Low-distortion imaging through a c-shaped planar optical architecture

Abstract

Embodiments include optical systems that can be included in waveguide displays. Waveguide devices according to some embodiments include an incoupler grating having a first grating vector G1 substantially normal to a first axis x; a first eye pupil expander grating having a second grating vector G2 and a first angle Φ G relative to the first axis; a second eye pupil expander grating having a third grating vector G3 and an angle substantially equal to 90° + Φ G relative to the first axis; and an outcoupler grating having a fourth grating vector G4 substantially normal to the first axis. Exemplary embodiments describe relationships between grating vectors, angle Φ G and related parameters to achieve a satisfactory field of view while reducing distortion.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to European patent application No. EP20305928 entitled “LOW DISTORTION IMAGING THROUGH AC-SHAPE FLAT OPTICAL ARCHITECTURE”, filed on August 13, 2020. Background Technology

[0003] This disclosure relates to the fields of optics and photonics, and more specifically to optical devices comprising at least one diffraction grating. It can be applied in the field of conformal and wearable optics (e.g., AR / VR glasses (augmented reality / virtual reality)) and in a variety of other consumer electronics products including displays and / or lightweight imaging systems (including head-up displays (HUDs)), such as in the automotive industry.

[0004] This section is intended to introduce the reader to various aspects of the art that may relate to the various aspects of this disclosure described below and / or claimed. This discussion is intended to help provide the reader with background information to facilitate a better understanding of the various aspects of the systems and methods described herein. Therefore, it should be understood that these statements should be interpreted in this context, rather than as an admission of prior art.

[0005] AR / VR glasses are considered the next generation of human-computer interfaces. The development of AR / VR glasses (and more generally, protective electronic devices for glasses) is associated with many challenges, including reducing the size and weight of such devices and improving image quality (in terms of contrast, field of view, color depth, etc.) to achieve a truly immersive user experience.

[0006] The trade-off between image quality and physical size in optics has spurred research into ultracompact optical components that could serve as building blocks for more complex optical systems, such as AR / VR glasses. It is hoped that such optical components will be easy to manufacture and replicate.

[0007] In such AR / VR glasses, various types of refractive and diffractive lenses and beamforming components are used to guide light from a microdisplay or projector to the human eye, thereby allowing the formation of virtual images that are superimposed on the physical world seen with the naked eye (in the case of AR glasses) or captured by a camera (in the case of VR glasses).

[0008] Some types of AR / VR glasses utilize optical waveguides, where light propagates into the waveguide only within a limited internal angle range via TIR (Total Internal Reflection). The FoV (Field of View) of the waveguide depends on the waveguide material and other factors.

[0009] The FoV of a waveguide can be expressed as the value of the waveguide propagating through the TIR. The maximum span. In some cases, such as Figure 2 As shown, the maximum angular span that can be coupled into a waveguide can be expressed by two rays: one with an incident angle of incidence. Critical ray ( Figure 2 In ) and having an angle of incidence Grazing rays ( Figure 2 In The critical ray is just the right distance from the critical ray. Limited critical angle The light rays diffracted into the waveguide, where n² is the refractive index of the waveguide material and λ is the wavelength of the incident light. Above the critical angle... Total internal reflection (TIR) ​​occurs. A grazing ray is a ray with an input angle that can be... The grazing incident diffracted into the waveguide. The theoretical FoV of the waveguide presented above is for a single-mode system, where a single diffraction mode is used to carry the image: +1 or -1 diffraction mode.

[0010] Figure 3 A graph is shown showing a reasonable range for n2. For n2 = 1.5, the total field of view of the single-mode system is more precisely limited to Δθ1 = 28.96 degrees. It can be seen that 60 degrees FoV is a practical limitation for some types of waveguides, as it is generally not feasible to use materials with a refractive index higher than 2.0.

[0011] By utilizing a second propagation direction within the waveguide, the field of view of the optical waveguide can be further expanded, effectively doubling the field of view.

[0012] In WO2017180403, a waveguide with extended field of view (ultra-high FoV) was proposed, which uses dual-mode image propagation. In this method, a diffraction mode +1 is used to carry one side of the image in one direction, and a -1 mode is used to propagate the opposite side of the image in the opposite direction in the waveguide. The two half-images are combined using a pupil dimmer and an external coupler at the waveguide exit, allowing the user to see a single image.

[0013] Using a diffraction order higher than one has the effect of multiplying the wavelength by the order used in the diffraction equation. Since the grating spacing is directly a function of the product Mλ, this means the grating spacing is multiplied by M. This allows for larger structures for internal couplers and opens up new possibilities in fabrication techniques. For example, nanoimprinting can be used. Furthermore, fewer lines are required per mm of grating density, resulting in a simpler fabrication process because the structure will have an over-wavelength dimension rather than a sub-wavelength dimension. Such an optical waveguide using ±2 diffraction orders provides a FoV of approximately 60° with a refractive index of 1.5. Therefore, a 60° field of view can be obtained using a material with a refractive index of 1.5 instead of 2 in a single mode.

[0014] However, 60° FoV is still limited relative to the total human field of vision, in which stereoscopic vision is effective for human vision and is approximately 114°.

[0015] An architecture using two waveguides as a full RGB combiner has been studied, in which the green FoV is shared between the first and second waveguides, as described in BCKress, “Optical waveguide combiners for AR headsets: features and limitation,” Proc. of SPIE, Vol. 11062, p. 110620J, 2019.

[0016] Waveguide-based AR / VR glasses can exhibit a wide field of view along one direction (e.g., horizontal) but may have a narrower field of view along another direction (e.g., vertical). However, since AR / VR applications typically require a specific aspect ratio, for practical purposes, limiting the field of view along one direction may effectively limit the field of view along another direction. Summary of the Invention

[0017] References to "an embodiment," "an embodiment," and "an exemplary embodiment" in the specification indicate that the described embodiment may include a particular feature, structure, or characteristic, but not every embodiment is required to include that particular feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Additionally, when a particular feature, structure, or characteristic is described in connection with an embodiment, such feature, structure, or characteristic may be used in conjunction with other embodiments, whether or not it is explicitly described.

[0018] In some embodiments, a waveguide device includes an inner coupler grating configured to use a diffraction order M1, the inner coupler grating having a first grating spacing Λ1 and being substantially perpendicular to a first axis. First grating vector A first pupil dilator grating, configured to use diffraction order M2, has a second grating vector. The second grating spacing Λ2 and the first angle Φ relative to the first axis G A second pupil dilator grating configured to use diffraction order M3, the second pupil dilator having a third grating vector. The third grating spacing Λ3 and the angle between 80° and Φ relative to the first axis G and 100°+Φ G The angle between; and the external coupler grating, which is configured to use diffraction order M4, having a fourth grating spacing Λ4 and a fourth grating vector substantially perpendicular to the first axis. In some implementations, the third grating spacing Λ3 of the second pupil dilator essentially satisfies:

[0019]

[0020] In some implementations, the outer coupler grating is configured to use a first diffraction order such that |M4|=1, and at least one of the inner coupler grating and the pupil dilator grating is configured to use a second diffraction order.

[0021] In some implementations, the outer coupler grating is configured to use a first diffraction order such that |M4| = 1, and the inner coupler grating, the first pupil dilator grating, and the second pupil dilator grating are configured to use a second diffraction order such that |M1| = |M2| = |M3| = 2.

[0022] In some implementations of waveguide devices, the fourth grating spacing Λ4 of the external coupler essentially satisfies:

[0023]

[0024] In some implementations, the grating spacings Λ2 and Λ3 essentially satisfy:

[0025]

[0026] in

[0027]

[0028] In some implementations, the grating spacing Λ1 essentially satisfies:

[0029]

[0030] In some implementations, the grating spacing is within 20% of the following values:

[0031] Λ1 = 851.38nm

[0032] Λ2 = 729.46 nm

[0033] Λ3 = 729.46nm

[0034] Λ4 = 1308.64 nm.

[0035] In some implementations, the grating spacing is within 10% of the following values:

[0036] Λ1 = 851.38nm

[0037] Λ2 = 729.46 nm

[0038] Λ3 = 729.46nm

[0039] Λ4 = 1308.64 nm.

[0040] In some implementation schemes, the following relationship is essentially satisfied:

[0041]

[0042] In some implementations, the following relationship is essentially satisfied, where Φ K =90°-Φ G :

[0043]

[0044] and

[0045]

[0046] in

[0047]

[0048] In some implementation schemes, the following relationship is essentially satisfied:

[0049]

[0050] and

[0051] Λ2=M2λsin(φ K -Δφ / 2)

[0052] in

[0053] Δφ=sin -1 (sin(2φ K -N)).

[0054] In some implementation schemes, the following relationship is essentially satisfied:

[0055]

[0056] and

[0057]

[0058] in

[0059]

[0060] in

[0061]

[0062] and

[0063] Δ=(cosφ K ) 2 -4α(α+sinφ K ).

[0064] In some implementation schemes, the following relationship is essentially satisfied:

[0065]

[0066] and

[0067]

[0068] in

[0069]

[0070] In some implementations, the waveguide device also includes an image generator configured to generate an image, wherein an inner coupler grating is configured to couple the image to an outer coupler grating along at least one optical path.

[0071] A waveguide device according to some embodiments includes an inner coupler grating, at least one pupil dilatator grating, and an outer coupler grating, wherein each of the inner coupler grating, the pupil dilatator grating, and the outer coupler grating has a grating spacing greater than 600 nm.

[0072] A waveguide device according to some embodiments includes an inner coupler grating, at least one pupil expander grating, and an outer coupler grating, wherein the outer coupler grating is configured to use a first diffraction order, and at least one of the inner coupler grating and the pupil expander grating is configured to use a second diffraction order. In some embodiments, both the inner coupler grating and the pupil expander grating are configured to use a second diffraction order.

[0073] According to some implementation methods, the method includes: coupling light into a waveguide using an inner coupler grating configured to use a diffraction order M1, the inner coupler grating having a first grating spacing Λ1 and being substantially perpendicular to a first axis. First grating vector Light is diffracted using a first pupil dilatator grating configured to use diffraction order M2, the first pupil dilatator having a second grating spacing Λ2 and a second grating vector. Having a first angle Φ relative to the first axis G Light is diffracted using a second pupil dilatator grating configured to use diffraction order M3, the second pupil dilatator having a third grating spacing Λ3 and a third grating vector. Having an angle of 80°+Φ relative to the first axis G and 100°+Φ G The second angle between; and the use of an external coupler grating configured to couple light out of the waveguide using a diffraction order M4, the external coupler grating having a fourth grating spacing Λ4 and a fourth grating vector substantially perpendicular to the first axis. Attached Figure Description

[0074] Figure 1A This is a schematic diagram of the cross-section of a waveguide display.

[0075] Figure 1B This is a schematic diagram of a binocular waveguide display with a first layout featuring diffractive optical components.

[0076] Figure 1C This is a schematic diagram of a binocular waveguide display with a second layout featuring diffractive optical components.

[0077] Figure 1D This is a schematic exploded view of a dual-waveguide display based on some implementation schemes.

[0078] Figure 1E This is a cross-sectional schematic diagram of a dual-waveguide display according to some implementation schemes.

[0079] Figure 2 This is a schematic diagram of a single-mode system, in which a single diffraction mode is used to carry the image using either a +1 or -1 diffraction mode.

[0080] Figure 3 This is an exemplary graph showing the waveguide's field of view as a function of the refractive index of its material.

[0081] Figure 4 It is a cross-sectional side view of a lens system that provides a true exit pupil.

[0082] Figure 5 This is a cross-sectional side view of a lens system suitable for use in some implementation schemes.

[0083] Figure 6 This is a cross-sectional view of a symmetrical diffraction grating.

[0084] Figure 7 This is a cross-sectional view of another symmetrical diffraction grating.

[0085] Figure 8 This is a cross-sectional view of a tilted diffraction grating.

[0086] Figure 9 The application of symmetrical diffraction with asymmetric gratings using two different diffraction gratings is shown.

[0087] Figure 10 It schematically shows the target Figure 9 The typical diffraction efficiency of a grating is a function of the incident angle.

[0088] Figure 11A It is a cross-sectional view of the diffraction grating profile used in some implementations.

[0089] Figure 11B Is it used as Figure 11A A schematic diagram of the grating profile in the image coupling light across different incident angles.

[0090] Figure 12 This is a schematic plan view of the arrangement of diffraction gratings on a waveguide display according to some implementation schemes.

[0091] Figure 13 This is a schematic diagram illustrating the unwanted distortion that occurs in some arrangements of diffraction gratings on a waveguide.

[0092] Figure 14A and Figure 14B It is a schematic isometric view of a grating on a surface, showing the vectors used in the grating equation.

[0093] Figure 15 This is a schematic plan view of the arrangement of diffraction gratings on a waveguide display according to some implementation schemes.

[0094] Figure 16A This is a schematic side view showing the wave vector of light incident on the inner coupler grating and the wave vector of the resulting diffracted light.

[0095] Figure 16B It is light passing through Figure 15 A schematic unfolded side view of waveguide propagation.

[0096] Figure 17 This is a graph showing the relationship between the pupil dilator and the grating spacing, which can be implemented in some embodiments.

[0097] Figure 18 This is a schematic plan view showing the arrangement of diffraction gratings on a waveguide display with parameters used in some embodiments.

[0098] Figure 19A and Figure 19B This is a schematic diagram of the wave vectors representing the propagation of light through an exemplary waveguide system. Figure 19A The propagation is shown as half of the field of view. Figure 19B The propagation of a single ray of light is shown.

[0099] Figure 20 The image is illustrated by waveguide imaging of two rectangles according to some embodiments. The rectangle on the right represents the display side, and the rectangle on the left represents the system's image output.

[0100] Figure 21 This shows Λ2(Φ) G sin(Φ) G For Φ G A graph showing the variations of different values. Detailed Implementation

[0101] Overview of exemplary waveguide architectures

[0102] This paper describes waveguide display systems and methods. Figure 1A An exemplary waveguide display device is shown in the figure. Figure 1A This is a schematic cross-sectional side view of the waveguide display device in operation. The image is projected by image generator 102. Image generator 102 can project the image using one or more of a variety of technologies. For example, image generator 102 can be a laser beam scanning (LBS) projector, a liquid crystal display (LCD), a light-emitting diode (LED) display (including organic LED (OLED) or micro LED (μLED) displays), a digital light processor (DLP), a liquid crystal on silicon (LCoS) display, or other types of image generators or light engines.

[0103] The light representing the image 112 generated by the image generator 102 is coupled into the waveguide 104 via a diffraction inner coupler 106. The inner coupler 106 diffracts the light representing the image 112 into one or more diffraction orders. For example, a ray 108 that is part of the bottom of the image is diffracted by the inner coupler 106, and one of the diffraction orders 110 (e.g., second order) is at an angle that can propagate through the waveguide 104 by total internal reflection.

[0104] At least a portion of the light 110 coupled into waveguide 104 via diffractive inner coupler 106 is coupled out of the waveguide via diffractive outer coupler 114. At least some of the light coupled out of waveguide 104 replicates the angle of incidence of the light coupled into the waveguide. For example, in the illustration, the externally coupled rays 116a, 116b, and 116c replicate the angle of the internally coupled ray 108. Since the light leaving the outer coupler replicates the direction of the light entering the inner coupler, the waveguide essentially replicates the original image 112. The user's eye 118 can focus on the replicated image.

[0105] exist Figure 1A In the example, the external coupler 114 allows a single input beam (such as beam 108) to generate multiple parallel output beams (such as beams 116a, 116b, and 116c) by reflecting only a portion of the externally coupled light each time. In this way, even if the eye is not perfectly aligned with the center of the external coupler, at least some light from each part of the image may reach the user's eye. For example, if the eye 118 moves downwards, beam 116c can enter the eye even if beams 116a and 116b do not, so the user can still perceive the bottom of image 112 despite the positional shift. Therefore, the external coupler 114 partially operates as an exit pupil dilator in the vertical direction. The waveguide may also include one or more additional exit pupil dilators (…). Figure 1A (not shown in the image) to expand the exit pupil in the horizontal direction.

[0106] In some implementations, waveguide 104 is at least partially transparent to light originating from outside the waveguide display. For example, at least some light 120 from a real-world object (such as object 122) passes through the waveguide 104, allowing the user to see the real-world object while using the waveguide display. Since the light 120 from the real-world object also passes through diffraction grating 114, there will be multiple diffraction orders and therefore multiple images. To minimize the visibility of multiple images, it is desirable that the zeroth order diffraction (not deflected by 114) has a high diffraction efficiency for light 120, while higher diffraction orders have lower energy. Therefore, in addition to extending and externally coupling virtual images, external coupler 114 is preferably configured to pass through the zeroth order of the actual image. In such implementations, the image displayed by the waveguide display may appear to be superimposed on the real world.

[0107] In some implementations, as described further in detail below, the waveguide display includes more than one waveguide layer. Each waveguide layer can be configured to preferentially deliver light with a specific wavelength range and / or angle of incidence from the image generator to the viewer.

[0108] like Figure 1B and Figure 1CAs shown, waveguide displays with internal couplers, external couplers, and pupil expanders can have various different configurations. Figure 1B An exemplary layout of a binocular waveguide display is shown. Figure 1B In the example, the display includes waveguides 152a and 152b for the left and right eyes, respectively. The waveguides include inner couplers 154a and 154b, pupil dilators 156a and 156b, and components 158a and 158b, which operate as outer couplers and horizontal pupil dilators. The pupil dilators 156a and 156b are arranged along an optical path between the inner and outer couplers. An image generator (not shown) can be provided to each eye and is arranged to project light representing the image on the corresponding inner coupler.

[0109] Figure 1C Another exemplary layout of a binocular waveguide display is shown in the image. Figure 1C In the example, the display includes waveguides 160a and 160b for the left and right eyes, respectively. The waveguides include inner couplers 162a and 162b. Light from different parts of the image can be coupled by the inner couplers 162a and 162b to different directions within the waveguides. Inner-coupled light traveling to the left passes through pupil dilatators 164a, 164b and 165a, 165b, while inner-coupled light traveling to the right passes through pupil dilatators 166a, 166b and 167a, 167b. Having passed through the pupil dilatators, the light is coupled out of the waveguides using outer couplers 168a and 168b to substantially replicate the image provided at the inner couplers 162a and 162b.

[0110] In different implementations, different features of the waveguide display can be disposed on different surfaces of the waveguide. For example (e.g.) Figure 1A In some configurations, both the inner and outer couplers can be positioned on the front surface of the waveguide (away from the user's eye). In other embodiments, the inner and / or outer couplers can be positioned on the rear surface of the waveguide (facing the user's eye). The inner and outer couplers can be positioned on opposite surfaces of the waveguide. In some embodiments, one or more of the inner coupler, outer coupler, and pupil dilator can be present on both surfaces of the waveguide. The image generator can be positioned facing either the front or rear surface of the waveguide. The inner coupler is not necessarily on the same side of the waveguide as the image generator. Any pupil dilator in the waveguide can be positioned on the front, rear, or both surfaces of the waveguide. In displays with more than one waveguide layer, different layers can have different configurations of inner couplers, outer couplers, and pupil dilators.

[0111] Figure 1D This is a schematic exploded view of a dual-waveguide display according to some embodiments, including an image generator 170, a first waveguide (WG1) 172 and a second waveguide (WG2) 174. Figure 1E This is a schematic side view of a dual-waveguide display according to some embodiments, including an image generator 176, a first waveguide (WG1) 178, and a second waveguide (WG2) 180. The first waveguide includes a first transmission diffraction inner coupler (DG1) 180 and a first diffraction outer coupler (DG6) 182. The second waveguide has a second transmission diffraction inner coupler (DG2) 184, a reflection diffraction inner coupler (DG3) 186, a second diffraction outer coupler (DG4) 188, and a third diffraction outer coupler (DG5) 190. Different embodiments may use different arrangements of optical components (such as different arrangements of pupil dilatators) on the first and second waveguides.

[0112] Although Figures 1A to 1E The example demonstrates the use of waveguides in near-eye displays, but the same principle can be applied to other display technologies, such as head-up displays for automobiles or other applications.

[0113] Overview of exemplary coupling optical devices .

[0114] For a waveguide based on a diffraction grating with an optical system that generates a composite image to be superimposed in the field of view, it is desirable for the lens system to have a real, rather than virtual, exit pupil. In other words, its exit pupil is located outside the lens and is also the aperture stop of the lens.

[0115] Figure 4 The lens system provides a suitable exit pupil. The system has a disc-shaped aperture stop, the diameter of which depends on the diameter of the lens, which primarily limits the system size. Since there is no lens behind the aperture stop, it is the image of the aperture stop itself, and therefore the exit pupil. It is located where an internal coupler can be placed, or in its vicinity.

[0116] If any of the objects or images is at infinity, the lens system can be called afocal. Figure 4 The lens system is focalless on the image side because the light rays leaving the lens are parallel for every field, and the image exists at infinity.

[0117] The position of a point on an object can be called a field. Figure 4 The diagram shows light rays exiting five different fields. In some cases, a pixel can be considered a field. Compared to other quantities in the system, the size of a pixel can be assumed to be negligible.

[0118] like Figure 4As seen in the image, light from each field pours through the entire exit pupil. Therefore, if we reduce the aperture of the exit pupil, we will also uniformly block the amount of light from each pixel simultaneously across all fields, meaning the light intensity will decrease. This is the function of the aperture stop, and it confirms that the exit pupil and the aperture stop are the same in this lens, and that the exit pupil is real, not virtual.

[0119] The pupil can be tessellated in space. This means that light rays striking the pupil from the positive side (y>0) will undergo one diffraction process, while light rays striking the pupil from the negative side (y<0) will undergo another diffraction process. The origin of the y-axis is the optical axis. Light rays striking the pupil with a certain angular sign will undergo a specific process, while those striking with the opposite sign will undergo another diffraction process. Alternatively, tessellation of the pupil angle can result in light rays with a range of [θ1, θ2] being diffracted in one direction of the waveguide, while light rays with a range of [-θ1, -θ2] are diffracted in the opposite direction.

[0120] Another characteristic of a focalless lens is that it maps all pixels from the display to a spherical coordinate system, where each pixel is referenced by its corresponding position in Cartesian coordinates via its (x, y) coordinates on the display. Relative to Figure 4 The image plane can be considered as an xy-plane, where the y-axis extends vertically across the page and the x-axis is perpendicular to the page. After a focal-free lens system, rays emanating from a single field cannot be referenced by x or y because they diffuse, but they each have a unique direction distinct from one another between pixels. The lens transforms pixel (x,y) coordinates into spherical (θ,Φ) pairs. This means that for each ray direction in the exit pupil (or inner coupler), we process another pixel.

[0121] exist Figure 5 In the example, rays from a field y>0 and rays from a field y<0 have angles with opposite signs at the exit pupil in polar coordinates. If we use a spherical coordinate system with the z-axis pointing along the optical axis, the polar angles are always between 0 and pi (positive), and only the azimuth direction sign will distinguish whether a ray strikes the exit pupil 'from above' or 'from below'. At each location along the exit pupil, we have positive and negative ray directions in polar coordinates.

[0122] When using symmetric diffraction modes, the diffraction grating will diffract the incoming light in either an additive or subtractive order. In some cases, if the light has a particular sign orientation, it will diffract in one mode, and if that sign changes, it will diffract into the opposite mode. In fact, mathematically, diffraction always occurs in all modes. Therefore, what we mean here is that if, for an incoming light in a particular direction, we diffract into a particular mode, then the energy in that mode is stronger than in the mode with the opposite sign. The symmetry here means that if the additive direction diffracts efficiently into mode M, then the subtractive direction will diffract efficiently into the -M direction. (M is a relative natural number.)

[0123] Symmetric diffraction gratings typically allow for the pre-existing characteristics of symmetrical diffraction modes. This characteristic can be achieved by using a basic structure (fundamental spacing) with left-right geometric symmetry. Blazed tilt gratings are not symmetrical diffraction gratings. Gratings based on square-shaped stepped (gate-shaped) structures can be symmetrical diffraction gratings. Figure 6 and Figure 7 An example of a symmetrical diffraction grating is provided.

[0124] Exemplary implementations use symmetric diffraction gratings that enable very efficient symmetric diffraction modes. For incident angles with opposite signs, some implementations provide highly efficient +M or -M diffraction modes.

[0125] Figure 8 The diagram shows a tilted grating that, when illuminated from above, will be effective for light tilted to the left (a negative angle in our case) and will have the optimal diffraction pattern towards the right side. When illuminated from the right side (a positive angle), the diffraction pattern towards the left will be very weak.

[0126] Figure 9 The application of symmetrical diffraction with asymmetric gratings using two different diffraction gratings is shown. Figure 9 The internally coupled grating in the [structure] has an asymmetric groove profile. The grating is divided into two parts, each primarily coupled in one direction. Figure 9 In this system, for a limited angular range, light rays from the left-hand side will diffract with high efficiency to the left, and light rays from the right-hand side will diffract with high efficiency to the right. In addition to this process, a small fraction of the energy will also be diffracted in the opposite direction for the opposite diffraction pattern.

[0127] In such Figure 9In the diffraction grating, only light rays with a negative propagation direction striking the right-hand side grating will diffract efficiently into the right-hand side diffraction mode. Light rays with a negative incident angle striking the right-hand side diffraction grating will not diffract into the right-hand side diffraction mode (but they will actually have low intensity). Only light rays with a positive propagation direction striking the left-hand side grating will diffract efficiently into the left-hand side diffraction mode. Light rays with a negative incident angle striking the left-hand side diffraction grating will only diffract into the left-hand side diffraction mode with low intensity. Thus, at each position of the exit pupil, there is an equal distribution of positive and negative angle propagation, and approximately half of the light will be lost. Figure 10 The typical diffraction efficiency for two gratings as a function of the incident angle is shown.

[0128] In contrast, some implementations use features such as Figure 11A The diffraction grating with the outline shown provides more uniform light coupling across different incident angles, such as... Figure 11B It is shown schematically in the middle.

[0129] Overview of exemplary waveguides with C-shaped geometry .

[0130] Figure 12 This is a schematic diagram of a waveguide with a C-shaped geometry used in some implementations. The inner coupler grating 1202 diffracts half of the angular exit pupil from the image generator into the positive x-direction (in...). Figure 12 (from center to left) positive level (in) Figure 12 In the example (secondary), the inner coupler diffracts the remaining half of the exit pupil into a negative diffraction mode in the negative x-direction. (In some implementations, a central overlap region may exist near the vertical incident direction, from which diffraction occurs in both directions.) Therefore, Figure 12 The waveguide provides two optical paths. Light in each path is deflected approximately downwards by a first set of pupil dilators 1204a, 1204b (and the pupil expands approximately horizontally simultaneously). Then, a second set of pupil dilators 1206a, 1206b expands the pupil approximately vertically, while simultaneously deflecting the optical path toward a downward diffraction grating into an external coupler 1208. The external coupler extracts the two optical paths from the waveguide, where they are bounced by total internal reflection, and the final image can then be observed by an eye placed (along the z-axis) perpendicular to the plane of the diagram.

[0131] The inner coupler spacing can be set based on parameters such as the waveguide's refractive index, the angular overlap near vertical incidence, and the grazing angle in the waveguide. The inner coupler spacing can also be selected based on the desired horizontal field of view; for example, the spacing can be chosen to substantially maximize the horizontal field of view.

[0132] In the example provided below, the parameters of the inner coupler are indexed as 1. The first pupil dilator is indexed as 2, the second pupil dilator as 3, and the outer coupler as 4. The incident ray is indexed as 0. The ray diffracted by element 1 is indexed as 1, and so on. Therefore, the ray emitted from the system is indexed as 4. For a waveguide with a refractive index of n2 = 1.52 nm and for a red wavelength of λ = 625 nm, for the case of no angular overlap... The grazing angle, using the second diffraction order (M=2), allows the spacing Λ1 of the inner coupler to be selected according to the following formula:

[0133]

[0134] in

[0135] Then, for a 45° pupil dilator, the pupil dilator spacing Λ2 and Λ3 can be selected according to the following formula.

[0136] A2=A3=Wλsin(45-φ / 2)

[0137] in

[0138] sinφ=lw

[0139] A spacing of 729.46 nm was obtained. Then, the outer coupler can be selected with the same spacing size as the inner coupler. With this parameter selection, using the second diffraction order for each grating, and for each grating |M| = 2, the following is obtained: Figure 13 A schematic diagram.

[0140] exist Figure 13 In the schematic diagram, regular rectangle 1302 represents half of the pixels of the display before propagation through the waveguide with the parameters described above. These pixels are mapped to the output array shown by region 1304, which has been distorted into a more trapezoidal shape. Pixels within the original region 1302 do not overlap onto the distorted region 1305, and the rectangular half-display does not image as a rectangle. Furthermore, nearby pixels (such as those in rectangle 1306) have been mapped to the center at rectangle 1308. This type of distortion cannot typically be corrected electronically.

[0141] To ensure compatibility with pupil stitching inner couplers used in very high field-of-view systems, it is desirable to have little to no distortion in the C-shaped geometry.

[0142] Example parameters for distortion reduction .

[0143] The grating equation describing the relationship between the incident beam and one or more diffracted beams can be used as follows: Figures 14A to 14B The vectors shown are represented in vector format. For clarity, Figures 14A to 14B A single diffraction grating on a substrate is shown, where the substrate can be considered as part of a waveguide. Grating vector. like Figure 14A As shown, the direction pointing parallel to the lines of the diffraction grating has a magnitude of Where Λ is the grating spacing. (To avoid confusion, it can be noted that in some sources, the direction of the "grating vector" is considered perpendicular to the grating lines, and the grating equation is changed accordingly.) Outward normal It is a unit vector perpendicular to the grating plane and pointing outwards from the grating surface. (Inward normal) It is a unit vector perpendicular to the grating plane and pointing inward from the grating surface, such that...

[0144] like Figure 14B As shown, the wave vector of the incident beam is represented as It points in the direction of the incident beam and has The magnitude of λ is given by λ, where n1 is the refractive index of the medium through which the incident beam travels, and λ is the wavelength of the beam in vacuum. Similarly, the wave vector of the diffracted beam is expressed as λ = n1 / λ. It points in the direction of the diffracted beam and has The size of is given by , where n2 is the refractive index of the medium in which the diffracted beam travels (which can be the same as the medium of the incident beam). It can be noted that multiple diffracted beams can be generated from a single incident beam, including some diffracted beams that are directed outside the substrate; however, for simplicity, only a single diffracted beam is shown.

[0145] use Figures 14A to 14B The grating equation, which represents the relationship between the incident beam and one or more diffracted beams, and the grating vector and wave vector, can be expressed as:

[0146]

[0147] Where M is an integer representing the diffraction order. The operator “∧” here represents the cross product of vectors (sometimes represented by “x” in other sources). This equation is satisfied in the case of the reflection diffraction order (in which case the medium of the incident beam is the same as the medium of the diffracted beam, such that n1 = n2) and in the case of the transmission diffraction order (in which case the medium of the incident beam is not necessarily the same as the medium of the diffracted beam).

[0148] Not every mathematical solution to the above equation necessarily represents a physical situation. For example, if If the equation is satisfied, then the vector This equation also applies to any value p. That is, the above grating equation itself does not provide a unique solution for the wave vector component perpendicular to the grating plane, referred to here as the z-component. However, the z-component k...z The size can be recovered based on the norm.

[0149]

[0150] Where the z component k z The notation is determined based on physical constraints. For example, k z The sign of the beam is reversed when the beam is reflected, but remains the same when the beam is transmitted.

[0151] Figure 15 The diagram illustrates a diffraction grating layout for a portion of a waveguide display according to some embodiments. Figure 12 Compared to waveguide layouts, for simplicity, Figure 15 The pupil dilator on the right side was omitted (similar to...). Figure 12 (referring to 1204b and 1206b), but it should be understood that some implementations include a right-side pupil dilator, and they can be used with... Figure 15 The pupil dilators on the left eye are arranged symmetrically.

[0152] like Figure 15 As shown, the inner coupler grating 1502 has a grating vector. It is oriented at a 90° angle relative to the x-axis in the grating plane. The first pupil dilator 1504 has a grating vector. Its angle relative to the x-axis Orientation. The second pupil dilator 1506 has a grating vector. Its angle relative to the x-axis Orientation. In some implementation schemes, and They are perpendicular to each other and the angle Φ is defined. G Make

[0153] and

[0154] The output coupling grating 1508 has a grating vector It is oriented at an angle of 90° relative to the x-axis.

[0155] In operation, it has a wave vector. The beam (which can be generated by an image generator) is coupled into the waveguide using a transmission diffraction stage M1 via an internal coupler 1502. The internally coupled beam has a wave vector. At least a portion of the internally coupled beam is diffracted by the first pupil dilator 1504 to the reflection diffraction order M2, thereby producing a beam with a wave vector. The beam. At least a portion of this beam is diffracted by the second pupil dilator 1506 to the reflection diffraction order M3, thereby producing a beam with a wave vector. The beam. At least a portion of the beam is externally coupled to grating 1508 using diffraction order M4, wherein the externally coupled beam has a wave vector In some implementations, each of the first three gratings 1502, 1504, and 1506 uses a +2 diffraction order, while the fourth grating 1508 uses a -2 diffraction order. However, different diffraction orders can be used in different implementations.

[0156] Figure 16A This is a schematic side view illustrating the operation of the inner coupler grating 1502 on the wave vector of the beam. It has a wave vector. and angle The incident beam (in the plane of the attached figure) is diffracted into a beam with a wave vector. and glancing angle A beam of light. It has a wave vector. The incident beam diffracts onto the wave vector Its critical angle Orientation is used for total internal reflection. It has the ability to... and The wave vector at the incident angle between the two propagates to the left (in this example) through the waveguide. The wave vector with a symmetrical orientation (having an inverted x-component) propagates to the right through the waveguide. There may be some overlap between propagation to the left and to the right; for example, a portion of the incident light with a near-perpendicular incident wave vector may propagate in both directions to avoid a visible gap between the left and right halves of the field of view.

[0157] In some implementations, the spacing Λ1 of the inner coupler grating is based on the grazing angle. and the angle of incidence diffracted to the grazing angle Choose an angle. This can be used to represent the angular overlap between the left and right halves of the field of view. Using the grating equations (whose geometric interpretation is...) Figure 16A (As shown in the diagram), the spacing Λ1 can be selected as follows:

[0158]

[0159]

[0160]

[0161] For example, taking values and Where n1 = 1 and n2 = 1.52, and for wavelength λ = 625nm, the spacing Λ1 = 882.5nm can be selected.

[0162] Figure 16B It is light passing through Figure 15 A schematic "unfolded" side view of the waveguide.

[0163] Using the grating equations described above, the wave vector can be described by the following relationship:

[0164]

[0165]

[0166]

[0167]

[0168] Remove from these equations and Incident beam and the emitted beam The relationship between them can be described as follows:

[0169]

[0170] To avoid distortion, it is desirable for the incident beam to... and the emitted beam The difference between the x and y components is small, for example, essentially equal to 0. The z component... and The signs of the z-components can be opposite, depending on the waveguide configuration. For example, if the image generator and the viewer are on the same side of the waveguide, the signs of the z-components can be opposite, and if the image generator and the viewer are on opposite sides of the waveguide, they can have the same sign.

[0171] Given the above equation, and setting the conditions... As can be seen, the following grating characteristics do not provide distortion.

[0172]

[0173] It can be noted that this relationship is satisfied in some implementations using diffraction orders different from the first diffraction order. For example, in some implementations, a system in which some or all of the diffraction gratings use a second diffraction order substantially satisfies the above relationship. In some implementations, different diffraction orders are used for different gratings while substantially satisfying the above relationship. For example, in some implementations, all gratings except the external coupler are configured to use the second diffraction order, while the external coupler is configured to use the first diffraction order. Using the first diffraction order at the external coupler can help reduce stray light effects that might otherwise be caused by diffraction of real-world images.

[0174] Because the grating equation is insensitive to changes in the z-component of the wave vector, it can be used regardless of the z-component. Is it relative to the z-component? Reverse.

[0175] Because of the sum of vectors Since the sum is 0, the x and y components of the sum are both added to 0. For the x component, this gives...

[0176] 0 = M4G 4x +M3G 3x +M2G 2x -M1G 1x

[0177] 0 = M3|G3|cos(90°+Φ) G )+M2|G2|cos(Φ G )

[0178] 0 = -M3|G3|sin(Φ) G )+M2|G2|cos(Φ G )

[0179] 0 = M3|G3|tan(Φ) G )-M2|G2|

[0180] 0 = 2πM³ tan(Φ) G ) / Λ3-2πM2 / Λ2

[0181] M2 / Λ2=M3tan(Φ G ) / Λ3

[0182]

[0183] In some implementations, the spacing Λ2 and angle Φ of the first pupillary dilator G Chosen to essentially maximize the field of view and spacing, and the spacing Λ3 and angle of the second pupil dilator. Use the above equations to select for reducing or minimizing distortion.

[0184] In some implementations, in order to substantially maximize the vertical field of view, the spacing Λ2 and angle φ of the first pupil dilator are... G It has one or more of the following relationships. In the following implementation, parameter φ is used. K It is convenient, among which

[0185] φ K =90°-Φ G .

[0186] As pointed out above, further review is possible.

[0187] In the first set of implementation schemes, the angle φ K Falling within the following range:

[0188]

[0189] In the first set of implementation schemes, the spacing Λ2 of the first pupil dilator can be selected according to the following formula.

[0190]

[0191] in

[0192]

[0193] In the second set of implementation schemes, the angle φ K Falling within the following range:

[0194]

[0195] In the second implementation scheme, the spacing Λ2 of the first pupil dilator can be selected according to the following formula.

[0196] Λ2=M2λsin(φ K -Δφ / 2)

[0197] in

[0198] Δφ=sin -1 (sin(2Φ K -N)).

[0199] In the third set of implementation schemes, the angle φ K Falling within the following range:

[0200]

[0201] In the third implementation scheme, the spacing Λ2 of the first pupil dilator can be selected according to the following formula.

[0202]

[0203] in

[0204]

[0205] in

[0206]

[0207] and

[0208] Δ=(cosφ K ) 2 -4α(α+sinφ K ).

[0209] In the fourth set of implementation schemes, angle ΦK satisfy:

[0210]

[0211] In the fourth implementation scheme, the spacing Λ2 of the first pupil dilator can be selected according to the following formula.

[0212]

[0213] in

[0214]

[0215] In some implementations, where Φ G At approximately 45°, Λ2 and Λ3 can be selected as follows:

[0216]

[0217] in

[0218]

[0219] And among them This is the selected grazing angle, which can be 75°. An exemplary solution Φ for different grating orientations. G like Figure 17 As shown.

[0220] Again from the sum of vectors Starting with the condition that the value is 0, the conditions for adding 0 to each y-component are given.

[0221] 0 = M4G 4y +M3G 3y +M2G 2y -M1G 1y

[0222]

[0223] 0 = M4 / Λ4 + M3cos(Φ) G ) / Λ3+M2sin(Φ G ) / Λ2-M1 / Λ1

[0224] Substituting Λ3 into the above expression gives

[0225]

[0226] It is reduced to using trigonometric identities.

[0227]

[0228] The above expression can be used to determine the spacing Λ4 of the external coupler.

[0229] Using the above expression, in some implementations, for exemplary implementations where the overlap angle is zero, Φ G =45°, the spacing and sequence of different gratings can be selected as follows:

[0230] Λ1 = 851.38 nm, M1 = 2

[0231] Λ2 = 729.46 nm, M2 = 2

[0232] Λ3 = 729.46 nm, M3 = 2

[0233] Λ4 = 1308.64 nm, M4 = -2

[0234] Using only the first diffraction order, the spacing and grating order in some implementations can be selected as follows:

[0235] Λ1 = 425.69 nm, M1 = 1

[0236] Λ2 = 364.73 nm, M2 = 1

[0237] Λ3 = 364.73 nm, M3 = 1

[0238] Λ4 = 654.32 nm, M4 = -1

[0239] In some implementations, different gratings use different diffraction orders. In one example of such an implementation, the spacing and grating order may be selected as follows:

[0240] Λ1 = 851.38 nm, M1 = 2

[0241] Λ2 = 729.46 nm, M2 = 2

[0242] Λ3 = 729.46 nm, M3 = 2

[0243] Λ4 = 654.32 nm, M4 = -1

[0244] In some implementations, all grating spacing is greater than 600 nm.

[0245] In some embodiments, one or more grating spacings have a value within 5% of the aforementioned values. In some embodiments, one or more grating spacings have a value within 10% of the aforementioned values. In some embodiments, one or more grating spacings have a value within 20% of the aforementioned values.

[0246] In some implementations, the external coupler grating is configured to use a first diffraction order such that |M4| = 1, and at least one of the internal coupler grating and the pupil dilatator grating is configured to use a second diffraction order. Using a first diffraction order with the external coupler grating typically provides the external coupler waveguide with better control over light from the surrounding scene (e.g., Figure 1A The better transparency of the light (120) is achieved, while the use of a second diffraction order for one or more other gratings simplifies the fabrication of these gratings by allowing for larger grating spacing. In some embodiments, the outer coupler grating is configured to use a first diffraction order such that |M4| = 1, and the inner coupler grating, as well as the first and second pupil dilatation gratings, are configured to use a second diffraction order such that |M1| = |M2| = |M3| = 2.

[0247] Figure 18 This is a schematic diagram of a portion of a waveguide display based on an implementation using the dimensions selected above. It should be noted that... Figure 18 The waveguide display may also include an additional pupil dilator on the right side of the inner and outer couplers, for example, in a symmetrical configuration relative to the pupil dilator shown on the left.

[0248] It can be noted that other relationships can be achieved based on the above configuration. For example, in some implementations, the grating spacing can be selected to substantially satisfy...

[0249]

[0250] Figure 19A and Figure 19B This is a schematic diagram of the wave vectors representing the propagation of light through an exemplary waveguide system. Figure 19A The propagation is shown as half of the field of view. Figure 19B The propagation of a single ray of light is shown.

[0251] Figure 20 The image is illustrated by waveguide imaging of two rectangles according to some embodiments. The rectangle 2002 on the right represents the display side, and the rectangle on the left represents the system's image output.

[0252] When selecting the grating spacing and orientation in a waveguide display, the limitations on the parameters need to be considered. Figure 21 This shows the different values ​​of Ф G Λ2 (as Φ) G The functions of ) and sin(Φ G A graph of the product of ). Figure 21 The curve in and angle Φ G The maximum value is at 37.48°. The minimum value is at... and angle Φ G=49.59°.

[0253] These values ​​can vary depending on the refractive index of the waveguide and the grazing angle within the waveguide. The spacing varies linearly with the diffraction order. Then, depending on the amount of overlap between the field of view coupled to the left and the field of view coupled to the right, this can cause variations in Λ1, and the range of Λ4 can be determined using the equations described above. In the case of no overlap in the system and using only the second diffraction order, the value of Λ4 can be chosen between 1211 nm and 1409 nm.

[0254] In the overview of the exemplary implementation, the inner coupler grating spacing Λ1 is selected based on the field of view to be coupled into the waveguide. The orientation of the first pupil expander can be selected, for example, to allow for an outer coupler with a relatively minimal spacing size, which can help minimize stray light. In some implementations, the first pupil expander may be oriented at an angle greater than 45 degrees, which may be desirable in implementations where the second pupil expander and the outer coupler are fused together to form a grating.

[0255] Once the orientation of the first pupillator has been chosen, the spacing Λ2 of the first pupillator can be selected to substantially maximize the field of view, or it can be chosen based on other considerations. The spacing Λ2 of the first pupillator can be, for example, determined based on... Figure 17 The spacing of the second pupil dilator can be selected using a curve graph. Then, the spacing of the second pupil dilator can be selected by solving the x-component of the distortion-free equation. The spacing of the external coupler can be derived using the y-component of the same equation.

[0256] In an exemplary implementation, the horizontal field of view can be magnified (e.g., maximized) by selecting the spacing Λ1 and diffraction order M1 of the inner coupler, and the vertical field of view can be magnified (e.g., maximized) by selecting the spacing Λ2 and diffraction order M2 of the first pupil dilator, and other parameters can be selected according to one or both of the following relationships to avoid distortion:

[0257]

[0258]

[0259] The parameters selected according to the embodiments described herein may deviate from the exact solution of the equations provided for practical reasons (e.g., tolerances in manufacturing processes) or other design considerations. In some embodiments, the grating spacing Λ is selected within 5% of the value satisfying the above equations. In some embodiments, the grating spacing Λ is selected within 10% of the value satisfying the above equations. In some embodiments, the angle Φ G Choose within 5° of the value that satisfies the above equation. In some implementations, the angle Φ GThe value is selected within 10° of the value satisfying the above equation. In some implementations, the grating vector... and It is not an exact 90° angle separation. In some implementations... and Between 85° and 95°. In some implementations... and Between 80° and 100°.

[0260] In some embodiments, all diffraction gratings of the waveguide are on the same surface of the waveguide (e.g., all on the user-facing surface or all on opposite surfaces). In various different embodiments, diffraction gratings may be disposed on different surfaces of the waveguide. For example, one or more gratings may be on the user-facing surface of the waveguide, while one or more other gratings may be on opposite surfaces of the waveguide. In some embodiments, waveguide gratings may overlap each other. Overlapping gratings may be on opposite sides of the waveguide, or they may at least partially overlap on the same surface of the waveguide. Overlapping gratings on the same surface may take the form of crosshairs in the overlapping regions.

[0261] In some implementations, instead of using two pupil dilatators for each half of the field of view, four polarization-selective pupil dilatators can be used for each half of the field of view. For example, the upper left quarter of the field of view can be handled using two pupil dilatators configured for a first polarization state, and the lower left quarter can be handled using two pupil dilatators configured for a second (e.g., orthogonal) polarization state. A similar (e.g., symmetrical) arrangement of polarization-sensitive pupil dilatators can be used to handle the upper right and lower right quadrants of the field of view. In such implementations, the pupil dilatators associated with each quarter of the field of view, together with the inner coupler grating and the outer coupler grating, form a set that substantially satisfies the relationships described herein.

[0262] The exemplary implementation provides a wide field of view, while also using the C-shaped geometry of the diffraction grating to provide imaging with little or no distortion.

[0263] In this disclosure, modifiers such as “first,” “second,” and “third” are sometimes used to distinguish different features. These modifiers do not imply any particular order of operation or arrangement of components. Furthermore, the terms “first,” “second,” “third,” etc., may have different meanings in different embodiments. For example, in one embodiment, a component that is a “first” component may be a “second” component in a different embodiment.

[0264] Although the features and elements have been described above in specific combinations, those skilled in the art will understand that each feature or element may be used alone or in any combination with other features and elements.

Claims

1. A waveguide device, the waveguide device comprising: Internal coupler grating, the internal coupler grating being configured to use a diffraction order The inner coupler grating has a first grating spacing. and substantially perpendicular to the first axis First grating vector ; A first pupil dilator grating, configured to use a diffraction order. The first pupil dilator has a second grating spacing. Second grating vector Having a first angle relative to the first axis ; A second pupil dilator grating, configured to use a diffraction order. The second pupil dilator has a third grating spacing. and the third grating vector Having a relative to the first axis between and The second angle between; and External coupler grating, the external coupler grating being configured to use diffraction order The external coupler grating has a fourth grating spacing. and a fourth grating vector substantially perpendicular to the first axis ; The external coupler grating is configured to diffract light in a first diffraction order, and at least one of the internal coupler grating and the pupil dilatator grating is configured to diffract light in a second diffraction order different from the first diffraction order. The first, second, third, and fourth diffraction orders are selected such that the following relationship is substantially satisfied to reduce or minimize distortion: ;and in The following relationship must be satisfied: and ,in , , It is the refractive index of the waveguide. It is the grazing angle, and λ is the wavelength of the incident beam. .

2. The device according to claim 1, wherein the second angle is between the first axis and the second angle. and between.

3. The device of claim 1, wherein the second angle is substantially equal to the first axis. .

4. The device according to any one of claims 1-3, wherein the external coupler grating is configured to use a first diffraction order, and the internal coupler grating, the first pupil dilator grating, and the second pupil dilator grating are configured to use a second diffraction order.

5. The device according to any one of claims 1-3, wherein the third grating spacing of the second pupil dilator is... Basically meets the requirements: 。 6. The device according to any one of claims 1-3, wherein the fourth grating spacing of the external coupler Basically meets the requirements: 。 7. The device according to any one of claims 1-3, wherein the grating spacing and Basically meets the requirements: Where M is the diffraction order and λ is the wavelength of the incident beam. , It is the refractive index of the waveguide, and It is the glancing angle.

8. The device according to any one of claims 1-3, wherein the grating spacing Basically meets the requirements: Where λ is the wavelength of the incident light beam. It is the refractive index of the medium in which the incident light beam travels. It is the refractive index of the waveguide. It is the glancing angle, and It is diffracted into a grazing angle The angle of the incident beam.

9. The device according to any one of claims 1-3, wherein the grating spacing is within 20% of the following values: 。 10. The device according to any one of claims 1-3, wherein the grating spacing is within 10% of the following values: 。 11. The device according to any one of claims 1-3, wherein the following relationship is substantially satisfied: 。 12. The apparatus according to any one of claims 1-11, further comprising an image generator configured to generate an image, wherein the inner coupler grating is configured to couple the image to the outer coupler grating along at least one optical path.

13. A waveguide display method, the method comprising: Used to use diffraction levels An inner coupler grating couples light into the waveguide, the inner coupler grating having a first grating spacing. and substantially perpendicular to the first axis First grating vector ; Utilizing the configuration to use diffraction level The first pupil dilatator grating diffracts the light, and the first pupil dilatator has a second grating spacing. Second grating vector Having a first angle relative to the first axis ; Utilizing the configuration to use diffraction level The second pupil dilatator grating diffracts the light, and the second pupil dilatator has a third grating spacing. and the third grating vector Having a relative to the first axis between and The second angle between; as well as Used to use diffraction levels An external coupler grating couples the light out of the waveguide, and the external coupler grating has a fourth grating spacing. and a fourth grating vector substantially perpendicular to the first axis ; The external coupler grating is configured to diffract light in a first diffraction order, and at least one of the internal coupler grating and the pupil dilatator grating is configured to diffract light in a second diffraction order different from the first diffraction order. The first, second, third, and fourth diffraction orders are selected such that the following relationship is substantially satisfied to reduce or minimize distortion: ;and in The following relationship must be satisfied: and ,in , , It is the refractive index of the waveguide. It is the grazing angle, and λ is the wavelength of the incident beam. .

14. The method of claim 13, wherein the second angle is between the first axis and the second angle. and between.

Images