Diffractive optical waveguide and display device having the same

Abstract

A diffractive optical waveguide and a display device having the same are disclosed. The diffractive optical waveguide includes a grating structure formed on a surface of a waveguide substrate, the grating structure including a plurality of grating lines arranged in a plane, the grating lines each extending along a first direction in the plane and arranged at a predetermined interval in a second direction perpendicular to the first direction; at least one sidewall of each grating line having a periodic structure along the first direction; and the grating structure configured to diffract light incident thereon at a non-zero angle with respect to the plane out of the plane through a predetermined diffraction order. The grating structure employed in the above-described diffractive optical waveguide can be used to adjust the diffraction efficiency at different angles and / or different diffraction orders, thereby providing a new effective and flexible means for improving the angular uniformity and / or the out-coupling efficiency of the diffractive optical waveguide.

Description

[0001] This application is a divisional application of the invention patent application with application number 202210254157.1, application date March 15, 2022, applicant Jiaxing Yuguang Optoelectronics Technology Co., Ltd., and invention title "Diffractive Waveguide and Display Device Having the Thereof". Technical Field

[0002] This invention relates to diffraction-based display technology, particularly diffractive waveguides and display devices having diffractive waveguides. Background Technology

[0003] Diffraction-based display technology has developed rapidly in recent years and can be applied to display devices such as near-eye displays, head-mounted displays, and head-up displays. Diffractive waveguides are an important optical device that can be used in diffraction display technology. Figure 1 A diffractive optical waveguide that can be used for display is schematically shown; Figure 2 It shows along Figure 1 The diagram shows a cross-sectional view of the diffractive waveguide taken at the cut position, and further illustrates the propagation of light within the diffractive waveguide. Figure 1 and Figure 2 As shown, a coupling grating b and a coupling grating c are disposed on the waveguide substrate a of the diffractive waveguide. The coupling grating b couples the incident light IN carrying image information into the waveguide substrate a. The coupling grating b propagates and expands the light carrying image information while coupling the light out of the waveguide substrate, forming a coupled light field OUT. The eye E receives the light from the coupled light field OUT, thereby, for example, being able to observe the image carried by the incident light IN.

[0004] Diffractive waveguides have advantages such as high mass production capability and thinness, but they are not without their drawbacks. For example, their brightness and uniformity in displayed images still need improvement.

[0005] In existing diffractive waveguide devices, the coupling grating is generally a straight-tooth grating (also known as a "rectangular grating"), with the +1st or -1st order diffraction order selected as the coupling order. However, the straight-tooth grating is a symmetrical structure, and after light passes through it, the energy of the ±1st order diffraction is evenly distributed, but only one order is actually used, resulting in low coupling efficiency. Using a blazed grating or a helical-tooth grating can concentrate the diffraction energy to the +1st or -1st order, improving coupling efficiency. However, the template processing for blazed and helical-tooth gratings is difficult, and transfer and demolding are also significant challenges, often making it difficult for actual products to meet the design performance requirements.

[0006] Furthermore, the uniformity of the coupled light field of a diffracting waveguide includes uniformity across different regions of the entire coupled light field, as well as uniformity (also known as "angular uniformity") across different field angles (corresponding to the incident angle of the incident light IN on the coupled grating) within the field of view. Researchers have been exploring ways to improve the uniformity of diffracting waveguides and have proposed improvements to the optical unit structure of two-dimensional coupled gratings, for example, see CN111194422A and CN212460098U. However, controlling the fine and accurate shape (especially the angular shape) and dimensions of the optical unit structure of the two-dimensional grating during manufacturing remains difficult; moreover, significant design limitations exist. Summary of the Invention

[0007] The purpose of this invention is to provide a diffractive waveguide for diffractive displays and a display device including the diffractive waveguide, so as to at least partially overcome the shortcomings of the prior art.

[0008] According to one aspect of the present invention, a diffractive waveguide is provided, comprising a waveguide substrate and a grating structure formed on the surface of the waveguide substrate, wherein the grating structure comprises a plurality of grating lines arranged in a plane, each of the plurality of grating lines extending along a first direction in the plane and arranged at predetermined intervals in a second direction perpendicular to the first direction; each grating line has a first sidewall and a second sidewall opposite to each other in the second direction, at least one of the first sidewall and the second sidewall having a periodic structure along the first direction; and the grating structure is configured to diffract light incident thereon at a non-zero angle relative to the plane outward through a predetermined diffraction order.

[0009] In some embodiments, the grating structure is configured to couple a light beam that is incident on the waveguide substrate at an incident angle within a predetermined range into the waveguide substrate through diffraction of the predetermined diffraction order, so that the light beam propagates within the waveguide substrate by total internal reflection.

[0010] Advantageously, only the first sidewall has a periodic structure along the first direction, and the periodic structures on the first sidewalls of different gate lines are aligned with each other in the second direction.

[0011] Advantageously, the diffractive waveguide further includes an output grating formed on the waveguide substrate, the output grating being configured such that at least a portion of the light propagating therefrom from the waveguide substrate by total internal reflection from the input grating is coupled out by diffraction; and the first sidewall faces the output grating.

[0012] In some embodiments, the grating structure is configured to couple at least a portion of the light that propagates into the waveguide substrate via total internal reflection out of the waveguide substrate via diffraction.

[0013] Advantageously, only the first sidewall has a periodic structure along the first direction, and the periodic structures on the sidewalls of adjacent grid lines are offset by a predetermined distance s along the first direction, s = P / n, where P is the period of the periodic structure in the first direction, and n is 2 or 3, preferably n is 2.

[0014] Advantageously, the diffractive waveguide further includes an additional grating structure, which is a one-dimensional grating and is arranged and adjacent to at least one side of the grating structure in the first direction for coupling at least a portion of the light propagating therein out of the waveguide substrate by diffraction.

[0015] Advantageously, the diffractive waveguide further includes a coupling grating formed on the waveguide substrate, the coupling grating being configured to couple a light beam incident on the waveguide substrate into the waveguide substrate so that it propagates within the waveguide substrate by total internal reflection, and the first sidewall faces the coupling grating.

[0016] Advantageously, the periodic structure forms a plurality of prominent tooth-like structures, each tooth having a tooth tip and a tooth root, and the width of the tooth-like structure in the first direction gradually decreases from the tooth root to the tooth tip.

[0017] Advantageously, the tooth-like structure has an axisymmetric structure about an axis parallel to the second direction.

[0018] Advantageously, the tooth-like structure has a polygonal shape, an arc shape, or a shape formed by a combination of arcs and straight lines; preferably, the tooth-like structure has a triangular, trapezoidal, or arc shape.

[0019] Advantageously, the grid lines are divided into a first region and a second region along the second direction, and the plurality of tooth-like structures are located in the second region; the grid lines have different heights perpendicular to the plane or different refractive indices in the first region and the second region.

[0020] Advantageously, the periodic structure has a period of 100 to 500 nm in the first direction.

[0021] According to another aspect of the invention, a display device is provided, which includes a diffractive waveguide as described above.

[0022] Advantageously, 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 diffractive waveguide.

[0023] Advantageously, the display device is an augmented reality display device or a virtual reality display device.

[0024] According to an embodiment of the present invention, a novel grating structure is used in the diffraction waveguide. This grating structure can be used to adjust the diffraction efficiency at different angles and / or different diffraction orders, thereby providing a new, effective and flexible means to improve the angular uniformity and / or coupling efficiency of the diffraction waveguide. Attached Figure Description

[0025] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0026] Figure 1 This is a schematic diagram of a diffractive optical waveguide that can be used for display purposes;

[0027] Figure 2 for Figure 1 A schematic cross-sectional view of the diffractive waveguide shown;

[0028] Figure 3 This is a schematic diagram of a diffractive optical waveguide according to Embodiment 1 of the present invention;

[0029] Figure 4 , Figure 5 and Figure 6 Different examples of gratings according to embodiments of the present invention are shown respectively;

[0030] Figure 7 This is a schematic diagram of a cross-section of the grating line 11 of the grating structure 10 along the second direction y.

[0031] Figure 8 The graph shows the +1st order diffraction efficiency of a straight-tooth grating without periodic structure on the grating line sidewalls and a grating with periodic structure of different shapes on the grating line sidewalls in Data Example 1 as a function of the incident angle, where the grating lines have a uniform height.

[0032] Figure 9 The graph shows the +1st order diffraction efficiency of a grating with a circular arc-shaped toothed periodic structure with different heights on the sidewalls of the grating lines in Example 2 as a function of the incident angle.

[0033] Figure 10 The graph shows the +1st order diffraction efficiency of a straight-tooth grating without a periodic structure on the grating sidewalls and a grating with a periodic structure of different shapes on the grating sidewalls in Example 3, as a function of the incident angle. The periodic structure has a different height than other parts of the grating.

[0034] Figure 11 The graph shows the coupling energy of the coupling grating in Example 4 as a function of the incident angle.

[0035] Figure 12The graph shows the coupling energy of the diffractive waveguide in Data Example 4 as a function of the incident angle. This waveguide uses the gratings from Data Example 3 as coupling gratings and is configured with features such as... Figure 11 The coupling grating is shown as a curve of the coupling energy as a function of the incident angle.

[0036] Figure 13 The graph shows the +1st order diffraction efficiency of a grating with a periodic arc-shaped tooth structure with different periods on the sidewalls of the grating lines in Example 5 as a function of the incident angle.

[0037] Figure 14 This is a schematic diagram of a diffractive optical waveguide according to Embodiment 2 of the present invention;

[0038] Figure 15 The image shows the energy distribution of the coupled optical field in the 0° field of view of the diffractive waveguide obtained from the simulation in Example 6.

[0039] Figure 16 This is a schematic diagram of a diffractive optical waveguide according to Embodiment 3 of the present invention;

[0040] Figure 17 , Figure 18 and Figure 19 Different examples of gratings according to other embodiments of the present invention are shown, wherein the two sidewalls of the grating lines are formed with periodic structures. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. For ease of description, only the parts relevant to the invention are shown in the drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0042] According to an embodiment of the present invention, a novel grating structure is used in the diffractive waveguide. The grating structure is formed on the surface of the waveguide substrate and includes multiple grating lines arranged in a plane. These grating lines extend along a first direction in the plane and are arranged at predetermined intervals in a second direction perpendicular to the first direction. Each grating line has a first sidewall and a second sidewall that are opposite to each other in the second direction, wherein at least one sidewall has a periodic structure along the first direction.

[0043] The inventors of this invention have discovered that when the grating structure is used to diffract light incident on the plane of the grating structure at a non-zero angle through a predetermined diffraction order outward, these periodic structures formed on the sidewalls can be used to adjust the diffraction efficiency at different incident angles and / or different diffraction orders, thereby providing a new, effective, and flexible means to improve the uniformity (especially angular uniformity) and / or optical coupling efficiency of the diffracted waveguide.

[0044] The following describes a diffractive waveguide according to Embodiment 1 of the present invention, wherein the novel grating structure described above is used as a coupling grating.

[0045] Figure 3 An example of a diffractive optical waveguide according to Embodiment 1 of the present invention is shown. Figure 3 As shown, the diffractive waveguide 100 according to Embodiment 1 of the present invention includes a waveguide substrate 100a and a coupling grating 110 formed on the surface of the waveguide substrate 100a. The coupling grating 110 includes a grating structure 10 configured to couple a light beam irradiated thereon into the waveguide substrate 100a through diffraction of a predetermined diffraction order, so that the light beam propagates within the waveguide substrate 100a through total internal reflection.

[0046] Figure 3 The right-hand side of the diagram is an enlarged view of the grating structure 10. As shown, the grating structure 10 includes multiple grating lines 11 arranged in a plane xy. Each grating line 11 extends along a first direction x in the plane xy and is arranged at a predetermined interval d1 in a second direction y perpendicular to the first direction x. Each grating line 11 has a first sidewall 11a and a second sidewall 11b that are opposite to each other in the second direction y. According to this embodiment, in the grating structure 10, the first sidewall 11a has a periodic structure 12 with a period of d2 along the first direction x, and the periodic structures 12 on the first sidewalls 11a of different grating lines 11 are aligned with each other in the second direction y. Such a grating structure 10 can function as a one-dimensional grating.

[0047] like Figure 3 As shown, the diffractive waveguide 100 may further include a coupling grating 120 formed on the waveguide substrate 100a, the coupling grating 120 being configured to couple at least a portion of the light propagating therefrom from the coupling grating 110 via total internal reflection out of the waveguide substrate 100a via diffraction. Preferably, a first sidewall 11a having a periodic structure 12 faces the coupling grating 120.

[0048] In some implementations, the periodic structure 12 can form a plurality of protruding tooth-like structures, each tooth having a tooth tip 12a and a tooth root 12b, and the width of the tooth-like structure in the first direction x gradually decreases from the tooth root 12b to the tooth tip 12a. Advantageously, the periodic structure 12 / tooth-like structure has an axisymmetric structure about an axis (not shown) parallel to the second direction y, thereby facilitating the provision of correspondingly symmetrical diffraction properties for the coupling grating 110.

[0049] exist Figure 3 In the example shown, the periodic structure 12 forms a symmetrical triangular tooth-like structure. However, Figure 3 The examples shown are for illustrative purposes only and are not intended to be restrictive. Figures 4 to 6 Examples of grating structures in which the toothed structure has asymmetrical triangular, arc-shaped, and trapezoidal shapes are shown. It should be understood that, depending on the specific application, the toothed structure can have a polygonal shape, an arc shape, or a shape formed by a combination of arcs and straight lines. As will be described below with reference to data examples, the diffraction efficiency of the grating structure 10 can be adjusted by changing the shape of the periodic structure 12.

[0050] In some other implementations, although not shown, the periodic structure 12 may be an undulating structure without forming a distinct tooth-like structure.

[0051] Figure 7 This is a schematic cross-sectional view of the grating line 11 of the grating structure 10 taken along the second direction y, where figures (a), (b), (c), (d), and (e) show different examples. Figure 7 As shown, the gate line 11 can be divided into a first region H1 and a second region H2 along the second direction y. Here, the first region H1 mainly corresponds to the part of the gate line 11 that extends continuously along the first direction x, and can be called the gate line body; the second region H2 is the region where the tooth structure (periodic structure 12) is located, which may include most or all of the tooth structure, and may also include a part of the gate line body.

[0052] Preferably, the first region H1 has a rectangular cross-section. In this case, the first region H1 (the main body of the grating lines) of the multiple grating lines 11 in the grating structure 10 can be equivalent to a one-dimensional straight-tooth grating (also known as a "rectangular grating"); the periodic structure 12 is equivalent to an additional structure added on the basis of this straight-tooth grating. This additional structure can be used to make the originally symmetrical straight-tooth grating no longer symmetrical on both sides of the first sidewall 11a and the second sidewall 11b, and to make the grating structure 10 as a whole asymmetrical on both sides in the second direction y. For example, in the diffractive waveguide 100 according to Embodiment 1 of the present invention, the periodic structure is formed only on the first sidewall 11a of the grating lines 11. Using a straight-tooth grating as the main body of the grating structure 10 can effectively reduce the manufacturing difficulty of the grating, which is beneficial to improving the yield and realizing mass production.

[0053] According to embodiments of the present invention, the height of the periodic structure 12 can be adjusted to regulate the diffraction efficiency of the grating structure 10. Figure 7 In the example shown in figure (a), the first region H1 and the second region H2 have the same height. Such a structure is very advantageous for the fabrication of gratings because the top of the grating structure 10 is flat, making the corresponding template processing and transfer demolding easier. Figure 7 Figures (b) to (e) illustrate different cases where the height h1 of the first region H1 differs from the height h2 of the second region H2. In figures (b) and (c), the height of the second region H2 is uniform, without any tilt. In figures (d) and (e), the second region H2 can have a gradually varying height. As will be explained below, by setting the first region H1 and the second region H2 to have different heights h1 and h2, the diffraction energy can be effectively concentrated towards the +1st or -1st order diffraction order, greatly improving the coupling efficiency. Furthermore, compared to blazed gratings and oblique tooth gratings, the grating structure described above is relatively easier to process and transfer due to the absence of a tilt at the top or the ability to be designed with only a small, localized tilt, which facilitates manufacturing.

[0054] As an alternative or supplement, the grating lines 11 can have different refractive indices in the first region H1 and the second region H2. Similar to the height difference, the refractive index difference also affects the phase difference of light in the first region H1 and the second region H2, which can be used to adjust the diffraction efficiency of the grating structure 10.

[0055] Below, using simulation data examples, we will illustrate, in a demonstrative rather than restrictive manner, the effect of the periodic structure on the sidewalls of the grating lines on the diffraction efficiency at different incident angles and / or different diffraction orders. The wavelength of light used in the following data examples is 532 nm.

[0056] (Data Example 1)

[0057] In Example 1, the +1st order diffraction efficiency of a straight-tooth grating without periodic sidewalls and a grating with a periodic structure 12 of different shapes (grating structure 10) were compared. The gratings being compared all have the same grating height, the grating material has a refractive index of 1.8, the grating period (i.e., the spacing of grating lines 11 in the second direction) d1 = 450 nm, and the period of the periodic structure 12 d2 = 450 nm. Other parameters are shown in Table 1.

[0058] [Table 1]

[0059] h1 w1 h2 w2 w3 w4 Straight-tooth grating 300nm 315nm —— —— —— —— Symmetrical triangle 300nm 225nm 300nm 90nm 450nm —— Asymmetrical triangle 300nm 225nm 300nm 90nm 225nm —— arc 300nm 225nm 300nm 140nm 90nm —— trapezoid 300nm 225nm 300nm 90nm 450nm 167nm

[0060] Where w1 is the width of the main body of the grid line 11 in the second direction y, w2 is the width of the periodic structure 12 in the second direction y, w3 is the width of the tooth root 12b of the tooth-like structure formed by the periodic structure 12 in the first direction x, and w4 is the width of the tooth tip 12a of the tooth-like structure formed by the periodic structure 12 in the first direction x (if the width is greater than 0). See details. Figures 3 to 6 The symbols in the text. The above parameters have the same meaning in the following data examples.

[0061] Figure 8 The graph shows the +1st order diffraction efficiency of each grating in Data Example 1 as a function of the incident angle. Figure 8 And the following will be discussed Figures 9 to 13 In the curve diagram, the incident angle is the angle between the incident light and the normal to the plane xy of the grating (grating structure 10), and the corresponding data examples and curve diagrams only examine and show the case when the incident angle changes about the axis along the first direction x.

[0062] from Figure 8 As can be seen, compared to a straight-tooth grating, the periodic structure 12 on the sidewall of the grating line of the grating structure 10 can change the distribution of the +1st order diffraction efficiency with the incident angle, and the shape of the periodic structure 12 has a direct and significant influence on the distribution of diffraction efficiency with the incident angle.

[0063] (Data Example 2)

[0064] In Example 2, the +1st order diffraction efficiency of gratings (grating structure 10) with toothed periodic structures 12 having the same arc shape on the sidewalls of the grating lines but different heights was compared. The refractive index of the grating material is 1.8, the grating period (i.e., the arrangement interval of the grating lines 11 in the second direction) d1 = 450 nm, the period of the periodic structure 12 d2 = 450 nm, and other parameters are shown in Table 2.

[0065] [Table 2]

[0066] h1 w1 h2 w2 w3 Arc-shaped 0 300nm 225nm 300nm 140nm 90nm Arc 1 300nm 225nm 450nm 140nm 90nm Arc 2 300nm 225nm 375nm 140nm 90nm

[0067] Figure 9 The graph shows the +1st order diffraction efficiency of each grating in Data Example 2 as a function of the incident angle. From... Figure 9 As can be seen, the height of the periodic structure 12 can significantly affect the distribution of the +1 order diffraction efficiency of the grating with the incident angle. By optimizing the height of the periodic structure 12, the overall diffraction efficiency of the +1 order can be greatly improved. See the changes of the curves of "circular arc 1" and "circular arc 2" relative to the curve of "circular arc 0".

[0068] (Data Example 3)

[0069] Example 3 compares the +1st order diffraction efficiency of a straight-tooth grating without periodic sidewalls and a grating with periodic sidewalls of different shapes and heights. The height of the periodic structure in the compared gratings differs from the height of the rest of the grating. The grating material has a refractive index of 1.8, the grating period (i.e., the spacing of grating lines 11 in the second direction) d1 = 450 nm, and the period of periodic structure 12 d2 = 450 nm. Other parameters are shown in Table 3.

[0070] [Table 3]

[0071] h1 w1 h2 w2 w3 w4 Straight-tooth grating 300nm 315nm —— —— —— —— Symmetrical triangle 300nm 225nm 450nm 90nm 450nm —— Asymmetrical triangle 300nm 225nm 450nm 90nm 225nm —— arc 300nm 225nm 450nm 140nm 90nm —— trapezoid 300nm 225nm 450nm 90nm 450nm 167nm

[0072] Figure 10 The graphs showing the +1st order diffraction efficiency of each grating as a function of the incident angle are presented. From Figure 10 As can be seen, by changing / optimizing the shape and height of the periodic structure 12, the +1st order diffraction efficiency of the grating can be improved overall, and the distribution of diffraction efficiency with the incident angle can be adjusted.

[0073] (Data Example 4)

[0074] The data examples 1-3 above were all analyzed and compared individually for the diffraction efficiency of the grating structure 10. Data example 4 will be examined as a whole for the diffraction waveguide 100 according to Embodiment 1 of the present invention.

[0075] In Example 4, it is assumed that the coupling grating 110 of the diffractive waveguide 100 adopts the various gratings analyzed in Example 3. The structural parameters and diffraction efficiency curves as a function of the incident angle are shown in Table 3 and... Figure 10 Furthermore, the +1 order of the coupling grating 110 is used as a predetermined diffraction order to couple the incident light into the waveguide substrate and propagate it to the coupling grating 120.

[0076] Meanwhile, in Example 4, it is assumed that the coupling grating 120 of the diffractive waveguide 100 is a two-dimensional grating, and the cross-section of the optical unit structure of this two-dimensional grating is as follows: Figure 11The improved parallelogram shown in the upper left corner has two vertices of 60° each, four vertices of 120° each, four long sides of 248 nm in length, and four short sides of 47 nm in length. The coupling grating 120 with the improved parallelogram optical unit structure is a grating structure already proposed in the prior art, which reduces the bright central fringes of the coupled light field, thus improving the uniformity between different regions of the coupled light field. However, referring to… Figure 11 The curve of the coupling energy of the coupling grating 120 as a function of the incident angle (the vertical axis is the normalized value, and it is assumed that the light energy coupled into the coupling grating is uniformly distributed with the incident angle) shows that this "improved parallelogram" shaped optical unit structure cannot simultaneously improve the angular uniformity of the coupled light field. On the contrary, the coupling energy (coupling efficiency) changes greatly with the change of the incident angle.

[0077] Figure 12 This is a graph showing the coupling energy of the diffracting waveguide 100, which has the aforementioned coupling grating 110 and coupling grating 120, as a function of the incident angle. The overall coupling energy of the diffracting waveguide 100 as a function of the incident angle is simultaneously affected by the +1st order diffraction efficiency of the coupling grating 110 and the coupling efficiency of the coupling grating 120. From... Figure 12 As can be seen, compared to the insertion grating with a straight-tooth grating, the insertion grating 120, when paired with the insertion grating 110 which has a periodic structure on the sidewalls of the grating lines, significantly improves the overall coupling efficiency within the field of view (FOV) of the diffracted waveguide 100, and also significantly improves the uniformity within the FOV. Figure 12 In the examples shown, the diffractive waveguide with a periodic triangular tooth structure has the highest efficiency, while the diffractive waveguide with a periodic asymmetric triangular structure has the best in-FOV uniformity.

[0078] It should be understood that the aforementioned coupling grating with the improved parallelogram optical unit structure is merely exemplary. According to Embodiment 1 of the present invention, in specific applications, the specific parameters of the periodic structure 12 in the coupling grating 110 can be adjusted according to the specific circumstances of the coupling grating 120 to be used, thereby adjusting the diffraction efficiency of the coupling diffraction order (e.g., +1st or -1st order) of the coupling grating 110, so that when paired with a specific coupling grating 120, the overall optical energy distribution of the coupling light field tends to be uniform with the field of view (FOV). Compared to simply improving the uniformity of the coupling light field through the optical structure design of the coupling grating, the diffractive waveguide 100 according to Embodiment 1 of the present invention provides an additional, effective, and flexible means to improve the angular uniformity of the coupling light field by employing a novel grating structure 10 in the coupling grating 110.

[0079] (Data Example 5)

[0080] Example 5 compares the +1st order diffraction efficiencies of gratings with different periods but the same arc shape on the sidewalls of the grating lines. The refractive index of each grating is 1.8, the grating period (i.e., the spacing between grating lines 11 in the second direction) d1 = 450 nm, and the period d2 of the periodic structure 12 is as follows: Figure 13 As marked on the curve graph. From Figure 13 As can be seen, the smaller the period d2 of the periodic structure, the higher the +1 order diffraction efficiency of the grating.

[0081] According to an embodiment of the present invention, the period d2 of the periodic structure 12 in the grating structure 10 is preferably below 600 nm; while considering manufacturability, the period d2 is preferably above 100 nm. More preferably, the period d2 of the periodic structure is between 100 and 500 nm.

[0082] Next, refer to Figure 14 and Figure 15 A diffractive waveguide according to Embodiment 2 of the present invention is introduced, wherein a novel grating structure is used as the coupling grating of the diffractive waveguide.

[0083] Figure 14 An example of a diffractive optical waveguide according to Embodiment 2 of the present invention is shown. Figure 14 As shown, the diffractive waveguide 200 according to Embodiment 2 of the present invention includes a waveguide substrate 200a and a coupling grating 220 formed on the surface of the waveguide substrate 200a. The coupling grating 220 includes a grating structure 20 configured to couple at least a portion of the light propagating into the waveguide substrate 200a by total internal reflection out of the waveguide substrate 200a by diffraction.

[0084] Figure 14 The right-hand side of the diagram is an enlarged view of the grating structure 20. As shown in the diagram, the grating structure 20 includes multiple grating lines 21 arranged in a plane xy. Each of the multiple grating lines 21 extends along a first direction x in the plane xy and is arranged at a predetermined interval d1 in a second direction y perpendicular to the first direction x. Each grating line 21 has a first sidewall 21a and a second sidewall 21b that are opposite to each other in the second direction y. According to this embodiment, the first sidewall 11a has a periodic structure 22 with a period of d2 along the first direction x, and the periodic structures 22 on the sidewalls of adjacent grating lines 22 are staggered along the first direction x by a predetermined distance s = d2 / n, where n is 2 or 3. Figure 14 In the preferred example shown, n is 2.

[0085] like Figure 14As shown, the diffractive waveguide 200 may further include a coupling grating 210 formed on the waveguide substrate 200a. The coupling grating 210 is configured to couple a light beam incident upon it into the waveguide substrate 200a, allowing it to propagate within the waveguide substrate 200a via total internal reflection. Preferably, the first sidewall 21a of the grating line 21 in the grating structure 20 faces the coupling grating 210, thereby causing the periodic structure 22 to face the coupling region. This reduces the coupling out of the centerline region of the coupling out grating 220, allowing energy to spread to both sides and thus improving uniformity.

[0086] In some implementations, the periodic structure 22 can form multiple protruding tooth-like structures, each tooth having a tooth tip 22a and a tooth root 22b, and the width of the tooth in the first direction x gradually decreases from the tooth root 22b to the tooth tip 22a. Advantageously, the periodic structure 22 / tooth-like structure has an axisymmetric structure about an axis (not shown) parallel to the second direction y, thereby facilitating the provision of correspondingly symmetrical diffraction properties for the coupling grating 220.

[0087] exist Figure 14 In the example shown, the periodic structure 22 forms a trapezoidal toothed structure. However, the toothed structure formed by the periodic structure 22 can also have structures such as triangles, arcs, and trapezoids; more broadly, depending on the needs of the specific application, it can have polygonal shapes, arc shapes, or shapes formed by a combination of arcs and straight lines.

[0088] In some other implementations, although not shown, the periodic structure 22 may be an undulating structure without forming a distinct tooth-like structure.

[0089] Furthermore, the gate line 21 can be divided into a first region H1 and a second region H2 along the second direction y (see reference). Figure 7 The second region H2 is the region where the tooth-like structure (periodic structure 22) is located, and has the same or different heights and / or refractive indices in the first region H1 and the second region H2. Preferably, the first region H1 has a rectangular cross-section.

[0090] (Data Example 6)

[0091] In Example 6, the coupled optical field of the diffracting waveguide 200, with grating structure 20 as the coupled grating 220, was simulated. The refractive index of the grating material is 1.8, the grating period (i.e., the arrangement interval of grating lines 21 in the second direction y) d1 = 450 nm, the period of the periodic structure 22 d2 = 450 nm, and other parameters are shown in Table 4.

[0092] [Table 4]

[0093] h1 w1 h2 w2 w3 w4 trapezoid 300nm 225nm 450nm 90nm 450nm 167nm

[0094] Figure 15 This is the energy distribution diagram of the coupled optical field of the diffracted waveguide obtained from the simulation in Example 6. From... Figure 15 As can be seen, the grating structure 20 can function as a two-dimensional grating, and when used as a coupling grating, it can achieve two-dimensional pupil expansion.

[0095] Figure 16 This is a schematic diagram of a diffractive optical waveguide according to Embodiment 3 of the present invention. Figure 16 As shown, the diffractive waveguide 200' according to Embodiment 3 of the present invention has a structure that is substantially the same as that of the diffractive waveguide 200 according to Embodiment 2. The main difference is that the coupling grating 220' in the diffractive waveguide 200' includes additional grating structures 221 and 222 in addition to the grating structure 20. The additional grating structures 221 and 222 are one-dimensional gratings and are arranged on both sides of and adjacent to the grating structure 20 in the first direction x, for coupling at least a portion of the light propagating therein out of the waveguide substrate by diffraction. Since the diffraction efficiency of a one-dimensional grating is generally higher than that of a two-dimensional grating, the additional grating structures 221 and 222 are beneficial to improving the coupling efficiency of the entire coupling grating 220', and also beneficial to improving the brightness of the two sides of the coupled light field, thereby improving uniformity.

[0096] Advantageously, such as Figure 16 As shown, the coupling grating 210' of the diffractive waveguide 200' can also adopt a novel grating structure 10. The grating structure 10 here can be the same as or similar to the grating structure 10 used in the diffractive waveguide 100 according to Embodiment 1 of the present invention, and will not be described in detail here.

[0097] In the diffractive waveguides described above according to embodiments of the present invention, the periodic structures 12 and 22 in the grating structures 10 and 20 are formed only on one sidewall of the grating lines 11 and 21. However, the present invention is not limited thereto. Figure 17 , Figure 18 and Figure 19 Different examples of grating structures 30 that can be used in diffractive waveguides according to other embodiments of the present invention are shown, wherein the two sidewalls 31a and 31b of the grating line 31 of the grating structure 30 are both formed with periodic structures. Specifically, the first sidewall 31a of the grating line 31 has a first periodic structure 32 along a first direction, and the second sidewall 31b has a second periodic structure 33 along the first direction. Advantageously, the first periodic structure 32 and the second periodic structure 33 can have different structures (e.g., shape, size, position, etc.) so that the grating structure 30 as a whole exhibits asymmetry in the direction perpendicular to the grating line 31 (i.e., in the second direction y).

[0098] The diffractive waveguide according to embodiments of the present invention can be applied in display devices. Such display devices are, for example, near-eye display devices, which include lenses and a frame for holding the lenses close to the eyes, wherein the lenses may include the diffractive waveguide described above according to embodiments of the present invention. Preferably, the display device can be an augmented reality display device or a virtual reality display device.

[0099] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A diffractive optical waveguide comprising a waveguide substrate and a grating structure formed on a surface of the waveguide substrate, wherein the grating structure comprises a plurality of grating lines arranged in a plane, each of the plurality of grating lines extending along a first direction in the plane and arranged at a predetermined interval in a second direction perpendicular to the first direction; each of the grating lines has a first sidewall and a second sidewall opposite to each other in the second direction, at least one of the first sidewall and the second sidewall having a periodic structure along the first direction; the grating structure is configured to diffract light incident thereon at a non-zero angle with respect to the plane out of the plane by a predetermined diffraction order; the grating structure is configured as a coupling-out grating that couples out at least a portion of light propagating into the waveguide substrate by total reflection therefrom by diffraction; only the first sidewall has the periodic structure along the first direction, and the periodic structures on the sidewalls of adjacent grating lines are staggered by a predetermined distance s along the first direction, s=P / n, where P is a period of the periodic structure in the first direction, and n is 2 or 3; the diffractive optical waveguide further comprises a coupling-in grating formed on the waveguide substrate, the coupling-in grating being configured to couple a light beam irradiated onto the waveguide substrate into the waveguide substrate to propagate therein by total reflection, and the first sidewall faces the coupling-in grating. 2.The diffractive optical waveguide of claim 1, further comprising an additional grating structure, the additional grating structure being a one-dimensional grating and arranged on at least one side of the grating structure and contiguous thereto in the first direction, for coupling out at least a portion of light propagating thereinto by diffraction.

3. The diffractive optical waveguide of claim 1, wherein, the periodic structure is formed as a plurality of protruding tooth-like structures having a tooth top and a tooth root, and a width of the tooth-like structure in the first direction gradually decreases from the tooth root to the tooth top.

4. The diffractive optical waveguide of claim 3, wherein, the tooth-like structure has an axisymmetric structure about an axis parallel to the second direction.

5. The diffractive optical waveguide of claim 3, wherein, the tooth-like structure has a polygonal shape, a circular arc shape, or a shape formed by a combination of an arc and a straight line.

6. The diffractive optical waveguide of claim 3, wherein, the tooth-like structure has a triangular shape, a trapezoidal shape, or a circular arc shape.

7. The diffractive optical waveguide of any of claims 3-6, wherein, the grating line is divided into a first region and a second region in the second direction, and the plurality of tooth-like structures are located in the second region; the grating line has different heights perpendicular to the plane and / or different refractive indices in the first region and the second region.

8. The diffractive optical waveguide of any of claims 1-6, wherein, a period of the periodic structure in the first direction is between 100 nm and 500 nm. 9.A display device comprising the diffractive optical waveguide of any one of claims 1-8.

10. The display device of claim 9, wherein, the display device is a near-eye display device, and comprises a lens and a frame for holding the lens close to an eye, the lens comprising the diffractive optical waveguide.

11. The display device of claim 9 or 10, wherein, the display device is an augmented reality display device or a virtual reality display device.

Images