A filter structure based on multi-channel controlled nonlinear metasurface

Abstract

The present invention discloses a filter structure based on a multi-channel controlled nonlinear metasurface, comprising a high-resistance silicon substrate, on which two U-shaped metal rings are symmetrically arranged, the openings of the U-shaped metal rings being arranged opposite to each other, and two rectangular metal sheets being symmetrically arranged on both sides of the two U-shaped metal rings, one end of one of the U-shaped metal rings being provided with a missing section, and the missing section being filled with a vanadium dioxide temperature-sensitive material; the filter structure is capable of separating a wide passband to generate two narrow passbands.

Description

Technical Field

[0001] The present invention relates to the field of nonlinear optical control devices, and in particular to a filter structure based on multi-channel control nonlinear metasurface. Background Art

[0002] Terahertz (THz) waves, which range from 0.1THz to 10THz, lie at the intersection of electronics and photonics. Compared to electromagnetic waves in other frequency bands, they exhibit a range of unique electromagnetic properties. Their non-ionizing and coherent properties prevent them from destroying the internal structure and intrinsic properties of the material being detected, nor do they harm the human body. Therefore, THz imaging can be widely used in various safety and health monitoring applications, holding significant significance in national security, medical diagnosis, quality control, and other fields.

[0003] To achieve widespread application of terahertz technology, in addition to effectively generating and detecting terahertz waves, practical applications also require filtering out unwanted frequency ranges and noise to improve system performance, due to environmental noise and application limitations. In recent years, filtering technology has become a crucial component of signal detection and parameter extraction in modern signal processing. The fundamental research question is how to filter out various noises from the received signal, either the target signal or the reflected signal, to obtain the true signal. Therefore, terahertz filters have become a crucial component in enabling widespread application of terahertz technology.

[0004] Communication systems often need to transmit frequency signals across multiple, discrete channels using a single beam, necessitating dual-passband or even multi-passband filters. The single-band communication systems commonly used in the past no longer adequately meet the demands of miniaturization and integration. To improve spectrum efficiency, it is essential to have multiple, simultaneously operating frequency bands within a communication system. Researchers both domestically and internationally have focused on the research and design of multi-passband filters, achieving significant results in this area.

[0005] Metasurfaces, also known as metastructured surfaces, are artificial electromagnetic materials composed of planar subwavelength units arranged in a regular pattern. They possess electromagnetic response properties not possessed by many traditional materials. Due to their high design flexibility and relatively simple fabrication process, metamaterials are widely used in filter design. Metamaterial filters achieve electrical and magnetic resonance with incident electromagnetic waves by rationally designing the metamaterial's geometric structure and parameters. At the resonant frequency, the majority of the incident wave is reflected and absorbed, forming a stopband. At the non-resonant frequency, the incident wave transmits through the metamaterial, forming a passband, thereby enabling the manipulation of terahertz waves. High-performance metasurfaces are key to manipulating terahertz waves and can be used to realize high-performance multi-band filters. Research on terahertz filters based on metamaterials has brought new opportunities for their development and application. However, current metasurface filters, once their structure is determined, only exhibit static and unique properties and cannot be dynamically adjusted.

[0006] Bound states in the continuum (BIC) are a powerful interaction recently introduced into metasurface systems, capable of trapping energy from electromagnetic waves with wavelengths larger than the diffraction limit without radiative leakage. Bound states in the continuum (BIC) have emerged as a physical mechanism that can support high-quality (Q) metasurfaces for enhancing nonlinear optical responses. BICs are highly localized states embedded in a continuous spectrum that coexists with radiative modes, allowing them to carry away energy without any radiation. True BICs are unavailable and exist only in mathematical models. For periodically arranged metasurfaces, if the lattice unit cell is symmetric, each resonant Bloch wave can support a non-leaking mode associated with a BIC. When the system is ideally perturbed, the BIC mode couples to an extended wave and leaks into a Fano resonance with a finitely high Q factor, a so-called "quasi-BIC." Furthermore, by adjusting the symmetry parameters of the metasurface unit cell, the amplitude, frequency, linewidth, and Q factor of the optical response can be manipulated. By utilizing the optical resonances generated by quasi-BICs and plasmon polaritons, multiple nonlinear optical signals on the metasurface can be tuned simultaneously. Due to their high Q factors, metasurfaces supporting BICs have potential applications in lasers, sensors, filters, and nonlinear optics.

[0007] Therefore, future wireless and satellite communication systems will require filters with very high Q factors. However, most current filters are unable to achieve ultra-high Q-factor resonant modes. Furthermore, the response of currently designed and fabricated terahertz metamaterial filters to electromagnetic waves depends primarily on their structural units. Once their shape and size are determined, the corresponding operating wavelength and bandwidth are also fixed, meaning they can only achieve a single function within a limited operating bandwidth, severely restricting their application. Summary of the Invention

[0008] The purpose of the present invention is to overcome the shortcomings of the existing technology, realize the transition from continuous domain bound states (BICs) to quasi-continuous domain bound states (quasi-BICs) through symmetry breaking, generate nonlinear response, realize the function of multi-band transmission path, and realize dynamic regulation of terahertz waves by integrating tunable dielectric materials, thereby realizing real-time control and dynamic tuning of electromagnetic properties, so as to obtain a filter structure of a tunable terahertz nonlinear electromagnetic metasurface.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A filter structure based on a multi-channel controlled nonlinear metasurface comprises a high-resistance silicon substrate on which two U-shaped metal rings are symmetrically arranged, the openings of the U-shaped metal rings being arranged opposite to each other, and two rectangular metal sheets being symmetrically arranged on either side of the two U-shaped metal rings, wherein one end of one of the U-shaped metal rings is provided with a missing section filled with a vanadium dioxide temperature-sensitive material; the filter structure is capable of generating four narrow passbands in a polarization direction perpendicular to the rectangular metal sheets.

[0011] Furthermore, the near-field coupling between the symmetrical U-shaped metal ring with a missing segment and the symmetrical rectangular metal piece can excite the LC resonance of the two rectangular metal pieces and generate a stopband, which ultimately separates the wide passband to produce two narrow passbands at 0.76 THz and 0.86 THz.

[0012] Furthermore, the symmetrical U-shaped metal ring with a missing segment can itself excite the continuum bound state, generating a narrow passband caused by a Fano resonance at 0.53 THz; the passband at 1.18 THz is generated by the symmetrical rectangular metal piece generating high-order continuum bound states to excite the U-shaped metal ring.

[0013] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0014] 1. The filter structure of the present invention realizes the transformation of continuous domain bound states (BICs) to quasi-continuous domain bound states (quasi-BICs) with ultra-high quality factors through symmetry breaking, generates sharp Fano resonance, and obtains a narrow stopband within a wide passband, thereby realizing multi-bandpass filtering function. The multi-bandpass filter can meet the needs of communication systems to transmit frequency signals of multiple discontinuous channels through a single beam, meet the requirements of miniaturization and integration of communication systems, and at the same time improve spectrum utilization.

[0015] 2. The LC resonance caused by the unique U-shaped metal ring structure of the filter structure of the present invention absorbs terahertz waves of a specific frequency, thereby realizing a band-stop filtering function and achieving an efficient terahertz filtering function, effectively filtering out various noises in the received signal to obtain a real signal.

[0016] 3. The addition of the temperature-sensitive material vanadium dioxide gives the filter a multi-band filtering switch function, and can control the opening and closing of the two passbands by temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention.

[0018] Figure 2 It is the transmittance of the filter structure of the present invention to terahertz signals of different frequencies at different operating temperatures.

[0019] Figure 3 is the transmittance of the filter structure under different degrees of symmetry breaking. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] like Figure 1 As shown, the present invention provides a filter structure based on a multi-channel controlled nonlinear metasurface, comprising a high-resistance silicon substrate, on which two U-shaped metal rings are symmetrically arranged, the openings of the U-shaped metal rings being arranged opposite to each other, and two rectangular metal sheets being symmetrically arranged on both sides of the two U-shaped metal rings, forming a completely symmetrical metasurface on the high-resistance silicon substrate as a whole; a missing section is provided at one end of one of the U-shaped metal rings, and the missing section is filled with a vanadium dioxide temperature-sensitive material.

[0022] Since the physical parameters that affect the nonlinear response are mainly the degree of symmetry breaking, the incident polarization state and the material conductivity, the present invention designs a nonlinear metasurface based on symmetry protection BIC containing temperature-sensitive materials by regulating the degree of symmetry breaking and the material conductivity to realize the function of terahertz multi-band filter. Figure 1The polarization direction shown shows typical localized surface plasmon (LSP) resonances, while the two U-shaped metal rings that support inductor-capacitor (LC) resonances at the same frequency are inactive in this polarization direction. The filter structure resonates only at 0.76 THz and 1.18 THz due to the inhibition of certain modes symmetrically controlled on the surface of the high-resistance silicon substrate.

[0023] The present invention slightly destroys the symmetry of the filter structure by providing a missing segment at one end of one of the U-shaped metal rings. The electromagnetic field distribution in the asymmetric mode supported by this asymmetric structure enables the BICs to be converted into an ultra-sharp Fano resonance, which can obtain an ultra-high Q-factor resonance mode, and the Q factor can be easily adjusted by the degree of asymmetry. The near-field coupling of the interaction between the symmetrical U-shaped metal ring with the missing segment and the symmetrical rectangular metal sheet will excite the LC resonance of the two U-shaped metal rings, and its destructive interference will produce a sharp stopband, thereby separating the wide passband to produce two narrower passbands located near 0.76THz and 0.86THz. The symmetrical U-shaped metal ring with the missing segment itself will also excite the continuous domain bound state, generating a narrow passband caused by the Fano resonance near 0.53THz. The passband near 1.18THz is generated by the high-order continuous domain bound state generated by the symmetrical rectangular metal sheet to excite the U-shaped metal ring.

[0024] Specifically, based on the designed filter structure with missing segments, a temperature-sensitive material is used to complete the broken symmetry, resulting in a filter structure that can change the material conductivity through temperature control, thereby affecting the symmetry of the filter structure with missing segments. The temperature-sensitive material selected in this embodiment is vanadium dioxide. Vanadium oxide (VO2) is a typical reversible phase-change material that exhibits a low-conductivity insulating state at room temperature and changes to a metallic state at 68°C. It can be used as an adjustable medium. The phase change can cause the conductivity of VO2 to change by nearly 4 orders of magnitude. Moreover, after the temperature drops, VO2 can change from a metallic state back to an insulating state. Therefore, it is used as a temperature-sensitive switch to regulate the nonlinear response of the filter structure.

[0025] Figure 2 In the figure, the transmittance of the filter structure for signals with frequencies ranging from 0.4 THz to 1 THz at different operating temperatures proves the influence of material conductivity on nonlinear response, and proves that the filter structure in this embodiment achieves efficient terahertz channel regulation effect near 0.76 THz and 0.86 THz.

[0026] Figure 3 The transmittance variation of the filter structure under different degrees of symmetry breaking further proves that the degree of symmetry breaking is an important physical parameter affecting the nonlinear response. The value after symmetry breaking represents the length of the missing segment in the U-shaped metal ring.

[0027] The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention. The above specific embodiments are merely illustrative and not restrictive. Without departing from the scope of the present invention and the scope of protection of the claims, those skilled in the art may make various specific modifications based on the teachings of the present invention, all of which fall within the scope of protection of the present invention.

Claims

1. A filter structure based on multi-channel controlled nonlinear metasurface, characterized in that: The invention comprises a high-resistance silicon substrate, on which two U-shaped metal rings are symmetrically arranged, the openings of the U-shaped metal rings are arranged opposite to each other, and two rectangular metal sheets are symmetrically arranged on two sides perpendicular to the opening directions of the two U-shaped metal rings, one end of one of the U-shaped metal rings is provided with a missing section, and the missing section is filled with vanadium dioxide temperature-sensitive material; the filter structure can generate four narrow passbands in a polarization direction perpendicular to the rectangular metal sheet.

2. The filter structure based on multi-channel controlled nonlinear metasurface according to claim 1, characterized in that: The near-field coupling between the symmetrical U-shaped metal ring with a missing segment and the symmetrical rectangular metal piece can excite the LC resonance of the two rectangular metal pieces and generate a stopband, which ultimately separates the wide passband to produce two narrow passbands at 0.76 THz and 0.86 THz.

3. The filter structure based on multi-channel controlled nonlinear metasurface according to claim 1, characterized in that: The symmetrical U-shaped metal ring with a missing segment can itself excite the continuum bound state, generating a narrow passband caused by a Fano resonance at 0.53THz; the passband at 1.18THz is caused by the symmetrical rectangular metal piece generating high-order continuum bound states to excite the U-shaped metal ring.

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