CN110082907B

CN110082907B - Optical waveguide structure and display device

Info

Publication number: CN110082907B
Application number: CN201810078000.1A
Authority: CN
Inventors: 戴杰; 郭帮辉; 阮望超
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2018-01-26
Filing date: 2018-01-26
Publication date: 2021-02-23
Anticipated expiration: 2038-01-26
Also published as: WO2019144596A1; CN110082907A

Abstract

An optical waveguide structure and a display device are used for solving the problem that stray light in an augmented reality waveguide is difficult to inhibit in the prior art. The optical waveguide structure comprises an upper layer waveguide, a lower layer waveguide and a first light splitting layer positioned between the upper layer waveguide and the lower layer waveguide; the upper waveguide comprises a first upper surface, a first lower surface and a second light splitting film array positioned between the first upper surface and the first lower surface, the second light splitting film array comprises at least two wavelength light splitting films, an acute included angle is formed between the at least two wavelength light splitting films and the first lower surface, the at least two wavelength light splitting films are used for reflecting light in at least three bands in visible light, the rest bands are transmitted, and the at least three bands are bands for projection imaging; the lower waveguide comprises a second upper surface and a second lower surface, and the second upper surface is parallel to the second lower surface; the first light splitting layer is used for reflecting one part of incident light and transmitting the other part of the incident light.

Description

Optical waveguide structure and display device

Technical Field

The present application relates to the field of optical technologies, and in particular, to an optical waveguide structure and a display device.

Background

The Augmented Reality (AR) technology is a new technology for seamlessly integrating real world information and virtual world information, and is a technology for superimposing entity information (such as visual information, three-dimensional appearance, sound, taste, touch and the like) which is difficult to experience in a certain time space range of the real world originally through simulation by optics, computers, electronics and the like, so that not only is the information of the real world displayed, but also the virtual information is displayed simultaneously, and the two kinds of information are mutually supplemented and superimposed. In visual augmented reality, a user combines the real world and a virtual image together by using an optical display device to form virtual-real combined immersive visual experience.

The stacked reflective waveguide shown in fig. 1 is a widely used implementation of an AR waveguide, and referring to fig. 1, the stacked reflective waveguide is provided with a spectroscopic film array that is capable of reflecting a portion of incident light and transmitting a portion of the incident light. Taking incident light ray a as an example, after the incident laminated reflection waveguide, the incident light ray is reflected to the light splitting film array through the light path b, one part of the light is reflected to human eyes through the light path c, the other part of the light is transmitted through the light path d, the transmitted light continues to propagate forwards, the light is separated when the light is incident to the light splitting film array every time, one part of the light is reflected to the human eyes along the light path d-e-f-g-h, one part of the light is reflected to the human eyes along the light path d-e-f-g-i-j, and the light rays are all normal light rays. However, after the light e enters the light splitting film array, a part of the light is reflected and reflected to human eyes along the light path k-l-m, the emergent direction of the light m is deflected, imaging deviation is caused after the light enters the human eyes, and the part of the light is stray light. In the prior art, the stray light is difficult to inhibit.

Disclosure of Invention

The application provides an optical waveguide structure and a display device, which are used for solving the problem that stray light in an AR waveguide is difficult to inhibit in the prior art.

In a first aspect, the present application provides an optical waveguide structure comprising an upper waveguide, a lower waveguide, and a first light splitting layer located between the upper waveguide and the lower waveguide. The upper waveguide comprises a first upper surface, a first lower surface and a second light splitting film array located between the first upper surface and the first lower surface, the first upper surface is parallel to the first lower surface, the second light splitting film array comprises at least two wavelength light splitting films, the at least two wavelength light splitting films are parallel to each other and form an acute included angle with the first lower surface, the at least two wavelength light splitting films are used for reflecting light in at least three bands of visible light, and the rest bands are transmitted, wherein the at least three bands are bands used for projection imaging, for example, the at least three bands are respectively one band of a red light spectrum, one band of a green light spectrum and one band of a blue light spectrum. The lower layer waveguide comprises a second upper surface and a second lower surface, and the second upper surface is parallel to the second lower surface. Two surfaces of the first light splitting layer are respectively contacted with the first lower surface and the second upper surface, and the first light splitting layer is used for reflecting one part of incident light and transmitting the other part of the incident light.

In the optical waveguide structure, the side end of the lower waveguide can receive projection light, the projection light is split into two parts by the first light splitting layer after entering the first light splitting layer, one part of the light enters the upper waveguide through the first light splitting layer, and is reflected back to the lower waveguide after entering the second light splitting film array, and then the light is emitted from the second lower surface and can finally enter human eyes; the other part of the projection light separated by the first light splitting layer is reflected to the second lower surface, is reflected to the first light splitting layer through the second lower surface and continues to be separated by the first light splitting layer. When the projection light propagates in the optical waveguide structure, stray light is less. Moreover, the first light splitting layer only needs to reflect one part of incident light and transmit the other part of the incident light, so that the process difficulty is low, and the cost is low; moreover, if the optical adhesive is used for bonding the first light splitting layer, the optical adhesive bonded with the first light splitting layer is not required to have an extremely high refractive index because the characteristic of the first light splitting layer is easy to realize, and the cost of the optical adhesive is low.

In some optional implementations of the first aspect, the first light splitting layer comprises a light splitting film or a grating array. The light splitting film can be a light intensity light splitting film, a polarization light splitting film and the like.

In some optional implementations of the first aspect, the first light splitting layer is to: the incident angle is from 0 DEG to theta₁A 90% to 99% partial transmission, a 10% to 1% partial reflection of light rays in the range, and an angle of incidence at θ₁5% to 20% of the light in the range to 90 ° is transmitted, 95% to 80% is partially reflected, θ₁Greater than 0 ° and less than 90 °. According to the technical scheme, the energy of the stray light can be controlled at an extremely low level, the projection light can be emitted from the second lower surface of the lower-layer waveguide within a wide range, and the display effect of the light emitted from the second lower surface of the lower-layer waveguide is improved. Furthermore, the above-mentioned angle selection characteristic of the first light splitting layer can also significantly improve the field of view (FOV) of the optical waveguide, thereby improving the viewing immersion of the user.

In some optional implementations of the first aspect, the refractive index of the upper waveguide is equal to the refractive index of the lower waveguide, and stray light caused by a refractive index difference between the upper waveguide and the lower waveguide is reduced.

In some optional implementations of the first aspect, the first light splitting layer is a piece of light splitting film, and a splitting ratio of the piece of light splitting film changes from small to large along the first direction; or the first light splitting layer comprises at least two light splitting films, and the light splitting ratio of the light splitting films, close to the first side end of the lower waveguide, of the two adjacent light splitting films is not greater than the light splitting ratio of the light splitting films, close to the second side end of the lower waveguide; or the first light splitting layer comprises at least two light splitting films, and the spacing distance between two adjacent light splitting films changes from large to small along the first direction; or, the first light splitting layer is a grating array, and the energy proportion of 0-order reflected light of the grating array changes from large to small along the first direction, and/or the diffraction efficiency of the effective diffraction order of the grating array changes from small to large along the first direction; wherein the first direction is a direction in which the first side end points to the second side end. The change in the splitting ratio of the splitting film can be realized by a change in the thickness, refractive index, or the like of the splitting film.

In the above technical solution, the transmittance of the first light splitting layer to light changes from small to large along the transverse propagation direction of the projection light in the lower waveguide, so that the energy of light emitted from the position of the second lower surface close to the incident side of the projection light can be reduced, and is not too strong, and the energy of light emitted from the position of the second lower surface far away from the incident side of the projection light can be increased, so that is not too weak, so that the energy of light emitted from different positions of the lower waveguide is more balanced, and the imaging effect of the emitted light is improved.

In some optional implementations of the first aspect, the first upper surface of the upper waveguide and/or the second lower surface of the lower waveguide are further provided with an antireflection film to enhance transmittance of the first upper surface and/or the second lower surface.

In an alternative design, the second dichroic film array in the upper waveguide of the first aspect is replaced with a reflective film array to reduce the cost of the yellow waveguide structure.

In a second aspect, the present application provides a display device comprising: a frame, an optical waveguide structure of the first aspect or any alternative implementation thereof, and a projection module. The optical waveguide structure and the projection module are fixed on the frame, and the projection module is used for inputting projection light to the lower layer waveguide, wherein the projection light comprises light rays in at least three wave bands, such as red, blue and green light.

In the display device, after the projection light generated by the projection module enters the lower waveguide 120, the projection light can be separated by the first light splitting layer 130, and finally exits from a plurality of positions of the second lower surface 122 to enter human eyes, while the ambient light can enter the upper waveguide 110 from the first upper surface and finally exits from the second lower surface 122, and is superposed with the projection light exiting from the second lower surface 122, so that the augmented reality effect is realized, and the display device can effectively increase the FOV of the projection light and effectively inhibit the generation of stray light.

In some optional implementations of the second aspect, the display device further comprises: the first light homogenizing layer comprises a first light homogenizing film arranged on the second lower surface or a first light homogenizing sheet arranged below the lower layer waveguide and fixed on the frame, the transmittance of the first light homogenizing layer changes from small to large along a first direction, and the first direction is a direction in which the first side end of the lower layer waveguide points to the second side end of the lower layer waveguide. The change in transmittance of the first light uniformizing film or the first light uniformizing sheet can be realized based on the change in shape, thickness, refractive index, and the like. The first dodging layer can enable the light intensity of projection light entering human eyes to be more uniform.

In some optional implementations of the second aspect, when the display device includes the first light uniformizing layer, the display device further includes a second light uniformizing layer, the second light uniformizing layer may be a second light uniformizing film disposed on the first upper surface or a second light uniformizing sheet disposed above the upper waveguide and fixed on the frame, and a transmittance of the second light uniformizing layer changes from large to small along the first direction. The second light homogenizing layer can compensate the influence of the first light homogenizing layer on the distribution of the ambient light, so that the ambient light entering human eyes is more balanced.

In some optional implementations of the second aspect, the display device further comprises an out-coupling waveguide positioned below the second lower surface and fixed to the frame for receiving, propagating and outputting light rays exiting from the second lower surface. The coupling-out waveguide can change the light path, and is convenient for designing products such as AR glasses and the like. In addition, the coupling-out waveguide is a single-layer waveguide, the thickness of the coupling-out waveguide is smaller than that of the upper-layer waveguide and the formed double-layer waveguide structure, and the thickness of the position where the user views the image can be obviously reduced compared with the case that the light is directly emitted to the user by the lower-layer waveguide due to the fact that the single-layer coupling-out waveguide is adopted to guide the light emitted by the user. Furthermore, the light path of the emergent light of the lower waveguide is changed through the coupling-out waveguide, so that the ambient light incident from the upper waveguide can be checked through the coupling-out waveguide, and the periscope-based augmented reality is realized.

In some optional implementations of the second aspect, the outcoupling waveguide includes an incoupling grating disposed on a third upper surface of the outcoupling waveguide opposite to the second lower surface, for coupling light received from the second lower surface into the outcoupling waveguide. The structure is simple to realize, and the effect of coupling light into the grating is better.

In some optional implementations of the second aspect, the outcoupling waveguide includes a first surface and a second surface, wherein the first surface is configured to receive the light emitted from the second lower surface and transmit the received light to the second surface, the second surface is configured to totally reflect the light transmitted through the first surface, the first surface is located on a surface of the outcoupling waveguide, the second surface is located on or inside the outcoupling waveguide, and the first surface is not parallel to the second surface. The coupling waveguide utilizes the film layer of the coupling waveguide to couple light into the coupling waveguide, a light coupling structure is not additionally arranged, the cost is low, and the effect of coupling light into the coupling grating is good.

In some optional implementations of the second aspect, one of the first and second faces is a wedge face or is provided with an optical structure comprising a wedge face when the second face is located at a surface of the out-coupling waveguide.

In some optional implementations of the second aspect, the outcoupling waveguide comprises an outcoupling grating arranged at a waveguide wall of the outcoupling waveguide for reflecting a part of light propagating within the outcoupling waveguide and incident on the outcoupling grating out of the waveguide wall and another part reflecting. The light-coupling waveguide has a simple structure for emitting light, and has a good light-emitting effect.

Optionally, the energy ratio of the 0 th order reflected light of the coupling-out grating changes from large to small along the propagation direction of the light in the coupling-out waveguide, and/or the diffraction efficiency of the effective diffraction order of the coupling-out grating changes from small to large along the propagation direction of the light in the coupling-out waveguide. The light coupling grating can enable the energy of light emitted from the light coupling grating to be more balanced, and the film watching experience of a user is improved.

In some optional implementations of the second aspect, the outcoupling waveguide comprises a third light-dividing film array disposed inside the outcoupling waveguide, and the third light-dividing film array is configured to reflect a part of light propagating in the outcoupling waveguide and incident on the third light-dividing film array to a waveguide wall of the outcoupling waveguide for exit, and transmit the rest. The light-coupling waveguide has a simple structure for emitting light, and has a good light-emitting effect.

Optionally, in the plurality of light splitting films of the third light splitting film array, the transmittance of the light splitting film at a position close to the waveguide where the light is incident and coupled out from the lower waveguide is relatively low, and the transmittance of the light splitting film at a position far from the waveguide where the light is incident and coupled out from the lower waveguide is relatively high. The third light splitting film array can enable the energy of light rays emitted from the coupling-out waveguide to be more balanced, and the film watching experience of users is improved.

Drawings

FIG. 1 is a schematic illustration of a prior art optical waveguide structure;

FIG. 2 is a schematic diagram of the wavelength range of the reflected light of the light splitting film;

FIGS. 3-4 are schematic diagrams of optical waveguide structures in embodiments of the present application;

FIGS. 5 a-5 b are schematic diagrams of possible implementations of a first light splitting layer in embodiments of the present application;

FIG. 6 is a schematic diagram of the propagation of the projected light in an embodiment of the present application;

FIGS. 7 a-7 d are schematic diagrams illustrating propagation of ambient light in an embodiment of the present application;

FIG. 8 is a schematic view of a display device according to an embodiment of the present application;

FIGS. 9-10 are schematic diagrams of possible implementations of a display device;

fig. 11 a-11 d are schematic diagrams of the structure of the out-coupling waveguide.

Detailed Description

The plural in the present application means two or more. In addition, in the description of the present application, the terms "first," "second," and the like are used for descriptive purposes only and are not intended to indicate or imply relative importance nor order to be construed. The term "and/or" in this application is only one kind of association relationship describing the associated object, and means that there may be three kinds of relationships, for example, a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone.

In the prior art, in order to suppress the stray light shown in fig. 1, a reflective film sensitive to an incident angle is plated on the surface of the light splitting film array, and the reflective film can reflect about 10% of incident light with a small incident angle and transmit 95-99% of incident light with a large incident angle. The characteristic of the reflective film that most of incident light with large incident angle is transmitted can reduce the stray light in fig. 1 caused by the reflection of the light e incident on the light splitting film array via the light path k. However, high transmission at high angles of incidence is very difficult to achieve, the process cost of the incident angle sensitive reflective film is high, and high index of refraction optical glue is also required to bond the reflective film to the array of dichroic films, which is also expensive.

In order to facilitate understanding of the technical solutions provided in the present application, some concepts are first introduced below.

An optical waveguide, referred to simply as a waveguide in the embodiments of the present application, is a dielectric device that guides light waves to propagate therein. The waveguide comprises an upper surface and a lower surface, when light rays in the waveguide are incident on the upper surface and the lower surface of the waveguide, if the incident angle is larger than a critical angle, the light rays are totally reflected on an interface between the surface of the waveguide and air, and the critical angle depends on the refractive index of the waveguide.

The light splitting film is a thin film which can reflect a part of incident light and transmit a part of the incident light to split the light into two parts. According to different light splitting modes, the light splitting film comprises a wavelength light splitting film, a light intensity light splitting film, a polarization light splitting film and the like.

The wavelength splitting film is a thin film that splits light into two parts according to wavelength regions. For example, after the light is incident on the wavelength-splitting film, the wavelength-splitting film reflects the light having the wavelength in the first range and transmits the remaining portion. It should be noted that the wavelength splitting film is not limited to reflecting light within a continuous bandwidth (see the left side of fig. 2), but may reflect light within a plurality of spaced narrow bands in the spectrum (see the right side of fig. 2).

The light intensity splitting film divides incident light into two parts of emission light and transmission light according to a certain light intensity ratio. For example, the light intensity splitting film may reflect 10% of the incident light and transmit the remaining 90% of the incident light.

The polarization splitting film is a film that separates a parallel direction component from a perpendicular direction component of light.

The grating array comprises a large number of parallel slits with equal width and equal spacing, and can be made of a large number of parallel scores engraved on a glass sheet. The grating array may reflect a portion of the incident light back and the rest pass through by diffraction.

It should be understood that, when the light splitting film or the grating splits the light, the sum of the energy of the reflected light and the energy of the transmitted light may be less than the energy of the incident light, because the energy of the light may be partially absorbed by the light splitting film or the grating, which results in energy loss.

The light homogenizing sheet is also called as a light homogenizing sheet and is a light guide plate, and due to the design of the size, the shape, the density and the like of the light homogenizing sheet, the intensity distribution of light is changed after a beam of light passes through the light homogenizing sheet.

The light homogenizing film is a light transmitting film, and the intensity distribution of light after penetrating the light homogenizing film can be changed due to the change of the thickness, the refractive index and the like of the light homogenizing film.

Fig. 3 and fig. 4 show an optical waveguide structure 100 provided in an embodiment of the present application, where fig. 4 is a schematic diagram of components of the optical waveguide structure 100 when separated. Referring to fig. 3 and 4, the optical waveguide structure 100 includes: an upper waveguide 110, a lower waveguide 120, and a first light splitting layer 130 between the upper and lower waveguides.

The upper waveguide 110 includes a first upper surface 111, a first lower surface 112, and a second dichroic film array 113. The first upper surface 111 is parallel to the first lower surface 112, the second dichroic film array 113 includes two or more wavelength dichroic films, the wavelength dichroic films are parallel to each other and form an acute angle with the first lower surface 112, the wavelength dichroic films are used for reflecting light in at least three bands of visible light, and the other bands are transmitted, where the at least three bands are bands used for projection imaging, for example, the wavelength reflective film is used for reflecting light in one band of a red light spectrum, one band of a green light spectrum, and one band of a blue light spectrum, and transmitting light in the other ranges of the spectrum. In some embodiments, referring to fig. 3, two ends of the wavelength-splitting film are respectively connected to the first upper surface 111 and the first lower surface 112. In other embodiments, the two ends of the wavelength splitting film may not be connected to the first upper surface 111 and the first lower surface 112. One possible implementation of the upper waveguide 110 is: the upper-layer waveguide structure internally containing the laminated wavelength light splitting film is formed by precisely grinding and polishing a plurality of optical glass or resin optical parts (such as commercial optical flat sheets, window sheets and the like) with certain thickness (such as 0.5-5 mm, and the thicknesses of different layers can be equal or unequal), plating the wavelength light splitting film (such as a metal film, a dielectric film or a grating structure), bonding by optical glue or directly gluing, cutting according to a certain angle (the included angle is 10-45 degrees), and precisely grinding and polishing the cut surface (the parallelism of the upper and lower planes is less than 1 angle). It should be understood that fig. 3 shows a segment of the waveguide structure, and the number of the wavelength splitting films in the second dichroic film array 113 in the upper waveguide 110 is not limited to 2 shown in fig. 3, and may be more, for example, the number of the wavelength splitting films shown in fig. 4 is 4.

The lower layer waveguide 120 includes a second upper surface 121 and a second lower surface 122 that are parallel. One possible implementation of the lower layer waveguide 120 is: the waveguide is formed by optical components (such as commercial optical flat sheets, window sheets and the like) made of optical glass or resin materials with certain thickness (such as 0.5-20 mm) and subjected to precision grinding and polishing (the parallelism of an upper plane and a lower plane is less than 1 angle), the material of the lower layer waveguide 120 can be the same as or different from that of the upper layer waveguide 110, and the refractive index of the lower layer waveguide 120 can be the same as or similar to that of the upper layer waveguide 110.

The first light splitting layer 130 may be a light splitting film or a grating array. The light splitting film included in the first light splitting layer 130 may be a light intensity splitting film or a polarization splitting film, and the following description of the present application takes the light intensity splitting film as an example. When the first light splitting layer 130 is a light intensity splitting film, there may be a plurality of implementation manners, for example, the first light splitting layer 130 is a light intensity splitting film, or the first light splitting layer 130 is formed by a plurality of light intensity splitting films, as shown in fig. 5a, the plurality of light intensity splitting films may be spliced together, as shown in fig. 5b, the plurality of light intensity splitting films may not be spliced together, and a distance is provided between adjacent light intensity splitting films. The following description will be given by taking the first light splitting layer as a light splitting film as an example.

The first light splitting layer 130 is disposed between the first lower surface 112 and the second upper surface 121, and both surfaces of the first light splitting layer 130 are in contact with the first lower surface 112 and the second upper surface 121, respectively. The first light splitting layer 130 may be adhered to the first lower surface 112 or the second upper surface 121 by an optical glue, or the first lower surface 112, the first light splitting layer 130, and the second upper surface 121 may be pressed together by a physical pressing method, for example, the upper waveguide 110, the first light splitting layer 130, and the lower waveguide 120 may be fixed together by a fixing member (e.g., a clamp).

Referring to fig. 6, the projected light may be coupled into the lower waveguide 120 from the side end of the lower waveguide 120, wherein after the light ray a1 enters the first light splitting layer 130, a portion of the light is transmitted to the upper waveguide 110 along the light path b1, and is reflected back to the lower waveguide 120 along the light path c1 after entering the second light splitting film array 113 of the upper waveguide 110, and exits from the second lower surface 122 of the lower waveguide 120. Another part d1 of the projection light a1 is reflected by the first light splitting layer 130 to the second lower surface 122 of the lower waveguide 120 and is reflected back to the first light splitting layer 130 along e1 by total reflection, after the e1 enters the first light splitting layer 130, the separation continues, a part of the light exits from the second lower surface 122 of the lower waveguide 120 along the optical path f1-g1, and another part of the light is reflected by the first light splitting layer 130 along the optical path h1 and continues to propagate in the lower waveguide 120. Similarly, after the projection light a2 enters the lower layer waveguide, the projection light a2 is split multiple times in the first light splitting layer 130, and can respectively exit from the second lower surface 122 of the lower layer waveguide 120 along the light paths a2-b2-c2, a2-d2-e2-f2-g2, and a2-d2-e2-h2-i2-j2-k 2. In addition, light rays (e.g., d1, d2, g1, g2, k2, etc.) exiting from the second lower surface 122 of the lower waveguide 120 may be refracted due to the difference in refractive index between the lower waveguide 120 and air. In order to reflect the light entering the upper waveguide 110 by the second dichroic film array 113, the wavelength range of the projection light is required to be within the wavelength range of the reflected light of the wavelength-splitting film of the second dichroic film array 113, or the wavelength range of the reflected light of the wavelength-splitting film of the second dichroic film array 113 is required to cover the wavelength range of the projection light. In addition, in order to realize that the reflected light formed after the projection light is incident on the first light splitting layer 130 in the lower waveguide can be totally reflected on the second lower surface 122, the incident angle of the projection light may be larger than the critical angle at which the total reflection occurs on the second lower surface 122.

In the optical waveguide structure 100, the first light splitting layer 130 is used to split the projection light incident from the lower waveguide 120, a part of the split projection light enters the upper waveguide 110, is reflected back to the lower waveguide 120 through the second light splitting film array 113 and exits from the second lower surface 122 of the lower waveguide 120, another part of the projection light split by the first light splitting layer 130 is reflected back to the second lower surface 122 of the lower waveguide 120 and is reflected back to the first light splitting layer 130 through the second lower surface 122, and the first light splitting layer 130 continues to split the light. When the projection light propagates through the optical waveguide structure 100, the stray light is less. Moreover, the first light splitting layer 130 only needs to reflect a part of the incident light and transmit a part of the incident light, so that the process difficulty is low, and the cost is low; furthermore, if the optical adhesive is used to bond the first light splitting layer 130, the optical adhesive to which the first light splitting layer 130 is bonded is not required to have a very high refractive index because the characteristics of the first light splitting layer 130 are easily implemented, and the cost of the optical adhesive is low.

As an alternative design, first light splitting layer 130 can split incident angles from 0 to θ₁A 90% to 99% partial transmission, a 10% to 1% partial reflection of light rays in the range, and an angle of incidence at θ₁5% to 20% of the light in the range to 90 ° is transmitted, 95% to 80% is partially reflected, θ₁Greater than 0 ° and less than 90 °. The implementation of the above angle selection characteristic can refer to various existing technical means, and the embodiments of the present application are not described in detail.

In the embodiment of the application, theta can be expressed₁Is set to be greater than 45 deg., and the projected light is projected into the lower waveguide 120 at a larger angle (greater than theta)₁) After entering the first light splitting layer 130 at the incident angle, a small portion of the incident light enters the upper waveguide 110 through the first light splitting layer 130, is reflected by the second light splitting film array 113, and then enters the lower waveguide at a small angle (smaller than θ)₁) The incident second dichroic film array 113, then, most (90% to 99%) of the light enters the lower waveguide 120 through the first dichroic film array 130 and exits from the second lower surface 122, and since most of the projection light reflected by the second dichroic film array 113 can pass through the first dichroic film array 130 and exit from the second lower surface, the light intensity loss can be reduced, the brightness of the image can be ensured, the stray light formed by the reflection of the projection light reflected by the second dichroic film array by the first dichroic film array can be suppressed, and the energy of the stray light can be controlled at an extremely low level. In addition, since the first light splitting layer 130 can reflect most of the projection light incident from the lower waveguide 120, the reflected projection light is continuously reflected back to the first light splitting layer 130 to be continuously split, so that the projection light can be emitted from the second lower surface 122 of the lower waveguide 120 in a wider range, and the display effect of the light emitted from the second lower surface 122 of the lower waveguide 120 is improved.

Further, the above-described angle selection characteristic of the first light splitting layer can also significantly improve the field of view (FOV) of the optical waveguide, and referring to fig. 6, the FOV is one of the key indicators of the AR optical waveguide, and a larger FOV can be closer to the observation habit of the human eye, thereby improving the immersion feeling. The following description will be made with reference to tables 1 and 2. Table 1 shows FOV related parameters of the conventional waveguide structure of fig. 1.

TABLE 1

As shown in table 1, in the conventional structure shown in fig. 1, when the FOV is 50 ° and the refractive index of the substrate of the waveguide is 1.72, the half field angle in the substrate is 14.22 °. The maximum and minimum values of the incidence angle e of the high-angle light on the light separation interface (i.e. the light splitting film array in fig. 1) satisfy: e.g. of the type_min≥h+t＝55.55°；e_max＝e_min+2·θ。

E.g. e_min55.55 deg. then e_maxAt 84 deg.. In order to transmit most of the energy of the large-angle light from the light separation interface and reflect a very small amount (1% -3%) of the energy to form stray light, the light separation interface film is required to be on e_min55.55 ° to e_maxHigh transmission (97-99%) was maintained over a range of 84 °. In a conventional waveguide, the angle e is such that when the FOV is further increased_maxWill also increase further. When e is_maxWhen the angle is more than 85 degrees, the coating film with the transmittance higher than 97-99% in the visible light wavelength range (400-700 nm) is difficult to meet by combining the existing coating film processing technology, the stray light intensity is rapidly increased along with the increase of the reflectivity, a strong ghost image is formed, and the film viewing quality under a large FOV is directly deteriorated. Therefore, since the light separation interface and the light reflection interface are the same interface and are not parallel to the upper and lower surfaces of the waveguide, the maximum and minimum angles of the large-angle light are respectively limited by the total reflection condition and the coating processing capability, and the theoretical upper limit of the FOV angle of the conventional waveguide shown in fig. 1 is about 50 degrees, which is difficult to be expanded continuously.

Table 2 shows FOV-related parameters of one possible implementation of the waveguide structure of fig. 3.

TABLE 2

In the double-layered optical waveguide structure 100 of the present application, the first light splitting layer 130 as a light splitting interface is parallel to the upper and lower surfaces of the optical waveguide structure 100 (i.e., the first upper surface 111 of the upper waveguide 110 and the second lower surface 122 of the lower waveguide 120), so that the included angle t is 0, and the first light splitting layer 130 is separated from the second light splitting film array 113 as a light reflecting interface. Therefore, the maximum and minimum limits of the incident angle of the light on the first light splitting layer 130 are: e.g. of the type_min≥h＝35.55；e_max＝e_min+2·θ。

When the FOV is 80 °, the upper waveguide 110 and the lower waveguide 120 use a substrate having the same refractive index of 1.72, and the half field angle in the substrate is θ₂21.94. Get e_minIf 35.55 is 38.06 deg., then e_max81.94. After the light is totally reflected at the second lower surface 122 of the lower waveguide 120 and enters the first light splitting layer 130, a small part of the light (10% -20%) is transmitted into the upper waveguide 110, and a large part of the light is reflected back to the lower waveguide 120 for continuous transmission. By designing the angle between the second dichroic film array 113 and the first lower surface 112 of the upper waveguide 110, it can be ensured that the incident angle of the light reflected from the upper waveguide 110 to the lower waveguide 120 at the first dichroic layer 130 is less than 22 °. The characteristic of high realizability, for example, the first light splitting layer 130 is a partial reflecting film, which is easily realized under the existing process conditions, can ensure that stray light in the full FOV is less than 1% when the transmittance of incident light in a small angle (0 ° -22 °) is higher than 99%. Therefore, using the same refractive index substrate, the double-layer optical waveguide structure 100 provided by the present application can extend the FOV from 50 ° to 80 ° with reduced ghost-image light energy, thereby improving the user's appearanceAnd (5) shadow experience.

Referring to fig. 7a, the reflection spectrum range of the second dichroic film array can only cover the wavelength range of the projection light, and the projection light includes three or more reference light rays, and the reference light rays with the same intensity are overlapped together to form white light, so that the ambient light enters the upper waveguide 110 through the first upper surface 111, and after being incident on the second dichroic film array 113, only a small portion of light rays (light rays with wavelengths overlapping with the wavelength range of the projection light) are reflected, and most of the rest of light rays pass through the second dichroic film array 113, and since the effect of overlapping the reflected light rays is white light, the imaging chromatic aberration of the light rays passing through the second dichroic film array 113 can be ignored. The light transmitted through the second dichroic film array 113 enters the first light splitting layer 130, and due to the small incident angle (smaller than θ 1), most of the ambient light enters the lower waveguide 120 through the first light splitting layer 130 and exits from the second lower surface 122.

In the above implementation manner, the ambient light may exit from the second lower surface 122 of the lower waveguide 120 through the optical waveguide structure 100 together with the projection light to form a real world image (natural light) and a virtual world image (projection light) to be fused, so as to implement the function of augmented reality.

Optionally, the reflection spectrum range of the second dichroic film array is a set of a plurality of narrow bands. Taking a Red Green Blue (RGB) mode as an example, the spectral range of the projection light can be controlled in a narrow range, that is, the wavelength of the red light in the projection light occupies a narrow range in the whole red light spectrum, the wavelength of the green light in the projection light occupies a narrow range in the whole green light spectrum, the wavelength of the blue light in the projection light occupies a narrow range in the whole blue light spectrum, correspondingly, the wavelength of the red light reflected by the wavelength splitting film in the second dichroic film array occupies a narrow range in the whole red light spectrum, the wavelength of the green light reflected occupies a narrow range in the whole green light spectrum, and the wavelength of the blue light reflected occupies a narrow range in the whole blue light spectrum. Therefore, only a part of the red, blue and green light in the ambient light is reflected by the second dichroic film array 113, and the deviation of the color and intensity of the light passing through the second dichroic film array 113 is small or even negligible, thereby improving the display effect of the optical waveguide structure 100 when used for AR imaging.

Alternatively, the second dichroic film array 113 may be replaced with a reflective film. Referring to fig. 7b to 7d, in this implementation, ambient light may also be incident from the first upper surface 111 and exit from the second lower surface 122. As in fig. 7b, the ambient light may not be incident on the reflective film, but may be directly incident on the first lower surface 112 of the upper waveguide 110, transmitted to the lower waveguide 120, and transmitted out of the second lower surface 122 of the lower waveguide 120. As shown in fig. 7c and 7d, although the ambient light enters the reflective film, the ambient light may finally enter another reflective film after being reflected by the reflective film, and may enter the first lower surface 112 of the upper waveguide 110 after being reflected by the reflective film, and further may be transmitted to the lower waveguide 120, and may be transmitted from the second lower surface 122 of the lower waveguide 120.

In the above implementation, the wavelength division film in the upper waveguide 110 is replaced by the reflective film, so that the cost is further reduced, and the ambient light can be incident from the first upper surface 111 and emitted from the second lower surface 122, thereby implementing the function of augmented reality AR.

As an alternative design, the transmittance ratio (also referred to as transmittance) of the first light splitting layer 130 to the incident light may be non-uniform, and may vary from small to large along the lateral propagation direction of the projection light in the lower waveguide 120, and referring to fig. 6, the lateral propagation direction is a direction in which the left end of the lower waveguide (the side end where the projection light enters the lower waveguide) points to the right end of the lower waveguide. The implementation manner of the light transmission ratio change may be as follows:

in the mode 1, the first light splitting layer is a light intensity light splitting film, the splitting ratio of the light intensity light splitting film changes from small to large along the first direction, and the splitting ratio refers to the ratio of the transmittance and the reflectance of the light splitting film to incident light. In this embodiment, the first side end is a side end of the lower waveguide designed to receive the projection light, such as a left side end of the lower waveguide 120 in fig. 6, and the second side end is a side end opposite to the first side end, such as a right side end of the lower waveguide in fig. 6. It should be understood that in the embodiments of the present application, the splitting ratio of the splitting film can be varied in various ways, for example, the thickness of the splitting film varies from large to small along the first direction, or the refractive index of the splitting film varies along the first direction, and various prior art methods can be referred to for other ways of varying the splitting ratio of the light splitting film.

In the mode 2, the first light splitting layer includes at least two light intensity splitting films, and the splitting ratio of the light intensity splitting film close to the first side end of the lower waveguide between the two adjacent light intensity splitting films is not greater than the splitting ratio of the light intensity splitting film close to the second side end of the lower waveguide. Taking fig. 5a or 5b as an example, the splitting ratio of the wavelength splitting film positioned on the right of the two adjacent wavelength splitting films is not smaller than the splitting ratio of the wavelength splitting film positioned on the left. In one possible implementation, the splitting ratio of each wavelength splitting film may be a fixed value, wherein the splitting ratio of the wavelength splitting film far away from the first side end of the lower waveguide is larger; in another possible implementation, the splitting ratio of the partial or full wavelength splitting film itself varies from small to large along the first direction.

In the mode 3, the first light splitting layer 130 includes at least two light intensity splitting films, and the separation distance between two adjacent light intensity splitting films changes from large to small along the first direction. As shown in fig. 5b, the distance between the left light-splitting films is large, and the distance between the right light-splitting films is small, so that the duty ratio of the light-splitting films changes from small to large along the first direction.

In the mode 4, the first light splitting layer is a grating array, and the energy proportion of 0-level reflected light of the grating array changes from large to small along the first direction, and/or the diffraction efficiency of the effective diffraction order of the grating array changes from small to large along the first direction. Various prior arts can be referred to for the implementation of the energy ratio change of the 0 th order reflected light of the grating array and the diffraction efficiency change of the effective diffraction order.

The advantage of the small to large variation of the transmission of the first light-splitting layer along the first direction is described below. Suppose that the first light splitting layer 130 is paired with 0-theta₁Of light incident at a range of angles of incidenceThe transmittance is uniform and is 10 percent, namely the light ray is in a range of 0 to theta₁Upon incidence of the first light splitting layer 130 at a range of incidence angles, 10% of the energy is transmitted and 90% of the energy is reflected. Taking the light ray a2 shown in fig. 6 as an example, assuming that the light energy is 100 units, after entering the first light splitting layer 130, 10 units of energy are emitted through the light path b2-c2, 100% 90% 10% 9 units of energy are emitted through the light path d2-e2-f2-g2, 100% 90% 10% 8.1 units of energy are emitted through the light path d2-e2-h2-i2-j2-k2, and so on. It can be seen that a light ray a2 incident on the lower layer waveguide is split into a plurality of light rays exiting from different positions on the second lower surface 122 of the lower layer waveguide 120, and the energy of the exiting light rays at different positions is different, which affects the imaging effect of the exiting light rays.

With any of the above-described embodiments 1 to 4, the pair of first light-splitting layers 130 is formed to have a length of 0 to θ₁The transmittance of light incident at an incident angle within the range changes from small to large along the lateral propagation direction of the projection light in the lower waveguide, so that the energy of light (such as light c1 and c2 in fig. 6) emitted from the position of the second lower surface 122 close to the first side end can be reduced and prevented from being too strong, and the energy of light (such as light g1, g2 and k2 in fig. 6) emitted from the position of the second lower surface 122 far from the first side end can be increased and prevented from being too weak, so that the energy of light emitted from different positions of the lower waveguide 120 is more balanced, and the imaging effect of the emitted light is improved.

As an alternative design, the first upper surface 111 of the upper waveguide 110 and/or the second lower surface 122 of the lower waveguide 120 are further provided with an antireflection film to enhance the transmittance of the first upper surface 111 and/or the second lower surface 122.

Fig. 8 is a schematic diagram of a display device provided in an embodiment of the present application, where the display device includes: the frame 200, the projection module 300, and the optical waveguide structure 100, wherein the projection module 300 and the optical waveguide structure 100 are fixed on the frame 200, the specific form of the frame 200 is not limited, for example, the form of the frame 200 may be smart glasses or a head-mounted display device. The projection module 300 is used to generate projection light and to inject the projection light into the lower layer waveguide 120.

As an alternative design, referring to fig. 9, the display device further includes: the first light uniformizing layer 400 may be a first light uniformizing film disposed on the second lower surface 122, or may be a first light uniformizing film disposed below the second lower surface. The transmittance of the first light homogenizing layer changes from small to large along a first direction, where the first side end of the lower waveguide 120 points to the second side end of the lower waveguide.

In this optional design, after the projection light emitted from the first lower surface passes through the first light uniformizing layer, the light intensity distribution changes, and the light intensity of the light near the first side end of the lower waveguide 120 becomes weaker than the light intensity of the light far from the first side end of the lower waveguide 120, thereby playing the same role as the aforementioned mode 1-mode 4, and making the light intensity of the projection light entering the human eye more uniform.

It should be understood that, when the first light uniformizing layer 400 is provided, the transmittance of the first light splitting layer 130 may be kept unchanged, or the transmittance of the first light splitting layer 130 may be changed from small to large along the first direction in the manners described in the foregoing manners (1) to (4), and in the latter case, the balance of the energy of the light emitted from different positions of the lower waveguide 120 can be further enhanced, and the imaging effect of the emitted light can be improved.

As an alternative design, with continued reference to fig. 9, in providing the first levelling layer 400, the display device further comprises: the second light uniformizing layer 500 may be a second light uniformizing film disposed on the first upper surface 111, or may be a first light uniformizing sheet disposed above the first upper surface 111. The transmittance of the second light uniformizing layer 500 varies from large to small along the first direction.

Since the transmittance of the first light uniformizing layer 400 near the first side end is small, the ambient light energy emitted from the first light uniformizing layer 400 near the first side end is small, and thus the ambient light incident to the human eyes of the user is unbalanced by the first light uniformizing layer 400. The second light uniformizing layer 500 has an effect of reversely compensating the influence of the first light uniformizing layer 400 on the balance of the ambient light, as shown in fig. 9, the transmittance of the left side of the second light uniformizing layer 500 is high, the transmittance of the right side of the second light uniformizing layer is low, and the ambient light energy incident to the left side of the upper waveguide 110 is stronger than the ambient light incident to the right side of the upper waveguide 110, and the energy of the ambient light emitted from the left side of the lower waveguide 120 to the first light uniformizing layer 400 is stronger than the energy of the ambient light emitted from the right side of the lower waveguide to the first light uniformizing layer 400, and after the light uniformizing processing of the first light uniformizing layer 400, the energy of the ambient light transmitted from the first light uniformizing layer 400 tends to be balanced, so that the intensity of the ambient light entering the eyes of the user can be more balanced, and the imaging.

As an alternative design, referring to fig. 10, the display device further includes an out-coupling waveguide 600, and the out-coupling waveguide 600 is used for receiving light (projection light and natural light) emitted from the second lower surface 122 of the lower waveguide 120, propagating inside the out-coupling waveguide 600 and emitting for the user to see. The coupling-out waveguide 600 may be made of optical glass, optical resin, or the like. The out-coupling waveguide 600 can change the optical path, facilitating the design of products such as AR glasses. In addition, the coupling-out waveguide 600 is a single-layer waveguide, and the thickness of the coupling-out waveguide 600 is smaller than that of a double-layer waveguide structure formed by the upper-layer waveguide 110 and the lower-layer waveguide 120, and because the light is emitted to the user by the single-layer coupling-out waveguide 600, compared with the case that the light is directly emitted to the user by the lower-layer waveguide 120, the thickness of the position where the user views the image can be significantly reduced. Furthermore, by changing the optical path of the light emitted from the lower waveguide 120 through the coupling-out waveguide 600, the ambient light incident from the upper waveguide 110 can be viewed through the coupling-out waveguide 600, and thus periscopic augmented reality is realized.

Fig. 11a to 11d show a number of possible propagation ways of light in the outcoupling waveguide 600. The mode of coupling light emitted from the lower waveguide 120 into the out-coupling waveguide 600 includes:

in-coupling mode 1, referring to fig. 11a, the out-coupling waveguide 600 includes an in-coupling grating 610 for receiving the outgoing light from the lower waveguide and changing the direction of the received light to couple the received light into the out-coupling waveguide 600.

In the coupling-in mode 2, referring to fig. 11b to 11d, the coupling-out waveguide 600 includes a first surface 630 and a second surface 640, wherein the first surface 630 is used for receiving the outgoing light of the lower waveguide and transmitting the received light to the second surface 640, and the second surface 640 is used for totally reflecting the light transmitted through the first surface 630. The first surface 630 is located on the surface of the coupling-out waveguide, the second surface 640 may be located on the surface of the coupling-out waveguide 600 (as shown in fig. 11c and 11 d), or may be located inside the coupling-out waveguide 600 (as shown in fig. 11 b), and the first surface 630 and the second surface 640 are not parallel. Optionally, when the second surface is located on the surface of the outcoupling waveguide, one of the first surface and the second surface is a wedge surface or is provided with an optical structure including a wedge surface.

The emission method of light propagating through the coupling waveguide 600 includes:

in the emission mode 1, referring to fig. 11a, the outcoupling waveguide 600 includes an outcoupling grating 620 provided on a waveguide wall, and is configured to emit a part of light propagating in the outcoupling waveguide 600 and entering the outcoupling grating 620 from the waveguide wall and reflect another part.

In the emission method 2, referring to fig. 11b to 11d, the coupling waveguide 600 includes a third light splitting film array 650 disposed inside the coupling waveguide 600, the third light splitting film array 650 reflects a part of light incident on the third light splitting film array 650 and propagating through the coupling waveguide 600 to the coupling waveguide wall for emission, and transmits the other part of the light, and the light splitting film in the third light splitting film array 650 may be a light intensity splitting film or a polarization splitting film.

Taking fig. 11a as an example, the light emitted from the lower waveguide 120 enters the coupling-in grating 610 of the coupling-out waveguide 600, changes the direction of the side wall of the coupling-out waveguide, and is reflected to the coupling-out grating 620 disposed on the other side wall of the coupling-out waveguide through total reflection, a part of the light exits from the coupling-out grating 620, and the other part of the light is reflected back to the inside of the coupling-out waveguide 600 to continue propagating, and the light that continues propagating continues to be separated after entering the coupling-out grating again, a part of the light exits from the coupling-out grating 620, and the other part of the light continues to propagate in the coupling-out waveguide.

Optionally, the energy ratio of the 0 th order reflected light of the coupling-out grating 620 varies from large to small along the propagation direction of the light in the coupling-out waveguide 600, and/or the diffraction efficiency of the effective diffraction order of the coupling-out grating 620 varies from small to large along the propagation direction of the light in the coupling-out waveguide 600. The coupling-out grating 620 can balance the energy of the light emitted from the grating, thereby improving the viewing experience of the user.

Taking fig. 11b to 11d as an example, the light emitted from the lower waveguide 120 is transmitted from the first surface 630 to the second surface 640 of the coupling-out waveguide 600, and is incident to the third optical splitter film array 650 via total reflection, a part of the light is reflected to be incident on the sidewall of the coupling-out waveguide at a small angle and is transmitted from the sidewall, another part of the light is transmitted via the third optical splitter film array 650 and continues to propagate in the coupling-out waveguide, and continues to be separated after being incident on the third optical splitter film array 650 again, a part of the light is reflected by the third optical splitter film array 650 and is projected from the sidewall of the coupling-out waveguide, and another part of the light is transmitted via the third optical splitter film array 650 and continues to propagate in the coupling-out waveguide.

Optionally, of the plurality of splitting films of the third splitting film array 650, the transmittance of the splitting film near the position (or the first side end) where the light is incident and outcoupled from the lower waveguide 120 to the waveguide 600 is smaller, and the transmittance of the splitting film far from the position (or the first side end) where the light is incident and outcoupled from the lower waveguide 120 to the waveguide 600 is larger, for example, in two adjacent splitting films of the third splitting film array 650 in fig. 11b, the transmittance of the splitting film on the left side is not greater than that of the splitting film on the right side. The third light splitting film array 650 may balance the energy of the light emitted from the coupling waveguide 600, thereby improving the viewing experience of the user.

It should be understood that the outcoupling waveguide 600 may have other implementations besides the implementations shown in fig. 11a to 11d, for example, the outcoupling waveguide may implement the incoupling of the outgoing light from the lower layer waveguide 120 in the incoupling mode 1 and the outgoing light based on the outcoupling mode 2. For example, the coupling-out waveguide can realize the coupling-in of the light emitted from the lower waveguide 120 by the coupling-in method 2 and the emission of the light based on the coupling-out method 1.

The multiple coupling-out waveguide structures are simple in implementation mode and low in cost, light can be emitted from a wide area, the area of the light emitting area is increased, the imaging effect is improved, moreover, the thickness of the position where a user views an image can be effectively reduced through the coupling-out waveguide structures, the structure shown in fig. 11a is taken as an example, the thickness of the position where the user views the image is the thickness of the coupling-out waveguide, and compared with a double-layer waveguide structure formed by the upper-layer waveguide 110 and the lower-layer waveguide 120, the thickness is remarkably reduced.

It should be understood that the display devices shown in fig. 10 to 11d may also include the first light-diffusing layer 400 and/or the second light-diffusing layer 500, etc., which are not all shown in the drawings.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An optical waveguide structure comprising an upper waveguide, a lower waveguide, and a first light splitting layer between the upper waveguide and the lower waveguide;

the upper waveguide comprises a first upper surface, a first lower surface and a second light splitting film array located between the first upper surface and the first lower surface, the first upper surface is parallel to the first lower surface, the second light splitting film array comprises at least two wavelength light splitting films, the at least two wavelength light splitting films are parallel to each other and form an acute included angle with the first lower surface, the at least two wavelength light splitting films are used for reflecting light in at least three bands of visible light, and the rest bands are transmitted, wherein the at least three bands are bands used for projection imaging;

the lower layer waveguide comprises a second upper surface and a second lower surface, the second upper surface is parallel to the second lower surface, and the lower layer waveguide is used for receiving light rays in the at least three wave bands;

two surfaces of the first light splitting layer are respectively contacted with the first lower surface and the second upper surface, and the first light splitting layer is used for reflecting one part of incident light and transmitting the other part of the incident light.

2. The optical waveguide structure of claim 1, wherein the first light splitting layer comprises a light splitting film or a grating array for: the incident angle is from 0 DEG to theta₁A 90% to 99% partial transmission, a 10% to 1% partial reflection of light rays in the range, and an angle of incidence at θ₁5% to 20% of the light in the range to 90 ° is transmitted, 95% to 80% is partially reflected, θ₁Greater than 0 ° and less than 90 °.

3. The optical waveguide structure of claim 1 or 2, wherein the refractive index of the upper layer waveguide is equal to the refractive index of the lower layer waveguide.

4. The optical waveguide structure of claim 1 or 2, wherein:

the first light splitting layer is a light splitting film, and the light splitting ratio of the light splitting film changes from small to large along the first direction; or

The first light splitting layer comprises at least two light splitting films, and the light splitting ratio of the light splitting film close to the first side end of the lower waveguide of the two adjacent light splitting films is not greater than the light splitting ratio of the light splitting film close to the second side end of the lower waveguide; or

The first light splitting layer comprises at least two light splitting films, and the spacing distance between two adjacent light splitting films changes from large to small along the first direction; or

The first light splitting layer is a grating array, and the energy proportion of 0-order reflected light of the grating array changes from large to small along the first direction, and/or the diffraction efficiency of the effective diffraction order of the grating array changes from small to large along the first direction;

wherein the first direction is a direction in which the first side end points to the second side end.

5. A display device, comprising:

a frame;

the optical waveguide structure of any one of claims 1 to 4, secured to the frame; and

and the projection module is fixed on the frame and used for inputting the light rays in the at least three wave bands to the lower layer waveguide.

6. The display device according to claim 5, further comprising:

the first light homogenizing layer comprises a first light homogenizing film arranged on the second lower surface or a first light homogenizing sheet arranged below the lower layer waveguide and fixed on the frame, the transmittance of the first light homogenizing layer changes from small to large along a first direction, and the first direction is a direction in which the first side end of the lower layer waveguide points to the second side end of the lower layer waveguide.

7. The display device according to claim 6, further comprising:

and the second light homogenizing layer comprises a second light homogenizing film arranged on the first upper surface or a second light homogenizing sheet arranged above the upper waveguide and fixed on the frame, and the transmittance of the second light homogenizing layer changes from large to small along the first direction.

8. The display device according to any one of claims 5 to 7, further comprising:

and the coupling-out waveguide is positioned below the second lower surface, is fixed on the frame and is used for receiving, transmitting and outputting the light rays emitted from the second lower surface.

9. The display device according to claim 8, wherein the outcoupling waveguide comprises an incoupling grating disposed on a third upper surface of the outcoupling waveguide opposite to the second lower surface for coupling light received from the second lower surface into the outcoupling waveguide.

10. The display device according to claim 8, wherein the outcoupling waveguide comprises a first surface and a second surface, wherein the first surface is used for receiving the light emitted from the second lower surface and transmitting the received light to the second surface, the second surface is used for totally reflecting the light transmitted through the first surface, the first surface is located on the surface of the outcoupling waveguide, the second surface is located on the surface or inside the outcoupling waveguide, and the first surface is not parallel to the second surface.

11. A display device as claimed in claim 10, characterized in that one of the first and second faces is a wedge face or is provided with an optical structure comprising a wedge face, when the second face is located at a surface of the outcoupling waveguide.

12. A display device as claimed in claim 8, characterized in that the outcoupling waveguide comprises an outcoupling grating arranged at a waveguide wall of the outcoupling waveguide for reflecting a part of the light propagating in the outcoupling waveguide and entering the outcoupling grating out of the waveguide wall and reflecting another part.

13. The display device according to claim 8, wherein the outcoupling waveguide comprises a third array of light-dividing films disposed inside the outcoupling waveguide, and the third array of light-dividing films is configured to reflect a part of light propagating in the outcoupling waveguide and incident on the third array of light-dividing films to the waveguide wall of the outcoupling waveguide to exit, and transmit the rest of light.