The present invention relates to a display technology based on diffraction, in particular to a diffractive optical waveguide, its design method and formation method, and a display device with the diffractive optical waveguide.
Diffraction-based display technology has developed rapidly in recent years, and it can be applied to display devices such as near-eye display devices, head-mounted display devices, and head-up display devices. A diffractive optical waveguide is an important optical device that can be used in diffraction display technology. The diffractive optical waveguide that can be used for display is provided with a coupling-in grating and a coupling-out grating on the waveguide substrate; the coupling-in grating couples incident light carrying image information into the waveguide substrate; the coupling-out grating propagates and expands the light carrying image information, and at the same time couples the light out of the waveguide substrate to form a coupled-out light field. Eyes receive the light of the coupled-out light field so that, for example, an image carried by the incident light can be observed.
A coupling-out grating of a diffractive optical waveguide can adopt a two-dimensional grating structure, and in the two-dimensional grating structure, an optical unit structure usually adopts a circular, rectangular, or rhombic structure in cross-section. When light is coupled into such a coupling-out grating, there will be a bright line in the middle in the image. At the same time, it will lead to the reduction of splitted light energy on both sides, which is unfavorable for the expansion of light energy to both sides and affects the light uniformity of the waveguide.
In order to improve brightness and uniformity, different cross-sectional shapes of the optical unit structure have been proposed. However, on one hand, it is difficult to design a cross-sectional shape of a unit structure that can significantly improve brightness and uniformity; on the other hand, it is difficult to guarantee the processing accuracy of some cross-sectional shapes, and the shape after processing has poor conformity with respect to the designed shape, which is unfavorable for regulating the distribution of diffraction performance of the diffractive optical waveguide. Therefore, it is urgent to propose a new diffractive optical waveguide and design and formation methods for the same to overcome the above problems.
The invention aims to provide a diffractive optical waveguide, its design method and formation method, and a display device comprising the diffractive optical waveguide, so as to at least partly overcome the deficiencies in the prior art.
According to one aspect of the present invention, a diffractive optical waveguide is provided, which comprises a waveguide substrate and a grating structure formed on the waveguide substrate, wherein: the grating structure is used to couple at least a part of light that propagates into it within the waveguide substrate along a coupling-in direction, out of the waveguide substrate through diffraction, the grating structure comprises a plurality of optical unit structures arranged in an array along a plane, and the optical unit structures are columnar structures, and have cross-sections parallel to the plane;
the cross-section as a whole has a shape with two small ends and a large middle part in a first direction and has an upper vertex and a lower vertex in a first direction and a left vertex and a right vertex in a second direction perpendicular to the first direction, and the upper vertex, the lower vertex, the left vertex, and the right vertex are respectively convex extreme points of the contour of the cross-section;
a distance between the upper vertex and the lower vertex of the cross-section in the first direction is length L of the cross-section, a maximum distance between the left vertex and the right vertex in the second direction is the maximum width W of the cross-section, and 0.4≤W≤0.8L;
a first contour curve, a second contour curve, a third contour curve, and a fourth contour curve are respectively formed between the upper vertex and the left vertex, between the upper vertex and the right vertex, between the lower vertex and the left vertex, and between the lower vertex and the right vertex, the first contour curve and the second contour curve are configured such that as approaching the upper vertex, a width of the cross-section in the second direction gradually decreases, and the third contour curve and the fourth contour curve are configured such that as approaching the lower vertex, a width of the cross-section in the second direction gradually decreases;
the first contour curve and the second contour curve are smooth and continuous at the upper vertex and have an upper radius of curvature R1, and the third contour curve and the fourth contour curve are smooth and continuous at the lower vertex and have a lower radius of curvature R2, where R1≤L/19, R2≤L/19.
In some embodiments, a connecting line connecting between the upper vertex and the lower vertex is parallel to the first direction, and the cross-section is symmetrical about the connecting line.
In some embodiments, the cross-section is symmetrical about an axis which is parallel to the second direction.
In some embodiments, the left vertex comprises an upper left vertex and a lower left vertex, and a left depression is formed between the upper left vertex and the lower left vertex; the right vertex comprises an upper right vertex and a lower right vertex, and a right depression is formed between the upper right vertex and the lower right vertex; and the first contour curve is formed between the upper vertex and the upper left vertex, the second contour curve is formed between the upper vertex and the upper right vertex, the third contour curve is formed between the lower vertex and the lower left vertex, and the fourth contour curve is formed between the lower vertex and the right lower vertex.
Advantageously, a distance between the upper left vertex and the lower left vertex in the first direction is a first distance di, and a distance between the upper right vertex and the lower right vertex in the first direction is a second distance d2, d1≤0.5L, and d20.5L. Preferably, d1≤0.3L, and d2≤0.3L.
Advantageously, the left depression and the right depression have arc-shaped contours.
Advantageously, the cross-section of the optical unit structure has a curve contour which is continuously differentiable at the upper vertex, the lower vertex, the left vertex, and the right vertex.
According to another aspect of the present invention, a display device is provided, comprising the diffractive optical waveguide.
In some embodiments, the display device is a near-eye display device and comprises a lens and a frame for holding the lens close to the eye, and the lens comprises the diffractive optical waveguide.
In some embodiments, the display device is an augmented reality display device or a virtual reality display device.
According to yet another aspect of the present invention, A waveguide design method for the diffractive optical waveguide is provided, comprising:
In some embodiments, the optimization variables further comprise at least one selected from a group consisted of number of the curve equations, depth/height of the optical unit structure in a direction perpendicular to the plane, and parameters of the array in which the optical unit structures are arranged.
In some embodiments, the number of the curve equations is 2, 3, or 4.
In some embodiments, the array comprises a plurality of rows extending along the second direction and formed by the arrangement of the plurality of optical unit structures, and the optimization variable comprises at least one of the following parameters of the array: a predetermined interval D of the plurality of rows in the first direction, a period P of the optical unit structure in the row, and a misalignment amount of the optical unit structure in the second direction in the two adjacent rows of the plurality of rows.
According to another aspect of the present invention, a waveguide formation method for the diffractive optical waveguide of claim 1 is provided, comprising: designing the diffractive optical waveguide by using the waveguide design method; and based on the output optimized configuration of the diffractive optical waveguide, forming the diffractive optical waveguide by using micro-nano or semiconductor processing technology.
In the diffractive optical waveguide according to embodiments of the present invention, the cross-section of the optical unit structure has a specific curved contour, whose edges are smooth and have very good processability. This is conducive to realizing high-precision conformity and mass production. In addition, the cross-section with curve contour of the optical unit structure has a very high degree of design freedom, which can be used to realize a better control of the distribution of the coupling-out efficiency of the diffractive optical waveguide, and thus is conducive to achieving high coupling-out efficiency and high uniformity. A display device having such a diffractive optical waveguide has the advantages of high brightness and high uniformity accordingly.
The waveguide design method according to embodiments of the present invention has a very high degree of design freedom, and can have a better control of the distribution of the coupling-out efficiency of the diffractive optical waveguide, by designing the cross-section of the optical unit structure based on curve equations, which is conducive to obtaining a better design for the diffractive optical waveguide with better performance. The waveguide formation method based on this waveguide design method has corresponding advantages.
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. It should be noted that, without conflicts, the embodiments in the present application and the features of the embodiments can be combined with each other.
Diffractive optical waveguides according to embodiments of the present invention will be described below with reference to the drawings.
The grating structure 1 comprises a plurality of optical unit structures 10 arranged in an array along/in a plane. This array of grating structures 1 is shown in the dashed box in the right part of
Only as an example but not a limitation, as shown in
As shown in
As shown in
According to embodiments of the present invention, a first contour curve 10a, a second contour curve 10b, a third contour curve 10c, and a fourth contour curve 10d are formed between the upper vertex 11 and the left vertex 13, between the upper vertex 11 and the right vertex 14, between the lower vertex 12 and the left vertex 13, and between the lower vertex 12 and the right vertex 14, respectively. The first contour curve 10a and the second contour curve 10b are configured such that as approaching the upper vertex 11, the width of the cross-section in the y direction gradually decreases, and the third contour curve 10c and the fourth contour curve 10d are configured such that as approaching the lower vertex 12, the width of the cross-section in the y direction gradually decreases.
Preferably, each of the first contour curve 10a, the second contour curve 10b, the third contour curve 10c, and the fourth contour curve 10d is of a curved shape that arches toward the outside of the cross-section.
In this embodiment, the four contour curves can be expressed by four high-order curve equations, and high-order curve coefficient parameters of the contour curves can be adjusted to meet requirements for various coupling-out efficiency distributions for beam propagating in the coupling-out region.
In the example shown in
In order to illustrate the technical effect of the diffractive optical waveguide 100 having the optical unit structure with the cross-section 10A shown in
In the various data examples given below, the wavelength of light is 532 nm; the refractive index of the material of the waveguide substrate and the grating structure is 1.82; the optical unit structure is formed as a concave structure with a depth of 57 nm; in the array of the optical unit structure, the interval D=450 nm, the period P=420 nm, and misalignment amount s=P/2 as described above.
Graph (a) in
the first contour curve 10a: x=0.011y2−0.786y−265.85;
the second contour curve 10b: x=0.011y2+0.786y−265.85;
the third contour curve 10c: x=−0.011y2+0.786y+265.85;
the fourth contour curve 10d: x=−0.011y2−0.786y+265.85,
wherein, the origin of the coordinates (x, y) in the above equations is located at the center of the cross-section as shown in
Based on the grating structure shown in
In this data example and the data examples below, “field of view on both sides” refers to the field of view with a field of view angle FOVX in the range of −15°˜−6° and 6°˜15°, wherein the field of view angle FOVX is an angle formed with respect to the normal of the x-y plane in the direction of turning around the x-axis; and “middle field of view” refers to the field of view with the field of view angle FOVX in the range of −5°˜5°. The above-mentioned average efficiency is the ratio of the average value of the light intensity of the coupled-out light field at each field of view angle to the light intensity of the coupling-in light of the grating structure, and the larger the value of the average efficiency means the higher the coupling-out efficiency. A middle bright line shown in the displayed image of the waveguide will be caused with a too high middle coupling-out efficiency.
In this data example and the following data examples, “nonuniformity” is the absolute value of the difference between the average efficiency of the field of view on both sides and the average efficiency of the middle field of view divided by the sum of the two, and the smaller the value of nonuniformity, the better the uniformity.
The light intensity distributions within the field of view angle range calculated by simulation are shown in
It can be seen from Table 1 and
As a variant of the cross-section of the optical unit structure shown in
Simulation calculation shows that the preferred radii of curvature are R1≤L/8 and R2≤L/8. For details, see Data Example 2 below.
Based on the above-mentioned grating structure shown in
The light intensity distribution diagrams within the field of view angle range obtained by simulation calculations are shown in
It can be seen from Table 2 and
Next, another example of the cross-section of the optical unit structure according to embodiments of the present invention and its variant will be introduced with reference to
Graph (a) and graph (b) in
An optical unit structure with the cross-sections 10B, 10B′ and a diffractive optical waveguide comprising such an optical unit structure have the advantage of being simple in design, and it is easy for the shapes of the left vertex 13 and the right vertex 14 to meet the design requirements during processing, that is to have conformity, which is beneficial for the control of the diffraction efficiency distribution of the diffractive optical waveguide.
The effect of the example shown in
In Data Example 3, two grating structures composed of optical unit structures with cross-sections 10B, 10B′ shown in
left contour curve 10e: y=0.00148x2−107.659;
right contour curve 10f: y=−0.00148x2+107.659,
wherein, the origin of the coordinates (x, y) in the above equations is located at the center of each cross-section, and the unit of the x, y coordinate values is “nm”. The length of the cross-section thus constructed is L=540 nm, and the maximum width is W=215 nm.
The cross-section 10B′ is of a shape obtained by rounding the upper and the lower vertices of the cross-section with a radius of curvature R=15 nm based on the cross-section 10B.
Based on the above-mentioned grating structure shown in
For the convenience of comparison, Table 3 also lists the relevant data of a grating structure formed by the optical unit structure with the conventional rhombic cross-section in Data Example 1.
The light intensity distribution diagram within the field of view angle range obtained by simulation calculation is shown in
It can be seen from Table 1 and
Next, another example of the cross-section of the optical unit structure according to embodiments of the present invention and its variant will be introduced with reference to
In the example shown in
As shown in
Preferably, the left depression and the right depression have arc-shaped contours, so as to facilitate processing and conform with the design.
Graph (b) in
The effect of the example shown in
Graph (a) in
The side length of the rhombus of the cross-section of the optical unit structure in the grating structure 2′ is 295.8 nm, and the upper and the lower vertex angles are 50°.
The curve equations of the first to the fourth contour curves of the cross-section 10C of the optical unit structure in the grating structure 1C are as follows:
y=a
11
x
8
+a
12
x
7
+a
13
x
6
+a
14
x
5
+a
15
x
4
+a
16
x
3
+a
17
x
2
+a
18
x+a
19,
y=a
21
x
8
+a
22
x
7
+a
23
x
6
+a
24
x
5
+a
25
x
4
+a
26
x
3
+a
27
x
2
+a
28
x+a
29,
y=a
31
x
8
+a
32
x
7
+a
33
x
6
+a
34
x
5
+a
35
x
4
+a
36
x
3
+a
37
x
2
+a
38
x+a
39,
y=a
41
x
8
+a
42
x
7
+a
43
x
6
+a
44
x
5
+a
45
x
4
+a
46
x
3
+a
47
x
2
+a
48
x+a
49,
wherein, the coefficients are:
wherein, the origin of the coordinates (x, y) in the above equations is located at the center of the cross-section, and the unit of the x, y coordinate values is “nm”. The length of the cross-section thus constructed is L=530 nm, and the maximum width is W=234 nm.
The curve equations of the first to the fourth contour curves of the cross-section 10C of the optical unit structure in the grating structure 1C′ are as follows:
y=a
11
x
8
+a
12
x
7
+a
13
x
6
+a
14
x
5
+a
15
x
4
+a
16
x
3
+a
17
x
2
+a
18
x+a
19,
y=a
21
x
8
+a
22
x
7
+a
23
x
6
+a
24
x
5
+a
25
x
4
+a
26
x
3
+a
27
x
2
+a
28
x+a
29,
y=a
31
x
8
+a
32
x
7
+a
33
x
6
+a
34
x
5
+a
35
x
4
+a
36
x
3
+a
37
x
2
+a
38
x+a
39,
y=a
41
x
8
+a
42
x
7
+a
43
x
6
+a
44
x
5
+a
45
x
4
+a
46
x
3
+a
47
x
2
+a
48
x+a
49,
wherein, the coefficients are:
wherein, the origin of the coordinates (x, y) in the above equations is located at the center of the cross-section, and the unit of the x, y coordinate values is “nm”. The length of the cross-section thus constructed is L=560 nm, and the maximum width is W=240 nm.
Based on the grating structure shown in
The light intensity distribution diagrams within the field of view angle range obtained by simulation calculations are shown in
It can be seen from Table 4 and
Some examples of the cross-section of the optical unit structure that can be used in the diffractive optical waveguide according to embodiments of the present invention have been specifically introduced above in conjunction with the data examples. For ease of understanding, and only for purposes of illustration but not limitation,
In
The diffractive optical waveguide according to embodiments of the present invention can be applied to a display device. Such a display device can be, for example, a near-eye display device, which comprises a lens and a frame for holding the lens close to the eye, wherein the lens can comprise a diffractive optical waveguide according to embodiments of the present invention as described above. Preferably, the display device can be an augmented reality display device or a virtual reality display device.
A waveguide design method for designing the above-described diffractive optical waveguide according to embodiments of the present invention will be described below with reference to
The basic parameters obtained in the process S110 comprise a refractive index of the waveguide substrate, a refractive index of the grating structure layer, and a working wavelength of the waveguide substrate. Optionally, in some embodiments, some other parameters can be further obtained in the process S110, such as a thickness of the waveguide substrate, and a desired range of the field of view angle of the waveguide grating.
In the process S120, initializing the grating structure can comprise setting relevant parameters of the array formed by the optical unit structure. For example, the grating structure can be initialized so that the array comprises a plurality of rows extending along the y direction formed by arranging a plurality of optical unit structures, the plurality of rows are arranged at a predetermined interval D in the x direction, and the optical unit structures 10 in each row are arranged at a period P, and the optical unit structures in two adjacent rows have a predetermined misalignment amount s in the y direction.
In the process S120, different numbers of curve equations can be established for the contour curve of the cross-section of the optical unit structure as required, and the number includes but is not limited to 2, 3, or 4.
In the process S130, the optimization target comprises uniformity of light energy distribution of the outgoing light field of the diffractive optical waveguide and/or light energy coupling efficiency of the diffractive optical waveguide.
In some embodiments, the optimization variables can comprise at least one of number of curve equations, depth/height of the optical unit structures in a direction perpendicular to the plane, and parameters of the array in which the optical unit structures are arranged.
In some embodiments, the optimization variables can comprise at least one of the following parameters of the aforementioned array: the predetermined interval D of a plurality of rows in the x direction, the period P of the optical unit structure in a row, and the misalignment amount s of the optical unit structures in two adjacent rows in the y direction.
During the optimization process of process S130, as needed for coupling-out efficiency and uniformity of the waveguide, appropriate optimization methods, such as genetic algorithm, particle swarm algorithm, etc., can be used to optimize variables.
The optimized configuration output in process S140 comprises the optimized parameters obtained through the optimization process in process S130.
According to other embodiments of the present invention, based on the waveguide design method described above with reference to
As discussed above with reference to the illustration of the figures, the followings are provided in this application:
The above description is merely an illustration of the preferred embodiments of the present application and the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solution formed by the specific combination of the above technical features, but also covers other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the technical solution is formed by replacing the above features with (but not limited to) the technical features with similar functions disclosed in the present application.
Number | Date | Country | Kind |
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202210522591.3 | May 2022 | CN | national |