Grating coupler, optical waveguide device, and display device

Abstract

The application discloses a grating coupler, an optical waveguide device and a display device. The grating coupler couples input light incident thereon into a waveguide substrate and makes it propagate in the waveguide by total reflection, and comprises a grating body and an optical coating. The grating body comprises a plurality of unit structures arranged according to a predetermined grating period, and the optical coating covers the grating body and comprises 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 gradually decreases in the direction of the at least one grating vector within a single grating period. By adopting the optical film layer with the thickness gradually decreasing in the coupling-in direction / grating vector direction, the grating coupler has a higher positive first-order diffraction efficiency in the upstream area of the coupling-in direction / grating vector direction and a lower coupling-out loss in the downstream area, so that the overall 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 same. Background Art

[0002] With the advancement of science and technology, technologies such as augmented reality (AR) and virtual reality (VR) displays have become increasingly popular as highly intelligent and portable display technologies. Optical waveguide devices incorporating grating couplers are also known as diffractive waveguides when used in these display technologies, and diffractive waveguide technology has become a mainstream approach for AR displays. In a diffractive waveguide, the grating coupler serves as the input element, coupling incident light carrying image information into the waveguide substrate and allowing it to propagate through the waveguide via total internal reflection. A diffractive waveguide also includes an output grating, and in some cases, a deflection grating. Both the deflection grating and the deflection grating generally have pupil expansion functions, forming a pupil expansion grating element. The deflection grating dilates the pupil in at least one dimension and deflects light toward the deflection grating. The deflection grating not only expands the pupil but also couples light out of the waveguide substrate, forming an outcoupling light field. The eye receives light from the decoupled light field, allowing it to observe the image carried by the incident light.

[0003] Diffractive waveguides, with their advantages of lightweight, strong pupil expansion, and ease of mass production, have become a core component in AR display devices. However, they are not without drawbacks, including insufficient brightness and uneven image display. Therefore, there is an urgent need to improve the coupling efficiency and uniformity of grating couplers to overcome these shortcomings.

[0004] In addition, optical waveguide devices combined with grating couplers are also used in a wide range of other applications, such as light-uniform 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, an optical waveguide device is provided, 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 a coupling-in direction within the waveguide substrate by total internal 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 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.

[0016] In some embodiments, the grating body forms a blazed grating; the optical coating includes a first film layer overlying the grating body and a second film layer overlying the first film layer, wherein the first film layer has a refractive index less than that of the grating body, and the second film layer has a refractive index greater than that of the grating body; and the at least one film layer includes the second film layer. In such embodiments, 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 skew tooth grating, a blazed grating or a multi-step grating.

[0018] In some embodiments, within a single grating period, portions of the at least one film layer located on respective surfaces of the grating body have the same thickness.

[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 is different.

[0021] In other embodiments, the average thickness can vary in a step-wise manner 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 isopach, and the isopach is arc-shaped.

[0023] Advantageously, the isopach 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 configured to couple input light incident thereon into a waveguide substrate and cause the input light to propagate in the waveguide substrate by total internal 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. The predetermined order of diffraction in the direction of the at least one grating vector is used to couple the light irradiated by the grating coupler into the waveguide substrate and cause it to propagate in the waveguide substrate by total internal 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 yet another aspect of the present invention, there is provided a display device comprising the optical waveguide device 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 an embodiment of the present invention, by employing an optical film layer whose thickness gradually decreases along the in-coupling direction / grating vector direction, the upstream region of the grating coupler along the in-coupling direction / grating vector direction has a high positive first-order diffraction efficiency, while the downstream region has a low out-coupling loss, thereby maximizing the overall in-coupling efficiency of the grating coupler. The optical waveguide device and display device according to the embodiment of the present invention accordingly possess the aforementioned technical advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] 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:

[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 diffraction 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 internal 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 FIG. 1 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] Figure 9 A graph showing the coupling efficiency versus field angle / incident angle for different film thickness variations in Data Example 1 is shown;

[0045] Figure 10 A graph showing the coupling efficiency versus field angle / incident angle for different film thickness variations in Data Example 2 is shown;

[0046] Figure 11 Different graphs showing the thickness of the second film layer in Data Example 3 changing along the grating vector direction;

[0047] Figure 12 、 Figure 13 and Figure 14 Graphs showing how the coupling efficiency of red light, green light, and blue light changes with the field of view angle / incident angle under different film thickness variations in Data Example 3 are shown;

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

[0049] Figure 16 、 Figure 17 and Figure 18 Graphs showing how the coupling efficiency of red light, green light, and blue light changes with the field of view angle / incident angle when the film thickness varies in Data Example 4 are shown. DETAILED DESCRIPTION

[0050] 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.

[0051] Figure 1 FIG 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. Figure 1 As shown in FIG. (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, which is configured to couple the input light L incident thereon to the optical waveguide device 1. in Coupled into the waveguide substrate 1a, and propagated in the waveguide substrate 1a along the coupling direction I through total reflection. Figure 1In 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 structures 11a include, for example, grating lines in a one-dimensional grating and columnar structures arranged in an array in a two-dimensional grating. Figure 1 In the illustrated example, 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, the average thickness of at least one film layer in the optical coating 12 within a single grating period P gradually decreases along the coupling direction.

[0052] For illustrative purposes only, Figure 1 Only a few grating periods P of the grating coupler 10 are shown, and within these few grating periods P, the variation in the film thickness of the optical coating 12 is shown, for example, thickness H' being significantly reduced compared to thickness H. However, it should be understood that, because the grating coupler includes a structure with a very large number of grating periods, and the film thickness of the optical coating itself is very limited, the variation in average thickness shown in the reduction within adjacent grating periods is very small, let alone within a single grating period. Within a single grating period, the reduction in average thickness does not result in a significant observable or measurable variation in 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 underlying 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 includes an optical element 20 that receives light from the grating coupler 10 and performs a predetermined function based on the received light. The direction from the grating coupler 10 toward the optical element 20 along the plane of the waveguide substrate 1a of the optical waveguide device 1 is the coupling-in direction I.

[0055] The grating coupler 10 has one or more grating vectors G. When designing and manufacturing optical waveguide devices, the grating coupler is typically configured so that the direction of one of the grating vectors coincides with, or substantially coincides with, the desired coupling direction I. Therefore, discussed 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. Diffraction of a predetermined order in the direction of the at least one grating vector is used to couple light incident on the grating coupler into the waveguide substrate, causing it to propagate within the waveguide substrate via total internal reflection.

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

[0057] Figure 2 Plan views schematically showing different examples of diffractive optical waveguides (optical waveguide devices) according to embodiments of the present invention. Figure 2 Figures (a), (b), and (c) illustrate diffractive optical waveguides 1A, 1B, and 1C, respectively. Each of these includes a waveguide substrate 1a, grating couplers 10A, 10B, and 10C disposed on the waveguide substrate 1a, and an outcoupling grating 21. In diffractive optical waveguides 1A and 1C, the outcoupling grating 21 receives light from the grating couplers 10A and 10C, expands the pupil of the received light, and couples it out of the waveguide substrate 1a. In this case, the coupling direction I is from the coupling grating couplers 10A and 10C toward the outcoupling grating 21. The diffractive 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 toward the outcoupling grating 21. In this case, the coupling direction I is from the coupling grating couplers 10A and 10C toward the turning grating.

[0058] Furthermore, in the examples shown in Figures (a) and (b), the grating couplers 10A and 10B in the diffractive optical waveguides 1A and 1B are one-dimensional gratings having a single grating vector G. Positive first-order diffraction in the direction of grating vector G is used to couple light from the outside into the waveguide substrate 1a, and the coupling direction I can be aligned with the direction of grating vector G. In the example shown in Figure (c), the grating coupler 10C in the diffractive optical waveguide 1C is a two-dimensional grating having three grating vectors G1, G2, and G3. Light incident on the grating coupler 10C is coupled into the waveguide substrate 1a via positive first-order diffraction in the directions of grating vectors G1, G2, and G3. In this case, the coupling direction includes sub-directions I1, I2, and I3, and these sub-directions I1, I2, and I3 can be aligned with the directions of grating vectors G1, G2, and G3, respectively. It should be understood that the number of grating vectors described above is merely exemplary and non-limiting. For example, in other examples not shown, the grating coupler according to an embodiment of the present invention may be a two-dimensional grating having two grating vectors perpendicular to each other.

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

[0060] Specifically, after the input light is coupled into the waveguide substrate 1a via the grating coupler 10, it 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 figure illustrates the outcoupling loss when light propagates through total internal reflection in the region of the grating coupler, where the outcoupling loss is as follows: Figure 3 As shown by the dashed arrows in the middle, when light propagates through the grating coupler 10 by total internal reflection, the number of reflections at different positions of the grating coupler 10 is different, so the outcoupling losses at these positions are also different. Figure 3 The dotted circles R1, R2, R3, and R4 in the figure represent the footprints of the light spots reflected from the first to the fourth time 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 downstream region of the grating coupler 10 along the coupling direction I, the number of light reflections is greater, and therefore the coupling loss is greater. At the same time, the diffraction efficiency of the specific order (e.g., positive first order) diffraction used to achieve the coupling function of the grating coupler 10 is often positively correlated with the coupling loss, that is, when the diffraction efficiency increases, the coupling loss of light in the grating region also increases. Existing grating couplers usually have a single grating structure, and while improving the diffraction efficiency of a specific order, it often leads to high coupling loss. Unlike the prior art, in the grating coupler and 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 region of the grating coupler 10 along the coupling direction / grating vector direction has a higher specific order (e.g., positive first order) diffraction efficiency, while the downstream region 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 variation is the same at different positions along the coupling direction I.

[0063] In other embodiments of the present invention, the average thickness per cycle (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 gradient of the variation of the average thickness per cycle gradually increases along the coupling direction. This can help to more significantly suppress outcoupling losses in the downstream region of the grating coupler 10 along the coupling direction, thereby improving coupling efficiency.

[0064] According to different embodiments of the present invention, the average thickness of a single period of at least one film layer of the optical coating 12 can vary continuously or in a stepwise manner along the coupling direction. In the case of continuous variation, the average thicknesses within any two adjacent grating periods in the coupling direction are different. In the case of stepwise variation, 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 film thickness variation 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 iso-thickness line of the film layer with a gradual thickness change 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 FIG. 5 (a), the film layer has a straight constant thickness line ct, which indicates 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 isothickness lines ct are arc-shaped, indicating that the film thickness can also vary in the direction perpendicular to the grating vector G. In this way, the degree of freedom in modulating 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 isothickness lines ct are symmetrical with respect to the central axis aa, in the grating coupler 10 shown in Figure (c), the isothickness 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 4Figure (d) illustrates that the thickness of the optical coating 12 in a grating coupler 10 composed of a two-dimensional grating can gradually decrease along 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 coating gradually decreases along each of the sub-directions 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 multiple 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 tooth grating (see Figure 7 Figure (b) Figure 8 Figure (a)), blazed grating (see Figure 5 ) or multi-step grating structure (see Figure 8 (b) The optical coating may include more than two layers. The average thickness per cycle of multiple or all layers of the optical coating may gradually decrease along the coupling direction / grating vector direction.

[0068] Preferably, the average thickness per cycle of the outermost layer in the optical coating gradually decreases along the incoupling direction / grating vector direction. Simulations and experiments have shown that gradually decreasing the average thickness of the outermost layer significantly improves incoupling efficiency. Advantageously, layers other than the outermost layer can each have a constant average thickness per cycle.

[0069] In the case where the optical coating includes an underlying layer adjacent to the outermost layer, it is preferred that the refractive index of the outermost layer is greater than the refractive index of the underlying 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 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. 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. 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 Figure (b), the portion of the first film layer C1 located on the first sidewall S1 has a thickness of d1, and the portion of the first film layer C1 located on the second sidewall S2 has a thickness of d2. Furthermore, the portion of the second film layer C2 located on the first sidewall S1 has a thickness of d3, and the portion of the second film layer C2 located on the second sidewall S2 has a thickness of d4. Preferably, the optical coating 12' is constructed to satisfy the following conditions: 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 fact that the average thickness of the second film layer C2 within a single grating period gradually decreases 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. For example, in Figure 8 In the example shown in FIG, the thickness of the film layer on a portion 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, an optical coating having the above-mentioned directivity difference is preferably used.

[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 it are shown. 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 are given.

[0079] Specifically, Data Example 1 is based on the following structure and usage 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 onto it from the bottom surface side of the grating body through the waveguide substrate), and the optical coating includes a single film layer and is as follows 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 = 522 nm (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 variations 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 film thickness 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] Incoupling efficiency Uniformity Single thickness 0.189 0.297 Gradual film thickness-increasing 0.182 0.227 Gradual film thickness-decreasing 0.209 0.499

[0093] 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 carrying image information used to diffract the optical waveguide. In other words, uniformity = minimum coupling efficiency / maximum coupling efficiency. A larger uniformity value indicates better uniformity.

[0094] Accordingly, Figure 9 A graph showing how the coupling efficiency changes with the field of view angle / incident angle when the film thickness changes in Data Example 1.

[0095] From Table 1 and Figure 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, both the coupling efficiency and uniformity have been improved. The increase in coupling efficiency exceeds 10%, and the improvement in uniformity is even 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 it 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 based on Data Example 2 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 variations 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 film thickness 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] Incoupling efficiency Uniformity Single thickness 0.167 0.403 Gradual film thickness-increasing 0.166 0.304 Gradual film thickness-decreasing 0.17.9 0.490

[0112] Accordingly, Figure 10 A graph showing how the coupling efficiency changes with the field of view angle / incident angle when the film thickness changes in Data Example 2.

[0113] From Table 2 and Figure 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, both the coupling efficiency and uniformity have been improved, with the increase in coupling efficiency exceeding 7% and the improvement in uniformity exceeding 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 it 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 a blazed grating (a one-dimensional grating) shown in FIG is used as a reflective grating in a diffraction waveguide (a grating coupler receives input light irradiated onto it from the bottom surface side of the grating body through a 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) The input light has a red wavelength of λ1 = 624 nm, a green wavelength of λ2 = 522 nm, and a blue wavelength of λ3 = 455 nm. The field of view (FOV) 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 variations 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 different film thickness changes, Figure 11 The corresponding graph shows 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 variations 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 Nonlinear 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, Figure 12 、 Figure 13 and Figure 14 Graphs showing how the coupling efficiency of red light, green light, and blue light changes with the field of view angle / incident angle when the film thickness varies in Data Example 3 are shown.

[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, the coupling efficiency and uniformity under the "non-linear gradient thickness" condition are further improved overall compared to the "linear gradient thickness".

[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 it 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 set of parameter conditions mentioned above includes:

[0140] (1) In the input light, the wavelength of red light is λ1 = 624 nm, the wavelength of green light is λ2 = 522 nm, and the wavelength of blue light is λ3 = 455 nm. 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 (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 variations 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 different film thickness changes, Figure 15 The corresponding graph shows 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 variations 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 Nonlinear 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, Figure 16 、 Figure 17 and Figure 18 Graphs showing how the coupling efficiency of red light, green light, and blue light changes with the field of view angle / incident angle when the film thickness varies in Data Example 4 are shown.

[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, the coupling efficiency and uniformity of green and blue light are further improved under the "non-linear gradient thickness" condition compared to the "linear gradient thickness" condition.

[0158] The grating coupler and optical waveguide device 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 the optical waveguide device or the grating coupler described above. The display device is preferably a near-eye display device and further comprises a lens and a frame for holding the lens close to the eye, with the optical waveguide device or grating coupler disposed 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 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. 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 a coupling-in direction within the waveguide substrate by total internal 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 gradually increases 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 includes 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 includes a first film layer covering the grating body and a second film layer covering the first film layer, wherein the refractive index of the first film layer is lower than the refractive index of the grating body, and the refractive index of the second film layer is higher 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 skew tooth grating, a blazed grating or a multi-step grating.

10. The optical waveguide device according to claim 1 or 9, wherein: 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; 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 varies 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 in a step-wise manner 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 isopach 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, 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 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.

17. The optical waveguide device according to claim 1, wherein 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 of the light in at least one dimension, wherein the coupling direction is the direction from the grating coupler toward the pupil expansion grating element.

18. A grating coupler, configured to couple input light incident thereon into a waveguide substrate and cause the input light to propagate along a coupling direction in the waveguide substrate by total internal 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. The predetermined order of diffraction in the direction of the at least one grating vector is used to couple the light irradiated by the grating coupler into the waveguide substrate and cause it to propagate in the waveguide substrate by total internal reflection.

19. The grating coupler of claim 18, 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.

20. The grating coupler of claim 18, wherein The refractive index of the at least one film layer is greater than the refractive index of the grating body.

21. The grating coupler according to any one of claims 18 to 20, wherein: The at least one film layer includes an outermost film layer in the optical coating.

22. A display device comprising the optical waveguide device according to any one of claims 1 to 17 or the grating coupler according to any one of claims 18 to 21.

23. The display device according to claim 22, 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 disposed on the lens.

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