Nano resonator-based metasurface and design method for realizing wavelength classification deflection

Abstract

The invention discloses a metasurface based on a nano resonator and a design method for realizing wavelength classification deflection. The metasurface is formed by periodically arranging three unit silicon nano resonators, wherein the widths of middle layers of the unit silicon nano resonators change in a gradient mode along the x axis, and the metasurface is of the sub-wavelength scale. The substrate of the unit resonator is a silver substrate, the surface of the silver substrate is provided with a silicon nanometer strip, and the top of the silicon nanometer strip and the top of the silver substrate are respectively deposited and covered with a layer of silver film; by adjusting the thickness of the middle silicon layer of the resonator, the working wavelength of a near-infrared band can be regulated and controlled, normal incident y polarized light with a specific wavelength is deflected to a diffraction order, light with other wavelengths is vertically reflected, and meanwhile, a phase modulation function is achieved. The device has the remarkable advantages of simple structure and convenience in preparation, has the advantages of high throughput and large-area preparation, and has important application prospects in new technologies such as optical imaging, spectrum detection and machine vision.

Description

Technical Field

[0001] The present invention relates to the field of micro-nano optical technology, and in particular to a nano-resonator-based metasurface and a design method for achieving wavelength classification deflection. Background Art

[0002] Metasurfaces have demonstrated remarkable light manipulation capabilities through various physical mechanisms, enabling a range of novel functionalities in areas such as structural color, optical imaging, and holographic displays. Fabry-Pérot (FP) resonance, one of the most fundamental physical mechanisms in nanophotonics, has been widely used to precisely control light fields due to its cavity effect's excellent resonant interference properties, showing promising applications in a wide range of fields. However, the lack of phase modulation in conventional FP metasurfaces hinders their application, particularly in wavefront reconstruction. To enhance the wavefront shaping capabilities of FP metasurfaces, current approaches involve integrating FP metasurfaces with phase-based metasurfaces in the direction of light propagation or designing the top metal layer into various structural shapes to introduce phase. These approaches not only increase manufacturing complexity and cost but also introduce additional resonances, reducing the spectral selectivity of the metasurface. Therefore, maintaining the narrowband spectral selectivity of the FP cavity while arbitrarily manipulating both the spectrum and phase within a simple structure remains a core challenge in this field. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides a metasurface based on nanoresonators and a design method for achieving wavelength classification deflection.

[0004] To achieve the above object, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a metasurface based on silicon nanoresonators, wherein the core structure includes three unit silicon nanoresonators, wherein the middle layer of these unit silicon nanoresonators has a width gradient. x They are arranged periodically in the direction, forming a large period of the metasurface, and the large period is along x Direction arrangement. Among them, the width of the middle layer of the three unit silicon nanoresonators changes in a gradient, and the width gradually increases. The gradient width of the middle layer is not a fixed value, but is determined according to the working band of the metasurface. y It extends periodically in the axial direction and is equivalent to a grating as a whole.

[0005] In terms of its specific structure, the unit resonator is based on a metal substrate with a thickness greater than 100 nm, and its material can be selected from gold, silver, or aluminum. Silicon nanostrips are arranged on the metal substrate surface, and a metal film with a thickness of 20 nm to 40 nm is deposited on top of the silicon nanostrips and the metal substrate, and its material can also be selected from gold, silver, or aluminum. The operating wavelength of the metasurface is determined by the thickness of the central silicon nanostrip. The width of the silicon nanostrips ranges from 50 nm to 200 nm, and the gradient width can produce a phase difference at the resonant wavelength while maintaining narrowband filtering characteristics. When the operating wavelength is 1000 nm, the intermediate layer thickness is 160 nm, and the three widths are 70 nm, 80 nm, and 90 nm, respectively. When the operating wavelength is 1300 nm, the intermediate layer thickness is 200 nm, and the three widths are 115 nm, 130 nm, and 150 nm, respectively. When the operating wavelength is 1600 nm, the intermediate layer thickness is 260 nm, and the three widths are 140 nm, 150 nm, and 185 nm, respectively. The intermediate layer thickness determines the optical path difference of light within the resonant cavity, and the optical path difference is the core variable for satisfying the FP resonance phase matching condition. Therefore, changing the intermediate layer thickness directly changes the resonant wavelength—only when the thickness matches the optical path difference of a specific wavelength will that wavelength be selectively enhanced, that is, the wavelength selectivity is dominated by the intermediate layer thickness.

[0006] The metasurface is x The unit resonator with a width gradient arrangement in the axial direction can have a phase modulation function at the working wavelength and only y Polarized light takes effect. For silicon nanoresonators arranged in a width gradient, when the resonant wavelength bandwidth is less than 100 nm, the phase shift is greater than π. By adjusting the thickness of the metasurface's intermediate silicon layer, the metasurface's operating wavelength can be effectively and freely customized within the infrared band of 1000 nm to 1600 nm. Simultaneously, its narrowband characteristics, less than a 100 nm bandwidth, enable near-infrared wavelength classification and deflection.

[0007] In addition, the operating wavelength of the metasurface can be adjusted by the thickness of the intermediate silicon layer, and any of 400 nm, 500 nm, or 600 nm can be selected as the unit resonator. x period to match the desired wavelength and diffraction angle; select 400 nm, 500 nm or 600 nm as the unit resonator yperiod. It can match the required wavelength and diffraction angle. In terms of material selection, high refractive index and low loss materials are used to enhance the interference and diffraction effects of light. In addition, the metasurface can achieve wavelength classification deflection and monochromatic beam deflection by re-optimizing the structure, and can be used as a universal platform for simultaneous manipulation of spectrum and wavefront phase. Re-optimizing the structure means first redesigning the period of the resonator, and then designing the thickness and width of the nanoblock according to the reflection spectrum diagram and phase change diagram of the nanoblock. According to the phase line diagram, three suitable widths are selected as the width of the resonator. x Width gradient arrangement is performed in the direction.

[0008] In the second aspect, the present invention also provides a design method for realizing wavelength classification deflection based on a metasurface of silicon nanoresonators. The metasurface of arrayed nanoresonators has a simple structure and narrowband characteristics, and the spectral characteristic is a narrowband absorption peak, and the peak value is determined by the thickness of the intermediate silicon layer. The metasurface perfectly inherits the spectral selectivity of the FP resonance of the unit resonator, while creating a certain degree of phase modulation freedom near the resonant wavelength. y When polarized light is irradiated perpendicularly, the metasurface effectively deflects only light with wavelengths close to the resonant absorption condition to a specific diffraction angle, while other light is directly reflected, achieving wavelength-selective deflection. By adjusting the thickness of the intermediate silicon layer, the operating wavelength of the wavelength-selective metasurface can be effectively and freely customized within the infrared band of 1000 nm to 1600 nm, with its narrowband characteristics less than 100 nm.

[0009] In addition, the diffraction angle at a specific wavelength can be effectively adjusted by changing the period of the resonator without affecting the performance of monochromatic diffraction, achieving arbitrary deflection of the monochromatic light beam, thus meeting the design requirements of any wavelength and steering angle in the infrared region.

[0010] Thirdly, the nanoresonator-based metasurface of the present invention can be applied to multiple technical fields or scenarios, including but not limited to: spectral analysis, wavelength routing, and multispectral imaging. For example: An application of a metasurface based on a nanoresonator, wherein the metasurface is applied to the field of spectral analysis, and its wavelength classification and deflection function is utilized to achieve high-precision identification of spectral components.

[0011] An application of a metasurface based on nanoresonators is described. The metasurface is applied to a wavelength routing scenario. By adjusting the resonator period and the thickness of the intermediate silicon layer, arbitrary angle deflection and wavelength routing control of a monochromatic light beam in the near-infrared band can be achieved.

[0012] A multispectral imaging device comprises the nanoresonator-based metasurface, and is used to realize classification deflection and spectral imaging of multi-wavelength light signals.

[0013] In summary, the nanoresonator-based metasurface of the present invention can serve as a novel wavelength classification device. This device utilizes the aforementioned metasurface to achieve monochromatic beam control while providing a degree of phase modulation freedom greater than π. This combination of monochromatic beam control and a certain degree of phase modulation freedom, combined with flexible design capabilities and ease of fabrication, demonstrates broad application prospects in multiple cutting-edge scientific fields.

[0014] The advantages and beneficial effects of the present invention are as follows: The present invention has the significant advantages of a streamlined structure and convenient preparation, enabling high-throughput, large-scale production and large-area fabrication. In the field of optical imaging, it can provide precise wavelength control for high-resolution imaging; in the field of spectral detection, it can efficiently implement wavelength classification and deflection, improving detection sensitivity; in the field of machine vision, it provides innovative solutions for multi-spectral recognition and dynamic beam control, demonstrating important application value and broad prospects in cutting-edge scientific and technological fields. Specific advantages are: 1. By adjusting the structural parameters of the unit resonator, and more than one adjustable structural parameter, such as the interlayer material, thickness and width of the interlayer, and the period of the unit resonator, wavelength-classified deflection and arbitrary deflection of monochromatic light beams can be achieved. This high-precision control is difficult to achieve in most optical components.

[0015] 2. While perfectly inheriting the spectral selectivity of the FP resonance of the unit resonator, the metasurface creates a certain degree of phase modulation freedom near the resonance wavelength. This integration not only simplifies the design of the optical system, but also improves the compactness and efficiency of the system, and broadens the application scenarios, especially in wavefront reconstruction.

[0016] 3. By adjusting the parameters of the unit resonator's intermediate layer and the resonator's period, the operating wavelength and diffraction angle can be arbitrarily customized. This customization enables the nanoresonator metasurface to adapt to different optical scenarios, with strong adaptability and versatility.

[0017] 4. The metasurface has ultra-micro dimensions, is compatible with semiconductor processing technology, is simple and easy to process, and is easy to reintegrate with other optical devices, with high flexibility.

[0018] In summary, the silicon nanoresonator-based metasurface of the present invention is innovative in many aspects. The silicon nanoresonator-based metasurface of the present invention achieves a certain degree of phase modulation freedom near the resonance wavelength while perfectly inheriting the spectral selectivity of the FP resonance, thereby realizing wavelength classification deflection; by changing the resonator period, arbitrary angle deflection of a monochromatic light beam can be achieved. It is compatible with semiconductor processing technology, simple and easy to process, and easy to reintegrate with other optical devices. It also has important advantages such as ultra-micro size. By adjusting the thickness and width of the silicon layer of the unit resonator, the working wavelength and diffraction angle of the metasurface can be arbitrarily customized, thereby enabling flexible application in different optical scenarios. It has strong adaptability and versatility and has high promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the silicon nanoresonator-based metasurface and unit resonator that can achieve wavelength classification deflection in the present invention; Figure 2 3 is a simulation diagram of the electric field distribution of light reflection waves at three different wavelengths when the thickness of the metasurface intermediate layer in an embodiment of the present invention is 160 nm, 200 nm, and 260 nm, respectively; Figure 3 The reflection of a single resonant cavity varies with wavelength and width when the thickness of the silicon layer in the middle of the unit resonator is 160 nm, 200 nm and 260 nm in the embodiment of the present invention. w Simulation diagram of changes in Figure 4 The phase delay of the unit resonator at wavelengths of 1000 nm, 1300 nm and 1600 nm varies with the width of the unit resonator in the embodiment of the present invention. w the changing relationship; Figure 5 3 is a reflection simulation diagram of the intermediate silicon layer of the metasurface in an embodiment of the present invention at thicknesses of 160 nm, 200 nm, and 260 nm; Figure 6 3 is a simulation diagram of the angle-resolved reflection intensity of the silicon layer of the metasurface in an embodiment of the present invention at thicknesses of 160 nm, 200 nm, and 260 nm; Figure 7 yes Figure 6 Polar coordinate diagram of far-field reflection intensity corresponding to the corresponding wavelength; Figure 8 is a schematic diagram of the structure and function of the metasurface at different periods in an embodiment of the present invention; Figure 9 3 is a simulation diagram of the angle-resolved reflection intensity of the metasurface period at 1200 nm, 1500 nm, and 1800 nm in an embodiment of the present invention; Figure 10 yes Figure 9 Polar plot of far-field reflection intensity corresponding to the corresponding period in ; In the picture: w 1. w 2. w 3 is the width of the middle layer of the unit silicon nanoresonator with three width gradients; λ 1. λ 2. λ 3 are three different working wavelengths; t is the thickness of the middle layer of the silicon nanoresonator; p is the period of the unit silicon nanoresonator; P x The metasurface x Direction cycle, P y The metasurface y Direction cycle. DETAILED DESCRIPTION

[0020] In order to more clearly illustrate the structure of the present invention and the functions achieved by it, the present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0021] Example 1 This embodiment is a metasurface based on silicon nanoresonators and the specific process of achieving wavelength classification deflection, as well as simulation and experimental results.

[0022] As an embodiment, in order to more clearly illustrate the structural design and performance of the invention, electromagnetic field simulation software is used to design and optimize structural parameters and characterize the performance of the device.

[0023] Figure 1 Schematic diagram of the function and structure of this metasurface based on silicon nanoresonators. y When polarized broadband infrared light is irradiated, the metasurface deflects light of different specific wavelengths, achieving wavelength classification deflection. First, silver is selected as the substrate of the unit resonator, then silicon nanostrips are plated on the silver substrate, and finally a layer of silver is deposited on the surface; the initial structure of a single silicon resonator is as follows: x The directional period is set to 600 nm, and the period of the metasurface is 1800 nm. y The directional period is set to 400 nm, and the thickness of the top silver layer is 30 nm. The thickness and width of the middle silicon layer can be changed as needed. Figure 2 The reflection wavefront profiles of the metasurface in different wavelength channels are shown when the silicon layer thickness is 160nm, 200nm and 260nm, revealing the wavelength classification deflection capability. The phase modulation is derived from the width gradient design of the three resonators. When the wavelength matches the structural parameters, the metasurface will control the phase at a specific wavelength. y Polarized light is reflected directly at other wavelengths. Figure 3 Demonstrates wavelength and width dependence of reflection from a single silicon resonator at three different silicon thicknesses w When the thickness of the intermediate layer of a single resonator is 160 nm, 200 nm, and 260 nm, as the width increases from 50 nm to 200 nm, the FP resonance becomes stronger and undergoes a certain red shift. Figure 4 Wavelengths are plotted λ 1 = 1000 nm, λ 2 = 1300 nm and λ 3 = Phase retardation at 1600 nm varies with wavelength w With the change curve of width w The phase retardation changes significantly only at a single wavelength, while it changes steadily at the other two wavelengths (when the silicon thickness is 260 nm, the wavelength is λ 2 also changes the phase of light, but due to a mismatch in width and thickness, it cannot inherit the spectral selectivity of FP. This study reveals the working mechanism of wavelength-selective beam control achieved by metasurfaces. At the operating wavelength, three silicon resonator structural parameters were selected, each with a width variation of less than 40 nm and significant phase delay, to achieve directional deflection control of a monochromatic beam. Figure 5 The reflectivity of the metasurface at three different thicknesses is demonstrated, showing that the metasurface inherits the spectral characteristics of the silicon unit resonator. Figure 6 It was shown that as the thickness of the silicon layer increased from 160 nm to 260 nm, the wavelength of the first-order diffraction changed from 1000 nm to 1600 nm, and the bandwidth was less than 100 nm, once again confirming that the metasurface perfectly combines FP resonance and anomalous reflection. Figure 7 The results show that the first-order diffraction angles are 33.8°, 46.3° and 62.7° at wavelengths of 1000 nm, 1300 nm and 1600 nm respectively. θ = arcsin ( mλ / P ) calculation results are consistent. Figure 8 It was demonstrated that at different periods, the metasurface still maintains its narrowband wavelength selectivity and can deflect 1000 nm light to different angles, demonstrating the ability to adjust the abnormal reflection angle of monochromatic light. Figure 9 It was demonstrated that the diffraction angle at a wavelength of 1000 nm can be continuously adjusted from 56.4° to 33.8°, demonstrating that the diffraction angle can be arbitrarily adjusted by changing the period of the metasurface without affecting the wavelength selection properties. Figure 10 The polar coordinate diagrams of the far-field reflection intensity corresponding to metasurface periods of 1200 nm, 1500 nm, and 1800 nm are shown, which are consistent with the results calculated using the grating equation.

[0024] The present invention designs a metasurface based on silicon nanoresonators and a method for achieving wavelength-classified deflection. This metasurface has spectral and phase-independent modulation capabilities and can be used to control monochromatic beams in the infrared band, achieve wavelength-classified deflection, and deflect the monochromatic beam at any angle by adjusting the period of the resonator. The present invention can be easily fabricated using mature semiconductor processes and has the advantages of high throughput and large area. The metasurface of the present invention will provide a universal and effective strategy for infrared monochromatic wavefront engineering and promote the development of new technologies such as optical imaging, spectral detection, and machine vision.

Claims

1. A metasurface based on silicon nanoresonators, characterized by: A unit resonator comprising three intermediate layers having a width gradient; The three unit resonators are x The direction is periodically arranged to form a metasurface x-direction period The super surface is y The axial direction is also periodically arranged to form a metasurface y Direction cycle, x Direction cycle and y The grating structure is formed as a whole by the periodicity of the direction; the metasurface is formed by x The unit resonators are arranged with a gradient change in the width of the middle layer in the axial direction, so that the metasurface has a phase modulation function at the working wavelength and only y Polarized light effect; The width of the middle layer of the three unit resonators is x The direction changes gradually, and the width of the intermediate layer is selected according to the target working band of the metasurface. The gradient change range of the width of the intermediate layer is 50 nm-200 nm.

2. The metasurface according to claim 1, wherein: The base of the unit resonator is a metal base, and silicon nano strips are arranged on the surface of the metal base; a layer of metal film is deposited on the top of the silicon nano strips and the metal base respectively.

3. The metasurface according to claim 2, wherein: The metal substrate is any one of gold, silver or aluminum; the metal film is any one of gold, silver or aluminum; the thickness of the metal substrate is greater than 100 nm, and the thickness of the metal film is 20 nm-40 nm.

4. A design method for achieving wavelength classification deflection, characterized by: The operating wavelength of the metasurface according to claim 3 is determined by the thickness of the silicon nanostrip in the middle, that is: By adjusting the thickness of the middle silicon layer of the metasurface, the operating wavelength of the metasurface can be effectively and freely customized within the infrared band of 1000 nm to 1600 nm, and its narrowband characteristics are less than 100 nm bandwidth. The silicon nanoresonators arranged in a gradient variation have a phase change greater than π when the resonant wavelength bandwidth is less than 100 nm, thereby realizing the function of near-infrared wavelength classification deflection.

5. The design method according to claim 4, characterized in that: The operating wavelength of the metasurface is adjusted by the thickness of the intermediate silicon layer. The metasurface achieves wavelength classification deflection and monochromatic beam deflection by re-optimizing its structure, serving as a universal platform capable of simultaneously manipulating the spectrum and wavefront phase. Specifically: First, the period of the unit resonator is redesigned, and then the thickness and width of the nanoblock are designed according to the reflection spectrum and phase change diagram of the nanoblock in the unit resonator; finally, several appropriate widths are selected as the width of the unit resonator according to the phase line diagram. x Arrange the gradient in the direction.

6. The design method according to claim 5, characterized in that: The metasurface selects any one of 400 nm, 500 nm or 600 nm as the unit resonator x period to match the required wavelength and diffraction angle; the metasurface selects any one of 400nm, 500nm or 600nm as the unit resonator y period; the metal material of the metal substrate and the metal film is selected to use a material with a high refractive index and low loss to enhance the interference and diffraction effects of light.

7. A wavelength classification device based on a nanoresonator metasurface, characterized in that: The metasurface described in any one of claims 1 to 3 is used to achieve monochromatic light beam control while providing a phase modulation degree of freedom greater than π.

8. An application of a metasurface based on a nanoresonator, characterized by: The metasurface described in any one of claims 1 to 3 is applied to the field of spectral analysis, and its wavelength classification and deflection function is utilized to achieve high-precision identification of spectral components.

9. An application of a metasurface based on a nanoresonator, characterized by: The metasurface described in any one of claims 1 to 3 is applied to a wavelength routing scenario, and arbitrary angle deflection and wavelength routing control of a monochromatic light beam in the near-infrared band are achieved by adjusting the resonator period and the thickness of the intermediate silicon layer.

10. A multispectral imaging device, characterized in that: A nanoresonator-based metasurface comprising any one of claims 1 to 3, for realizing classification deflection and spectral imaging of multi-wavelength optical signals.

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