Actively Tunable Terahertz Switches Based on Subwavelength Graphene Waveguide

Logic operation and all-optical switch characteristics of graphene surface plasmons

Terahertz logic gates play a crucial role in optical signal processing and THz digitization. In this paper, we propose a design strategy for graphene-based metamaterial THz all-optical logic gate devices based on the induced transparency effect of surface isolated. Theoretically, we realize Boolean operations by coupling of a hexagonal graphene resonant cavity with dual embedded rotatable ellipses. Based on the coupled mode theory, the elliptical rotation angle of the resonator is an important factor affecting the PIT phenomenon. We control the logic input by adjusting the rotation angles of the two embedded ellipses. The analysis results show that: under the incidence of y-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 30° represents the input signal '1'. Through numerical simulation, the structure realizes two logical operations of NAND and AND. Under the incidence of x-polarized light, the ellipse deflection angle of 0° represents the input signal '0', and the ellipse deflection angle of 90° represents the input signal '1'. Through numerical simulation, the structure realizes three logical operations of NAND, XNOR and OR. Finally, we analyze the performance of the logic gates by extinction ratio. The extinction ratio of the logic gate is up to 10.38 dB when performing OR Boolean operations. Numerically simulated all-optical logic gates can be key components of optical processing and telecommunication equipment.

First designing of a silicene-based optical MOSFET with outstanding performance

Miniaturized integrated optical devices with low power consumption have long been considered hot candidates for plasmonic applications. While 2D materials such as graphene have been proposed for this purpose, they suffer from large propagation loss and low controllability at room temperature. Here, a silicene-based optical MOSFET with excellent performance is designed to achieve integrated circuit optical technology. The designed device is comprised of a silicene optical waveguide whose switching operation is performed by a gate and has a structure similar to an enhancement MOSFET with a formed channel. Unlike graphene, the surface conductivity of silicene can be controlled by both chemical potential and an electric field perpendicular to its surface. This unique feature of silicene is used to design and simulate an optical-MOSFET with transverse electric polarization at 300 K. The salient characteristics of the optical device include its nanoscale dimensions, ultra-low insertion loss of 0.13 dB, infinite extinction ratio, and quality factor of 688, proposing it as a promising tool for optical integration.

Tunable Thermal Camouflage Based on GST Plasmonic Metamaterial

Thermal radiation control has attracted increasing attention in a wide range of field, including infrared detection, radiative cooling, thermal management, and thermal camouflage. Previously reported thermal emitters for thermal camouflage presented disadvantages of lacking either tunability or thermal stability. In this paper, we propose a tunable thermal emitter consisting of metal-insulator-metal (MIM) plasmonic metamaterial based on phase-change material Ge₂Sb₂Te₅ (GST) to realize tunable control of thermal radiation in wavelength ranges from 3 μm to 14 μm. Meanwhile, the proposed thermal emitter possesses near unity emissivity at the wavelength of 6.3 μm to increase radiation heat dissipation, maintaining the thermal stability of the system. The underlying mechanism relies on fundamental magnetic resonance and the interaction between the high-order magnetic resonance and anti-reflection resonance. When the environmental background is blackbody, the tunable emitter maintains signal reduction rates greater than 80% in middle-IR and longer-IR regions from 450 K to 800 K and from room temperature to 800 K, respectively. The dependences of thermal camouflage on crystallization fraction of GST, incident angles and polarization angles have been investigated in detail. In addition, the thermal emitter can continuously realize thermal camouflage for various background temperatures and environmental background in atmospheric window in the range of 3–5 μm.

Graphene-Coated Nanowire Waveguides and Their Applications

In recent years, graphene-coated nanowires (GCNWs) have attracted considerable research interest due to the unprecedented optical properties of graphene in terahertz (THz) and mid-infrared bands. Graphene plasmons in GCNWs have become an attractive platform for nanoscale applications in subwavelength waveguides, polarizers, modulators, nonlinear devices, etc. Here, we provide a comprehensive overview of the surface conductivity of graphene, GCNW-based plasmon waveguides, and applications of GCNWs in optical devices, nonlinear optics, and other intriguing fields. In terms of nonlinear optical properties, the focus is on saturable absorption. We also discuss some limitations of the GCNWs. It is believed that the research of GCNWs in the field of nanophotonics will continue to deepen, thus laying a solid foundation for its practical application.

All-Plasmonic Switching Effect in the Graphene Nanostructures Containing Quantum Emitters

Nonlinear plasmonic effects in perspective 2D materials containing low-dimensional quantum emitters can be a basis of a novel technological platform for the fabrication of fast all-plasmonic triggers, transistors, and sensors. This article considers the conditions for achieving a strong coupling between the surface plasmon-polariton (SPP) and quantum emitter taking into account the modification of local density of optical states in graphene waveguide. In the condition of strong coupling, nonlinear interaction between two SPP modes propagating along the graphene waveguide integrated with a stub nanoresonator loaded with core-shell semiconductor nanowires (NWs) was investigated. Using the 2D full-wave electromagnetic simulation, we studied the different transmittance regimes of the stub with NW for both the strong pump SPP and weak signal SPP tuned to interband and intraband transition in NW, respectively. We solved the practical problem of parameters optimization of graphene waveguide and semiconductor nanostructures and found such a regime of NW-SPP interaction that corresponds to the destructive interference with the signal SPP transmittance through the stub less than 7 % in the case for pump SPP to be turned off. In contrast, the turning on the pump SPP leads to a transition to constructive interference in the stub and enhancement of signal SPP transmittance to 93 % . In our model, the effect of plasmonic switching occurs with a rate of 50 GHz at wavelength 8 µ m for signal SPP localized inside 20 nm graphene stub loaded with core-shell InAs/ZnS NW.

High-Performance Transmission of Surface Plasmons in Graphene-Covered Nanowire Pairs with Substrate

Graphene was recently proposed as a promising alternative to support surface plasmons with superior performances in the mid-infrared range. Here, we theoretically show that high-performance and low-loss transmission of graphene plasmons can be achieved by adding a silica substrate to the graphene-covered nanowire pairs. The effect of the substrate layer on mode properties has been intensively investigated by using the finite element method. Furthermore, the results show that inserting a low index material layer between the nanowire and substrate could compensate for the loss accompanied by the substrate, thus the mode properties could be adjusted to fulfill better performance. A reasonable propagation length of 15 μm and an ultra-small normalized mode area about ~10⁻⁴ could be obtained at 30 THz. The introduction of the substrate layer is crucial for practical fabrication, which provides additional freedom to tune the mode properties. The graphene-covered nanowire pairs with an extra substrate may inspire potential applications in tunable integrated nanophotonic devices.

Coupled Resonance Enhanced Modulation for a Graphene-Loaded Metamaterial Absorber

A graphene-loaded metamaterial absorber is investigated in the mid-infrared region. The light-graphene interaction is greatly enhanced by virtue of the coupled resonance through a cross-shaped slot. The absorption peaks show a significant blueshift with increasing Fermi level, enabling a wide range of tunability for the absorber. A simple circuit model well explains and predicts this modulation behavior. Our proposal may find applications in a variety of areas such as switching, sensing, modulating, and biochemical detecting.

Dynamically Tunable Light Absorbers as Color Filters Based on Electrowetting Technology

A device that uses the electrowetting fluid manipulation technology to realize the reversible and dynamical modulation of the local surface plasmon resonance is invented. By varying the electrowetting voltage, the distribution of fluids media surrounding the grating structure get changed accordingly, causing the modulation of the plasmonic resonance peak. The simulation results indicated that three primary colors, that are cyan, magenta and yellow (CMY) can be respectively reflected through selecting suitable structural parameters. More importantly, for the first time, the invented fluid-based devices have exhibited fine-tuning characteristics for each primary color. Finally, the device has been proved to have a large color gamut range in the Commission International De L’E’clairage (CIE) 1931 color space.