阅读说明：本技术 Ar光波导的设计方法及用于ar眼镜的光波导 (Method for designing AR optical waveguide and optical waveguide for AR glasses ) 是由 赵兴明 范真涛 朱庆峰 隋磊 田克汉 于 2021-07-15 设计创作，主要内容包括：本发明提供了一种AR光波导的设计方法,所述AR光波导包括耦入光栅、光波导主体以及耦出光栅,所述设计方法包括：S101：根据光束入射至所述耦入光栅的角度、所述光束的波长对所述耦入光栅的光栅参数进行优化,所述光栅参数包括光栅周期、光栅深度以及光栅占空比；S102：根据所述耦入光栅的光栅周期以及光栅深度确定所述耦出光栅的光栅周期以及光栅深度；S103：对所述耦出光栅进行分区；S104：以所述耦出光栅的耦出总光功率以及非均匀性为优化目标,得到所述耦出光栅的各分区的光栅占空比。本发明所提供的AR光波导的设计方法,从多个侧面改善了通过AR光波导传输的图像,在佩戴者的视野中呈现明暗变化的情况。(The invention provides a design method of an AR optical waveguide, wherein the AR optical waveguide comprises a coupling-in grating, an optical waveguide main body and a coupling-out grating, and the design method comprises the following steps: s101: optimizing grating parameters of the incoupling grating according to the angle of the light beam incident to the incoupling grating and the wavelength of the light beam, wherein the grating parameters comprise a grating period, a grating depth and a grating duty ratio; s102: determining the grating period and the grating depth of the coupling-out grating according to the grating period and the grating depth of the coupling-in grating; s103: partitioning the coupling grating; s104: and obtaining the grating duty ratio of each subarea of the coupled-out grating by taking the coupled-out total optical power and the non-uniformity of the coupled-out grating as optimization targets. The design method of the AR optical waveguide improves images transmitted through the AR optical waveguide from a plurality of sides, and the situation of brightness change in the visual field of a wearer is presented.)

1. A method of designing an AR optical waveguide including an incoupling grating, an optical waveguide body, and an outcoupling grating, the method comprising:

s101: optimizing grating parameters of the incoupling grating according to the angle of the light beam incident to the incoupling grating and the wavelength of the light beam, wherein the grating parameters comprise a grating period, a grating depth and a grating duty ratio;

s102: determining the grating period and the grating depth of the coupling-out grating according to the grating period and the grating depth of the coupling-in grating;

s103: partitioning the coupling grating;

s104: and obtaining the grating duty ratio of each subarea of the coupled-out grating by taking the coupled-out total optical power and the non-uniformity of the coupled-out grating as optimization targets.

2. The design method of claim 1, wherein step S101 further comprises:

s1011: setting an optimization range of the grating parameters;

s1012: setting a coupling angle step length, and calculating diffraction efficiencies under different coupling angles;

s1013: calculating the average diffraction efficiency and the non-uniformity parameter of the coupling-in grating according to the diffraction efficiencies under different coupling-in angles;

s1014: and obtaining the grating period, the modulation depth and the duty ratio of the coupled-in grating after optimization by taking the average diffraction efficiency and the nonuniformity as optimization targets.

3. The design method of claim 2, wherein step S1014 further comprises:

and optimizing by adopting a steepest descent method, a genetic algorithm, a particle swarm algorithm or a simulated annealing algorithm.

4. The design method of any one of claims 1-3, wherein step S102 further comprises:

the coupling grating is designed to have the same grating depth and grating period as the coupling grating.

5. The design method of any one of claims 1-3, wherein step S103 further comprises:

s1031: calculating a diffraction coupling-in angle at which the light beam is diffracted and coupled into the optical waveguide body through the coupling-in grating according to an angle at which the light beam is incident to the coupling-in grating, the wavelength of the light beam and a grating period of the coupling-in grating;

s1032: calculating the distance between two adjacent coupling-out positions of the light beam on the coupling-out grating according to the diffraction coupling-in angle and the thickness of the optical waveguide main body;

s1033: calculating the brightness difference rate of the light beams after being coupled out by the coupling-out grating for multiple times according to the maximum diffraction efficiency of the coupling-out grating;

s1034: and calculating the number of the subareas of the coupling-out grating according to the length of the coupling-out grating, the sensitivity of human eyes to the light beams, the brightness difference rate and the distance between the two adjacent coupling-out positions.

6. The design method of claim 5, wherein the light beam is incident in a cone beam having a certain field angle, and the step S1031 further comprises:

and calculating the diffraction coupling-in angle according to the central incident angle of the cone beam or the positive pole value/negative pole value of the incident angle of the cone beam.

7. The design method of any one of claims 1-3, wherein step S104 further comprises:

s1041: dividing the eye movement range of the coupling-out grating into a plurality of eye movement sub-regions according to the size of the pupil, and calculating the coupling-out light power of each eye movement sub-region;

s1042: calculating the non-uniformity parameter of the coupled-out optical power in the eye movement range of the coupled-out grating according to the coupled-out optical power of each eye movement subregion;

s1043: and obtaining the optimized grating duty ratio of the subarea by taking the coupled total optical power of the coupled grating and the non-uniformity parameter as optimization targets.

8. The design method of claim 7, wherein the step S1044 further comprises:

and optimizing by adopting a steepest descent method, a genetic algorithm, a particle swarm algorithm or a simulated annealing algorithm.

9. An optical waveguide for AR glasses, designed by the design method according to any one of claims 1 to 8.

Technical Field

The present invention generally relates to the field of near-eye display technologies, and in particular, to a design method of an AR optical waveguide and an optical waveguide for AR glasses.

Background

With the development of computer technology and display technology, Virtual Reality (VR) technology for experiencing a Virtual world through a computer simulation system, and Augmented Reality (AR) technology and Mixed Reality (MR) technology for fusing display contents into a real environment background have been rapidly developed.

Near-eye display is an important technical hotspot in the development of VR, AR and MR technologies as described above. The near-eye display VR technology mainly pursues an immersion type large-view-field virtual display, and corresponds to a virtual reality display helmet. And the near-eye AR and MR technologies aim to realize perspective virtual-real fusion, and correspondingly, the near-eye AR and MR technologies are augmented reality intelligent glasses.

At present, a free-form surface geometric optical scheme is mostly used for a near-to-eye display device for AR/MR, but the size of the near-to-eye display device is limited, so that the popularization of AR/MR glasses is restricted; the array optical waveguide and the diffraction optical waveguide gradually appear in the visual field, the design principle of the array optical waveguide is relatively simple, but the process difficulty is high, the large-scale mass production is not suitable, and the large-scale popularization is also restricted due to the fact that the array optical waveguide needs to be matched with a specific optical machine.

And the diffraction optical waveguide is used as an augmented reality optical engine, and functions of image coupling-in, coupling-out, pupil expanding and the like are realized. The diffractive light waveguide has the advantages of high mass productivity, light weight, and the like, and is gradually recognized in the AR/MR field, and is used as a mainstream technical development direction in the AR/MR field in the future. However, AR/MR glasses using diffractive optical waveguides typically exhibit non-uniform image shading in the field of view of the wearer.

The statements in this background section merely represent techniques known to the public and are not, of course, representative of the prior art.

Disclosure of Invention

In view of at least one of the drawbacks of the prior art, the present invention provides a method for designing an AR optical waveguide including an incoupling grating, an optical waveguide body, and an outcoupling grating, the method comprising:

s101: optimizing grating parameters of the incoupling grating according to the angle of the light beam incident to the incoupling grating and the wavelength of the light beam, wherein the grating parameters comprise a grating period, a grating depth and a grating duty ratio;

s102: determining the grating period and the grating depth of the coupling-out grating according to the grating period and the grating depth of the coupling-in grating;

s103: partitioning the coupling grating;

s104: and obtaining the grating duty ratio of each subarea of the coupled-out grating by taking the coupled-out total optical power and the non-uniformity of the coupled-out grating as optimization targets.

According to an aspect of the present invention, wherein step S101 further comprises:

s1011: setting an optimization range of the grating parameters;

s1012: setting a coupling angle step length, and calculating diffraction efficiencies under different coupling angles;

s1013: calculating the average diffraction efficiency and the non-uniformity parameter of the coupling-in grating according to the diffraction efficiencies under different coupling-in angles;

s1014: and obtaining the grating period, the modulation depth and the duty ratio of the coupled-in grating after optimization by taking the average diffraction efficiency and the nonuniformity as optimization targets.

According to an aspect of the invention, wherein step S1014 further comprises:

and optimizing by adopting a steepest descent method, a genetic algorithm, a particle swarm algorithm or a simulated annealing algorithm.

According to an aspect of the present invention, wherein step S102 further comprises:

the coupling grating is designed to have the same grating depth and grating period as the coupling grating.

According to an aspect of the invention, wherein step S103 further comprises:

s1031: calculating a diffraction coupling-in angle at which the light beam is diffracted and coupled into the optical waveguide body through the coupling-in grating according to an angle at which the light beam is incident to the coupling-in grating, the wavelength of the light beam and a grating period of the coupling-in grating;

s1032: calculating the distance between two adjacent coupling-out positions of the light beam on the coupling-out grating according to the diffraction coupling-in angle and the thickness of the optical waveguide main body;

s1033: calculating the brightness difference rate of the light beams after being coupled out by the coupling-out grating for multiple times according to the maximum diffraction efficiency of the coupling-out grating;

s1034: and calculating the number of the subareas of the coupling-out grating according to the length of the coupling-out grating, the sensitivity of human eyes to the light beams, the brightness difference rate and the distance between the two adjacent coupling-out positions.

According to an aspect of the invention, wherein the light beam is incident as a cone beam having a certain field angle, the step S1031 further comprises:

and calculating the diffraction coupling-in angle according to the central incident angle of the cone beam or the positive pole value/negative pole value of the incident angle of the cone beam.

According to an aspect of the invention, wherein step S104 further comprises:

s1041: dividing the eye movement range of the coupling-out grating into a plurality of eye movement sub-regions according to the size of the pupil, and calculating the coupling-out light power of each eye movement sub-region;

s1042: calculating the non-uniformity parameter of the coupled-out optical power in the eye movement range of the coupled-out grating according to the coupled-out optical power of each eye movement subregion;

s1043: and obtaining the optimized grating duty ratio of the subarea by taking the coupled total optical power of the coupled grating and the non-uniformity parameter as optimization targets.

According to an aspect of the present invention, wherein the step S1044 further comprises:

and optimizing by adopting a steepest descent method, a genetic algorithm, a particle swarm algorithm or a simulated annealing algorithm.

The invention also provides an optical waveguide for AR glasses, which is designed and manufactured by the design method.

The preferred embodiment of the invention provides a design method of an AR optical waveguide, which is characterized in that various grating parameters of an incoupling grating are optimized to enable the diffraction efficiencies of light beams incoupling into the optical waveguide from different angles to be similar, the grating parameters of an outcoupling grating are set according to the grating parameters of the incoupling grating, the outcoupling grating is partitioned according to the parameters of the outcoupling grating and the optical waveguide and the sensitivity of human eyes to light and shade, so that human eyes can not easily perceive the change of light and shade in the same partition, and for different partitions, the outcoupling diffraction efficiencies of the partitions are different by optimizing the grating duty cycles in the partitions, images transmitted through the AR optical waveguide are improved from multiple sides, and the change of light and shade is presented in the visual field of a wearer.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 shows an AR optical waveguide in accordance with a preferred embodiment of the present invention;

FIG. 2 illustrates a method of designing an AR optical waveguide in accordance with a preferred embodiment of the present invention;

FIG. 3 shows the diffraction efficiency of an incoupling grating as a function of the incoupling angle;

FIG. 4 illustrates an optimization for an incoupling grating in accordance with a preferred embodiment of the present invention;

FIG. 5 shows the diffraction efficiency of an incoupling grating as a function of the incoupling angle after optimization for the incoupling grating in accordance with a preferred embodiment of the present invention;

FIG. 6 illustrates partitioning of an outcoupling grating according to a preferred embodiment of the present invention;

FIG. 7 illustrates various parameters of an optical waveguide body in accordance with a preferred embodiment of the present invention;

FIG. 8 illustrates the optimization of the out-coupling grating according to a preferred embodiment of the present invention;

FIG. 9 illustrates the division of the eye movement range into sub-regions according to pupil size in accordance with a preferred embodiment of the present invention;

fig. 10 shows the display effect after optimization of the incoupling grating, division of the outcoupling grating and optimization of the outcoupling grating according to a preferred embodiment of the present invention.

Detailed Description

In the following, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like, indicate orientations and positional relationships based on those shown in the drawings, and are used only for convenience of description and simplicity of description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be considered as limiting the present invention. Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.

In the description of the present invention, it should be noted that unless otherwise explicitly stated or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection, either mechanically, electrically, or in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly above and obliquely above the second feature, or simply meaning that the first feature is at a lesser level than the second feature.

The following disclosure provides many different embodiments or examples for implementing different features of the invention. To simplify the disclosure of the present invention, the components and arrangements of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, such repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art may recognize applications of other processes and/or uses of other materials.

The embodiments of the present invention will be described in conjunction with the accompanying drawings, and it should be understood that the embodiments described herein are only for the purpose of illustrating and explaining the present invention, and are not intended to limit the present invention.

As shown in fig. 1, the AR optical waveguide 100 includes an incoupling grating 110, an optical waveguide body 120, and an outcoupling grating 130. The AR optical waveguide 100 provides an incident light beam from the optical engine 140, and the optical engine 140 is configured to form a light beam group with a light cone distribution, wherein light beams in different directions in the light beam group may carry color information and/or brightness information of different image pixels, for example.

As shown in fig. 1, the optical engine 140 generates a light beam group with a divergence angle θ in a light cone distribution, wherein the diffraction efficiency of the light beams coupled into the AR optical waveguide 100 from different angles is different, and as the light beams are continuously coupled out during transmission, the luminous flux in the eye movement range (Eyebox) is gradually reduced, which causes the phenomenon that the brightness of the observed image changes when the human eye moves in the eye movement range.

In order to solve the above technical problem, the present invention provides a method 10 for designing an AR optical waveguide. According to a preferred embodiment of the present invention, as shown in fig. 1, an AR optical waveguide 100 includes an incoupling grating 110, an optical waveguide body 120, and an outcoupling grating 130. Fig. 2 shows a flow chart of the design method 10, comprising steps S101-S104. Wherein:

in step S101, the grating parameters of the incoupling grating 110 are optimized according to the angle of the light beam incident on the incoupling grating 110 and the wavelength of the light beam, where the grating parameters include a grating period, a grating depth, and a grating duty cycle.

For example, the incoupling grating 110 is designed for +1 order diffraction, that is, the +1 order diffraction light is totally reflected and propagates after being coupled into the optical waveguide body 120 through the incoupling grating 110. Whereas the diffraction efficiency of +1 order diffraction is asymmetric with respect to 0 °, i.e. the diffraction efficiency of the light beams coupled into the AR optical waveguide 100 from different angles is different. Fig. 3 shows the diffraction efficiency as a function of different coupling angles in the +1 diffraction order. As shown in fig. 1, the light beam L1 generated by the optical engine 140 is coupled into the AR optical waveguide 100 at an angle of-10 °, and the light beam L2 generated by the optical engine 140 is coupled into the AR optical waveguide 100 at an angle of 10 °. As can be seen from fig. 3, the diffraction efficiency of the +1 order of the light beam L1 is 16.8%, and the diffraction efficiency of the +1 order of the light beam L2 is 6.5%. Without optimizing the incoupling grating 110, the light beams L1, L2 propagate through the light guide body 120 and are coupled out by the outcoupling grating 130, and the brightness of the image information conveyed by the light beam L1 as viewed by the human eye will be significantly greater than the brightness of the image information conveyed by the light beam L2 due to the light loss caused by the different +1 order diffraction efficiencies of the incoupling light beams at different angles.

The +1 order diffraction efficiency of the incoupling grating 110 is related to the wavelength of the incoupling beam and the incoupling angle of the beam, and therefore, in step S101, the grating parameters of the incoupling grating 110 are optimized according to the angle of the beam incident on the incoupling grating 110 and the wavelength of the beam, where the optimized parameters include the grating period, the grating depth and the grating duty ratio. The optimized incoupling grating 110 can make the +1 order diffraction efficiency of the light beams incoupled into the AR optical waveguide 100 at different angles more uniform, and also take into account the light-exiting rate of the incoupling grating 110, i.e. the average diffraction efficiency of the incoupling grating 110.

Step S101 of the design method 10 overcomes or improves the problem of different imaging brightnesses of different fields of view caused by different diffraction efficiencies of the light beams coupled into the AR optical waveguide 100 from different angles, so that the light beams emitted by the optical machine 140 are coupled in by the coupling-in grating 110, are propagated by total reflection through the optical waveguide main body 120, and are coupled out by the coupling-out grating 130, and then the brightness of the image observed by human eyes is relatively uniform.

In step S102, the grating period and the grating depth of the outcoupling grating 130 are determined according to the grating period and the grating depth of the incoupling grating 110.

In step S101, the grating parameters of the incoupling grating 110 may be determined, and then the grating period and the grating depth of the outcoupling grating 130 may be determined according to the grating period and the grating depth of the incoupling grating 110. When the grating period of the incoupling grating 110 is set to be the same as that of the outcoupling grating 130, the light beam L1 generated by the optical engine 140 is incoupled into the incoupling grating 110 of the AR optical waveguide 100 at an incident angle of-10 °, for example, and is still outcoupled from the AR optical waveguide 100 at an exit angle of-10 ° by the outcoupling grating 130 after propagating through the optical waveguide body 120. Moreover, the grating depths of the coupling grating 110 and the coupling grating 130 are set to be the same, which is friendly to the process and convenient for processing and manufacturing, and the etching depth-to-width ratio of the same standard is adopted in the grating imprinting and etching processes, so that the difficulty of the etching process is reduced.

In step S103, the outcoupling grating 130 is partitioned.

As shown in fig. 1, the light beams L1 and L2 are propagated by total reflection in the optical waveguide body 120 of the AR optical waveguide 100, and as the light beams L1 and L2 are coupled and emitted in the range of the region where the coupling grating 130 is located, the luminance of the light beams L1 and L2 is reduced continuously if the diffraction efficiency of the coupling grating 130 is constant. This is one of the reasons why AR/MR glasses using a diffractive optical waveguide cause bright-dark images to appear in the field of view of the observer. In the preferred embodiment of the present invention, the coupling-out area corresponding to the coupling-out grating 130 is partitioned according to the sensitivity of human eyes to light variation, the same grating parameters are set in the same partition, and human eyes cannot be attenuated in the partition; in different subareas, the grating parameters are adjusted to ensure that the light-emitting rates (diffraction efficiencies) of the light beams are different, and after each attenuation, the diffraction efficiency is increased, so that the brightness change of the light beams is not obvious. The method of partitioning the coupled-out grating will be described in detail below.

In step S104, the grating duty cycles of the respective partitions of the outcoupling grating are obtained with the outcoupling total optical power and the non-uniformity of the outcoupling grating as optimization objectives.

The grating partition of the outcoupling grating 130 is determined by step S103, and the grating duty ratio in each partition is determined with the total outcoupling power and non-uniformity in the eye movement range as optimization targets.

According to a preferred embodiment of the present invention, as shown in fig. 4, in the design method 10, the optimization of the grating parameters of the coupled-in grating in step S101 is implemented by the following method, which includes steps S1011 to S1014.

In step S1011, an optimized range of the coupled grating parameters is set.

The optimum range of grating parameters is determined according to the wavelength of the light beam coupled into the AR optical waveguide 100. For example, for green light, the optimized range of the grating period is 300nm-500nm, the optimized range of the duty ratio is 30% -70%, and considering the process limitation, the depth-to-width ratio of the grating ridge does not exceed 2:1, and then the optimized range of the grating depth is 100nm-300 nm.

In step S1012, a step size of the coupling angle is set, and diffraction efficiencies at different coupling angles are calculated.

Diffraction efficiencies at different coupling angles were calculated, respectively. For example, the coupling-in angle is divided by a step size of 0.2 °, the light-out angle range of the optical engine 140 is set to be θ, and the coupling-in angle is symmetric about 0 °, and is divided into m coupling-in angles, that is, m is θ/0.2. The diffraction efficiency was recorded every 0.2 deg. for a total of m times, assuming that the diffraction efficiency at different coupling angles is Ei, where i is in the range of (-theta/2, … -0.4, -0.2,0,0.2,0.4 … theta/2).

In step S1013, an average diffraction efficiency and a non-uniformity parameter of the coupling-in grating are calculated from the diffraction efficiencies at the different coupling-in angles.

By designing the grating parameters of the incoupling grating 110, the +1 order diffraction efficiency as a function of the incoupling angle is optimized to be approximately uniformly distributed. However, it is also not desirable to improve the uniformity of the diffraction efficiency of only the +1 order, sacrificing the light extraction (characterized by the average diffraction efficiency) into the grating 110. Therefore, in a preferred embodiment of the present invention, the uniformity of the +1 st order diffraction efficiency and the average diffraction efficiency are both optimization targets. Wherein the average diffraction efficiency is:

the non-uniformity parameters of the diffraction efficiency are:

in step S1014, the optimized grating period, modulation depth and duty ratio of the coupled-in grating 110 are obtained by using the average diffraction efficiency and the non-uniformity parameter as optimization targets.

Will maximize the average diffraction efficiency E_{mean-efficiency}Minimizing the non-uniformity parameter E_non-uniformAs an optimization target, a steepest descent method (DS), a Genetic Algorithm (GA), a Particle Swarm Optimization (PSO), or a simulated annealing algorithm (SA) is used to optimize the grating period, modulation depth, and duty ratio.

As shown in fig. 5, the optimized coupling-in grating 110 has a diffraction efficiency as a function of the coupling-in angle of the light beam. If the optimized incoupling grating 110 is used, as shown in FIG. 1, the light beam L1 generated by the optical engine 140 is coupled into the AR optical waveguide 100 at an angle of-10, and the light beam L2 generated by the optical engine 140 is coupled into the AR optical waveguide 100 at an angle of 10. As can be seen from fig. 5, the diffraction efficiency of the +1 order of the light beam L1 is 17.75%, and the diffraction efficiency of the +1 order of the light beam L2 is 17.5%. After the light beams L1 and L2 propagate through the optical waveguide body 120 and are coupled out by the coupling-out grating 130, the brightness of the image information transmitted by the light beam L1 observed by the human eye is not much different from the brightness of the image information transmitted by the light beam L2.

According to a preferred embodiment of the present invention, as shown in fig. 6, in the design method 10, the partitioning of the out-coupling grating 130 in step S103 is implemented by the following method, which includes steps S1031 to S1034.

In step S1031, a diffraction incoupling angle at which the light beam is diffracted and coupled into the optical waveguide body 120 through the incoupling grating 110 is calculated from the angle at which the light beam is incident on the incoupling grating 110, the wavelength of the light beam, and the grating period of the incoupling grating 110.

As shown in fig. 7, the light beam L1 emitted from the optical device 140 is coupled into the AR optical waveguide 100 via the coupling-in grating 110, and then is totally reflected and propagated in the optical waveguide body 120, whereby the diffraction coupling-in angle of the light beam L1Comprises the following steps:

where λ is the wavelength of beam L1, Λ is the grating period coupled into grating 110, θ_inThe incident angle of the light beam L1 incident on the incoupling grating 110, n is the diffraction order.

In step S1032, the angle is coupled according to diffractionAnd the thickness of the optical waveguide body 120, the distance between two adjacent outcoupling sites of the light beam on the outcoupling grating 130 is calculated.

As shown in fig. 7, if the thickness of the optical waveguide body 120 is h, the distance between the positions where two adjacent light beams are coupled out in the coupling-out region of the coupling-out grating 130 is:

in step S1033, a brightness difference rate of the light beam after being coupled out by the coupling-out grating 130 for a plurality of times is calculated according to the maximum diffraction efficiency of the coupling-out grating 130.

Assuming that the maximum diffraction efficiency of the outcoupling grating 130 is a, the m-th light extraction efficiency is:

a_m＝a(1-a)^m-1

the brightness difference rate of the p-th coupled light-out and the m-th coupled light-out is as follows:

Δa＝a((1-a)^m-1-(1-a)^p-1)

since the light beam is most attenuated when it is first coupled out during the propagation of the optical waveguide body 120, when m is 1, the attenuation is the largest

Δa＝a(1-(1-a)^p-1)

In step S1034, the number of partitions of the outcoupling grating 130 is calculated according to the length of the outcoupling grating 130, the sensitivity of the human eye to the light beam, the luminance difference ratio Δ a, and the distance d1 between the two adjacent outcoupling positions.

The brightness sensitivity of human eyes to light with fixed wavelength is set as delta b, under different light intensities, a coefficient alpha needs to be added to the brightness sensitivity of human eyes to light, and in order to ensure that human eyes cannot feel obvious brightness change when receiving light information, the brightness difference rate delta a < alpha delta b needs to be ensured, namely:

a(1-(1-a)^p-1)<αΔb

from the above formula, the number p of outcoupling within the same partition of the outcoupling grating 130 can be obtained on the premise that the human eye cannot perceive the change in brightness:

the coupling-out area of the coupling-out grating 130 is divided by the coupling-out times p, and in the same partition, the brightness attenuation observed by human eyes is not obvious by adopting the same grating parameters. In the same partition, if the maximum outcoupling time is p, the partition length is p × d1, that is, the product of the distance between two adjacent outcoupling positions and the maximum outcoupling time, and the length of the outcoupling grating 130 is d2, the number of partitions on the outcoupling grating 130 is:

f＝d2/(p*d1)，

taking f as an integer.

In different subareas, the diffraction efficiency of different subareas is different by adjusting the grating duty ratio or other grating parameters, and the light intensity is attenuated continuously along with the total reflection propagation of the light beam in the optical waveguide main body 120, so that the diffraction coupling-out efficiency of each subarea arranged on the light propagation path is increased continuously to make up for the brightness difference caused by the attenuation of the light intensity.

According to a preferred embodiment of the present invention, in the designing method 10, the light beam is incident as a cone light beam having a certain field angle, and the step S1031 further includes:

calculating a diffraction coupling-in angle according to the central incident angle of the cone beam or the positive/negative value of the incident angle of the cone beam

According to a preferred embodiment of the present invention, as shown in fig. 8, in the design method 10, the step S104 is implemented by taking the total coupled optical power and the non-uniformity of the coupled grating 130 as the optimization objectives, and obtaining the grating duty ratio of each partition of the coupled grating 130 includes steps S1041 to S1043.

In step S1041, the eye movement range of the coupling grating 130 is divided into a plurality of eye movement sub-regions according to the pupil size, and the coupling optical power of each eye movement sub-region is calculated.

As shown in fig. 9, the eye movement range of the coupled-out grating is divided into 12 sub-regions according to the pupil size, and the coupled-out optical power Uj of each eye movement sub-region is calculated, where j ∈ (1,2, … 12).

In step S1042, a non-uniformity parameter of the coupled-out optical power in the eye movement range of the coupled-out grating 130 is calculated according to the coupled-out optical power Uj of each eye movement sub-region.

The non-uniformity parameters of the outcoupled optical power in the eye movement range (Eyebox) are:

the total power of the outcoupled light in the eye movement range (Eyebox) is:

U_total＝∑Uj

since the light intensity of the light engine 140 is generally constant, the coupling efficiency of the AR optical waveguide 100 is consistent with the total light-coupled power of the light-coupling grating 130, and in the preferred embodiment of the present invention, the total light-coupled power of the light-coupling grating 130 and the non-uniformity of the light-coupled power of each eye movement sub-region are used as optimization targets.

In step S1043, the total optical power U of the grating 130 is coupled out_totalAnd a non-uniformity parameter U_non-uniformAnd obtaining the optimized grating duty ratio of the subarea as an optimization target. Preferably, the optimization is performed by a steepest descent method, a genetic algorithm, a particle swarm algorithm or a simulated annealing algorithm.

The design method 10 provided by the present invention is further described below by way of a specific embodiment.

Let human eye sensitivity coefficient α equal to 1, human eye brightness sensitivity Δ b under ambient light approximately equal to 1: 20-0.05. The thickness h of the optical waveguide body 120 of the AR optical waveguide 100 is 1mm, the width d2 of the coupling-out grating 130 is 23mm, and the refractive indices of the grating and the optical waveguide are both 1.816.

Aiming at green light, the optimization range of the grating period is 300nm-500nm, the optimization range of the duty ratio is 30% -70%, and considering that the depth-to-width ratio of the grating ridge is not more than 2:1 due to process limitation, the optimization range of the grating depth is 100nm-300 nm.

The grating period of the incoupling grating 110 is 390nm, the duty ratio is 50%, and the grating depth is 190nm as the initial grating parameter.

And dividing the coupling angle by taking 0.2 degrees as a step length, and optimizing an optimization target by adopting a steepest Descent (DS) algorithm.

The average diffraction efficiency of the coupled grating 110 is converged between 10% and 20% through optimization, and the perturbation interval of the non-uniformity coefficient is large. And analyzing the optimized result, and selecting the grating period, the duty cycle and the modulation depth, wherein the grating period is preferably 420nm-450nm, the modulation depth is preferably 160nm-200nm, and the duty cycle of the coupled grating 110 is preferably 44% -53%. The average diffraction efficiency of the incoupling grating 110 can be up to 17% with a non-uniformity coefficient of 3%.

Calculated as the maximum angle at which total reflection occurs in the optical waveguide body 120 isThe outcoupling grating 130 is partitioned by the above-mentioned method, so that p is 1.9, and the distance d1 between two adjacent outcoupling positions is 2.36mm, so that the number f of partitions of the outcoupling grating 130 is 23/(1.9 × 2.36), and the integer f is 5.

In the 5 sections of the coupling-out grating 130, the grating period and the modulation depth are the same as those of the coupling-in grating 110. The eye movement range (Eyebox) is divided according to the pupil size using the grating duty cycle in the 5 sections of the coupled-out grating 130 as an optimization variable. Wherein the eye movement range (Eyebox) is 15mm 10mm, the eye movement range (Eyebox) is divided into 12 areas of 4 x 3, and the optical power Uj is calculated in each area. The grating duty ratio fi inside each partition is used as an optimization variable to couple out the total optical power U of the grating 130_totalAnd a non-uniformity parameter U_non-uniformAs an optimization target, the target was optimized using a Particle Swarm Optimization (PSO), and the optical power non-uniformity within the eye movement range (Eyebox) gradually converged to 15% -20%. After the optimization results are analyzed, the optimal optimization combination is obtained, and the result parameters are shown in table 1.

TABLE 1

The optimized result is used for reconstructing a waveguide model for simulation, and the simulation result is shown in fig. 10, which shows that the uniformity of light is greatly improved in the range of the eye movement range (Eyebox) compared with the situation before optimization as shown in fig. 9.

The present invention also provides an optical waveguide for AR glasses, designed according to a preferred embodiment of the present invention, using the design method 10 as described above.

The preferred embodiment of the invention provides a design method of an AR optical waveguide, which is characterized in that various grating parameters of an incoupling grating are optimized to enable the diffraction efficiencies of light beams incoupling into the optical waveguide from different angles to be similar, the grating parameters of an outcoupling grating are set according to the grating parameters of the incoupling grating, the outcoupling grating is partitioned according to the parameters of the outcoupling grating and the optical waveguide and the sensitivity of human eyes to light and shade, so that human eyes can not easily perceive the change of light and shade in the same partition, and for different partitions, the outcoupling diffraction efficiencies of the partitions are different by optimizing the grating duty cycles in the partitions, images transmitted through the AR optical waveguide are improved from multiple sides, and the change of light and shade is presented in the visual field of a wearer.

Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.