Metasurface-based coupling waveguide structure and AR display system

Abstract

The invention relates to a coupling waveguide structure based on a metasurface and an AR display system, and belongs to the technical field of optical display, the coupling waveguide structure sequentially comprises a main lens, a first metasurface and a combined second metasurface in the light incidence direction, and the combined second metasurface is fixedly connected with the first metasurface; the first metasurface has the following functions that left-handed polarized light incident from the main lens is reflected, and a reflected light field is changed into right-handed polarized light; the right-handed polarized light incident from the main lens is projected, transmission light is converted into left-handed polarized light, and the left-handed polarized light continues to be propagated forwards; the combined second metasurface has the following functions: reflecting the left-handed polarized light transmitted by the first metasurface, and changing the reflected light into right-handed polarized light; the light reflected by the second metasurface is subjected to total reflection propagation in the main lens. According to the invention, one-dimensional pupil expansion is realized through the design of the two metasurfaces.

Description

Technical Field

[0001] The present invention belongs to the field of optical display technology, and in particular relates to a coupled waveguide structure based on a metasurface and an AR display system. Background Art

[0002] With the development of science and technology, three-dimensional display and human-computer interaction have gradually entered people's lives. For example, intelligent driving assistance for vehicles, AR swimming goggles, head-mounted VR somatosensory games, etc. At present, the mainstream AR display solutions include holographic diffraction waveguide solution, diffraction waveguide solution, and free-form surface solution.

[0003] However, the traditional AR display system has a small eye movement range, which reduces the wearer's viewing experience. At the same time, the problem of low coupling efficiency leads to a decrease in display effect in strong light environments. Summary of the invention

[0004] The present application provides a coupled waveguide structure and an AR display system based on a metasurface to at least solve the above technical problems existing in the prior art.

[0005] On the one hand, an embodiment of the present application provides a coupled waveguide structure based on a metasurface, which includes a main lens, a first metasurface, and a combined second metasurface in sequence along the incident direction of light, wherein the combined second metasurface is fixedly connected to the first metasurface;

[0006] The first metasurface has the following functions:

[0007] a. Reflecting the left-handed polarized light incident from the main lens and converting the reflected light field into right-handed polarized light;

[0008] b. Projecting the right-handed polarized light incident from the main lens and converting the transmitted light into left-handed polarized light, which continues to propagate forward;

[0009] The combined second metasurface has the following functions:

[0010] a. reflecting the left-handed polarized light transmitted by the first metasurface and converting the reflected light into right-handed polarized light;

[0011] b. The light reflected by the second metasurface is transmitted through total reflection in the primary lens.

[0012] In one possible implementation manner, the deflection angle of the first metasurface for left-handed circularly polarized light should satisfy:

[0013]

[0014] The refractive index of the main lens is n1, and the incident angle of the light reflected from the first metasurface to the main lens is θ l1 .

[0015] In one embodiment, the incident angle θ of the reflected light propagating to the first metasurface is l2 The incident angle of the light reflected from the first metasurface onto the main lens is θ l1 The angles are the same.

[0016] In one possible implementation manner, the first metasurface is a rectangular structure or a combination of multiple rectangular structures to achieve control of polarization characteristics.

[0017] In one possible implementation manner, the first supersurface is composed of a plurality of nanocolumns, and the length L, width W and orientation angle θ of any nanocolumn can be adjusted according to design requirements.

[0018] In one possible implementation manner, the combined second supersurface includes a bonding layer and a second supersurface attached to the bonding layer, and the bonding layer is used to fixedly connect the first supersurface and the second supersurface.

[0019] In one possible implementation, the thickness of the second metasurface is adjustable, and the reflection angle is determined by a total reflection condition.

[0020] In one possible implementation, the modulation angle of the second metasurface satisfies:

[0021]

[0022] n m is the refractive index of the bonding layer, and n1 is the refractive index of the first metasurface substrate.

[0023] In one embodiment, the right-handed polarized light after the combination of the second metasurface reflection and the first metasurface base refraction is θ l2 It is transmitted by total reflection in the primary mirror.

[0024] On the other hand, an embodiment of the present application provides an AR display system, including a display device, a collimation device and any one of the above-mentioned coupled waveguide structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the optical path of light propagating on the first metasurface and the combined second metasurface in an embodiment of the present application.

[0026] Figure 2 is a structural diagram of an AR display system in an embodiment of the present application;

[0027] Figure 3 is a schematic diagram of phase distribution of a rectangular structure under x-polarization in an embodiment of the present application;

[0028] Figure 4 is a schematic diagram of phase distribution of a rectangular structure under y polarization in an embodiment of the present application;

[0029] Figure 5 is a schematic diagram of phase distribution of a rectangular structure under x and y polarizations in an embodiment of the present application;

[0030] Figure 6 This is a typical schematic diagram of the arrangement of polarization metasurface nanostructures in the embodiment of the present application;

[0031] Figure 7 This is another typical schematic diagram of polarization metasurface nanostructure arrangement in the embodiment of the present application; DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0033] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application 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 operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0034] refer to Figure 1 The present application discloses a coupled waveguide structure based on a metasurface, which includes a main lens 11, a first metasurface 12 and a combined second metasurface in sequence along the incident direction of light, and the combined second metasurface is fixedly connected to the first metasurface 12.

[0035] One of the functions of the first metasurface 12 attached to the main lens 11 is to reflect all left-handed polarized light incident on the first metasurface 12 from the main lens 11, and the reflected light field becomes right-handed polarized light. The reflection angle is determined by the total reflection condition. If the refractive index of the main lens 11 is n1, the deflection angle of the first metasurface 12 to the left-handed circularly polarized light should satisfy:

[0036]

[0037] At the same time, the second function of the first metasurface 12 is to transmit all the right-handed polarized light incident on the first metasurface 12 from the main lens in the original propagation direction, and convert it into left-handed polarized light, which continues to propagate forward.

[0038] The super surface microstructure uses a rectangular structure or a combination of multiple rectangular structures to achieve the control of polarization characteristics. The length L and width W of the nanocolumn and the orientation angle θ can be adjusted according to the design requirements. The material is mainly a-si, and the height is adjustable from 200 to 1000nm.

[0039] The combined second metasurface includes a bonding layer 13 and a second metasurface 14 attached to the bonding layer 13. The bonding layer 13 is used to firmly connect the first metasurface 12 with the second metasurface 14. Since the refractive index of the material is not 1, the bonding layer 13 needs to participate in the optimization process of the second metasurface 14. Therefore, the bonding layer 13 and the second metasurface 14 can be regarded as the same device. That is, the combined second metasurface needs to be optimized.

[0040] The function of the combined second metasurface is to reflect all the left-handed polarized light transmitted by the first metasurface 12, and the reflected light becomes right-handed polarized light. The incident angle of the reflected light propagating to the first metasurface 12 is θ l2 , the incident angle of the light reflected by the first metasurface 12 to the main lens is θ l1 . Both should meet:

[0041] θ l2 =θ l1

[0042] The refractive index of the bonding layer 13 is n m , the refractive index of the first metasurface 12 substrate is n1, and the modulation angle of the second metasurface 14 should satisfy:

[0043]

[0044] The right-handed polarized light after the combination of the second metasurface reflection and the first metasurface 12 base refraction is θ l2 The light is totally reflected in the main mirror 11.

[0045] The present application also discloses an AR display system, such as Figure 2 The figure shows the overall structure of the AR display system. The AR display system includes a display device, a collimating device arranged at the front end of the display device, and any of the above-mentioned coupled waveguide structures 1. The coupled waveguide structure 1 includes a main lens 11, a first metasurface 12, a bonding layer 13, and a second metasurface 14. The collimating device can be a collimating mirror 2, and the display device can be a display 3. The display 3 has a built-in polarization modulation device that can generate left-handed and right-handed polarized light in time. Similarly, an external optical system can be used to achieve the generation of left-handed and right-handed polarized light. The display 3 is loaded with the image to be displayed, and the virtual scene is dynamically switched. The collimating mirror 2 is used to collimate the light emitted by the display 3 and then vertically incident on the main lens 11. The distance from the collimating mirror 2 to the light-emitting plane of the display 3 is the back focal length of the collimating mirror 2, and f is the back focal length of the collimating mirror 2.

[0046] The material of the main lens 11 is glass, and its refractive index is 1.74. According to the formula:

[0047]

[0048] It can be seen that the minimum transmission angle of the primary lens 11 is 35.07°. To increase the bandwidth of the transmission in the waveguide, a material with a higher refractive index is required.

[0049] After the light is vertically incident on the first metasurface 12, the first metasurface 12 is a-si, with a height of 600nm and a refractive index of 3.2; as follows Figure 3 The phase distribution of the nanorod length and width under x-polarized incidence. Its length is 50nm and the cut-off length is 400nm; as follows Figure 4 is the phase distribution of the length and width of the nanorod under y-polarized incidence. Its length is 50nm and the cut-off length is 400nm; according to Figure 3 and Figure 4 The data can be used to solve the phase difference under two polarization states, and the following is obtained: Figure 5 The phase difference distribution shown in FIG. The black circled points are points with a phase difference of pi. Considering the actual processing technology, 170*270nm nanorods are selected. The selection method of the second metasurface 14 is the same. However, considering the actual deflection angle difference, the arrangement of the PB phase is different. Figure 6 The change in the rotation angle θ of the nanorods shown determines the actual distribution of the PB phase. The relationship is

[0050]

[0051] In addition, Figure 7 As shown, the same modulation function can also be achieved by multiple rectangular structures.

[0052] The left-handed polarized light is modulated by the first metasurface 12 and reflected, and enters the main lens at an angle of 36°. At the same time, the left-handed polarized light is converted into right-handed polarized light. The right-handed polarized light part directly passes through the first metasurface 12, and the propagation direction does not change, but the polarization state is converted from right-handed to left-handed. Figure 1 As shown, the light propagates to the bonding layer 13 without any deflection, and only a linear optical path accumulation is generated. The light continues to propagate forward to the second metasurface 14, at which time the left-handed polarized light transmitted by the first metasurface 12 is completely reflected, and the reflected light becomes right-handed polarized light. The incident angle of the reflected light propagating to the first metasurface 12 is θ l2 , the incident angle of the light reflected by the first metasurface 12 to the main lens is θ l1 Both should satisfy

[0053] θ l1 =θ l2

[0054] Refractive index n m , the refractive index of the first metasurface 12 substrate is n1,

[0055]

[0056] The right-handed polarized light after being reflected by the second metasurface 14 and refracted by the first metasurface 12 is θ l2 Total reflection propagates in the primary lens 11. Due to the existence of the bonding layer 13 and the second metasurface 12, the thickness of the bonding layer 13 is d m , and a one-dimensional pupil dilation is achieved. The pupil dilation value is calculated as follows:

[0057] Δl=d m tanθ

[0058] After multiple total reflections by the primary lens 11, the image loaded on the display 3 is transmitted to the human eye through the outcoupling waveguide, thereby realizing the viewing of the virtual scene. At the same time, the human eye can directly observe the real scene through the primary lens.

[0059] The above are only specific embodiments of the present disclosure, but the protection scope of the present disclosure is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present disclosure, which should be included in the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.

Claims

1. A coupled waveguide structure based on a metasurface, characterized in that: The main lens, the first metasurface and the combined second metasurface are sequentially included along the incident direction of the light, and the combined second metasurface is fixedly connected to the first metasurface; The first metasurface has the following functions: a. Reflecting the left-handed polarized light incident from the main lens and converting the reflected light field into right-handed polarized light; b. Projecting the right-handed polarized light incident from the primary lens and converting the transmitted light into left-handed polarized light, which continues to propagate forward; The combined second metasurface has the following functions: a. reflecting the left-handed polarized light transmitted by the first metasurface and converting the reflected light into right-handed polarized light; b. The light reflected by the second metasurface is transmitted through total reflection in the primary lens.

2. A coupled waveguide structure based on a metasurface according to claim 1, characterized in that: The deflection angle of the first metasurface for left-handed circularly polarized light should satisfy: The refractive index of the main lens is n1, and the incident angle of the light reflected from the first metasurface to the main lens is θ l1 .

3. A coupled waveguide structure based on a metasurface according to claim 2, characterized in that: The incident angle θ of the reflected light propagating to the first metasurface l2 The incident angle of the light reflected from the first metasurface onto the main lens is θ l1 The angles are the same.

4. The coupled waveguide structure based on a metasurface according to claim 1, characterized in that: The first metasurface is a rectangular structure or a combination of multiple rectangular structures to achieve control of polarization characteristics.

5. The coupled waveguide structure based on a metasurface according to claim 4, characterized in that: The first super surface is composed of a plurality of nano-columns, and the length L, width W and orientation angle θ of any nano-column can be adjusted according to design requirements.

6. The coupled waveguide structure based on a metasurface according to claim 1, characterized in that: The combined second supersurface includes a bonding layer and a second supersurface attached to the bonding layer, and the bonding layer is used to fixedly connect the first supersurface and the second supersurface.

7. The coupled waveguide structure based on a metasurface according to claim 6, characterized in that: The thickness of the second metasurface is adjustable, and the reflection angle is determined by the total reflection condition.

8. The coupled waveguide structure based on a metasurface according to claim 6, characterized in that: The modulation angle of the second metasurface satisfies: n m is the refractive index of the bonding layer, and n1 is the refractive index of the first metasurface substrate.

9. The coupled waveguide structure based on a metasurface according to claim 6, characterized in that: The right-handed polarized light after the combination of the second metasurface reflection and the first metasurface base refraction is θ l2 It is transmitted by total reflection in the primary mirror.

10. An AR display system, characterized in that: The invention comprises a display device, a collimating device and any one of the coupled waveguide structures in claims 1-9.

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