Volume holographic grating waveguide, manufacturing method thereof and near-eye display equipment

Abstract

The invention provides a volume holographic grating waveguide, a manufacturing method thereof and near-to-eye display equipment. The problem that coupled light intensity is not uniform due to transmission light intensity attenuation when light is transmitted in a waveguide substrate can be solved. The volume holographic grating waveguide includes: a waveguide substrate having an in-coupling region and an out-coupling region for transmitting image light from the in-coupling region to the out-coupling region; the coupling-in element is correspondingly arranged in the coupling-in area of the waveguide substrate, and is used for coupling the image light into the waveguide substrate from the coupling-in area; and a volume hologram out-coupling grating, which is correspondingly disposed in the out-coupling area of the waveguide substrate, and is used for coupling the image light out of the waveguide substrate from the out-coupling area. Wherein a thickness of the volume holographic decoupling grating increases along an image light transmission direction at the decoupling region.

Description

Technical Field

[0001] The present invention relates to the field of augmented reality technology, and in particular to a volume holographic grating waveguide, a manufacturing method thereof, and a near-eye display device. Background Art

[0002] In recent years, although the technology of diffractive optical waveguides in augmented reality (AR) has become increasingly mature, the efficiency and uniformity of diffractive optical waveguides are still hot topics in waveguide design.

[0003] At present, as an excellent optical coupling device, volume holographic grating has the characteristics of high efficiency, wide response bandwidth and reusability, and has a simple process, low cost, high production efficiency, and great market potential. In addition, since most of the external ambient light can directly pass through the volume holographic grating, the volume holographic grating has good transparency, which is an obvious advantage in the field of augmented reality technology.

[0004] However, since the volume holographic grating has good incident light wavelength selectivity and incident angle selectivity, its diffraction efficiency for incident light whose angle and wavelength meet the Bragg conditions is very high (theoretical efficiency is close to 100%). Therefore, along the light transmission direction in the waveguide, the light intensity transmitted in the existing volume holographic grating waveguide will decay rapidly as the light is coupled out, resulting in large differences in the intensity of light coupled out from different areas of the volume holographic grating, resulting in poor uniformity of display brightness of the existing volume holographic grating waveguide, which seriously affects the display effect of near-eye display devices. Summary of the invention

[0005] One advantage of the present invention is that it provides a volume holographic grating waveguide and a manufacturing method thereof and a near-eye display device, which can solve the problem of uneven outcoupled light intensity caused by attenuation of transmission light intensity when light is transmitted in a waveguide substrate.

[0006] Another advantage of the present invention is to provide a volume holographic grating waveguide and a manufacturing method thereof and a near-eye display device. In one embodiment of the present invention, the volume holographic grating waveguide can enhance the uniformity of display brightness and improve the display effect of the near-eye display device.

[0007] Another advantage of the present invention is that it provides a volume holographic grating waveguide, a manufacturing method thereof, and a near-eye display device. In one embodiment of the present invention, the volume holographic grating waveguide can adjust the diffraction efficiency of different areas on the volume holographic out-coupling grating by changing the grating thickness, so that the volume holographic out-coupling grating can diffract the out-coupled light and emit it into the human eye with uniform light intensity, which helps to improve the overall display uniformity.

[0008] Another advantage of the present invention is to provide a volume holographic grating waveguide, a manufacturing method thereof, and a near-eye display device. In one embodiment of the present invention, the volume holographic grating waveguide can adjust the diffraction efficiency of different areas on the volume holographic turning grating by changing the grating thickness, so that the volume holographic turning grating can diffract the turning light and propagate it to the volume holographic out-coupling grating with uniform light intensity, which helps to improve the overall display uniformity.

[0009] Another advantage of the present invention is to provide a volume holographic grating waveguide, a method for manufacturing the same, and a near-eye display device, wherein in order to achieve the above-mentioned purpose, no expensive materials or complex structures are required in the present invention. Therefore, the present invention successfully and effectively provides a solution, not only providing a simple volume holographic grating waveguide, a method for manufacturing the same, and a near-eye display device, but also increasing the practicality and reliability of the volume holographic grating waveguide, a method for manufacturing the same, and a near-eye display device.

[0010] In order to achieve at least one of the above advantages or other advantages and purposes of the present invention, the present invention provides a volume holographic grating waveguide, comprising:

[0011] A waveguide substrate having an incoupling region and an outcoupling region for transmitting image light from the incoupling region to the outcoupling region;

[0012] a coupling element, the coupling element being correspondingly disposed in the coupling region of the waveguide substrate, and being used for coupling the image light from the coupling region into the waveguide substrate; and

[0013] A volume holographic out-coupling grating is correspondingly arranged in the out-coupling region of the waveguide substrate, and is used to couple the image light from the out-coupling region out of the waveguide substrate; wherein the thickness of the volume holographic out-coupling grating increases along the image light transmission direction at the out-coupling region.

[0014] According to one embodiment of the present application, the thickness of the volume holographic outcoupling grating gradually increases along the image light transmission direction at the outcoupling region.

[0015] According to one embodiment of the present application, the thickness of the volume holographic outcoupling grating increases stepwise along the image light transmission direction at the outcoupling region.

[0016] According to an embodiment of the present application, the thickness difference between two adjacent step portions in the volume holographic outcoupling grating is between 100 nm and 20 um.

[0017] According to one embodiment of the present application, the number of longitudinal periods in the thickest part of the volume holographic outcoupling grating is less than 10.

[0018] According to one embodiment of the present application, the volume holographic outcoupling grating has a thickness ranging from 100 nm to 100 um.

[0019] According to one embodiment of the present application, the volume holographic outcoupling grating includes an orientation layer and a liquid crystal layer, the orientation layer is located between the liquid crystal layer and the waveguide substrate, and the liquid crystal layer is composed of liquid crystal groups doped with chiral materials to present a three-dimensional rotation structure.

[0020] According to one embodiment of the present application, the waveguide substrate further has a pupil expansion region located in the optical path between the coupling-in region and the coupling-out region; the volume holographic grating waveguide further includes a pupil expansion element, which is correspondingly arranged in the pupil expansion region of the waveguide substrate.

[0021] According to one embodiment of the present application, the pupil expansion element is a volume holographic turning grating; the thickness of the volume holographic turning grating increases gradually or stepwise along the image light transmission direction at the pupil expansion area.

[0022] According to an embodiment of the present application, the coupling element is a volume holographic coupling grating.

[0023] According to another aspect of the present application, the present application further provides a near-eye display device, including:

[0024] Display light machine; and

[0025] Any of the above-mentioned volume holographic grating waveguides, wherein the volume holographic grating waveguide is located at the projection side of the display optical machine.

[0026] According to another aspect of the present application, the present application further provides a method for manufacturing a volume holographic grating waveguide, comprising the steps of:

[0027] Spin coating an alignment layer solution on the outcoupling region of the waveguide substrate to solidify and expose to form an alignment layer of a volume holographic outcoupling grating;

[0028] Spraying a liquid crystal mixture solution on the alignment layer, and curing it by light to form a liquid crystal layer with uneven thickness in the volume holographic outcoupling grating, so that the thickness of the volume holographic outcoupling grating increases along the image light transmission direction at the outcoupling area; and

[0029] The coupling element is arranged in the coupling region of the waveguide substrate.

[0030] According to one embodiment of the present application, the liquid crystal mixture solution is formed by mixing a solvent, a liquid crystal material, a chiral material and a photoinitiator.

[0031] According to one embodiment of the present application, the step of spin coating the alignment layer solution on the outcoupling region of the waveguide substrate to solidify and expose the alignment layer of the volume holographic outcoupling grating comprises the steps of:

[0032] preparing a BY solution as the alignment layer solution;

[0033] Spin coating the alignment layer solution on the outcoupling region;

[0034] baking the alignment layer solution to form an alignment layer semi-finished product fixed to the outcoupling region; and

[0035] After the semi-finished product of the alignment layer is cooled, the semi-finished product of the alignment layer is subjected to polarization holographic exposure to obtain the alignment layer.

[0036] According to one embodiment of the present application, the method for manufacturing the volume holographic grating waveguide further comprises the steps of:

[0037] The pupil expansion element is arranged in the pupil expansion area of ​​the waveguide substrate.

[0038] According to one embodiment of the present application, the step of setting a pupil expansion element in the pupil expansion area of ​​the waveguide substrate comprises the steps of:

[0039] Spin coating an alignment layer solution on the pupil expansion area to cure and expose the alignment layer to form a volume holographic turning grating; and

[0040] A liquid crystal mixed solution is sprayed on the alignment layer and cured by light to form a liquid crystal layer with uneven thickness in the volume holographic turning grating, so that the thickness of the volume holographic turning grating increases gradually or stepwise along the image light transmission method at the pupil expansion area. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is a schematic structural diagram of a near-eye display device according to an embodiment of the present application;

[0042] Figure 2 A schematic structural diagram of a volume holographic grating waveguide in a near-eye display device according to the above embodiment of the present application is shown;

[0043] Figure 3 A first example of a volume holographic grating waveguide according to the above embodiment of the present application is shown;

[0044] Figure 4 A schematic diagram showing the relationship between the diffraction efficiency of a volume holographic grating and the number of longitudinal periods;

[0045] Figure 5 A second example of the volume holographic grating waveguide according to the above embodiment of the present application is shown;

[0046] Figure 6A third example of the volume holographic grating waveguide according to the above embodiment of the present application is shown;

[0047] Figure 7 is a schematic flow chart of a method for manufacturing a volume holographic grating waveguide according to an embodiment of the present application;

[0048] Figure 8 An example of a step of preparing an alignment layer in the method for manufacturing a volume holographic grating waveguide according to the above embodiment of the present application is shown;

[0049] Fig. 9 An example of a volume holographic pupil expansion grating preparation step in the method for manufacturing a volume holographic grating waveguide according to the above embodiment of the present application is shown.

[0050] Explanation of the main component symbols: 1. Volume holographic grating waveguide; 10. Waveguide substrate; 11. Coupling region; 12. Decoupling region; 13. Pupil expansion region; 20. Coupling element; 21. Volume holographic coupling-in grating; 30. Volume holographic decoupling grating; 301. First step portion; 302. Second step portion; 303. Third step portion; 304. Fourth step portion; 31. Orientation layer; 32. Liquid crystal layer; 40. Pupil expansion element; 41. Volume holographic turning grating; 2. Display optical machine.

[0051] The above description of the main component symbols is combined with the accompanying drawings and specific implementation methods to further illustrate the present application in detail. DETAILED DESCRIPTION

[0052] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art can think of other obvious variations. The basic principles of the present invention defined in the following description can be applied to other embodiments, variations, improvements, equivalents, and other technical solutions that do not deviate from the spirit and scope of the present invention.

[0053] Those skilled in the art should understand that, in the disclosure of the present invention, the terms "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the above terms should not be understood as limiting the present invention.

[0054] In the present invention, the term "one" in the claims and the specification should be understood as "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple. Unless it is clearly indicated in the disclosure of the present invention that the number of the element is only one, the term "one" cannot be understood as unique or single, and the term "one" cannot be understood as a limitation on the quantity.

[0055] In the description of the present invention, it should be understood that "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through a medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0056] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0057] Considering that the intensity of light transmitted in the existing volume holographic grating waveguide will decay rapidly along the light transmission direction in the waveguide, the intensity of light coupled out through different areas of the volume holographic grating will vary greatly, resulting in poor uniformity of display brightness of the existing volume holographic grating waveguide, which seriously affects the display effect of the near-eye display device. Therefore, the present application creatively proposes a volume holographic grating waveguide, a manufacturing method thereof, and a near-eye display device, which can solve the problem of uneven out-coupling light intensity caused by the attenuation of the transmission light intensity when the light is transmitted in the waveguide substrate, improve the uniformity of the display brightness, and improve the display effect of the near-eye display device.

[0058] Specifically, refer to the accompanying drawings of the specification of this application. Figure 1According to an embodiment of the present application, a near-eye display device is provided, which may include a volume holographic grating waveguide 1 and a display optical machine 2. The volume holographic grating waveguide 1 is located on the projection side of the display optical machine 2, and is used to transmit the image light projected by the display optical machine 2 to the human eye for near-eye display. It can be understood that the near-eye display device mentioned in the present application can be implemented as AR glasses or AR helmets, but is not limited to it.

[0059] More specifically, if Figures 1 to 6 As shown, the volume holographic grating waveguide 1 may include a waveguide substrate 10, a coupling element 20, and a volume holographic outcoupling grating 30. The waveguide substrate 10 has a coupling region 11 and an outcoupling region 12, which are used to transmit the image light from the coupling region 11 to the outcoupling region 12. The coupling element 20 is correspondingly arranged in the coupling region 11 of the waveguide substrate 10, and is used to couple the image light from the coupling region 11 into the waveguide substrate 10. The volume holographic outcoupling grating 30 is correspondingly arranged in the outcoupling region 12 of the waveguide substrate 10, and is used to couple the image light from the outcoupling region 12 out of the waveguide substrate 10; wherein the thickness of the volume holographic outcoupling grating 30 increases along the image light transmission direction at the outcoupling region 12.

[0060] It is worth noting that, although the image light transmitted through the waveguide substrate 10 will be diffracted through the volume holographic out-coupling grating 30 during the transmission process in the out-coupling region 12 and continuously coupled out of the waveguide substrate 10, so that the light intensity of the image light will be continuously weakened along the image light transmission direction of the out-coupling region 12, the thickness of the volume holographic out-coupling grating 30 of the present application increases along the image light transmission direction at the out-coupling region 12, so that the image light transmitted in the out-coupling region 12 will be diffracted and coupled out through the thinner thickness portion of the volume holographic out-coupling grating 30 when the light intensity is large, and will be diffracted and coupled out through the thicker thickness portion of the volume holographic out-coupling grating 30 when the light intensity is small; at the same time, due to the The outcoupling diffraction efficiency of the volume holographic outcoupling grating 30 will increase with the increase of the grating thickness, that is, the outcoupling diffraction efficiency of the thinner portion of the volume holographic outcoupling grating 30 is less than the outcoupling diffraction efficiency of the thicker portion of the volume holographic outcoupling grating 30. Therefore, the volume holographic outcoupling grating 30 of the present application can compensate for the attenuation of the light intensity of the image light when it is transmitted in the outcoupling area 12 by changing the outcoupling diffraction efficiency, so that the image light intensity coupled through the thinner portion of the volume holographic outcoupling grating 30 can be basically consistent with the image light intensity coupled through the thicker portion of the volume holographic outcoupling grating 30, which helps to improve the uniformity of display brightness and improve the display effect of near-eye display devices.

[0061] For example, in the first example of the present application, Figure 2 and Figure 3As shown in FIG. 1 , the coupling-in region 11 and the coupling-out region 12 in the waveguide substrate 10 are sequentially arranged along the image light transmission direction at the coupling-out region 12, that is, the thickness of the volume holographic coupling-out grating 30 increases from the direction close to the coupling-in region 11 to the direction away from the coupling-in region 11. It can be understood that in this example of the present application, the image light transmission direction at the coupling-out region 12 refers to the direction from the direction close to the coupling-in region 11 to the direction away from the coupling-in region 11, that is, the direction from the coupling-in region 11 to the coupling-out region 12, as shown in FIG. Figure 2 The X direction in .

[0062] Alternatively, if Figure 3 As shown, the thickness of the volume holographic out-coupling grating 30 gradually increases along the image light transmission direction at the out-coupling region 12, that is, the thickness of the volume holographic out-coupling grating 30 gradually increases from close to the coupling region 11 to far away from the coupling region 11, so that the thickness of the portion of the volume holographic out-coupling grating 30 close to the coupling region 11 is smaller than the thickness of the portion of the volume holographic out-coupling grating 30 far away from the coupling region 11.

[0063] Alternatively, if Figure 3 As shown, the volume holographic outcoupling grating 30 of the present application may include an orientation layer 31 and a liquid crystal layer 32, wherein the orientation layer 31 is located between the liquid crystal layer 32 and the waveguide substrate 10, and the liquid crystal layer 32 is composed of liquid crystal molecules doped with chiral materials to present a three-dimensional rotating structure in three-dimensional space. In this way, the thickness of the volume holographic outcoupling grating 30 determines the number n of longitudinal periods of the volume holographic outcoupling grating 30, that is, the number n of longitudinal periods of the volume holographic outcoupling grating 30 refers to the number of periods of the volume holographic outcoupling grating 30 in the grating thickness direction; and since the number of longitudinal periods of the volume holographic grating and the diffraction efficiency show a strong linear relationship within a specific range, the volume holographic grating waveguide 1 of the present application can enhance the uniformity of the waveguide display through the volume holographic outcoupling grating 30 with a variable thickness, so as to improve the display effect of the near-eye display device as a whole.

[0064] Optionally, the number of longitudinal periods n at different locations on the volume holographic outcoupling grating 30 is i It can be equal to the thickness d of the corresponding part of the volume holographic outcoupling grating 30 i The ratio between the twist pitch p of the liquid crystal layer 32, that is, n i =d i / p. It can be understood that the longitudinal period of the volume holographic outcoupling grating 30 of the present application is mainly determined by the characteristics and concentration of the chiral material in the liquid crystal layer 32: the twist pitch p of the liquid crystal layer 32 = (HTP*c) -1 The longitudinal period of the volume holographic outcoupling grating 30 is y=p / 2; wherein p is the distance that the liquid crystal molecules in the liquid crystal layer 32 rotate 360°; HTP is the helical twisting force constant of the liquid crystal material, which is determined by the properties of the liquid crystal material itself; and c is the concentration of liquid crystal molecules in the liquid crystal layer 32.

[0065] It is worth noting that according to Figure 4 From the relationship curve between the diffraction efficiency and the number of longitudinal periods of the volume holographic grating shown in FIG. 1 , it is easy to see that: in the interval where the number of longitudinal periods n is less than 10, the diffraction efficiency of the volume holographic grating and the number of longitudinal periods show a strong linear relationship; while in the interval where the number of longitudinal periods n is greater than 10, the diffraction efficiency of the volume holographic grating approaches 1, and at this time, increasing the number of longitudinal periods (i.e., increasing the thickness of the volume holographic grating) does not increase the diffraction efficiency of the volume holographic grating. Therefore, the number of longitudinal periods of the volume holographic outcoupling grating 30 of the present application needs to be less than 10, that is, the number of longitudinal periods n of the thickest part of the volume holographic outcoupling grating 30 is greater than 10. max Need to be less than 10, that is, n max <10.

[0066] Optionally, the thickness of the volume holographic outcoupling grating 30 can be less than 100um, ensuring that the diffraction efficiency of the volume holographic outcoupling grating 30 increases with the increase of the grating thickness, so as to compensate for the shortcoming of the existing volume holographic grating waveguide that the outcoupling light intensity gradually attenuates along the light transmission direction, thereby improving the uniformity of the overall display of the waveguide.

[0067] Optionally, the thickness of the volume holographic out-coupling grating 30 ranges from 100nm to 100um, that is, the thickness of the smallest thickness portion of the volume holographic out-coupling grating 30 can be equal to 100nm, and the thickness of the largest thickness portion of the volume holographic out-coupling grating 30 can be equal to 100um. For example, in the first example of the present application, the thickness of the edge portion of the volume holographic out-coupling grating 30 close to the coupling-in region 11 can be equal to 100nm, and the thickness of the edge portion of the volume holographic out-coupling grating 30 far from the coupling-in region 11 can be equal to 100um.

[0068] Preferably, the volume holographic outcoupling grating 30 has a thickness ranging from 500 nm to 100 um.

[0069] It is worth noting that in the second example of the present application, Figure 5As shown, the thickness of the volume holographic out-coupling grating 30 increases stepwise along the image light transmission direction at the out-coupling region 12, that is, the thickness of the volume holographic out-coupling grating 30 increases stepwise from the direction close to the coupling-in region 11 to the direction far away from the coupling-in region 11, which can still compensate for the light intensity attenuation of the image light when it is transmitted in the out-coupling region 12 to a certain extent, so that the image light intensity coupled through the smaller thickness portion of the volume holographic out-coupling grating 30 can be basically consistent with the image light intensity coupled through the larger thickness portion of the volume holographic out-coupling grating 30.

[0070] For example, Figure 5 As shown, the volume holographic out-coupling grating 30 includes a first step portion 301, a second step portion 302, a third step portion 303 and a fourth step portion 304 in sequence along the image light transmission direction at the out-coupling region 12, and the thicknesses of the first step portion 301, the second step portion 302, the third step portion 303 and the fourth step portion 304 increase in sequence. It can be understood that in other examples of the present application, the volume holographic out-coupling grating 30 may further include a fifth or more step portions, which will not be described in detail in the present application.

[0071] Optionally, the thickness difference between two adjacent step portions in the volume holographic outcoupling grating 30 may be between 100 nm and 20 um.

[0072] According to the above embodiments of the present application, Figure 3 and Figure 5 As shown, the coupling element 20 mentioned in the present application can be implemented as, but not limited to, a volume holographic coupling grating 21, for diffracting the image light projected via the display light machine 2 to couple into the waveguide substrate 10. It can be understood that in other examples of the present application, the coupling element 20 can also be implemented as other coupling devices such as a coupling prism or an embossed coupling grating, as long as the image light projected via the display light machine 2 can be coupled into the waveguide substrate 10, and this application will not go into details.

[0073] Optionally, the thickness of the volume holographic coupling-in grating 21 may be greater than 100 um, so as to ensure that the volume holographic coupling-in grating 21 has a higher diffraction efficiency, which helps to reduce the light energy coupling loss and improve the light energy utilization efficiency.

[0074] Optionally, the volume holographic coupling-in grating 21 has a uniform thickness, that is, the thickness of each part of the volume holographic coupling-in grating 21 is substantially consistent / the same, so as to reduce the difficulty of preparing the volume holographic coupling-in grating 21 .

[0075] It is worth noting that in waveguide applications, in addition to the in-coupling and out-coupling functions, the grating can also perform one-dimensional pupil expansion or two-dimensional pupil expansion to ensure that the image light has a larger eye box range when it is displayed through the waveguide. Figure 6 As shown, in the third example of the present application, the waveguide substrate 10 may further have a pupil expansion region 13 located in the optical path between the coupling-in region 11 and the coupling-out region 12; the volume holographic grating waveguide 1 may further include a pupil expansion element 40, which is correspondingly arranged in the pupil expansion region 13 of the waveguide substrate 10, and is used to modulate the image light transmitted from the coupling-in region 11 to be extendedly transmitted to the coupling-out region 12, so as to realize the pupil expansion function of the waveguide. It can be understood that in this example of the present application, the image light transmission direction at the coupling-out region 12 refers to the direction from close to the pupil expansion region 13 to away from the pupil expansion region 13, that is, the direction from the pupil expansion region 13 to the coupling-out region 12, as shown in FIG. Figure 6 in the Y direction.

[0076] Alternatively, if Figure 6 As shown, the pupil expansion element 40 can be implemented as, but not limited to, a volume holographic turning grating 41, which is used to diffract the image light transmitted from the coupling-in area 11 to be transmitted to the coupling-out area 12 in a redirected manner, thereby realizing the one-dimensional pupil expansion function of the waveguide. It can be understood that in other examples of the present application, the pupil expansion element 40 can also be implemented as other types of pupil expansion elements such as an embossed pupil expansion grating or a semi-reflective semi-transparent film, which will not be described in detail in the present application.

[0077] Optionally, the thickness of the volume holographic turning grating 41 increases along the image light transmission direction at the pupil expansion area 13, and the turning diffraction efficiency of the volume holographic turning grating 41 increases with the increase of the grating thickness. It can be understood that in this example of the present application, the image light transmission direction at the pupil expansion area 13 refers to the direction from close to the coupling area 11 to away from the coupling area 11, that is, the direction from the coupling area 11 to the pupil expansion area 13, as shown in FIG. Figure 6 The X direction in .

[0078] In this way, although the image light transmitted through the waveguide substrate 10 will be diffracted by the volume holographic turning grating 41 during the transmission process in the pupil expansion area 13 and will be continuously turned to the coupling-out area 12, so that the light intensity of the image light will be continuously weakened along the image light transmission direction of the pupil expansion area 13, the thickness of the volume holographic coupling-out grating 30 of the present application increases along the image light transmission direction at the pupil expansion area 13, so that the image light transmitted in the pupil expansion area 13 will be diffracted and turned through the smaller thickness portion of the volume holographic turning grating 41 when the light intensity is large, and will be diffracted and turned through the larger thickness portion of the volume holographic turning grating 41 when the light intensity is small; at the same time, due to the diffraction efficiency of the volume holographic turning grating 41 of the present application It increases with the increase of grating thickness, that is, the diffraction efficiency of the thinner part of the volume holographic turning grating 41 is less than the diffraction efficiency of the thicker part of the volume holographic turning grating 41. Therefore, the volume holographic turning grating 41 of the present application can compensate for the light intensity attenuation of the image light when it is transmitted in the pupil expansion area 13 by changing the diffraction efficiency, so that the image light intensity diffracted and turned through the thinner part of the volume holographic turning grating 41 can be basically consistent with the image light intensity diffracted and turned through the thicker part of the volume holographic turning grating 41, ensuring that the light intensity propagated to various places in the coupling-out area 12 is basically consistent, which is beneficial for the volume holographic coupling-out grating 30 to couple out image light with uniform brightness, thereby improving the display effect of the near-eye display device.

[0079] It is worth noting that the thickness of the volume holographic turning grating 41 of the present application can be gradually increased along the image light transmission direction at the pupil expansion area 13, or can be increased in a step-by-step manner, as long as the required diffraction efficiency adjustment can be achieved, and the present application will not repeat it. It can be understood that, similar to the volume holographic outcoupling grating 30: the thickness range of the volume holographic turning grating 41 can be between 100nm and 100um; the thickness difference between adjacent parts in the volume holographic turning grating 41 can be between 100nm and 20um.

[0080] In addition, although the volume holographic turning grating 41 and the volume holographic out-coupling grating 30 mentioned in the present application can have the same structure, that is, the volume holographic turning grating 41 can also be composed of an orientation layer and a liquid crystal layer; however, the thickness increase trends of the volume holographic turning grating 41 and the volume holographic out-coupling grating 30 are unrelated, that is, the thickness change of the volume holographic turning grating 41 is relatively independent of the thickness change of the volume holographic out-coupling grating 30. It can be understood that the volume holographic turning grating 41 and the volume holographic out-coupling grating 30 mentioned in the present application can be prepared in the same way. For the convenience of description, the volume holographic out-coupling grating 30 is taken as an example for explanation below.

[0081] Optionally, the liquid crystal layer 32 of the volume holographic outcoupling grating 30 can be formed by spraying a liquid crystal mixture solution on the alignment layer 31 and curing the solution, wherein the liquid crystal mixture solution consists of a solvent, a liquid crystal material, a chiral material and a photoinitiator.

[0082] Optionally, the solvent may be, but is not limited to, toluene; the liquid crystal material may be, but is not limited to, RM257; the chiral material may be, but is not limited to, R5011 or S5011; the photoinitiator may be, but is not limited to, IRGACURE 651, i.e., photoinitiator-651.

[0083] Optionally, the alignment layer 31 of the volume holographic outcoupling grating 30 can be formed by spin coating an alignment layer solution on the waveguide substrate 10 and curing the solution, wherein the alignment layer solution can be composed of a solvent and an alignment layer material.

[0084] Optionally, the alignment layer material may be, but is not limited to, Bright Yellow (BY for short). It is understood that the solvent in the alignment layer solution mentioned in the present application may be, but is not limited to, water.

[0085] It is worth mentioning that according to another aspect of the present application, Figure 7 As shown, an embodiment of the present application further provides a method for manufacturing a volume holographic grating waveguide, which may include the steps of:

[0086] S100: spin coating an alignment layer solution on the outcoupling region of the waveguide substrate to solidify and expose to form an alignment layer of a volume holographic outcoupling grating;

[0087] S200: spraying a liquid crystal mixture solution on the orientation layer and curing it by light to form a liquid crystal layer with uneven thickness in the volume holographic out-coupling grating, so that the thickness of the volume holographic out-coupling grating increases along the image light transmission direction at the out-coupling area; and S300: setting a coupling element in the coupling area of ​​the waveguide substrate.

[0088] It is worth noting that in step S200 of the present application: the thickness of the liquid crystal layer in different parts of the volume holographic outcoupling grating can be controlled by controlling the flow rate or time of the spraying, and then the grating thickness can be modulated so that the thickness of the volume holographic outcoupling grating gradually increases or increases in steps along the image light transmission direction at the outcoupling area.

[0089] Optionally, the light curing mentioned in step S200 of the present application may be, but is not limited to, implemented as UV curing, and nitrogen protection is performed during UV curing. It is understandable that since RM257 as a liquid crystal material has an obvious oxygen inhibition effect, it is difficult to cure in the air, so the liquid crystal mixture solution of the present application can be UV cured in nitrogen protection.

[0090] Optionally, in the step S200 of the present application, the liquid crystal mixture solution may be formed by mixing toluene as a solvent, RM257 as a liquid crystal material, R5011 as a chiral material, and IRGACURE 651 as a photoinitiator.

[0091] In one example of this application, Figure 8 As shown, step S100 in the method for manufacturing the volume holographic grating waveguide may include the following steps:

[0092] S110: preparing a BY solution as the alignment layer solution;

[0093] S120: spin coating the alignment layer solution on the outcoupling region;

[0094] S130: baking the alignment layer solution to form an alignment layer semi-finished product fixed to the outcoupling region; and

[0095] S140: After the semi-finished product of the alignment layer is cooled, polarization holographic exposure is performed on the semi-finished product of the alignment layer to obtain the alignment layer.

[0096] Optionally, in step S140 of the present application: first build an exposure optical path; then place the waveguide substrate with the semi-finished product of the alignment layer on a clamping device in the exposure optical path, ensuring that the normal direction of the waveguide substrate is parallel to the angle bisector direction of the exposure angle in the exposure optical path; finally determine the exposure time and exposure energy according to the light intensity density at the waveguide substrate to perform polarization holographic exposure. It can be understood that the alignment layer solution mentioned in the present application can be implemented as a BY solution but is not limited to it.

[0097] It is worth noting that in the above embodiments of the present application, Figure 7 As shown, the method for manufacturing the volume holographic grating waveguide may further include the steps of:

[0098] S400: Disposing a pupil expansion element in a pupil expansion area of ​​the waveguide substrate.

[0099] Optionally, in an example of the present application, Fig. 9 As shown, step S400 may include the following steps:

[0100] S410: spin coating an alignment layer solution on the pupil expansion area to cure and expose to form an alignment layer of a volume holographic turning grating; and

[0101] S420: Spraying a liquid crystal mixture solution on the alignment layer, and curing it by light to form a liquid crystal layer with uneven thickness in the volume holographic turning grating, so that the thickness of the volume holographic turning grating increases gradually or stepwise along the image light transmission direction in the pupil expansion area.

[0102] It can be understood that the volume holographic turning grating and volume holographic out-coupling grating mentioned in the present application can be prepared in time-sharing or simultaneously; that is, step S100 and step S410 can be executed at different times or at the same time; similarly, step S200 and step S420 can be executed at different times or at the same time.

[0103] It is worth noting that when the coupling element mentioned in the present application is implemented as a volume holographic coupling-in grating, the volume holographic coupling-in grating can be prepared by the same preparation material as the volume holographic coupling-out grating in different time periods or simultaneously, and this application will not elaborate on this.

[0104] In addition, the method for manufacturing the volume holographic grating waveguide of the present application may further include the step of cleaning the waveguide substrate before step S100 to ensure that the surface of the waveguide substrate is clean, which helps to obtain a high-quality volume holographic grating waveguide.

[0105] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention.

Claims

1. Volume holographic grating waveguide, characterized in that include: A waveguide substrate having an incoupling region and an outcoupling region for transmitting image light from the incoupling region to the outcoupling region; A coupling element, the coupling element being correspondingly arranged at the coupling region of the waveguide substrate, and being used for coupling the image light from the coupling region into the waveguide substrate; as well as A volume holographic out-coupling grating is correspondingly arranged in the out-coupling region of the waveguide substrate, and is used to couple the image light from the out-coupling region out of the waveguide substrate; wherein the thickness of the volume holographic out-coupling grating increases along the image light transmission direction at the out-coupling region.

2. The volume holographic grating waveguide according to claim 1, characterized in that: The thickness of the volume holographic outcoupling grating gradually increases along the image light transmission direction at the outcoupling region.

3. The volume holographic grating waveguide according to claim 1, characterized in that: The thickness of the volume holographic outcoupling grating increases stepwise along the image light transmission direction at the outcoupling region.

4. The volume holographic grating waveguide according to claim 3, characterized in that: The thickness difference between two adjacent step portions in the volume holographic outcoupling grating is between 100 nm and 20 um.

5. The volume holographic grating waveguide according to any one of claims 2 to 4, characterized in that: The number of longitudinal periods at the thickest part of the volume holographic outcoupling grating is less than 10.

6. The volume holographic grating waveguide according to any one of claims 2 to 4, characterized in that: The thickness of the volume holographic outcoupling grating ranges from 100 nm to 100 um.

7. The volume holographic grating waveguide according to any one of claims 1 to 4, characterized in that: The volume holographic outcoupling grating comprises an orientation layer and a liquid crystal layer, wherein the orientation layer is located between the liquid crystal layer and the waveguide substrate, and the liquid crystal layer is composed of liquid crystal groups doped with chiral materials to present a three-dimensional rotating structure.

8. The volume holographic grating waveguide according to any one of claims 1 to 4, characterized in that: The waveguide substrate further has a pupil expansion region located in the optical path between the coupling-in region and the coupling-out region; the volume holographic grating waveguide further includes a pupil expansion element, which is correspondingly arranged in the pupil expansion region of the waveguide substrate.

9. The volume holographic grating waveguide according to claim 8, characterized in that: The pupil expansion element is a volume holographic turning grating; the thickness of the volume holographic turning grating increases gradually or stepwise along the image light transmission direction at the pupil expansion area.

10. The volume holographic grating waveguide according to any one of claims 1 to 4, characterized in that: The coupling element is a volume holographic coupling grating.

11. A near-eye display device, characterized in that include: Display light machine; and The volume holographic grating waveguide according to any one of claims 1 to 10, wherein the volume holographic grating waveguide is located at the projection side of the display optical engine.

12. A method for manufacturing a volume holographic grating waveguide, characterized in that: Includes steps: Spin coating an alignment layer solution on the outcoupling region of the waveguide substrate to solidify and expose to form an alignment layer of a volume holographic outcoupling grating; Spraying a liquid crystal mixture solution on the alignment layer, and curing it by light to form a liquid crystal layer with uneven thickness in the volume holographic outcoupling grating, so that the thickness of the volume holographic outcoupling grating increases along the image light transmission direction at the outcoupling area; and The coupling element is arranged in the coupling region of the waveguide substrate.

13. The method for manufacturing a volume holographic grating waveguide according to claim 12, characterized in that: The liquid crystal mixture solution is formed by mixing a solvent, a liquid crystal material, a chiral material and a photoinitiator.

14. The method for manufacturing a volume holographic grating waveguide according to claim 12, characterized in that: The step of spin coating the orientation layer solution on the outcoupling area of ​​the waveguide substrate to solidify and expose the orientation layer of the volume holographic outcoupling grating comprises the steps of: preparing a BY solution as the alignment layer solution; Spin coating the alignment layer solution on the outcoupling region; baking the alignment layer solution to form an alignment layer semi-finished product fixed to the outcoupling region; as well as After the semi-finished product of the alignment layer is cooled, the semi-finished product of the alignment layer is subjected to polarization holographic exposure to obtain the alignment layer.

15. The method for manufacturing a volume holographic grating waveguide according to any one of claims 12 to 14, characterized in that: The method for manufacturing the volume holographic grating waveguide further comprises the steps of: The pupil expansion element is arranged in the pupil expansion area of ​​the waveguide substrate.

16. The method for manufacturing a volume holographic grating waveguide according to claim 15, characterized in that: The step of arranging the pupil expansion element in the pupil expansion area of ​​the waveguide substrate comprises the steps of: Spin coating an alignment layer solution on the pupil expansion area to solidify and expose to form an alignment layer of a volume holographic turning grating; and A liquid crystal mixed solution is sprayed on the alignment layer and cured by light to form a liquid crystal layer with uneven thickness in the volume holographic turning grating, so that the thickness of the volume holographic turning grating increases gradually or stepwise along the image light transmission method at the pupil expansion area.

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