A terahertz metamaterial sensor based on graphene plasmon-induced transparency and Fano resonance

Abstract

This invention addresses the shortcomings of existing terahertz sensors in terms of sensitivity and tunability by proposing a high-sensitivity metamaterial sensor based on plasmon-induced transparency (PIT) and Fano resonance in monolayer graphene. The specific graphene sensing structure of this invention consists of a vertical graphene strip and proportionally designed graphene resonant rings on both sides. This symmetrical graphene structure is attached to a SiO2 dielectric layer with a suitable relative permittivity, forming a typical transmission-type metamaterial sensor. The resulting terahertz metamaterial sensor possesses an excellent sensitivity of up to 2.84 THz / RIU, a superior quality factor, and insensitivity to changes in polarization and incident angle. Furthermore, by adjusting the structural parameters, flexible switching between dual functions can be achieved, significantly enhancing the accuracy of material detection and the range of sensing applications. This invention offers advantages such as high sensitivity, strong tunability, simple structure, and high stability. This design integrates the excellent characteristics of Fano resonance and the PIT effect, achieving the high sensitivity requirements of the sensor and successfully overcoming the performance limitations of traditional single-function sensors.

Description

Technical Field

[0001] This invention belongs to the field of terahertz metamaterials, specifically relating to a graphene terahertz metamaterial sensor capable of generating plasma-induced transparency and Fano resonance. Background Technology

[0002] Terahertz waves are a segment of the electromagnetic spectrum between microwaves and infrared waves, with frequencies ranging from 0.1 to 10 THz and wavelengths from 3 mm to 0.03 mm. Due to their unique spectral position, terahertz waves have enormous potential value in scientific research and various practical applications. However, the early development of terahertz technology encountered significant challenges, particularly the lack of efficient terahertz sources and sensitive detectors, leading to the so-called "terahertz gap."

[0003] Since the 1990s, with the significant advancements in semiconductor and ultrafast laser technologies, terahertz technology has seen remarkable development. Due to its unique properties such as low energy, high penetration, and fingerprint spectrum, terahertz waves have demonstrated outstanding application potential in fields such as medical non-destructive testing, quality inspection, and security checks. Scientific research and technological development activities are flourishing, thus it has important application prospects in fields such as chemistry, biology, and medicine.

[0004] Metamaterials are materials with unique electromagnetic properties not found in nature, designed through artificial periodic structures. Their uniqueness lies in the fact that the scale of their structure is typically much smaller than the wavelength of the electromagnetic wave they interact with, allowing control of electromagnetic waves by manipulating the material's structure rather than its chemical composition. This enables metamaterials to exhibit many properties in the interaction, propagation, and control of electromagnetic waves that are impossible with traditional materials. With the theoretical predictions and experimental verification of negative refractive index materials, metamaterial research has rapidly become a hot field. Metamaterials have overturned traditional electromagnetic wave propagation laws, providing entirely new ideas for the design of novel optical devices. Subsequently, the research scope of metamaterials has expanded to multiple application areas such as electromagnetic stealth, super-resolution imaging, tunable filters, and antennas.

[0005] Plasma-induced transparency (PIT) is an optical phenomenon similar to electromagnetically induced transparency (EIT) in atomic physics, producing very narrow transmission peaks, analogous to the narrow transparent window in EIT. This narrow bandwidth characteristic enables metamaterials to achieve highly selective light transmission at specific frequencies, while the accompanying slow-light effect can significantly slow down the speed of light, which has potential applications in optical storage and optical delay lines. Plasma-induced transparent metamaterials can be designed to be sensitive to environmental changes, allowing the metamaterial to dynamically change the position and width of the transparent window by adjusting external electric or magnetic fields, achieving tunable optical responses. Simultaneously, the metamaterial structure can be optimized to achieve low-loss plasma-induced transparency, greatly improving the performance and efficiency of metamaterial sensors. Fano resonance can be achieved through resonant coupling between "bright" and "bright" or "bright" and "dark" modes. Its core mechanism originates from the interaction between discrete-state excitation (related to resonance) and continuous-state scattering (related to background). This interference effect only manifests when the resonance energy of the discrete state is within the energy range of the continuous state. Observing the transmission spectrum of Fano resonance reveals significant differences from the spectral characteristics of the induced transparency effect. The spectral characteristics of Fano resonances are often sharper due to the interference splitting between discrete and continuous states within the same resonance energy range. It is worth noting that the boundary between the transparency effect and the Fano resonance is not absolute; designers can achieve interconversion between the two by adjusting structural parameters.

[0006] Currently, the main problem with high-performance sensors is that overly complex designs increase manufacturing difficulty, while overly simplified designs may fail to achieve the desired results. Furthermore, many lack the necessary anti-interference capabilities. Therefore, there is an urgent need to design a high-performance metamaterial sensor with a simple structure and strong anti-interference performance to address these issues. Summary of the Invention

[0007] To address the aforementioned shortcomings, this invention provides a graphene-based plasma-induced transparent terahertz metamaterial sensor. This sensor features a simple structure and enhances sensitivity through plasma-induced transparency. By investigating the influence of structural parameter adjustments, the invention confirms that the sensor can flexibly switch between dual functions while maintaining a simple structural design. Furthermore, through resonance mechanism analysis of the transmission spectrum, high-quality Fano resonance is introduced without disrupting the PIT effect. This provides a novel solution to the existing problems.

[0008] To achieve the above objectives, this invention provides a terahertz metamaterial sensor based on graphene plasmon-induced transparency and Fano resonance, offering the following solution:

[0009] It should be noted that since the terahertz metamaterial sensor is composed of a periodic arrangement of unit structures, the size of which can be arranged according to one's own needs, the following steps only introduce the design of the unit structures.

[0010] The sensor is a transmission type, consisting of a vertical graphene strip and proportionally designed graphene resonant rings on both sides, with each structure in contact with the substrate. The graphene strip is located at the center of the structure.

[0011] Preferably, the substrate is a silicon dioxide (SiO2) substrate;

[0012] Preferably, the patterned structure material is graphene;

[0013] Preferably, the graphene strip has a width of 1.6µm and a length of 20µm; the left-side ring of the graphene has a radius of 4µm and an inner diameter of 2.2µm. The right-side ring has a radius of 2.8µm and an inner diameter of 1.6µm.

[0014] Preferably, the thickness of the patterned structure is 0.1 µm, and the electrical conductivity of the graphene structure is 6 × 10⁻⁶. 6 S / m;

[0015] Preferably, the substrate has a thickness of 5µm and a dielectric constant ε=3.9.

[0016] This invention relates to the field of terahertz metamaterials, providing a terahertz metamaterial sensor based on graphene plasmon-induced transparency and Fano resonance. Specifically, it comprises a symmetrical graphene metamaterial sensor consisting of a vertical graphene strip, graphene resonant rings on both sides with appropriately patterned structural layers, and a substrate. The invention uses a periodic arrangement of unit structures, with this symmetrical graphene structure attached to a SiO2 dielectric layer with a suitable relative permittivity, collectively forming a typical transmission-type metamaterial sensor. The resulting terahertz metamaterial sensor possesses an excellent sensitivity of up to 2.84 THz / RIU, a superior quality factor, and insensitivity to changes in polarization and incident angle. Furthermore, by adjusting structural parameters, flexible switching between dual functions can be achieved, significantly enhancing the accuracy of material detection and the range of sensing applications. This invention offers advantages such as high sensitivity, strong tunability, simple structure, and high stability, effectively addressing the shortcomings of current terahertz materials in practical applications. Attached Figure Description

[0017] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0018] Figure 1 This is a surface view of the terahertz metamaterial sensor based on graphene plasmon-induced transparency and Fano resonance, as described in this invention.

[0019] Figure 2 This is a structural diagram of the sensor unit described in this invention.

[0020] Figure 3 It is the sensor periodic array described in this invention.

[0021] Figure 4 This is the transmission spectrum of the sensor described in this invention when the radius variable is 0.

[0022] Figure 5 This is a transmission spectrum of the sensor described in this invention under different radius variations.

[0023] Figure 6 This is a simulation diagram of the sensor described in this invention with different refractive index detection objects placed on it. Detailed Implementation

[0024] The technical methods of this invention will be fully and clearly described below with reference to the accompanying drawings, enabling those skilled in the art to easily and smoothly understand the advantages and details of this invention. Obviously, the examples described below are merely specific examples of this invention, and this invention can be implemented through different examples. Details such as dimensions and positions described in this invention can also be slightly modified for different examples without departing from the spirit of this invention. Therefore, other examples obtained without inventive modifications also fall within the scope of this invention.

[0025] Please see Figures 1 to 5 As shown, this invention relates to the field of terahertz metamaterials and provides a terahertz metamaterial sensor based on graphene plasmon-induced transparency and Fano resonance. Specifically, a symmetrical graphene metamaterial sensor is constructed using a vertical graphene strip, a graphene resonant ring on both sides with a structurally patterned layer of suitable values, and a substrate. The invention consists of a periodically arranged unit structure, with this symmetrical graphene structure attached to a SiO2 dielectric layer with a suitable relative permittivity, forming a typical transmission-type metamaterial sensor. The terahertz metamaterial sensor formed by this invention possesses excellent sensitivity up to 2.84 THz / RIU, a good quality factor, and insensitivity to changes in polarization and incident angle. Furthermore, by adjusting the structural parameters, flexible switching between dual functions can be achieved, significantly enhancing the accuracy of material detection and the range of sensing applications. This invention has advantages such as high sensitivity, strong tunability, simple structure, and high stability, thus effectively addressing the shortcomings of current terahertz band materials in practical applications.

[0026] In this example, the substrate is a dielectric layer formed of silicon dioxide. Silicon dioxide has a low dielectric constant, which can effectively improve the performance of the sensor. At the same time, silicon dioxide maintains relatively stable physical dimensions under different temperature and humidity conditions and is not easily deformed or expanded due to environmental changes.

[0027] As described above, in this example, the vertical strip and the two circular rings on the left and right are all made of graphene. The terahertz metamaterial sensor is intended for use in fields requiring high-precision measurement. Graphene has extremely high conductivity and electron mobility, which gives it extremely low intrinsic loss, allows it to support narrower linewidths, and has high sensitivity to changes in the external dielectric environment. Therefore, the use of graphene as a structural layer in this invention further improves the accuracy of the sensor.

[0028] As described above, in this example, the present invention utilizes plasma-induced transparency (PIT), an optical phenomenon similar to electromagnetically induced transparency (EIT) in atomic physics, which can produce a very narrow transmission peak, analogous to the narrow transparent window in EIT. This narrow bandwidth characteristic enables metamaterials to achieve highly selective light transmission at specific frequencies, while the accompanying slow-light effect can significantly slow down the speed of light, which has potential applications in fields such as optical storage and optical delay lines. Plasma-induced transparent metamaterials can be designed to be sensitive to environmental changes, allowing the metamaterial to dynamically change the position and width of the transparent window by adjusting external electric or magnetic fields, achieving a tunable optical response. Simultaneously, the metamaterial structure can be optimized to achieve a low-loss plasma-induced transparency effect, which can greatly improve the performance and efficiency of metamaterial sensors.

[0029] The structural diagram of the sensor described in this example is as follows: Figure 1 As shown, the side length P of the unit structure is 20µm; the width of the graphene strip is 1.6µm and the length is 20µm; the radius of the left ring is 4µm and the inner diameter is 2.2µm; the radius of the right ring is 2.8µm and the inner diameter is 1.6µm.

[0030] The sensor 3D structure diagram shown in this example is as follows: Figure 2 As shown, the substrate has a thickness of 0.5µm and is made of silicon dioxide; the structural layer has a thickness of 0.1µm and is made of graphene.

[0031] The sensor periodic array and sensor coordination simulation diagram shown in this example are as follows: Figure 3 As shown, TM waves are incident perpendicularly on the sensor surface; the Fermi level of graphene is changed by altering the voltage across the external metal electrode, thereby coordinating the sensor's sensitivity parameters.

[0032] Based on the specific parameters and structure described above, the sensor proposed in this example is a transmission-type sensor, such as... Figure 4 As shown, when the radius variable dx remains constant, the sensor exhibits perfect transmission valleys at frequencies of 3.529 THz, 3.947 THz, and 4.649 THz, while possessing deeper transparent windows at frequencies of 3.502 THz and 4.191 THz. Each transmission valley is caused by the direct coupling of each individual structure with the incident light; the two transparent windows result from the destructive interference of the bright and dark modes of each structure. The proposed sensor possesses a good Q value. The specific formula for the Q value is as follows: ,in This is the frequency at the highest point of the resonance peak. The Q value is the full width at half maximum (FWHM) of the peak. Therefore, the FWHM of the resonant peak at 3.502 THz is 0.213 THz, resulting in a Q value of 18.06 for the transmission peak P1. The FWHM of the resonant peak at 4.191 THz is 0.284 THz, resulting in a Q value of 11.27 for the transmission peak P2. The Q value is an important parameter for evaluating sensor performance; a higher Q value indicates stronger frequency selectivity and thus better sensor performance. In this invention, the Q value of the sensor is further improved through plasmon-induced transparency.

[0033] Based on the specific parameters and structure described above, the transmission maps of the sensor proposed in this example for different radius variables dx are as follows: Figure 5As shown, as the radius variable dx increases from 0µm to 1.5µm, the profile of the Fano transmission valley D2 gradually becomes sharper, and its intensity also increases significantly. This phenomenon stems from the fact that the increase in the radius variable dx exacerbates the difference in coupling strength between the two resonant cavities, and it is this difference in strong and weak coupling under the same resonance background that contributes to the formation of the Fano transmission valley D2. Since the introduction of Fano resonance does not completely destroy the PIT effect, the overall waveform of the PIT effect does not change much. As previously analyzed, the transmission valley D1 originates from the coupling of the quadrupole resonance, and the adjustment of the radius variable dx has a relatively limited impact on the quadrupole resonance mode, so the resonance frequency in the transmission spectrum remains stable. However, in the dipole resonance system, the coupling strength and the coupling distance are significantly proportional. This is reflected in the dynamic control in this study as the resonance frequency redshifts with the increase of the radius variable dx, thus causing the resonance frequency of the transmission valley D3 to exhibit a redshift. When the radius variable dx varies within the range of 0.3µm to 1.5µm, the Fano resonance still maintains its high Q factor, while the bandwidth of the Fano transmission valley shows a certain degree of broadening. The results show that when the radius variable dx is 0, only the PIT effect of a single resonance exists in the metasurface's resonance mode; however, when the radius variable dx is adjusted within a range less than 1.2µm, both the Fano resonance with varying strengths and the PIT effect coexist in the metasurface's resonance mode, and the sensor's sensitivity is also increased due to the introduction of asymmetric spectral lines. This phenomenon confirms the feasibility and superiority of using the radius variable dx as a control switch.

[0034] Based on the above description, a detection material with a fixed thickness of 5 μm is placed on the surface of the sensor. This detection material is then simulated by having different refractive indices *n*. As the refractive index of the detection material increases, such as... Figure 5 As shown, the sensor's simulated resonant frequency exhibits a redshift. This is because as the refractive index of the detected object increases, its dielectric constant also increases. According to equivalent circuit theory, an increase in the dielectric constant of the detected object leads to an increase in the equivalent capacitance formed between it and the sensor surface, thus lowering the sensor's resonant frequency and causing a redshift. Sensor sensitivity is a crucial parameter for evaluating sensor performance; higher sensitivity indicates better sensor performance. The commonly defined formula for sensitivity is: ,in, This represents the frequency shift of the transparent window. This represents the change in the refractive index of the medium. When RI increases from 1.0 to 1.1, the frequency shift of the PIT transmission peak P2 reaches 0.284 THz, while the frequency shift of the transmission peak P1 is 0.213 THz. At this point, the sensor sensitivity reaches 2.13 THz / RIU (Fano resonance) and 2.84 THz / RIU (PIT effect), respectively. Compared with traditional metamaterial sensors, the proposed graphene metamaterial sensor exhibits extremely high sensitivity at the peak values.

[0035] In summary, this invention relates to the field of terahertz metamaterials, providing a terahertz metamaterial sensor based on graphene plasmon-induced transparency and Fano resonance. Specifically, the graphene metamaterial sensor is constructed using a vertical graphene strip, graphene resonant rings on both sides with appropriately patterned structural layers, and a substrate. This invention consists of a periodically arranged unit structure, with this symmetrical graphene structure attached to a SiO2 dielectric layer with a suitable relative permittivity, collectively forming a typical transmission-type metamaterial sensor. The resulting terahertz metamaterial sensor possesses an excellent sensitivity of up to 2.84 THz / RIU, a superior quality factor, and insensitivity to changes in polarization and incident angle. Furthermore, by adjusting structural parameters, flexible switching between dual functions can be achieved, significantly enhancing the accuracy of material detection and the range of sensing applications. Addressing the issues of complex structures and poor detection performance in terahertz metamaterial sensors, this invention offers advantages such as high sensitivity, strong tunability, simple structure, and high stability, effectively solving the shortcomings of current terahertz materials in practical applications and possessing high commercial value.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to specific embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A terahertz metamaterial sensor, characterized in that, The terahertz metamaterial sensor is a transmission type, and its unit structure includes a bottom substrate and a top graphene pattern. The pattern consists of a vertical graphene strip and graphene resonant rings designed proportionally on the left and right sides. The terahertz metamaterial sensor is composed of unit structures arranged periodically, and the size of the actual finished product can be arranged independently according to one's own needs.

2. According to claim 1, in the unit structure, the substrate is selected as SiO2 with a dielectric constant of 3.9, and the top pattern is selected as graphene with a conductivity of 6 × 10⁻⁶. 6 S / m.

3. According to claim 1, in the unit structure, the thickness of the graphene pattern is 1µm and the thickness of the substrate is 5µm.

4. According to claim 1, in the unit structure, the radius of the left circular ring is 4µm and the inner diameter is 2.2µm.

5. According to claim 1, in the unit structure, the radius of the right-side ring is 2.8µm and the inner diameter is 1.6µm.

6. According to claim 1, in the unit structure, the graphene strip has a width of 1.6µm and a length of 20µm.

7. According to claim 1, the period of the terahertz metamaterial sensor unit structure is 20 µm.

8. According to claims 1-7, the terahertz metamaterial sensor generates three resonant peaks at 3.529 THz, 3.947 THz and 4.649 THz, and forms two transparent windows at 3.502 THz and 4.191 THz.

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