Two-dimensional grating structure, pupil expansion structure and outcoupling structure

Abstract

The present invention provides a two-dimensional grating structure for use in pupil expansion and / or outcoupling structures of diffractive optical waveguides. The two-dimensional grating structure comprises a plurality of grating elements arranged periodically in at least two directions. The plurality of grating elements arranged periodically in at least two directions are configured such that the propagation path of a light beam in the diffractive optical waveguide is affected only by the periodic structure formed by the plurality of grating elements in one direction. The technical solution provided by the present invention optimizes the degree of freedom in modulating diffraction efficiency by modulating the duty cycle by increasing the periodic dimension of the grating structure, while also preventing the added periodic structure in other dimensions from affecting the existing light beam propagation path.

Description

Technical Field

[0001] The present invention relates to the field of optical waveguides, and in particular to a two-dimensional grating structure, a pupil expansion structure and an outcoupling structure. Background Art

[0002] Augmented reality (AR) is a technology that integrates the real world and virtual information. The AR display system usually includes a micro projector and an optical display screen. The virtual content provided by the micro display is projected into the human eye through the optical display screen, and the user sees the real world through the optical display screen at the same time.

[0003] Optical waveguides are a promising approach for optical displays. Currently, commercially available waveguides are generally categorized into geometric array waveguides and diffraction waveguides. These are further divided into volume holographic waveguides and surface relief grating waveguides. Surface relief grating waveguides offer significant advantages over other approaches due to their high degree of design freedom. Uniformity is a key performance metric for diffraction waveguides, and waveguide design typically optimizes this by modulating grating parameters (such as grating depth or duty cycle).

[0004] Currently, the most commonly used architecture for surface relief grating waveguides is a combination of a one-dimensional coupling-in grating, a one-dimensional pupil expansion grating, and a one-dimensional coupling-out grating. In this architecture, optimizing uniformity by modulating the grating depth theoretically has good results, but the manufacturing process is relatively complex. Optimizing uniformity by modulating the grating duty cycle has a certain degree of modulation capability at the same depth, but achieving a larger modulation range usually requires a relatively extreme line width and is difficult to manufacture.

[0005] Therefore, those skilled in the art hope to design a grating structure to optimize the aforementioned architecture, thereby increasing the degree of freedom in modulating the diffraction efficiency while reducing the difficulty of process manufacturing. Summary of the Invention

[0006] The present invention provides a two-dimensional grating structure, a pupil expansion structure and an outcoupling structure to solve the problems of limited freedom and high process difficulty when optimizing uniformity by modulating the duty cycle.

[0007] According to a first aspect of the present invention, a two-dimensional grating structure is provided for use as a pupil expansion structure and / or an outcoupling structure of a diffractive optical waveguide, the two-dimensional grating structure comprising:

[0008] A plurality of grating units are periodically arranged in at least two directions, wherein the plurality of grating units periodically arranged in the at least two directions are configured so that a propagation path of a light beam in the diffraction optical waveguide is only affected by the periodic structure formed by the plurality of grating units in one direction.

[0009] Optionally, one of the directions is a target direction, and directions other than the target direction among the at least two directions are other directions, and the periodic structures formed by the multiple grating units in the other directions are configured as follows: the period of the periodic structure formed in the other directions is adapted to the wavelength of the light beam and the refractive index of the waveguide substrate of the diffraction light waveguide, so that the propagation path of the light beam in the diffraction light waveguide is not affected by the periodic structure formed in the other directions.

[0010] Optionally, the period of the periodic structure formed by the multiple grating units in the i-th direction among the other directions is configured as a maximum value within an optional range, and the optional range represents the value of the period of the periodic structure formed by the multiple grating units in the i-th direction when the propagation path of the light beam in the diffraction optical waveguide is only affected by the periodic structure formed by the multiple grating units in the target direction.

[0011] Optionally, the periodic structures formed by the multiple grating units in other directions are further configured so that the diffraction efficiency of the light beam in the diffraction waveguide is jointly affected by the periodic structures formed by the multiple grating units in the target direction and the other directions.

[0012] Optionally, different positions of the two-dimensional grating structure have different grating parameters that affect the diffraction efficiency of the two-dimensional grating structure, so as to adjust the uniformity of pupil expansion and / or outcoupling of the light beam under the action of the two-dimensional grating structure.

[0013] Optionally, the two-dimensional grating structure is configured as follows: by configuring the grating duty ratio of different areas of the two-dimensional grating structure, the diffraction efficiency of the two-dimensional grating structure gradually increases along the direction of propagation of the light beam in the diffraction waveguide, so as to adjust the uniformity of pupil expansion or outcoupling of the light beam under the action of the two-dimensional grating structure.

[0014] According to a second aspect of the present invention, a pupil expansion structure is provided, comprising the grating structure according to any one of the first aspects of the present invention.

[0015] Optionally, the pupil expansion structure further includes a one-dimensional grating structure, and the turning efficiency in the pupil expansion structure increases successively along the direction of light beam propagation.

[0016] According to a third aspect of the present invention, there is provided a coupling-out structure comprising the grating structure described in the first aspect of the present invention.

[0017] Optionally, the outcoupling structure further includes a one-dimensional grating structure, and the outcoupling efficiency in the outcoupling structure increases successively along the direction of light beam propagation.

[0018] The present invention provides a two-dimensional grating structure comprising a plurality of grating units. These grating units are periodically arranged in at least two directions and configured such that, when used as a pupil expansion structure and / or an outcoupling structure of a diffractive optical waveguide, the propagation path of a light beam in the diffractive optical waveguide is affected only by the periodic structure formed by the grating units in one direction, thereby controlling the propagation path of the light beam within the waveguide substrate; while the periodic structures formed in other directions do not affect the propagation direction of the light beam in the two-dimensional grating structure. It can be seen that, when the two-dimensional grating structure provided by the present invention is used as a pupil expansion structure and / or an outcoupling structure of a diffractive optical waveguide, compared to the scenario where the existing one-dimensional grating structure is used as a pupil expansion structure and / or an outcoupling structure of a diffractive optical waveguide, the propagation path of the light beam in the diffractive optical waveguide is not affected by the configuration, and the arrangement of the grating units can greatly increase the degree of freedom for optimizing uniformity by modulating the duty cycle. In addition, the increased degree of freedom in optimizing the grating duty cycle can also reduce process difficulty and process cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 Schematic diagram of the diffraction waveguide architecture and grating arrangement consisting of a one-dimensional grating;

[0021] Figure 2 is a schematic diagram of the curve showing the diffraction efficiency of a one-dimensional grating structure changing with the duty cycle;

[0022] Figure 3 Schematic diagram of the duty cycle of a one-dimensional grating structure and a two-dimensional grating structure;

[0023] Figure 4 is a schematic diagram of a curve showing how the diffraction efficiency of a two-dimensional grating structure varies with the duty cycle in a specific embodiment of the present invention;

[0024] Figure 5 is a schematic diagram of a main grating and an auxiliary grating in a two-dimensional grating structure provided in one embodiment of the present invention;

[0025] Figure 6 It is a schematic diagram of the K domain of a light beam propagating in a diffraction optical waveguide;

[0026] Figure 7 FIG. 1 is a schematic diagram of a diffraction optical waveguide provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0028] The embodiments described are clearly and completely. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative work are within the scope of protection of the present invention.

[0029] The terms "first," "second," "third," "fourth," and the like (if any) in the description and claims of the present invention and in the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions, e.g., a process, method, system, product, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to these processes, methods, products, or apparatus.

[0030] It can be understood that uniformity is one of the key indicators for evaluating the performance of diffraction waveguides, which includes FOV uniformity and eyebox uniformity. A commonly used method to optimize the uniformity of a diffraction waveguide is to modulate the diffraction efficiency of the pupil expansion grating and / or the outcoupling grating in the diffraction waveguide; specifically, the diffraction efficiency of the pupil expansion grating and / or the outcoupling grating is modulated to increase with the increase in the propagation distance of the light beam. Although the light beam will lose energy each time it encounters the pupil expansion grating and / or the outcoupling grating, the diffraction efficiency increases as the light beam propagates. Therefore, the light beam can remain uniform at different positions along the propagation direction of the diffraction waveguide. A commonly used method to modulate the diffraction efficiency of the grating is to modulate the parameters of the grating, such as the grating depth or the grating duty cycle.

[0031] Among them, when modulating the diffraction efficiency by modulating the grating duty cycle to optimize uniformity, the pupil expansion grating and / or the outcoupling grating are set to different duty cycles along the light propagation path, and the duty cycle modulation has a certain modulation capability at the same grating depth. Figure 1 The diffraction waveguide 100 of the one-dimensional grating structure shown includes a coupling-in structure 101, a pupil expansion structure 102, a coupling-out structure 103 and a waveguide substrate 104, wherein the coupling-in structure 101, the pupil expansion structure 102 and the coupling-out structure 103 are all implemented as one-dimensional gratings. Figure 2, we can see that when other parameters remain unchanged and only the duty cycle is modulated, the one-dimensional grating can reach the upper limit of diffraction efficiency when the duty cycle FF=50%, which is also relatively easy to achieve in the process; if the lower limit of diffraction efficiency needs to be lowered to a value such as 0.5%, the duty cycle needs to be set to a very extreme value such as 15% or 90%, which is more difficult to achieve in the process. Figure 3 (a) The duty cycle FF of a one-dimensional grating is the ratio of the grating unit width W to the grating period T.

[0032] To solve this problem, the present application proposes a two-dimensional grating structure. Since the two-dimensional grating structure has a grating duty cycle in at least two directions, compared with a one-dimensional grating structure with only one duty cycle, it has a larger solution space for optimizing uniformity through duty cycle modulation. From the larger solution space, it is easier to find a structure that is easier to implement in the process to reduce the difficulty of the process.

[0033] Exemplary, reference Figure 4 , this figure takes a two-dimensional orthogonal grating as an example and shows the relationship between the diffraction efficiency and duty cycle of a two-dimensional grating structure. Figure 4 The horizontal axis is the X-direction duty cycle (FF_x), and the vertical axis is the first-order diffraction efficiency. Different curves correspond to different Y-direction duty cycles (FF_y). For example, the black solid line represents the curve of the first-order diffraction efficiency changing with the X-direction duty cycle when the Y-direction duty cycle is fixed at 80%. From this figure, it can be seen that if the lower limit of the diffraction efficiency needs to reach a lower value such as about 0.5%, there are multiple solutions, and the process is relatively easy to achieve, such as: FF_x = 50%, FF_y = 60%. Reference Figure 3 (b) The X-direction duty cycle (FF_x) of the two-dimensional orthogonal grating is the ratio of the X-direction width Wx of the grating unit to the X-direction grating period Tx, and the Y-direction duty cycle (FF_y) is the ratio of the Y-direction width Wy of the grating unit to the Y-direction grating period Ty.

[0034] In light of this, the present invention provides a two-dimensional grating structure for use as a pupil expansion structure and / or outcoupling structure in a diffractive optical waveguide. The two-dimensional grating structure comprises: a plurality of grating elements arranged periodically in at least two directions. The plurality of grating elements arranged periodically in at least two directions are configured such that the propagation path of a light beam in the diffractive optical waveguide is affected only by the periodic structure formed by the plurality of grating elements in one direction. In other words, although this novel two-dimensional grating structure is structurally two-dimensional, it only produces diffraction orders in one direction.

[0035] For the convenience of description, the two-dimensional grating structure includes a plurality of grating units arranged periodically in at least two directions. The direction of the periodic structure that affects the light beam propagation path in the at least two directions is defined as the target direction, and the directions other than the target direction are defined as other directions. It can be understood that, for example, Figure 1 In the illustrated diffraction waveguide architecture, the use of a two-dimensional grating as a pupil expansion grating and / or an outcoupling grating may affect the original beam propagation path in the diffraction waveguide, compared to the use of a one-dimensional grating (with the periodic structure oriented in the target direction) as a pupil expansion grating and / or an outcoupling grating, thereby potentially increasing the complexity of optimizing the uniformity of the diffraction waveguide. Therefore, the present application proposes optimizing the grating period, configuring the grating period in one direction of the two-dimensional grating so that the grating structure at this grating period can function in the K-domain to control the propagation path of the light beam within the waveguide substrate, while simultaneously configuring the grating period in other directions so that the grating structure at this grating period does not function in the K-domain, i.e., does not affect the original beam propagation path.

[0036] It can be seen that the technical solution provided by the present invention can optimize the duty cycle selection freedom by selecting a two-dimensional grating, while ensuring that the grating periodic structure in one direction of the two-dimensional grating does not affect the light beam propagation path in the diffraction waveguide, without increasing the complexity of uniformity adjustment.

[0037] The technical solution of the present invention is described in detail below with reference to specific embodiments.

[0038] According to one embodiment of the present invention, a two-dimensional grating structure is provided for use in a pupil expansion structure and / or an outcoupling structure of a diffraction light waveguide. The two-dimensional grating structure includes: a plurality of grating units periodically arranged in at least two directions, wherein the plurality of grating units periodically arranged in at least two directions are configured such that a propagation path of a light beam in the diffraction light waveguide is affected only by the periodic structure formed by the plurality of grating units in one direction.

[0039] The grating unit may be shaped like a circle, ellipse, rectangle, or polygon; other implementations are also possible. Any grating unit shape that can achieve the technical effects of this application is within the scope of protection of this application, and this application is not limited thereto. Furthermore, the shapes of grating units at different locations in the two-dimensional grating structure may be the same or different.

[0040] In one embodiment, one direction is a target direction, and directions other than the target direction in at least two directions are other directions. The periodic structure formed by the multiple grating units in the target direction is configured as follows: the period of the periodic structure formed in the target direction is adapted to the wavelength of the light beam and the refractive index of the waveguide substrate of the diffraction light waveguide, so that the propagation path of the light beam in the diffraction light waveguide is affected by the periodic structure formed in the target direction; and the periodic structures formed by the multiple grating units in other directions are configured as follows: the period of the periodic structure formed in other directions is adapted to the wavelength of the light beam and the refractive index of the waveguide substrate of the diffraction light waveguide, so that the propagation path of the light beam in the diffraction light waveguide is not affected by the periodic structures formed in other directions.

[0041] Wherein, any grating unit is periodically arranged in any of the at least two directions, that is, any grating unit has at least two periodicities.

[0042] The following describes the specific configuration requirements for the periodic structure formed by multiple grating units in other directions: For the convenience of explanation, the concepts of main grating and auxiliary grating are introduced. The main grating refers to the grating structure that is periodically arranged along the target direction in the two-dimensional grating structure. The auxiliary grating structure refers to the grating structure that is periodically arranged along other directions in the two-dimensional grating structure. There is only one main grating, but there can be multiple auxiliary gratings. Figure 5 The two-dimensional grating structure includes a main grating G1 and an auxiliary grating G2.

[0043] like Figure 6 As shown in the K-domain diagram, it is assumed that the K vector coordinate of the initial light beam coupled into the waveguide is (K x0 ,K y0 ); the grating period of the grating is d, and the angle between the grating vector and the X axis is θ, then the coordinates of the K vector after grating diffraction are

[0044] Wherein, m is the diffraction order, preferably, m=±1.

[0045] When a two-dimensional grating structure is used for the pupil expansion structure of a diffractive optical waveguide, after the light beam is diffracted by the main grating of the pupil expansion structure (i.e., the main grating of the two-dimensional grating structure), the K vector coordinate must satisfy the following relationship:

[0046]

[0047] After the light beam is diffracted by any auxiliary grating of the pupil expansion structure (i.e., any auxiliary grating of the two-dimensional grating structure), the K vector coordinates must satisfy the following relationship:

[0048]

[0049] Where n is the refractive index of the waveguide substrate, λ is the wavelength of the beam, and d i is the period of the i-th auxiliary grating.

[0050] It should be noted that the inner circle in the K-domain diagram represents the total reflection condition of the waveguide substrate, and the outer circle represents the maximum K value that the waveguide substrate material can achieve. Usually, the coupling-in structure shifts the K value of the light beam to the annular area, so that the light beam meets the conditions for total reflection propagation in the waveguide substrate and is coupled into the waveguide substrate; the expansion structure shifts the K value of part of the light beam within the annular area, so that the light beam is expanded. If it expands in multiple directions, there are multiple light beam propagation paths; the coupling-out structure shifts the K value of part of the light beam from the annular area to the inner circle area, so that the light beam is coupled out to the human eye.

[0051] In the present application, since the main grating of the pupil expansion structure is a grating used to control the propagation path of the light beam, and the auxiliary grating of the pupil expansion structure does not affect the propagation path of the light beam, the K vector coordinates obtained after the main grating of the pupil expansion structure acts on it must be located within the annular area in the K domain diagram, that is, it satisfies formula (1), and the K vector coordinates obtained after the auxiliary grating of the pupil expansion structure acts on it must be located outside the outer circle in the K domain diagram, that is, it satisfies formula (2). In this way, the light beam diffracted by the main grating of the pupil expansion structure can remain in the waveguide and continue to transmit through total reflection, and the light beam diffracted by the auxiliary grating of the pupil expansion structure will not generate another light beam propagation path, nor will it be coupled out of the waveguide substrate to generate light leakage. Continue to refer to Figure 6 (a) The light beam passes through the main grating K of the pupil expansion structure epe1 After the action, the vector coordinates are located in the annular area of ​​the K domain diagram and continue to transmit in the waveguide substrate. After the pupil expansion structure, the main grating K epe2 After the action, the vector coordinates are outside the outer circle in the K-domain diagram and no longer exist.

[0052] When a two-dimensional grating structure is used as an outcoupling structure of a diffractive optical waveguide, after the light beam is diffracted by the main grating of the outcoupling structure (i.e., the main grating of the two-dimensional grating structure), the K vector coordinates must satisfy the following relationship:

[0053]

[0054] After the light beam is diffracted by any auxiliary grating of the outcoupling structure (ie, any auxiliary grating of the two-dimensional grating structure), the K vector coordinate must also satisfy the above formula (2).

[0055] In the present application, since the main grating of the outcoupling structure is a grating used to control the light beam propagation path and light beam outcoupling, the auxiliary grating of the outcoupling structure does not affect the light beam propagation path and does not need to cause light outcoupling, then the K vector coordinates obtained after the main grating of the outcoupling structure acts on it must be located within the inner circle of the K domain diagram, that is, it satisfies formula (3), and the K vector coordinates obtained after the auxiliary grating of the outcoupling structure acts on it must be located outside the outer circle of the K domain diagram, that is, it satisfies formula (2). In this way, after the main grating of the outcoupling structure diffracts, light beam outcoupling occurs, and the partial light beam diffracted by the auxiliary grating of the outcoupling structure will not generate another light beam propagation path, nor will it be coupled out of the waveguide substrate. Continue to refer to Figure 6 (b) The light beam passes through the main grating K of the outcoupling structure out1 After the action, the vector coordinates are located in the inner circle of the K domain diagram, coupled out of the waveguide substrate, and through the main grating K of the pupil expansion structure out2 After the action, the vector coordinates are outside the outer circle in the K-domain diagram and no longer exist.

[0056] To facilitate process manufacturing, preferably, the period of the periodic structure formed by the multiple grating units in the i-th direction is configured to be a maximum value within an optional range. The optional range represents the value of the period of the periodic structure formed by the multiple grating units in the i-th direction when the propagation path of the light beam in the diffraction waveguide is only affected by the periodic structure formed by the multiple grating units in one direction.

[0057] In a specific example, the angle between the periodic structure formed by the multiple grating units in one direction and the periodic structure formed in other directions is 45°; in another specific example, the angle between the periodic structure formed by the multiple grating units in one direction and the periodic structure formed in other directions is 60°; of course, other implementation forms are also possible. Any implementation form of the angle between the main grating and the auxiliary grating that can achieve the technical effect of the present application is within the scope of protection of the present invention, and the present application is not limited to this.

[0058] The above is an explanation of how to maintain the original light beam propagation path unchanged after replacing the one-dimensional grating structure in the pupil expansion structure and / or the outcoupling structure in the diffraction waveguide with a two-dimensional grating structure.

[0059] In one embodiment, the periodic structures formed by the multiple grating units in other directions are further configured such that the diffraction efficiency of the light beam in the diffractive waveguide is jointly affected by the periodic structures formed by the multiple grating units in other directions. In other words, when the one-dimensional grating structure in the pupil expansion structure and / or the outcoupling structure of the diffractive waveguide is replaced with a two-dimensional grating structure, the grating diffraction efficiency changes.

[0060] In one embodiment, the grating duty cycles at different positions of the two-dimensional grating structure are different to adjust the uniformity of pupil expansion or outcoupling of the light beam under the action of the two-dimensional grating structure.

[0061] In one embodiment, the two-dimensional grating structure is configured as follows: by configuring the grating duty cycle of different regions of the two-dimensional grating structure, the diffraction efficiency of the two-dimensional grating structure gradually increases along the direction of light beam propagation in the diffraction waveguide, so as to adjust the uniformity of pupil expansion or outcoupling of the light beam under the action of the two-dimensional grating structure.

[0062] In one embodiment, the grating depth of the two-dimensional grating structure may also be modulated simultaneously, so that the diffraction efficiency of the two-dimensional grating structure gradually increases along the propagation direction of the light beam in the diffraction waveguide.

[0063] In one embodiment, the two-dimensional grating structure is configured such that, by adjusting the grating duty cycle of different regions of the two-dimensional grating structure, the diffraction efficiency of the two-dimensional grating structure gradually increases along the direction of light beam propagation in the diffractive waveguide. In this case, the two-dimensional grating structure can be considered as being divided into multiple regions, each with a consistent grating duty cycle. Furthermore, the grating depth of the two-dimensional grating structure can be further modulated to gradually increase the diffraction efficiency along the direction of light beam propagation within each region, while also gradually increasing the diffraction efficiency along the direction of light beam propagation within the entire two-dimensional grating structure.

[0064] In other embodiments, the diffraction efficiency of the two-dimensional grating structure may also show other changing trends. As long as the implementation form of the diffraction efficiency changing trend can adjust the pupil expansion or coupling uniformity of the light beam under the action of the two-dimensional grating structure, it is within the protection scope of the present invention, and the present invention is not limited to this.

[0065] On the other hand, the present invention further provides a pupil expansion structure, comprising the two-dimensional grating structure of the aforementioned embodiment of the present invention.

[0066] For example, the angle between the periodic structure formed by the multiple grating units in one direction and the periodic structure formed by the multiple grating units in the other direction is 45°. That is, the angle between the main grating and the auxiliary grating is 45°. Of course, other angles, such as 60°, are also possible. The 60° and 45° values ​​here are merely illustrative, and the present invention does not impose any limitations on the value of this angle, which ranges from greater than 0° to less than 180°.

[0067] In one embodiment, the diffraction efficiency in the pupil expansion structure increases successively along the direction of light beam propagation.

[0068] Specifically, along the direction of light beam propagation, the duty cycle of the two-dimensional grating structure is modulated so that the diffraction efficiency in the pupil expansion structure along the direction of light beam propagation increases successively, thereby optimizing pupil expansion uniformity.

[0069] In another embodiment, the grating depth of the two-dimensional grating structure can be modulated simultaneously along the direction of light beam propagation, so that the diffraction efficiency of the pupil expansion structure gradually increases along the direction of light beam propagation.

[0070] In one embodiment, the pupil expansion structure further includes a one-dimensional grating structure, and the turning efficiency in the pupil expansion structure increases successively along the direction of light beam propagation.

[0071] It should be noted that, continue to refer to Figure 3 and Figure 4 , it can be seen that the one-dimensional grating structure can obtain higher diffraction efficiency than the two-dimensional grating structure, and the duty cycle of the one-dimensional grating structure when obtaining high diffraction efficiency is also a structure that is easy to achieve in terms of technology. It can be seen that the one-dimensional grating structure has an advantage when modulating the duty cycle to achieve high diffraction efficiency, and the two-dimensional grating structure has an advantage when modulating the duty cycle to achieve lower diffraction efficiency. In this way, the position where high diffraction efficiency is required in the pupil expansion structure can also use a one-dimensional grating structure. Figure 7 The diffraction waveguide 200 includes an incoupling structure 201, a pupil expansion structure 202, an outcoupling structure 203, and a waveguide substrate 204. Different regions of the pupil expansion structure 202 are two-dimensional grating structures 10 or one-dimensional grating structures 20 with different duty cycles. Regions where the light beam propagates closer do not require high diffraction efficiency and may use the two-dimensional grating structure 10. Regions where the light beam propagates farther require relatively high diffraction efficiency and may use the one-dimensional grating structure 20. It should be noted that Figure 7 The partitioning arrangement of the pupil expansion structure is only for illustration, and there may be more two-dimensional grating structures or one-dimensional grating structures with different duty cycles.

[0072] Of course, in other embodiments, the two-dimensional grating structure and the one-dimensional grating structure can be arranged alternately within the pupil expansion structure. It will be appreciated that when designing the specific grating structure within the pupil expansion structure, the design is based on turning efficiency, such that the turning efficiency increases sequentially along the direction of beam propagation within the pupil expansion structure, thereby improving beam expansion uniformity. Therefore, for any location or region within the pupil expansion structure, any grating structure (whether two-dimensional or one-dimensional) that achieves the required turning efficiency and has a relatively easy-to-implement duty cycle can be considered a solution.

[0073] On the other hand, the present invention further provides an outcoupling structure comprising the two-dimensional grating structure of the aforementioned embodiment of the present invention.

[0074] For example, the angle formed between the periodic structure formed by the multiple grating units in one direction and the periodic structure formed by the multiple grating units in the other direction is 90°. That is, the angle between the main grating and the auxiliary grating is 90°. Of course, other angles, such as 60°, are also possible. The 60° or 90° values ​​here are merely illustrative, and the present invention does not impose any limitations on the value of this angle, which ranges from greater than 0° to less than 180°.

[0075] In one embodiment, the diffraction efficiency in the outcoupling structure increases successively along the direction of light beam propagation.

[0076] Specifically, along the direction of light beam propagation, the duty cycle of the two-dimensional grating structure is modulated so that the diffraction efficiency in the outcoupling structure along the direction of light beam propagation increases successively, thereby optimizing pupil expansion and outcoupling uniformity.

[0077] In another embodiment, the grating depth of the two-dimensional grating structure can be modulated simultaneously along the direction of light beam propagation, so that the diffraction efficiency of the outcoupling structure along the direction of light beam propagation gradually increases.

[0078] In one embodiment, the outcoupling structure further includes a one-dimensional grating structure, and the diffraction efficiency in the outcoupling structure increases successively along the direction of light beam propagation.

[0079] Similar to the pupil expansion structure, a one-dimensional grating structure can also be used in the outcoupling structure where high diffraction efficiency is required. Figure 7 Different regions of the outcoupling structure 203 are two-dimensional grating structures 10 or one-dimensional grating structures 20 with different duty cycles. The region where the light beam propagates closer does not require high diffraction efficiency and may use the two-dimensional grating structure 10. The region where the light beam propagates farther away requires relatively high diffraction efficiency and may use the one-dimensional grating structure 20. It should be noted that Figure 7 The partitioning arrangement of the outcoupling structure is only for illustration, and there may be more two-dimensional grating structures or one-dimensional grating structures with different duty cycles.

[0080] Of course, in other embodiments, the two-dimensional grating structure and the one-dimensional grating structure can also be arranged alternately in the outcoupling structure. It will be appreciated that when designing the specific grating structure in the outcoupling structure, the design is based on outcoupling efficiency, such that the outcoupling efficiency increases along the direction of beam propagation, thereby improving the uniformity of beam expansion. Therefore, for any location or region in the outcoupling structure, any grating structure (whether a two-dimensional grating structure or a one-dimensional grating structure) that can achieve the required outcoupling efficiency for that region and has a relatively easy-to-implement process footprint can be the solution.

[0081] On the other hand, the present invention also provides a diffraction optical waveguide 200, including a waveguide substrate 204, a coupling-in structure 201, a pupil expansion structure 202 and a coupling-out structure 203, wherein the pupil expansion structure 202 and / or the coupling-out structure 203 include the two-dimensional grating structure 10 of the aforementioned embodiment of the present invention.

[0082] Furthermore, the pupil expansion structure 202 and / or the outcoupling structure 203 further includes a one-dimensional grating structure 20 .

[0083] In one embodiment, the grating structures of the pupil expansion structure and the outcoupling structure have the same depth.

[0084] In one embodiment, the grating depths of the grating structures in the pupil expansion structure and / or the outcoupling structure are consistent;

[0085] Preferably, the grating depths of the grating structures in the pupil expansion structure are consistent;

[0086] Practically, the grating depths of the grating structures in the outcoupling structure are consistent;

[0087] Practically, the grating depths of the grating structure in the pupil expansion structure are consistent, and the grating depths of the grating structure in the outcoupling structure are consistent, but the grating depths of the two are different.

[0088] In one embodiment, the grating depth of the grating structure in the pupil expansion structure and / or the outcoupling structure varies along the propagation direction of the light beam.

[0089] In addition, another most commonly used architecture and grating layout for diffraction waveguides includes an in-coupling structure and an out-coupling structure arranged sequentially along the propagation direction of the image beam. In this case, the diffraction waveguide no longer includes a separate pupil expansion structure. The out-coupling structure uses a conventional two-dimensional grating to simultaneously achieve two-dimensional pupil expansion and out-coupling. Here, the conventional two-dimensional grating can diffract to produce beam propagation paths in multiple directions. For this architecture, in order to improve uniformity and efficiency, the out-coupling structure is usually partitioned and then a one-dimensional grating is arranged. For example, conventional one-dimensional gratings are used in the two side areas of the out-coupling structure, and conventional two-dimensional gratings are used in the middle area of ​​the out-coupling structure. In this case, the aforementioned problems of limited optimization freedom and high process difficulty will also exist.

[0090] On the other hand, the present invention also provides a diffraction optical waveguide, including a waveguide substrate, a coupling-in structure and a coupling-out structure, wherein the coupling-out structure is divided into a first coupling-out structure, a second coupling-out structure and a third coupling-out structure, the second coupling-out structure is located between the first coupling-out structure and the third coupling-out structure, and the first coupling-out structure and the third coupling-out structure include a two-dimensional grating structure 10.

[0091] Practically, the first outcoupling structure and the third outcoupling structure also include a one-dimensional grating structure, and the grating duty ratios of different regions of the two-dimensional grating structure in the first outcoupling structure and the third outcoupling structure and the grating duty ratio of the one-dimensional grating structure are modulated so that in the diffraction optical waveguide, along the direction of propagation of the image light beam, the diffraction efficiency of the first outcoupling structure and the third outcoupling structure gradually increases.

[0092] Among them, based on the respective advantages of different grating structures in achieving different diffraction efficiencies by modulating the duty cycle, similar to the setting of the grating structure type in the aforementioned embodiment, the positions in the first outcoupling structure and the third outcoupling structure that require high diffraction efficiency can adopt a one-dimensional grating structure, and the positions in the first outcoupling structure and the third outcoupling structure that require lower diffraction efficiency can adopt the new two-dimensional grating structure provided by the present invention.

[0093] In this way, when the area where the conventional one-dimensional grating structure is located is partially or completely replaced with the two-dimensional grating structure 10 provided in the aforementioned embodiment of the present invention, the propagation path of the light beam in the diffractive optical waveguide is only affected by the periodic structure formed in one direction, while the periodic structures formed in other directions do not affect the propagation direction of the light beam in the two-dimensional grating, thus maintaining the original light beam propagation path. This allows the outcoupling structure of the diffractive optical waveguide to greatly increase the degree of freedom in optimizing uniformity by modulating the duty cycle by increasing the dimension of the periodic structure. This does not increase the complexity of optimizing uniformity by introducing a new light beam propagation path due to the increased dimension of the periodic structure. The increased degree of freedom in optimizing the grating duty cycle also reduces process difficulty and cost.

[0094] Practically, the grating depths of the grating structures in the outcoupling structure are consistent.

[0095] In practice, the grating depth of the grating structure in the outcoupling structure varies along the propagation direction of the light beam.

[0096] Of course, when the novel two-dimensional grating structure and one-dimensional grating structure provided by the present invention are used together for the pupil expansion structure and / or outcoupling structure of the diffraction waveguide, the choice of setting a two-dimensional grating structure or a one-dimensional grating structure at different positions may also depend on the difficulty of implementing the duty cycle of the two-dimensional grating structure or the one-dimensional grating structure in the preparation process when the diffraction efficiency required at the position is achieved by the two-dimensional grating structure or the one-dimensional grating structure. It is not necessarily limited to using a one-dimensional grating structure at a position requiring higher diffraction efficiency and using a two-dimensional grating structure at a position requiring lower diffraction efficiency.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A two-dimensional grating structure for a pupil expansion structure and / or an outcoupling structure of a diffractive optical waveguide, characterized in that: The two-dimensional grating structure comprises: a plurality of grating units periodically arranged in at least two directions, wherein the plurality of grating units periodically arranged in the at least two directions are configured such that a propagation path of a light beam in the diffraction optical waveguide is only affected by the periodic structure formed by the plurality of grating units in one direction; One of the directions is a target direction, and directions other than the target direction among the at least two directions are other directions. The periodic structures formed by the plurality of grating units in the other directions are configured such that: a period of the periodic structures formed in the other directions is adapted to the wavelength of the light beam and the refractive index of the waveguide substrate of the diffractive optical waveguide, so that a propagation path of the light beam in the diffractive optical waveguide is not affected by the periodic structures formed in the other directions; and a diffraction efficiency of the light beam in the diffractive optical waveguide is jointly affected by the duty ratios of the periodic structures formed by the plurality of grating units in the target direction and the other directions. The plurality of grating units in the other directions The period of the periodic structure formed in the first direction is configured as a maximum value within an optional range, and the optional range represents that the propagation path of the light beam in the diffraction optical waveguide is only affected by the periodic structure formed by the multiple grating units in the target direction. The value of the period of the periodic structure formed in the direction; The two-dimensional grating structure includes a main grating and an auxiliary grating; the main grating is a grating structure in the two-dimensional grating structure that is periodically arranged along the target direction; the auxiliary grating is a grating structure in the two-dimensional grating structure that is periodically arranged along other directions; When the two-dimensional grating structure is used for the pupil expansion structure of the diffraction light waveguide, after the light beam is diffracted by the main grating of the pupil expansion structure, the light beam is initially coupled into the waveguide. The vector coordinates must satisfy the following relationship: + (1) in, represents the K vector coordinate of the initial coupling of the light beam into the diffraction waveguide, represents the grating period of the master grating, represents the angle between the grating vector of the grating and the X axis, represents the diffraction order, is the refractive index of the waveguide substrate, is the wavelength of the light beam; After the beam is diffracted by any auxiliary grating of the pupil expansion structure, the initial coupling of the beam into the waveguide The vector coordinates must satisfy the following relationship: + (2) in, For the The period of the auxiliary grating.

2. The two-dimensional grating structure according to claim 1, characterized in that The grating parameters affecting the diffraction efficiency of the two-dimensional grating structure are different at different positions of the two-dimensional grating structure, so as to adjust the uniformity of pupil expansion and / or outcoupling of the light beam under the action of the two-dimensional grating structure.

3. The two-dimensional grating structure according to claim 2, wherein: The two-dimensional grating structure is configured as follows: by configuring the grating duty ratio of different areas of the two-dimensional grating structure, the diffraction efficiency of the two-dimensional grating structure gradually increases along the direction of light beam propagation in the diffraction waveguide, so as to adjust the uniformity of pupil expansion or outcoupling of the light beam under the action of the two-dimensional grating structure.

4. A pupil expansion structure, comprising the grating structure according to any one of claims 1 to 3.

5. The pupil expansion structure according to claim 4, characterized in that: The pupil expansion structure further includes a one-dimensional grating structure, and the turning efficiency in the pupil expansion structure increases successively along the direction of light beam propagation.

6. An outcoupling structure comprising the grating structure according to any one of claims 1 to 3.

7. The outcoupling structure according to claim 6, characterized in that: The outcoupling structure further includes a one-dimensional grating structure, and the outcoupling efficiency in the outcoupling structure increases sequentially along the direction of light beam propagation.

8. A diffraction optical waveguide, characterized in that: The diffraction optical waveguide includes a coupling-in structure, a pupil expansion structure and a coupling-out structure, the pupil expansion structure includes a plurality of pupil expansion regions, the pupil expansion region close to the coupling-in structure is implemented as the two-dimensional grating structure according to any one of claims 1 to 3, and the pupil expansion region away from the coupling-in structure is implemented as a one-dimensional grating structure; the coupling-out structure includes a plurality of coupling-out regions, the coupling-out region close to the pupil expansion structure is implemented as the two-dimensional grating structure according to any one of claims 1 to 3, and the coupling-out region away from the pupil expansion structure is implemented as a one-dimensional grating structure.

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