Optical array for displays

Abstract

A folded optical array for use in transmitting an image from an image source to a user's eye within a view-through display, wherein the folded optical array is a folded optical array providing a folded light transmission path, comprising a first optical element including a first plurality of optically powered surfaces and a second optical element including at least one optically powered surface, configured to receive light forming an image from an image source, and an optical system for providing a virtual image of the image source at an apparent focus between a predetermined distance and optical infinity; wherein the first plurality of optically powered surfaces and at least one optically powered surface of the second optical element are arranged to define a plurality of interfaces along the folded light path, and a change in refractive index at each interface is predetermined to control the direction of light passing through said interface or each interface, and one surface of the first optical element and one surface of the second optical element are adjacent to each other, the adjacent surfaces are different, and each of the adjacent surfaces is relative to the adjacent surfaces A folded optical array comprising: defining individual different surfaces and angles of the relevant optical elements at opposite ends, wherein the angles of opposite ends are not identical; and a compensator element positioned between the first optical element and the external view to receive an external view to be combined with an image output from the optical system.

Description

Technology Field

[0001] The present invention relates to improving an optical device for use in a display, such as, for example, a head-mounted display; a head-worn display; and / or a head-up display, or to such an optical device. Background Technology

[0002] Some displays, such as head-mounted displays (HMDs); head-worn displays (HWDs) or head-up displays (HUDs), aim to be as small and lightweight as possible. An exemplary HMD (100) is shown in FIG. 1.

[0003] An HMD, such as the HMD (100), can be worn by a user using a suitable support (102). The support includes one or more optical elements (104) that can be viewed by one or both eyes of the user. Although not illustrated in detail, the optical elements (104) include a substantially transparent display medium. The user can see the external environment through the optical elements (104). Additionally, the user can see an image transmitted through the HMD to the user's eyes while in use.

[0004] In a conventional system, an image is transmitted to the user's eye using a lens array or a folded optical design. The lens array or the folded optical design is integrated within the HMD (100). Conventionally, the lens array or the folded optical design is typically located within the support (102) of the HMD (100).

[0005] Conventional optical lens arrays are linear and non-folding for the sake of simplicity. Typically, multiple elements are used to achieve the required performance. For this reason, they are not particularly suitable for modern HMDs that are required to be compact, lightweight, and optimized for anthropometric data.

[0006] Conventional folded optical designs can be more compact, but they may introduce optical loss mechanisms and reduce system efficiency. One of the simplest folded optical designs consists of an optical array (200) as shown in FIG. 2.

[0007] The optical array (200) includes a beam splitter (202) and a spherical coupler (204). In use, an image is directed from a display source (206) or a relay lens onto the beam splitter (202). The beam splitter (202) partially reflects the image onto the concave surface of the spherical coupler (204). It can be understood that the surface is concave with respect to the input light. The spherical coupler (204) reflects the collimated outgoing pupil through the beam splitter (202) toward the user's eye (208).

[0008] However, if used within an HMD, the optical array (200) must be adapted to allow the user to see the external environment (210). To achieve this, the beam splitter (202) and the spherical coupler (204) must be at least semi-transparent. Consequently, some image source light is lost during interaction with each element because light is lost when only partial reflection occurs. Therefore, the image provided to the eye is blurrier than desired. Additionally, the light must pass through the beam splitter (202) twice, which can also increase loss and cause a ghost image.

[0009] An additional disadvantage of the optical array (200) is that they are often not sufficiently lightweight and compact. The geometry of the beam splitter (202) and the spherical coupler (204) must match the output pupil requirements and thus must be large enough to fit the required anthropometric range, thereby increasing the size of the geometry of the optical device.

[0010] Improvements to the optical array are provided in the expired patents US 5093567 and US 4969724. These patents show a folded optical array having a multi-part folded eyepiece and a relay lens assembly.

[0011] An example of a known folded optical array (300) found in these patents is illustrated in FIG. 3. The optical array (300) has a compact eyepiece within an off-axis solid array. The array (300) includes a wedge (302), a prism (304), and a bonded makeup piece (306). The prism (304) receives an image from a relay lens (308) or a display source. The wedge (302) and the prism (304) can together form a collimated image to be viewed by the user's eye (310). The makeup piece (306) optically manipulates light to cancel out the effects of the prism (304) and the wedge (302), allowing the user to see the external environment (312) accurately. The makeup piece (306) is typically bonded to the prism (304) using an optical adhesive.

[0012] As can be seen in FIG. 3, the prism uses a transmission surface and a conventional curved coupling surface. Similarly, the wedge has two transmission surfaces. The makeup piece also has a surface that matches the coupling surface of the prism.

[0013] While the folded optical array (300) solves some of the problems recognized in the optical array (200), new issues may arise. For example, the optical array (300) of FIG. 3 includes off-axis components that are simple surface shapes, such as spherical and cylindrical surfaces, which result in residual aberrations such as astigmatism and distortion within the viewed image.

[0014] Additionally, the optical array (300) of FIG. 3 is suitable for use with an image source of an ideally controlled numerical aperture (NA). In such an array, a relay lens with an internal hard-stop is used to vignette unwanted light / rays to control the size of the resulting system output pupil.

[0015] However, if such an optical array is paired with a flat panel display, a radial display, or a direct image source having an uncontrolled NA (excluding the use of relay lenses), the output pupil size may not be controlled, and unwanted light may propagate through the optical system, resulting in a large output pupil that cannot be fully corrected to eliminate aberrations. In FIG. 3, the unwanted light is indicated by reference number 314. In this scenario, if the user's pupil is aligned axially with the center of the output pupil, the display appears well corrected. Conversely, if the eye or the optical array moves, uncorrected light is present primarily in the user's viewing area of ​​the output pupil. Within this area, the image may appear blurry, distorted, or inaccurate, which is an obvious disadvantage for high-performance conformal displays. The problem to be solved

[0016] Therefore, one objective of the present invention is to overcome the problems of existing folded optical arrays for use in HMDs. means of solving the problem

[0017] According to one aspect of the present invention, a folded optical array for use in transmitting an image from an image source to a user's eye within a view-through display, wherein the folded optical array provides a folded light transmission path and has a first optical element comprising a first plurality of optically powered surfaces and a second optical element comprising at least one optically powered surface, configured to receive light forming an image from an image source and an optical system for presenting a virtual image of the image source to a user at an apparent focus between a predetermined distance and optical infinity, wherein the first and second plurality of optically powered surfaces are arranged to define a plurality of interfaces along the folded light path, and a change in refractive index at each interface is predetermined to control the direction of light passing through said interface or said interface, and one surface of the first optical element and one surface of the second optical element are adjacent to each other, and each of the adjacent surfaces is at an angle with each other surface of the relevant optical element at the ends opposite to each other of the adjacent surfaces A folded optical array is provided, comprising a first optical element and a compensator element positioned between the external view to receive an external view to be combined with an image output from the optical system, wherein the angles on opposite sides are not identical.

[0018] Preferably, the compensator element is adapted to minimize the refractive error induced on the external view by either the first optical element or the second optical element.

[0019] Preferably, the compensator element is optically coupled to the first optical element.

[0020] Preferably, one surface of the compensator element is matched to the surface of the first optical element.

[0021] Preferably, the first optical element includes at least three optical power surfaces.

[0022] Preferably, the first optical element is a three-sided prism.

[0023] Preferably, the first optical element comprises a single-piece triangular element having an elongated substantial triangular cross-section.

[0024] Preferably, the second optical element has at least two optical power surfaces.

[0025] Preferably, the second optical element is a wedge.

[0026] Preferably, the second optical element includes an elongated element having a quadrilateral cross-section.

[0027] Preferably, the first optical element and the second optical element are arranged in juxtaposition with each other so that at least one optical power surface of each optical element is substantially aligned.

[0028] Preferably, at least one optical power surface of each optical element is separated by a gap.

[0029] Preferably, the gap is a void.

[0030] Preferably, the first optical element is a substantially concave surface.

[0031] Preferably, the substantial concave surface is optically coated so as to be substantially reflective.

[0032] Preferably, at least one optical power surface among the optical power surfaces on the first optical element is described by a multi-order polynomial.

[0033] Preferably, one of the angles is less than 30°.

[0034] Preferably, the first and second optical elements are made of different materials.

[0035] Preferably, the predetermined distance is about 30 cm.

[0036] According to another embodiment of the present invention, a display comprising a folded optical array according to another aspect of the present invention is provided.

[0037] Preferably, such displays are in the form of head-mounted displays, head-worn displays, and head-up displays, or at least one of these. Brief explanation of the drawing

[0038] Embodiments of the present invention will be described only by example with reference to the following drawings: FIG. 1 is a representation of a head-mounted display; FIG. 2 is a cross-sectional view of a conventional optical array; FIG. 3 is a cross-sectional view of a conventional off-axis solid optical array; FIG. 4 is a cross-sectional view of a folded optical array according to one embodiment of the present invention; FIG. 5 is a more detailed cross-sectional view of a folded optical array according to one embodiment of the present invention; FIG. 6 is a cross-sectional view of an optical element showing an angle difference according to one embodiment of the present invention; FIGS. 7a and 7d are top-down and side views, respectively, of various different orientations of the positioning of the optical array of the present invention for the user; Figures 8a and 8b are representations of a combination of a prism, a wedge, and a compensator. Specific details for implementing the invention

[0039] Generally, the present invention relates to improvements to displays, such as, for example, head-mounted or head-worn displays (HMD, HWD, respectively) or head-up displays (HUD), or to optical improvements to such displays. In particular, the present invention relates to a folded optical array to be used within a display for transmitting an image from an image plane to a user's eye, and a display comprising such a folded optical array.

[0040] For example, an exemplary display such as an HMD or HWD according to the present invention includes a folded optical array, such as the optical array of FIG. 5 (described later), to overcome the problems of existing arrays in the industry.

[0041] FIG. 4 illustrates a cross-sectional view of a folded optical array (600) according to one embodiment of the present invention. FIG. 4 shows the path of a light beam traveling from a source (602) to a user's eye (604) through the optical array (600), an optical field lens (606), and a focusing optical device (608). Additionally, the light travels from an external environment (607) to a user's eye (604) through a focusing optical device (608) and a compensator element (609).

[0042] The optical array (600) includes an optical system (608), also described as a focusing optical device. Light forming an image from an image source (602) is directed toward the optical system (608). The optical system (608) receives the light forming the image. The light is focused by the optical system (608) to create a virtual image at an apparent focal distance. The virtual image is output from the optical system (608) and transmitted to the position of the user's eye (604). Additionally, light travels from the external view toward the eye through the focusing optical device. Therefore, the user can view the virtual image simultaneously with the external view of the outside world. Typically, the virtual image will be focused at a predetermined apparent distance between, for example, about 30 cm and optical infinity.

[0043] For the purposes of the drawings, it will be assumed that the user's eye (604) is in the indicated position, and the reference to the user's eye should be interpreted to mean that a typical use case is being described. However, it will be understood that the user's eye is not required to operate according to the theory described in this specification for the present invention. The optical array described below ultimately generates an emitting pupil in the direction of the assumed position of the user's eye when the device is used, regardless of the actual position of the user's eye.

[0044] An enlarged view of the optical system (608) is shown in FIG. 5. The optical system (608) includes a first optical power optical element (612) (hereinafter referred to as a prism element) and a second optical power element (614) (hereinafter referred to as a wedge element). The prism element (612) and the wedge element (614) operate as an optical lens system for focusing light to be output toward the eye (604). Additionally, the prism element (612) and the wedge element (614) may be configured to optimize or cancel out unwanted optical aberrations typically introduced by an optical lens array. For example, surface features of the prism element (612) and / or the wedge element (614) may be configured to reduce aberrations and / or correct any other optical defects. By using two elements while maintaining a space such as an air space between them, the collimation element acts as an air-separated optical doublet to improve color correction. Furthermore, a third optical element, such as a field lens (606) as shown in FIG. 5, may be added between the prism element (612) and the image source to provide additional optical correction.

[0045] FIG. 6 shows a simplified representation of a prism element (612) and a wedge element (614) to illustrate an exemplary angular orientation. In FIG. 6, the surfaces of the elements are depicted as flat for convenience, but it should be noted that the surfaces may be curved as described with reference to FIG. 4 and FIG. 5. FIG. 6 shows a normal (900) for the wedge surface (628) through which light exits the focusing element. The normal is located at the center of the surface (628) and intersects the surface (628) at point K. The normal extends to point L, which intersects the surface (626); point M, which intersects the surface (620); and point N, which intersects the surface (622). Additionally, two angles (902 and 904, respectively) for the prism element and for the wedge element at point J are indicated. Angle (902) is defined by surfaces (622 and 620), and angle (904) is defined by surfaces (628 and 626). Angle (904) can be determined based on the tangent of the angle. The tangent of angle (904) is:

[0046] Tan(angle(904)) = KL / JK.

[0047] Surfaces (620 and 626) are referred to herein as adjacent surfaces of each wedge element and prism element, because they are adjacent to each other in the normal orientation of the focusing element. One of the angles (902, 904) is defined at one end of one of the adjacent surfaces, and the other angle is defined at the other end of the adjacent surface. In other words, the angles are located at opposite ends of the adjacent surfaces. The interface between the adjacent surfaces is referred to herein as the adjacent interface.

[0048] The two angles can be changed to obtain the optimal orientation of the two elements, which now allows optimal optical properties to be obtained for the focusing element. The angular difference between the two angles is predetermined, and generally the angles are not equal, with angle (904) being smaller than angle (902). Although specific angles are not mandatory, the angular difference is determined to ensure an accurate path for the light coming from each source. As an example, the angle (904) may be, for example, less than 30°.

[0049] In the present invention, the prism element is used throughout the specification for ease of description and is not intended to limit the form and shape of the element (612). Accordingly, the prism element is intended to include any optical element comprising a plurality of optical power surfaces. This may be a three-sided prism or may have two or more surfaces. A preferred form is a three-sided prism, but other forms and shapes are likewise applicable. Similarly, the wedge element is used for ease of reference but may be of a different form and shape. Accordingly, the wedge element is intended to include any optical element comprising one or more optically powered surfaces. At least one of the optically powered surfaces on the prism element or the wedge element may be described by a polynomial of a higher degree.

[0050] The combination of prism and wedge elements defines multiple interfaces between the optical power surfaces of each element. When light passes through this combination (also called a focusing element), a change in refractive index exists as a result of the existence of the interfaces, which causes the direction of the light passing through the interfaces to change. This allows the light beam to be directed by this combination. Due to the relative positions of the prism and wedge, different interfaces and different interface shapes exist, which help to form a "folded path" passing through the focusing element.

[0051] The prism and wedge elements may be in direct contact or have a gap between their surfaces. The gap may be an air void or may contain other materials such as adhesive. Adding an air void adds an additional interface (e.g., an interface from the prism to the air; from the air to the wedge, etc.). The additional interface has the effect of further directing the light. The overall direction of the light is described in detail later. The result of this combination is that, due to multiple interfaces, light can be directed in a highly controlled manner and within a compact and lightweight component, which is optimal for head-mount optics. When the first and second optical power elements are juxtaposed (with or without a gap), a compact folded path through which the light can pass is defined.

[0052] The optical system (608) produces an output pupil that is well-corrected while maintaining a small volume and size. As used herein, 'well-corrected' is intended to mean that optical defects such as aberrations, artifacts, and color distortion are minimized in order to provide a predetermined standard of optical performance that may vary for different applications.

[0053] The prism (612), whose 3D representation is also shown in FIGS. 4 and 5, is, as an example, a single-piece triangular element having an elongated substantial triangular cross-section. Thus, the prism (612) has two three-edged bases (only one of which is shown in FIG. 9) (616) and three surfaces (618, 620, 622) that combine the corresponding edges of the two bases (616). Any number of surfaces (618, 620, 622) of the prism (612) are optically powered surfaces, and the surface power may differ from surface to surface. In the embodiment of FIG. 5, the prism element (612) and the wedge element are separated by a gap (624), such as an air gap, for example. The gap (624), wedge (614), and prism (612) can be any combination of materials, and since each can be different, the interface between these three can provide a difference in refractive index for each element. This can be utilized in the present invention to control the direction of light passing through the combination of elements. The gap can be formed of any type of gap material having a refractive index different from that of the other elements. In the example of FIG. 5, the prism (612) is surrounded by air having a lower refractive index than the other elements. Many other combinations of materials can be used.

[0054] The operation of the prism element (612) alone and the operation of the prism element combined with the wedge element (614) and the gap (624) will now be described. Light from the image source (602) enters the prism element (612) through a field lens at the light receiving surface (618), which is the first surface. The light receiving surface (618) is an optical power surface and can be described by a spherical, aspherical, cylindrical, toroidal, or multi-order polynomial surface shape.

[0055] Light travels through the prism element (612) and experiences total internal reflection (TIR) ​​at the second surface (620). TIR occurs because the surrounding material, air, has a lower refractive index than the material of the prism (612), and because the angle of incidence of the light is greater than the critical angle for the interface at the surface (620) between the prism element (612) and the air. The surface (620) is also an optical power surface and can be described by spherical, aspherical, cylindrical, toroidal, or multi-order polynomial surface shapes. Partial internal reflection or reflection due to a reflective coating can be used instead of TIR, but it should be noted that this may result in reduced efficiency.

[0056] The surface (620) is tilted relative to the central axis A of the prism (612). The tilting surface (620) relative to the vertical axis can help reduce TIR breakdown that would occur if the transmission plane were aligned closer to the vertical axis. Preferably, the tilting surface (620) allows the image plane to be oriented at a smaller angle with respect to the vertical axis in this way, and makes the array more compact.

[0057] Thanks to passing through TIR on the surface (620), light is reflected toward the surface (622). Since it is also required to be transparent so that the user can view the outside world, the surface (622) is partially reflective. The coating may be a simple partially reflective coating, or a better-fit coating specifically designed for a defined wavelength of light. The surface (622) is also an optical power surface and can be described by spherical, aspherical, cylindrical, toroidal, or multi-order polynomial surface shapes. The surface (622) is optically coated to reflect light. Therefore, light reflected toward the surface (622) within the prism (612) experiences the surface (622) as a second surface mirror. The surface (622) may not be tilted or may be tilted minimally about the vertical axis A to reduce off-axis aberrations. Light reflected by the coating applied to the surface (622) returns toward the surface (620).

[0058] Light is reflected from the surface (622) and re-enters the surface (620) at an angle smaller than the critical angle for the interface between the prism element (612) and the air on the surface (620), so that the light passes through the surface (620), is transmitted, and exits the prism element (612). The light exits the prism element (612) and proceeds into the gap (624) between the prism element (612) and the wedge element (614).

[0059] Light travels through the gap (624) and enters the wedge element (614). The refractive index of the air within the gap (624) is lower than the refractive index of the material of the wedge element (614). The wedge element (614) is, for example, an elongated element having a quadrilateral cross section and thus has two surfaces (626, 628) connected by an upper and lower end (630, 632). The surfaces (626, 628) and the end (630, 632) extend between the bases (not shown in FIG. 6). The wedge element (614) also has a substantially triangular cross section and lacks an upper end (630).

[0060] The wedge element (614) receives light from the gap (624) at the first surface, the incident surface (626). The light exits the wedge (614) at the second surface, the exit surface (628).

[0061] In the embodiment of FIG. 5, the incident surface (626) of the wedge (614) may also be described by a spherical, aspherical, cylindrical, toroidal, or multi-order polynomial surface shape. Light is transmitted through the wedge (614) from the incident surface (626) to the exit surface (628).

[0062] The exit surface (628) is typically planar, but can be described by a spherical, aspherical, cylindrical, toroidal, or multi-order polynomial surface shape. At the exit surface (628), light exits the wedge element (614) because the light is incident on the exit surface (628) at an angle smaller than the critical angle for the corresponding surface. The light exiting the wedge element (614) is now collimated and forms a well-corrected exit pupil.

[0063] As mentioned above, the shape of the surface, which may be a polynomial or an extended polynomial shape, can be modeled by determining the parameters of the lens. One parameter used is the determination of surface sag. For a surface using such a surface shape, the surface sag can be described by the following mathematical formula (for example), which introduces oscillation into the conical aspherical surface by adding an additional polynomial term.

[0064]

[0065] Here

[0066] c = base surface curvature,

[0067] r = radial distance from base surface,

[0068] k = base surface cone constant,

[0069] N = the number of polynomial coefficients, and

[0070] Ai is the coefficient of the i-th polynomial term.

[0071] It will be understood that this is just one example of surface modeling; others can also be used.

[0072] In the embodiment of FIG. 5, the prism element (612), gap (624), wedge element (614), and compensator element provide multiple degrees of freedom used to manipulate light to obtain a collimated and well-corrected outgoing pupil as a result. The collimated light exits the optical system (608) at the wedge element (614). In some embodiments, additional components may be included to increase the number of degrees of freedom of the array, and the collimated light may enter or exit the optical system (608) through different components. For example, a field lens, which is an additional optical element, may be included in the optical system (608) to further reduce residual aberrations such as distortion and / or field curvature. In some embodiments, an additional correction element may be included in the optical system (608) to chromatically correct the light. These elements may include additional refractive, reflective, holographic, or diffractive optical components for further manipulating source light to improve or enhance optical performance together with prism and wedge optical elements.

[0073] Furthermore, in the embodiment of FIG. 5, any of the three surfaces (618, 620, 622) of the prism element (612) and any of the two surfaces (626, 628) of the wedge (614) may have altered optical power and surface shape. In some embodiments, the optical properties of the surface (620) of the prism element (612) and the incident surface (626) of the wedge element (614) may be matched or designed to be complementary for a specific application. For the compensator element, it has a matching / complementary surface shape corresponding to the prism coupler surface.

[0074] The materials of the prism element (612), wedge element (614), and compensator element (609) may be the same, or they may be different to utilize optical properties such as the refractive indices of different materials. Similarly, the surrounding material and / or the gap material of the gap (624) may be changed to optimize the optical properties of the optical system (608). The material for the optical element may have any suitable properties. For example, the material may include one or more of the following optical glasses, polymers, and plastics with varying refractive indices, and Abbe numbers may be used: N-BK7 (low refractive index glass), N-SF6 (high refractive index glass), 7980_0F (low refractive index fused silica), PMMA (low refractive index polymer), and E48R (low refractive index polymer). To combine materials having different indices and different dispersion properties, it may be advantageous to have both optical elements made of different materials. For example, an optical wedge can be manufactured from a low-dispersion material to mitigate chromatic splitting of light while interacting with a powered surface.

[0075] Returning to FIG. 4 or FIG. 5, the compensator element (609) is positioned to be sympathetic with the surface (622) of the prism element. The compensator element (609) is illustrated in more detail in FIG. 11. The compensator element (609) is an optical element that allows light from an image source to be combined with external light from the outside world before the combined image is provided to the user. The first surface of the compensator element (609) is designed to be sympathetic or matched with the surface (622), so that the two surfaces can be optically bonded or combined using an optical adhesive (613). The thickness and surface shape of the second surface of the compensator element (609) can be optimized to minimize the introduction of refractive error, such as distortion, into the user's view of the outside world. Otherwise, such refractive error would be clearly visible without the use of the compensator element and thus degrade the user's view of the outside world.

[0076] The surface (620) of the prism element and the surface (624) of the wedge element (adjacent surfaces) are depicted in FIGS. 4 and 5 as partially matching or synchronous due to the two-dimensional properties of the drawings, but it should be noted that the surfaces are not required to be matching or synchronous. For example, the surface (624) of the wedge element may have optical power and / or be curved, and the surface (620) may not have optical power and / or be linear, and thus the adjacent surfaces may not be matching or synchronous. In some examples, the adjacent surfaces are different and not complementary, so that the adjacent surfaces may not be synchronous and / or matching. Non-complementary or non-synchronous shapes may refer to shapes where there is always a gap between the surfaces when the shapes are placed together.

[0077] Non-complementary shapes or other shapes allow for additional optical surface shapes to correct aberrations.

[0078] Referring to FIGS. 7a and 7b, if the display is an HMD or HWD, it may be worn using a suitable support (not shown). The support may include one or more optical elements that can be seen by one or both eyes (604) of the user. The HMD may further include a control system. The optical elements (608) of FIG. 4 or 5 may be positioned relative to the arc or shape of the head. FIG. 7a shows a view from above, and FIG. 7b shows a side view. It will be understood that many alternatives to the illustrated array exist, and the scale of the drawings is not limited to easy readability.

[0079] To be used with the present invention or as the present invention itself, the HMD may be any suitable type including goggles, glasses, a helmet, or a helmet visor suitable for use in various fields. Ideally, the device is portable or adapted to be carried using a support. Although not illustrated in detail, the support may include a support adapted to support the optical element in front of the eyes. The support may include: a frame; side arms and supports for goggles and glasses; a helmet or visor; a headband; a neck or shoulder support; a gaming headset; or any other support that can be worn to maintain the optical element in the required position.

[0080] The control system may be modified depending on the use of the HMD. The control unit may be in-situ or separate from the HMD. The control device may include a communication module for communicating with optical elements and other modules on or remotely from the HMD. Communication may be wireless and / or wired. The control module may include different modules for performing different functions. These functions are not limited in any way and may include imaging, tracking, scene generation, processing, storage, power supply, audio, etc.

[0081] To display an image to a user through an optical array, the HMD may further include an image source corresponding to the optical array. The image source may have a controlled numerical aperture or an uncontrolled numerical aperture and may include a flat panel display, an emission display, a reflective display, a projection optical device, a relay lens, or any other type of display source, image or light generating unit.

[0082] FIGS. 8A and 8B illustrate a 2D view of a prism, a wedge, and a compensator, showing the ray path, and a 3D view of a combination of a prism, a wedge, and a compensator, showing the optical power surface.

[0083] Although the present invention has been described in connection with several embodiments, it is not limited to the specific forms described herein. Accordingly, the scope of the invention is limited only by the appended claims. Furthermore, while certain features may appear to be described in connection with specific embodiments, those skilled in the art will recognize that various features of the described embodiments may be combined according to the present invention. In the claims, the term "comprising" does not exclude the presence of other elements or steps.

[0084] Furthermore, the order of features within a claim does not imply any specific order in which the features must be performed, and in particular, the order of individual steps in a method claim does not imply that these steps must be performed in such an order. Rather, the steps may be performed in any suitable order. Additionally, singular reference does not exclude the plural. Thus, expressions such as 'a', 'an', 'first', 'second', etc., do not exclude the plural. In a claim, 'comprising' or "including" does not exclude the presence of other elements.

Claims

Claim 1 An optical system comprising a folded optical array for use in transmitting an image from an image source to a user's eye within a view-through display, wherein the folded optical array provides a folded light transmission path and has a first optical element comprising a first plurality of optically powered surfaces and a second optical element comprising at least one optically powered surface, configured to receive light forming an image from an image source and configured to present a virtual image of the image source to the user at an apparent focus between a predetermined distance and optical infinity; wherein the first plurality of optically powered surfaces and at least one optically powered surface of the second optical element are arranged to define a plurality of interfaces along the folded light path, and a change in refractive index at each interface is predetermined to control the direction of light passing through said interface or each interface, and one surface of the first optical element and one surface of the second optical element are adjacent to each other, and the adjacent surfaces are non-complementary or non-synchronous so as not to have a gap between the surfaces A folded optical array comprising: a first optical element having no way of being placed together, wherein one surface of the first optical element defines an angle with another surface of the first optical element and one surface of the second optical element defines an angle with another surface of the second optical element, wherein the angles are located at opposite ends of the adjacent surfaces and the opposite angles are not the same; and a compensator element located between the first optical element and the external view to receive an external view to be combined with an image output from the optical system. Claim 2 In claim 1, the compensator element is a folded optical array adapted to minimize a refractive error induced on the external view by either the first optical element or the second optical element. Claim 3 In claim 1 or 2, the compensator element is a folded optical array optically coupled to the first optical element. Claim 4 In claim 1 or 2, one surface of the compensator element is a folded optical array that matches the surface of the first optical element. Claim 5 A folded optical array according to claim 1 or 2, wherein the first optical element comprises at least three optical power surfaces. Claim 6 A folded optical array according to claim 1 or 2, wherein the first optical element comprises a single-piece triangular element having an elongated substantial triangular cross-section. Claim 7 A folded optical array according to claim 1 or 2, wherein the second optical element comprises at least two optical power surfaces. Claim 8 A folded optical array according to claim 1 or 2, wherein the second optical element is a wedge. Claim 9 A folded optical array according to claim 1 or 2, wherein the first optical element and the second optical element are arranged in juxtaposition with each other such that at least one optical power surface of each optical element is substantially aligned. Claim 10 A folded optical array, wherein at least one optical power surface of each optical element is separated by a gap in claim 1 or 2. Claim 11 A folded optical array according to claim 1 or 2, wherein the first optical element comprises a substantially concave surface. Claim 12 In claim 1 or 2, at least one optical power surface on the first optical element is a folded optical array described by a multi-order polynomial. Claim 13 A folded optical array according to claim 1 or 2, wherein one of the angles is less than 30°. Claim 14 A display comprising a folded optical array according to claim 1 or 2. Claim 15 In claim 14, a display in the form of a head-mounted display, a head-worn display, and a head-up display, or at least one of these.

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