A diffractive optical waveguide and its design method

Abstract

This invention discloses a diffractive waveguide and its design method. The diffractive waveguide includes a waveguide substrate and a coupling-in region and a coupling-out region disposed on at least one side of the waveguide substrate. A beam of light projected from an image source is coupled into the waveguide substrate through the coupling-in region and transmitted to the coupling-out region by total internal reflection. The second coupling-out region of the coupling-out region includes multiple coupling-out sub-regions. At least two coupling-out sub-regions are filled with one-dimensional gratings with different grating directions to satisfy the requirement of pupil expansion and coupling-out of the beam through the second coupling-out region. The one-dimensional grating filled in the first coupling-out region of the coupling-out region has the same grating vector as one of the one-dimensional gratings in the coupling-out sub-regions to increase the coupling-out of edge rays and compensate for the coupling-out energy at the edges. Furthermore, the sum of the grating vectors of the one-dimensional gratings in the coupling-in region and the one-dimensional gratings in the coupling-out region is set to zero, so that the beam can be effectively coupled into the waveguide substrate and coupled out without dispersion, effectively improving the visual imaging effect of the diffractive waveguide.

Description

[0001] This application is a divisional application, with parent application number 2022110139388 and application date of August 23, 2022. Technical Field

[0002] This invention relates to the field of display technology, and more particularly to a diffractive waveguide and its design method. Background Technology

[0003] Augmented Reality (AR) is a technology that blends the real world with virtual information, and the optical waveguide system is one of the key components for realizing AR technology. In an augmented reality display scenario, an image source projects a beam of light, which is to be superimposed on the real scene, onto the optical waveguide system. The optical waveguide system then deflects the direction of the image beam, allowing it to enter the viewer's eye.

[0004] Existing optical waveguide systems typically use one-dimensional gratings for pupil expansion and coupling. However, their grating layout clearly distinguishes between a pupil expansion grating and a coupling grating. A drawback is that the presence of the pupil expansion structure affects the design of the eyeglasses' appearance, such as... Figure 1 As shown, the lens usually needs to be designed to be very large, affecting the aesthetics. In contrast, a two-dimensional diffraction waveguide only has one coupling-in structure and one coupling-out structure, such as... Figure 2 As shown, a two-dimensional grating with a coupling structure can simultaneously achieve pupil expansion and coupling, thus allowing for more flexible eyeglass design using two-dimensional diffraction waveguides. However, on the one hand, the fabrication process of two-dimensional gratings is relatively more complex and requires higher precision; on the other hand, due to its higher diffraction orders, its efficiency is far lower than that of a one-dimensional grating, resulting in a significant waste of energy. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide a diffractive waveguide and its design method. By dividing the coupling region into multiple coupling sub-regions and filling the coupling sub-regions with one-dimensional gratings of different grating directions, a one-dimensional grating is used to replace a two-dimensional grating, thereby achieving pupil expansion and coupling of the beam. Based on a relatively more convenient fabrication process, the visual imaging effect of the diffractive waveguide is effectively improved.

[0006] In a first aspect, embodiments of the present invention provide a diffractive optical waveguide, the diffractive optical waveguide comprising a waveguide substrate and a coupling-in region and a coupling-out region disposed on at least one side of the waveguide substrate;

[0007] The waveguide substrate has a first surface and a second surface that are parallel to each other. The coupling region is used to couple a beam of light projected by an image source into the waveguide substrate so that the beam is transmitted to the coupling region by total internal reflection between the first surface and the second surface of the waveguide substrate.

[0008] The coupling region includes a first coupling region and a second coupling region; the second coupling region includes multiple coupling sub-regions, and at least two different grating orientations of one-dimensional gratings are provided in the second coupling region. Each of the coupling sub-regions is provided with one of the at least two different grating orientations of one-dimensional gratings. The second coupling region is used to expand the pupil of the light beam and couple it out of the waveguide substrate by diffraction. The one-dimensional grating provided in the first coupling region has the same grating vector as one of the one-dimensional gratings in the coupling sub-regions. The first coupling region is used to couple the light beam out of the waveguide substrate by diffraction.

[0009] Wherein, the sum of the grating vectors of the one-dimensional grating in the coupling-in region and the coupling-out region is zero.

[0010] Secondly, embodiments of the present invention also provide a design method for a diffractive optical waveguide, the method comprising:

[0011] A coupling-in region and a coupling-out region are defined on at least one surface of the waveguide substrate; the at least one surface is selected from a first surface and a second surface of the waveguide substrate that are parallel to each other; the coupling-in region is used to couple a beam of light projected by an image source into the waveguide substrate so that the beam of light is transmitted by total internal reflection between the first surface and the second surface of the waveguide substrate to the coupling-out region and then coupled out of the waveguide substrate.

[0012] The coupling region is divided into a first coupling region and a second coupling region, and the second coupling region is further divided into multiple coupling sub-regions;

[0013] One-dimensional gratings are filled in the coupling-in region, the first coupling-out region, and the plurality of coupling-out sub-regions, respectively; wherein, the grating directions of the one-dimensional gratings in at least two of the coupling-out sub-regions are different, the grating vector of the one-dimensional grating in the first coupling-out region is the same as that of one of the one-dimensional gratings in the coupling-out sub-regions, and the sum of the grating vectors of the one-dimensional gratings in the coupling-in region and the coupling-out region is zero.

[0014] The diffractive waveguide provided in this invention includes a waveguide substrate and a coupling-in region and a coupling-out region disposed on at least one side of the waveguide substrate. A beam of light projected from an image source is coupled into the waveguide substrate through the coupling-in region and transmitted to the coupling-out region by total internal reflection between two opposing surfaces of the waveguide substrate. The coupling-out region is divided into a first coupling-out region and a second coupling-out region. The second coupling-out region is further divided into multiple coupling-out sub-regions. Each coupling-out sub-region is filled with a one-dimensional grating with a grating direction. The grating directions of the one-dimensional gratings in at least two coupling-out sub-regions are different to satisfy the requirement of pupil expansion and coupling-out of the beam through the second coupling-out region. At the same time, the grating vector of the one-dimensional grating filled in the first coupling-out region is the same as that of the one-dimensional grating in the coupling-out sub-region, which increases the coupling-out of edge light rays and compensates for the coupling-out energy at the edge. Furthermore, the sum of the grating vectors of the one-dimensional gratings in the coupling-in region and the one-dimensional gratings in the coupling-out region is set to zero, so that the beam can be effectively coupled into the waveguide substrate and coupled out without dispersion, which effectively improves the visual imaging effect of the diffractive waveguide. Attached Figure Description

[0015] 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:

[0016] Figure 1 This is a schematic diagram of a diffractive optical waveguide in the prior art;

[0017] Figure 2 This is a schematic diagram of a diffractive optical waveguide in the prior art;

[0018] Figure 3 A schematic diagram of a planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0019] Figure 4 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0020] Figure 5 for Figure 4 A schematic diagram of a three-dimensional structure of a diffractive optical waveguide is shown.

[0021] Figure 6 A longitudinal cross-sectional view of a one-dimensional grating provided in an embodiment of the present invention;

[0022] Figure 7 for Figure 5 Wave vector space diagram of the mid-beam (K-space);

[0023] Figure 8 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0024] Figure 9A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0025] Figure 10 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0026] Figure 11 This is a schematic diagram of an coupled sub-region provided in an embodiment of the present invention;

[0027] Figure 12 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention;

[0028] Figure 13 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0029] Figure 14 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0030] Figure 15 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention;

[0031] Figure 16 This is a schematic diagram of another coupled sub-region provided in an embodiment of the present invention.

[0032] Figure 17 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention;

[0033] Figure 18 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention;

[0034] Figure 19 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention;

[0035] Figure 20 A schematic diagram of an coupling region provided in an embodiment of the present invention;

[0036] Figure 21 A schematic diagram of another coupling region provided in an embodiment of the present invention;

[0037] Figure 22 A schematic diagram of another coupling region provided in an embodiment of the present invention;

[0038] Figure 23 A schematic diagram of another coupling region provided in an embodiment of the present invention;

[0039] Figure 24 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0040] Figure 25 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention;

[0041] Figure 26 This is a flowchart illustrating a design method for a diffractive optical waveguide provided in an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be fully described below with reference to the accompanying drawings in the embodiments of this invention, through specific implementation methods. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort fall within the protection scope of this invention.

[0043] Example

[0044] This invention provides a diffractive optical waveguide, comprising a waveguide substrate having a first surface and a second surface parallel to each other. An insertion region and an exit region are disposed on the first surface and / or the second surface. The insertion region is used to couple a light beam projected from an image source into the waveguide substrate, so that the light beam is transmitted to the exit region by total internal reflection between the first and second surfaces of the waveguide substrate. The exit region includes a first exit region and a second exit region. The second exit region includes multiple exit sub-regions, each containing at least two different one-dimensional gratings with varying grating orientations. Each one-dimensional grating in the exit sub-region is one of these at least two different grating orientations. The second exit region is used to expand the pupil of the light beam and couple it out of the waveguide substrate by diffraction. The one-dimensional grating in the first exit region has the same grating vector as one of the one-dimensional gratings in the exit sub-regions. The first exit region is used to couple the light beam out of the waveguide substrate by diffraction. The sum of the grating vectors of the one-dimensional gratings in the insertion and exit regions is zero.

[0045] In this context, the grating direction refers to the direction in which the grating units are periodically arranged. The propagation direction of the grating after diffraction is related to the grating direction. The presence of at least two different grating directions in the second coupling region allows the light beam to be deflected by diffraction in at least two directions, effectively expanding the pupil and further improving its uniformity. The grating vector of the one-dimensional grating in the first coupling region is the same as that of one of the one-dimensional gratings in the coupling sub-region, ensuring effective coupling of the light beam propagating from the second coupling region. Since non-monochromatic light undergoes dispersion through grating diffraction, which affects imaging, the light beam emitted from the image source enters the eye after diffraction in both the input and output regions. When the sum of the grating vectors of the one-dimensional gratings in the input and output regions is zero, the dispersion generated by the multiple diffractions before entering the eye can be canceled out.

[0046] For example, Figure 3 A schematic diagram of a planar structure of a diffractive waveguide provided in an embodiment of the present invention; Figure 4 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention; Figure 5 for Figure 4 A schematic diagram of a three-dimensional structure of a diffractive optical waveguide is shown. Figure 6 A longitudinal cross-sectional view of a one-dimensional straight-tooth grating provided in an embodiment of the present invention; Figure 7 for Figure 5 The (K-space) wave vector space diagram of the mid-beam. Combined with... Figures 3-7 As shown, the diffractive waveguide includes a waveguide substrate 1, which has a first surface M1 and a second surface M2 that are parallel to each other. A coupling region 2 and a coupling region 3 are disposed on the first surface M1 of the waveguide substrate 1. The coupling region 2 is used to couple a beam of light projected from an image source into the waveguide substrate 1, so that the beam is transmitted to the coupling region 3 by total internal reflection between the first surface M1 and the second surface M2. The coupling region 3 includes a first coupling region 31 and a second coupling region 32. The second coupling region 32 includes multiple coupling sub-regions 321, each of which is provided with a one-dimensional grating. The grating directions of the one-dimensional gratings in at least two coupling sub-regions 321 are different. The second coupling region 32 is used to expand the pupil of the beam and couple it out of the waveguide substrate 1 by diffraction. The one-dimensional grating in the first coupling region 31 has the same grating vector as one of the one-dimensional gratings in the coupling sub-regions 321. The first coupling region 31 is used to couple the beam out of the waveguide substrate 1 by diffraction.

[0047] For example, the waveguide substrate 1 can be optical glass, the thickness of the waveguide substrate 1 is between 0.5mm and 3mm, and the length of the waveguide substrate 1 can be set according to the needs of the actual scenario. One-dimensional gratings are set in both the coupling region 2 and the coupling region 3, which can be straight tooth gratings, blazed gratings, oblique tooth gratings, volume holographic gratings, etc.

[0048] It should be noted that, to avoid the complex manufacturing process associated with using two-dimensional gratings, both the insertion and extraction regions of this application employ one-dimensional grating structures. To achieve a larger field of view and a better viewing experience, sufficient pupil expansion is required in the extraction region. This application divides the extraction region into a first extraction region and a second extraction region based on their relative positions, and arranges one-dimensional gratings according to the pupil expansion requirements of each region. Specifically, for the region in the extraction region corresponding to the insertion region (the second extraction region), since most of the light beam coupled from the insertion region directly enters the second extraction region, this portion of the beam concentrates most of its energy. This application further divides this region into multiple extraction sub-regions, and sets at least two different types of one-dimensional gratings in these extraction sub-regions, with one type of grating set in each extraction sub-region, allowing the light beam propagating from the insertion region to expand and extract to one or both sides. For the first coupling region, the light source is mainly the boundary field beam and the extended beam from the second coupling region. This part of the light has less energy. At this time, it is necessary to reduce pupil expansion and increase coupling to compensate for the coupling energy at the edge. Therefore, sub-region partitioning is no longer performed, and only a one-dimensional grating is filled.

[0049] Combination Figure 4 As shown, the light beam incident on the first coupling region 31 mainly originates from the pupil-expanded beam of the second coupling region 32. Since the energy remaining to propagate in the waveguide substrate 1 decreases after each diffraction coupling, the energy obtained at the boundary between the first coupling region 31 and the second coupling region 32 is already very low. Therefore, it is necessary to reduce pupil expansion and increase coupling to compensate for the coupling energy at the edges. The first coupling region 31 is no longer subdivided; it is simply filled with a one-dimensional grating. Simultaneously, through parameter optimization, the sum of the grating vectors of the one-dimensional grating in the coupling region 2 and the one-dimensional grating in the coupling region 3 is zero, ensuring that light can be coupled out of the waveguide substrate 1 without dispersion and enter the user's eye. By using a one-dimensional grating instead of a two-dimensional grating, higher diffraction efficiency can be obtained. In the figure, S represents the incident beam, and S' represents the pupil-expanded coupling beam after waveguide substrate 1.

[0050] Combination Figures 3-7 As shown in the schematic diagram of the light transmission process in k-space, at least two one-dimensional gratings in the coupling sub-regions 321 must have different grating vectors to achieve simultaneous pupil expansion and coupling within the coupling region 3. Figure 7 The mid-wave vector space diagram is a two-dimensional projection of the three-dimensional k-space, omitting the Z-direction component. This will be illustrated using a rectangular incident beam as an example. Figure 7 The rectangular frame in the k-space shown represents the field of view, and any point within the frame corresponds to a field of view angle FOV:(θ).n , φ n The incident light ray. Combined Figure 4 and Figure 7 As shown, the incident beam S is coupled into the waveguide substrate 1 by diffraction of Kin1 and Kin2 through the coupling grating. The Kin2 component propagates along the positive Y-axis and becomes the useful beam. When the Kin2 component is incident on the coupling grating 41 (or coupling grating 42) in the second coupling region 32, the Kout11 component is diffracted by the coupling grating 41 (or coupling grating 42) and continues to propagate in the waveguide in the positive X-axis direction within the ring (actually does not exist); or the Kout21 component is diffracted by the coupling grating 42 and continues to propagate in the waveguide substrate 1 in the positive X-axis direction within the ring (actually does not exist). When the Kout11 component is incident on the coupling grating 41 (or coupling grating 42), the Kout21 component is diffracted by the coupling grating 41 (or coupling grating 42) and continues to propagate in the waveguide in the positive Y-axis direction within the ring (actually does not exist); or the Kout21 component is diffracted by the coupling grating 42 and couples out of the waveguide in the inner ring (actually does not exist). The above example shows two types of coupling gratings filling the coupling region 3, but it is not limited to this.

[0051] In summary, the diffractive waveguide provided by this invention includes a waveguide substrate and a coupling-in region and a coupling-out region disposed on one side of the waveguide substrate. The light beam projected by the image source is coupled into the waveguide substrate through the coupling-in region and transmitted to the coupling-out region by total internal reflection between two opposing surfaces of the waveguide substrate. The coupling-out region is divided into a first coupling-out region and a second coupling-out region. The second coupling-out region is further divided into multiple coupling-out sub-regions. Each coupling-out sub-region is filled with a one-dimensional grating with a grating vector. The grating vectors of the one-dimensional gratings in at least two coupling-out sub-regions are different, satisfying the requirement that the light beam expands its pupil and couples out of the waveguide substrate through the second coupling-out region. At the same time, the one-dimensional grating filled in the first coupling-out region has the same grating vector as the one-dimensional grating in the coupling-out sub-region, which increases the coupling out of edge light and compensates for the coupling out energy at the edge. Furthermore, the sum of the grating vectors of the one-dimensional gratings in the coupling-in region and the one-dimensional gratings in the coupling-out region is set to zero, achieving dispersion-free coupling out of the light beam and effectively improving the visual imaging effect of the diffractive waveguide.

[0052] Based on the above embodiments, the second coupling region can be divided into multiple coupling sub-regions, which can be regular partitions or irregular partitions, i.e., random partitions.

[0053] In some embodiments, the second coupling region is a regular partition, and all coupling sub-regions except those located on the boundary of the second coupling region have the same shape. Alternatively, when the second coupling region is a regular partition, the second coupling region is divided into multiple coupling sub-regions along one direction, or the second coupling region is divided into multiple coupling sub-regions along two different directions.

[0054] In practice, the second coupling region can be divided into multiple coupling sub-regions along one direction, with the grating directions of the one-dimensional gratings in adjacent coupling sub-regions being different. The dimensions of these multiple coupling sub-regions are random along this direction, but the maximum size of each coupling sub-region in this direction should be smaller than the spot size of the beam incident on the coupling region, and the center distance between two adjacent coupling sub-regions should be greater than or equal to λ / nsinθ; where, The refractive index of the waveguide substrate, The smallest angle that the human eye can distinguish. The wavelength of the beam projected from the image source is denoted by λ. This division of the coupled sub-regions and the distribution of the grating effectively expand the pupil and ensures that the distance between adjacent diffraction orders is beyond the human eye's ability to distinguish and is not directly perceived by the human eye. This effectively avoids and reduces the problem of multiple diffraction orders and improves the clarity of the displayed image from the diffraction waveguide.

[0055] For example, Figure 8 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention; Figure 9 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention. As can be seen, Figure 8 To divide the second coupling region into multiple coupling sub-regions in the Y direction, one-dimensional gratings B and C are filled in each coupling sub-region 321 along the Y direction in the figure, forming an arrangement of B, C, B, C... so that the grating directions of the one-dimensional gratings in two adjacent coupling sub-regions are different. Figure 9 To divide the second coupling region into multiple coupling sub-regions in the X direction, one-dimensional gratings A, B, and C are filled in each coupling sub-region 321 along the X direction in the figure, forming an arrangement of A, B, C... so that the grating directions of the one-dimensional gratings in two adjacent coupling sub-regions are different. Figure 10 The second coupling region is divided into multiple coupling sub-regions in a direction that deviates from the Y direction by a certain angle in the X direction. The grating directions of the one-dimensional gratings in two adjacent coupling sub-regions along this direction are different.

[0056] In practice, the second coupling region can be divided into multiple coupling sub-regions along two directions, with the grating directions of the one-dimensional gratings in adjacent coupling sub-regions being different. The size constraints of the coupling sub-regions are the same as those of the coupling sub-regions divided along one direction. Optionally, under this division method, except for the coupling sub-regions located on the boundary of the second coupling region, all other coupling sub-regions have the same shape.

[0057] For example, Figure 11This is a schematic diagram of an coupled sub-region provided in an embodiment of the present invention; Figure 12 This is a schematic diagram of an coupled sub-region provided in an embodiment of the present invention; Figure 13 A schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention; Figure 14 This is a schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention. (Reference) Figure 3 and Figure 4 In the figure, the second coupling region is divided into multiple coupling sub-regions 321 in the X and Y directions. Except for the coupling sub-regions located on the boundary of the second coupling region, the remaining coupling sub-regions are all rectangular in shape. The shape of the coupling sub-regions 321 can also be other regular shapes, such as hexagons (e.g.,...). Figure 12 (as shown) or triangle (as shown) Figure 13 (As shown) etc. Reference Figure 13 and 14 The diagram also shows the second coupling region divided into multiple coupling sub-regions 321 in two directions. For example... Figure 13 In the second coupling region 32, the coupling sub-region 321 at the center is rhomboid. The coupling sub-regions 321 are nested sequentially along the two sides of the rhombus. The width d0 of each coupling sub-region 321 can be the same or different. A one-dimensional grating is filled in each coupling sub-region 321, and the one-dimensional gratings in adjacent coupling sub-regions 321 are different, such as one-dimensional grating B and one-dimensional grating C respectively. When the one-dimensional grating B acts, the light diffracts. The +1 order light is deflected towards the second sub-coupling region 312 and propagates, while the 0th order light continues to propagate in its original direction until it interacts with the one-dimensional grating C, generating a -1 order light. This light is then deflected towards the first sub-coupling region 311 and propagates, while the 0th order light continues to propagate in its original direction, and so on. The deflected +1 and -1 order light interacts with the one-dimensional gratings B and C during propagation, thus generating coupled rays. In particular, a one-dimensional grating A can also exist in the middle region of the second coupling region. The interaction between the 0th order grating and the one-dimensional grating A will directly couple out, thereby improving the efficiency in this field of view.

[0058] It should be noted that the accompanying drawings only schematically show the filling of a few one-dimensional gratings within the coupled sub-regions 321; the filling methods of other coupled sub-regions 321 are not shown.

[0059] It should be noted that the "regular division" mentioned in the above examples refers to the consistent shape of the sub-regions, such as triangles, quadrilaterals, or squares, but not necessarily their consistent size. For example, in the case of regularly divided quadrilateral sub-regions, it is not required that each sub-region be exactly the same size. Except for the boundary of the second region, where there may be sub-regions of different shapes, all other sub-regions should be quadrilaterals.

[0060] Furthermore, the method of performing regular partitioning of the second coupled region is not limited to the method mentioned in this application; any method that can achieve regular partitioning of the second coupled region is included.

[0061] It should be noted that when the second coupling region is designed with regular partitions, and the structure is arranged in a periodic pattern with the coupling sub-regions as units, this structure may have the problem of multiple diffraction orders. By reasonably setting the size of the coupling sub-regions, and ensuring that the center distance between two adjacent coupling sub-regions is greater than or equal to d≥λ / nsinθ, the distance between adjacent diffraction orders can be kept beyond the human eye's ability to distinguish and not directly perceived by the human eye. This can effectively avoid and reduce the problem of multiple diffraction orders and improve the clarity of the displayed image of the diffraction waveguide.

[0062] In some embodiments, when the second coupling region is a regular partition, each coupling sub-region may further include at least two coupling secondary sub-regions, and the grating directions of each coupling secondary sub-region are different.

[0063] For example, Figure 15 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention; Figure 16 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention. Each coupling sub-region 321 includes multiple coupling secondary sub-regions 3211, and the grating vector directions of each coupling secondary sub-region 3211 are different. Specifically, in conjunction with... Figure 15 and Figure 16 As shown, for the second coupled region 32 after one partitioning, multiple coupled secondary sub-regions 3211 can be obtained by further partitioning within each coupled sub-region 321. For example, in Figure 15 The central region of the rectangular coupling sub-region 321 is divided into a secondary coupling sub-region 3211. Figure 16 The hexagonal coupling sub-region 321 is divided into coupling secondary sub-regions 3211. When filling multiple coupling secondary sub-regions 3211 with one-dimensional gratings, it is only necessary to fill multiple coupling secondary sub-regions 3211 with one-dimensional gratings of different grating vectors in each coupling sub-region 321, so that the grating vectors of the one-dimensional gratings in two adjacent coupling secondary sub-regions 3211 are different, thereby realizing the pupil expansion and coupling of the beam.

[0064] In some embodiments, the second detached region is an irregular partition, i.e., a random partition. The second detached region is irregularly partitioned, meaning that, except for the detached sub-regions located on the boundary of the second detached region, each of the remaining detached sub-regions has at least two detached sub-regions with different shapes. With irregular partitioning, the detached sub-regions are no longer periodically arranged, which can avoid or reduce multi-order diffraction problems and eliminates the need for additional size lower limits.

[0065] Based on the above embodiments, optionally, when the second coupling region is an irregular partition, the coupling sub-region is a Thiessen polygon partition; wherein, the discrete point dividing the Thiessen polygon partition is the intersection point of the beam inserted into the optical waveguide substrate and the second coupling region; and / or, the offset point is obtained based on the offset of the reference point of the initial coupling sub-region of the regular partition.

[0066] Figure 19 This is a schematic diagram of another coupling sub-region provided in an embodiment of the present invention. (Refer to...) Figure 19 As shown, based on a regular shape, the Thiessen polygon partitioning can be optimized by dividing it according to the Voronoi diagram, breaking the periodic arrangement of the coupled sub-regions in the case of regular partitioning, thus avoiding multi-order diffraction problems. In another embodiment, when the second coupled region is an irregular partition, the target points for dividing the Thiessen polygon partitions can be selected by optical path tracing. Based on these target points, a set of perpendicular bisectors of line segments connecting any two adjacent target points is determined, dividing the second coupled region into multiple coupled sub-regions 321. One-dimensional gratings with different grating vectors are filled into them in the same way as regular rectangular partitioning, forming the irregularly partitioned second coupled region 32, which can effectively avoid or reduce the diffraction problems of multiple diffraction orders of pupil expansion and coupled rays.

[0067] It should be noted that the method of irregular partitioning of the second coupled region is not limited to the method mentioned in this application. Any method that can achieve irregular partitioning of the second coupled region is included.

[0068] In some embodiments, the second coupling region includes each coupling sub-region having a size smaller than the spot size of the beam in at least one direction. Optionally, it is at least smaller than the spot size of the beam reaching the second coupling region.

[0069] For example, combined Figures 8-10 , Figures 13-14 As shown, the size d0 of each coupling sub-region 321 in at least one direction is smaller than the spot size of the beam A' reaching the second coupling region 32, so as to ensure that light rays are diffracted on the grating in different vector directions, thereby expanding the pupil or coupling out.

[0070] In some embodiments, at least three different grating orientations of one-dimensional gratings are provided in the second coupling region, and the first one-dimensional grating among these one-dimensional gratings is the same as the one-dimensional grating provided in the coupling region; in the coupling sub-region of the second coupling region, the size of the coupling sub-region filling the first one-dimensional grating in at least one direction is smaller than the size of the coupling sub-region filling the remaining one-dimensional gratings among these one-dimensional gratings in that direction.

[0071] It is understood that the first one-dimensional grating is the same as the one-dimensional grating in the coupling region. When the light beam is incident on the coupling region where the first one-dimensional grating is provided, it can be deflected and directly coupled out, resulting in high coupling efficiency. Thus, the coupling efficiency can be improved by locally setting the first one-dimensional grating in the coupling region. However, precisely because of its high coupling efficiency, if the size of the coupling sub-region where the first one-dimensional grating is set is too large, it will cause the efficiency of the coupling sub-region to concentrate, forming bright spots or bright bars, which is not conducive to coupling uniformity. Therefore, in this application, the size of the coupling sub-region filling the first one-dimensional grating in at least one direction is smaller than the size of the coupling sub-region filling the remaining one-dimensional gratings in these one-dimensional gratings in that direction, so as to balance the coupling efficiency and uniformity.

[0072] For example, Figure 17 This illustration shows a schematic diagram of the second coupling region partitioning and filling of a one-dimensional grating in one embodiment of this application. Figure 18 A schematic diagram of the second coupling region partitioning and filling of a one-dimensional grating in one embodiment of this application is shown. (Reference) Figure 17 The coupled sub-region 321(03) is filled with a first one-dimensional grating, which is the same one-dimensional grating as the coupled-in grating. The coupled sub-regions 321(01) and 321(02) are provided with one-dimensional gratings different from the coupled-in grating. The size of the coupled sub-region 321' in the X direction is smaller than the size of the coupled sub-regions 321(01) and 321(02) in the X direction. Reference Figure 18 The coupled sub-regions 321(06) and 321(07) are filled with a first one-dimensional grating, which is the same one-dimensional grating as the coupled grating. The coupled sub-regions 321(04) and 321(05) are set with a one-dimensional grating different from the coupled grating. The size of the coupled sub-region 321(06) in the Y direction and the X direction is smaller than that of the coupled sub-regions 321(04) and 321(05) in the Y direction and the X direction, respectively. The size of the coupled sub-region 321(07) in the Y direction is smaller than that of the coupled sub-regions 321(04) and 321(05) in the Y direction, respectively.

[0073] Based on the above embodiments, the second coupling region includes a first side and a second side disposed opposite to each other; the first side is close to the coupling region; the length of the first side is greater than the length of the second side, and the width of the second coupling region gradually decreases along a first direction; the first direction is the direction from the first side to the second side, and the width of the second coupling region is the length in a second direction perpendicular to the first direction.

[0074] It should be noted that the second coupling region includes a first side and a second side arranged opposite to each other; the first side is close to the coupling region; the first direction is defined as the direction from the first side to the second side, and the width of the second coupling region is its length in a second direction perpendicular to the first direction. Since the grating structure of the second coupling region is used to both extend the beam to one or both sides and couple the beam out of the waveguide substrate, and the light energy continuously attenuates as the beam is extended to one or both sides, the length of the first side of the second coupling region is greater than the length of the second side, and the width of the second coupling region gradually decreases along the first direction to improve coupling uniformity.

[0075] For example, Figure 20 A schematic diagram of an coupling region provided in an embodiment of the present invention; Figure 21 A schematic diagram of another coupling region provided in an embodiment of the present invention; Figure 22 A schematic diagram of another coupling region provided in an embodiment of the present invention; Figure 23 A schematic diagram of another coupling region provided in an embodiment of the present invention. Figure 24 This is a schematic diagram of another coupling region provided in an embodiment of the present invention. (See reference...) Figures 20-24 As shown, optionally, the second coupling region 32 includes a first side L1 and a second side L2 that are disposed opposite to each other; the first side L1 is close to the coupling region 2; the length of the first side L1 is greater than the length of the second side L2, and the width H1 of the second coupling region 32 gradually decreases along the first direction.

[0076] It is understandable that the energy carried by a light beam attenuates continuously as the beam propagates and diffracts, decreasing with distance from the coupling region. Therefore, it is necessary to reduce the number of pupil dilation actions and increase the number of coupling-out actions to compensate for the coupling energy at the edges. Therefore, preferably, the dimensions of the first sub-coupling region 311 and the second sub-coupling region 312 can be set to gradually increase with distance from the coupling region. For example, the length of the first side L1 can be greater than the length of the second side L2, so that the width H1 of the second coupling region 32 gradually decreases along the direction from the first side L1 to the second side L2. Based on the above embodiment, the length of the first side satisfies the boundary condition for the boundary field angle light emitted from the image source to reach the second coupling region. This avoids the situation where the coupled light enters the first coupling region directly without passing through the diffraction pupil of the second coupling region, potentially leading to ineffective coupling.

[0077] Figure 25 This is a schematic diagram of another planar structure of a diffractive waveguide provided in an embodiment of the present invention. (Reference) Figure 21 Figure 25 As shown, optionally, the length of the first side L1 satisfies the boundary condition that the boundary field angle ray (101) emitted from the image source reaches the second coupling region 32.

[0078] Optionally, combined Figures 21-25 As shown, the grating depth of the one-dimensional grating gradually increases along the direction from the first side L1 to the second side L2. In addition to grating partitioning, the height of the one-dimensional grating can be further partitioned, following the principle of gradually increasing grating depth along the direction away from coupling, which is beneficial for improving the diffraction efficiency of the grating. The grating depth is between 10nm and 200nm, and the value can be continuous or discrete.

[0079] Based on the above embodiments, the second coupling region further includes a third side; the third side is the boundary edge between the first coupling region and the second coupling region; the third side is one or more combinations of a straight edge, a curved edge, and a zigzag edge.

[0080] Specifically, the second coupling region is the region in the coupling region corresponding to the coupling-in region. The distribution of the first coupling region is related to the positional relationship between the coupling-in region and the coupling region. When the coupling-in region deviates from one side of the coupling region, the first coupling region may be distributed only on one side of the second coupling region. When the coupling-in region does not deviate from one side of the coupling region, the first coupling region is distributed on both sides of the second coupling region, i.e., the first sub-coupling region and the second sub-coupling region. In addition, the width of the first sub-coupling region and the second sub-coupling region is also related to the positional relationship between the coupling-in region and the coupling region. When the coupling-in region and the coupling region are aligned with the central axis in the first direction, the first sub-coupling region and the second sub-coupling region are symmetrically arranged about the central axis; when the coupling-in region deviates from the central axis in the first direction, the widths of the first sub-coupling region and the second sub-coupling region are unequal, with the width of the first sub-coupling region, which is closer to the coupling region, being greater than the width of the second sub-coupling region.

[0081] For example, refer to Figures 20-24 As shown, optionally, the second coupling region 32 further includes a third side L3 disposed opposite to it. The third side L3 is the boundary between the first coupling region 31 and the second coupling region 32. The third side L3 can be one or more combinations of a straight edge, a curved edge, and a zigzag edge. The first coupling region 31 can gradually increase in size along the direction from the first side L1 to the second side L2, so as to reduce the number of pupil expansion actions, increase the number of coupling actions, compensate for the coupling energy at the edge, and improve the uniformity of the light energy distribution of the emitted light field in the coupling region of the diffractive waveguide. Figure 24 In the process, when the coupling-in region deviates to one side of the coupling-out region, the first coupling-out region can be distributed on one side of the second coupling-out region. Figure 20-23 In the case where the coupling-in region does not deviate to one side of the coupling-out region, the first coupling-out region is distributed on both sides of the second coupling-out region, including the first sub-coupling-out region and the second sub-coupling-out region.

[0082] Based on the same inventive concept, the present invention also provides a design method for a diffractive waveguide, used to design the diffractive waveguide provided in the above embodiments. Figure 26 This is a flowchart illustrating a design method for a diffractive optical waveguide provided in an embodiment of the present invention. (Combined with...) Figures 3-7 and Figure 26 As shown, the design method includes:

[0083] S101. Determine the coupling-in region and the coupling-out region on at least one surface of the waveguide substrate.

[0084] Specifically, a waveguide substrate 1 is provided, and a coupling region 2 and a coupling region 3 are defined on at least one surface of the waveguide substrate 1.

[0085] At least one surface is selected from the first surface M1 and the second surface M2 of the waveguide substrate that are parallel to each other. The coupling region 1 is used to couple the beam of light projected by the image source into the waveguide substrate 1 so that the beam is transmitted through total internal reflection between the first surface M1 and the second surface M2 of the waveguide substrate 1 to the coupling region 3 and then coupled out of the waveguide substrate 1.

[0086] S102. Divide the coupling region into a first coupling region and a second coupling region, and further divide the second coupling region into multiple coupling sub-regions.

[0087] S103. Fill the coupling-in region, the first coupling-out region, and the multiple coupling-out sub-regions with one-dimensional gratings. Among them, the grating directions of the one-dimensional gratings in at least two coupling-out sub-regions are different, the grating vectors of the one-dimensional gratings in the first coupling-out region are the same as those of one type of one-dimensional grating in the coupling-out sub-regions, and the sum of the grating vectors of the one-dimensional gratings in the coupling-in region and the coupling-out region is zero.

[0088] In summary, the design method for the diffractive waveguide provided in this embodiment of the invention produces a diffractive waveguide comprising a waveguide substrate and a coupling region and a coupling region disposed on at least one side of the waveguide substrate. A beam projected from an image source is coupled into the waveguide substrate via the coupling region and transmitted through total internal reflection between two opposing surfaces of the waveguide substrate to the coupling region. The coupling region is divided into a first coupling region and a second coupling region. The second coupling region is further divided into multiple coupling sub-regions, each filled with a one-dimensional grating of a specific grating direction. At least two coupling sub-regions have different one-dimensional gratings to satisfy the requirement of pupil expansion and coupling of the beam through the second coupling region to the waveguide substrate. Simultaneously, the one-dimensional grating filled in the first coupling region is the same as one of the one-dimensional gratings in the coupling sub-regions, which increases edge light coupling and compensates for the coupling energy at the edges. Furthermore, the sum of the grating vectors of the one-dimensional gratings in the coupling region and the one-dimensional gratings in the coupling region is zero, achieving dispersion-free beam coupling and effectively improving the visual imaging effect of the diffractive waveguide.

[0089] Based on the above embodiments, step 102 includes:

[0090] S1. Divide the coupling region into a first coupling region and a second coupling region.

[0091] The second coupling region includes a first side and a second side that are arranged opposite to each other. The first side is close to the coupling region, and the length of the first side is greater than the length of the second side. The width of the second coupling region gradually decreases along a first direction, which is the direction from the first side to the second side. The width of the second coupling region is the length in a second direction that is perpendicular to the first direction.

[0092] S2. The second coupling region is regularly divided into multiple coupling sub-regions, and all coupling sub-regions except those located on the boundary of the second coupling region have the same shape; or, the second coupling region is irregularly divided into multiple coupling sub-regions, and at least two coupling sub-regions except those located on the boundary of the second coupling region have different shapes.

[0093] Based on the above embodiments, combined with Figure 20 As shown, in step S2, the second coupling region is irregularly divided into multiple coupling sub-regions, including:

[0094] S21. Regularize the second coupled region into multiple coupled sub-regions with the same shape.

[0095] S22. Select the center point of each coupled sub-region and use the center point as the initial point.

[0096] S23. Randomly offset the initial point in at least one direction to obtain the target point.

[0097] S24. Based on the target point, determine a set of perpendicular bisectors of line segments connecting any two adjacent target points to divide the second coupling region into multiple coupling sub-regions.

[0098] Specifically, in combination Figure 19As shown, the second coupling region 32 is pre-defined with multiple primary coupling sub-regions (not shown in the figure) of regular partitions. The center point coordinates (xi, yi) of each primary coupling sub-region under the regular partition are obtained. The center point is used as the initial point. The center point coordinates (xi, yi) are randomly offset in at least one direction to obtain the target point coordinates (xi'=xi+Δxi, yi'=yi+Δyi). Based on the target point, a set of perpendicular bisectors of line segments connecting any two adjacent target points are determined to divide the second coupling region 32 into multiple coupling sub-regions 321. Then, one-dimensional gratings with different grating vectors are filled in in the same way as the regular rectangular partitions to form the second coupling region 32 of irregular partitions. For example, the regular partition is set as a rectangular partition, the short side of the rectangle is a, and Δx and Δy follow a uniform distribution of (-a / 2, a / 2). Of course, the variables Δx and Δy can also follow different distributions, or they can not be uniformly distributed. There are no specific restrictions here. By breaking the periodic arrangement of the coupled sub-regions through random offset partitioning, the diffraction problems of multiple diffraction orders of the pupil expansion and coupled rays can be effectively avoided or reduced, thereby improving the clarity of the displayed image of the diffracted waveguide.

[0099] Based on the above embodiments, combined with Figure 19 As shown, in step S2, the second coupling region is irregularly divided into multiple coupling sub-regions, including:

[0100] S25. Determine the intersection point of the beam coupled into the optical waveguide substrate and the second coupling region to obtain the target point.

[0101] S26. Based on the target point, determine a set of perpendicular bisectors of line segments connecting any two adjacent target points to divide the second coupling region into multiple coupling sub-regions.

[0102] Specifically, the optical path of the beam coupled to the optical waveguide substrate can be traced to determine the intersection of the beam's path with the second coupling region 32, i.e., the total reflection point of the beam within the second coupling region 32. These total reflection points are used as target points for constructing the von Lono diagram to divide the Thiessen polygon partitions. Based on these target points, a set of perpendicular bisectors of line segments connecting any two adjacent target points are determined to divide the second coupling region 32 into multiple coupling sub-regions 321. Then, one-dimensional gratings with different grating vectors are filled in in the same way as regular rectangular partitions to form an irregularly partitioned second coupling region 32, which can effectively avoid or reduce the diffraction problems of pupil expansion and multiple diffraction orders of coupling rays.

[0103] It should be noted that the energy carried by a beam usually decreases as the beam propagates. The distribution of total reflection points can characterize the energy distribution to a certain extent, while the von Runnoy diagram is used to describe spatial proximity. Thus, when designing partitions based on the von Runnoy diagram with the total reflection point of the beam in the coupling region as the target point, combining the light energy distribution with the spatial proximity relationship is more conducive to improving the uniformity of the light energy distribution of the outgoing light field in the coupling region of the diffractive waveguide.

[0104] Based on the above embodiments, combined with Figures 21-24 As shown, step S102 further includes:

[0105] The coupling region is divided into a first coupling region and a second coupling region along the third side.

[0106] The third side is the boundary between the first and second coupled regions; the third side is one or more combinations of a straight edge, a curved edge, and a zigzag edge.

[0107] Specifically, the coupling region 3 is divided into a first coupling region 31 and a second coupling region 32 along the third side L3. The plane containing the third side L3 can be one or a combination of planes, arcs, and zigzags, and its surface design is not limited to satisfying the following conditions. Figures 21-24 The first coupling region 31 can be gradually increased along the direction from the first side L1 to the second side L2 to reduce the number of pupil expansion actions, increase the number of coupling actions, compensate for the coupling energy at the edge, and improve the uniformity of the light energy distribution of the output light field in the coupling region of the diffraction waveguide.

[0108] Based on the above embodiments, combined with Figure 4 , Figure 11 and Figure 12 As shown, in step S102, the second coupling region is divided into multiple coupling sub-regions, including:

[0109] The second coupling region is divided into multiple coupling sub-regions, and the area D1 of the coupling sub-region is set to be smaller than the spot area D2 of the beam reaching the second coupling region.

[0110] Continue to refer to Figure 4 , Figure 11 and Figure 12As shown, since the lateral propagation distance of the beam projected by the image source after total internal reflection in the waveguide substrate 1 is several hundred micrometers to several millimeters, and the beam spot diameter is usually four to five millimeters, in order to ensure that light is diffracted on the one-dimensional grating in different vector directions to expand the pupil or couple out, the second coupling region 32 is divided into multiple coupling sub-regions 321. The area D1 of the coupling sub-region 321 is set to be located within the spot area D2 of the beam reaching the second coupling region 32. That is, the spot area D2 of the beam reaching the second coupling region 32 covers at least one one-dimensional grating in the coupling sub-region 321, ensuring that light is diffracted on the grating to expand the pupil or couple out.

[0111] Preferably, the area D1 of the coupling sub-region 321 is set to ensure that the coverage area of ​​the light spot (i.e., the area D2 of the light spot reaching the second coupling region 32) includes all types of one-dimensional gratings within the second coupling region 32. This ensures that light rays are diffracted on gratings in different vector directions, thereby expanding the pupil or coupling out. It should be noted that, as described in the above embodiment, the types of one-dimensional gratings are classified here based on the grating vector direction.

[0112] Based on the above embodiments, optionally, the grating depth of the one-dimensional grating in the first and second coupling regions gradually increases along the direction away from the coupling region.

[0113] Specifically, the grating has the following parameters: n is the refractive index of the waveguide substrate material, γ is the grating tilt angle, Λ is the grating period, W is the grating width, and H is the grating depth. Along the direction away from the coupling region, the grating depth H of the one-dimensional grating in the first coupling region 31 and the second coupling region 32 gradually increases, improving the diffraction efficiency of light in the first and second coupling regions 31 and 32, thus ensuring a uniform distribution of light energy in the outgoing light field of the diffracted waveguide substrate and providing uniform brightness for image display.

[0114] Based on the above embodiments, the duty cycle and grating tilt angle of the grating in the coupling region vary along the direction away from the coupling region. Furthermore, by reasonably adjusting parameters such as the grating tilt angle γ and duty cycle ff of the one-dimensional grating in the first coupling region 31 and the second coupling region 32 along the direction away from the coupling region, the total internal reflection condition of light within the diffraction waveguide can be matched, thereby improving the diffraction efficiency in the first coupling region 31 and the second coupling region 32 and achieving a uniform distribution of light energy in the emitted light field of the diffraction waveguide substrate. Wherein, the duty cycle ff = W / Λ.

[0115] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and the features of various embodiments of the present invention can be combined partially or entirely with each other, and can cooperate and be technically driven in various ways. Various obvious changes, readjustments, combinations, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A diffractive optical waveguide, characterized in that, It includes a waveguide substrate and a coupling-in region and a coupling-out region disposed on at least one side of the waveguide substrate; The waveguide substrate has a first surface and a second surface that are parallel to each other. The coupling region is used to couple a beam of light projected by an image source into the waveguide substrate so that the beam is transmitted to the coupling region by total internal reflection between the first surface and the second surface of the waveguide substrate. The coupling region includes a first coupling region and a second coupling region; the second coupling region includes multiple coupling sub-regions, and at least two different grating orientations of one-dimensional gratings are provided in the second coupling region, and one of the at least two different grating orientations of one-dimensional gratings is provided in each of the coupling sub-regions; the grating vector of the one-dimensional grating provided in the first coupling region is the same as that of one of the one-dimensional gratings in the coupling sub-regions. The second coupling region is a regular partition, and except for the coupling sub-region located on the boundary of the second coupling region, the remaining coupling sub-regions have the same shape.

2. The diffractive waveguide according to claim 1, characterized in that, The second coupling region is divided into multiple coupling sub-regions along one direction, or the second coupling region is divided into multiple coupling sub-regions along two different directions.

3. The diffractive waveguide according to claim 1, characterized in that, The center distance between two adjacent coupled sub-regions is: ； Where d is the center distance between two adjacent coupling sub-regions, and n is the refractive index of the waveguide substrate. The smallest angle that the human eye can distinguish. The wavelength of the light beam projected from the image source.

4. The diffractive waveguide according to claim 1, characterized in that, Each of the said coupled sub-regions includes at least two coupled secondary sub-regions, and the grating vectors of the one-dimensional gratings in two adjacent coupled secondary sub-regions are different.

5. The diffractive waveguide according to claim 1, characterized in that, The second coupling region includes a first side and a second side disposed opposite to each other; the first side is close to the coupling region; the length of the first side is greater than the length of the second side, and the width of the second coupling region gradually decreases along a first direction; the first direction is the direction from the first side to the second side, and the width of the second coupling region is the length in a second direction perpendicular to the first direction.

6. The diffractive waveguide according to claim 5, characterized in that, The length of the first side satisfies the boundary condition for the boundary field angle light emitted from the image source to reach the second coupling region, so that the incoming light light passes through the second coupling region and then enters the first coupling region.

7. The diffractive waveguide according to claim 5, characterized in that, The second coupling region further includes a third side; the third side is the boundary edge between the first coupling region and the second coupling region; the third side is one or more combinations of a straight edge, a curved edge, and a zigzag edge.

8. The diffractive waveguide according to claim 1, characterized in that, The first coupling region includes a first sub-coupling region and a second sub-coupling region. The grating vector of the one-dimensional grating set in the first sub-coupling region is the same as the grating vector of the first type of one-dimensional grating in the coupling sub-region. The grating vector of the second sub-coupling region is the same as the grating vector of the second type of one-dimensional grating in the coupling sub-region.

9. The diffractive waveguide according to claim 1, characterized in that, The second coupling region includes each coupling sub-region whose size in at least one direction is smaller than the spot size of the light beam reaching the beam.

10. The diffractive waveguide according to claim 1, characterized in that, The second coupling region is provided with at least three different grating orientations of one-dimensional gratings, and the first one-dimensional grating of the at least three different grating orientations of one-dimensional gratings has the same grating vector as the one-dimensional grating provided in the coupling region; in the coupling sub-region of the second coupling region, the dimension of the coupling sub-region filling the first one-dimensional grating in at least one direction is smaller than the dimension of the coupling sub-region filling the remaining one-dimensional grating in that direction.

Images