CN113625446B - Design method of AR optical waveguide and optical waveguide for AR glasses - Google Patents
Design method of AR optical waveguide and optical waveguide for AR glasses Download PDFInfo
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Abstract
The invention provides a design method of an AR optical waveguide, which comprises a coupling-in grating, an optical waveguide main body and a coupling-out grating, and comprises the following steps: s101: optimizing grating parameters of the coupling-in grating according to the angle of incidence of the light beam to the coupling-in grating and the wavelength of the light beam, wherein the grating parameters comprise grating period, grating depth and grating duty ratio; s102: determining the grating period and the grating depth of the coupled grating according to the grating period and the grating depth of the coupled grating; s103: partitioning the coupling-out grating; s104: and taking the total coupling-out light power and the non-uniformity of the coupling-out grating as optimization targets to obtain grating duty ratios of all the subareas of the coupling-out grating. The design method of the AR optical waveguide provided by the invention improves the image transmitted by the AR optical waveguide from a plurality of sides, and the light and shade change condition appears in the visual field of a wearer.
Description
Technical Field
The invention relates to the technical field of near-to-eye display, 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 of experiencing a Virtual world through a computer simulation system and augmented Reality (Augmented Reality, AR) technology and Mixed Reality (MR) technology of fusing display contents into a real environment background have been rapidly developed.
Near-eye display is an important technical hotspot for the development of VR, AR and MR technologies as described above. VR technology for near-eye display mainly pursues virtual display of submerged large field of view, corresponding to virtual reality display helmets. The purpose of the near-eye AR and MR technology is to realize perspective virtual-real fusion, and the purpose is to augment reality intelligent glasses.
At present, the near-to-eye display device for AR/MR mostly uses a geometrical optical scheme of a free-form surface, but has the limitation of size, and restricts the popularization of AR/MR glasses; 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 array optical waveguide is not suitable for large-scale mass production, and the array optical waveguide is restricted from large-scale popularization due to the fact that the array optical waveguide is required to be matched with a specific optical machine.
The diffraction optical waveguide is used as an augmented reality optical engine, so that the functions of image in-coupling, out-coupling, pupil expansion and the like are realized. The diffractive optical waveguide has the advantages of high mass productivity, light weight, and the like, is gradually accepted in the AR/MR field, and is used as a main technical development direction in the AR/MR field in the future. However, AR/MR glasses using a diffractive optical waveguide generally exhibit a phenomenon that the brightness of an image is not uniform in the field of view of a wearer.
The matters in the background section are only those known to the public and do not, of course, represent prior art in the field.
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, the AR optical waveguide including an in-coupling grating, an optical waveguide body, and an out-coupling grating, the method comprising:
s101: optimizing grating parameters of the coupling-in grating according to the angle of incidence of the light beam to the coupling-in grating and the wavelength of the light beam, wherein the grating parameters comprise grating period, grating depth and grating duty ratio;
s102: determining the grating period and the grating depth of the coupled grating according to the grating period and the grating depth of the coupled grating;
s103: partitioning the coupling-out grating;
s104: and taking the total coupling-out light power and the non-uniformity of the coupling-out grating as optimization targets to obtain grating duty ratios of all the subareas of the coupling-out grating.
According to one 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 efficiency under different coupling angles;
s1013: calculating average diffraction efficiency and non-uniformity parameters of the coupling grating according to the diffraction efficiency at the different coupling angles;
s1014: and taking the average diffraction efficiency and the non-uniformity parameter as optimization targets to obtain the optimized grating period, modulation depth and duty ratio of the coupling grating.
According to one 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 one aspect of the present invention, wherein step S102 further comprises:
the out-coupling grating is designed to have a uniform grating depth, grating period, as the in-coupling grating.
According to one aspect of the present invention, wherein step S103 further comprises:
s1031: calculating a diffraction coupling angle of the light beam, which is diffracted and coupled into the optical waveguide main body through the coupling grating, according to the angle of incidence of the light beam to the coupling grating, the wavelength of the light beam and the grating period of the coupling 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 beam after being coupled out for many times by the coupling-out grating according to the maximum diffraction efficiency of the coupling-out grating;
s1034: and calculating the partition number of the out-coupling gratings according to the length of the out-coupling gratings, the sensitivity of human eyes to the light beams, the brightness difference rate and the distance between the two adjacent out-coupling positions.
According to an aspect of the present invention, wherein the light beam is incident in a cone beam having a certain angle of view, step S1031 further includes:
the diffraction in-coupling angle is calculated from the center angle of incidence of the cone beam or the positive/negative value of the cone beam angle of incidence.
According to one aspect of the present invention, wherein step S104 further comprises:
s1041: dividing the eye movement range of the coupling-out grating into a plurality of eye sub-regions according to pupil sizes, and calculating the coupling-out light power of each eye sub-region;
s1042: according to the coupled light power of each eye subarea, calculating the non-uniformity parameter of the coupled light power in the eye movement range of the coupled grating;
s1043: and taking the total coupling-out light power of the coupling-out grating and the non-uniformity parameter as optimization targets to obtain the optimized grating duty ratio of the subarea.
According to one aspect of the present invention, 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 adopting 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 a coupling-in grating are optimized, so that the diffraction efficiency of light beams coupled into the optical waveguide from different angles is similar, the grating parameters of a coupling-out grating are set according to the grating parameters of the coupling-in grating, the coupling-out grating is partitioned according to the parameters of the coupling-out grating and the optical waveguide and the sensitivity degree of human eyes to light brightness, so that the human eyes are not easy to perceive the change of the brightness in the same partition, and the coupling-out diffraction efficiency of each partition is different by optimizing the duty ratio of the grating in the partition for different partitions, the image transmitted through the AR optical waveguide is improved from a plurality of sides, and the condition of brightness change is presented in the visual field of a wearer.
Drawings
The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate the invention and together with the embodiments of the invention, serve to explain the invention. In the drawings:
FIG. 1 illustrates 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 the incoupling grating as a function of incoupling angle;
FIG. 4 illustrates optimization of the coupling-in grating according to a preferred embodiment of the present invention;
FIG. 5 shows the diffraction efficiency of the coupling-in grating as a function of coupling-in angle after optimization of the coupling-in grating according to a preferred embodiment of the invention;
FIG. 6 illustrates partitioning of an out-coupling grating according to a preferred embodiment of the present invention;
FIG. 7 illustrates parameters of an optical waveguide body in accordance with a preferred embodiment of the present invention;
FIG. 8 illustrates optimization of an out-coupling grating according to a preferred embodiment of the present invention;
FIG. 9 illustrates dividing the eye movement range into a plurality of sub-regions according to pupil size in accordance with a preferred embodiment of the present invention;
FIG. 10 illustrates the display effect after the in-grating optimization, out-grating partitioning, and out-grating optimization is performed according to a preferred embodiment of the present invention.
Detailed Description
Hereinafter, only certain exemplary embodiments are briefly described. As will be recognized by those of skill in the pertinent art, the described embodiments may be modified in various different ways 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 should 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", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
In the description of the present invention, it should be noted that, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be fixedly connected, detachably connected, or integrally connected, and may be mechanically connected, electrically connected, or may communicate with each other, for example; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.
In the present invention, unless expressly stated or limited otherwise, a first feature "above" or "below" a second feature may include both the first and second features being in direct contact, as well as the first and second features not being in direct contact but being in contact with each other through additional features therebetween. Moreover, a first feature being "above," "over" and "on" a second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is higher in level than the second feature. The first feature being "under", "below" and "beneath" the second feature includes the first feature being directly above and obliquely above the second feature, or simply indicating that the first feature is less level than the second feature.
The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. In order to simplify the present disclosure, components and arrangements of specific examples are described below. They are, of course, merely examples and are not intended to limit the invention. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples, which are for the purpose of brevity and clarity, and which do not themselves indicate the relationship between the various embodiments and/or arrangements discussed. In addition, the present invention provides examples of various specific processes and materials, but one of ordinary skill in the art will recognize the application of other processes and/or the use of other materials.
The embodiments of the present invention will be described below with reference to the accompanying drawings, and it should be understood that the embodiments described herein are for illustration and explanation of the present invention only, and are not intended to limit the present invention.
As shown in fig. 1, AR optical waveguide 100 includes an in-coupling grating 110, an optical waveguide body 120, and an out-coupling grating 130. The AR light guide 100 is provided with an incident light beam by a light engine 140, the light engine 140 being configured to form a light beam group of light cone distribution, wherein light beams of different directions in the light beam group may carry, for example, color information and/or brightness information of different image pixels.
As shown in fig. 1, the optical engine 140 generates a light beam group with a divergence angle θ and in a light cone distribution, wherein the diffraction efficiency of light beams coupled into the AR light waveguide 100 from different angles is different, and as the light beams are continuously coupled out during transmission, the light flux in the eye movement range (Eyebox) gradually decreases, so that the observed image appears as a bright-dark change when the human eye moves in the eye movement range.
In order to solve the above technical problems, the present invention provides a design method 10 of an AR optical waveguide. According to a preferred embodiment of the present invention, as shown in FIG. 1, AR optical waveguide 100 includes an in-coupling grating 110, an optical waveguide body 120, and an out-coupling grating 130. Fig. 2 shows a flow chart of the design method 10, comprising steps S101-S104. Wherein:
in step S101, grating parameters of the coupling-in grating 110 are optimized according to an angle of incidence of the light beam to the coupling-in grating 110, a wavelength of the light beam, the grating parameters including a grating period, a grating depth, and a grating duty cycle.
For example, the coupling-in grating 110 is designed for +1 diffraction, i.e. the +1 diffraction light propagates by total reflection after coupling into the optical waveguide body 120 via the coupling-in grating 110. Whereas the diffraction efficiency of the +1st order diffraction is asymmetric with respect to 0 deg., i.e. the diffraction efficiency of the light beam 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 bench 140 is coupled into the AR light guide 100 at an angle of-10 °, and the light beam L2 generated by the optical bench 140 is coupled into the AR light guide 100 at an angle of 10 °. As can be seen from fig. 3, the +1 order diffraction efficiency of the light beam L1 is 16.8%, while the +1 order diffraction efficiency of the light beam L2 is 6.5%. Without the coupling-in grating 110 being optimized, the light beams L1, L2 propagate through the optical waveguide body 120, and after being coupled out by the coupling-out grating 130, the brightness of the image information transmitted by the light beam L1, which is observed by the human eye, will be significantly greater than the brightness of the image information transmitted by the light beam L2 due to the light loss caused by the difference in +1 diffraction efficiency of the light beams coupled in at different angles.
The +1 diffraction efficiency of the coupling-in grating 110 is related to the wavelength of the coupling-in beam and the coupling-in angle of the beam, so in step S101, the grating parameters of the coupling-in grating 110 are optimized according to the angle of incidence of the beam to the coupling-in grating 110 and the wavelength of the beam, and the optimized parameters include the grating period, the grating depth and the grating duty cycle. The optimized coupling-in grating 110 can make the +1 diffraction efficiency of the light beams coupled into the AR optical waveguide 100 at different angles more uniform, and also give consideration to the light extraction rate of the coupling-in grating 110, that is, the average diffraction efficiency of the coupling-in grating 110.
Step S101 of the design method 10 overcomes or improves the problem of different imaging brightness 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 beam emitted by the optical engine 140 is coupled in by the coupling-in grating 110, is transmitted through the optical waveguide body 120 by total reflection, and is coupled out by the coupling-out grating 130, and the brightness of the image observed by human eyes is uniform.
In step S102, the grating period and the grating depth of the coupling-out grating 130 are determined according to the grating period and the grating depth of the coupling-in grating 110.
Through step S101, the grating parameters of the coupling-in grating 110 can be determined, and then the grating period and the grating depth of the coupling-out grating 130 can be determined according to the grating period and the grating depth of the coupling-in grating 110. When the grating period of the coupling-in grating 110 is set to be the same as the grating period of the coupling-out grating 130, the light beam L1 generated by the optical machine 140 is coupled into the coupling-in grating 110 of the AR optical waveguide 100, for example, at an incident angle of-10 °, and is still coupled out from the AR optical waveguide 100 at an exit angle of-10 ° by the coupling-out grating 130 after propagating through the optical waveguide body 120. And, the grating depth of the coupling-in grating 110 and the coupling-out grating 130 is set to be the same, so that the process is friendly, the processing and the manufacturing are convenient, and the etching depth-to-width ratio of the same standard is adopted in the grating embossing and etching processes, so that the etching process difficulty is reduced.
In step S103, the out-coupling grating 130 is partitioned.
As shown in fig. 1, the light beams L1 and L2 propagate through the optical waveguide body 120 of the AR optical waveguide 100 by total reflection, and as the light beams L1 and L2 are continuously coupled and emitted within the area where the coupling-out grating 130 is located, the brightness of the light beams L1 and L2 is continuously reduced if the diffraction efficiency of the coupling-out grating 130 is constant. This is also one of the reasons for the appearance of an image with a light-dark change in the field of view of the observer using AR/MR glasses with diffractive optical waveguides. According to the preferred embodiment of the 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 the human eyes can not feel the attenuation of brightness in the partition; in different subareas, the grating parameters are adjusted to ensure that the light extraction rate (diffraction efficiency) of the light beam is different, and after each attenuation, the diffraction efficiency is increased, so that the brightness change of the light beam is not obvious. The partitioning method for coupling out the grating is described in more detail below.
In step S104, the total light power and the non-uniformity of the out-coupling grating are used as optimization targets to obtain the grating duty ratio of each partition of the out-coupling grating.
The grating partitions of the coupling-out grating 130 are determined in step S103, and the grating duty cycle in each partition is determined with the total power and the non-uniformity of the coupling-out light 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 coupled into the grating in step S101 is achieved by the following method, including steps S1011-S1014.
In step S1011, an optimized range of the coupling-in grating parameters is set.
The optimal range of grating parameters is determined according to the wavelength of the light beam coupled into the AR light guide 100. For example, for green light, the optimal range of grating period is 300nm-500nm, the optimal range of duty cycle is 30% -70%, and considering the process limitation, the depth-to-width ratio of grating ridge is not more than 2:1, the optimal range of grating depth is 100nm-300nm.
In step S1012, a coupling angle step is set, and diffraction efficiency at different coupling angles is calculated.
Diffraction efficiencies at different coupling angles were calculated separately. For example, the coupling angles are divided according to the step size of 0.2 °, let the light exit angle range of the light machine 140 be θ, and are symmetrical about 0 °, and divided into m coupling angles altogether, i.e., m=θ/0.2. The diffraction efficiency was recorded every 0.2 ° and m times in total, with the diffraction efficiency at different coupling angles being Ei, where i e (- θ/2, … -0.4, -0.2,0,0.2,0.4 … θ/2).
In step S1013, average diffraction efficiency and non-uniformity parameters of the coupling grating are calculated from the diffraction efficiencies at the different coupling angles.
By designing the various grating parameters of the coupling-in grating 110, the function of +1st-order diffraction efficiency with respect to the coupling-in angle is optimized to be approximately uniformly distributed. However, merely increasing the uniformity of the +1 order diffraction efficiency, sacrificing the etendue (characterized by the average diffraction efficiency) of the coupling-in grating 110, is also undesirable. Therefore, in a preferred embodiment of the present invention, uniformity of +1 order diffraction efficiency and average diffraction efficiency are simultaneously taken as optimization targets. Wherein the average diffraction efficiency is:
the non-uniformity parameters for diffraction efficiency were:
in step S1014, the optimized grating period, modulation depth and duty cycle of the coupling-in grating 110 are obtained with the average diffraction efficiency and the non-uniformity parameter as optimization targets.
Will maximize the average diffraction efficiency E mean-efficiency Minimizing non-uniformity parameter E non-uniform As an optimization target, a steepest descent method (DS), a Genetic Algorithm (GA), a particle swarm algorithm (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 diffraction efficiency of the optimized incoupling grating 110 is obtained as a function of the beam incoupling angle. If the optimized coupling-in grating 110 is used, as shown in fig. 1, the light beam L1 generated by the optical bench 140 is coupled into the AR light guide 100 at an angle of-10 °, and the light beam L2 generated by the optical bench 140 is coupled into the AR light guide 100 at an angle of 10 °. As can be seen from fig. 5, the +1 order diffraction efficiency of the light beam L1 is 17.75%, while the +1 order diffraction efficiency 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 and the brightness of the image information transmitted by the light beam L2, which are observed by the human eye, do not greatly differ.
According to a preferred embodiment of the present invention, as shown in fig. 6, in the design method 10, the partitioning of the coupling-out grating 130 in step S103 is achieved by the following method, including steps S1031-S1034.
In step S1031, a diffraction coupling-in angle at which the light beam is diffraction-coupled into the optical waveguide body 120 through the coupling-in grating 110 is calculated according to an angle at which the light beam is incident to the coupling-in grating 110, a wavelength of the light beam, and a grating period of the coupling-in grating 110.
As shown in fig. 7, after the light beam L1 emitted from the optical machine 140 is coupled into the AR optical waveguide 100 through the coupling grating 110, the light beam L1 propagates through the optical waveguide body 120 by total reflection, and the diffraction coupling angle of the light beam L1 isThe method comprises the following steps:
where lambda is the wavelength of the light beam L1, lambda is the grating period coupled into the grating 110, θ in The incident angle of the light beam L1 to the coupling-in grating 110 is n, which is the diffraction order.
In step S1032, the coupling angle is determined according to diffractionAnd the thickness of the optical waveguide body 120 calculates the distance between two adjacent outcoupling sites of the light beam on the outcoupling grating 130.
As shown in fig. 7, assuming that the thickness of the optical waveguide body 120 is h, the distance between the positions of the coupling-out grating 130, where two adjacent light beams are coupled out, is:
in step S1033, the brightness difference ratio of the light beam after being coupled out of the coupling-out grating 130 for a plurality of times is calculated according to the maximum diffraction efficiency of the coupling-out grating 130.
Let the maximum diffraction efficiency of the coupling-out grating 130 be a, the mth light extraction efficiency is:
a m ＝a(1-a) m-1
the brightness difference ratio of the p-th coupled light and the m-th coupled light is as follows:
Δa＝a((1-a) m-1 -(1-a) p-1 )
since the light beam attenuates most at the beginning of the coupling-out during propagation of the optical waveguide body 120, let m=1
Δa＝a(1-(1-a) p-1 )
In step S1034, the number of partitions of the coupling-out grating 130 is calculated according to the length of the coupling-out grating 130, the sensitivity of the human eye to the light beam, the brightness difference rate Δa, and the distance d1 between the two adjacent coupling-out positions.
Let the light and shade sensitivity of human eyes to light with fixed wavelength be deltab, under different light intensities, a coefficient alpha needs to be added to the light and shade sensitivity of human eyes, in order to ensure that human eyes can not feel obvious light and shade changes when receiving light information, the brightness difference rate deltaa < deltab needs to be ensured, namely:
a(1-(1-a) p-1 )<αΔb
the number of times p of coupling out in the same partition of the coupling-out grating 130 can be obtained by the above method under the precondition that the human eye cannot perceive the brightness change:
the outcoupling region of the outcoupling grating 130 is divided by the number of outcoupling times p, and the luminance attenuation observed by human eyes is not obvious by adopting the same grating parameters in the same partition. In the same partition, the maximum number of out-coupling times is p, the partition length is p×d1, that is, the product of the distance between two adjacent out-coupling positions and the maximum number of out-coupling times, and the length of the out-coupling grating 130 is d2, and the number of partitions on the out-coupling grating 130 is:
f＝d2/(p*d1)，
taking f as an integer.
In different partitions, the diffraction efficiency of the different partitions is different by adjusting the duty ratio of the grating or other grating parameters, and as the light beam is totally reflected and propagated in the optical waveguide main body 120, the light intensity is continuously attenuated, so that the diffraction coupling-out efficiency of each partition is continuously improved on the light propagation path, and the brightness difference caused by the light intensity attenuation is compensated.
According to a preferred embodiment of the present invention, in the design method 10, the light beam is incident in a cone beam having a certain angle of view, and the step S1031 further includes:
calculating diffraction coupling angle according to the central incidence angle of the conical light beam or the positive/negative value of the incidence angle of the conical light beam
According to a preferred embodiment of the present invention, as shown in fig. 8, in the design method 10, with the total light power and the non-uniformity of the coupled-out grating 130 as optimization targets in step S104, the grating duty cycle of each partition of the coupled-out grating 130 is obtained by the following method, which includes steps S1041 to S1043.
In step S1041, the eye movement range of the coupling-out grating 130 is divided into a plurality of eye sub-regions according to pupil sizes, and the coupling-out light power of each eye sub-region is calculated.
As shown in fig. 9, the eye movement range of the coupling-out grating is divided into 12 sub-regions according to pupil sizes, and the coupling-out light power Uj of each eye sub-region is calculated, wherein j e (1, 2, … 12).
In step S1042, a non-uniformity parameter of the coupled light power in the eye movement range of the coupled grating 130 is calculated according to the coupled light power Uj of each eye sub-region.
The non-uniformity parameters of the coupled-out light power in the eye movement range (Eyebox) are:
the total power of the coupled-out light in the eye movement range (Eyebox) is:
U total ＝∑Uj
since the light intensity of the light emitted from the light machine 140 is fixed under normal conditions, the coupling efficiency of the AR optical waveguide 100 is consistent with the total coupled light power of the coupling-out grating 130, and in the preferred embodiment of the present invention, the total coupled light power of the coupling-out grating 130 and the non-uniformity of the coupled light power of each eye subarea are adopted as optimization targets.
In step S1043, the total light power U of the out-coupling grating 130 is used total Non-uniformity parameter U non-uniform And obtaining the optimized grating duty ratio of the subarea as an optimization target. Preferably, the optimization is performed using 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 in the following by way of one specific example.
Let the human eye sensitivity coefficient α=1, the bright-dark sensitivity Δb≡1 of the human eye under ambient light: 20 =0.05. The thickness h=1 mm of the optical waveguide body 120 of the AR optical waveguide 100, the width d2=23 mm of the coupling-out grating 130, and the refractive indexes of the grating and the optical waveguide are 1.816.
For green light, the optimization range of the grating period is 300-500 nm, the optimization range of the duty ratio is 30-70%, and the optimization range of the grating depth is 100-300 nm in consideration of the process limit grating ridge depth-width ratio not exceeding 2:1.
The grating period coupled into the grating 110 was 390nm, the duty cycle was 50% and the grating depth was 190nm as initial grating parameters.
The coupling-in angle is divided by taking 0.2 DEG as a step length, and the optimization target is optimized by adopting a steepest Descent (DS) algorithm.
The average diffraction efficiency of the coupling-in grating 110 is converged between 10% and 20% by optimization, and the disturbance interval of the non-uniformity coefficient is large. The optimization result is analyzed and the grating period, the duty cycle and the modulation depth are selected, wherein the grating period is preferably 420nm-450nm, the modulation depth is preferably 160nm-200nm, and the duty cycle of the coupling grating 110 is preferably 44% -53%. The average diffraction efficiency of the coupling-in grating 110 may reach 17% with a non-uniformity coefficient of 3%.
Calculated, the optical waveguide body 120, the maximum angle at which total reflection occurs isThe coupling-out grating 130 is partitioned by the method described above, to obtain p=1.9, and the distance d1=2.36 mm between two adjacent coupling-out positions, where the number of partitions f=23/(1.9×2.36) of the coupling-out grating 130 is taken as an integer f=5.
Within 5 sections of the coupling-out grating 130, the grating period, modulation depth is the same as the grating period, modulation depth of the coupling-in grating 110. The eye movement range (Eyebox) is divided according to pupil size using the grating duty cycles in the 5 partitions of the out-coupling grating 130 as optimization variables. Wherein the eye movement range (Eyebox) is 15mm by 10mm, the eye movement range (Eyebox) is divided into 4*3 total 12 areas, and the optical power Uj is calculated in each area. Taking the grating duty ratio fi inside each partition as an optimization variable to couple out the total light power U of the grating 130 total Non-uniformity parameter U non-uniform As an optimization target, the target is optimized using a particle swarm algorithm (PSO), and the optical power non-uniformity within the eye movement range (Eyebox) gradually converges to 15% -20%. After the optimization result is 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 the waveguide model, and simulation is performed, and the simulation result is shown in fig. 10, so that the light uniformity is greatly improved in the range of the eye movement range (Eyebox) compared with the condition before the optimization shown in fig. 9.
According to a preferred embodiment of the present invention, the present invention also provides an optical waveguide for AR glasses, designed 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 a coupling-in grating are optimized, so that the diffraction efficiency of light beams coupled into the optical waveguide from different angles is similar, the grating parameters of a coupling-out grating are set according to the grating parameters of the coupling-in grating, the coupling-out grating is partitioned according to the parameters of the coupling-out grating and the optical waveguide and the sensitivity degree of human eyes to light brightness, so that the human eyes are not easy to perceive the change of the brightness in the same partition, and the coupling-out diffraction efficiency of each partition is different by optimizing the duty ratio of the grating in the partition for different partitions, the image transmitted through the AR optical waveguide is improved from a plurality of sides, and the condition of brightness change is presented in the visual field of a wearer.
Finally, it should be noted that: the foregoing description is only a preferred embodiment of the present invention, and the present invention is not limited thereto, but it is to be understood that modifications and equivalents of some of the technical features described in the foregoing embodiments may be made by those skilled in the art, although the present invention has been described in detail with reference to the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A design method of an AR optical waveguide including an in-grating, an optical waveguide body, and an out-grating, the design method comprising:
s101: optimizing grating parameters of the coupling-in grating according to the angle of incidence of the light beam to the coupling-in grating and the wavelength of the light beam, wherein the grating parameters comprise grating period, grating depth and grating duty ratio;
s102: determining the grating period and the grating depth of the coupled grating according to the grating period and the grating depth of the coupled grating;
s103: partitioning the coupling-out grating;
s104: taking the total coupling-out light power and the non-uniformity of the coupling-out grating as optimization targets to obtain grating duty ratios of all the subareas of the coupling-out grating;
wherein step S103 further comprises:
setting the same grating parameters in the same partition;
different diffraction efficiencies are set in different partitions;
the setting of different diffraction efficiencies includes; and adjusting grating parameters to continuously improve diffraction coupling-out efficiency of each partition on an optical propagation path so as to make up brightness difference caused by light intensity attenuation caused by light beam propagation in the optical waveguide main body.
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 efficiency under different coupling angles;
s1013: calculating average diffraction efficiency and non-uniformity parameters of the coupling grating according to the diffraction efficiency at the different coupling angles;
s1014: and taking the average diffraction efficiency and the non-uniformity parameter as optimization targets to obtain the optimized grating period, modulation depth and duty ratio of the coupling grating.
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. A design method according to any one of claims 1-3, wherein step S102 further comprises:
the out-coupling grating is designed to have a uniform grating depth, grating period, as the in-coupling grating.
5.A design method according to any one of claims 1-3, wherein step S103 further comprises:
s1031: calculating a diffraction coupling angle of the light beam, which is diffracted and coupled into the optical waveguide main body through the coupling grating, according to the angle of incidence of the light beam to the coupling grating, the wavelength of the light beam and the grating period of the coupling 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 beam after being coupled out for many times by the coupling-out grating according to the maximum diffraction efficiency of the coupling-out grating;
s1034: and calculating the partition number of the out-coupling gratings according to the length of the out-coupling gratings, the sensitivity of human eyes to the light beams, the brightness difference rate and the distance between the two adjacent out-coupling positions.
6. The design method according to claim 5, wherein the light beam is incident in a cone beam having a certain angle of view, step S1031 further comprising:
the diffraction in-coupling angle is calculated from the center angle of incidence of the cone beam or the positive/negative value of the cone beam angle of incidence.
7. A design method according to 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 sub-regions according to pupil sizes, and calculating the coupling-out light power of each eye sub-region;
s1042: according to the coupled light power of each eye subarea, calculating the non-uniformity parameter of the coupled light power in the eye movement range of the coupled grating;
s1043: and taking the total coupling-out light power of the coupling-out grating and the non-uniformity parameter as optimization targets to obtain the optimized grating duty ratio of the subarea.
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.
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