Turning light pipe for a pupil expansion system and method

Abstract

A display system includes a light pipe including elongated surfaces. The light pipe is configured to expand the image in a first direction through one of the elongated surfaces. The display also includes a waveguide including an output grating, a first surface, a second surface, and a side surface. The first surface and the second surface have a larger area than the side surface, the output grating being configured to provide the image expanded in a second direction. The second direction is different than the first direction. The image enters the waveguide from the one of the elongated surfaces.

Description

BACKGROUND

The present disclosure relates to substrate guided displays including but not limited to head up displays (HUDs), helmet mounted displays (HMDs), wearable displays, near eye displays, head down displays (HDDs), etc.

Substrate guided displays have been proposed which use waveguide technology with diffraction gratings to preserve eye box size while reducing lens size. U.S. Pat. No. 4,309,070 issued to St. Leger Searle and U.S. Pat. No. 4,711,512 issued to Upatnieks disclose head up displays including a waveguide where the pupil of a collimating optical system is effectively expanded by the waveguide. The U.S. patent applications listed in the Cross Reference to Related Applications above disclose compact head up displays (HUDS) and near eye displays using multiple gratings, multiple waveguides, and/or multiple waveguide layers for pupil expansion.

Pupil expansion using multiple layers or multiple waveguides with input and output diffraction gratings adds to the complexity of the waveguide display. For example, pupil expansion using multiple layers, multiple waveguides, and/or multiple gratings can add to the size, weight and cost of the display and can reduce the brightness and contrast of the display. Further, expanding the pupil from a small round collimating lens in two directions using two or more waveguides or using three or more gratings to produce a final expanded pupil can be lossy due to air gaps and the number of gratings. The air gaps can induce geometric coupling losses. Further, expanding the pupil from a small round collimating lens in two directions using two or more waveguides or using three or more gratings to produce a final expanded pupil can add haze to the final image.

Therefore, there is a need for a display with reduced complexity, size, cost, and weight. There is further a need for a compact wearable display that uses diffraction gratings and is not susceptible to haze. Further, there is a need for a compact HUD which uses collimating optics optimized for constrained spaces associated with smaller aircraft. Yet further still, there is also a need for a small volume, lightweight, lower cost waveguide display with less lossiness and haze. Yet further, there is a need for a substrate waveguide near eye display or HUD that requires fewer gratings for pupil expansion. Yet further, there is a need for a wearable display or HMD that requires fewer gratings for pupil expansion. Yet further, there is a need to mitigate solar flare effects associated with waveguide displays.

SUMMARY

In one aspect, the inventive concepts disclosed herein are directed to a near eye optical display. The near eye display includes a light pipe including elongated surfaces. The light pipe is configured to expand an image in a first direction through one of the elongated surfaces. The near eye display also includes a waveguide including an output grating, a first surface, a second surface, and a side surface. The first surface and the second surface have a larger area than the side surface, and the output grating is configured to provide the image expanded in a second direction. The second direction is different than the first direction. The image enters the waveguide from the one of the elongated surfaces at the side surface.

In one aspect, the inventive concepts disclosed herein are directed to a method of displaying information. The method includes receiving light in a light pipe, receiving the light in a waveguide having a first surface and a second surface, and providing the light to an output grating via total internal reflection between the first surface and the second surface. The method also includes providing the light from the waveguide via the output grating, where the light is provided with dual axis pupil expansion with respect to the light received in the light pipe.

In one aspect, the inventive concepts disclosed herein are directed to an apparatus for providing an image. The apparatus includes a light pipe and a waveguide comprising an input surface and an output surface. The input surface is non-planar with respect to the output surface. Light from the non-gradient or gradient reflective coating is received at the input surface, and the light is ejected from the output surface of the waveguide by an output grating.

BRIEF DESCRIPTION OF THE DRAWINGS

The exemplary embodiments will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements, in which:

FIG. 1 is a general block diagram of a display system according to some exemplary embodiments;

FIG. 2A is a perspective view schematic drawing of a display system worn by a user according to some exemplary embodiments;

FIG. 2B is a more detailed perspective view schematic drawing of the display system illustrated in FIG. 2A without showing the user according to some exemplary embodiments;

FIG. 2C is a planar front view schematic drawing of the display system illustrated in FIG. 2B according to some exemplary embodiments;

FIG. 3 is planar side view schematic drawing of a light pipe for the display system illustrated in FIG. 2A according to some exemplary embodiments;

FIG. 4 is a planar top view schematic drawing of the light pipe illustrated in FIG. 3 according to some exemplary embodiments;

FIG. 5 is a perspective view schematic drawing of the of the light pipe illustrated in FIG. 3 according to some exemplary embodiments;

FIG. 6 is planar front view schematic drawing of the light pipe and the waveguide for the display system illustrated in FIG. 2 according to some exemplary embodiments;

FIG. 7 is a graph showing reflectance versus thickness at a number of angles for a gradient reflection coating associated with the light pipe illustrated in FIG. 3 according to some exemplary embodiments;

FIG. 8 is a graph showing reflectance and light output versus number of bounces for a gradient reflection coating associated with the light pipe illustrated in FIG. 3 according to some exemplary embodiments;

FIG. 9 is a planar side view schematic drawing of a projector and a light pipe and waveguide assembly at a first orientation for the display system illustrated in FIG. 1 according to some exemplary embodiments;

FIG. 10 is a planar back view schematic drawing of the projector and the light pipe and waveguide assembly at the first orientation illustrated in FIG. 9 according to some exemplary embodiments;

FIG. 11 is a planar side view schematic drawing of a projector and a light pipe and waveguide assembly at a second orientation for the display system illustrated in FIG. 1 according to some exemplary embodiments;

FIG. 12 is a planar back view schematic drawing of the projector and the light pipe and waveguide assembly at the second orientation illustrated in FIG. 11 according to some exemplary embodiments;

FIG. 13 is a planar side view schematic drawing of a projector and a light pipe and waveguide assembly at a third orientation for the display system illustrated in FIG. 1 according to some exemplary embodiments; and

FIG. 14 is a planar side back schematic drawing of the projector and the light pipe and waveguide assembly at the third orientation illustrated in FIG. 13 according to some exemplary embodiments.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Following below are more detailed descriptions of various concepts related to, and embodiments of, an optical display and methods of displaying information. The display system and method can be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular manner of implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

Exemplary embodiments will now be further described by way of example with reference to the accompanying drawings. It will be apparent to those skilled in the art that the some embodiments may be practiced with none, one, some or all of the features and advantages as disclosed in the following description. For the purposes of explaining aspects the invention, well-known features of optical technology known to those skilled in the art of optical design and visual displays have been omitted or simplified in order not to obscure the basic principles of some embodiments. In the following description, the terms light, ray, beam and direction may be used interchangeably and in association with each other to indicate the direction of propagation of light energy along rectilinear trajectories. Parts of the following description will be presented using terminology commonly employed by those skilled in the art of optical design.

Referring generally to the Figures, systems and methods relating to near-eye display systems, HUD systems, worn display systems, HMD systems, and HDD systems are shown according to various embodiments. The display system of some embodiments advantageously provides dual axis expansion with less reduction in brightness and contrast as well as less susceptibility to haze. The display system advantageously can be utilized in HMDs or head mounted/worn displays, near eye displays, and HUDs for many applications, including but not limited to military applications, aviation applications, medical applications, entertainment applications, simulation applications, vehicle applications and consumer applications (e.g., augmented reality glasses, etc.) in some embodiments. The display system uses a light pipe to increase the pupil in one direction and a waveguide with a grating to increase the pupil in another direction in some embodiments. Using the systems and methods disclosed herein, a highly integrated, low cost, light weight, display system can be provided which is less susceptible to solar flare effects, brightness, contrast, and haze issues according to some embodiments.

With reference to FIG. 1, a display system 100 can be embodied as a HUD, an HMD, a near-eye display, a worn display, HDD, etc. Display system 100 includes a projector 102, a light pipe 104, and a waveguide 106. Waveguide 106 includes an output coupler or grating 108. Display system 100 provides light in the form of an image into light pipe 104. In some embodiments, light pipe 104 has an input coupler or grating that is responsible for turning the light from projector 102 down light pipe 104 for expansion. Light pipe 104 expands the image in one direction (e.g. from right to left in FIG. 1) and provides the image into waveguide 106 (e.g., via a leaky transmissive coating) in some embodiments. Light travels partially by total internal reflection in waveguide 106 and is ejected by grating 108. Grating 108 expands the pupil in a direction (e.g., vertically) different than the direction that light pipe 104 expands the pupil in some embodiments.

In some embodiments, grating 108 expands the pupil vertically while light pipe 104 expands the pupil horizontally. Light pipe 104 can be disposed as a horizontal beam expander, and waveguide 106 can be disposed as a vertical beam expander and combiner in some embodiments. Light pipe 104 can be disposed as the vertical beam expander, and waveguide 106 can be disposed as the horizontal beam expander and combiner in some embodiments. In some embodiments, the display system 100 provides additional field of view by implementing additional layers of light pipe 104 and waveguide 106.

Projector 102 provides the image with a single color of light or multiple colors of light to light pipe 104. Projector 102 is a collimating projector, such as, a catadioptric collimating system. Projector 102 is comprised of multiple optical components integrated to provide a compact package in some embodiments. Projector 102 is physically attached to light pipe 104 and provides near collimated or collimated P-type or S-type polarized light in some embodiments. In some embodiments, an air gap exists between projector 102 and light pipe 104.

Light pipe 104 is a tube, waveguide or other optical assembly that allows light to travel from a first location to a second location in some embodiments. Light pipe 104 is an optical component that allows light to gradually leak into waveguide 106 as light travels within light pipe 104 in some embodiments. Advantageously, light pipe 104 does not add significant haze or grating losses to the image provided by display system 100 in some embodiments. Light pipe 104 captures the field of view in three dimensions and guides the field of view along the length of light pipe 104 in some embodiments.

In some embodiments, light pipe 104 is a waveguide embodied as an elongated rectangular prism with a square or rectangular cross sectional area. Light travels through light pipe 104 in a corkscrew, spiral, helical, or other fashion where all four sides of the rectangular prismatic shape are struck by light as light travels from a first end to a second end. In some embodiments, light pipe 104 is made from optical glass and includes a gradient reflection coating disposing an interface between light pipe 104 and waveguide 106. In some embodiments, the light travels by total internal reflection on three sides of light pipe 104 and by reflection off the gradient reflection coating on a fourth side.

In some embodiments, the gradient reflection coating is disposed directly on light pipe 104. Waveguide 106 receives light from the gradient reflective coating associated with light pipe 104. Light can be input to an edge of waveguide 106 and can be output via grating 108. Grating 108 can be a holographic grating, a volume grating, a surface relief grating, or other output coupler. Grating 108 can provide pupil expansion in a vertical direction while light pipe 104 provides pupil expansion in a horizontal direction. Other directions for pupil expansion are possible. Grating 108 can have a circular, oval, rectangular, or square shape.

With reference to FIG. 2A-C, a display system 200 includes a projector 202, a light pipe 204 and a waveguide 206 and is similar to display system 100 discussed with reference to FIG. 1. Projector 202, light pipe 204 and waveguide 206 can be similar to projector 102, light pipe 104 and waveguide 106, respectively, described above with reference to FIG. 1. Projector 202 is disposed to be worn at approximately an eyebrow level associated with a user 212. User 212 views the environment through waveguide 206 operating as a combiner where light is ejected from a grating 218 of waveguide 206 into the eye of user 212 in some embodiments. Although a monocular display system 200 is described below, display system 200 can be a binocular system in some embodiments. Light pipe 204 is not required to be at a 90 degree angle with respect to waveguide 206 in some embodiments. Waveguide 206 can have a variety of shapes including an irregular shape with a flat interface facing a side of light pipe 204. Light pipe 204 can have a slanted orientation relative to the eye of the user in some embodiments.

With reference to FIGS. 2B-C, projector 202 is a low cost projector system in some embodiments. Projector 202 includes a mirror 222, beam splitter 224, a lens 226, a beam splitter 228, a lens 230, a light emitting diode source 232, and an image source 234. Projector 202 can be embodied as a catadioptric collimating system, such as a folded catadioptric projector.

Projector 202 can be implemented in any variety of fashions. Other projectors for some embodiments are discussed in U.S. application Ser. No. 13/251,087, U.S. patent application Ser. No. 13/250,940, U.S. patent application Ser. No. 13/250,858, U.S. patent application Ser. No. 13/250,970, U.S. patent application Ser. No. 13/250,994, and U.S. patent application Ser. No. 13/250,621. The components shown in FIGS. 2A-C are not shown in a limiting fashion.

Lens 226 and 230 can be an assembly of lenses and can include a field flattening lens, collimating lenses, etc. Mirror 222 can be a powered, collimating mirror in some embodiments. Laser source 232 is a laser diode or other device for providing laser light at a single wavelength through lens 230 in some embodiments. Laser source 232 can include a board for a light emitting diode (LED). Beam splitter 228 reflects the light from lens 230 to image source 234. Lens 230 can include a convex or spherical lens, polarizing film, retarder films, etc. Beam splitter 228 is a polarizing beam splitter in some embodiments. An image from image source 234 is provided through beam splitter 228 to lens 226 in some embodiments. Lens 226 can include a convex lens, a polarizing film, and/or a retarder film in some embodiments. Image source 234 is a liquid crystal display (LCD) or other image source in some embodiments.

Light received by lens 226 is provided to beam splitter 224. Beam splitter 224 can be a polarizing beam splitter. Beam splitter provides the light from lens 226 to mirror 222. Mirror 222 provides the light through beam splitter 224 to light pipe 204 in some embodiments. In some embodiments, beam splitter 224 and mirror 222 are provided as an integrated package attached to light pipe 204 and physically separate from lens 226.

Light pipe 204 includes an input coupler or input grating 242. Input grating 242 injects light from beam splitter 224 into light pipe 204. Light pipe 204 guides light to waveguide 206 which is ejected into the eye via grating 218. Input grating 242 is a reflection type grating disposed on an opposite side 244 of light pipe from a side 246 closest to beam splitter 224 in some embodiments. In some embodiments, input grating 242 is a transmission type grating on side 244 or embedded within light pipe 204. In some embodiments, display system 200 is compatible with dispersion compensation which allows use of LED and reduces the banding effect typically associated with lasers. For dispersion compensation, the input and output gratings are “matched” (e.g., grating line orientations are either parallel to each other or mirror symmetric to each other (with respect to the interface facet), and that their surface pitches are identical) in some embodiments.

In some embodiments, light pipe 204 injects light into waveguide 206 along its top edge. Alternatively, light can be ejected into an outside or inside main surface of waveguide 206. In one embodiment, light pipe 204 has a cross sectional area of five millimeters by five millimeters and a length of approximately 25 millimeters. In one embodiment, waveguide 206 touches light pipe 204 such that total internal reflection does not occur on the bottom surface of light pipe 204.

With reference to FIGS. 3 and 4, a light pipe 400 can be utilized as light pipe 104 or 204 described above with reference to FIGS. 1 and 2A-C. Light pipe 400 includes an input grating 402, a beam splitting coating 404, and an output coupler or a gradient reflection coating 406. Input grating 402 can be provided on a first side 421 of light pipe 400. First side 421 can correspond to a side closest to the user's eye in some embodiments. Alternatively, input grating 402 can be provided on a side 423 away from the user's eye.

Input grating 402 can be integral with light pipe 400 or can be externally attached to light pipe 400. In some embodiments, input grating 402 is a surface relief grating having a period of approximately 400 to 450 nanometers. Input grating 402 can be rotated to various orientations depending upon system criteria and design parameters. Although shown at a first end 428 on a surface 421, input grating 402 can be placed along any external surface of or within light pipe 400 at various locations. Input grating 402 can be a holographic grating, a volume grating, a surface relief grating, or other input coupler. Input grating 402 can be embedded, or embossed in some embodiments.

In some embodiments, light pipe 400 is optical glass (e.g., fused silica), plastic, or other material for transporting light. In some embodiments, light pipe 400 has neighboring sides at 90 degree angles with respect to each other (e.g., square or rectangular in cross section). The end of light pipe 400 can be coated with an absorptive material to reduce stray light in some embodiments. Beam splitting coating 404 can be disposed in a middle of light pipe 400. In one embodiment, light pipe 400 includes two plates with beam splitting coating 404 disposed between the two plates. Beam splitting coating 404 is parallel to a surface 434 and a surface 436. Beam splitting coating 404 advantageously increases the number of rays propagating from input coupler 402 to reflection coating 406. Beam splitting coating 404 fills in, bounces, and blends the image for uniformity in some embodiments. Beam splitting coating 404 can be manufactured from a metallic or dichroic optical coating.

Gradient reflection coating 406 can be a dichroic coating or a silver coating covering surface 436 that gradually leaks light from light pipe 400 into waveguide 106 or 206. Gradient reflection coating 406 is disposed on surface of waveguide 106 or 206 associated with surface 436 in some embodiments. Gradient reflection coating 406 provides very low haze and does not require a grating for ejection of light. Gradient reflection coating 406 is configured to leak light from light pipe 400 to waveguide 106 or 206 such that the light is received with relative uniformity and the pupil is expanded in some embodiments. In some embodiments, gradient reflection coating 406 is non-gradient reflection coating (e.g, a uniform reflection coating).

With reference to FIG. 5, light 412 entering light pipe 400 is diffracted along a light path by input coupler 402 to travel along light pipe 400. Light striking gradient reflection coating leaves light pipe 400. In one embodiment, gradient reflection coating 406 is configured to leak about 15% of light into waveguide 106 or 206 embodied as a vertical beam expander at an upper portion and gradually leaks a higher percentage (up to 50%) producing uniform light output. Absorption by coating 406 is preferably relatively low (e.g. less than 3%).

With reference to FIG. 6, a light pipe 604 includes an input grating 602 and is attached to waveguide 606. Light pipe 604 and waveguide 606 can be similar to light pipes 400, 204 and 104 and waveguides 206 and 106, respectively. A gradient reflection coating 610 is disposed in an interface between light pipe 604 and waveguide 606. Light 612 travels through light pipe 604 and is gradually released into waveguide 606. In some embodiments, gradient reflection coating 610 is a half silver coating of variable thickness. Gradient reflection coating 610 can be monochromatic or polychromatic. In some embodiments, the facet of light pipe 604 opposite to gradient interface coating 610 (the interface facet to waveguide 606) can be mirror-coated to reflect light even beyond a total internal reflection condition to increase field of view.

With reference to FIG. 7, reflectance of p-polarized light is shown in a graph 700. Graph 700 includes a Y axis 904 showing reflectance in percentage and an X axis 706 showing thickness of the coating in nanometers. Graph 700 shows a number of lines indicating reflectance at particular angles from 40 to 65 degrees. As shown, reflectance is relatively uniform for a silver coating across varying angles. Accordingly, by controlling the thickness of gradient reflection coating 610, an appropriate light output can be provided in some embodiments.

With reference to FIG. 8, a graph 800 shows reflectivity in percentage on Y axis 804 and the number of bounces in light pipe 604 on an X axis 806. As shown in FIG. 8, the thickness of gradient reflective coating 610 can be chosen according to line 804 to provide a uniform output according to line 802 in some embodiments. The number of bounces in light pipe 604 is correlated to a position in light pipe 604 along its elongated surface.

With reference to FIGS. 9 and 10, a light pipe and waveguide assembly 1003 is disposed at a right angle 1005 with respect to projector 1002 for display system 1000. Light pipe and waveguide assembly 1003 includes light pipe 1004 and waveguide 1006 in some embodiments. Grating 1012 of light pipe 1004 and grating 1014 of waveguide 1006 are disposed compensate for angle 1005 in some embodiments. In some embodiments, the angles of orientation of gratings 1012 and 1014 match.

With reference to FIGS. 11 and 12, light pipe and waveguide assembly 1005 is disposed at an acute angle 1015 with respect to projector 1002 for display system 1000. Gratings 1022 and 1024 are oriented to compensate for angle 1015. Gratings 1022 and 1024 can be disposed at a similar angle. In some embodiments, the angles of orientation of gratings 1022 and 1024 match.

With reference to FIGS. 13 and 14, light pipe and waveguide assembly 1003 is disposed at an obtuse angle 1025 with respect to projector 1002 for display system 1000. Grating 1032 in light pipe 1004 and grating 1034 in waveguide 1006 are disposed to compensate for angle 1025 in some embodiments. In some embodiments, the angles of orientation of gratings 1032 and 1034 match. Angles 1005, 1015 and 1025 can be used to provide a more compact design.

Different configurations of light pipes 104, 204 and waveguides 106 and 206 are possible. Although edge coupled structures are shown, other arrangements are possible. In some embodiments, the configurations are used in a sand wind and dust goggle or a frame for glasses. In some embodiments, the output gratings are displaced so that they line up with the eye location in the goggle or the frame. In some embodiments, a display system uses more than one light pipe and waveguide to increase the field of view. Such a display system can use a projector designed to output a higher field of view than a projector for single light pipe waveguide projectors (given its numerical aperture) in some embodiments.

The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.

Although the figures may show a specific order of method steps, the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure.

The construction and arrangement of the systems and methods as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements may be reversed or otherwise varied and the nature or number of discrete elements or positions may be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. The order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes, and omissions may be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.

Although the figures may show a specific order of method steps, the order of the steps may differ from what is depicted. Also two or more steps may be performed concurrently or with partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure.

Claims

1. A near eye optical display, comprising: a projector configured to provide an image;a light pipe comprising a plurality of elongated surfaces, the light pipe being configured to expand the image in a first direction through one of the elongated surfaces, wherein light associated with the image travels through the light pipe by striking three or more of the elongated surfaces; anda waveguide comprising an output grating, a first surface, a second surface, and a side surface, the first surface and the second surface being an opposing surfaces, and having a larger area than the side surface, the output grating being configured to provide the image expanded in a second direction, the second direction being different than the first direction, wherein the image enters the waveguide from the one of the elongated surfaces of the light pipe.

2. The near eye optical display of claim 1, wherein the first direction is orthogonal to the second direction.

3. The near eye optical display of claim 1, wherein the one elongated surface, the side surface, the first surface and the second surface are planar surfaces.

4. The near eye optical display of claim 1, wherein the projector: is comprised of a display source comprising a collimating mirror, a pair of beam splitters, a light source, and a lens configured to provide the image as collimated light to the light pipe.

5. The near eye optical display of claim 1, further comprising: a gradient reflective coating disposed on the one elongated surface.

6. The near eye optical display of claim 5, further comprising a beam splitting coating between an input coupler on the light pipe and the gradient reflective coating.

7. The near eye optical display of claim 6, wherein the input coupler is a volume hologram or a surface relief grating.

8. The near eye optical display of claim 1, wherein the light pipe is disposed at an angle less than 90 degrees and greater than 0 degrees between the one elongated surface and the first surface.

9. The near eye optical display of claim 8, wherein an input coupler associated with the light pipe and the output grating are disposed to compensate for the angle to the side surface.

10. The near eye optical display of claim 9, wherein angle orientations for the output grating and the input grating match.

11. A method of displaying information, the method comprising: receiving light in a light pipe having at least four elongated surfaces, the light striking the four elongated surfaces and traveling at least partially by total internal reflection within the light pipe;receiving the light from one of the at least four elongated surfaces in a waveguide having a first surface and a second surface;providing the light to an output grating via total internal reflection between the first surface and the second surface; andproviding the light from the waveguide via the output grating, where the light is provided with dual axis pupil expansion with respect to the light received in the light pipe.

12. The method of claim 11, wherein the output grating is a volume hologram or surface relief grating.

13. The method of claim 11, further comprising beam splitting the light received in the light pipe before the light enters the waveguide.

14. The method of claim 11, wherein the light pipe includes an input coupler.

15. The method of claim 14, wherein the input coupler is a surface relief grating.

16. An apparatus for providing an image, the apparatus comprising: a light pipe comprising at least four elongated surfaces, each elongated surface connecting to at least two other of the elongated surfaces, the light pipe being configured such that light associated with an image strikes the at least four elongated surfaces as the light travels in a corkscrew or helical fashion within the light pipe; anda waveguide comprising an input surface and an output surface, wherein the light from the light pipe is received at the input surface and the light is ejected from the output surface of the waveguide by an output grating.

17. The apparatus of claim 16, wherein the apparatus provides dual axis pupil expansion.

18. The apparatus of claim 16, wherein the light pipe comprises an input grating.

19. The apparatus of claim 16, further comprising a first beam splitting coating disposed in the waveguide and a second beam splitting coating disposed in the light pipe.

20. The apparatus of claim 16, wherein the light pipe has a rectangular prismatic shape.