Grating coupler, diffraction optical waveguide and display device having the same

Abstract

The present application discloses a grating coupler, a diffractive optical waveguide having the same, and a display device. The grating coupler includes a grating body and an optical film layer. At least a part of the grating lines of the grating body includes a first sidewall and a second sidewall. The first sidewall and the second sidewall respectively form an included angle θ1 and an included angle θ2 with respect to the plane where the grating body is located, and θ1 < θ2. The optical film layer includes a first film layer covering the grating body and a second film layer covering the first film layer. The grating body has a grating refractive index n0, the first film layer has a refractive index n1, and the second film layer has a refractive index n2, where n1 < n0 < n2. The parts of the first film layer located on the first and second sidewalls respectively have an average thickness d1 and d2, and d1 > d2. And the parts of the second film layer located on the first and second sidewalls respectively have an average thickness d3 and d4, and d3 > d4. By providing an optical film layer with specific asymmetry, the coupling efficiency is significantly improved, and at the same time, an additional means for uniformity adjustment is provided.

Description

Technical Field

[0001] The present invention relates to a display technology based on a diffraction optical waveguide; in particular, to a grating coupler, a diffraction optical waveguide and a display device having the same. Background Art

[0002] With the development of science and technology, AR (Augmented Reality) technology, as a very intelligent and portable display technology, is slowly becoming popular. Diffraction light waveguides are currently a mainstream solution for realizing AR display. A waveguide grating is provided on a waveguide substrate. The waveguide grating includes an in-coupling grating and an out-coupling grating. The in-coupling grating couples the incident light carrying image information into the waveguide substrate. The out-coupling grating propagates and expands the light carrying image information while coupling the light out of the waveguide substrate to form an out-coupling light field. The eye receives light from the out-coupling light field, so that, for example, the image carried by the incident light can be observed.

[0003] However, the image display based on the diffraction light waveguide has the problems of insufficient brightness and uniformity deviation. The coupling grating of the diffraction light waveguide has a significant impact on this. For the coupling grating, it is hoped that the diffraction efficiency of the specific order (usually the positive first order) used to couple light into the waveguide substrate is high, while the diffraction efficiency of other orders (especially the zeroth order and the negative first order) is sufficiently low. For this reason, people choose to use a blazed grating as the coupling grating in the diffraction light waveguide, and propose improvements to the structure of the grating (such as the cross-section of the grating line). However, the adjustment capability that can be obtained based on a single refractive index is still limited, and it is impossible to achieve a breakthrough in efficiency, especially it is difficult to further improve the efficiency while taking into account uniformity. Summary of the Invention

[0004] An object of the present invention is to provide a grating coupler, a diffractive optical waveguide and a display device having the same, which at least partially overcome the problems in the prior art.

[0005] According to one aspect of the present invention, a grating coupler is provided for coupling light incident from the outside into a waveguide, the grating coupler comprising:

[0006] a grating body, the grating body comprising a plurality of grating lines arranged along a plane, the plurality of grating lines being periodically arranged in a first direction, each grating line extending in a second direction perpendicular to the first direction, at least some of the grating lines comprising a first sidewall and a second sidewall extending along the second direction, the first sidewall and the second sidewall forming a first angle θ1 and a second angle θ2 with respect to the plane, respectively, θ1<θ2; and

[0007] an optical film layer, the optical film layer comprising a first film layer covering the grating body and a second film layer covering the first film layer,

[0008] The grating body has a grating refractive index n0, the first film layer has a first refractive index n1, and the second film layer has a second refractive index n2, n1 <n0<n2;

[0009] The portion of the first film layer located on the first sidewall has an average thickness d1, and the portion of the first film layer located on the second sidewall has an average thickness d2, d1>d2; and

[0010] The portion of the second film layer located on the first sidewall has an average thickness d3 , and the portion of the second film layer located on the second sidewall has an average thickness d4 , where d3 > d4 .

[0011] Advantageously, the optical film layer satisfies at least one of the following relationships:

[0012] n1≤1.5;

[0013] n2≥2.0;

[0014] n2-n1≥0.4;

[0015] n0-n1≥0.3;

[0016] n2-n0≥0.3; and

[0017] n1+n2≤2n0+0.2.

[0018] Advantageously, the optical film layer also satisfies: n2-n1≥0.6.

[0019] Advantageously, the optical film layer further satisfies: n0-n1≥0.4, and n2-n0≥0.4.

[0020] Advantageously, the optical film layer also satisfies: d1 / d2=d3 / d4.

[0021] Advantageously, the optical film layer further satisfies at least one of the following relationships:

[0022] d1 / d2≥1.5;

[0023] d3 / d4 ≥ 1.5;

[0024] d2≤40nm≤d1≤100nm; and

[0025] d4≤40nm≤d3≤120nm.

[0026] Advantageously, the optical film layer further satisfies: d1 / d2≥3, or d3 / d4≥3.

[0027] In some embodiments, at least a portion of the gate lines has a cross-section perpendicular to the second direction, and the first side wall corresponds to a side edge in the cross-section, the side edge is composed of two or more straight lines and / or curves, and the first angle θ1 is the angle formed by the line connecting the two ends of the side edge relative to the plane.

[0028] In some embodiments, the at least part of the gate line further includes a top wall connected between the first sidewall and the second sidewall, and the top wall forms a flattened or rounded ridge.

[0029] In some embodiments, the optical film layer further includes a third film layer covering the second film layer and a fourth film layer covering the third film layer, wherein the third film layer has a third refractive index n3, and the fourth film layer has a fourth refractive index n4, n3 <n2,n3<n4;

[0030] The portion of the third film layer located on the first sidewall has an average thickness of d'1, and the portion of the third film layer located on the second sidewall has an average thickness of d'2, d'1>d'2; and

[0031] The portion of the fourth film layer located on the first sidewall has an average thickness of d'3, and the portion of the fourth film layer located on the second sidewall has an average thickness of d'4, where d'3>d'4.

[0032] According to another aspect of the present invention, a diffraction optical waveguide is provided, comprising a waveguide substrate and an in-coupling grating and an out-coupling grating arranged on the waveguide substrate, wherein the in-coupling grating is used to couple input light carrying image information into the waveguide substrate and cause it to propagate in the waveguide substrate along a coupling direction by total internal reflection, and the out-coupling grating is used to expand the pupil of the light propagated therein and couple it out of the waveguide substrate to achieve image display, wherein the in-coupling grating is the grating coupler described above.

[0033] In some embodiments, the coupling-in grating may be a reflective grating that receives input light irradiated thereon from one side of the grating body through the waveguide substrate; and the second sidewall faces the coupling-in direction.

[0034] In some embodiments, the coupling-in grating may be a transmissive grating that receives input light irradiated thereon from one side of the optical film layer; and the first sidewall faces the coupling-in direction.

[0035] According to yet another aspect of the present invention, a display device is provided. The display device includes a lens, wherein the lens includes the diffractive optical waveguide as described above.

[0036] Advantageously, the display device is a near-eye display device and further comprises a frame for holding the lenses close to the eyes.

[0037] In the grating coupler according to the embodiments of the present invention, by providing a composite optical film layer with specific asymmetry on the asymmetric grating body, the coupling efficiency is significantly improved. This also provides an additional means for adjusting uniformity, further improving efficiency while maintaining uniformity. Accordingly, the diffractive optical waveguide and practical device according to the embodiments of the present invention also possess the aforementioned technical advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0039] Figure 1 is a schematic plan view of a diffraction optical waveguide according to an embodiment of the present invention, wherein the diffraction optical waveguide adopts a grating coupler according to an embodiment of the present invention as an in-coupling grating;

[0040] Figure 2 Schematic cross-sectional views of an example of a grating coupler according to an embodiment of the present invention are shown, including Figure (a) and Figure (b), wherein for clarity, the optical film layer is not shown in Figure (a);

[0041] Figure 3 Schematic cross-sectional views showing different examples of grating couplers according to embodiments of the present invention;

[0042] Figure 4 shows a schematic cross-sectional view of another example of a grating coupler according to an embodiment of the present invention;

[0043] Figure 5 A schematic cross-sectional view showing an example of a diffractive optical waveguide according to an embodiment of the present invention;

[0044] Figure 6 A schematic cross-sectional view showing another example of a diffractive optical waveguide according to an embodiment of the present invention;

[0045] Figure 7 A graph showing the coupling efficiency of different grating couplers used in Data Example 1 as a function of field angle / incident angle is shown;

[0046] Figure 8 A graph showing the coupling efficiency of different grating couplers used in Data Example 2 as a function of field angle / incident angle is shown;

[0047] Figure 9A graph showing the red light coupling efficiency of different grating couplers used in Data Example 3 as a function of field angle / incident angle is shown;

[0048] Figure 10 A graph showing the green light coupling efficiency of different grating couplers used in Data Example 3 as a function of field angle / incident angle is shown;

[0049] Figure 11 A graph showing how the blue light coupling efficiency of different grating couplers used in Data Example 3 varies with the field angle / incident angle; and

[0050] Figure 12 4 is a chart showing the simulation calculation results of the coupling efficiency and uniformity of the grating coupler according to the embodiment of the present invention when using different film refractive indices in Data Example 5. DETAILED DESCRIPTION

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to explain the relevant invention and are not intended to limit the invention. For ease of description, only portions relevant to the invention are shown in the accompanying drawings. It should be noted that the embodiments and features in the embodiments of this application may be combined with each other unless there is a conflict.

[0052] First refer to Figure 1 The diffraction optical waveguide according to the embodiment of the present invention is briefly introduced.

[0053] Figure 1 FIG is a schematic plan view of a diffraction optical waveguide 1 according to an embodiment of the present invention. Figure 1 As shown, the diffraction optical waveguide 1 includes a waveguide substrate 1a and an in-coupling grating 10 and an out-coupling grating 20 arranged on the waveguide substrate 1a. The in-coupling grating (i.e., grating coupler) 10 is used to couple the input light L carrying image information into the waveguide substrate 1a. in (See Figure 5 and Figure 6 ) and propagates in the waveguide substrate 1a along the incoupling direction IN via total internal reflection. The outcoupling grating 20 is used to expand the pupil of the light propagating therein and couple it out of the waveguide substrate 1a to achieve image display. The diffraction optical waveguide 1 employs a grating coupler according to an embodiment of the present invention as the incoupling grating 10.

[0054] In the grating coupler according to an embodiment of the present invention, an optical film layer with specific asymmetry is provided on the basis of a grating body (also called a "blazed grating") having two side walls with asymmetric inclinations, thereby achieving a significant improvement in the coupling efficiency of the grating coupler at the target diffraction order.

[0055] Although not shown, it should be understood that the diffraction optical waveguide 1 according to the embodiment of the present invention may also include other gratings besides the coupling-in grating and the coupling-out grating, such as a turning grating for expanding the pupil of light from the coupling-in grating and deflecting it to propagate toward the coupling-out grating, and a return grating for returning light that propagates beyond the range of the coupling-out grating to the coupling-out grating (so as to be coupled out for display), etc.

[0056] The following will refer to Figures 2 to 4 The grating coupler according to the embodiment of the present invention is described in detail.

[0057] In this application, a grating coupler refers to a grating device for coupling light incident from the outside into a waveguide (eg, a waveguide substrate). Figure 1 The diffraction waveguide used for image display can be used as an input grating. The same reference numeral "10" is used throughout this application to designate both the grating coupler and the input grating. It should be understood that the grating coupler according to embodiments of the present invention is not limited to use as an input grating in a diffraction waveguide. It can also be used as an optical coupling input device in other non-display optical waveguide devices (e.g., light-homogenizing waveguide devices in optical machines and optical waveguide illumination devices in eye tracking equipment).

[0058] Figure 2 Figure 1 is a schematic cross-sectional view of an example of a grating coupler 10 according to an embodiment of the present invention, including Figure (a) and Figure (b). Figure (a) illustrates the structure of the grating body in the grating coupler 10, with the optical film layer omitted for clarity; Figure (b) shows the overall structure of the grating coupler 10.

[0059] like Figure 2 As shown in FIG. (b), the grating coupler 10 includes a grating body 11 and an optical film layer 12 covering the grating body 11. Figure 2 In the example shown, the grating coupler 10 further includes a waveguide substrate 10a, and the grating body 11 is disposed on the waveguide substrate 10a. The grating coupler 10 may be formed of a material different from the waveguide substrate 10a, or may be formed of the same material as the waveguide substrate 10a, or may even be formed integrally with the latter. However, it should be understood that the grating coupler 10 according to the embodiment of the present invention is not limited to including a waveguide substrate. For example, in some implementations, the grating coupler 10 may be combined with a waveguide substrate provided separately (e.g., a waveguide substrate of other optical devices, such as Figure 1 On the waveguide substrate 1a) of the diffractive optical waveguide 1 shown.

[0060] Combined with reference Figure 1 and Figure 2 The grating body 11 includes a plane P (ie Figure 1The plurality of gate lines 11a are arranged in a periodic manner in a first direction x, and each gate line 11a extends in a second direction y perpendicular to the first direction x. Figure 2 As shown in the middle figure (a), at least part of the grating lines 11a of the grating body 11 includes a first side wall S1 and a second side wall S2 extending along the second direction y, and the first side wall S1 and the second side wall S2 form a first angle θ1 and a second angle θ2 relative to the plane P, respectively, θ1<θ2.

[0061] like Figure 2 As shown in Figure (b), the optical film layer 12 includes a first film layer C1 covering the grating body 11 and a second film layer C2 covering the first film layer C1. The grating body 11 has a grating refractive index n0, the first film layer C1 has a first refractive index n1, and the second film layer C2 has a second refractive index n2. According to an embodiment of the present invention, the optical film layer 12 is constructed to meet the following requirements: n1 <n0<n2。

[0062] Continue to refer to Figure 2 In figure (b), the portion of the first film layer C1 located on the first sidewall S1 has an average thickness of d1, and the portion of the first film layer C1 located on the second sidewall S2 has an average thickness of d2. The portion of the second film layer C2 located on the first sidewall S1 has an average thickness of d3, and the portion of the second film layer C2 located on the second sidewall S2 has an average thickness of d4. According to an embodiment of the present invention, the optical film layer 12 is constructed to further satisfy the following conditions: d1>d2, d3>d4. In this application, the thickness of a film layer refers to the thickness in a direction perpendicular to the surface on which the film layer is located.

[0063] As will be described in detail below with reference to data examples, in the grating coupler 10 according to an embodiment of the present invention, a grating body 11 is provided with a specific refractive index relationship (ie, n1 <n0<n 2) The composite optical film layer 12 is configured such that the portions of the film layer 12 on the two differently inclined sidewalls S1 and S2 of the grating body 11 have a specific thickness relationship (i.e., d1>d2, d3>d4). This significantly improves the coupling efficiency of the grating coupler 10 and provides a new means / variable for uniformity adjustment, further improving the coupling efficiency while also taking uniformity into account. Here, uniformity refers to the uniformity of the distribution of the coupling efficiency of the grating coupler within the field angle (i.e., incident angle) of the input light.

[0064] In actual manufacturing, the grating coupler 10 according to an embodiment of the present invention can be implemented, for example, through physical vapor deposition. Specifically, the thickness of each film layer C1 and C2 on the two sidewalls S1 and S2 of the grating body 11 can be controlled by controlling the coating direction (e.g., sputtering direction) during physical vapor deposition. Preferably, the optical film layer 12 of the grating coupler 10 can be designed and / or fabricated to further satisfy d1 / d2=d3 / d4. This advantageously enables the first film layer C1 and the second film layer C2 to be continuously formed during manufacturing using a single coating process.

[0065] exist Figure 2 In the example shown, the first side wall S1 and the second side wall S2 of the grating body 11 are respectively plane and adjacent to each other, thereby forming an angle in a cross section of the grating body 11 perpendicular to the second direction y. However, it should be understood that Figure 2 The illustrations are merely exemplary and non-restrictive. The grating coupler 10 according to the embodiment of the present invention is not limited to the first side wall S1 and the second side wall S2 of the grating body 11 being planar side walls or being adjacent to each other. Figure 3 Schematic cross-sectional views of three different examples of grating couplers 10 according to embodiments of the present invention are shown.

[0066] Figure 3 In the grating coupler 10A shown in Figure (a), the first sidewall S1 of at least some of the lines 11a of the grating body 11 is a non-planar wall. More specifically, at least some of the lines 11a of the grating body 11 have a cross-section perpendicular to the second direction y, and the first sidewall S1 corresponds to a side edge (the left side edge shown in the figure) of the cross-section, which is formed by a combination of two or more straight lines and / or curves (e.g., line segments l1, l2, and l3 shown in the figure). By way of example only and not limitation, such a non-planar wall may include, for example, a stepped wall edge.

[0067] When the first sidewall S1 is a non-planar wall, the angle formed by a line connecting two ends of the side corresponding to the first sidewall S1 and the plane P can be used as the first angle θ1 of the first sidewall S1 relative to the plane P.

[0068] Although not shown in the figures, it should be understood that, as an alternative or in addition, the second side wall S2 of the grating body 11 of the grating coupler 10 according to an embodiment of the present invention may also be a non-planar wall, so that similarly in the cross section of the grating line perpendicular to the second direction y, the side corresponding to the second side wall S2 may be composed of two or more straight lines and / or curves.

[0069] Figure 3Figures (b) and (c) show that at least part of the grating lines 11a of the grating body 11 may also include a top wall S3 / S3' connected between the first side wall S1 and the second side wall S2, wherein in the grating coupler 10B shown in Figure (b), the top wall S3 is formed as a flattened ridge, and in the grating coupler 10C shown in Figure (c), the top wall S3' is formed as a rounded ridge.

[0070] Except for Figure 3 The grating body 11 shown may have different Figure 2 In addition to the structure shown, according to some embodiments of the present invention, the optical film layer in the grating coupler may also have a modified structure, wherein the optical film layer further includes a third film layer and a fourth film layer.

[0071] For example, see Figure 4 Schematic cross-sectional view of the grating coupler 10D shown. Figure 4 As shown, the optical film layer 12 of the grating coupler 10D further includes a third film layer C3 covering the second film layer C2 and a fourth film layer C4 covering the third film layer C3. According to an embodiment of the present invention, the third film layer C3 has a third refractive index n3, and the fourth film layer C4 has a fourth refractive index n4, n3 <n2,n3<n4。

[0072] Continue to refer to Figure 4 The portion of the third film layer C3 located on the first sidewall S1 has an average thickness of d'1, and the portion of the third film layer C3 located on the second sidewall S2 has an average thickness of d'2. The portion of the fourth film layer C4 located on the first sidewall S1 has an average thickness of d'3, and the portion of the fourth film layer C4 located on the second sidewall S2 has an average thickness of d'4. According to some embodiments of the present invention, the optical film layer 12 is constructed to further satisfy the following conditions: d'1>d'2, d'3>d'4.

[0073] Figure 4 In the grating coupler 10D shown, the modulation capability of the grating is further improved by adding a composite structure of optical film layers. Furthermore, by adjusting the film thickness and refractive index, the grating coupling efficiency and uniformity of more wavelengths or wider bands can be improved.

[0074] Referenced above Figure 1 The diffraction optical waveguide according to the embodiment of the present invention has been briefly introduced. Figure 5 and Figure 6 A further detailed introduction is given, in particular, an introduction to the application of the grating coupler in the diffraction optical waveguide according to the embodiment of the present invention.

[0075] Figure 5 An example of a diffractive optical waveguide according to an embodiment of the present invention, namely a diffractive optical waveguide 1' is schematically shown in a cross-sectional view. Figure 5 In the example shown, the diffraction optical waveguide 1' adopts the grating coupler 10 according to the embodiment of the present invention as the coupling grating, and the coupling grating 10 is used as a reflective grating, wherein Figure 5 As shown, the coupling grating 10 receives the input light L from the grating body 11 side through the waveguide substrate 1a. in Input light L in The diffraction of the coupling grating 10 is "reflected" back into the waveguide substrate 1a and is reflected in the waveguide substrate 1a along the coupling direction IN (see Figure 1 and Figure 5 In this case, according to an embodiment of the present invention, the coupling-in grating 10 is arranged in the diffraction optical waveguide 1' so that its second side wall S2 faces the coupling-in direction.

[0076] Similarly, Figure 6 An example of a diffractive optical waveguide according to an embodiment of the present invention, namely a diffractive optical waveguide 1, is schematically shown in a cross-sectional view. Figure 6 In the example shown, the diffraction optical waveguide 1" adopts the grating coupler 10 according to the embodiment of the present invention as the coupling grating, and the coupling grating 10 is used as a transmission grating, wherein Figure 6 As shown, the coupling grating 10 receives the input light L from the optical film layer 12 side through the waveguide substrate 1a. in Input light L in The diffraction of the coupling grating 10 is "transmitted" into the waveguide substrate 1a and is reflected in the waveguide substrate 1a along the coupling direction IN (see Figure 1 and Figure 5 In this case, according to an embodiment of the present invention, the coupling-in grating 10 is arranged in the diffraction optical waveguide 1 ″ so that its first side wall S1 faces the coupling-in direction.

[0077] The diffractive optical waveguide according to the embodiment of the present invention correspondingly has the technical advantages of the grating coupler according to the present invention.

[0078] The technical advantages of the grating coupler and the diffraction optical waveguide according to the embodiments of the present invention will be described below through data examples.

[0079] (Data Example 1)

[0080] In Data Example 1, the simulation calculation and comparison analysis of the following grating coupler used as a reflective grating (the grating coupler receives the input light from the bottom side of the grating body through the waveguide substrate, see Figure 5 The coupling efficiency and uniformity of the grating coupler 10 shown in FIG.

[0081] Grating coupler 1A: A grating coupler according to an embodiment of the present invention, comprising the grating coupler as described above with reference to Figure 2 The grating body, the first film layer covering the grating body, and the second film layer covering the first film layer are introduced;

[0082] Grating coupler 1B: a blazed grating without an optical film layer, which is composed of the same structure as the grating body in grating coupler 1A;

[0083] Grating coupler 1C: a grating coupler having a single film layer, which has a grating body identical to the grating body in grating coupler 1A and a single film layer covering the grating body, wherein the single film layer has the same refractive index as the first film layer in grating coupler 1A;

[0084] Grating coupler 1D: A grating coupler having two film layers, comprising a grating body identical to the grating body in grating coupler 1A, a lower film layer covering the grating body, and an upper film layer covering the lower film layer, wherein the lower film layer and the upper film layer have the same refractive index as the first film layer and the second film layer in grating coupler 1A, respectively, and each film layer has the same film thickness on the first sidewall and the second sidewall of the grating body; and

[0085] Grating coupler 1E: A grating coupler having two film layers, which has a grating body identical to the grating body in the grating coupler 1A, a lower film layer covering the grating body, and an upper film layer covering the lower film layer, wherein the lower film layer and the upper film layer respectively have the same refractive index and film thickness as the second film layer and the first film layer in the grating coupler 1A (that is, having a film layer structure obtained by reversing the order of the first film layer and the second film layer).

[0086] In Data Example 1, the grating coupler is optimized based on the following parameters:

[0087] (1) Input light wavelength λ = 522 nm (green light), field of view angle / incident angle range is 25° × 18°;

[0088] (2) The refractive index of the waveguide substrate is 1.8, the thickness is 0.7 mm, and the grating period is 400 nm;

[0089] (3) The refractive index of the grating body is n0 = 1.8, the refractive index of the first film layer is n1 = 1.4, and the refractive index of the second film layer is n2 = 2.3.

[0090] During the optimization process, the optimizable parameters of the grating coupler include the height of the blazed grating, the first angle (blaze angle), and the thickness of the film layer. The primary optimization objective is coupling efficiency, with uniformity as a secondary optimization objective (preferably achieving a uniformity of 45% or greater). In this application, uniformity is characterized by the ratio of the minimum to maximum coupling efficiency of the grating coupler over the range of the incident angle / field of view (FOV) of the input light used for image display: uniformity = minimum coupling efficiency / maximum coupling efficiency.

[0091] The grating coupler 1A is a grating coupler according to an embodiment of the present invention. The optimized parameters of the grating coupler 1A that enable better coupling efficiency and uniformity include:

[0092] The grating height is 170 nm, and the first angle θ1 is 25.2°;

[0093] The thickness of the portion of the first film layer on the first sidewall is d1 = 54.3 nm;

[0094] The thickness of the portion of the first film layer on the second sidewall is d2 = 13.3 nm;

[0095] The thickness of the portion of the second film layer on the first sidewall is d3 = 67.9 nm;

[0096] The thickness d4 of the portion of the second film layer on the second sidewall is 16.7 nm.

[0097] The optimized parameters of the grating coupler 1C, which enable better coupling efficiency and uniformity, include: the thickness of the single film layer on the first side wall of the grating body is 58.8 nm, and the thickness on the second side wall is 14.0 nm.

[0098] The parameters of the grating coupler 1D obtained after optimization, which can achieve better coupling efficiency and uniformity, include: the thickness of the lower film layer is 30 nm, and the thickness of the upper film layer is 65.5 nm.

[0099] The coupling efficiency and uniformity of the grating couplers 1A to 1E after the above optimization are shown in Table 1:

[0100] [Table 1]

[0101] Incoupling efficiency Uniformity (min / max) Grating Coupler 1A 0.244 0.540 Grating coupler 1B (comparative example) 0.123 0.641 Grating Coupler 1C (Comparative Example) 0.193 0.392 Grating coupler 1D (comparative example) 0.196 0.541 Grating coupler 1E (comparative example) 0.137 0.462

[0102] at the same time, Figure 7 2 is a graph showing how the coupling efficiency of the grating couplers 1A to 1E in Data Example 1 changes with the field angle / incident angle of the input light.

[0103] From Table 1 and Figure 7As can be seen in the figure, the coupling efficiency of grating coupler 1A according to an embodiment of the present invention is significantly better than that of grating couplers 1B to 1E. Specifically, the coupling efficiency of grating coupler 1A is improved by 98.4% compared to grating coupler 1B, and by 24.5% compared to grating coupler 1D.

[0104] In addition, from Table 2 and Figure 8 As can be seen in the figure, the grating coupler 1A also maintains relatively good coupling uniformity, overcoming the problem in existing grating couplers that it is difficult to improve the coupling efficiency while taking uniformity into account.

[0105] Data Example 1 shows that the grating coupler according to the embodiment of the present invention can significantly improve the coupling efficiency and maintain good uniformity when used as a reflective grating.

[0106] (Data Example 2)

[0107] In Data Example 2, simulation calculations are performed to compare and analyze the case where grating couplers 2A, 2B, 2C, 2D, and 2E are used as transmission gratings (the grating coupler receives input light from the top surface of the optical film layer / grating body, see Figure 6 The coupling efficiency and uniformity of the grating coupler 10' shown in the usage state) are shown.

[0108] Grating couplers 2A to 2E respectively have the structures of grating couplers 1A to 1E in Data Example 1. Specifically, grating coupler 2A is a grating coupler according to an embodiment of the present invention; grating coupler 2B is a blazed grating without an optical film layer; grating coupler 2C is a grating coupler with a single film layer; grating coupler 2D is a grating coupler with two film layers, wherein the two film layers have the same film layer thickness on the first and second sidewalls of the grating body; and grating coupler 2E is a grating coupler with two film layers, wherein the two film layers are obtained by reversing the order of the first and second film layers in grating coupler 2A. For a more detailed description, please refer to Data Example 1 and will not be repeated here.

[0109] In Data Example 2, the grating coupler is optimized based on the following parameters:

[0110] (1) Input light wavelength λ = 522nm (green light), field of view (FOV) range is 25° × 18°; the optical machine that projects the input light is Figure 1 The xz plane shown is tilted 9° relative to the z-axis (normal direction of the waveguide substrate);

[0111] (2) The refractive index of the waveguide substrate is 1.8, the thickness is 0.7 mm, and the grating period is 420 nm;

[0112] (3) The refractive index of the grating body is n0 = 1.8, the refractive index of the first film layer is n1 = 1.4, and the refractive index of the second film layer is n2 = 2.3.

[0113] During the optimization process, the optimizable parameters of the above-mentioned grating coupler include the height of the blazed grating, the first angle (blaze angle) and the thickness of the film layer, and the coupling efficiency is the main optimization target, and the uniformity is the secondary optimization target (preferably the uniformity reaches above 0.45).

[0114] The grating coupler 2A is a grating coupler according to an embodiment of the present invention. The optimized parameters of the grating coupler 2A that enable better coupling efficiency and uniformity include:

[0115] The grating height is 220 nm, and the first angle θ1 is 30.2°;

[0116] The thickness of the portion of the first film layer on the first sidewall is d1 = 26.0 nm;

[0117] The thickness of the portion of the first film layer on the second sidewall is d2 = 5.2 nm;

[0118] The thickness of the portion of the second film layer on the first sidewall is d3 = 48.0 nm;

[0119] The thickness d4 of the portion of the second film layer on the second side wall is 9.6 nm.

[0120] The optimized parameters of the grating coupler 2C, which can achieve better coupling efficiency and uniformity, include: the thickness of the single film layer on the first side wall of the grating body is 26.0 nm, and the thickness of the single film layer on the second side wall is 5.2 nm.

[0121] The parameters of the grating coupler 2D obtained after optimization, which can achieve better coupling efficiency and uniformity, include: the thickness of the lower film layer is 30.0 nm, and the thickness of the upper film layer is 50.0 nm.

[0122] The coupling efficiency and uniformity of the grating couplers 2A to 2E after the above optimization are shown in Table 2:

[0123] [Table 2]

[0124] Incoupling efficiency Uniformity (min / max) Grating Coupler 2A 0.229 0.788 Grating coupler 2B (comparative example) 0.141 0.779 Grating coupler 2C (comparative example) 0.196 0.771 Grating Coupler 2D (Comparative Example) 0.184 0.558 Grating coupler 2E (comparative example) 0.182 0.659

[0125] at the same time, Figure 8 2 is a graph showing how the coupling efficiency of the grating couplers 2A to 2E in Data Example 2 changes with the field angle / incident angle of the input light.

[0126] From Table 2 and Figure 8As can be seen in the figure, the coupling efficiency of grating coupler 2A according to the embodiment of the present invention is significantly better than that of grating couplers 2B to 2E. Specifically, the coupling efficiency of grating coupler 2A is improved by 62.4% compared to grating coupler 2B, and by 16.8% compared to grating coupler 2C.

[0127] In addition, from Table 2 and Figure 8 As can be seen in the figure, the grating coupler 2A can also achieve very good uniformity, taking into account the improvement of coupling efficiency and uniformity.

[0128] Data Example 2 shows that the grating coupler according to the embodiment of the present invention can significantly improve the coupling efficiency when used as a transmission grating, while also improving the uniformity.

[0129] (Data Example 3)

[0130] In Data Example 3, the coupling efficiency and uniformity of grating couplers 3A, 3B, 3C and 3D at different wavelengths are compared and analyzed through simulation calculation.

[0131] Grating couplers 3A-3D respectively have the structures of grating couplers 1A-1D in Data Example 1. Specifically, grating coupler 3A is a grating coupler according to an embodiment of the present invention; grating coupler 3B is a blazed grating without an optical film layer; grating coupler 3C is a grating coupler with a single film layer; and grating coupler 3D is a grating coupler with two film layers, where the two film layers have the same film thickness on the first and second sidewalls of the grating body. For a more detailed description, please refer to Data Example 1 and will not be repeated here.

[0132] In Data Example 3, the grating coupler described above is optimized as a reflective grating based on the following parameters:

[0133] (1) The input light has a red wavelength of λ1 = 622 nm, a green wavelength of λ2 = 532 nm, and a blue wavelength of λ3 = 455 nm. The field of view (FOV) is 20° × 20°.

[0134] (2) The refractive index of the waveguide substrate is 1.9, the thickness is 0.7 mm, and the grating period is 390 nm;

[0135] (3) The refractive index of the grating body is n0 = 1.9, the refractive index of the first film layer is n1 = 1.45, and the refractive index of the second film layer is n2 = 2.5.

[0136] During the optimization process, the optimizable parameters of the above-mentioned grating coupler include the height of the blazed grating, the first angle (blaze angle) and the thickness of the film layer, and the coupling efficiency is the main optimization target, and the uniformity is the secondary optimization target (preferably the uniformity reaches above 0.45).

[0137] The grating coupler 3A is a grating coupler according to an embodiment of the present invention. The optimized parameters of the grating coupler 3A that enable better coupling efficiency and uniformity include:

[0138] The grating height is 175 nm, and the first angle θ1 is 25.7°;

[0139] The thickness of the portion of the first film layer on the first sidewall is d1 = 67.7 nm;

[0140] The thickness of the portion of the first film layer on the second sidewall is d2 = 23.2 nm;

[0141] The thickness of the portion of the second film layer on the first sidewall is d3 = 72.2 nm;

[0142] The thickness d4 of the portion of the second film layer on the second side wall is 26.3 nm.

[0143] The optimized parameters of the grating coupler 3C, which can achieve better coupling efficiency and uniformity, include: the thickness of the single film layer on the first side wall of the grating body is 40.5 nm, and the thickness on the second side wall is 13.9 nm.

[0144] The parameters of the grating coupler 3D obtained after optimization, which can achieve better coupling efficiency and uniformity, include: the thickness of the lower film layer is 33.0 nm, and the thickness of the upper film layer is 70.3 nm.

[0145] The coupling efficiency and uniformity of the grating couplers 3A to 3D after the above optimization are shown in Table 3:

[0146] [Table 3]

[0147] R-efficiency G-Efficiency B-Efficiency R-uniformity G-Uniformity B-Uniformity Grating Coupler 3A 0.380 0.317 0.152 0.784 0.597 0.409 Grating coupler 3B (comparative example) 0.113 0.162 0.127 0.568 0.783 0.356 Grating coupler 3C (comparative example) 0.238 0.223 0.104 0.827 0.603 0.213 Grating Coupler 3D (Comparative Example) 0.274 0.238 0.096 0.806 0.615 0.186

[0148] In Table 3, R, G, and B represent red light, green light, and blue light, respectively.

[0149] at the same time, Figure 9 、 Figure 10 and Figure 11 Graphs showing how the coupling efficiency of different grating couplers used in Data Example 3 changes with the field of view angle / incident angle under red light, green light, and blue light, respectively.

[0150] From Table 3 and Figures 9 to 11As can be seen in the figure, the grating coupler 3A according to the embodiment of the present invention achieves a coupling efficiency of 38% and a uniformity of 78% for red light; a coupling efficiency of 32% and a uniformity of 60% for green light; and a coupling efficiency of 15.2% and a uniformity of 41% for blue light. These coupling efficiencies of the grating coupler 3A are significantly superior to those of the other grating couplers 3B, 3C, and 3D.

[0151] From the perspective of uniformity, although the uniformity obtained by the grating coupler 3A for red and green light is not optimal, it can be maintained at a very good level; and for blue light, the uniformity obtained by the grating coupler 3A is optimal, and the improvement is significant.

[0152] Data Example 3 shows that the grating coupler according to an embodiment of the present invention can comprehensively improve the coupling efficiency at different wavelengths (eg, red, green, and blue wavelengths used for full-color display) while also taking uniformity into consideration.

[0153] Referring to the optimized thicknesses of the first film layer and the second film layer in the grating couplers 1A, 2A and 3A according to embodiments of the present invention in data examples 1 to 3, in the grating coupler according to embodiments of the present invention, the optical film layer can be advantageously constructed to satisfy at least one of the following conditions: d2≤40nm≤d1≤100nm; and d4≤40nm≤d3≤120nm.

[0154] The above data examples 1 to 3 show the technical advantages of the grating coupler according to the embodiment of the present invention in terms of coupling efficiency and uniformity. Next, the influence of film thickness and refractive index in the grating coupler according to the embodiment of the present invention will be further analyzed through data examples 4 and 5.

[0155] (Data Example 4)

[0156] In Data Example 4, the coupling efficiency and uniformity of the grating coupler 4A according to the embodiment of the present invention are simulated and analyzed under different film thickness ratios d1 / d2 and d3 / d4. The grating coupler 4A includes the above reference Figure 2 The grating body, the first film layer covering the grating body, and the second film layer covering the first film layer are introduced and will not be described in detail here.

[0157] In Data Example 4, the coupling efficiency and uniformity of the grating coupler 4A when used as a reflective grating are simulated based on the following parameters:

[0158] (1) Input light wavelength λ = 522 nm (green light), field of view angle / incident angle range is 25° × 18°;

[0159] (2) The refractive index of the waveguide substrate is 1.8, the thickness is 0.7 mm, and the grating period is 400 nm;

[0160] (3) The refractive index of the grating body n0 = 1.8, the refractive index of the first film layer n1 = 1.4, and the refractive index of the second film layer n2 = 2.3; and

[0161] (4) The grating height is 170 nm, and the first angle θ1 = 25.2°.

[0162] Furthermore, the simulation calculations for Data Example 4 are divided into three groups, among which:

[0163] The first group: Calculate the coupling efficiency and uniformity under different film thickness ratios d3 / d4 under the condition that d1 / d2 is fixed (about 4);

[0164] The second group: Calculate the coupling efficiency and uniformity under different film thickness ratios d1 / d2, with d3 / d4 being a fixed value (approximately 4); and

[0165] Group 3: Under the condition of d1 / d2 = d3 / d4 (considering the design and processing accuracy of the film thickness, there may be a slight deviation between the two ratios. In this application, it is considered that such a situation meets the condition of d1 / d2 = d3 / d4). The coupling efficiency and uniformity are calculated for different film thickness ratios.

[0166] The coupling efficiency and uniformity of the grating coupler 4A obtained through the above three sets of simulation calculations are shown in Table 4.1, Table 4.2 and Table 4.3 respectively: [Table 4.1]

[0167] d3 / d4 d1 d2 d3 d4 Incoupling efficiency Uniformity (min / max) 1 54.3 13.3 70.3 70.3 0.211 0.563 1.25 54.3 13.3 70.1 56.1 0.215 0.562 1.5 54.3 13.3 69.6 46.4 0.225 0.550 2 54.3 13.3 69.0 34.5 0.232 0.544 3 54.3 13.3 68.4 22.8 0.239 0.541 4 54.3 13.3 67.9 16.7 0.244 0.540 6 54.3 13.3 66.0 11.0 0.246 0.528

[0168] [Table 4.2]

[0169] d1 / d2 d1 d2 d3 d4 Incoupling efficiency Uniformity (min / max) 1 33.0 33.0 67.9 16.7 0.247 0.456 1.25 36.0 28.8 67.9 16.7 0.246 0.478 1.5 39.2 26.1 67.9 16.7 0.246 0.472 2 43.0 21.5 67.9 16.7 0.247 0.482 3 49.0 16.3 67.9 16.7 0.246 0.509 4 54.3 13.3 67.9 16.7 0.244 0.540 6 60.0 10.0 67.9 16.7 0.244 0.534

[0170] [Table 4.3]

[0171] d1 / d2=d3 / d4 d1 d2 d3 d4 Incoupling efficiency Uniformity (min / max) 1 33.0 33.0 70.3 70.3 0.196 0.541 1.25 36.0 28.8 70.1 56.1 0.206 0.513 1.5 39.2 26.1 69.6 46.4 0.224 0.494 2 43.0 21.5 69.0 34.5 0.231 0.498 3 49.0 16.3 68.4 22.8 0.236 0.506 4 54.3 13.3 67.9 16.7 0.244 0.540 6 60.0 10.0 66.0 11.0 0.243 0.547

[0172] Table 4.1 shows that, with d1 / d2 fixed, the coupling efficiency of the grating coupler 4A increases significantly with the increase of the ratio d3 / d4, while the uniformity decreases slightly but remains at a good level.

[0173] Table 4.2 shows that when d3 / d4 is fixed, the coupling efficiency of the grating coupler 4A does not change significantly with the increase of the ratio d1 / d2, while the uniformity is significantly improved.

[0174] Table 4.3 shows that under the condition of d1 / d2=d3 / d4, the coupling efficiency of the grating coupler 4A increases more significantly with the increase of the ratios d1 / d2 and d3 / d4. At the same time, the uniformity decreases slightly and then increases again, thus maintaining a good level overall.

[0175] Taking into account the influence of the film thickness ratios shown in Tables 4.1, 4.2 and 4.3, in the grating coupler according to an embodiment of the present invention, the optical film layer can be advantageously constructed to meet at least one of the following conditions: d1 / d2≥1.5; and d3 / d4≥1.5.

[0176] In some embodiments, preferably, the optical film layer can be constructed to satisfy: d1 / d2≥3, or d3 / d4≥3, to obtain higher coupling efficiency.

[0177] (Data Example 5)

[0178] In Data Example 5, the coupling efficiency and uniformity of the grating coupler 5A according to the embodiment of the present invention are simulated and analyzed under the conditions of using different refractive indices n1 and n2. The grating coupler 5A includes the grating coupler 5A as described above. Figure 2 The grating body, the first film layer covering the grating body, and the second film layer covering the first film layer are introduced and will not be described in detail here.

[0179] In Data Example 5, the coupling efficiency and uniformity of the grating coupler 5A when used as a reflective grating are simulated based on the following parameters:

[0180] (1) Input light wavelength λ = 522 nm (green light), field of view angle / incident angle range is 25° × 18°;

[0181] (2) The refractive index of the waveguide substrate is 1.8, the thickness is 0.7 mm, and the grating period is 400 nm;

[0182] (3) The refractive index of the grating body n0 = 1.8; and

[0183] (4) The grating height is 170 nm, and the first angle θ1 = 25.2°.

[0184] The coupling efficiency and uniformity of the grating coupler 5A obtained by simulation are Figure 12 Shown in tabular form.

[0185] Figure 12 The table shows that as the refractive index n1 of the first film layer decreases, the coupling efficiency increases; and as the refractive index n2 of the second film layer increases, the coupling efficiency also increases.

[0186] Considering that it is a common trend to use a waveguide substrate with a higher refractive index n0 (for example, a waveguide substrate with a refractive index n0 above 1.8) in order to improve the field of view of the diffraction optical waveguide, in the grating coupler according to an embodiment of the present invention, the optical film layer is constructed to satisfy n1≤1.5 and / or n2≥2.0, which will help to more significantly improve the coupling efficiency.

[0187] The influence of the film refractive indices n1 and n2 on the coupling efficiency can also be examined in combination with the refractive index n0 of the grating body. Figure 12 The table further shows that as the value of n0-n1 increases, the coupling efficiency improves; as the values ​​of n2-n0 and n2-n1 increase, the coupling efficiency also improves. Even when n2-n0 is only 0.1, if n0-n1 ≥ 0.3, a relatively good coupling efficiency of 0.180 is achieved; even when n0-n1 is only 0.1, if n2-n0 ≥ 0.3, a relatively good coupling efficiency of 0.182 is achieved. Therefore, in the optical coupler according to the embodiment of the present invention, the optical film layer structure that satisfies n0-n1 ≥ 0.3 and / or n2-n0 ≥ 0.3 will help to significantly improve the coupling efficiency.

[0188] In addition, from Figure 12 It can be found from the table that if the optical film layer is constructed to satisfy (n2-n0)+(n0-n1)≥0.4, that is, n2-n1≥0.4, the coupling efficiency can also be improved to a better level.

[0189] Figure 12 The table also shows that as the refractive index n1 of the first film decreases, n0-n1 increases, and uniformity improves; while as the refractive index n2 of the second film increases, n2-n1 increases, and uniformity deteriorates. This demonstrates that while improving coupling efficiency by decreasing n1 and increasing n2, as discussed above, uniformity can be maintained, and in some cases even improved, by controlling and balancing the opposing effects of n0-n1 and n2-n1 on uniformity.

[0190] from Figure 12 The table shows that if the optical film is constructed to satisfy n0-n1≥n2-n0, that is, n1+n2≤2n0 (in Data Example 5, this means n1+n2≤3.6), uniformity can be maintained at a relatively good level. Considering that in applications such as diffractive waveguides for image display, a uniformity above 0.45 is acceptable, while improving coupling efficiency is a more pressing need, the optical film can be constructed to satisfy n1+n2≤2n0+0.2, thereby further improving coupling efficiency while maintaining uniformity.

[0191] In summary, in the grating coupler according to the embodiment of the present invention, it is advantageous for the optical film layer to satisfy at least one of the following relationships:

[0192] n1≤1.5;

[0193] n2≥2.0;

[0194] n0-n1≥0.3;

[0195] n2-n0≥0.3;

[0196] n2-n1≥0.4; and

[0197] n1+n2≤2n0+0.2.

[0198] Advantageously, in some cases, the coupling efficiency can be further improved by constructing the optical film layer to satisfy n2-n1≥0.6.

[0199] Advantageously, in some cases, the coupling efficiency can be further improved by constructing the optical film layer to satisfy n0-n1≥0.4 and n2-n0≥0.4.

[0200] The grating coupler and diffractive optical waveguide according to embodiments of the present invention have been described above. According to embodiments of the present invention, a display device is also provided, comprising a diffractive optical waveguide according to embodiments of the present invention. Specifically, the display device may include a lens, and the lens includes the diffractive optical waveguide described above. The display device is preferably a near-eye display device, such as an augmented reality display device or a virtual reality display device, and further includes a frame for holding the lens close to the eye.

[0201] Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but also includes other technical solutions formed by any combination of the above-mentioned technical features or their equivalents without departing from the inventive concept. For example, the above-mentioned features can be replaced with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A grating coupler for coupling light incident from the outside into a waveguide, the grating coupler comprising: a grating body, the grating body comprising a plurality of grating lines arranged along a plane, the plurality of grating lines being periodically arranged in a first direction, each grating line extending in a second direction perpendicular to the first direction, at least some of the grating lines comprising a first sidewall and a second sidewall extending along the second direction, the first sidewall and the second sidewall forming a first angle θ1 and a second angle θ2 with respect to the plane, respectively, θ1<θ2; and an optical film layer, the optical film layer comprising a first film layer covering the grating body and a second film layer covering the first film layer, The grating body has a grating refractive index n0, the first film layer has a first refractive index n1, and the second film layer has a second refractive index n2, n1 <n0<n2; The portion of the first film layer located on the first sidewall has an average thickness d1, and the portion of the first film layer located on the second sidewall has an average thickness d2, d1>d2; and The portion of the second film layer located on the first sidewall has an average thickness d3 , and the portion of the second film layer located on the second sidewall has an average thickness d4 , where d3 > d4 .

2. The grating coupler according to claim 1, wherein The optical film layer satisfies at least one of the following relationships: n1≤1.5； n2≥2.0； n2-n1≥0.4; n0-n1≥0.3; n2-n0≥0.3; and n1+n2≤2n0+0.

2.

3. The grating coupler according to claim 2, wherein n2-n1≥0.

6.

4. The grating coupler according to claim 1, wherein n0-n1≥0.4, and n2-n0≥0.

4.

5. The grating coupler according to claim 1, wherein d1 / d2=d3 / d4.

6. The grating coupler according to any one of claims 1 to 5, wherein: The optical film layer also satisfies at least one of the following relationships: d1 / d2≥1.5; d3 / d4 ≥ 1.5; d2≤40nm≤d1≤100nm; and d4≤40nm≤d3≤120nm.

7. The grating coupler according to claim 6, wherein d1 / d2≥3, or d3 / d4≥3.

8. The grating coupler according to claim 1, wherein At least part of the gate line has a cross section perpendicular to the second direction, and the first side wall corresponds to a side edge in the cross section, the side edge is composed of two or more straight lines and / or curves, and the first angle θ1 is the angle formed by the line connecting the two ends of the side edge relative to the plane.

9. The grating coupler according to claim 1 or 8, wherein: The at least part of the gate line further includes a top wall connected between the first side wall and the second side wall, and the top wall forms a flattened or rounded ridge.

10. The grating coupler according to any one of claims 1 to 5 and 8, wherein: The optical film layer further includes a third film layer covering the second film layer and a fourth film layer covering the third film layer, wherein the third film layer has a third refractive index n3, and the fourth film layer has a fourth refractive index n4, n3 <n2,n3<n4; The portion of the third film layer located on the first sidewall has an average thickness of d'1, and the portion of the third film layer located on the second sidewall has an average thickness of d'2, d'1>d'2; and The portion of the fourth film layer located on the first sidewall has an average thickness of d'3, and the portion of the fourth film layer located on the second sidewall has an average thickness of d'4, where d'3>d'4.

11. A diffraction optical waveguide comprising a waveguide substrate and an in-coupling grating and an out-coupling grating disposed on the waveguide substrate. The in-coupling grating is configured to couple input light carrying image information into the waveguide substrate and cause the light to propagate in the waveguide substrate along an in-coupling direction by total internal reflection. The out-coupling grating is configured to expand the pupil of the light propagating therein and couple it out of the waveguide substrate to achieve image display. in, The coupling-in grating is a grating coupler according to any one of claims 1 to 10.

12. The diffractive optical waveguide according to claim 11, wherein: The coupling-in grating is a reflective grating that receives input light that passes through the waveguide substrate and is irradiated onto it from one side of the grating body; and the second side wall faces the coupling-in direction.

13. The diffractive optical waveguide according to claim 11, wherein: The coupling-in grating is a transmission grating, which receives input light irradiated thereon from one side of the optical film layer; and the first side wall faces the coupling-in direction.

14. A display device comprising a lens, wherein the lens comprises the diffractive optical waveguide according to any one of claims 11 to 13.

15. The display device according to claim 14, wherein The display device is a near-eye display device and further comprises a frame for holding the lens close to the eye.

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