Display device and head-up display system

Abstract

The utility model discloses a display device and a head-up display system, and relates to the technical field of augmented reality, the display device comprises a light source, an optical waveguide structure and a light recovery structure, the light source is used for emitting light rays with at least two different wavelengths, and the optical waveguide structure comprises at least two stacked waveguide layers; the light of each wavelength is coupled into the corresponding waveguide layer to be propagated and then is emitted to form target light; the light of each wavelength is diffracted by the at least one waveguide layer to form various stray light, and the light recovery structure is used for diffracting at least one stray light formed by the light of at least part of wavelengths so as to change the emergent angle of the at least one stray light to be consistent with the emergent angle of the target light. The light recovery structure is arranged for the multi-layer waveguide display device, so that the light recovery structure recovers stray light formed by light propagating in the multi-layer optical waveguide, the stray light effect of the multi-layer optical waveguide is remarkably reduced, and the efficiency of the display device is improved.

Description

Technical Field

[0001] The present application relates to the field of augmented reality technology, and more specifically, to a display device and a head-up display system. Background Art

[0002] With the development of augmented reality (AR) technology, AR displays are becoming more widely used in people's lives. Diffraction waveguides (DWGs), commonly used light propagation devices in displays, can confine light and transmit it through total internal reflection to achieve pupil expansion.

[0003] Currently, the mainstream solution in the industry to improve the color uniformity of images output by display devices is to stack multiple layers of waveguides, allowing incident light of different wavelengths to propagate between different waveguide layers. However, a significant drawback of multi-layer waveguides is that waveguide layers designed for a particular wavelength cannot completely isolate the diffraction effects of other wavelengths. This results in a significant amount of stray light, reducing waveguide efficiency and impacting the user experience. Therefore, reducing stray light generated by waveguide layers in display devices is an urgent issue. Utility Model Content

[0004] The present application proposes a display device and a head-up display system to improve the above-mentioned defects.

[0005] In a first aspect, an embodiment of the present application provides a display device, characterized by comprising: a light source, an optical waveguide structure, and a light recycling structure, wherein the light source is configured to emit light of at least two different wavelengths, the optical waveguide structure comprises at least two stacked waveguide layers, different waveguide layers are configured to propagate light of different wavelengths, and at least two of the waveguide layers have respective coupling-in gratings and coupling-out gratings. After coupling-into the corresponding waveguide layer and propagating therethrough, the light is coupled-out and emitted from the optical waveguide structure to form a target light. Light of each wavelength is diffracted by the coupling-in grating or coupling-out grating of at least one of the waveguide layers and then emitted from the optical waveguide structure to form a plurality of stray light rays, the angles at which the stray light rays exit the optical waveguide structure being different from the angles at which the target light rays exit the optical waveguide structure. The light recycling structure is configured to diffract at least one stray light ray formed by light of at least some wavelengths emitted from the optical waveguide structure, thereby changing the angle of exit of the at least one stray light ray to be consistent with the angle of exit of the target light ray.

[0006] Optionally, the light recycling structure includes at least one group of light recycling components, one group of light recycling components corresponding to stray light formed by light of a certain wavelength, and the light recycling components are used to diffract the stray light formed by light of the corresponding wavelength, and pass the stray light formed by light of other wavelengths, and change the exit angle of the stray light formed by the corresponding wavelength to be consistent with the exit angle of the target light.

[0007] Optionally, the multiple stray light rays formed by the light of one wavelength have different exit angles, and the light recycling member includes at least one light recycling layer, which corresponds to the stray light of one exit angle, and the light recycling layer is used to diffract the stray light of the corresponding exit angle and transmit the light of the remaining exit angles, so as to change the exit angle of the stray light of the corresponding angle to be consistent with the exit angle of the target light.

[0008] Optionally, the intensity of the stray light generated by the light of each wavelength is negatively correlated with the total number of diffraction of the light in the at least two waveguide layers, and the light recycling member is used to recycle the stray light generated when the total number of diffraction of the light of the corresponding wavelength in the at least two waveguide layers does not exceed 2 times.

[0009] Optionally, the light recycling layer is a one-dimensional grating, and each light recycling layer has a recycling grating vector, and the recycling grating vector is used to change the exit angle of the stray light corresponding to the light recycling layer to be consistent with the exit angle of the target light.

[0010] Optionally, the light recycling member includes a first type of light recycling layer, which is used to recycle a first type of stray light, and the first type of stray light is formed by the light of the corresponding wavelength being diffracted through one of the at least two waveguide layers; each of the waveguide layers has a different diffraction grating vector for light of different wavelengths, and the recycling grating vector of the first type of light recycling layer is the opposite vector of the diffraction grating vector of the waveguide layer that diffracts the light of the corresponding wavelength corresponding to the wavelength.

[0011] Optionally, the light recycling member includes a second type of light recycling layer, which is used to recycle a second type of stray light, and the second type of stray light is formed by diffraction of light of corresponding wavelength through two waveguide layers of the at least two waveguide layers; each of the waveguide layers has different diffraction grating vectors for light of different wavelengths, and the recycling grating vector of the second type of light recycling layer is the opposite vector of the superposition vector of the two diffraction grating vectors corresponding to the wavelength of the two waveguide layers that diffract the light of the corresponding wavelength.

[0012] Optionally, the light recycling layer is in the form of a thin film, and a plurality of the light recycling layers are sequentially attached to the surface of the optical waveguide structure for emitting light.

[0013] Optionally, the light recycling layer is a Bragg grating, a volume Bragg grating, a volume holographic grating, a polarization volume holographic grating, a liquid crystal grating or a metasurface grating.

[0014] In a second aspect, an embodiment of the present application provides a head-up display system, comprising display glass and the display device as described above, wherein the target light emitted by the display device and the stray light after the angle of incidence is changed reach the display glass and are reflected to an observation position.

[0015] Therefore, the present application provides a display device and a head-up display system. The display device includes: a light source, an optical waveguide structure, and a light recycling structure. The light source is configured to emit light of at least two different wavelengths. The optical waveguide structure includes at least two stacked waveguide layers, with different waveguide layers configured to propagate light of different wavelengths. The at least two waveguide layers have respective coupling-in gratings and coupling-out gratings. After coupling into the corresponding waveguide layer and propagating, the light is coupled out and emitted from the optical waveguide structure to form a target light. Light of each wavelength is diffracted by the coupling-in grating or coupling-out grating of at least one waveguide layer and then emitted from the optical waveguide structure to form multiple stray light rays. The angles at which the stray light rays exit the optical waveguide structure are different from the angles at which the target light rays exit the optical waveguide structure. The light recycling structure is configured to diffract at least one stray light ray formed by light of at least some wavelengths emitted from the optical waveguide structure, thereby changing the angle of exit of the at least one stray light ray to be consistent with the angle of exit of the target light. Therefore, the present application sets a light recycling structure for a display device with a multi-layer optical waveguide, so that the light recycling structure can recycle stray light generated when the light propagates in the multi-layer optical waveguide, and adjust the output angle of the stray light to be consistent with the target light, thereby significantly reducing the stray light effect of the multi-layer optical waveguide and improving the efficiency of the display device.

[0016] Other features and advantages of the embodiments of the present application will be described in the following description and, in part, will become apparent from the description or be understood by practicing the embodiments of the present application. The objectives and other advantages of the embodiments of the present application can be achieved and obtained through the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 A schematic diagram showing stray light generated by a multilayer waveguide is shown;

[0019] Figure 2 A schematic diagram of grating vector distribution of a multilayer waveguide is shown;

[0020] Figure 3 A schematic structural diagram of a display device proposed in an embodiment of the present application is shown;

[0021] Figure 4 A schematic diagram showing the distribution of grating vectors of the optical waveguide structure for light of a second wavelength in a display device according to one embodiment of the present application is shown;

[0022] Figure 5 A schematic diagram showing the distribution of recycling grating vectors of a light recycling structure in a display device proposed in one embodiment of the present application is shown;

[0023] Figure 6 shows a wave vector distribution diagram of a portion of stray light generated by a second wavelength light in a display device according to one embodiment of the present application;

[0024] Figure 7 A schematic diagram showing the propagation of a portion of stray light generated by a second wavelength of light in a display device in an optical waveguide structure according to one embodiment of the present application is shown;

[0025] Figure 8 A schematic structural diagram of a head-up display system proposed in one embodiment of the present application is shown. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for which protection is claimed, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work fall within the scope of protection of the present application.

[0027] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0028] See also Figure 1 , Figure 1 FIG2 shows a schematic diagram of a multilayer waveguide generating stray light, wherein the diffraction waveguide 100 includes a first waveguide layer 110 and a second waveguide layer 120. The first waveguide layer 110 is used to propagate and emit light of a first wavelength (shown by a solid line in the figure), and the second waveguide layer 120 is used to propagate and emit light of a second wavelength (shown by a dotted line in the figure).

[0029] Specifically, the first waveguide layer 110 and the second waveguide layer 120 are able to filter and propagate light of corresponding wavelengths because the coupling gratings of the first waveguide layer 110 and the second waveguide layer 120 have different grating vectors and are set corresponding to the light of corresponding wavelengths. Figure 2 , Figure 2 A schematic diagram of the grating vector distribution of the coupling grating of a multilayer waveguide is shown. Figure 2 (a) shows a schematic diagram of the grating vector distribution of the coupling grating of the first waveguide layer 110, Figure 2 (b) shows a schematic diagram of the grating vector distribution of the coupling grating of the second waveguide layer 120. Specifically, Figure 2 (a) or Figure 2 The K-vector circle shown in (b) can reflect the diffraction of light of different wavelengths by the coupling grating of the first waveguide layer 110 or the second waveguide layer 120. It should be noted that the rectangular area contained in the K-vector circle represents the wave vector distribution of light at all angles in the incident light. When light enters the waveguide layer from the outside, the wave vector distribution area of the light is considered to be located at the center of the K-vector circle. In addition, the grating vector of the waveguide layer will move the wave vector distribution of the light from the center area of the K-vector circle to other areas. Only light with the shifted wave vector distribution located in the area between the small circle and the large circle in the K-vector circle can be diffracted into the waveguide layer and undergo total internal reflection propagation in the waveguide layer. Light with the shifted wave vector distribution located in the area inside the small circle in the K-vector circle cannot be diffracted into the waveguide layer and undergoes total internal reflection propagation. Light with the shifted wave vector distribution located in the area outside the large circle in the K-vector circle means that the corresponding diffraction order does not exist.

[0030] Therefore, if Figure 2 As shown, the grating vector K1 set by the coupling grating of the first waveguide layer 110 for the first wavelength light can move the first wavelength light from the initial wave vector distribution area A0 to the wave vector distribution area A1, and the grating vector K2 set by the coupling grating of the first waveguide layer 110 for the second wavelength light can move the second wavelength light from the initial wave vector distribution area A0 to the wave vector distribution area Similarly, the grating vector of the coupling grating of the second waveguide layer 120 is set for the second wavelength light Able to move the second wavelength light from the initial wave vector distribution area A0 to the wave vector distribution area , and the grating vector of the coupling grating of the second waveguide layer 120 is set for the first wavelength light The first wavelength light can be moved from the initial wave vector distribution area A0 to the wave vector distribution area A1. Combining the grating vector settings of the first waveguide layer 110 and the second waveguide layer 120 and the above analysis, it can be seen that since only the wave vector distribution area of the first wavelength light of the light incident on the first waveguide layer 110 is moved to the middle of the double ring of the K vector circle, the first waveguide layer 110 is used to propagate the first wavelength light. Similarly, the second waveguide layer 120 is used to propagate the second wavelength light, which is reflected in Figure 1 The result is that the first wavelength light (shown by the solid line) incident on the first waveguide layer 110 can be coupled into the first waveguide layer and propagated by total reflection, while the second wavelength light (shown by the dotted line) incident on the first waveguide layer 110 cannot be coupled into the first waveguide layer and propagated by total reflection. Therefore, ideally, the second wavelength light should transmit through the first waveguide layer 110 and enter the second waveguide layer 120, where it will be diffracted by the second waveguide layer 120 and propagated into the layer before being emitted.

[0031] However, although the second wavelength light cannot be diffracted into the layer by the first waveguide layer 110 and propagated, the first waveguide layer 110 cannot completely isolate the diffraction effect on the second wavelength light. For example, because the grating vector K2 set by the first waveguide layer 110 for the second wavelength light can move the second wavelength light from the wave vector distribution area A0 to the wave vector distribution area Therefore, the second wavelength light may still undergo transmission diffraction or reflection diffraction on the first waveguide layer 110, and be reflected in Figure 1 In this case, the second wavelength light undergoes transmission diffraction on the first waveguide layer 110 and then travels to the second waveguide layer 120. Furthermore, the transmitted diffracted second wavelength light is incident on the outcoupling grating of the second waveguide layer 120, reflected back to the first waveguide layer 110 by the outcoupling grating of the second waveguide layer 120, and transmits through the first waveguide layer 110 to form the final output light. Since only light with a wave vector distribution in the middle of the ring can be accommodated and propagated by the waveguide layer, and ultimately emerge from the waveguide layer at an angle observable to the human eye, the second wavelength light will, due to the diffraction effect of the first waveguide layer 110 and the second waveguide layer, form stray light at an output angle inconsistent with the output angle of the normal propagation light when it is finally emitted. It should be understood that Figure 1 The diagram illustrates only one way stray light is generated in various waveguides and at one angle. In reality, multi-layer waveguides can generate stray light at many angles. Since stray light originates from normal image light sources, the more stray light there is, the lower the waveguide efficiency. Furthermore, stray light entering the human eye not only severely impacts the user experience but, when excessive, can even be dangerous. Therefore, controlling the formation of stray light between multi-layer waveguides is crucial.

[0032] Therefore, see Figure 3 , Figure 3 The structure of a display device proposed in an embodiment of the present application is shown in FIG. Specifically, the display device 300 includes a light source 310, an optical waveguide structure 320, and a light recycling structure 330. The light source 310 is used to emit light of at least two different wavelengths. The optical waveguide structure 320 includes at least two stacked waveguide layers, each of which is used to propagate light of different wavelengths. The at least two waveguide layers have respective coupling-in gratings and coupling-out gratings. Combined with the above analysis of the prior art, it can be seen that light of each wavelength is coupled into the corresponding waveguide layer, propagates, and then coupled out and emitted from the optical waveguide structure to form a target light. In addition, light of each wavelength is diffracted by the coupling-in grating or coupling-out grating of at least one waveguide layer in the optical waveguide structure 320 to form a plurality of stray light rays. The angles of the plurality of stray light rays when they exit the optical waveguide structure 320 are different from the angles of the target light rays when they exit the optical waveguide structure. Furthermore, the light recycling structure 330 is used to diffract at least one stray light emitted from the optical waveguide structure, and change the emission angle of the at least one stray light to be consistent with the emission angle of the target light.

[0033] In some specific embodiments, the light recycling structure may include at least one group of light recycling members, one group of light recycling members corresponding to stray light formed by a wavelength of light, the light recycling members being used to diffract the stray light formed by the corresponding wavelength of light, and transmit the stray light formed by other wavelengths of light, so as to change the exit angle of the stray light formed by the corresponding wavelength of light to be consistent with the exit angle of the target light. For example, when the light source emits a first wavelength of light and a second wavelength of light, the light recycling structure may include a first light recycling member and a second light recycling member, the first light recycling member being used to diffract the stray light formed by the first wavelength of light to change the exit angle of the stray light formed by the first wavelength of light to be consistent with the exit angle of the target light and transmit the stray light formed by the second wavelength of light, the second light recycling member transmitting the stray light formed by the first wavelength of light whose exit angle has been changed and diffracting the stray light formed by the second wavelength of light to change the exit angle of the stray light formed by the second wavelength of light to be consistent with the exit angle of the target light.

[0034] In some more specific embodiments, since the multiple stray light rays formed by a wavelength of light have different exit angles, each of the light recycling members may further include at least one light recycling layer, the light recycling layer corresponding to the stray light of a certain exit angle, the light recycling layer being used to diffract the stray light of the corresponding exit angle and transmit the light of the remaining exit angles, thereby changing the exit angle of the stray light of the corresponding angle to be consistent with the exit angle of the target light. Exemplarily, the light source may emit a first wavelength of light and a second wavelength of light, the optical waveguide structure may include a first waveguide layer and a second waveguide layer, the light recycling member may include a first light recycling member corresponding to the first wavelength of light and a second light recycling member corresponding to the second wavelength of light, further, the first light recycling member may include only one light recycling layer corresponding to one exit angle of the first wavelength of light, or may include multiple light recycling layers corresponding to multiple exit angles of the first wavelength of light; similarly, the second light recycling member may include one light recycling layer corresponding to one exit angle of the second wavelength of light, or may include multiple light recycling layers corresponding to multiple exit angles of the second wavelength of light.

[0035] Ideally, a corresponding recycling layer should be set for each possible stray light. However, as the types of light wavelengths included in the image light increase and the number of layers of the light waveguide structure 320 increases, the amount of stray light that may be generated is very large. As an embodiment, a corresponding light recycling layer can be set only for the stray light with the highest intensity generated by the device. It can be understood that each time light is diffracted on the waveguide layer, a certain amount of energy loss will be generated. Therefore, the intensity of the stray light formed is negatively correlated with the number of diffractions that occur in at least two waveguide layers. In other words, the more times the light is diffracted (including diffraction transmission and diffraction reflection) in multiple waveguide layers, the lower the intensity of the stray light formed. In some embodiments, the light recycling element is used to recycle stray light formed when the total number of diffractions of light of the corresponding wavelength in multiple waveguide layers does not exceed 2 times.

[0036] Specifically, the light recycling layer may be a one-dimensional grating, and the light recycling layer may recycle stray light in such a manner that each light recycling layer has a recycling grating vector, which is used to change the exit angle of the stray light corresponding to the light recycling layer to be consistent with the exit angle of the target light. That is, the recycling grating vector is capable of shifting the wave vector of the stray light incident on the light recycling layer back to the initial wave vector distribution area A0 within the K vector circle, thereby making the exit angle of the stray light corresponding to the light recycling layer consistent with the exit angle of the target light. Specifically, the recycling grating vector of each light recycling layer may be determined based on the superposition of diffraction grating vectors experienced by the original light beam that formed the corresponding stray light when propagating through multiple waveguide layers in the optical waveguide structure.

[0037] As a specific embodiment, the light recycling member includes a first type of light recycling layer, which is used to recycle a first type of stray light. The first type of stray light is formed by the light of the corresponding wavelength being diffracted by one of the at least two waveguide layers. The first type of light recycling layer is used to diffract the first type of stray light and change the exit angle of the first type of stray light to be consistent with the exit angle of the target light. Since the first type of stray light is formed by the light of the corresponding wavelength being diffracted once by one of the at least two waveguide layers, the angle at which the first type of stray light exits the optical waveguide layer is mainly determined by the diffraction grating vector of the waveguide layer that diffracts the light of the corresponding wavelength. Therefore, the first type of light recycling layer is the opposite vector of the diffraction grating vector of the waveguide layer that diffracts the light of the corresponding wavelength. The diffraction grating vector of the waveguide layer can be the grating vector of the coupling-in grating of the waveguide layer or the grating vector of the coupling-out grating of the waveguide layer.

[0038] In a specific embodiment, the light recycling member includes a second type of light recycling layer, which is used to recycle a second type of stray light. The second type of stray light is formed by diffracting light of a corresponding wavelength through two of the at least two waveguide layers. The second type of light recycling layer is used to diffract the second type of stray light and change the exit angle of the second type of stray light to be consistent with the exit angle of the target light. Because the second type of stray light is emitted after diffraction by the two waveguide layers, the angle at which the second type of stray light exits the optical waveguide structure is determined by the grating vectors of the two waveguides. Therefore, the recycling grating vector of the second type of light recycling layer is the opposite vector of the superposition vector of the two diffraction grating vectors corresponding to the wavelength of the two waveguide layers that diffract light of the corresponding wavelength.

[0039] As a specific embodiment, the light recycling member may include both a first type of light recycling layer and a second type of light recycling layer.

[0040] For ease of understanding, the light source emits two different wavelengths of light, and the corresponding optical waveguide structure 320 has two waveguide layers as an example for description. Figure 3 As shown, the light source emits a first wavelength light L1 and a second wavelength light L2. The optical waveguide structure 320 includes a first waveguide layer 321 and a second waveguide layer 322. The first waveguide layer 321 includes a first coupling grating 323 and a first coupling grating 324. The second waveguide layer 322 includes a second coupling grating 325 and a second coupling grating 326. The first waveguide layer 321 is used to transmit the first wavelength light L1 and then emit it to form a target light. The second waveguide layer is used to transmit the second wavelength light L2 and then emit it to form the target light , and the target light and target light The exit angle is the same.

[0041] Furthermore, in this embodiment, several stray lights formed by the diffraction of the second wavelength light L2 in the optical waveguide structure 320 are used as an example for explanation. Figure 4 , Figure 4 FIG. 1 shows a schematic diagram of the grating vector distribution of the optical waveguide structure in the display device according to one embodiment of the present application for the second wavelength light, wherein: Figure 4 (a) shows a schematic diagram of the grating vector distribution of the first coupling grating 323 of the first waveguide layer 321 for the second wavelength light L2. Figure 4 (b) shows a schematic diagram of the grating vector distribution of the second wavelength light L2 of the second coupling grating 325 of the second waveguide layer 322. Furthermore, the first coupling grating 323 of the first waveguide layer 321 has a diffraction grating vector K1 for the second wavelength light. The diffraction grating vector K1 is used to move the wave vector of the second wavelength light incident on the first coupling grating 323 of the first waveguide layer 321 from the initial wave vector distribution area A0 to any one of the wave vector distribution areas A1-A6. The second coupling grating 325 of the second waveguide layer 322 has a diffraction grating vector K2. The diffraction grating vector K2 is used to move the wave vector of the second wavelength light incident on the second coupling grating 325 of the second waveguide layer 322 from the initial wave vector distribution area A0 to any one of the wave vector distribution areas A1-A6. - According to the above analysis of the principle of K vector circle and combined with Figure 4 As can be seen from the content, when the second wavelength light L2 is incident on the first waveguide layer 321 at an initial predetermined angle, it cannot be coupled into the first waveguide layer 321 to cause total reflection propagation, but may cause any one or more of transmission diffraction, reflection diffraction, direct transmission and direct reflection on the first waveguide layer 321; when the second wavelength light L2 is incident on the second coupling grating 325 of the second waveguide layer 322 at an initial predetermined angle, it may cause any one or more of transmission diffraction, reflection diffraction, direct transmission and direct reflection on the second waveguide layer 322, among which only the following three conditions can be met: Figure 4 The diffracted lights corresponding to the six diffraction orders shown in (b) can be coupled into the second waveguide layer 322 to undergo total reflection propagation.

[0042] Therefore, in Figure 3 As can be seen in the figure, after the second wavelength light L2 enters the first waveguide layer 321, a portion of the light directly transmits through the first waveguide layer 321, and another portion undergoes transmission diffraction on the first waveguide layer 321. The portion of light that directly transmits through the first waveguide layer 321 is then diffracted by the second coupling grating 325 on the second waveguide layer and coupled into the second waveguide layer 322, where it undergoes total internal reflection and propagates to form the target light. , and the light diffracted by the first waveguide layer 321 and then directly passes through the second waveguide layer 322 forms stray light. It should be noted that, considering the simplicity of the description, Figure 3 Only two kinds of stray light with different emission angles are shown, namely stray light L3 and stray light L4, but according to Figure 4 As can be seen from (a), the second wavelength light L2 may be diffracted and transmitted in the first waveguide layer 321 to form stray light. Depending on the different wave vector distribution areas A1-A6, there should actually be six different types of stray light with different exit angles. Here, the stray light L3 can be regarded as the exit light formed after the wave vector of the second wavelength light L2 is moved by the diffraction grating vector to the wave vector distribution area A3 in the first waveguide layer 321 and is not affected by the diffraction grating vector of the second waveguide layer 322. The stray light L4 can be regarded as the exit light formed after the wave vector of the second wavelength light L2 is moved by the diffraction grating vector to the wave vector distribution area A4 in the first waveguide layer 321 and is not affected by the diffraction grating vector of the second waveguide layer 322. That is, the light emitted from the first waveguide layer 321 is directly transmitted through the second waveguide layer 322 to form the stray light L3, and the light emitted from the first waveguide layer 321 is also directly transmitted through the second waveguide layer 322 to form the stray light L4. Finally, the stray light L3 and the stray light L4 emitted from the optical waveguide structure are as shown in FIG. Figure 3 Since the stray light L3 and the stray light L4 are both formed by the second wavelength light being diffracted once by the first waveguide layer, the stray light L3 and the stray light L4 both belong to the first type of stray light.

[0043] Furthermore, Figure 3 The light recycling structure 330 shown in the figure can accordingly have a first light recycling layer 331 for recycling stray light L3 and a second light recycling layer 332 for recycling stray light L4. The first light recycling layer 331 and the second light recycling layer 332 both belong to the first type of light recycling layer. Specifically, the first light recycling layer 331 can change the emission angle of the stray light L3 to the same as the target light. The second light recycling layer 332 can change the exit angle of the stray light L4 to the same as the target light. Furthermore, since both the first light recycling layer and the second light recycling layer are used to recycle stray light generated by the light of the second wavelength, the two light recycling layers belong to the same light recycling member.

[0044] According to the above analysis, different waveguide layers in the optical waveguide structure have different diffraction grating vectors for light of the same wavelength. Figure 4As shown in FIG, the first coupling-in grating 323 of the first waveguide layer 321 has a diffraction grating vector K1 for diffracting the second wavelength light L2, and the second coupling-in grating 325 of the second waveguide layer 322 has a diffraction grating vector K2 for diffracting the second wavelength light L2. Therefore, when the second wavelength light L2 is diffracted by different waveguide layers, stray light with different output angles is generated.

[0045] In some embodiments, the recycling grating vector can be determined based on the superposition of diffraction grating vectors encountered by the original light beam that forms the stray light when propagating through multiple waveguide layers in the optical waveguide structure. For example, see Figure 5 , Figure 5 A schematic diagram of the recycling grating vector distribution of the light recycling structure in a display device according to one embodiment of the present application is shown, wherein the first light recycling layer 331 has a recycling grating vector K3, and the second light recycling layer 332 has a recycling grating vector K4. Furthermore, a plane rectangular coordinate system can be established within the K-vector circle, with the center of the K-vector circle as the origin, the direction from wave vector distribution area A0 to wave vector distribution area A4 as the x-axis, and the direction perpendicular to wave vector distribution area A0 pointing to wave vector distribution area A4 as the y-axis. Thus, based on the above analysis of the light recycling layers and their recycling grating vectors, it can be seen that the recycling grating vector of each light recycling layer is related to the superposition result of the diffraction grating vectors experienced by the light corresponding to the stray light to be recycled by the light recycling layer when propagating in the optical waveguide structure. Furthermore, the recycling grating vector is the opposite vector of this superposition result.

[0046] In a specific embodiment, when the first type of light recycling layer is used to recycle stray light generated by the diffraction of light of the corresponding wavelength by only one of the waveguide layers in the optical waveguide structure, the recycling grating vector of the first type of light recycling layer is the opposite vector of the diffraction grating vector of the waveguide layer that diffracts the light of the corresponding wavelength corresponding to the wavelength. Figure 4 It can be seen that when the stray light L3 propagates in the optical waveguide structure 320, it is only affected by the diffraction grating vector K1 of the first waveguide layer 321, which points from the wave vector distribution area A0 to the wave vector distribution area A3. That is, the corresponding diffraction grating vector superposition result points from the wave vector distribution area A0 to the wave vector distribution area A3. If the corresponding diffraction grating vector superposition result is decomposed along the plane rectangular coordinate system, its expression can be obtained as { }, then the recycling grating vector K3 of the first light recycling layer 331 for recycling the stray light L3 is the opposite vector of the superposition result, that is, pointing from the wave vector distribution area A3 to the wave vector distribution area A0, and the expression of the recycling grating vector is: { Similarly, when the stray light L4 propagates in the optical waveguide structure 320, it is only affected by the diffraction grating vector K1 of the first waveguide layer 321, which points from the wave vector distribution area A0 to the wave vector distribution area A4. That is, the corresponding diffraction grating vector superposition result points from the wave vector distribution area A0 to the wave vector distribution area A4. If the corresponding diffraction grating vector superposition result is decomposed along the plane rectangular coordinate system, its expression can be obtained as { }, then the recycling grating vector K4 of the second light recycling layer 332 for recycling the stray light L4 is the opposite vector of the superposition result, that is, it points from the wave vector distribution area A4 to the wave vector distribution area A0, and the expression of the recycling grating vector is { }.

[0047] Therefore, according to the above analysis, it can be seen that based on the process of each wavelength of light propagating in the optical waveguide structure and forming stray light, all the diffraction grating vectors affected by the optical waveguide structure on the stray light can be obtained, and the superposition result can be obtained based on all the diffraction grating vectors. Then, the opposite vector of the superposition result is used as the recycling grating vector of the light recycling layer corresponding to the stray light. This can enable the light recycling layer to change the output angle of the corresponding stray light to be consistent with the output angle of the target light.

[0048] In a specific embodiment, the light recycling member may further include a second type of light recycling layer, the second type of light recycling layer being used to recycle second stray light, the second stray light being formed by light of corresponding wavelengths diffracting through two of the at least two waveguide layers. For example, see Figure 6 and Figure 7 , Figure 6 FIG2 shows a wave vector distribution diagram of a portion of stray light formed in the display device proposed in an embodiment of the present application. Figure 7 A schematic diagram showing the propagation of a portion of stray light generated by the second wavelength light in the display device in an embodiment of the present application in the optical waveguide structure is shown. Figure 6 and Figure 7 , the stray light shown includes: L4, L41, L42, and L43. Among them, L4 is the stray light formed by the second wavelength light L2 being directly transmitted in the second waveguide layer 322 after being transmitted and diffracted in the first waveguide layer 321. The wave vector of the stray light L4 is moved from the wave vector distribution area A0 to the wave vector distribution area A4 by the diffraction grating vector K1 of the first waveguide layer 321; L41, L42, and L43 are the stray lights formed by the second wavelength light L2 being further diffracted in the second waveguide layer after being transmitted and diffracted in the first waveguide layer 321. When the type Figure 5 When the rectangular coordinate system is established by the model, the corresponding diffraction grating vector superposition results of the three new stray lights when propagating in the optical waveguide structure are obtained as follows: }、{}and{ },in is the angle between the corresponding vector and the x-axis. Further, the recycling vector grating of the light recycling layer can be set according to the superposition result of the diffraction grating vectors corresponding to the above stray light. For example, Figure 6 and Figure 7 The stray light L41, L42 and L43 shown in the figure can be provided with three light recycling layers, which belong to the second type of light recycling layer, and the recycling vector gratings thereof are respectively: }、{ }and{ According to the above analysis, it can be inferred that the wave vectors corresponding to the various stray lights emitted after each wavelength of light is diffracted by the optical waveguide structure are all formed by the superposition of the diffraction grating vectors of the waveguide layers that diffract them, and since the diffraction grating vectors of each waveguide layer are different for light of the same wavelength, the superposition results of these various stray lights after at least one superposition of the diffraction grating vectors are also different, and the light emission angle is related to the superposition result of the diffraction grating vectors, that is, the emission angles of the various stray lights emerging from the optical waveguide structure are also different. When the recycling grating vector of the light recycling layer is determined according to the superposition result of the diffraction grating vectors to which each stray light is subjected when propagating in the optical waveguide structure, it can be ensured that each light recycling layer is used to diffract stray light of a certain emission angle and convert its emission direction to be consistent with the emission direction of the target light.

[0049] Further, combined with Figure 6 and Figure 7 From the relevant analysis, it can be inferred that the amount of stray light diffracted by the second wavelength light L2 in the optical waveguide structure 320 is actually still much greater than Figure 6 In the case shown in FIG. 3 , for example, the second wavelength light L2 has an exit angle after being incident on the first waveguide layer 321 and diffracted and transmitted. Figure 4 The six scenarios shown in (a) can each be diffracted and transmitted through the second waveguide layer 322. For another example, the second wavelength light L2, after entering the first waveguide layer 321 and diffracting and transmitting therethrough, then enters the second waveguide layer 322, undergoing diffraction and reflection. It then returns to the first waveguide layer 321 and is again diffracted and reflected back to the second waveguide layer, ultimately exiting the optical waveguide structure 320. Similarly, the propagation of the first wavelength light L1 in the optical waveguide structure 320 is similar to that of the second wavelength light L2. In other embodiments, corresponding light recycling layers may be provided for other stray light sources, which is not a limitation in this case. The principles for providing such light recycling layers are similar to those for the first and second stray light sources described above and are not further elaborated here.

[0050] Furthermore, it should be noted that the same waveguide layer also has different diffraction grating vectors for different wavelengths. The above analysis only analyzes the stray light generated by the second wavelength. When considering the stray light generated by the first wavelength, the recycling grating vector of the light recycling layer set for the stray light generated by the first wavelength is different from the recycling grating vector of the light recycling layer set for the stray light generated by the second wavelength. Specifically, it can be based on Figure 2 It can be inferred that the diffraction grating vectors of the first waveguide layer 321 for the first wavelength light L1 and the second wavelength light L2 are different, and the diffraction grating vectors of the second waveguide layer 322 for the first wavelength light L1 and the second wavelength light L2 are also different. In other words, when light of different wavelengths propagates through the optical waveguide structure 320, the diffraction grating vectors experienced by the stray light of the corresponding wavelength will differ depending on the wavelength, resulting in different superposition results. Therefore, the light recycling layer can be wavelength-selective. Specifically, the recycling grating vector of each light recycling layer is determined solely based on the superposition result of the diffraction grating vectors experienced by the stray light of the corresponding wavelength when propagating through the optical waveguide structure. This ensures that each light recycling layer is dedicated to diffracting stray light of a specific wavelength and converting its exit direction to align with the exit direction of the target light.

[0051] In other embodiments, the light recycling structure may further include a second light recycling component for the first wavelength of light, and the second light recycling component may further specifically include a first type of light recycling layer and / or a second type of light recycling layer. The recycling grating vectors of the first type of light recycling layer and the second type of light recycling layer of the second light recycling component are different from the recycling grating vectors of the first type of light recycling layer and the second type of light recycling layer of the aforementioned light recycling component for the first wavelength of light. When it is necessary to recycle the stray light generated by the first wavelength of light, the principle of the method for determining the recycling grating vector of the light recycling layer corresponding to the second light recycling component is similar to the principle of determining the recycling grating vector of the light recycling layer of the recycling component corresponding to the first wavelength of light, and will not be repeated here.

[0052] Furthermore, each waveguide layer is provided with an in-coupling grating and an out-coupling grating. Figure 3The first waveguide layer 321 and the second waveguide layer 322 of the optical waveguide structure 320 are provided with corresponding coupling-in gratings and coupling-out gratings, wherein the first waveguide layer 321 is provided with a first coupling-in grating 323 and a first coupling-out grating 324, and the second waveguide layer 322 is provided with a second coupling-in grating 325 and a second coupling-out grating 326. Furthermore, the diffraction grating vector of each waveguide layer may include a coupling-in grating vector and a coupling-out grating vector. Furthermore, the coupling-in grating vector is a grating vector of the coupling-in grating, which is generally used to couple the corresponding light into the waveguide layer for total reflection propagation. The coupling-out grating vector is a grating vector of the coupling-out grating, which is generally used to couple the corresponding light out of the waveguide layer. It should be understood that the diffraction grating vectors mentioned in the above embodiments are all based on the coupling-in grating vector as an example, but can also be applied to the case where light is diffracted by the coupling-out grating vector on the coupling-out grating. When light of a wavelength that it cannot propagate is incident on a waveguide layer, it may be affected by the combined effects of the waveguide layer's in-coupling grating vector, out-coupling grating vector, or both, resulting in stray light. For example, in the aforementioned embodiment, light of a second wavelength is incident on the first waveguide layer. The first waveguide layer may have an in-coupling grating and an out-coupling grating. In this case, the second wavelength may be diffracted by the in-coupling grating vector on the in-coupling grating of the first waveguide layer and then directly transmitted through the out-coupling grating. Alternatively, the second wavelength may be directly transmitted through the in-coupling grating of the first waveguide layer and then diffracted by the out-coupling grating vector through the out-coupling grating. Alternatively, the second wavelength may be diffracted by both the in-coupling grating vector and the out-coupling grating vector on the in-coupling grating and the out-coupling grating of the first waveguide layer. Considering that the light recycling layer is only provided for stray light diffracted once or / and twice, that is, the recycling grating vector of the light recycling layer can be the opposite vector of the coupling-in grating vector of one waveguide layer, or the opposite vector of the coupling-out grating vector of one waveguide layer, or the opposite vector of the superposition vector of the coupling-in grating vector of one waveguide layer and the coupling-in grating vector of another waveguide layer, or the opposite vector of the superposition vector of the coupling-out grating vector of one waveguide layer and the coupling-out grating vector of another waveguide layer, or the opposite vector of the superposition vector of the coupling-out grating vector of one waveguide layer and the coupling-in grating of another waveguide layer.

[0053] Furthermore, the types of stray light generated are different depending on the type of the coupling grating and the coupling grating on each waveguide layer. Taking the coupling grating of the waveguide layer in some optical waveguide structures as a two-dimensional grating as an example, the specific type of stray light generated can be based on Figure 4The result shows that, for light that cannot propagate within each waveguide layer, at least six of the possible stray light angles emitted are formed after only one diffraction. This means that, regardless of the number of waveguide layers in the optical waveguide structure, to save costs, the stray light with the highest intensity can be considered to be the light that has only been diffracted once within the waveguide layer. For some optical waveguide structures where the coupling grating of the waveguide layer is a one-dimensional grating, since the one-dimensional grating only has a coupling grating vector in one direction, that is, if only one diffraction is considered for each waveguide layer, the amount of stray light that can be recovered is relatively small. In this case, the requirement for stray light intensity can be appropriately relaxed, and stray light that has been diffracted twice or more within the optical waveguide structure can also be included in the range that needs to be recovered, and a light recycling layer can be provided accordingly. Furthermore, to achieve the pupil expansion effect of the optical waveguide, the coupling grating is generally configured as a two-dimensional grating. Here, the implementation of the coupling grating, whether the coupling grating is a one-dimensional grating or a two-dimensional grating, can refer to the description of the coupling grating and will not be repeated here.

[0054] As an embodiment, to further reduce the size of the display device, the light recycling layer can be configured as a thin film, with multiple light recycling layers sequentially attached to the surface of the optical waveguide structure used to emit light. Furthermore, the light recycling layer can be any of a Bragg grating, a volume Bragg grating, a volume holographic grating, a polarization volume holographic grating, a liquid crystal grating, or a metasurface grating.

[0055] Therefore, the present application provides a display device comprising: a light source, an optical waveguide structure, and a light recycling structure. The light source is for light of at least two different wavelengths. The optical waveguide structure comprises at least two stacked waveguide layers. Light is coupled into corresponding waveguide layers for propagation and then coupled out to form a target light. Light of each wavelength is diffracted by at least one waveguide layer and then emerges from the optical waveguide structure to form multiple stray light rays. The light recycling structure is for diffracting at least some of the wavelengths of light, forming at least one stray light ray, to change the exit angle of the at least one stray light ray to be consistent with the exit angle of the target light ray. The present application provides a light recycling structure for a display device with a multilayer optical waveguide. The light recycling structure is capable of recycling stray light rays formed when light propagates through the multilayer optical waveguide and adjusting the exit angle of the stray light rays to be consistent with the exit angle of the target light ray. This significantly reduces the stray light effect of the multilayer optical waveguide and improves the efficiency of the display device.

[0056] See also Figure 8 , Figure 8A schematic diagram of the structure of a head-up display system according to one embodiment of the present application is shown. Specifically, head-up display system 800 includes display glass 801 and a display device 802 as described in any one of the claims. Image light emitted from display device 802 is reflected by display glass 801 and enters the observation position (human eye), providing the driver with various information such as navigation, road conditions, and vehicle data. Because the display device in this application significantly reduces the amount of stray light, the display quality of the head-up display system is improved, effectively preventing the problem of a large amount of stray light entering the human eye and posing a threat to personal safety.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A display device, characterized in that: include: A light source, an optical waveguide structure, and a light recycling structure, wherein the light source is configured to emit light of at least two different wavelengths. The optical waveguide structure comprises at least two stacked waveguide layers, wherein different waveguide layers are configured to propagate light of different wavelengths. At least two of the waveguide layers have respective coupling-in gratings and coupling-out gratings. The light is coupled into the corresponding waveguide layer, propagates, and then coupled out from the optical waveguide structure to form target light. wherein each wavelength of light is diffracted by at least one coupling-in grating or coupling-out grating of the waveguide layer and then emerges from the optical waveguide structure to form a plurality of stray light rays, and the angle at which the stray light rays emerge from the optical waveguide structure is different from the angle at which the target light rays emerge from the optical waveguide structure; The light recycling structure is used to diffract at least one stray light formed by at least a portion of the wavelengths of light emitted from the optical waveguide structure, so as to change the emission angle of the at least one stray light to be consistent with the emission angle of the target light.

2. The display device according to claim 1, wherein The light recycling structure includes at least one group of light recycling components, one group of light recycling components corresponds to the stray light formed by a wavelength of light, and the light recycling components are used to diffract the stray light formed by the light of the corresponding wavelength, and pass the stray light formed by the light of other wavelengths, and change the exit angle of the stray light formed by the light of the corresponding wavelength to be consistent with the exit angle of the target light.

3. The display device according to claim 2, wherein: The multiple stray light rays formed by the light of one wavelength have different exit angles. The light recycling component includes at least one light recycling layer, and the light recycling layer corresponds to the stray light of one exit angle. The light recycling layer is used to diffract the stray light of the corresponding exit angle and transmit the light of the remaining exit angles, so as to change the exit angle of the stray light of the corresponding exit angle to be consistent with the exit angle of the target light.

4. The display device according to claim 3, wherein: The intensity of the stray light generated by the light of each wavelength is negatively correlated with the total number of diffractions of the light in the at least two waveguide layers. The light recycling member is used to recycle the stray light generated when the total number of diffractions of the light of the corresponding wavelength in the at least two waveguide layers does not exceed 2 times.

5. The display device according to claim 4, wherein: The light recycling layer is a one-dimensional grating, and each light recycling layer has a recycling grating vector. The recycling grating vector is used to change the exit angle of the stray light corresponding to the light recycling layer to be consistent with the exit angle of the target light.

6. The display device according to claim 5, wherein: The light recycling member includes a first type of light recycling layer, the first type of light recycling layer is used to recycle a first type of stray light, the first type of stray light is formed by the light of the corresponding wavelength being diffracted through one of the at least two waveguide layers; Each of the waveguide layers has a different diffraction grating vector for light of different wavelengths. The recycling grating vector of the first type of light recycling layer is the opposite vector of the diffraction grating vector corresponding to the wavelength of the waveguide layer that diffracts the light of the corresponding wavelength.

7. The display device according to claim 5 or 6, characterized in that: The light recycling member includes a second type of light recycling layer, the second type of light recycling layer is used to recycle a second type of stray light, the second type of stray light is formed by the diffraction of light of corresponding wavelength through two waveguide layers of the at least two waveguide layers; Each of the waveguide layers has a different diffraction grating vector for light of different wavelengths. The recycling grating vector of the second type of light recycling layer is the opposite vector of the superposition vector of the two diffraction grating vectors corresponding to the wavelength of the two waveguide layers that diffract the light of the corresponding wavelength.

8. The display device according to claim 3, wherein The light recycling layer is in the form of a thin film, and a plurality of light recycling layers are sequentially attached to the surface of the optical waveguide structure for emitting light.

9. The display device according to claim 8, wherein The light recycling layer is a Bragg grating, a volume Bragg grating, a volume holographic grating, a polarization volume holographic grating, a liquid crystal grating or a metasurface grating.

10. A head-up display system, characterized in that: The display device comprises display glass and any one of claims 1 to 9, wherein the target light emitted by the display device and the stray light after the emission angle is changed reach the display glass and are reflected to an observation position.

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