Single-entrance-pupil binocular head-mounted display product

Abstract

The utility model discloses a single-entrance-pupil binocular head-mounted display product. The single-entrance-pupil binocular head-mounted display product comprises a micro-projection light machine and an optical waveguide. The optical waveguide comprises a waveguide layer and a grating layer, and the grating layer comprises a coupling-in grating, a first coupling-out grating and a second coupling-out grating. The coupling-in grating is a volume holographic grating and is arranged opposite to the micro-projection light machine. The volume holographic grating is provided with two grating surfaces which are parallel and opposite to each other, and a first grating and a second grating which are arranged between the two grating surfaces, the first grating is provided with a first grating vector, and the second grating is provided with a second grating vector; the first grating vector and the second grating vector are symmetrical in plane and are provided with a symmetry plane M. The symmetry plane M is perpendicular to the grating surface, so that first diffraction light generated after a light beam is diffracted by the first grating is transmitted to one side of the symmetry plane M, and second diffraction light generated after the light beam is diffracted by the second grating is transmitted to the other side of the symmetry plane M. Diffraction energy of the first diffracted light and the second diffracted light is balanced; the first coupling-out grating and the second coupling-out grating are located on the two sides of the symmetry plane M.

Description

Technical Field

[0001] This solution belongs to the field of optical waveguide technology, and specifically relates to a single-pupil binocular head-mounted display product. 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] A piece of optical waveguide is usually matched with a micro-projection optical machine to form an augmented reality display module. If you want to realize a pair of optical waveguide glasses with binocular display, you usually need two sets of modules, which have high power consumption and weight. Using a micro-projection optical machine with a binocular integrated optical waveguide can reduce power consumption and weight. For the surface relief grating, its coupling-in grating uses the positive and negative first-order diffraction orders to diffract the image beam output by the optical machine into evenly distributed left and right transmission beams. The integrated waveguide sheet can include a left-right symmetrical turning grating and a left-right symmetrical coupling-out grating, that is, binocular display is realized. At the same time, this solution can also easily realize binocular fusion. However, for a volume holographic grating with an inclined grating surface, due to the characteristics of Bragg diffraction, the energy is concentrated in the zero-order and positive first-order diffraction, and the image beam cannot be transmitted symmetrically left and right. If the volume holographic grating is set to be perpendicular to the grating surface, the field of view angle of the optical machine output beam often cannot match the Bragg diffraction condition, and the positive and negative first-order diffraction energies are very low. Utility Model Content

[0004] The present invention aims to overcome at least one defect in the prior art and provide a single-pupil binocular head-mounted display product to solve the problem that a volume holographic grating cannot be used to couple and transmit image beams symmetrically.

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

[0006] In the first aspect, a volume holographic grating is proposed. The volume holographic grating is used for coupling light beams, and has two parallel and opposite grating surfaces, and a first grating and a second grating arranged between the two grating surfaces, wherein the first grating has a first grating vector, and the second grating has a second grating vector. The first grating vector is plane-symmetrical with the second grating vector, and has a symmetry plane M, wherein the symmetry plane M is perpendicular to the grating surface, so that the first diffracted light generated after the light beam is diffracted by the first grating propagates to one side of the symmetry plane M, and the second diffracted light generated after the light beam is diffracted by the second grating propagates to the other side of the symmetry plane M, and the diffraction energy of the first diffracted light and the second diffracted light is balanced.

[0007] This solution uses two gratings (first grating and second grating) with symmetric grating vector planes to generate first diffracted light and second diffracted light with symmetrical propagation directions and balanced diffraction energy after the light beam is diffracted, wherein the first diffracted light propagates to one side of the symmetry plane M, and the second diffracted light propagates to the other side of the symmetry plane M. If the symmetry plane M is perpendicular to the left and right directions, the first diffracted light and the second diffracted light will propagate symmetrically in the left and right directions, and when the coupled grating is used as an optical waveguide, binocular display can be realized, which is conducive to binocular fusion.

[0008] The first grating and the second grating diffract the light beam successively. If the ratio of the first grating to diffract the light beam before the second grating is ρ, the first-order diffraction efficiency η1 of the first grating and the first-order diffraction efficiency η2 of the second grating satisfy: η1 / η2=(1-ρη1) / (1-(1-ρ)η2), and the first diffracted light and the second diffracted light can be conveniently controlled to balance their diffraction energies. Specifically, the first grating and the second grating can be stacked, and the stacking direction is perpendicular to the grating surface. At this time, if the first grating and the second grating diffract the light beam successively, the first-order diffraction efficiency η1 of the first grating and the first-order diffraction efficiency η2 of the second grating satisfy: η1 / η2=1-η1, and the first diffracted light and the second diffracted light can be conveniently controlled to balance their diffraction energies. In addition, the first grating and the second grating can also completely overlap.

[0009] The first grating and the second grating can also diffract the light beam at the same time, so that the first grating's first-order diffraction efficiency η1 and the second grating's first-order diffraction efficiency η2 satisfy: η1=η2, the first grating's area s1 and the second grating's area s2 satisfy: s1=s2, the first grating's thickness h1 and the second grating's thickness h2 satisfy: h1=h2, and the first diffracted light and the second diffracted light can be conveniently controlled to balance their diffraction energies. Specifically, the first grating and the second grating can be tiled, and the tiled direction is perpendicular to the symmetry plane M.

[0010] In addition, the first grating and the second grating can also be arranged in a tiled manner and partially overlap, and the tiling direction is perpendicular to the symmetry plane M.

[0011] The first grating can have more than two first grating vectors, and the second grating can have more than two second grating vectors. The number of the first grating vectors is the same as the number of the second grating vectors, which are used to expand the angular bandwidth of each grating so that the incident light beam within the field of view angle range can be coupled to the left and right sides of the optical waveguide with high and balanced diffraction efficiency.

[0012] In the second aspect, a single-entry-pupil binocular waveguide is proposed. The optical waveguide includes a waveguide layer and a grating layer that are stacked, the grating layer includes an input grating, a first output grating, and a second output grating, the input grating uses the above-mentioned volume holographic grating, the first output grating is located on one side of the symmetry plane M, and the second output grating is located on the other side of the symmetry plane M.

[0013] This solution uses the above-mentioned volume holographic grating as a coupling-in grating, which can diffract the image light beam to produce a first diffraction light and a second diffraction light with symmetrical propagation directions and balanced diffraction energy. The first diffraction light propagates to one side of the symmetry plane M to the first coupling-out grating, is coupled out by the first coupling-out grating and realizes one-dimensional pupil expansion, and the second diffraction light propagates to the other side of the symmetry plane M to the second coupling-out grating, is coupled out by the second coupling-out grating and realizes one-dimensional pupil expansion, thereby realizing binocular display while improving light efficiency and reducing light leakage, and is also conducive to realizing binocular fusion.

[0014] The grating layer also includes a first turning grating and a second turning grating, wherein the first turning grating is located on one side of the symmetry plane M, and the second turning grating is located on the other side of the symmetry plane M. The first diffraction light propagating to one side of the symmetry plane M first propagates to the first turning grating and then to the first out-coupling grating, and the second diffraction light propagating to the other side of the symmetry plane M first propagates to the second turning grating and then to the second out-coupling grating, thereby realizing two-dimensional pupil expansion.

[0015] In a third aspect, a single-entry-pupil binocular head-mounted display product is provided, which includes a micro-projection optical machine and the above-mentioned optical waveguide, wherein the micro-projection optical machine is arranged opposite to the coupling grating in the optical waveguide.

[0016] The present solution adopts the above-mentioned optical waveguide, which adopts the above-mentioned volume holographic grating as the coupling-in grating, and can diffract the image light beam to produce the first diffraction light and the second diffraction light with symmetrical propagation directions and balanced diffraction energy. The first diffraction light propagates to one side of the symmetry plane M to the first coupling-out grating, is coupled out by the first coupling-out grating and realizes one-dimensional pupil expansion, and the second diffraction light propagates to the other side of the symmetry plane M to the second coupling-out grating, is coupled out by the second coupling-out grating and realizes one-dimensional pupil expansion, thereby realizing binocular display while improving the light efficiency and reducing light leakage, and is also conducive to realizing binocular fusion.

[0017] Compared with the prior art, the present solution has the following beneficial effects: the volume holographic grating in the present solution uses two gratings (a first grating and a second grating) that are symmetrical in the grating vector plane so that after the light beam is diffracted, a first diffracted light and a second diffracted light with symmetrical propagation directions and balanced diffraction energies can be generated, thereby realizing binocular display and facilitating binocular fusion. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 This is the main view of a one-dimensional pupil expansion single-entry binocular waveguide.

[0020] Figure 2 This is the front view of a 2D pupil expansion single-entry binocular waveguide.

[0021] Figure 3 This is a top view of a double-stacked bidirectional volume holographic grating.

[0022] Figure 4 This is a top view of a single-layer multiplexed bidirectional volume holographic grating.

[0023] Figure 5 This is a top view of the spatially divided bidirectional volume holographic grating.

[0024] Figure 6 A top view of a partially single-layer multiplexed spatially partitioned bidirectional volume holographic grating.

[0025] Figure 7 The coupling grating adopts Figure 3 A top view of a head-mounted display product with a double-layer stacked holographic grating is shown.

[0026] Figure 8 The coupling grating adopts Figure 4 A top view of a head-mounted display product with a single-layer multiplexed volume holographic grating.

[0027] Fig. 9 The coupling grating adopts Figure 5 A top view of a head-mounted display product with a spatially divided volume holographic grating is shown.

[0028] Fig.10 The coupling grating adopts Figure 6 A top view of a head-mounted display product with a spatially divided volume holographic grating is shown.

[0029] Fig.11 A top view of a spatially partitioned bidirectional volume holographic grating with extended angular bandwidth.

[0030] Description of the reference numerals: micro-projection optical engine 100 , waveguide layer 200 , coupling-in grating 310 , first grating 311 , second grating 312 , first coupling-out grating 321 , second coupling-out grating 322 , first turning grating 331 , second turning grating 332 . 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] Figures 7-10 The diagram shows a possible head-mounted display product. The head-mounted display product is a single-pupil binocular head-mounted display product, which is equipped with a micro-projection optical machine 100 and an optical waveguide. The optical waveguide is a single-pupil binocular optical waveguide, which can be divided into a left area, a middle area and a right area. The left area is located on the left side of the middle area, and the right area is located on the right side of the middle area. The middle area is opposite to the micro-projection optical machine 100. The micro-projection optical machine 100 is similar to a projector, and projects an image beam with a virtual image from the middle area of ​​the optical waveguide into the optical waveguide. The optical waveguide transmits the image beam from the micro-projection optical machine 100 to the left and right sides and couples it out into the left and right eyes of the person to form a virtual image, realizing different effects such as virtual reality (VR), augmented reality (AR), and mixed reality (MR). According to different effects, head-mounted display products can be divided into different types. Among them, VR head-mounted display products are the carriers of virtual reality technology. Through computer technology, etc., a three-dimensional virtual world that allows the wearer to interact with it is generated, so that the wearer has an immersive feeling. AR head-mounted display products are the carriers of augmented reality technology. Through computer technology, virtual information is applied 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 head-mounted display products are the carriers of mixed reality technology, combining the characteristics of VR and AR, allowing the wearer to interact with the real and virtual environment.

[0033] The head display product generally includes a bracket, which is used to install and fix the micro-projection optical machine 100 and the optical waveguide so that the relative positions of the micro-projection optical machine 100 and the optical waveguide are fixed, and is also used to achieve wearing so that the optical waveguide is directly in front of the wearer's eyes when the wearer wears the head display product.

[0034] Figures 1-2A possible single-entry-pupil binocular waveguide is illustrated, and the optical waveguide is configured with a waveguide layer 200 and a grating layer, and both the waveguide layer 200 and the grating layer are layered structures and are stacked. The waveguide layer 200 runs through the left region, the middle region, and the right region of the optical waveguide, and has two opposite surfaces, namely, a first surface and a second surface. The grating layer can be arranged on the surface or inside of the waveguide layer 200, specifically, it can be arranged on the first surface of the waveguide layer 200, it can also be arranged on the second surface of the waveguide layer 200, and it can also be arranged between the first surface and the second surface of the waveguide layer 200 to form a stacked structure with the waveguide layer 200.

[0035] The waveguide layer 200 is generally made of a material with a high refractive index. The waveguide layer 200 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 200 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 θ of total reflection. 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 200 are attached with only the incident angle absolute value 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 r The 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 200. This propagation can be called high reflection propagation. Whether it is total reflection propagation or high reflection propagation, the waveguide layer 200 can realize back and forth reflection propagation of light.

[0036] Figure 1 In the optical waveguide shown, the grating layer is configured with an in-coupling grating 310, a first out-coupling grating 321, and a second out-coupling grating 322. The in-coupling grating 310 is located in the middle area of ​​the optical waveguide, and is used to couple the image beam into the waveguide layer 200, so that the image beam can be reflected back and forth in the waveguide layer 200 and evenly distribute the image beam to the left and right areas of the optical waveguide. The first out-coupling grating 321 is located in the left area of ​​the optical waveguide, and the second out-coupling grating 322 is located in the right area of ​​the optical waveguide, and is used to expand the range of the image beam in one direction to achieve one-dimensional pupil expansion, and couple the image beam out of the waveguide layer 200, so that the image beam that is reflected back and forth in the waveguide layer 200 can be emitted outside the waveguide layer 200 and enter the left eye and the right eye of the person respectively.

[0037] Figure 2In the optical waveguide shown, the grating layer is not only configured with an in-coupling grating 310, a first out-coupling grating 321 and a second out-coupling grating 322, but also configured with a first turning grating 331 and a second turning grating 332. The first turning grating 331 is located in the left region of the optical waveguide, and the second turning grating 332 is located in the right region of the optical waveguide, and is used to change the propagation direction of the image light beam in the waveguide layer 200 and expand the light beam range in another direction to achieve two-dimensional pupil expansion.

[0038] The coupling-in grating 310, the first coupling-out grating 321, the second coupling-out grating 322, the first turning grating 331 and the second turning grating 332 can all adopt volume holographic gratings or surface relief gratings. In contrast, the optical waveguide using volume holographic gratings has the advantages of improving light efficiency and reducing light leakage. In particular, the volume holographic grating used in the coupling-in grating 310 is a bidirectional volume holographic grating, which is different from an ordinary volume holographic grating and can propagate the image light beam symmetrically in the left and right directions and evenly distribute the diffraction energy propagating in two directions.

[0039] Figures 3 to 6 FIG. 4 illustrates possible bidirectional volume holographic gratings, which are used to couple into the light beam L0 and can be used as coupling gratings 310 in a single-entry-pupil binocular waveguide. Figures 3 to 7 As shown, the bidirectional volume holographic grating is a layered structure with two parallel and opposite surfaces, which can be called grating surfaces. The bidirectional volume holographic grating includes a first grating 311 and a second grating 312, which are arranged between the two grating surfaces and can diffract the light beam into direct light (zero-order light) and diffracted light (first-order light). The grating vector of the volume holographic grating is usually defined as a vector with a value of 2π / P perpendicular to the grating Bragg plane. In the present bidirectional volume holographic grating, the first grating 311 has a first grating 311 vector, and the second grating 312 has a second grating 312 vector. The first grating 311 vector is symmetrical with the second grating 312 vector, and has a symmetry plane M, which is perpendicular to the grating surface, so that the first diffracted light generated by the light beam after diffracting the first grating 311 propagates to one side of the symmetry plane M, and the second diffracted light generated after diffracting the second grating 312 propagates to the other side of the symmetry plane M, and the diffraction energy of the first diffracted light and the second diffracted light is balanced.

[0040] When used as the coupling grating 310 of the single-entry-pupil binocular optical waveguide, the symmetry plane M of the two-way volume holographic grating can be made perpendicular to the left-right direction of the optical waveguide, so that the left area of ​​the single-entry-pupil binocular optical waveguide is located on one side of the symmetry plane M, the right area is located on the other side of the symmetry plane M, the first coupling-out grating 321 and the first turning grating 331 are located on one side of the symmetry plane M, and the second coupling-out grating 322 and the second turning grating 332 are located on the other side of the symmetry plane M. After the image light beam is projected into the two-way volume holographic grating, it will be diffracted by the first grating 311 and the second grating 312 to generate the first diffracted light and the second diffracted light with balanced diffraction energy and symmetrical propagation in the left and right directions, wherein the first diffracted light propagates to the left, and after being coupled out by the first coupling-out grating 321, enters the left eye E of the person. L , and the second diffracted light propagates to the right, is coupled out by the second coupling grating 322, and then enters the right eye E of the human body. R ,like Figures 7-10 , realizing binocular display, is conducive to binocular fusion.

[0041] When the light beam L0 is projected into the bidirectional volume holographic grating, it can first be incident on the first grating 311 and then on the second grating 312. When incident on the first grating 311, it will be diffracted into the first diffracted light L 11 And the first straight light L 12 , where the first diffracted light L 11 When the incident light continues to enter the second grating 312, most of it will be directly transmitted and enter the waveguide layer 200 due to the deviation from the Bragg wave vector matching condition, while the first straight light L 12 When it continues to be incident on the second grating 312, it will be diffracted into the second diffracted light L 21 and the second straight light L 22 , where the second diffracted light L 21 will enter the waveguide layer 200, and the second straight light L 22 The light will pass through the waveguide layer 200 and become loss light.

[0042] When the light beam L0 is projected into the bidirectional volume holographic grating, it can also be incident on the second grating 312 first and then on the first grating 311. When incident on the second grating 312, it will be diffracted into the second diffracted light L 21 and the second straight light L 22 , where the second diffracted light L 21 When the light continues to be incident on the first grating 311, most of it will be directly transmitted and enter the waveguide layer 200 due to the deviation from the Bragg wave vector matching condition, while the second straight light L 22 When it continues to be incident on the first grating 311, it will be diffracted into the first diffracted light L 11 And the first straight light L 12 , where the first diffracted light L 11 will enter the waveguide layer 200, and the first straight light L 12The light will pass through the waveguide layer 200 and become loss light.

[0043] For the case where the light beam L0 is incident on the first grating 311 and the second grating 312 successively, assuming that the energy of the light beam L0 is A, the first-order diffraction efficiency of the first grating 311 is η1, the first-order diffraction efficiency of the second grating 312 is η2, and the ratio of the first grating 311 to diffract the light beam before the second grating 312 is ρ. Considering that the energy of volume holographic diffraction mainly exists in the zero-order light and the first-order light, and the energy of other orders is negligible, the energy of the light beam L0 incident on the first grating 311 and the energy of the light beam L0 incident on the second grating 312 are Aρ and A(1-ρ) respectively. For the part incident on the first grating 311 first, the first diffracted light L0 generated by diffraction is 11 And the first straight light L 12 The energies of are Aρη1 and Aρ(1-η1) respectively, and the second diffraction light L generated by continued diffraction 21 and the second straight light L 22 The energies of are Aρ(1-η1)η2 and Aρ(1-η1)(1-η2) respectively. For the part that first enters the second grating 312, the diffraction generated by the second diffraction light L 21 and the second straight light L 22 The energies of are A(1-ρ)η2 and A(1-ρ)(1-η2), and the first diffraction light L generated by continued diffraction 11 And the first straight light L 12 The energies of are A(1-ρ)(1-η2)η1 and A(1-ρ)(1-η2)(1-η1) respectively. Therefore, the first diffracted light L generated by the light beam L0 diffracting through the bidirectional volume holographic grating is 11 and the second diffracted light L 21 The energies of are Aρη1+A(1-ρ)(1-η2)η1 and Aρ(1-η1)η2+A(1-ρ)η2 respectively. When Aρη1+A(1-ρ)(1-η2)η1=Aρ(1-η1)η2+A(1-ρ)η2 holds true, that is, the first-order diffraction efficiency η1 of the first grating 311 and the first-order diffraction efficiency η2 of the second grating 312 satisfy: η1 / η2=(1-ρη1) / (1-(1-ρ)η2), the diffraction energies of the first diffracted light and the second diffracted light are balanced. The first-order diffraction efficiency η1 of the first grating 311 and the first-order diffraction efficiency η2 of the second grating 312 can be adjusted by adjusting parameters such as the refractive index modulation of the first grating 311 and the second grating 312 respectively, so that their first-order diffraction efficiencies satisfy the above relationship. The refractive index modulation of the grating can be precisely controlled by adjusting the material ratio, exposure dose (exposure power and time), etc.

[0044] When the light beam L0 is projected into the bidirectional volume holographic grating, it can also be incident on the first grating 311 and the second grating 312 in no particular order, and is diffracted by the first grating 311 into the first diffracted light L 11 And the first straight light L 12 , is diffracted by the second grating 312 into the second diffracted light L 21 and the second straight light L 22 Among them, the first diffracted light L 11 and the second diffracted light L 21 will enter the waveguide layer 200, and the first straight light L 12 and the second straight light L 22 The light will pass through the waveguide layer 200 and become loss light.

[0045] For the case where the light beam L0 is incident on the first grating 311 and the second grating 312 at the same time, assuming that the energy of the light beam L0 is A, the probability of it being incident on the first grating 311 is σ1, the probability of it being incident on the second grating 312 is σ2, the first-order diffraction efficiency of the first grating 311 is η1, and the first-order diffraction efficiency of the second grating 312 is η2, then the first diffraction light L generated by diffraction is 11 and the second diffracted light L 21 The energies of the first diffracted light and the second diffracted light are Aσ1η1 and Aσ2η2 respectively. When Aσ1η1=Aσ1η2 holds true, the diffraction energies of the first diffracted light and the second diffracted light are balanced. The probability σ1 of the light beam L0 incident on the first grating 311 is related to the area s1 and thickness h1 of the first grating 311, and the probability σ1 of the light beam L0 incident on the second grating 312 is related to the area s2 and thickness h2 of the second grating 312. If s1 and s2 are large enough or equal, and h1 and h2 are large enough or equal, then σ1=σ2. Therefore, as long as the first-order diffraction efficiency η1 of the first grating 311 and the first-order diffraction efficiency η2 of the second grating 312 are equal, and at the same time, the area s1 of the first grating 311 and the area s2 of the second grating 312 are large enough or equal, and the thickness h1 of the first grating 311 and the thickness h2 of the second grating 312 are large enough or equal, the diffraction energies of the first diffracted light and the second diffracted light can be balanced.

[0046] The bidirectional volume holographic grating can be configured as a double-layer stacked structure, such as Figure 3As shown, the first grating 311 and the second grating 312 are stacked, and the stacking direction is perpendicular to the grating surface. The double-layer stacked bidirectional volume holographic grating belongs to the situation where the light beam is incident on the first grating 311 and the second grating 312 successively, and the proportion ρ of the first grating 311 diffracting the light beam before the second grating 312 is either 100% or 0%. If the first grating 311 and the second grating 312 diffract the light beam in sequence, that is, ρ = 100%, then the first-order diffraction efficiency η1 of the first grating 311 and the first-order diffraction efficiency η2 of the second grating 312 meet: When η1 / η2 = 1-η1, the diffraction energy of the first diffracted light and the second diffracted light is balanced. If the second grating 312 and the first grating 311 diffract the light beam in sequence, that is, ρ=0%, the first-order diffraction efficiency η1 of the first grating 311 and the first-order diffraction efficiency η2 of the second grating 312 satisfy: η1 / η2=1-η2, and the diffraction energy of the first diffracted light and the second diffracted light is balanced.

[0047] Bidirectional volume holographic gratings can also be configured as single-layer multiplexing structures, such as Figure 4 As shown, the first grating 311 and the second grating 312 completely overlap. The single-layer multiplexed bidirectional volume holographic grating belongs to the situation that the light beam is incident on the first grating 311 and the second grating 312 successively. The proportion ρ of the first grating 311 diffracting the light beam before the second grating 312 is close to or equal to 50%, and the first-order diffraction efficiency η1 of the first grating 311 is close to or equal to the first-order diffraction efficiency η2 of the second grating 312. Volume holographic gratings are generally made by exposing photosensitive materials. The single-layer multiplexed bidirectional volume holographic grating needs to be exposed twice, one time to make the first grating 311, and the other time to make the second grating 312. Based on the characteristics of the photosensitive material, the two exposure processes should avoid full exposure, and generally speaking, the exposure doses of the two exposures should be different. The diffraction efficiency of the first grating 311 and the second grating 312 can be measured experimentally and the exposure doses of the two exposures can be continuously adjusted to obtain the best exposure dose data.

[0048] Bidirectional volume holographic gratings can also be configured as space-dividing structures, such as Figure 5 As shown, the first grating 311 and the second grating 312 are arranged in a tiled manner, and the tiled direction is perpendicular to the symmetry plane M. The space-divided bidirectional volume holographic grating belongs to the case where the light beam is incident on the first grating 311 and the second grating 312 at the same time. The first grating 311 and the second grating 312 can be fully exposed to obtain the maximum first-order diffraction efficiency. Since the first grating 311 vector and the second grating 312 vector are symmetrical in the plane, the maximum first-order diffraction efficiency of the first grating 311 and the second grating 312 must be equal. As long as the area s1 of the first grating 311 and the area s2 of the second grating 312 are large enough or equal, and the thickness h1 of the first grating 311 and the thickness h2 of the second grating 312 are large enough or equal, the diffraction energy of the first diffracted light and the second diffracted light can be balanced.

[0049] The bidirectional volume holographic grating can also be configured as a combination of the above three structures. Figure 6 A partially single-layer multiplexed spatially divided bidirectional volume holographic grating is illustrated, wherein the first grating 311 and the second grating 312 are tiled and partially overlapped, and the tiled direction is perpendicular to the symmetry plane M.

[0050] In order to expand the field of view, the volume holographic grating often expands the angular bandwidth of the grating by spatial distribution of the grating vector or angle multiplexing. This method of expanding the angular bandwidth can also be used in combination with the above-mentioned bidirectional volume holographic grating. For example, Fig.11 The illustrated spatially divided bidirectional volume holographic grating reuses two sets of grating vectors on the first grating 311 and the second grating 312 respectively to expand the angular bandwidth of each grating, so that the incident light beam within the field of view angle range can be coupled to the left and right sides of the optical waveguide with high and balanced diffraction efficiency.

[0051] 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. A single-entry-pupil binocular head-mounted display product, comprising a micro-projection optical engine and an optical waveguide, wherein the optical waveguide comprises a waveguide layer and a grating layer stacked in layers, wherein the grating layer comprises an in-coupling grating, a first out-coupling grating and a second out-coupling grating, and wherein the micro-projection optical engine is arranged opposite to the in-coupling grating; characterized in that: The coupling-in grating is a volume holographic grating, which has two parallel and opposite grating surfaces, and a first grating and a second grating arranged between the two grating surfaces, the first grating has a first grating vector, and the second grating has a second grating vector; the first grating vector is symmetrical with the second grating vector, and has a symmetry plane M, and the symmetry plane M is perpendicular to the grating surface, so that the first diffraction light generated after the light beam is diffracted by the first grating propagates to one side of the symmetry plane M, and the second diffraction light generated after the light beam is diffracted by the second grating propagates to the other side of the symmetry plane M, and the diffraction energy of the first diffraction light and the second diffraction light is balanced; the first coupling-out grating is located on one side of the symmetry plane M, and the second coupling-out grating is located on the other side of the symmetry plane M.

2. The single-entry-pupil binocular head-mounted display product according to claim 1, characterized in that: The ratio of the first grating diffracting the light beam before the second grating is ρ, and the first-order diffraction efficiency η1 of the first grating and the first-order diffraction efficiency η2 of the second grating satisfy: η1 / η2=(1-ρη1) / (1-(1-ρ)η2).

3. The single-entry-pupil binocular head-mounted display product according to claim 1 or 2, characterized in that: The first grating and the second grating are stacked, and the stacking direction is perpendicular to the grating surface.

4. The single-entry-pupil binocular head-mounted display product according to claim 3, characterized in that: The first grating and the second grating diffract the light beam in sequence, and the first-order diffraction efficiency η1 of the first grating and the first-order diffraction efficiency η2 of the second grating satisfy: η1 / η2=1-η1.

5. The single-entry-pupil binocular head-mounted display product according to claim 1 or 2, characterized in that: The first grating and the second grating completely overlap.

6. The single-entry-pupil binocular head-mounted display product according to claim 1, characterized in that: The first grating and the second grating diffract the light beam simultaneously, the first-order diffraction efficiency η1 of the first grating and the first-order diffraction efficiency η2 of the second grating satisfy: η1=η2, the area s1 of the first grating and the area s2 of the second grating satisfy: s1=s2, the thickness h1 of the first grating and the thickness h2 of the second grating satisfy: h1=h2.

7. The single-entry-pupil binocular head-mounted display product according to claim 1 or 6, characterized in that: The first grating and the second grating are tiled, and the tiling direction is perpendicular to the symmetry plane M.

8. The single-entry-pupil binocular head-mounted display product according to any one of claims 1, 2 or 6, characterized in that: The first grating and the second grating are tiled and partially overlapped, and the tiling direction is perpendicular to the symmetry plane M.

9. The single-entry-pupil binocular head-mounted display product according to any one of claims 1, 2 or 6, characterized in that: The first grating has more than two first grating vectors, the second grating has more than two second grating vectors, and the number of the first grating vectors is the same as the number of the second grating vectors.

10. The single-entry-pupil binocular head-mounted display product according to any one of claims 1, 2 or 6, characterized in that: The grating layer further includes a first turning grating and a second turning grating. The first turning grating is located on one side of the symmetry plane M, and the second turning grating is located on the other side of the symmetry plane M.

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