Metalens

Abstract

A meta-lens includes a substrate and a plurality of meta atoms. These meta atoms are distributed on the substrate, and each meta atom includes two phase retardation structures intersecting in a direction parallel to the substrate, wherein these meta atoms have not exactly the same pitch and not exactly the same focal length.

Description

Technical Field

[0001] This invention relates to an optical element, and more particularly to a metalen. Prior Technology

[0002] For decades, optical lenses have been indispensable components in optical systems, used for applications such as imaging, focusing, and telescoping. However, traditional lenses have limitations, such as the impact of thickness and shape on image quality, and interference from refraction and scattering of the light field, which can produce stray light or ghosting in the image. These limitations lead to constraints in some applications.

[0003] Subsequently, meta-lenses were developed. However, there is still room for improvement in the modulation transfer function (MTF) of images produced by meta-lenses that generally use circular meta-atoms. Summary of the Invention

[0004] This invention provides a super-lens that can effectively improve the modulation conversion function value and imaging quality.

[0005] One embodiment of the present invention provides a meta-lens comprising a substrate and a plurality of meta atoms. These meta atoms are distributed on the substrate, and each meta atom includes two phase retardation structures intersecting in a direction parallel to the substrate, wherein these meta atoms have not exactly the same pitch and not exactly the same focal length.

[0006] In the metalens of the embodiments of the present invention, each metaatom includes two phase retardation structures intersecting in a direction parallel to the substrate, and these metaatoms have not exactly the same pitch and not exactly the same focal length. Therefore, the metalens of the embodiments of the present invention can achieve a higher modulation conversion function value compared with metalenses using circular metaatoms, thereby effectively improving the imaging quality of the metalens. Simple Explanation of the Diagram

[0007] Figure 1A is a frontal view of a super-lens according to an embodiment of the present invention. Figure 1B is a magnified view of a portion of region M1 in Figure 1A. Figure 2A is a frontal view of a superatom in Figure 1A. Figure 2B is a three-dimensional schematic diagram of one of the superatoms in Figure 1A. Figure 3 is a cross-sectional schematic diagram of the optical system of the superlens in Figure 1A. Figure 4A shows the light energy distribution curve of the superlens in Figure 1A, which focuses perpendicularly incident parallel light onto the imaging plane on the line Y=0. Figure 4B shows the light energy distribution curve of the superlens in Figure 1A, which focuses perpendicularly incident parallel light onto the imaging plane on the line X=0. Figure 5A is a light energy distribution curve on the line Y=0 of another embodiment of the superlens of Figure 1A, which shows the light energy of the perpendicularly incident parallel light focused on the imaging plane. Figure 5B is a light energy distribution curve on a straight line X=10 micrometers, which shows the light energy of a vertically incident parallel light focused onto the imaging plane in another embodiment of the superlens of Figure 1A. Figure 6 is a graph showing the modulation conversion function of the images formed by the light energy in Figures 4A and 4B on the imaging plane on the line X=0 and the line Y=0. Figure 7 is a graph showing the modulation conversion function of the images formed by the light energy in Figures 5A and 5B on the imaging surface, on the line X=10 micrometers and the line Y=0. Figure 8 shows the modulation conversion function of the image formed by the light energy in Figures 4A and 4B on the imaging surface, and the modulation conversion function of a conventional super-lens using circular super-atoms at a viewing angle of 0 degrees. Figure 9 shows the modulation conversion function of the image formed by the light energy in Figures 5A and 5B on the imaging surface, and the modulation conversion function of a conventional metalens using circular metaatoms at a viewing angle of 20 degrees. Figure 10A shows the distribution of the transverse index of a single metaatom in the Y direction in the metalens of Figure 1A. Figure 10B shows the distribution of the lateral index of a single metaatom in the X direction in the metalens of Figure 1A. Figure 11 shows the distribution of total transmittance and total reflectance of a single metaatom in the visible light band at different light exit angles in the metalens of Figure 1A. Implementation

[0008] Figure 1A is a front view of a meta-lens according to an embodiment of the present invention; Figure 1B is a partially enlarged view of region M1 in Figure 1A; Figure 2A is a front view of a meta-atom in Figure 1A; Figure 2B is a three-dimensional view of a meta-atom in Figure 1A; and Figure 3 is a cross-sectional view of the optical system of the meta-lens of Figure 1A. Referring to Figures 1A, 1B, 2A, 2B, and 3, the meta-lens 100 of this embodiment includes a substrate 110 and a plurality of meta-atoms 200. These meta-atoms 200 are distributed on the substrate 110, and each meta-atom 200 includes two phase retardation structures 210 and 220 intersecting in a direction parallel to the substrate 110, wherein these meta-atoms 200 have not exactly the same pitch P and not exactly the same focal length. In this embodiment, the design of these meta-atoms 200 conforms to Babinet's principle.

[0009] In this embodiment, the two phase delay structures 210 and 220 intersect at a 90-degree angle. In this embodiment, each of the two phase delay structures 210 and 220 is a rectangular column. That is, in this embodiment, the two intersecting phase delay structures 210 and 220 form a cross-shaped column, and their cross-section parallel to the substrate 110 is cross-shaped.

[0010] Furthermore, in this embodiment, each superatom 200 further includes multiple fillet structures 230 located near the intersection of the two phase retardation structures 210 and 220 (Figure 2A shows an example with four fillet structures 230). In this embodiment, the angles θ1 and θ2 between the side surface 232 of these fillet structures 230 and the adjacent side surfaces 212 and 222 of the two phase retardation structures 210 and 220 are, for example, both 135 degrees.

[0011] In this embodiment, the metaatoms 200 are distributed on two opposing surfaces 112 and 114 of the substrate 110 (as shown in FIG. 3). Furthermore, in this embodiment, the metaatoms 200 on surface 112 and the metaatoms 200 on surface 114 are mirror-symmetrical with respect to the substrate 110. In this embodiment, the material of the metaatoms 200 is, for example, titanium dioxide, and the material of the substrate 110 is, for example, gallium nitride, but the invention is not limited thereto. In this embodiment, the left side of surface 114 and the metaatoms 200 on it in FIG. 3 is, for example, air, and the right side of surface 112 and the metaatoms 200 on it in FIG. 3 is, for example, air. The refractive index of air is, for example, 1. The "phase retardation" of phase retardation structures 210 and 220 refers to the fact that their materials have a large phase retardation effect relative to air. The material of the filler structure 230 can be the same as the material of phase retardation structures 210 and 220, and the filler structure 230 and phase retardation structures 210 and 220 are, for example, integrally formed. In addition, in this embodiment, the substrate 110 is, for example, a circular substrate, and these metaatoms 200 are arranged in an array on the substrate 110.

[0012] In the meta-lens 100 of this embodiment, each meta-atom 200 includes two phase retardation structures 210 and 220 intersecting in a direction parallel to the substrate 110, and these meta-atoms 200 have not exactly the same pitch P and not exactly the same focal length. Therefore, the meta-lens 100 of this embodiment can achieve a higher modulation transfer function value than a meta-lens using circular meta-atoms, thereby effectively improving the imaging quality of the meta-lens 100. For example, for incident light with a wavelength of 520 nanometers, under the same effective focal length and within a field of view of 0 to 20 degrees, the meta-lens 100 of this embodiment can achieve a higher modulation transfer function value than a general meta-lens using circular meta-atoms. Furthermore, compared to conventional refractive lenses, the meta-lens 100 of this embodiment can be thinner and is less affected by light field refraction and scattering, thus reducing the generation of stray light or ghosting in the image.

[0013] In this embodiment, these meta-lenses 100 conform to: 0.25 micrometers < P < 0.5 micrometers Where P is the pitch of these superatoms 200.

[0014] In this embodiment, each metaatom 200 of the metalens 100 conforms to: 0.25 micrometers < W < 0.5 micrometers; and 0.25 micrometers < H < 0.5 micrometers Where W is the length of one of the two phase delay structures 210 and 220 (such as phase delay structure 210) in the direction parallel to the substrate 110, and H is the length of the other of the two phase delay structures 210 and 220 (such as phase delay structure 220) in the direction parallel to the substrate 110.

[0015] In this embodiment, each metaatom 200 of the metalens 100 conforms to: 0.5 micrometers < L < 1 micrometer Where L is the height of the superatom 200 in the direction perpendicular to the substrate 110.

[0016] Figure 4A shows the light energy distribution curve of the superlens 100 on the imaging surface along the line Y=0, where the perpendicularly incident parallel light is focused onto the imaging surface. Figure 4B shows the light energy distribution curve of the superlens 100 on the imaging surface along the line X=0, where the perpendicularly incident parallel light is focused onto the imaging surface. In Figure 1A, the X and Y directions are parallel to the substrate 110, and the Z direction is perpendicular to the substrate 110. Furthermore, the X, Y, and Z directions are perpendicular to each other. As can be seen from Figures 4A and 4B, the light energy distribution is concentrated, and the superlens 100 exhibits good imaging quality.

[0017] Figure 5A shows the light energy distribution curve of the vertically incident parallel light focused on the imaging plane along the line Y=0, representing another embodiment of the metalens of Figure 1A. Figure 5B shows the light energy distribution curve of the vertically incident parallel light focused on the imaging plane along the line X=10 micrometers, representing another embodiment of the metalens of Figure 1A. Referring to Figures 5A and 5B, the metalens 100 of this embodiment, through the appropriate distribution of not entirely identical pitch P, causes the light emitted from the metalens 100 to be deflected by a field of view of 20 degrees in the X direction. As shown in Figures 5A and 5B, even with the emitted light deflected by a field of view of 20 degrees, the light energy distribution remains concentrated, thus the metalens 100 still has good imaging quality under these conditions.

[0018] Figure 6 shows the modulation conversion function curves of the images formed by the light energy of Figures 4A and 4B on the imaging surface along the line X=0 and the line Y=0. Figure 7 shows the modulation conversion function curves of the images formed by the light energy of Figures 5A and 5B on the imaging surface along the line X=10 micrometers and the line Y=0. Figure 8 shows the modulation conversion function curves of the images formed by the light energy of Figures 4A and 4B on the imaging surface and the modulation conversion function curves of a conventional super-lens using circular super-atoms at a viewing angle of 0 degrees. These two modulation conversion functions are labeled "this embodiment" and "conventional super-lens" in Figure 8, respectively. Figure 9 shows the modulation conversion function curves of the images formed by the light energy of Figures 5A and 5B on the imaging surface and the modulation conversion function curves of a conventional super-lens using circular super-atoms at a viewing angle of 20 degrees. These two modulation conversion functions are labeled "this embodiment" and "conventional super-lens" in Figure 9, respectively. As shown in Figures 6 to 9, under the same effective focal length and within a field of view of 0 to 20 degrees, the superlens 100 of this embodiment can achieve a higher modulation conversion function value compared to a general superlens using circular super-atoms.

[0019] Figure 10A shows the refractive index distribution of a single metaatom in the metalens of Figure 1A in the Y direction, Figure 10B shows the refractive index distribution of a single metaatom in the metalens of Figure 1A in the X direction, and Figure 11 shows the distribution of the total transmittance and total reflectance of a single metaatom in the metalens of Figure 1A in the visible light band at different light exit angles. Referring to Figures 10A, 10B, and 11, Figures 10A and 10B show the refractive index distribution of the metalens 100 at different positions in the X and Y directions, and Figure 11 shows that the metaatom 200 in this embodiment has good transmittance, where high diffraction efficiency indicates high transmittance.

[0020] In summary, in the meta-lens of the embodiments of the present invention, each meta-atom includes two phase retardation structures intersecting in a direction parallel to the substrate, and these meta-atoms have not exactly the same pitch and not exactly the same focal length. Therefore, the meta-lens of the embodiments of the present invention can achieve a higher modulation conversion function value compared with a meta-lens using circular meta-atoms, thereby effectively improving the imaging quality of the meta-lens.

[0021] 100: Super Lens 110:Substrate 112, 114: Surface 200: Super-intelligent Atom 210, 220: Phase delay structure 212, 222, 232: Side view 230: Fill-in structure H, W: Length L: Height P: Pitch X, Y, Z: Direction θ1, θ2: included angle

Claims

1. A meta-lens, comprising: One substrate; And a plurality of superatoms are distributed on the substrate, each superatom including two phase retardation structures intersecting in a direction parallel to the substrate, wherein the superatoms have not exactly the same pitch and not exactly the same focal length, and each superatom further includes a plurality of filler structures located next to the intersection of the two phase retardation structures.

2. The super-lens as claimed in claim 1, wherein the side surfaces of the filler structures form a 135-degree angle with the side surfaces adjacent to the two phase delay structures.

3. The super-lens as claimed in claim 2, wherein the two phase delay structures intersect at 90 degrees.

4. The super-lens as claimed in claim 3, wherein each of the two phase delay structures is rectangular columnar.

5. The meta-lens as claimed in claim 1, wherein the meta-atoms are made of titanium dioxide and the substrate is made of gallium nitride.

6. The meta-lens as claimed in claim 1, wherein the meta-lens conforms to the condition: 0.25 micrometers < P < 0.5 micrometers, where P is the pitch of the meta-atoms.

7. The meta-lens as claimed in claim 1, wherein each meta-atom of the meta-lens conforms to: 0.25 μm < W < 0.5 μm; and 0.25 μm < H < 0.5 μm, where W is the length of one of the two phase retardation structures in a direction parallel to the substrate, and H is the length of the other of the two phase retardation structures in a direction parallel to the substrate.

8. The meta-lens as claimed in claim 1, wherein each meta-atom of the meta-lens conforms to the following condition: 0.5 micrometers < L < 1 micrometer, where L is the height of the meta-atom in a direction perpendicular to the substrate.

9. The meta-lens as claimed in claim 1, wherein the meta atoms are distributed on opposite surfaces of the substrate.

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