Grating coupler, optical waveguide device and display equipment

Abstract

The invention discloses a grating coupler, an optical waveguide device and display equipment. The grating coupler couples input light incident on the grating coupler into a waveguide substrate and enables the input light to be propagated in a waveguide through total reflection. The grating coupler comprises a grating body and an optical coating. The grating body comprises a plurality of unit structures arranged according to a preset grating period, the optical coating film covers the grating body and comprises one or more film layers, and the grating coupler is provided with one or more grating vectors. And the average thickness of at least one film layer in the optical coating film in a single grating period is gradually reduced along the direction of at least one grating vector. By adopting the optical film layer of which the thickness is gradually reduced along the coupling-in direction / the grating vector direction, the upstream region of the grating coupler along the coupling-in direction / the grating vector direction has higher positive first-order diffraction efficiency, and the downstream region has lower coupling-out loss, so that the comprehensive coupling-in efficiency of the grating coupler is maximized.

Description

Technical Field

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

[0002] With the development of science and technology, technologies such as augmented reality display and virtual reality display have become popular as very intelligent and portable display technologies. Optical waveguide devices combined with grating couplers are also called diffraction optical waveguides when used in these display technologies, and diffraction optical waveguide technology has become the mainstream solution for augmented reality display technology. In diffraction optical waveguides, grating couplers are used as input elements to couple incident light carrying image information into the waveguide substrate and propagate it in the waveguide through total reflection. The diffraction optical waveguide also includes an outcoupling grating used as an output element, and in some cases further includes a turning grating. The turning grating and the outcoupling grating generally have a pupil expansion function, and therefore constitute a pupil expansion grating element, wherein the turning grating is used to expand the pupil in at least one dimension and deflect the light to propagate toward the outcoupling grating, and the outcoupling grating is used to expand the pupil on the one hand, and couple the light out of the waveguide substrate on the other hand to form an outcoupling light field. The eye receives the light of the outcoupling light field, so that the image carried by the incident light can be observed.

[0003] Diffractive waveguides have the advantages of being thin, light, capable of expanding pupils, and easy to mass produce, and have become the core components of AR display devices. However, diffractive waveguides are not without disadvantages. They have problems such as insufficient brightness and uniformity deviation in image display. Therefore, it is urgent to improve the coupling efficiency and coupling uniformity of grating couplers to help overcome the above-mentioned shortcomings in diffractive waveguides.

[0004] In addition, optical waveguide devices combined with grating couplers are also used in a wide range of other applications, such as light homogenizing waveguide devices in optical machines and optical waveguide lighting devices in eye tracking equipment. The coupling efficiency of grating couplers and optical waveguide devices containing grating couplers also needs to be improved in these applications. Summary of the invention

[0005] An object of the present invention is to provide a grating coupler, an optical waveguide device and a display apparatus having the same, which at least partially overcome the problems in the prior art.

[0006] According to one aspect of the present invention, there is provided an optical waveguide device, comprising a waveguide substrate and a grating coupler disposed on the waveguide substrate, wherein the grating coupler is configured to couple input light incident thereon into the waveguide substrate and cause the input light to propagate in the waveguide substrate along a coupling direction by total reflection.

[0007] The grating coupler comprises:

[0008] A grating body comprising a plurality of unit structures arranged according to a predetermined grating period; and

[0009] an optical coating covering the grating body and comprising one or more film layers,

[0010] Wherein, along the coupling direction, the average thickness of at least one film layer in the optical coating within a single grating period gradually decreases.

[0011] In some embodiments, the average thickness varies linearly along the coupling direction.

[0012] In some other embodiments, the average thickness changes nonlinearly along the coupling direction, and the change gradient gradually increases along the coupling direction.

[0013] Advantageously, the refractive index of the at least one film layer is greater than the refractive index of the grating body.

[0014] Advantageously, the at least one film layer comprises the outermost film layer in the optical coating.

[0015] Advantageously, the optical coating comprises a lower film layer adjacent to the outermost film layer, and the refractive index of the outermost film layer is greater than the refractive index of the lower film layer.

[0016] In some embodiments, the grating body forms a blazed grating; the optical coating includes a first film layer covering the grating body and a second film layer covering the first film layer, the refractive index of the first film layer is less than the refractive index of the grating body, and the refractive index of the second film layer is greater than the refractive index of the grating body; and the at least one film layer includes the second film layer. In such an embodiment, the average thickness of the first film layer within a single grating period may be constant.

[0017] Advantageously, the grating body forms a straight-tooth grating, a slanted-tooth grating, a blazed grating or a multi-step grating.

[0018] In some embodiments, within a single grating period, the thickness of the portion of the at least one film layer located on each surface of the grating body is the same.

[0019] In some other embodiments, within a single grating period, thicknesses of portions of the at least one film layer located on at least two surfaces of the grating body are different.

[0020] In some embodiments, the average thickness may vary continuously along the coupling direction, wherein the average thickness in any two adjacent grating periods in the coupling direction are different.

[0021] In other embodiments, the average thickness can vary in steps along the coupling direction, wherein the grating coupler is divided into a plurality of equal-thickness regions along the coupling direction, and the at least one film layer of the optical coating in each equal-thickness region has the same average thickness.

[0022] Advantageously, the at least one film layer has an isopycnic line, and the isopycnic line is arc-shaped.

[0023] Advantageously, the equal thickness lines are asymmetric with respect to a central axis passing through the center of the grating body and parallel to the coupling direction.

[0024] In some embodiments, the grating coupler has at least two grating vectors, the coupling direction includes at least two sub-directions each parallel to a corresponding one of the grating vectors, and the average thickness of the at least one film layer gradually decreases along each of the sub-directions.

[0025] In some embodiments, the optical waveguide device is a diffraction optical waveguide for image display, and further includes a pupil expansion grating element, which receives light from the grating coupler and expands the pupil in at least one dimension, wherein the coupling direction is from the grating coupler toward the pupil expansion element.

[0026] According to another aspect of the present invention, there is provided a grating coupler, the grating coupler being configured to couple input light incident thereon into a waveguide substrate and cause the input light to propagate in the waveguide substrate by total reflection, the grating coupler comprising:

[0027] A grating body comprising a plurality of unit structures arranged according to a predetermined grating period; and

[0028] an optical coating covering the grating body and comprising one or more film layers,

[0029] The grating coupler has one or more grating vectors, and the average thickness of at least one film layer in the optical coating within a single grating period gradually decreases along the direction of at least one grating vector, and the diffraction of a predetermined order in the direction of the at least one grating vector is used to couple the light irradiated to the grating coupler into the waveguide substrate and make it propagate in the waveguide substrate by total reflection.

[0030] Advantageously, the average thickness varies nonlinearly along the coupling direction, and the variation gradient gradually increases along the direction of the at least one grating vector.

[0031] Advantageously, the refractive index of the at least one film layer is greater than the refractive index of the grating body.

[0032] Advantageously, the at least one film layer comprises the outermost film layer in the optical coating.

[0033] According to still another aspect of the present invention, there is provided a display device comprising the optical waveguide device as described above or the grating coupler as described above.

[0034] In some embodiments, the display device may be a near-eye display device and further include a lens and a frame for holding the lens close to the eye, the optical waveguide device or the grating coupler being disposed on the lens.

[0035] In the grating coupler according to the embodiment of the present invention, by using an optical film layer whose thickness gradually decreases along the coupling direction / grating vector direction, the upstream region of the grating coupler along the coupling direction / grating vector direction has a higher positive first-order diffraction efficiency, while the downstream region has a lower coupling-out loss, thereby maximizing the comprehensive coupling-in efficiency of the grating coupler. The optical waveguide device and the display device according to the embodiment of the present invention have the above technical advantages accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0037] Figure 1 is a schematic cross-sectional view of an example of an optical waveguide device and a grating coupler according to an embodiment of the present invention;

[0038] Figure 2 Schematic plan views of different examples of diffractive optical waveguides as examples of optical waveguide devices according to embodiments of the present invention;

[0039] Figure 3 Illustration of the outcoupling loss when light propagates by total reflection in the region of the grating coupler;

[0040] Figure 4 Schematically illustrating different examples of equal thickness lines in a grating coupler according to an embodiment of the present invention;

[0041] Figure 5 is a schematic cross-sectional view of another example of a grating coupler according to an embodiment of the present invention;

[0042] Figure 6 is a schematic cross-sectional view of another example of an optical waveguide device according to an embodiment of the present invention, wherein the optical waveguide device adopts Figure 5 The grating coupler shown;

[0043] Figure 7 and Figure 8Schematic cross-sectional views of different examples of grating couplers according to embodiments of the present invention;

[0044] Fig. 9 A curve diagram showing the coupling efficiency as a function of the field of view angle / incident angle when the film thickness varies in Data Example 1 is shown;

[0045] Fig.10 A curve diagram showing the coupling efficiency as a function of the field of view angle / incident angle when the film thickness varies in Data Example 2;

[0046] Fig.11 Different curves showing the variation of the thickness of the second film layer along the grating vector direction in Data Example 3;

[0047] Fig.12 , Fig.13 and Fig.14 The graphs showing the coupling efficiency of red light, green light and blue light as a function of the viewing angle / incident angle under different film thickness changes in Data Example 3 are shown respectively;

[0048] Fig.15 Different graphs showing the thickness of the second film layer in Data Example 4 changing along the grating vector direction; and

[0049] Fig.16 , Fig.17 and Fig.18 The graphs showing the coupling efficiency of red light, green light and blue light as a function of the viewing angle / incident angle when the film thickness varies in Data Example 4 are shown respectively. DETAILED DESCRIPTION

[0050] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It will be appreciated that the specific embodiments described herein are only used to explain the relevant inventions, rather than to limit the invention. For ease of description, only the parts related to the invention are shown in the accompanying drawings. It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments may be combined with each other.

[0051] Figure 1 Schematic cross-sectional view of an example of an optical waveguide device and a grating coupler according to an embodiment of the present invention. Figure 1 As shown in FIG. 1 (a), the optical waveguide device 1 includes a waveguide substrate 1a and a grating coupler 10 disposed on the waveguide substrate 1a. The grating coupler 10 is a grating coupler according to an embodiment of the present invention, and is configured to couple the input light L incident thereon to the optical waveguide substrate 1a. in Coupled into the waveguide substrate 1a, and propagated in the waveguide substrate 1a along the coupling direction I through total reflection. Figure 1In the middle figure (b), the grating coupler 10 includes a grating body 11 and an optical coating 12. The grating body 11 includes a plurality of unit structures 11a arranged according to a predetermined grating period P, and the optical coating 12 covers the grating body 11. The unit structure 11a includes, for example, grating lines in a one-dimensional grating and a columnar structure arranged in an array in a two-dimensional grating. Figure 1 In the example shown, the optical coating 12 includes one film layer C; however, the optical coating 12 may also include two or more film layers. According to an embodiment of the present invention, along the coupling direction, the average thickness of at least one film layer in the optical coating 12 within a single grating period P gradually decreases.

[0052] For illustrative purposes only, Figure 1 Only a few grating periods P of the grating coupler 10 are shown in the figure, and the change of the film thickness of the optical coating 12 is shown in these few grating periods P, for example, the thickness H' is significantly reduced compared to the thickness H. However, it should be understood that since the grating coupler contains a structure of a very large number of grating periods, and the film thickness of the optical coating itself is very limited, the change of the average thickness shown in the adjacent grating periods is very small, not to mention in a single grating period. In a single grating period, the reduction of the average thickness does not lead to a significant observable or measurable change in the film thickness.

[0053] In the present application, the thickness of the film layer of the optical coating 12 refers to the thickness in the normal direction of the lower surface covered by the film layer, which is usually the thickness in the normal direction of the surface of the grating body located below the film layer.

[0054] like Figure 1 The optical waveguide device 1 further comprises a subsequent optical element 20, which receives light from the grating coupler 10 and implements a predetermined function based on the received light. Along the plane where the waveguide substrate 1a of the optical waveguide device 1 is located, the direction from the grating coupler 10 toward the optical element 20 is the coupling direction I.

[0055] The grating coupler 10 has one or more grating vectors G. Generally, when designing and manufacturing an optical waveguide device, people configure the grating coupler so that the direction of one of the grating vectors is consistent or substantially consistent with the desired coupling direction I. Therefore, independently of the optical waveguide device 1, the grating coupler 10 according to an embodiment of the present invention is configured so that the average thickness of at least one film layer in the optical coating 12 within a single grating period P gradually decreases along the direction of at least one of the grating vectors G. The predetermined order of diffraction in the direction of the at least one grating vector is used to couple the light irradiated to the grating coupler into the waveguide substrate and propagate it in the waveguide substrate by total reflection.

[0056] As an example, the optical waveguide device 1 according to the embodiment of the present invention may be a diffractive optical waveguide for image display. In this case, the subsequent optical element 20 may be a pupil expansion grating element, which may be an out-coupling grating or a turning grating; the coupling direction I is the direction from the grating coupler 10 toward the pupil expansion grating element 20.

[0057] Figure 2 Plan views schematically show different examples of diffractive optical waveguides (optical waveguide devices) according to embodiments of the present invention. Figure 2 Figures (a), (b), and (c) in the middle respectively show diffraction optical waveguides 1A, 1B, and 1C, which respectively include a waveguide substrate 1a, grating couplers 10A, 10B, and 10C disposed on the waveguide substrate 1a, and an outcoupling grating 21. In the diffraction optical waveguides 1A and 1C, the outcoupling grating 21 receives light from the grating couplers 10A and 10C, and expands the pupil of the received light while coupling it out of the waveguide substrate 1a; in this case, the coupling direction I is the direction from the coupling grating couplers 10A and 10C toward the outcoupling grating 21. The diffraction optical waveguide 1B further includes a turning grating 22, which receives light from the grating coupler 10B, expands the pupil of the received light, and deflects it to propagate toward the outcoupling grating 21; in this case, the coupling direction I is the direction from the coupling grating couplers 10A and 10C toward the turning grating.

[0058] In addition, in the examples shown in Figures (a) and (b), the grating couplers 10A and 10B in the diffraction optical waveguides 1A and 1B are one-dimensional gratings and have a single grating vector G, and the positive first-order diffraction in the direction of the grating vector G is used to couple light from the outside into the waveguide substrate 1a, and the coupling direction I can be consistent with the direction of the grating vector G. In the example shown in Figure (c), the grating coupler 10C in the diffraction optical waveguide 1C is a two-dimensional grating and has three grating vectors G1, G2 and G3, wherein the light incident on the grating coupler 10C is coupled into the waveguide substrate 1a through the positive first-order diffraction in the direction of the grating vectors G1, G2 and G3; at this time, the coupling direction includes sub-directions I1, I2 and I3, and the sub-directions I1, I2 and I3 can be consistent with the directions of the grating vectors G1, G2 and G3, respectively. It should be understood that the number of the above grating vectors is only exemplary and not restrictive. For example, in other examples not shown, the grating coupler according to the embodiment of the present invention may be a two-dimensional grating having two grating vectors perpendicular to each other.

[0059] The grating coupler and the optical waveguide device according to the embodiments of the present invention can advantageously improve the comprehensive coupling efficiency of light.

[0060] Specifically, after the input light is coupled into the waveguide substrate 1a via the grating coupler 10, the light is totally reflected in the waveguide substrate 1a and re-irradiated onto the grating coupler 10. Due to the microstructure of the grating coupler 10 on the surface of the waveguide substrate 1a, part of the light is totally reflected, while part of the light is directly coupled out or coupled out from the opposite surface after diffraction and lost (i.e., coupling loss). For ease of understanding, Figure 3 The outcoupling loss of light when it propagates by total reflection in the region of the grating coupler is illustrated, where the outcoupling loss is Figure 3 As shown by the dashed arrow in the middle, when light propagates through the grating coupler 10 by total reflection, the number of reflections at different positions of the grating coupler 10 is different, so the coupling loss at these positions is also different. Figure 3 The dashed circles indicated by R1, R2, R3, and R4 in FIG. 1 respectively represent the light spot footprints of the first to fourth reflections on the waveguide surface where the grating coupler 10 is located after the light is coupled into the waveguide substrate 1a. Figure 3 As shown, in the area of ​​the grating coupler 10 located downstream along the coupling direction I, the number of light reflections is greater, so the coupling loss is greater. At the same time, the diffraction efficiency of the specific order (e.g., positive first order) diffraction of the grating coupler 10 used to achieve the coupling function is often positively correlated with the coupling loss, that is, when the diffraction efficiency is improved, the coupling loss of light in the grating area is also improved. Existing grating couplers usually have a single grating structure, and while improving the diffraction efficiency of a specific order, the coupling loss is often also high. Different from the prior art, in the grating coupler and the optical waveguide device according to the embodiment of the present invention, by using an optical film layer whose thickness gradually decreases along the coupling direction / grating vector direction, the upstream area of ​​the grating coupler 10 along the coupling direction / grating vector direction has a higher specific order (e.g., positive first order) diffraction efficiency, and the downstream area has a lower coupling loss, thereby maximizing the comprehensive coupling efficiency of the grating coupler.

[0061] Preferably, the refractive index of the at least one film layer of the optical coating 12 is greater than the refractive index of the grating body 11 .

[0062] In some embodiments of the present invention, the single-period average thickness (i.e., the average thickness within a single grating period) of at least one film layer of the optical coating 12 of the grating coupler 10 varies linearly along the coupling direction I, wherein the gradient of the change is the same at different positions along the coupling direction I.

[0063] In other embodiments of the present invention, the single-period average thickness (i.e., the average thickness within a single grating period) of at least one film layer of the optical coating 12 of the grating coupler 10 varies nonlinearly along the coupling direction I, wherein the gradient of the variation varies at different positions along the coupling direction I. Preferably, the variation gradient of the single-period average thickness gradually increases along the coupling direction. This can help to more significantly suppress the outcoupling loss in the region of the grating coupler 10 located downstream along the coupling direction, thereby improving the coupling efficiency.

[0064] According to different embodiments of the present invention, the single-period average thickness of at least one film layer of the optical coating 12 can change continuously or in steps along the coupling direction, wherein in the case of continuous change, the average thicknesses in any two adjacent grating periods in the coupling direction are different, and in the case of step-by-step change, the grating coupler 10 is divided into a plurality of equal-thickness regions along the coupling direction I / grating vector G, and the film layer in each equal-thickness region has the same average thickness.

[0065] In the grating coupler 10 according to the embodiment of the present invention, the change of the single-period average thickness of at least one film layer of the optical coating 12 can also have more characteristics to provide more flexible control means and more detailed control effects. As an example, Figure 4 In the figure, equal thickness lines are used to represent some possible situations of the variation of the film thickness in the grating coupler according to the embodiment of the present invention.

[0066] Figure 4 The dotted line indicated by the reference sign “ct” is the equal thickness line of the film layer with a gradual thickness in the optical coating 12 , and the center line aa represents the center axis passing through the center of the grating coupler 10 and parallel to the grating vector G. Figure 4 In the example shown in the middle figure (a), the film layer has a straight line of equal thickness ct, which means that the thickness of the film layer simply changes / decreases gradually along one direction (eg, the direction of the grating vector G). Figure 4 In the examples shown in Figures (b) and (c), the equal thickness lines ct are arc-shaped, indicating that the thickness of the film layer can also vary in the direction perpendicular to the grating vector G. In this way, the degree of freedom of modulation of the structure of the grating coupler 10 is increased, and the flexibility and effect of regulating the coupling efficiency and uniformity are correspondingly improved. Unlike the case in Figure (b) where the equal thickness lines ct are symmetrical with respect to the central axis aa, in the grating coupler 10 shown in Figure (c), the equal thickness lines ct are asymmetric with respect to the central axis aa. This asymmetric design is suitable for situations where the light source (such as an optical machine) is tilted relative to the grating coupler 10, causing the functional version of the input light irradiated on the grating coupler 10 to be asymmetric with respect to the central axis aa. Figure 4The middle figure (d) is intended to indicate that the thickness of the film layer of the optical coating 12 in the grating coupler 10 composed of a two-dimensional grating can be gradually reduced along the direction of at least two grating vectors of the two-dimensional grating. Specifically, figure (d) shows that corresponding to the three grating vectors G1, G2 and G3 of the grating coupler 10, the coupling direction I includes three sub-directions I1, I2 and I3 each parallel to a corresponding grating vector, and the average thickness of the film layer gradually decreases along each sub-direction I1, I2 and I3.

[0067] Return to reference Figure 1 , Figure 1 In the example shown, the grating body 11 in the grating coupler 10 is a straight tooth grating, and the optical coating 12 includes a single film layer and covers the grating body 11 only in a direction perpendicular to the plane PL where the plurality of unit structures 11a of the grating body 11 are located. However, it should be understood that Figure 1 The above is only an example. In the grating coupler according to the embodiment of the present invention, the grating body and the optical coating may have different structures and combinations thereof. For example, the grating body may also have a slanted grating (see Figure 7 Middle figure (b), Figure 8 Figure (a)), blazed grating (see Figure 5 ) or multi-step grating structure (see Figure 8 Figure (b) in the figure). The optical coating may include more than two film layers. The single-period average thickness of multiple or all film layers of the optical coating may gradually decrease along the coupling direction / grating vector direction.

[0068] Preferably, the average single-period thickness of the outermost film layer in the optical coating gradually decreases along the coupling direction / grating vector direction. Through simulation and experiments, the gradual decrease in the average thickness of the outermost film layer has a significant effect on improving the coupling efficiency. Advantageously, the film layers other than the outermost film layer can each have a constant average single-period thickness.

[0069] In the case where the optical coating includes an underlying film layer adjacent to the outermost film layer, it is preferred that the refractive index of the outermost film layer is greater than the refractive index of the underlying film layer.

[0070] As an example, Figure 5 FIG. 1 shows a grating coupler 10' according to an embodiment of the present invention. Figure 5As shown in the figure (a), in the grating coupler 10', the grating body 11' forms a blazed grating. Specifically, the grating body 11' includes a plurality of grating lines (unit structures) 11a', and the grating line 11a' includes a first side wall S1 and a second side wall S2, and the angle θ1 (i.e., the blaze angle) formed by the first side wall S1 relative to the plane PL where the grating body 11' is located is smaller than the angle θ2 formed by the second side wall S2 relative to the plane PL. The optical coating 12' includes a first film layer C1 covering the grating body 11' and a second film layer C2 covering the first film layer C1, and the refractive index n1 of the first film layer C1 is smaller than the refractive index n0 of the grating body 11', and the refractive index n2 of the second film layer C2 is greater than the refractive index of the grating body 11'. According to a preferred embodiment of the present invention, the average thickness of a single period of the second film layer C2 gradually decreases along the direction of the grating vector G (i.e., the direction perpendicular to the grating line 11a).

[0071] According to some embodiments of the present invention, the first film layer C1 and the second film layer C2 may have different thicknesses on the first side wall S1 and the second side wall S2. Figure 5 As shown in the middle figure (b), the portion of the first film layer C1 located on the first side wall S1 has a thickness of d1, and the portion of the first film layer C1 located on the second side wall S2 has a thickness of d2; and the portion of the second film layer C2 located on the first side wall S1 has a thickness of d3, and the portion of the second film layer C2 located on the second side wall S2 has a thickness of d4. Preferably, the optical coating 12' is constructed to satisfy: d1>d2, and d3>d4.

[0072] In such an embodiment, along the direction of the grating vector G, the thickness d2 of the second film layer C2 in one grating period P may be smaller than the thickness d1 in the next grating period. It should be understood that this does not conflict with the average thickness of the second film layer C2 in a single grating period gradually decreasing along the grating period direction.

[0073] Preferably, along the direction of the grating vector G, the first film layer C1 has a constant single-period average thickness.

[0074] Figure 6 Shows the use of Figure 5 The optical waveguide device 1' of the grating coupler 10' is shown. According to a preferred embodiment of the present invention, Figure 6 As shown, the grating coupler 10' is arranged in the optical waveguide device 1' so that the second side wall S2 of the grating body 11' faces the coupling direction I, and the input light L in The light is incident on the grating coupler 10' from the bottom surface of the grating body 11'.

[0075] In addition, depending on the coating method, the coverage and thickness of the film layer in the optical coating on the grating body will have different characteristics. For example, the film layer formed by atomic layer deposition (ALD) technology will evenly cover the structural surface of the grating body, so that within a single grating period, the thickness of the film layer on each surface of the grating body is the same, such as Figure 7 As shown in . For another example, the coverage of the film layer formed by chemical vapor deposition (CVD) and physical vapor deposition (PVD) technology on the grating body will show certain directional differences, wherein within a single grating period, the thickness of the film layer located on at least two surfaces of the grating body is different. Figure 8 In the example shown in , the thickness of the film layer on a part of the surface of the grating body (such as the surface indicated by the curved arrow) is 0. In the grating coupler according to the embodiment of the present invention, it is preferred to use an optical coating in which the film layer has the above-mentioned directivity difference.

[0076] The technical advantages of the grating coupler and the optical waveguide device according to the embodiments of the present invention will be described below through data examples.

[0077] (Data Example 1)

[0078] In data example 1, based on reference Figure 1 The structure of the grating coupler and the diffraction optical waveguide including the grating coupler are given, through simulation calculation, the coupling efficiency and uniformity indicators corresponding to different changes in the film thickness of the optical coating under the first set of parameter conditions.

[0079] Specifically, Data Example 1 is based on the following structure and use of a grating coupler: the grating coupler has a structure of a straight tooth grating (a one-dimensional grating), is used as a reflective grating in a diffraction optical waveguide (the grating coupler receives input light irradiated thereon from the bottom surface side of the grating body through the waveguide substrate), and the optical coating includes a single film layer and as Figure 1 Shown is coverage only on the top surface of the grating body.

[0080] The first set of parameter conditions mentioned above includes:

[0081] (1) Input light wavelength λ = 522nm (green light), field of view angle range 20° × 16°;

[0082] (2) The refractive index of the waveguide substrate is 1.9 and the thickness is 0.7 mm;

[0083] (3) The diameter of the grating coupler is 4 mm, the grating period P = 330 nm, the grating line height is 230 nm, and the duty cycle is 0.5; and

[0084] (4) The refractive index of the grating body is n0=1.9, and the refractive index of the optical coating layer is 2.5.

[0085] Data Example 1 compares and analyzes the thickness changes of the following optical coatings:

[0086] Single thickness: The thickness of the film layer is kept at 80nm along the grating vector direction;

[0087] Gradient film thickness - incremental: the thickness of the film layer gradually changes from 50nm to 105nm over a span of 4mm along the grating vector direction; and

[0088] Gradient film thickness - decreasing: The thickness of the film layer gradually changes from 105nm to 50nm over a span of 4mm along the grating vector direction.

[0089] The above “gradual film thickness-decreasing” corresponds to the case of the grating coupler according to the embodiment of the present invention.

[0090] The coupling efficiency and uniformity of the grating coupler calculated under the above different film thickness changes are shown in Table 1:

[0091] [Table 1]

[0092] Coupling efficiency Uniformity Single thickness 0.189 0.297 Gradient film thickness-increasing 0.182 0.227 Gradient film thickness-decreasing 0.209 0.499

[0093] In this application, uniformity is characterized by the ratio of the minimum value to the maximum value of the coupling efficiency of the grating coupler in the range of the incident angle / field of view (FOV) of the input light carrying image information for the diffraction optical waveguide, that is, uniformity = minimum coupling efficiency / maximum coupling efficiency. The larger the uniformity value, the better the uniformity.

[0094] Accordingly, Fig. 9 A curve diagram showing the coupling efficiency as a function of the field of view angle / incident angle when the film thickness varies in Data Example 1 is shown.

[0095] From Table 1 and Fig. 9 It can be seen that the coupling efficiency obtained in the "gradual film thickness-decreasing" case is 20.9%, and the uniformity is 49.9%. Compared with the coupling efficiency of 18.9% and uniformity of 29.7% obtained in the "single film thickness" case and the coupling efficiency of 18.2% and uniformity of 22.7% obtained in the "gradual film thickness-increasing" case, the coupling efficiency and uniformity are improved, among which the improvement rate of coupling efficiency exceeds 10%, and the improvement of uniformity is more significant, exceeding 60%.

[0096] (Data Example 2)

[0097] Data Example 2 is similar to Data Example 1, where the reference Figure 1The structure of the grating coupler and the diffraction optical waveguide including the grating coupler are given, through simulation calculation, the coupling efficiency and uniformity indicators corresponding to different changes in the film thickness of the optical coating under the second set of parameter conditions.

[0098] The structure and usage of the grating coupler on which Data Example 2 is based are the same as those in Data Example 1 and will not be repeated here.

[0099] The second set of parameter conditions mentioned above includes:

[0100] (1) Input light wavelength λ = 530 nm (green light), field of view angle range 20° × 16°;

[0101] (2) The refractive index of the waveguide substrate is 1.9 and the thickness is 0.7 mm;

[0102] (3) The diameter of the grating coupler is 4 mm, the grating period P = 360 nm, the grating line height is 240 nm, and the duty cycle is 0.4; and

[0103] (4) The refractive index of the grating body is n0=1.9, and the refractive index of the optical coating layer is 2.5.

[0104] Data Example 2 compares and analyzes the thickness changes of the following optical coatings:

[0105] Single thickness: The thickness of the film layer is kept at 100nm along the grating vector direction;

[0106] Gradient film thickness - incremental: the thickness of the film layer gradually changes from 70nm to 130nm over a span of 4mm along the grating vector direction; and

[0107] Gradient film thickness - decreasing: The thickness of the film layer gradually changes from 130nm to 70nm over a span of 4mm along the grating vector direction.

[0108] The above “gradual film thickness-decreasing” corresponds to the case of the grating coupler according to the embodiment of the present invention.

[0109] The coupling efficiency and uniformity of the grating coupler calculated under the above different film thickness changes are shown in Table 2:

[0110] [Table 2]

[0111] Coupling efficiency Uniformity Single thickness 0.167 0.403 Gradient film thickness-increasing 0.166 0.304 Gradient film thickness-decreasing 0.17.9 0.490

[0112] Accordingly, Fig.10 A curve diagram showing the coupling efficiency as a function of the field of view angle / incident angle when the film thickness varies in Data Example 2 is shown.

[0113] From Table 2 and Fig.10It can be seen that the coupling efficiency obtained in the "gradual film thickness-decreasing" case is 17.9%, and the uniformity is 49.0%. Compared with the coupling efficiency of 16.7% and uniformity of 40.3% obtained in the "single film thickness" case and the coupling efficiency of 16.6% and uniformity of 30.4% obtained in the "gradual film thickness-increasing" case, the coupling efficiency and uniformity are improved, among which the improvement ratio of coupling efficiency exceeds 7%, and the improvement ratio of uniformity exceeds 20%.

[0114] (Data Example 3)

[0115] In data example 3, based on reference Figure 5 The structure of the grating coupler and the diffraction optical waveguide including the grating coupler are shown, and the coupling efficiency and uniformity indicators corresponding to different changes in the film thickness of the optical coating under the third set of parameter conditions are given through simulation calculation.

[0116] Specifically, Data Example 3 is based on the following structure and usage of the grating coupler: The grating coupler has Figure 5 The structure of the blazed grating (a one-dimensional grating) shown in the figure is used as a reflective grating in a diffraction optical waveguide (the grating coupler receives input light irradiated thereon from the bottom surface side of the grating body through the waveguide substrate), and the optical coating includes a first film layer covering the grating body and a second film layer covering the first film layer.

[0117] The third set of parameter conditions mentioned above includes:

[0118] (1) In the input light, the wavelength of red light is λ1=624nm, the wavelength of green light is λ2=522nm, the wavelength of blue light is λ3=455nm, and the field of view (FOV) range is 20°×20°;

[0119] (2) The refractive index of the waveguide substrate is 1.9 and the thickness is 0.7 mm;

[0120] (3) The diameter of the grating coupler is 4 mm, the grating period P = 390 nm, the grating line height is 170 nm, and the blaze angle θ1 = 25.7°;

[0121] (4) the refractive index of the grating body n0=1.9, the refractive index of the first film layer n1=1.45, and the refractive index of the second film layer n2=2.5; and

[0122] (5) The thickness of the first film layer is 75 nm.

[0123] Data Example 3 compares and analyzes the thickness changes of the second film layer of the following optical coatings:

[0124] Single thickness: The thickness of the second film layer is kept at 80nm along the grating vector direction;

[0125] Linearly graded thickness: the thickness of the second film layer is linearly graded from 115nm to 55nm over a span of 4mm along the grating vector direction; and

[0126] Non-linear gradient thickness: The thickness of the second film layer is non-linearly graded from 100nm to 45nm over a span of 4mm along the grating vector direction.

[0127] In order to intuitively display the above-mentioned different film thickness changes, Fig.11 The corresponding graph showing the thickness of the second film layer changing along the grating vector direction.

[0128] The above “linearly gradient thickness” and “non-linearly gradient thickness” both belong to the case of film thickness variation in the grating coupler according to the embodiment of the present invention.

[0129] The coupling efficiency and uniformity of the grating coupler calculated under different changes in the thickness of the second film layer are shown in Table 3:

[0130] [Table 3]

[0131] R - Efficiency G-Efficiency B-Efficiency R-Uniformity G-Uniformity B-Uniformity Single thickness 0.378 0.317 0.151 0.755 0.597 0.409 Linear gradient thickness 0.386 0.338 0.179 0.886 0.695 0.507 Non-linear gradient thickness 0.394 0.347 0.198 0.835 0.770 0.564

[0132] In Table 3, R, G, and B represent red light, green light, and blue light, respectively.

[0133] at the same time, Fig.12 , Fig.13 and Fig.14 The graphs showing the coupling efficiency of red light, green light and blue light as a function of the viewing angle / incident angle when the thickness of the film layer changes in Data Example 3 are shown respectively.

[0134] From Table 3 and Figures 11 to 14 It can be seen that under the "linear gradient thickness" condition, the red light coupling efficiency is 38.6%, the red light uniformity is 88.6%, the green light coupling efficiency is 33.8%, the green light uniformity is 69.5%, the blue light coupling efficiency is 17.9%, and the blue light uniformity is 50.7%; compared with the red light coupling efficiency of 37.8%, red light uniformity of 75.5%, green light coupling efficiency of 31.7%, green light uniformity of 59.7%, blue light coupling efficiency of 15.1%, and blue light uniformity of 40.9% obtained under the "single film thickness" condition, the coupling efficiency and uniformity have been significantly improved.

[0135] From Table 3 and Figures 11 to 14It can also be seen that under the "non-linear gradient thickness" condition, the red light coupling efficiency is 39.4%, the red light uniformity is 83.5%, the green light coupling efficiency is 34.7%, the green light uniformity is 77%, the blue light coupling efficiency is 19.8%, and the blue light uniformity is 56.4%; except for a slight decrease in red light uniformity, compared with the "linear gradient thickness", the coupling efficiency and uniformity under the "non-linear gradient thickness" condition are further improved as a whole.

[0136] (Data Example 4)

[0137] Data Example 4 is similar to Data Example 3, where the reference Figure 5 The structure of the grating coupler and the diffraction optical waveguide including the grating coupler are shown, and the coupling efficiency and uniformity indicators corresponding to different changes in the film thickness of the optical coating under the fourth set of parameter conditions are given through simulation calculation.

[0138] The structure and usage of the grating coupler on which Data Example 4 is based are the same as those in Data Example 3 and will not be repeated here.

[0139] The fourth group of parameter conditions mentioned above includes:

[0140] (1) In the input light, the wavelength of red light λ1=624nm, the wavelength of green light λ2=522nm, the wavelength of blue light λ3=455nm, and the field of view (FOV) range is 20°×20°; the optical machine for projecting the input light is Figure 1 The xz plane is tilted 8 degrees relative to the z-axis (the normal direction of the waveguide substrate)

[0141] (2) The refractive index of the waveguide substrate is 1.9 and the thickness is 0.7 mm;

[0142] (3) The diameter of the grating coupler is 4 mm, the grating period P = 420 nm, the grating line height is 160 nm, and the blaze angle θ1 = 23.8°;

[0143] (4) the refractive index of the grating body n0=1.9, the refractive index of the first film layer n1=1.45, and the refractive index of the second film layer n2=2.5; and

[0144] (5) The thickness of the first film layer is 65 nm.

[0145] Data Example 4 compares and analyzes the thickness changes of the second film layer of the following optical coatings:

[0146] Single thickness: The thickness of the second film layer is kept at 75nm along the grating vector direction;

[0147] Linearly graded thickness: the thickness of the second film layer is linearly graded from 100nm to 55nm over a span of 4mm along the grating vector direction; and

[0148] Non-linear gradient thickness: The thickness of the second film layer is non-linearly graded from 95nm to 40nm over a span of 4mm along the grating vector direction.

[0149] In order to intuitively display the above-mentioned different film thickness changes, Fig.15 The corresponding graph showing the thickness of the second film layer changing along the grating vector direction.

[0150] The above “linearly gradient thickness” and “non-linearly gradient thickness” both belong to the case of film thickness variation in the grating coupler according to the embodiment of the present invention.

[0151] The coupling efficiency and uniformity of the grating coupler calculated under different changes in the thickness of the second film layer are shown in Table 4:

[0152] [Table 4]

[0153] R - Efficiency G-Efficiency B-Efficiency R-Uniformity G-Uniformity B-Uniformity Single thickness 0.332 0.303 0.198 0.807 0.619 0.341 Linear gradient thickness 0.340 0.323 0.234 0.786 0.737 0.433 Non-linear gradient thickness 0.348 0.347 0.257 0.735 0.843 0.498

[0154] In Table 3, R, G, and B represent red light, green light, and blue light, respectively.

[0155] at the same time, Fig.16 , Fig.17 and Fig.18 The graphs showing the coupling efficiency of red light, green light and blue light as a function of the viewing angle / incident angle when the thickness of the film layer changes in Data Example 4 are shown respectively.

[0156] From Table 4 and Figures 15 to 18 It can be seen that under the "linear gradient thickness" condition, the red light coupling efficiency is 34.0%, the red light uniformity is 78.6%, the green light coupling efficiency is 32.3%, the green light uniformity is 73.7%, the blue light coupling efficiency is 23.4%, and the blue light uniformity is 43.3%; compared with the red light coupling efficiency of 37.8%, red light uniformity of 75%, green light coupling efficiency of 31.7%, green light uniformity of 59.7%, blue light coupling efficiency of 15.1%, and blue light uniformity of 40.9% obtained under the "single film thickness" condition, the red light performance is similar, while the coupling efficiency and uniformity of green and blue light are significantly improved.

[0157] From Table 4 and Figures 15 to 18 It can also be seen that under the “non-linear gradient thickness” condition, the red light coupling efficiency is 34.8%, the red light uniformity is 73.5%, the green light coupling efficiency is 34.7%, the green light uniformity is 84.3%, the blue light coupling efficiency is 25.7%, and the blue light uniformity is 49.8%; except for a slight decrease in red light uniformity, compared with the “linear gradient thickness” condition, the coupling efficiency and uniformity of green and blue light are further improved under the “non-linear gradient thickness” condition.

[0158] The grating coupler and the optical waveguide device according to the embodiments of the present invention are described above. According to the embodiments of the present invention, a display device is also provided, which includes the optical waveguide device described above or the grating coupler described above. The display device is preferably a near-eye display device, and further includes a lens and a frame for holding the lens close to the eye, and the optical waveguide device or the grating coupler is arranged on the lens.

[0159] 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 a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept. For example, the above features are replaced with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An optical waveguide device, comprising a waveguide substrate and a grating coupler disposed on the waveguide substrate, wherein the grating coupler is configured to couple input light incident thereon into the waveguide substrate and cause the input light to propagate in the waveguide substrate along a coupling direction by total reflection, in, The grating coupler comprises: A grating body comprising a plurality of unit structures arranged according to a predetermined grating period; and an optical coating covering the grating body and comprising one or more film layers, Wherein, along the coupling direction, the average thickness of at least one film layer in the optical coating within a single grating period gradually decreases.

2. The optical waveguide device according to claim 1, wherein: The average thickness varies linearly along the coupling direction.

3. The optical waveguide device according to claim 1, wherein: The average thickness changes nonlinearly along the coupling direction, and the change gradient increases gradually along the coupling direction.

4. The optical waveguide device according to claim 1, wherein: The refractive index of the at least one film layer is greater than the refractive index of the grating body.

5. The optical waveguide device according to any one of claims 1 to 4, wherein: The at least one film layer comprises an outermost film layer in the optical coating.

6. The optical waveguide device according to claim 5, wherein: The optical coating includes a lower film layer adjacent to the outermost film layer, and the refractive index of the outermost film layer is greater than the refractive index of the lower film layer.

7. The optical waveguide device according to claim 5, wherein: The grating body forms a blazed grating; The optical coating comprises a first film layer covering the grating body and a second film layer covering the first film layer, the refractive index of the first film layer is smaller than the refractive index of the grating body, and the refractive index of the second film layer is larger than the refractive index of the grating body; and The at least one film layer includes the second film layer.

8. The optical waveguide device according to claim 7, wherein: The average thickness of the first film layer within a single grating period is constant.

9. The optical waveguide device according to claim 5, wherein: The grating body forms a straight tooth grating, a slanted tooth grating, a blazed grating or a multi-step grating.

10. The optical waveguide device according to claim 1 or 9, wherein: In a single grating period, the thickness of the portion of the at least one film layer located on each surface of the grating body is the same; or Within a single grating period, thicknesses of portions of the at least one film layer located on at least two surfaces of the grating body are different.

11. The optical waveguide device according to claim 1, wherein: The average thickness changes continuously along the coupling direction, wherein the average thickness in any two adjacent grating periods in the coupling direction are different.

12. The optical waveguide device according to claim 1, wherein: The average thickness changes stepwise along the coupling direction, wherein the grating coupler is divided into a plurality of equal-thickness regions along the coupling direction, and the at least one film layer of the optical coating in each equal-thickness region has the same average thickness.

13. The optical waveguide device according to claim 11 or 12, wherein: The at least one film layer has an equal thickness line, and the equal thickness line is arc-shaped.

14. The optical waveguide device according to claim 13, wherein: The equal thickness lines are asymmetric with respect to a central axis passing through the center of the grating body and parallel to the coupling direction.

15. The optical waveguide device according to claim 1 or 5, wherein: The grating coupler has at least two grating vectors, the coupling direction includes at least two sub-directions each parallel to a corresponding one of the grating vectors, and the average thickness of the at least one film layer gradually decreases along each of the sub-directions.

16. The optical waveguide device according to claim 1, wherein: The optical waveguide device is a diffraction optical waveguide for image display, and further comprises a pupil expansion grating element, which receives light from the grating coupler and expands the pupil in at least one dimension, wherein the coupling direction is the direction from the grating coupler toward the pupil expansion element.

17. A grating coupler, the grating coupler being configured to couple input light incident thereon into a waveguide substrate and propagate the input light in the waveguide substrate by total reflection, the grating coupler comprising: A grating body, comprising a plurality of unit structures arranged according to a predetermined grating period; and an optical coating covering the grating body and comprising one or more film layers, The grating coupler has one or more grating vectors, and the average thickness of at least one film layer in the optical coating within a single grating period gradually decreases along the direction of at least one grating vector, and the diffraction of a predetermined order in the direction of the at least one grating vector is used to couple the light irradiated to the grating coupler into the waveguide substrate and make it propagate in the waveguide substrate by total reflection.

18. The grating coupler of claim 17, wherein: The average thickness changes nonlinearly along the coupling direction, and the change gradient gradually increases along the direction of the at least one grating vector.

19. The grating coupler of claim 17, wherein: The refractive index of the at least one film layer is greater than the refractive index of the grating body.

20. The grating coupler according to any one of claims 17 to 19, wherein: The at least one film layer comprises an outermost film layer in the optical coating.

21. A display device comprising the optical waveguide device according to any one of claims 1 to 16 or the grating coupler according to any one of claims 17 to 20.

22. The display device according to claim 21, wherein: The display device is a near-eye display device and further includes a lens and a frame for holding the lens close to the eye, the optical waveguide device or the grating coupler being arranged on the lens.

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