Intermediate infrared multi-peak narrow-band high-quality-factor metasurface filter and method

Abstract

The invention discloses a mid-infrared multi-peak narrow-band high-quality factor metasurface filter and a method. The filter comprises a dielectric layer; the metasurface is arranged on the dielectric layer and comprises a plurality of semiconductor structures which are arranged periodically, and each semiconductor structure is composed of a plurality of cuboids with different sizes; according to the metasurface, under vertical incidence of electromagnetic waves in a TE polarization mode, the electromagnetic waves generate multiple electromagnetic resonance modes in the semiconductor structure, so that the filtering effect is achieved; wherein the multiple electromagnetic resonance modes comprise electric dipole resonance, magnetic dipole resonance, multi-dipole resonance or Fano resonance. According to the invention, the red shift or blue shift of the filtering frequency is carried out by adjusting the geometric dimension parameters of the semiconductor structure, so that the filtering effect with a multi-peak high-quality factor is realized, and the excellent narrow-band filtering and gas detection functions are realized. The method can be widely applied to the field of special gas sensor design.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic metasurface device design and special gas sensor design in the mid-infrared band, and in particular to a mid-infrared multi-peak narrow-band high quality factor metasurface filter and method. Background Art

[0002] Metasurface is a composite material with an artificially designed structure, which exhibits extraordinary physical properties that natural materials do not have. These properties mainly come from the artificial special structure of the material, which is composed of a periodic arrangement of subwavelength unit structures. It has extraordinary electromagnetic properties that natural materials do not have, such as negative magnetic permeability, negative refractive index, negative dielectric constant, etc. Therefore, metasurface technology has been an attractive research frontier in recent years. Fano-type resonance is constructed by the interference between the continuous spectrum of the radiation wave and a non-radiative (dark) mode overlapping in the spectrum. Compared with the symmetrical Lorentz line shape, the resonant spectral line of Fano resonance is asymmetric and can be used in nonlinear optics and optical filters. In addition, Fano resonance can increase the field strength of the local electromagnetic field and is extremely sensitive to changes in the surrounding environment. Therefore, it can also be used in the development of sensors.

[0003] Each gas molecule has unique vibration and rotation energy levels, and the corresponding infrared spectrum will show specific absorption or emission wavelengths. For example, carbon dioxide (CO2) has a strong absorption peak near 4.26μm, while methane (CH4) has a characteristic peak near 3.3μm. By designing a specific metasurface structure, the sensor can be tuned to only transmit the infrared characteristic wavelength corresponding to a specific gas, while filtering out infrared radiation of other wavelengths. This selective transmission property enables the sensor to accurately detect the presence and concentration of the target gas. The mid-infrared band sensor has the advantages of high sensitivity, high resolution and non-contact measurement. Using the metasurface as a gas sensor, through precise optical design, it can selectively transmit the characteristic infrared wavelength of a specific gas. This metasurface-based sensor has a wide range of applications in the field of gas detection, especially in environmental monitoring, industrial emission control and medical diagnosis. It can achieve high-sensitivity and high-selectivity gas detection, and is suitable for detecting various greenhouse gases, harmful gases and volatile organic compounds. This method has great potential in the field of gas detection. Summary of the invention

[0004] In order to solve at least one of the technical problems existing in the prior art to a certain extent, the object of the present invention is to provide a mid-infrared multi-peak narrow-band high quality factor metasurface filter and method.

[0005] The first technical solution adopted by the present invention is:

[0006] A mid-infrared multi-peak narrow-band high quality factor metasurface filter, comprising:

[0007] dielectric layer;

[0008] A metasurface is arranged on the dielectric layer and includes a plurality of periodically arranged semiconductor structures, wherein the semiconductor structure is composed of a plurality of cuboids of different sizes; when an electromagnetic wave in a TE polarization mode is vertically incident on the metasurface, the electromagnetic wave generates a plurality of electromagnetic resonance modes in the semiconductor structure to achieve a filtering effect; wherein the plurality of electromagnetic resonance modes include electric dipole resonance, magnetic dipole resonance, multi-dipole resonance or Fano resonance.

[0009] Furthermore, by adjusting the geometrical dimension parameters of the semiconductor structure within a single period to break the symmetry of the structure, the asymmetry of the structure is utilized to form a filtering effect with multiple high transmission peaks.

[0010] Furthermore, the material of the dielectric layer is BaF2 and the thickness of the dielectric layer is 2-8 μm.

[0011] Furthermore, the semiconductor structure is germanium Ge.

[0012] Furthermore, the semiconductor structure includes four cuboids.

[0013] Furthermore, the area corresponding to the semiconductor structure of a single period is a square, and the square is evenly divided into four regions according to the midpoints of the four sides of the square, and the four cuboids are respectively distributed in the four regions.

[0014] Furthermore, the four cuboids are located at the center of the four areas.

[0015] Furthermore, the four cuboids have the same height and width but different lengths.

[0016] Furthermore, the four cuboids have a length of 1-5 μm, a width of 1-5 μm, and a thickness of 1-5 μm.

[0017] The second technical solution adopted by the present invention is:

[0018] A design method for the above-mentioned mid-infrared multi-peak narrow-band high-quality factor metasurface filter comprises the following steps:

[0019] For semiconductor structures, multi-dipole resonance is excited by design to perform narrow-band filtering at multiple frequency points.

[0020] The beneficial effects of the present invention include:

[0021] (1) Multi-band selectivity: The metasurface can be designed to respond to multiple specific infrared wavelengths. For complex gas mixtures, the metasurface can simultaneously transmit or reflect the characteristic absorption wavelengths of these gases, thereby achieving simultaneous detection of multiple gases.

[0022] (2) High sensitivity: Since the metasurface can significantly enhance the local electromagnetic field, the intensity of the detection signal can be increased, and even trace components in complex gas mixtures can be detected.

[0023] (3) High resolution: The precise design of metasurface materials enables them to exhibit extremely high optical selectivity at specific wavelengths, and even when these wavelengths are very close, they can distinguish the characteristic wavelengths of each component in a complex gas mixture. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the embodiments of the present invention or the drawings of related technical solutions in the prior art are introduced below. It should be understood that the drawings introduced below are only for the convenience of clearly describing some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a schematic diagram of a single-period semiconductor structure of a mid-infrared multi-peak narrow-band high-quality factor metasurface filter proposed by the present invention;

[0026] Figure 2 yes Figure 1 The transmittance curve of the middle filter in TE polarization mode with 4-8μm wavelength electromagnetic wave incident;

[0027] Figure 3 yes Figure 1 XOY profile of the electric field distribution of the filter with an electromagnetic wave wavelength of 6.46 μm;

[0028] Figure 4 yes Figure 1 XOY profile of the electric field distribution of the medium filter with an electromagnetic wave wavelength of 6.97 μm;

[0029] Figure 5 yes Figure 1 YOZ cross-section diagram of the electric field distribution of the filter electromagnetic wave with a wavelength of 7.63μm.

[0030] Figure numerals: 1 - dielectric layer; 2 - first rectangular parallelepiped semiconductor germanium block; 3 - second rectangular parallelepiped semiconductor germanium block; 4 - third rectangular parallelepiped semiconductor germanium block; 5 - fourth rectangular parallelepiped semiconductor germanium block. DETAILED DESCRIPTION

[0031] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limitations of the present invention. For the step numbers in the following embodiments, they are only provided for the convenience of explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0032] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0033] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0034] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0035] In the existing metasurface filter design, the more common design structural shapes are rectangular, U-shaped, cross-shaped, elliptical, H-shaped, etc. Multiple structures are used in a single period to form a symmetrical structure. The symmetry of the structure can enhance the resonance effect of a specific mode, such as the electric dipole mode or the magnetic dipole mode, and even achieve multiple resonances in the same structure. This feature can be used to design filters with high Q factors. In order to achieve the design of more high-Q transmission peaks, according to the principle of Fano resonance, within a single period structure, a part of a symmetrical structure is slightly offset, or asymmetric cracks or gaps are introduced into the structure. These tiny offsets can break the symmetry and introduce new resonance modes and interference effects, thereby achieving more transmission peaks in the design.

[0036] See also Figure 1 This embodiment provides a mid-infrared multi-peak narrow-band high quality factor metasurface filter, including:

[0037] Dielectric layer 1;

[0038] A metasurface is arranged on the dielectric layer and includes a plurality of periodically arranged semiconductor structures, wherein the semiconductor structure is composed of a plurality of cuboids of different sizes; when an electromagnetic wave in a TE polarization mode is vertically incident on the metasurface, the electromagnetic wave generates a plurality of electromagnetic resonance modes in the semiconductor structure to achieve a filtering effect; wherein the plurality of electromagnetic resonance modes include electric dipole resonance, magnetic dipole resonance, multi-dipole resonance or Fano resonance.

[0039] The principle of the filter of this embodiment is: when the electromagnetic wave is incident on a structure close to the wavelength size, the electromagnetic wave will generate different modes of electromagnetic resonance resonance modes in the semiconductor bulk structure, including magnetic dipole resonance, multi-dipole resonance, Fano resonance and other modes. Under certain circumstances, the coupling between the non-radiative (dark) mode and the radiative (bright) mode of the metasurface will lead to the Fano resonance phenomenon, that is, an asymmetric resonance line shape. By breaking the symmetrical structure of the device, the non-radiative (dark) mode generated by the asymmetric structure is introduced, and the filtering frequency can be red-shifted or blue-shifted by adjusting the geometric size parameters of the semiconductor structure, thereby achieving a filtering effect with a high quality factor with multiple peaks, and then achieving excellent narrow-band filtering and gas detection functions.

[0040] In some embodiments, the semiconductor structure is implemented by using the material germanium Ge, that is, a semiconductor germanium structure. In other embodiments, the semiconductor structure can also be implemented by using some high-k (dielectric constant) dielectric materials, such as gallium arsenide.

[0041] As an optional implementation, see Figure 1 The shape corresponding to a single-period semiconductor structure is a square. The semiconductor structure includes four cuboids. The square is evenly divided into four regions by the midpoints of the four sides of the square. The four cuboids are distributed in the four regions. It should be noted that the number of cuboids in the semiconductor structure is not limited to 4, and may include more or less cuboids, which can be determined according to actual conditions.

[0042] Specifically, the material selected for the dielectric layer is BaF2, and the dielectric layer of a single periodic structure has a length of 2-8 μm, a width of 2-8 μm, and a thickness of 2-8 μm.

[0043] The following is a detailed description of a specific embodiment in which a semiconductor germanium structure is composed of four rectangular blocks of different sizes. In addition, based on the advantages of simpler processing technology and more adjustable parameters, this embodiment uses a cube as the basic structure, and uses four cubes to form a single periodic structure to increase adjustable parameters. This embodiment simulates the filter structure in the mid-infrared band to obtain a transmission coefficient parameter curve of the electric field mode (TE) under vertical irradiation at an electromagnetic wave wavelength of 4-8μm.

[0044] Figure 1 This is a schematic diagram of a single period semiconductor germanium structure of the filter. The filter is an extension of this periodic structure. Figure 1 As shown, the bottom dielectric layer 1 occupies the entire periodic unit, and the semiconductor structure includes four cuboids, which are respectively called: a first cuboid semiconductor germanium block 2, a second cuboid semiconductor germanium block 3, a third cuboid semiconductor germanium block 4 and a fourth cuboid semiconductor germanium block 5. The four cuboid semiconductor germanium blocks have the same thickness and width, but different lengths.

[0045] Each rectangular semiconductor germanium block has its corresponding resonant frequency. After adjusting the structural dimensions to make the structural frequencies of the two close, they will affect each other, produce more frequency transmission peaks, and achieve the best filtering effect. In addition, the lengths of different rectangular semiconductor germanium blocks will affect the absorption performance and quality factors between different peaks, and if the heights are inconsistent, it will directly affect the filtering effect, affect the resonant frequency, and result in poor filtering effect. The semiconductor germanium structure is made of semiconductor germanium material. Ge is selected in this embodiment. In the mid-infrared band, the dielectric constant changes only slightly with the change of wavelength. The refractive index of Ge is about 15.7; the material selected for the bottom layer is BaF2, and the dielectric constant decreases slightly with the increase of wavelength in the mid-infrared band.

[0046] In this embodiment, when the incident electromagnetic wave enters the periodic structure perpendicular to the structure along the Z direction in the TE polarization mode, the following is obtained: Figure 2 The transmittance curve shown in the figure has a wavelength range of 4-8 μm, the average transmittance of the transmission peak can reach above 0.85, and the average value of the quality factor Q value is above 100. In this embodiment, the resonance mode analysis is not performed on each transmission peak, and some representative transmission peaks are selected for analysis: the XOY cross-sectional diagrams of the electric field distribution measured at the transmission peak at a wavelength of 6.46 μm are shown in FIG. Figure 3 As shown, the XOY cross-sectional diagrams of the electric field distribution measured at the transmission peak at a wavelength of 6.97 μm are shown in Figure 4 As shown, the electric field distribution patterns at wavelengths of 6.46 μm and 6.97 μm are given by Figure 3 and Figure 4By comparison, it can be found that the resonance modes of their structures are relatively similar. Among them, there are relatively obvious magnetic resonance characteristics in the rectangular semiconductor germanium blocks 2, 3, and 4, and relatively obvious electric resonance characteristics in the rectangular semiconductor germanium block 5. The frequency of the incident electromagnetic wave matches the collective oscillation frequency of the free electrons in the rectangular semiconductor germanium block, which will form a strong local resonance effect. At this time, the energy transfer efficiency is the highest, forming a resonant mode with a high Q value. The places with greater electric field intensity all appear in positions perpendicular to the direction of the electric field. This is because when an electromagnetic wave is incident, a semiconductor germanium structure with a size close to that perpendicular to the direction of the electric field can be equivalent to a capacitor and produce electrical resonance with the electromagnetic wave, so the electric field intensity at the corresponding position is greater.

[0047] Figure 5 The YOZ cross-sectional diagram of the electric field distribution in the TE mode was measured at the transmission peak of the filter at a wavelength of 7.63μm; unlike the magnetic resonance generated before, the electromagnetic wave at this wavelength did not resonate in the XOY plane perpendicular to the propagation direction of the electromagnetic wave, but produced a resonance effect in the YOZ plane with the same propagation direction. When the electromagnetic wave is incident on the semiconductor germanium structure, it can excite the electromagnetic polarization effect of the semiconductor germanium bulk structure, forming electric resonance and magnetic resonance modes of the fundamental and higher-order modes, resulting in a significant enhancement of the electric field or magnetic field intensity in the special wavelength mode. It causes the excitation and radiation of the electric dipole or magnetic dipole or higher-order electromagnetic resonance mode inside the structure, achieving efficient coupling with the incident electromagnetic field, further enhancing the local electromagnetic field to form electric (or magnetic) dipole and multipole resonance, that is, introducing a dark mode in the bright mode, thereby achieving a transmission peak with a high Q value; the rising edge of the transmission peak is relatively gentle, while the falling edge is very steep, which is the same as the resonance effect formed by Fano resonance.

[0048] This embodiment also provides a mid-infrared multi-peak narrow-band high-quality factor metasurface filter, which achieves excellent multi-peak filtering effects by simultaneously realizing multi-dipole excitation to generate electric resonance and magnetic resonance. It can achieve the advantages of multi-band selectivity, high sensitivity, and high resolution in special gas detection, and can cope with complex gas mixtures and electromagnetic wave background environments to achieve good detection effects.

[0049] In the above description of this specification, the description with reference to the terms "one embodiment / example", "another embodiment / example" or "certain embodiments / examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0050] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

[0051] The above is a specific description of the preferred implementation of the present invention, but the present invention is not limited to the above embodiments. Those skilled in the art may make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A mid-infrared multi-peak narrow-band high quality factor metasurface filter, characterized in that: include: dielectric layer; A metasurface is arranged on the dielectric layer, and includes a plurality of periodically arranged semiconductor structures, wherein the semiconductor structure is composed of a plurality of cuboids of different sizes; when an electromagnetic wave in a TE polarization mode is vertically incident on the metasurface, the electromagnetic wave generates a plurality of electromagnetic resonance modes in the semiconductor structure to achieve a filtering effect; wherein the plurality of electromagnetic resonance modes include electric dipole resonance, magnetic dipole resonance, multi-dipole resonance or Fano resonance.

2. A mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 1, characterized in that: By adjusting the geometric size parameters of the semiconductor structure within a single period, the symmetry of the structure is broken, and the asymmetry of the structure is used to form a filtering effect with multiple high transmission peaks.

3. The mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 1, characterized in that: The material of the dielectric layer is BaF2.

4. The mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 1, characterized in that: The semiconductor structure is germanium.

5. The mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 1, characterized in that: The semiconductor structure includes four cuboids.

6. A mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 5, characterized in that: The area corresponding to a single-period semiconductor structure is a square, which is evenly divided into four regions according to the midpoints of the four sides of the square, and the four cuboids are respectively distributed in the four regions.

7. A mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 6, characterized in that: The four cuboids are located at the center of the four areas.

8. The mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 5, characterized in that: The four cuboids have the same height and width but different lengths.

9. A mid-infrared multi-peak narrow-band high quality factor metasurface filter according to claim 8, characterized in that: The lengths of the four cuboids are 1-5 μm.

10. A design method for a mid-infrared multi-peak narrow-band high quality factor metasurface filter according to any one of claims 1 to 9, characterized in that: The following steps are involved: For semiconductor structures, multi-dipole resonance is excited by design to perform narrow-band filtering at multiple frequency points.

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