Variable-focus super-structure lens system

Abstract

The invention relates to a variable-focus metamaterial lens system. The system comprises a first metasurface and a second metasurface. A first metasurface and a second metasurface are sequentially arranged on the same optical axis, and a preset distance is reserved between the first metasurface and the second metasurface. A group of sub-wavelength structure units are constructed on the surface of the first metasurface; a group of sub-wavelength structure units are constructed on the second metasurface, and the second metasurface rotates by an angle theta around the normal direction relative to the first metasurface; the equivalent phase distribution of the composite device can be adjusted through the relative rotation between the first metasurface and the second metasurface, and the continuous regulation and control of the focal length are realized along with the change of the numerical aperture. Therefore, the complexity is reduced, and the response speed is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of planar optics and metasurface, and particularly relates to a variable-focus metasurface lens system. BACKGROUND

[0002] As a planar optical device based on subwavelength scale nanostructures, a metalens has the advantages of compact size, high integration and flexible light control. However, the focal length and numerical aperture (NA) of a conventional metalens are fixed once designed, which limits its application in adjustable-focus, variable-focus imaging and composite imaging systems. To realize the adjustable-focus function, some studies have introduced mechanical adjustment, liquid crystal control and other methods, but the system complexity and response speed are still insufficient. SUMMARY

[0003] Therefore, it is necessary to provide a variable-focus metasurface lens system capable of reducing complexity and improving response speed in view of the above technical problems.

[0004] A variable-focus metasurface lens system, the system comprising: a first metasurface and a second metasurface;

[0005] The first metasurface and the second metasurface are sequentially arranged on the same optical axis, and the first metasurface and the second metasurface are spaced apart by a preset interval;

[0006] The first metasurface is configured with a group of subwavelength structure units;

[0007] The second metasurface is configured with a group of subwavelength structure units, and the second metasurface is rotated by an angle θ relative to the first metasurface around the normal direction;

[0008] The relative rotation between the first metasurface and the second metasurface can adjust the equivalent phase distribution of the composite device, realize continuous regulation of the focal length, and accompany the change of the numerical aperture.

[0009] In one of the embodiments, the phase of the subwavelength structure unit configured on the first metasurface conforms to a first target phase function, and the first target phase function Φ1(x1, y1) is:

[0010]

[0011] Wherein, a is a phase control factor, (x1, y1) is a two-dimensional coordinate point on the first metasurface, actan(y, x) is a polar angle, which represents the angular direction of point (y, x) relative to the origin.

[0012] In one of the embodiments, the phase of the subwavelength structure unit constructed on the second metasurface is consistent with a second target phase function, the second target phase function Φ2(x2, y2) is:

[0013]

[0014] Wherein, a is a phase control factor, (x2, y2) is a two-dimensional coordinate point on the second metasurface, actan(y, x) is a polar angle, which represents the angle direction of the point (y, x) relative to the origin.

[0015] In one of the embodiments, the preset interval is between 50 nm and 500 μm.

[0016] In one of the embodiments, the angle θ ranges from 0° to 360°.

[0017] In one of the embodiments, the working wavelength range of the first metasurface and the second metasurface is ultraviolet wavelength.

[0018] In one of the embodiments, the material used by the first metasurface and the second metasurface is one or more of titanium dioxide, silicon, silicon nitride, hafnium oxide, SiC, metal, and zinc oxide material.

[0019] In one of the embodiments, the focal length ranges from f = π / (a × θ × λ), wherein f is the focal length, a is the phase control factor, λ is the wavelength, and θ is the rotation angle.

[0020] In one of the embodiments, the rotation between the first metasurface and the second metasurface is rotated by MEMS, motor or manual method.

[0021] Compared with the prior art, the variable focus metasurface lens system has the following advantages:

[0022] 1. Simple structure, no need to change the element interval, continuous focusing can be achieved by rotation, and the response speed is improved;

[0023] 2. The numerical aperture (NA) can be adjusted while adjusting the focal length, which is suitable for multi-mode imaging;

[0024] 3. Easy to miniaturize and integrate, suitable for portable microscopes, near-eye displays, light field control systems, etc.;

[0025] 4. Strong adaptability of materials and wave bands, which can be used in multiple spectral intervals. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the variable focus metasurface lens system in one of the embodiments;

[0027] Figure 2 A schematic diagram of the phase of a first metasurface and a second metasurface in an embodiment;

[0028] Figure 3 A partial example of the light intensity distribution of the corresponding cross section at different rotation angles in an embodiment;

[0029] Figure 4 A schematic diagram of the corresponding change of focal length as the rotation angle changes from 0 degrees to 360 degrees in an embodiment. DETAILED DESCRIPTION

[0030] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0031] In an embodiment, as shown in Figure 1 , a variable-focus metasurface lens system is provided, the system comprising: a first metasurface and a second metasurface;

[0032] The first metasurface and the second metasurface are sequentially arranged on the same optical axis, and the first metasurface and the second metasurface are spaced apart by a predetermined distance; a group of subwavelength structure units are constructed on the first metasurface; a group of subwavelength structure units are constructed on the second metasurface, and the second metasurface is rotated by an angle θ around the normal direction relative to the first metasurface; the relative rotation between the first metasurface and the second metasurface can adjust the equivalent phase distribution of the composite device, realize the continuous regulation of the focal length, and accompany the change of the numerical aperture.

[0033] Among them, the key to realizing a metasurface with a set phase distribution is to accurately map the target phase function into a two-dimensional metasurface unit array. Usually, by controlling the geometric shape, size or rotation angle of each subwavelength unit (such as nanocolumn, nanobar or H-shaped structure), the required optical phase delay at the specified wavelength is generated to form continuous or discrete 0-2π phase coverage. According to the different phase regulation mechanisms, the common methods include propagation phase and geometric phase design, where the geometric phase method realizes polarization-selective control by rotating each unit, which is suitable for preparing circular polarization-sensitive devices; the propagation phase realizes polarization-independent regulation by changing the structure size, which is suitable for wide-band or high-transmittance applications. The above structures are usually prepared by high-precision nanofabrication technologies such as electron beam exposure, nanoimprinting, focused ion beam etching, etc., so as to obtain a functional metasurface with accurate phase regulation capability.

[0034] Wherein, a certain interval d is provided between the two pieces of superstructures, which ranges from about 50 nm to 500 μm.

[0035] Wherein, the first piece of superstructure and the second piece of superstructure are sequentially arranged on the same optical axis, the front surface of the first piece of superstructure is spaced apart from the back surface of the second piece of superstructure by an interval d, the incident light is incident from the back surface of the first piece of superstructure, the light is transmitted to the back surface of the second piece of superstructure through the front surface of the first piece of superstructure, and then is emitted from the front surface of the second piece of superstructure, as shown in Figure 1 The relative rotation between the first piece of superstructure and the second piece of superstructure can adjust the equivalent phase distribution of the compound device, so as to realize continuous regulation of focal length, accompanied by change of numerical aperture.

[0036] Wherein, the variable-focus superlens system can be applied to integrated imaging, microscopy, optical communication and light field regulation, etc.

[0037] Wherein, the high-precision rotation of the two pieces of superstructures can be realized by micro-electro-mechanical system (MEMS), motor or manual method.

[0038] The above variable-focus superlens system can realize continuous focal length adjustment and numerical aperture change by rotating the two pieces of superstructures with a set phase distribution, which expands its application potential in the fields of imaging, display, sensing, etc.

[0039] In one embodiment, the phase of the subwavelength structure unit constructed on the first piece of superstructure conforms to a first target phase function, and the first target phase function Φ1(x1, y1) is:

[0040]

[0041] Wherein, a is a phase control factor, which adjusts the strength or curvature of the overall phase; (x1, y1) is a two-dimensional coordinate point on the first piece of superstructure, and actan(y, x) is a polar angle, which represents the angular direction of the point (y, x) relative to the origin.

[0042] Wherein, represents the square of the radial distance from (x1, y1) on the first piece of superstructure to the origin on the first piece of superstructure, reflecting how far from the center (reflecting the radial variation trend).

[0043] In one example, the phase of the first piece of superstructure is as shown in the first piece of sample phase in Figure 2

[0044] ​In one embodiment, the phase of the subwavelength structure units constructed on the second metasurface sheet conforms to a first target phase function, the first target phase function Φ2(x2, y2) is:

[0045]

[0046] wherein a is a phase control factor, (x2, y2) is a two-dimensional coordinate point on the second metasurface sheet, actan(y, x) is a polar angle, indicating the angular direction of the point (y, x) relative to the origin.

[0047] wherein, represents the square of the radial distance of (x2, y2) on the second metasurface sheet to the origin on the second metasurface sheet, reflecting how far away from the center (reflecting the radial variation trend).

[0048] In one example, the phase of the second metasurface sheet is as shown in the second sample phase in Figure 2 .

[0049] In one embodiment, the preset interval is between 50 nm and 500 μm.

[0050] In one embodiment, the angle θ ranges from 0° to 360°.

[0051] In one embodiment, the working wavelength range of the first metasurface sheet and the second metasurface sheet is the ultraviolet wavelength.

[0052] wherein the ultraviolet wavelength refers to a section of the electromagnetic wave with a wavelength range of 10 nanometers to 400 nanometers.

[0053] In one embodiment, the material used by the first metasurface sheet and the second metasurface sheet is one or more of titanium dioxide (TiO2), silicon (Si), silicon nitride (Si3N4), hafnium oxide (HfO2), SiC, metal, zinc oxide (ZnO) material.

[0054] wherein the metal can be gold, silver, aluminum, etc.

[0055] In one embodiment, the focal length varies in the range of f = π / (a × θ × λ), wherein f is the focal length, a is the phase control factor, λ is the wavelength, and θ is the rotation angle.

[0056] wherein, as shown in Figure 3 , the light intensity distribution of the corresponding cross section at different rotation angles, some examples are shown in Figure 4 , as the rotation angle changes from 0 degrees to 360 degrees, the focal length changes accordingly.

[0057] In one embodiment, the rotation between the first piece of metasurface and the second piece of metasurface is rotated by MEMS, motor or manually.

[0058] Compared with the prior art, the variable-focus metasurface lens system has the following advantages:

[0059] 1. Simple structure, no need to change the element spacing, continuous focusing can be achieved by rotation, and the response speed is improved;

[0060] 2. Numerical aperture (NA) can be adjusted while adjusting the focal length, suitable for multi-mode imaging;

[0061] 3. Easy to miniaturize and integrate, suitable for portable microscopes, near-eye displays, light field control systems, etc.;

[0062] 4. Strong adaptability of materials and wave bands, can be used in multiple spectral intervals.

[0063] The technical features of the above embodiments can be combined in any way. In order to make the description simple, all possible combinations of the technical features in the above embodiments are not described, but as long as the combination of the technical features does not exist contradictory, it should be considered as the scope of the description.

[0064] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the scope of the patent of the present application should be subject to the appended claims.

Claims

1. A variable-focus meta-lens system, characterized in that, The system includes: a first metasurface and a second metasurface; The first metasurface and the second metasurface are sequentially arranged on the same optical axis, with a preset distance between the first metasurface and the second metasurface; A set of subwavelength structural units is constructed on the first metasurface; A set of subwavelength structural units are constructed on the second metasurface, and the second metasurface is rotated by an angle θ relative to the first metasurface about the normal direction. By adjusting the equivalent phase distribution of the composite device through the relative rotation between the first and second metasurfaces, continuous control of the focal length is achieved, accompanied by changes in the numerical aperture.

2. The variable focal length meta-lens system according to claim 1, characterized in that, The phase of the subwavelength structural unit constructed on the first metasurface conforms to a first target phase function, Φ1(x1, y1), which is: Where a is the phase adjustment factor, (x1, y1) is the two-dimensional coordinate point on the first metasurface, and actan(y,x) is the polar angle, representing the angular direction of point (y,x) relative to the origin.

3. The variable focal length meta-lens system according to claim 1, characterized in that, The phase of the subwavelength structural unit constructed on the second metasurface conforms to the second target phase function, Φ2(x2, y2), which is: Where a is the phase control factor, (x2, y2) is the two-dimensional coordinate point on the second metasurface, and actan(y,x) is the polar angle, representing the angular direction of point (y,x) relative to the origin.

4. The variable focal length meta-lens system according to claim 1, characterized in that, The preset spacing is between 50nm and 500μm.

5. The variable focal length meta-lens system according to claim 1, characterized in that, The angle θ ranges from 0° to 360°.

6. The variable focal length meta-lens system according to claim 1, characterized in that, The operating wavelength range of the first metasurface and the second metasurface is ultraviolet wavelength.

7. The variable focal length meta-lens system according to claim 1, characterized in that, The first metasurface and the second metasurface are made of one or more of the following materials: titanium dioxide, silicon, silicon nitride, hafnium oxide, SiC, metal, and zinc oxide.

8. The variable focal length meta-lens system according to claim 1, characterized in that, The range of the focal length variation is f = π / (a × θ × λ), where f is the focal length, a is the phase adjustment factor, λ is the wavelength, and θ is the rotation angle.

9. The variable focal length meta-lens system according to claim 1, characterized in that, The rotation between the first metasurface and the second metasurface is achieved via MEMS, a motor, or manual means.

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