Image light guide device with light security

Abstract

An image light guide with light security.SOLUTION: An image projection system includes an image source for generating an image-bearing light beam, an in-coupling diffractive optical element including a waveguide for propagating the image-bearing light beam and formed along the waveguide and operable to diffract a portion of the image-bearing light beam from the image source into the waveguide in an angularly encoded form, and an out-coupling diffractive optical element formed along the waveguide and operable to expand the image-bearing light beam and direct a first portion of the expanded image-bearing light beam from the waveguide in a first direction toward an eyebox in an angularly decoded form and a second portion of the expanded image-bearing light beam from the waveguide in a second direction different from the first direction. The image light guide further includes an optical device operable to reduce, eliminate, and / or block a second portion of the expanded image-bearing light beams output from the image light guide in a second direction.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to electronic display devices, and more particularly to display devices that utilize an image light guide having a diffractive optical element for transmitting image-bearing light to a viewer. [Background technology]

[0002] Head-mounted displays (HMDs) and virtual image near-eye displays are being developed for a wide range of applications, including military, commercial, industrial, firefighting, and entertainment applications. In many of these applications, there is value in creating a virtual image that can be visually superimposed on a real-world image in the HMD user's field of view. Optical image light guides can deliver image-bearing light to the viewer in a small space to direct the virtual image toward the viewer's pupil and enable this superimposition function.

[0003] While conventional image light guide arrangements have resulted in significant reductions in the bulk, weight, and overall cost of near-eye display optics, further improvements are needed. In some instances, light is output from a near-eye display in more directions than toward the viewer's eyebox. However, many applications utilizing near-eye displays would benefit from near-eye displays operable to control and / or eliminate light output in undesired directions. For example, near-eye displays with optical security may be attractive to commercial and general consumers because the near-eye display can appear like conventional eyewear (i.e., aesthetic improvement), while military applications may benefit from optical security for purposes of concealment and visibility. Thus, there is a need for an image light guide system operable to produce desired virtual image brightness and resolution while managing light output in undesired directions. Summary of the Invention

[0004] In a first exemplary embodiment, the present disclosure provides an optically secure image light guide including an image source operable to generate an image-bearing light beam and a waveguide operable to propagate the image-bearing light beam. An incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into the waveguide in an angularly coded manner, and an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand a portion of the image-bearing light beam and direct a first portion of the expanded image-bearing light beam from the waveguide in an angularly coded manner in a first direction toward the eyebox and direct a second portion of the expanded image-bearing light beam from the waveguide in a second direction different from the first direction. The image light guide further includes an optical device operable to reduce, eliminate, and / or block a second portion of the expanded image-bearing light beam output from the image light guide in the second direction. [Brief explanation of the drawings]

[0005] The accompanying drawings are incorporated herein as part of this specification. The drawings described herein illustrate embodiments of the disclosed subject matter and illustrate selected principles and teachings of the present disclosure. However, the drawings do not illustrate every possible implementation of the disclosed subject matter and are not intended to limit the scope of the present disclosure in any way.

[0006] [Figure 1] FIG. 1 shows a simplified cross-sectional view of an image light guide showing the expansion of an image-bearing beam along the propagation direction to expand one direction of the eyebox. [Figure 2] FIG. 2 shows a perspective view of an image light guide with a turning grating showing the expansion of the image-bearing beam perpendicular to the propagation direction to expand in a second direction in the eyebox. [Figure 3]FIG. 3 shows a schematic side view of an image light guide having a waveguide and a liquid crystal shutter according to an exemplary embodiment of the disclosed subject matter. [Figure 4A] FIG. 4A shows a schematic side view of a portion of the liquid crystal shutter according to FIG. [Figure 4B] FIG. 4B shows a schematic side view of a portion of the liquid crystal shutter according to FIG. [Figure 5A] FIG. 5A shows a graph of a projector voltage signal versus duty cycle, according to an exemplary embodiment of the disclosed subject matter. [Figure 5B] FIG. 5B shows a graph of the projector voltage signal versus duty cycle, according to an exemplary embodiment of the disclosed subject matter. [Figure 5C] FIG. 5C shows a graph of the projector voltage signal versus duty cycle, according to an exemplary embodiment of the disclosed subject matter. [Figure 6] FIG. 6 shows a schematic side view of an image light guide having a waveguide according to an exemplary embodiment of the disclosed subject matter. [Figure 7] FIG. 7 shows a schematic side view of a portion of the outcoupling diffractive optical element according to FIG. [Figure 8] FIG. 8 shows a schematic side view of a portion of the outcoupling diffractive optical element according to FIG. [Figure 9A] FIG. 9A shows one or more diffraction orders of light incident on an outcoupling diffractive optical element according to FIG. [Figure 9B] FIG. 9B shows one or more diffraction orders of light incident on an outcoupling diffractive optical element according to FIG. [Figure 10A] FIG. 10A shows a schematic side view of a portion of an outcoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 10B] FIG. 10B shows a schematic side view of a portion of an incoupling diffractive optical element, according to an exemplary embodiment of the disclosed subject matter. [Figure 11] FIG. 11 shows a schematic side view of an image light guide having a waveguide and a photonic crystal shield according to an exemplary embodiment of the disclosed subject matter. [Figure 12] FIG. 12 shows a portion of the photonic crystal shield according to FIG. [Figure 13A] FIG. 13A shows a schematic perspective view of a near-eye display having an image light guide with an overshield, according to an exemplary embodiment of the disclosed subject matter. [Figure 13B] FIG. 13B shows a schematic perspective view of a near-eye display having an image light guide with an overshield, according to an exemplary embodiment of the disclosed subject matter. [Figure 14A] FIG. 14A shows a schematic perspective view of a near-eye display having an image light guide with an overshield, according to another exemplary embodiment of the disclosed subject matter. [Figure 14B] FIG. 14B shows a schematic perspective view of a near-eye display having an image light guide with an overshield, according to another exemplary embodiment of the disclosed subject matter. [Figure 14C] FIG. 14C shows a schematic perspective view of a near-eye display having an image light guide with an overshield, according to yet another exemplary embodiment of the disclosed subject matter. [Figure 14D] FIG. 14D shows a schematic perspective view of a near-eye display having an image light guide with an overshield, according to yet another exemplary embodiment of the disclosed subject matter. [Figure 15] FIG. 15 shows a side view of a portion of a photodiode according to an exemplary embodiment of the disclosed subject matter. [Figure 16] FIG. 16 shows a schematic side view of an image light guide having a waveguide according to an exemplary embodiment of the disclosed subject matter. [Figure 17] FIG. 17 shows a schematic side view of an image light guide having a waveguide according to FIG. 16 with a photodiode located at the distal end of the waveguide. [Figure 18] FIG. 18 shows a schematic side view of an image light guide with a waveguide according to FIG. 16, with an optional photodiode positioned between the projector and the incoupling optics. [Figure 19A]FIG. 19A shows a schematic side view of an image light guide having a waveguide according to FIG. 18, with a quarter-wave plate positioned between the photodiode and the incoupling optic, and a specular reflective surface positioned adjacent to the waveguide on the opposite side of the projector. [Figure 19B] FIG. 19B shows a schematic side view of an image light guide with a waveguide according to FIG. 19A and a light path incident on a specular reflective surface. [Figure 20] FIG. 20 shows a schematic side view of an image light guide having a waveguide and an electrochromic filter according to an exemplary embodiment of the disclosed subject matter. [Figure 21A] FIG. 21A shows a schematic side view of a portion of the electrochromic filter according to FIG. [Figure 21B] FIG. 21B shows a schematic side view of a portion of the electrochromic filter according to FIG. [Figure 22] FIG. 22 shows a schematic side view of an image light guide having a waveguide and multiple electrochromic filters according to an exemplary embodiment of the disclosed subject matter. [Figure 23] FIG. 23 shows a schematic side view of an image light guide having a waveguide and a volume hologram according to an exemplary embodiment of the disclosed subject matter. [Figure 24] FIG. 24 shows a schematic side view of a portion of the image light guide according to FIG. [Figure 25] FIG. 25 shows a schematic side view of an image light guide having a waveguide and a volume hologram layer according to an exemplary embodiment of the disclosed subject matter. [Figure 26] FIG. 26 shows a schematic side view of a portion of the image light guide according to FIG. [Figure 27A] FIG. 27A shows a schematic side view of an image light guide having a waveguide and a switchable mirror in a reflective state according to an exemplary embodiment of the disclosed subject matter. [Figure 27B] FIG. 27B shows a schematic side view of an image light guide according to FIG. 27A with a switchable mirror in a partially reflective state, according to an exemplary embodiment of the presently disclosed subject matter. [Figure 27C]FIG. 27C shows a schematic side view of an image light guide according to FIG. 27A with a switchable mirror in a transmissive state, according to an exemplary embodiment of the presently disclosed subject matter. [Figure 28] FIG. 28 shows a schematic perspective view of an HMD. DETAILED DESCRIPTION OF THE INVENTION

[0007] It should be understood that the present invention may assume various alternative orientations and step arrangements unless expressly specified to the contrary. It should also be understood that the specific assemblies and systems illustrated in the accompanying drawings and described in the following specification are merely exemplary embodiments of the inventive concepts defined herein. Accordingly, specific dimensions, orientations, or other physical characteristics relating to the disclosed embodiments are not to be considered limiting unless expressly stated otherwise. Also, although not applicable, like elements in the various embodiments described herein may be generally referred to within this section of the specification using like reference numerals.

[0008] As used herein, terms such as "first," "second," etc. do not necessarily imply any order, sequence, or priority relationship, but are merely used to more clearly distinguish one element or set of elements from another, unless otherwise specified.

[0009] As used herein, the terms "viewer," "operator," "observer," and "user" are considered equivalent and refer to a person or machine wearing a device having an imaging light guide and / or viewing an image using a device having an imaging light guide.

[0010] As used herein, the term "set" refers to a non-empty set, as the concept of a collection of elements or members of a set is commonly understood in elementary mathematics. As used herein, the term "subset," unless explicitly stated otherwise, is used to refer to a non-empty proper subset, i.e., a subset of a larger set that has one or more members. For a set S, a subset may include the complete set S. However, a "proper subset" of set S is strictly contained in set S and excludes at least one member of set S.

[0011] As used herein, the terms "coupled" and "coupled" in the optical context refer to a connection in which light travels from one optical medium or device to another optical medium or device.

[0012] As used herein, the terms "wavelength band" and "wavelength range" are equivalent and have the standard meaning used by those skilled in the art of color imaging, and refer to a continuous range of light wavelengths used to represent a multicolor image.

[0013] As used herein, the term "beam expansion" is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions. Similarly, as used herein, "expanding" a beam or a portion of a beam is intended to mean the duplication of a beam through multiple encounters with optical elements to provide an exit pupil expansion in one or more directions.

[0014] Optical systems such as HMDs can generate virtual images. Unlike methods for forming real images, virtual images are not formed on a display surface. That is, when a display surface is positioned at the perceived location of the virtual image, no image is formed on the surface. Virtual images have many advantages unique to augmented reality displays. For example, the apparent size of the virtual image is not limited by the size or location of the display surface. Furthermore, the source object of the virtual image can be small; for example, a magnifying glass provides a virtual image of the object. Compared to systems that project real images, a more realistic viewing experience can be provided by forming a virtual image that appears to be at a certain distance. Providing a virtual image also eliminates the need to correct for screen artifacts, which may be required when projecting a real image.

[0015] An image light guide may display a virtual image using image-bearing light from a light source, such as a projector. For example, a collimated, relative angle-encoded light beam from the projector is coupled into the waveguide by an input coupling, such as an in-coupling diffractive optical element, which can be attached to or formed on the surface of the waveguide or embedded within the waveguide. Such a diffractive optical element can be formed as a diffraction grating, a holographic optical element (HOE), or by other known methods. For example, a diffraction grating can be formed by a surface relief. After propagating along the waveguide, the diffracted light can be redirected out of the waveguide by a similar output coupling, such as an out-coupling diffractive optical element, which can be configured to provide pupil dilation along at least one direction. Additionally, a rotating optical element (e.g., a diffraction grating) can be positioned on or in the waveguide to provide pupil dilation in at least one other direction. The image-bearing light output from the waveguide provides an expanded eyebox for the viewer.

[0016] As shown in FIG. 1 , the image light guide 10 may include a planar waveguide 22 having plane-parallel surfaces. The waveguide 22 comprises a transparent substrate S having an outer surface 12 and an inner surface 14 opposite the outer surface 12. In this example, an incoupling diffractive optical element IDO and an outcoupling diffractive optical element ODO are disposed on the inner surface 14. The incoupling diffractive optical element IDO is a reflective diffraction grating through which the image-bearing light WI is coupled into the planar waveguide 22. However, the incoupling diffractive optical element IDO may alternatively be a volume hologram, other holographic diffractive element, or other type of optical component that provides diffraction for the incident image-bearing light WI. The incoupling diffractive optical element IDO may be located on the outer surface 12 or the inner surface 14 of the planar waveguide 22 and may be a transmissive or reflective optical element depending on the direction from which the image-bearing light WI approaches the planar waveguide 22.

[0017] When used as part of a virtual image display system, the incoupling diffractive optical element IDO couples image-bearing light WI from a real image source into the substrate S of the planar waveguide 22. Any real image or image dimension is first converted into an array of overlapping, angle-related beams that encode different pixel locations within the image for presentation to the incoupling diffractive optical element IDO. The image-bearing light WI is diffracted, and at least a portion of the image-bearing light WI is thereby redirected by the incoupling diffractive optical element IDO into the planar waveguide 22 by total internal reflection (“TIR”) as image-bearing light WG for further propagation along the planar waveguide 22. Although diffracted along the boundaries set by TIR into a generally more condensed range of angle-related beams, the image-bearing light WG preserves the image information in coded form. The outcoupling diffractive optical element ODO receives the coded image-bearing light WG and diffracts at least a portion of the image-bearing light WG exiting the planar waveguide 22 as image-bearing light WO toward the intended location of the viewer's eye. Generally, the outcoupling diffractive optical element ODO is designed symmetrically with respect to the incoupling diffractive optical element IDO to restore the original angular relationship of the image-bearing light WI from the output angle-related beams of the image-bearing light WO. However, to increase one direction of overlap between the angle-related beams within the so-called eyebox E, where the virtual image can be seen, the outcoupling diffractive optical element ODO is positioned to encounter the image-bearing light WG multiple times and diffract only a portion of the image-bearing light WG at each encounter. The multiple encounters along the length of the outcoupling optic in the propagation direction have the effect of expanding one direction of the eyebox in which the image-bearing light beams overlap. The expanded eyebox E reduces the sensitivity to the position of the viewer's eye for viewing the virtual image.

[0018] An outcoupling diffractive optical element having a refractive index variation along a single direction can expand the eyebox in one direction in the propagation direction along the waveguide through multiple encounters of the image-bearing light beam with the outcoupling diffractive optical element, which produce copies of the outcoupled image-bearing light beam. Furthermore, an outcoupling diffractive optical element having a refractive index variation along a second direction can expand the eyebox in a second direction, providing bidirectional expansion of the eyebox. The refractive index variation along the first direction of the outcoupling diffractive optical element can be arranged to diffract a portion of the energy of each beam emerging from the waveguide upon each encounter through a preferred first-order diffraction, while another portion of the beam's energy is preserved for further propagation in the original direction through a zeroth-order diffraction. The refractive index variation along the second direction of the outcoupling diffractive optical element can be arranged to diffract a portion of the energy of each beam upon each encounter through a preferred first-order diffraction into a direction angled relative to the beam's original propagation direction, while another portion of the beam's energy is preserved for further propagation in the original direction through a zeroth-order diffraction.

[0019] The outcoupling diffractive optical element ODO is shown as a transmissive diffraction grating disposed on the inner surface 14 of the planar waveguide 22. However, like the incoupling diffractive optical element IDO, the outcoupling diffractive optical element ODO may be located on the outer surface 12 or the inner surface 14 of the planar waveguide 22 and may be transmissive, reflective, or a combination depending on the intended direction in which the image-bearing light WG exits the planar waveguide 22.

[0020] As shown in FIG. 2 , the image light guide 10 may be positioned to expand the eyebox E in two directions, i.e., along both the x-axis and the y-axis of the intended image. To achieve the second dimension of beam expansion, the incoupling diffractive optical element IDO with grating vector k0 is oriented to diffract a portion of the image-bearing light WI toward the intermediate turning grating TG with grating vector k1, which is oriented to diffract a portion of the image-bearing light WG in a reflective mode toward the outcoupling diffractive optical element ODO. Only a portion of the image-bearing light WG is diffracted by each of multiple encounters with the intermediate turning grating TG, thereby laterally expanding each angle-related beam of the image-bearing light WG that approaches the outcoupling diffractive optical element ODO. The image-bearing light WO exits the planar waveguide 22 after the turning grating TG redirects the image-bearing light WG toward the outcoupling diffractive optical element ODO to longitudinally expand the angle-related beam of the image-bearing light WG into the second dimension. The grating vectors, such as the depicted grating vectors k0, k1, k2, extend in a direction perpendicular to the diffractive features (e.g., grooves, lines, or rulings) of the diffractive optical elements and have a magnitude that is the reciprocal of the period or pitch d (i.e., the center-to-center distance between grooves) of the diffractive optical elements IDO, TG, ODO. The incoupling diffractive optical element IDO, turning grating TG, and outcoupling diffractive optical element ODO may each have a different period or pitch d.

[0021] As shown in FIG. 2, the incoupling diffractive optical element IDO receives incident image-bearing light WI, which includes a series of angle-related beams corresponding to individual pixels or equivalent locations in an image generated by the image source 16. The image source 16, operable to generate a range of angle-encoded beams to generate a virtual image, may be a combination of, but is not limited to, an actual display device combined with focusing optics, a beam scanner to more directly set the beam angles, or a one-dimensional actual display device used with a scanner. The image light guide 20 outputs a series of expanded angle-related beams in the two dimensions of the image by providing multiple encounters of the image-bearing light WG with both the intermediate turning grating TG and the outcoupling diffractive optical element ODO at different orientations. In the original orientation of the planar waveguide 22, the intermediate grating TG provides beam expansion in the y-axis direction, and the outcoupling diffractive optical element ODO provides a similar beam expansion in the x-axis direction. The reflective properties of the diffractive optical elements IDO, ODO, TG and their respective periods d, together with the orientation of their respective grating vectors, provide beam expansion in two dimensions while maintaining the intended relationship between the angularly related beams of image-bearing light WI that are output from the image light guide 20 as image-bearing light WO.

[0022] Although the image-bearing light WI input to the image light guide 20 is coded into a series of different angle-related beams by the incoupling diffractive optical element IDO, the information necessary to reconstruct the image is preserved by taking into account the systematic effects of the incoupling diffractive optical element IDO. The turning grating TG, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically positioned so as not to induce any significant changes to the coding of the image-bearing light WG. In some embodiments, the combined diffractive effects of the incoupling diffractive optical element IDO and the turning grating TG operate to code the image-bearing light WG, while the diffractive effect of the outcoupling diffractive optical element ODO operates to decode the combined coding. The outcoupling diffractive optical element ODO is typically positioned symmetrically with respect to the incoupling diffractive optical element IDO, e.g., including diffractive features that share the same period. Similarly, the period of the turning grating TG typically matches the common period of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO. 2, the grating vector k1 of the turning grating TG may be oriented at 45 degrees relative to the other grating vectors k0, k2 (all as undirected lines). However, in one embodiment, the grating vector k1 of the turning grating TG is oriented at 60 degrees relative to the grating vectors k0, k2 of the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO in such a way that the image-bearing light WG is turned by 120 degrees. By orienting the grating vector k1 of the intermediate turning grating TG at 60 degrees relative to the grating vector k0 of the incoupling diffractive optical element IDO and the grating vector k2 of the outcoupling diffractive optical element ODO, the grating vectors k0, k2 are also oriented at 60 degrees relative to each other (again, considered as undirected lines).Taking the common pitch of the turning grating TG, the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO as the basis for the magnitude of the grating vectors, the three grating vectors k0, k1, k2 (as directed line segments) form an equilateral triangle and sum to a zero vector magnitude, thereby avoiding asymmetric effects that may result in undesirable aberrations, including chromatic dispersion.

[0023] The image-bearing light WI diffracted into the planar waveguide 22 is effectively encoded by the incoupling diffractive optical element IDO, regardless of whether the incoupling diffractive optical element IDO uses a grating, hologram, prism, mirror, or some other mechanism. The reflection, refraction, and / or diffraction of light that occurs at the incoupling diffractive optical element IDO must be decoded accordingly by the outcoupling diffractive optical element ODO to recreate the virtual image presented to the viewer. The turning grating TG, located at an intermediate position between the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, is typically designed and oriented so as not to induce any changes in the encoded light. The outcoupling diffractive optical element ODO decodes the image-bearing light WG into its original or desired form of an angle-related beam expanded to fill the eyebox E.

[0024] It is relevant whether any symmetry is maintained between the turning grating TG and the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, or whether changes to the angle-related beam coding of the image-bearing light WI occur along the planar waveguide 22, the turning grating TG, the incoupling diffractive optical element IDO and the outcoupling diffractive optical element ODO, so that the image-bearing light WO output from the planar waveguide 22 retains or otherwise maintains the original or desired form of the image-bearing light WI for generating the intended virtual image.

[0025] The letter R represents the orientation of the virtual image as seen by a viewer positioned in the eyebox E. As shown, the orientation of the letter R in the represented virtual image coincides with the orientation of the letter R encoded by the image-bearing light WI. A change in rotation about the z-axis or angular orientation of the incident image-bearing light WI relative to the xy plane causes a corresponding symmetric change in the rotation or angular orientation of the output light from the outcoupling diffractive optical element ODO. From the image orientation perspective, the turning grating TG simply acts as a type of optical relay, providing expansion of the angle-encoded beam of the image-bearing light WG along one axis of the image (e.g., along the y-axis). The outcoupling diffractive optical element ODO further expands the angle-encoded beam of the image-bearing light WG along another axis of the image (e.g., along the x-axis) while maintaining the original orientation of the virtual image encoded by the image-bearing light WI. As shown in FIG. 2, the turning grating TG may be a tilted or square diffraction grating disposed on the front or back surface of the planar waveguide 22. Alternatively, the turning grating TG may be a blazed grating.

[0026] The present disclosure provides image light guide arrangements with improved control of image-bearing light output. More specifically, the present disclosure provides image light guide systems and AR display systems that, among other things, have means for reducing, eliminating, and / or blocking light output from the image light guide generally in a direction opposite the eyebox.

[0027] As shown in FIG. 3 , in one embodiment, image light guide system 50 includes a planar waveguide 100A having a first surface 102 and a second surface 104. Waveguide first surface 102 is positioned generally parallel to waveguide second surface 104. A first incoupling diffractive optical element IDO1 and a first outcoupling diffractive optical element ODO1 are formed on or within first surface 102. In one embodiment, waveguide 100A includes additional diffractive optical elements, such as a second incoupling diffractive optical element, an intermediate diffractive optical element (e.g., a turning grating), and / or a second outcoupling diffractive optical element. First outcoupling diffractive optical element ODO1 may include a composite diffractive optical element. In another embodiment, image source 16 is a color-field sequential projector system operable to pulse image-bearing light in red, green, and blue wavelength ranges to a digital light modulator / micromirror array (“DLP”) or liquid crystal on silicon (“LCOS”) display. Image source 16 may be operable to operate in a low-light mode using image-bearing light in only one of the red, green, and blue wavelength ranges. For example, in the low-light mode, image source 16 may emit image-bearing light for about 33% or less of the time that image source 16 is on.

[0028] Image-bearing light WI from the image source 16 is incident on the first incoupling diffractive optical element IDO1, and at least a portion of the image-bearing light WI is diffracted by the first incoupling diffractive optical element IDO1 and generally propagates as image-bearing light WG toward the outcoupling diffractive optical element ODO1 via TIR. At least a portion of the image-bearing light WG incident on the outcoupling diffractive optical element ODO1 may be expanded in at least one direction and directed from the first planar waveguide 100A by the outcoupling diffractive optical element ODO1 as outcoupled image-bearing light beams WO1, WO2 (representing central rays of the outcoupled image-bearing light beams). The first outcoupled image-bearing light beam WO1 is emitted in a first direction toward the eyebox E, where the viewer's eye is operable to see a virtual image. The second outcoupled image-bearing light beam WO2 is emitted in a second direction opposite the eyebox E.

[0029] 3, 4A, and 4B, in one embodiment, the image light guide system 50 includes an optical device comprising a liquid crystal shutter 150. In some exemplary embodiments, the liquid crystal shutter 150 may include a first glass substrate 152A and a second glass substrate 152B coated on their inner surfaces with a transparent conductive material 154, respectively, so that an electric field can be created between the first glass substrate 152A and the second glass substrate 152B. When the electric field is on, the liquid crystal 156 (“LC”) located between the first glass substrate 152A and the second glass substrate 152B aligns in a first direction, as shown in FIG. 4A, and when the electric field is off, the LC 156 aligns in a second, different direction, as shown in FIG. 4B. The liquid crystal shutter 150 may also include a first polarizing film 158A and a second polarizing film 158B located on the outer surfaces of the first glass substrate 152A and the second glass substrate 152B, respectively. The polarizing films 158A, 158B may, for example, have polarization axes that are generally crossed relative to one another.

[0030] LC 156 is operable to rotate the polarization direction of image-bearing light WO2, effectively similar to a wave plate. For example, LC 156 may be operable to rotate the polarization of light polarized by 158A by 90 degrees. When the electric field is on, second outcoupled image-bearing light WO2 incident on liquid crystal shutter 150 in a first linear polarization state is absorbed. When the electric field is in the off state, second outcoupled image-bearing light WO2 transmitted by LC 156 is transmitted by second polarizing film 158B.

[0031] In one embodiment, first polarizing film 158A is replaced by a wave plate, and waveguide 100A utilizes a polarization grating. It should be understood that the above-described exemplary configuration of liquid crystal shutter 150 is not intended to be limiting, but merely one potential exemplary configuration. Those skilled in the art will recognize that other configurations are possible.

[0032] Liquid crystal shutter 150 may block approximately 50% of the ambient light incident thereon due to the absorptivity of first polarizer 158A and second polarizer 158B. For example, if image source 16 operates at a frame rate of approximately 60 Hz, pixels of a particular wavelength range are displayed for a portion of the frame rate. For example, if image source 16 operates at a duty cycle where the frame rate is one-sixtieth (1 / 60) of a second, the duty cycle will be one-third (1 / 3) or less of the frame rate.

[0033] Thus, image source 16 emits image-bearing light WI in at least one of the red, green, and blue wavelength ranges for less than half (<1 / 2) the frame rate of image source 16. Liquid crystal shutter 150 is operable to reduce the transmission of the second outcoupled image-bearing light WO2 to approximately zero during periods when image source 16 is emitting image-bearing light WI. In one embodiment, liquid crystal shutter 150 is configured to operate completely in the dark during periods when image source 16 is emitting image-bearing light in low-light mode.

[0034] In one embodiment, liquid crystal shutter 150 is configured to block a red light wavelength range while generally allowing green and blue light wavelength ranges transmitted therethrough. For example, image source 16 may be operable to emit image-bearing light WI in a first wavelength range, and first polarizer 158A is limited to the first wavelength range. In this embodiment, ambient light transmission through liquid crystal shutter 150 increases to approximately 75% (e.g., absorption decreases from approximately 50% to one-third of 50%). In other words, utilizing liquid crystal shutter 150 to block only one light wavelength range changes the amount of time liquid crystal shutter 150 needs to be in an on state. Therefore, the on / off timing is different from when attempting to block all color wavelength ranges. In one embodiment, programmable image source 16 includes an operating mode in which only the red light wavelength range is emitted, and liquid crystal shutter 150 is on only for the red light wavelength range R portion of the frame rate shown in FIG. 5A.

[0035] 5A, 5B, and 5C, in one embodiment, the brightness of the first outcoupled image-bearing light WO1 and the second outcoupled image-bearing light WO2 may be adjusted by changing the voltage of the image source 16 and / or by changing the duty cycle (i.e., the amount of time per frame that the red, green, and / or blue light wavelength ranges R, G, B are on). For example, as shown in FIG. 5B, the brightness of the first outcoupled image-bearing light WO1 and the second outcoupled image-bearing light WO2 may be decreased by reducing the voltage to the LEDs for each light wavelength range R, G, B in the image source 16. Similarly, as shown in FIG. 5C, the brightness of the first outcoupled image-bearing light WO1 and the second outcoupled image-bearing light WO2 may be decreased by reducing the duty cycle to the LEDs for each light wavelength range R, G, B in the image source 16.

[0036] In one embodiment, the liquid crystal shutter 150 may include a polymer dispersed liquid crystal (PDLC) adhesive smart film such as that developed by Gauzy Ltd., having a place of business at 14 Hathiya Street, Tel Aviv - Yafo, Israel 6816914. For example, the smart film is typically 560 μm thick and operates with a switching time of 10 milliseconds.

[0037] In one embodiment, as shown in FIG. 6 , the image light guide system 50 includes a planar waveguide 100B having at least an incoupling diffractive optical element IDO2 and an outcoupling diffractive optical element ODO2 formed on or in the first surface 102. As shown in FIGS. 7 and 8 , in one embodiment, the outcoupling diffractive optical element ODO2 includes diffractive features 170 forming a blazed grating. The blazed grating's diffractive features 170 each form a right-angled triangle with a blaze angle α. The blaze angle α may be utilized to optimize the diffraction efficiency of the outcoupling diffractive optical element ODO2 for a given range of optical wavelengths. In one embodiment, the blazed diffractive features 170 each form a triangle with a blaze angle α. In one embodiment, one or more surfaces of the blazed diffractive features 170 may be curved.

[0038] In one embodiment, an antireflective coating 172 is located on a generally vertical surface of each blazed diffractive feature 170. An antireflective coating 172 that is one-quarter of the wavelength of the image-bearing light WG when the image-bearing light WG is within the antireflective coating 172 is also referred to as a quarter (1 / 4) wavelength thick. In one embodiment, the refractive index of the antireflective coating 172 can be calculated by taking the geometric mean of the refractive index of the waveguide substrate S (which is generally the same for the diffractive feature 170) and the refractive index of the surrounding material (e.g., air). n C =√n A n S

[0039] For example, the refractive index n of the substrate S Sis 1.65, and the blazed grating feature 170 has a refractive index n A When exposed to air with a refractive index of n = 1.0, the refractive index of the anti-reflective coating 172 is C = 1.28. However, those skilled in the art will recognize that the refractive index of the anti-reflection coating 172 can also be calculated in other ways. As shown in FIG. 8 and as illustrated in the graphs of FIGS. 9A and 9B, the anti-reflection coating 172 is operable to destroy, by destructive interference, a portion of the image-bearing light WG incident on the outcoupling diffractive optical element ODO2, which would propagate as second-order diffracted light and be output in the opposite direction from the eyebox E. Because the outcoupling diffractive optical element ODO2 is formed by a blazed grating, the first-order diffracted light is not outcoupled in the opposite direction from the eyebox E. Thus, the design of the planar waveguide 100B reduces or eliminates the second outcoupled image-bearing light beam WO2.

[0040] In one embodiment, as shown in FIG. 10A , the image light guide system 50 includes a planar waveguide 100C having an outcoupling diffractive optical element ODO3 formed on or in the first surface 102. The outcoupling diffractive optical element ODO3 includes blazed diffractive features 180 that are randomly or pseudo-randomly (collectively referred to herein as “randomly” or “random”) displaced across a distribution. In one embodiment, as shown in FIG. 10B , the outcoupling diffractive optical element ODO3 is a linear grating with approximately rectangular features 190 that are randomly displaced across a distribution. The period of the diffractive features 180, 190 is randomized according to a cosine probability distribution. ρ(s)=-π / Dcos(2πs / D)rect((2s / D)-1)

[0041] By randomizing the period of the diffractive features 180, 190 according to a cosine probability distribution, second-order diffraction of the image-bearing light WG incident on the outcoupling diffractive optical element ODO3 is reduced or eliminated, whereby the second outcoupled image-bearing light beam WO2 normally output by the outcoupling diffractive optical element ODO3 is reduced and / or eliminated in the direction opposite to the eyebox E.

[0042] Randomly varying the positions of the diffractive features 180, 190, as described in Nan Gao and Changqing Xie, "High-Order Diffraction Suppression Using Modulated Groove Position Gratings," Optics Letters, Vol. 36, No. 21 (Nov. 1, 2011), the entirety of which is incorporated herein by reference, suppresses second-order diffraction by a small amount. Furthermore, first-order diffracted image-bearing light is increased in intensity and is not outcoupled in a direction opposite to the eyebox E formed by the outcoupling diffractive optical element IDO3 with a blazed grating. In one embodiment, as shown in FIG. 10B , the period of the linear diffractive features 190 of the incoupling diffractive optical element IDO3 is randomized according to a cosine probability distribution so that second-order diffraction of the image-bearing light WG incident on the incoupling diffractive optical element IDO3 is reduced or eliminated.

[0043] In one embodiment, as shown in FIG. 11 , an image light guide system 50 having a planar waveguide 100A including an incoupling diffractive optical element IDO1 and an outcoupling diffractive optical element ODO1 formed on or within a first surface 102 includes an optical device including a photonic crystal shield 200. In one embodiment, the photonic crystal shield 200 is a fixed layer of the image light guide system 50. The photonic crystal shield 200 includes a three-dimensional photonic crystal 202 having a periodic refractive index variation along three axes. The periodic variation along three axes provides the three-dimensional photonic crystal 202 with a complete photonic bandgap, enabling complex light emission control. As shown in FIG. 12 , in one embodiment, the three-dimensional photonic crystal 202 is of wood construction, including silicon nitride with a nanoporous silicon dioxide interstitial material. In one embodiment, the projector 16 includes an LED operable to emit a wavelength range, such as red light. The photonic crystal shield 200 is operable to reflect light within at least one or a portion of the wavelength range of the projector LED. Accordingly, light in the wavelength range of the projector LED incident on photonic crystal shield 200 from the environment is reflected before reaching waveguide 100A.

[0044] In one embodiment, photonic crystal shield 200 is configured to block a first range of optical wavelengths while generally allowing second and third ranges of optical wavelengths to be transmitted therethrough. For example, programmable image source 16 may be operable to emit only image-bearing light WI in a first range of wavelengths, and photonic crystal shield 200 is configured to block the first range of wavelengths while generally allowing second and third ranges of optical wavelengths to be transmitted therethrough.

[0045] 13A-14B, liquid crystal shutter 150 or photonic crystal shield 200 may be embodied in an overshield 1000 operable to translate in and out of the path of light from the environment through image light guide system 50. As shown in Figures 13A and 13B, in one embodiment, liquid crystal shutter 150 or photonic crystal shield 200 is coupled to the frame of near-eye display 60 via hinge 1002. For example, hinge 1002 may be coupled to a rim 1004 of the eyepiece to allow rotation of liquid crystal shutter 150 or photonic crystal shield 200 about the longitudinal axis of hinge 1002 relative to planar waveguide 100A. Additionally, as described, any of the optical devices 150, 200, 400, 800, 900, 1100 operable to reduce a portion of the expanded image-bearing light beam output from the image light guide in a direction opposite the eyebox may be embodied within the overshield 1000.

[0046] 14A and 14B , any of the optical devices described herein, such as liquid crystal shutter 150, photonic crystal shield 200, photodiode 400, electrochromic filter 800, volume hologram 900, electro-optically switchable mirror 1100, or any combination thereof, may be embodied in an overshield 1000A that is slidably coupled to the frame of near-eye display 60 via slot 1006 in eyepiece rim 1004. For example, slot 1006 may allow liquid crystal shutter 150 or photonic crystal shield 200 to translate in and out of the path of light from the environment through image light guide system 50, relative to planar waveguide 100A.

[0047] 14C and 14D , liquid crystal shutter 150 or photonic crystal shield 200 may be embodied in an overshield 1000B slidably coupled to a portion of a frame of monocular near-eye display 62. Overshield 1000B may include a sleeve 1010 operable to cover at least a portion of waveguide 100A of image light guide system 50. Sleeve 1010 may include electrical contacts 1012 located at an end of sleeve 1010 and operable to connect to a power source of monocular near-eye display 62 to provide voltage to liquid crystal shutter 150, photonic crystal shield 200, or switchable mirror 1100.

[0048] In one embodiment, as shown in FIGS. 15-17 , an image light guide system 500 having a planar waveguide 504 including an incoupling diffractive optical element 506 and an outcoupling diffractive optical element 508 formed on or within a first surface 510 includes an optical device 400 with a photodiode, also referred to herein as an optical isolator. The photodiode 400 may be constructed by stacking multiple component layers 410 including a plasmonic material 412 and a dielectric material 414 with low optical loss. The article, B. Janaszek, et al., Nonlocality-Enabled Magnetic-Free Optical Isolation in Hyperbolic Metamaterials, Materials 2021, 14, 2865, is incorporated herein by reference in its entirety. Multiple layers 420 of the component layers 410 may be fabricated on a photodiode substrate 416. In one embodiment, the photodiode 400 includes ten of the component layers 410. In another embodiment, photodiode 400 includes fewer than 10 component layers 410, and in yet another embodiment, photodiode 400 includes more than 10 component layers 410. In one embodiment, plasmonic material 412 is graphene. In one embodiment, plasmonic material 412 is a single layer of graphene, dielectric material 414 is silicon nitride, and photodiode substrate 416 is zinc selenide (ZnSe). In another embodiment, photodiode substrate 416 may be another high refractive index, transparent optical material, such as glass or a polymer material.

[0049] In one embodiment, the thickness of the plasmonic material 412 is the same for each component layer 410 of the photodiode 400. In another embodiment, the thickness of the plasmonic material 412 may not be the same for all component layers 410. In one embodiment, the thickness of the dielectric material 414 is the same for each component layer 410 of the photodiode 400. In another embodiment, the thickness of the dielectric material 414 may not all be the same.

[0050] In one embodiment, the plasmonic material 412 is the same for each component layer 410 of the photodiode 400. In another embodiment, the plasmonic material 412 is not the same for each component layer 410 of the photodiode 400.

[0051] In one embodiment, the dielectric material 414 is the same material for each component layer 410 of the photodiode 400. In another embodiment, the dielectric material 414 is not the same material for each component layer 410 of the photodiode 400.

[0052] In some embodiments, the chemical potential of each component layer 410 can be altered to change the dielectric constant of the photodiode 400. In one embodiment, chemical doping of the component layers 410 causes a change in the chemical potential of the component layers 410, which results in a change in the dielectric constant of each respective component layer 410. In other embodiments, a voltage is applied across one or more component layers 410 during operation, changing the chemical potential of each respective component layer 410 and resulting in a change in the dielectric constant. In an exemplary embodiment, in which the plasmonic material 412 is graphene, the graphene layer may be electrically connected to a thin film transistor TFT having one or more electrically addressable portions. When a current or voltage is applied across one or more electrically addressable portions of the TFT, the corresponding portion of the connected graphene layer will experience a change in chemical potential and therefore a change in the dielectric constant of its respective portion. In some embodiments, the dielectric constant of an individual component layer 410 of graphene may be altered across the entire layer or across only a limited number of portions of the layer. For example, the dielectric constant of one or more portions of the graphene layers that are coaxially aligned about an imaginary axis passing through the eyebox and the planar waveguide 504 may be modified to prevent transmission of the second outcoupled image-bearing light beam WO2. In some embodiments, the voltage applied across one or more portions of the one or more graphene layers is between 0 and 1 eV.

[0053] FIG. 16 shows a portion of an image light guide system 500 operable in a head-mounted augmented reality (AR) display system. The image light guide system 500 includes a microprojector 502 and a parallel-plate waveguide 504. A wearer of the system 500 can view a virtual image via an image-bearing light beam from the system 500 entering the wearer's eye 501. The parallel-plate waveguide 504 includes parallel surfaces 510, 512. The parallel-plate waveguide 504 also includes an incoupling diffractive optical element 506 and an outcoupling diffractive optical element 508. The incoupling diffractive optical element 506 may be a diffraction grating, a holographic optical element, or the like, that optically couples an image-bearing light beam 520 incident from the projector 502 into the parallel-plate waveguide 504. Generally, when the light beam 520 is incident on the diffraction grating 506, there are both one or more reflected beams 524 and one or more transmitted beams 522. A portion of the transmitted beam 522 of a particular diffraction order (e.g., ±1 diffraction order) has an angle of incidence at the waveguide surface 512 that satisfies the total internal reflection (TIR) ​​condition and therefore reflects from the surface 512. Similarly, the beam 522 after reflecting from the surface 512 satisfies the TIR condition for reflection from the waveguide surface 510. Thus, the incoupled beam 522 propagates through the parallel-plate waveguide 504 by TIR from the proximal end 536 to the distal end 538 of the waveguide 504.

[0054] The parallel plate waveguide 504 further includes an outcoupling diffractive optical element 508. The outcoupling diffractive optical element 508 may be a diffraction grating, a holographic optical element, or the like, which optically outcouples at least a portion of the incoupled beam 522 from the parallel plate waveguide 504, typically as beam 526 directed toward the wearer's eye 501. A portion of the incoupled beam 522 reflects back from the outcoupling optical element 508 as reflected beam 532. A portion of the reflected beam 532 no longer meets the requirements for TIR at the waveguide surface 512 and refracts out of the parallel plate waveguide 504 as beam 534.

[0055] When a person is observing a person wearing image light guide system 500, beam 534 may be visible to the observer. This may detract from the wearer of image light guide system 500 or from the information the wearer is viewing. Furthermore, such beam 534 exiting the parallel plate waveguide away from the wearer is aesthetically undesirable. Therefore, it is desirable to reduce or eliminate the observation of beam 534.

[0056] 16 further shows incident light beams or rays 530 from the environment. A portion of these ambient rays 530 passes through the parallel plate waveguide 504 and through the outcoupling optics 508 where they are observed by the wearer's eye 501.

[0057] FIG. 17 shows a portion of an image light guide system 600 as detailed in FIG. 16 with a photodiode 400 oriented to reflect a beam 534 exiting a parallel-plate waveguide 504 through a waveguide surface 512. The photodiode 400 may be constructed as described above and / or as shown in FIG. 15. The alignment of the photodiode 400 is parallel to the waveguide surface 512. The photodiode 400 may cover the same area as the outcoupling diffractive optical element 508. In another embodiment, the area of ​​the photodiode 400 covers another portion of the waveguide surface 512 in addition to the area of ​​the outcoupling diffractive optical element 508. In another embodiment, the area of ​​the photodiode 400 covers the entire area of ​​the waveguide surface 512.

[0058] In one embodiment, the space between the photodiode 400 and the surface 512 is filled with air. In another embodiment, the space between the photodiode 400 and the surface 512 forms a closed cavity and is filled with a fluid such as, but not limited to, dry air, air, argon gas, or nitrogen gas. In yet another embodiment, the space between the photodiode 400 and the waveguide surface 512 is filled with a material having a low refractive index, such as materials provided by PiBond Oy, having offices at Kutojantie 2, 02630 Espoo, Finland. The material having a low refractive index may be based on a siloxane material, resulting in a material having a refractive index as low as 1.25.

[0059] Photodiode 400 is oriented relative to parallel-plate waveguide 504 so that beam 534 exiting parallel-plate waveguide 504 through waveguide surface 512 reflects back toward parallel-plate waveguide 504 as reflected beam 540. A portion of reflected beam 540 may re-enter parallel-plate waveguide 504 as beam 542. A portion of beam 542 may encounter outcoupling diffractive optical element 508 and exit parallel-plate waveguide 504 as beam 544. Beam 544 is essentially parallel to beam 526 that is outcoupled by outcoupling diffractive optical element 508. The degree to which beam 544 is parallel to beam 526 depends, at least in part, on the degree to which photodiode 400 can be collimated to waveguide surface 512 of parallel-plate waveguide 504. Alignment of photodiode 400 with waveguide surface 512 is such that a wearer viewing a virtual image sees only one image. Misalignment of the photodiodes 400 can cause double images to be observed by the wearer.

[0060] When photodiode 400 is properly aligned, beam 544 enhances the intensity (i.e., increases brightness) of the total light emitted from waveguide 504 toward wearer's eye 501. By adding outcoupled beam 544 to outcoupled beam 526, the virtual image observed by the wearer will be brighter than it would be without photodiode 400. With photodiode 400 in place and producing a brighter virtual image, the power of projector 502 can be reduced. That is, the amount of light generated by projector 502 can be decreased to achieve the same level of observed brightness of the virtual image as without photodiode 400 in place. Thus, system 600 may require less power to drive projector 502, thus increasing battery life per battery charge. Furthermore, requiring less power, system 600 may reduce heating issues. Thus, there are advantages beyond security for a head-mounted AR system having photodiode 400 constructed and positioned as disclosed herein.

[0061] As shown in FIG. 17, ambient light rays 530 pass through the photodiode 400, allowing the wearer a real-world view that approximates the real-world view without the photodiode 400 in place.

[0062] In one embodiment, photodiode 400 is configured to block a first range of light wavelengths while generally allowing other ranges of light wavelengths to be transmitted therethrough. For example, image source 502 may be operable to emit image-bearing light 520 in a first range of wavelengths, and photodiode 400 is configured to block / reflect the first range of wavelengths.

[0063] FIG. 18 illustrates a portion of an image light guide system 700 operable in a head-mounted AR display system, having one or more features and / or components described above with respect to systems 500, 600 of FIGS. 16 or 17 . Correspondingly, like elements are generally referred to by like reference numerals. As shown in FIG. 18 , image light guide system 700 includes a photodiode 550 optically positioned between projector 502 and an incoupling diffractive optical element 506 on waveguide surface 510 of parallel-plate waveguide 504. Photodiode 550 is oriented such that beam 520 from projector 502 passes through photodiode 550 and is incident on incoupling diffractive optical element 506. At incoupling optic 506, incident beam 520 is partially reflected to become beam 524 (which may be one or more diffraction orders, not shown) and partially transmitted through incoupling optic 506 to become incoupled beam 522 (which may be one or more diffraction orders, not shown). Photodiode 550 is oriented such that reflected beam 524 is reflected from photodiode 550. Thus, a portion of beam 524 reflects back toward waveguide 504 as beam 552. A portion of beam 552 may be incident on incoupling optic 506 and then become incoupled beam 554. Incoupled beam 554 would not propagate within waveguide 504 in the absence of photodiode 550. Thus, photodiode 550 provides additional beam 554 for coupling into waveguide 504, which then outcouples with beam 522 to result in a brighter image observed by a wearer of image light guide system 700. Thus, the advantages of a brighter virtual image, reduced battery demand, and reduced heat generation may be achieved with the introduction of photodiode 550.

[0064] The photodiode 550 is positioned so that it is parallel to the waveguide surface 510. In one embodiment, the photodiode 550 is fabricated on the waveguide surface 510. In another embodiment, the photodiode 550 is in mechanical contact with the surface 510. The alignment of the photodiode 550 is such that multiple images are not produced and are viewed by the wearer.

[0065] 19A shows a portion of an image light guide system 750. Like elements of the image light guide system 750 are generally referred to with like reference numerals from the previous embodiments. As shown in FIG. 19A, in one embodiment, a quarter-wave plate 556 is optically positioned between the photodiode 550 and the incoupling optic 506. The quarter-wave plate 556 rotates the polarization of the image-bearing light beam.

[0066] 19A and 19B , the AR display system 750 may also include a specular reflective surface 560, such as a mirror optically positioned after the surface 512. The mirror 560 reflects at least a portion of the image-bearing light beam, for example, but not limited to, a zero-order diffraction beam from the incoupling optic 506 that does not satisfy the TIR condition for coupling into the waveguide 504. The portion of the beam reflected from the mirror 506 into the waveguide 504 may be incident on the incoupling optic 506 and may pass through the incoupling optic 506 to the photodiode 550. The portion of the beam reflected from the mirror 506 onto the photodiode 550 may be reflected again so that it is incident on the incoupling optic 506 and is incoupled as beams 522, 554 that propagate via TIR to the outcoupling optic 508.

[0067] It should be understood that the location of incoupling optical element 506 and / or outcoupling optical element 508 may be on or within waveguide surface 510 or waveguide surface 512 .

[0068] 20 , in one embodiment, image light guide system 50 includes an optical device comprising an electrochromic filter 800. Electrochromic filter 800 may include a first glass substrate 802A and a second glass substrate 802B coated on their inner surfaces with a transparent conductive material 804, respectively, such that an electric field can be created between first glass substrate 802A and second glass substrate 802B. When the electric field is on, liquid crystals 806 (“LC”) located between first glass substrate 802A and second glass substrate 802B align in a first direction, as shown in FIG. 21A , and when the electric field is off, LC 806 aligns in a second, different direction, as shown in FIG. 21B . Electrochromic filter 800 functions similarly to liquid crystal shutter 150. However, instead of using an electric field to change the polarization of LC 806 to block image-bearing light WO2, LC 806 in electrochromic filter 800 is structured such that, at a particular orientation of LC 806, the dichroic filter blocks a particular wavelength range of image-bearing light WO2. For example, when the electric field is on, LC 806 can act as a dichroic filter operable to block a first range of light wavelengths.

[0069] In one embodiment, the LC 806 is operable across the visible spectrum of light, and the on / off states of the LC 806 are timed so that the LC 806 is completely opaque when the image source 16 emits image-bearing light. The image source 16 may be controllable so that a portion of the frame rate includes a state where all of the LEDs of the image source 16 are off, and the LC 806 is controllable so that when the LEDs are off, the dichroic filter is off and the electrochromic filter 800 is completely transparent. Synchronizing the image source 16 and the electrochromic filter 800 allows for the transmission of light from the surrounding environment to the user's eyes, so that the image light guide system 50 appears transparent to the user even as it propagates the image to the eyebox. Increasing the frame rate period that the LEDs are off increases the apparent transparency of the image light guide system 50.

[0070] In one embodiment, the LC 806 of the electrochromic filter 800 is operable over a specific wavelength range rather than the visible spectrum. In this embodiment, the image source 16 may be controllable so that a portion of the frame rate includes a state in which the LEDs corresponding to the specific wavelength range in which the LC 806 is operable are off, such that the image light guide system 50 is operable to transmit at least a portion of the light from the surrounding environment to the user's eyes. By increasing the frame rate period in which the LEDs corresponding to the specific wavelength range in which the dichroic filter is operable are off, the apparent transparency of the image light guide system 50 may be increased.

[0071] In one embodiment, the electrochromic filter 800 includes a first polarizing film 808A and a second polarizing film 808B positioned on the outer surfaces of a first glass substrate 802A and a second glass substrate 802B, respectively. The polarizing films 808A, 808B may, for example, have generally crossed polarization axes relative to each other.

[0072] 22 , in one embodiment, image light guide system 50 includes multiple electrochromic filters 800A, 800B, and 800C. Each of electrochromic filters 800A, 800B, and 800C may be timed (e.g., with image source 16) to operate at a separate subframe (e.g., a fraction of the frame rate) within the video signal corresponding to a different wavelength range of image-bearing light. For example, first electrochromic filter 800A may be operable to block light in a first wavelength range (e.g., red), second electrochromic filter 800B may be operable to block light in a second wavelength range (e.g., green), and third electrochromic filter 800C may be operable to block light in a third wavelength range (e.g., blue).

[0073] Referring now to FIG. 23, in one embodiment, the image light guide system 50 includes an optical device comprising a volume hologram 900 formed on the second surface 104 of a planar waveguide 100A. The volume hologram 900 includes diffractive elements spaced apart to affect a specific range of optical wavelengths. As shown in FIG. 24, the diffractive elements of the volume hologram 900 are configured such that image-bearing light WO2 incident on the volume hologram 900 is directed substantially orthogonally to the image-bearing light WO2 as image-bearing light WO3, rather than in a TIR condition. Due to the configuration of the diffractive elements of the volume hologram 900, light from the surrounding environment is operable to be transmitted through the volume hologram 900 and the planar waveguide 100A to a user's eye. In one embodiment, one extreme field angle of the central ray of image-bearing light WO2 entering the volume hologram 900 is directed approximately perpendicular to the second surface 104 as image-bearing light WO3', and the opposite field angle of the central ray of image-bearing light WO2 entering the volume hologram 900 is directed to exit the volume hologram 900 under non-TIR conditions approximately perpendicular to the central ray of image-bearing light WO2 as image-bearing light WO3.

[0074] In one embodiment, image-bearing light WO2 incident on volume hologram 900 and directed as image-bearing light WO3 in a substantially orthogonal direction in non-TIR conditions is directed toward an absorbing material 904 located at end 902 of planar waveguide 100A. For example, absorbing material 904 may be, but is not limited to, a flat black coating or a light-absorbing film. In one embodiment, the propagation angle of image-bearing light WO3 prevents a significant portion of image-bearing light WO3 from being diffracted by volume hologram 900.

[0075] 25, in one embodiment, the planar waveguide 100A of the image light guide system 50 includes a material layer 906 formed on its second surface 104 between the volume hologram 900 and the planar waveguide substrate. As shown in FIG. 26, the diffractive elements of the volume hologram 900 are configured such that the image-bearing light WO2 incident on the volume hologram 900 is directed substantially orthogonally to the image-bearing light WO2, as image-bearing light WO3, rather than in a TIR condition. The material layer 906 allows some rays of the image-bearing light WO3′ to reflect from the waveguide surface 104 on their way to the absorbing material 904.

[0076] In one embodiment, volume hologram 900 is configured to block a first range of optical wavelengths while generally allowing second and third ranges of optical wavelengths to be transmitted therethrough. For example, programmable image source 16 may be operable to emit only image-bearing light WI in a first range of wavelengths, and volume hologram 900 is configured to block the first range of wavelengths while generally allowing second and third ranges of optical wavelengths to be transmitted therethrough.

[0077] FIG. 27A illustrates a portion of an image light guide system 600 having one or more features and / or components described above with respect to image light guide systems 500, 600 of FIG. 16 or 17 . Correspondingly, like elements are generally referred to by like reference numerals. In one embodiment, as shown in FIG. 27A , image light guide system 600 includes an optical device comprising an electro-optically switchable mirror 1100 operable in a reflective state to reflect beam 534 exiting parallel-plate waveguide 504 through waveguide surface 512. As shown in FIG. 27C , switchable mirror 1100 is also operable in an optically transmissive state to allow a portion of incident light beam 530 from the environment to pass therethrough.

[0078] In one embodiment, the switchable mirror 1100 is located at 40 Corporate Park The switchable mirror 1100 may include an e-TransFlector™ developed by Kent Optronics, Inc., having a business address at 1000 Angstrom Dr., Hopewell Junction, NY 12533. For example, the switchable mirror 1100 operates with a switching time of 10 milliseconds to 100 milliseconds and has a reflection bandwidth range selected from 50 nm to 1,000 nm. The alignment of the switchable mirror 1100 is parallel to the waveguide surface 512. The switchable mirror 1100 may cover the same area as the outcoupling diffractive optical element 508. In another embodiment, the area of ​​the switchable mirror 1100 covers a different portion of the waveguide surface 512 in addition to the area of ​​the outcoupling diffractive optical element 508. In another embodiment, the area of ​​the switchable mirror 1100 covers the entire area of ​​the waveguide surface 512.

[0079] Synchronizing the image source 502 and the switchable mirror 1100 allows for the transmission of light from the surrounding environment to the user's eyes, so that the display system 600 appears transparent to the user, even as it propagates an image to the eyebox. As shown in FIG. 27C , when the switchable mirror 1100 is in a light-transmitting state (as opposed to a reflective state), a portion of an incident light beam or ray 530 from the environment passes through the switchable mirror 1100, the parallel-plate waveguide 504, and the outcoupling optics 508 to be observed by the wearer's eye 501. In embodiments in which the image source 502 is synchronized with the reflective / transmissive state of the switchable mirror 1100, the image source 502 does not emit image-bearing light while the switchable mirror 1100 is in the transmissive state.

[0080] 27B , in one embodiment, the switchable mirror 1100 is operable in a partially reflective state in which a portion of the image-bearing light beam 534 exiting the parallel-plate waveguide 504 through the waveguide surface 512 is reflected back by the switchable mirror 1100 toward the parallel-plate waveguide 504 as a reflected beam 540, and another portion of the image-bearing light beam 534 exiting the parallel-plate waveguide 504 through the waveguide surface 512 is transmitted through the switchable mirror 1100. Similarly, a portion of an incident light beam or ray 530 from the environment passes through the switchable mirror 1100, and another portion of the incident light beam 530 is reflected by the switchable mirror 1100. The partially reflective state of the switchable mirror 1100 has the advantage of increasing the brightness / intensity of the total light emitted from the waveguide 504 toward the wearer's eye 501 by reflecting a portion of the image-bearing light beam 534 back into the waveguide 504. By adding outcoupled beam 544 to outcoupled beam 526, the virtual image observed by the wearer will be brighter than it would be without switchable mirror 1100. Furthermore, by reflecting a portion of incident light beam 530 from the environment, the real-world image perceived by the user is reduced in intensity. Thus, the observed brightness of the virtual image may be further increased relative to the environment. As described above, system 600 may require less power to drive projector 502 at a desired brightness, thus increasing battery life per battery charge.

[0081] In one embodiment, the switchable mirror 1100 is operable between at least a reflective state shown in FIG. 27A , a partially reflective state shown in FIG. 27B , and a light-transmitting state shown in FIG. 27C . In one embodiment, the switchable mirror 1100 is configured to block a first range of optical wavelengths while generally allowing other ranges of optical wavelengths to be transmitted therethrough. For example, the image source 502 may be operable to emit image-bearing light 520 in a first wavelength range, and the switchable mirror 1100 is configured to block / reflect the first wavelength range. Using the switchable mirror 1100 to block only one range of optical wavelengths changes the amount of time the switchable mirror 1100 needs to be in an on state. Thus, the on / off timing is different than when attempting to block all color wavelength ranges. In one embodiment, the programmable image source 502 includes an operating mode in which only the red wavelength range is emitted, and the switchable mirror 1100 is on only for the red optical wavelength range R portion of the frame rate.

[0082] The perspective view of FIG. 28 illustrates a display system 60 for augmented reality viewing using one or more image light guides, image light guide systems, and / or AR display systems of the present disclosure. The display system 60 is shown as an HMD having a right-eye optical system 64R with a right-eye image light guide 66R. The display system 60 includes an image source 16, such as a picoprojector or similar device, and is energizable to generate images. In one embodiment, the display system 60 includes one or more image light guides 66L and a left-eye optical system 64L including a second image source. The generated images can be a stereoscopic pair of images for 3D viewing. The virtual image formed by the display system 60 may appear to be superimposed or overlaid on real-world scene content viewed by a viewer through the right-eye image light guide 66R and / or the left-eye image light guide 66L. Additional components well known to those skilled in the art of augmented reality visualization may also be provided, such as one or more cameras attached to the frame of the HMD for viewing scene content or for tracking the viewer's gaze.

[0083] Those skilled in the art will recognize that the incoupling and outcoupling diffractive optical elements of the embodiments described herein may be located on the outer or inner surface of the planar waveguide and may be transmissive or reflective depending on the direction from which the image-bearing light approaches the planar waveguide. Similarly, the diffractive optical elements may alternatively be volume holograms or other types of optical components that provide diffraction of the image-bearing light.

[0084] In addition to the foregoing, the present disclosure contemplates the following non-limiting examples. In an exemplary embodiment, an optically secure image light guide system includes an image source operable to generate an image-bearing light beam; a waveguide operable to propagate the image-bearing light beam; an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source to the first waveguide in an angularly coded manner; an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand the portion of the image-bearing light beam, the outcoupling diffractive optical element directing a first portion of the expanded image-bearing light beam from the waveguide in an angularly decoded manner in a first direction towards an eyebox and directing a second portion of the expanded image-bearing light beam from the waveguide in a second direction different from the first direction; and an optical device operable to reduce the second portion of the expanded image-bearing light beam output from the image light guide in the second direction.

[0085] In another exemplary embodiment of the image light guide system with optical security, the optical device comprises a liquid crystal shutter, for example, the liquid crystal shutter includes: a first substrate having first and second opposing surfaces, a second substrate having first and second opposing surfaces, a first layer of conductive material disposed on the second surface of the first substrate, a second layer of conductive material disposed on the first surface of the second substrate, the first and second layers of conductive material operable to generate an electric field between the first and second substrates, liquid crystal disposed between the first and second layers of conductive material, the liquid crystal operable to align in a first direction in an electric field on state and in a second direction in an electric field off state, and a polarizer disposed on the second surface of the second substrate.

[0086] In an exemplary embodiment, the polarizer located on the second surface of the second substrate is a second polarizer, and a first polarizer is located on the first surface of the first substrate. For example, the first polarizer and the second polarizer have crossed polarization axes, and / or in the on state of the electric field, a first linear polarization state of the second portion of the expanded image-bearing light beam incident on the liquid crystal is absorbed. The first linear polarization state and the second linear polarization state may be substantially orthogonal.

[0087] In another exemplary embodiment of an image light guide system with optical security, the optical device comprises a three-dimensional photonic crystal having periodic variations on three axes, the image source operable to emit image-bearing light in a first wavelength range, and the three-dimensional photonic crystal operable to reflect light in the first wavelength range. For example, a second photodiode may be optically positioned between the image source and the incoupling diffractive optical element, and a portion of the image-bearing light directed from the incoupling diffractive optical element towards the second photodiode is reflected by the second photodiode towards the incoupling diffractive optical element and thereby incoupled.

[0088] In another exemplary embodiment of an image light guide system with optical security, an optical device includes an electrochromic filter having a first substrate having first and second opposing surfaces; a second substrate having first and second opposing surfaces; a first layer of conductive material located on the second surface of the first substrate; a second layer of conductive material located on the first surface of the second substrate, the first and second layers of conductive material operable to generate an electric field between the first substrate and the second substrate; liquid crystals located between the first and second layers of conductive material, the liquid crystals operable to align in a first direction in an on state of the electric field and in a second direction in an off state of the electric field; and a polarizer located on the second surface of the second substrate.

[0089] In an exemplary embodiment, the liquid crystal presents a dichroic filter operable to block a first wavelength range of the image-bearing light, e.g., the electrochromic filter is opaque to the first wavelength range of the image-bearing light when the image source emits the first wavelength range of the image-bearing light.

[0090] In an exemplary embodiment, the image source and the electrochromic filter are synchronized such that when a virtual image is visible in the eyebox, the environment is perceptible through the electrochromic filter.

[0091] In another exemplary embodiment of an image light guide system with optical security, the optical device comprises a first electrochromic filter, a second electrochromic filter, and a third electrochromic filter, each of the first, second, and third electrochromic filters synchronized with the image source to block the image-bearing light during different sub-frames of a frame rate of the image source.

[0092] For example, the first electrochromic filter is operable to block image-bearing light in a first wavelength range, the second electrochromic filter is operable to block image-bearing light in a second wavelength range, and the third electrochromic filter is operable to block image-bearing light in a third wavelength range.

[0093] In another exemplary embodiment, an image light guide system with optical security includes an image source operable to generate an image-bearing light beam; a waveguide operable to propagate the image-bearing light beam; an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into the waveguide in an angularly coded manner; an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand the portion of the image-bearing light beam and direct a first portion of the expanded image-bearing light beam from the waveguide in an angularly decoded manner in a first direction towards an eyebox, the outcoupling diffractive optical element comprising blazed grating features; and an anti-reflective coating positioned on a surface of the blazed grating features operable to reduce light output from the image light guide in a second direction opposite the first direction.

[0094] In an exemplary embodiment, the blazed grating feature comprises a substantially right triangle and the anti-reflective coating is located on a substantially vertical surface of the blazed grating feature, e.g., the anti-reflective coating is operable to cancel, via destructive interference, a subset of the image-bearing light beam incident on the outcoupling diffractive optical element to reduce a second portion of the expanded image-bearing light beam from being output from the waveguide in the second direction.

[0095] In an exemplary embodiment, the anti-reflective coating has a refractive index that is a function of the geometric mean of the refractive index of the waveguide and the refractive index of the surrounding material, hi an exemplary embodiment, the anti-reflective coating has a thickness that is substantially one-quarter wavelength of the image-bearing light.

[0096] In another exemplary embodiment, an optically secure image light guide system includes an image source operable to generate an image-bearing light beam, a waveguide operable to propagate the image-bearing light beam, an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into the waveguide in an angularly coded manner, and an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand the portion of the image-bearing light beam and direct a first portion of the expanded image-bearing light beam from the waveguide in an angularly decoded manner in a first direction toward an eyebox, the outcoupling diffractive optical element comprising diffractive features randomly displaced across a distribution and operable to reduce light output from the image light guide in a second direction opposite the first direction. For example, the period of the diffractive features is randomized as a function of a cosine probability distribution.

[0097] In exemplary embodiments, second order diffraction of the image-bearing light beam incident on the outcoupling diffractive optical element is suppressed, thereby substantially eliminating light output from the image light guide in the second direction. In exemplary embodiments, first order diffraction of the image-bearing light beam incident on the outcoupling diffractive optical element is enhanced, thereby increasing the intensity of light output from the image light guide in the first direction.

[0098] In another exemplary embodiment, an optically secure image light guide system includes an image source operable to generate an image-bearing light beam, a waveguide operable to propagate the image-bearing light beam, an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into the waveguide in an angularly coded manner, and an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element diffracting a portion of the image-bearing light beam from the image source into the waveguide in an angularly coded manner. an outcoupling diffractive optical element operable to expand a portion and direct a first portion of the expanded image-bearing light beam from the waveguide in a first direction towards the eyebox in an angularly decoded form; a wave plate located between the incoupling diffractive optical element and the image source; and a specular reflective surface located proximate a surface of the wave plate opposite the image source, the reflective surface operable towards the incoupling diffractive optical element such that at least a portion of the image-bearing light beam is not incoupled by the incoupling diffractive optical element.

[0099] In an exemplary embodiment, a photodiode is optically positioned between the image source and the incoupling diffractive optical element, and a portion of the image-bearing light reflected from the reflective surface and directed from the incoupling diffractive optical element toward the second photodiode is reflected by the photodiode toward the incoupling diffractive optical element and thereby incoupled.

[0100] One or more features of the embodiments described herein may be combined to create additional embodiments not shown. While various embodiments have been described in detail above, it should be understood that they are presented for illustrative purposes, and not for limiting purposes. It will be apparent to those skilled in the relevant art that the subject matter of the present disclosure may be embodied in other specific forms, variations, and modifications without departing from the scope, spirit, or essential characteristics thereof. The above-described embodiments are therefore to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated by the appended claims, and all changes that come within the meaning and range of equivalents thereof are intended to be embraced therein.

Claims

1. An image light guide system with optical security, comprising: an image source operable to generate an image-bearing light beam; a waveguide operable to propagate said image-bearing light beam; an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into a first of the waveguides in an angularly coded manner; an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand a portion of the image-bearing light beam and to direct a first portion of the expanded image-bearing light beam from the waveguide in an angularly decoded manner in a first direction towards an eyebox; the outcoupling diffractive optical element includes blazed grating features; and an anti-reflective coating disposed on a surface of the blazed grating features, the anti-reflective coating operable to reduce light output from the image light guiding system in a second direction opposite the first direction.

2. 10. The image light guide system of claim 1, wherein the blazed grating features comprise substantially right-angled triangles, and the anti-reflective coating is disposed on substantially vertical surfaces of the blazed grating features.

3. 2. The image light guide system of claim 1, wherein the anti-reflection coating is operable to destroy a subset of the image-bearing light beam incident on the outcoupling diffractive optical element via destructive interference to reduce a second portion of the expanded image-bearing light beam from being output from the waveguide in the second direction.

4. 4. The image light guide system of claim 3, wherein the first portion of the expanded image-bearing light beam comprises first-order diffracted light and the subset of the image-bearing light beam comprises second-order diffracted light.

5. The imaging light guide system of claim 1 , wherein the anti-reflective coating comprises a refractive index that is a function of the geometric mean of the refractive index of the waveguide and the refractive index of a surrounding material.

6. The image light guide system of claim 1 , wherein the anti-reflective coating has a thickness substantially one-quarter of a wavelength of the image-bearing light beam.

7. 10. The image light guide system of claim 1, wherein the blazed grating features have a blaze angle operable to optimize diffraction efficiency of light in the first wavelength range.

8. An image light guide system with optical security, comprising: an image source operable to generate an image-bearing light beam; a waveguide operable to propagate said image-bearing light beam; an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into a first of the waveguides in an angularly coded manner; an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand a portion of the image-bearing light beam and to direct a first portion of the expanded image-bearing light beam from the waveguide in an angularly decoded manner in a first direction towards an eyebox; an image light guiding system, wherein the outcoupling diffractive optical element comprises diffractive features randomly displaced across a distribution, the diffractive features operable to reduce light output from the image light guiding system in a second direction opposite the first direction.

9. The image light guiding system of claim 8 , wherein the period of the diffractive features is randomized as a function of a cosine probability distribution.

10. 9. The image light guide system of claim 8, wherein second-order diffraction of the image-bearing light beam incident on the outcoupling diffractive optical element is suppressed, thereby substantially eliminating light output from the image light guide system in the second direction.

11. 9. The image light guide system of claim 8, wherein first order diffraction of the image-bearing light beam incident on the outcoupling diffractive optical element is enhanced, thereby increasing the intensity of light output from the image light guide system in the first direction.

12. The image light guide system of claim 8 , wherein the diffractive features comprise surface relief gratings.

13. The image light guide system of claim 12 , wherein the diffractive features comprise a blazed grating.

14. an image source operable to generate an image-bearing light beam; a waveguide operable to propagate said image-bearing light beam; an incoupling diffractive optical element formed along the waveguide, the incoupling diffractive optical element operable to diffract a portion of the image-bearing light beam from the image source into a first of the waveguides in an angularly coded manner; an outcoupling diffractive optical element formed along the waveguide, the outcoupling diffractive optical element operable to expand a portion of the image-bearing light beam and to direct a first portion of the expanded image-bearing light beam from the waveguide in an angularly decoded manner in a first direction towards an eyebox; a waveplate optically positioned between the incoupling diffractive optical element and the image source; a mirrored reflective surface disposed proximate a face of the waveguide opposite the image source, the reflective surface operable to reflect at least a portion of the image-bearing light beam not incoupled by the incoupling diffractive optical element towards the incoupling diffractive optical element; An image light guide system comprising:

15. further comprising a photodiode optically positioned between the image source and the incoupling diffractive optical element; 15. The image light guide system of claim 14, wherein a portion of the image-bearing light beam reflected from the reflective surface and directed from the incoupling diffractive optical element toward the photodiode is reflected by the photodiode toward the incoupling diffractive optical element and thereby incoupled.

16. The image light guiding system of claim 15 , wherein the wave plate is optically positioned between the incoupling diffractive optical element and the photodiode.

17. The image light guide system of claim 14 , wherein the wave plate is a quarter wave plate.

Images