A wavelength multiplexing metamaterial based on calcite crystal and application thereof

Abstract

The application belongs to the field of electromagnetic regulation, and particularly relates to a wavelength multiplexing metamaterial based on calcite crystals and application thereof, which can realize wavelength multiplexing device application in the near-infrared waveband. The wavelength multiplexing metamaterial based on calcite crystals is divided into two layers, including a bottom base layer and a metasurface structure unit covering the upper surface of the base layer, the metasurface structure unit is a nano-cylindrical pair arranged in a periodic interval, and the base layer is composed of calcite crystals with birefringence characteristics. The application also relates to a new use of the wavelength multiplexing metamaterial based on calcite crystals, specifically application in preparation of wavelength multiplexing devices. The base layer of the metamaterial is replaced with calcite material in the application, and the structure is simple and convenient to manufacture. The wavelength multiplexing in the near-infrared waveband is realized by using the birefringence characteristics of calcite, which is helpful to realize integration and miniaturization of the device.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic control, specifically relating to a metamaterial based on calcite crystals for wavelength multiplexing and its applications, which can realize wavelength multiplexing device applications in the near-infrared band. Background Technology

[0002] Metamaterials refer to a class of man-made materials with extraordinary physical properties, possessing characteristics not found in natural materials, such as negative permittivity and negative permeability—effects that traditional materials cannot achieve. The properties of metamaterials are not determined by their intrinsic materials; their unique properties stem from their intricate geometry and size. Their microstructures, smaller than the wavelength of light they interact with, thus allow them to influence waves.

[0003] In recent years, metamaterials technology has developed rapidly, achieving significant breakthroughs in many technological fields. One phenomenon that has attracted widespread attention is the electromagnetically induced transparency (EIT) effect. EIT is a special electromagnetic effect, characterized by a narrow and sharp transmission spectrum within a broad absorption spectrum. The generation of EIT is always accompanied by a strong dispersion effect, thus it can be applied to realize nonlinear and slow-light effects and to fabricate high-sensitivity sensors. However, due to technological limitations, current research on EIT mainly focuses on the terahertz field, with relatively little research in the near-infrared field. In recent years, researchers have designed some ingenious structures to reuse electromagnetic effects; however, these structures are usually quite complex and have many limitations.

[0004] Natural calcium carbonate, also known as calcite, is an ideal birefringent material, possessing a natural dual controllability over incident photoelectric and magnetic fields. When light is incident on a calcite crystal, it undergoes birefringence and decomposes into two beams of polarized light with perpendicular vibration directions, different propagation speeds, and unequal refractive indices, except along the crystal axis. Due to this natural birefringence property, combining calcite with metamaterials will bring more unexpected properties to the metamaterials. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing metamaterials in the near-infrared field, such as low precision and high structural complexity, and provides a metamaterial based on calcite crystals that achieves wavelength multiplexing and its application, thereby overcoming the above-mentioned shortcomings.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a metamaterial based on calcite crystals for wavelength reuse, characterized in that the metamaterial is divided into upper and lower layers, including a bottom substrate layer and a metasurface structure unit covering the upper surface of the substrate layer, wherein the metasurface structure unit is a pair of nanocylinders arranged in a periodic interval, and the substrate layer is composed of calcite crystals with birefringence properties.

[0007] The inventors have combined calcite materials with birefringence properties with metamaterials. The metamaterials in this invention consist of two layers: a lower layer composed of calcite crystals and an upper layer composed of periodically spaced pairs of nanocylinders covering the base layer. Furthermore, due to the birefringence of calcite crystals, when incident light is incident along the crystal axis of the calcite crystal, the structure achieves electromagnetic induction transparency at a specific wavelength. When the incident light is not incident along the crystal axis, it undergoes birefringence, becoming ordinary and extraordinary rays. The refractive index of the calcite crystal corresponding to the ordinary ray is called the ordinary ray refractive index, and the refractive index of the calcite crystal corresponding to the extraordinary ray is called the extraordinary ray refractive index. This allows for electromagnetic induction transparency at two different wavelengths. Based on the birefringence properties of calcite crystals, the metamaterials can utilize the coupling effect between microstructures and combine the birefringence of calcite crystals to achieve electromagnetic induction transparency at different wavelengths, thus achieving wavelength multiplexing in the near-infrared band.

[0008] Preferably, the thickness of the substrate layer is 150 nm-250 nm.

[0009] During the testing process, the inventors discovered that changing the thickness of the calcite base layer affects the light transmittance as follows: as the thickness increases, the light transmittance decreases slightly.

[0010] Preferably, the material of the nanocylinder pair is silicon.

[0011] Preferably, the nanocylinder pair includes a first nanocylinder and a second nanocylinder, wherein the first nanocylinder has a radius of 170 nm-220 nm and the second nanocylinder has a radius of 100 nm-150 nm.

[0012] During the testing process, the inventors discovered that changing the radius of the first nanocylinder affects the light transmittance as follows: as the radius increases, the light transmittance increases slightly; while changing the radius of the second nanocylinder affects the light transmittance as follows: as the radius increases, the light transmittance remains basically unchanged, but the quality factor decreases.

[0013] Preferably, the distance between the first nanocylinder and the second nanocylinder is 150 nm-200 nm.

[0014] During the testing process, the inventors discovered that changing the distance between the first and second nanocylinders affects the light transmittance as follows: as the distance increases, the light transmittance remains basically unchanged, but the quality factor improves.

[0015] Preferably, the first nanocylinder and the second nanocylinder have the same height.

[0016] Preferably, the height of the first nanocylinder and the second nanocylinder is 150 nm-250 nm.

[0017] During the testing process, the inventors discovered that changing the height of the first and second nanocylinders affects the light transmittance as follows: as the height increases, the light transmittance decreases slightly.

[0018] Preferably, the period of the metasurface structural unit is 1400 nm-1600 nm.

[0019] The period of a metasurface structural unit is the width of a single unit structure.

[0020] The significance of the aforementioned constraints on structural dimensions lies in the fact that the response of metamaterials to ordinary and extraordinary light can be controlled by adjusting parameters such as the thickness of the substrate layer, the height of the nanocylinders, the radius of the first nanocylinder, the radius of the second nanocylinder, and the period of the metasurface structural units. Furthermore, through the rational design of structural dimensions, electromagnetic induction transparency with high quality factors can be achieved.

[0021] This invention also relates to the application of the above-mentioned wavelength-multiplexing metamaterial based on calcite crystal in the fabrication of wavelength-multiplexing devices.

[0022] When applied to wavelength multiplexing devices, different refractive indices of the extraordinary wavelength are obtained by processing calcite crystals, thereby achieving the electromagnetic induction transparency effect of the metamaterial at different wavelengths and thus realizing wavelength multiplexing. Specifically, by processing the calcite crystals, the refractive index of the extraordinary wavelength can be selected between 1.48 and 1.66, while the refractive index of the ordinary wavelength remains constant at 1.66. Due to the coupling effect between the structures, the ordinary and extraordinary wavelengths can each achieve a high-quality factor electromagnetic induction transparency effect, thus realizing wavelength multiplexing. Furthermore, by processing the calcite crystals, the refractive index of the extraordinary wavelength can be continuously varied within a certain range, so the electromagnetic induction transparency window of the extraordinary wavelength can appear at any position within a specific wavelength range.

[0023] This involves the application of metamaterials based on calcite crystals that achieve wavelength multiplexing in the fabrication of multifunctional electromagnetic control devices in the near-infrared band.

[0024] Therefore, the present invention has the following beneficial effects:

[0025] (1) Based on metamaterials, this invention replaces the substrate with calcite material, which has a simple structure and is easy to manufacture; in particular, the birefringence properties of calcite are used to realize wavelength reuse in the near-infrared band, which helps to realize the integration and miniaturization of devices.

[0026] (2) This invention combines calcite with metamaterials, providing a new approach for reusing metamaterials, and has certain technical reference value for the development of multifunctional electromagnetic control devices in the near-infrared band, and has important practical significance.

[0027] (3) The present invention utilizes the strong electromagnetic coupling effect between microstructures to generate an electromagnetic induction transparency effect with a high quality factor, which can be used to achieve a more significant slow light effect and nonlinear effect. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a metasurface according to an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the unit structure according to an embodiment of the present invention;

[0030] Figure 3 This is a top view of the unit structure according to an embodiment of the present invention;

[0031] Figure 4 The transmittance spectrum of ordinary light in an embodiment of the present invention;

[0032] Figure 5 The following are the transmittance curves of the extraordinary light under different extraordinary light refractive indices according to embodiments of the present invention;

[0033] Figure 6 These are the time-delay spectra of the extraordinary light under different extraordinary light refractive indices in embodiments of the present invention;

[0034] Figure 7 This is a transmittance spectrum of the nanocylinder with varying height at two extreme values ​​of the optical refractive index in an embodiment of the present invention.

[0035] Figure 8 This is a transmittance curve spectrum of the periodicity of the extraordinary refractive index at two extreme values ​​in an embodiment of the present invention.

[0036] Figure 9 This is a transmittance curve spectrum of the second nanocylinder radius with varying refractive index at two extreme values ​​in an embodiment of the present invention.

[0037] In the figure, the symbols represent the following meanings: 1. Substrate layer; 2. Nanocylinder pair; 21. First nanocylinder; 22. Second nanocylinder; h, height of the first and second nanocylinders; h1, thickness of the substrate layer; r1, radius of the first nanocylinder; r2, radius of the second nanocylinder; d, spacing between the first and second nanocylinders; p, period of the metasurface structural unit. Detailed Implementation

[0038] To illustrate the technical solutions in the embodiments of the present invention more specifically, the present invention will be further described below with reference to the accompanying drawings. Obviously, the drawings and corresponding technical solutions described below represent only embodiments of the present invention. For those skilled in the art, other drawings and results can be obtained based on these drawings and the corresponding descriptions without any creative effort.

[0039] The present invention will be further described below with reference to specific embodiments and accompanying drawings:

[0040] This invention provides an application of a wavelength-reusing metamaterial based on calcite crystals. Utilizing the coupling effect between the microstructures of the metamaterial, with calcite crystal as the substrate layer 1, and the birefringence inherent in calcite, an electromagnetic induction transparency effect is achieved at different wavelengths, thus achieving wavelength reuse. The metamaterial used to implement this method consists of two layers: the lower substrate layer 1 is composed of calcite crystals with birefringence; the upper metasurface structure unit covers the substrate layer 1, wherein the metasurface structure unit is composed of periodically spaced pairs of nanocylinders 2, and the nanocylinder pairs 2 are composed of first nanocylinders 21 and second nanocylinders 22 with different radii. By optimizing parameters such as the height h of the nanocylinders, the radius r2 of the second nanocylinder 21, and the period p of the metasurface structure unit, the electromagnetic induction transparency window for both ordinary and extraordinary light can be controlled simultaneously within a certain range. By processing the calcite crystal to obtain different extraordinary light refractive indices, the electromagnetic induction transparency effect of the metamaterial at different wavelengths is achieved, thus realizing the wavelength reuse effect. Because the refractive index of an electromagnetic induction transparent window can vary continuously within a certain range, it can appear at any position within a specific wavelength range. This technical solution will improve the integration of devices and provide new ideas for the development of optoelectronic integrated devices.

[0041] The embodiments of the present invention are simulated and optimized using electromagnetic simulation software CST. The polarization direction of the incident light is selected as the y-direction, and it is incident along the negative z-axis.

[0042] An ideal and feasible implementation scheme obtained through simulation optimization in this invention is as follows: r1=192 nm, r2=130 nm, h=205 nm, h1=195 nm, d=170 nm, p=1500 nm. The nanocylinder pair is made of silicon with a dielectric constant of 14, and the substrate material is calcite crystal, wherein the ordinary refractive index ε o The constant is fixed at 1.66 (corresponding to a relative permittivity of 2.75), and the optical refractive index ε is... e The value can be any value between 1.48 and 1.66 depending on the processing of the calcite crystal (the corresponding relative permittivity is 2.19-2.75).

[0043] Based on the above conditions, with a fixed dielectric constant of 2.75, when incident light is incident along the crystal axis, the ordinary refractive index spectrum at 1440 nm-1500 nm is measured as follows: Figure 4 As shown. By Figure 4 It can be seen that a distinct and sharp EIT window appears near the center wavelength of 1471 nm. To further describe the properties of the EIT window, a quality factor (Q-factor) is introduced. The quality factor used can be obtained from the following formula:

[0044]

[0045] Where λ0 is the center wavelength of the EIT window and FWHM is the half-width.

[0046] Thus, the FWHM and Q values ​​of the EIT window under y-polarized light excitation are 0.9 nm and 1634, respectively.

[0047] Keeping other conditions constant, processing calcite crystals to make the incident light and crystal axis at different angles alters the dielectric constants to 2.19, 2.33, 2.47, 2.61, and 2.75, respectively. The corresponding extraordinary light transmittance curves are shown below. Figure 5 As shown. By Figure 5 It can be seen that the EIT effect can be clearly observed under different dielectric constants. When the dielectric constant is in the range of 2.19-2.75, as the dielectric constant increases, the corresponding transmission spectrum undergoes a red shift, the EIT window has a high quality factor, and the corresponding center wavelength changes.

[0048] Figure 4 The results show that when incident light is incident along the crystal axis of the calcite crystal to excite the embodiment of the present invention, the EIT window is excited at only one wavelength. This indicates that when incident light is incident along the crystal axis of the calcite crystal, the structure achieves an electromagnetically induced transparency effect at a specific wavelength.

[0049] Even when the incident light is not incident along the crystal axis of the calcite crystal, ordinary light still exists, and... Figure 4 The results are the same; furthermore, an EIT window excited by the extraordinary ray also appears at this time. Therefore, it can be shown that calcite crystals undergo birefringence when the incident light is along the amorphous axis, splitting the incident light into ordinary and extraordinary rays. Both beams can achieve electromagnetically induced transparency at two wavelengths, thus enabling the multiplexing of the electromagnetically induced transparency effect across wavelengths. Furthermore, due to the refractive index ε of the extraordinary ray... e It can vary continuously within a certain range, and the electromagnetically induced transparent window of very light can appear at any position in the range of 1434nm-1474nm.

[0050] Keeping other conditions constant, the dielectric constants were changed to 2.19, 2.33, 2.47, 2.61, and 2.75, and the corresponding extraordinary optical time-delay spectra were measured as follows: Figure 6 As shown, its group delay values ​​are mainly distributed between 2 ps and 3.5 ps, exhibiting a significant delay effect; metasurfaces can be designed according to actual needs to achieve a slow light effect at a specific wavelength.

[0051] Furthermore, to investigate the influence of structural size parameters on the ordinary and extraordinary light responses in the embodiments of the present invention, the extraordinary light refractive index ε was selected. e The two endpoints (ε) e =2.19 and ε e =2.75=ε o (These will be discussed separately.)

[0052] Figure 7 In this embodiment of the invention, the refractive index ε is... e The transmittance spectra of the nanocylinder at different heights (h) were varied under two extreme conditions. The results show that the refractive index ε... e At both endpoints, the response to changes in h is consistent. As h increases, the overall transmittance spectrum redshifts, while the transmittance decreases slightly. Notably, changing h1 yields the same trend; conversely, as r1 increases, the transmittance increases slightly.

[0053] Figure 8 In this embodiment of the invention, the refractive index ε is... e Transmittance spectra were measured with varying period p under two extreme conditions. The results show that the extreme refractive index ε... e At both endpoints, the response to changes in p is consistent. As p increases, the overall transmittance spectrum redshifts, but still maintains a high-quality EIT window.

[0054] Figure 9 In this embodiment of the invention, the refractive index ε is... eTransmittance spectra were plotted under two extreme conditions, varying the radius r2 of the second nanocylinder. The results show that the refractive index ε... e At both extreme values, the response to changes in r2 is consistent. As r2 increases, the EIT window widens, the quality factor decreases, while the spectral line only undergoes a slight redshift. Conversely, as d increases, the corresponding quality factor increases.

[0055] When the above parameters vary within a certain range, the high quality of the electromagnetic induction transparent window can still be maintained, and its effect on ordinary light and extraordinary light response is consistent. This will greatly enhance the application capability of the device and reduce the development difficulty of the device. Therefore, the present invention has important practical significance.

[0056] In summary, this invention achieves electromagnetic induction transparency in the near-infrared band through ingenious structural design. Furthermore, due to the birefringence of calcite crystals, ordinary and extraordinary light can achieve electromagnetic induction transparency at two different wavelengths. Since the refractive index of the extraordinary light is continuously changing, the electromagnetic induction transparency window of the extraordinary light can be continuously adjusted within a certain wavelength range. This provides flexible adjustment space for the two operating wavelengths of the device, improving device integration and enabling miniaturization. This invention has significant application potential in areas such as slow light effects and nonlinear effects.

[0057] The above embodiments are for supplementary illustration only and are not intended to limit the present invention. Any modifications made to the present invention within the scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A metamaterial that achieves wavelength reuse based on electromagnetic induction transparency in the near-infrared band, characterized in that, The metamaterial is divided into two layers, including a bottom base layer (1) and a metasurface structure unit covering the upper surface of the base layer (1). The metasurface structure unit is a pair of nanocylinders (2) arranged in a periodic interval. The base layer (1) is composed of calcite crystals with birefringence properties. The pair of nanocylinders (2) includes a first nanocylinder (21) and a second nanocylinder (22). The first nanocylinder (21) and the second nanocylinder (22) have different radii.

2. The metamaterial for wavelength reuse based on electromagnetic induction transparency in the near-infrared band according to claim 1, characterized in that, The thickness of the substrate layer (1) is 150 nm-250 nm.

3. The metamaterial for wavelength reuse based on electromagnetic induction transparency in the near-infrared band according to claim 1, characterized in that, The material of the nanocylinder pair (2) is silicon.

4. The metamaterial for wavelength reuse in the near-infrared band based on electromagnetic induction transparency effect according to claim 3, characterized in that, The first nanocylinder (21) has a radius of 170 nm-220 nm, and the second nanocylinder (22) has a radius of 100 nm-150 nm.

5. The metamaterial for wavelength reuse in the near-infrared band based on electromagnetic induction transparency effect according to claim 3, characterized in that, The distance between the first nanocylinder (21) and the second nanocylinder (22) is 150 nm-200 nm.

6. The metamaterial for wavelength reuse in the near-infrared band based on electromagnetic induction transparency effect according to claim 5, characterized in that, The first nanocylinder (21) and the second nanocylinder (22) have the same height.

7. The metamaterial for wavelength reuse in the near-infrared band based on electromagnetic induction transparency effect according to claim 6, characterized in that, The heights of the first nanocylinder (21) and the second nanocylinder (22) are 150 nm to 250 nm.

8. The metamaterial for wavelength reuse based on electromagnetic induction transparency in the near-infrared band according to claim 1, characterized in that, The period of the metasurface structural unit is 1400 nm-1600 nm.

9. The application of the metamaterial for wavelength multiplexing based on electromagnetic induction transparency effect in the near-infrared band as described in any one of claims 1-8 in the fabrication of wavelength multiplexing devices.

10. The application of the metamaterial for wavelength reuse based on electromagnetic induction transparency effect in the near-infrared band, as described in any one of claims 1-8, in the fabrication of multifunctional electromagnetic control devices in the near-infrared band.

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