CN114355502B - Diffraction grating waveguide and AR display device - Google Patents
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Abstract
The application provides a diffraction grating waveguide and an AR display device, comprising: a waveguide plate; the coupling-in grating, the turning grating and the coupling-out grating are used for enabling incident light to enter the waveguide plate after entering the coupling-in grating, enter the turning grating after being totally reflected in the waveguide plate, enter the waveguide plate after being totally reflected in the waveguide plate, enter the coupling-out grating after being totally reflected in the waveguide plate, and exit after being subjected to direction change in the coupling-out grating; wherein, the relative phase angle rho of the coupling-in grating and the turning grating is equal to the relative phase angle rho of the turning grating and the coupling-out grating; the grating period of the coupling-in grating and the coupling-out grating is d, and the grating period of the turning grating is d/2cos rho. The diffraction grating waveguide and the AR display device provided by the application can reproduce information of the coupled light beam, reduce distortion in light beam propagation, and enable a user to see a picture consistent with an image source.
Description
Technical Field
The invention relates to the field of near-to-eye display optics, in particular to a diffraction grating waveguide and an AR display device.
Background
Near-eye display systems such as AR typically include a core assembly of an image source, a beam collimating lens assembly, a transmission waveguide, and the like. The image of the image source is typically displayed by a micro display screen, a beam collimating lens group is used to convert the light beams with different angle information emitted by the image points into parallel light, and a transmission waveguide is used to transmit the image from the display screen to the human eye, and the collimated light beams are modulated. The transmission waveguide element may include a lens, a mirror, a waveguide plate (tube), a hologram, a diffraction grating, and the like.
Diffraction grating waveguides are transmission waveguides currently being appreciated and widely used by the industry, and include coupling-in gratings, turning gratings, and coupling-out gratings. Because diffraction occurs at each grating, ghost images occur after the images are emitted in the propagation process, and the coupled-in light beam cannot completely restore the information of the coupled-in light beam, so that the images are distorted.
Disclosure of Invention
The present application provides a diffraction grating waveguide and an AR display device that enable an out-coupled light beam to reproduce information of an in-coupled light beam, and a user can see a picture consistent with an image source.
A first aspect of the present application discloses a diffraction grating waveguide comprising: a waveguide plate; the coupling-in grating, the turning grating and the coupling-out grating are arranged on the surface of the waveguide plate, when incident light enters the coupling-in grating, the incident light changes in direction and enters the waveguide plate, the incident light enters the turning grating after total reflection in the waveguide plate, enters the waveguide plate after the incident light changes in direction in the turning grating, enters the coupling-out grating after total reflection in the waveguide plate, and exits after the incident light changes in direction in the coupling-out grating; wherein, the relative phase angle rho of the coupling-in grating and the turning grating is equal to the relative phase angle rho of the turning grating and the coupling-out grating; the grating period of the coupling-in grating and the coupling-out grating is d, and the grating period of the turning grating is d/2cos rho.
In a possible implementation manner of the first aspect, the relative phase angle ρ=60°, where the grating periods of the coupling-in grating, the turning grating and the coupling-out grating are d.
In a possible implementation manner of the first aspect, an area of the coupling-in grating is smaller than an area of the coupling-out grating, one side of the turning grating is close to the coupling-in grating, and another side of the turning grating is close to the coupling-out grating.
In a possible implementation manner of the first aspect, the turning grating includes a first portion and a second portion that are disposed in series and are offset, the first portion is close to the coupling-in grating, and the second portion is far away from the coupling-in grating, so that a light beam entering the first portion diffracts earlier than a light beam entering the second portion.
In a possible implementation manner of the first aspect, one or more of the coupling-in grating, the turning grating and the coupling-out grating is a surface grating, a grating period of the surface grating is 250-500nm, a groove depth is 30-400nm, and a groove inclination angle is 0-45 °.
In a possible implementation of the first aspect, the coupling-in grating diffracts the incident light beam to generate a diffracted light beam, where a diffraction polar angle Φ of the diffracted light beam satisfies: phi is greater than or equal to sin (-1) (1/n), where n is the refractive index of the waveguide plate where the incoupling grating is located.
In a possible implementation of the first aspect, one or more of the in-coupling grating, the turning grating, and the out-coupling grating is a trapezoidal surface relief grating, a sinusoidal surface relief grating, a holographic grating.
In a possible implementation of the first aspect, the in-coupling grating, the turning grating, and the out-coupling grating are located on the same side of the waveguide plate.
In a possible implementation of the first aspect, the waveguide plate is a glass substrate, an optical cement substrate, or a glass layer with an optical cement layer on a surface.
A second aspect of the present application discloses an AR display device comprising the diffraction grating waveguide in the first aspect described above.
According to the diffraction grating waveguide and the display device, the coupling-in grating and the turning grating, the turning grating and the coupling-out grating, and the grating periods of the coupling-in grating, the turning grating and the coupling-out grating are arranged, so that the information of the coupling-in light beam can be reproduced by the coupling-out light beam, and the coupling-out light beam is the restoration of the coupling-in light beam. At this time, distortion in light beam propagation is greatly reduced, and a user can see a picture consistent with an image source.
Drawings
FIG. 1 is a schematic plan view of a related art near-eye display system;
FIGS. 2 (a) - (b) are schematic illustrations of diffraction grating waveguides according to one embodiment of the present application;
FIGS. 3 (a) - (c) are schematic cross-sectional views of SRGs according to one embodiment of the present application;
FIG. 4 is a schematic diagram of a diffraction grating waveguide according to another embodiment of the present application;
FIGS. 5 (a) - (f) are schematic diagrams showing propagation paths of different angles of the coupled-in light beam in the diffraction grating waveguide of the embodiment of FIG. 4;
FIG. 6 shows a schematic view of the extent of the coupling-out grating in the embodiment of FIG. 4.
Detailed Description
The present application is further described below with reference to specific embodiments and figures. It is to be understood that the illustrative embodiments of the present disclosure, including but not limited to diffraction grating waveguides and AR display devices, are described herein in terms of specific embodiments only, and are not limiting of, the present application. Furthermore, for ease of description, only some, but not all, of the structures or processes associated with the present application are shown in the drawings.
Further advantages and effects of the present application will be readily apparent to those skilled in the art from the present disclosure, by describing embodiments of the present application with specific examples. While the description of the present application will be presented in conjunction with the preferred embodiments, it is not intended that the invention be limited to this embodiment. Rather, the invention has been described in connection with specific embodiments, and is intended to cover various alternatives or modifications, which may be extended by the claims based on this application. The following description contains many specific details in order to provide a thorough understanding of the present application. The present application may be practiced without these specific details. Furthermore, some specific details are omitted from the description in order to avoid obscuring the focus of the application. It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other.
Moreover, various operations will be described as multiple discrete operations in a manner that is most helpful in understanding the illustrative embodiments; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.
The terms "comprising," "having," and "including" are synonymous, unless the context dictates otherwise. The phrase "A/B" means "A or B". The phrase "a and/or B" means "(a and B) or (a or B)".
In the drawings, some structural or methodological features are shown in a particular arrangement and/or order. However, it should be understood that such a particular arrangement and/or ordering may not be required. In some embodiments, these features may be arranged in a different manner and/or order than shown in the illustrative figures. Additionally, the inclusion of structural or methodological features in a particular figure is not meant to imply that such features are required in all embodiments, and in some embodiments, may not be included or may be combined with other features.
It will be understood that, although the terms "first," "second," etc. may be used herein to describe various elements or data, these elements or data should not be limited by these terms. These terms are only used to distinguish one feature from another. For example, a first feature may be referred to as a second feature, and similarly a second feature may be referred to as a first feature, without departing from the scope of the example embodiments.
It should be noted that in this specification, like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
For the purpose of making the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.
Referring to fig. 1, fig. 1 shows a schematic plan view of a near-eye display system in the related art. The near-eye display system comprises an image source 20, a beam collimating lens group 21, a transmission waveguide and other core components. The scale of the elements in fig. 1 is merely an example and not true scale, and the light beam in the optical path is represented by its central ray to clearly show its propagation path. The image of the image source 20 is typically generated by a MICRO display screen, such as digital Light processing (Digital Light Procession, DLP), liquid crystal on silicon (Liquid Crystal On Silicon, LCOS), organic Light-Emitting Diode (OLED), MICRO Light-Emitting Diode (MICRO-LED), or the like. Image source 20 also includes a processor (not shown) that is capable of activating the various pixels of the display screen to generate an image. Each active pixel provides substantially uniform illumination for the exit pupil 22 region of the beam collimating lens group 21. The arrangement of the beam collimating lens group 21 may substantially collimate an image on the micro-display screen into a plurality of input beams, each corresponding to and propagating in a unique direction determined by the position of a respective active image point. The exit pupil 22 region is generally circular with a diameter D that is dependent on factors such as the parameters of the lenses making up the lens group and the size of the display screen, typically about 1-10mm. The beam collimator lens group 21 converts the light beams having different angle information emitted from the image source into parallel light. The beam collimator lens group 21 in fig. 1 is shown as a single lens, and may be any lens group. The substantially collimated beam from the pixel is deflected by the optical path of the deflection prism 23 to compress the system volume. The light beam is turned by the turning prism 23 and is guided to a transmission waveguide for modulating the collimated light beam, changing its transmission direction or redistributing energy, etc. The light beam enters human eyes for imaging after being modulated by the waveguide. The human eye 30 may restore the parallel light beam to an image point.
In the related art, a diffraction grating waveguide is a widely used transmission waveguide, which couples a light beam into a waveguide plate in a diffraction manner, when a total reflection condition is met, the coupled parallel light periodically propagates forward in a total reflection manner, and when the coupled grating is encountered, the light beam is coupled out in a diffraction manner, and finally enters a human eye for imaging. Diffraction gratings are used for expansion of the exit pupil, and in order to increase the viewable area of the human eye to be able to expand the exit pupil in two directions, multiple diffraction gratings are used to couple light beams. The human eye can make the image visible in a wider area by receiving the light beam emitted from the diffraction grating waveguide than by directly viewing the microdisplay. If the eye is located in a region that receives part of the light of almost all the light beams, the entire image is visible to the user, this region becomes an "eye box".
When the transmission waveguide in fig. 1 is a diffraction grating waveguide, the transmission waveguide may include a waveguide plate 10, an in-coupling grating 11, a turning grating 12, an out-coupling grating 13, a protection sheet 14, and the like. The light beam entering the transmission waveguide is coupled into the waveguide plate 10 by diffraction action of the coupling-in grating 11. The coupled light is then guided to the turning grating 12 and the outcoupling grating 13 by a mechanism involving diffraction and total internal reflection (Total Internal Reflection, TIR), where the light beam is coupled out of the waveguide plate 10 towards the eye of the user. The coupling grating is an entrance pupil, the turning grating is an expansion pupil, and the coupling grating is an exit pupil.
The transmission beam is distorted after the beam passes through the propagation process because diffraction occurs at the coupling-in grating, the turning grating and the coupling-out grating. To mitigate distortion and improve the quality of the final image, one embodiment of the present application provides a diffraction grating waveguide that restores the image source view, see FIG. 2 (a), which includes a waveguide plate; the coupling-in grating, the turning grating and the coupling-out grating are arranged in different areas on the surface of the waveguide plate, the coupling-in grating is configured to enable light emitted from the coupling-in grating to enter the turning grating after being reflected in the waveguide plate, the turning grating is configured to enable light emitted from the turning grating to enter the coupling-out grating after being reflected in the waveguide plate, and the coupling-out grating is configured to enable light emitted from the coupling-out grating to be coupled out of the waveguide plate; wherein, the relative phase angle rho of the coupling-in grating and the turning grating is equal to the relative phase angle rho of the turning grating and the coupling-out grating; the grating period of the coupling-in grating and the coupling-out grating is d, and the grating period of the turning grating is d/2cos rho.
In fig. 2 (a), the diffraction grating waveguide includes a waveguide plate 10, an in-coupling grating 11, a turning grating 12, and an out-coupling grating 13. Wherein the area of the coupling-in grating 11 is smaller than the area of the coupling-out grating 13, one side of the turning grating 12 is close to the coupling-in grating 11, and the other side of the turning grating 12 is close to the coupling-out grating 13.
Each grating screens the incident light for diffraction orders and changes the direction of propagation of the light. When incident light enters the coupling-in grating 11 at a certain angle, the incident light is diffracted and enters the waveguide plate 10, total reflection occurs in the waveguide plate 10, the incident light enters the turning grating 12, the light emitted from the turning grating 12 enters the coupling-out grating 13 after the total reflection occurs in the waveguide plate 10, and the coupling-out grating 13 couples the light out of the waveguide plate 10 and enters human eyes.
In some embodiments, the outer contour of the coupling-in grating 11 in fig. 2 (a) is circular, the turning grating 12 is arranged in a trapezoid shape, the short bottom side of the turning grating 12 is arranged near the coupling-in grating 11, the coupling-out grating 13 is arranged in a rectangle shape, and the area of the coupling-out grating 13 is larger than the area of the coupling-in grating 11. The triangular arrangement of the coupling-in grating 11, the turning grating 12 and the coupling-out grating 13 is compact. Typically the light sources in a near-eye display system are arranged in a circular shape, so that the light field provided by the light sources is circular, and the arrangement of the coupling-in grating in fig. 2 in a circular shape can be matched to the light field provided by the light sources. The coupling-out grating 13 is rectangular and has a large area, so that a large emergent light field can be formed. The trapezoid arrangement of the turning grating 12 with the shorter side close to the coupling-in grating can transfer the incident light beam with smaller angle to the coupling-out grating with larger angle.
Those skilled in the art will appreciate that the shapes of the in-coupling grating 11, the turning grating 12 and the out-coupling grating 13 in fig. 2 are not limited to the above-described shapes, but may be provided in other shapes.
After entering the waveguide, the light source first enters the incoupling grating 11, where the coupled light is guided to the turning grating 12 and the outcoupling grating 13 by mechanisms involving diffraction and TIR, where the light beam is coupled out of the waveguide plate 10 towards the eye of the user. The coupling-in grating 11 and the turning grating 12 are arranged according to a certain phase angle ρ, and the turning grating 12 and the coupling-out grating 13 are arranged according to a certain phase angle ρ. In some embodiments, ρ=45°.
Fig. 2 (b) shows a schematic diagram of three light rays a, b, c entering the turning grating 12 and the outcoupling grating 13 from the light ray coupled into the grating 11 at ρ=45°. The light ray a propagates in the turning grating 12 along the arrow a1 shown after exiting the coupling-in grating 11, and propagates in the turning grating 12 and the coupling-out grating 13 along the arrow a2 shown. Similarly, the light ray b propagates in the turning grating 12 along the arrow b1 shown after exiting the coupling-in grating 11, and propagates in the turning grating 12 and the coupling-out grating 13 along the arrow b2 shown; the light ray c propagates in the turning grating 12 along the arrow c1 shown after exiting the coupling-in grating 11, and propagates in the turning grating 12 and the coupling-out grating 13 along the arrow c2 shown. The rectangular area of the out-coupling grating 13 in fig. 2b is only schematically shown and is not an overlapping area of the beam path surfaces of a2, b2, c 2.
In order to make the coupled-out beam reproduce the information of the coupled-in beam, the grating period of both the coupling-in grating 11 and the coupling-out grating 13 in fig. 2 may be set to d, and the grating period of the turning grating 12 is set to d/2cos ρ. When the diffraction grating waveguide is arranged in this way, the coupled-out beam is a restoration of the coupled-in beam. At this time, distortion in light beam propagation is greatly reduced, and a user can see a picture consistent with an image source. The waveguide plate 10 shown in fig. 2 is circular, and the profile of the transmission waveguide is not limited to the circular profile in fig. 2, but the profile of the waveguide plate in fig. 2 may be other shapes including all grating structures.
The coupled-out beam in fig. 2 is restored by deducting from the following equations (1) - (6). With spherical coordinates, the angular pair of the incident beam with respect to the coordinate system of the incoupling grating 11 is denoted (phi) 0 ，θ 0 ) The angle pair of the +1 diffracted beam after coupling into the grating 11 with respect to the coordinate system of the coupling into the grating 11 is denoted (phi) 1 ，θ 1 ) These two angle pairs satisfy the grating equation:
where d is the grating period and λ is the wavelength of visible light, approximately between 390-700 nm.
The turning grating 12 then diffracts the beam back to-1 order, and the angle pair (phi) of the diffracted beam after passing through the turning grating 12 with respect to the coordinate system of the turning grating 12 2 ，θ 2 ) The grating equation is satisfied:
as the light beam propagatesBy the time the out-coupling grating 13 is reached, the angle pair (phi) of the +1-order diffracted beam after the out-coupling grating 13 with respect to the out-coupling grating 13 coordinate system 3 ，θ 3 ) The grating equation is satisfied:
beam (phi) 3 ，θ 3 ) Is refracted by the waveguide plate 10 and finally enters the human eye, and the angle pair (phi) out ，θ out ) The transformation into the coordinate system of the first incoupling grating 11 should be such that:
it is possible to obtain a solution,
that is to say,
as can be seen from the deductions of the formulas (1) - (6), when the relative phase angle ρ of the coupling-in grating and the turning grating is equal to the relative phase angle ρ of the turning grating and the coupling-out grating; and the grating period of the coupling-in grating and the coupling-out grating is d, when the grating period of the turning grating is d/2cos rho, the coupling-out light beam reproduces the information of the coupling-in light beam, and the user can see the picture consistent with the image source.
In some embodiments, ρ=45°, the grating period of the in-coupling and out-coupling gratings are both d, and the grating period of the turning grating is
In some embodiments, ρ=60°, the period of the turning grating is d/2cos ρ=d, and the periods of the coupling-in grating, the turning grating, and the coupling-out grating are equal and d, which can reduce the complexity of the grating processing process.
In some embodiments, the in-grating, the turning grating, and the out-grating are located on the same side of the diffraction grating waveguide. Typically, the waveguide is a slab of glass or resin, and the waveguide shape may be a curved shape with an arc. The waveguide has two surfaces, and diffraction gratings are distributed on the same side of the waveguide plate, so that the easiness in grating processing can be improved.
In some embodiments, the diffractive structure in fig. 2 has periodicity, and diffractive effects occur when the propagating beam interacts with structures such as periodic obstructions or slits. In some examples, the periodic structure is a surface grating, which is located at the surface of the optical element.
In some embodiments, the surface grating may be a surface relief grating (Surface Relief Grating, SRG) whose periodic structure is due to modulation of the surface itself. In addition to the wavelength of light incident on the grating, the optical characteristics of the SRG, such as groove pitch, groove depth, and groove tilt angle, can also affect the diffraction characteristics of the SRG.
FIG. 3 illustrates several examples of SRGs, respectively (a) vertical binary SRGs; (b) tilting binary SRGs; and (c) a overhanging triangular SRG. The SRG of fig. 3 has a spatial period d with a groove depth h. The grating ridge width w is the product of the period d and the fraction f, i.e. w=f×d. The grating ridge width w may be the same in height h (see fig. 3 (a) and 3 (b)), and the grating ridge width w may also be different in height h (see fig. 3 (c)). The inclined binary SRG is inclined at an angle β relative to the surface normal compared to the vertical binary SRG. The overhanging triangular SRG is a triangular groove arrangement with identifiable tips on the surface, the groove walls on both sides being inclined at angles β, r relative to the surface normal. In some embodiments, the grating grooves of the out-coupling SRG13 and in-coupling SRG11 are mirror symmetric. In some embodiments, the period d is 250-500nm, the groove depth h is 30-400nm, the groove inclination angle beta is 0-45 degrees, the arrangement of the grating can eliminate dispersion, and high coupling-out diffraction efficiency can be obtained.
In some embodiments, the surface grating may be one or more of a trapezoidal SRG, a sinusoidal SRG, and a holographic grating.
In the diffraction grating waveguide of fig. 2 (a), the coupling-in and turning gratings are separated by a small gap, and the coupling-out grating is located generally directly below the turning grating. The grating structure is compact, but when the relative phase angle ρ of the coupling-in grating 11 and the turning grating 12, the relative phase angle ρ of the turning grating 12 and the coupling-out grating 13 are all 45 degrees, the grating period (d/2 cos ρ) of the turning grating 12 is inconsistent with the grating period (d) of the coupling-in grating 11 and the coupling-out grating 13 due to the phase angle limitation between the gratings, so that the overlapping area of the path surfaces of the light beams at each angle in the coupling-out grating 13 is smaller, that is, the area of the eye box is smaller, and the light energy utilization rate is lower. This also does not facilitate optimization of the uniformity of the intensity of the coupled-out beam.
To address this problem, another embodiment of the present application provides a shaped diffraction grating waveguide, as shown in fig. 4. The main difference between the diffraction grating waveguides in fig. 2 (a) and fig. 4 is the shaped structure of the turning grating 12.
In fig. 4, the relative phase angles of the coupling-in grating and the turning grating are equal to the relative phase angles of the turning grating and the coupling-out grating, which are 60 °, and the grating periods of the coupling-in grating, the turning grating and the coupling-out grating are d. The special-shaped structure of the turning grating 12 is that the turning grating 12 includes a first portion 121 and a second portion 122 (divided into two by a line L) that are disposed continuously and are offset, the first portion 121 is close to the coupling grating, the second portion 122 is far from the coupling grating, and the first portion and the second portion may include light beams with all incident angles. The first part is close to the coupling-in grating, so that the light beam entering the first part can diffract earlier than the light beam entering the second part, the coupling-out grating area range is enlarged, and the eye box is enlarged. The lower part is slightly far away from the coupling-in grating, so that diffraction action is generated after the lower angle beam, and unnecessary light energy loss is reduced. The turning gratings arranged as the upper part and the lower part can reduce light energy loss and are beneficial to optimizing the uniformity of the light intensity of the coupled light beam.
Fig. 4 is not limited to the shapes of the turning grating and the coupling-out grating as another embodiment of the present application, and those skilled in the art will understand that the turning grating may have other shapes that reduce the light energy loss and optimize the uniformity of the light intensity of the coupling-out beam, for example, the turning grating 12 may include a first portion 121 and a second portion that are disposed in series, and the first portion 121 is closer to the coupling-in grating than the second portion 122, where the first portion 121 and the second portion 122 are trapezoidal, or the first portion 121 and the second portion 122 are fan-shaped, or the first portion 121 and the second portion 122 are different combinations of shapes. In addition, the shape of the coupling-out grating in fig. 4 is not limited to the hexagonal shape in the drawing.
To illustrate the distinction of the light beam entering the first portion and the light beam entering the second portion in fig. 4, (a) - (f) in fig. 5 show the propagation paths of the coupled-in light beams at different angles in the turning grating as shown in fig. 4. In fig. 5, the coupling-in grating causes incident light beams of different angles to produce first order diffraction order light beams having different diffraction azimuth angles θ. The different first order diffracted order light beams are represented by circular outlines of different propagation periods. Similarly, turning the grating causes incident light beams at different angles (i.e., diffracted light beams produced by the coupling-in grating) to produce first-order diffracted-order light beams having different diffraction azimuth angles θ, which propagate in a direction toward the coupling-out grating. In fig. 5, the beam in the direction of the outcoupling grating is shown with an outer contour for clarity. As can be seen from fig. 4, the start-stop positions of the contours actually used for the light beams with different angles towards the coupling-out grating are different, and for the first part of the turning grating close to the coupling-in grating, the light beams entering the first part can be diffracted first (see fig. 5 (a) - (c)) due to the fact that the first part is closer to the coupling-in grating, so that a wider contour is formed, and the area range of the coupling-out grating is further increased; for the second portion of the turning grating, since it is slightly far from the coupling-in grating, diffraction can be performed after the light beam enters the second portion (see fig. 5 (d) - (f)), so that light energy loss can be reduced.
As can be seen from fig. 5, the different angles of light rays in different fields of view in the transmission waveguide cause the different angles of the diffracted light beams and transmission periods. The coupling-in grating causes the incident beam to produce a first order (+ -1) diffracted order beam, which then propagates toward the new direction of the turning SRG 12. If the diffraction order beam meets the total internal reflection standard, the diffraction polar angle phi of the diffraction order beam meets the following conditions:
where n is the refractive index of the waveguide plate where the grating is located.
The hexagonal areas in the areas of the coupling-out grating in fig. 4-5 are only illustrative and the outer contour shape of the coupling-out grating is not limited thereto. For better illustration, fig. 6 shows the area range of the coupling-out grating, i.e. the shadow area therein is the light path overlapping area after diffraction of the incident light beams with different angles, after turning the grating to generate the first-order diffraction order light beams with different diffraction azimuth angles θ. The shape of the outcoupling grating may be arranged as the overlap region, or it may be arranged as any other shape comprising the overlap region.
In some embodiments, the area of the out-coupling grating includes a common area encompassed by the various angular beam profiles to enable the eye to receive the beams of all image points. One or more of these beams are received by the eye and focused onto a single retinal spot so that the image point is reconstructed on the retina as if the light were received directly from the microdisplay. Because the light beam for each active image point is received, the eye can reconstruct the entire image currently on the microdisplay so that the user can see an infinite virtual image.
In some embodiments, the waveguide plate is a glass substrate, an optical cement substrate, or a glass layer with an optical cement layer on the surface.
One embodiment of the present application also provides an AR display device including a diffraction grating waveguide as described above with respect to fig. 2-4. The AR display device may include components such as the image source, the beam collimating lens group, etc. described above with reference to fig. 1, and are not described herein.
The scheme of the application is described in detail by combining with fig. 2-6, and according to the diffraction grating waveguide of the specific embodiment of the application, the image distortion can be reduced, the imaging quality can be improved, the light energy utilization rate can be improved, the eye box area can be increased, and the uniformity of the light intensity of the coupled light beam can be optimized.
While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
Claims (9)
1. A diffraction grating waveguide comprising:
a waveguide plate;
the coupling-in grating, the turning grating and the coupling-out grating are arranged in different areas on the surface of the waveguide plate, when incident light enters the coupling-in grating, the incident light changes in direction and enters the waveguide plate, the incident light enters the turning grating after total reflection in the waveguide plate, enters the waveguide plate after the direction change in the turning grating, enters the coupling-out grating after total reflection in the waveguide plate, and exits after the direction change in the coupling-out grating;
wherein, the relative phase angle rho of the coupling-in grating and the turning grating is equal to the relative phase angle rho of the turning grating and the coupling-out grating;
the grating period of the coupling-in grating and the coupling-out grating is d, and the grating period of the turning grating is d/2cos rho;
the turning grating comprises a first part and a second part which are arranged continuously and staggered, the first part is close to the coupling grating, and the second part is far away from the coupling grating, so that light beams entering the first part diffract earlier than light beams entering the second part.
2. The diffraction grating waveguide of claim 1, wherein the relative phase angle ρ = 60 °, where the grating periods of the in-coupling grating, the turning grating, and the out-coupling grating are d.
3. The diffraction grating waveguide of claim 1 or 2, wherein the area of the in-coupling grating is smaller than the area of the out-coupling grating, one side of the turning grating being adjacent to the in-coupling grating, the other side of the turning grating being adjacent to the out-coupling grating.
4. The diffraction grating waveguide of claim 1, wherein one or more of the in-coupling grating, the turning grating, and the out-coupling grating is a surface grating, the surface grating has a grating period of 250-500nm, a groove depth of 30-400nm, and a groove tilt angle of 0-45 °.
5. A diffraction grating waveguide according to claim 1, wherein the coupling grating diffracts the incident beam to produce a diffracted beam having a diffraction polar angle Φ that satisfies:
wherein n is the refractive index of the waveguide plate.
6. The diffraction grating waveguide of claim 1, wherein one or more of the in-coupling grating, the turning grating, and the out-coupling grating is a trapezoidal surface relief grating, a sinusoidal surface relief grating, or a holographic grating.
7. The diffraction grating waveguide of claim 1, wherein the in-coupling grating, the turning grating, and the out-coupling grating are located on the same side of the waveguide plate.
8. The diffraction grating waveguide of claim 1, wherein the waveguide plate is a glass substrate, an optical cement substrate, or a glass layer with an optical cement layer on the surface.
9. An AR display device, the AR display device comprising: the diffraction grating waveguide of any one of claims 1 to 8.
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| CN115128810A (en) * | 2022-06-01 | 2022-09-30 | 上海蜃微科技有限公司 | Grating structure, waveguide device and display system |
| CN115016061A (en) * | 2022-06-28 | 2022-09-06 | 珠海莫界科技有限公司 | Diffraction light waveguide structure, optical device and near-to-eye display equipment |
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