CN117930419A - Optical waveguide and display device - Google Patents

Abstract

The embodiment of the invention discloses an optical waveguide and a display device. The optical waveguide specifically comprises a first waveguide layer and a second waveguide layer which are stacked; the first waveguide layer comprises a geometric coupling-in structure positioned at the end part and a geometric coupling-out structure positioned at the middle part, and image light rays emitted by the image source are coupled into the first waveguide layer through the geometric coupling-in structure, coupled out of the first waveguide layer through the geometric coupling-out structure and then are incident into the second waveguide layer; the second waveguide layer comprises a diffraction structure, and the image light is coupled into the second waveguide layer from the middle part through the diffraction structure, then continuously passes through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer to enter human eyes. The optical waveguide provided by the embodiment of the invention has high energy utilization rate and is easy to modulate in image uniformity.

Description

Optical waveguide and display device

Technical Field

The embodiment of the invention relates to the technical field of optics, in particular to an optical waveguide and a display device.

Background

Augmented reality is a technology of integrating virtual world information and real world information in a "seamless" manner, in which virtual content and real environment provided by a miniature projection system are superimposed on the same screen or space to coexist, so that a user obtains a virtual and real fused experience.

The existing common waveguide display scheme using the diffraction optical waveguide mainly utilizes the diffraction characteristic of the diffraction grating to design an optical path, so that image light propagates on the designed path and is guided into human eyes. However, light diffraction produces multiple orders, and typically only a limited number of diffraction orders can be coupled into the optical waveguide for use, and the diffraction efficiency is low, resulting in low energy utilization of the diffractive optical waveguide.

Disclosure of Invention

The embodiment of the application provides an optical waveguide and a display device, which can improve the energy utilization efficiency of a diffraction optical waveguide.

According to an aspect of the present application, there is provided an optical waveguide, specifically including a first waveguide layer and a second waveguide layer which are stacked;

The first waveguide layer comprises a geometric coupling-in structure positioned at the end part and a geometric coupling-out structure positioned at the middle part, and image light rays emitted by the image source are coupled into the first waveguide layer through the geometric coupling-in structure, coupled out of the first waveguide layer through the geometric coupling-out structure and then are incident into the second waveguide layer;

The second waveguide layer comprises a diffraction structure, and the image light is coupled into the second waveguide layer from the middle part through the diffraction structure, then continuously passes through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer to enter human eyes.

Optionally, the second waveguide layer is located between the first waveguide layer and the human eye, after the image light is incident on the second waveguide layer, part of the light enters the human eye through the second waveguide layer, and part of the light continues to pass through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer to enter the human eye after being coupled into the second waveguide layer through the diffraction structure.

Optionally, the diffraction structure has a zero-order transmission diffraction order with a smaller efficiency than the other diffraction orders.

Optionally, the first waveguide layer is located between the second waveguide layer and the human eye, after the image light is incident to the second waveguide layer, part of the light exits from the human eye through the second waveguide layer, and part of the light continues to pass through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer to enter the human eye after being coupled into the second waveguide layer through the diffraction structure.

Optionally, an absorption component or a reflection component is arranged on the side of the second waveguide layer away from the human eye; the absorption component is used for absorbing the image light rays which are transmitted through the second waveguide layer and are emitted away from human eyes, and the reflection component is used for reflecting the image light rays which are transmitted through the second waveguide layer and are emitted away from human eyes back to the second waveguide layer.

Optionally, the geometric coupling-in structure includes a coupling-in prism or a coupling-in inclined plane, the geometric coupling-out structure includes a total reflection film, the image light is coupled into the first waveguide layer through the coupling-in prism or the coupling-in inclined plane, and is coupled out of the first waveguide layer through the total reflection film after being transmitted to the total reflection film through total reflection in the first waveguide layer.

Optionally, the diffraction structure comprises a two-dimensional grating, the grating diffraction efficiency of the two-dimensional grating being symmetrically distributed about the center of the viewing window.

Optionally, the diffraction efficiency of the two-dimensional grating increases along the direction of the periphery of the symmetrical area of the two-dimensional grating and the center of the window.

Optionally, the second waveguide layer has a plurality of light propagation paths, different light propagation paths carry different local view field information, and each local view field information is spliced to obtain complete view field information.

According to another aspect of the present application, there is provided a display device specifically including an image source and any one of the above optical waveguides; the image source is configured to output image light toward the geometrically incoupling structure of the first waveguide layer. Optionally, the display device is an augmented reality display device or a virtual reality display device.

The optical waveguide provided by the embodiment of the invention specifically comprises a first waveguide layer and a second waveguide layer which are stacked; the first waveguide layer comprises a geometric coupling-in structure positioned at the end part and a geometric coupling-out structure positioned at the middle part, and image light rays emitted by the image source are coupled into the first waveguide layer through the geometric coupling-in structure, coupled out of the first waveguide layer through the geometric coupling-out structure and then are incident into the second waveguide layer; the second waveguide layer comprises a diffraction structure, and the image light is coupled into the second waveguide layer through the diffraction structure, then continuously passes through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer to enter human eyes. Therefore, the first waveguide layer geometrically couples light into the waveguide and transmits most of energy to the center of the window and then transmits the energy to the second waveguide layer so as to couple the light into the second waveguide layer from the center of the window, thereby avoiding energy waste caused by diffraction efficiency of the traditional diffraction waveguide at the coupling-in grating, and the pupil expansion and coupling-out of the second waveguide layer begin from the center of the window, avoiding pupil expansion energy waste of the traditional diffraction waveguide outside the window, and greatly improving the energy utilization rate. In addition, when the uniformity of the image is optimized, the pupil expansion and coupling-out of the second waveguide layer are started from the center of the window, so that the unidirectional distance of the modulation is short, the range is small, and the uniformity is easier to optimize.

It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the invention or to delineate the scope of the invention. Other features of the present invention will become apparent from the description that follows.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a schematic diagram of an optical waveguide in the prior art;

FIG. 2 is a schematic diagram of an optical waveguide according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of another optical waveguide according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of another optical waveguide according to an embodiment of the present invention;

FIG. 5 is a schematic top view of a two-dimensional grating waveguide according to an embodiment of the present invention;

FIG. 6 is a K-domain diagram of light transmitted in a second waveguide layer according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of a two-dimensional coupling-out grating and a K-domain diagram of light transmission in a second waveguide layer according to an embodiment of the present invention;

fig. 8 is a diagram of an optical waveguide display device according to an embodiment of the present invention.

Detailed Description

In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.

It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

Fig. 1 is a schematic diagram of an optical waveguide in the prior art. Referring to fig. 1, the optical waveguide includes a coupling-in grating 01 and a coupling-out grating 02, light is coupled into the optical waveguide by the coupling-in grating 01, then part of the light is totally reflected in the optical waveguide and transmitted to the coupling-out grating 02, and the light is coupled out to the human eye 03 through the coupling-out grating 02 in the transmission process. During this coupling of light into the light guide, most of the light (0 th order diffracted light a) is lost due to the fact that the total reflection condition is not fulfilled, only a small part of the light (+1 th order diffracted light b) is utilized, and the energy of 0 th order is usually higher than the energy of +1 th order, so that the energy available for the existing diffraction-based light guide is very limited.

In order to solve the above-described problems, an embodiment of the present invention provides an optical waveguide including a first waveguide layer and a second waveguide layer that are stacked; the first waveguide layer comprises a geometric coupling-in structure positioned at the end part and a geometric coupling-out structure positioned at the middle part, image light rays emitted by the image source are coupled into the first waveguide layer through the geometric coupling-in structure, and the geometric coupling-out structure is coupled out of the first waveguide layer and then is incident into the second waveguide layer; the second waveguide layer comprises a diffraction structure, and the image light is coupled into the second waveguide layer through the diffraction structure, then continuously passes through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer to enter human eyes.

Wherein the geometric coupling-in structure is used for coupling light into the waveguide for transmission, and can include, but is not limited to, a prism or a coupling-in inclined plane; geometric out-coupling structures for coupling light out of a waveguide may include, but are not limited to, prisms or total reflection films; the diffractive structure is used to couple light into, pupil out of, and out of the waveguide and may include, but is not limited to, gratings. The optical waveguide provided by the invention couples light into the waveguide in a geometric mode through the first waveguide layer, transmits most of energy to the center of the window and then transmits the energy to the second waveguide layer so as to couple the light into the second waveguide layer from the center of the window, thereby avoiding energy waste caused by diffraction efficiency of the traditional diffraction waveguide at the coupling-in grating, and avoiding pupil expansion and coupling-out of the second waveguide layer from the center of the window, thereby avoiding pupil expansion energy waste of the traditional diffraction waveguide outside the window, and greatly improving the energy utilization rate. In addition, when the uniformity of the image is optimized, the pupil expansion and coupling-out of the second waveguide layer are started from the center of the window, so that the unidirectional distance of the modulation is short, the range is small, and the uniformity is easier to optimize.

Fig. 2 is a schematic structural diagram of an optical waveguide according to an embodiment of the present invention. Referring to fig. 2, the optical waveguide specifically includes a first waveguide layer 10 and a second waveguide layer 20 that are stacked; the first waveguide layer 10 includes a geometric coupling-in structure 11 at the end and a geometric coupling-out structure 12 at the middle, and an image light ray c emitted from an image source (not shown in fig. 1) is coupled into the first waveguide layer 10 through the geometric coupling-in structure 11, coupled out of the first waveguide layer 10 through the geometric coupling-out structure 12, and then incident into the second waveguide layer 20; the second waveguide layer 20 comprises a diffractive structure 21, and the image light is coupled into the second waveguide layer 20 via the diffractive structure 21, then further pupil-expanded via the diffractive structure 21 and coupled out of the second waveguide layer 20, and output from the first surface 100 of the optical waveguide into the human eye 3.

In the embodiment shown in fig. 2, the second waveguide layer 20 is located between the first waveguide layer 10 and the human eye 3, after the image light is incident on the second waveguide layer 20, part of the light enters the human eye through the second waveguide layer 20, and part of the light continues to pass through the diffraction structure 21 to expand the pupil of the second waveguide layer 20 and is coupled out of the second waveguide layer 20 to enter the human eye 3 after being coupled into the second waveguide layer 20 through the diffraction structure 21. Therefore, after the image light rays are incident on the second waveguide layer, partial energy which is not diffracted can directly enter human eyes, and the energy utilization rate is further improved.

Alternatively, for an optical waveguide as shown in fig. 2, the diffraction structure has a zero-order transmission diffraction order with a smaller efficiency than the other diffraction orders.

Specifically, according to the grating diffraction principle, diffracted light rays of multiple orders are generated after being diffracted by the diffraction structure 21, the zero-order transmission order is directly transmitted through the waveguide, the other part of the orders are diffracted by the diffraction structure to enter the waveguide substrate for total internal reflection transmission, the energy is coupled out by the variable pupil expansion side through multiple actions with the diffraction structure, and the energy is gradually attenuated along with pupil expansion and coupling out of the light rays. It will be appreciated that the order that is not diffracted into the waveguide (zero-order transmission order) is directly transmitted into the human eye at the position of the second waveguide layer corresponding to the geometric coupling-out structure, and the diffraction order that is diffracted into the waveguide substrate needs to be coupled out at the region outside the position of the second waveguide layer corresponding to the geometric coupling-out structure, so as to improve the uniformity of the image, avoid that the transmitted light is high in energy and affects the viewing of human eyes, and cause discomfort to the observer, the efficiency of the zero-order transmission diffraction order of the diffraction structure should be smaller than the diffraction efficiency of other diffraction orders, and preferably, the efficiency of the zero-order transmission diffraction order of the diffraction structure should be far smaller than the diffraction efficiency of the other diffraction orders.

According to the optical waveguide provided by the embodiment of the invention, the image light is geometrically coupled into (such as prism coupled into) the first waveguide layer through the geometrical coupling-in structure, the image light is transmitted in the waveguide in a total reflection way, and then the image light is coupled out of the first waveguide layer through the geometrical coupling-out structure (reflection occurs at the total reflection film). Because the first waveguide layer adopts a geometric coupling-in and coupling-out mode to transmit image light, almost no energy is lost in the whole working process of the first waveguide layer, and all light energy is coupled out to the center of a window for eye observation and transmitted to the second waveguide. After the light coupled out by the first waveguide layer is incident to the diffraction structure of the second waveguide layer to be diffracted, a part of energy (such as 0 level) directly penetrates through the waveguide and enters human eyes, and the other part of energy is diffracted by the diffraction structure (such as a two-dimensional grating) of the second waveguide layer and enters the waveguide substrate to be transmitted in a total reflection mode, so that the energy utilization efficiency of the optical waveguide is greatly improved. According to the embodiment of the invention, most of energy of image light is firstly transmitted to the center of the window (eyebox) through the first waveguide layer and is coupled in again from the middle of the second waveguide layer, so that partial energy which is not diffracted by the second waveguide layer directly enters human eyes, and energy waste caused by diffraction efficiency of a traditional diffraction waveguide at a coupling grating is avoided.

In another embodiment, fig. 3 is a schematic structural diagram of another optical waveguide provided in this embodiment, referring to fig. 3, the first waveguide layer 10 is located between the second waveguide layer 20 and the human eye, after the image light c is incident on the first waveguide layer 10, part of the light exits from the human eye 3 through the first waveguide layer 10, and part of the light is coupled into the second waveguide layer through the diffraction structure, then continues to pass through the diffraction structure to expand pupil and is coupled out of the second waveguide layer 20 to enter the human eye 3.

In this embodiment, the light and the window are on the same side of the waveguide layer and are incident into the first waveguide layer 10 at a certain angle, the image light c is totally reflected inside the first waveguide layer 10, leaves the first waveguide layer 10 via the coupling-out structure, and is diffracted into the second waveguide layer 20 via the diffraction structure (such as a two-dimensional grating) of the second waveguide layer 20 for total reflection transmission.

Since the above solution has a certain energy loss, in another embodiment, optionally, the side of the second waveguide layer away from the human eye is provided with an absorption component or a reflection component; the absorption component is used for absorbing the image light rays which are transmitted through the second waveguide layer and are emitted away from human eyes, and the reflection component is used for reflecting the image light rays which are transmitted through the second waveguide layer and are emitted away from human eyes back to the second waveguide layer for recycling.

Fig. 4 is a schematic structural diagram of another optical waveguide according to an embodiment of the present invention, referring to fig. 4, on the basis of the above embodiment, an absorption component or a reflection component 31 is disposed on a surface of the second waveguide layer 20 on a side away from the first waveguide layer 10, where the reflection component includes, but is not limited to, a total reflection film layer, and may reflect, back to the second waveguide layer 20, image light emitted from the human eye 3 through the second waveguide layer 20, and the absorption component includes, but is not limited to, an organic absorption layer, and may absorb image light emitted from the human eye through the second waveguide layer. Wherein the reflective or absorptive component should be transmissive to ambient light.

It can be appreciated that in this embodiment, the light is coupled into the second waveguide layer 20 by the diffraction structure 21 and is diffracted, so that zero-order diffraction order light and secondary diffraction order light are generated, a part of energy (such as zero-order diffraction order light) directly passes through the second waveguide layer 20, is absorbed by the absorption component or the reflection component 31 disposed on the side of the second waveguide layer 20 away from the human eye 3 or is reflected back to the second waveguide layer 20, the reflected light passes through the first waveguide layer 10 and can be observed, the energy utilization efficiency of the optical waveguide is greatly improved, meanwhile, the added absorption component can absorb the image light exiting from the human eye and passing through the second waveguide layer 20, so that the light can be prevented from leaking out and being observed by the outside, thereby protecting the privacy of the observer, and the reflection component can be observed by the human eye 3 through the second waveguide layer 20 and the first waveguide layer 10, so that the part of energy is recovered.

Optionally, the geometric coupling-in structure includes a coupling-in prism or a coupling-in inclined plane, the geometric coupling-out structure includes a total reflection film, the image light is coupled into the first waveguide layer through the coupling-in prism or the coupling-in inclined plane, and is coupled out of the first waveguide layer through the total reflection film after being transmitted to the total reflection film through total reflection in the first waveguide layer. The geometric coupling-in structure comprises a coupling-in prism or a coupling-in inclined plane, the geometric coupling-out structure comprises a total reflection film layer, and various structures can be combined into optical waveguides with different structures after optical parameter matching.

Optionally, the diffraction structure comprises a grating structure, the diffraction efficiency of which is symmetrically distributed about the center of the field of view (Eyebox) to improve the uniformity of the brightness coupled out by the second waveguide layer. The grating structure is a one-dimensional or two-dimensional grating including, but not limited to, a partially reflective micromirror array coupled (PARTIALLY-REFLECTIVE MIRRORS ARRAY, PRMA) Surface relief grating (Surface RELIEF GRATING, SRG), a volume holographic grating (Holographic Volume Grating, VHG), and a polarizer coupled grating (Polarization Volume Grating, PVG).

Illustratively, when incident light impinges on the SRG, the light rays will diffract at different azimuth and polar angles, including reflection orders (R0, r±1, r±2,) and transmission orders (T0, t±1, t±2,). The diffraction angle (θm, m= ±1, ±2, …) of each diffraction order is determined by the incidence angle (θ) of the incident light and the grating period (T). The diffraction efficiency of each diffraction order is then affected by the grating depth/height (h), duty cycle (W/T), refractive index (n), tilt angle, and grating shape (straight, skewed, blaze, etc.) of the grating structure. For example, the larger the grating depth/height (h), the greater the diffraction efficiency.

In particular, a two-dimensional grating can be equivalently regarded as a superposition of a first grating along a first direction and a second grating along a second direction, the angle between the first direction and the second direction being greater than or equal to 20 ° and less than or equal to 90 °. The direction is the direction of the grating line, and the included angle between the first direction and the second direction is the included angle of the two-dimensional coupling-out grating.

Fig. 5 is a schematic diagram of a two-dimensional outcoupling grating and a K-domain diagram of light propagating in a second layer waveguide according to an embodiment of the present invention. In fig. 5 a), the left graph is a two-dimensional coupling-out grating with an included angle θ=90°, and the right graph is a K-domain graph when a light beam propagates therein; in fig. 5 b), the left graph is a two-dimensional coupling-out grating with an included angle θ=60°, and the right graph is a K-domain graph when the light beam propagates in the second layer waveguide.

Fig. 6 is a schematic top view of a two-dimensional grating waveguide according to an embodiment of the present invention, and referring to fig. 6, a dashed frame is a window range, and light is uniformly transmitted from the center of the window into the window regions around the window. After the light is coupled into the waveguide layer, the propagation energy is gradually attenuated, so that the intensity of the propagation light is kept unchanged basically, the uniformity of the image is ensured, and relatively low diffraction efficiency can be obtained by modulating grating parameters close to the area of the coupling structure; relatively high diffraction efficiency can be achieved by modulating grating parameters away from the region of the incoupling structure to gradually increase diffraction efficiency as light propagates to modulate the uniformity of the intensity of propagating light in the waveguide. When parameters are modulated, the range of the traditional pupil expansion mode which needs to be optimized along with the image transmission direction is larger than the size of the whole window, the optimization difficulty is high, and the light transmission of the invention starts to symmetrically optimize from the center of the window, the optimization range is small, and the optimization difficulty is reduced. Optionally, the grating depth of the two-dimensional grating is gradually increased along the direction of the periphery of the position of the two-dimensional grating corresponding to the center of the window.

In some embodiments of the present invention, the diffraction structure of the second grating layer selects a two-dimensional grating, when the two-dimensional grating diffracts the image light into the second layer waveguide, the two-dimensional grating can diffract the image light to generate a plurality of propagation light rays in different directions, so that a plurality of light propagation paths exist in the second layer waveguide, different local view field information is carried by different light propagation paths through the grating parameter design of the two-dimensional grating, and the local view field information is spliced to obtain complete view field information, so as to obtain a larger view field angle range.

As shown in fig. 7, which is a K-domain plot of light propagating in the second waveguide layer. In fig. 7, a), b) and c) correspond to the K-domain diagrams of the propagation of the green light, the red light and the blue light in the second waveguide layer, respectively, and the left-hand diagram is the K-domain diagram of the propagation of the light under the action of the one-dimensional grating, and the right-hand diagram is the K-domain diagram of the propagation of the light under the action of the two-dimensional grating with an included angle of 90 degrees. The rectangular box represents complete field of view information, and only field of view information falling into the circular ring area in the rectangular box can propagate through total reflection in the second layer waveguide layer. As can be seen from fig. 7, under the action of the one-dimensional grating, only one light propagation path exists, and in a large-view field scene, it is easy to cause that a part of view field areas of long and short wavelengths cannot be coupled into the second-layer waveguide, and further, a view field of an image observed by human eyes is lost. Under the action of the two-dimensional grating, a plurality of light propagation paths exist, and although a part of view field areas cannot be coupled into the second-layer waveguide under the single light propagation path, the plurality of propagation paths can carry different local view field information through the grating parameter design of the two-dimensional grating, and the local view field information is spliced to obtain complete view field information, so that a large view field is realized. It should be noted that, in fig. 7, only a two-dimensional grating with an included angle of 90 degrees is taken as an example for illustration, and two-dimensional gratings with other included angles can also realize a large field of view by designing field of view stitching.

Fig. 8 is a schematic structural diagram of a display device according to an embodiment of the present application. According to another aspect of the present application, there is provided a display device specifically including an image source and any one of the above optical waveguides; the image source is configured to output image light toward the geometrically incoupling structure of the first waveguide layer. Referring to fig. 8, the display device includes an image source 1 and any one of the optical waveguides 2 provided in the above-described embodiments; the image source 1 is arranged to output image light towards the geometrical incoupling structure 11 of the first waveguide layer 10; image light is incident into the first waveguide layer 10 from the geometric coupling-in structure 11 of the first waveguide layer 2, is transmitted through the geometric coupling-out structure 12 of the first waveguide layer 10 and is coupled to the second waveguide layer 20; the diffraction structure of the second waveguide layer 20 diffracts and transmits the imaging light to be output from the first surface 100 of the optical waveguide to the human eye 3.

In particular, the image light emitted from the image source 1 may be coupled into the first waveguide layer 10 through a prism (geometric coupling structure), and the image light is transmitted through total reflection in the waveguide, and then coupled out of the first waveguide layer 10 through reflection at the total reflection film. Since the first waveguide layer transmits image light by total reflection, there is little loss of energy during operation of the entire first waveguide layer, and all of the light energy is coupled out into the eye's viewing window and transferred to the second waveguide layer 20. After the light coupled out by the first waveguide layer 10 is incident to the diffraction structure of the second waveguide layer 20 to be diffracted, a part of energy (for example, 0 level) directly penetrates through the waveguide, enters the human eye through the first surface 100, and the other part of energy is diffracted by the diffraction structure (for example, a two-dimensional grating) of the second waveguide layer 20 to enter the waveguide layer to be transmitted in a total reflection way, and is coupled out to the human eye 3 for many times in the transmission process, so that the energy utilization efficiency of the optical waveguide display device is greatly improved.

Optionally, the display device is an augmented reality display device, such as a near-eye display device or a vehicle head-up display device. Of course, the display device may be a virtual reality display device when it does not transmit ambient light.

The above embodiments do not limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.

Claims (10)

1. An optical waveguide comprising a first waveguide layer and a second waveguide layer arranged in a stack;

The first waveguide layer comprises a geometric coupling-in structure positioned at the end part and a geometric coupling-out structure positioned at the middle part, and image light rays emitted by an image source are coupled into the first waveguide layer through the geometric coupling-in structure, coupled out of the first waveguide layer through the geometric coupling-out structure and then are incident into the second waveguide layer;

the second waveguide layer comprises a diffraction structure, and the image light is coupled into the second waveguide layer from the middle part through the diffraction structure, then continuously passes through the diffraction structure to expand the pupil and is coupled out of the second layer waveguide to enter human eyes.

2. The optical waveguide of claim 1, wherein the second waveguide layer is located between the first waveguide layer and the human eye, and after the image light is incident on the second waveguide layer, a portion of the light enters the human eye through the second waveguide layer, and a portion of the light continues to pass through the diffraction structure to expand the pupil and couple out of the second waveguide layer into the human eye after coupling into the second waveguide layer through the diffraction structure.

3. The optical waveguide of claim 2, wherein the diffraction structure has a zero-order transmission diffraction order with a lower efficiency than the other diffraction orders.

4. The optical waveguide of claim 1, wherein the first waveguide layer is located between the second waveguide layer and the human eye, and after the image light is incident on the second waveguide layer, a portion of the light exits from the human eye through the second waveguide layer, and after the portion of the light is coupled into the second waveguide layer through the diffraction structure, the portion of the light continues to pass through the diffraction structure to expand the pupil and is coupled out of the second waveguide layer into the human eye.

5. The optical waveguide according to claim 4, wherein the side of the second waveguide layer remote from the human eye is provided with an absorbing component or a reflecting component; the absorption component is used for absorbing the image light rays which are transmitted through the second layer waveguide and are emitted away from human eyes, and the reflection component is used for reflecting the image light rays which are transmitted through the second layer waveguide and are emitted away from human eyes back to the second waveguide layer.

6. The optical waveguide of claim 1, wherein the geometric coupling-in structure comprises a coupling-in prism or a coupling-in slope, the geometric coupling-out structure comprises a total reflection film, the image light is coupled into the first waveguide layer through the coupling-in prism or the coupling-in slope, and the image light is coupled out of the first waveguide layer through the total reflection film after being transmitted to the total reflection film through the total reflection layer in the first waveguide layer.

7. The optical waveguide of claim 1, wherein the diffractive structure comprises a two-dimensional grating having a grating diffraction efficiency symmetrically distributed about a window center.

8. The optical waveguide according to claim 7, wherein the diffraction efficiency of the two-dimensional grating increases in a direction along a periphery of a region of the two-dimensional grating corresponding to the center of the window.

9. The optical waveguide of claim 7, wherein the second waveguide layer has a plurality of light propagation paths, different light propagation paths carrying different local field of view information, each of the local field of view information being spliced to obtain complete field of view information.

10. A display device comprising an image source and the optical waveguide of any one of claims 1 to 9; the image source is configured to output image light toward the geometric in-coupling structure.