CN114740621A

CN114740621A - Optical system for head-mounted display

Info

Publication number: CN114740621A
Application number: CN202210219936.8A
Authority: CN
Inventors: S·A·卡恩; N·朱; G·B·米勒; B·J·博尔曼; T·安德森; W·程; J·N·波德
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2016-08-02
Filing date: 2017-07-27
Publication date: 2022-07-12
Also published as: CN110703444B; CN110703444A; CN110268301A; CN110268301B

Abstract

The head mounted display may include a display system and an optical system in a housing. The display system may have an array of pixels that generate light associated with an image. The display system may also have a linear polarizer through which light from the pixel array passes and a quarter wave plate through which the light passes after passing through the quarter wave plate. The optical system may be a catadioptric optical system having one or more lens elements. The lens elements may include plano-convex and plano-concave lenses. The partial mirror may be formed on a convex surface of the plano-convex lens. The reflective polarizer may be formed on a planar surface of a plano-convex lens or a concave surface of a plano-concave lens. An additional quarter-wave plate may be located between the reflective polarizer and the partial mirror.

Description

Optical system for head-mounted display

The present application is a divisional application of an invention patent application having an application date of 2017, month 7, and day 27, an application number of 201780046188.5, entitled "optical system for head-mounted display".

Cross Reference to Related Applications

This application claims 2016, provisional patent application 62/370,170 filed 8, month 2; provisional patent application No.62/383,911 filed on 6/9/2016; and us patent application 15/434,623 filed on 16.2.2017, which is hereby incorporated by reference in its entirety.

Technical Field

The present disclosure relates generally to optical systems, and more particularly to optical systems for head mounted displays.

Background

Head mounted displays, such as virtual reality glasses, use lenses to display images for a user. The microdisplay can generate an image for each eye of the user. A lens may be placed between each eye of the user and a portion of the microdisplay so that the user can view virtual reality content.

Head mounted displays can be cumbersome and tiring to wear if not noticed. Optical systems for head-mounted displays may use bulky and heavy lens arrangements. It may be uncomfortable to use head mounted displays more with this type of optical system.

Accordingly, it is desirable to be able to provide an improved head mounted display.

Disclosure of Invention

A head mounted display may include a display system and an optical system. The display system and the optical system may be supported by a housing worn on the head of the user. The head mounted display may present images to a user using the display system and the optical system while the housing is worn on the user's head.

The display system may have an array of pixels that generate image light associated with an image. The display system may also have a linear polarizer through which image light from the pixel array passes and a quarter wave plate through which the light passes after passing through the linear polarizer.

The optical system may be a catadioptric optical system having one or more lens elements formed of a transparent material, such as glass or plastic, and having a reflective structure. The lens elements may include plano-convex lens elements and plano-concave lens elements. The plano-convex lens element may have a convex surface and an opposing planar surface. The plano-concave lens element may have a concave surface and an opposite planar surface facing the planar surface of the convex lens element.

The partial mirror may be formed on a convex surface of the plano-convex lens element. The reflective polarizer may be formed on a planar surface of a plano-convex lens or a concave surface of a plano-concave lens. An additional quarter-wave plate may be located between the reflective polarizer and the partial mirror.

Drawings

FIG. 1 is a diagram of an exemplary head mounted display according to one embodiment.

Fig. 2 is a diagram of an illustrative head mounted display showing components of an illustrative optical system in the head mounted display, according to one embodiment.

FIG. 3 is a diagram of a head mounted display with another exemplary optical system according to an embodiment.

Fig. 4 and 5 are cross-sectional side views of exemplary lens elements of the type that may be incorporated into a head-mounted display optical system according to one embodiment.

Fig. 6 and 7 are diagrams of additional exemplary head mounted displays according to an implementation.

Fig. 8 and 9 are top and side views, respectively, of a lens element having a cylindrical surface according to one embodiment.

FIG. 10 is a diagram of exemplary lens elements and a reflective polarizer during a molding operation of a mold, according to one embodiment.

Detailed Description

Head mounted displays may be used for virtual reality and augmented reality systems. For example, a pair of virtual reality glasses worn on the head of a user may be used to provide virtual reality content to the user.

An illustrative system is shown in fig. 1 in which a head mounted display, such as a pair of virtual reality glasses, is used to provide virtual reality content to a user. As shown in fig. 1, virtual reality glasses (head mounted display) 10 may include a display system, such as display system 40, that forms an image and may have an optical system, such as optical system 20, through which a user (e.g., a user's eye 46) may view an image produced by display system 40 looking in direction 48.

The display system 40 may be based on a liquid crystal display, an organic light emitting diode display, a light emitting display with an array of crystalline semiconductor light emitting diode dies, and/or a display based on other display technologies. Separate left and right displays may be included in the system 40 for the left and right eyes of the user or a single display may span both eyes.

Virtual content (e.g., image data for still and/or moving images) may be provided to the display system (display) 40 using control circuitry 42 mounted in the eyewear (head mounted display) 10 and/or control circuitry mounted external to the eyewear 42 (e.g., associated with a portable electronic device, laptop computer, or other computing device). Control circuitry 42 may include storage devices such as hard disk storage, volatile and non-volatile memory, electrically programmable storage devices used to form solid state drives, and other memory. Control circuitry 42 may also include one or more microprocessors, microcontrollers, digital signal processors, graphics processors, baseband processors, application specific integrated circuits, and other processing circuitry. The communication circuitry in circuitry 42 may be used to transmit and receive data (e.g., wirelessly and/or over a wired path). The control circuitry 42 may use the display system 40 to display visual content, such as virtual reality content (e.g., computer-generated content associated with a virtual world), pre-recorded video or other images for a movie or other media. An illustrative configuration for the control circuit 42 to provide virtual reality content to a user using the display system 40 may sometimes be described herein as an example. In general, however, any suitable content may be presented to the user by the control circuit 42 using the display system 40 and the optical system 20 of the eyewear 10.

An input-output device 44 may be coupled to the control circuit 42. The input-output device 44 may be used to collect user input from a user, may be used to make measurements of the environment surrounding the eyewear 10, may be used to provide output to a user, and/or may be used to provide output to an external electronic device. The input-output devices 44 may include buttons, joysticks, keypads, keyboard keys, touch sensors, track pads, displays, touch screen displays, microphones, speakers, light emitting diodes for providing visual output to a user, sensors (e.g., force sensors, temperature sensors, magnetic sensors, accelerometers, gyroscopes, and/or other sensors for measuring orientation, position, and/or motion of the eyewear 10, proximity sensors, capacitive touch sensors, strain gauges, gas sensors, pressure sensors, ambient light sensors, and/or other sensors). If desired, the input-output devices 44 may include one or more cameras (e.g., a camera for capturing images of the user's environment, a camera for gaze detection operations by viewing the eyes 46, and/or other cameras).

Fig. 2 is a cross-sectional side view of the eyeglass 10 that illustrates how the optical system 20 and the display system 40 can be supported by a head-mounted support structure, such as the housing 12 of the eyeglass 10. The housing 12 may have the shape of a frame for a pair of eyeglasses (e.g., the eyeglasses 10 may resemble eyeglasses), may have the shape of a helmet (e.g., the eyeglasses 10 may form a helmet-mounted display), may have the shape of a pair of goggles, or may have any other suitable housing shape that allows the housing 12 to be worn on a user's head. The following configurations may sometimes be described herein as examples: housing 12 supports optical system 20 and display system 40 in front of a user's eyes (e.g., eye 46) when the user views system 20 and display system 40 in direction 48. The housing 12 may have other suitable configurations, if desired.

The housing 12 may be formed of plastic, metal, fiber composite materials such as carbon fiber materials, wood and other natural materials, glass, other materials, and/or combinations of two or more of these materials.

The input-output device 44 and the control circuit 42 may be mounted in the housing 12 with the optical system 20 and the display system 40, and/or portions of the input-output device 44 and the control circuit 42 may be coupled to the eyewear 10 using a cable, wireless connection, or other signal path.

The display system 40 and optical components of the eyewear 10 may be configured to display images for the user 46 using a lightweight and compact arrangement. The optical system 10 may for example be based on a catadioptric lens.

Display system 40 may include an image source such as pixel array 14. The pixel array 14 may include a two-dimensional array of pixels P that emit image light (e.g., organic light emitting diode pixels, light emitting diode pixels formed from semiconductor dies, liquid crystal display pixels with backlighting, liquid crystal on silicon pixels with front lighting, etc.). A polarizer, such as linear polarizer 16, may be placed in front of pixel array 14 and/or may be laminated to pixel array 14 to provide polarized image light. Linear polarizer 16 may have a pass axis (e.g., aligned with the X-axis of fig. 2). The display system 40 may also include a wave plate, such as a quarter wave plate 18, to provide circularly polarized image light. The fast axis 18 of the quarter-wave plate may be aligned at 45 degrees with respect to the pass axis of the linear polarizer 16. Quarter-wave plate 18 may be mounted in front of polarizer 16 (between polarizer 16 and optical system 20). If desired, quarter-wave plate 18 may be attached to polarizer 16 (and display 14).

Optical system 20 may include lens elements, such as

lens elements

26 and 32. The lens element 26 may be a plano-convex lens (lens element) having a convex surface facing the display system 40. The optional lens element 32 may be a plano-concave lens (lens element) having a concave surface S3 facing the user (eye 46).

Optical structures, such as partially reflective coatings, wave plates, reflective polarizers, linear polarizers, anti-reflective coatings, and/or other optical components, may be incorporated into the eyewear 10 (e.g., system 20, etc.). These optical structures may allow light rays from display system 40 to pass through and/or reflect from surfaces in optical system 20, such as surfaces S1, S2, and S3, thereby providing optical system 20 with the required lens power.

For example, consider image ray R1. As image light ray R1 exits display 14 and passes through linear polarizer 16, light ray R1 becomes linearly polarized in alignment with the pass axis of linear polarizer 16. The transmission axis of linear polarizer 16 may be aligned, for example, with the X-axis of fig. 2. After passing through polarizer 16, light ray R1 passes through wave plate 18, which may be a quarter wave plate. When the light ray R1 passes through the quarter-wave plate 18, the light ray R1 becomes circularly polarized.

A partially reflective mirror (e.g., a metal mirror coating or other mirror coating such as a dielectric multilayer coating having 50% transmission and 50% reflection), such as partially reflective mirror 22, may be formed on the convex surface of lens element 26. When circularly polarized light ray R1 strikes the partial mirror 22, a portion of the light ray R1 will pass through the partial mirror 22 as reduced intensity light ray R2. Ray R2 will be refracted (partially focused) by the shape of convex surface S1 of lenticular element 26.

The light ray R2 is circularly polarized light. A second quarter wave plate, such as quarter wave plate 28, may be included in optical system 20 to convert the circular polarization of light ray R2 to a linear polarization. Quarter wave plate 28 may, for example, convert circularly polarized light ray R2 into light ray R3 having a linear polarization aligned with the Y-axis of fig. 2.

A reflective polarizer 30 may be formed adjacent to the quarter wave plate 28. In one exemplary configuration, the reflective polarizer 30 and the quarter-wave plate 28 are planar layers and may be formed on a planar surface of the lens element 26. The reflective polarizer 30 may have orthogonal reflection and transmission axes. Light polarized parallel to the reflection axis of the reflective polarizer 30 will be reflected by the reflective polarizer 30. Light polarized perpendicular to the reflection axis of the reflective polarizer 30, and thus parallel to the transmission axis, will pass through the reflective polarizer 30. In the exemplary arrangement of FIG. 2, the reflective polarizer 30 has a reflection axis aligned with the Y-axis, so the light ray R3 will reflect from the reflective polarizer 30 at surface S2 as reflected light ray R4.

The reflected ray R4 has a linear polarization aligned with the Y-axis. After passing through quarter-wave plate 28, the linear polarization of ray R4 will be converted to circular polarization (i.e., ray R4 will become circularly polarized ray R5).

The circularly polarized light ray R5 will travel through the lens element 26 and a portion of the light ray R5 will be reflected in the Z direction by the partial mirror 22 on the convex surface S1 of the lens element 26 as reflected light ray R6. The curved shape of the reflection from surface S1 provides additional optical power for optical system 20. At the same time, the portion of light ray R5 transmitted through partial mirror 22 is converted from circularly polarized light to linearly polarized light by quarter wave plate 18. This linearly polarized light has a polarization that is aligned with the Y-axis so that it is absorbed by linear polarizer 16. Thus, contrast degradation and stray light artifacts from the transmitted portion of light ray R5 are prevented in the image viewable by the user.

Light ray R6 is circularly polarized. After passing through the lens element 26 and the quarter-wave plate 28, the light ray R6 will become linearly polarized (light ray R7), with the linear polarization of the light ray R7 aligned with the X-axis of FIG. 2, which is parallel to the pass axis of the reflective polarizer 30. Thus, the light ray R7 will pass through the reflective polarizer 30 to provide a visual image to the user.

If desired, the eyewear 10 may include an additional linear polarizer, such as a clean linear polarizer 34. The clean linear polarizer 34 has a pass axis that is aligned with the pass axis of the reflective polarizer 30 (i.e., parallel to the X-axis in this example), and thus will remove any residual non-X-axis polarization from the light ray R7 before the light ray R7 reaches the viewer's eye 46.

Additional lens elements, such as element 32, having additional lens element surfaces (surface S3) may be incorporated into optical system 20, if desired. Surface S3 may be concave and/or convex and may be used for additional focusing, distortion correction, and the like. The element 32 may have a planar surface facing the lens element 26 and a curved surface facing the viewer 46 (S3). Surface S3 may be concave, convex, aspheric, freeform, partially concave and partially convex, or may have other suitable shapes. Curved surfaces in system 20, such as surfaces S1 and/or S3, may be aspheric to improve sharpness or reduce distortion in images presented to a user. For example, lens element 32 may be positioned with its planar surface adjacent to the planar surfaces of reflective polarizer 30, quarter-wave plate 28, and element 26 (i.e., reflective polarizer 30 and quarter-wave plate 28 may be sandwiched between the planar surfaces of

lens elements

32 and 26 without voids).

Although element 32 provides additional focusing power, the complexity and weight of the optical system can be reduced by omitting element 32, if desired. Furthermore, the quarter-wave plate 28 need not be located on the planar surface of the element 26, but may be located anywhere between the partially reflective mirror 22 and the reflective polarizer 30. For example, quarter wave plate 28 may be moved to position 24 between curved partial mirror 22 and the convex surface of element 26.

Fig. 3 is a cross-sectional side view of eyewear 10 in an exemplary configuration in which the optical system includes plano-convex lens elements 26 and a curved lens element 32 (e.g., plano-concave, plano-aspheric, etc.), and in which reflective polarizer 30 is formed on curved surface S3 of lens element 32. Because surface S3 is curved, additional optical power and/or distortion correction capability or a larger display field of view may be provided by allowing image light to reflect from reflective polarizer 30 when reflective polarizer 30 has been curved into the shape of surface S3. If desired, the quarter-wave plate 28 may be moved from the position shown in FIG. 3 to a position adjacent to the reflective polarizer 30 of FIG. 3 (e.g., in position 50) or may be moved to position 24 of FIG. 2. The configuration of fig. 3 is merely exemplary.

Fig. 4 shows how

lens elements

32 and 26 may be separated by a gap in system 20, if desired. If desired, an anti-reflective coating may be provided on the planar surface of elements 32 and/or 26 to reduce reflections.

In the exemplary configuration of fig. 5, system 20 is formed from lens elements having additional curved surfaces. In this arrangement, the

elements

32 and 26 are meniscus lenses and meet at a curved mating surface 52. The optical system of fig. 4 and 5 may include a quarter-wave plate, a partial mirror, and a reflective polarizer to form a catadioptric lens as described in connection with catadioptric lens system (lens) 20 of fig. 2 and 3.

In the exemplary configuration of FIG. 6, the reflective polarizer 30 has been formed on the surface of the additional lens element 54. The reflective polarizer 30 and the lens element 54 may be attached to adjacent curved surfaces of the lens element 32 using an optically clear adhesive, for example. The surface of the lens element 54 facing the user 46 may have a curved surface, if desired. If desired, the thickness of the lens element 54 may be constant (e.g., the thickness of the element 54 may vary by less than 10% or less than 5% or other suitable amount across its diameter). In addition, linear polarizer 34 may be formed on the curved surface of lens element 54 facing user 46 to help suppress reflections of stray ambient light. The linear polarizer 34 may be oriented such that the transmission axis of the linear polarizer 34 is aligned with the X-axis, such that rays of image light, such as ray R7 of fig. 2, will pass to the user 46 for viewing, while ambient light rays passing through the polarizer 34 (in the-Z direction) will become X-polarized due to the X-axis transmission axis orientation of the linear polarizer 34 and will therefore not be reflected by the reflective polarizer 30 (which has a reflection axis with a Y-axis orientation). Obliquely oriented ambient light rays will also tend to reflect off of the user 46 due to the curved surfaces of the lens elements in the system 20. Thus, the presence of the linear polarizer 34 will help to reduce stray light reflections from the inward side of the system 20 towards the user 46.

The outward facing surface S4 of lens element 54 may be curved (e.g., convex) and the opposing mating inward facing surface S5 of lens element 32 may be correspondingly curved (e.g., concave). For one illustrative configuration, surfaces S4 and S5 may be rotationally symmetric about the Z-axis of fig. 6 (e.g.,

lens elements

54 and 32 may be dome lenses and surfaces S4 and S5 may be dome lens surfaces). This allows the lens element 54 to be rotated relative to the lens element 32 (e.g., to align the reflective polarizer 30 to the quarter wave plate 28, etc.).

In the example of fig. 6, surfaces S6 and S7 are planar. This helps to avoid applying undesirable stress on the quarter-wave plate 28 (which may be formed, for example, by a birefringent stretched film). Another exemplary arrangement for minimizing quarter wave plate stress is shown in fig. 7. In the example of fig. 7, surfaces S6 and S7 have cylindrical curved shapes (S6 is convex and S7 is concave so that the cylindrical shapes fit together). Although the quarter-wave plate 28 of fig. 7 is curved, the quarter-wave plate 28 is bent (curved) only about a single axis (Y-axis) and not about the X-axis. Thus, the quarter-wave plate 28 has no compound curvature, which may place undesirable stresses on the quarter-wave plate 28. For comparison, fig. 8 and 9 show cross-sectional side views of

lens elements

32 and 26 of fig. 7. Fig. 8 is a cross-sectional side view looking along the Y-axis. Quarter wave plate 28 is interposed between cylindrical surface S6 of lens element 32 and cylindrical surface S7 of lens element 26 and is bent about an axis parallel to the Y-axis, as shown in fig. 8. FIG. 9 is a cross-sectional side view of

lens elements

32 and 26 of FIG. 7 viewed along the X-axis, showing how surfaces S6 and S7 do not bend about the X-axis. Because the surfaces S6 and S7 have such a cylindrical shape, the quarter-wave plate 28 does not exhibit compound curvature and is not exposed to an undesirable amount of stress, such that the quarter-wave plate 28 provides a relatively uniform retardation across the lens assembly.

Fig. 10 illustrates how a lens element, such as lens element 54, may be formed by injection molding a plastic (polymer) or other material into mold 56. The reflective polarizer 30 may be placed in the mold 56 such that the reflective surface of the reflective polarizer 30 abuts the mold surface S5' when plastic is injected into the interior cavity of the mold 56 to form the lens element 54. Mold surface S5 'can be machined with high precision so that pressing reflective polarizer 30 against surface S5' during the molding operation will help enhance the smoothness and precision of the reflective surface of reflective polarizer 30. Similarly, if desired, the reflective polarizer 30 may be formed by molding the reflective polarizer 30 against the opposing surface 58 during an injection molding operation.

The lens elements used in optical system 20 may be thin and formed of lightweight materials (e.g., plastic) and/or may be formed of materials such as glass. The reduction in weight may help provide a comfortable viewing experience for the user 46. Where lens elements such as element 54 have a uniform thickness, it may be easier to mold one or more lens elements having uniform optical properties, including low birefringence.

As described in connection with fig. 8 and 9, the quarter wave plate 28 may be interposed between the

lens elements

32 and 26 when the

elements

32 and 26 are bonded together (e.g., using adhesive layers on opposite sides of the quarter wave plate 28). As described in connection with fig. 6, surfaces S6 and S7 may be planar (e.g., element 32 may be a plano-concave element and element 26 may be a plano-convex element), or surfaces S6 and S7 may be curved (e.g., see fig. 7). As described in connection with fig. 8 and 9, the surfaces S6 and S7 may be cylindrical surfaces (surfaces that are bent around an axis). In such a configuration, the quarter-wave plate 28 may be bent along only one axis (e.g., the quarter-wave plate 28 may not have any compound curves), thereby reducing distortion in the quarter-wave plate 28 and helping to ensure that the retardation provided by the quarter-wave plate 28 is uniform.

During assembly of the optical system 20, a planar piece of quarter wave film may be placed between the

elements

32 and 26, with optical adhesive on either side of the quarter wave film. The

elements

32 and 26 may then be forced together to distribute the adhesive and fold the quarter wave film about axis Y (an axis parallel to axis Y). Providing surfaces S6 and S7 with a cylindrically curved shape enables the thickness of

lens elements

32 and 26 to be reduced. The use of a cylindrically curved shape for surfaces S6 and S7 may help achieve a more uniform thickness across the lens element and thereby improve the moldability of the lens element. In forming injection molded lens elements, uniformity of thickness in the mold cavity can help improve the uniformity of flow of the molten plastic as it is injected into the mold and the melt front flows through the mold cavity. The presence of uniform flow during molding can be important to prevent flow lines in the molded lens, especially when the lens elements are thicker at the edges than in the center. More uniform flow may also result in low birefringence in the molded lens element. For catadioptric optical systems such as system 20, low birefringence in the lens elements helps to maintain control over the polarization state of the image light, so that stray light and ghosting are reduced, and thus a high contrast image free of stray light artifacts is provided to user 46. Furthermore, the cylindrical curved shape of the wave plate 28 in configurations of the type shown in fig. 8 and 9 can help ensure that light rays in the system 20 pass through the quarter wave plate 28 at angles closer to normal incidence than in planar wave plate configurations. As a result, the retardation provided by the quarter-wave plate 28 may be more uniform across the lens elements, and thus the image provided to the user 46 may be more uniform in contrast with less ghosting artifacts.

In the device 10, the image light is converted from unpolarized light to linearly polarized light, to circularly polarized light, then back to linearly polarized light, back to circularly polarized light and finally back to linearly polarized light. In order to fully convert linearly polarized light into circularly polarized light, thereby reducing the ellipticity of polarization, it may be desirable to precisely orient quarter-

wave plates

28 and 18 with respect to the polarization axis of the polarizers. For example, it may be desirable to precisely orient the fast axis of quarter-wave plate 18 at 45 degrees relative to the polarization axis (transmission axis) of linear polarizer 16, and to precisely orient the fast axis of quarter-wave plate 28 at 45 degrees relative to the polarization axis (transmission axis) of reflective polarizer 30. For example, the fast axis of the quarter-wave plate may be oriented at 45 degrees relative to the polarization axis of the corresponding polarizer, within +/-1.5 degrees or other suitable alignment tolerance. The precise alignment of the quarter-wave plate to the polarization axis of the polarizer helps to ensure that the light is not mixed polarization (non-elliptical polarization). Thus, precise alignment prevents portions of the image light from following undesired paths that form ghost images, which can reduce contrast and present stray light artifacts.

The linear polarizer 16 and the quarter-wave plate 18 may be aligned during lamination. For example, rolls of polarizing film and quarter wave film may be precisely aligned with each other during rewinding and laminated together with an optically clear adhesive so that alignment is maintained. The laminated polarizer/quarter wave film may then be attached to a substrate for installation into an optical system or directly to a cover glass or other structure associated with the pixel array 14. Light emitting displays, such as organic light emitting diode displays and light emitting diode displays formed from arrays of crystalline semiconductor light emitting diode dies, can provide non-deflected image light, such that attaching a laminated polarizer/quarter wave film to the pixel array allows the display system to emit circularly polarized light.

The quarter wave plate 28 may also be precisely aligned with the reflective polarizer 30. Reflective polarizer 30 may be formed in a curved shape (e.g., by thermoforming with heat and differential pressure or pressure forming) directly to the concave surface of lens element 32 or to a mold (e.g., mold 56 of fig. 10) that matches the concave surface of lens element 32. The quarter wave plate 28 or the reflective polarizer 30 may then be aligned in an assembly process, with the two

lens elements

32 and 54 bonded to the reflective polarizer 30 and the curved quarter wave plate 28. Reflective polarizer 30 or curved quarter wave plate 28 may, for example, be bonded to one of

lens elements

32 or 54, and the remaining elements of system 20 may be oriented with the desired alignment accuracy. A polarimeter can be used to measure through optical system 20 during alignment to determine how much ovality is present and use this information to guide alignment during assembly. In a configuration of the type shown in fig. 6, the interface between

lens elements

32 and 26 is planar. In this configuration, the quarter wave plate 28 may be bonded to the planar side of the plano-convex lens element 26, and the reflective polarizer 30 may be bonded to the concave side of the plano-concave lens element 32.

Lens elements

32 and 26 may then be rotated relative to each other while measuring the polarization ellipticity. Once it is determined that the quarter-wave plate 28 is satisfactorily aligned to the reflective polarizer 30, the components of the optical system 20 may be bonded together to maintain alignment.

A dome optical system (a lens element having a dome-shaped surface) may be used to facilitate alignment of the polarizer 30 and the quarter-wave plate 28, if desired. For example, the convex surface S4 of element 54 and the concave surface S5 of element 32 may be dome-shaped, allowing these dome lens elements to rotate relative to each other during an alignment operation. The quarter wave plate 28 may be bonded between

lens elements

32 and 26. Polarizer 30 may be formed on the surface of lens element 54. Dome lens element 54 may then be bonded to surface S5 of lens element 32 while polarizer 30 and quarter wave plate 28 are aligned. Dome lens element 54 may be rotated as desired prior to bonding to lens element 32 while polarization measurements are taken to assess alignment accuracy. If desired, the reflective polarizer 30 may be molded to the surface S4 of the lens element 54, as described in connection with FIG. 10 (e.g., using the reflective polarizer 30 as an insert in the mold 56). Applying pressure to the optical plastic for elements 54 during molding presses reflective polarizer 30 against the walls of mold 56 during molding, such that the precision and smoothness of the reflective surface of reflective polarizer 30 (e.g., the outward surface of reflective polarizer 30) is determined by the precision and smoothness of the walls of mold 56, which may be formed to conform to optical specifications. The thickness of molded dome lens 54 (e.g., 1-3mm) maintains the surface finish of the reflective surface of reflective polarizer 30 after molding for ease of handling during assembly. The force used in the process of bonding the dome lens 54 to the mating dome-shaped surface S5 of the lens element 32 (e.g., using a liquid optically clear adhesive) may then be sufficiently small so as not to degrade the as-molded surface accuracy of the reflective surface of the reflective polarizer 30 on the surface S4 of the element 54.

As shown in fig. 6, a linear polarizer 34 may be formed on the eye side (concave surface S8) of element 54 to help prevent stray reflections of light from the environment. Linear polarizer 34 may be a flat or curved separate layer located between optical system 20 and user's eye 46. The linear polarizer 34 may also be attached to the surface S8 of the lens element 54 (e.g., the inner dome lens surface), or may be laminated to the reflective polarizer 30 before the polarizer 30 is formed on the surface S4 of the lens element 54. The linear polarizer 34 may be aligned relative to the reflective polarizer 30 such that the transmission axes of the two polarizers are aligned. In this way, the linear polarizer 34 absorbs light from the environment having a polarization state that will be reflected by the reflective polarizer 30. Light from the environment having the polarization state transmitted by linear polarizer 34 and reflective polarizer 30 passes through quarter-wave plate 28 and quarter-wave plate 18, eventually having the linear polarization state absorbed by linear polarizer 16. This helps reduce stray light reflections because the reflective polarizer 30 reflects light of this polarization state with a high reflectivity, which may create diffuse reflections of light entering the device 10 from behind or beside the user 46. At the same time, aligning linear polarizer 34 such that the transmission axis of linear polarizer 34 is parallel to the transmission axis of reflective polarizer 30 helps enable linear polarizer 34 to act as a cleaning polarizer to improve the image quality from pixel array 14 while reducing the brightness of the image light presented to the user's eye by a small amount (e.g., < 20% if the transmission of linear polarizer 34 is 40%, and < 10% if the transmission of linear polarizer 34 is 45%). The linear polarizer 34 may be a high transmission polarizer having a transmission of at least 40%, at least 43%, or at least 45% compared to unpolarized light.

In one embodiment, the quarter-wave plate in system 28 may be formed from multiple layers of retardation film laminated together. The layers of the retardation film may be oriented at an angle to each other such that together they act as a quarter-wave plate, the retardation variation being reduced when measured in waves over a wider spectral bandwidth (also referred to as achromatic quarter-waves). For example, the retardation of the quarter-wave plates 18 and/or 28 may be within +/-1.5 over the wavelength range of 450 and 650 nm.

A primer (e.g., an adhesion promoter polymer) may be applied to one or more surfaces of reflective polarizer 30 prior to molding of the intervening dome lens elements 54. This may help increase the strength of the bond between reflective polarizer 30 and dome lens element 54 after molding.

If desired, reflective polarizer 30 may have a substrate formed from a material such as polycarbonate or a cyclic olefin that matches the thermal expansion of the lens elements (e.g., acrylate or cyclic olefin lens elements) in system 20, thereby reducing interfacial stress when optical system 20 is exposed to heat from display system 40 or the environment.

If desired, the lens element 26 interposed between the other lens elements of the system 20 and the display system 40 may be made of glass (which may have a lower thermal expansion and higher heat resistance than plastic) to help resist thermal effects from the display system 20. In addition, a soft adhesive or optical grease may be used for the quarter wave plate 28 between the

lens elements

54 and 32 to achieve some differential thermal expansion with reduced interfacial stress between the two lens elements and the quarter wave plate 28.

According to one embodiment, there is provided a head mounted display configured to display an image viewable by a user, comprising an array of pixels configured to produce the image; a linear polarizer through which light associated with the image passes; a first planar quarter wave plate receiving light from the linear polarizer; a plano-convex lens element having a convex surface and an opposing planar surface; a partial mirror on the convex surface; a reflective polarizer and a second planar quarter wave plate between the reflective polarizer and the partial mirror.

According to another embodiment, the head mounted display includes an additional linear polarizer through which the light passes after passing through the reflective polarizer.

According to another embodiment, the second planar quarter wave plate is formed at the planar surface of the plano-convex lens element.

According to another embodiment, the head-mounted display includes a plano-concave lens element having a concave surface and an opposing planar surface, the planar surface of the plano-concave element being parallel to the planar surface of the plano-convex lens element.

According to another embodiment, the planar surface of the plano-convex lens element faces the planar surface of the plano-concave lens element.

According to another embodiment, the reflective polarizer is formed at the concave surface of the plano-concave lens.

According to another embodiment, the head mounted display comprises an additional lens element, the reflective polarizer being interposed between the additional lens element and the plano-concave lens element.

According to another embodiment, the head mounted display comprises an additional linear polarizer at a surface of the additional lens element, the additional lens element being interposed between the additional linear polarizer and the reflective polarizer.

According to another embodiment, the head mounted display includes control circuitry configured to provide image data to the pixel array and an input-output device coupled to the control circuitry.

According to another embodiment, the input-output device includes a camera.

According to one embodiment, there is provided a head mounted display configured to display an image viewable by a user, comprising an array of pixels configured to produce the image; a linear polarizer through which light associated with the image passes; a first quarter wave plate receiving light from the linear polarizer; a first lens element having a first opposing surface and a second opposing surface; a second lens element having a third opposing surface and a fourth opposing surface, the third surface facing the second surface; a third lens element having a fifth opposing surface and a sixth opposing surface, the fifth surface facing the fourth surface; a partial mirror on the first surface; a second quarter wave plate interposed between the second surface and the third surface; and a reflective polarizer between the fourth surface and the fifth surface.

According to another embodiment, the head-mounted display comprises an additional linear polarizer at the sixth surface, the light passing through the additional linear polarizer after passing through the reflective polarizer.

According to another embodiment, the first surface is a convex surface and the second surface is a planar surface.

According to another embodiment, the third surface is a planar surface, the fourth surface is a concave surface, the fifth surface is a convex surface, and the sixth surface is a concave surface.

According to another embodiment, the second surface is a concave surface and the third surface is a convex surface.

According to another embodiment, the first surface is a convex surface, the second surface is a concave surface, the third surface is a convex surface, and the second surface and the third surface have a cylindrical shape.

According to another embodiment, the fourth surface and the fifth surface are dome-shaped surfaces.

According to one embodiment, there is provided a head-mounted device configured to present images to a user, comprising: a support structure configured to be worn on a user's head; a display system supported by the support structure and generating light for an image; and a catadioptric optical system supported by the housing and focusing the light as it passes from the display system to the user, the catadioptric system comprising: a first lens element having a convex first surface and having an opposing second surface; a partial mirror on the first surface; a quarter wave plate at the second surface; a second lens element having a third surface at the quarter-wave plate and an opposing concave fourth surface; a reflective polarizer having a reflection axis at the fourth surface and having a transmission axis perpendicular to the reflection axis; and a third lens element having a convex fifth surface at the reflective polarizer and an opposing concave sixth surface.

According to another embodiment, the head-mounted device comprises a linear polarizer on the sixth surface.

According to another embodiment, the second and third surfaces are planar and the quarter wave plate is planar.

According to another embodiment, the second surface and the third surface have a mating cylindrical shape.

The foregoing is merely exemplary and various modifications may be made to the embodiments. The foregoing embodiments may be implemented independently or in any combination.

Claims

1. A head mounted display configured to display images viewable by a user, the head mounted display comprising:

a pixel array configured to generate the image;

a first linear polarizer through which light associated with the image passes;

a first quarter wave plate that receives the light from the first linear polarizer;

a first lens element having a convex first surface and having an opposing second surface;

a partial mirror on the first surface;

a second quarter wave plate on the second surface;

a second lens element having a third surface at the second quarter wave plate and an opposing fourth surface that is a concave surface;

a reflective polarizer at the fourth surface;

a third lens element having a fifth surface and an opposing sixth surface, wherein the second lens element is interposed between the first lens element and the third lens element; and

a second linear polarizer interposed between the second lens element and the third lens element.

2. The head mounted display of claim 1, wherein the third lens element is a dome lens.

3. The head mounted display of claim 1, wherein the second linear polarizer and the reflective polarizer have parallel transmission axes.

4. The head mounted display of claim 1, wherein the reflective polarizer has a reflection axis and a transmission axis orthogonal to the reflection axis.

5. The head mounted display of claim 1, wherein the first linear polarizer has a pass axis, and wherein the first quarter-wave plate has a fast axis at a 45 degree angle with respect to the pass axis.

6. The head mounted display of claim 1, wherein the reflective polarizer has a transmission axis, and wherein the second quarter wave plate has a fast axis at a 45 degree angle relative to the transmission axis.

7. The head mounted display of claim 1, wherein the second surface is a cylindrical concave surface, and wherein the third surface is a cylindrical convex surface.

8. The head mounted display of claim 1, wherein the second surface and the third surface are mated cylindrical surfaces.

9. The head mounted display of claim 1, wherein at least one of the fifth surface and the sixth surface is aspheric.

10. A head mounted display configured to display images viewable by a user, the head mounted display comprising:

an array of pixels configured to produce the image;

a first linear polarizer through which light associated with the image passes;

a first lens element having a first surface and having an opposing second surface, the first surface being a convex surface and the second surface being a concave surface;

a partial mirror on the first surface;

a second quarter wave plate on the second surface;

a second lens element having a third surface and an opposing fourth surface, the third surface being a convex surface and the fourth surface being a concave surface;

a reflective polarizer interposed between the first lens element and the second lens element; and

a second linear polarizer interposed between the first lens element and the second lens element.

11. The head mounted display of claim 10, wherein the second linear polarizer and the reflective polarizer have parallel transmission axes.

12. The head mounted display of claim 10, wherein the reflective polarizer has a reflection axis and a transmission axis orthogonal to the reflection axis.

13. The head mounted display of claim 10, wherein the first linear polarizer has a transmission axis, and wherein the first quarter wave plate has a fast axis at a 45 degree angle relative to the transmission axis.

14. The head mounted display of claim 10, wherein the reflective polarizer has a pass axis, and wherein the second quarter-wave plate has a fast axis at a 45 degree angle with respect to the pass axis.

15. The head mounted display of claim 10, wherein the second lens element is a dome lens.

16. A head mounted display configured to display images viewable by a user, the head mounted display comprising:

an array of pixels configured to produce the image;

a first linear polarizer through which light associated with the image passes;

a lens element having a first surface and having an opposing second surface, the first surface being a convex surface and the second surface being a concave surface;

a partial mirror on the first surface;

a second quarter wave plate on the second surface;

a reflective polarizer, wherein the second quarter-wave plate is interposed between the reflective polarizer and the lens element; and

a second linear polarizer, wherein the reflective polarizer is interposed between the second linear polarizer and the second quarter-wave plate.

17. The head mounted display of claim 16, wherein the second linear polarizer and the reflective polarizer have parallel transmission axes.

18. The head mounted display of claim 16, wherein the reflective polarizer has a reflection axis and a transmission axis orthogonal to the reflection axis.

19. The head mounted display of claim 16, wherein the first linear polarizer has a transmission axis, and wherein the first quarter wave plate has a fast axis at a 45 degree angle relative to the transmission axis.

20. The head mounted display of claim 16, wherein the reflective polarizer has a transmission axis, and wherein the second quarter wave plate has a fast axis at a 45 degree angle relative to the transmission axis.