Graphene-based Plasmonic Waveguide Research Articles

Minimum length modulator design with a graphene-based plasmonic waveguide.

In this study, we simulated and analyzed a plasmonic waveguide modulator based on a single layer of graphene. It includes a graphene sheet, which sandwiches between two layers of silicon dioxide. Then, some gates are arranged on either side of the waveguide on a periodic structure. When an electric field is applied perpendicular to the waveguide plate, the Fermi level of graphene under the gates changes. Detailed analysis is performed by the method of lines based on Maxwell's equations along the propagation direction of the waveguide. Computation of the multi-gate device starts by examining the effect of the Fermi level. The transmission coefficient of the magnetic-field norms of the modulator is calculated by varying the parameters, such as Fermi level, length, gates number, and distance between the gates to achieve optimized design of the modulator device with very small dimensions. The results show that at higher Fermi levels, where the imaginary part of the effective index of the waveguide is close to zero, the reflection is dominant and absorption is low. Therefore, the modulator length becomes so long that it is more than one hundred nanometers. At lower Fermi levels, where the amount of the imaginary part of the effective index is significant, the absorption is dominant. At this range, a one-gate device is sufficient for modulation. Consequently, the designed minimum device length becomes equal to six nanometers for the ten-micrometer wavelength. Furthermore, the design is carried out in other wavelengths.

Analog of midinfrared electromagnetically induced-transparency and slow rainbow trapping light based on graphene nanoribbon-coated silica substrate

A midinfrared band-tunable graphene-based plasmonic waveguide is analytically and numerically investigated to realize electromagnetically induced-transparency-like transmission and to slow rainbow trapping light. By applying different Fermi energy levels to the top and bottom graphene nanoribbons, a dynamic control of resonant wavelengths is thus obtained at the desired working regions. Plus, the structural size parameters play a significant role in modulating the resonant spectra and resonant depth. Combining the manipulation of the two sets of influential factors, the transparency window is therefore under control. Detailed investigations of the analytic mechanism of the device are made as well. Furthermore, the light signal that travels in the waveguide can be successfully slowed down to over 340 times the speed in a vacuum. If the nanoribbon width is gradiently distributed, the so-called rainbow trapping can be achieved. Hence, the device has potential applications in nanoimaging, sensing, integrated circuits, and light energy storage domains.

Hybrid Airy plasmons with dynamically steerable trajectories.

With their intriguing diffraction-free, self-accelerating, and self-healing properties, Airy plasmons show promise for use in the trapping, transporting, and sorting of micro-objects, imaging, and chip scale signal processing. However, high dissipative loss and lack of dynamical steerability restrict the implementation of Airy plasmons in these applications. Here we reveal hybrid Airy plasmons for the first time by taking a hybrid graphene-based plasmonic waveguide in the terahertz (THz) domain as an example. Due to coupling between optical modes and plasmonic modes, the hybrid Airy plasmons can have large propagation lengths and effective transverse deflections, where the transverse waveguide confinements are governed by the hybrid modes with moderate quality factors. Meanwhile, the propagation trajectories of the hybrid Airy plasmons are dynamically steerable by changing the chemical potential of graphene. These hybrid Airy plasmons may promote the further discovery of non-diffracting beams along with the emerging developments of optical tweezers and tractor beams.

Modeling of Graphene Coplanar Waveguide and its Discontinuities for THz Integrated Circuits Applications

Graphene, having extraordinary electronic and optical properties at THz frequencies, can be used in the design and development of miniaturized components, devices, and integrated circuits. Model of graphene-based transmission lines and their discontinuities play a crucial role in the realization of THz integrated circuits, which is not readily available in the literature. This paper reports the characteristics of graphene film deposited over a SiO2/Si wafer. Transmission line characteristics of graphene-based plasmonic coplanar waveguide (GPCPW) on SiO2/Si wafer have been determined from the electromagnetic modeling of the structure. Discontinuities in the GPCPW such as open end, series gap, and step junction have also been analyzed to obtain their lumped element electrical equivalent. Closed-form expressions are developed so that it can be used in the circuit design at later stage. It has been observed that GPCPW transmission lines have very high characteristic impedance values (∼1000–2500 Ω) which are not possible in non-graphene transmission line structures.

A symmetric terahertz graphene-based hybrid plasmonic waveguide

A graphene-based hybrid plasmonic waveguide (GHPW) structure, which works on the terahertz frequency and includes two identical cylinder robs symmetrically put on each side of graphene sheet with gaps g, has been proposed and investigated. The present waveguide not only significantly improves the propagation length but also maintains a compact mode area, which is due to the coupling between the dielectric waveguide mode and plasmonic mode. The graphene plasmons particularly differ from plasmons in noble metals of which propagation loss can be tuned by adjusting the Fermi energy level or carrier mobility. With a very good Fermi energy level and carrier mobility, a typical propagation length of 26.7mm, and mode area of optical field of approximately 4μm2 at 10THz are achieved. This waveguide structure shows great promise for designing kinds of functional elements in actively tunable integrated optical devices.

Graphene-based hybrid plasmonic waveguide with ultra long-ranged propagation length

We have investigated on a tunable graphene-based hybrid plasmonic terahertz waveguide with ultra-long-ranged propagation length at the frequency of 3 THz by using a finite-element method. The proposed structure consists of five graphene sheets, a curved semiconductor layer as a low-index material at the top of an air gap spacer, and gallium arsenide as a high-index material. The most important characteristic of this hybrid structure is its tunable, long-ranged propagation length. By tuning the waveguide dimensions, we can have a very long propagation length ranging from 20 to 15,000 μm, which is approximately 10 times higher than that in recently proposed structures. Moreover, we will show that with this increase in the propagation length, the normalized mode area does not change significantly and remains between 0.03% and 0.04%, indicating that this structure also poses a tight energy confinement.

Maximum modulation of plasmon-guided modes by graphene gating

The potential of graphene in plasmonic electro-optical waveguide modulators has been investigated in detail by finite-element method modelling of various widely used plasmonic waveguiding configurations. We estimated the maximum possible modulation depth values one can achieve with plasmonic devices operating at telecom wavelengths and exploiting the optical Pauli blocking effect in graphene. Conclusions and guidelines for optimization of modulation/intrinsic loss trade-off have been provided and generalized for any graphene-based plasmonic waveguide modulators, which should help in consideration and design of novel active-plasmonic devices.

Hybrid graphene plasmonic waveguide modulators

The unique optical and electronic properties of graphene make possible the fabrication of novel optoelectronic devices. One of the most exciting graphene characteristics is the tunability by gating which allows one to realize active optical devices. While several types of graphene-based photonic modulators have already been demonstrated, the potential of combining the versatility of graphene with subwavelength field confinement of plasmonic waveguides remains largely unexplored. Here we report fabrication and study of hybrid graphene–plasmonic waveguide modulators. We consider several types of modulators and identify the most promising one for telecom applications. The modulator working at the telecom range is demonstrated, showing a modulation depth of >0.03 dB μm−1 at low gating voltages for an active device area of just 10 μm2, characteristics which are already comparable to those of silicon-based waveguide modulators while retaining the benefit of further device miniaturization. Our proof-of-concept results pave the way towards on-chip realization of efficient graphene-based active plasmonic waveguide devices for optical communications.

Graphene-based hybrid plasmonic modulator

A graphene-based hybrid plasmonic modulator is designed based on an asymmetric double-electrode plasmonic waveguide structure. The photonic device consists of a monolayer graphene, a thin metal strip, and a thin dielectric layer that is inserted between the grapheme and the metal strip. By electrically tuning the graphene’s refractive index, the propagation loss of the hybrid long-range surface plasmon polariton strip mode in the proposed graphene-based hybrid plasmonic waveguide is switchable, and hence the intensity of the guided modes is modulated. The highest modulation depth is observed at the graphene’s epsilon-near-zero region. The device characteristics are characterized over the entire C-band (1.530–1.565 μm).

Subwavelength Graphene-Based Plasmonic THz Switches and Logic Gates

In this paper, we report on the design procedure for developing subwavelength graphene-based plasmonic waveguide, performing as a THz switch or an AND/OR logic gate. The propagation length of the surface plasmons (SPs), stimulated by a 6 THz TM polarized incident wave along this waveguide with a top graphene layer whose chemical potential is held at $\mu_{\rm C}=300~{\hbox{meV}}$ (ON state) is more than 35 times larger than that in the waveguide with $\mu_{\rm C}= 0~{\hbox{eV}}$ (OFF state). Numerical results, obtained from full wave simulations using a finite element method, also show that the modulation depth density obtained for the straight plasmonic switching waveguide, whose length is just about 20% of the incident wavelength, is larger than those reported to date. Moreover, we also designed a logic AND gate composed of a straight waveguide, a Y-branch switch, and a logic OR gate composed of two face to face Y-branches, whose total lengths are ${\sim} {\hbox{37\%}}$ , ${\sim} {\hbox{45\%}}$ , and ${\sim} {\hbox{53\%}}$ of the incident wavelength, respectively. Simulations show that the maximum ON/OFF ratios for these subwavelength plasmonic waveguides that occur between their ‘1 1’ and ‘0 0’ logical states are ${\sim} {\hbox{41.37}}$ , ${\sim} {\hbox{39.87}}$ , and ${\sim} {\hbox{40.76}}~{\hbox{dB}}$ , respectively. These numerical data also show that the modulation depth densities obtained for these devices are also greater than those reported to date. The proposed graphene-based plasmonic switches and gates offer potential building blocks for the future digital plasmonic circuits operating around 6 THz.

Enhanced graphene plasmon waveguiding in a layered graphene−metal structure

In this Letter, a graphene-based terahertz plasmonic waveguide is proposed. The proposed structure benefits from the enhanced confinement and increased attenuation length of graphene surface plasmon by placing the graphene sheet in proximity of metal layers. For a graphene-based slab waveguide, our data show a 20% increase in the plasmonic attenuation length and a 97% increase in the attenuation length normalized to the plasmonic wavelength, thus significantly increasing the propagation distance of the surface plasmon. Further, improvement is possible by optimizing dielectric mismatch, graphene−metal distance, waveguide width, and the Fermi energy of graphene.

Graphene-based photonic devices for soft hybrid optoelectronic systems

Graphene, a two-dimensional one-atom-thick planar sheet of carbon atoms densely packed in a honeycomb crystal lattice, has attracted appreciable attention due to its extraordinary mechanical, thermal, electrical, and optical properties. One of these properties, graphene’s outstanding tensile strength, allows graphene-based electronic and photonic devices to be flexible, stretchable, and foldable. In this work, we propose a novel platform technology and architecture of graphene-based flexible photonic devices for the development of high-performance flexible devices and components. We investigated the characteristics of the graphene-based plasmonic waveguide for the development of high-performance optical interconnection in flexible human-friendly optoelectronic devices. We concluded that graphene-based photonic devices have huge potential for the development of next-generation human-friendly flexible optoelectronic systems.

Graphene-based plasmonic waveguides for photonic integrated circuits

We perform experimental investigations on the characteristics of graphene-based plasmonic waveguides for development of photonic integrated circuits. By embedding chemical vapor deposited graphene strip in a photoactive UV curable perfluorinated acrylate polymer with a low refractive index and material loss, the two-dimensional metal-like plasmonic waveguide demonstrated as a light signal guiding medium for high-speed optical data transmission. The fabricated graphene-based plasmonic waveguide supports the transverse-magnetic (TM) polarization modes with the averaged extinction ratio of 19 dB at a wavelength of 1.31 µm. The 2.5 Gbps optical signals were successfully transmitted via 6 mm-long graphene plasmonic waveguides. The proposed graphene-based plasmonic waveguides can be exploited further for development of next-generation photonic integrated circuit and devices.