Patent Description:
Diffraction-based display technology has developed rapidly in recent years, and it can be applied to a display device such as a near-eye display device, a head-mounted display device, and a head-up display device. A diffraction optical waveguide is an important optical device that can be used in diffraction display technology. The diffraction optical waveguide that can be used for display is provided with a coupling-in grating and a coupling-out grating on a 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. The eye receives the light of the coupled-out light field so that, for example, an image carried by the incident light can be observed.

The coupling-out grating of the diffraction optical waveguide can adopt a two-dimensional grating structure. 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. At the same time, it will lead to the reduction of light splitting energy on both sides, which is adverse to expansion of light energy to both sides and affects a light uniformity of the waveguide.

In order to improve brightness and uniformity, <CIT> provides a two-dimensional grating for near-eye display device, which comprises repeating units periodically tiled on a waveguide sheet in the horizontal direction and the vertical direction. Each repeating unit comprises a first concave/convex part and a second concave/convex part which are arranged along a first horizontal line, and a strip-shaped part provided on the surface of the waveguide sheet in a concave/convex manner along a second horizontal line. The first concave/convex part and the second concave/convex part in two adjacent repeating units in the horizontal direction form a water drop-shaped structure.

<CIT> provides a waveguide or guiding light to eye motion box, which includes an input-coupling DOE, and expanding DOE and an out-coupling DOE. The output-coupling DOE outputting the light expanded in the waveguide by the expanding DOE to an outside of the waveguide, wherein the expanding DOE includes a plurality of expanding segments, the output-coupling DOE includes a plurality of output-coupling segments, and the plurality of expanding segments and/or the plurality of output-coupling segments have a circle shape, an arc shape, a sector shaper, a circle segment shape, or a polygon shape.

<CIT> describes an image light guide for conveying a virtual image having an in-coupling diffractive optic and an out-coupling diffractive optic formed on a waveguide plate. A compound grating pattern having a plurality of grating features in the form of a two-dimensional lattice can be used as the out-coupling diffractive optic. <CIT> mentions that relatively reducing the width of the grating features with respect to the length contributes to filling the eyebox with more even illumination.

<CIT> describes a waveguide structure comprises a plurality of grid structures, wherein a plurality of grid structures are arranged in first arrangement directions to form a multi-row grid structure, and a plurality of grid structures are arranged in second arrangement directions, and an acute angle is formed between first arrangement directions and second arrangement directions. Each of the grid structures is a flat polygon. The grid structure can achieve better two-dimensional grating performance and increase brightness and brightness uniformity of the two-dimensional diffraction waveguide.

A two-dimensional coupling-out grating with an improved parallelogram cross-section is also proposed. As shown in a unit structure design diagram of <FIG>, the left and right ends of the improved parallelogram form vertices of acute angles, two upper vertices and two lower vertices are formed in the middle, a small gap is formed between each two vertices, in addition, there are four long sides at both portions, in which two pairs of opposite sides are parallel, and there are two pairs of parallel short sides in the middle. A coupling-out grating with the improved parallelogram optical unit structure has an effect of weakening the middle bright line of the coupled-out light field, and significantly improves the uniformity among different fields of view of the coupled-out light field.

However, a size of the optical unit structure itself is of wavelength order, and multiple vertices and gaps in the above-mentioned improved parallelogram are smaller in size, and processing accuracy cannot be guaranteed, so there are great difficulties in processing and mass producibility.

The object of the present disclosure is to provide a diffraction optical waveguide for diffraction-based display and a display device comprising the diffraction optical waveguide, so as to at least partly overcome the deficiencies in the prior art.

According to one aspect of the present disclosure, a diffraction optical waveguide according to claim <NUM> is provided.

Advantageously, the predetermined distance d satisfies d≤<NUM>.

Advantageously, a length l of the predetermined section in the first direction satisfies <NUM>≤l≤<NUM>.

Advantageously, the optical unit structure is a concave hole structure formed on the waveguide substrate.

Advantageously, the first end has a first width w1 perpendicular to the first direction, where <NUM>≤w1≤W; and the second end has a second width w2 perpendicular to the first direction, where <NUM>≤w2≤<NUM>.

Advantageously, the length L and the maximum width W of the optical unit structure satisfy: <NUM>≤W≤<NUM>.

Advantageously, the optical unit structure has a first arc-shaped profile between the predetermined section and the first end, and the first arc-shaped profile is in the shape of an outwardly raised arc.

Advantageously, the optical unit structure has a second arc-shaped profile between the predetermined section and the second end, and the second arc-shaped profile is in the shape of an outwardly raised arc.

The optical unit structure can have a symmetry axis substantially parallel to the first direction.

In some embodiments, the first end has a form of a vertex, a straight side, or a concave side; and/or the second end has a form of has a form of a vertex, a straight side, or a concave side.

Advantageously, the array includes a plurality of rows perpendicular to the first direction formed by the arrangement of the plurality of optical unit structures; the plurality of rows are arranged at a predetermined interval in the first direction; the optical unit structures are arranged at a period P in the rows; and the optical unit structures in two adjacent rows of the plurality of rows are staggered by a predetermined distance s in a direction perpendicular to the first direction, where s=P/n and <NUM><n≤<NUM>, preferably n=<NUM>.

According to another aspect of the present disclosure, a display device is provided, including the diffraction optical waveguide.

In some embodiments, the display device is a near-eye display device and includes a lens and a frame for holding the lens close to the eye, the lens including the diffraction optical waveguide.

In some embodiments, the display device is an augmented reality display device or a virtual reality display device.

According to embodiments of the disclosure, the optical unit structure has a more freeform shape which is not necessary to form a vertex of a certain angle and is not limited to a straight side, without restriction of corresponding sides parallel to each other. The grating structure formed by such an optical unit structure as well as a correspondingly obtained diffraction optical waveguide may have the advantages of easy processing, a high coupled-out efficiency, and a good uniformity.

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

The present disclosure 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. For the convenience of description, only the parts related to the invention are shown in the drawings. It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other without conflict.

A diffraction optical waveguide according to an embodiment of the present invention will be described below with reference to the drawings.

<FIG> is a schematic diagram of an example of a diffraction optical waveguide according to an embodiment of the present invention. As shown in <FIG>, a diffraction optical waveguide <NUM> includes a waveguide substrate 100a and a grating structure <NUM> formed on the waveguide substrate 100a. In the example shown in <FIG>, the grating structure <NUM> is configured as a coupling-out grating <NUM> used for coupling at least a part of the light propagating thereinto along a coupling-in direction within the waveguide substrate 100a, out of the waveguide substrate 100a by diffraction. The diffraction optical waveguide <NUM> can further include a coupling-in grating <NUM>. The coupling-in direction is a direction in which light propagates from the coupling-in grating <NUM> to the coupling-out grating <NUM>, and the coupling-in direction is an x direction in the example shown in <FIG>.

Preferably, a first end <NUM> of an optical unit structure <NUM> is located upstream along the coupling-in direction (the x direction shown in <FIG>), and a second end <NUM> is located downstream along the coupling-in direction. Advantages of this orientation of the optical unit structure will be illustrated below with Data Examples.

Referring to <FIG>, the grating structure <NUM> includes a plurality of optical unit structures <NUM> arranged in an array along a plane x-y of the waveguide substrate 100a. The optical unit structure <NUM> can be a concave hole structure or a convex structure formed on the waveguide substrate 100a. Preferably, the optical unit structure <NUM> is a concave hole structure formed on the waveguide substrate.

<FIG> is an enlarged schematic diagram of the optical unit structure shown in <FIG>. As shown in <FIG>, the optical unit structure <NUM> has a first end <NUM> and a second end <NUM> in the x direction, and a distance between the first end <NUM> and the second end <NUM> along the x direction is a length L of the optical unit structure <NUM>; the optical unit structure <NUM> has a predetermined section <NUM> along the x direction (see <FIG>), and in the predetermined section <NUM> the optical unit structure <NUM> has a maximum width W perpendicular to the x direction (that is, along a y direction shown in the figure), where <NUM>≤W≤<NUM>; and a width of the optical unit structure <NUM> in the y direction gradually decreases from the predetermined section <NUM> to the first end <NUM> as well as from the predetermined section <NUM> to the second end <NUM>. According to the embodiment of the present invention, a central position 13a of the predetermined section <NUM> is at a predetermined distance d from the first end <NUM> in the x direction, and d<<NUM>, so that a centroid of a cross-section of the optical unit structure parallel to the plane is closer to the first end relative to the second end.

According to the embodiment of the present disclosure, the optical unit structure <NUM> has a more freeform shape, which is not necessary to form a vertex of a certain angle and is not limited to a straight side, without restriction of corresponding sides parallel to each other. The grating structure <NUM> formed by such an optical unit structure <NUM> is easy to process and has excellent diffraction characteristics, which will be described in more detail in the following Data Examples.

Continue to refer to <FIG>, in the optical unit structure <NUM>, the predetermined distance d satisfies d≤<NUM>.

Preferably, a length l of the predetermined section <NUM> in the x direction satisfies <NUM>≤l≤<NUM>.

As shown in <FIG>, the first end <NUM> has a first width w1 along the y direction, and the second end <NUM> has a second width w2 along the y direction. Preferably, the first width w1 and the second width w2 satisfy: <NUM>≤w1≤W; <NUM>≤w2≤<NUM>.

In addition, it is also preferable that the optical unit structure <NUM> has arc-shaped structures at both ends. Specifically, the optical unit structure <NUM> preferably has an outwardly raised arc profile between the predetermined section <NUM> and the first end <NUM>, as well as between the predetermined section <NUM> and the second end <NUM>. The two ends of the optical unit structure <NUM> have a structure with an arc-shaped profile, on the one hand, it is easy to process, and the shape obtained by processing is highly reproducible compared to a designed shape, on the other hand, according to optimization calculation, the grating formed by such an optical unit structure <NUM> has excellent diffraction characteristics and can achieve good brightness and uniformity of the coupled-out light field.

In the example shown in <FIG>, the optical unit structure <NUM> has an axisymmetric structure, and its axis of symmetry is parallel to the x direction. However, according to the embodiments of the present disclosure, the optical unit structure is not limited to a symmetrical structure, and may also be asymmetrical in the x direction, for example.

<FIG> shows a partially enlarged schematic diagram of the array/grating structure <NUM> formed by the arrangement of optical unit structures <NUM>. As shown in <FIG>, the array includes a plurality of rows perpendicular to the x direction (that is, along the y direction) formed by the arrangement of the plurality of optical unit structures <NUM>, the plurality of rows are arranged at a predetermined interval D in the x direction, the optical unit structures <NUM> are arranged at a period P in each row, and the optical unit structures <NUM> in two adjacent rows of the plurality of rows are staggered by a predetermined distance s in a direction perpendicular to the first direction, where s=P/n and <NUM><n≤<NUM>. Here, n can be an integer or a non-integer. When n is <NUM>, the grating structure <NUM> formed by the array is symmetrical in the y direction and can provide symmetrical and uniform diffraction characteristics and effects on both sides of the y direction.

<FIG> schematically shows different variants of a cross-section of an optical unit structure that can be used for a diffraction optical waveguide according to an embodiment of the present disclosure.

In the example shown in graph (a) of <FIG>, a second end 12A of an optical unit structure 10A has a straight side, which is different from the second end <NUM> with an arc vertex shown in <FIG>. In the example shown in graph (b) of <FIG>, a second end 12B of an optical unit structure 10B has a concave side. The first ends <NUM> of the optical unit structures shown in <FIG> all have a straight side. Although not shown, according to an embodiment of the present disclosure, the first end <NUM> of the optical unit structure can also have a vertex or a concave side.

In addition, in other examples of the embodiment of the present disclosure, the sidewall <NUM> of the optical unit structure can include a serrated side formed by a plurality of straight sides. Such a structure takes into account a precision that can be achieved in actual processing.

<FIG> is a schematic diagram of another example of a diffraction optical waveguide according to an embodiment of the present disclosure. As shown in <FIG>, a diffraction optical waveguide <NUM> includes a waveguide substrate 200a and a coupling-out grating <NUM> formed on a surface of the waveguide substrate 200a. The coupling-out grating <NUM> is configured to couple at least a part of the light propagating thereinto along a coupling-in direction within the waveguide substrate 200a, out of the waveguide substrate 200a by diffraction. The coupling-out grating <NUM> includes a grating structure <NUM> and additional grating structures <NUM> and <NUM>. The grating structure <NUM> is the same as the grating structure <NUM> described above with reference to <FIG>. The additional grating structures <NUM> and <NUM> are one-dimensional gratings, which are arranged respectively on both sides of the grating structure <NUM> in the x-direction and adjoin it. Since a diffraction efficiency of a one-dimensional grating is generally higher than that of a two-dimensional grating, the additional grating structures <NUM> and <NUM> are beneficial for improving a coupled-out efficiency of an entire coupling-out grating <NUM> and at the same time help to increase brightness of two sides of the coupled-out light field, thereby improving the uniformity.

As shown in <FIG>, the diffraction optical waveguide <NUM> may further include a coupling-in grating <NUM>. Preferably, the first end <NUM> of the optical unit structure <NUM> in the grating structure <NUM> is located upstream along the coupling-in direction (that is, the direction in which light propagates from the coupling-in grating <NUM> to the coupling-out grating <NUM>, that is, the x direction shown in <FIG>), and the second end <NUM> is located downstream along the coupling-in direction.

The diffraction optical waveguide according to the embodiment of the present disclosure can be applied in a display device. Such a display device is, for example, a near-eye display device, which includes a lens and a frame for holding the lens close to the eye, wherein the lens can include the diffraction optical waveguide according to the embodiment of the present invention as described above. Preferably, the display device may be an augmented reality display device or a virtual reality display device.

Finally, in order to illustrate the technical advantages of the diffraction optical waveguide according to the embodiment of the present disclosure in terms of a light coupled efficiency and a uniformity, and to illustrate an optimal value of structure parameters of the optical unit structure. Data Examples of simulation calculation will be given below. A wavelength of light used in the following Data Examples is <NUM>.

<FIG> shows grating structures with different optical unit structures and the same other parameters. In the grating structures shown in <FIG>, the optical unit structures in the grating structures 1A, 1B, and 1C are the optical unit structures described above in conjunction with <FIG> and have the same cross-section. For specific parameters of the cross-section of the optical unit structures in the grating structures 1A, 1B, and 1C, refer to Table <NUM> (unit: nm).

In the grating structure 1A, the optical unit structure is a concave hole structure formed on the waveguide substrate, and the first end is located upstream of the second end along the coupling-in direction. The grating structure 1B is different from the grating structure 1A in that the first end of the optical unit structure in the grating structure 1B is located downstream of the second end along the coupling-in direction. The grating structure 1C is different from the grating structure 1A in that the optical unit structure in the grating structure 1C is a convex structure formed on the waveguide substrate.

An optical unit structure in the grating structure <NUM> shown in <FIG> is a convex structure and has the improved parallelogram cross-section introduced above, the improved parallelogram has vertices of <NUM>°, in upper and lower directions shown in the figure, and four vertex angles in the middle are all <NUM>°, a length of four long sides is <NUM>, and a length of four short sides is <NUM>.

An optical unit structure in the grating structure <NUM> shown in <FIG> is a convex structure and has a rhombus cross-section, vertex angles of the rhombus in the upper and lower directions are <NUM>°, and a length of a side is <NUM>.

An optical unit structure in the grating structure <NUM> shown in <FIG> is a convex structure and has a circular cross-section, and the radius of a circle is <NUM>.

Based on the above-mentioned grating structures shown in <FIG> and based on the same conditions of light coupling into the grating structures, the coupled-out efficiencies EFF(s) and uniformity indices UNI(s) of the grating structures at the centers of their eye boxes obtained by simulation are shown in Table <NUM>.

Here, a uniformity index UNI is a ratio of a maximum light intensity to a minimum light intensity in the coupled-out light field, and the smaller the ratio, the better the uniformity; and a coupled-out efficiency EFF is a ratio of an average of light intensity at each field of view angle of the coupled-out light field to a light intensity of the coupled-in light of the grating structure. The larger the value of EFF, the higher the coupling-out efficiency.

Light intensity distribution diagrams within the range of the field of view obtained by simulation calculation are shown in <FIG>, in which distribution diagrams (a), (b), (c), (d), (e), and (f) correspond to the grating structures 1A, 1B, 1C, <NUM>, <NUM> and <NUM>, respectively. The maximum light intensity in each light intensity distribution diagram shown in <FIG> is displayed as the same brightness/grayscale in the drawing, but actual light intensities are different; similarly, the minimum light intensity in each light intensity distribution diagram is displayed as the same brightness/grayscale in the drawing, but actual light intensities are also different. The light intensity distribution situations shown in <FIG> should be seen in combination with the uniformity indices UNI(s) in Table <NUM>.

First, it can be seen from Table <NUM> that the uniformities of the coupled-out light field of the grating structure <NUM> with rhombic optical unit structures and the grating structure <NUM> with circular optical unit structures within the range of field of view angle are very poor; the grating structure <NUM> with the improved parallelogram optical unit structure has an excellent uniformity; the grating structures 1A, 1B, and 1C having the optical unit structures proposed in this application have significantly improved uniformities as a whole relative to the grating structures <NUM> and <NUM>, and the grating structure 1A has an excellent uniformity comparable to that of the grating structure <NUM> and is superior in uniformity with respect to the grating structures 1B and 1C. It can be further seen from <FIG> that, the grating structure 1A is better in uniformity than the grating structures 1B and 1C, and has a similar uniformity as the grating structure <NUM>.

From the coupled-out efficiencies EFF(s) in Table <NUM>, it can be seen that the grating structures 1A, 1B, and 1C with the optical unit structures proposed in this application have higher coupled-out efficiencies than the grating structure <NUM> with the improved parallelogram optical unit structure, wherein the coupled-out efficiency EFF of the grating structure 1A is about <NUM>% higher than the coupled-out efficiency EFF of the grating structure <NUM>.

The above Data Examples have shown that the grating structure/diffraction optical waveguide with the optical unit structure proposed in this application can advantageously obtain better coupled-out efficiency and uniformity, in terms of an effect that can be achieved only in theory. At the same time, further considering the ease of processing of the optical unit structure proposed in this application, it can be predicted that it is possible to realize further optimization of the efficiency and uniformity by the diffraction optical waveguide according to the embodiment of the present disclosure.

In Data Example <NUM>, the coupled-out efficiencies and uniformity indices of the grating structures in which optical unit structures have cross sections with different length-width ratios are simulated and compared.

<FIG> shows optical unit structures with different length-width ratios and three grating structures formed therefrom. As shown in <FIG>, for the three grating structures, the maximum widths W(s) of the optical unit structures are <NUM>, <NUM>, and <NUM> respectively, and other structure parameters are shown in Table <NUM> (unit: nm):.

Based on the structures shown in <FIG> and the same conditions of light coupled into the grating structures, the coupled-out efficiencies EFF(s) and uniformity indices UNI(s) of the grating structures at the centers of their eye boxes obtained by simulation are shown in Table <NUM>:.

It can be seen that, when the maximum width W=<NUM>, the coupled-out efficiency EFF decreases significantly, and the efficiency deteriorates seriously. When the maximum width W reaches W=<NUM>, the uniformity index UNI is up to <NUM>, and the uniformity deteriorates seriously. Therefore, the length-width ratio W/L of the optical unit structure in the waveguide grating according to the embodiment of the disclosure has a significant impact on performance of the grating structure, and its range should be limited.

In data example <NUM>, the coupled-out efficiencies and uniformity indices of grating structures formed by optical unit structures with different distances d between the predetermined sections and the first ends are simulated and compared.

<FIG> shows the optical unit structures with different distances d between the predetermined sections and the first ends, and four grating structures formed therefrom. As shown in <FIG>, the distances d(s) of these four grating structures are <NUM>, <NUM>, <NUM>, and <NUM> respectively, and other structure parameters are shown in Table <NUM> (unit: nm):.

Based on the structures shown in <FIG> and the same conditions of light coupling into the grating structures, the coupling-out efficiencies EFF(s) and uniformity indices UNI(s) of the grating structures at the centers of their eye boxes obtained by simulation are shown in Table <NUM>:.

It can be seen that, when the distance d is in a range of <NUM>~<NUM>, the coupled-out efficiency EFF and uniformity index UNI of the grating structure reach a better level; and when d=<NUM>, the coupled-out efficiency EFF remains at a better level, while the uniformity is significantly reduced.

In Data Example <NUM>, the coupled-out efficiencies and uniformity indices of grating structures formed by optical unit structures with predetermined sections having different lengths are simulated and compared.

<FIG> shows the optical unit structures with the predetermined sections having different lengths, and four grating structures formed therefrom. As shown in <FIG>, for the four grating structures, lengths l(s) of the predetermined sections of the optical unit structures are <NUM>, <NUM>, <NUM>, and <NUM> respectively, and other structure parameters are shown in Table <NUM> (unit: nm):.

Based on the structures shown in <FIG> and the same conditions of light coupled into the grating structures, the coupled-out efficiencies EFF(s) and uniformity index UNI(s) of the grating structures at the centers of their eye boxes obtained by simulation are shown in Table <NUM>:.

It can be seen that, when the length l of the predetermined section is less than <NUM>, the coupled-out efficiency EFF and uniformity index UNI of the grating structure reach a better level; and when l = <NUM>, the uniformity decreases slightly, and the index UNI rises to <NUM>.

In Data Example <NUM>, the coupled-out efficiencies and uniformity indices of grating structures formed by optical unit structures with different widths at the second ends are simulated and compared.

<FIG> shows optical unit structures with different widths at the second ends, and three grating structures formed therefrom. As shown in <FIG>, for the three grating structures, the widths w2(s) of the second ends of the optical unit structures are <NUM>. 16W, <NUM>. 5W, and <NUM>. 7W respectively, and other structure parameters are shown in Table <NUM> (unit: nm):.

Claim 1:
A diffraction optical waveguide (<NUM>, <NUM>), comprising a waveguide substrate (100a, 200a) and a grating structure (<NUM>) formed on the waveguide substrate (100a, 200a), wherein,
the grating structure (<NUM>) comprises a plurality of optical unit structures (<NUM>) arranged in an array along a plane (x-y), wherein each optical unit structure (<NUM>) is a concave hole structure or a convex structure formed on the waveguide substrate (100a, 200a) and has a first end (<NUM>) and a second end (<NUM>) in a first direction (x) parallel to the plane (x-y), and a distance between the first end (<NUM>) and the second end (<NUM>) along the first direction is a length L of each optical unit structure (<NUM>);
and
the grating structure (<NUM>) is configured as a coupling-out grating (<NUM>), the coupling-out grating (<NUM>) couples at least a part of the light propagating thereinto along a coupling-in direction within the waveguide substrate (100a, 200a), out of the waveguide substrate by diffraction, and the coupling-in direction is substantially parallel to the first direction (x);
characterized in that:
each optical unit structure (<NUM>) has a maximum width W perpendicular to the first direction (x) in a predetermined section (<NUM>) along the first direction, where <NUM>≤W≤<NUM>;
in the first direction (x), a central position (13a) of the predetermined section (<NUM>) is at a predetermined distance d from the first end (<NUM>), where d<<NUM>, and a width of the optical unit structure (<NUM>) in a direction perpendicular to the first direction (x) gradually decreases from the predetermined section (<NUM>) to the first end (<NUM>) as well as from the predetermined section (<NUM>) to the second end (<NUM>), so that a centroid of a cross-section of each optical unit structure (<NUM>) parallel to the plane (x-y) is closer to the first end (<NUM>) relative to the second end (<NUM>); and
the first end (<NUM>) of each optical unit structure (<NUM>) is located upstream along the coupling-in direction, and the second end (<NUM>) is located downstream along the coupling-in direction.