Energy flow regulation and control thin film structure based on multilayer film

Abstract

The invention relates to an energy flow regulation thin film structure based on a multilayer film, which comprises a substrate, the multilayer film and a metasurface which are arranged from bottom to top, the multilayer film comprises a high-reflective film, the metasurface comprises a super unit structure, the multilayer film further comprises a non-periodic film, and the non-periodic film is connected with the high-reflective film and the metasurface; and energy flow regulation and control in a wider range can be realized by adjusting the thickness of the non-periodic film layer. Compared with the prior art, the non-periodic film layer is arranged, so that wider and stronger energy flow regulation and control can be realized; the degree of freedom is higher in the metasurface design, and the design difficulty is reduced; the problem that the broadband regulation and control capability of the multilayer film is weak under the Littrow incident angle is solved; more super-unit structures are used, so that the transverse energy flow transmission capability of the whole super-surface is enhanced; the broadband Littrow reflection efficiency of more than 99% can be realized by the laser wavelength in the mid-infrared broadband range.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic wave energy flow regulation, and in particular to an energy flow regulation thin film structure based on a multilayer film. Background Art

[0002] As a two-dimensional metamaterial, metasurface can regulate the phase, amplitude and polarization of incident light through the design of unit structure, and has realized a variety of functions, including lens focusing, polarization conversion, holographic imaging, vortex beam and abnormal deflection.

[0003] Abnormal deflection is one of the basic functions of optical path regulation. Abnormal reflection under Littrow incidence plays a vital role in applications such as laser beam combining and spectral analysis, and Littrow reflection efficiency of more than 99% is the basis for realizing advanced functions of metasurfaces. Reflective abnormal deflection devices mainly use metal or dielectric metasurfaces to achieve the functions of high reflectivity and abnormal deflection. Due to the absorption characteristics of metals in the mid-infrared band, it is difficult to increase the efficiency of metal metasurfaces to more than 99%. At the same time, due to the lack of sufficient lateral energy flow transfer capability, the efficiency of existing dielectric metasurfaces decreases rapidly at the edge of the bandwidth, and can only achieve narrow-band Littrow perfect reflection, which is not conducive to the realization of more complex functions. It can be seen that there is currently a lack of a suitable design method to use all-dielectric metasurfaces to achieve broadband perfect Littrow reflection in the mid-infrared band.

[0004] The invention patent with publication number CN110727037A discloses a linear phase gradient metasurface structure based on a high-reflection film, comprising a substrate (1), a high-reflection film (2) and a metasurface (3) arranged in sequence from bottom to top, wherein the high-reflection film (2) is a dielectric film stack composed of a high-refractive index dielectric film layer H1 and a low-refractive index dielectric film layer L alternately arranged, the side of the high-reflection film (2) in contact with the metasurface (3) is a low-refractive index dielectric film layer L, the metasurface (3) adopts a high-refractive index dielectric film layer H2, and one period of the metasurface (3) is composed of a plurality of unit structures of different widths. The invention omits the traditional thick metal substrate and introduces a full dielectric high-reflection film, thereby improving the reflectivity of the metasurface and reducing the loss of the metasurface, but lacks the ability to regulate energy flow in a wider range.

[0005] At present, how to enhance the ability to regulate energy flow in a wider range and achieve mid-infrared broadband perfect Littrow reflection is an urgent problem to be solved for the practical application of anomalous reflection metasurfaces. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide an energy flow regulating thin film structure based on a multilayer film.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A thin film structure for energy flow regulation based on a multilayer film comprises a substrate, a multilayer film and a super surface arranged from bottom to top, wherein the multilayer film comprises a high-reflection film, the super surface comprises a super unit structure, and the multilayer film further comprises a non-periodic film, wherein the non-periodic film is respectively connected to the high-reflection film and the super surface; energy flow regulation in a wider range can be achieved by adjusting the thickness of the non-periodic film layer.

[0009] As a preferred technical solution, the high-reflective film and the non-periodic film are a dielectric film stack composed of alternating high-refractive index dielectric film layers H and low-refractive index dielectric film layers L; the contact side of the non-periodic film with the high-reflective film and the metasurface is the low-refractive index dielectric film layer L.

[0010] As a preferred technical solution, the high reflective film structure is (LH) 7 , the non-periodic membrane structure is LHL.

[0011] As a preferred technical solution, the material of the high refractive index dielectric film layer H is Si, and the material of the low refractive index dielectric film layer L is SiO2.

[0012] As a preferred technical solution, the thickness selection method of the non-periodic film layer is:

[0013] Based on the determined width of the superunit structure in the metasurface, the Littrow reflection efficiency of the non-periodic film layer with different thicknesses is scanned, and the thickness is locally fine-tuned to achieve the highest broadband Littrow reflection efficiency of the superunit structure of the metasurface.

[0014] As a preferred technical solution, the non-periodic film includes a dielectric film stack composed of three layers of high refractive index dielectric film layers H and low refractive index dielectric film layers L of different thicknesses arranged alternately, and the structures from bottom to top are the first low refractive index dielectric film layer L, the first high refractive index dielectric film layer H and the second low refractive index dielectric film layer L.

[0015] As a preferred technical solution, the metasurface includes a plurality of superunit periods with a period range of p, and the superunit period includes n superunit structures with different widths and the same height.

[0016] As a preferred technical solution, the super unit period range p and the number of super unit structures n are selected using the following formula:

[0017]

[0018] Where λ is the Littrow reflection wavelength and i is the Littrow incident angle.

[0019] As a preferred technical solution, the method for selecting the height of the supercell structure of the supersurface is:

[0020] The width of a single superunit structure of the metasurface is scanned so that the reflection phase of each superunit structure can cover a variation range of 0 to 2π; the phase variation is achieved by using n superunit structures of different widths and a superunit period with a period range of p; wherein n≥4, and n is a positive integer.

[0021] As a preferred technical solution, the method for selecting the width of the supercell structure of the supersurface is:

[0022] Through rigorous coupled wave analysis, the theoretical value of the Poynting vector inside the metasurface under different incident wavelengths is obtained. The widths of n superunit structures in the superunit period of the metasurface are scanned to obtain the Poynting vector inside the metasurface at this time, so that it matches the target value obtained by theoretical calculation.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention can achieve wider and stronger energy flow regulation by setting a non-periodic film layer.

[0025] 2. The present invention provides a non-periodic film layer, which allows greater freedom in the design of the metasurface and reduces the difficulty of design.

[0026] 3. The present invention solves the problem of weak broadband control capability of multilayer films under Littrow incident angle by setting a non-periodic film layer.

[0027] 4. The present invention uses more super unit structures to enhance the lateral energy flow transfer capability of the entire super surface.

[0028] 5. The present invention can achieve a broadband Littrow reflection efficiency of more than 99% at a laser wavelength within a mid-infrared broadband range by providing a non-periodic film layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the film structure of the present invention;

[0030] Figure 2 It is a schematic diagram of the structure of the super surface super unit of the present invention;

[0031] Figure 3 A graph showing the relationship between different wavelengths and the required lateral energy flow amplitude within a broadband range of the metasurface of the present invention;

[0032] Figure 4 The total energy flow amplitude scanning results corresponding to different widths of the super unit structure of the super surface of the present invention;

[0033] Figure 5 This is the Littrow reflection efficiency diagram of the supersurface of the present invention.

[0034] 1. Substrate; 2. High-reflective film; 3. Non-periodic film layer; 4. Super surface; 5. Super unit structure; H is a high-refractive index dielectric film layer; L is a low-refractive index dielectric film layer. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0036] Abnormal deflection is one of the basic functions of optical path regulation. Abnormal reflection under Littrow incidence plays a vital role in applications such as laser beam combining and spectral analysis, and Littrow reflection efficiency of more than 99% is the basis for realizing advanced functions of metasurfaces. Reflective abnormal deflection devices mainly use metal or dielectric metasurfaces to achieve the functions of high reflectivity and abnormal deflection. Due to the absorption characteristics of metals in the mid-infrared band, it is difficult to increase the efficiency of metal metasurfaces to more than 99%. At the same time, due to the lack of sufficient lateral energy flow transfer capability, the efficiency of existing dielectric metasurfaces decreases rapidly at the edge of the bandwidth, and can only achieve narrow-band Littrow perfect reflection, which is not conducive to the realization of more complex functions. It can be seen that there is currently a lack of a suitable design method to use all-dielectric metasurfaces to achieve broadband perfect Littrow reflection in the mid-infrared band.

[0037] The present invention can achieve stronger energy flow regulation by setting a non-periodic film layer, has greater freedom in metasurface design, and reduces the design difficulty; solves the problem of weak regulation ability of multilayer films under Littrow incidence, and enhances the lateral energy flow transfer ability of the entire metasurface; the laser wavelength in the mid-infrared broadband range can achieve a broadband Littrow reflection efficiency of more than 99%.

[0038] Example 1

[0039] Schematic diagram of film structure Figure 1 As shown, a thin film structure for energy flow regulation based on a multilayer film includes a substrate 1, a multilayer film and a supersurface 4 arranged from bottom to top, wherein the multilayer film includes a high-reflection film 2, the supersurface 4 includes a superunit structure 5, and the multilayer film also includes a non-periodic film 3, wherein the non-periodic film 3 is respectively connected to the high-reflection film 2 and the supersurface 4; energy flow regulation in a wider range can be achieved by adjusting the thickness of the non-periodic film layer 3.

[0040] The high-reflective film 2 and the non-periodic film 3 are dielectric film stacks composed of alternating high-refractive index dielectric film layers H and low-refractive index dielectric film layers L; the contact side of the non-periodic film 3 with the high-reflective film 2 and the metasurface 4 is the low-refractive index dielectric film layer L.

[0041] The structure of the high reflective film (2) is (LH) 7 , the non-periodic film (3) structure is LHL.

[0042] In this embodiment, the film structure is S|(LH) 7 LHL|G; wherein S and G are substrate 1 and super surface 4 respectively.

[0043] In this embodiment, the high-reflective film 2 adopts a dielectric film stack composed of seven layers of high-refractive index dielectric film layers H and seven layers of low-refractive index dielectric film layers L alternately arranged; the substrate 1 is a silicon wafer; the high-refractive index dielectric film layer H used in the high-reflective film 2 has a thickness of 258nm, and the low-refractive index dielectric film layer L has a thickness of 596nm.

[0044] The material of the high refractive index dielectric film layer H is Si, and the material of the low refractive index dielectric film layer L is SiO2.

[0045] The thickness of the non-periodic film layer 3 is selected as follows:

[0046] Based on the determined width of the superunit structure 5 in the metasurface 4, the Littrow reflection efficiency at different thicknesses of the non-periodic film layer 3 is scanned, and the thickness is locally fine-tuned so that the superunit structure 5 of the metasurface 4 can achieve the highest broadband Littrow reflection efficiency.

[0047] The non-periodic film 3 includes a dielectric film stack composed of three layers of high refractive index dielectric film layers H and low refractive index dielectric film layers L of different thicknesses arranged alternately, and the structure from bottom to top is a first low refractive index dielectric film layer L, a first high refractive index dielectric film layer H, and a second low refractive index dielectric film layer L.

[0048] In this embodiment, the thickness of the first low-refractive index dielectric film layer L is 634nm; the thickness of the first high-refractive index dielectric film layer H is 335nm; and the thickness of the second low-refractive index dielectric film layer L is 119nm. The energy flow regulation in a wider range can be achieved by adjusting the thickness of the non-periodic film layer 3. The non-periodic film layer 3 has three layers, and the number of layers can be increased. More film layers can be used to achieve energy flow regulation in a wider range.

[0049] Super unit structure Figure 2 As shown, the metasurface 4 includes a plurality of superunit periods with a period range of p, and the superunit period includes n superunit structures 5 with different widths and the same height.

[0050] The super unit period range p and the number n of super unit structures 5 are selected using the following formula:

[0051]

[0052] Where λ is the Littrow reflection wavelength and i is the Littrow incident angle.

[0053] In this embodiment, the super surface 4 is formed by four super unit structures 5 with the same height and different widths arranged in sequence, and the material of the super unit structure 5 is Si.

[0054] The method for selecting the height of the super unit structure 5 of the super surface 4 is:

[0055] The width of a single superunit structure 5 of the metasurface 4 is scanned so that the reflection phase of each superunit structure 5 can cover a variation range of 0 to 2π; phase variation is achieved using n superunit structures 5 with different widths and a superunit period with a period range of p; wherein n≥4, and n is a positive integer.

[0056] In this embodiment, the super unit period range p of the metasurface 4 is 465 nm, and the height of the super unit structure 5 is 1100 nm. Under such structural parameters, by changing the width of the super unit structure 5, the reflection phase coverage of 0 to 2π can be achieved.

[0057] The method for selecting the width of the super unit structure 5 of the super surface 4 is:

[0058] The theoretical value of the Poynting vector inside the metasurface 4 at different incident wavelengths is obtained through rigorous coupled wave analysis. The widths of n superunit structures 5 in the superunit period of the metasurface 4 are scanned to obtain the Poynting vector inside the metasurface 4 at this time, so that it matches the target value obtained by theoretical calculation.

[0059] In this embodiment, Figure 3 4 is a relationship diagram between different wavelengths and the required transverse energy flow amplitude within a broadband range of the metasurface 4. The metasurface 4 requires a greater transverse energy flow transmission capability when the incident wavelength is farther from the Littrow wavelength.

[0060] By scanning the total energy flow amplitude corresponding to the supersurface 4 at different widths of the superunit structure 5, as shown in Figure 4 As shown, the widths of the super unit structure 5 close to the target values ​​are selected, which are 207 nm, 116 nm, 302 nm, and 419 nm from left to right.

[0061] Electromagnetic simulations using finite-difference time-domain method or rigorous coupled wave analysis are performed to confirm the electromagnetic response of the metasurface 4, such as Figure 5As shown, the present invention can achieve broadband Littrow reflection with an efficiency of more than 99% at 3.12-3.52 μm.

[0062] The structural parameters of the metasurface 4 in the present invention are not limited thereto, and more superunit structures 5 can be used to achieve stronger lateral energy flow transmission capability, and more non-periodic film layers 3 can be used to achieve energy flow regulation in a wider range. The wavelength of the metasurface 4, the high refractive index material H, the low refractive index material L, the film system of the multilayer film, and the height of the superunit structure 5 can also be changed. The multilayer film can provide a reflectivity greater than 99%. The period of the superunit structure 5 needs to be designed according to the wavelength and the Littrow incident angle. The height of the superunit structure 5 only needs to cover 0 to 2π when the width changes.

[0063] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An energy flow control thin film structure based on a multilayer film, comprising a substrate (1), a multilayer film and a super surface (4) arranged from bottom to top, wherein the multilayer film comprises a high reflective film (2), and the super surface (4) comprises a super unit structure (5), characterized in that: The multilayer film further comprises a non-periodic film (3), wherein the non-periodic film (3) is respectively connected to the high-reflective film (2) and the super surface (4); energy flow regulation in a wider range is achieved by adjusting the thickness of the non-periodic film layer (3).

2. The energy flow control thin film structure based on a multilayer film according to claim 1, characterized in that: The high-reflective film (2) and the non-periodic film (3) are dielectric film stacks formed by alternating high-refractive index dielectric film layers H and low-refractive index dielectric film layers L; the contact side of the non-periodic film (3) with the high-reflective film (2) and the metasurface (4) is the low-refractive index dielectric film layer L.

3. The energy flow control thin film structure based on a multilayer film according to claim 2, characterized in that: The structure of the high reflective film (2) is (LH) 7 , the non-periodic film (3) structure is LHL.

4. The energy flow control thin film structure based on a multilayer film according to claim 2, characterized in that: The material of the high refractive index dielectric film layer H is Si, and the material of the low refractive index dielectric film layer L is SiO2.

5. The energy flow control thin film structure based on a multilayer film according to claim 2, characterized in that: The thickness of the non-periodic film layer (3) is selected by: Based on the determined width of the super unit structure (5) in the metasurface (4), the Littrow reflection efficiency of the non-periodic film layer (3) at different thicknesses is scanned, and the thickness is locally fine-tuned so that the super unit structure (5) of the metasurface (4) achieves the highest broadband Littrow reflection efficiency.

6. The energy flow control thin film structure based on a multilayer film according to claim 5, characterized in that: The non-periodic film (3) comprises a dielectric film stack consisting of three layers of high refractive index dielectric film layers H and low refractive index dielectric film layers L of different thicknesses arranged alternately, which are, from bottom to top, a first low refractive index dielectric film layer L, a first high refractive index dielectric film layer H, and a second low refractive index dielectric film layer L.

7. The energy flow control thin film structure based on a multilayer film according to claim 1, characterized in that: The super surface (4) includes a plurality of super unit periods with a period range of p, and the super unit period includes n super unit structures (5) with different widths and the same height.

8. The energy flow control thin film structure based on a multilayer film according to claim 7, characterized in that: The super unit period range p and the number n of super unit structures (5) are selected using the following formula: Where λ is the Littrow reflection wavelength and i is the Littrow incident angle.

9. The energy flow control thin film structure based on a multilayer film according to claim 7, characterized in that: The method for selecting the height of the super unit structure (5) of the super surface (4) is: The width of a single super unit structure (5) of the metasurface (4) is scanned so that the reflection phase of each super unit structure (5) can cover a variation range of 0 to 2π; phase variation is achieved using n super unit structures (5) with different widths and a super unit period with a period range of p; wherein n≥4, and n is a positive integer.

10. The energy flow control thin film structure based on a multilayer film according to claim 7, characterized in that: The method for selecting the width of the super unit structure (5) of the super surface (4) is: The theoretical value of the Poynting vector inside the metasurface at different incident wavelengths is obtained through rigorous coupled wave analysis. The width of n superunit structures (5) in the superunit period of the metasurface (4) is scanned to obtain the Poynting vector inside the metasurface (4) at this time, so that it matches the target value obtained by theoretical calculation.

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