Zhili Lin

Optimization of the Fano Resonance Lineshape Based on Graphene Plasmonic Hexamer in Mid-Infrared Frequencies

In this article, the lineshape of Fano-like resonance of graphene plasmonic oligomers is investigated as a function of the parameters of the nanostructures, such as disk size, chemical potential and electron momentum relaxation time in mid-infrared frequencies. Also, the mechanism of the optimization is discussed. Furthermore, the environmental index sensing effect of the proposed structure is revealed, and a figure of merit of 25.58 is achieved with the optimized graphene oligomer. The proposed nanostructure could find applications in the fields of chemical or biochemical sensing.

Generation of stochastic electromagnetic beams with complete controllable coherence.

We generate a stochastic electromagnetic beam (SEB) with complete controllable coherence, that is, the coherence degree can be controlled independently along two mutually perpendicular directions. We control the coherence of the SEB by adjusting the phase modulation magnitude applied onto two crossed phase only spatial light modulators. We measure the beams coherence properties using Youngs interference experiment, as well as the beam propagation factor. It is shown that the experimental results are consistent with our theoretical predictions.

Topologically protected edge states in graphene plasmonic crystals

A two-dimensional graphene plasmonic crystal composed of periodically arranged graphene nanodisks is proposed. We show that the band topology effect due to inversion symmetry broken in the proposed plasmonic crystals is obtained by tuning the chemical potential of graphene nanodisks. Utilizing this kind of plasmonic crystal, we constructed N-shaped channels and realized topologically edged transmission within the band gap. Furthermore, topologically protected exterior boundary propagation, which is immune to backscattering, was also achieved by modifying the chemical potential of graphene nanodisks. The proposed graphene plasmonic crystals with ultracompact size are subject only to intrinsic material loss, which may find potential applications in the fields of topological plasmonics and high density nanophotonic integrated systems.

Investigation of the Band Structure of Graphene-Based Plasmonic Photonic Crystals

In this paper, one-dimensional (1D) and two-dimensional (2D) graphene-based plasmonic photonic crystals (PhCs) are proposed. The band structures and density of states (DOS) have been numerically investigated. Photonic band gaps (PBGs) are found in both 1D and 2D PhCs. Meanwhile, graphene-based plasmonic PhC nanocavity with resonant frequency around 175 THz, is realized by introducing point defect, where the chemical potential is from 0.085 to 0.25 eV, in a 2D PhC. Also, the bending wvaguide and the beam splitter are realized by introducing the line defect into the 2D PhC.

Ultra-compact tunable graphene-based plasmonic multimode interference power splitter in mid infrared frequencies

In this paper, we propose graphene-based plasmonic multimode interference power splitters with ultra-compact size working in mid infrared range. Further, the arbitrary-ratio 1×2 power splitter with a size of 140 nm×232 nm, where the splitting ratio can be tuned continuously from 1:1 to 100:0, is numerically demonstrated. Meanwhile, the graphene-based arbitrary-ratio 1×2 power splitters with different frequencies and chemical potentials are also investigated. The proposed multimode interference structure with a deep nanoscale footprint might be a fundamental component of the future high density integrated plasmonic circuit or on-chip plasmonic interconnect techniques.

Modeling the ponderomotive interaction of high-power laser beams with collisional plasma: the FDTD-based approach

The ponderomotive interaction of high-power laser beams with collisional plasma is modeled in the nonrelativistic regime and is simulated using the powerful finite-difference time-domain (FDTD) method for the first time in literature. The nonlinear and dissipative dielectric constant function of the collisional plasma is deduced that takes the ponderomotive effect into account and is implemented in the discrete framework of FDTD algorithms. Maclaurin series expansion approach is applied for implementing the obtained physical model and the time average of the square of light field is extracted by numerically evaluating an integral identity based on the composite trapezoidal rule for numerical integration. Two numerical examples corresponding to two different types of laser beams, Gaussian beam and vortex Laguerre-Gaussian beam, propagating in collisional plasma, are presented for specified laser and plasma parameters to verify the validity of the proposed FDTD-based approach. Simulation results show the anticipated self-focusing and attenuation phenomena of laser beams and the deformation of the spatial density distributions of electron plasma along the beam propagation path. Due to the flexibility of FDTD method in light beam excitation and accurate complex material modeling, the proposed approach has a wide application prospect in the study of the complex laser-plasma interactions in a small scale.

Pseudospin Dependent One-Way Transmission in Graphene-Based Topological Plasmonic Crystals

Originating from the investigation of condensed matter states, the concept of quantum Hall effect and quantum spin Hall effect (QSHE) has recently been expanded to other field of physics and engineering, e.g., photonics and phononics, giving rise to strikingly unconventional edge modes immune to scattering. Here, we present the plasmonic analog of QSHE in graphene plasmonic crystal (GPC) in mid-infrared frequencies. The band inversion occurs when deforming the honeycomb lattice GPCs, which further leads to the topological band gaps and pseudospin features of the edge states. By overlapping the band gaps with different topologies, we numerically simulated the pseudospin-dependent one-way propagation of edge states. The designed GPC may find potential applications in the fields of topological plasmonics and trigger the exploration of the technique of the pseudospin multiplexing in high-density nanophotonic integrated circuits.

Investigation of beam splitter in a zero-refractive-index photonic crystal at the frequency of Dirac-like point

The Dirac-like cone dispersion of the photonic crystal induced by the three-fold accidental degeneracy at the Brillouin center is calculated in this paper. Such photonic crystals can be mapped to zero-refractive-index materials at the vicinity of the Dirac-like point frequency, and utilized to construct beam splitter of high transmission efficiency. The splitting ratio is studied as a function of the position of the input/output waveguides. Furthermore, variant beam splitters with asymmetric structures, bulk defects, and some certain bending angles are numerically simulated. Finally, we show that 1 × 2 to 1 × N beam splitting can be realized with high transmission efficiency in such a zero-refractive-index photonic crystal at the frequency of Dirac-like point. The proposed structure could be a fundamental component of the high density photonic integrated circuit technique.

Realization of conical dispersion and zero-refractive-index in graphene plasmonic crystal

Dirac cones discovered in classical periodic systems such as photonic and phononic crystals have exhibited many interesting properties, particularly conical dispersion at the Brillouin zone center can be related to a zero-refractive-index. Here, we theoretically and numerically explore the conical dispersion in plasmonic crystal of graphene nanodisks arranged in triangular lattice. We show that the plasmonic crystal of Dirac-like cone resulted from three-fold accidental degeneracy can be mapped to a zero-refractive-index medium around the Dirac-like point frequency of 65.5 THz. The isotropic behavior of Dirac-like point formed by a monopole and two dipoles is observed by calculating isofrequency contours. Furthermore, numerical simulations including cloaking, focusing and unidirectional transmission are implemented to demonstrate the zero-index characteristics of the graphene plasmonic crystal.