Polarization-insensitive infrared achromatic metamaterial lens and preparation method thereof

Abstract

The invention belongs to the technical field of super-structure lens imaging, and particularly discloses a polarization-insensitive infrared achromatic super-structure lens and a preparation method thereof.According to the infrared achromatic super-structure lens, a plurality of blind holes are formed in the front face and the back face of a base body at the same time and used for regulating and controlling the phase of incident light; the diameter of the blind holes is determined according to the working wave band and the phase size of the infrared achromatic metamaterial lens body, the metamaterial lens formed by the blind holes in the front face of the base body and the metamaterial lens formed by the back face of the base body show opposite focal power, and the infrared achromatic metamaterial lens can have the achromatic function within the wide wave band range. Meanwhile, the infrared achromatic super-structure lens is prepared on the two sides of the same base body through hole type achromatic super-structure lenses, the parameters such as focal power and focal length of the infrared achromatic super-structure lens are adjusted by adjusting the parameters such as the height of the base body and the depth of holes in the upper surface, and compared with a super-structure lens of a columnar structure, the infrared achromatic super-structure lens has the advantages that the manufacturing cost is reduced, and the manufacturing efficiency is improved. The hole type super-structure lens has better product stability.

Description

Technical Field

[0001] This invention belongs to the field of metalens imaging technology, and particularly relates to a polarization-insensitive infrared achromatic metalens and its preparation method. Background Technology

[0002] Metalenses exhibit superior performance in the miniaturization and polarization control of optical lenses, making their research a hot topic in scientific and engineering fields. However, metalenses are still some distance from practical engineering applications, mainly due to shortcomings in their design and fabrication performance. For example, design-related issues include chromatic aberration and low efficiency, while engineering-related issues include high precision requirements and long processing times for the unit structures. These problems severely restrict the practical application of metalenses. Among them, the chromatic aberration problem is a pressing issue that needs to be addressed. Chromatic aberration in metalenses arises from the different phases of light waves of different wavelengths after passing through the waveguide of the metacell unit. The cemented doublet lens scheme commonly used in traditional optical lens design can provide a solution to the chromatic aberration problem in metalenses. By cementing two lenses with different positive and negative optical powers together, the phases of the shortest and longest wavelengths at the focal point can be aligned. Summary of the Invention

[0003] This invention provides a polarization-insensitive infrared achromatic metalens and its fabrication method, in order to solve the problem of how to achieve achromatic effect using an infrared metalens.

[0004] In a first aspect, a polarization-insensitive infrared achromatic metalens is provided, the metalens comprising a substrate; the substrate comprising a front side and a back side;

[0005] The front side has a first number of blind holes; the back side has a second number of blind holes.

[0006] The first number of blind apertures and the second number of blind apertures are used to jointly modulate the phase of the incident light in order to achieve infrared achromatic light.

[0007] Secondly, a method for fabricating a polarization-insensitive infrared achromatic metalens is provided, the method comprising:

[0008] Configure the processing system: Configure the ultraviolet femtosecond laser processing system, adjust the position of the focusing objective, initially calibrate the laser position, and perform pre-positioning;

[0009] Fixing the material sample: First, clean the ZnS substrate with degreased cotton soaked in alcohol. After confirming that the substrate surface is clean under a 220x magnification electron microscope, fix the ZnS substrate on the processing platform, adjust the micro-motion platform, determine the processing origin, and import the meta-lens processing parameters designed by FDTD into the software.

[0010] Beam positioning: The beam generates a multifocal array through a microlens array. Adjusting the height of the focusing objective or the vertical height of the micro-motion platform allows the multifocal array of the laser to be focused on the sample surface.

[0011] Set the processing parameters: laser wavelength 350nm, pulse power 1W-100W, pulse width 250fs, and use a grid-like scanning pattern;

[0012] Real-time monitoring: Equipped with an online observation CCD to monitor the processing morphology in real time;

[0013] Start processing: Start the ultraviolet femtosecond laser processing system to process the ZnS sample and complete the processing of one side of the microarray;

[0014] After processing one side of the metalens, high-pressure nitrogen is used to purge the surface impurities. Then, the substrate is flipped over, and the other side of the metalens is processed according to the above process. After processing both sides, a perforated achromatic metalens is obtained.

[0015] This invention provides a polarization-insensitive infrared achromatic metalens and its fabrication method. Compared with the prior art, this polarization-insensitive infrared achromatic metalens can effectively reduce the chromatic aberration of the metalens and improve the image quality of the metalens. By using a single dielectric material as the substrate and a blind aperture as the metalens unit for adjusting the phase, the fabrication difficulty of the metalens is reduced, the processing technology is simplified, and the stability of the product is improved.

[0016] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1 A cross-sectional schematic diagram of a polarization-insensitive infrared achromatic metalens according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the principle of a porous metasurface provided according to an embodiment of the present invention;

[0020] Figure 3 This is a schematic diagram illustrating the relationship between the hole radius and phase according to an embodiment of the present invention;

[0021] Figure 4 A schematic diagram of the relationship between the target phase of a ZnS substrate positive front surface positive focal length meta-lens, the opening radius and the substrate surface position according to an embodiment of the application is shown in Figure 1;

[0022] Figure 5 A schematic diagram of the relationship between the target phase of a ZnS substrate negative back surface negative focal length meta-lens, the opening radius and the substrate surface position according to an embodiment of the application is shown in Figure 2;

[0023] Figure 6 A schematic diagram of the axial field intensity distribution of an infrared achromatic meta-lens at different wavelengths according to an embodiment of the application is shown in Figure 3;

[0024] Figure 7 A schematic diagram of the axial field intensity distribution of a single-layer meta-lens at different wavelengths according to an embodiment of the application is shown in Figure 4;

[0025] Figure 8 An implementation flowchart of a preparation method of a polarization-insensitive infrared achromatic meta-lens according to an embodiment of the application is shown in Figure 5. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below with reference to the embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0027] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the application described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, device, product or equipment including a series of steps or units does not have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or equipment.

[0028] The technical solutions provided by the embodiments of the present application will be described in detail below with reference to the drawings.

[0029] In order to realize infrared achromatism using a meta-lens, the embodiments of the present application provide a polarization-insensitive infrared achromatic meta-lens and a preparation method thereof.

[0030] Figure 1 A cross-sectional schematic view of a polarization-insensitive infrared achromatic meta-lens according to an embodiment of the present application is shown in FIG. 1. The infrared achromatic meta-lens includes a substrate. The substrate includes a front surface and a back surface. Figure 1

[0031] The front surface is provided with a first number of blind holes, and the back surface is provided with a second number of blind holes.

[0032] The first number of blind holes and the second number of blind holes are used to jointly regulate the phase of incident light to achieve infrared achromatism.

[0033] In one specific embodiment, the target phase of the infrared achromatic meta-lens is set according to the following formula: Figure 2

[0034]

[0035]

[0036] In the formula, φ denotes the target phase, λ denotes the wavelength of incident light, f denotes the focal length of the infrared achromatic meta-lens, and (x, y) denotes any point on the surface of the infrared achromatic meta-lens. In one specific embodiment, the diameters of the first number of blind holes and the second number of blind holes are determined according to the working wavelength range and the phase size of the infrared achromatic meta-lens body.

[0037]

[0038] In the same hole depth condition, different diameter sizes of holes correspond to different phase sizes. According to the distribution requirements of the target phase of the meta-lens, holes with the same depth and different diameter sizes are arranged.

[0039] In one specific embodiment, the long-wave infrared material ZnS is selected as the substrate. The meta-lens composed of the blind holes on the front surface of the substrate and the meta-lens composed of the blind holes on the back surface of the substrate exhibit opposite optical powers. The FDTD finite element analysis software is used for design to enable the infrared achromatic meta-lens to achieve achromatism in a wide wavelength range.

[0040] In one specific embodiment, the long-wave infrared material ZnS is selected as the substrate. The meta-lens composed of the blind holes on the front surface of the substrate and the meta-lens composed of the blind holes on the back surface of the substrate exhibit opposite optical powers. The FDTD finite element analysis software is used for design to enable the infrared achromatic meta-lens to achieve achromatism in a wide wavelength range.

[0041] In one specific embodiment, the long-wave infrared material ZnS is selected as the substrate. The meta-lens composed of the blind holes on the front surface of the substrate and the meta-lens composed of the blind holes on the back surface of the substrate exhibit opposite optical powers. The FDTD finite element analysis software is used for design to enable the infrared achromatic meta-lens to achieve achromatism in a wide wavelength range.

[0042] In one specific embodiment, the long-wave infrared material ZnS is selected as the substrate. The meta-lens composed of the blind holes on the front surface of the substrate and the meta-lens composed of the blind holes on the back surface of the substrate exhibit opposite optical powers. The FDTD finite element analysis software is used for design to enable the infrared achromatic meta-lens to achieve achromatism in a wide wavelength range.

[0043] ​​​​The infrared achromatic superlens has a diameter d of 200 μm, the blind hole depths h1 and h2 of the front and back superlenses are both 18 μm, the radius of the hole unit structure is scanned, when the radius is scanned from 1.6 μm to 2.4 μm, a phase range of 2π is obtained, and according to the distribution requirements of the target phase of the superlens, holes with the same depth and different diameters can be arranged, such as shown in Figure 3

[0044] It should be noted that the infrared achromatic superlens substrate can be a cylinder or a cuboid, and is selected and set according to actual needs.

[0045] In a specific embodiment,

[0046] The front surface with the first number of blind holes constitutes a positive focal length superlens, and the focal length is 500 μm; the target phase, the hole radius and the position relationship on the substrate surface are as shown in Figure 4

[0047] The back surface with the second number of blind holes constitutes a negative focal length superlens, and the focal length is -2000 μm. The target phase, the hole radius and the position relationship on the substrate surface are as shown in Figure 5

[0048] In a specific embodiment,

[0049] The total focal length of the lens formed by the front and back surfaces of the infrared achromatic superlens is as shown in Figure 6 The focal length is 763 nm when the incident light wave band is 8 μm and 10 μm, and the focal length is 820.89 μm when the incident light wave band is 9 μm, and the maximum chromatic aberration is only 57 μm. A single-layer superlens with a similar focal length is selected for comparison, that is, a single-layer positive focal length superlens with only a front surface has a focal length of 1013 μm, 903 μm and 828 μm at 8 μm, 9 μm and 10 μm respectively, and the maximum chromatic aberration difference is 185 μm, as shown in Figure 7 It can be seen that the double-layer achromatic lens has a significant achromatic function.

[0050] In a specific embodiment,

[0051] According to the focal length requirements of the superlenses on the front and back surfaces of the substrate, the blind hole array arrangement on the front and back surfaces, the blind hole radius, the depth and the period parameters are adjusted to form a processing model.

[0052] In a specific embodiment,

[0053] The processing model is introduced into a femtosecond laser processing device or an electron beam etching device for processing.

[0054] ​​​Based on the same inventive concept, this invention also provides a method for fabricating a polarization-insensitive infrared achromatic metalens, see [link to relevant documentation]. Figure 8 The method includes:

[0055] S800: Configure the processing system: Configure the ultraviolet femtosecond laser processing system, adjust the position of the focusing objective lens, initially calibrate the laser position, and perform pre-positioning;

[0056] S802: Fixing the material sample: First, clean the ZnS substrate with degreased cotton soaked in alcohol. After confirming that the substrate surface is clean under a 220x magnification electron microscope, fix the ZnS substrate on the processing platform, adjust the micro-motion platform, determine the processing origin, and import the meta-lens processing parameters designed by FDTD into the software.

[0057] S804: Beam positioning: The beam generates a multifocal array through a microlens array. Adjusting the height of the focusing objective or the vertical height of the micro-motion platform allows the multifocal array of the laser to be focused on the sample surface.

[0058] S806: Set processing parameters: laser wavelength 350nm, pulse power 1W-100W, pulse width 250fs, and use "grid" pattern scanning;

[0059] S808: Real-time monitoring: Equipped with an online observation CCD to monitor the processing morphology in real time;

[0060] S810: Start processing: Start the ultraviolet femtosecond laser processing system to process the ZnS sample and complete the processing of one side of the microarray;

[0061] S812: After processing one side of the metalens, high-pressure nitrogen is used to purge the surface impurities. Then the substrate is flipped over, and the other side of the metalens is processed according to the above process. After processing both sides, a perforated achromatic metalens is obtained.

[0062] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0063] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A polarization-insensitive infrared achromatic metalens, characterized in that, The infrared achromatic meta-lens includes a substrate; the substrate includes a front side and a back side; The front side has a first number of blind holes; the back side has a second number of blind holes. The first number of blind apertures and the second number of blind apertures are used to jointly modulate the phase of the incident light in order to achieve infrared achromatic light.

2. The infrared achromatic metalens according to claim 1, characterized in that, The target phase of the infrared achromatic metalens is set according to the following formula: In the formula, λ represents the target phase; λ represents the wavelength of the incident light; f represents the focal length of the infrared achromatic metalens; (x,y) represents any point on the surface of the infrared achromatic metalens.

3. The infrared achromatic metalens according to claim 2, characterized in that, The diameters of the first and second number of blind holes are determined based on the operating wavelength and phase magnitude of the infrared achromatic metalens body; Under the same hole depth, holes with different diameters correspond to different phase sizes. According to the distribution requirements of the target phase of the meta-lens, holes with the same depth but different diameters are arranged.

4. The infrared achromatic metalens according to claim 3, characterized in that, ZnS, a long-wave infrared material, was selected as the substrate. The metalens formed by the blind holes on the front side of the substrate and the metalens formed by the back side of the substrate exhibit opposite optical powers. The design was carried out using FDTD finite element analysis software to enable the infrared achromatic metalens to achieve achromaticity over a wide wavelength range.

5. The infrared achromatic metalens according to claim 4, characterized in that, The infrared achromatic metalens has a diameter d of 200 μm, and the blind hole depths h1 and h2 of the front and back metalenses are both 18 μm. The radius of the hole unit structure is scanned, and when the radius is scanned from 1.6 μm to 2.4 μm, a phase range of 2π is obtained.

6. The infrared achromatic metalens according to claim 5, characterized in that, The front side with a first number of blind holes constitutes a positive optical power super lens with a focal length of 500μm; A negative-formation superlens with a second number of blind holes has a focal length of -2000μm.

7. The infrared achromatic metalens according to claim 6, characterized in that, The total focal length formed by the two surfaces of the infrared achromatic meta-lens is 763nm when the incident light wavelength is 8μm and 10μm, and 820.89μm when it is 9μm, with a maximum chromatic aberration of only 57μm.

8. The infrared achromatic metalens according to claim 7, characterized in that, Based on the optical power requirements of the metalenses on both sides of the substrate, the arrangement of the blind aperture arrays on both sides, the size of the blind aperture radius, the size of the depth, and the period parameters are adjusted to form a processing model.

9. The infrared achromatic metalens according to claim 8, characterized in that, The processing model is imported into a femtosecond laser processing device or an electron beam etching device for processing.

10. A method for fabricating a polarization-insensitive infrared achromatic metalens, characterized in that, The method includes: Configure the processing system: Configure the ultraviolet femtosecond laser processing system, adjust the position of the focusing objective, initially calibrate the laser position, and perform pre-positioning; Fixing the material sample: First, clean the ZnS substrate with degreased cotton soaked in alcohol. After confirming that the substrate surface is clean under a 220x magnification electron microscope, fix the ZnS substrate on the processing platform, adjust the micro-motion platform, determine the processing origin, and import the meta-lens processing parameters designed by FDTD into the software. Beam positioning: The beam generates a multifocal array through a microlens array. Adjusting the height of the focusing objective or the vertical height of the micro-motion platform allows the multifocal array of the laser to be focused on the sample surface. Set the processing parameters: laser wavelength 350nm, pulse power 1W-100W, pulse width 250fs, and use "grid" scanning; Real-time monitoring: Equipped with an online observation CCD to monitor the processing morphology in real time; Start processing: Start the ultraviolet femtosecond laser processing system to process the ZnS sample and complete the processing of one side of the microarray; After processing one side of the metalens, high-pressure nitrogen is used to purge the surface impurities. Then, the substrate is flipped over, and the other side of the metalens is processed according to the above process. After processing both sides, a perforated achromatic metalens is obtained.

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