Optical waveguide and display product

Abstract

The utility model belongs to the technical field of optical waveguides, and discloses an optical waveguide and a display product, and the display product applies the optical waveguide. According to the optical waveguide, the reflection type volume holographic grating serving as the first grating is arranged on the side, back to the projection light machine, of the coupling-in grating to intercept zero-order diffraction light to be emitted, the zero-order diffraction light is re-coupled into the waveguide layer, the conduction angle is consistent with the conduction angle of light which is coupled into the waveguide layer by the coupling-in grating, energy loss is reduced, and the transmission efficiency is improved. And deformation or ghosting of the image in twice coupling and conduction is avoided. Moreover, the light beams which are recoupled into the waveguide layer are continuously conducted and are continuously coupled into the human eyes by the out-of-grating, so that the density of the light beams which are coupled into the human eyes is increased, and the out-of-coupling energy uniformity is improved.

Description

Technical Field

[0001] The present invention belongs to the field of optical waveguide technology, and specifically relates to optical waveguide and display products. Background Art

[0002] Diffraction waveguide display technology is the mainstream solution for achieving high transparency and lightweight augmented reality glasses, and has great potential in expanding the field of view and improving display effects. Light is transmitted in a transparent waveguide by total internal reflection, and coupling elements such as gratings are arranged in the waveguide to control light input, output, steering, pupil expansion, energy distribution, etc., thereby guiding the image beam into the human eye. Commonly used coupling elements mainly include surface relief gratings and volume holographic gratings. As a Bragg diffraction element, the volume holographic grating concentrates the diffraction energy on the zeroth and first orders. The ratio of the two can be adjusted by adjusting the grating parameters. Therefore, the volume holographic grating as an optical waveguide coupling element has special advantages in improving light efficiency and reducing light leakage.

[0003] Diffraction optical waveguides use coupling-in gratings to couple image light signals into the waveguide. It is necessary to take into account a certain field of view angle range so that light at all angles of the entire field of view can enter the waveguide with a relatively balanced diffraction efficiency. Therefore, in order to expand the angular bandwidth, the coupling-in grating needs to be specially designed, but it often also reduces the overall coupling efficiency. Most of the energy leaks out of the waveguide in the form of zero-order light, causing energy loss. Diffraction optical waveguides use coupling-out gratings to couple the image light signal transmitted in the waveguide to the human eye and ensure that the remaining light energy continues to be transmitted to expand the exit pupil, but some energy will also be coupled out to the other side of the waveguide, causing energy loss and image leakage. It is difficult for current technical solutions to solve these problems at the design level of coupling-in and coupling-out gratings. Utility Model Content

[0004] The present solution aims to overcome at least one defect in the prior art and provide an optical waveguide to solve the problem of energy loss caused by coupling of volume holographic grating.

[0005] In order to solve the above technical problems, the following technical solutions are adopted:

[0006] In a first aspect, an optical waveguide is proposed. The optical waveguide is used to transmit an image light beam, and its structure includes a waveguide layer and a grating layer. The grating layer includes at least a coupling-in grating and a coupling-out grating, both of which have a first surface and a second surface opposite to each other. The image light beam is incident into the optical waveguide from the first surface of the coupling-in region of the optical waveguide, and is emitted to the human eye from the first surface or the second surface of the coupling-out region of the optical waveguide. The optical waveguide is provided with at least a coupling-in region and a coupling-out region, and the waveguide layer runs through the coupling-in region and the coupling-out region. The coupling-in grating is located in the coupling-in region and is arranged on the first surface, the second surface or inside of the waveguide layer. The coupling-out grating is located in the coupling-out region and is arranged on the first surface, the second surface or inside of the waveguide layer. In particular, the coupling-in grating is a volume holographic grating, and the grating layer also includes a first grating. The first grating is a reflective volume holographic grating, whose grating vector surface component is equal to the grating vector surface component of the coupling-in grating, and whose grating vector normal component matches the Bragg diffraction condition of the image light beam, is opposite to the coupling-in grating and is located on the side of the second surface of the coupling-in grating, and is arranged on the second surface of the coupling-in grating, the second surface of the waveguide layer, or inside the waveguide layer.

[0007] The coupling grating has a first surface and a second surface facing each other. The image beam is incident from the first surface of the coupling grating, and the zero-order diffraction light and the first-order diffraction light generated by the diffraction of the coupling grating are emitted from the second surface of the coupling grating, wherein the transmission angle of the first-order diffraction light meets the reflection condition of the waveguide layer, and then the light is reflected back and forth in the waveguide layer, while the zero-order diffraction light does not meet the reflection condition of the waveguide layer, and then is emitted outside the waveguide layer, causing energy loss. In this scheme, a reflective volume holographic grating as a first grating is arranged on one side of the second surface of the coupling grating to intercept the zero-order diffraction light that is about to be emitted, and re-couple it into the waveguide layer, and the transmission angle is consistent with the transmission angle of the light coupled into the waveguide layer by the coupling grating, which not only reduces the energy loss, but also ensures that the image will not be deformed or ghosted during the two couplings and transmissions. Moreover, these light beams re-coupled into the waveguide layer continue to be transmitted and are continuously coupled into the human eye by the coupling grating, which increases the density of the light beams coupled into the human eye, thereby facilitating the improvement of the uniformity of the coupling energy.

[0008] The out-coupling grating is preferably a volume holographic grating, and the grating layer preferably includes a second grating, which is a reflective volume holographic grating, and the grating vector surface component of which is equal to the grating vector surface component of the out-coupling grating. If the image light beam is coupled out from the first surface of the optical waveguide out-coupling region, the second grating is directly opposite to the out-coupling grating and is located on the side of the second surface of the out-coupling grating, and is arranged on the second surface of the out-coupling grating, the second surface of the waveguide layer, or inside the waveguide layer; if the image light beam is coupled out from the second surface of the optical waveguide out-coupling region, the second grating is directly opposite to the out-coupling grating and is located on the side of the first surface of the out-coupling grating, and is arranged on the first surface of the out-coupling grating, the first surface of the waveguide layer, or inside the waveguide layer. The second grating can intercept the image light beam that is about to leak and re-couple it into the waveguide layer, and the transmission angle is consistent with that before the coupling with the out-coupling grating, which not only reduces or even avoids image leakage, improves the utilization rate of light energy, but also ensures that the image light beam will not be deformed or ghosted during the two couplings and transmissions. Moreover, these light beams recoupled into the waveguide layer continue to be transmitted and continuously coupled into the human eye by the outcoupling grating, increasing the density of the light beams coupled into the human eye, thereby facilitating the improvement of outcoupling energy uniformity. The grating vector normal component of the second grating preferably varies with the spatial position to optimize the exit pupil uniformity of the optical waveguide.

[0009] The first grating is preferably a multi-layer stacked reflective volume holographic grating or a single-layer multiplexed reflective volume holographic grating. The grating vectors of each layer of the multi-layer stacked reflective volume holographic grating are different, and the angular bandwidth of the grating can be expanded by using reflective volume holographic gratings with different grating vectors. The single-layer multiplexed reflective volume holographic grating can expand the angular bandwidth of the grating by spatial distribution of the grating vector or angle multiplexing, thereby expanding the field of view.

[0010] The second grating is preferably a multi-layer stacked reflective volume holographic grating or a single-layer multiplexed reflective volume holographic grating. The grating vectors of each layer of the multi-layer stacked reflective volume holographic grating are different, and the angular bandwidth of the grating can be expanded by using reflective volume holographic gratings with different grating vectors. The single-layer multiplexed reflective volume holographic grating can expand the angular bandwidth of the grating by spatial distribution of the grating vector or angle multiplexing, thereby expanding the field of view.

[0011] The size of the first grating is preferably greater than or equal to the size of the coupling-in grating, and the size of the second grating is preferably greater than or equal to the size of the coupling-out grating, so as to couple more possible leaked light beams back into the waveguide layer to further reduce energy loss and image leakage.

[0012] The transmittance of the waveguide layer, the outcoupling grating and the second grating to the external ambient light is preferably greater than 70%, so that the optical waveguide can be applied to augmented reality display products and mixed reality display products.

[0013] The optical waveguide preferably also includes a volume holographic optical element with a transmittance of more than 70% to external ambient light and a refractive power. The volume holographic optical element is arranged outside the waveguide layer and at least covers the outcoupling area, and can focus or diverge the light beam, so that the optical waveguide can be used as a prescription lens to correct vision, and can also manufacture lightweight eyeglass lenses that integrate vision correction and augmented reality / mixed reality display functions.

[0014] In a second aspect, a display product is provided, which includes a projection optical engine and the above-mentioned optical waveguide, wherein the projection optical engine emits an image light beam toward a first surface of a coupling-in region of the optical waveguide.

[0015] The optical waveguide used in this scheme intercepts the zero-order diffraction light that is about to be emitted by setting a reflective volume holographic grating as the first grating on the side of the coupling grating facing away from the projection optical machine, and recouples it into the waveguide layer, and the transmission angle is consistent with the transmission angle of the light coupled into the waveguide layer by the coupling grating, which not only reduces energy loss, but also ensures that the image will not be deformed or ghosted during the two coupling and transmission. Moreover, these light beams recoupled into the waveguide layer continue to be transmitted and continuously coupled into the human eye by the coupling grating, which increases the density of the light beams coupled into the human eye, thereby facilitating the improvement of the uniformity of the coupling energy.

[0016] Compared with the prior art, this solution has the following beneficial effects: this solution intercepts the zero-order diffraction light that is about to be emitted by the reflective volume holographic grating as the first grating, and recouples it into the waveguide layer, and the transmission angle is consistent with the transmission angle of the light coupled into the waveguide layer by the coupled grating, which not only reduces energy loss, but also ensures that the image will not be deformed or ghosted during the two couplings and transmissions. Moreover, these light beams recoupled into the waveguide layer continue to be transmitted and are continuously coupled into the human eye by the out-coupled grating, which increases the density of the light beams coupled into the human eye, thereby facilitating the improvement of the uniformity of the out-coupled energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings are for illustrative purposes only and should not be construed as limitations on the present invention. In order to better illustrate the present invention, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0018] Figure 1 It is a schematic diagram showing the structure of the product.

[0019] Figure 2 It is a schematic diagram of the structure of an optical waveguide.

[0020] Figure 3 It is a schematic diagram of the structure of a one-dimensional pupil expansion optical waveguide.

[0021] Figure 4It is a schematic diagram of the structure of a two-dimensional pupil expansion optical waveguide.

[0022] Figure 5 This is a schematic diagram of the structure and optical path of a traditional optical waveguide.

[0023] Figure 6 The diagram is a schematic diagram of the structure and optical path of an optical waveguide provided with a first grating.

[0024] Figure 7 The present invention is a schematic diagram of the structure and optical path of an optical waveguide provided with a first grating and a second grating.

[0025] Figure 8 This is a schematic diagram of the structure and optical path of the first grating optical waveguide using multi-layer stacked reflective volume holographic gratings.

[0026] Fig. 9 It is a schematic diagram of the structure and optical path of an optical waveguide in which the second grating adopts a multi-layer stacked reflective volume holographic grating.

[0027] Fig.10 The present invention is a schematic diagram of the structure and optical path of an optical waveguide in which the first grating and the second grating adopt single-layer multiplexed reflective volume holographic grating.

[0028] Fig.11 The invention is a schematic diagram of the structure and optical path of an optical waveguide provided with a first grating and a diopter holographic optical element.

[0029] Fig.12 The invention is a schematic diagram of the structure and optical path of an optical waveguide provided with a first grating, a second grating and a refractive body holographic optical element.

[0030] Description of reference numerals: projection optical machine 100, optical waveguide 200, first surface 201, second surface 202, waveguide layer 210, grating layer 220, coupling-in grating 221, coupling-out grating 222, turning grating 223, first grating 224, second grating 225, volume holographic optical element 230, image beam L IMG , the lost zero-order diffraction light L IMG-LOSS , the leaked image beam L IMG-OUT , the image beam L entering the eye IMG-IN , external ambient light L AMB , the ambient light L AMB . DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the present solution, the present solution is further described in detail below in conjunction with specific embodiments.

[0032] Figure 1A possible display product is illustrated, which is configured with a projection optical machine 100 and an optical waveguide 200. The projection optical machine 100 is similar to a projector, and projects an image beam with a virtual image into the optical waveguide 200. The optical waveguide 200 transmits and couples the image beam from the projection optical machine 100 into the human eye to form a virtual image, thereby achieving different effects such as virtual reality (VR), augmented reality (AR), and mixed reality (MR). According to different effects, display products can be divided into different types. Among them, VR display products are the carriers of virtual reality technology, which use computer technology to generate a three-dimensional virtual world that allows users to interact with it, so that users have an immersive feeling. AR display products are the carriers of augmented reality technology, which use computer technology to apply virtual information to the real world, so that the real environment and virtual objects are superimposed on the same screen or space in real time and exist simultaneously. MR display products are the carriers of mixed reality technology, combining the characteristics of VR and AR, allowing users to interact with real and virtual environments.

[0033] Figures 2 to 4 A possible optical waveguide 200 is illustrated, and the optical waveguide 200 includes a waveguide layer 210 and a grating layer 220, both of which are layered structures and are stacked. The optical waveguide 200 and its components (including the waveguide layer 210, the grating layer 220, and each grating in the grating layer 220) have two opposite surfaces, namely a first surface 201 and a second surface 202. Each grating in the grating layer 220 can be arranged on the surface or inside of the waveguide layer 210, specifically, it can be arranged on the first surface 201 of the waveguide layer 210, it can also be arranged on the second surface 202 of the waveguide layer 210, and it can also be arranged between the first surface 201 and the second surface 202 of the waveguide layer 210 to form a stacked structure with the waveguide layer 210.

[0034] The waveguide layer 210 is generally made of a material with a high refractive index. The waveguide layer 210 itself acts as a high refractive index medium, and the air around it acts as a low refractive index medium. The two surfaces of the waveguide layer 210 act as interfaces between the high refractive index medium and the low refractive index medium. When light is incident from the high refractive index medium to the interface with the low refractive index medium, the absolute value of the incident angle is greater than the critical angle of total reflection θ. c The light will be completely reflected back, and then propagate forward along the extension direction of the medium in the form of back and forth reflection in the high refractive index medium. This propagation can be called total reflection propagation. In addition, the two surfaces of the waveguide layer 210 are attached with only the incident angle greater than the high reflection critical angle θ. r The light has a high reflectivity material, and can also make most of the incident angles greater than the high reflection critical angle θ rThe light is reflected back and can also propagate forward along the extension direction of the medium in the form of back and forth reflection in the waveguide layer 210. This propagation can be called high reflection propagation. Whether it is total reflection propagation or high reflection propagation, the waveguide layer 210 can realize back and forth reflection propagation of light.

[0035] Figure 3 The optical waveguide 200 shown is provided with an in-coupling region and an out-coupling region, the waveguide layer 210 runs through the in-coupling region and the out-coupling region, and the grating layer 220 is provided with an in-coupling grating 221 and an out-coupling grating 222. The in-coupling grating 221 is located in the in-coupling region, and is used to couple the image light beam into the waveguide layer 210, so that the image light beam can be reflected back and forth in the waveguide layer 210 and propagate to the out-coupling region. The out-coupling grating 222 is located in the out-coupling region, and is used to couple the image light beam out of the waveguide layer 210, so that the image light beam that is reflected back and forth in the waveguide layer 210 can be emitted outside the waveguide layer 210 and enter the human eye, and the range of the image light beam is expanded in one direction, so as to realize one-dimensional pupil expansion.

[0036] Figure 4 The optical waveguide 200 shown is provided with an incoupling region, an outcoupling region and a turning region, the waveguide layer 210 runs through the incoupling region, the outcoupling region and the turning region, and the grating layer 220 is not only provided with an incoupling grating 221 and an outcoupling grating 222, but also provided with a turning grating 223. The turning grating 223 is located in the turning region, and is used to change the propagation direction of the image light beam in the waveguide layer 210, and to expand the range of the light beam in another direction to achieve two-dimensional pupil expansion. After the image light beam is coupled into the waveguide layer 210 by the incoupling grating 221 in the incoupling region, it is reflected back and forth in the waveguide layer 210 and propagates to the turning region, and then the propagation direction is changed by the turning grating 223 and propagates to the outcoupling region, and finally coupled out of the waveguide layer 210 by the outcoupling grating 222 and enters the human eye.

[0037] The coupling-in grating 221, the coupling-out grating 222 and the turning grating 223 can all be volume holographic gratings. In order to take into account a certain range of viewing angles, so that the light at all angles of the entire viewing field can enter the optical waveguide 200 with a relatively balanced diffraction efficiency, the coupling-in grating 221 using a volume holographic grating, in addition to coupling the image light beam incident from the first surface 201 of each component in the coupling-in area into the waveguide layer 210 in the form of first-order diffraction, most of it is lost in the form of zero-order diffraction. The lost zero-order diffraction light is emitted from the second surface 202 of each component in the coupling-in area, as shown in FIG. Figure 5 .

[0038] To reduce the zero-order diffraction loss, the grating layer 220 may be configured with a first grating 224, such as Figure 6The first grating 224 is located in the coupling region, facing the coupling grating 221, and located on the side of the second surface 202 of the coupling grating 221. Specifically, it can be set on the second surface 202 of the coupling grating 221, or on the second surface 202 of the waveguide layer 210, or inside the waveguide layer 210 (between the first surface 201 and the second surface 202), so that the zero-order diffraction light emitted from the coupling grating 221 can be incident on the first grating 224 instead of being directly emitted to the outside of the waveguide layer 210. The first grating 224 is a reflective volume holographic grating, and its grating vector surface component is equal to the grating vector surface component of the coupled grating 221, and its grating vector normal component matches the Bragg diffraction condition of the image light beam, so that most of the zero-order diffraction light incident on the first grating 224 can be coupled into the waveguide layer 210 in the form of first-order diffraction for back-and-forth reflection and propagation, and its transmission angle is consistent with the transmission angle of the light coupled into the waveguide layer 210 by the coupled grating 221, which not only saves energy loss and improves light efficiency, but also ensures that the image will not be deformed or ghosted during the two couplings and transmissions. Moreover, these light beams re-coupled into the waveguide layer 210 continue to be transmitted and are continuously coupled into the human eye by the coupled-out grating 222, which increases the density of the light beams coupled into the human eye, thereby facilitating the improvement of the uniformity of the coupled-out energy.

[0039] The projection area of ​​the image light beam emitted by the projection optical machine 100 on the coupling grating 221 may be smaller than the size of the coupling grating 221, or may be equal to the size of the coupling grating 221. For the former, the projection area of ​​the zero-order diffraction light generated by the diffraction of the coupling grating 221 on the first grating 224 may also be smaller than the size of the coupling grating 221. In this case, the size of the first grating 224 may be smaller than the size of the coupling grating 221. For the latter, the projection area of ​​the zero-order diffraction light generated by the diffraction of the coupling grating 221 on the first grating 224 is at least equal to the size of the coupling grating 221. In this case, the size of the first grating 224 may be approximately equal to the size of the coupling grating 221. Of course, in order to improve the universality of the optical waveguide 200, the size of the first grating 224 is preferably equal to the size of the coupling grating 221, or even larger than the size of the coupling grating 221.

[0040] In the optical waveguide 200 using the volume holographic grating as the out-coupling grating 222, since the diffraction energy of the volume holographic grating is relatively concentrated, most of the image light beam transmitted in the optical waveguide 200 is coupled out by the out-coupling grating 222 in the form of first-order diffraction to the eyes of the user located on one side of the optical waveguide 200, but a part of the image light beam is still output by the out-coupling grating 222 in the form of first-order diffraction to the other side of the optical waveguide 200 to form image leakage, such as Figure 5 Although this image leakage accounts for a small proportion and the image brightness is weak, it can still be felt by the human eye on the other side.

[0041] To reduce image leakage, the grating layer 220 may be configured with a second grating 225, such as Figure 7 The second grating 225 is located in the outcoupling region, facing the outcoupling grating 222, and located on the side of the outcoupling grating 222 where the image light beam leaks, so that the image light beam leaking outward can be incident on the second grating 225 instead of being directly emitted to the outside of the waveguide layer 210. Specifically, the image light beam can be coupled out from the first surface 201 of the outcoupling region of the optical waveguide 200, and can also be coupled out from the second surface 202 of the outcoupling region of the optical waveguide 200. If the image light beam is coupled out from the first surface 201 of the outcoupling region of the optical waveguide 200, the second grating 225 is opposite to the outcoupling grating 222 and is located on the side of the second surface 202 of the outcoupling grating 222. It can be set on the second surface 202 of the outcoupling grating 222, or on the second surface 202 of the waveguide layer 210, or inside the waveguide layer 210. If the image light beam is coupled out from the second surface 202 of the outcoupling region of the optical waveguide 200, the second grating 225 is opposite to the outcoupling grating 222 and is located on the side of the first surface 201 of the outcoupling grating 222. It can be set on the first surface 201 of the outcoupling grating 222, or on the first surface 201 of the waveguide layer 210, or inside the waveguide layer 210.

[0042] The second grating 225 is a reflective volume holographic grating, and its grating vector surface component is equal to the grating vector surface component of the out-coupling grating 222, so that the image light beam incident on the second grating 225 can be coupled back to the waveguide layer 210 in the form of first-order diffraction to continue to reflect and propagate back and forth, and its transmission angle is consistent with that before being coupled by the out-coupling grating 222, which not only reduces or even avoids image leakage, improves the utilization rate of light energy, but also ensures that the image light beam will not be deformed or ghosted during the two couplings and transmissions. Moreover, these light beams re-coupled into the waveguide layer 210 continue to be transmitted and continuously coupled into the human eye by the out-coupling grating 222, which increases the density of the light beams coupled into the human eye, thereby facilitating the improvement of the uniformity of the out-coupling energy. The grating vector normal component and the refractive index modulation degree of the second grating 225 can be changed in spatial position to optimize the uniformity of the exit pupil of the optical waveguide 200.

[0043] When the image light beam is projected onto the second grating 225 by the outcoupling grating 222 in the form of first-order diffraction, its projection area on the second grating 225 may be comparable to the size of the outcoupling grating 222, or may be smaller or larger than the size of the outcoupling grating 222. In order to minimize image leakage as much as possible, the size of the second grating 225 is preferably equal to the size of the outcoupling grating 222, or even larger than the size of the outcoupling grating 222.

[0044] The first grating 224 and the second grating 225 can be configured as a multi-layer stacked reflective volume holographic grating, each layer of which has a different grating vector, and the angular bandwidth of the grating is expanded by using reflective volume holographic gratings with different grating vectors. Figure 8 The optical waveguide 200 shown in the figure uses a multi-layer stacked reflective volume holographic grating as the first grating 224. Fig. 9 The illustrated optical waveguide 200 uses a multi-layer stacked reflective volume holographic grating as the second grating 225 to expand the angular bandwidth of each grating so that the incident light beams within the field of view angle range can be coupled into the return waveguide layer 210 with a higher diffraction efficiency.

[0045] The first grating 224 and the second grating 225 can also be configured as a single-layer multiplexed reflective volume holographic grating, and the angular bandwidth of the grating can be expanded by spatial distribution of grating vectors or angle multiplexing. Fig.10 The optical waveguide 200 shown in the figure multiplexes two groups of grating vectors in the first grating 224 and the second grating 225 respectively, so as to expand the angular bandwidth of each grating, so that the incident light beams within the field angle range can be coupled into the return waveguide layer 210 with higher diffraction efficiency.

[0046] Augmented reality display products and mixed reality display products require that all components in the outcoupling area have high transmittance to external ambient light. Therefore, when the above-mentioned optical waveguide 200 is applied to augmented reality display products and mixed reality display products, the waveguide layer 210, the outcoupling grating 222 and the second grating 225 in the outcoupling area should all have high transmittance (more than 70%) to the external ambient light.

[0047] As an optical waveguide 200 of an augmented reality head display product or a mixed reality head display product, a volume holographic optical element 230 may be configured outside the waveguide layer 210, such as Figures 10-11 The volume holographic optical element 230 covers at least the outcoupling area, has a high transmittance (more than 70%) to the ambient light, has a certain refractive power, can focus or diverge the light beam, and this optical waveguide 200 can be used as a prescription lens to correct vision, and can manufacture lightweight eyeglass lenses that integrate vision correction and augmented reality / mixed reality display functions. The volume holographic optical element 230 can be exposed and manufactured using a specially designed light beam to minimize aberrations.

[0048] The volume holographic optical element 230 can be configured separately (eg Fig.11 ), and can also be stacked with the second grating 225 to form a multi-layer volume holographic film layer to achieve a better effect (such as Fig.12). For the former, the volume holographic optical element 230 can be arranged on the first surface 201 of the waveguide layer 210, or on the second surface 202 of the waveguide layer 210. For the latter, if the second grating 225 is arranged inside the waveguide layer 210, the volume holographic optical element 230 can be arranged on the first surface 201 of the waveguide layer 210, or on the second surface 202 of the waveguide layer 210; if the second grating 225 is arranged on one surface of the waveguide layer 210 (first surface 201 / second surface 202), the volume holographic optical element 230 can be arranged on the side of the second grating 225 facing away from the waveguide layer 210, or on the other surface of the waveguide layer 210 (second surface 202 / first surface 201).

[0049] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. An optical waveguide, which is used to transmit an image light beam, and has a structure comprising a waveguide layer and a grating layer, wherein the grating layer at least comprises an in-coupling grating and an out-coupling grating, both of which have a first surface and a second surface opposite to each other, wherein the image light beam is incident into the optical waveguide from the first surface of the in-coupling region of the optical waveguide, and is emitted to a human eye from the first surface or the second surface of the out-coupling region of the optical waveguide; wherein the optical waveguide is at least provided with an in-coupling region and an out-coupling region, wherein the waveguide layer runs through the in-coupling region and the out-coupling region, wherein the in-coupling grating is located in the in-coupling region and is arranged on the first surface, the second surface or inside of the waveguide layer, wherein the out-coupling grating is located in the out-coupling region and is arranged on the first surface, the second surface or inside of the waveguide layer; wherein the The coupling-in grating is a volume holographic grating, and the grating layer further comprises a first grating, which is a reflective volume holographic grating, whose grating vector surface component is equal to the grating vector surface component of the coupling-in grating, whose grating vector normal component matches the Bragg diffraction condition of the image light beam, faces the coupling-in grating and is located on the side of the second surface of the coupling-in grating, and is arranged on the second surface of the coupling-in grating, the second surface of the waveguide layer, or inside the waveguide layer.

2. The optical waveguide according to claim 1, characterized in that The out-coupling grating is a volume holographic grating, the grating layer further comprises a second grating, the second grating is a reflective volume holographic grating, and the grating vector surface component of the second grating is equal to the grating vector surface component of the out-coupling grating; If the image light beam is coupled out from the first surface of the optical waveguide outcoupling region, the second grating is directly opposite to the outcoupling grating and is located on the side of the second surface of the outcoupling grating, and is arranged on the second surface of the outcoupling grating, the second surface of the waveguide layer, or inside the waveguide layer; If the image light beam is coupled out from the second surface of the optical waveguide outcoupling region, the second grating is opposite to the outcoupling grating and is located on the side of the first surface of the outcoupling grating, and is arranged on the first surface of the outcoupling grating, the first surface of the waveguide layer or inside the waveguide layer.

3. The optical waveguide according to claim 2, characterized in that The normal component of the grating vector of the second grating varies with the spatial position.

4. The optical waveguide according to claim 2, characterized in that The first grating is a multi-layer stacked reflective volume holographic grating or a single-layer multiplexed reflective volume holographic grating.

5. The optical waveguide according to claim 2, characterized in that The second grating is a multi-layer stacked reflective volume holographic grating or a single-layer multiplexed reflective volume holographic grating.

6. The optical waveguide according to claim 2, characterized in that The size of the first grating is greater than or equal to the size of the coupling-in grating; and / or The size of the second grating is greater than or equal to the size of the outcoupling grating.

7. The optical waveguide according to any one of claims 2 to 6, characterized in that: The waveguide layer, the out-coupling grating and the second grating have a transmittance of more than 70% to the external ambient light.

8. The optical waveguide according to claim 1, characterized in that The transmittance of the waveguide layer and the out-coupling grating to the external ambient light exceeds 70%.

9. The optical waveguide according to claim 8, characterized in that The optical waveguide also includes a volume holographic optical element with a transmittance of more than 70% to ambient light and a refractive power. The volume holographic optical element is arranged outside the waveguide layer and at least covers the outcoupling region.

10. A display product, comprising a projection light machine, characterized in that: The display product further comprises the optical waveguide according to any one of claims 1 to 9, and the optical projection engine emits an image light beam toward a first surface of the coupling-in region of the optical waveguide.

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