Planar metalens array for hemispherical ultra-wide-angle imaging and its fabrication method

Abstract

This invention provides a planar metalens array for hemispherical ultra-wide-angle imaging and its fabrication method. The planar metalens array for hemispherical ultra-wide-angle imaging includes: a substrate; and a plurality of planar metalenses located on the substrate, the plurality of planar metalenses being arranged according to a predetermined period, the rotation angle of each planar metalens corresponding to its position, and the position of each planar metalens corresponding to its order. This invention enables hemispherical ultra-wide-angle imaging using planar optical elements within an ultra-compact scale, reducing distortion while improving system integration.

Description

Technical Field

[0001] This invention relates to the field of optical imaging technology, and more specifically, to a planar meta-lens array for hemispherical ultra-wide-angle imaging and its fabrication method. Background Technology

[0002] Wide-angle imaging systems are imaging systems that can provide a wider field of view. Compared with ordinary imaging systems, wide-angle imaging can capture more information, and therefore has attracted much attention in fields such as satellite positioning, autonomous driving, and real-time monitoring. However, traditional wide-angle imaging systems are composed of multiple optical lenses, making them large and heavy. Fisheye lenses that can achieve a hemispherical field of view require even more precise assembly. Furthermore, because the front lens protrudes outward, it is difficult to install lens protection devices, which not only easily damages the system but also limits its application in integrated optics. Summary of the Invention

[0003] The main objective of this invention is to provide a planar meta-lens array for hemispherical ultra-wide-angle imaging and its fabrication method, which reduces distortion while improving system integration.

[0004] To achieve the above objectives, embodiments of the present invention provide a planar meta-lens array for hemispherical ultra-wide-angle imaging, comprising:

[0005] Substrate; and

[0006] Multiple planar metalenses are located on the substrate. The multiple planar metalenses are arranged according to a preset period. The rotation angle of the planar metalenses corresponds to the position of the planar metalenses, and the position of the planar metalenses corresponds to the order of the planar metalenses.

[0007] In one embodiment, the phase distribution of the planar metalens depends on the incident angle, wavelength, distance from the origin of the planar metalens, focal length of the planar metalens, and distance between the focal centers.

[0008] In one embodiment, the focal center distance depends on the incident angle and the focal length of the planar metalens.

[0009] In one embodiment, the period of the planar metalens array corresponds to the wavelength of the planar metalens.

[0010] In one embodiment, the rotation angle of the planar meta-lens corresponding to the position of the planar meta-lens includes:

[0011] The rotation angle of the planar meta-lens corresponds to the angle between the position coordinates of the planar meta-lens and the horizontal axis.

[0012] This invention also provides a method for fabricating a planar meta-lens array for hemispherical ultra-wide-angle imaging as described above, comprising:

[0013] Provide a base;

[0014] With the center of the substrate as the origin, planar metalenses of various orders are arranged on the corresponding coordinate axes;

[0015] Determine the corresponding order of planar metalenses based on the location to be filled;

[0016] Rotate the planar metalens according to the rotation angle of the planar metalens to obtain a planar metalens array.

[0017] In one embodiment, it further includes:

[0018] The rotation angle of the planar meta-lens is determined based on its position.

[0019] In one embodiment, arranging planar metalenses of various orders on corresponding coordinate axes includes:

[0020] Arrange planar metalenses of various orders sequentially on one of the coordinate axes to obtain a planar metalens coordinate axis array;

[0021] The planar meta-lens coordinate axis array is rotated 90° around the origin in sequence to arrange planar meta-lenses of various orders on the coordinate axes in each direction.

[0022] In one embodiment, determining the corresponding order of the planar metalens based on the location to be filled includes:

[0023] The corresponding angle is determined based on the distance from the position to be filled to the origin.

[0024] The corresponding order of planar metalens is determined based on the angle.

[0025] In one embodiment, determining the corresponding angle based on the distance from the location to be filled to the origin includes:

[0026] The corresponding basic coordinate axis distance is determined based on the distance from the location to be filled to the origin.

[0027] The corresponding angle is determined based on the distance of the basic coordinate axes.

[0028] The planar meta-lens array for hemispherical ultra-wide-angle imaging and its fabrication method in this invention can achieve hemispherical ultra-wide-angle imaging with planar optical elements in an ultra-compact scale, thereby reducing distortion and improving the system integration. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of a planar meta-lens array used for hemispherical ultra-wide-angle imaging in an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram illustrating the relationship between the field of view, the superconducting lens array, and the image plane in one embodiment of the present invention;

[0032] Figure 3 This is a schematic diagram showing the correspondence between the field of view, the superconducting lens array, and the image plane in one embodiment of the present invention;

[0033] Figure 4 This is a schematic diagram of light convergence of the metalens in an embodiment of the present invention;

[0034] Figure 5 In the embodiments of the present invention, d(θ) i )=f·tanθ i A schematic diagram of the phase distribution on the surface of the metalens;

[0035] Figure 6 In the embodiments of the present invention, d(θ) i )=f·sinθ i A schematic diagram of the phase distribution on the surface of the metalens;

[0036] Figure 7 In the embodiments of the present invention, d(θ) i )=f·θ i A schematic diagram of the phase distribution on the surface of the metalens;

[0037] Figure 8 This is a schematic diagram of the planar meta-lens array in an embodiment of the present invention;

[0038] Figure 9 This is a schematic diagram of the origin rotation of the planar meta-lens in an embodiment of the present invention;

[0039] Figure 10 This is a schematic diagram of the rotation of the planar meta-lens in an embodiment of the present invention;

[0040] Figure 11 This is a flowchart of the fabrication method of the planar meta-lens array for hemispherical ultra-wide-angle imaging in an embodiment of the present invention;

[0041] Figure 12This is a flowchart illustrating the arrangement of planar meta-lenses of various levels in an embodiment of the present invention;

[0042] Figure 13 This is a flowchart of S103 in an embodiment of the present invention;

[0043] Figure 14 This is a schematic diagram of the phase distribution of the metalens in an embodiment of the present invention;

[0044] Figure 15 This is a schematic diagram of the coordinate axis array of the planar metalens in an embodiment of the present invention;

[0045] Figure 16 This is a schematic diagram of planar meta-lenses of various orders arranged on coordinate axes in each direction in an embodiment of the present invention;

[0046] Figure 17 This is a schematic diagram illustrating the determination of a planar meta-lens in an embodiment of the present invention;

[0047] Figure 18 This is a schematic diagram of a rotating meta-lens in an embodiment of the present invention. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] Given that traditional wide-angle imaging systems are not only prone to damage but also limit their application in integrated optics, this invention provides a planar metalens array for hemispherical ultra-wide-angle imaging and its fabrication method. Each metalens in the constructed planar metalens array can converge oblique incident light at different angles, thereby imaging different regions. Ultimately, hemispherical ultra-wide-angle imaging can be achieved in an ultra-compact scale using planar optical elements, reducing distortion while improving the system's integration.

[0050] Taking a one-dimensional linear metalens array as an example, the phase distribution of the metalenses used in a conventional metalens array is completely uniform. It can only respond to perpendicularly incident light beams, thus greatly limiting its imaging angle. Taking the imaging of 'ABCDEFGHIJKLMN' as an example, the imaging angle of a conventional metalens array is limited, and only the words 'EFGHIJ' near the center position can be observed on the image plane.

[0051] The difference in this application lies in the fact that the phase distribution of each metalens is different. The central metalens is responsible for collecting normally incident light, while the metalenses further out to the edges can collect light at a larger angle of incidence. For example, the leftmost and rightmost metalenses are responsible for imaging the words 'KLMN' and 'ABCD', respectively. The invention will now be described in detail with reference to the accompanying drawings.

[0052] Figure 1 This is a schematic diagram of a planar metalens array used for hemispherical ultra-wide-angle imaging in an embodiment of the present invention. Figure 1 As shown, the planar metalens array for hemispherical ultra-wide-angle imaging includes:

[0053] substrate ( Figure 1 (not shown in the text); and

[0054] Multiple planar metalenses are located on the substrate. The multiple planar metalenses are arranged according to a preset period. The rotation angle of the planar metalenses corresponds to the position of the planar metalenses, and the position of the planar metalenses corresponds to the order of the planar metalenses.

[0055] In one embodiment, the period of the planar metalens array corresponds to the wavelength of the planar metalens.

[0056] In one embodiment, the phase distribution of the planar metalens depends on the incident angle, wavelength, distance from the origin of the planar metalens, focal length of the planar metalens, and focal center distance. The focal center distance depends on the incident angle and the focal length of the planar metalens.

[0057] Figure 2 This is a schematic diagram illustrating the relationship between the field of view, the superconducting lens array, and the image plane in one embodiment of the present invention. Figure 3 This is a schematic diagram illustrating the correspondence between the field of view, the superimposed lens array, and the image plane in one embodiment of the present invention. For example... Figures 2-3 As shown, each metalens M is responsible for imaging different regions in the hemispherical field of view S onto the P plane.

[0058] The spatial positions of each region in the hemispherical field of view are determined by two parameters, such as... Figure 3 As shown, θ represents the angle θ between the line connecting the center of the region and the center O of the hemisphere and the z-axis. i And the angle between the projection of the line connecting the center of the region and the center of the hemisphere O onto the xoy plane and the x-axis. Mark a region of the hemispherical field of view as The metalens responsible for imaging this region is denoted as Corresponding image plane is The relationship between the field of view S, the metalens array M, and the image plane P follows the formula below:

[0059]

[0060] Figure 4 This is a schematic diagram of light convergence using a metalens in an embodiment of the present invention. For example... Figure 4 As shown, the meta-lens M(θ) i ,0) can be incident at an angle θ i Since the light rays converge at point F, the optical path along GAF must be the same as that along HKF. Therefore, the phase compensated by the metalens is:

[0061]

[0062] Let K be any point on the metalens, with a distance r from the origin A, and let f be the focal length of the metalens. Let d(θ) be the distance between the focal point and the center. i If the phase distribution on the surface of the metalens needs to satisfy:

[0063]

[0064] Where d(θ) i With focal length f and incident angle θ i Regarding this, it can usually be set as follows:

[0065] d(θ i )=f·tanθ i ,f·sinθ i ,f·θ i ...

[0066] Figure 5 In the embodiments of the present invention, d(θ) i )=f·tanθ i A schematic diagram of the phase distribution on the surface of the metalens. Figure 6 In the embodiments of the present invention, d(θ) i )=f·sinθ i A schematic diagram of the phase distribution on the surface of the metalens. Figure 7 In the embodiments of the present invention, d(θ) i )=f·θ i A schematic diagram of the phase distribution on the surface of the metalens. (See diagram below.) Figures 5-7 As shown, d(θ) i The choice of d(θ) affects the required phase distribution of the metalens. Under the conditions of an incident light wavelength of 532 nm, a focal length of 10.64 μm, and a lens radius of 0.665 μm, different d(θ) values ​​will affect the desired phase distribution. i The surface phase distribution of the metalens is inconsistent.

[0067] In one embodiment, the rotation angle of the planar metalens corresponding to the position of the planar metalens includes:

[0068] The rotation angle of the planar meta-lens corresponds to the angle between the position coordinates of the planar meta-lens and the horizontal axis.

[0069] Figure 8 This is a schematic diagram of the planar meta-lens array in an embodiment of the present invention. Figure 9 This is a schematic diagram of the origin rotation of the planar meta-lens in an embodiment of the present invention. Figure 10 This is a schematic diagram of the rotation of the planar metalens in an embodiment of the present invention. For example... Figures 8-10 As shown, according to the phase calculation formula of a single metalens, the phase distribution is related to θ. i Related to Irrelevant. Therefore With M(θ) i The overall phase distribution of M(θ, 0) is consistent, so it is only necessary to make M(θ, 0) the same. i ,0) Perform a rotation operation on the entire object. The specific rotation operation is as follows: Figure 9 As shown, first M(θ) i ,0) Rotate around point O Angle, at this time With M(θ) i The coordinate correspondence between ,0) is as follows:

[0070]

[0071] Then Around point D Rotation Angle, such as Figure 10 , can be obtained and The coordinate correspondence between them:

[0072]

[0073] Where r (distance from the center) and the included angle k (angle from the center) are used to label the metalens. The positions of the different points.

[0074] The specific structural units of this invention can be arbitrarily changed according to preferences and objectives. For example, if the superlens array is to operate in the visible light band, its material can be gallium nitride or titanium dioxide; if the superlens array is to operate in the near-infrared band, materials such as silicon can also be selected. If the corresponding phase distribution is to be achieved using geometric phase, the structural unit can be designed as a cuboid or a triangular prism; if the corresponding phase distribution is to be achieved using propagation phase, the structural unit can be designed as a cylinder.

[0075] Based on the same inventive concept, this invention also provides a method for fabricating a planar meta-lens array for hemispherical ultra-wide-angle imaging. Since the principle of this method in solving the problem is similar to that of the planar meta-lens array for hemispherical ultra-wide-angle imaging, the implementation of this method can refer to the implementation of the planar meta-lens array for hemispherical ultra-wide-angle imaging, and the repeated parts will not be described again.

[0076] Figure 11 This is a flowchart illustrating the fabrication method of a planar metalens array for hemispherical ultra-wide-angle imaging in an embodiment of the present invention. Figure 11 As shown, the flowchart of the fabrication method of the planar metalens array for hemispherical ultra-wide-angle imaging includes:

[0077] S101: Provides a substrate.

[0078] S102: Arrange planar meta-lenses of various orders on the corresponding coordinate axes with the center of the substrate as the origin.

[0079] Figure 12 This is a flowchart illustrating the arrangement of planar metalenses at various levels in an embodiment of the present invention. For example... Figure 12 As shown, the planar metalenses of various orders arranged on the corresponding coordinate axes include:

[0080] S201: Arrange planar metalenses of various orders sequentially on one of the coordinate axes to obtain a planar metalens coordinate axis array.

[0081] In practice, multiple levels can be designed within the range of -90° to 0°, with the total number of levels being the size of the metalens array database. For example, in this case, [-90, 0] is divided into 10 levels: 0, -10, -20, -30, ..., -80, -90. This means that each metalens is responsible for imaging at incident light angles of 0, -10, -20, -30, ... . Although this embodiment sets 10 equally spaced levels, this is not a mandatory requirement. The total number of levels and the interval between each level can be freely changed; however, too few levels may lead to a decrease in image quality.

[0082] According to the phase distribution formula of the metalens surface:

[0083] The phase distribution of each order of the metalens can be calculated. Figure 14 This is a schematic diagram of the phase distribution of the metalens in an embodiment of the present invention. For example... Figure 14 As shown, the focal length, radius, operating wavelength, and period of each metalens are consistent. Here, it is assumed that the focal length is 500 micrometers, the radius is 250 micrometers, the unit period is 500 nanometers, the operating wavelength is 532 nanometers, and d(θ) = f*θ.

[0084] Figure 15 This is a schematic diagram of the coordinate axis array of the planar metalens in an embodiment of the present invention. For example... Figure 15 As shown, starting with the simplest -x-axis arrangement, the planar metalenses in the range of [-90,0] are arranged sequentially on the -x-axis, with the metalens corresponding to 0° located at the origin.

[0085] S202: Rotate the planar meta-lens coordinate axis array around the origin by 90° in sequence to arrange planar meta-lenses of various orders on the coordinate axes in each direction.

[0086] Figure 16 This is a schematic diagram illustrating the arrangement of planar metalenses of various orders on the coordinate axes in each direction, as described in an embodiment of the present invention. Taking the metalens corresponding to -10° as an example, the present invention establishes the arrangement of the metalens array on the +y, +x, and -y axes. For example... Figure 16 As shown, auxiliary arrows illustrate the definition of the 'rotation around the origin' operation. Rotating the metalens 90° clockwise around the origin completes the +y-axis arrangement, rotating it 180° clockwise around the origin completes the +x-axis arrangement, and rotating it 270° clockwise around the origin completes the -y-axis arrangement. Following this method, rotating and arranging the metalenses around the origin at -20°, -30°…, -90° sequentially allows for the collection of wide-field image information along the x and y axes, corresponding to angles from -90° to 90°.

[0087] S103: Determine the corresponding order of planar metalens based on the position to be filled.

[0088] Table 1

[0089]

[0090]

[0091] Table 1 shows the relationship between d(θ) and the distance from the center of the superlens to the origin O for each superlens in this embodiment of the invention. As shown in Table 1, f is the focal length and r is the radius of the superlens.

[0092] In practice, first determine which metalens from the database needs to be filled at any position in the array. Select any position in the array that needs to be filled with a metalens, calculate the distance from that position to the origin, assuming that the distance is X, find the distance G when the function F=|XG| reaches its minimum value in Table 1, and its corresponding angle θ, and then select the metalens corresponding to that angle from the database.

[0093] Figure 13 This is a flowchart of S103 in an embodiment of the present invention. For example... Figure 13 As shown, S103 includes:

[0094] S301: Determine the corresponding angle based on the distance from the position to be filled to the origin.

[0095] In one embodiment, S301 includes:

[0096] The corresponding basic coordinate axis distance is determined based on the distance from the position to be filled to the origin, and the corresponding angle is determined based on the basic coordinate axis distance.

[0097] S302: Determine the corresponding order of planar meta-lens based on the angle.

[0098] Figure 17 This is a schematic diagram illustrating the determination of a planar meta-lens in an embodiment of the present invention. For example... Figure 17 As shown, when the hyperlens at (4r, 6r) is determined (as indicated by the dashed box), the calculated distance X is 7.21r. When the distance G is 8r, the function F has a minimum value, corresponding to an angle of -40°. Therefore, the -40° hyperlens from the database is selected. The arrow indicates that the phase distribution of the hyperlens at point M is completely consistent with that of the -40° hyperlens in the database (located on the -x axis).

[0099] S104: Rotate the planar metalens according to the rotation angle of the planar metalens to obtain a planar metalens array.

[0100] In one embodiment, before performing S104, the method further includes: determining the rotation angle of the planar metalens based on the position of the planar metalens.

[0101] To achieve hemispherical imaging, the superlens needs to be rotated. Let the coordinates of the superlens be M(x0,y0). Then, we need to calculate the angle between the line MO connecting this position to the origin and the -x-axis using atan(y0,x0). The calculated angle is the rotation angle. Figure 18 This is a schematic diagram of a rotating metalens in an embodiment of the present invention. For example... Figure 18 As shown, the angle between MO and the -x axis is 124°. Therefore, the meta-lens at M needs to rotate 124° clockwise around its center position. It can be seen that the direction of the arrow has changed.

[0102] In summary, the planar metalens array for hemispherical ultra-wide-angle imaging and its fabrication method provided in this invention can achieve hemispherical ultra-wide-angle imaging on an ultra-compact scale, facilitating integration, eliminating spherical aberration and distortion, and playing a corresponding role in autonomous driving, real-time monitoring, and satellite positioning. Furthermore, this invention can achieve multi-wavelength or even broadband achromatic hemispherical ultra-wide-angle imaging by rationally setting the metalens material, arranging the metalens units, and optimizing the corresponding structural dimensions.

[0103] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A planar metalens array for hemispherical ultra-wide-angle imaging, characterized in that, include: Substrate; as well as Multiple planar metalenses are located on the substrate, and the multiple planar metalenses are arranged according to a preset period; The rotation angle of the planar meta-lens is determined based on the angle between the position coordinates of the planar meta-lens and the horizontal axis. The order of the planar meta-lens is determined based on the distance from the center of the planar meta-lens to the center of the substrate. The order is used to indicate the incident light angle corresponding to the planar meta-lens.

2. The planar meta-lens array for hemispherical ultra-wide-angle imaging according to claim 1, characterized in that, The phase distribution of the planar meta-lens depends on the incident angle, wavelength, distance from the origin of the planar meta-lens, focal length of the planar meta-lens, and distance between the focal points.

3. The planar metalens array for hemispherical ultra-wide-angle imaging according to claim 2, characterized in that, The distance between the focal centers depends on the incident angle and the focal length of the planar metalens.

4. The planar meta-lens array for hemispherical ultra-wide-angle imaging according to claim 1, characterized in that, The period of the planar metalens array corresponds to the wavelength of the planar metalens.

5. The planar meta-lens array for hemispherical ultra-wide-angle imaging according to claim 1, characterized in that, The rotation angle of the planar meta-lens corresponds to the position of the planar meta-lens, including: The rotation angle of the planar meta-lens corresponds to the angle between the position coordinates of the planar meta-lens and the horizontal axis.

6. A method for fabricating a planar metalens array for hemispherical ultra-wide-angle imaging as described in any one of claims 1-5, characterized in that, include: Provide a base; With the center of the substrate as the origin, planar metalenses of various orders are arranged on the corresponding coordinate axes; Determine the corresponding order of planar metalens based on the distance from the location to be filled to the center of the substrate; The rotation angle of the planar meta-lens is determined based on the angle between the position coordinates of the location to be filled and the horizontal axis. Rotate the planar metalens according to the rotation angle of the planar metalens to obtain a planar metalens array.

7. The method for fabricating a planar metalens array according to claim 6, characterized in that, Also includes: The rotation angle of the planar meta-lens is determined based on its position.

8. The method for fabricating a planar metalens array according to claim 6, characterized in that, The planar meta-lenses of various orders arranged on the corresponding coordinate axes include: Arrange planar metalenses of various orders sequentially on one of the coordinate axes to obtain a planar metalens coordinate axis array; The planar meta-lens coordinate axis array is rotated 90° around the origin in sequence to arrange planar meta-lenses of various orders on the coordinate axes in each direction.

9. The method for fabricating a planar metalens array according to claim 6, characterized in that, The planar meta-lens of the corresponding order, determined based on the location to be filled, includes: The corresponding angle is determined based on the distance from the position to be filled to the origin. The corresponding order of planar metalens is determined based on the angle.

10. The method for fabricating a planar metalens array according to claim 9, characterized in that, Determining the corresponding angle based on the distance from the location to be filled to the origin includes: The corresponding basic coordinate axis distance is determined based on the distance from the location to be filled to the origin. The corresponding angle is determined based on the distance of the basic coordinate axes.

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