Holographic Device

Abstract

A holographic device for a virtual retinal display and a method of forming the holographic device, the holographic device including a transparent substrate and a holographic element disposed on the substrate, the holographic element including a phase pattern, the phase pattern being a predetermined optical coma aberration constructed and arranged to diffract light from a light source to form a plurality of images at an image plane of the holographic element.A virtual retinal display including the holographic device.An augmented reality system including the virtual retinal device and smart glasses.

Description

[Technical field]

[0001] The present disclosure relates to a holographic device and a method for forming a holographic device. The present disclosure also relates to a virtual retinal display including a holographic device. The present disclosure also relates to an augmented reality display system including a virtual retinal display. Furthermore, the present disclosure also relates to an augmented reality display system including a holographic device, the augmented reality display being smart glasses. [Background technology]

[0002] A Virtual Retinal Display (VRD) system (also known as a Retinal Scanning Display (RSD) system or more simply a Retinal Projector (RP) system) is a display technology in which a displayed image is rapidly scanned or rastered onto the retina of a user's eye via an optical system. VRD systems allow a user to see what appears to be a traditional display floating in front of the user's field of view. Such VRD systems are now being incorporated within so-called smart glasses to enable augmented reality, where virtual images are displayed to the user wearing the smart glasses.

[0003] An example of a typical VRD system 100 is shown in FIG. 1. The VRD system of FIG. 1 includes a light source 102. The light source 102 can typically be a low-power RGB (red, green, blue) light source, such as a laser or laser diode. Such a VRD system 100 typically includes first and second microelectromechanical (MEMS) scanning mirrors, where the first scanning mirror functions as a raster line scanner that scans at a rate of several KHz. The second scanning mirror functions as a frame refresh scanner that is arranged to scan at a rate of about 60 Hz. The first and second microelectromechanical (MEMS) scanning mirrors can be replaced by a single MEMS tip-tilt mirror 104 that can simultaneously perform raster line and frame refresh scanning at a desired rate. The light source 102, MEMS scanning mirror 104, and lens 106 are collectively known as a projector system 110. An image from the light source is directed by the tip-tilt mirror 104 and lens 106 onto a holographic optical element (HOE) 108. An image scanned or rastered by scanner 104 is focused by lens 106 onto surface P. Surface P is midway between lens 106 and HOE 108. Midway surface P is perpendicular to axis AA of projector system 110.

[0004] VRD systems of the type mentioned above typically use a so-called holographic optical element (HOE) to refocus the light from the projector system 110 onto the user's eye. HOEs used for this purpose are known as point-to-point HOEs, and they take the light from the exit pupil of the projector system 110 and focus it onto a small spot known as the eyebox. The light that reaches the eyebox needs to be substantially or nearly collimated so that the user can see a sharp (resolved) image during use. In the context of a holographic optical element, the location of the eyebox is the location where the entire image generated by the VRD is visible to the user.

[0005] However, such VRD arrangements are known to suffer from image resolution problems. As shown diagrammatically in FIG. 2a, the light from the projector system 110 at the intermediate focal plane P is not optimally focused, and the ray bundles P1 and P3 from the projector system 110 appear blurred. As shown in FIG. 2b, the holographic optical element 108 reflects the ray bundles onto the eyebox such that only the on-axis point (P2 in this example) is focused on the eyebox. The intermediate surface P is perpendicular to the projector system 110 axis AA. Unfortunately, the off-axis points (P1 and P3 in this example) corresponding to points at the periphery of the image appear blurred at the user's eye plane. The blurred off-axis ray bundles are diffracted by the holographic optical element to the user, resulting in a blurred image. Usually, one of P1 or P3 is under-focused, while the other is hyper-focused. 2a and 2b show three ideal ray bundles P1, P2, and P3, but as one skilled in the art will appreciate, in reality there are an infinite number of ray bundles across the two-dimensional image plane, with the central axial ray bundle P2 appearing to be in focus. The central axial ray bundle corresponds to the central optical axis of projector system 110. Holographic optical element 108 is known as a point-to-point hologram in that it forms a single eyebox that appears to the user as a uniform image spot. Typically, the spot dimensions are less than 1 mm at the eye plane. 2 It is.

[0006] As shown in Figure 2b, spot 1 is under-focused (because the light rays are converging) and is perceived as too close, while spot 3 is hyper-focused and the user cannot perceive or accommodate (because it is converging beyond infinity) and the image appears blurry. As mentioned before, spot 2 is in focus.

[0007] The types of point-to-point holographic optical elements discussed above are designed to generate a single eyebox. The attraction of using point-to-point holograms to create an array of small eyeboxes is that it is easy for eye-tracking algorithms to select rays from the field of view that are visible or invisible to the viewer for superimposition (i.e., blending or adjustment) of images that penetrate the viewer's pupil. However, point-to-point holographic optical elements suffer from the resolution problem discussed above. Summary of the Invention

[0008] Various example embodiments are directed to problems such as those addressed above and / or others that may become apparent from the following disclosure.Objects and advantages of the illustrated embodiments are described below.

[0009] The present disclosure relates generally to holographic devices that overcome image resolution problems associated with known point-to-point type holographic optical elements.

[0010] Thus, according to an embodiment, there is provided a holographic device for virtual retinal display, the holographic device comprising a substrate and a holographic element disposed on said substrate, the holographic element comprising a phase pattern, said phase pattern comprising a predetermined optical coma constructed and arranged to diffract light from a light source to generate an eyebox at an eye plane of the holographic element, the eyebox being optionally a coma image of said light source.

[0011] The optical coma of the holographic element may be constructed and arranged to form an array of eyeboxes at the eye plane, and the array of separate eyeboxes may be a two-dimensional array of eyeboxes at the eye plane. The optical coma may be expressed as a cubic function in a phase profile across a horizontal axis of the holographic element, the horizontal axis may extend through a central portion of the holographic element between first and second distal edges of the holographic element. The optical coma may increase from the central portion of the holographic element toward the first and second distal sides of the holographic element, and the optical coma is antisymmetric about the central axis. The local light focusing ability of the holographic element may increase from the central portion toward a first side of the holographic element, and the local focusing ability decreases from the central portion toward a second side. The local light focusing ability of the holographic element may be substantially zero at the central portion, and the local light focusing ability varies substantially linearly across the width of the holographic element. The eye plane may be oriented perpendicular to a central ray of said light source from a central portion of the holographic element.

[0012] According to an embodiment, there is provided a method of forming a holographic device system for a virtual retinal display, the method comprising forming a holographic element on a substrate, the holographic element comprising a phase pattern, the phase pattern comprising a predetermined optical coma constructed and arranged to diffract light from a light source to generate an eyebox at an eye plane of the holographic element, the eyebox being a coma image of the light source.

[0013] Also provided is a virtual retinal display system including a holographic device according to an embodiment.

[0014] Also provided is an augmented reality system including such a virtual retinal display system according to an embodiment and smart glasses.

[0015] Advantageously, uniform resolution across the image is achieved by achieving a uniform focus on a plane at the eye using a holographic device according to embodiments, thereby improving image resolution compared to known VRD systems by introducing pupil aberration in the form of a predetermined optical coma aberration.

[0016] In order to allow the features of the present disclosure to be understood in detail, a more detailed description will be made with reference to embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only typical embodiments and are therefore not considered to be limiting of its scope. The drawings are for ease of understanding of the present disclosure and therefore are not necessarily drawn to scale. The advantages of the claimed subject matter will be apparent to those skilled in the art upon reading this description in conjunction with the accompanying drawings. In the accompanying drawings, like reference numerals are used to designate like elements. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 illustrates a known virtual retinal display system including a projector system and a point-to-point holographic optical element. [Figure 2a] FIG. 2 is a ray diagram from the exit pupil of the projector system of FIG. 1. [Figure 2b] FIG. 1 is a ray diagram of a known point-to-point holographic element. [Figure 3a] 1 is a schematic side view of a holographic device according to an embodiment. [Figure 3b] FIG. 2 is a schematic plan view of a holographic device according to an embodiment. [Figure 4a] 1 is a graph of a relative phase profile of a holographic device according to an embodiment. [Figure 4b] 13 is a graph of a parabolic ray crossing profile of a holographic device according to an embodiment. [Figure 4c] 1 is a graph of a substantially linear focusing ability profile of a holographic device according to an embodiment. [Figure 5a] FIG. 2 is a schematic ray diagram of light diffracted from a holographic device to an eye plane in accordance with an embodiment. [Figure 5b] 1A-1C are schematic diagrams illustrating light diffracted from a holographic device to an eye plane, according to an embodiment. [Figure 6] FIG. 1 illustrates a schematic virtual retinal display including a holographic device in conjunction with a projector system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Overview and with reference to FIG. 3a, the holographic device 300 includes a substrate or plate 302 on which a holographic element 304 is formed. The substrate or plate 302 can be formed of any suitable optical material, such as, for example, glass, polycarbonate plastic, or acrylic plastic, and can include a single unitary piece of optical material or can be formed by two or more layers of optical material. The substrate 302 can be substantially flat or planar, and can be transparent. Alternatively, the substrate 302 can be curved, the curvature of the substrate following, for example, the curvature of a lens. The holographic or interference pattern that constitutes the holographic element 304 is illustrated in FIG. 3b. FIG. 3b shows a diffractive structure formed using a suitable holographic material on the substrate 302. The holographic element 304 can be a reflection hologram.

[0019] Advantageously, the holographic element 304 of the holographic device 300 according to an embodiment incorporates a predetermined phase pattern to achieve improved resolution. Depending on the particular application and limitations of the VRD, the holographic device 300 can improve image resolution, for example, by up to a factor of two, when used with a VRD. For example, the holographic device 300 can achieve at least 10 line pairs per degree uniform across the entire field of view. This is compared to known point-to-point holographic optical elements that can provide 5 line pairs per degree.

[0020] The phase pattern of the holographic element 304 is recorded in the interference pattern that constitutes the holographic element 304. Contrary to known approaches, the phase pattern introduces coma aberration in the holographic element 304. Coma aberration may arise in certain optical systems, for example due to misalignment in optical components, and is undesirable as it results in a blurred image. However, according to an embodiment of the present disclosure, a predefined phase pattern in the form of coma aberration is intentionally introduced to achieve improved resolution. The inventive concept of the present disclosure is coma aberration, which can be characterized as the addition of a substantially third-order term in the phase profile across the holographic element 304, more specifically in the phase profile in the transverse lateral direction across the substrate (horizontal direction across the plane of the hologram when looking at FIG. 3b) in the direction of a plane that includes the viewer's eye and the projector system of the VRD system, as described below.

[0021] A phase profile according to an embodiment can be seen in FIG. 4a. FIG. 4a illustrates how the phase profile varies in a third order across the holographic device 300, which in this example is 10 mm wide (-5 mm to 5 mm). In this context, phase is the difference in phase delay across the wavefront and can be described as an addition or subtraction to the phase of the incident wavefront. In general, the holographic device 300 modifies the curvature of the optical wavefront of light diffracted by the holographic element according to a predetermined phase profile. The x-axis (horizontal or abscissa) of FIG. 4a represents the width of the hologram as previously described, and the y-axis (vertical or ordinate) of FIG. 4a represents the phase in a period of 2π radians. As will be appreciated by those skilled in the art, the third order term results in a phase profile that is relatively high at the edges of the holographic device 300 and relatively decreases according to the third order term towards the origin of the graph (or the center of the holographic optical element). In other words, the phase decreases relatively towards the center of the holographic device 300, thus defining an antisymmetric phase profile. The phase profile corresponding to a coordinate in the lateral direction across holographic device 300 is given by the function: Phase ∝x 3 Here, x is the coordinate in the lateral direction across holographic device 300.

[0022] Figure 4a illustrates the phase for a similarly sized point-to-point hologram. That is, the point-to-point hologram has a known phase profile, and Figure 4a shows the difference between the known phase profile and a further predetermined phase profile of the holographic device. The known phase profile of the point-to-point holographic element does not include a predetermined coma aberration to aberrate the exit pupil to intentionally widen the eyebox, as illustrated in Figures 5a and 5b.

[0023] On the right side of Fig. 4a, i.e., for a positive phase profile, holographic element 304 of holographic device 300 locally adds to the curvature of any wavefront incident on it, whereas on the left side of Fig. 4a, i.e., for a negative profile, holographic element 304 subtracts from the curvature of any wavefront incident on it, i.e., any wavefront incident at the origin experiences no substantial change in curvature.

[0024] FIG. 4b illustrates the parabolic nature of the ray intersection at the eye plane. In the context of the present disclosure, the eye plane of the holographic device 300 is considered to occur at or near the user's pupil. As will be appreciated by those skilled in the art, the graph in FIG. 4b is based on the first derivative of the phase profile in FIG. 4a, with the x-axis showing the lateral distance across the holographic device 300 and the y-axis illustrating the coordinates of the intersection with the eye plane. FIG. 4a shows that the wavefront diffracted from the holographic device 300 is locally tilted and therefore displaced in the eye plane according to a parabolic function as illustrated in FIG. 4b. The amount of tilt at any point is equal to the slope of the graph in FIG. 4a at that point of the holographic element. At the origin, there is no deviation in the amount at the intersection at the eye plane (similar to known point-to-point holographic optical elements). However, as light enters holographic device 300 away from the origin, the intersection point of the diffracted light at the eye plane also moves away from its central position on-axis at the eye plane (as shown in Figures 5a and 5b below).

[0025] With this third-order phase profile in mind, and looking at Figure 4c, one skilled in the art will appreciate that light incident on the center of the holographic optical element will experience zero or little focus shift. Similarly, light incident on the holographic device 300 away from the center will experience a focus shift that increases substantially linearly, resulting in a tilt of the focal plane, as described below.

[0026] FIG. 4c shows the relative focusing power (in diopters (m-1 )) illustrates the nearly or substantially linear nature of the phase profile of FIG. 4c. As will be appreciated by those skilled in the art, the graph of FIG. 4c is based on the second derivative of the phase profile of FIG. 4a and the first derivative of FIG. 4b. FIG. 4c illustrates on the x-axis the lateral distance across the holographic device 300 and on the y-axis the corresponding focusing power. The focusing power of the holographic device 300 is zero at the origin and increases linearly and positively from its center to the right. Similarly, the focusing power of the holographic device 300 decreases linearly from its center to the left. This has the effect of tilting the focal plane of the holographic device 300. Thus, as will be appreciated by those skilled in the art, the optical power across the device 300 varies in a nearly substantially linear manner. The tilting of the focal plane increases the curvature of the wavefront of light incident on one side of the holographic device 300 and decreases the curvature of the wavefront of light incident on the other opposite side.

[0027] In this regard, as will be appreciated by those skilled in the art, in order to practice the present invention, holographic element 304 of holographic device 300 must have an additional coma contribution in the form of a third order phase profile. The effect of coma in holographic device 300 is to vary the optical power in proportion to the distance of holographic element 304 from the origin.

[0028] Further performance improvements can be obtained from optimizing the phase function in other directions, such as orthogonal directions to the lateral horizontal direction mentioned above, along the holographic element surface. The above-mentioned embodiment describes a situation where the phase profile of FIG. 4a (and subsequent derivatives shown in FIGS. 4b and 4c) varies across the holographic device 300 (looking from left to right across FIG. 3b). However, as will be appreciated by those skilled in the art, the phase profile of FIG. 4a may be implemented in any suitable direction across the holographic device 300 without departing from the concept of the invention. For example, the phase profile may be defined along the orthogonal directions mentioned above, down the holographic device 300 (as seen in FIG. 3b), or along any suitable direction (provided that the plane of the projector's exit pupil is perpendicular to the major surface of the holographic device 300 on which the holographic element 304 is located).

[0029] How light is diffracted from the holographic device 300 is more clearly understood with reference to FIG. 5a. FIG. 5a illustrates an idealized view of how three ray bundles at points P1', P2', and P3' on an intermediate focal plane P' from a projector system are diffracted. Although FIG. 5a shows three ray bundles, those skilled in the art will appreciate that the number of ray bundles is in fact infinite. The ray bundles P1', P2', and P3' may be output ray bundles from the projector system (as described in more detail below with respect to FIG. 6).

[0030] The bundle of rays P2' leaves the optical system (such as a projector) and is focused at an intermediate focal plane P'. The bundle of rays P2' is known as an on-axis ray because it is on the optical axis of the projector system. The bundles of rays P1' and P3' are off-axis because they are not on the optical axis of the exit optics. The bundle of rays P2' enters the holographic device 300 and is diffracted therefrom. The bundle of rays P2' enters the center of the holographic device 300 (i.e., corresponding to the origin in FIG. 4a), so no further curvature is introduced. The bundle of rays P2' intersects at a point 2' in the user's eye plane. However, for the bundles of rays such as P1' and P3', a significant further tilt is introduced (i.e., corresponding to the largest focus shift) because they enter the periphery of the holographic device 300. The bundles of rays P1' and P3' are diffracted by the holographic device 300, so they are not incident on a single point P2'. The ray bundles P1' and P3' instead intersect at respective points 1' and 3' in the user's eye plane (said to be focused or collimated at infinity). The spreading of points 1', 2', 3' in the eye plane occurs due to the tilt of the wavefront, and the individual ray bundles P1' and P3' are imaged at respective points 1' and 3' in the eye plane above point 2'. Note that points 1', 2', and 3' spread across the user's eye plane, but there may be a small amount of overlap between adjacent points. This results in separate spread spots of the eyebox for the holographic device 300, eliminating variations in focus for each point P1', P2', P3' in the eye plane, and thus uniform resolution across the diffraction image. For clarity and understanding, a front view of the eyebox, i.e., as seen from the user's or viewer's point of view at the eye plane, is illustrated in FIG. 5b. This represents a front view that corresponds to the side view of FIG. 5a.

[0031] 5a and 5b, the holographic device 300 according to the embodiment diffracts light so that the light rays at the periphery, i.e., the light rays away from the central axis P2' (ray bundles P1' and P3'), appear as separate or as points 1', 2', and 3', which are formed in the eyebox plane on the side furthest from the projector. In other words, the points are formed on one side of the central axis, and as illustrated in FIG. 5a, they are formed above the central point 2' (formed by ray bundle P2'). This is due to the phase profile in the hologram pattern of the holographic device 300.

[0032] As described in more detail below, for example, during use in a VRD, the holographic device 300 induces pupil aberration. The hologram device 300 creates an image of the projector system's exit pupil aberrated by coma aberration. The image produced by the projector system may be focused at infinity, and the projector system's exit pupil is aberrated at the eye plane. That is, the eyebox at the eye plane is a coma aberrated image of the optical system's exit pupil (e.g., the projector system's exit pupil, which is relayed into a separate, coma aberrated eyebox). In this way, the coma aberration introduced by the holographic optical element 300 intentionally compensates or corrects the image aberration at the expense of the pupil aberration. In this way, as will be appreciated by those skilled in the art, the holographic device 300 according to the embodiment achieves uniform focus between different fields of view at the eye plane at the expense of widening the eyebox. Although the image generated by the projector system may be focused at infinity, the principles of this disclosure may be applied to different focal lengths across the field of view, such as 1 m (meter), depending on the particular AR system design. Typically, smart glasses applications require a focal length of 1 m, while head-up displays require a focal length at infinity.

[0033] The holographic device 300 according to the embodiment may be formed by any suitable holographic process. As will be appreciated by one skilled in the art, standard holographic techniques may be used to form the holographic element 304 on the substrate. In particular, the interference pattern used to form the holographic element 304 is formed by two beams, referred to as a reference beam and an object beam, and the interference pattern is recorded on the holographic element 304. The holographic element 304 is formed on the substrate 302 by coating or laminating a suitable holographic material onto the substrate 302. As will be appreciated by one skilled in the art, any suitable holographic material (e.g., photopolymer or silver halide) may be used to form or record the desired holographic or interference pattern on the substrate 302.

[0034] A further advantage of the holographic device 300 according to the embodiments is that it can be used with a projector system without the need to change the design of the projector system: the coma of the holographic device 300 is simply optimized for the particular optical design of the projector system.

[0035] As will be appreciated by those skilled in the art, holographic device 300 according to embodiments may be suitable for use in any number of optical applications, including, but not limited to, VRDs, lenses for smart glasses, smart glasses such as those used in conjunction with VRDs, smart glasses with eye tracking or head-up displays (HUDs).

[0036] The holographic device 300 may be embedded within one or both lenses of the smart glasses. As a non-limiting example, the lamination process may include the following steps: The holographic device 300 may be a thin film of the same size and profile of the lens. The thin film may be laminated between a first component part of the lens and a second component part of the lens. The first component part and the second component part are then attached to each other such that the thin film is fully enclosed within the lens or lenses. Similarly, the thin film may be laminated directly onto the outer surface of one or both lenses. Alternatively, the substrate 302 of the holographic device 300 may function as the lens or lenses of the smart glasses. Thus, as will be appreciated by those skilled in the art, any suitable embedding or lamination process may be used without departing from the scope of the inventive concept.

[0037] The holographic device 300 may be used with a VRD, an example of which is illustrated in FIG. 6. The VRD 600 may include any suitable light source or light sources 602, such as an array of RGB lasers. One or more tip-and-tilt mirrors 604, such as MEMS mirrors, may be included to scan or raster light from the light source 602 through an exit pupil 606 onto the holographic device 300 according to an embodiment. The light source 602, MEMS scanning mirror 604, and exit pupil 606 are depicted generally as a projector 610. The eye plane may be oriented perpendicular to the central ray bundle of the light source 602 diffracted from a central portion of the holographic element.

[0038] Thus, light incident on holographic device 300 is diffracted according to the principles previously described to form an eyebox as illustrated in Figures 5a and 5b, resulting in the light rays from light source 602 coming to the same focus at the eye plane for each field of view.

[0039] In the context of this application and optical systems generally, as will be appreciated by those skilled in the art, the exit pupil of projector system 610 may be real or virtual. An exit pupil may be defined as an aperture in an optical system, where only light rays passing through this aperture can exit the system. In the sense that it is real, it may be a lens, an aperture, or other suitable optical component. A virtual pupil may be generated by other refractive components.

[0040] As mentioned above, the holographic device 300 according to the embodiment may be incorporated in or on one or more lenses of the smart glasses. A VRD 600 of the type mentioned above may be included on the frame of the smart glasses. Typically, the VRD 600 is placed on one arm of the smart glasses and light from the VRD 600 is directed to one of the lenses incorporating the holographic device 300. The holographic device 300 according to the embodiment redirects the light from the VRD onto the eye plane, and the image is then seen by the wearer or user of the glasses during use. The third order phase profile is preferably implemented, for example, in the smart glasses, such that the projector system is directionally oriented relative to the holographic device 300.

[0041] Known point-to-point holographic elements can be multiplexed to generate multiple eyeboxes in an array. Similarly, holographic device 300 can be multiplexed to generate an array of eyeboxes. When multiple eyeboxes are generated, eye tracking may be used to select a particular eyebox for the user to view. In operation, light from VRD 600 is directed onto holographic device 300 into the user's eye to form an array of separate eyeboxes at the eye plane as described above. Images observed at different eyeboxes can be registered or overlaid by eye tracking techniques. For example, optical eye tracking head mounted systems typically have an infrared (IR) light source to illuminate the eye and an IR camera (e.g., a charge-coupled device, CCD) to capture images of the eye and track the eye position. The IR camera and IR light source may be mounted near the eye as a head mounted structure (e.g., a frame of smart glasses). A machine vision algorithm then determines the location of the corneal reflection (also referred to as a glint or first Purkinje image or spot) from the light source and the location of the pupil. This allows a particular eyebox to be imaged for the user to view. However, as will be appreciated by those skilled in the art, any suitable eye tracking technology, such as optical eye tracking (as described), eye-mounted tracking, or electrical potential measurements may be used without departing from the scope of the inventive concept.

[0042] Particular and preferred aspects of the present disclosure are set out in the accompanying independent claims. Combinations of features from the dependent and / or independent claims may be combined as appropriate and not merely as set out in the claims.

[0043] The scope of the present disclosure includes any novel feature or combination of features explicitly or implicitly disclosed therein, or any generalization thereof, regardless of whether it relates to the claimed disclosure or whether it alleviates some or all of the problems addressed by the present disclosure. The applicant hereby notifies that new claims may be formulated for such features during the prosecution of this application or any further application derived therefrom. In particular, with reference to the appended claims, features from the dependent claims may be combined with features of the independent claims, and features from each independent claim may be combined in any suitable manner and not merely in the specific combinations recited in the claims.

[0044] Features that are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination.

[0045] The word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. Reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

1. 1. A holographic device for a virtual retinal display, the holographic device comprising: A substrate; a holographic element disposed on the substrate; 1. A holographic device, wherein the holographic element includes a phase pattern, the phase pattern including a predetermined optical coma aberration constructed and arranged to diffract light from a light source to produce an eyebox at an eye plane of the holographic element.

2. The holographic device of claim 1 , wherein the eyebox is a coma image of the light source.

3. 10. The holographic device of claim 1, wherein the optical coma of the holographic elements is constructed and arranged to form an array of eyeboxes at the eye plane.

4. The holographic device of claim 3 , wherein the array of distinct eyeboxes is a two-dimensional array of eyeboxes at the eye plane.

5. The holographic device of claim 1 , wherein the optical coma is expressed as a cubic function in a phase profile across the horizontal axis of the holographic element.

6. The holographic device of claim 5 , wherein the transverse axis extends through a central portion of the holographic element between first and second distal edges of the holographic element.

7. 7. The holographic device of claim 6, wherein the optical coma increases from the central portion of the holographic element toward the first and second distal sides of the holographic element, and the optical coma is antisymmetric about a central axis.

8. 7. The holographic device of claim 6, wherein the local light focusing ability of the holographic element increases from the central portion toward a first side of the holographic element, and the local focusing ability decreases from the central portion toward a second side of the holographic element.

9. 9. The holographic device of claim 8, wherein the local light-focusing ability of the holographic element is substantially zero in the central portion and the local light-focusing ability varies substantially linearly across the width of the holographic element.

10. 10. The holographic device of claim 6, wherein the eye plane is oriented perpendicular to a central ray of the light source diffracted from the central portion of the holographic element.

11. 1. A method of forming a holographic device system for a virtual retinal display, the method comprising: forming a holographic element on a substrate, the holographic element comprising a phase pattern, the phase pattern comprising a predetermined optical coma constructed and arranged to diffract light from a light source to produce an eyebox at an eye plane of the holographic element, the eyebox being a coma image of the light source.

12. 12. The method of claim 11, wherein the optical coma of the holographic element is constructed and arranged to form an array of distinct eyeboxes at the eye plane.

13. The method of claim 12 , wherein the array of distinct eyeboxes is a two-dimensional array of eyeboxes at the eye plane.

14. The method of claim 11 , wherein the holographic element is formed by interference of an object beam and a reference beam that defines the optical coma aberration.

15. The method of claim 11 , wherein the optical coma is expressed as a cubic function in a phase profile across a horizontal axis of the holographic element.

16. The method of claim 11 , wherein the substrate is formed of a transparent material selected from one of glass, polycarbonate plastic, or acrylic plastic.

17. The method of claim 16 , wherein the substrate is curved or planar.

18. The method of any one of claims 11 to 16, wherein the holographic element is formed from a photopolymer or silver halide.

19. A virtual retinal display system comprising a holographic device according to any one of claims 1 to 9.

20. 20. The virtual retinal display system of claim 19, further comprising a projector system including a light source and one or more scanning mirrors constructed and arranged to direct light from the light source toward the holographic device.

21. 21. The virtual retinal display system of claim 20, wherein the holographic device is constructed and arranged to diffract light from the projector system to the eye plane, the eye plane corresponding in position to the pupil of a user's eye.

22. 21. The virtual retinal display system of claim 20, wherein the light source is an RGB laser and the one or more scanning mirrors are micro-electromechanical (MEMS) scanning mirrors.

23. 20. The virtual retinal display of claim 19, further comprising an eye-tracking system, the eye-tracking system constructed and arranged to select one or more of the distinct eyeboxes of the two-dimensional array.

24. 21. An augmented reality system comprising the virtual retinal display system of claim 20 and smart glasses.

25. 25. The augmented reality system of claim 24, wherein the projector system is located on one or more arms of the smart glasses and the holographic device is integrated into or on one or more lenses of the smart glasses.

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