Patent Description:
This relates generally to electronic devices and, more particularly, to electronic devices with displays.

Electronic devices often include displays. For example, a head-mounted device such as a pair of virtual reality or mixed reality glasses may have a display for displaying images for a user. An optical system can be used to direct image light from the display to the eyes of a user.

The process of using an optical system to provide images from a display to the eyes of a user in a head-mounted device has the potential to introduce image distortion. Challenges may also arise in forming an optical system that is sufficiently compact to wear on the head of a user. If care is not taken, an optical system for an electronic device may be overly bulky and may not exhibit satisfactory optical performance. <CIT> discloses a beam expanding optical element, a beam expansion method, an image display apparatus, and a head-mounted display.

An electronic device such as a head-mounted device has a pixel array. A light source illuminates the pixel array to produce image light. When illuminating the pixel array, light from the light source may pass through a prism. Reflected image light may pass through the prism to a multi-element lens.

The image light passes through the multi-element lens and is coupled into a waveguide using an input coupler such as a prism. An output coupler such as a diffraction grating may couple the image light out of the waveguide and towards a user. The user may view the image light and may simultaneously observe real-world objects through the waveguide.

The waveguide has a thickness and has locally modified lateral portions that define an aperture stop at a distance from the exit surface of the multi-element lens. The multi-element lens may have first and second achromatic doublets and first and second singlets between the first and second achromatic doublets. The lens elements of the multi-element lens may include lens elements with aspheric surfaces.

Head-mounted devices and other electronic devices may be used for virtual reality and mixed reality (augmented reality) systems. These devices may include portable consumer electronics (e.g., portable electronic devices such as cellular telephones, tablet computers, glasses, other wearable equipment), head-up displays in cockpits, vehicles, etc., display-based equipment (projectors, televisions, etc.). Devices such as these may include displays and other optical components. Device configurations in which virtual reality and/or mixed reality content is provided to a user (viewer) with a head-mounted display device are described herein as an example. This is, however, merely illustrative. Any suitable equipment may be used in providing a user with visual content such as virtual reality and/or mixed reality content.

A head-mounted device such as a pair of augmented reality glasses that is worn on the head of a user may be used to provide a user with computer-generated content that is overlaid on top of real-world content. The real-world content may be viewed directly by a user through a transparent portion of an optical system. The optical system may be used to route images from one or more pixel arrays in a display system to the eyes of a user. A waveguide such as a thin planar waveguide formed from a sheet of transparent material such as glass or plastic or other light guide may be included in the optical system to convey image light from the pixel arrays to the user. The display system may include reflective displays such as liquid-crystal-on-silicon displays, microelectromechanical systems (MEMs) displays, or other displays.

A schematic diagram of an illustrative electronic device such as a head-mounted device is shown in <FIG>. As shown in <FIG>, head-mounted device <NUM> may have a head-mountable support structure such as support structure <NUM>. The components of head-mounted display <NUM> may be supported by support structure <NUM>. Support structure <NUM>, which may sometimes be referred to as a housing, may be configured to form a frame of a pair of glasses (e.g., left and right temples and other frame members), may be configured to form a helmet, may be configured to form a pair of goggles, or may have other head-mountable configurations.

The operation of device <NUM> may be controlled using control circuitry <NUM>. Control circuitry <NUM> may include storage and processing circuitry for controlling the operation of head-mounted display <NUM>. Circuitry <NUM> may include storage such as hard disk drive storage, nonvolatile memory (e.g., electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry <NUM> may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, graphics processing units, application specific integrated circuits, and other integrated circuits. Software code may be stored on storage in circuitry <NUM> and run on processing circuitry in circuitry <NUM> to implement operations for head-mounted display <NUM> (e.g., data gathering operations, operations involving the adjustment of components using control signals, image rendering operations to produce image content to be displayed for a user, etc.).

Head-mounted device <NUM> may include input-output circuitry such as input-output devices <NUM>. Input-output devices <NUM> may be used to allow data to be received by head-mounted display <NUM> from external equipment (e.g., a tethered computer, a portable device such as a handheld device or laptop computer, or other electrical equipment) and to allow a user to provide head-mounted device <NUM> with user input. Input-output devices <NUM> may also be used to gather information on the environment in which head-mounted device <NUM> is operating. Output components in devices <NUM> may allow head-mounted device <NUM> to provide a user with output and may be used to communicate with external electrical equipment.

As shown in <FIG>, input-output devices <NUM> includes one or more displays such as display(s) <NUM>. Display(s) <NUM> may be used to display images for a user of head-mounted device <NUM>. Display(s) <NUM> have pixel array(s) to generate images that are presented to a user through an optical system. The optical system includes optical components such as waveguides waveguides and may include optical couplers, and lenses. The optical system may have a transparent portion through which the user (viewer) can observe real-world objects while computer-generated content is overlaid on top of the real-world objects by producing computer-generated images on the display(s) <NUM>.

<FIG> is a diagram of an illustrative optical system for presenting images on display <NUM> to the eye(s) of user <NUM>. As shown in <FIG>, system <NUM> includes an illumination source such as light source <NUM>. Light source <NUM> may have one or more light-emitting components <NUM> for producing output light. Light-emitting components <NUM> may be, for example, light-emitting diodes (e.g., red, green, and blue light-emitting diodes, white light-emitting diodes, and/or light-emitting diodes of other colors). Illumination may also be provided using light sources such as lasers or lamps.

The displays in device <NUM> such as illustrative display <NUM> may be reflective displays such as liquid-crystal-on-silicon displays, microelectromechanical systems (MEMs) displays (sometimes referred to as digital micromirror devices), or other displays. An optical component such as prism <NUM> may be interposed between light source <NUM> and pixel array <NUM> of display <NUM>. As illustrated by light ray <NUM>, prism <NUM> may be used to couple illumination from light source <NUM> to display <NUM> and may be used to couple reflected image light from pixel array <NUM> of display <NUM> to lens <NUM>. Lens <NUM> is used to provide image light from display <NUM> (e.g., reflected light <NUM>) to optical components <NUM>. Lens <NUM> may have a relatively wide field of view (e.g., at least <NUM>° x <NUM>°, at least <NUM>° by <NUM>°, etc.).

Optical components <NUM> includes a waveguide (e.g., a waveguide formed from a transparent layer of clear glass or plastic) and may include an input coupler for coupling image light (light <NUM>) into the waveguide, and an output coupler for coupling the image light out of the waveguide (e.g., to produce emitted light <NUM> that is viewed by user <NUM>).

<FIG> is a diagram of optical system <NUM> of <FIG> in which prism <NUM> has been omitted for clarity. As shown in <FIG>, the bundle of light rays reflected from each pixel <NUM> may be characterized by a chief ray 26C and marginal rays <NUM>. Chief rays 26C may be perpendicular to pixels <NUM> (e.g., within <NUM>°). Lens <NUM> may be telecentric (configured to accept telecentric light rays). Upon passing through lens <NUM>, the bundle of light rays from each pixel may be collimated. With one illustrative configuration for optical system <NUM>, the marginal and chief rays for any given pixel <NUM> in display <NUM> will vary in angular orientation by less than <NUM> arc min.

Upon exiting lens <NUM>, light rays <NUM> is coupled into waveguide <NUM> using an input coupler such as prism <NUM>. As shown in <FIG>, light rays <NUM> may, for example, enter surface <NUM> of waveguide <NUM> and coplanar surface <NUM> of prism <NUM> and thereafter propagate along the length of waveguide <NUM> (e.g., along dimension Z in the example of <FIG>) in accordance with the principal of total internal reflection. When the image light from display <NUM> that has been coupled into waveguide <NUM> in this way reaches output coupler <NUM> (e.g., a diffraction grating embedded in waveguide <NUM> and/or formed in a coating on the surface of waveguide <NUM> and/or other output coupler structures), output coupler <NUM> is used to couple the image light out of waveguide <NUM> as emitted light <NUM>, for viewing by user <NUM>. If desired, waveguide <NUM> may be transparent, so user <NUM> can view real-world objects such as object <NUM> through waveguide <NUM> when looking in direction <NUM>.

The image light propagating through waveguide <NUM> is confined vertically (relative to dimension X in the example of <FIG>) by the thickness TW of waveguide <NUM> (e.g., <NUM>, <NUM>-<NUM>, at least <NUM>, less than <NUM>, etc.). Lateral image light confinement is provided by locally modifying the properties of waveguide <NUM> (e.g., by incorporating absorbing material in selected regions of waveguide <NUM>, by covering selected portions of waveguide <NUM> with a coating of light-absorbing material and/or by otherwise incorporating light-absorbing material, reflecting structures, gratings, and/or other structures into waveguide <NUM>). As shown in <FIG>, portions 36B of waveguide <NUM> include light restricting structures that block light propagation while leaving portion 36C transparent to permit light propagation. In particular, portion of the width of waveguide <NUM> that is used for transmitting light is locally reduced from the full width FW of waveguide <NUM> (which is generally larger than thickness TW) to reduced width CW. This selective modification to waveguide <NUM> therefore confines image light laterally (along lateral dimension Y in the example of <FIG>).

Waveguide <NUM> is modified in this way (including portions 36B) at the entrance to waveguide <NUM> (e.g., in length L of waveguide <NUM> adjacent to entrance surface <NUM>). The value of L may be at least <NUM>, at least <NUM>, at least <NUM>, less than <NUM>, less than <NUM>, or other suitable value. The lateral confinement of light-restricting portions 36B (e.g., the width CW of transparent entrance portion 36C of waveguide <NUM>) and the vertical confinement due to the size of thickness TW of waveguide <NUM> form an aperture stop for system <NUM>. The aperture stop formed from these waveguide structures is located between the last surface of lens <NUM> and output coupler <NUM> (e.g., between lens <NUM> and user <NUM>). As an example, these structures may form an aperture of about <NUM> in diameter (or at least <NUM>, at least <NUM>, less than <NUM>, less than <NUM>, etc.) at a distance of <NUM> (or at least <NUM>, at least <NUM>, at least <NUM>, less than <NUM>, less than <NUM>, etc.) from the output surface of lens <NUM>.

The quality of lens <NUM> is enhanced by using multiple lens elements (lenses) in lens <NUM> and may be enhanced by incorporating multiple aspheric surfaces in these lens elements. An illustrative configuration for lens <NUM> is shown in <FIG>. As shown in <FIG>, lens <NUM> may include an initial lens element such as lens element <NUM>-<NUM> with an aspheric surface A1 (e. , the entrance surface for lens <NUM> that accepts image light <NUM>). Lens element <NUM>-<NUM> may be a negative lens and may have a concave output surface S1. Lens element <NUM>-<NUM> may be attached to positive lens element <NUM>-<NUM> to form an achromatic doublet. The entrance surface to lens element <NUM>-<NUM> may be a convex surface that is matched to the concave output surface S1 of lens element <NUM>-<NUM>. Lens element <NUM>-<NUM> may also have an output surface S2 that is convex. Surfaces S1 and S2 may be spherical.

At the exit of lens <NUM>, lens <NUM> may have another achromatic doublet formed from lens element <NUM>-<NUM> and final lens element <NUM>-<NUM>. Elements <NUM>-<NUM> and <NUM>-<NUM> are joined at surface S6. Lens element <NUM>-<NUM> may be a positive lens element and lens element <NUM>-<NUM> may be a negative lens element. Convex entrance surface S5 of lens element <NUM>-<NUM> and concave exit surface S7 of lens element <NUM>-<NUM> may be spherical. Surface S6, which forms a concave exit surface for lens element <NUM>-<NUM> and a matching convex input surface for lens element <NUM>-<NUM> may also be spherical. Surface S7 serves as the exit surface for lens <NUM> and may be located about <NUM> (or at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, less than <NUM>, or other suitable distance) from the aperture stop formed from waveguide <NUM>.

A pair of singlets such as lens element <NUM>-<NUM> and lens element <NUM>-<NUM> may be located between the entrance doublet and exit doublet of lens <NUM>. Lens element <NUM>-<NUM> may be a positive lens element having spherical convex entrance surface S3 and aspheric exit surface A2. Lens element <NUM>-<NUM> may be a positive lens element having spherical convex entrance surface S4 and aspheric exit surface A3.

Prism <NUM> may be formed from SF1 glass, lens element <NUM>-<NUM> may be formed from SF6 glass, lens element <NUM>-<NUM> may be formed from N-PK51 glass, lens element <NUM>-<NUM> may be formed from L-BAL42 glass, lens element <NUM>-<NUM> may be formed from L-LAL13 glass, lens element <NUM>-<NUM> may be formed from H-ZPK5 glass, and lens element <NUM>-<NUM> may be formed from N-BK10 glass. Display <NUM> may have a cover glass layer that covers pixels <NUM>. The cover glass layer for display <NUM> may be formed from BK7 glass.

Claim 1:
An electronic device, comprising:
a pixel array (<NUM>);
a light source (<NUM>) that illuminates the pixel array (<NUM>) to produce image light (<NUM>);
a lens (<NUM>) having multiple lens elements (<NUM>-<NUM>..<NUM>-<NUM>) including an initial lens element (<NUM>-<NUM>) with an entrance surface (A1) that receives the image light (<NUM>) and including a final lens element (<NUM>-<NUM>) with an exit surface (S7) through which the image light (<NUM>) exits; and
a waveguide (<NUM>) that receives the image (<NUM>) light from the lens (<NUM>) and that forms an aperture stop located at a distance from the exit surface (S7), wherein
the waveguide (<NUM>) has a thickness (TW) that extends along a first dimension (X), a length (L) that extends along a second dimension (Z) that is orthogonal to the first dimension (X), and a width (FW) that extends along a third dimension (Y) that is orthogonal to the first dimension (X) and to the second dimension (Z),
wherein the waveguide (<NUM>) has first and second opposing surfaces separated by the thickness (TW), wherein the image light (<NUM>) is configured to propagate along the waveguide (<NUM>) parallel to the second dimension (Z) by reflecting off of the first and second opposing surfaces using total internal reflection,
the electronic device being characterized in that the aperture stop is formed by portions of the waveguide that include light restricting structures (36B) that block propagation and locally reduce the width (FW) of the waveguide (<NUM>) while leaving a transparent portion (36C) that permits light propagation.