 116 is closer to the electronic display 112 than the optical lens element 118. The optical lens element 116 and 118 may be spaced apart from each other by an air gap 142. In some examples, the air gap 142 may be between about 1.7 millimeters (mm) to 2.1 mm wide. In certain examples, the air gap 142 may be at least about 1.892 mm wide. Generally, the telecentric folded lens 114 may include two or more optical lens elements (e.g., 3, 4, or more) arranged in series along the optical axis 102 of the telecentric folded lens 114.

[0065] To provide a folded optical path within the telecentric folded lens 114, the telecentric folded lens 114 further includes a reflective polarization optical element 122, a quarter-wave plate (QWP) 120, and a partially reflective optical element 124. The reflective polarization optical element 122 is disposed on a surface 103 of the optical lens element 118 facing the optical lens element 116. In some instances, the reflective polarization optical element 122 may be a coating applied to the surface 103. The reflective polarization optical element 122 may selectively transmit light waves with a specific polarization state while reflecting light waves with other polarization states.

[0066] The QWP 120 is disposed between the reflective polarization optical element 122 and the optical lens element 116 and 118. The QWP 120 may introduce a phase shift of a quarter wavelength (corresponding to 90 degrees) between polarization components of light passing through the QWP 120. Generally, the QWP 120 can be disposed on top of the reflective polarization optical element 122 on the optical lens element 118 as shown in FIG. 1 or on a surface 107 of the optical lens element 116 facing the optical lens element 118. In some instances, it may be desirable to place the QWP 120 on a flat surface.

[0067] The partially reflective optical element 124 is disposed on a surface 105 of the optical lens element 116 facing the electronic display 112. In some instances, the partially reflectiveoptical element 124 may be a coating applied to the surface 105. The partially reflective optical element 124 may reflect a portion of the light directing to the partially reflective optical element 124 and transmitting the remaining portion of the light. In certain examples, the partially reflective optical element 124 may reflect 50 percent (%) of the light and transmit the other 50% of the light. An example optical path for the telecentric folded lens 114 is provided in FIG. 2. The folded optical path property allows the telecentric folded lens 114 to be light-weight and compact in size, suitable for use for immersive displays (e.g., the HMD 110).

[0068] To provide the varifocal property, the HMD 110 further includes an adjustable mechanism for varying the distance 140 (represented by L in FIG. 1) between the electronic display 112 and the telecentric folded lens 114 along a direction substantially parallel to the optical axis 102 of the telecentric folded lens 114. Stated differently, the distance 140 can be decreased to move the electronic display 112 closer to the user’s eye or increased to move the electronic display 112 further away from the user’s eye along the z-axis. In some examples, the distance 140 may be adjusted to be between 0.5 mm and 15 mm. Examples of various adjustment mechanisms are provided in FIGS. 3 and 4. Generally, the varifocal property of the HMD 110 may be provided by adjusting the distance 140 between the electronic display 112 and the telecentric folded lens 114 while keeping the distance 144 between the telecentric folded lens 114 and the user’s eye constant. However, in some instances, the distance 144 may be adjustable (e.g., varying between 8 mm and 18 mm).

[0069] To provide the telecentric property where the magnification remains constant regardless of the image distance or the focal length of the telecentric folded lens 114, the telecentric folded lens 114 is designed such that all the chief rays 104 of the light 106 entering the telecentric folded lens 114 are parallel (or at least substantially parallel) to the optical axis 102 of the telecentric folded lens 114. As discussed above, a chief ray is a light ray that originates from an off-axis object point (shown by the solid circles on the electronic display 112) that passes through the center of the aperture stop of an optical system (e.g., the telecentric folded lens 114). In the example HMD arrangement 100 (a display system) illustrated in FIG. 1, the aperture stop of the telecentric folded lens 114 may correspond to the exit pupil 132, which is the aperture of opening (an apparent or virtual point) from which light appears to the user’s eye (e.g., at location 399 of the telecentric folded lens 114 shown in FIGS. 3 and 4). For ease of illustration, FIG. 1 only shows the chief rays of two off-axis object points with the label 104.

[0070] In an embodiment, the entrance pupil of the telecentric folded lens 114 may be greater than 10 meters (m) away from the telecentric folded lens 114. In certain examples, the entrance pupil of the telecentric folded lens 114 may be greater than 50 m away from the telecentric folded lens 114. In the example HMD arrangement 100 (the display system) illustrated in FIG. 1, the entrance pupil of the telecentric folded lens 114 may be at infinity to the left of the telecentric folded lens 114 so that the chief rays 104 may be parallel to the optical axis 102 when entering the telecentric folded lens 114. In an embodiment, the telecentric folded lens 114 may provide a constant halfFOV greater than 50 degrees for a plurality of image distances (the distance between the viewer’s eye and the virtual object plane 150). Stated differently, the telecentric folded lens 114 may provide a constant FOV greater than 100 degrees for a plurality of image distances. In certain examples, the telecentric folded lens 114 are optimized to provide a constant FOV at image distances for 1 diopter (corresponding to a focal length of 1 m), 2 diopters (corresponding to a focal length of 200 mm, and 3 diopters (corresponding to a focal length of 333 mm). Examples of the telecentric folded lens 114 providing a constant FOV at various image distances are provided in FIGS. 6-9.

[0071] In an embodiment, the optical lens element 116 includes a flint glass with a dispersion V-value lower (or less) than 50 and a refractive index higher (or greater) than 1.65 and less than 1.9 at a wavelength of 589.25 nanometer (nm). In a certain example, the optical lens elements 116 may include Schott® SF10 glass. Generally, the optical lens element 116 may include any crown glasses with a refractive index higher (or greater) than 1.65. In an embodiment, at least one of the surface 105 of the optical lens element 116 facing the electronic display 112 or the opposite surface 107 of the optical lens element 116 is aspherical. That is, in some examples, the surface 105 may be flat, and the surface 107 may be aspherical. In other examples, the surface 107 may be flat, and the surface 105 may be aspherical. In yet other examples, both the surfaces 105 and 107 may be aspherical. In an embodiment, the surface 105 (of the optical lens element 116 facing the electronic display 112) has a radius between 120 mm and 140 mm and a conic constant between -5 and -6. In certain examples, the surface 105 may have a radius of about 130 mm and a conic constant of about -5.604 with a 4thorder polynomial coefficient of 2.052* 10‘6. In an embodiment, the surface 107 of the optical lens element 116 facing the optical lens element 118 has a radius between -190 mm and -200 mm and a conic constant between 7 and 8. In certain examples, the surface 107 mayhave a radius of about -195.2 mm and a conic constant of about 7.576 with a 4thorder polynomial coefficient of 6.799x 10’6.

[0072] In an embodiment, the optical lens element 118 includes a crown glass with a dispersion V-value higher (or greater) than 50 and less than 90 and a refractive index greater than 1.4 and lower (or less) than 1.6 at a wavelength of 589.25 nm wavelength. In certain examples, the optical lens elements 118 may include Schott® PSK-series glass and a thickness of between 9 mm and 11 mm (e.g. about 10 mm). In an embodiment, the surface 109 of the optical lens element 118 (opposite the surface 103) has a radius between -8 mm and -9 mm and a conic constant between - 6.5 x lO14and -7.5 *1014In certain examples, the surface 109 of the optical lens element 118 has a radius of about -8.602 mm and a conic constant of about -6.92* 1014with a 4thorder polynomial coefficient of -2.523 x lO-5. In an embodiment, the surface 103 of the optical lens element 118 (facing the optical lens element 116) is flat, and the surface 109 of the optical lens element 118 opposite the surface 103 of the optical lens element 118 is aspherical.

[0073] FIG. 2 illustrates an example optical path of the telecentric folded lens 114 according to an embodiment of the present disclosure. The optical paths are in the direction along the z-axis. For ease of illustration, FIG. 2 illustrates the QWP 120 as a separate component from the optical lens elements 116 and 118. As shown in FIG. 2, the electronic display 112 may emit a light 202 (e.g., corresponding to the light 106 of FIG. 1) having a certain polarization state 204. The light 202 may travel towards the telecentric folded lens 114. When the light 202 reaches the optical lens element 116, a portion 206 (e g., about 50 %) of the light 202 may be reflected by the partially reflective optical element 124, and the remaining portion 208 (e.g., about 50 %) of the light 202 may continue to travel through the optical lens element 116. The QWP 120 may change the polarization of the light portion 208 by a quarter wavelength, which corresponds to 90 degrees (as shown by the polarization state 210).

[0074] When the light portion 208 with the polarization state 210 reaches the reflective polarization optical element 122, the reflective polarization optical element 122 may not allow the light portion 208 with the polarization state 210 to pass through (as shown by the symbol “X”). That is, the light portion 208 with the polarization state 210 may be reflected by the reflective polarization optical element 122 (shown by 212). Next, the reflected light portion 212 with the polarization state 210 may travel towards the optical lens element 116 and may reach the partially reflective optical element 124. The partially reflective optical element 124 may reflect a portion214 of the light portion 212 and pass a portion 216 of the light portion 212 through. Referring to the example of the partially reflective optical element 124 being a 50 / 50 coating. The light portion 216 may correspond to about 25 % of the original light 202. The light portion 216 may travel towards the QWP 120 and the optical lens element 118.

[0075] When the light portion 216 (with the polarization state 210) reaches the QWP 120, the QWP 120 may change the polarization state of the light portion 216 by a quarter wavelength, back to the original polarization state 204. When the light portion 216 with the polarization state 204 reaches the reflective polarization optical element 122, the reflective polarization optical element 122 may pass the light portion 216 (with the polarization state 204) through the optical lens element 118 towards the viewer’s eye 230 (e.g., similar to the eye model 130).

[0076] As can be observed in FIG. 2, the optical path of the telecentric folded lens 114 is folded within the telecentric folded lens 114. That is, light is directed through a series of optical elements, traveling back and forth as discussed above. The series of optical elements may fit into a smaller space (along the z-axis) that would otherwise require a significantly larger space (along the z-axis) to achieve the same focal length. In other words, the folded property can reduce the length (along the z-axis) of the telecentric folded lens 114 while achieving the desired focal length(s).

[0077] FIG. 3 is a block diagram illustrating an example adjustment arrangement 300 for the HMD arrangement 100 with the telecentric folded lens 114 according to an embodiment of the present disclosure. The arrangement 300 includes an adjustment element 310 configured to adjust the distance 140 between the electronic display 112 and the telecentric folded lens 114 (e.g., along a path substantially parallel to the optical axis 102 of the telecentric folded lens 114). For ease of illustration, FIG. 3 only shows the electronic display 112, the telecentric folded lens 114, and the adjustment element 310, which may be of the HMD 110.

[0078] As shown in FIG. 3, the adjustment element 310 is a sliding wedge system including a pair of wedge blocks 312 (individually shown as 312-1 and 312-2) with opposing inclined surfaces 302 and 304 extending across two ends 322 and 324 of respective wedge blocks 312. The sliding wedge system further includes a sliding mechanism for sliding the pair of wedge blocks 312 in opposite directions along an axis 306 substantially orthogonal to the optical axis 102 of the telecentric folded lens 114. For instance, to reduce the distance 140 (between the electronic display 112 and the telecentric folded lens 114), the sliding mechanism may be configured to cause the wedge blocks 312 to slide away from each other, where the wedge blocks 312-1 and 312-2 mayslide respectively in the directions 308 and 309 (shown by the solid arrows). Alternatively, to increase the distance 140 (between the electronic display 112 and the telecentric folded lens 114), the sliding mechanism may be configured to cause the wedge blocks 312 to slide towards each other, where the wedge blocks 312-1 and 312-2 may slide respectively in the directions 307 and 311 (shown by the dotted arrows).

[0079] The pair of wedge blocks 312-1 and 312-2 may be disposed between the electronic display 112 and the telecentric folded lens 114. In an embodiment, the pair of wedge blocks 312- 1 and 312-2 may comprise a glass material, such as Schott® SF10 glass which has a high refractive index and a low dispersion.

[0080] The sliding mechanism may include a pair of adjustment components 314 (individually shown as 314-1 and 314-2), each attached to the wider end 324 of the respective wedge block 312. For instance, the adjustment component 314-1 is attached to the wider end 324 of the wedge block 312-1, and the adjustment component 314-2 is attached to the wider end 324 of the wedge block 312-2. In some examples, the adjustment components 314 may also be coupled to the frame of the HMD 110. In an example, the adjustment components 314 may be in the form of a knob with screw threads that can be rotated to slide the respective wedge blocks 312.

[0081] In one embodiment, a user may manually adjust the adjustment components 314-1 and 314-2 to slide the wedge blocks 312 away from each other or towards each other. For instance, when the arrangement 300 is used to configure an HMD 110 as an eye-prescription adjustable immersive display, a user (or viewer) of the HMD 110 may adjust a prescription power by adjusting the distance 140 (between the electronic display 112 and the telecentric folded lens 114). That is, the user’s eyes may function as the sensor and the user may adjust the distance 140 (by adjusting the adjustment components 314) until the user can see an image with a best resolution and / or a sharp focus. In another embodiment, a processor (e.g., the processor(s) 1004 of FIG. 10) may control the adjustment components 314 to slide the wedge blocks 312 away from each other or towards each other. In one example, the processor may be configured to adjust the distance 140 based on a desired prescription power (e.g., selected by a user of the HMD). In another example, the processor may adjust the distance 140 based on a user gaze point or display image content as will be discussed more fully below with reference to FIG. 13.

[0082] FIGS. 4A-4B are block diagrams illustrating another example adjustment arrangement 400 for the HMD arrangement 100 with the telecentric folded lens 114 according to anembodiment of the present disclosure. As shown in FIG. 4A, the arrangement 400 includes an adjustment element 410 configured to adjust the distance 140 between the electronic display 112 and the telecentric folded lens 114 (e.g., along a path substantially parallel to the optical axis 102 of the telecentric folded lens 114). For ease of illustration, FIG. 4A only shows the electronic display 112, the telecentric folded lens 114, and the adjustment element 410, which may be part of the HMD 110. FIG. 4A illustrates the adjustment element 410 having portions 410-1, 410-2, and 410-3 attached to the electronic display 112 in a side view (e.g., in a y-z plane) of the HMD 110. FIG. 4B provides a front view of the adjustment element 410 and the electronic display 112 in a front view (e.g., in an x-y plane) of the HMD 110. As shown in FIG. 4B, the adjustment element 410 may be in a ring shape wrapped around the electronic display 112.

[0083] In the arrangement 400, the adjustment elements 410 may include actuators configured to move the electronic display 112 closer to the telecentric folded lens 114 (and the user’s eyes) or further away from the telecentric folded lens 114 (and the user’s eyes), thereby adjusting the distance 140. In one embodiment, the actuators may include voice coil motors (VCMs). A VCM may be a type of direct-drive actuator that produces linear motion by means of electromagnetic force. For instance, a cylindrical coil of wire is suspended in a magnetic field (e.g., created by magnets). When current flows through the coil, the resulting Lorentz force acts along the coil’s axis, causing the coil to move in a very controlled, frictionless manner. In another embodiment, the actuators may include step motors. A step motor may be a type of brushless direct-current (DC) motor that converts electrical pulses into precise mechanical movements. In yet another embodiment, the actuators may include ultrasonic motors (USMs). A USM may be a type of motor that uses high-frequency vibrations (e.g., generated by piezoelectric elements) to produce motion through friction. In USMs, an oscillating element (the stator) vibrates at ultrasonic frequencies and interacts with a contacting element (the rotor) to create motion in discrete steps. Generally, the adjustment elements 410 may include VCMs, step motors, USMs, or any combinations thereof. In an embodiment, a processor (e.g., the processor(s) 1004 of FIG. 10) may control the adjustment elements 410 (the actuators) to move the electronic display 112 closer to or further away from the telecentric folded lens 114 based on a user gaze point or display image content as will be discussed more fully below with reference to FIG. 13.

[0084] FIG. 5 is a schematic diagram illustrating the generation of a virtual image according to an embodiment of the present disclosure. A user’s eye 230 may view an image presented on theelectronic display 112 through the telecentric folded lens 114. The electronic display 112 and the telecentric folded lens 114 are part of an HMD 110 as discussed above with reference to FIGS. 1- 3 and 4A-4B. As shown in FIG. 5, the electronic display 112 may emit light 506 directed towards the telecentric folded lens 114. For instance, the light 506 may originate from various points (shown by the solid dots) on the electronic display 112. For ease of illustration, FIG. 5 only shows three of the points with labels 508a, 508b, and 508c. The light 506 may pass through the telecentric folded lens 114 to reach the user’s eye 230. The telecentric folded lens 114 may focus and shape the light 506 such that the light 506 appears to be projected from a virtual object plane 150 (or virtual image plane) that is on the far left behind the electronic display 112. The projection is shown by the dashed lines 502. That is, the virtual object plane 150 (or the virtual image) may appear to be further away from the user’s eye 230 than the actual distance from the electronic display 112. For instance, the rays of the light 506 originated from the points 508a, 508b, and 508c on the electronic display 112 may appear to be respectively from the points 504a, 504b, and 504c on the virtual object plane 150. As will be discussed more fully below with reference to FIGS. 6- 9, the distance 140 between the electronic display 112 and the telecentric folded lens 114 may be adjusted to vary the image distance 512 (virtual image distance) between the user’s eye 230 and the virtual object plane 150 (e.g., using the adjustment mechanisms discussed above with reference to FIGS. 3 and 4). As an example, when the distance 140 is configured to be about 12 mm, the image distance 512 may be about 300 mm. As another example, when the distance 140 is configured to be about 14.4 mm, the image distance 512 may be greater than 10 meters (e.g., becomes infinity).

[0085] FIGS. 6-9 illustrate image distance or depth adjustments through adjusting the distance (L) 140 between the electronic display 112 and the telecentric folded lens 114 in the HMD 110 (e g., using the adjustment mechanisms discussed above with reference to FIGS. 3 and 4). For ease of illustration, FIGS. 6-9 only show three groups of light 506 and corresponding projections 502 as discussed above with reference to FIG. 5.

[0086] FIG. 6 is a schematic diagram of an example adjustment configuration 600 for the HMD arrangement 100 with the telecentric folded lens 114 according to an embodiment of the present disclosure. In the configuration 600, the distance (L) 140 between the electronic display 112 and the telecentric folded lens 114 is set to an initial distance of about 14.4 mm, providing an about infinite virtual image distance (e.g., the image distance 512). As shown in FIG. 6, theelectronic display 112 may emit light 506a, 506b, and 506c towards the telecentric folded lens 114, and the telecentric folded lens 114 may provide corresponding projections 502a, 502b, and 502c.

[0087] FIG. 7 is a schematic diagram of another example adjustment configuration 700 for the HMD arrangement 100 with the telecentric folded lens 114 according to an embodiment of the present disclosure. In the configuration 700, the distance (L) 140 between the electronic display 112 and the telecentric folded lens 114 is configured (e.g., to about 12 mm) to provide an image distance (e g., the image distance 512) at about 300 mm away from the user’s eye 230 (e.g., corresponding to 3.3 D) with a certain half FOV 702 between the projections 502a and 502c. In some instances, the projection 502a may be referred to as a field angle (e.g., 10 degrees, 50 degrees, etc.)

[0088] FIG. 8 is a schematic diagram of yet another example adjustment configuration 800 for the HMD arrangement 100 with the telecentric folded lens 114 according to an embodiment of the present disclosure. In the configuration 800, the distance L 140 between the electronic display 112 and the telecentric folded lens 114 is further configured to provide an image distance (e.g., the image distance 512) at about 500 mm away from the user’s eye 230 (e.g., corresponding to 2D) with a half FOV 802 between the projections 502a and 502c. Because the telecentric folded lens 114 is designed to provide a constant FOV irrespective of the image distance, the half FOV 802 (for the 500 mm image distance) may be substantially the same as the half FOV 702 (for the 330 mm image distance) shown in FIG. 7.

[0089] FIG. 9 is a schematic diagram of a further example adjustment configuration 900 for the HMD arrangement 100 with the telecentric folded lens 114 according to an embodiment of the present disclosure. In the configuration 900, the distance L 140 between the electronic display 112 and the telecentric folded lens 114 is further configured to provide an image distance at about 1000 mm away from the user’s eye 230 (e.g., corresponding to ID) with a half FOV 902 between the projections 502a and 502c. Again, the half FOV 902 (for the 1000 mm image distance) may be substantially the same as the half FOV 802 (for the 500 mm image distance) shown in FIG. 8 and the half FOV 702 (for the 330 mm image distance) shown in FIG. 7.

[0090] FIG. 10 is a schematic diagram of a side view of another example HMD arrangement 1000 with the telecentric folded lens 114 according to an embodiment of the present disclosure. In the arrangement 1000, the HMD 1010 may be substantially the same as the HMD 110 of FIG. 1For instance, the HMD 1010 may include an electronic display 1 12 and a telecentric folded lens 114 arranged and operate in a similar way as the HMD 110 discussed above with reference to FIGS. 1-3, 4A-4B, and 5-9. However, FIG. 10 further illustrates the HMD 1010 including the sensor(s) 1002 and the processor(s) 1004. The HMD 1010 may generally include any suitable number of sensors 1002 (e.g., about 1, 2, 3, 4, 5, 6 or more) and any suitable number of processors 1004 (e.g., about 1, 2, 3 or more). The sensors(s) 1002 and the processor(s) 1004 may be located at any suitable locations of the HMD 1010. Examples of sensor(s) 1002 may include, but are not limited to, eye and / or facial tracking sensors, motion sensors, positional tracking sensors, and depth and environment sensors. The processor(s) 1004 may be communicatively coupled to the sensor(s) 1002 and the electronic display 112. As will be discussed more fully below with reference to FIG. 13, the processor(s) 1004 may determine an image distance (e.g., the image distance 512) for presenting a virtual image or a virtual scene based on feedback received from the sensors 1002 or based on the virtual image content and adjust the image distance by controlling the distance 140 between the electronic display 112 and the telecentric folded lens 114.

[0091] FIG. 11 is a schematic diagram of a side view (e.g., in the y-z plane) of an example camera arrangement 1100 with a telecentric folded lens 1114 according to an embodiment of the present disclosure. In an embodiment, the camera arrangement 1100 is part of a cell phone camera. For instance, a UE 1110 may include an image sensor 1112 and the telecentric folded lens 1114. Generally, the UE 1110 may be a smart phone, a personal digital assistance (PDA), a tablet computer, or any wirelessly equipped communication device. The image sensor 1 112 is configured to capture light 1106 and convert the captured light 1106 into an electrical signal to create a digital image. In some examples, the image sensor 1112 may be a complementary metal-oxide semiconductor (CMOS) image sensor. Generally, the image sensor 1112 can be any suitable sensor for converting light into electrical signals, acting as an “electronic eye” to capture digital images.

[0092] The telecentric folded lens 1114 may be substantially similar to the telecentric folded lens 114 discussed above with reference to FIGS. 1-3, 4A-4B, and 5-9. However, the telecentric folded lens 1114 has a reverse or flipped optical architecture compared to the telecentric folded lens 114. For instance, the telecentric folded lens 1114 may include an optical lens element 1116 (e.g., a first optical lens element) and an optical lens element 1118 (e.g., a second optical lens element) disposed along an optical axis 1102 of the telecentric folded lens 1114, where the optical lens element 1118 is closer to the image sensor 1112 than the optical lens element 1116. The opticallens element 1116 may be substantially similar to the optical lens element 118, and the optical lens element 1118 may be substantially similar to the optical lens element 116. Generally, the telecentric folded lens 1114 may include two or more optical lens elements (e.g., 3, 4, or more) arranged in series along the optical axis 1102 of the telecentric folded lens 1114. The telecentric folded lens 1114 and the image sensor 1112 may form an optical imaging device 1150.

[0093] To provide a folded optical path within the telecentric folded lens 1114, the telecentric folded lens 1114 further includes a reflective polarization optical element 1122, a QWP 1120, and a partially reflective optical element 1124. The reflective polarization optical element 1122, the QWP 1120, and the partially reflective optical element 1124 may be substantially similar to the reflective polarization optical element 122, the QWP 120, and the partially reflective optical element 124, respectively, discussed above with reference to FIG. 1. However, the reflective polarization optical element 1122, the QWP 1120, and the partially reflective optical element 1124 are arranged differently than the HMD arrangement 100 of FIG. 1. As shown in FIG. 11 , the reflective polarization optical element 1122 is disposed on the optical lens element 1118 (or more specifically, on a surface 1109 of the optical lens element 1118 facing the image sensor 1112). The reflective polarization optical element 1122 is placed close to the image sensor 1112 so that the ghost image (e.g., from multiple reflections and / or refractions) may be blocked. The partially reflective optical element 1124 is disposed on the optical lens element 1116 facing an entrance aperture or the entrance pupil 1130 (e.g., where light 1106 enters the telecentric folded lens 1114). For instance, the partially reflective optical element 1 124 is disposed on a surface 1107 of the optical lens element 1116 as shown. In other instances, the partially reflective optical element 1124 may be disposed on the opposite surface 1105 of the optical lens element 1116. The QWP 1120 is disposed between the reflective polarization optical element 1122 and the optical lens element 1118. Generally, the QWP 1120 can be disposed on top of the partially reflective optical element 1124 on the optical lens element 1116 as shown or on a surface 1103 of the optical lens element 1118 facing the optical lens element 1116. In some instances, it may be desirable to place the QWP 1120 on a flat surface (e.g., the surface 1107 as will be discussed more fully below).

[0094] The folded optical path provided by the telecentric folded lens 1114 may be substantially similar to the optical path illustrated in FIG. 2. For instance, a light 1106 from a light source (e.g., sun, lamp, flash, etc.) may illuminate a target 1101 (e.g., a target object or target plane). The target 1101 may reflect the light 1106 in various directions towards the telecentricfolded lens 1 114. The telecentric folded lens 1 114 may focus and direct the light 1106 towards the image sensor 1112. The light 1106 may have a certain polarization state (e.g., a first polarization state). The light 1106 may travel through the optical lens element 1116 and reach the partially reflective optical element 1124. The partially reflective optical element 1124 may reflect a portion (e g., a first portion) of the light 1106, and the remaining portion (e.g., a second portion) of the light 1106 may continue to travel through the optical lens element 1116. The QWP 120 may change the polarization of the second portion of the light 1106 by a quarter of the wavelength (e.g., to a second polarization state).

[0095] When the second portion of the light 1106 with the second polarization state 210 reaches the reflective polarization optical element 1122, the reflective polarization optical element 1122 may not allow the second portion of the light 1106 with the second polarization state to pass through. That is, the second portion of the light 1106 with the second polarization state may be reflected by the reflective polarization optical element 1122. The reflected light with the second polarization state may travel towards the optical lens element 1116 and may reach the partially reflective optical element 1124. The partially reflective optical element 1124 may reflect a portion (e.g., a third portion) of the reflected light and pass the remaining portion of the reflected light through.

[0096] When the third light portion with the second polarization state reaches the QWP 120, the QWP 120 may change the polarization state of the third light portion by quarter of a wavelength, back to the first polarization state. When the third light portion with the first polarization state reaches the reflective polarization optical element 1122, the reflective polarization optical element 122 may pass the third light portion with the first polarization state through the optical lens element 1118 towards the image sensor 1112.

[0097] To provide the varifocal property, the camera arrangement 1100 further includes an adjustable mechanism that can adjust the distance 1140 between the image sensor 1112 and the telecentric folded lens 1114 along a direction parallel to the optical axis 1102 of the telecentric folded lens 1114. In some examples, the distance 1140 may be adjusted to be between 0 mm and 15 mm depending on the diameter of the telecentric folded lens 1114. For example, if the diameter of the telecentric folded lens 1114 is about 10 mm, then the adjustable distance 1140 may be between 0 mm and 3 mm. In one embodiment, the adjustable mechanism may include the adjustment element 310 (e.g., including the sliding wedge blocks 312 and the adjustmentcomponents 314) discussed above with reference to FIG. 3. In another embodiment, the adjustable mechanism may include the adjustment element 410 (e.g., the VCM, step motor, and / or USM actuators) discussed above with reference to FIG. 4. In an example, the adjustment element 410 may be coupled to the telecentric folded lens 1114 to move the telecentric folded lens 1114 closer to or further away from the image sensor 1112. In some embodiments, the UE 1110 may include an application (e.g., software) executing on the UE 1110, and the application may provide a user interface where a user may control and configure the adjustment element 310 or 410 (to adjust the distance 1140). For instance, the application may send an instruction (e.g., indicating an amount of distance adjustment) to the adjustment element 310 or 410 based on the user input.

[0098] To provide the telecentric property where the magnification and the FOV remain constant regardless of the object distance 1142 or the focal length of the telecentric folded lens 114, the telecentric folded lens 114 is designed such that all the chief rays 1104 of the light exiting the telecentric folded lens 1114 are parallel (or at least substantially parallel) to the optical axis 1102 of the telecentric folded lens 1114. As discussed above, a chief ray is a light ray that originates from an off-axis object point (e.g., at a 25-degree field and a 50-degree field) that passes through the center of the aperture stop of an optical system (e.g., the telecentric folded lens 1114). In the example camera arrangement 1100 illustrated in FIG. 11, the aperture stop of the telecentric folded lens 1114 is shown by 1199, which corresponds to the entrance pupil 1130 of the telecentric folded lens 1114. The entrance pupil 1130 is the opening where the light 1106 converges after passing through the aperture stop 1199 (e.g., to the left of the telecentric folded lens 1 114 in FIG. 11). For ease of illustration, FIG. 11 only shows the chief rays of two off-axis object points exiting the telecentric folded lens 114 with the label 1104. Stated differently, the telecentric folded lens 1114 is configured to receive light 1106 associated with an external object (e.g., the target 1101) and propagate at least a portion of the light 1106 towards the image sensor 1112 and the at least the portion of the light 1106 includes the chief ray 1104.

[0099] In an embodiment, the exit pupil of the telecentric folded lens 1114 may be greater than 10 m away from the telecentric folded lens 1114. In some instances, the exit pupil of the telecentric folded lens 1114 may be greater than 50 m away from the telecentric folded lens 1114. In the example camera arrangement 1100 illustrated in FIG. 11, the exit pupil of the telecentric folded lens 1114 may may be at infinity to the right of the telecentric folded lens 1114..

[0100] In an embodiment, the telecentric folded lens 1114 may have a diameter between 4 mm and 20 mm. In an embodiment, the optical lens element 1118 includes a flint glass with a dispersion V-value lower (or less) than 50 and a refractive index higher (or greater) than 1.65 at a wavelength of 589.25 nanometer (nm). In a certain example, the optical lens elements 1118 may include Schott® SF10 glass. Generally, the optical lens element 1118 may include any crown glasses with a refractive index higher (or greater) than 1.65. In an embodiment, at least one of the surface 1103 of the optical lens element 1118 facing the image sensor 1112 or the opposite surface 1109 of the optical lens element 1118 is aspherical. That is, in some examples, the surface 1103 may be flat, and the surface 1109 may be aspherical. In other examples, the surface 1109 may be flat, and the surface 1103 may be aspherical. In yet other examples, both the surfaces 1103 and 1109 may be aspherical. In an embodiment, the optical lens element 1116 includes a crown glass with a dispersion V-value higher (or greater) than 50 and a refractive index lower (or less) than 1.60 at a wavelength of 589.25nm wavelength. In certain examples, the optical lens elements 1116 may include Schott® PSK-series glass. In an embodiment, the surface 1107 of the optical lens element 1116 (facing the optical lens element 1118) is flat, and the surface 1105 of the optical lens element 1116 opposite the surface 1107 of the optical lens element 118 (facing the entrance aperture or the entrance pupil 1130) is aspherical. In other instances, the optical lens elements 1116 and 1118 may be moldable lens, and thus may comprise different glass materials than the optical lens element 116 and 118, respectively.

[0101] The adjustment configurations 600-900 discussed above with reference to FIGS. 6-9 may generally apply to the camera arrangement 1100. However, for the camera arrangement 1100, instead of the virtual object plane 150, a real object (for imaging) may replace the virtual object plane 150 (as shown by the target 1101). The capability of focusing or varying the focal length while maintaining the magnification and / or FOV provided by the camera arrangement 1100 imitates the human eye (providing natural human vision), enabling smooth and steady video recording and making it visually comfortable for the user.

[0102] FIG. 12 is a schematic diagram of a side view of an example camera arrangement 1200 with a zoomable telecentric folded lens 1214 according to an embodiment of the present disclosure. In an embodiment, the camera arrangement 1200 is part of a cell phone camera (e.g., of the UE 1110). For instance, the camera arrangement 1200 may include a telecentric folded lens 1214. The telecentric folded lens 1214 may be substantially similar to the telecentric folded lens 1114 andmay be arranged to be in front of an image sensor similar to the image sensor 11 12 as shown in FIG. 11. For instance, the telecentric folded lens 1214 may include an optical lens element 1116 and an optical lens element 1118 with a reflective polarization optical element 1122, a QWP 1120, and a partially reflective optical element 1124 arranged in the same way as in the telecentric folded lens 1114 of FIG. 11. However, the telecentric folded lens 1214 further includes an adjustable mechanism (shown by the air gap adjustment 1204) to adjust the air gap 1242 between the optical lens elements 1116 and 1118. Adjusting the air gap 1242 may vary a magnification ratio or an FOV provided by the telecentric folded lens 1214 (with the varying focal lengths). Using separate adjustable mechanisms to adjust the zoom ratio and the focal lengths (e.g., a first adjustable mechanism for adjusting the distance 140 to vary the focal length and a second, separate adjustable mechanism for adjusting the air gap 1242 to vary the zoom ratio) can decouple the zoom and focus operations of optics, allowing for a compact size and a large FOV telecentric folded lens 1214.

[0103] In an embodiment, the air gap 1242 may be adjusted to be between 1 mm and 2 mm to provide focal lengths between 8 mm and 17 mm as shown by 1204. In an example, the air gap 1242 may be configured to have a gap width of about 1.95 mm to provide a focal length of about 10.27 mm. In another example, the air gap 1242 may be configured to have a gap width of about 1.1 mm to provide a focal length of about 15 mm. In an embodiment, the adjustable mechanism may include the adjustment element (e.g., the VCM, step motor, and / or UCM actuators) discussed above with reference to FIG. 4. Generally, the camera arrangement 1200 can further include an image sensor (e.g., the image sensor 11 12) and an adjustable mechanism to adjust the distance (e.g., the distance 1140) between the image sensor and the telecentric folded lens 1214 as discussed above with reference to FIG. 11.

[0104] While the zooming capability is discussed in the context of the camera arrangement 1200, similar mechanisms may be implemented in an HMD arrangement (e.g., HMD arrangement 100 of FIG. 1 or the HMD arrangement 1100 of FIG. 11 ) to provide zooming, where an additional separate adjustable mechanism may be integrated into the HMD arrangement for adjusting the width of the air gap 142 between the optical lens elements 116 and 118.

[0105] FIG. 13 is a flowchart of an example method 1300 for operations of an HMD (e.g., the HMD 110 or the HMD 1010) with a telecentric folded lens (e.g., the telecentric folded lens 114) according to an embodiment of the present disclosure. In embodiments, the HMD may implement the method 1300 using a computer system with components as shown in FIG. 14. The method1300 may use similar mechanisms as discussed above with reference to FIGS. 1-3, 4A-4B, and 5- 10. As illustrated, FIG. 13 includes a number of enumerated operations, but embodiments of the operations in FIG. 13 may include additional operations before, after, and in between the enumerated operations. In some embodiments, one or more of the enumerated operations may be omitted or performed in a different order.

[0106] At operation 1302, a distance (e.g., the image distance 512) between a user’s eye (e.g., the eye model 130 or the user’s eye 230) and a virtual object plane (e.g., the virtual object plane 150) is determined by a processor (e.g., the processor 1004) of the HMD. For instance, the HMD may include a telecentric folded lens (e.g., the telecentric folded lens 114) and an electronic display (e.g., the electronic display 112) arranged as discussed above with reference to FIGS. 1-3, 4A-4B, and 5-110 so that the user’s eye may perceive that the images are from the virtual object plane, which is farther away from the user’s eye than the actual electronic display.

[0107] In one embodiment, the distance between the user’s eye and the virtual object plane is determined based on a gaze (e.g., a gaze point) of the user’s eye. The gaze point is a point or location at which the user is looking at or wants to see. Stated differently, the gaze point is a point of focus in the visual field that the user is perceiving. In an embodiment, the gaze of the user’s eye may be tracked by one or more sensors (e.g., the sensor(s) 1002) of the HMD 110.

[0108] In another embodiment, the distance between the user’s eye and the virtual object plane may be based on an image content to be projected onto the virtual object plane by the electronic display and through the telecentric folded lens. For instance, the image content may be intended for a user to perceive a certain depth, and thus the distance between the user’s eye and the virtual object plane may correspond to that depth.

[0109] At operation 1304, a distance (e.g., the distance 140) between the electronic display and the telecentric folded lens is adjusted by the processor based on the distance between the user’s eye and the virtual object plane while maintaining a constant distance between the user’s eye and the telecentric folded lens. For instance, the processor may be coupled to an adjustment element (e g., the adjustment element 310 or 410 as discussed above with reference to FIGS. 3 or 4, respectively) that is configured to adjust the distance between the electronic display and the telecentric folded lens, and thus the process may send an instruction (e.g., indicating the desired amount of distance adjustment) to the adjustment element.

[0110] FIG. 14 is a schematic diagram of a computer apparatus 1400 (e.g., part of the HMD 110, the HMD 1010, or the optical imaging device 1150, etc.). The computer apparatus 1400 is suitable for implementing the disclosed embodiments as described herein. The computer apparatus 1400 comprises ingress ports / ingress means 1410 (a.k.a., upstream ports) and receiver units (Rx) / receiving means 1420 for receiving data; a processor, logic unit, or central processing unit (CPU) / processing means 1430 to process the data; transmitter units (Tx) / transmitting means 1440 and egress ports / egress means 1450 (a.k.a., downstream ports) for transmitting the data; and a memory / memory means 1460 for storing the data. The computer apparatus 1400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports / ingress means 1410, the receiver units / receiving means 1420, the transmitter units / transmitting means 1440, and the egress ports / egress means 1450 for egress or ingress of optical or electrical signals.[0U1] The processor / processing means 1430 is implemented by hardware and software. The processor / processing means 1430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor / processing means 1430 is in communication with the ingress ports / ingress means 1410, receiver units / receiving means 1420, transmitter units / transmitting means 1440, egress ports / egress means 1450, and memory / memory means 1460. The processor / processing means 1430 comprises an adjustment module 1470. The adjustment module 1470 is able to implement the methods disclosed herein. For example, in one embodiment, the computer apparatus 1400 may be part of an HMD 110 or 1010, and the adjustment module 1470 may control and adjust the distance 140 between the electronic display 112 and the telecentric folded lens 114 in the HMD 110 or 1010. In another embodiment, the computer apparatus 1400 may be part of an optical imaging device 1150, and the adjustment module 1470 may control and adjust the distance 1140 between the image sensor 1112 and the telecentric folded lens 1114 at the optical image device 1150 or the air gap 1242 between the optical lens elements 1116 and 1118 (of the telecentric folded lens 1114). The inclusion of the adjustment module 1470 therefore provides a substantial improvement to the functionality of the computer apparatus 1400 and effects a transformation of the computer apparatus 1400 to a different state. Alternatively, the adjustment module 1470 is implemented as instructions stored in the memory / memory means 1460 and executed by the processor / processing means 1430.

[0112] The computer apparatus 1400 may also include input and / or output (I / O) devices or I / O means 1480 for communicating data to and from a user. The I / O devices or I / O means 1480 may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. The I / O devices or I / O means 1480 may also include input devices, such as a keyboard, mouse, trackball, etc., and / or corresponding interfaces for interacting with such output devices.

[0113] The memory / memory means 1460 comprises one or more disks, tape drives, and solid- state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory / memory means 1460 may be volatile and / or non-volatile and may be readonly memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and / or static random-access memory (SRAM).

[0114] It should also be understood that the steps of the exemplary methods set forth herein are not necessarily required to be performed in the order described, and the order of the steps of such methods should be understood to be merely exemplary. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments of the present disclosure.

[0115] While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.

[0116] In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.

Claims

CLAIMSWhat is claimed is:

1. A head-mounted display (HMD), comprising: an electronic display configured to emit light; a telecentric folded lens configured to direct the light to an exit pupil of the HMD, the telecentric folded lens comprising: a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, wherein the first optical lens element is closer to the electronic display than the second optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element facing the first optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, disposed such that an optical path of a chief ray of the light entering the telecentric folded lens is parallel to the optical axis of the telecentric folded lens, and wherein the chief ray is a ray that passes through a center of an aperture stop of the telecentric folded lens; and an adjustment element configured to adjust a focal length of the telecentric folded lens.

2. The HMD of claim 1, wherein the adjustment element is configured to adjust the focal length of the telecentric folded lens by adjusting a distance between the electronic display and the telecentric folded lens.

3. The HMD of any of claims 1-2, wherein an entrance pupil of the telecentric folded lens is greater than 10 meters away from the telecentric folded lens.

4. The HMD of any of claims 1-3, wherein the telecentric folded lens provides a constant half field of view greater than 50 degrees for a plurality of image distances.

5. The HMD of any of claims 1 -4, wherein the first optical lens element comprises a flint glass, which has a dispersion V-value less than 50 and a refractive index greater than 1.65 and less than 1.9 at a wavelength of 589.25 nanometers (nm) wavelength.

6. The HMD of any of claims 1-5, wherein at least one of a first surface of the first optical lens element facing the electronic display or a second surface of the first optical lens element opposite the first surface is aspherical.

7. The HMD of any of claims 1-6, wherein: a radius of a surface of the first optical lens element facing the electronic display is between 120 millimeters (mm) and 140 mm, and a conic constant of the surface is between -5 and -6.

8. The HMD of any of claims 1-7, wherein: a radius of a surface of the first optical lens element facing the second optical lens element is between -190 millimeter (mm) and -200 mm, and a conic constant of the surface is between 7 and 8.

9. The HMD of any of claims 1-8, wherein the second optical lens element comprises a crown glass with a refractive index greater than 1.4 and less than 1.6 at a wavelength of 589.25 nanometers (nm) and a dispersion V-value greater than 50 and less than 90.

10. The HMD of any of claims 1-9, wherein: a radius of a second surface of the second optical lens element opposite the surface of the second optical lens element facing the first optical lens element is between -8 millimeters (mm) and -9 mm, and a conic constant of the second surface is between -6.5* 1014and -7.5x 1014.

11. The HMD of any of claims 1-10, wherein: the surface of the second optical lens element facing the first optical lens element is flat, anda second surface of the second optical lens element opposite the surface of the second optical lens element facing the first optical lens element is aspherical.

12. The HMD of any of claims 1-11, wherein the telecentric folded lens further comprises a partially reflective optical element disposed on a surface of the first optical lens element facing the electronic display.

13. The HMD of any of claims 1-12, wherein a distance between the telecentric folded lens and an eye of a user of the HMD is adjustable.

14. The HMD of any of claims 1-13, wherein the adjustment element is between the electronic display and the telecentric folded lens and comprises a sliding wedge system comprising: a pair of wedge blocks with opposing inclined planes; and a sliding mechanism for sliding the pair of wedge blocks in opposite directions along an axis different than the optical axis of the telecentric folded lens.

15. The HMD of any of claims 1-13, wherein the adjustment element is coupled to the electronic display and comprises an actuator.

16. The HMD of claim 15, wherein the actuator comprises at least one of a voice coil motor (VCM), a step motor, or an ultrasonic motor (USM).

17. The HMD of any of claims 1-16, wherein the HMD is a varifocal immersive display device.

18. The HMD of any of claims 1-16, wherein the HMD is an eye-prescription adjustable immersive display device, wherein a prescription power of the HMD is based on at least one of a manual or automatic adjustment of the distance between the electronic display and the telecentric folded lens.

19. An apparatus comprising: an optical imaging device comprising: an image sensor configured to convert first light to an electrical signal; a telecentric folded lens configured to receive second light associated with an external object and propagate at least a portion of the second light towards the image sensor, wherein the at least the portion of the second light corresponds to the first light, and wherein the telecentric folded lens comprises: a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, wherein the second optical lens element is closer to the image sensor than the first optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, disposed such that an optical path of a chief ray of the second light exiting the telecentric folded lens is parallel to the optical axis of the telecentric folded lens; and an adjustment element configured to adjust a focal length of the telecentric folded lens.

20. The apparatus of claim 19, wherein the adjustment element is configured to adjust the focal length of the telecentric folded lens by adjusting a distance between the image sensor and the telecentric folded lens.

21. The apparatus of any of claims 19-20, wherein an exit pupil of the telecentric folded lens is greater than 10 meters away from the telecentric folded lens.

22. The apparatus of any of claims 19-21, wherein a diameter of the telecentric folded lens is between 4 millimeters (mm) to 20 mm.

23. The apparatus of any of claims 19-22, wherein the telecentric folded lens further comprises a partially reflective optical element disposed on a surface of the first optical lens element facing an entrance aperture.

24. The apparatus of any of claims 19-23, wherein the adjustment element comprises at least one of: a sliding wedge system, or an electronically adjustable actuator comprising at least one of a voice coil motor (VCM), a step motor, or an ultrasonic motor (USM).

25. The apparatus of any of claims 19-24, wherein the optical capturing device further comprises: a second adjustment element configured to adjust a distance between the first optical lens element and the second optical lens element of the telecentric folded lens.

26. The apparatus of any of claims 19-25, wherein the apparatus is a user equipment (UE).

27. A method comprising: determining, by a processor of a head-mounted display (HMD), comprising an electronic display and a telecentric folded lens, that is configured to place the telecentric folded lens in front of a user’s eye, a distance between the user’s eye and a virtual object plane that is farther away from the user’s eye than the electronic display; and adjusting, by the processor, based on the distance between the user’s eye and the virtual object plane, a distance between the electronic display and the telecentric folded lens while maintaining a constant distance between the telecentric folded lens and the user’s eye.

28. The method of claim 27, further comprising: tracking, by a sensing device, a gaze of the user’s eye, wherein the determining the distance between the virtual object plane and the user’s eye is based on the gaze of the user’s eye.

29. The method of any of claims 27, wherein the determining the distance between the virtual object plane and the user’s eye is based on an image content to be projected on to the virtual object plane.

30. The method of any of claims 27-29, wherein: the telecentric folded lens comprises: a first optical lens element and a second optical lens element disposed along an optical axis of the telecentric folded lens, wherein the first optical lens element is closer to the electronic display than the second optical lens element; a reflective polarization optical element disposed on a surface of the second optical lens element facing the first optical lens element; and a quarter-wave plate disposed between the reflective polarization optical element and the first optical lens element, and an optical path of a chief ray entering the telecentric folded lens is parallel to the optical axis of the telecentric folded lens.

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