Graphene-based Waveguide Research Articles

Evanescent field engineering to reduce cross-talk in pattern-free suspended graphene-based plasmonic waveguides using nano-strips

Suppression of the cross-talk between neighboring photonic components has been considered one of the most efficient methods for increasing the packing density of photonic integrated circuits. In this study, an effective cross-talk reduction approach is developed for plasmonic waveguides. Firstly, the mode characteristics of the waveguide are investigated, and then two silicon strips are placed beside the two adjacent waveguides. The mechanism of the cross-talk suppression method highly relies on the evanescent waves. The designed strips in this study manipulate the wave vectors of surface plasmon polaritons. The tangential component of the wave vector is conserved along the interface, while the perpendicular component in the surroundings can be equal to zero or imaginary, leading to evanescent waves. Placing the strips increases the perpendicular component of the wave vector in the surroundings, resulting in less cross-talk. So, the coupling length of the waveguide with the strips at the wavelength of 10 μm increases up to 345 μm which is 25 times longer than that in its non-strip counterpart. Also, the figure-of-merit and loss of the designed structure are up to 1000 and 0.13 dB/μm at a chemical potential of 0.8 eV and a wavelength of 10 μm, respectively. So, high figure-of-merit and low loss along with long coupling length are the interesting features of the designed plasmonic waveguide which propose promising structures with high performance in the near-infrared.

Analytical formulation of spatiotemporal modulated graphene-based waveguides using Floquet-Bloch theory

In this work, an analytical model to study graphene-based spatiotemporal modulated structures is developed and verified through comparison with full wave numerical simulations. Graphene is an ideal material for realizing spatiotemporal modulated structures at high frequencies of THz and optics. In this analysis, the electromagnetic response of studied structures is expressed in terms of weighted Floquet-Bloch modes supported by the structure, while graphene is modeled by a spatiotemporal modulated surface current that imposes certain boundary conditions on the modes. The developed analytical technique is a comprehensive tool and can be used for accurate modeling of different kinds of spatiotemporal devices including lossy, guided, and leaky wave structures. To demonstrate the accuracy of the model, two plasmonic waveguides with space and time modulated graphene conductivity are analyzed and their interband and intraband transition between modes are thoroughly investigated. Using the developed analytical model, spatiotemporal modulation phenomena such as mode conversion, wave amplification and nonreciprocal response are explored and discussed for the studied structures.

Design of a graphene-based ridge gap waveguide coupler for THz applications

Design of a graphene-based ridge gap waveguide coupler for THz applications

Graphene based waveguide fed hybrid plasmonic terahertz patch antenna

Abstract The terahertz (THz) technology has fascinated lot of attention due to its enormous potential for a wide range of applications in the public, private and enterprise domains. This research work demonstrates the design structure and analysis of graphene based waveguide fed hybrid plasmonic THz patch antenna (HPTPA) constructed at around 3 THz. Hybrid plasmonic THz waveguide (HPTW) as a feeding line for the proposed THz patch antenna can increases antenna efficiency. The graphene is sandwiched between gallium arsenide (GaAs) and silver (Ag) to confine THz waves efficiently. Using mode analysis in finite element method for the proposed HPTW the propagation length, effective refractive index has been thoroughly examined. Based on the finite element method (FEM) approach, the results of the designed graphene-based waveguide fed HPTPA shows a high effective refractive index of 2.9, large propagation length of 230 µm, gain of 2.29 dBi, bandwidth of 200 GHz and efficiency of 85 % has obtained. The proposed graphene-based waveguide fed HPTPA could be beneficial to enable several photonic integrated circuit applications in next-generation wireless communication.

Design and simulation of a dynamically tunable 1× 2 power splitter using MZI configuration in the telecom regime

We propose an ultra-broadband, ultra-compact and a dynamically tunable power splitter on a silicon on Insulator (SOI) platform with a 220 nm thick silicon light-guiding layer, using two multimode interference (MMI) couplers connected with graphene-based waveguides as the phase-tuning section through a Mach-Zehnder Interferometer (MZI) configuration. First, we theoretically present and demonstrate a novel design for the MMI couplers by combining the plane wave expansion method (PWEM) and the mode expansion conjecture concept. To verify the proposed theory, a center-fed MMI coupler and a MMI coupler, respectively, as the input and output sections of our proposed device, are designed and simulated. The simulation results achieved by Lumerical FDTD show good agreement with the design theory. Then, a highly tunable graphene-embedded silicon waveguide, for the highly efficient modulation of the effective mod index (EMI), is duly designed using Lumerical Mode Solutions. As the two MZI arms, a pair of the proposed waveguides is introduced into the middle of the cascaded MMI couplers. Accordingly, the integration properties of the analytically designed MMI couplers and the numerically designed waveguide is demonstrated through our proposed device for the aim of achieving any wanted power splitting ratio. To this end, we consider the case that the real part of the EMI of the waveguide in the lower MZI arm is modulated by varying the graphene Fermi level values, being the same for all the layers belonging to the same waveguide, while that of the upper arm is constant. The corresponding power splitting ratio can be dynamically tuned in the range of All reported results assume TE polarization. The designed MZI-based splitter possesses a bandwidth of over the wavelength range from to for various power splitting ratios, maintaining the averaged insertion loss and the averaged power imbalance, respectively, below as low as and The overall footprint of the proposed device is also highly small, i.e., about

Simulation optimized design of graphene-based hybrid plasmonic waveguide

Simulation optimized design of graphene-based hybrid plasmonic waveguide

Pulsed Four-Wave Mixing at Telecom Wavelengths in Si3N4 Waveguides Locally Covered by Graphene.

Recently, the nonlinear optical response of graphene has been widely investigated, as has the integration of this 2D material onto dielectric waveguides so as to enhance the various nonlinear phenomena that underpin all-optical signal processing applications at telecom wavelengths. However, a great disparity continues to exist from these experimental reports, depending on the used conditions or the hybrid devices under test. Most importantly, hybrid graphene-based waveguides were tested under relatively low powers, and/or combined with waveguide materials that already exhibited a nonnegligible nonlinear contribution, thereby limiting the practical use of graphene for nonlinear applications. Here, we experimentally investigate the nonlinear response of Si3N4 waveguides that are locally covered by submillimeter-long graphene patches by means of pulsed degenerate four-wave mixing at telecom wavelength under 7 W peak powers. Our measurements and comparison with simulations allow us to estimate a local change of the nonlinearity sign as well as a moderate increase of the nonlinear waveguide parameter (γ∼-10 m-1W-1) provided by graphene. Our analysis also clarifies the tradeoff associated with the loss penalty and nonlinear benefit afforded by graphene patches integrated onto passive photonic circuits, thereby providing some guidelines for the design of hybrid integrated nonlinear devices, coated with graphene, or, more generally, any other 2D material.

Graphene-Based Hybrid Plasmonic Waveguide with Deep Subwavelength Confinement

Graphene-Based Hybrid Plasmonic Waveguide with Deep Subwavelength Confinement

Systematic design and analysis of a compact ultra-low loss graphene-based multilayer hybrid plasmonic waveguide

This paper presents systematic design and analysis of a compact ultra-low loss graphene-based multilayer hybrid plasmonic waveguide (GMLHPW). The simulation results indicate that the propagation length of the surface plasmon polaritons (LSPP) is equal to 45.28 mm at the wavelength of 1550 nm for moderate value of the graphene’s chemical potential and a small carrier mobility. To our knowledge, the obtained LSPP is the highest value among the hybrid plasmonic waveguides proposed to date. However, more enhancement of LSPP is realizable by increasing the graphene’s chemical potential and carrier mobility. Also, the effective mode area and the dimensions of the GMLHPW core are 0.0547 µm2 and 180 × 640 nm2, respectively; indicating the potential of the designed waveguide to realize compact optical integrated circuits. An add-drop microring resonator has been designed based on the GMLHPW with a higher Q factor than that of the recent work. This device is a good candidate in the signal processing applications.

Surface plasmon polariton waves in cylindrical single-layer and bilayer graphene-based waveguides: a comparative simulation study

Surface plasmon polariton waves in cylindrical single-layer and bilayer graphene-based waveguides: a comparative simulation study

Theory and Modeling of Slab Waveguide Based Surface Plasmon Resonance

The current study proposes a developing surface plasmon resonance (SPR) sensor that has been widely employed to detect viruses, such as environmental analytes, biological and chemical analytes, and monitoring and medical diagnostics. Optical waveguides have much potential for developing new chemical and biological sensors. Graphene is the world's most vital substance and can be used to enhance other materials. A composite silver film-based SPR sensor with the waveguide. To enhance the silver film's stability, detect the best thickness with the best resonance using different types of analyte: air than 1.1, 1.2, 1.3, and water. The resonance wavelength numerically calculated, loss, sensitivity, Figure of merit FOM, and Refractive index using Lumerical FDE. The numerical data showed the differences in the electric field of SPR in the number of refractive indexes after applying the silver coating layer, and the performance parameters improved. Moreover, Graphene has much promise, yet almost most of it is still unexplored. The fundamentals of graphene-based waveguides and devices were investigated using two layers with FDE. The primary purpose of this study is to show the effective thickness of the Graphene and the analyte's refractive index to get high absorption.

Tunable plasmon-induced transparency in graphene-based plasmonic waveguide for terahertz band-stop filters

Terahertz (THz) tunable filters have great advantages in miniaturizing integrated and multiband communication systems. Here, THz band-stop filter with switchable single/double plasmon-induced transparency (PIT) based on metal-dielectric-metal waveguide consisting of a ring-stub cavity and two graphene ribbons (GRs) on stub sidewalls is proposed. The switchable characteristics of single and dual-PIT are investigated numerically and theoretically by the finite-difference time-domain and the radiating multi-oscillator theory, displaying good correspondence. The single-PIT is excited by the destructive interference between bright mode and dark mode, which possesses significant tunability of resonant frequency and transmission amplitude due to the existence of GRs. When independently regulating chemical potentials of GRs on the left and right sidewalls, the dual-PIT emerges. And the filter based on dual-PIT switches from single stopband to dual-stopband or even multi-stopband filtering. Besides, the band-stop filtering performance of the tunable PIT can be further optimized by increasing the number of ring-stub cavities. The tunable PIT in graphene-based plasmonic waveguide holds potential for THz multiband communications and subwavelength plasmonic devices, such as filters, switches, modulators.

Optical amplification of surface plasmon polaritons in a graphene single layer integrated with a random grating

In this paper, we design and simulate a terahertz (THz) controllable active plasmonic waveguide structure based on a single graphene layer that is placed on a random SiC grating substrate whose grooves are filled with CaF2. Optical gain in the proposed THz active plasmonic waveguide structure is provided by the stimulated emission process in the photoexcited graphene monolayer that leads to the amplification of surface plasmon polariton (SPP) waves. We use a random grating substrate to introduce Anderson localization of the SPP waves propagating through the graphene monolayer to enhance their optical amplification at resonance frequencies in which more amplification occurs due to multi-scattering and interference effects. It is shown that the input SPP wave can be amplified by 130 times at resonance frequencies of the random system. Significant amplification occurs only for frequencies that are equal to the resonance frequencies corresponding to the passive structure and are located within the gain bandwidth of graphene. The effects of depth and width of filled grooves on the amplification characteristics are also investigated. Furthermore, we show that increasing the ambient temperature by 30 K can reduce the output intensity by a factor of 12. This property of the proposed graphene-based THz plasmonic waveguide structure makes it useful in temperature sensing applications and on/off switchable laser devices.

Cross-talk reduction in a graphene-based ultra-compact plasmonic encoder using an Au nano-ridge on a silicon substrate

Plasmonic waveguides have been widely studied in the rapid development of optically integrated circuits. The cross talk between plasmonic waveguides is a critical issue that should be considered. Nano-plasmonic waveguides with tunable graphene-free patterns on silicon ridge have very attractive features. Despite these attractive features, the low confinement in plasmonic waveguides reduces the coupling length. This issue results in high cross talk in optical integrated circuits. We present a solution to the mentioned problem. A metal ridge under the plasmonic channel helps to reduce the cross-talk value. A new graphene-based plasmonic waveguide has been proposed for achieving the switching operation at terahertz frequencies. Based on the designed waveguide, a 4-to-2 plasmonic encoder with the cross talk of -17.33dB has been presented. Using six waveguides, the encoder is designed with a contrast ratio of 14.44 dB and an area of 0.36µm2. Concerning the obtained results, the presented structure can be used in optical integrated circuits.

Free-carrier-induced nonlinear dynamics in hybrid graphene-based photonic waveguides

We develop from first principles a theoretical model for infrared pulse propagation in graphene-covered hybrid waveguides. We model electron dynamics in graphene by Bloch equations, enabling the derivation of the nonlinear conductivity and of a rate equation accounting for free-carrier generation. Radiation propagation is modeled through a generalized nonlinear Schr\"{o}dinger equation for the field envelope coupled with the rate equation accounting for the generation of free carriers in graphene. Our numerical simulations clearly indicate that unperturbed Kerr solitons accelerate due to the carrier-induced index change and experience a strong self-induced spectral blueshift. Our numerical results are fully explained by semianalytical predictions based on soliton perturbation theory.

Terahertz hybrid plasmonic waveguides with ultra-long propagation lengths based on multilayer graphene-dielectric stacks.

To develop on-chip photonic devices capable of transmitting terahertz signals beyond the propagation distance of millimeter while keeping deep subwavelength field confinement has been a challenging task. Herein, we propose a novel multilayer graphene-based hybrid plasmonic waveguide (MLGHPW) consisting of a cylindrical dielectric waveguide and hyperbolic metamaterials. The device is based on alternating graphene and dielectric layers on a rib substrate, operating in the terahertz range (f = 3 THz). We couple the fundamental dielectric waveguide mode with the fundamental volume plasmon polarition modes originated from the coupling of plasmon polaritons at individual graphene sheets. The resulting hybrid mode shows ultra-low loss compared with the conventional GHPW modes at the comparable mode sizes. The present MLGHPW demonstrated a few millimeters of propagation length while keeping the mode area of 10-3A0, where A0 is the diffraction-limited area, thus possessing a thirty times larger figure of merit (FoM) compared to other GHPWs. The additional degree of freedom (the number of graphene layers) makes the proposed MLGHPW more flexible to control the mode properties. We investigated the geometry and physical parameters of the device and identified optimal FoM. Moreover, we analyzed the crosstalk between waveguides and confirmed the potential to construct compact on-chip terahertz devices. The present design might have the possible extensibility to other graphene-like materials, like silicene, germanen, stanene etc.

Ultra-Low-Loss Mid-Infrared Plasmonic Waveguides Based on Multilayer Graphene Metamaterials.

Manipulating optical signals in the mid-infrared (mid-IR) range is a highly desired task for applications in chemical sensing, thermal imaging, and subwavelength optical waveguiding. To guide highly confined mid-IR light in photonic chips, graphene-based plasmonics capable of breaking the optical diffraction limit offer a promising solution. However, the propagation lengths of these materials are, to date, limited to approximately 10 µm at the working frequency f = 20 THz. In this study, we proposed a waveguide structure consisting of multilayer graphene metamaterials (MLGMTs). The MLGMTs support the fundamental volume plasmon polariton mode by coupling plasmon polaritons at individual graphene sheets over a silicon nano-rib structure. Benefiting from the high conductivity of the MLGMTs, the guided mode shows ultralow loss compared with that of conventional graphene-based plasmonic waveguides at comparable mode sizes. The proposed design demonstrated propagation lengths of approximately 20 µm (four times the current limitations) at an extremely tight mode area of 10−6 A0, where A0 is the diffraction-limited mode area. The dependence of modal characteristics on geometry and material parameters are investigated in detail to identify optimal device performance. Moreover, fabrication imperfections are also addressed to evaluate the robustness of the proposed structure. Moreover, the crosstalk between two adjacent present waveguides is also investigated to demonstrate the high mode confinement to realize high-density on-chip devices. The present design offers a potential waveguiding approach for building tunable and large-area photonic integrated circuits.

All-dielectric graphene-induced waveguide electro-optic modulators with offset nanowires

All-dielectric waveguide modulators nowadays are critical for on-chip photonic circuit’s integration. We propose and theoretically demonstrate a graphene-based all-dielectric waveguide modulator with offset nanowires. The displacement between the nanowires causes the electric field parallel to the graphene to increase, thereby realizing an enhanced field modulation effect. We obtain the best modulation performance by optimizing the structural parameters and changing the offset distance of the nanowires. Analysis of the simulation results indicate that the structure offers a high modulation depth (>0.13 dB / μm) covering the S , C, and L bands. Benefitting from the strong subwavelength confinement and excellent broadband modulation performance, the proposed optical waveguide modulators offer a significant potential to realize various long-wave integrated modulators, interconnects, and optoelectronic devices.

Graphene-based terahertz closed-stopband tunable composite right/left-handed leaky-wave antennas

A simple scheme for the realization of the terahertz (THz) fundamental-mode tunable closed-stopband composite right/left-handed leaky-wave antennas (CRLH LWAs) is presented. The proposed CRLH LWAs are reconstructed by graphene-based coplanar waveguide (CPW) transmission line supercells. Their shunt inductances achieved by narrow graphene strips of two unit cell structures are halved. The CRLH LWAs are designed and confirmed by numerical simulations. They also exhibit frequency-scanning behaviors at THz with narrower bandwidth than that of the conventional graphene-based fundamental-mode CPW unit cell CRLH LWAs at THz. Besides, the LWAs also exhibit strong tunable characteristics and achieve the closed-stopband condition more effectively. Therefore, the proposed supercell CRLH LWAs could further improve the performance of the beam-steering antennas at THz.

Second harmonic generation in a graphene-based plasmonic waveguide

Second harmonic generation in a graphene-based plasmonic waveguide