Optical waveguide device and display device

Abstract

An optical waveguide device comprises a waveguide substrate with two opposing surfaces, the first having an input coupling region and the second having a reflection region. An input coupling grating couples input light into the substrate within a field of view by diffracting it to produce positive first-order and zero-order light that propagates by total internal reflection. The output coupling grating decouples a portion of the light from the substrate. A reflection grating in the reflection region of the second surface diffracts the zero-order light again to produce positive first-order reflected light, which also propagates to the output coupling grating. The projection of the reflection region onto the first surface only partially overlaps the input coupling region, up to a maximum of 40%.

Description

Field of the InventionThe present invention relates to the technical field of optics, and more particularly to an optical waveguide device and a display device.Prior ArtOptical waveguide devices have many advantages, e.g., they are light and thin, easily reproducible, and have a high processing yield. Compared with the low processing yield of the array optical waveguides and the difficulty of mass production of the holographic waveguides, optical waveguide devices with surface relief are ideal solutions for waveguide glasses in consumer electronics. In the optical waveguide device, regardless of whether it is a rotation type one-dimensional pupil expansion optical waveguide device, a butterfly type pupil expansion optical waveguide device, or a two-dimensional pupil expansion optical waveguide device, the launch grating serves as a source for the introduction of the entire light emitting device into the waveguide. Its coupling efficiency plays an important role for the overall efficiency of the entire waveguide.Due to the need for adaptation to the diameter of the light emitting device and for other reasons, the dimension of the launch region is generally larger. Because of the requirement for ease and thinness, the thickness of the lens is small. The launch order +1 hits the launch grid several times and the substrate on the other side of the launch grid. Due to the high number of reflections in a dense field of view, the coupling efficiency is normally lower than in a sparse field of view. Moreover, on the other side of the transmissive launch grating, there is a separate region between the launch order zero and the launch order +1. However, the zeroth-order light propagates in the direction away from the extraction grating, thereby wasting much energy. Overall, there is a high probability of obscuring the dense field of view.Therefore, it is necessary to improve the optical waveguide device and the display apparatus in order to solve at least one technical problem.Object of the InventionIn order to solve at least one of the above problems, the invention has been developed. The invention provides, on the one hand, an optical waveguide device comprising:a waveguide substrate having opposing first surfaces and second surfaces, the first surface having an incoupling region and the second surface having a reflecting region, and the waveguide substrate further comprising an outcoupling region;an launch grating disposed in the launch region of the first surface of the waveguide substrate, the launch grating operable to receive the input light within a predetermined field of view range and diffract at least a portion of the input light to generate and launch a positive first order diffracted light and a zeroth order diffracted light into the waveguide substrate such that the light can propagate within the waveguide substrate by total reflection, wherein the light spot of the zeroth order diffracted light first illuminated onto the second surface has a first profile, the first profile being at least partially in the reflection region; a decoupling grating disposed in the decoupling region of the waveguide substrate, the decoupling grating serving to couple at least a portion of the light propagating into the decoupling grating out of the waveguide substrate by diffraction; anda reflection grating disposed in the reflection region of the second surface, the reflection grating serving to diffract a portion of the zeroth-order diffracted light to form a positive first-order reflection light and to propagate the positive first-order reflection light inside the waveguide substrate to the extraction grating by total reflection;wherein the projection of the reflection region on the first surface at least partially overlaps with the coupling region, wherein the ratio of the area of the overlapping part to the area of the coupling region is less than or equal to 40%.In the optical waveguide device according to the present invention, the reflection grating is used to use the energy of the zeroth-order diffracted light, which improves the input efficiency of the dense field of view, thereby increasing the output brightness of the dense field of view, so that the uniformity of the entire field of view is improved.Optionally, the ratio of the area of the overlapping part to the area of the coupling region is less than or equal to 20%.Optionally, the angle of incidence of the positive first order reflection light on the first surface and / or the second surface is equal to the angle of incidence of the positive first order diffracted light on the first surface and / or the second surface.Optionally, the projection of the reflection grating on the first surface lies within the coupling-in region.Optionally, the reflection grating has a first section and a second section, wherein the projection of the first section on the first surface lies within the coupling-in region and the projection of the second section on the first surface lies outside the coupling-in region, and wherein the length of the second section along the first direction is less than or equal to twice the length of the first section along the first direction.Optionally, the light spot of the positive first order diffracted light first illuminated onto the second surface has a second profile, wherein the area of the second profile located in the reflection region is less than or equal to 20% of the area of the second profile.Optionally, the second profile lies outside the reflection region.Optionally, the first profile and the second profile partially overlap such that the first profile has a non-overlapping region and an overlapping region, wherein the non-overlapping region is located in the reflection region.Optionally, the first profile and the second profile are circles with a diameter D or ellipses with a minor axis D, wherein the thickness of the waveguide substrate is L, wherein, when 0.5 mm<L≤0.75 mm, the ratio of the area of the overlapping region to the area of the first profile and / or of the second profile is less than or equal to 80%.Optionally, the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.8.Optionally, when 0.75 mm<L≤1.0 mm, the ratio of the area of the overlapping region to the area of the first profile and / or the second profile is less than 75%.Optionally, the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.72.Optionally, when 1.0 mm<L≤1.5 mm, the area of the overlapping region to the area of the first profile and / or the second profile is less than 70%.Optionally, the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.65.Optionally, when 1.5 mm<L≤2.0 mm, the area of the overlapping region to the area of the first profile and / or the second profile is less than 65%.Optionally, the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.5.Optionally, the waveguide substrate has a first refractive index (n 1) and the coupling grating has a second refractive index (n 2) where 0≤n 2- n 1≤0.4.Optionally 0 ≤ n 2- n 1 ≤ 0.2.Optionally, the area of the coupling-in region is less than or equal to 144 mm 2, and / or the shape of the coupling-in region is circular, oval, square or rectangular.Optionally, the area of the engagement region is less than or equal to 64 mm 2.Optionally, the periods of the input coupling grating and of the reflection grating are the same and / or the input coupling grating and the reflection grating have different duty cycles.Optionally, the coupling efficiency of the reflection grating for the positive first-order diffracted light is greater than the coupling efficiency of the input grating for the input light.The invention, on the other hand, provides a display device comprising:the above optical waveguide device, andA light emitting device that radiates the input light within a predetermined field of view range onto the launch grating of the optical waveguide device.Optionally, the value along the first direction is within the predetermined field of view range V and the value along the second direction is within the predetermined field of view range H, the second direction being orthogonal to the first direction, the plane formed by the intersection of the first direction and the second direction being substantially parallel to the first surface; the angle between the optical axis of the light emitting device and the first direction α and the angle between the optical axis of the light emitting device and the second direction being horizontal β; the sampling interval along the first direction being h and the sampling interval along the second direction being v and the number of sampling points being c, H=c×h, V=c×v; wherein the angle formed by the light beam at the edge vertex along the first direction of the light spot of the input light on the first surface and the first surface is k 1 × h + α, where 0 ≤ k 1< c; wherein the angle formed by the light beam at the edge vertex along the second direction of the light spot of the input light on the first surface and the first surface is k 2 × v + β, where 0 < k 2< c; and wherein by adjusting the values of k 1 and k 2 the shape of the light spot can be changed.Brief Description of the DrawingsIn order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings to be used in the description of the embodiments will be briefly presented below. Obviously, the drawings in the following description are only some embodiments of the present invention. Other drawings may be made by those skilled in the art based on these drawings without requiring any curative efforts. FIG. 1 is a side view of the optical waveguide device of a preferred embodiment of the invention, FIG. 2 shows an illustration of the overlap of the first profile and the second profile, FIGS. 3A and 3B are schematic diagrams showing the path of the positive first-order diffracted light and the zeroth-order diffracted light at the 100% overlap ratio of the projection of the reflection grating on the first surface and the injection grating, FIGS. 4A and 4B are schematic diagrams showing the path of the positive first-order diffracted light and the zeroth-order diffracted light at the 60% overlap ratio of the projection of the reflection grating on the first surface and the coupling grating, FIGS. 5A and 5B are schematic diagrams showing the path of the positive first-order diffracted light and the zeroth-order diffracted light at the 40% overlap ratio of the projection of the reflection grating on the first surface and the coupling grating, FIGS. 6A and 6B are schematic diagrams showing the path of the positive first-order diffracted light and the zeroth-order diffracted light at the 20% overlap ratio of the projection of the reflection grating on the first surface and the injection grating, FIGS. 7A and 7B are schematic views of the reflection grating extending beyond the covering area of the coupling grating, FIGS. 8A, 8B and 8C are schematic views of the reflection regions of different shapes, FIG. 9 is a schematic illustration of the display apparatus of a preferred embodiment of the present invention, FIG. 10A is a schematic illustration of the angle between the optical axis of the light emitting device and the first direction, FIG. 10B is a schematic illustration of the angle between the optical axis of the light emitting device and the second direction, FIGS. 11A, 11B, 11C and 11D are schematic views showing the irradiation of the input light into the launch grating at different deflection angles of the light emitting device.DESCRIPTION OF THE PREFERRED EMBODIMENTSIn order to make the purpose, technical solutions, and advantages of the present invention clearer, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention and not all the embodiments of the present invention. It should be understood that the present invention is not limited by the exemplary embodiments described herein. Based on the embodiments of the present invention described in this invention, all other embodiments obtained by those skilled in the art without any creative efforts should fall within the scope of the present invention.In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without one or more of these details. In other embodiments, some technical features well known in the art are not described to avoid confusion with the present invention.It is to be understood that the present invention may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.The terms used herein are merely for describing particular embodiments and are not intended to limit the invention. As used herein, the singular forms "a", "an", and "these" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will also be understood that the terms "include" and / or "comprise," when used in the present invention, represent the presence of feature, integer, step, operation, element, and / or part without excluding one or more features, integers, steps, operations, elements, parts, and / or combinations thereof. As used herein, the term "and / or" includes all combinations of the associated listed items.In order to thoroughly understand the present invention, detailed structures will be described in the following description to illustrate the technical solutions provided by the present invention. Optional embodiments of the present invention will be described in detail below. However, in addition to these detailed descriptions, the present invention may have other embodiments.In order to solve the above technical problems, the invention provides an optical waveguide device 100 including a waveguide substrate 110, an input grating 120, an output grating 130, and a reflection grating 140.The waveguide substrate 110 has opposing first surface 111 and second surface 112. The first surface 111 has an incoupling region and the second surface 112 has a reflecting region. The waveguide substrate 110 also has an extraction region. The launch grating 120 is disposed in the launch region of the first surface 111 of the waveguide substrate 110. The launch grating 120 serves to receive the input light L within a predetermined field of view range and diffract at least a portion of the input light L to generate and launch a positive first order diffracted light L 1 and a zeroth order diffracted light L 0 into the waveguide substrate 110 so that the light can propagate within the waveguide substrate 110 by total reflection. The light spot of the zero-order diffracted light L 0 that is first radiated onto the second surface 112 has a first profile P 1, wherein the first profile P 1 is at least partially located in the reflection region. The decoupling grating 130 is arranged in the decoupling region of the waveguide substrate 110. The decoupling grating 130 serves to couple at least a portion of the light propagating into the decoupling grating 130 out of the waveguide substrate 110 by diffraction. The reflection grating 140 is arranged in the reflection region of the second surface 112. The reflection grating 140 functions to diffract a part of the zeroth-order diffracted light L 0 to form a positive first-order reflection light L 3 and to propagate the positive first-order reflection light L 3 inside the waveguide substrate 110 to the extraction grating 130 by total reflection.The projection of the reflection region on the first surface 111 overlaps at least partially with the coupling region, and the ratio of the area of the overlapping part to the area of the coupling region is less than or equal to 40%.The optical waveguide device of the present invention uses the energy of the zeroth-order diffracted light by using the reflection grating, which increases the input efficiency of the dense field of view and thus the output brightness of the dense field of view, so that the uniformity of the entire field of view is improved.The optical waveguide device 100 of the present invention will be described below with reference to Figs. 1 to 8C. The features of various embodiments of the present invention may be combined with each other as long as no conflict exists.The present invention provides an optical waveguide device 100. The optical waveguide device 100 includes a waveguide substrate 110. The shape of the waveguide substrate 110 may be any suitable shape, for example, it may be rectangular, dumbbell-shaped, butterfly-shaped, etc. The waveguide substrate 110 may be made of glass, optical plastic, or other optically transmissive materials. The waveguide substrate 110 may have a substantially flat first surface 111 and second surface 112, wherein the first surface 111 and the second surface 112 are opposite each other. The first surface 111 may be the surface of the display device 10 facing the eyes of the observer provided with the waveguide substrate 110. The waveguide substrate 110 may propagate light by total reflection in a direction generally parallel to the first surface 111 and the second surface 112.The optical waveguide device 100 of the present invention also includes an input coupling grating 120 and an output coupling grating 130. The waveguide substrate 110 has an in-coupling region and an out-coupling region. The launch grating 120 is disposed on or in the waveguide substrate 110 and is located in the launch region. It serves to diffract at least a part of the input light L to generate and couple a positive first-order diffracted light L1 and a zeroth-order diffracted light L0 into the waveguide substrate 110 so that the light propagates inside the waveguide substrate 110.The decoupling grating 130 is arranged on or in the waveguide substrate 110 and is located in the decoupling region. The decoupling grating 130 serves to couple at least a portion of the light propagated therein out of the waveguide substrate 110 by diffraction, so that the coupled-out light can be received by the viewer's eyes.The launch grid 120 may be a one-dimensional grid, such as a linear grid (which may also be referred to as a helical grid), or may be a helical grid, a non-blazed grid, and other suitable types of grids. Or the launch grid 120 may also be a metasurface coupling structure. In some examples, the launch grid 120 is a one-dimensional grid, a two-dimensional grid, or consists of two assembled grids with different grid vectors. The launch grating 120 may be a periodic structure optical element that may be manufactured by any suitable microlithography process. For example, the grating may be formed on the surface or inside the waveguide substrate 110 by photolithography technology. Or it may be formed by nanoimprinting on the waveguide substrate 110, thereby forming a surface relief diffraction grating.The decoupling grid 130 may be fabricated by any suitable micro-fabrication process. For example, the grating may be formed on the surface or inside the waveguide substrate 110 by photolithography technology. Or it may be formed by nanoimprinting on the waveguide substrate 110, thereby forming a surface relief diffraction grating. Note that the shapes of the various gratings in the present invention are the shapes of the upper surfaces that are parallel to the surface of the optical waveguide (i.e., the surface on which the extraction grating 130 or the injection grating 120 is located). It may be a cross-sectional shape substantially parallel to the surface of the optical waveguide or a projected shape on a plane parallel to the surface of the optical waveguide.For example, when the light entering the input grating 120 is the image light projected from a projector, the light output by the output grating 130 is at least a part of the image light. The portion of the image light is guided from the output grating 130 to the viewer's eyes so that the viewer's eyes can see the image projected from the projector. The decoupling grating 130 has the effect of pupil widening. Upon receiving the thinner incident light beam from the launch grating 120, the launch grating 130 diffracts the light beam continuously in two directions in the plane and simultaneously partially couples it out of the waveguide substrate 110 to realize in-plane pupil widening so that the viewer can observe the display information carried by the incident light beam in a larger viewing window.The launch grating 120 and the launch grating 130 may be arranged on the same side of the waveguide substrate 110, for example they are both arranged on the first surface 111 of the waveguide substrate 110. They can also be arranged on different sides, i.e. in each case on the first surface 111 and the second surface 112 of the waveguide substrate 110. In a preferred embodiment, the coupling-in region is located on the first surface 111 and the decoupling region is likewise located on the first surface 111. Therefore, the light emitting device 20 disposed on one side of the eyes radiates the input light L to the coupling region, and after diffraction, the input light L is radiated from the coupling region to the eye.In the present invention, as shown in FIG. 2, the second surface 112 also has a reflection region. The light spot of the zero-order diffracted light L 0 that is first radiated onto the second surface 112 has a first profile P 1, wherein the first profile P 1 is at least partially located in the reflection region. The light spot of the positive first-order diffracted light L 1 irradiated on the second surface 112 for the first time has a second profile P 2.Moreover, the reflection region is provided with a reflection grating 140. The reflection grating 140 functions to diffract the zeroth-order diffracted light L 0 to form a positive first-order reflection light L 3 and to propagate the positive first-order reflection light L 3 inside the waveguide substrate 110 to the extraction grating 130 by total reflection. Preferably, the angle of the positive first-order reflection light L 3 and the positive first-order diffracted light L 1 is the same. In other words, the angle of incidence of the positive first order reflection light L 3 on the first surface 111 and / or the second surface 112 is equal to the angle of incidence of the positive first order diffracted light L 1 on the first surface 111 and / or the second surface 112. More specifically, after the zeroth-order diffracted light L 0 impinges on the reflection grating 140, the reflection grating 140 diffracts the zeroth-order diffracted light L 0 to form a plurality of divided light beams (reflected shapes) propagating in the opposite direction of the reflection grating 140, including negative first-order reflected light and positive first-order reflected light L 3. The positive first-order reflection light L 3 propagates in the direction from the input grating 120 to the output grating 130, and satisfies the total reflection condition between the first surface 111 and the second surface 112, so that it can propagate and be used to the output grating 130. The negative first order reflection light propagates in the direction from the extraction grating 130 to the input grating 120 and cannot propagate to the extraction grating 130. Even if it satisfies the total reflection condition, it cannot be used. The direction from the decoupling grating 130 to the coupling grating 120 and the direction from the coupling grating 120 to the decoupling grating 130 are opposite directions to each other and may collectively be referred to as a first direction D 1.The reflective grating 140 may be a one-dimensional grating, such as a linear grating (which may also be referred to as a helical grating), or may be a helical grating, a non-blazed grating, and other suitable types of gratings. It may be manufactured by any suitable microlithography process. For example, the grating may be formed on the surface or inside the waveguide substrate 110 by photolithography technology. Or it may be formed by nanoimprinting on the waveguide substrate 110, thereby forming a surface relief diffraction grating. Or, the reflection grating 140 may also be separately manufactured and then bonded to the surface of the waveguide substrate 110.Here, the projection of the reflection region on the first surface 111 overlaps at least partially with the coupling region, and the ratio of the area of the overlapping part to the area of the coupling region is less than or equal to 40%. As a variant embodiment, the surface of the second profile P 2 located in the reflection region is less than or equal to 20% of the surface of the second profile P 2.In other words, when the area of the second profile P 2 located in the reflection region is less than or equal to 20% of the area of the second profile P 2, the ratio of the area of the required overlapping part to the area of the coupling region is less than or equal to 40%.After the input light L is irradiated on the input grating 120, the positive first-order diffracted light L 1 formed by diffraction is irradiated on the first surface 111 after total reflection at the second surface 112, thereafter propagates between the first surface 111 and the second surface 112 to the output grating 130 by total reflection, and is then output from the output grating 130. The input grating 120 irradiates the zeroth-order diffracted light L 0 formed by the diffraction of the input light L onto the reflection grating 140. The reflection grating 140 makes diffraction to form the positive first-order reflection light L 3. The positive first-order reflection light L 3 is then radiated onto the first surface 111 by reflection, thereafter propagates to the extraction grating 130 by total reflection between the first surface 111 and the second surface 112, and is then extracted from the extraction grating 130. Thereby, the zeroth-order diffracted light L 0 originally radiated from the second surface 112 is reused, so that the extraction efficiency of the dense field of view and the overall uniformity are increased.As a preferred embodiment, the second profile P 2 is outside the reflection region. Thereby, the energy of the original positive first-order diffracted light L 1 is not affected by the reflection grating 140, so that the highest extraction efficiency is achieved. As an embodiment, the ratio of the area of the overlapping part to the area of the engagement portion is less than or equal to 20%.In other words, when the second profile P 2 is located outside the reflection region, the ratio of the area of the required overlapping part to the area of the coupling region is less than or equal to 20%. Table 1 Table 1Embodiment 140 %34,1 %21,7 %Embodiment 230 %34,9 %22,6 %Embodiment 320 %35,4 %23,9 %Comparative Example 150 %31,3 %19,2 %Comparative Example 2No reflection grating34,5 %20,3 %Table 1 shows the change in the extraction efficiency according to the overlap ratio of the projection of the reflection grating 140 on the first surface 111 and the input grating 120. Among them, Comparative Example 1 having the reflection grating 140 has reduced input efficiency and output efficiency in a dense field of view, as compared with Comparative Example 2 without the reflection grating 140 due to the excessive overlap ratio of the projection of the reflection grating 140 on the first surface and the input grating 120. In Embodiment 1, the overlap ratio of the projection of the reflection grating 140 on the first surface and the input grating 120 is 40%. Although its coupling-in efficiency is slightly lower than that of Comparative Example 2, its coupling-out efficiency at a dense field of view is higher than that of Comparative Example 2, it already has a realization value. When the overlap ratio of the projection of the reflection grating 140 on the first surface and the launch grating 120 gradually decreases to 20%, both the launch efficiency and the dense field of view launch efficiency increase significantly. Table 2 Table 2Embodiment 120 %34,1 %21,9%Embodiment 210 %35,4%23,1 %Embodiment 30 (The second profile is outside the reflection region)35,8 %24.3 %Comparative Example 130 %32,4 %17,8 %Comparative Example 2No reflection grating34,5 %20,3 %Table 2 shows the change in the decoupling efficiency corresponding to different overlapping areas of the second profile P 2 and the reflection grating 140. Among them, Comparative Example 1 including the reflection grating 140 has reduced input efficiency and output efficiency in a dense field of view, as compared with Comparative Example 2 without the reflection grating 140 due to the excessively large overlap area ratio of the second profile P 2 and the reflection grating 140. The overlap area ratio of the second profile P 2 and the reflection grating 140 in Embodiment 1 is 20%. Although its coupling-in efficiency is slightly lower than that in Comparative Example 2, its coupling-out efficiency at a dense field of view is higher than that in Comparative Example 2, it already has a conversion value. When the overlap area ratio of the second profile P 2 and the reflection grating 140 gradually decreases to 0, both the input efficiency and the output efficiency in the dense field of view increase significantly.Obviously, it is a preferred solution that the second profile P 2 does not overlap with the reflection grating 140. It is preferable that the overlap ratio of the projection of the reflection grating 140 on the first surface and the launch grating 120 does not exceed 20%. The best solution is that the second profile P 2 does not overlap with the reflection grating 140 and that the overlap ratio of the projection of the reflection grating 140 on the first surface and the injection grating 120 does not exceed 20%. It is simultaneously possible to increase the coupling-in efficiency and the decoupling efficiency in the dense field of view. The objective of total good non-uniformity can be achieved without loss of efficiency.To further explain the influence of the overlap ratio of the projection of the reflection grating 140 on the first surface 111 and the input grating on the output efficiency in the dense field of view, reference is made to FIGS. 3A to 6B.FIGS. 3A and 3B are schematic diagrams illustrating the path of the positive first-order diffracted light L 1 and the zeroth-order diffracted light L 0 when the overlap ratio of the projection of the reflection grating 140 on the first surface 111 and the launch grating is 100%. It is seen from the figure that when the reflection grating 140 entirely corresponds to the launch grating 120, a large portion of the positive first-order diffracted light L1 is radiated onto the reflection grating 140, resulting in a large energy loss of the positive first-order diffracted light L1. The gain of the return of the zeroth-order diffracted light L0 by the reflection grating 140 cannot compensate for the energy loss of the positive first-order diffracted light L1. Therefore, this is not an optional solution.FIGS. 4A and 4B are schematic diagrams illustrating the path of the positive first-order diffracted light L 1 and the zeroth-order diffracted light L 0 when the overlap ratio of the projection of the reflection grating 140 on the first surface 111 and the launch grating is 60%. Similarly to the above, a large part of the positive first-order diffracted light L 1 is irradiated on the reflection grating 140. The gain of the return of the zeroth-order diffracted light L0 by the reflection grating 140 cannot compensate for the energy loss of the positive first-order diffracted light L1, either. Therefore, this is also not an optional solution.FIGS. 5A and 5B are schematic diagrams illustrating the path of the positive first-order diffracted light L 1 and the zeroth-order diffracted light L 0 when the overlap ratio of the projection of the reflection grating 140 on the first surface 111 and the launch grating is 40%. When the overlap ratio is 40%, a smaller part of the positive first-order diffracted light L1 is irradiated on the reflection grating 140. The gain of the return of the zeroth-order diffracted light L 0 by the reflection grating 140 can compensate for the energy loss of the positive first-order diffracted light L 1. Therefore, although a part of the energy of the positive first-order diffracted light L 1 is lost, this solution still improves the extraction efficiency in the dense field of view.FIGS. 6A and 6B are schematic diagrams illustrating the path of the positive first-order diffracted light L 1 and the zeroth-order diffracted light L 0 when the overlap ratio of the projection of the reflection grating 140 on the first surface 111 and the launch grating is 20%. In this case, the second profile of the positive first-order diffracted light L 1 is completely outside the reflection region. In other words, the positive first-order diffracted light L 1 is not radiated to the reflection grating 140 at all. The gain of the return of the zero-order diffracted light L 0 by the reflection grating 140 may all be superimposed to increase the extraction efficiency at the dense field of view. Therefore, this is the optimum solution.As shown in FIG. 2, the first profile P 1 and the second profile P 2 partially overlap each other, so that the first profile P 1 has a non-overlapping region S 2 and an overlapping region S 1, the non-overlapping region S 2 being located in the reflection region. In order to use as much energy of the zeroth-order diffracted light L0 as possible, the ratio of the area of the overlapping region S1 and the area of the first profile P1 needs to correspond to an appropriate range.As an optional embodiment, the ratio of the area of the overlapping region S 1 to the area of the first profile P 1 is less than or equal to 80%. The ratio of the area of the overlapping region S 1 to the area of the second profile P 2 is less than or equal to 80%. Within the above range, the smaller the ratio of the area of the overlapping region S 1 to the area of the first profile P 1 and / or the second profile P 2, the more favorable the utilization of the energy of the zeroth-order diffracted light L 0.In practice, however, the maximum utilization range of the above-mentioned ratio is related to the thickness L of the waveguide substrate 110. The thickness L of the waveguide substrate 110 is the size of the waveguide substrate 110 in a direction substantially vertical to the first surface 111 and the second surface 112.Specifically, the positive first-order diffracted light spot L 1 and the zeroth-order diffracted light spot L 0 are generally circles or almost circular ellipses. In other words, the first profile P 1 and the second profile P 2 are circles having a diameter D or ellipses having a minor axis D.When 0.5 mm<L≤0.75 mm, the ratio of the area of the overlapping region S 2 to the area of the first profile P 1 and / or the second profile P 2 is preferably less than or equal to 80%. Moreover, the distance from the geometric center of the second profile P 2 to the side closest to the geometric center of the reflection grating 140 is greater than (D / 2)×0.8.When 0.75 mm<L≤1.0 mm, the ratio of the area of the overlapping region S 2 to the area of the first profile P 1 and / or the second profile P 2 is preferably less than 75%. Moreover, the distance from the geometric center of the second profile P 2 to the side closest to the geometric center of the reflection grating 140 is greater than (D / 2)×0.72.When 1.0 mm<L≤1.5 mm, the area of the overlapping region S 2 to the area of the first profile P 1 and / or the second profile P 2 is preferably less than 70%. Moreover, the distance from the geometric center of the second profile P 2 to the side closest to the geometric center of the reflection grating 140 is greater than (D / 2)×0.65.When 1.5 mm<L≤2.0 mm, the area of the overlapping region S 2 to the area of the first profile P 1 and / or the second profile P 2 is preferably less than 65%. Moreover, the distance from the geometric center of the second profile P 2 to the side closest to the geometric center of the reflection grating 140 is greater than (D / 2)×0.5.In addition, the waveguide substrate 110 has a first refractive index n 1 and the coupling grating 120 has a second refractive index n 2 where 0≤n 2- n 1≤0.4. Preferably, 0≤n 2- n 1≤0.2. the combination of the high refractive index of the launch grating 120 and the low refractive index of the waveguide substrate 110 allows the first profile P 1 and the second profile P 2 to be further apart from each other. In other words, the area ratio of the overlapping region S 1 is reduced, thereby increasing the area ratio of the first profile P 1 in the reflection region, which is more favorable for utilizing the energy of the zeroth-order diffracted light L 0.The shape of the coupling-in region is circular, oval, square or rectangular. The area of the engagement region is less than or equal to 144 mm 2. For example, when the shape of the engaging portion is square, the side length of the engaging portion is less than or equal to 12 mm and its area is less than or equal to 144 mm 2. When the shape of the engaging portion is circular, its radius is less than or equal to 6 mm and its area is less than or equal to 115 mm 2.Preferably, the area of the coupling-in region is less than or equal to 64 mm 2. For example, when the shape of the engaging portion is square, the side length of the engaging portion is less than or equal to 8 mm and its area is less than or equal to 64 mm 2. When the shape of the engaging portion is circular, its radius is less than or equal to 4 mm and its area is less than or equal to 51 mm 2. By reducing the area of the launch grid 120, the number of light reflections from the dense field of view to the launch grid 120 may be reduced and the energy loss may be reduced.As an optional embodiment, the periods of the launch grating 120 and the reflective grating 140 are the same. The input grating 120 and the reflection grating 140 have different duty ratios.In the present invention, the launch grating 120 needs to take into account the energy and reflection efficiency of the positive first-order diffracted light L 1, while the reflection grating 140 needs to deal only with the energy of the zeroth-order diffracted light L 0. Therefore, the coupling efficiency of the reflection grating 140 for the positive first-order diffracted light L 1 is greater than the coupling efficiency of the input grating 120 for the input light L.The shape of the reflection grating 140 or the reflection region may be circular, rectangular (FIG. 8A ), etc. In order to further extend the area where the reflection grating 140 can come into contact with the zeroth-order diffracted light L0, the shape of the reflection grating 140 or the reflection region may also be a butterfly shape as shown in FIG. 8B or a crescent shape as shown in FIG. 8C. The butterfly-shaped reflection grating 140 shown in FIG. 8B and the crescent-shaped reflection grating 140 shown in FIG. 8C have a main portion 141 that is located at the center and overlaps with most of the first profile P 1, and an extending portion 142 that extends along the first direction D 1 from both sides of the main portion 141.It should be noted that the projection of the reflection region on the first surface 111 may be entirely in the coupling-in region, i.e. the reflection grating 140 is entirely covered by the coupling-in grating 120 in the thickness direction of the waveguide substrate 110. However, the projection of the reflection region on the first surface 111 can also be situated partially outside the coupling region. In other words, the reflection grating 140 is not completely covered by the launch grating 120 in the thickness direction of the waveguide substrate 110. As shown in FIGS. 7A and 7B, the reflection grating 140 extends beyond the coverage area of the launch grating 120 in the first direction D 1. Specifically, the reflection grating 140 has a first section 141 and a second section 142, wherein the projection of the first section 141 on the first surface 111 lies within the coupling-in region and the projection of the second section 142 on the first surface 111 lies outside the coupling-in region.Optionally, the reflection grating 140 can also extend in the second direction D 2 beyond the covering region of the coupling-in grating 120. The plane formed by the intersection of the first direction D 1 and the second direction D 2 is substantially parallel to the first surface 111. The second direction D 2 is orthogonal to the first direction D 1. As mentioned above, the first direction D 1 includes the direction from the launch grid 120 to the launch grid 130 and the direction from the launch grid 130 to the launch grid 120. For simplicity, the direction from the launch grid 120 to the launch grid 130 may be referred to as a forward direction and the direction from the launch grid 130 to the launch grid 120 may be referred to as a rearward direction.That is, the reflection grating 140 extends beyond the coverage area of the input grating 120 in the first direction D 1 means that the reflection grating 140 extends beyond the coverage area of the input grating 120 along the direction from the output grating 130 to the input grating 120 (i.e., in the backward direction).Preferably, the size of the portion of the reflection grating 140 extending beyond the coverage area of the launch grating 120 in the rearward direction does not exceed 2 times the size of the reflection grating 140 itself, or in other words, the size of the second portion 142 along the first direction D 1 is less than or equal to 2 times the size of the reflection grating 140 along the first direction D 1.Particularly preferably, the size of the portion of the reflection grating 140 extending beyond the coverage area of the launch grating 120 in the rearward direction does not exceed 1 times the size of the reflection grating 140 itself, or the size of the second portion 142 along the first direction D 1 is less than or equal to the size of the reflection grating 140 along the first direction D 1.Such a reflection grating 140, which extends beyond the covering region of the coupling-in grating 120 in the direction from the coupling-out grating 130 to the coupling-in grating 120, is helpful for production and processing and favorable for increasing the yield and the production efficiency. Moreover, the reflective grating 140 extending in the direction from the coupling-out grating 130 to the coupling-in grating 120 beyond the coverage area of the coupling-in grating 120 may help to collect the zeroth-order diffracted light L 0 formed by diffraction of the incident light at different fields of view from the coupling-in grating 120 and generate the positive first-order reflected light L 3 by diffraction. Thereby, the utilization of the zeroth-order diffracted light L0 is maximized.The present invention, on the other hand, provides a display device 10. The display apparatus 10 includes the above-mentioned optical waveguide device 100 and the light emitting device 20. The light emitting device 20 may radiate the input light L onto the optical waveguide device 100, for example, the input light L within a predetermined field of view range into the region where the launch grating 120 of the optical waveguide device 100 is located.The display device 10 may be an augmented reality display device 10 or a virtual reality display device 10. Among them, the augmented reality display device 10 includes augmented reality (AR) glasses, vehicle head-up displays (HUD), and other devices, among others.For example, as shown in FIG. 9, the display device 10 may be a near-eye display device 10 including glasses 30 and a mount 40 that holds glasses 30 close to the eyes. The socket 40 may be provided with the above-mentioned light emitting device 20, and the glasses 30 may contain the optical waveguide device 100.The light emitting device 20 may be laser beam scanning (LBS), digital light processing (DLP), digital micromirror device (DMD), liquid crystal on silicon (LCOS), micro electro mechanical system (MEMS), organic light emitting diode (OLED), microLED, and other micro display devices. The light emitted from the light emitting device 20 is visible light.As an optional embodiment, the display device 10 may also be a driving device. The driving apparatus is used to drive the light emitting device 20 to radiate the input light L to the launch grating 120 of the optical waveguide device 100. The driving device may include a driving circuit. The drive circuit may include MOS tubes, capacitors, resistors, or other suitable components. The display device 10 may also include a controller that may be electrically connected to the drive circuit. The driving apparatus drives the light emitting device 20 under the control of the controller to radiate the input light L to the launch grating 120 of the optical waveguide device 100.As an embodiment variant, the value of the input light L from the light emitting device 20 along the first direction D 1 is within the predetermined field-of-view range V and the value along the second direction D 2 is within the predetermined field-of-view range H. Optionally, when the display device 10 is worn on the eyes, the first direction D 1 may be the horizontal direction and the second direction D 2 may be the vertical direction.The angle between the optical axis AX of the light emitting device 20 and the first direction D 1 is α as shown in FIG. 10A. The angle between the optical axis AX of the light emitting device 20 and the second direction D 2 is horizontal β as shown in FIG. 10B. FIGS. 11A, 11B, 11C, and 11D show the influence of the deflection angle of the optical axis AX of the light emitting device 20 on the position of the light spot of the input light L. Here, the outer circle stands for the input grating 120 and the inner circle stands for the light beam of the input light L. In the figures, the input grating 120 and the light spot of the input light L are, for example, circular. In actual applications, they may have a slightly elliptical shape.In FIG. 11A, the optical axis AX of the light emitting device 20 is vertical to the launch grating 120, that is, α and β are both 0. At this time, the light spot of the input light L is located at the center of the input grating 120. In other words, the light of the light emitting device 20 just enters the launch grating 120.In FIG. 11B, the optical axis AX of the light emitting device 20 forms an angle with the launch grating 120. Specifically, α is 0 and β is not 0. At this time, the light spot of the input light L is slightly offset along the perpendicular direction relative to the center of the input grating 120. In other words, the light of the light emitting device 20 is incident into the input grating 120 from above or below.In FIG. 11C, the optical axis AX of the light emitting device 20 forms an angle with the launch grating 120.In particular, α is not 0 and β is 0. At this time, the light spot of the input light L is slightly offset along the horizontal direction relative to the center of the input grating 120. In other words, the light of the light emitting device 20 is incident into the input grating 120 from the left or right.In FIG. 11D, the optical axis AX of the light emitting device 20 forms an angle with the launch grating 120. In particular, α and β are both not 0. At this time, the light spot of the input light L inclines slightly along the perpendicular direction relative to the center of the input grating 120. In other words, the light of the light emitting device 20 obliquely enters the launch grating 120.The sampling interval along the first direction D 1 is h, the sampling interval along the second direction D 2 is v, the number of sampling points is c, H=c×h, V=c×v.The angle formed by the light beam at the edge vertex along the first direction D 1 of the light spot of the input light L on the first surface 111 and the first surface 111 is k 1 × h + α, where 0<k 1< c. The angle formed by the light beam at the edge vertex along the second direction D 2 of the light spot of the input light L on the first surface 111 and the first surface 111 is k 2 × v + β, where 0<k 2< c.By adjusting the values of k 1 and k 2 the shape of the light spot can be changed. For example, the light spot may be changed to a rectangular, circular, elliptical shape, etc.The wavelength of the input light L is λ, and the period of the input grating 120 is d.The diffraction angle of the positive first-order diffracted light L1 in the spherical coordinate system is defined as follows:The diffraction angle of the zeroth-order diffracted light L0 in the spherical coordinate system is defined as follows:By the above formulas, the area of the reflection grating 140 or the reflection surface can be limited in an appropriate range.It should be noted that the above-described embodiments are only for the purpose of illustrating the invention and not for the purpose of limiting it. Those skilled in the art may design alternative embodiments without departing from the scope of the appended claims. In the claims, the parenthetical reference numerals should not be interpreted as limiting the claims. The invention may be implemented by means of hardware consisting of several different components and by means of a suitably programmed computer. In the individual claims, in which multiple devices are recited, the multiple devices may be embodied by the same hardware. The terms "first", "second", "third", etc. do not indicate an order. These terms may be interpreted as being used as labels.List of reference characters10 Display device 20 Light emitting device AX Optical axis 30 Glass 40 Mount 100 Optical waveguide device 110 Waveguide substrate 111 First surface 112 Second surface 120 Input grating 130 Output grating 140 Reflection grating 141 Main portion 142 Extension portion P 1 First profile P 2 Second profile S 1 Overlapping region S 2 Non-overlapping region L Input light L 0 Zeroth-order diffracted light L 1 Positive first-order diffracted light D 1 First direction D 2 Second direction L 3 Positive first-order reflection light 141 First portion 142 Second portion

Claims

An optical waveguide device comprising: a waveguide substrate having opposing first surface and second surface, wherein the first surface has an incoupling region and the second surface has a reflecting region, and wherein the waveguide substrate further comprises an outcoupling region; an launch grating disposed in the launch region of the first surface of the waveguide substrate, the launch grating operable to receive the input light within a predetermined field of view range and diffract at least a portion of the input light to generate and launch a positive first order diffracted light and a zeroth order diffracted light into the waveguide substrate such that the light can propagate within the waveguide substrate by total reflection, wherein the light spot of the zeroth order diffracted light first illuminated onto the second surface has a first profile, the first profile being at least partially in the reflection region; a decoupling grating disposed in the decoupling region of the waveguide substrate, the decoupling grating serving to couple at least a portion of the light propagating into the decoupling grating out of the waveguide substrate by diffraction; and a reflection grating disposed in the reflection region of the second surface, the reflection grating serving to diffract a portion of the zeroth-order diffracted light to form a positive first-order reflection light and to propagate the positive first-order reflection light within the waveguide substrate to the decoupling grating by total reflection; wherein the projection of the reflection region on the first surface overlaps at least partially with the coupling region, wherein the ratio of the area of the overlapping portion to the area of the coupling region is less than or equal to 40%.The optical waveguide device according to claim 1, characterized in that the ratio of the area of the overlapping part to the area of the coupling region is less than or equal to 20%.The optical waveguide device according to claim 1, characterized in that the incident angle of the positive first-order reflection light on the first surface and / or the second surface is equal to the incident angle of the positive first-order diffracted light on the first surface and / or the second surface.The optical waveguide device according to claim 1, characterized in that the projection of the reflection grating on the first surface is within the launch region.The optical waveguide device according to claim 1, characterized in that the reflection grating has a first portion and a second portion, wherein the projection of the first portion on the first surface is inside the coupling region and the projection of the second portion on the first surface is outside the coupling region, and wherein the length of the second portion along the first direction is less than or equal to twice the length of the first portion along the first direction.Optical waveguide device according to claim 5, characterised in that the length of the second section along the first direction is less than or equal to the length of the first section along the first direction.Optical waveguide device according to Claim 1, characterized in that the light spot of the diffracted light of positive first order, which is first illuminated on the second surface, has a second profile, the area of the second profile which is situated in the reflection region being less than or equal to 20% of the area of the second profile.The optical waveguide device according to claim 7, characterized in that the second profile is outside the reflection region.The optical waveguide device according to claim 7, characterized in that the first profile (P1) and the second profile partially overlap, such that the first profile (P1) has a non-overlapping area and an overlapping area, the non-overlapping area being located in the reflection area.Optical waveguide device according to claim 9, characterized in that the first profile and the second profile are circles with a diameter D or ellipses with a minor axis D, the thickness of the waveguide substrate being L, wherein, when 0.5 mm < L ≤ 0.75 mm, the ratio of the area of the overlapping area to the area of the first profile and / or of the second profile is less than or equal to 80%.Optical waveguide device according to claim 10, characterized in that the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.8.Optical waveguide device according to claim 10, characterized in that when 0.75 mm < L ≤ 1.0 mm, the ratio of the area of the overlapping area to the area of the first profile and / or the second profile is less than 75 %.Optical waveguide device according to claim 12, characterized in that the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.72.Optical waveguide device according to claim 10, characterized in that, when 1.0 mm < L ≤ 1.5 mm, the area of the overlapping area to the area of the first profile and / or the second profile is less than 70%.Optical waveguide device according to claim 14, characterized in that the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.65.Optical waveguide device according to claim 10, characterized in that, when 1.5 mm < L ≤ 2.0 mm, the area of the overlapping area to the area of the first profile and / or the second profile is less than 65%.Optical waveguide device according to claim 16, characterized in that the distance from the geometric center of the second profile to the side closest to the geometric center of the reflection grating is greater than (D / 2)×0.5.Optical waveguide device according to one of Claims 1 to 17, characterized in that the waveguide substrate has a first refractive index n 1 and the coupling-in grating has a second refractive index n 2 where 0 ≤ n 2- n 1 ≤ 0.4.The optical waveguide device according to claim 18, characterized in that 0 ≤ n 2- n 1 ≤ 0.2.Optical waveguide device according to one of Claims 1 to 17, characterized in that the area of the coupling-in region is less than or equal to 144 mm 2 and / or the shape of the coupling-in region is circular, oval, square or rectangular.Optical waveguide device according to Claim 20, characterized in that the area of the coupling-in region is less than or equal to 64 mm 2.Optical waveguide device according to one of Claims 1 to 17, characterized in that the periods of the input coupling grating and of the reflection grating are identical and / or the input coupling grating and the reflection grating have different duty cycles.The optical waveguide device according to any one of claims 1 to 17, characterized in that the coupling efficiency of the reflection grating for the positive first-order diffracted light is greater than the coupling efficiency of the input grating for the input light.A display apparatus comprising: an optical waveguide device according to any one of claims 1 to 23, and a light emitting device that radiates the input light onto the launch grating of the optical waveguide device within a predetermined field of view range.The display apparatus according to claim 24, characterized in that the value along the first direction within the predetermined field of view range V and the value along the second direction within the predetermined field of view range is H, the second direction being orthogonal to the first direction, the plane formed by the intersection of the first direction and the second direction being substantially parallel to the first surface; the angle between the optical axis of the light emitting device and the first direction being α and the angle between the optical axis of the light emitting device and the second direction being horizontally β; the sampling interval along the first direction being h and the sampling interval along the second direction being v and the number of sampling points being c, H = c × h, V = c × v; wherein the angle formed by the light beam at the edge vertex along the first direction of the light spot of the input light on the first surface and the first surface is k 1 × h + α, where 0 < k 1< c; wherein the angle formed by the light beam at the edge vertex along the second direction of the light spot of the input light on the first surface and the first surface is k 2 × v + β, where 0 < k 2< c; and wherein by adjusting the values of k 1 and k 2 the shape of the light spot can be changed.

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