Exit pupil expander

Abstract

According to an exemplary aspect of the invention, an exit pupil expander (EPE) grating is provided, which is divided into at least two segments, wherein the EPE grating includes a plurality of grating strips in a first segment and a plurality of grating strips in a second segment, the plurality of grating strips in the first segment being oriented in a direction substantially the same as the plurality of grating strips in the second segment, and not aligned in a direction perpendicular to the direction of the grating strips.

Description

Technical Field

[0001] Embodiments of the present invention generally relate to an exit pupil expander (EPE), for example for optical waveguide arrangements, such as for waveguide-based displays. Background Technology

[0002] Generally, improvements are needed related to the exit pupil expander (EPE). Light rays typically interfere with the EPE grating, thus causing non-uniformity in the coupled image. Therefore, it is necessary to reduce the interference caused by light rays interfering with the EPE grating.

[0003] For example, US2018 / 0052501A1 discusses an EPE that presents wave interference caused by a uniform grating in an orthogonal pupil expander (OPE). For example, wave interference can be reduced and the brightness uniformity of the output image can be increased by changing the grating parameters or materials at different locations.

[0004] However, this solution cannot independently tune the phase of the diffracted rays without altering the amplitude response of the grating. In other words, considering US2018 / 0052501A1, more degrees of freedom are needed to modify the operation of the optical waveguide. Changing the width, height, and / or fill factor of the grating strips does not provide the desired effect. Therefore, an improved EPE grating is needed, for example, for optical waveguide arrangements. Summary of the Invention

[0005] The subject matter of the independent claims is provided according to several aspects. Several embodiments are defined in the dependent claims.

[0006] According to a first aspect of the invention, an exit pupil expander (EPE) grating is provided, which is divided into at least two segments, wherein the EPE grating includes a plurality of grating strips in a first segment and a plurality of grating strips in a second segment, the plurality of grating strips in the first segment being oriented in a direction substantially the same as the plurality of grating strips in the second segment, and not aligned in a direction perpendicular to the direction of the grating strips.

[0007] The implementation of the first aspect may include at least one feature from the following list or any combination of the following features:

[0008] • The plurality of grating strips in the first segment and the plurality of grating strips in the second segment are misaligned, so that light rays propagating along different paths in the EPE grating experience different phase shifts;

[0009] • Each of the plurality of grating strips in the second segment is offset by a certain distance in a direction perpendicular to the direction of the grating strip, compared to the corresponding grating strip in the first segment;

[0010] • The first grating strip of the first segment is the corresponding grating strip of the first grating strip of the second segment, and the second grating strip of the first segment is the corresponding grating strip of the second grating strip of the second segment;

[0011] • The distance is less than the period of the EPE grating;

[0012] • Each of the plurality of strips in the second segment is offset laterally from the corresponding grating strip in the first segment by the distance;

[0013] • Each of the plurality of strips in the second segment is offset by the distance from the corresponding grating strip in the first segment in the vertical direction;

[0014] • The EPE grating is a dual-period grating;

[0015] • The first segment of the EPE grating is arranged to cause a first phase shift of light rays deflected in the first segment, and the second segment of the EPE grating is arranged to cause a second phase shift of light rays deflected in the second segment;

[0016] • The first phase shift is different from the second phase shift;

[0017] • The amplitude of the light ray deflected in the first segment is the same as the amplitude of the light ray deflected in the second segment;

[0018] • For light rays guided to the EPE grating, the second segment follows the first segment;

[0019] • The EPE grating also includes a plurality of grating strips in the third segment, and each of the plurality of strips in the third segment is offset by a certain distance from the corresponding grating strip in the first segment in a direction perpendicular to the direction of the grating strip;

[0020] • The distance between subsequent raster strips of the first segment is the same as the distance between subsequent raster strips of the second segment;

[0021] • The EPE grating is arranged to propagate and couple light from the EPE grating, and is preferably also arranged to operate as an internal coupler;

[0022] • The EPE grating is arranged to keep the amplitude of light rays propagating through different paths in the EPE grating constant.

[0023] According to a second aspect of the present invention, an optical waveguide arrangement for displaying an image is provided, comprising: an optical waveguide; an input grating for diffractically coupling the image to the optical waveguide; an output grating for diffractically coupling the image to the optical waveguide; and an EPE grating as described in any of the preceding claims, wherein the EPE grating is located between the input grating and the output grating to extend the exit pupil of the image on the output grating.

[0024] According to a third aspect of the invention, a personal display device is provided that includes an optical waveguide arrangement of the second aspect, the personal display device being a head-mounted display (HMD) or a head-up display (HUD). Attached Figure Description

[0025] Figure 1 An exemplary system according to at least some embodiments of the present invention is shown;

[0026] Figure 2a Examples of optical waveguide arrangements according to at least some embodiments of the present invention are shown;

[0027] Figure 2b Examples of coupling gratings, exit pupil expanders and coupling gratings according to at least some embodiments of the present invention are shown;

[0028] Figure 3 An example of an exit pupil expander according to at least some embodiments of the present invention is shown;

[0029] Figure 4 A first example of an offset grating strip according to at least some embodiments of the present invention is shown;

[0030] Figure 5a and 5b A second example of an offset grating strip according to at least some embodiments of the present invention is shown;

[0031] Figure 6 Examples of phase shifts according to at least some embodiments of the present invention are shown;

[0032] Figure 7a and 7b Examples of offset two-dimensional grating strips according to at least some embodiments of the present invention are shown;

[0033] Figure 8 An exemplary distribution of travel distances in different segments according to at least some embodiments of the present invention is shown. Detailed Implementation

[0034] Embodiments of the present invention relate to, for example, exit pupil expander (EPE) gratings for optical waveguide arrangements. More specifically, embodiments of the present invention provide an EPE grating that reduces interference effects caused by light rays interfering with the EPE grating. According to embodiments of the present invention, the EPE grating is divided into at least two segments with different phase shifts. Each of the at least two segments may include a plurality of grating strips, and the grating strips of each segment may be arranged to cause different phase shifts as light propagates along different paths through the segment, such as different phase shifts controlled according to Lohmann's detour-phase principle. Thus, the EPE grating can be arranged to keep the amplitude of light rays propagating along different paths the same, i.e., unchanged, to provide more degrees of freedom for modifying the operation of the optical waveguide. For example, interference caused by light rays interfering with the EPE grating can be reduced.

[0035] An EPE grating may include multiple grating strips in a first segment and multiple grating strips in a second segment, wherein the multiple grating strips in the first segment are misaligned compared to the multiple grating strips in the second segment. That is, the grating strips in the first and second segments may not be coaxial, and each of the multiple strips in the second segment may be offset by a certain distance from the corresponding grating strip in the first segment in a direction perpendicular to the direction of the grating strip. In other words, offset can refer to the distance by which a grating strip is misaligned with its corresponding grating strip.

[0036] Figure 1 An example system according to at least some embodiments of the present invention is shown. The system may include at least one light source 140. For example, at least one light source 140 may include a laser or a light-emitting diode (LED), wherein a laser source has the advantage of being more strictly monochromatic than an LED. Embodiments of the invention are not limited to any particular light source and may be implemented using more than one type of light source 140. At least one light source 140 may be arranged together with an optional reflector 130 to generate a light field in angular space, which can be used to enable a waveguide-based display to generate its image.

[0037] Images can be encoded within a light field. The light field is... Figure 1The light field 100 is schematically shown as a field. In some embodiments, a physical main display may show an image of the light field 100, while in other embodiments, the system may not include a physical main display, and the image is encoded only in the light field 100 distributed in angular space. Light rays 104 or optical signals from the light field 100 may be transmitted directly or via a light guide 102 comprising, for example, mirrors and / or lenses, to a waveguide 110 to generate a waveguide-based display. The light guides 102 are optional in the sense of details according to a particular embodiment; they may be absent. In other words, the light guide 102 is absent in all embodiments.

[0038] In waveguide 110, light ray 104 can propagate by repeated reflections within the waveguide and interact with element 112a until it interacts with element 112, which deflects light ray 104 from waveguide 110 into the air, resulting in an image of light ray 114 directed toward eye 120. For example, elements 112 and 112a may include a semi-reflective mirror, a surface-embossed grating, or other diffraction structures. Element 112a can be arranged, for example, to propagate light ray 104 within waveguide 110, thereby correctly generating an image for the waveguide display. Light from different angular aspects of light field 100 will interact with element 112, causing light ray 114 to produce an image encoded in light field 100 on the retina of eye 120.

[0039] Then, element 112 can cause light 104 to exit the waveguide 110 at the exit position. As a result, the user will perceive an image encoded in the light field 100 in front of their eyes 120. Since the waveguide 110 can be at least partially transparent, the user can also advantageously see their real-life environment through the waveguide 110, for example, in the case where the waveguide-based display is a head-mounted display. Due to the action of elements 112a and 112, light is emitted from the waveguide 110 at multiple angles at multiple elements 112. In a waveguide-based display, multiple waveguides 110 can be present, which transmit light at different apparent depths simulating in front of the eyes 120, and optionally, for illustrative purposes, not shown in the diagram. Figure 1 The user's other eye is shown in the image.

[0040] In particular, embodiments of the present invention relate to an outgoing pupil expander (EPE), for example for use in optical waveguide arrangements for diffractive displays such as those based on optical waveguides, including, for example, an input grating, an EPE grating, and an outgoing grating. The optical waveguide is capable of transmitting light at optical frequencies. Optical frequencies, or visible light frequencies, refer to light with wavelengths between approximately 400 and 700 nanometers. Optical waveguides can be employed in displays where one or more waveguides can be used to direct light from an optical field to a suitable location for the release of one or both eyes of a user.

[0041] Embodiments of the present invention can be used, for example, in head-mounted displays (HMDs) and head-up displays (HUDs) utilizing diffraction gratings. HMDs and HUDs can be implemented using optical waveguide technology, for example, for augmented reality or virtual reality applications. In augmented reality, the user sees a view of the real world with supplementary instructions overlaid on it. In virtual reality, the user is deprived of their view of the real world and instead provided with a view of a software-defined scene. Typically, improvements related to EPE gratings are required, such as for optical waveguide arrangements.

[0042] Figure 2a An example of an optical waveguide arrangement according to at least some embodiments of the present invention is shown. The optical waveguide arrangement 200 may include an optical waveguide 110, a coupling grating 202, a coupling grating 204, and an EPE grating 206. Figure 2a In the example, the exit pupil of the optical waveguide arrangement 200 can be extended using the EPE grating 206 between the input grating 202 and the output grating 204 of the optical waveguide arrangement 200.

[0043] like Figure 2a As shown, for example from Figure 1 The light 104 from a light source 140 (such as a projector) can be guided to a coupling grating 202. The coupling grating 202 can be arranged to guide the light 104 into the light waveguide 110. That is, the coupling region 202 can diffractically couple an image into the light waveguide 110. Figure 2a As shown, in some embodiments, for example, the coupling grating 202 may be on the surface of the optical waveguide 110. However, in some embodiments, the optical waveguide 110 may include the coupling grating 202. Similarly, the optical waveguide 110 may include the coupling out grating 204 and / or the EPE grating 206, or the coupling grating 202 and / or the EPE grating 206 may be on the surface of the optical waveguide 110.

[0044] Light 104 can propagate towards the output grating 204 via internal reflection within the waveguide through the EPE grating 206 to laterally extend the visible area of ​​the display. In some example embodiments, the EPE grating 206 can therefore extend the exit pupil of the image on the output grating 204 along the path of light 104 between the input grating 202 and the output grating 204. Furthermore, the output grating 204 can diffractically couple the image from the light waveguide 110 towards the eye 120 via light 114.

[0045] Figure 2aAn example is shown including an input grating 202, an output grating 204, and an EPE grating 206. However, in some embodiments, the EPE grating 206 may be arranged to extend and couple light out of the EPE grating 206. The EPE grating 206 may also be arranged to operate as an internal coupler. For example, in the case of a 2D structure, the entire grating region may be made of the same grating from which light is coupled in, extended, and coupled out.

[0046] Figure 2b Examples of in-coupling (IC) gratings, EPE gratings, and out-coupling (OC) gratings according to at least some embodiments of the present invention are shown. For example, when an LED projector is used as the light source 140, the light typically interferes with the EPE grating 206, resulting in inhomogeneities (e.g., streaks) in the output image. Therefore, embodiments of the present invention provide an improved EPE that offers more degrees of freedom for modifying the operation of the optical waveguide, for example, to minimize inhomogeneities in the image.

[0047] Figure 3 Examples of EPE gratings according to at least some embodiments of the present invention are shown. For example... Figure 3 As shown in the example, the EPE grating, for example Figure 2b The EPE grating 206 in the image can be divided into segments. Figure 3 The dashed lines in the diagram indicate the boundaries of the segments. For example, as... Figure 3 As shown, the EPE grating can be divided into at least a first segment 310 and a second segment 320. More specifically, the EPE grating can be divided into segments that cause different phase shifts, such as phase shifts controlled according to Lohmann's detour-phase principle. By appropriately selecting the phase shift, interference effects can be reduced.

[0048] Each segment of the EPE grating 206 may include multiple grating strips, and the grating strips of different segments may be arranged to produce diffracted versions of incident light with different phase shifts at each segment as light propagates along different paths through the segment. For example, the first segment 310 of the EPE grating 206 may include at least a first grating strip and a second grating strip, and the second segment 320 of the EPE grating 206 may include at least a first grating strip and a second grating strip, and the grating strips of the first and second segments may be arranged to cause different phase shifts to reduce interference caused by light interfering with the EPE grating 206.

[0049] In some exemplary embodiments of the invention, Lohmann's detour-phase principle can be used to reduce interference in EPE gratings, such that when light diffracts from the grating, it produces a set of reflection and transmission diffraction orders with specific phases and amplitudes determined by the characteristics of the grating. If the relative positions of the grating strips shift within the period of the grating, a phase shift occurs, which can be determined according to the following equation, for example, in the 1-dimensional case:

[0050] (1)

[0051] Where d represents the period of the grating, ds is the offset of the grating strip position, m is the diffraction order of the optical signal under discussion (e.g., -2, -1, 0, 1, 2), and t m =t m (0) is the amplitude of the grating without the grating strips being shifted. Therefore, the phase of the non-zero diffraction order can be adjusted by shifting the grating strips, while the amplitude of all diffraction orders remains the same compared to the grating without shifting. Equation (1) can be generalized to two-dimensional gratings, for example, using periods dx and dy, where the m and n diffraction orders are in the x and y directions, respectively. The period of grating d can also be referred to as the distance between subsequent grating strips in a segment. The phase shift can be controlled according to Lohmann's detour-phase principle, as described by Joseph W. Goodman in the 3rd edition, 2004 (page 360).

[0052] Therefore, for example, according to Lohmann's detour-phase principle, different phase shifts can be achieved by shifting the grating strip by one segment (such as the second segment 320) compared to an adjacent segment (such as the first segment 310). This reduces interference caused by the rays from the interference EPE grating 206. The amplitude of the diffracted rays remains unchanged.

[0053] In other words, the amplitude distribution can be altered by the entire EPE grating 206, but the EPE grating 206 can be arranged to control the phase shift, for example, according to Lohmann's detour-phase principle, so that the amplitude remains unchanged in the case of a single grating. Therefore, the phase of the diffracted rays can be controlled without altering the amplitude. This provides more degrees of freedom for modifying the waveguide's operation. For example, during the initial design phase, a waveguide without phase can be designed first, and then the amplitude can be kept constant when modifying the phase shift to reduce interference.

[0054] The magnitude of the offset can also vary depending on the segment and can be optimized to minimize the effects of interference. Alternatively or additionally, the size of the segment can vary. That is, the first segment 310 can have a first size and the second segment 320 can have a second size, wherein the first size is different from the second size.

[0055] about Figure 3 For example, incident ray 104 can be guided toward the grating strips of the first segment 310 of the EPE grating. The grating strips of the first segment 310 can diffract the incident ray 104 into 0th order ray 104a and 1st order ray 104b. The position of the grating strips in the first segment 310 does not affect the phase of the 0th order ray 104a, but it does affect the phase of the 1st order ray 104b. The 0th order ray 104a can be referred to as a non-deflected ray, while the 1st order ray 104b can be referred to as a deflected ray. Other non-zero diffraction orders of rays (i.e., m = (-2, -1, 1, 2)) can be referred to as deflected rays.

[0056] In other words, a 0th-order ray 104a can be a straight, continuous ray that does not turn. A 1st-order ray 104b can be a ray that does not continue in a straight line, that is, a ray that turns.

[0057] The diffracted 0th-order ray 104a can be further guided from the first segment 310 toward the grating strip of the second segment 320, and the grating strip of the second segment 320 can diffract the input 0th-order ray 104a into 0th-order ray 104c and 1st-order ray 104d. Similarly, the position of the grating strip in the second segment 320 does not affect the phase of the 0th-order ray 104c, but it does affect the phase of the 1st-order ray 104d. Furthermore, the 0th-order ray 104c can be referred to as an undeflected ray, while the 1st-order ray 104d can be referred to as a deflected ray.

[0058] Furthermore, the first-order diffracted ray 104b can be further guided from the first segment 310 toward the grating strip of the third segment 330, and the grating strip of the third segment 330 can diffract the ray 104b into an undeflected ray 104e and a deflected ray 104f. The ray can be similarly guided through several segments of the EPE.

[0059] Light rays deflected in different segments can have different phases; that is, different segments can cause different phase shifts to deflect the light rays, but the amplitudes of the deflected (and undeflected) light rays can be the same. For example, a first segment 310 can be arranged to cause a first phase shift in the light ray 104b deflected in the first segment 310, and a second segment 320 can be arranged to cause a second phase shift in the light ray 104d deflected in the second segment 320. The first phase shift can be different from the second phase shift, while the amplitude of the light ray deflected in the first segment 310 can be the same as the amplitude of the light ray deflected in the second segment 320. Light rays propagating along different paths may collide at the same location and interfere, but this interference can be controlled by adjusting the phase of the light rays.

[0060] The grating strips of each segment can be arranged in the same direction 305, but at least some segments can be offset relative to their corresponding grating strips in adjacent segments in a direction 315 perpendicular to the direction 305 of the grating strips, so that the diffracted rays propagating along different paths have different phase shifts. For example, each of the plurality of strips of the second segment 320 can be moved, i.e. offset, by a certain distance from the corresponding grating strip of the first segment 310 in a direction 315 perpendicular to the direction 305 of the grating strips.

[0061] In other words, phase shift can be achieved as deflected rays by moving the grating strips within the distance between subsequent grating strips in a segment. The phases of the undeflected rays 104a, 104c, and 104e can remain unchanged, and the amplitudes of all diffraction orders can remain the same regardless of the phase shift.

[0062] Figure 4 A first example of an offset grating strip according to at least some embodiments of the present invention is shown. More specifically, Figure 4 The diagram illustrates how the first grating strip 321 and the second grating strip 322 of the second segment are offset by a distance 410 in a direction 315 perpendicular to the direction 305 of the grating strips, respectively. That is, the first grating strip 311 of the first segment 310 can be the corresponding grating strip of the first grating strip 321 of the second segment 320, and the second grating strip 312 of the first segment 310 can be the corresponding grating strip of the second grating strip 322 of the second segment 320.

[0063] Therefore, the first grating strip 321 of the second segment 320 can be offset by a distance 410 from the corresponding grating strip 311 of the first segment 310. Similarly, the second grating strip 322 of the second segment 320 can also be offset by a distance 410 from the corresponding grating strip 312 of the first segment 310. Therefore, compared with the corresponding first grating strip 321 and second grating strip 322 of the second segment 320, the first grating strip 311 and second grating strip 312 of the first segment 310 will be misaligned in the direction 315 perpendicular to the direction 305 of the grating strip, so that the light rays propagating along different paths in the EPE grating experience different phase shifts, even if the amplitude of the diffracted light rays remains the same. That is, compared with the corresponding grating strip of the first segment 310, all the grating strips of the second segment 320 can be offset by the same distance 410.

[0064] The distance 410 can be less than the distance 420 between adjacent grating strips in a segment. That is, the distance 410 can be less than the period of the EPE grating. For example, if the EPE grating includes two grating strips within the period of the EPE grating, the two grating strips can be offset by the same amount.

[0065] Figure 5a and 5b A second example of an offset grating strip according to at least some embodiments of the present invention is shown. More specifically, Figure 5a and 5b This illustrates how each of the plurality of strips in the second segment 320 is offset by a distance ds from the corresponding strip of the first segment 310 in a direction 315 perpendicular to the direction 305 of the grating strip (e.g., laterally). The distance ds (as shown in equation (1)) can correspond to Figure 4 The distance 410 in the middle. The distance between subsequent raster strips of a segment (such as the first raster strip 311 and the second raster strip 312 of the first segment 310) is represented by d (as shown in equation (1)), which can correspond to Figure 4 The distance is 420.

[0066] In other words, Figure 5b The first grating strip 321 of the second segment 320 in the middle and Figure 5a The first grating strip 311 of the first segment 310 can be offset by a distance ds, and Figure 5b The second grating strip 322 of the second segment 320 and Figure 5a The second grating strip 312 of the first segment can be offset by a distance ds. Therefore, by moving the grating strip of one segment within the distance between subsequent grating strips in a segment (i.e., within the period d) compared to the grating strip of another segment, a phase shift can be achieved as a diffraction order, i.e., deflected light rays. Figure 5bAs shown, for example, in the case of a one-dimensional grating strip, on the plane of the grating strip, for example in the lateral direction, the first grating strip 321 of the second segment 320 may be offset by a distance ds compared to the first grating strip 311 of the first segment 310. The lateral direction can refer to the direction extending from one side of the EPE grating to the other side of the EPE grating.

[0067] Figure 5a and 5b Cross-sectional views of grating strips 311, 312, 321, and 322 are shown. Grating strips can typically have various shapes. However, embodiments of the invention are not limited to any particular shape of grating strips. For example, the cross-sectional profile of a grating strip can also be rectangular or triangular. Furthermore, the width, height, fill factor, or any other characteristics of the grating strips can vary depending on the segment; for example, the grating strip of the first segment 310 can have a different width compared to the second segment 320.

[0068] Figure 6 Examples of phase shifts according to at least some embodiments of the present invention are shown. More specifically, Figure 6 An example of phase shift as a function of the ds / d ratio is shown. Figure 6 In this context, the phase of the electric field component of the first diffraction order is used as a function of the Lohmann displacement ds.

[0069] Figure 7a and 7b Examples of offset two-dimensional grating strips according to at least some embodiments of the present invention are shown. That is, Figure 7a and 7b An example of a dual-period grating strip is shown.

[0070] More specifically, Figure 7a and 7b This illustrates how embodiments of the present invention can be applied to two-dimensional EPE gratings. Figure 7a The position of the first raster strip 311 of the first segment 310 is shown, and Figure 7b This shows the position of the first raster strip 321 of the second segment 320. Figure 7b It can be seen that, in the case of a two-dimensional grating, the first grating strip 321 of the second segment 320 can be offset on the plane of the grating strip, that is, offset in the horizontal direction dx, and can also be offset on a plane perpendicular to the plane of the grating strip, that is, offset in the vertical direction dy. The vertical direction can refer to the direction extending from the bottom of the EPE grating to the top of the EPE grating. Similar to... Figure 5a and 5b The example shown, Figure 7a and 7b The grating strips shown can also have any shape or other characteristics, such as rectangular or triangular shapes.

[0071] Figure 8 An exemplary distribution of travel distances in different segments according to at least some embodiments of the present invention is shown. Figure 8 The image shows the input grating 202, the output grating 204, and the EPE grating 206. (See image for details.) Figure 8 As shown, segments of the EPE grating 206 (e.g., the first segment 310 and the second segment 320) can be arranged to cause different phase shifts in the diffracted light, while the amplitude of the diffracted light is kept the same by moving the grating strips of different segments by different distances, thereby reducing interference caused by the light interfering with the EPE grating 206.

[0072] It should be understood that the embodiments of the present invention disclosed herein are not limited to the specific structures, process steps, or materials disclosed herein, but extend to equivalents that will be recognized by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0073] In this specification, reference to an embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the phrases "in one embodiment" or "in one embodiment" appearing in various places in this specification do not necessarily refer to the same embodiment. Precise numerical values ​​are also disclosed where terms such as approximately or substantially are used to refer to numerical values.

[0074] As used herein, for convenience, multiple items, structural elements, constituent elements, and / or materials may be presented in a common list. However, these lists should be interpreted as each member of the list being individually identified as a separate and unique member. Therefore, any single member in these lists should not be construed as being factually equivalent to any other member in the same list solely based on its statement in the common group, without any indication to the contrary. Furthermore, various embodiments and examples of the invention may be referenced herein along with alternatives to its various components. It should be understood that such embodiments, examples, and alternatives should not be construed as factual equivalents of each other, but should be considered as independent and autonomous representations of the invention.

[0075] Furthermore, in one or more embodiments, the described features, structures, or properties can be combined in any suitable manner. Numerous specific details, such as examples of length, width, shape, etc., have been provided in the foregoing description to provide a thorough understanding of embodiments of the invention. However, those skilled in the art will recognize that the invention can be practiced without one or more specific details, or using other methods, components, materials, etc. In other instances, well-known structures, materials, or operations have not been shown or described in detail to avoid obscuring aspects of the invention.

[0076] While the foregoing examples illustrate the principles of the invention in one or more specific applications, it will be apparent to those skilled in the art that many modifications can be made in form, use, and implementation details without requiring inventive effort and without departing from the principles and concepts of the invention. Therefore, the invention is not intended to be limited except by the claims set forth below.

[0077] The verbs “comprising” and “including” are used in this document as open-ended restrictions; they neither exclude nor require the presence of any unmentioned features. Unless otherwise expressly stated, the features described in the dependent claims may be freely combined with each other. Furthermore, it should be understood that the use of singular forms such as “a” or “an” in this document does not exclude a plurality.

[0078] Industrial application

[0079] At least some embodiments of the present invention have been found to have industrial applications in HMDs and HUDs.

[0080] List of abbreviations

[0081] HMD: Head-mounted display;

[0082] HUD: Head-up display;

[0083] LCOS: Liquid Crystal on Silicon;

[0084] LED: Light Emitting Diode;

[0085] MEMS: Microelectromechanical Systems.

[0086] Reference tag list

[0087] 100 light field 102 Light guide tube 104 Light 110 waveguide 112 element 114 Directional light 120 Eye 130 mirror 140 light source 202 Coupled grating 204 Output grating 206 Exit pupil expander 310，320 EPE fragments 311，312，321，322 grating strip 305，315 direction 410 Distance ds 420 Distance d

Claims

1. An exit pupil expander (EPE) grating, which is divided into at least two segments, wherein, The EPE grating includes a plurality of grating strips in a first segment and a plurality of grating strips in a second segment, wherein the plurality of grating strips in the first segment are oriented in the same direction as the plurality of grating strips in the second segment, and are not aligned in a direction perpendicular to the direction of the grating strips; The plurality of grating strips in the first segment and the plurality of grating strips in the second segment are misaligned so that light rays propagating along different paths in the EPE grating experience different phase shifts; The distance between adjacent grating strips in the first segment is the same as the distance between adjacent grating strips in the second segment.

2. The EPE grating according to claim 1, wherein, Each of the plurality of grating strips in the second segment is offset by a certain distance in a direction perpendicular to the direction of the grating strip, compared to the corresponding grating strip in the first segment.

3. The EPE grating according to claim 2, wherein, The first grating strip of the first segment is the corresponding grating strip of the first grating strip of the second segment, and the second grating strip of the first segment is the corresponding grating strip of the second grating strip of the second segment.

4. The EPE grating according to claim 2 or 3, wherein, The distance is less than the period of the EPE grating.

5. The EPE grating according to claim 2, wherein, Each of the plurality of grating strips in the second segment is offset laterally from the corresponding grating strip in the first segment by the distance described above.

6. The EPE grating according to claim 2, wherein, Each of the plurality of grating strips in the second segment is offset by the distance from the corresponding grating strip in the first segment in the vertical direction.

7. The EPE grating according to claim 1, wherein, The EPE grating is a dual-period grating.

8. The EPE grating according to claim 1, wherein, The first segment of the EPE grating is arranged to cause a first phase shift in light rays deflected in the first segment, and the second segment of the EPE grating is arranged to cause a second phase shift in light rays deflected in the second segment.

9. The EPE grating according to claim 8, wherein, The first phase shift is different from the second phase shift.

10. The EPE grating according to claim 8 or 9, wherein, The amplitude of the light ray deflected in the first segment is the same as the amplitude of the light ray deflected in the second segment.

11. The EPE grating according to claim 1, wherein, For light rays guided to the EPE grating, the second segment follows the first segment.

12. The EPE grating according to claim 1, wherein, The EPE grating also includes a plurality of grating strips in the third segment, and each of the plurality of grating strips in the third segment is offset by a certain distance from the corresponding grating strip in the first segment in a direction perpendicular to the direction of the grating strip.

13. The EPE grating according to claim 1, wherein, The EPE grating is arranged to propagate and couple light from the EPE grating, and is also arranged to operate as an internal coupler.

14. The EPE grating according to claim 1, wherein, The EPE grating is arranged to keep the amplitude of light rays propagating through different paths in the EPE grating constant.

15. An optical waveguide arrangement for displaying images, comprising: Optical waveguide; A coupling grating is used to diffractively couple the image to the optical waveguide; A coupling grating is used to diffractically couple the image out of the optical waveguide; as well as The EPE grating of any one of claims 1 to 14, wherein the EPE grating is located between the input grating and the output grating for extending the image on the output grating as the exit pupil.

16. A personal display device comprising the optical waveguide arrangement of claim 15, wherein the personal display device is a head-mounted display (HMD) or a head-up display (HUD).

Images