Patent Description:
With the high development of semiconductor technology, the way of interaction between humans and computers is developing rapidly. Among them, Augmented Reality (AR) display can provide human beings with more dimensional information, and has attracted widespread attention. AR glasses are one of the important mediums in the field of augmented reality display. Diffractive optical waveguide has the advantages of strong mass production, thinness, etc. It has gradually been recognized in the field of AR display and is expected to become the mainstream technology development direction in the field of AR in the future.

Current diffractive optical waveguides for AR display have deficiencies. For example, the overall optical coupling efficiency of the diffractive optical waveguide is not high enough, resulting in the field of view displayed by AR is not bright enough. In addition, for example, the optical energy distribution uniformity of the optical output field of the diffractive optical waveguide still needs to be improved. In order to improve the optical coupling efficiency of the diffractive optical waveguide and improve the optical energy distribution uniformity of the optical output field, people have proposed a diffractive optical waveguide as shown in <FIG>, in which a coupling-in grating a, a coupling-out grating b, and a light-return grating c are arranged on a waveguide substrate. The coupling-in grating a couples incident light carrying image information into the waveguide substrate. The coupling-out grating b expands the light carrying image information in a plane where the waveguide substrate is located, and at the same time couples the light out of the waveguide substrate. The light-return grating c is arranged around the end of the coupling-out grating b away from the coupling-in grating a, and is used to return the light that leaves the coupling-out grating b and continues to propagate in the waveguide substrate to the coupling-out grating b. However, the improvement of the overall optical coupling efficiency of the diffractive optical waveguide by the design shown in <FIG> is still very limited. In addition, the optical output field of the coupling-out grating b tends to be in a non-uniform state where the central area (as shown by the dotted line box in <FIG> ) is dark and the surrounding area is bright, resulting in a poor display effect.

<CIT> discloses a diffractive display element comprising a waveguide body, an in-coupling region, an out-coupling region and at least one grating mirror outside a primary route, along which light propagate from the in-coupling region to the out-coupling region, for mirroring light strayed from the primary route back. The grating mirror and its associated grating can be located on opposite surfaces of the waveguide body.

<CIT> discloses an optical waveguide comprising a waveguide substrate and a coupling-in region, a coupling-out region and a light return region arranged on the waveguide substrate, in which the light return region is used for reversely returning the light beam with the image information to the coupling-out region.

<CIT> discloses a light guide arrangement comprising an optical deflection device, which is arranged between the coupling arrangement and the decoupling arrangement and is designed to deflect light ray bundles, emerging from the coupling arrangement towards the decoupling arrangement.

The invention aims to provide a diffractive optical waveguide and a display device comprising the diffractive optical waveguide, so as to at least partly address the deficiencies in the prior art.

According to embodiments of the invention, by providing the coupling-in end light-return grating and/or improving the arrangement of the coupling-in end light-return grating, the optical coupling efficiency of the diffractive optical waveguide is improved, and the optical energy distribution uniformity of the optical output field of the diffractive optical waveguide is advantageously improved.

Other features, objects, and advantages of the invention will become more apparent by reading the following detailed description of non-limitative embodiments with reference to the following drawings.

The invention will be further described in detail in conjunction with drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the related invention, but not to limit the invention. In addition, it should be noted that, for the convenience of description, only the parts related to the invention are shown in the drawings.

The invention will be described in detail below with reference to drawings and embodiments.

Firstly, a diffractive optical waveguide according to Embodiment <NUM> of the disclosure, which is not covered by the subject-matter of the claims, will be introduced with reference to <FIG>.

<FIG> shows Example <NUM>, which is not covered by the subject-matter of the claims, of the diffractive optical waveguide according to Embodiment <NUM>, that is, diffractive optical waveguide <NUM>. As shown in <FIG>, the diffractive optical waveguide <NUM> comprises a waveguide substrate 10a, and the waveguide substrate 10a is formed with a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, and a coupling-out grating <NUM>.

The coupling-in grating <NUM> is a one-dimensional grating, which is configured to couple an input beam irradiated on the coupling-in grating <NUM> into the waveguide substrate 10a so that it propagates in the waveguide substrate 10a through total reflection and forms a first beam of light propagating toward the coupling-out grating <NUM> (for example, as shown by a leftward arrow in <FIG>) and a second beam of light not propagating toward the coupling-out grating <NUM> (for example, as shown by a rightward arrow in <FIG>). The coupling-in end light-return grating <NUM> is configured to diffract the second beam of light, so as to make it propagate towards the coupling-out grating <NUM>. The coupling-out grating <NUM> is a two-dimensional grating configured to couple at least a part of the light propagating therein out of the waveguide substrate 10a by diffraction.

Specifically, in the example shown in <FIG>, the coupling-in grating <NUM> has a plurality of linear grooves periodically arranged along the direction indicated by the arrow in <FIG> (see the figure in the lower left corner of <FIG>). That is, the extension direction of the linear grooves of the coupling-in grating <NUM> is perpendicular to the direction shown by the arrow. The input beam (such as light carrying image information) irradiated on the coupling-in grating <NUM> from the outside of the waveguide substrate 10a is diffracted by the coupling-in grating <NUM> to form positive first-order diffracted light and negative first-order diffracted light. The positive first-order diffracted light propagates in the waveguide substrate 10a through total reflection (total internal reflection) along the leftward arrow in <FIG> to form the first beam of light; The negative first-order diffracted light propagates in the waveguide substrate 10a through total reflection along the rightward arrow in <FIG> to form the second beam of light.

In this case, the coupling-in grating <NUM> has a grating vector G11 as shown in the figure in the lower left corner of <FIG>. In this application, "grating vector" is used to describe the periodic characteristics of the grating structure, wherein the direction of the "grating vector" is parallel to the direction along which the structure of the grating is periodically changed/arranged (for example, perpendicular to the grating lines/grooves direction) and is consistent with the propagation direction of the positive first-order diffracted light of the grating; the magnitude of the "grating vector" is 2π/d, where d is the period of the grating structure in the direction of the "grating vector", also known as "grating period ".

In the example shown in <FIG>, the coupling-in end light-return grating <NUM> is arranged on the opposite side of the coupling-in grating <NUM> to the coupling-out grating <NUM>. The coupling-in end light-return grating <NUM> is configured to diffract the second beam of light to form a third beam of light. According to this embodiment, the third beam of light propagates along the same direction as the first beam of light (for example, along the leftward arrow in <FIG>), so as to enter the coupling-out grating <NUM>. In order to enable the light incident on the waveguide substrate 10a at the same incident angle to be coupled out from the waveguide substrate at the same angle of emergence through the coupling-out grating <NUM>, according to this embodiment, the coupling-in end light-return grating <NUM> is configured so that the third beam of light propagates in the waveguide substrate at the same total reflection angle as the first beam of light.

To this end, according to this embodiment, the coupling-in end light-return grating <NUM> can have a grating vector G12 as shown in the figure in the lower right corner of <FIG>, the grating vector G12 has a direction that is the same as the direction of G11, and a magnitude that is twice of that of the grating vector G11. In other words, the grating period d<NUM> of the coupled-in grating <NUM> in the direction of the grating vector G11 and the grating period d<NUM> of the coupling-in end light-return grating <NUM> in the direction of the grating vector G12 satisfy d<NUM>=2d<NUM>. Light diffracted by grating has complicated angle changes, which is difficult to introduce here concisely and clearly. However, an intuitive explanation can be provided from a grating vector perspective. For example, referring to the figure in the lower right corner of <FIG>, the negative first-order diffracted light (the second beam of light) of the coupling-in grating <NUM> is equivalent to that obtained by applying the influence of a grating vector -G11 opposite to the direction of the grating vector G11 on the input beam; the second beam of light diffracted by the coupling-in end light-return grating <NUM> is equivalent to superimposing the influence of the coupling-in end light-return grating <NUM> on the influence of the grating vector -G11, such that the third beam of light is obtained. As shown in the figure in the lower right corner of <FIG>, the overall effect of the grating vectors -G11 and G12 on the third beam of light is equivalent to the influence of the grating vector G11 on the input beam, which is the same as the first beam of light. This is consistent with the result of calculating the light angle based on the refraction, diffraction, and reflection of the input beam incident on the diffractive optical waveguide <NUM>.

As shown in <FIG>, preferably, the coupling-in end light-return grating <NUM> has a trapezoidal shape, and two sides parallel to each other of the trapezoidal shape are perpendicular to the first grating vector G11 of the coupling-in grating <NUM>; the width of the coupling-in end light-return grating <NUM> increases along the propagation direction of the second beam of light. This structure is provided in consideration of that when the diffractive optical waveguide is used to display images, the received input beam is not completely perpendicular to the surface of the waveguide substrate 10a, but has a certain field of view (FOV), which results in that each of the first beam of light and the second beam of light obtained through the diffraction of the coupling-in grating <NUM> propagates through total reflection in the waveguide substrate 10a with a certain expanding angle with respect to the direction shown by the arrow in <FIG>. According to the embodiment of the disclosure, in order to sufficiently "return" the second beam of light to the coupling-out grating <NUM> to improve the utilization efficiency of the light, the coupling-in end light-return grating <NUM> preferably has the trapezoidal shape. However, it should be understood that the coupling-in end light-return grating <NUM> can also have any other suitable shape whose width in the direction perpendicular to the grating vector G11 of the coupling-in grating is greater than or equal to the width of the coupling-in grating <NUM>. This is applicable to any coupling-in end light-return grating in diffractive optical waveguides of each embodiment described below, and will not be repeated in the following.

<FIG> shows Example <NUM>, which is not covered by the subject-matter of the claims, of the diffractive optical waveguide according to Embodiment <NUM>, that is, diffractive optical waveguide <NUM>. As shown in <FIG>, the diffractive optical waveguide <NUM> comprises a waveguide substrate 20a, and the waveguide substrate 20a is formed with a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, a coupling-out grating <NUM> and a turning grating <NUM>.

The coupling-in grating <NUM> is a one-dimensional grating, which has a grating vector G21 as shown in the lower left corner of <FIG>. The coupling-in end light-return grating <NUM> has a grating vector G22, and the direction of the grating vector G22 is the same as that of the grating vector G21, and its magnitude is twice of that of the latter. The coupling-in grating <NUM> and the coupling-in end light-return grating <NUM> can have the same structure and function as the coupling-in grating <NUM> and the coupling-in end light-return grating <NUM> in the diffractive optical waveguide <NUM> introduced above with reference to <FIG>, and will not be repeated here.

As an example only, as shown in <FIG>, the coupling-in end light-return grating <NUM> can have a rectangular shape with a width greater than the coupling-in grating <NUM> in the direction perpendicular to the grating vector G21.

In the example shown in <FIG>, the coupling-out grating <NUM> and the turning grating <NUM> are one-dimensional gratings, and the light from the coupling-in grating <NUM> propagates towards the coupling-out grating <NUM> after deflection and one-dimensional expansion of the turning grating <NUM> in one direction (such as the left and right directions in <FIG>). The coupling-out grating <NUM> expands the received light in another direction (such as the up and down directions in <FIG>) and gradually couples the light out of the waveguide substrate 20a during the expansion process. In applications for image display, this can provide image display after two-dimensional pupil expansion.

In order to study the effect of the coupling-in end light-return grating on the optical coupling efficiency of the diffractive optical waveguide, based on the diffractive optical waveguide <NUM> shown in <FIG>, a simulation example is designed, in which:.

Based on the above conditions, the optical energy detected by the photodetector with or without the coupling-in end light-return grating <NUM> is calculated respectively with a certain input beam angle, and the following results are obtained:.

In the above calculation, the optical energy of the input beam is fixed.

It should be understood that the influence of the turning grating <NUM> and the coupling-out grating <NUM> on the coupling efficiency of light is fixed, the structure and efficiency of the turning grating <NUM> and the coupling-out grating <NUM>, as well as size and position of the detection surface D of the photodetector, do not have a significant impact on the improvement of the optical coupling efficiency brought by the coupling-in end light-return grating in the above example.

From the results of the above calculation example, it can be seen that the coupling-in end light-return grating helps to improve the optical coupling efficiency of the diffractive optical waveguide, and corresponding to a certain range of field of view, it can greatly improve the optical coupling efficiency. This advantageously improves the brightness of image displays based on diffractive optical waveguide.

In the diffractive optical waveguide according to Embodiment <NUM> of the disclosure shown in <FIG>, both the coupling-in gratings <NUM> and <NUM> are one-dimensional gratings. It should be understood that the invention is not limited to this, and in other embodiments, a two-dimensional grating can also be used as the coupling-in grating. In this case, the coupling-in grating has more than one grating vector, and the grating vector of the coupling-in end light-return grating can be in the same/parallel direction as one of the grating vectors of the coupling-in grating, as long as the diffraction through the coupling-in end light-return grating can make the second beam of light from the coupling-in grating propagate toward the coupling-out grating.

<FIG> show different examples of diffractive optical waveguide according to Embodiment <NUM> of the disclosure, which is not covered by the subject-matter of the claims. In these examples, a direction of a grating vector of coupling-in end light-return grating is at a predetermined angle with respect to a direction of a grating vector of a coupling-in grating.

In the example shown in <FIG>, which is not covered by the subject-matter of the claims, a diffractive optical waveguide <NUM> comprises a waveguide substrate 30a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, and a coupling-out grating <NUM> formed on the waveguide substrate 30a. The coupling-in grating <NUM> is a one-dimensional grating and has a grating vector G31 (the figure on the right of <FIG> shows a grating vector -G31 which is opposite to the grating vector G31 and has the same magnitude). The coupling-in end light-return grating <NUM> is a one-dimensional grating and has a grating vector G32. As shown in <FIG>, the direction of the grating vector G32 is at an angle to the direction of the grating vector G31.

The coupling-out grating <NUM> is a two-dimensional grating, and one of the grating vectors of the two-dimensional grating is G33. According to this embodiment, the coupling-in end light-return grating <NUM> is configured so that the vector sum of the grating vector G32, the grating vector -G31 and the grating vector G33 is zero. In this way, the input beam is diffracted by the coupling-in grating <NUM> to form positive first-order diffracted light (a first beam of light) propagating toward the coupling-out grating <NUM> and negative first-order diffracted light (a second beam of light) not propagating toward the coupling-out grating <NUM>; The second beam of light passes through the diffraction of the coupling-in end light-return grating <NUM>, propagates toward the coupling-out grating <NUM>, and finally couples out from the waveguide substrate 30a through the diffraction of the coupling-out grating <NUM>, and the light coupled out from the waveguide substrate 30a remains the same angle as the input beam, so that the image information carried by the input beam can be restored.

As shown in <FIG>, in the case where the coupling-in grating <NUM> is not centered with respect to the coupling-out grating <NUM>, the coupling-in end light-return grating <NUM> can be arranged so that the light follows, for example, the direction shown by the parallel arrow in the figure on the right of <FIG> to propagate toward the coupling-out grating <NUM> to supplement the insufficient brightness of the lower half of the coupling-out grating <NUM> caused by the upward bias of the coupling-in grating <NUM>.

In the example shown in <FIG>, which is not covered by the subject-matter of the claims, the diffractive optical waveguide <NUM> comprises a waveguide substrate 40a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, and a coupling-out grating <NUM> formed on the waveguide substrate 40a. The coupling-in grating <NUM> is a one-dimensional grating and has a grating vector G41 (the figure on the right of <FIG> shows a grating vector -G41 which is opposite to the grating vector G41 and has the same magnitude). The coupling-in end light-return grating <NUM> comprises a first one-dimensional grating 42a and a second one-dimensional grating 42b, a grating vector G42a of the first one-dimensional grating 42a forms a first angle with respect to the grating vector G41 and a grating vector G42b of the second one-dimensional grating 42b forms a second angle with respect to the grating vector G41. In the example shown in <FIG>, the light diffracted by the first one-dimensional grating 42a and the second one-dimensional grating 42b converges toward the coupling-out grating <NUM>; In other examples, the diffracted light can also diverge toward the coupling-out grating <NUM>. Preferably, the first angle and the second angle are in opposite directions, and both are <NUM>°.

The coupling-out grating <NUM> is a two-dimensional grating, and the two grating vectors of the two-dimensional grating are G43a and G43b. According to this embodiment, the coupling-in end light-return grating <NUM> is configured so that the vector sum of the grating vector G42a, the grating vector -G41, and the grating vector G43a is zero (as shown in the figure in the lower left corner of <FIG>), and the vector sum of the grating vector G42b, the grating vector -G41 and the grating vector G43b is zero (as shown in the figure in the lower right corner of <FIG>). In this way, negative first-order diffracted light (a second beam of light) formed by the input beam through the diffraction of the coupling-in grating <NUM> is coupled out from the waveguide substrate 40a through the diffraction of the coupling-in end light-return grating <NUM> and the coupling-out grating <NUM>, and the light coupled out from the waveguide substrate 40a maintains the same angle as the input beam, so that the image information carried by the input beam can be restored.

As shown in <FIG>, the design of the diffractive optical waveguide <NUM> helps to supplement the insufficient light intensity at the two corners of the coupling-out grating <NUM> near the coupling-in grating <NUM>, thereby improving the uniformity of the optical output field of the diffractive optical waveguide.

In the example shown in <FIG>, which is not covered by the subject-matter of the claims, the diffractive optical waveguide <NUM> comprises a waveguide substrate 50a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, and a coupling-out grating <NUM> formed on the waveguide substrate 50a. The coupling-in grating <NUM> is a one-dimensional grating and has a grating vector G51 (the figure on the right of <FIG> shows a grating vector -G51 which is opposite to the grating vector G51 and has the same magnitude). The coupling-in end light-return grating <NUM> comprises a first one-dimensional grating 52a and a second one-dimensional grating 52b, a grating vector G52a of the first one-dimensional grating 52a forms a first angle with respect to the grating vector G51 and a grating vector G52b of the second one-dimensional grating 52b forms a second angle with respect to the grating vector G51. In the example shown in <FIG>, a deflection grating <NUM> is formed on the waveguide substrate 50a, comprising a grating 57a and a grating 57b, which is configured to deflect light from the coupling-in end light-return grating toward the coupling-out grating <NUM>. Preferably, the first angle and the second angle are in opposite directions, and both are <NUM>°.

The coupling-out grating <NUM> is a two-dimensional grating, and two grating vectors of the two-dimensional grating are G53a and G53b. The deflection gratings 57a and 57b have grating vectors G57a and G57b respectively. According to this embodiment, the coupling-in end light-return grating and the deflection grating are configured so that the vector sum of the grating vector G52a, the grating vector -G51, the grating vector 57a, and the grating vector G53a is zero (as shown in the figure in the lower left corner of <FIG>), the vector sum of the grating vector G52b, the grating vector -G51, the grating vector 57b and the grating vector G53b is zero (as shown in the figure in the lower right corner of <FIG>). In this way, negative first-order diffracted light (a second beam of light) formed by the input beam through the diffraction of the coupling-in grating <NUM> is coupled out from the waveguide substrate 50a through the diffraction of the coupling-in end light-return grating <NUM>, the deflection grating <NUM>, and the coupling-out grating <NUM>, and the light coupled out from the waveguide substrate 50a maintains the same angle as the input beam so that the image information carried by the input beam can be restored.

As shown in <FIG>, the design of the diffraction waveguide <NUM> helps to supplement the insufficient light intensity at the two corners of the coupling-out grating <NUM> near the coupling-in grating <NUM>, thereby improving the uniformity of the optical output field of the diffractive optical waveguide. Compared with the diffractive optical waveguide <NUM> shown in <FIG>, the arrangement of the deflection gratings 57a and 57b helps to make the light from the coupling-in end light-return grating <NUM> propagate a longer distance in the coupling-out grating <NUM>, thereby being coupled out more fully by the out-coupling grating <NUM> to the outside of the waveguide substrate 60a, thereby improving the optical coupling efficiency. Similarly, in the diffractive optical waveguide <NUM> shown in <FIG>, a deflection grating can also be provided near the lower right corner of the coupling-out grating <NUM>.

<FIG> and <FIG> show different examples of diffractive optical waveguide according to Embodiment <NUM> of the disclosure, which is not covered by the subject-matter of the claims. In these examples, a coupling-in grating and a coupling-in end light-return grating are respectively formed on two opposite surfaces of the waveguide substrate.

A diffractive optical waveguide <NUM> according to Embodiment <NUM> of the disclosure shown in <FIG>, which is not covered by the subject-matter of the claims, comprises a waveguide substrate 60a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, and a coupling-out grating <NUM> formed on the waveguide substrate 60a. The coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, and the coupling-out grating <NUM> of the diffractive optical waveguide <NUM> have the same configuration as the coupling-in grating <NUM>, the coupling-in end light-return grating <NUM> and the coupling-out grating <NUM> of the diffractive optical waveguide <NUM> shown in <FIG>, and will not be repeated here. According to this embodiment, in the diffractive optical waveguide <NUM>, the coupling-in grating <NUM> and the coupling-in end light-return grating <NUM> are respectively formed on two opposite surfaces A and B of the waveguide substrate 60a. As an example only, as shown in <FIG>, the coupling-in grating <NUM> and the coupling-out grating <NUM> are formed on the surface A of the waveguide substrate 60a, and the coupling-in end light-return grating <NUM> is formed on the surface B of the waveguide substrate 60a. In other examples, the coupling-out grating <NUM> and the coupling-in end light-return grating <NUM> can also be formed on the same surface.

As shown in <FIG>, which is not covered by the subject-matter of the claims, a diffractive optical waveguide <NUM> according to Embodiment <NUM> of the disclosure comprises a waveguide substrate 70a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, a coupling-out grating <NUM> and a turning grating <NUM> formed on the waveguide substrate 70a. The coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, the coupling-out grating <NUM>, and the turning grating <NUM> of the diffractive optical waveguide <NUM> have the same configuration as the coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, the coupling-out grating <NUM> and the turning grating <NUM> of the diffractive optical waveguide <NUM> shown in <FIG>, and will not be repeated here. According to the present embodiment, in the diffractive optical waveguide <NUM>, the coupling-in grating <NUM> and the coupling-in end light-return grating <NUM> are respectively formed on two opposite surfaces A and B of the waveguide substrate 70a. As an example only, as shown in <FIG>, the coupling-in grating <NUM>, the coupling-out grating <NUM>, and the turning grating <NUM> are formed on the surface A of the waveguide substrate 70a, and the coupling-in end light-return grating <NUM> is formed on the surface B of the waveguide substrate 70a. In other examples, the coupling-out grating <NUM> and the turning grating <NUM> can also be formed on the same surface as the coupling-in end light-return grating <NUM>, or be formed on different surfaces, respectively.

For the sake of clarity, in <FIG> and <FIG>, the structure on the surface A is shown with dotted lines in the figure of the surface B of the waveguide substrate of the diffractive optical waveguide, and the structure on the surface B is not shown in the figure of the surface A.

As shown in <FIG> and <FIG>, especially as shown in the figure of the surface B of the waveguide substrate, in the projection perpendicular to the surfaces A and B, the coupling-in end light-return grating <NUM> partially overlaps the coupling-in grating <NUM>, the coupling-in end light-return grating <NUM> partially overlaps the coupling-in grating <NUM>.

Since the second beam of light from the coupling-in grating is gradually diffracted back in the coupling-in end light-return grating, the longer the length of the coupling-in end light-return grating in the propagation direction of the second beam of light is, the more conducive it is to fully diffract the second beam of light back to the coupling-out grating. However, diffractive optical waveguides usually have size limitations in specific applications, and for a diffractive optical waveguide of a certain size, people usually hope to provide the largest possible exit pupil (corresponding to the largest possible coupling-out grating), so the area of diffractive optical waveguides that can be used for optical coupling-in is limited, which leads to the area that can be used for coupling-in grating and coupling-in end light-return grating is very limited. According to Embodiment <NUM> of the disclosure, since the coupling-in end light-return grating is arranged on the surface of the waveguide opposite to the surface where the coupling-in grating is located, it is allowed to increase the length of the coupling-in end light-return grating along the propagation direction of the second beam of light without increasing the overall area occupied by the coupling-in grating and the coupling-in end light-return grating, or reduce the overall area of the coupling-in grating and the coupling-in end light-return grating without reducing the length of the coupling-in end light-return grating. This is very advantageous for AR head-mounted display devices, for example.

It should be understood that the concept that the coupling-in grating and the coupling-in end light-return grating are respectively arranged on two surfaces of the waveguide substrate in Embodiment <NUM> and overlap in the projection perpendicular to the surface can also be applied to, for example, referring to Embodiment <NUM> introduced in <FIG> and other embodiments comprising the coupling-in grating and the coupling-in end light-return grating.

<FIG> and <FIG> show different examples of a diffractive optical waveguide according to Embodiment <NUM> of the disclosure, which examples are part of the present invention. In these examples, the diffractive optical waveguide further comprises a coupling-out end light-return grating, and the coupling-out end light-return grating and a coupling-out grating are formed on two opposite surfaces of the waveguide substrate.

The diffractive optical waveguide <NUM> according to Embodiment <NUM> of the disclosure shown in <FIG> comprises a waveguide substrate 80a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, a coupling-out grating <NUM>, and a coupling-out end light-return grating <NUM> formed on the waveguide substrate 80a. The coupling-out end light-return grating <NUM> is configured to receive light from the coupling-out grating <NUM> and diffract the light back to the coupling-out grating <NUM>. The coupling-out end light-return grating <NUM> can be a one-dimensional grating or a two-dimensional grating, or can comprise different gratings in different regions. The invention is not limited in this respect.

The coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, and the coupling-out grating <NUM> of the diffractive optical waveguide <NUM> can have the same configuration as the coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, and the coupling-out grating <NUM> of the diffractive optical waveguide <NUM> shown in <FIG>, and will not be repeated here.

According to Embodiment <NUM>, the coupling-out grating <NUM> and the coupling-out end light-return grating <NUM> are respectively formed on two opposite surfaces A and B of the waveguide substrate 80a. As an example only, as shown in <FIG>, the coupling-in grating <NUM> and the coupling-out grating <NUM> are formed on the surface A of the waveguide substrate 80a, and the coupling-out end light-return grating <NUM> is formed on the surface B of the waveguide substrate 80a. In other examples, the coupling-out end light-return grating <NUM> can also be located on the same surface as the coupling-in grating <NUM>, for example, on the surface A. Similarly, the coupling-in grating <NUM> and the coupling-in end light-return grating <NUM> can be respectively formed on two opposite surfaces of the waveguide substrate, but the diffractive optical waveguide according to Embodiment <NUM> is not limited to such an arrangement.

According to Embodiment <NUM>, as shown in <FIG>, in the projection perpendicular to the two surfaces A and B of the waveguide substrate 80a, the coupling-out end light-return grating <NUM> partially overlaps the coupling-out grating <NUM> but does not cover the entire coupling-out grating <NUM>. For the sake of clarity, in <FIG>, the structure on the surface A is shown with dotted lines only in the figure of the surface B of the waveguide substrate of the diffractive optical waveguide <NUM>.

The coupling-out grating <NUM> has a first side L1 for receiving light from the coupling-in grating <NUM>, a second side L2 opposite to the first side L1, and a third side L3 and a fourth side L4 between the first side L1 and the second side L2. In the example shown in <FIG>, the coupling-out end light-return grating is formed in a U shape and lies across the second side L2, the third side L3, and the fourth side L4 in the projection perpendicular to the surfaces A and B.

Although not shown, it should be understood that in some examples according to this embodiment, the coupling-out end light-return grating <NUM> can comprise three separate grating parts that are respectively lying across the second side L2, the third side L3 and the fourth side L4 of the coupling-out grating <NUM> in the projection; In some other examples, the coupling-out end light-return grating <NUM> can lie across the second side L2, the third side L3 and the fourth side L4 in the projection; In further examples, the coupling-out end light-return grating <NUM> can only lie across the second side L2 of the coupling-out grating <NUM> in the projection.

The diffractive optical waveguide <NUM> shown in <FIG> is particularly beneficial to overcome the problem that the central area (as shown by the dotted line box in <FIG>) is dark and the surrounding area is bright in the prior art diffractive optical waveguide shown in <FIG>. This is because the overlapping part of the coupling-out end light-return grating <NUM> and the coupling-out grating <NUM> in the projection perpendicular to the surfaces A and B is closer to the central area of the coupling-out grating <NUM>. Through the diffraction of this part of the coupling-out end light-return grating <NUM>, the light is gradually diffracted back when it is transmitted and coupled out in the area of the coupling-out grating, so that the light can return to the central area of the coupling-out grating <NUM>, thus increasing the brightness of the central area of the optical output field and improving the uniformity of the light field.

Different positions of the coupling-out end light-return grating <NUM> can have different light-return efficiencies. Preferably, the further out, the higher the light-return efficiency, so as to improve the uniformity of the overall optical output field. The coupling-out end light-return grating <NUM> have different light-return efficiencies at different positions, which can be achieved by changing the grating structure within a period, including shape and depth, at different positions.

<FIG> shows another example according to Embodiment <NUM> of the disclosure. As shown in <FIG>, a diffractive optical waveguide <NUM> comprises a waveguide substrate 90a and a coupling-in grating <NUM>, a coupling-out grating <NUM>, and a coupling-out end light-return grating <NUM> formed on the waveguide substrate 90a. The diffractive optical waveguide <NUM> further comprises a coupling-in end light-return grating formed on the waveguide substrate 90a. The coupling-out end light-return grating <NUM> is configured to receive light from the coupling-out grating <NUM> and diffract the light back to the outcoupling grating <NUM>. The coupling-out end light-return grating <NUM> can be a one-dimensional grating or a two-dimensional grating, or can comprise different gratings in different regions. The invention is not limited in this respect.

According to Embodiment <NUM>, the coupling-out grating <NUM> and the coupling-out end light-return grating <NUM> are respectively formed on two opposite surfaces A and B of the waveguide substrate 90a, as shown in <FIG>. In addition, as shown in <FIG>, in the projection perpendicular to the two surfaces A and B of the waveguide substrate 90a, the coupling-out end light-return grating <NUM> partially overlaps the coupling-out grating <NUM> and does not cover the entire coupling-out grating <NUM>. In the example shown in <FIG>, the coupling-out end light-return grating <NUM> comprises a grating region 94a formed with a grating structure and several grating-free regions 94b distributed in the grating region 94a. For the sake of clarity, in <FIG>, the structure on the surface A is shown with dotted lines only in the figure of the surface B of the waveguide substrate of the diffractive optical waveguide <NUM>.

In the diffractive optical waveguide <NUM> shown in <FIG>, by setting "blank" regions (i.e., grating-free regions 94b), it is convenient and beneficial to adjust the light-return efficiency from different positions of the coupling-out end light-return grating <NUM>, thereby improving the uniformity of the optical output field of the coupling-out grating <NUM>. Preferably, different positions in the grating region 94a of the coupling-out end light-return grating <NUM> can also have different grating structures, comprising shape and depth of the grating, so as to adjust the light-return efficiency at different positions and help to further improve the uniformity of the overall optical output field.

<FIG> is a schematic diagram of an example of a diffractive optical waveguide according to Embodiment <NUM> of the disclosure, which example is part of the present invention. As shown in <FIG>, the diffractive optical waveguide <NUM> comprises a waveguide substrate 100a and a coupling-in grating <NUM>, a coupling-in end light-return grating <NUM>, a coupling-out grating <NUM>, a coupling-out end light-return grating <NUM>, a turning grating <NUM> and an intermediate light-return grating <NUM> formed on the waveguide substrate 100a. The intermediate light-return grating <NUM> is configured to receive light from the turning grating <NUM> and diffract it back to the turning grating <NUM>.

The coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, the coupling-out grating <NUM>, and the turning grating <NUM> can be configured in the same or similar way as the coupling-in grating <NUM>, the coupling-in end light-return grating <NUM>, the coupling-out grating <NUM> and the turning grating <NUM> in the diffractive optical waveguide <NUM> introduced with reference to <FIG>, and will not be repeated here. As shown in <FIG>, the coupling-in grating <NUM> and the coupling-in end light-return grating <NUM> can be respectively formed on two opposite surfaces of the waveguide substrate. The coupling-out grating <NUM> and the coupling-out end light-return grating <NUM> are respectively formed on two opposite surfaces of the waveguide substrate.

According to Embodiment <NUM>, as shown in <FIG>, the turning grating <NUM> and the intermediate light-return grating <NUM> are respectively formed on the two surfaces A and B of the waveguide substrate 100a, and in the projection perpendicular to the surfaces A and B, the intermediate light-return grating <NUM> partially overlaps the turning grating <NUM>.

In the example shown in <FIG>, the turning grating <NUM> has a first edge E1 opposite to the coupling-in grating <NUM> and a second edge E2 opposite to the coupling-out grating <NUM>; the intermediate light-return grating <NUM> comprises a first grating 106a and a second grating 106b, in the projection perpendicular to the surfaces A and B, the first grating 106a and the second grating 106b lie across the first edge E1 and the second edge E2 of the turning grating <NUM>, respectively.

The diffractive optical waveguides according to different embodiments of the disclosure have been described above with reference to the accompanying drawings. It should be understood that different embodiments and features in the embodiments can be combined with each other under the condition of no conflict.

Finally, a display device according to an embodiment of the disclosure will be described with reference to <FIG> is a schematic diagram of a display device <NUM> according to an embodiment of the disclosure, and <FIG> is a schematic diagram of lens/diffractive optical waveguide in the display device <NUM>.

As shown in <FIG>, a display device <NUM> according to an embodiment of the disclosure can be a near-eye display device, comprising a lens <NUM> and a frame <NUM> for keeping the lens <NUM> close to the eye, wherein the lens <NUM> comprises the diffractive optical waveguide according to embodiment <NUM> or <NUM> of the disclosure. In <FIG>, the diffractive optical waveguide according to embodiment <NUM> or <NUM> of the disclosure is marked with reference numeral "<NUM>".

In the example shown in <FIG>, the lens <NUM> can consist of the diffractive optical waveguide <NUM> as a whole; in other cases, the lens <NUM> can comprise a carrier sheet, and the diffractive optical waveguide <NUM> is attached or otherwise fixed on the carrier sheet.

Referring to <FIG> in conjunction, the frame <NUM> can comprise a holder <NUM> abutting against the lens <NUM> to hold the lens <NUM> (for example, the leg form formed into a spectacle frame), and the coupling-in end light-return grating <NUM> of the diffractive optical waveguide <NUM> is located in a region r (see <FIG>) where the lens <NUM> abuts against the holder <NUM>.

The display device <NUM> can further comprise an optical machine <NUM> for projecting light with image information onto the coupling-in grating <NUM> of the diffractive optical waveguide <NUM>, as shown in <FIG>, the optical mechanism <NUM> can be mounted on the holder <NUM> and face the coupling-in grating <NUM>.

Claim 1:
A diffractive optical waveguide (<NUM>, <NUM>, <NUM>), comprising a waveguide substrate (80a, 90a, 100a), the waveguide substrate being formed with a coupling-in grating (<NUM>, <NUM>, <NUM>) and a coupling-out grating (<NUM>, <NUM>, <NUM>), the coupling-in grating (<NUM>, <NUM>, <NUM>) being configured to couple an input beam into the waveguide substrate (80a, 90a, 100a) so that the input beam propagates in the waveguide substrate through total reflection and forms a first beam of light propagating toward the coupling-out grating (<NUM>, <NUM>, <NUM>) and a second beam of light not propagating toward the coupling-out grating, and the coupling-out grating being configured to couple at least a part of the light propagating therein out of the waveguide substrate by diffraction,
wherein the waveguide substrate (80a, 100a) is further formed with a coupling-in end light-return grating (<NUM>, <NUM>), and the coupling-in end light-return grating is configured to diffract the second beam of light, so as to make it propagate towards the coupling-out grating;
the waveguide substrate (80a, 90a, 100a) is further formed with a coupling-out end light-return grating (<NUM>, <NUM>, <NUM>), and the coupling-out end light-return grating is configured to receive light from the coupling-out grating (<NUM>, <NUM>, <NUM>) and diffract the light back to the coupling-out grating; and
the coupling-out grating (<NUM>, <NUM>, <NUM>) and the coupling-out end light-return grating (<NUM>, <NUM>, <NUM>) are respectively formed on two opposite surfaces of the waveguide substrate (80a, 90a, 100a),
characterized in that:
in a projection perpendicular to the two opposite surfaces, the coupling-out end light-return grating (<NUM>, <NUM>, <NUM>) partially overlaps the coupling-out grating (<NUM>, <NUM>, <NUM>).