A hybrid bullseye antenna for focusing terahertz waves and a method of operating the same

Abstract

The application discloses a hybrid bull's eye antenna for focusing terahertz waves and a working method thereof, comprising a substrate, a metal film and a center hole; a layer of metal film is arranged on the substrate, and a center hole is arranged at the center position of the metal film; a silicon column is fixed in the center hole, and a metal hemisphere is further fixed on the silicon column; an incident light source is located on one side of the metal hemisphere; the hybrid bull's eye antenna with the introduced hemisphere particle has the advantages of high gain, small volume, high signal-to-noise ratio and insensitivity to the polarization direction of the incident light.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of terahertz metamaterials, and particularly to a hybrid bullseye antenna for focusing terahertz waves and a working method thereof. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] According to the classical electromagnetic theory, the transmittance of light is proportional to the fourth power of the ratio of the aperture to the wavelength. In order to break the diffraction limit of traditional optics, people design complex metamaterial structures to achieve extraordinary optical transmission (EOT). Surface plasmon polaritons (SPPs) are hybrid excited states produced by the interaction of incident photons and metal surface plasmons, and the scientific community generally believes that SPPs play a key role in achieving the EOT phenomenon. Local surface plasmon resonance (LSPRs) is the local oscillation of charges inside the metal under the excitation of light, which can assist the transmission of light and greatly improve the transmittance. Under certain conditions, SPPs and LSPRs are coupled, which can effectively increase the transmittance and enhance the local electric field, further enhancing the EOT phenomenon.

[0004] The bullseye structure is an array structure surrounded by periodic grooves, which can convert incident light into SPPs on the metal surface and converge a wide range of incident electromagnetic waves into a small range. The hybrid bullseye antenna formed by improving the center hole of the bullseye structure can realize the coupling of SPPs and LSPRs, and further realize the transmission enhancement. The hybrid bullseye antenna has great effect in realizing local transmission enhancement, and its main application is photodetector. Photodetectors can absorb photons and convert them into electrical signals, which are the core components of target detection, photoelectric sensing and other applications. However, the transmission enhancement of the bullseye antenna in the terahertz wave band is small, and the corresponding device size is large. SUMMARY

[0005] In order to solve the problems of the prior art, the present application provides a hybrid bullseye antenna for focusing terahertz waves and a working method thereof. The hybrid bullseye antenna with hemispherical particles introduced has the advantages of high gain, small volume, high signal-to-noise ratio, and insensitivity to the polarization direction of incident light.

[0006] In the first aspect, the present application provides a hybrid bullseye antenna for focusing terahertz waves, comprising a substrate, a metal film and a center hole; a layer of metal film is arranged on the substrate;

[0007] The metal thin film is provided with a plurality of uniform and periodic annular grooves, and a center hole is provided at the center position of the metal thin film; a silicon column is fixed in the center hole, and a metal hemisphere is further fixed on the silicon column; an incident light source is located on one side of the metal hemisphere and the annular groove.

[0008] Further, the annular groove and the center hole have the same center.

[0009] Further, the distance between the center of the center hole and the first layer of annular grooves is 50-70um.

[0010] Further, the periodic distance of the annular groove is 50-65um.

[0011] Further, the height of the center hole is consistent with the height of the metal thin film.

[0012] Further, the height of the metal thin film is consistent with the height of the silicon column.

[0013] Further, the silicon column is a cylindrical silicon column.

[0014] Further, the diameter of the silicon column is consistent with that of the metal hemisphere.

[0015] Further, the metal thin film is made of gold material.

[0016] Further, the metal hemisphere is made of gold material.

[0017] In a second aspect, the application provides a working method of the hybrid bull's eye antenna for focusing terahertz waves, comprising:

[0018] The plane wave polarized in any direction is incident on the surface of the hybrid bull's eye antenna vertically on the side with the groove, so as to realize the transmission of the plane wave.

[0019] Compared with the prior art, the application has the following beneficial effects:

[0020] The present application introduces hemispherical particles, combined with periodic ring grooves, and the terahertz wave is incident from the side of the periodic ring grooves and the metal hemispherical structure. The distance from the center hole to the first layer of grooves affects the optical path difference of SPPs after the action of the metal grooves at the center hole position. Since the incident plane electromagnetic wave vector direction is perpendicular to the surface of the hybrid cow eye antenna, this distance is approximately equal to the size of the resonance wavelength. The single metal hemispherical particle will generate LSPRs with the center hole slit. When the resonance wavelength of SPPs is equal to the resonance wavelength of LSPRs, the two resonance modes will be strongly coupled, greatly enhancing the normalized transmission of the center hole. This EOT effect can be used for photodetectors to increase the light absorption of the active region under the center hole. For two kinds of cow eye structures with different groove numbers, the transmission enhancement of the hybrid cow eye structure is significantly higher than that of the conventional cow eye structure. The maximum transmission enhancement peak that can be achieved by the hybrid cow eye antenna is 556, while the maximum transmission enhancement peak that can be achieved by the conventional cow eye antenna is 102, so the improved structure can achieve a peak of about 5.5 times that of the conventional structure. BRIEF DESCRIPTION OF DRAWINGS

[0021] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification. The embodiments of the application, and their

[0022] Figure 1 Structure schematic diagram of the hybrid cow eye antenna in the embodiment of the present application;

[0023] Figure 2 Structure schematic diagram of the center hole position of the hybrid cow eye antenna in the embodiment of the present application;

[0024] Figure 3 Sectional view of the hybrid cow eye antenna in the embodiment of the present application;

[0025] Figure 4 Transmission enhancement spectrum comparison schematic diagram of the hybrid cow eye antenna and the conventional cow eye antenna in the embodiment of the present application;

[0026] Figure 5 Transmission enhancement spectrum comparison schematic diagram of the cow eye antenna and the cow eye antenna with only a center hole structure in the embodiment of the present application;

[0027] Figure 6 Transmission enhancement peak of the hybrid cow eye antenna and the conventional cow eye antenna in the embodiment of the present application changes with N;

[0028] In the figure: 1-ring groove; 2-metal film; 3-substrate; 4-metal hemisphere; 5-silicon column. DETAILED DESCRIPTION

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on this invention.

[0032] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0033] Example 1

[0034] like Figures 1-6 As shown, this embodiment discloses a hybrid bullseye for focusing terahertz waves, including a substrate 3, a metal thin film 2, and a central hole; a metal thin film 2 is disposed on the substrate; the height of the metal thin film is 5-10 μm;

[0035] The metal film 2 has multiple uniformly and periodically arranged annular grooves 1, and a central hole is formed at the center of the metal film 2; a silicon pillar 5 is fixed in the central hole, and a metal hemisphere 4 is also fixed on the silicon pillar 5; the incident light source is located on one side of the metal hemisphere 4 and the annular grooves 1.

[0036] Specifically, the annular groove is concentric with the central hole, and the height of the annular groove is 1-8 μm and the width is 15-40 μm.

[0037] The distance between the center of the central hole and the annular groove in the first layer is 50-70 μm; this distance can affect the optical path difference of SPPs at the central hole position, thus greatly affecting the coupling between SPPs and LSPRs. The periodic distance of the annular groove is 50-65 μm, which is approximately the size of the SPPs resonant wavelength, and is used to excite SPPs with a fixed wavelength.

[0038] The height of the center hole is consistent with the height of the metal film; the height of the metal film is consistent with the height of the silicon column; the diameter of the center hole is 15-20um.

[0039] The silicon column is a cylindrical silicon column; the diameter of the silicon column is consistent with the diameter of the metal hemisphere, both of which are 12-16um, and the diameters of the hemispheres are different, so the resonance frequencies of the excited LSPRs are different.

[0040] The material of the metal film and the metal hemisphere is Au, which has a negative dielectric constant in the terahertz wave band, can effectively excite SPPs, and has high conductivity and magnetic permeability, so the skin depth is smaller, and the light loss in the metal is smaller.

[0041] In this example, the metal film material is Au, the thickness of the metal film is 5-10um, the thickness of the silicon substrate is greater than 5 times the thickness of the metal film, the groove depth is 1-4um, the groove width is 15-40um, the center hole center distance from the center of the first layer of grooves is 50-70um, the period of the uniform period groove is 50-65um, and the diameter of the center hole is 15-20um. The above parameter settings can make the thickness of the metal film at any position greater than the skin depth.

[0042] In order to meet the Bragg coupling condition The period of the metal groove is set to be slightly smaller than the wavelength of SPPs. The period of the uniform metal groove is slightly smaller than λ spp The reason is that the interaction of the field with the groove increases the optical path of SPPs.

[0043] The transmission enhancement of the hybrid bullseye antenna to terahertz waves in this example is simulated and calculated, and the terahertz waves are incident from one side with a periodic concentric groove and a metal hemisphere structure. In the simulation calculation, the Drude model is used to describe the dielectric refractive index of Au.

[0044] The calculation method of transmission enhancement is:

[0045]

[0046] is the Poynting vector, A r is the fraction of the hole occupied area.

[0047] Figure 4Figure 6 is a transmission enhancement spectrum of the HIHB structure and the NIHB structure from 3.5 THz to 7.0 THz. The corresponding structure parameters are b = 4 um, w = 17.5 um, a = 60 um, and p = 55 um. It can be seen from the figure that the HIHB structure with 5 layers of groove enclosures and the NIHB structure with 16 layers of groove enclosures can achieve the same transmission enhancement peak value, and thus the improved bullseye antenna can effectively reduce the size of the device. The transmission enhancement spectrum of the HIHB structure with 5 layers of groove enclosures and the NIHB structure with 5 layers of groove enclosures is also compared in the figure, and it is obvious that the transmission enhancement of the HIHB structure is significantly higher than that of the NIHB structure for the same size. The reason for this phenomenon is that the SPPs generated by the periodic grating are coupled with the LSPRs generated by the center hole and the hemispherical gap, further enhancing the transmission.

[0048] Figure 5 Figure 7 is a transmission enhancement spectrum of the HIHB structure, the NIHB structure, and the structure without groove enclosures from 3.5 THz to 7.0 THz. The corresponding structure parameters are b = 4 um, w = 17.5 um, a = 60 um, and p = 55 um. It can be seen from the figure that the structure with concentric grooves has much higher transmission enhancement than the structure with only a single hole, and the normalized value is much larger than 1, so the direct transmission of the incident light no longer plays a major role. The corresponding number of grooves N for the saturation of the HIHB structure and the NIHB structure is 20, and the corresponding transmission enhancement spectrum is given in the figure. It can be seen from the figure that the transmission enhancement peak value of the HIHB structure is 556 when N = 20, and the transmission enhancement peak value of the NIHB structure is 102 when N = 20, and the improved structure can achieve a peak value about 5.5 times that of the conventional structure.

[0049] Figure 6 Figure 8 is a transmission enhancement peak value of the HIHB structure and the NIHB structure with respect to N. It can be seen that the transmission enhancement peak value of both structures increases with the increase of N at the beginning, and both reach saturation at N = 20. For the range of N ≤ 7 which has more application prospects, the transmission enhancement peak value of the HIHB structure is more than 7 times that of the NIHB structure. In the range of N > 7, the transmission enhancement peak value of the HIHB structure is about 6 times that of the NIHB structure.

[0050] Example Two

[0051] The embodiment provides a working method of the hybrid bull's eye antenna for focusing terahertz waves, and the working method comprises the following steps of:

[0052] A plane wave polarized in any direction, with a frequency of 3.5THz to 7THz, is incident on the surface of the hybrid bull's eye antenna with a groove in a vertical direction, so that the plane wave is transmitted.

[0053] The periodic groove occupies a large area and can interact with a large area of incident light, and the electromagnetic energy is converged to the center hole along with the propagation of SPPs. Then the SPPs excited by the periodic groove are coupled with the LSPRs excited by the semispherical and the slit of the center hole, so that the transmission of the center hole is enhanced. The transmission enhancement can be obtained by measuring the electromagnetic transmission at the outlet of the hybrid bull's eye antenna, calculating the normalized transmission value.

[0054] The above merely describes the preferred embodiments of the present application but is not intended to limit the present application. The present application can be variously changed and modified by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A hybrid bull's eye antenna for focusing terahertz waves, characterized by, It comprises a substrate, a metal film and a center hole; the substrate is provided with a layer of metal film; A plurality of uniform and periodic annular grooves are arranged on the metal film, and a center hole is arranged at the center position of the metal film; a silicon column is fixed in the center hole, and a metal hemisphere is further fixed on the silicon column; an incident light source is located on one side of the metal hemisphere and the annular groove; The annular groove and the center hole have the same center; The distance between the center of the center hole and the first layer of annular grooves is 50-70um, which is the size of the resonance wavelength; the diameter of the center hole is 15-20um; The thickness of the metal film is 5-10um, the thickness of the substrate is more than 5 times the thickness of the metal film, the depth of the annular groove is 1-4um, and the width of the annular groove is 15-40um; The period distance of the annular groove is 50-65um; The diameter of the silicon column and the metal hemisphere is consistent, which is 12-16um; The above parameter settings make the thickness of the metal film at any position greater than the skin depth; The maximum transmission enhancement peak of the hybrid cow eye antenna is 556, which is 5.5 times that of the traditional structure; The calculation method of transmission enhancement is: is the Poynting vector, is the fraction of the area occupied by the holes; The height of the center hole is consistent with the height of the metal film; The height of the metal film is consistent with the height of the silicon column.

2. The hybrid bull's eye antenna for focusing terahertz waves according to claim 1, wherein The silicon column is a cylindrical silicon column.

3. The hybrid bull's eye antenna for focusing terahertz waves according to claim 1, wherein The metal film and the metal hemisphere are made of gold material.

4. The working method of the hybrid cow eye antenna for focusing terahertz waves according to any one of claims 1-3, characterized in that, The plane wave polarized in any direction is incident on the side with grooves perpendicular to the surface of the hybrid cow eye antenna, realizing the transmission of the plane wave.

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