A High-Sensitivity Graphene Metasurface and Four-Frequency Switch Application Based on Plasmon-Induced Transparency Effects

At a Glance

Metadata	Details
Publication Date	2025-02-28
Journal	Photonics
Authors	Aijun Zhu, Mingjie Zhang, Weigang Hou, Cheng Lei, Cong Hu
Institutions	Guangxi Normal University, Chongqing University of Posts and Telecommunications
Citations	3
Analysis	Full AI Review Included

Executive Summary

This analysis summarizes the design and performance of a high-sensitivity, tunable monolayer graphene metasurface operating in the terahertz (THz) regime, leveraging the Plasmon-Induced Transparency (PIT) effect.

Core Value Proposition: Achieves simultaneous, high-performance functionality as a four-frequency optical switch, a high-sensitivity sensor, and a tunable filter, all controlled by adjusting the graphene Fermi level (E_F).
High Sensitivity: The sensor demonstrated a maximum sensitivity (S) of 3.70 THz/RIU (Refractive Index Unit) and an exceptional Figure of Merit (FOM) of 22.40 RIU^-1.
Tunable Switching: Functions as a four-frequency switch modulator (4.6, 5.3, 5.9, and 6.7 THz) by modulating the E_F between 0.9 eV and 1.2 eV.
Switch Performance: Achieved a maximum Modulation Depth (MD) of 95.04% and a low minimum Insertion Loss (IL) of 0.04 dB.
Structural Design: The unit cell consists of a diamond-shaped cross resonator coupled with a pentagon graphene resonator, generating PIT via destructive interference of two bright modes.
Robustness: The device exhibits insensitivity to incident angle variations, maintaining performance stability up to 60° oblique incidence.
Mechanism: Tunability is achieved by applying a bias voltage (0 to 3 V) to the graphene layer, which dynamically shifts the PIT transparent window toward higher frequencies as the E_F increases.

Technical Specifications

Parameter	Value	Unit	Context
Operating Frequency Range	1 to 9	THz	Simulation range
PIT Transparent Window	6.0	THz	Central frequency
Maximum Sensitivity (S)	3.70	THz/RIU	Sensing performance (at dip2)
Maximum Figure of Merit (FOM)	22.40	RIU^-1	Sensing performance
Refractive Index (n) Range	1.0 to 1.5	RIU	Tested range for sensing
Fermi Level (E_F) Tuning Range	0.8 to 1.2	eV	Full spectral tuning range
Switching E_F Range	0.9 to 1.2	eV	Used for 4-frequency modulator
Graphene Carrier Mobility (µ)	1.8	m²/Vs	Used for switching analysis
Graphene Thickness	1	nm	Monolayer structure
Substrate Material	Silica (SiO₂)	N/A	Dielectric constant: 3.9
Substrate Thickness	100	nm	N/A
Unit Cell Periodicity (P_x = P_y)	7	µm	N/A
Max Modulation Depth (MD)	95.04	%	Optical switch performance
Min Insertion Loss (IL)	0.04	dB	Optical switch performance
Max Extinction Ratio (ER)	13.00	dB	Optical switch performance
Incident Angle Stability	0 to 60	°	Minimal transmittance change
Operating Temperature (T)	300	K	Room temperature

Key Methodologies

The proposed graphene metasurface structure and its PIT effect were analyzed using a combination of theoretical modeling and numerical simulation.

Structural Design:
- The unit cell was designed with sub-wavelength dimensions (7 µm periodicity) on a 100 nm thick silica substrate.
- The resonators included a central diamond-shaped cross (r₁ = 2.6 µm, r₂ = 0.6 µm) and four edge pentagon structures (L = 1.5 µm).
Graphene Modeling:
- The surface conductivity (σ) of the monolayer graphene was calculated using the Kubo formula, simplified to the Drude model in the THz regime, assuming E_F is much greater than ħω and k_BT.
- The propagation constant (β) was derived from Maxwell’s equations to characterize graphene properties.
Numerical Simulation:
- The transmission spectrum was simulated using the Finite-Integration Time-Domain (FITD) method via CST STUDIO SUITE 2018.
- Boundary conditions included periodic boundaries in the x and y directions and open boundaries in the z direction.
Mechanism Analysis:
- The PIT phenomenon was confirmed to result from the destructive interference (coupling) of two bright modes (the diamond cross and the pentagon resonator).
- The Lorentz oscillation coupling model was used to accurately fit the simulated transmission curve, confirming the physical mechanism.
Performance Evaluation:
- Tuning: E_F was modulated (0.8 eV to 1.2 eV) to observe the spectral shift of the PIT window.
- Switching: MD, IL, and ER were calculated at four specific frequencies (4.6, 5.3, 5.9, 6.7 THz) to validate the four-frequency modulator function.
- Sensing: Sensitivity (S = Δf/Δn) and Figure of Merit (FOM = S/FWHM) were calculated by varying the surrounding medium’s refractive index (n).
Fabrication Feasibility (Conceptual):
- The structure is compatible with standard fabrication techniques, including Chemical Vapor Deposition (CVD) for uniform graphene growth and Electron Beam Lithography (EBL) for patterning the sub-wavelength features.

Commercial Applications

This multifunctional graphene metasurface technology is highly relevant for next-generation THz systems, offering dynamic control and high sensitivity in a compact, planar format.

THz Communication and Imaging:
- Tunable Filters: The ability to shift the PIT window across the THz band allows for dynamic frequency selection in THz communication links.
- Multi-Frequency Modulators: The four-frequency optical switch capability is ideal for high-speed, multi-channel THz data encoding and modulation systems.
Advanced Sensing and Detection:
- Ultra-Sensitive Biosensors: The high sensitivity (3.70 THz/RIU) and high FOM make the device suitable for detecting trace amounts of biological or chemical analytes in the THz fingerprint region.
- Refractive Index Sensors: Used for real-time monitoring of chemical reactions or material composition analysis.
Photonic Devices and Integrated Optics:
- Slow Light Devices: The narrow PIT window inherently supports slow light effects, crucial for buffering and processing optical signals in integrated circuits.
- Tunable Optoelectronic Devices: Graphene’s electrical tunability (0-3 V bias) enables integration into compact, voltage-controlled photonic chips, replacing bulky, fixed-frequency components.

View Original Abstract

In this paper, we propose the use of a monolayer graphene metasurface to achieve various excellent functions, such as sensing, slow light, and optical switching through the phenomenon of plasmon-induced transparency (PIT). The designed structure of the metasurface consists of a diamond-shaped cross and a pentagon graphene resonator. We conducted an analysis of the electric field distribution and utilized Lorentz resonance theory to study the PIT window that is generated by the coupling of bright-bright modes. Additionally, by adjusting the Fermi level of graphene, we were able to achieve tunable dual frequency switching modulators. Furthermore, the metasurface also demonstrates exceptional sensing performance, with sensitivity and figure of merit (FOM) reaching values of 3.70 THz/RIU (refractive index unit) and 22.40 RIU-1, respectively. As a result, our numerical findings hold significant guiding significance for the design of outstanding terahertz sensors and photonic devices.

Tech Support

Original Source

DOI: https://doi.org/10.3390/photonics12030218

References

2022 - Optical sensing based on classical analogy of double Electromagnetically induced transparencies [Crossref]
2023 - An EIT-based piezoresistive sensing skin with a lattice structure [Crossref]
2023 - Triple frequency bands terahertz metasurface sensor based on EIT and BIC effects [Crossref]
2022 - Electromagnetically induced transparency for efficient optical modulation in a graphene-dielectric metasurface with surface roughness [Crossref]
2024 - Optically implemented deep terahertz switch based on perovskite film and electromagnetically induced transparency metasurface [Crossref]
2024 - Triple-band graphene-based tunable electromagnetically induced transparency terahertz metamaterial with multi-frequency optical switching [Crossref]
2023 - Frequency-tunable hybrid metamaterial terahertz logic gate with liquid crystal based on electromagnetically induced transparency [Crossref]
2020 - Tunable plasmon induced transparency in the ellipse-shaped resonators coupled waveguide [Crossref]
2009 - Low-Loss Metamaterials Based on Classical Electromagnetically Induced Transparency [Crossref]
2022 - Optical modulated graphene metamaterial based on plasmon-induced transparency in the terahertz band: Application for sensing [Crossref]