Grating coupler and diffractive optical waveguide comprising same, and display device

Abstract

A grating coupler and a diffractive optical waveguide comprising same, and a display device. The grating coupler comprises a grating body (11) and an optical film layer (12). At least part of each gate line (11a) of the grating body (11) comprises a first side wall S1 and a second side wall S2, and the first side wall S1 and the second side wall S2 respectively form a first angle θ1 and a second angle θ2 with respect to a plane P where the grating body (11) is located, wherein θ1<θ2. The optical film layer (12) comprises a first film layer C1 covering the grating body (11) and a second film layer C2 covering the first film layer C1. The grating body (11) has a grating refractive index n0, the first film layer C1 has a refractive index n1, and the second film layer C2 has a refractive index n2, wherein n1<n0<n2. The portions of the first film layer C1 located on the first side walls S1 and the portions of the first film layer located on the second side walls S2 respectively have an average thickness d1 and an average thickness d2, wherein d1>d2; and in addition, the portions of the second film layer C2 located on the first side walls S1 and the portions of the second film layer located on the second side wall S2 respectively have an average thickness d3 and an average thickness d4, wherein d3>d4. By providing the optical film layer (12) having specific asymmetry, in-coupling efficiency and uniformity are improved.

Description

Grating couplers, as well as diffractive waveguides and display devices incorporating them. Technical Field

[0001] This invention relates to display technology based on diffractive waveguides; specifically, it relates to a grating coupler and a diffractive waveguide and display device having the same. Background Technology

[0002] With the development of science and technology, Augmented Reality (AR) technology, as a highly intelligent and portable display technology, is gradually becoming more widely used. Diffractive waveguides are currently a mainstream solution for realizing AR displays. These waveguides consist of waveguide gratings on a waveguide substrate, including coupling-in gratings and coupling-out gratings. The coupling-in grating couples incident light carrying image information into the waveguide substrate. The coupling-out grating propagates and expands the light carrying image information while simultaneously coupling the light out of the waveguide substrate, forming an outgoing light field. The eye receives the light from this outgoing light field, allowing it to observe, for example, the image carried by the incident light.

[0003] However, image displays based on diffractive waveguides suffer from insufficient brightness and uniformity deviations. The coupling grating of the diffractive waveguide has a significant impact on this. For the coupling grating, it is desirable to have high diffraction efficiency for a specific order (typically the positive first order) used to couple light into the waveguide substrate, while the diffraction efficiency for other orders (especially the zeroth and negative orders) should be sufficiently low. To address this, blazed gratings have been chosen as the coupling gratings in diffractive waveguides, and improvements have been made to the grating structure (e.g., the cross-section of the grating lines). However, the tuning capability achievable based on a single refractive index remains limited, making it difficult to achieve a breakthrough in efficiency, particularly in improving efficiency while maintaining uniformity. Summary of the Invention

[0004] The purpose of this invention is to provide a grating coupler, as well as a diffractive waveguide and display device having the same, which at least partially overcomes the problems in the prior art.

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

[0006] A grating body includes a plurality of grating lines arranged along a plane. The grating lines are periodically arranged in a first direction, and each grating line extends in a second direction perpendicular to the first direction. At least a portion of the grating lines includes a first sidewall and a second sidewall extending along the second direction. The first sidewall and the second sidewall form a first angle θ1 and a second angle θ2 with respect to the plane, respectively, where θ1 < θ2.

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

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

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

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

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

[0012] n1≤1.5;

[0013] n² ≥ 2.0;

[0014] n2-n1≥0.4;

[0015] n0-n1≥0.3;

[0016] n² - n₀ ≥ 0.3; and

[0017] n1+n2≤2n0+0.2.

[0018] Advantageously, the optical film also satisfies: n 2- n1≥0.6.

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

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

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

[0022] d1 / d2≥1.5;

[0023] d3 / d4 ≥ 1.5;

[0024] d2≤40nm≤d1≤100nm; and

[0025] d4≤40nm≤d3≤120nm.

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

[0027] In some embodiments, at least a portion of the grid lines have a cross section perpendicular to the second direction, and the first sidewall corresponds to one side of the cross section, the side being composed of a combination of two or more straight lines and / or curves, and the first included angle θ1 is the included angle formed by the lines connecting the two ends of the side with respect to the plane.

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

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

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

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

[0032] According to another aspect of the present invention, a diffractive waveguide is provided, comprising a waveguide substrate and an input grating and an output grating disposed on the waveguide substrate. The input grating is used to couple input light carrying image information into the waveguide substrate and propagate it in the waveguide substrate by total internal reflection along the coupling direction. The output grating is used to expand the pupil of the light propagating therein and couple it out of the waveguide substrate to achieve image display. The input grating is a grating coupler as described above.

[0033] In some embodiments, the coupling grating may be a reflective grating that receives input light that passes through the waveguide substrate and is incident on one side of the grating body; and the second sidewall faces the coupling direction.

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

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

[0036] Advantageously, the display device is a near-eye display device and also includes a frame for holding the lens close to the eye.

[0037] In the grating coupler according to embodiments of the present invention, by providing a composite optical film layer with specific asymmetry on the grating body having an asymmetric structure, the coupling efficiency is significantly improved, and at the same time, additional means are provided for uniformity adjustment, enabling further improvement in efficiency while maintaining uniformity. Accordingly, the diffractive waveguide and the actual device according to embodiments of the present invention also possess the above-mentioned technical advantages. Attached Figure Description

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

[0039] Figure 1 is a schematic plan view of a diffractive waveguide according to an embodiment of the present invention, wherein a grating coupler according to an embodiment of the present invention is used as a coupling grating in the diffractive waveguide.

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

[0041] Figure 3 shows a schematic cross-sectional view of different examples of grating couplers according to embodiments of the present invention;

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

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

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

[0045] Figure 7 shows the curves of coupling efficiency of different grating couplers used in Data Example 1 as a function of field of view / incident angle;

[0046] Figure 8 shows the curves of coupling efficiency of different grating couplers used in Data Example 2 as a function of field of view / incident angle;

[0047] Figure 9 shows the curves of red light coupling efficiency of different grating couplers used in Data Example 3 as a function of field of view / incident angle:

[0048] Figure 10 shows the green light coupling efficiency of the different grating couplers used in Data Example 3 as a function of field of view / incident angle;

[0049] Figure 11 shows the curves of blue light coupling efficiency as a function of field of view / incident angle for the different grating couplers used in Data Example 3; and

[0050] Figure 12 is a graph showing the simulation results of the coupling efficiency and uniformity of the grating coupler according to the embodiment of the present invention in Data Example 5, under different film refractive indices. Detailed Implementation

[0051] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. For ease of description, only the parts relevant to the invention are shown in the drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0052] First, let's briefly introduce the diffractive waveguide according to an embodiment of the present invention with reference to Figure 1.

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

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

[0055] Although not shown, it should be understood that the diffractive waveguide 1 according to embodiments of the present invention may also include other gratings besides the input grating and the output grating, such as a deflection grating for expanding the pupil of light from the input grating and deflecting it toward the output grating, or a return grating for returning light that has propagated beyond the range of the output grating to the output grating (so that it can be coupled out for display), etc.

[0056] The grating coupler according to an embodiment of the present invention will be described in detail below with reference to Figures 2 to 4.

[0057] In this application, a grating coupler refers to a grating device used to couple externally incident light into a waveguide (e.g., a waveguide substrate), which can serve as a coupling grating in a diffractive waveguide for image display as shown in FIG. 1. The same reference numeral "10" is used in this application to denote both the grating coupler and the coupling grating. It should be understood that the grating coupler according to embodiments of the present invention is not limited to use as a coupling grating in a diffractive waveguide, but can also be applied as an optical coupling input device in other optical waveguide devices for non-display purposes (e.g., uniform waveguide devices in optomechanics and optical waveguide illumination devices in eye-tracking devices).

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

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

[0060] Referring to Figures 1 and 2, the grating body 11 includes a plurality of grating lines 11a arranged along plane P (i.e., the xy plane shown in Figure 1). The plurality of grating lines 11a are arranged periodically in a first direction x, and each grating line 11a extends in a second direction y perpendicular to the first direction x. As shown in Figure 2(a), at least a portion of the grating lines 11a of the grating body 11 includes a first sidewall S1 and a second sidewall S2 extending along the second direction y. The first sidewall S1 and the second sidewall S2 form a first angle θ1 and a second angle θ2 with respect to plane P, respectively, where θ1 < θ2.

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

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

[0063] As will be specifically explained below with reference to data examples, in the grating coupler 10 according to an embodiment of the present invention, by providing a composite optical film layer 12 with a specific refractive index relationship (i.e., n1 < n0 < n2) on the grating body 11 and making the portions of the film layer 12 on the two sidewalls S1 and S2 of the grating body 11 with different inclinations have a specific thickness relationship (i.e., d1 > d2, d3 > d4), the coupling efficiency of the grating coupler 10 can be significantly improved, and a new means / variable for uniformity adjustment can be provided, enabling further improvement of coupling efficiency while taking uniformity into account. Here, uniformity refers to the uniformity of the distribution of the coupling efficiency of the grating coupler within the field of view (i.e., incident angle) of the input light.

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

[0065] In the example shown in FIG2, the first sidewall S1 and the second sidewall S2 of the grating body 11 are each planar and adjacent to each other, thereby forming an included angle in a cross-section of the grating body 11 perpendicular to the second direction y. However, it should be understood that FIG2 is merely exemplary and not limiting. The grating coupler 10 according to embodiments of the present invention is not limited to the first sidewall S1 and the second sidewall S2 of the grating body 11 being planar sidewalls or adjacent to each other. For ease of understanding, FIG3 shows schematic cross-sectional views of three different examples of the grating coupler 10 according to embodiments of the present invention.

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

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

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

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

[0070] In addition to the grating body 11 shown in FIG3 having a structure different from that shown in FIG2, according to some embodiments of the present invention, the optical film layer in the grating coupler may also have a modified structure, wherein the optical film layer further includes a third film layer and a fourth film layer.

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

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

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

[0074] The diffractive waveguide according to an embodiment of the present invention has been briefly introduced above with reference to FIG1. ​​The following will provide a more detailed description with reference to FIG5 and FIG6, especially the application of the grating coupler in the diffractive waveguide according to an embodiment of the present invention.

[0075] Figure 5 schematically illustrates an example of a diffractive waveguide 1' according to an embodiment of the present invention in a cross-sectional view. In the example shown in Figure 5, a grating coupler 10 according to an embodiment of the present invention is used as a coupling grating in the diffractive waveguide 1', and the coupling grating 10 is used as a reflective grating, wherein, as shown in Figure 5, the coupling grating 10 receives input light L that passes through the waveguide substrate 1a and is incident on it from one side of the grating body 11. in Input light L in The diffraction after the coupling grating 10 is "reflected" back into the waveguide substrate 1a and propagates in the waveguide substrate 1a by total internal reflection along the coupling direction IN (see the bold black arrows in Figures 1 and 5). In this case, according to an embodiment of the invention, the coupling grating 10 is configured in the diffracting waveguide 1' such that its second sidewall S2 faces the coupling direction.

[0076] Similarly, FIG6 schematically illustrates an example of a diffractive waveguide according to an embodiment of the present invention, namely diffractive waveguide 1”, in a cross-sectional view. In the example shown in FIG6, a grating coupler 10 according to an embodiment of the present invention is used as a coupling grating in diffractive waveguide 1”, and the coupling grating 10 is used as a transmission grating, wherein, as shown in FIG6, the coupling grating 10 receives input light L that passes through the waveguide substrate 1a and is incident on it from one side of the optical film layer 12. in Input light L in The diffraction through the coupling grating 10 is "transmitted" into the waveguide substrate 1a and propagates in the waveguide substrate 1a by total internal reflection along the coupling direction IN (see the bold black arrows in Figures 1 and 5). In this case, according to an embodiment of the invention, the coupling grating 10 is configured in the diffracting waveguide 1” such that its first sidewall S1 faces the coupling direction.

[0077] The diffractive waveguide according to embodiments of the present invention correspondingly possesses the technical advantages of the grating coupler according to the present invention.

[0078] The technical advantages of the grating coupler and diffractive waveguide according to embodiments of the present invention will be illustrated below with data examples.

[0079] (Data Example 1)

[0080] In Example 1, simulation calculations were used to compare and analyze the coupling efficiency and uniformity of the following grating coupler when it is used as a reflective grating (in this case, the grating coupler receives input light that passes through the waveguide substrate and is incident on one side of the bottom surface of the grating body, see the usage state of grating coupler 10 shown in Figure 5):

[0081] Grating Coupler 1A: According to an embodiment of the present invention, the grating coupler includes a grating body as described above with reference to FIG2, a first film layer covering the grating body, and a second film layer covering the first film layer;

[0082] Grating Coupler 1B: A blazed grating without an optical coating, which is constructed with the same structure as the grating body in grating coupler 1A;

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

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

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

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

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

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

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

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

[0091] The grating coupler 1A is a grating coupler according to an embodiment of the present invention. The parameters of the grating coupler 1A obtained after optimization, which can achieve better coupling efficiency and uniformity, include:

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

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

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

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

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

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

[0098] The optimized parameters of the grating coupler 1D, which achieves better coupling efficiency and uniformity, include: a lower film thickness of 30 nm and an upper film thickness of 65.5 nm.

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

[0100] [Table 1]

[0101] Meanwhile, Figure 7 shows the coupling efficiency of grating couplers 1A to 1E in Data Example 1 as a function of the field of view / incident angle of the input light.

[0102] As can be seen from Table 1 and Figure 7, the coupling efficiency of grating coupler 1A according to the embodiment of the present invention is superior to that of other grating couplers 1B to 1E, and the improvement is considerable. Specifically, the coupling efficiency of grating coupler 1A is improved by 98.4% compared to grating coupler 1B; and the coupling efficiency is improved by 24.5% compared to grating coupler 1D.

[0103] Furthermore, as can be seen from Table 2 and Figure 8, the grating coupler 1A also maintains better coupling uniformity, overcoming the problem in existing grating couplers that it is difficult to improve coupling efficiency while taking uniformity into account.

[0104] Example 1 shows that when the grating coupler according to the embodiment of the present invention is used as a reflective grating, it can significantly improve the coupling efficiency and maintain good uniformity.

[0105] (Data Example 2)

[0106] In Example 2, simulation calculations were used to compare and analyze the coupling efficiency and uniformity of grating couplers 2A, 2B, 2C, 2D and 2E when they are used as transmission gratings (in this case, the grating coupler receives input light that is incident on it from the top surface of the optical film / grating body, see the usage state of grating coupler 10' shown in Figure 6).

[0107] Grating couplers 2A to 2E each have the structure of grating couplers 1A to 1E in Data Example 1. Specifically, grating coupler 2A is a grating coupler according to an embodiment of the present invention; grating coupler 2B is a blazed grating without an optical film layer; grating coupler 2C is a grating coupler with a single film layer; grating coupler 2D is a grating coupler with two film layers, wherein the two film layers have the same film layer thickness on the first and second sidewalls of the grating body; grating coupler 2E is a grating coupler with two film layers, wherein the two film layers are obtained by reversing the order of the first and second film layers in grating coupler 2A. For a more detailed description, please refer to Data Example 1, which will not be repeated here.

[0108] In Example 2, the above grating coupler is optimized based on the following parameters:

[0109] (1) The input light wavelength λ = 522nm (green light) and the field of view (FOV) range is 25° × 18°; the optical engine that projects the input light is tilted 9° relative to the z-axis (the normal direction of the waveguide substrate) in the xz plane shown in Figure 1;

[0110] (2) The refractive index of the waveguide substrate is 1.8, the thickness is 0.7 mm, and the grating period is 420 nm;

[0111] (3) The refractive index of the grating body is n0 = 1.8, the refractive index of the first film layer is n1 = 1.4, and the refractive index of the second film layer is n2 = 2.3.

[0112] During the optimization process, the optimizable parameters of the above-mentioned grating coupler include the height of the blazed grating, the first included angle (blazed angle), and the thickness of the film layer. The coupling efficiency is the primary optimization objective, and uniformity is the secondary optimization objective (preferably uniformity of 0.45 or higher).

[0113] The grating coupler 2A is a grating coupler according to an embodiment of the present invention. The parameters of the grating coupler 2A obtained after optimization, which can achieve better coupling efficiency and uniformity, include:

[0114] The grating height is 220 nm, and the first included angle θ1 = 30.2°;

[0115] The thickness of the portion of the first film layer on the first sidewall is d1 = 26.0 nm;

[0116] The thickness of the portion of the first film layer on the second sidewall is d2 = 5.2 nm;

[0117] The thickness of the portion of the second film layer on the first sidewall is d3 = 48.0 nm;

[0118] The thickness of the second film layer on the second sidewall is d4 = 9.6 nm.

[0119] The optimized parameters of the grating coupler 2C, which achieves better coupling efficiency and uniformity, include: the thickness of the single film layer on the first sidewall of the grating body is 26.0 nm, and the thickness on the second sidewall is 5.2 nm.

[0120] The optimized parameters for the grating coupler 2D, which achieve better coupling efficiency and uniformity, include: a lower film thickness of 30.0 nm and an upper film thickness of 50.0 nm.

[0121] Table 2 shows the coupling efficiency and uniformity of the grating couplers 2A-2E after the above optimization:

[0122] [Table 2]

[0123] Meanwhile, Figure 8 shows the coupling efficiency of grating couplers 2A to 2E in Data Example 2 as a function of the field of view / incident angle of the input light.

[0124] As can be seen from Table 2 and Figure 8, the coupling efficiency of grating coupler 2A according to the embodiment of the present invention is superior to that of other grating couplers 2B to 2E, and the improvement is considerable. Specifically, the coupling efficiency of grating coupler 2A is improved by 62.4% compared to grating coupler 2B; and by 16.8% compared to grating coupler 2C.

[0125] Furthermore, as can be seen from Table 2 and Figure 8, the grating coupler 2A also achieves very good uniformity, balancing the improvement of coupling efficiency and uniformity.

[0126] Data Example 2 shows that when the grating coupler according to the embodiment of the present invention is used as a transmissive grating, it can significantly improve the coupling efficiency and also improve the uniformity.

[0127] (Data Example 3)

[0128] In Example 3, the coupling efficiency and uniformity of grating couplers 3A, 3B, 3C and 3D at different wavelengths were compared and analyzed through simulation calculations.

[0129] Grating couplers 3A to 3D each have the structure of grating couplers 1A to 1D in Data Example 1. Specifically, grating coupler 3A is a grating coupler according to an embodiment of the present invention; grating coupler 3B is a blazed grating without an optical coating; grating coupler 3C is a grating coupler with a single coating; and grating coupler 3D is a grating coupler with two coatings, wherein the two coatings have the same coating thickness on the first and second sidewalls of the grating body. For a more detailed description, please refer to Data Example 1, which will not be repeated here.

[0130] In Example 3, the above grating coupler is optimized as a reflective grating based on the following parameters:

[0131] (1) In the input light, the wavelength of red light λ1 = 622nm, the wavelength of green light λ2 = 532nm, the wavelength of blue light λ3 = 455nm, and the field of view (FOV) range is 20° × 20°;

[0132] (2) The refractive index of the waveguide substrate is 1.9, the thickness is 0.7 mm, and the grating period is 390 nm;

[0133] (3) The refractive index of the grating body is n0 = 1.9, the refractive index of the first film layer is n1 = 1.45, and the refractive index of the second film layer is n2 = 2.5.

[0134] During the optimization process, the optimizable parameters of the above-mentioned grating coupler include the height of the blazed grating, the first included angle (blazed angle), and the thickness of the film layer. The coupling efficiency is the primary optimization objective, and uniformity is the secondary optimization objective (preferably uniformity of 0.45 or higher).

[0135] The grating coupler 3A is a grating coupler according to an embodiment of the present invention. The parameters of the grating coupler 3A, which are optimized to achieve better coupling efficiency and uniformity, include:

[0136] The grating height is 175nm, and the first included angle θ1 = 25.7°;

[0137] The thickness of the portion of the first film layer on the first sidewall is d1 = 67.7 nm;

[0138] The thickness of the portion of the first film layer on the second sidewall is d2 = 23.2 nm;

[0139] The thickness of the portion of the second film layer on the first sidewall is d3 = 72.2 nm;

[0140] The thickness of the portion of the second film layer on the second sidewall is d4 = 26.3 nm.

[0141] The optimized parameters of the grating coupler 3C, which achieve better coupling efficiency and uniformity, include: the thickness of the single film layer on the first sidewall of the grating body is 40.5 nm, and the thickness on the second sidewall is 13.9 nm.

[0142] The optimized parameters for the grating coupler 3D, which achieve better coupling efficiency and uniformity, include: a lower film thickness of 33.0 nm and an upper film thickness of 70.3 nm.

[0143] Table 3 shows the coupling efficiency and uniformity of the grating couplers 3A-3D after the above optimization:

[0144] [Table 3]

[0145] In Table 3, R, G, and B represent red light, green light, and blue light, respectively.

[0146] Meanwhile, Figures 9, 10, and 11 show the coupling efficiency of different grating couplers used in Data Example 3 under red, green, and blue light as a function of field of view / incident angle.

[0147] As can be seen from Table 3 and Figures 9 to 11, the grating coupler 3A according to the embodiment of the present invention achieves a coupling efficiency of 38% and a uniformity of 78% for red light; a coupling efficiency of 32% and a uniformity of 60% for green light; and a coupling efficiency of 15.2% and a uniformity of 41% for blue light. The coupling efficiency of grating coupler 3A is superior to that of other grating couplers 3B, 3C, and 3D, and the improvement is considerable.

[0148] In terms of uniformity, although the uniformity obtained by grating coupler 3A is not optimal for red and green light, it can be maintained at a very good level; while for blue light, the uniformity obtained by grating coupler 3A is optimal, and the improvement is significant.

[0149] Data Example 3 shows that the grating coupler according to the embodiment of the present invention can comprehensively improve coupling efficiency at different wavelengths (e.g., red, green, and blue light wavelengths for full-color displays) and can also take into account uniformity.

[0150] Referring to the optimized thicknesses of the first and second films in the grating couplers 1A, 2A and 3A according to embodiments of the present invention in Examples 1 to 3, the optical films in the grating couplers according to embodiments of the present invention can be advantageously configured to satisfy at least one of the following conditions: d2≤40nm≤d1≤100nm; and d4≤40nm≤d3≤120nm.

[0151] Examples 1-3 above demonstrate the technical advantages of the grating coupler according to embodiments of the present invention in terms of coupling efficiency and uniformity. Next, examples 4 and 5 will further analyze the influence of film thickness and refractive index in the grating coupler according to embodiments of the present invention.

[0152] (Data Example 4)

[0153] Example 4 presents a simulation analysis of the coupling efficiency and uniformity of the grating coupler 4A according to an embodiment of the present invention under different film thickness ratios d1 / d2 and d3 / d4. The grating coupler 4A includes a grating body as described above with reference to FIG2, a first film layer covering the grating body, and a second film layer covering the first film layer, which will not be described in detail here.

[0154] In Example 4, the coupling efficiency and uniformity of grating coupler 4A when used as a reflective grating were simulated based on the following parameters:

[0155] (1) The input light wavelength λ = 522nm (green light) and the field of view / incident angle range is 25° × 18°;

[0156] (2) The waveguide substrate has a refractive index of 1.8, a thickness of 0.7 mm, and a grating period of 400 nm;

[0157] (3) The refractive index of the grating body is n0 = 1.8, the refractive index of the first film layer is B1 = 1.4, and the refractive index of the second film layer is n2 = 2.3; and

[0158] (4) The grating height is 170nm and the first included angle θ1 = 25.2°.

[0159] Furthermore, the simulation calculations for Data Example 4 are divided into three groups, among which:

[0160] Group 1: Under the condition that d1 / d2 is a fixed value (approximately 4), calculate the coupling efficiency and uniformity under different film thickness ratios d3 / d4;

[0161] Group 2: With d3 / d4 as a fixed value (approximately 4), calculate the coupling efficiency and uniformity for different film thickness ratios d1 / d2: and

[0162] Group 3: Under the condition that d1 / d2 = d3 / d4 (considering the design and processing accuracy of the film thickness, there may be slight deviations between the two ratios. In this application, it is assumed that such a situation meets the condition that d1 / d2 = d3 / d4), the coupling efficiency and uniformity under different film thickness ratios are calculated.

[0163] The coupling efficiency and uniformity of the grating coupler 4A obtained from the above three sets of simulation calculations are shown in Tables 4.1, 4.2, and 4.3, respectively:

[0164] [Table 4.1]

[0165] [Table 4.2]

[0166] [Table 4.3]

[0167] Table 4.1 shows that, with d1 / d2 fixed, the coupling efficiency of grating coupler 4A increases significantly with the increase of the ratio d3 / d4, while the uniformity decreases slightly but remains at a good level.

[0168] Table 4.2 shows that, with d3 / d4 fixed, the coupling efficiency of grating coupler 4A does not change significantly with the increase of the ratio d1 / d2, while the uniformity is significantly improved.

[0169] Table 4.3 shows that, under the condition that d1 / d2 = d3 / d4, the coupling efficiency of the grating coupler 4A increases more significantly with the increase of the ratios d1 / d2 and d3 / d4. At the same time, the uniformity decreases slightly and then increases again, thus maintaining a good level overall.

[0170] Taking into account the influence of the film thickness ratios shown in Tables 4.1, 4.2 and 4.3, in the grating coupler according to an embodiment of the present invention, the optical film can be advantageously constructed to satisfy at least one of the following conditions: d1 / d2 ≥ 1.5; and d3 / d4 ≥ 1.5.

[0171] In some embodiments, preferably, the optical film layer can be configured to satisfy: d1 / d2≥3, or d3 / d4≥3, to obtain higher coupling efficiency.

[0172] (Data Example 5)

[0173] Example 5 presents a simulation analysis of the coupling efficiency and uniformity of the grating coupler 5A according to an embodiment of the present invention under different refractive indices n1 and n2. The grating coupler 5A includes a grating body as described above with reference to FIG2, a first film layer covering the grating body, and a second film layer covering the first film layer, which will not be described in detail here.

[0174] In Example 5, the coupling efficiency and uniformity of the grating coupler 5A when used as a reflective grating were simulated based on the following parameters:

[0175] (1) Input light wavelength λ = 522nm (green light), field of view / incident angle range is 25°×18°;

[0176] (2) The waveguide substrate has a refractive index of 1.8, a thickness of 0.7 mm, and a grating period of 400 nm;

[0177] (3) The refractive index of the grating body is n0 = 1.8; and

[0178] (4) The grating height is 170nm and the first included angle θ1 = 25.2°.

[0179] The coupling efficiency and uniformity of the grating coupler 5A obtained from simulation calculations are shown in tabular form in Figure 12.

[0180] The table in Figure 12 shows that the coupling efficiency increases as the refractive index n1 of the first film decreases, and the coupling efficiency also increases as the refractive index n2 of the second film increases.

[0181] Considering that the current trend is to use waveguide substrates with higher refractive index n0 (e.g., waveguide substrates with refractive index n0 above 1.8) in order to improve the field of view of diffractive waveguides, in the grating coupler according to the embodiments of the present invention, the optical film structure that satisfies n1≤1.5 and / or n2≥2.0 will help to significantly improve the coupling efficiency.

[0182] The influence of the film refractive indices n1 and n2 on the coupling efficiency can also be examined in conjunction with the refractive index n0 of the grating body. The table in Figure 12 further shows that: as the value of n0-n1 increases, the coupling efficiency improves; as the value of n2-n0 increases, the coupling efficiency also improves; even when n2-n0 is only 0.1, a relatively good coupling efficiency of 0.180 can be obtained if n0-n1 ≥ 0.3; even when n0-n1 is only 0.1, a relatively good coupling efficiency of 0.182 can be obtained if n2-n0 ≥ 0.3. Therefore, in the optical coupler according to the embodiments of the present invention, an optical film structure that satisfies n0-n1 ≥ 0.3 and / or n2-n0 ≥ 0.3 will significantly improve the coupling efficiency.

[0183] Furthermore, as can be seen from the table in Figure 12, if the optical film is constructed to satisfy (n2-n0)+(n0-n1)≥0.4, i.e. n2-n1≥0.4, the coupling efficiency can also be improved to a better level.

[0184] The table in Figure 12 also shows that as the refractive index n1 of the first film layer decreases, n0-n1 increases, and the uniformity improves; as the refractive index n2 of the second film layer increases, n2-n1 increases, and the uniformity deteriorates. This indicates that while improving coupling efficiency by decreasing n1 and increasing n2 as discussed above, uniformity can be maintained by controlling and balancing the opposing effects of n0-n1 and n2-n1 on uniformity, and in some cases, even improved uniformity can be achieved.

[0185] As can be seen from the table in Figure 12, if the optical film is constructed to satisfy n0-n1≥n2-n0, i.e., n1+n2≤2n0 (or n1+n2≤3.6 in Data Example 5), the uniformity can be maintained at a relatively good level. Considering that in applications such as diffractive waveguides used for image displays, a uniformity above 0.45 is acceptable while improving coupling efficiency is a more pressing need, the optical film can be constructed to satisfy n1+n2≤2n0+0.2 to further improve coupling efficiency while maintaining uniformity.

[0186] In summary, in the grating coupler according to embodiments of the present invention, it is advantageous for the optical film layer to satisfy at least one of the following relationships:

[0187] n1≤1.5;

[0188] n² ≥ 2.0;

[0189] n0-n1≥0.3;

[0190] n² - n₀ ≥ 0.3;

[0191] n2-n1≥0.4; and

[0192] n1+n2≤2n0+0.2.

[0193] Advantageously, in some cases, the coupling efficiency can be further improved by constructing the optical film to satisfy n2-n1≥0.6.

[0194] Advantageously, in some cases, the coupling efficiency can be further improved by constructing the optical film to satisfy n0-n1≥0.4 and n2-n0≥0.4.

[0195] The grating coupler and diffractive waveguide according to embodiments of the present invention have been described above. According to embodiments of the present invention, a display device is also provided, which includes a diffractive waveguide according to embodiments of the present invention. Specifically, the display device may include a lens, and the lens includes the diffractive waveguide described above. The display device is preferably a near-eye display device, such as an augmented reality display device or a virtual reality display device, and further includes a frame for holding the lens close to the eye.

[0196] Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-mentioned technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by substituting the above-mentioned features with technical features disclosed in this application (but not limited to) that have similar functions.

Claims

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

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

2.

3. The grating coupler as described in claim 2, wherein, n2-n1≥0.

6.

4. The grating coupler as described in claim 1, wherein, n0-n1≥0.4, and n2-n0≥0.

4.

5. The grating coupler as claimed in claim 1, wherein, d1 / d2 = d3 / d4.

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

7. The grating coupler as claimed in claim 6, wherein, d1 / d2≥3, or d3 / d4≥3.

8. The grating coupler as claimed in claim 1, wherein, The at least part of the grid lines have a cross section perpendicular to the second direction, and the first sidewall corresponds to one side of the cross section, the side being composed of a combination of two or more straight lines and / or curves, and the first included angle θ1 is the included angle formed by the lines connecting the two ends of the side with respect to the plane.

9. The grating coupler as claimed in claim 1 or 8, wherein, The at least part of the grid lines also includes a top wall connecting the first sidewall and the second sidewall, the top wall forming a flattened or rounded ridge.

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

11. A diffractive waveguide, comprising a waveguide substrate and a coupling grating and a coupling grating disposed on the waveguide substrate, wherein the coupling grating is used to couple input light carrying image information into the waveguide substrate and propagate it along the coupling direction by total internal reflection within the waveguide substrate, and the coupling grating is used to dilate the light propagating therein and couple it out from the waveguide substrate to achieve image display. in, The coupled grating is a grating coupler as described in any one of claims 1-10.

12. The diffractive waveguide as described in claim 11, wherein, The coupling grating is a reflective grating that receives input light that passes through the waveguide substrate and is incident on it from one side of the grating body; and the second sidewall faces the coupling direction.

13. The diffractive waveguide as described in claim 11, wherein, The coupling grating is a transmission grating that receives input light incident on it from one side of the optical film layer; and the first sidewall faces the coupling direction.

14. A display device comprising a lens, the lens comprising a grating coupler as claimed in claims 1-10 or a diffractive waveguide as claimed in any one of claims 11-13.

15. The display device as claimed in claim 14, wherein, The display device is a near-eye display device and also includes a frame for holding the lens close to the eye.

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