Terahertz super surface resonator based on band folding

Abstract

The application discloses a terahertz super surface resonator based on band folding, comprising a silicon substrate, a plurality of "middle" type cells formed on the silicon substrate and arranged in a two-dimensional plane periodic array to form a super surface, each "middle" type cell comprising two hollow frames oppositely arranged along a first direction and a rectangular strip arranged between the two hollow frames, the two ends of the rectangular strip along a second direction extending to the edges of the "middle" type cell to completely separate the two hollow frames, and the width of the rectangular strip being adjustable, the radiation loss of the terahertz resonator being adjusted by changing the width of the rectangular strip to adjust the size of the quality factor. The structure of the application induces Brillouin zone band folding, folds the non-radiation guide mode originally below the light into a radiation continuous spectrum to form a quasi-continuous domain bound state induced by Brillouin zone folding, and can adjust the Q factor of the quasi-BIC, and the structure is simple and robust.

Description

Technical Field

[0001] The present invention relates to the technical fields of novel artificial electromagnetic materials and terahertz science and technology, and specifically relates to a terahertz metasurface resonator based on energy band folding. Background Art

[0002] Terahertz waves refer to electromagnetic waves with a frequency between 0.1 THz and 10 THz, and a wavelength ranging from approximately 3 millimeters to 30 micrometers. With unique advantages such as high penetrability, broad spectral characteristics and biological safety, terahertz waves have shown great application value in many fields such as high-speed communication, radar stealth and sensing. The terahertz resonator with a high Q factor is the core device for realizing the above high-performance applications, and the magnitude of the Q factor directly determines the spectral resolution, sensing sensitivity of the device and the intensity of light-matter interaction. However, in the field of terahertz metasurfaces, since traditional metal and dielectric metasurfaces cannot avoid ohmic loss or radiation loss, their resonant Q factor is usually low, which greatly suppresses the efficiency of light-matter interaction.

[0003] Bound states in the continuum (BIC) are a class of localized states that exist in the continuous spectrum but do not radiate energy outward. Theoretically, they are completely decoupled from the radiation channel without energy leakage, and have an infinitely high Q factor, which provides a brand-new idea for realizing strong light-matter interaction, and has been widely applied in the design of high-performance devices such as metasurface perfect absorbers, sensors, and frequency doublers. Therefore, there is a need for an all-silicon terahertz metasurface device that has better structural robustness and can construct a stably tunable terahertz high-Q resonance. Summary of the Invention

[0004] In view of the above problems, the present invention provides a terahertz metasurface resonator based on energy band folding, so as to solve at least part of the above problems.

[0005] A terahertz metasurface resonator based on energy band folding, comprising: a silicon substrate; a plurality of "zhong"-shaped unit cells, which are formed on the silicon substrate and arranged in a periodic array along a two-dimensional plane to form a metasurface; each of the "zhong"-shaped unit cells comprises two hollow frames disposed oppositely along a first direction, and a rectangular strip arranged between the two hollow frames, wherein both ends of the rectangular strip along a second direction extend to the edges of the "zhong"-shaped unit cell to completely separate the two hollow frames; the metasurface is configured to double the lattice constant of the "zhong"-shaped unit cells in the first direction through the periodic arrangement of the plurality of "zhong"-shaped unit cells, so as to induce the Brillouin zone energy band folding effect, fold the non-radiative guided mode into the radiation continuum, and form a quasi-bound state in the continuum; The width of the rectangular strip is adjustable, and the radiation loss of the terahertz resonator is adjusted by changing the width of the rectangular strip, so as to adjust the magnitude of the quality factor.

[0006] Further, the two hollow frames are symmetrically arranged with respect to the rectangular strip, and the "zhong"-shaped unit cell has rotational symmetry; when the width of the rectangular strip is within the preset adjustment range, the rotational symmetry remains unchanged.

[0007] Further, the two hollow frames and the rectangular strip are integrally formed.

[0008] Further, the hollow frame is a square hollow frame, the width of the square hollow frame is 160 μm, and the side length of the square hollow hole of the square hollow frame is 80 μm.

[0009] Further, the silicon substrate is a high-resistivity silicon wafer, and the thickness of the high-resistivity silicon wafer is 200 μm.

[0010] Further, the value range of the width of the rectangular strip is 10 μm to 80 μm.

[0011] Further, the quality factor decreases as the width of the rectangular strip increases. When the width of the rectangular strip increases from 10 μm to 80 μm, the quality factor decreases from attenuates to .

[0012] The beneficial effects of the present invention are as follows: 1. The present invention first proposes a metasurface configuration with a "zhong"-shaped structure as the unit cell to realize resonance regulation. By introducing a vertical rectangular strip between two adjacent square hollow regions, the lattice constant of the unit cell in the first direction is doubled, so that the non-radiative guided mode originally located below the light cone is folded into the radiation continuum, forming a quasi-BIC induced by Brillouin zone folding. At the same time, the unit cell always maintains symmetry during the whole process of adjusting the width of the rectangular strip, and the quasi-BIC induced by Brillouin zone folding is obtained, so that the device has better robustness to disordered disturbance of processing dimensions, and effectively avoids the problem of significant attenuation of the quality factor of symmetry-protected BIC caused by processing errors.

[0013] 2. The present invention is fabricated by using all high-resistivity silicon dielectric materials, which eliminates the inherent ohmic loss of the traditional metal resonance structure, reduces the intrinsic material loss to an extremely low level, provides a material basis for realizing ultra-high quality factor resonance, and obtains a tunable ultra-high quality factor.

[0014] 3. According to the present invention, the radiation loss of the resonance mode can be continuously adjusted only by adjusting the width of the rectangular strip, so as to realize continuous adjustability of the quality factor. Brief Description of the Drawings

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings described below only relate to some embodiments of the present invention, rather than limiting the present invention.

[0016] Figure 1 is a schematic diagram of the overall structure of the present invention; wherein, (a) is a plan view of the basic structural unit, (b) is a plan view of the "zhong"-shaped unit cell, and (c) is a three-dimensional schematic diagram of the metasurface arranged in a periodic array; Figure 2 is a band diagram of the metadevice along the high-symmetry path; Figure 3 is the width of the rectangular strip in the embodiment of the present invention diagram of the regulation relationship on resonance characteristics; wherein, (a) is the regulation relationship curve with the quality factor Q, (b) is a partial enlarged view of the Q value in the range of 20-40 μm, (c) is the narrow-band transmission curve under different values, (d) is the overall variation diagram of the transmission spectrum when increasing from 30 μm to 80 μm.

[0017] Figure 4 is an experimental verification diagram of the embodiment of the present invention; wherein, (a) is the scanning electron microscope photograph of the device when =80 μm, and (b) is the comparison diagram between the experimental test result and the simulation result. Detailed Description of the Embodiments

[0018] To make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be described clearly and completely below with reference to the drawings of 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 described embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without creative labor shall fall within the protection scope of the present invention.

[0019] The present invention will be further described below with reference to the drawings and embodiments.

[0020] As Figure 1As shown, a terahertz metasurface resonator based on energy band folding comprises: a silicon substrate; a plurality of "zhong"-shaped unit cells formed on the silicon substrate and periodically arranged in an array along a two-dimensional plane to form a metasurface; each of the "zhong"-shaped unit cells includes two hollow frames disposed opposite to each other along a first direction, and a rectangular strip disposed between the two hollow frames, wherein both ends of the rectangular strip along a second direction extend to the edges of the "zhong"-shaped unit cell to completely separate the two hollow frames; the two hollow frames and the rectangular strip are integrally formed. The hollow frames are square hollow frames, the width of the square hollow frame is W=160μm, and the side length of the square hollow hole of the square hollow frame is =80μm, and the period constant P=320μm. The terahertz resonator is an all-silicon dielectric structure, the silicon substrate is a high-resistivity silicon wafer, and the thickness of the high-resistivity silicon wafer is H=200μm. The width of the rectangular strip is adjustable, with a value range from 10μm to 80μm; the radiation loss of the terahertz resonator is adjusted by changing the width of the rectangular strip, so as to adjust the magnitude of the quality factor Q. The two hollow frames are arranged symmetrically with respect to the rectangular strip, and the "zhong"-shaped unit cell has rotational symmetry; when the width of the rectangular strip is within a preset adjustment range, the rotational symmetry remains unchanged. The metasurface is configured to double the lattice constant of the "zhong"-shaped unit cells in the first direction through the periodic arrangement of the plurality of "zhong"-shaped unit cells, so as to induce the Brillouin zone energy band folding effect, fold the non-radiative guided mode originally located below the light cone into the radiation continuum, and form a quasi-bound state in the continuum. (In this embodiment, the first direction is the x direction, and the second direction is the y direction) In the present invention, the metasurface is a two-dimensional planar structure formed by periodically arranging a plurality of "zhong"-shaped unit cells in an array along a two-dimensional plane. The function of the metasurface is as follows: a single "zhong"-shaped unit cell can only form a localized mode and cannot produce the energy band folding effect; only through the periodic arrangement of a plurality of "zhong"-shaped unit cells can a periodic photonic system with a specific Brillouin zone structure be constructed, so that the lattice constant of the unit cells in the first direction is doubled, and the non-radiative guided mode originally located below the light cone is folded into the radiation continuum to form a quasi-bound state in the continuum. Therefore, the periodic arrangement of the metasurface is a structural prerequisite for realizing energy band folding and high-Q resonance.

[0021] The present invention relies on the vertical rectangular silicon strip to regulate resonant radiation, and maintains the unit cell throughout the process rotational symmetry, and can realize quasi-BIC excitation without introducing geometric asymmetric distortion. When the width of the vertical rectangular silicon strip approaches zero, the resonance approaches a non-radiative BIC. As the width of the vertical rectangular silicon strip gradually increases, the radiation loss gradually increases, and the resonant quality factor decreases accordingly.

[0022] As shown in Figure 2 as shown in =0.01μm, which is the energy band diagram under the extreme state. The non-radiative guided mode originally located below the light line is folded into the radiation continuum, forming a Brillouin zone folding-induced quasi-BIC near 0.475 THz.

[0023] As Figure 3 shows, when there is no rectangular strip, that is =0μm, the mode in the device is a conventional bound mode at this time; after introducing the rectangular strip, that is is not zero, this mode is transformed into a quasi-BIC. As increases, the resonant Q factor decreases exponentially. As Figure 3 (a-b) shows, when increases from 10μm to 80μm, the Q factor changes from decays to . As Figure 3 (c-d) shows, obvious resonance is exhibited on the transmission spectrum, and the resonant frequency shifts accordingly.

[0024] As Figure 4 shows, a device with =80μm was fabricated and tested. The quasi-BIC resonance of this device is located at 0.46 THz. The experimental results are basically consistent with the simulation results, which proves the effectiveness of the device design.

[0025] The present invention proposes a high-Q factor terahertz resonator based on energy band folding. For the first time, the "zhong"-shaped structure is used to induce the Brillouin zone energy band folding effect, folding the non-radiative guided mode originally located below the light line into the range of the radiation continuum, thereby forming a quasi-BIC. The present invention relies on vertical rectangular silicon strips to regulate resonance, and maintains the unit cell rotational symmetry throughout the process, and quasi-BIC excitation can be realized without introducing geometric asymmetric distortion. When the width of the vertical rectangular silicon strip approaches zero, the resonance approaches the non-radiative BIC. As the width of the vertical rectangular silicon strip gradually increases, the radiation loss of the resonance gradually increases, and the quality factor decreases accordingly.

[0026] The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, may make minor modifications or equivalent variations to form equivalent embodiments using the technical content disclosed above. However, any simple modifications, equivalent variations and modifications made to the above embodiments according to the technical essence of the present invention that do not depart from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A terahertz metasurface resonator based on band folding, characterized in that, comprising: a silicon substrate; a plurality of "zhong"-shaped unit cells, formed on the silicon substrate and periodically arranged in a two-dimensional plane to form a metasurface; each of the "zhong"-shaped unit cells comprises two hollow frames disposed opposite to each other along a first direction, and a rectangular strip disposed between the two hollow frames, wherein both ends of the rectangular strip along a second direction extend to the edges of the "zhong"-shaped unit cell, so as to completely separate the two hollow frames; the metasurface is configured to, through the periodic arrangement of the plurality of "zhong"-shaped unit cells, double the lattice constant of the "zhong"-shaped unit cells in the first direction, so as to induce the Brillouin zone band folding effect, fold the non-radiative guided mode into the radiation continuum, and form a quasi-bound state in the continuum; the width of the rectangular strip is adjustable, and the radiation loss of the terahertz resonator is adjusted by changing the width of the rectangular strip, so as to adjust the magnitude of the quality factor.

2. A terahertz metasurface resonator based on band folding according to claim 1, characterized in that, The two hollow frames are symmetrically arranged with respect to the rectangular strip, and the "middle"-shaped unit cell has rotational symmetry; when the width of the rectangular strip is within the preset adjustment range, the rotational symmetry remains unchanged.

3. A terahertz metasurface resonator based on band folding according to claim 1, characterized in that, the two hollow frames and the rectangular strip are integrally formed.

4. A terahertz metasurface resonator based on band folding according to claim 1, characterized in that, the hollow frame is a square hollow frame, the width of the square hollow frame is 160μm, and the side length of the square hollow hole of the square hollow frame is 80μm.

5. A terahertz metasurface resonator based on band folding according to claim 1, characterized in that, the silicon substrate is a high-resistivity silicon wafer, and the thickness of the high-resistivity silicon wafer is 200μm.

6. A terahertz metasurface resonator based on band folding according to claim 1, characterized in that, the width of the rectangular strip ranges from 10μm to 80μm.

7. A terahertz metasurface resonator based on band folding according to claim 6, characterized in that, The quality factor decreases as the width of the rectangular strip increases. When the width of the rectangular strip increases from 10 μm to 80 μm, the quality factor decreases from... decay to .

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