KR20180117180A - Wide field holographic skew mirror - Google Patents

Abstract

A holographic skew mirror has a reflective or skew axis that can be tilted with respect to its surface normal. Tilting the skew axis in two dimensions with respect to the surface normal extends the possible field of view of the holographic skew mirror to, for example, 60 or more. These additional angles can be accessed using an out-of-plane fill geometry with matching total internal grazing extension rotation (TIGER) prisms.

Description

Wide field holographic skew mirror

Cross-reference to related application

This application is a continuation of application PCT / US16 / 48499, filed on August 24, 2016, entitled " Skew Mirrors, Methods of Use, and Methods of Manufacture " Which is a continuation-in-part of U.S. Application No. 15 / 174,938 entitled " Skew Mirrors, Methods of Use, and Methods of Manufacture ", filed on April 6, 2016, Methods of Use, and Methods of Manufacture, filed on August 24, 2015 and entitled " Multiwavelength Diffraction Grating Mirrors, Methods of Use, and Methods of Manufacture & US Patent Application No. 62 / 209,290, Claims priority benefit under §119. This application is also related to U.S. Serial No. 62 / 435,676, filed December 16, 2016, entitled " Wide Field of View Skew Mirror ", filed on October 13, 2016, US Patent Application < RTI ID = 0.0 > 35 USC < / RTI > of US Provisional Application No. 62 / 407,994, Claims priority benefit under §119. Each of these applications is incorporated herein by reference.

A holographic skew mirror is a holographic optical element that reflects incident light to a reflective axis that does not have to be perpendicular to the surface where the incident light impinges. In other words, the reflection axis of the holographic skew mirror need not be parallel to or coincident with the surface normal of the holographic optical element. The angle between the reflective axis and the surface normal is referred to as the reflective axis angle and can be selected based on the desired application of the holographic skew mirror.

The terms " reflection " and similar terms are used in the present invention in some cases where " diffraction " The use of this " reflection " is consistent with the mirrored properties exhibited by the skew mirrors and helps to avoid potentially confusing terms. For example, when a grating or skew mirror is said to be structured to " reflect " incident light, a conventional artisan may prefer to say that the grating structure is structured to " Because structures are generally thought to act on light by diffraction. However, such use of the term " diffraction " will produce expressions such as " incident light is diffracted with respect to substantially constant reflection axes ", which can lead to confusion.

Thus, when incident light is referred to as being " reflected " by a grating structure, one of ordinary skill in the art will recognize that the grating structure is in effect " reflecting " light by the diffraction mechanism, taking into account the advantages of the present invention. Such use of " reflection " is not unprecedented in the optical system, since conventional dielectric mirrors are generally referred to as " reflecting " light, despite the primary role of diffraction in such reflection. Thus, those skilled in the art will recognize that most " reflections " include the characteristics of diffraction and that " reflection " by the skew mirror or its components also includes diffraction.

Embodiments of the present invention include holographic optical elements including, but not limited to, holographic skew mirrors, holographic input / output couplers, and other holographic optical reflective devices. An example is an optically reflective device comprising a grating structure present in the grating media. Such a grating structure is structured to primarily reflect incident light as reflected light, wherein both incident light and reflected light comprise a first wavelength. The incident light of the first wavelength and the reflected light of the first wavelength form an angle bisecting by the reflection axis and the reflection axis is at least one degree when incident on the lattice medium in the range of the internal angles of incidence, Lt; / RTI > Also, the reflection axis is at least 2.0 degrees different from the surface normal of the lattice medium.

In some embodiments of such an optically reflective device, the reflective axis changes less than one degree when incident light is incident on the grating medium in the range of internal angles of incidence over which the incident light spans at least 30 degrees. Similarly, the grid structure is in grid frequency over a range of at least 2.00 × 10 ⁵ radians per meter may include one or more holograms having a (| | K _G).

In some cases, both incident light and reflected light include a second wavelength that is different from the first wavelength by at least about 50 nm (e.g., the first wavelength is 50 nm, 60 nm, 70 nm, 80 nm , 90 nm, 100 nm, or more). And, in some of these cases, the incident light and the reflected light include a third wavelength that is different by at least about 50 nm from each of the first wavelength and the second wavelength (e.g., the first wavelength is 50 to 100 nm, where the second wavelength may then be 50 to 100 nm larger than the third wavelength). For example, the first wavelength may be in the red region of the electromagnetic spectrum, the second wavelength may be in the green region, and the third wavelength may be in the blue region.

The lattice structure of the optical reflective device is at least a meter of 1.68 × 10 ⁶ radians, at least a meter of 5.01 × 10 ⁶ radians, or grid frequency over a range of at least a meter of 1.24 × 10 ⁷ radians more than one having a (| | K _G) Holograms. For example, the lattice structure of the meter and greater than 5.10 × 10 ⁵ radian frequency grid that spans the range of less than 3.15 × 10 ⁷ radians per meter may include one or more holograms having a (| | K _G).

In some examples, the grating structure includes at least nine holograms. The average contiguity | K _G | of these holograms may be in the range of 5.0 × 10 ³ rad / m to 1.0 × 10 ⁷ rad / m.

An optically reflective device can be constructed or structured to act as an output coupler, wherein the incident light is incident on the grating structure from within the optically reflective device, and the reflected light comes from the optically reflective device.

The optically reflective device may further include at least one substrate adjacent to the lattice media. For example, an optically reflective device may include two substrates, with a lattice medium disposed between the two substrates. In this case, the grating medium may comprise a photopolymer medium of at least 100 [mu] m thickness, and the two substrates may transmit at least 60% of the incident light and at least 60% of the reflected light. The refractive indices of the grating medium and the two substrates may be within about 0.1 of each other.

Other embodiments of the invention include a method of using an optically reflective device. The method includes illuminating a grating structure present in the grating medium with incident light of a first wavelength. This incident light is reflected in the lattice structure to produce the reflected light of the first wavelength. The incident light and the reflected light form an angle bisecting by a reflection axis that is at least about 2.0 degrees from the surface normal of the grating medium. This reflection axis changes to less than one degree when the incident light is incident on the grating structure in the grating medium in the range of the internal incident angles spanning at least 15 degrees. In some cases, the reflection axis changes to less than one degree when the incident light is incident on the grating medium in the range of internal angles of incidence spanning at least 30 degrees.

In the examples of this method, the step of illuminating the grating structure comprises coupling the incident light into the grating medium, for example via a holographic input coupler, a prism, or an edge coupling, and an inner total reflection of the incident light in the grating medium . In other words, the grating medium can at least partially guide the incident light to the grating structure.

As noted above, incident light and reflected light may comprise a second wavelength that is different from the first wavelength by at least about 50 nm. The incident light and the reflected light may also include a third wavelength that is different by at least about 50 nm from each of the first wavelength and the second wavelength.

Examples of this method may also include coupling the reflected light out of the grating medium at an angle of about 25 degrees to the surface normal of the grating medium. The grating medium may couple this reflected light to the eye of the person in optical communication with the grating medium such that the reflected beam at least partially illuminates the human eye. In this case, illuminating the grating structure may include illuminating the grating structure with the image such that the reflected image is visible to the human eye.

Another example of the present invention includes a method of imaging. The method includes placing a grating medium including a grating structure in a state of optical communication with a human eye. These lattice media have a proximity surface that defines the surface normal. The visible image is coupled into the grating medium and guided into the grating structure through at least one total internal reflection in the grating medium. The grating structure reflects the visible image against a reflective axis that forms an angle of at least about 2 degrees with respect to the surface normal. The visible image is coupled out of the grating medium towards the human eye through the proximity surface. The visible image spans the field of view in at least about 30 degrees of free space.

Another example of the invention includes a method of writing holographic gratings in a photosensitive medium. The method includes disposing a photosensitive medium between an oblique surface of the first prism and an oblique surface of the second prism. A first beam is coupled into the photosensitive medium through the first surface of the photosensitive medium and the oblique surface of the first prism. This first beam forms a first angle with respect to the surface normal of the first surface. A second beam is coupled into the photosensitive medium through the second surface of the photosensitive medium and the oblique surface of the second prism. This second beam has a size that is substantially the same as the magnitude of the first angle and forms a second angle to the surface normal of the second surface. In some cases, the method also includes interfering the third beam and the fourth beam with the photosensitive medium to form a second holographic grating in the photosensitive medium.

Yet another example of the present invention includes a device having a holographic optical element having at least one grating structured to reflect visible light over a field of view of at least about 50 degrees in a first dimension. The field of view is measured outside the holographic optical element and is substantially centered on the surface normal of the holographic optical element. And the lattice has a lattice vector oriented at an angle of at least about 15 [deg.] To about 45 [deg.] With respect to the surface normal.

In some embodiments, the holographic optical element includes a single grating structured to reflect visible light at wavelengths ranging from about 400 nm to about 700 nm across the field of view. In other embodiments, the holographic optical element includes a plurality of gratings, each of which is structured to reflect incident light at one wavelength of visible light at different angles within the field of view. In such embodiments, the device may also include at least one light source in optical communication with the holographic optical element to illuminate the plurality of gratings with visible light.

The view may be at least about 30 [deg.] In a second dimension orthogonal to the first dimension. Also, the angle formed by the reflective axis and the surface normal may be between about 20 degrees and about 40 degrees. And, the holographic optical element may have substantially no photoinitiators sensitive to visible light.

Another aspect of the invention includes a method of reflecting light. The method includes illuminating at least one grating in the holographic optical element with visible light. The grating reflects at least a portion of the light over a field of view of at least about 50 [deg.]. This view is centered on the reflective axis which forms an angle of at least about 15 [deg.] To about 45 [deg.] With respect to the surface normal of the holographic optical element.

Yet another aspect of the present invention includes a method of producing a holographic optical element (and a generated holographic optical element). The method includes interfering the first beam and the second beam within the holographic recording medium to form a first grating. The holographic recording medium has a flat surface. The first grating is structured to reflect incident light of a first visible light wavelength over a field of view of at least about 50 [deg.]. This view is centered on the reflective axis which forms an angle of at least about 15 [deg.] To about 45 [deg.] With respect to the surface normal of the planar surface of the holographic optical element. In some cases, interfering the first beam and the second beam includes coupling the first beam into the holographic recording medium through the oblique surface of the first prism and coupling the second beam through the oblique surface of the second prism, Into the holographic recording medium.

Yet another aspect of the present invention includes a device comprising a holographic optical element having a plurality of reflective gratings. A plurality of reflection gratings, each of the reflection grating of the can, alone vector lattice to form a surface angle in the normal and about 15 ° to about 45 ° of the graphic optical element (K _G) and at least a meter of 2.00 × 10 ⁵ radians of the grid frequency ( | K _G |).

All of the above concepts and all combinations of additional concepts discussed in more detail below are part of the subject matter of the invention disclosed herein (unless such concepts are mutually contradictory). In particular, all combinations of claimed subject matter appearing at the end of the present invention are part of the subject matter of the present disclosure disclosed herein. The terms used herein, which may also appear in the context of any disclosure included herein, are to be accorded the best meaning consistent with the specific concepts disclosed herein.

Those skilled in the art will appreciate that the drawings are primarily for illustrative purposes and are not intended to limit the scope of the subject matter of the invention described herein. The drawings are not necessarily drawn to scale; In some instances, various aspects of the inventive subject matter disclosed herein may be exaggerated or enlarged in the drawings to facilitate an understanding of the different features. In the drawings, like reference numbers generally refer to similar features (e.g., functionally similar and / or structurally similar elements).
Figure 1 shows a holographic skew mirror with a relatively narrow field of view.
2A and 2B illustrate a k-space representation of the holographic skew mirror shown in FIG. 1, respectively, when and without an incident beam.
Figures 3A and 3B illustrate an in-plane holographic recording system suitable for manufacturing holographic skew mirrors.
Figures 4A and 4B illustrate k-space representations of fabricating a holographic skew mirror using the in-plane holographic recording geometry of Figures 3A and 3B, respectively.
Figures 5A and 5C show actual spatial views of an out-of-plane holographic skew mirror fill geometry.
Figures 5B and 5D show k-space representations of the actual spatial representations shown in Figures 5A and 5C, respectively.
Figure 6 is a plot showing the angular recording bands achievable both in in-plane and out-of-plane holographic skew mirror recording geometries.
Figures 7A-7C show different views of a holographic recording medium interposed between total internal Grazing-Extension Rotation (TIGER) prisms for writing holographic skew mirrors with wide fields of view .
Figure 7d shows a perspective view of TIGER prisms used in the holographic recording geometry of Figures 7a-7c.
Figures 8A-8C illustrate a holographic recording system with TIGER prisms and out-of-plane holographic recording geometries shown in Figures 7A-7C.
Figure 9 illustrates an angle correction using pairs of wedges.
Figure 10 shows a plan view of a holographic skew input / output coupler having a 60 ° diagonal view (53.4 ° horizontal view, 31.6 ° horizontal view, and 16: 9 aspect ratio) made using an out-of-plane holographic recording system.
11 shows a k-space representation of the recording beams for the first and 228 grids in the holographic skew mirror of FIG.
12 is a plot of skew mirror internal angle write bands for a 53.4 < RTI ID = 0.0 > viewfield holographic skew mirror output coupler. ≪ / RTI >
Figure 13 illustrates an experimentally realized holographic skew output coupler having a 53.4 degree horizontal view and a 31.6 degree vertical view coupled to a waveguide.
Figure 14 is a mosaic of modulation transfer function (MTF) plots of the holographic skew mirror of Figure 13;
Figure 15 shows a head-mounted display with a wide field of view holographic skew mirror.

Holographic skew mirror

FIG. 1 shows an actual spatial representation of a holographic skew mirror 100. These holographic skew mirror 100 has a holographic grating medium 110, e.g., Colorado, USA Longmont of Akonia Holographics Tapestry ^® holographic photopolymer medium from LLC, or Leverkusen, Germany Bayfol from Covestro AG material ^® Lt; RTI ID = 0.0 > HX200 < / RTI > photoreceptive self-developing photopolymer film. The grating structure 120 may include many discrete holographic gratings, each of which reflects light over a narrow range of angles and / or wavelengths.

In this case, the grating structure 120 includes many holographic gratings that define both the skew axis 121 and the reflective axis. Lattice vector for each holographic grating forms a skew angle (Ø) to the surface normal 111 of the in parallel to or match the skew shaft 121, the skew lattice axes graphic medium 110 alone. As mentioned briefly above, each holographic grating reflects light of a particular wavelength or range of wavelengths over a certain range of internal angles of incidence, wherein the internal angles of incidence are measured in the holographic grating medium 110, Are incident angles on the same grating structure 120. The axis through which each holographic grating reflects incident light is called the reflective axis.

The reflection axis of each holographic grating may differ slightly from the skew axis 121 by, for example, less than about 0.1 DEG, less than 0.01 DEG, less than 0.001 DEG, etc. depending on the wavelength. In view of this very slight deviation, the skew axis / reflection axis can be used as a skew axis when referring to the manufacture of a skew mirror (for example, when describing the recording of a hologram in a skew mirror grating medium) When referring to light reflection properties, it can be referred to as the reflection axis.

The average skew angle for the hologram (which includes the average skew angle for the set of holograms) may be substantially the same as the angle of the reflection axis, which means that the skew angle or average skew angle is 1.0, 0.1, 0.05 °, 0.02 °, 0.0167 ° (1 arcmin), or less. In view of the advantages of the present invention, those skilled in the art will recognize that the skew angle and the angle of the reflection axis can be theoretically the same. However, due to limitations of system accuracy and accuracy, shrinkage of the recording medium that occurs while recording the holograms, and other sources of error, the skew angle or the average skew angle, as measured or estimated based on the recording beam angles, May not perfectly match the reflection axis angles as measured by the reflection angles and incidence angles of light reflected by the skew mirror. This deviation occurs at a single hologram level and is inversely proportional to the thickness of the hologram. Nonetheless, even if media shrinkage and system defects contribute to errors in estimating the skew angle and the reflective axis angle, the skew angle determined based on the recording beam angles is based on the angles of the incident light and its reflection 0.1 degrees, 0.05 degrees, 0.02 degrees, 0.0167 degrees, or less of the angle of the reflection axis determined by the following equation.

In FIG. 1, an incident beam 101 'of visible light impinges on the surface 112 of the holographic grating medium 110 at an angle ? _I ' relative to the skew axis 121. This beam 101 'may be a monochromatic, multicolor, or broadband visible light beam. The holographic grating medium 110 has a refractive index that is higher than ambient air so that the incident beam 101 'is refracted at the surface 112 to form the refracted incident beam 101. The refracted incident beam 101 illuminates the volume hologram 120 at an angle [ theta] _i with respect to the skew axis 121. [ The angle [ theta] _i is also referred to as the internal angle of incidence because it is the angle of incidence on the volume hologram 120 measured inside the holographic grating medium 110. [

The volume hologram 120 reflects at least a portion of the refracted incident beam 101 at an angle ? _R with respect to the skew axis 121. The angle [ theta] _r is also referred to as an internal reflection angle and is equal to the internal incident angle [ theta] _i as shown in Fig. In other words, the skew axis 121 bisects an angle equal to twice the internal incidence angle [ theta] _i .

The reflected portion of the refracted incident beam 101 is referred to as the primarily reflected beam 103. The primary reflected beam 103 impinges on the surface 112 of the holographic grating medium 110. It is refracted at this boundary to form a primarily reflected beam 103 'that is refracted at an angle _r ' relative to the skew axis 121. The field of view of the holographic skew mirror, as measured in the free space outside the holographic grating medium 110, is determined by the range of external reflection angles ? _R ^' .

K-space representation of holographic skew mirrors

2A and 2B illustrate a k-space representation of the holographic skew mirror 100 shown in FIG. 1 in the case of and without the incident beam 101 and the primarily reflected beam 103, respectively. As will be readily understood by those skilled in the art, this k-space representation comprises a plurality of concentric circles, each of which is a k-space representation of optical propagation vectors or wave numbers vectors for light of a particular wavelength in a holographic medium, Is a two-dimensional projection of a k-sphere. The length of the wavenumber vector can be expressed as:

,

,

Here, n is the refractive index and ? Is the wavelength.

In a generally distributed medium, including the holographic grating medium 110, the wavevectors vectors (and hence the k-spherical radii) are longer than the shorter wavelengths. Thus, the innermost circle 290 represents the wavenumber vectors for the red light in the holographic grating medium 110, the second innermost circle 291 represents the wavenumber vectors for the red light in the holographic grating medium 110, The second outermost circle 292 represents the wavenumber vectors for the blue light in the holographic grating medium 110 and the outermost circle 293 represents the wavenumber vectors for the blue light in the holographic grating medium 110, And expresses the wave number vectors of the recording wavelength.

2A and 2B also show a volume hologram 120 in which the distribution of the grating vectors K _G in k-space appears as a line segmented distribution parallel to the reflection / skew axis 121. Figure 2B also shows the wave number vectors of the incident refracted beam 101 and the primarily reflected beam 103 for the lattice vector of the volume hologram. In the k-space, the wave number vector of the primarily reflected beam 103 is the vector sum of the lattice vector of the volume hologram and the wave number vector of the incident refracted beam 101.

In-plane holographic skew mirror recording system

3A and 3B illustrate a holographic recording medium 310 using a pair of in-plane recording prisms 330a and 330b (collectively, in-plane recording prisms 330) - to couple the light into it. The recording medium 310 and the substrates are interposed between the in-plane recording prisms 330 such that the signal beam 331a and the reference beam 331b, which are also referred to as recording beams 331, To be introduced into the holographic recording medium 310 at angles that produce an internal total reflection (TIR) at the substrate-air interface. The in-plane recording prisms are typically index-matched to the substrates, and a refractive-matching fluid (not shown) is formed at the interface between the prisms 330 and the substrates (not shown) to reduce reflections and reflections at the prism / Can be applied. Indeed, the refractive index-matching may mean that the refractive indices of the holographic recording medium 310, the substrates, and the prisms 330 are within about 0.1 or less.

The mirrors 350a and 350b (collectively, the mirrors 350) reflect the recording beams 331a and 331b, respectively, into the holographic recording medium 310 through the prisms 330a and 330b. Each of the mirrors 350a and 350b is oriented so that the corresponding recording beam 331a or 331b directs the recording beam to illuminate the base of the corresponding prism 330a or 330b. Recording beams 331 are refracted at the air / base interface and then propagated into the holographic media 310 where they interfere to produce a (reflective) grating that is recorded by the holographic recording medium 310 . The holographic recording medium 310 and the prisms 330 are translated back and forth along the z _G axis with respect to the mirrors 350 using a translation stage (not shown) Is rotated to record a series of gratings that make up the skew mirror as shown.

Figures 3a and 3b also illustrate global or recorder coordinates ( x _G , y _G , z _G ) for the case of in-plane prisms. The origin of the global coordinates shown in FIGS. 3A and 3B is defined as being at the center of the output coupler at the center of the recording layer of the holographic recording medium 310. Global angle (θ _G) for recording is defined as the angle of the recording beam (331a) on the x-axis _G in the holographic recording medium 310 / prism (330a). Note that the nominal angle of the other recording beam 331b is 180 ^o -? _G (not shown), so that the recorded lattice vectors are substantially aligned with the x _G axis. Alone angle between graphical recording medium (310) / prism (330a) in the recording beams 331, or bimgan angle is denoted as α. The global skew angle is the angle between the x _G and z axes, _denoted as Ø _G.

In view of the advantages of the present invention, those skilled in the art will appreciate that standard coordinates (Cartesian coordinates in the reference frame of the holographic recording medium 310) can be transformed into global coordinates for the case of in-plane prisms by I will confirm

Conversion of global coordinates to standard coordinates can also be easily derived.

In the global coordinate frame, the surface normal of the graphic recording medium 310 alone, forms an angle (Ø _G) (global skew angle) for the _G z axis. In other words, the angle between the holographic recording medium 310 and the z _G axis sets the skew axis of the holographic skew mirror. This skew axis can be changed by rotating the holographic recording medium 310 and the prisms 330, for example, with respect to the recording beams 331, using an appropriate combination of stages and mounts.

For more information on methods of making and using holographic skew mirrors and holographic skew mirrors, refer to Skew Mirrors, filed June 6, 2016, the entirety of which is incorporated herein by reference, Methods of Use, and Methods of Manufacture ", which is incorporated herein by reference in its entirety.

Constraints on field of view by in-plane recording

Unfortunately, in-plane recording systems can not generally be used to fabricate holographic skew mirrors with wide fields of view. This is due to constraints on the wavelengths and geometry of the beams used to record the volume holographic gratings for the holographic skew mirror. These constraints include the difference between the skew angle, the grating frequency that determines the angle of reflection, and the difference between the write beam wavelength in the dark blue region (typically 400 nm to 430 nm) of the normal electromagnetic spectrum and the read beam wavelength in the visible region of the electromagnetic spectrum .

As briefly mentioned above, the grating frequency (| K _G |) of the holographic grating, which can be expressed as the magnitude of the lattice wavevector, determines its reflection angle: the smaller the grating frequency, the greater the reflection angle. In the case of a skew mirror, it is necessary to increase the range of grating vector sizes in the grating structure to increase or widen the field of view. However, both the refractive index and the skew angle of the holographic recording medium limit the range of recording angles that can be accessed through in-plane prisms, such as those shown in Figs. 3A and 3B. In the case of certain combinations of skew angles and angles between recording beams, one or both of the recording beams become parallel to the holographic recording medium surface, which, if not impossible, interferes with recording beams in the holographic recording medium It can be difficult.

To see how these geometric constraints limit the field of view of the holographic skew mirror, consider the in-plane recording system 300 shown in Figures 3A and 3B. As shown in FIG. 3B, one recording beam 331b 'makes a steep (higher) surface angle with respect to the surface of the recording medium 310 than that made by the other recording beam 331a'. Increasing such an angle of the land reduces the spatial frequency (size) of the holographic grating recorded by the holographic recording medium, which in turn increases the field of view of the skew mirror. Unfortunately, increasing the ground angle can degrade the recording quality because it enlarges the refractive index mismatching and aberration effects between the prisms 330 and the holographic recording medium 310.

In addition, Snell's Law can limit the maximum surface angle (exact limits depend on the recording wavelength, the refractive indices of the recording medium and the surrounding medium, and the skew angle). Exceeding this limit, the recording beam 331b 'may be reflected at it instead of coupling into the holographic recording medium 310. The upper limit for the ground angle may limit the ability to record lower frequency holograms, which may limit the view of the skew mirror for some colors, especially for large skew angles.

Figures 4A and 4B show k-space representations of in-plane record geometry in Figures 3A and 3B, respectively. In Figure 4a, the recording beams (331a, 331b) will alone be incident on the graphic recording media, their frequency vectors alone having bimgan angle (α) lattice vector (K _G), is formed parallel to the skew axis 421, the Record the graphical grid. 4B, the recording beams 331a 'and 331b' are incident on the holographic recording medium so that their wavefront vectors form an inter-beam angle α ' and a grating vector K _G (which is also parallel to the skew axis 421) &Apos;')< / RTI >

The size of the grating vector determines the internal angle of incidence (s) at which the corresponding holographic grating reflects the incident light. Holographic gratings with smaller gratings reflect light of larger internal angles of incidence as measured from the skew axis and holographic gratings with larger gratings reflect light of smaller internal angles of incidence as measured from the skew axis . The maximum possible grid vector is recorded when the wavenumber vectors of the recording beams are antiparallel and aligned with the skew axis 421. The corresponding holographic grating retroreflects the light incident on the grating medium along the skew axis 421 (" vertical incidence " for the holographic skew mirror).

According to a reduced angle between the recording beams (331b ') and the x-axis, bimgan the angle (α) it is also reduced, thereby reducing the size of the grating vector (K _G) to increase the available field of view. The angle between the recording beam 331b 'and the x- axis is such that the recording beam 331b' is parallel to the surface of the holographic recording medium 310 instead of being refracted into the holographic recording medium 310 Lt; / RTI > In other words, a limitation occurs when the lattice vector of the recording beam 331b 'is aligned with k _x , that is, when the recording beam 331b' is parallel to the surface of the holographic recording medium 310. At this time, the recording beam 331b 'no longer interferes with the other recording beam 331a' in the holographic recording medium 310, thereby recording the reflection grating. This limits the minimum size of the grating vector and thus the field of view. While rotating the skew axis can compensate for this effect, it also limits the range of allowable skew angle / field combinations.

In summary, FIGS. 3A, 3B, 4A and 4B illustrate a tradeoff between the permissible field of view and acceptable skew angle in the in-plane recording geometry: In general, It is possible to have a field of view, but not both.

The minimum accessible angular difference between the recording beams depends in part on the wavelengths of the recording beams and reading beams and the dispersion of the holographic recording medium. Most holographic recording media are optimized to record lattices at deep blue wavelengths, e.g., 405 nm, and to be insensitive to visible light of longer wavelengths. However, it is impossible or difficult to interfere the dark blue beams in the holographic recording medium with angular differences small enough to produce reflective gratings at spatial frequencies that are low enough to produce a wide field of view at visible wavelengths in the in-plane recording system .

Increasing the write beam wavelength will alleviate this problem, but will also require a holographic recording medium that is sensitive to longer wavelength light. However, increasing the sensitivity of the holographic recording medium to longer wavelength light will make the holographic recording medium more susceptible to incomplete bleaching at visible light wavelengths. This is because the holographic recording medium having photoinitiators sensitive to visible light can be polymerized when exposed to visible light and thus less suitable for manufacturing holographic optical elements operating at visible light wavelengths. Also, photoinitiators sensitive to visible light can cause undesirable visible light absorbance in the lattice media. This will make the holographic recording medium less suitable for use in a skew mirror that reflects light of visible light wavelengths.

Out-of-plane recording for manufacturing a wide-angle holographic skew mirror

As described above, the geometry limits the range of accessible beam angles (and hence the maximum field of view) for writing holographic skew mirrors by in-plane recording systems. However, the inventors have recognized that it is possible to access smaller inter-beam angles by tilting the surface normal from a plane accessed by the in-plane recording system. In other words, it is to skew the medium 90 ^o rotation about the axis thereby mitigate the constraints shown in Figure 3a, Figure 3b, Figure 4a and 4b.

Figure 5a to Figure 5d, the holographic recording medium x of (310) - y _G recording axis centered beams in the z plane (531a, 531b), (collectively, the recording beams 531) by rotating the in-plane recording Lt; RTI ID = 0.0 > holographic grids < / RTI > shorter than possible in a geometric shape. Figs. 5A and 5C are graphs showing the relationship between z _G Shows the actual spatial views at different views of the recording beams 531 that are incident on the holographic recording medium 510 that is tilted with respect to the axis (i.e., the y-axis of the holographic recording medium 510). Recording beams 531 x _G - is rotated in the plane _G z, _G x - it writes the grating vector lies also in _G z plane.

Figures 5B and 5D are k-space representations of the actual spatial representations shown in Figures 5A and 5C, respectively. As shown in both FIGS. 5B and 5D, the wavenumber vectors of the recording beams 531 lie within the x _G - z _G plane, which means that the k-number of the recording beams 531 representing the momentum of the recording beams in the holographic recording medium 510, To form an off-axis slice of the sphere 591. As in the in-plane recording geometry, changing the angle of beam between recording beams 531 changes the length of the grating vector. The longest lattice vector (maximum | K _G |) is written when the recording beams 531 are propagating in the opposite direction along the x _G axis, and recording beams 531 'are recorded along the z _G axis (y axis) The smallest grid vector (minimum | K _G |) is generated. This is an index angular condition for both recording beams 531 'as shown in FIG. 5A.

Those skilled in the art will recognize that Figures 5A-5C illustrate only one of many possible orientations of write beams and skew angles. The skew angle and each recording beam can be adjusted as desired within the constraints imposed by the write wavelength and the refractive index of the holographic recording medium, in order to record the holographic gratings at a great variety of spatial frequencies. The exact number of the holographic gratings and the spatial frequencies depend, among other things, on the desired field of view of the holographic skew mirror.

In-plane vs. out-of-plane recording

Figure 6 is a plot illustrating the capabilities of out-of-plane recording prisms for a particular recording geometry. This plot shows the spatial grating frequencies for a waveguided head mounted display (HMD) skew mirror output coupler with skew axis Ø = -30.25 °, which supports a horizontal field of view of 53.4 °. The horizontal axis is the lattice frequency (in rad / m units) and the vertical axis is the Bragg-matching angle for the lattice vector / skew axis. The five curves illustrate the Bragg-matching angle for five different represented wavelengths: Curve 690 is for the wavelength (405 nm) at which holograms are recorded; Curve 691 is for 463 nm (blue); Curve 692 is for 522 nm (green); Curve 693 is for 622 nm (red); Curve 694 is for 860 nm. The horizontal lines at 47.75 DEG and 12.75 DEG demark a range of spatial grid frequencies required for the red, green, and blue wavelengths, coded by color.

According to the in-plane recording prisms, the reference beam index angular condition occurs when the write wavelength curve intersects 59.75 DEG (= 90 DEG -Ø), as indicated by the hollow arrow. This indicates that the in-plane recording system can not record the gratings on the left side of the cheeky arrow. The gratings near the right side of the hollow arrow may experience degradation because the reference beam is incident on a refractive-matched boundary at a very shallow angle.

However, according to the out-of-plane recording, the ground angular conditions do not occur until the write wavelength curve crosses 90 degrees at the left edge of the plot. The lowest writing angle, indicated by hollow arrows, makes angles of about 22 degrees with respect to the inner boundaries for both the reference beam and the signal beam, which is easily feasible.

TIGER prism for the out-of-plane holographic skew mirror recording system

7A-7C illustrate different aspects of an out-of-plane holographic recording system 700 that can record holographic skew mirrors having wide fields of view. In this holographic recording system 700, the holographic recording medium 710 is arranged between a pair of full internal surface angularly expanded TIGER prisms 730a, 730b (collectively, TIGER prisms 730) . The holographic recording medium 710 may also be interposed between a pair of transparent substrates (not shown), wherein a refractive index-matching fluid is disposed on the surfaces of the transparent substrates in contact with the prisms 730 . Such substrates can transmit 60%, 70%, 80%, 90%, or more of light of visible light wavelengths. TIGER prisms 730 make it possible to introduce recording beams into the holographic recording medium 710 at an inaccessible angle using in-plane recording geometries because of the total internal reflection (TIR) and surface angle constraints.

Figs. 7A to 7C (and Figs. 5A to 5D) also show the symmetry of the recording beams 731a and 731b (531a and 531b in Figs. 5A to 5D). More specifically, these figures show that the magnitudes of the angles between the recording beams and the surface normals of the holographic recording medium 710 are substantially the same. In other words, when the recording beam 731a forms a first angle (for example, 32 degrees) with respect to the surface normal of the holographic recording medium, the surface normal of the recording beam 731b and the holographic recording medium have the same size (E.g., -32 [deg.]). (Here, the recording beams 731 are incident on the surfaces of the parallel holographic recording medium 710, and therefore have matching / parallel surface normal lines.) This is the same as that shown in Figs. 5A to 5D Likewise, as the recording beams 731 are rotated relative to the holographic recording medium 710, they are held.

As shown in FIG. 7D, each TIGER prism 730 has prism surfaces 732a and 732b (collectively, major surfaces 732) that are inclined relative to the prism base. In this example, the main surface 732 of each TIGER prism 730 is parallel to the holographic recording medium 710 when the prism 730 and the holographic recording medium 710 are present in the skew mirror recording system And immediately adjacent hexagonal faces. The tilting of the main surface 730 makes it possible to access out-of-plane recording beam angles and skew angles as illustrated in Figs. 5A to 5D.

The TIGER prisms 730 can be visualized by assuming that the glass rectangular parallelepiped, or the right prism, is cut into two sections. The cutting in the rectangular parallelepiped forms the diagonal line connecting the adjacent side surfaces (prism surfaces 734a and 734b) of one of the surfaces of the rectangular parallelepipeds to the other two sides (prism surfaces 736a and 736b) of the opposite surface of the rectangular parallelepiped, Lt; RTI ID = 0.0 > diagonal < / RTI > The resulting sections of the rectangular parallelepiped form a matched pair of TIGER prisms 730.

In practice, the TIGER prisms may be of any suitable shape as long as they have angled facets or facets angled to enable access to out-of-plane recording angles. For example, a TIGER prism may be formed as a section of any suitable polyhedron including parallelepipeds and an angle of horn (geometric prisms). Likewise, the facets / facets can be oriented or angled as desired, and it is not necessary to necessarily cause a symmetric division of the facets. The surface (and the holographic recording medium) may also be curved, for example, to form at least a portion of a spherical, cylindrical, or conical surface. Other surfaces are also possible, including optionally curved or warped surfaces.

The beveled surfaces 732 and other surfaces (e.g., surfaces 734 and 736) of the TIGER prisms may be used to define the two different coordinate systems shown in Figures 7A-7C. As in the in-plane recording system shown in FIGS. 3A and 3B, the axes ( x _G , y _G , z _G ) are the Cartesian coordinates in the reference frame of the TIGER prisms 730. The axes ( x , y , z ) are orthogonal coordinates (also known as standard coordinates) in the reference frame of the holographic recording medium 710, where the z axis extends perpendicular to the surface of the holographic recording medium 710 do. The axes ( x , y , z ) are the actual spatial equivalents of the k -space axes ( k _x , k _y , k _z ) shown in Figures 5A-5D.

7C illustrates how the standard coordinate axes are aligned in prisms of a skew mirror writer for the case of TIGER prisms. More specifically, it shows a view of TIGER prisms 730 along the z _G axis, wherein the holographic recording medium 710 is interposed therebetween at the same angle as?. Note that in the illustrated geometry, Ø has a negative sign (eg, Ø = -30.25 °). Since the holographic recording medium 710 is tilted with respect to the y _G axis, in the case of the TIGER prism recording system 700, the conversion from standard coordinates to global coordinates is performed using the in-plane recording system 300 shown in Figs. 3A and 3B ). In view of the advantages of the present invention, those skilled in the art will recognize that for the case of TIGER prisms, the standard coordinates can be converted to global coordinates by equation (2): < EMI ID =

Recording beam (331b), "in-plane" configuration of the surface, to impose an angle of the worst case for each of Figs. 3a and 3b and in contrast to, TIGER prisms 730 is the central axis is x _G recording medium (710) To divide the " difference " between the land angles of the recording beams 731a and 731b. Both the TIGER prism configuration 700 and the in-plane configuration 300 may record the grating vectors aligned with the x _G axis, thus causing equivalent written skew mirrors. However, the TIGER prism configuration 700 can also access smaller recording angles and thus record gratings with lower spatial frequencies than in-plane configurations.

8A-8C illustrate a TIGER prism-based skew mirror writer (FIG. 8A) that implements the recording geometry 700 shown in FIGS. 7A-7C for producing wide field holographic skew mirrors using TIGER prisms 730 800). It includes mirrors 850a and 850b (collectively, mirrors 850) that direct recording beams 731a and 731b to a holographic recording medium 710, 860) to the TIGER prisms 730. The TIGER prism-based skew mirror recorder 800 also includes stages for adjusting the angular and translational alignment of the recording beams 731 relative to the holographic recording medium 730. These stages include three goniometers 870a through 870c (collectively, goniometers 870), a vertical translation stage 880, rotation stages 872a and 872b for each mirror 850, (Collectively, rotation stages 872), and a horizontal translation stage (not shown) for moving the loaded holographic recording medium 710 and TIGER prisms 730 back and forth.

For in-plane recording prisms, refraction correction and other adjustments are typically performed by rotating the mirrors 350 and translating the holographic recording medium. However, according to the TIGER prisms, there may be desired out-of-plane angular adjustments that can not be made by rotating the mirrors 850 or translating the holographic recording medium. This is why other actuators, such as goniometers 870 and vertical stage 880, can be mounted on the TIGER prism skew recorder 800 to perform out-of-plane angular adjustments.

The first goniometer 870a is located below the rotating mirror 850a and is located above the first rotating stage 872a so that the mirror 850a of the mirror 850a centered on the axis substantially aligned with the horizontal midline of the mirror surface Allow rotation. The actuation of the first goniometer 870a causes the recording beam 731a to be reflected up or down from the x _G - z _G plane up to several degrees. Similarly, the second goniometer 870b is positioned such that the recording beam 731b is also reflected either upwards or downwards independently by the mirror 850b. Similarly, the third goniometer 870c causes the mirror (unlabeled) on the upstream side of the rotating mirror 850a to be turned up and down so that the first and third goniometers 870a and 870c ) Can be combined to create any desired beam 731a height and vertical angle combination (within mechanical limits). Vertical stage 880 may raise or lower the height ( y _G coordinate) of the entire prism package 860, including recording medium 710.

An additional way to perform the correction is to create the desired height and vertical angle combination in substantially the same manner as the first and third goniometers 870a, 870c produce the desired height and vertical angle combinations And to add an additional goniometer (not shown) to adjust the path of the recording beam 731b.

Figure 9 illustrates another method for achieving such a refractive correction using a pair of optical wedges in the rotating mounts that can be aligned with respect to each other to achieve angles within twice the cone of the size that one wedge achieves do.

In view of the advantages of the present invention, those skilled in the art will recognize that such an arrangement will cause small, arbitrary, vertical angular components to also be introduced into each recording beam while maintaining overlap between the beams and the recording medium. For example, the goniometer 870b may be used to set the desired vertical angle component of the reference beam 731b, and then the vertical stage height may be set such that the reference beam 731b passes through the desired recording area. The goniometers 870a and 870c can then be set such that the signal beam 731a is introduced at the desired vertical angle at a height that matches that set by the vertical stage. Typically, only a few degrees of vertical angular range and a few centimeters of vertical motion will suffice to implement the desired refraction correction and other adjustments.

Choosing Beam Angle and Skew Angle for Out-of-Plane Holographic Skew Mirror

The out-of-plane skew mirror recorder 800 shown in Figs. 8A to 8C can be used to manufacture a wide-field holographic skew mirror by recording one or more volume holograms within the volume of the holographic recording medium. The inter-beam and skew angles selected for recording these holograms depend on the operating wavelength range and the desired field of view of the holographic skew mirror.

In some cases, the out-of-plane skew mirror writer 800 can be used to record many discrete gratings, each of which reflects primarily one or more wavelengths of light across different narrow angles of incidence. If these ranges of incident angles are overlapping or close to each other, the gratings will reflect light over a wide range of incident angles to provide a wide field of view. Alternatively, the holographic skew mirror may include a holographic grating that is written by successively recording interference between a pair of recording beams as the beam angle changes. This successively recorded grating reflects light over a wide range of angles of incidence to provide a broad field of view. For example, to create a holographic skew mirror that reflects light over a range of incident angles but not others, or that reflects light over a range of wavelengths but not others, other combinations of gratings It is also possible.

In at least one example, the vector form of Snell's law can be used to calculate the direction of the recording beam at refraction at the inner boundary between the recording medium and the prism. As will be understood by those skilled in the art of holography, the vector form of Snell's law describes what happens to rays that impinge on an optical boundary, such as a prism surface, at an angle that includes non-zero components in more than one coordinate axis . The vector form of Snell's law provides the resulting refraction at such a surface as follows:

은 광학 경계의 단위 법선 벡터이고,

및

는 정규화된 입사 및 굴절된 광선 방향 벡터들이고, n ₁ 및 n ₂ 는 제1 및 제2 재료들의 굴절률들이다. TIGER 프리즘들의 경우, 그러한 굴절은 전형적으로 글로벌 좌표계의 하나 초과의 축에서 0이 아닌 성분들을 포함한다.here,

Is the unit normal vector of the optical boundary,

And

Are normalized incident and refracted ray direction vectors, and n ₁ and n ₂ are the refractive indices of the first and second materials. For TIGER prisms, such refraction typically includes non-zero components on more than one axis of the global coordinate system.

)가 요구될 수 있다. 매체(710) 내에서 내부 각도(θ_G)로

를 생성하기 위해 적용되어야 하는 외부 각도를 결정하기 위하여. 이 목적을 위해, 스넬의 법칙은 기록 프리즘(730a)과 기록 매체(710) 사이의 내부 경계에 적용되어,

, 즉, 프리즘(730a) 내의 광선 방향 벡터를 결정할 수 있다(작은 굴절률 미스매칭이라도 상당한 굴절을 생성할 수 있음에 유의한다). 이어서, 스넬의 법칙은 기록 프리즘(730b)의 외부 표면에 다시 적용되어,

로부터 외부 광선 방향 벡터(

)를 결정할 수 있다. 따라서, 외부 광선 방향 벡터(

)는 θ _G 를 직접 결정하는데, 이는 회전 미러(850b)에 의해 설정될 수 있다. 유사하게, 회전 미러(850a)에 대한 각도는, 기록 프리즘(730a)의 내부 및 외부 표면들을 통해 추적함으로써 원하는 참조 광선 방향 벡터(

)로부터 결정될 수 있다.In some embodiments, refractive index mismatches between optical elements, such as a recording medium and a recording prism, are corrected using Snell's law. For example, for the signal beam within the recording medium 710 (Figures 7A-7D and Figures 8A-8C) during recording exposure,

) May be required. In the medium 710 to the internal angle (θ _G)

To determine the external angle that should be applied to generate the angle. For this purpose, Snell's law is applied to the inner boundary between the recording prism 730a and the recording medium 710,

, I.e., the ray direction vector in the prism 730a (note that even a small refractive index mismatch can generate significant refraction). The Snell's law is then applied again to the outer surface of the recording prism 730b,

To the outer ray direction vector (

Can be determined. Thus, the outer ray direction vector (

) Directly determines ? _G , which can be set by the rotating mirror 850b. Similarly, the angle to the rotating mirror 850a may be determined by tracing through the inner and outer surfaces of the recording prism 730a,

). ≪ / RTI >

In some embodiments, adjustments to recording angles may be performed for reasons other than refractive correction. Examples of other adjustments include dispersion compensation, media shrink precompensation, and empirical adjustments to improve the modulation transfer function (MTF) or color plane separation. For example, such adjustments may be made to compensate for device error, contraction, refractive index mismatch, and the like. This error can be empirically determined by writing a complete test skew mirror with (incomplete) holograms and identifying the defects of the holograms by measuring the angular dispersion of the test skew mirror as a function of wavelength. These measurements can be used to adjust the design angles. Once the design angles have been adjusted, it is possible to record virtually defect-free holographic skew mirrors.

Wide field holographic skew mirror

Indeed, the out-of-plane skew mirror recorder can create a holographic skew mirror with a wide field of view by recording one or more (e.g., several tens, hundreds, or even thousands) of holographic grids in the holographic recording medium. Writing discrete sets of gratings over a series of exposures, in contrast to a single grating at a single continuous exposure using angular scanning beams, offers several advantages. First, it reduces the need to suppress or compensate for vibrations during exposure. Second, compared to continuous gratings, discrete gratings preserve the change in refractive index (DELTA n ) at the expense of spectrally subsampling the incoming light (discrete gratings reflect the light illuminating the skew mirror) Function). Third, by selecting the lattice spacing to match the spectrum of the light source, the device becomes more efficient.

Figure 10 shows a wide field of view holographic input / output coupler 1000 fabricated using an out-of-plane fill geometry. The holographic skew input / output coupler 1000 includes a holographic grating structure 1020 that is recorded in a holographic grating medium 1010, which may be about 100 micrometers thick or thicker. The grating structure 1020 includes 228 gratings, each of which is written at a different inter-beam recording beam angle, and thus has a different grating frequency (| K _G |) at the recording wavelength. These gratings are oriented with respect to the skew axis 1021 which forms a skew angle of about -30.25 占 with respect to the surface normal 1011 of the holographic grating medium 1010. [ In practice, skew angles greater than other skew angles are possible, such as 2.0, 5.0, 10.0, 15.0, 30.0, 45.0, 60.0, The skew angles may range from about 15.0 DEG to about 45.0 DEG (e.g., from about 20.0 DEG to about 40.0 DEG, from about 25.0 DEG to about 35.0 DEG, from about 27.5 DEG to about 32.5 DEG, and the like).

Together, the gratings together cause the holographic squeak mirror 1000 to be positioned at an angle of incidence in the range of 13.1 to 47.6 degrees with respect to the range of incident angles ? _RAI = 34.5 degrees, as measured from the reflective axis 1021, Thereby causing the incident light to be reflected on the substantially constant reflective axis 1021. This corresponds to the field of view as measured in air outside the holographic grating medium at about &thetas; _FOV = 54.3 DEG. Light rays that propagate within the shaded area 1001, which spans a range of angles (an angular range of about 34.5 DEG) from 13.1 DEG to 47.6 DEG with respect to the skew axis 1021 illuminates the grating structure 1020. The grating structure 1020 mainly reflects this light to the shaded area 1003 that extends over the same angular range (-13.1 DEG to -47.6 DEG) on the other side of the skew axis 1021. [ The primarily reflected light for the third shaded area 1003 is refracted into a fourth shaded area 1003 'that spans a horizontal view of about 54.3 ° at the surface 1020.

10, it can be seen that incident light along a ray 1091 of an angle of 47.6 degrees measured from the skew axis 1021 is directed along a ray 1093 symmetrical to the ray 1091 relative to the skew axis 1021, (1020). ≪ / RTI > This primarily reflected light 1093 is refracted along the light ray 1093 'at the surface 1012. Similarly, incident light along ray 1081 'is totally internally reflected at surface 1012 of holographic skew mirror 1000 along ray 1081 at an angle of 13.1 ° measured from skew axis 1021. The grating structure 1020 reflects this incident light along a beam 1083 symmetric to the beam 1081 with respect to the skew axis 1021. This primarily reflected light 1083 is then refracted along the ray 1083 'at the surface 1012.

FIG. 11 shows a k-space representation of the grating vectors for the first grating (K _G1 ) and the 228th grating (K _G228 ), along with the _wavevectors for the recording beams used to record the gratings. The lattice and wavenumber vectors are shown with respect to k-sphere 1191 for a holographic grating medium 1020 having a refractive index of about 1.5471 at a recording wavelength of 405 nm. When projected in a plane, the edges of the lattice and wavenumber vectors lie on the ellipse. The first and second recording beam wave number vector of the first grating (R1 _1, R2 ₁₎ are, respectively, about 4.1 × 10 ⁷ rad / m axis of reflection (10 21) to produce a first grating having a grating frequency of the Lt; RTI ID = 0.0 > 32. < / RTI > The wavenelve vectors for the 228th grids (R1 ₂₂₈ , R2 ₂₂₈ ) are respectively 64.1 ° and 115.9 ° relative to the skew axis 1021 to produce a 228 grating with a grating frequency of about 2.1x10 ⁷ rad / m Lt; / RTI > of the holographic grating medium. Each lattice vector forms an angle of -30.25 with respect to the surface normal 1011.

The lattice vector in the lattice structure (1020) of Figure 10 are, and over a range of grating frequencies extending to about 2.0 × 10 ⁷ rad / m. Other grating frequencies and ranges of grating frequencies are also possible; In practice, the difference between the range of the grid frequency, or up to the grid frequency and the minimum grid frequency may be approximately 2.00 × 10 ⁵ radian to meter about 3.15 × 10 ⁷ radians per meter (for example, per meter of about 2.00 × 10 ⁵ radians, per meter 1.68 × 10 ⁶ radians, per meter 5.01 × 10 ⁶ radians, per meter 1.24 × 10 ⁷ radians, per meter 3.15 × 10 ⁷ radians, or any other value or sub-range).

The gratings may be uniformly or non-uniformly spaced in the k-space. About 2.1 × 10 ⁷ rad / m to about 4.1 × 10 ⁷ In the case of the approximately 228 uniformly spaced grid having a grid frequency in rad / m, the difference in lattice frequency between adjacent lattice vectors of about 8.68 × 10 ⁴ rad / m. Other interval containing interval in the range of about 5.0 × 10 ³ rad / m, and 1.0 × 10 ⁷ rad / m are also possible. For example, if the holographic skew mirror should reflect light at some wavelengths or angles but not others, then non-uniform spacing is also possible. For example, the grating frequencies may be selected based on the spectrum of the incident light and / or the range of expected incident angles for increased efficiency.

Since each grating has a different grating frequency, each grating reflects light from different angles of incidence with different principal reflection angles. The range of possible angles of incidence depends on the range of grating frequencies and determines the field of view. For example, each grating can have one wavelength (e.g., 460 nm, 518 nm, or 618 nm), two wavelengths (e.g., 460 nm and 518 nm or 518 nm and 618 nm), three wavelengths For example, 460 nm, 518 nm, and 618 nm), or higher wavelengths. The gratings can reflect light in visible light wavelengths, near-infrared (NIR) wavelengths, near-ultraviolet wavelengths, or combinations thereof. This enables the skew mirror to reflect narrowband light (e.g., light from a laser), broadband light (e.g., light from an organic light emitting diode (OLED)), and even natural light (e.g., sunlight).

In the case of input / output couplers, for example as shown in FIG. 10, the skew axis may be selected to couple light into or out of the grating medium at an angle close to the surface normal. In this case, the skew angle may be based on the critical angle for total internal reflection of about 40.81 degrees at the boundary between air and the lattice medium (e.g., n = 1.53 at visible light wavelengths).

Table 1 lists the recording beam angles and the grating frequencies for each of the 228 uniformly spaced gratings. The first recording beam angle? _R1 and the second recording beam angle? _R2 are for a skew axis having a skew angle of -30.25 degrees with respect to the surface normal of the recording medium. Thus, the lattice vectors listed in Table 1 are oriented at -30.25 degrees relative to the surface normal of the recording medium, which is referred to as the grating medium after all 228 gratings have been recorded. As it illustrated in Figure 7b, except that the θ θ _R1 and _R2 are measured in a non-prism 730, the medium (710), θ _R1 and θ _R2 is similar to the θ and θ _{GR1 GR2,} respectively.

Collectively, the 228 gratings in Table 1 reflect incident light of 460 nm, 518 nm, and 618 nm with respect to their reflective axes at an incident angle in the range of 13.1 to 47.6 degrees (a range of 34.5 degrees) for a substantially constant reflective axis . The reflection axis has a reflection axis angle of -30.25 degrees with respect to the surface normal. The gratings can be grouped into three overlapping subsets, each of which is structured to reflect incident light of a particular wavelength with respect to the reflection axis, in the range of incident angles.

Subset 1 comprising gratings 1 through 146 may be formed at an angle of incidence in the range of 13.1 to 47.7 degrees for a substantially constant reflective axis, at or near 460 nm (e.g., in the 20 to 40 nm band centered at 460 nm) (Which may be referred to as a probe beam) with respect to its reflective axis. Lattice 1 through grating 228 (i.e., all the gratings in Table 1) collectively reflect incident light at 460 nm in the range of 13.1 to 59.8 degrees (range of 46.7 degrees) for a substantially constant reflective axis, And can be reflected with respect to the axis. The range of 13.1 to 47.6 degrees is of interest for structured skew mirrors to reflect blue, green, and red light at a common incident angle to a substantially constant reflective axis.

Subset 2 comprising gratings 53 through 182 is structured to reflect 518 nm incident light with respect to its reflective axis at incident angles ranging from 12.8 to 47.7 degrees for a substantially constant reflective axis. Collectively, gratings 43 through 228 can reflect 518 nm of incident light with respect to their reflective axis at incident angles in the range of 3.1 to 55.6 degrees (a range of 52.5 degrees) with respect to a substantially constant reflective axis. The ranges 13.1 to 47.6 are of interest for the purposes of this discussion.

Subset 3 comprising gratings 120 through 228 is structured to reflect incident light at 618 nm with respect to its reflective axis at incident angles ranging from 12.5 to 47.6 degrees with respect to a substantially constant reflective axis. Gratings 112 through 228 are structured to reflect incident light at 618 nm with respect to its reflective axis at incident angles in the range of 3.0 to 47.6 degrees (a range of 44.6 degrees) with respect to a substantially constant reflective axis. The ranges 13.1 to 47.6 are of interest for the purposes of this discussion.

At least gratings 198 to 228 can not be recorded using in-plane recording as illustrated in FIGS. 3A and 3B because the in-plane recording geometry causes unacceptable write beam angles of 90 degrees or more with respect to the surface normal of the recording medium . Practically speaking, even though gratings 115 to 198 are theoretically possible, it is likely to be a problem using the in-plane architecture because the recording beam angles approach the land angular condition (i.e., at 90 degrees Because it is approaching). As exemplified in Figs. 7A-7C, out-of-plane recording using TIGER prisms makes it possible to write all the gratings in Table 1.

Select recording beam angle and exposure time

Computer code may be used to calculate write beam angles and exposure times to produce a holographic squirrel with out-of-plane fill geometry. The sub-pieces of the computer code calculate horizontal and vertical fields of view from the diagonal field of view. As noted above, this holographic skew mirror 1000 has a 60 [deg.] Diagonal field of view (measured outside the holographic recording medium 1020). When the variable g.aspect is 9/16, it also has an aspect ratio of 16: 9, which is common for many displays:

g.dFoV = 60; % Diagonal angle

g.dia = 2 * tand (g.dFoV / 2); % diagonal size at dist = 1.0

g.width = g.dia * cos (atan (g.aspect));

g.height = g.dia * sin (assign (g.aspect));

g.vFoV = 2 * atand (g.height / 2);

g.hFoV = 2 * atand (g.width / 2);

The 60 [deg.] Diagonal field of view and the 16: 9 aspect ratio correspond to a 53.4 [deg.] Horizontal field of view and a 31.6 [deg.] Vertical (Bragg degeneration) field of view (also as measured from the outside of the holographic recording medium). (The choice of orientation may be arbitrary and invert, i. E., The horizontal field of view may be 31.6 and the vertical field of view may be 53.4). A holographic recording medium having a refractive index of about 1.5 (e.g., n = 1.53) The range of horizontal incidence angles on the holographic grating measured inside the medium is about 35 degrees (e.g., 34.17 degrees).

Figure 12 illustrates a set of curves generated by different computer codes, illustrating holograms (holographic gratings) for each color band. These curves represent the skew mirror internal angular wave bands 1201a through 1201e for the holographic output coupler with a 53.4 degree horizontal view. Left bands 1201a represent holograms that reflect red light. Middle bands 1201c represent holograms used for all three color bands. Left middle bands 1201b represent holograms shared for the green and red bands. The right middle bands 1201d represent holograms shared for the blue and green bands. The right bands 1201e represent holograms that reflect blue light.

The code also generated a table of recording parameters, shown in Table 1 below. The parameters were selected to support a 53.4 ° horizontal field of view for the output coupler in red-green-blue (RGB) color bands centered at 620 nm, 520 nm, and 460 nm, respectively.

The 228 rows of Table 1 correspond to 228 exposures for programming the skew mirror using the out-of-plane fill geometry and system shown in Figures 7A-7D and 8A-8C. The first column, the global angle, represents the angle [theta] _G of the signal beam 731a (Figure 7A) relative to the x _G axis within the media, which is set by the rotating mirror 850a (Figure 8A). The rotating mirror 850b is set to transmit the reference beam 731b at an angle of 180 [deg.] - [theta] _G inside the medium. An adjustment angle of row 3 is used to set the goniometers 870 to produce out-of-plane angular components shown for both beams 731 inside the media. The adjustments have the same size but opposite signs for the two beams 731 so that the signal beam is transmitted at an upward angle or the reference beam is delivered at the same downward angle or vice versa. The linear stage and vertical stage 880 are set to center the recording medium 710 at the intersection of the recording beams 731. The shutter is then opened to expose the recording medium 710 for the time shown in column 2. All exposures in Table 1 are thus recorded, and then the recording medium 710 is removed from the skew mirror recorder immediately after exposure and postcured to a non-coherent UV LED source.

[Table 1]

Proof of experiment

13 shows a slab waveguide 1350 having a holographic skew mirror output coupler 1300 (e.g., the same as the output coupler 1000 shown in FIG. 10) that was fabricated according to the parameters shown in Table 1. The holographic skew output coupler 1300 had a 53.4 ° horizontal field of view and a 31.6 ° vertical (Bragg degeneration field of view). The skew mirror output coupler was programmed into the recording medium according to the parameters in Table 1. An optically flat waveguide package was fabricated using two 1 " x 2 " 500 μm thick Eagle XG glass substrates 1354 having a 500 μm recording layer 1310 of Akonia form AK291 photopolymer medium. These substrates transmit about 90% of the incident visible light in both directions. The TIGER prism skew recorder delivered collimated signals and reference beams with a diameter of approximately 40 mm at an optical power of approximately 2 mW / cm 2 for each beam. Each beam was apodized by a rectangular aperture of 25 x 21 mm (width x height).

The resulting waveguide 1350 and output coupler 1300 have been tested to verify their properties. A coupling prism was attached to the left ( x < 0) end of the waveguide 1350 using an optical adhesive and the image 1301 was projected into the waveguide through the coupling prism using a ready-made picoprojector. This image was guided in the recording layer through total internal reflection at the substrate boundaries to the gratings within the output coupler 1300. [ These gratings reflect the image from the coupler 1300 (e.g., toward the eye) with respect to the reflective axis forming an angle of about -30.25 degrees with respect to the surface normal. The output image 1303 'was visually inspected to approximate a horizontal view of 53.4 ° (the pico projector had only about 30 ° view, which was manually rotated to examine both ends of the waveguide range).

A Modulation Transfer Function (MTF) test was performed across the field of view to verify the projected image quality. Figure 14 shows a mosaic of nine plots of MTF measured across the field of view where the position of the plot in the figure corresponds to the position in the field of view (i.e., the upper left plot corresponds to the upper left of the field of view, The plot corresponds to the center of view and so on). The horizontal axis of each plot of FIG. 14 is the spatial frequency (cycle / degree) and the vertical axis is the contrast ratio CR. The darker lines correspond to the vertical MTF, and the brighter lines correspond to the horizontal MTF. Much of the deterioration is due to the projector lens, which is evidenced by the low CR of vertical MTF, which is not adversely affected by the output coupler.

Skew Mirror Based Head Mount Display

15 illustrates a head-mounted display 1500 having wide field-of-view skew mirror-based couplers for projecting images onto an observer's eye 1599. An image source 1502, such as a microdisplay, illuminated by one or more lasers or light emitting diodes (LEDs) disposed in or along the eyeglass temple 1504 is coupled to an image light 1501 (E.g., red, green, and blue light) in a direction substantially parallel to the eyeglass temple 1504. A skew input coupler 1510 including a grating structure recorded in a grating medium interposed between a pair of transparent substrates 1512 couples light into the slab waveguide 1520. (A prism or edge coupling may also be used to couple light 1501 from image source 1502 into slab waveguide 1520.) Slab waveguide 1520 directs such light 1511 To a skew output coupler 1530 as shown.

This skew output coupler 1530 includes other grating structures recorded in more grating media interposed between the transparent substrates 1512. Skew output coupler 1530 couples this light 1531 out towards the observer over a field of view, e.g., a field of view that spans approximately 50 degrees horizontally and approximately 30 degrees vertically as perceived by an observer. This allows the observer to perceive the image in a wide field of view. 15, the skew input coupler 1510 has a skew angle of about +30.25 degrees and the skew output coupler 1530 has a skew angle of about -30.25 degrees (e.g., the skew input / output Coupler).

conclusion

While various embodiments of the present invention have been described and illustrated herein, those skilled in the art will readily appreciate that various other means and / or structures for performing the functions and / or obtaining one or more of the results and / And each of these variations and / or modifications are considered within the scope of the embodiments of the invention described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are intended to be exemplary and that the actual parameters, dimensions, materials, and / or configurations may vary depending upon a particular application or application in which the teachings of the present invention are employed Lt; RTI ID = 0.0 &gt; a &lt; / RTI &gt; Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation with the specific embodiments of the invention described herein, many equivalents. It is therefore to be understood that the above-described embodiments are presented by way of example only, and that within the scope of the appended claims and their equivalents, the embodiments of the invention may be practiced otherwise than as specifically described and claimed. The inventive embodiments of the invention are intended as respective individual features, systems, articles, materials, kits and / or methods described herein. It should also be understood that any combination of two or more such features, systems, articles, materials, kits and / or methods is intended to cover the modifications and variations of the inventive subject matter, systems, articles, materials, .

The above-described embodiments may be implemented in any of various ways. For example, embodiments for designing and performing the techniques disclosed herein may be implemented using hardware, software, or a combination thereof. When implemented in software, the software code may be executed on any suitable processor or collection of processors, whether provided in a single computer or distributed among multiple computers.

The various methods or processes described in this specification (e.g., for designing and performing the techniques described above) may be coded as software executable on one or more processors employing any of a variety of operating systems or platforms . Additionally, such software may be written using any of a number of suitable programming languages and / or programming or scripting tools, and may also include executable machine language code or intermediate code Lt; / RTI &gt;

In this regard, the various inventive concepts may be embodied in a computer-readable storage medium (or a plurality of computer-readable instructions) encoded in one or more programs that, when executed on one or more computers or other processors, (E.g., a computer memory, one or more floppy disks, a compact disk, an optical disk, a magnetic tape, a flash memory, a circuitry within a field programmable gate array or other semiconductor device, Or tangible computer storage media). The computer readable medium or media may be transportable such that the programs or programs stored thereon may be loaded onto one or more different computers or other processors to implement the various aspects of the present invention discussed above.

The term "program" or "software" or "code" is used herein to refer to any type of computer code Lt; / RTI &gt; is used in the general sense to refer to a set of possible instructions. Additionally, in accordance with one aspect, one or more computer programs that, when executed, perform the method of the present invention, need not reside on a single computer or processor, but may be implemented on a number of different computers or processors to implement various aspects of the invention. Lt; RTI ID = 0.0 &gt; modular &lt; / RTI &gt;

The computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

Further, the data structure may be stored in a computer readable medium in any suitable form. For simplicity of illustration, the data structure may be shown as having a field associated therewith through the location of the data structure. This relationship can likewise be achieved by assigning locations in a computer readable medium that carry relationships between fields to a repository for a field. However, any appropriate mechanism may be used to establish the relationship between the information in the fields of the data structure, including through the use of pointers, tags, or other mechanisms to establish relationships between data elements.

Furthermore, the various inventive concepts may be embodied in one or more ways, one example of which has been provided. The operations performed as part of the method may be ordered in any suitable manner. Thus, even when illustrated in sequential operation in an exemplary embodiment, an embodiment may be constructed in which operations are performed in a different order than the illustrated, which may include performing some operations concurrently.

All definitions defined and used herein should be understood as dictionary definitions, definitions in documents incorporated by reference, and / or control over the ordinary meaning of defined terms.

The indefinite articles "a" and "an" used in the specification and claims should be understood to mean "at least one" unless explicitly indicated to the contrary.

The phrase " and / or " as used in this specification and claims means either such combined elements, that is, either or both of the elements that in some cases are present in combination and in other cases exist separately . Many of the elements listed as " and / or " should be interpreted in the same manner, i.e., as " one or more " Elements other than those specifically identified by " and / or " phrases may optionally be present, whether specifically associated with those elements being specifically identified or not. Thus, as a non-limiting example, references to " A and / or B ", when used in conjunction with an open-ended language such as " &Lt; / RTI &gt; In other embodiments only B (optionally including elements other than A); In another embodiment, both A and B (optionally including other elements) and the like can be referred to.

As used in the specification and claims, " or " should be understood to have the same meaning as " and / or " as defined above. For example, to separate items in a list, it is to be understood that "or" or "and / or" is inclusive, i.e., includes at least one inclusion, as well as more than one of a plurality of elements or lists of elements, It will be interpreted as inclusion of unlisted items. It will be understood that, by way of contrast, the term explicitly used, for example, " only one of " or " exactly one of &Quot; element " In general, the term " or " as used herein refers to an exclusive alternative when preceded by exclusivity terms such as "any one," "one of," "only one," or "exactly one of. (I.e., one or the other, but not both). &Quot; Essentially consisting of, " as used in the claims shall have its ordinary meaning as used in the field of patent law.

As used in this specification and the claims, the phrase " at least one " in reference to a list of one or more elements necessarily includes at least one of each and every element specifically listed in the list of elements, Quot; is understood to mean at least one element selected from any one or more of the elements in the list of elements, not excluding any combination of elements within the list. This definition is also intended to encompass elements that are selectively present in the list of elements referred to by the phrase " at least one ", whether or not the elements other than the specifically identified elements are specifically identified as being specifically related . Thus, as a non-limiting example, "at least one of A and B" (or equivalently, "at least one of A or B," or equivalently, "at least one of A and / or B" In the example, A and B none (and optionally including elements other than B) of at least one - optionally more than one -; In another embodiment, at least one - optionally including more than one - B, and no A (and optionally including elements other than A); In another embodiment, it may refer to at least one - optionally including more than one - A and at least one - optionally including more than one - B (and optionally including other elements), and the like.

As used in the specification, as well as in the claims, the terms "comprising," "including," "carrying," "having," "containing," " quot ;, " involving ", " holding ", " composed of, " and the like, are to be understood as being extendable, i.e., including but not limited to. However, the transitional phrases "consisting essentially of" and "consisting essentially of" shall each be a closed or semi-closed transitional phrase, as described in the Patent and Trademark Office's Patent Examination Procedures Manual, Section 2111.03.

Claims (41)

As an optical reflection type device,
Comprising a grating structure present in a grating medium,
The grating structure is structured to primarily reflect incident light as reflected light,
Wherein the incident light includes a first wavelength,
Wherein the reflected light comprises the first wavelength,
Wherein the incident light of the first wavelength and the reflected light of the first wavelength form an angle bisecting by the reflection axis,
The reflection axis changes to less than one degree when the incident light is incident on the grating medium in a range of internal incident angles spanning at least 15 degrees,
Wherein the reflective axis is at least 2.0 degrees different from the surface normal of the grating medium. 2. The optically reflective device of claim 1, wherein the reflective axis varies less than one degree when the incident light is incident on the grating medium in a range of internal angles of incidence that span at least 30 degrees. According to claim 1 or 2, wherein the lattice structure is in grid frequency over a range of at least 2.00 × 10 ⁵ radians per meter (| K _G |), the optical reflective device comprising one or more hologram having. 4. The method according to any one of claims 1 to 3,
Wherein the incident light includes a second wavelength,
Wherein the reflected light comprises the second wavelength,
Wherein the second wavelength is different by at least about 50 nm from the first wavelength. 5. The method according to any one of claims 1 to 4,
Wherein the incident light includes a third wavelength,
Wherein the reflected light comprises the third wavelength,
Wherein the third wavelength is different by at least about 50 nm from each of the first wavelength and the second wavelength. 6. The device of claim 5, wherein the first wavelength is in a red region, the second wavelength is in a green region, and the third region is in a blue region. ^7. Optical system according to any one of the preceding claims, wherein the grating structure comprises at least one hologram with a grating frequency (| K _G |) that spans a range of at least 1.68 x 10 radians per meter. device. Any one of claims 1 to claim 7 as set forth in wherein the grating structure has at least a meter of 5.01 × 10 ⁶ radians grid frequency over a range of (| K _G |), an optical reflection type, which comprises one or more holograms having device. 9. Optical system according to any one of the preceding claims, wherein the grating structure comprises at least one hologram with a grating frequency (| K _G |) spanning a range of at least 1.24 x 10 ⁷ radians per meter. device. The method according to any one of claims 2 to 6, wherein the lattice structure of the meter 5.10 × 10 ⁵ radians excess and grid frequencies over the range of the meter 3.15 × less than 10 ⁷ radians one having a (| | K _G) RTI ID = 0.0 &gt; holograms. &Lt; / RTI &gt; 11. An optically reflective device according to any one of claims 7 to 10, wherein the at least one hologram comprises at least nine holograms. 12. The method of claim 11, wherein at least an average of nine adjacent hologram | ΔK _G | is 5.0 × 10 ³ rad / m to 1.0 × 10 ⁷ rad / m, the optical reflective devices existing in the range of. 13. The method according to any one of claims 1 to 12,
The incident light is incident on the grating structure from the inside of the optical reflection type device,
Wherein the reflected light emanates from the optically reflective device. 14. The optically reflective device of any one of claims 1 to 13, further comprising at least one substrate adjacent the grating medium. 15. The optically reflective device of claim 14, wherein the at least one substrate comprises two substrates, wherein the grating medium is disposed between the two substrates. 16. The optically reflective device of claim 15, wherein the grating medium comprises a photopolymer medium at least 100 microns thick and wherein the two substrates transmit at least 60 percent of the incident light and at least 60 percent of the reflected light. 16. The optically reflective device of claim 15, wherein the grating medium has a first index of refraction and the two substrates have a second index of refraction less than about 0.1 of the first index of refraction. As a method,
Illuminating a grating structure present in the grating medium with incident light of a first wavelength, wherein the incident light is reflected in the grating structure to produce reflected light of the first wavelength,
Wherein the incident light and the reflected light form an angle bisecting by a reflection axis which is inclined by at least about 2.0 degrees with respect to the surface normal of the grating medium,
Wherein the reflective axis changes less than one degree when the incident light is incident on the grating structure in the grating medium in a range of internal angles of incidence that span at least 15 degrees. 19. The method of claim 18, wherein the reflective axis changes less than one degree when the incident light is incident on the grating medium in a range of internal angles of incidence that span at least 30 degrees. 19. The method of claim 18, wherein illuminating the grating structure comprises:
Coupling the incident light into the grating medium; And
And total internal reflection of the incident light in the grating medium. 19. The method of claim 18, wherein illuminating the grating structure comprises:
And at least partially guiding the incident light to the grating structure through the grating medium. 19. The method of claim 18, wherein the incident light and the reflected light comprise a second wavelength that is different by at least about 50 nm from the first wavelength. 24. The method of claim 22, wherein the incident light and the reflected light comprise a third wavelength that is different by at least about 50 nm from each of the first wavelength and the second wavelength. 19. The method of claim 18,
Further comprising coupling the reflected light out of the grating medium at an angle of about 25 degrees to the surface normal of the grating medium. 19. The method of claim 18,
Further comprising the step of placing the grating medium in optical communication with the eye of the person so that the reflected beam at least partially illuminates the human eye. 26. The method of claim 25, wherein illuminating the grating structure comprises illuminating the grating structure with an image such that the reflected image is visible to a human eye. As a method,
Disposing a grating medium including a grating structure in optical communication with a human eye, the grating medium having a proximity surface defining a surface normal;
Coupling a visible image into the grating medium;
Directing the visible image into the grating structure through at least one total internal reflection in the grating medium;
Reflecting the visible image from the grating structure with respect to a reflective axis forming an angle of at least about 2 degrees with respect to the surface normal; And
And coupling the visible image out of the grating medium towards the human eye through the proximity surface, wherein the visible image spans a field of view in at least about 30 degrees of free space. A method of writing holographic gratings to a photosensitive medium,
Disposing the photosensitive medium between an oblique surface of the first prism and an oblique surface of the second prism;
Coupling a first beam into the photosensitive medium through a first surface of the photosensitive medium and the oblique surface of the first prism, the first beam forming a first angle relative to a surface normal of the first surface, The first angle having a first magnitude; And
Coupling a second beam into the photosensitive medium through a second surface of the photosensitive medium and the oblique surface of the second prism, the second beam forming a second angle relative to a surface normal of the second surface, And wherein the second angle has a second magnitude substantially equal to the first magnitude. 29. The method of claim 28,
Further comprising interfering the third beam and the fourth beam in the photosensitive medium to form a second holographic grating in the photosensitive medium. As a device,
A holographic optical element having at least one grating structured to reflect visible light over a field of view of at least about 50 degrees in a first dimension, the field of view being measured outside the holographic optical element, Wherein the at least one grating has a grating vector oriented at an angle of at least about 15 to about 45 relative to the surface normal. 31. The device of claim 30, wherein the at least one grating comprises a single grating structured to reflect visible light at wavelengths ranging from about 400 nm to about 700 nm over the field of view. 31. The device of claim 30, wherein the at least one grating comprises a plurality of gratings, each of the gratings being structured to reflect incident light at one wavelength of the visible light at different angles within the field of view. 31. The method of claim 30,
And at least one light source in optical communication with the holographic optical element to illuminate the plurality of gratings with the visible light. 32. The device of claim 30, wherein the field of view is at least about 30 degrees at a second dimension orthogonal to the first dimension. 31. The device of claim 30, wherein the angle formed by the reflective axis and the surface normal is between about 20 degrees and about 40 degrees. 31. The device of claim 30, wherein the holographic optical element is substantially free of visible light-sensitive photoinitiators. As a method of reflecting light,
Wherein the at least one grating reflects at least a portion of the light over a field of view of at least about 50 [deg.], The field of view of the at least one grating of the holographic optical element Centered on a reflective axis that forms an angle of at least about 15 [deg.] To about 45 [deg.] With respect to the surface normal. A method of manufacturing a holographic optical element,
Interfering with a first beam and a second beam within a holographic recording medium to form a first grating, the holographic recording medium having a planar surface, the first grating having a viewing angle of at least about 50 [ Wherein the field of view is centered on a reflective axis that forms an angle of at least about 15 to about 45 with respect to a surface normal of the planar surface of the holographic optical element How to put it. 39. The method of claim 38, wherein interfering the first beam and the second beam comprises:
Coupling the first beam into the holographic recording medium through an oblique surface of the first prism; And
And coupling the second beam into the holographic recording medium through an oblique surface of the second prism. A holographic optical element produced according to the method of claims 38 or 39. As a device,
Wherein each reflective grating of the plurality of reflective gratings comprises a grating element that forms an angle of about 15 to about 45 with the surface normal of the holographic optical element, (K _G) and the grid frequency of the meter at least 2.00 × 10 ⁵ radians (| K _G |), the device having a.

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