Graphene-based Photonic Crystal Research Articles

Impact of truncation on absorption spectra in a graphene-based random photonic crystal

The present study investigates the influence of randomness on achieving multimode broadband and narrowband absorption of graphene-embedded photonic structures. In the first proposed photonic configuration, with a change in randomness parameter, it is possible to achieve single-mode and multimode broadband absorption up to 0.8. This value is further enhanced up to 0.99 by varying the Fermi level to −0.9 eV. The position of absorption peaks can be tuned by varying the thickness of the silicon carbide layer. Further, an investigation is carried out on the influence of adding a defective periodic photonic crystal to the first photonic configuration, which provides a multimode narrowband absorption with a value of up to 0.99, and the strength and location of absorption peaks can be altered to the desired value by changing the graphene Fermi level and the thickness of the silicon carbide layer. Finally, the authors also survey the influence of a magnetic field B on the absorption behaviour of left-handed circularly polarised (LCP) and right-handed circularly polarised (RCP) waves. The results indicate that the full width at half-maximum of absorption peaks expands with the application of a positive magnetic field for LCP waves, whereas it shrinks for RCP waves. This has applications in the design of tunable broadband and narrowband absorbers and sensors.

Multi-channel THz perfect absorber using graphene-based Fibonacci photonic crystals

A graphene-based multi-channel THz perfect absorber is proposed in this paper. The absorber consists of a graphene layer, a Fibonacci quasi-periodic layer, a spacer, and a substrate. We demonstrate that the structure we proposed can lead to multi-channel perfect THz absorption because of the graphene surface plasmon polaritons and multiple photonic stop bands in this structure. The multi-channel working frequencies and absorption peaks can be flexibly tuned by controlling the incidence angle, size of component materials, and Fermi energy. Moreover, by adjusting the Fibonacci quasi-period orders of the structure, the number of working channels can be flexibly expanded without reoptimizing the structure size. Moreover, by adjusting the Fibonacci quasi-period orders of the structure, the number of working channels can be flexibly expanded without reoptimizing the structure size. Using existing technology, our design scheme is easy to realize, which will be helpful to promote the development and application of novel tunable optoelectronic devices.

Tunable bidirectional perfect THz absorber realized by graphene-based one-dimensional photonic crystals

In this paper, a perfect absorption structure of graphene-based one-dimensional photonic crystals (1DPC) with tunable absorption channels and absorptivity is proposed. The proposed structure can achieve four perfect absorption peaks with the absorptivity of 99.31%, 99.88%, 99.74% and 99.32% at the same time, and the absorptivity of all absorption peaks is more than 95%. By adjusting the period number of 1DPC, the number of absorption peaks and absorption efficiency can be changed. By changing the chemical potential and relaxation rate of graphene, the absorption of the proposed structure can be dynamically tuned. And the influence of structural layer thickness on absorption property is also explored. In addition, we use this structure to design two different bidirectional absorbers. The designed bidirectional absorber can tailor the perfect absorption frequency with the absorptivity of more than 99.51%, and can change the absorption channel from single channel to double channel and double channel to multi-channel under the forward and backward incidence. This work not only fills the gap in the design of bidirectional perfect absorbers for 1DPC, but also provides a scheme for the design of multifunctional devices.

Graphene-VO2-based-defect-induced tunable multiple narrowband unidirectional photonic terahertz absorber

This work demonstrates a one-dimensional unidirectional terahertz (THz) absorber with thermal switching from broadband to narrowband and tunable multiple narrowband absorption with vanadium dioxide (VO2)-graphene-based defective photonic crystal. The thermal tuning of defect layer switches the phase of VO2 and obtain multiple narrowband optical absorptance with 70-90% peak at 4.12, 4.86 and 5.23THz respectively with a Q factor around 291 for 4.86 THz peak. The thermal dependent Q factor of the stack varies from 19 to 291 with phase transition from metal to the insulating state of the defect. The optical non-magnetic THz unidirectional absorber has switchable propagation functions within the metallic phase from non-absorption to higher peak absorption with forward and backward propagated wave. The asymmetrical dual defect layer with dual absorption peaks can be switched and the wavelength can be changed by changing the distance between the two peaks. Multiple graphene-based VO2 defects have increased peaks of narrowband absorption. This novel phase changing material (PCM) based asymmetric defective photonic layer can tune the defect layer for optimum and adjustable absorption at THz range and non-magnetic reciprocal and unidirectional structure with temperature dependent dual band switchable, which leads to this structure for terahertz wireless communication systems as well as other THz sensing devices.

Multimode absorption in single-layer graphene: Disordered photonics and magneto-optic effect

The current study theoretically investigates the effect of disordered thickness and the position of layers on optical absorption properties of the graphene-based photonic crystal in the THz frequency regime. The results show that single, as well as multiple narrow-band peaks, are formed by changing the disorder strength and twisting unicells (defect). It is also found that multiple narrow-band absorption peaks with absorption up to 0.997 can be formed in highly disordered photonic structures with a single graphene layer. On the other hand, single as well as multiple near-unity absorption peak strength is increased by twisting the two most right dielectric layers as well as by increasing the disorderedness of the structures. The presence of magnetic fields has a strong impact on the optical absorption of LCP and RCP waves. The bandwidth of absorption peaks increases for LCP and decreases for RCP. This effect can be interchanged by reversing the magnetic field. Therefore, the proposed structure can be effectively used for the design of tunable THz optical absorbers, sensors as well as different optoelectronic devices.

High-performance electro-optical switch using an anisotropic graphene-based one-dimensional photonic crystal.

A novel electro-optical switch is proposed and investigated using the transfer matrix method (TMM) and three-dimensional finite-difference time-domain (3D FDTD) analysis at the near-infrared range. The structure is made of a defect at the middle of a one-dimensional photonic crystal. The defect consists of two anisotropic graphene (AG) sheets separated by a dielectric layer. As a result, a sharp transmission peak with a high quality factor of 5000 appears at the wavelength of 1552.4 nm where light is trapped by the defect. When an external voltage is applied across the AG sheets, their chemical potentials shift in such a way that the trapped photons are absorbed and the switch changes to ON state. According to the presented results, a high extinction ratio of 14.26 dB with a very low insertion loss of 0.18 dB are obtained. The required switching voltage and energy consumption are as low as 4.68 V and 226 fJ/bit, respectively. The 3 dB bandwidth is also calculated to be as high as 17.5 GHz, which makes our proposed switch promising for high speed optical systems.

Omnidirectional cylindrical graphene-based Bragg fiber in terahertz

The optical properties of a graphene-based cylindrical photonic crystal are theoretically investigated based on the generalized cylindrical transfer matrix method to include the out-of-plane propagation of the cylindrical waves. It is found that Maxwell's equations have solutions for both E- and H-polarized waves only at the azimuthal mode number m = 1 . We study the reflectance spectrum of the structure to obtain its photonic bandgaps. We show that the reflection spectrum, in addition to the usual Bragg gaps, contains an omnidirectional bandgap at low terahertz frequencies for both E and H-polarized cylindrical waves. The robustness of this bandgap under random variations of geometrical parameters is investigated. This few-period structure is an ideal candidate for guiding waves at the low terahertz region because of its weak absorption and transmission losses. In contrast to the usual Bragg gap, the results show that in both polarizations, the width of graphene-produces bandgap reaches its maximum value when the refractive indices of the two cylindrical shells have their lowest possible values. The width of this unusual omnidirectional bandgap increases by decreasing the thicknesses of the cylindrical shells and increasing the chemical potential of the graphene monolayers.

Spectral statistics of light in one-dimensional graphene-based photonic crystals.

The optical properties and spectral statistics of light in one-dimensional photonic crystals in the representative classes of (AB)^{N} (composed of dielectric layers) and (AGBG)^{N} (composed of periodic stacking of graphene-dielectric layers) have been investigated using the transfer matrix method and random matrix theory. The proposed method provides new predictions to determine the chaos and regularity of the optical systems. In this analysis, the chaoticity parameter with q=0 for Poisson distribution and q→1 for Wigner distribution is determined based on the random matrix theory. It has been shown that two kinds of chaos and regularity modes can be found with Brody distribution. Also, as a part of this work, we found out the regular pattern in both classes of (AB)^{N} and (AGBG)^{N} when results were fit to a Brody distribution. Moreover, the effects of different parameters such as the number of unit cells, incident angle, state of polarization, and chemical potential of the graphene nanolayers on the structures' regularity are discussed. It is found that the regular patterns are seen in the band gaps. The results show that the structure (AGBG)^{N} has an extra photonic band gap compared to (AB)^{N}, which is tunable by changing the chemical potential of the graphene nanolayers. Therefore, the possibility of external control of the regularity using a gate voltage in the graphene-based photonic crystals is obtained. Finally, comparing of TE and TM waves based on the random matrix theory, which interpolates between regular and chaotic systems, indicates that the Poisson statistics well describes the TE waves.

Multi-band absorption characteristics of a metal-loaded graphene-based photonic crystal

In this paper, the absorption characteristics of a metal-photonic crystal-metal structure in the visible light region have been investigated by the transfer matrix method. The metal-photonic crystal-metal composite structure is formed by loading a metal layer on both sides of a one-dimensional graphene photonic crystal composed of dielectric material and graphene. The calculation results show that the multi-band absorption can be achieved for this structure. The influence of structural parameters on the multi-band absorption characteristics of the structure was investigated detailly. It is found that the center wavelength of the absorption band basically keeps invariant with the change of the chemical potential of graphene. It is also found that the number of absorption bands is tunable by changing the periodic number of graphene photonic crystals or the thickness of the dielectric material. These results provide a useful reference for the development of graphene-based multi-band light absorbers. • A M-GPC-M structure which can realize multi-band absorption in the visible wavelength region is proposed. • The number of absorption bands is adjustable. • The influence of structural parameters on the multi-band absorption characteristics is investigated.

Photonic Hall effect for a 1D-dimensional graphene-based photonic crystal with two defects

The presence of two defect layers in a one-dimensional photonic crystal which could be described numerically by the transfer matrix model becomes important when two defects modes might be controlled by the number of the middle layers. In this work, we compute the transmission spectra of a 1D photonic crystal with two graphene-based defect layers in the presence of an applied constant magnetic field. It is observed that an additional defect mode shows up at the lower edge of the photonic bandgap of the optical structure which could to be tuned by the Fermi energy, the intensity of the magnetic field and also the number of the layers between the defects. In addition, we investigated the effect of decreasing the number of middle layers on the transmission spectra of the photonic device.

Effect of nonlinear cap layer on TM-polarized surface waves in a graphene-based photonic crystal

In this paper, we investigated the effect of nonlinear cap layer and the chemical potential of the graphene on the p-polarized surface waves (SWs) in a one-dimensional graphene-based photonic crystal (GBPC). Three different cases were considered for the dielectric tensor of the nonlinear cap layer: (1) perpendicular uniaxial approximation, (2) parallel uniaxial approximation and (3) generic case. The results of the study indicated that the effect of nonlinear cap layer on TM SWs may be neglected due to the perpendicular approximation. On the other hand, in parallel approximation as well as generic form of dielectric function, the frequency of the TM SWs within the graphene-induced band gap (GIPBG) may be controlled by the nonlinear cap layer and the chemical potential of the graphene. Moreover, according to the results, in the GIPBG of GBPC with self-defocusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the same direction. However, with respect to the self-focusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the opposite direction. Consequently, by adjusting the chemical potential in the self-defocusing cap layer, the tunability range of the SW frequency may be extended and in the case of self-focusing, optical nonlinear effects may be eliminated.

Tunable Tamm states at the interface of a 1D graphene-based photonic crystal and a nonlinear dielectric slab

We investigate the dispersion of the Tamm states at the interface of a 1D graphene-based photonic crystal and a nonlinear dielectric slab. We use the nonlinear transfer matrix method to obtain the dispersion of the Tamm states in both the graphene induced and Bragg gaps in the terahertz region. We explore the spectral tunability of the surface modes by adjusting parameters such as the thickness of the nonlinear slab, the intensity of the surface modes, and the chemical potential of graphene layers. We reveal that the penetration depth of the graphene induced bandgap modes in the uniform environment is several times greater than that of the conventional Bragg gap modes. Also, it is shown that we can improve the penetration depth of the surface modes by adjusting the thickness of the nonlinear slab, the intensity of the Tamm states, or the chemical potential of the graphene layers.

Plasmonic mode coupling in graphene-based photonic crystals

Abstract Plasmonic bands in 1D graphene-based photonic crystals have recently been reported for transverse magnetic polarization in the low THz regime. In this work, we demonstrate that plasmon coupling, giving rise to plasmonic bands, is also present for transverse electric polarization at IR frequencies corresponding to the region of interband transitions in graphene. Due to the doping level dependence of graphene interband optical conductivity, plasmonic band region can be shifted in the IR frequency regime for different doping levels. We have analyzed graphene-based photonic crystals with a homogeneous and periodic doping level sequence along crystal growth direction in the unit cell; our results prove that plasmonic band opening is obtained for these two different graphene doping sequences, in the frequency region such that imaginary optical conductivity turns negative, displaying different levels of attenuation due interband absorption processes. Finally, we show that TE plasmonic modes in a finite multilayer can be excited by attenuated total reflection technique in Otto configuration.

Tunable wave localization for Tamm modes in graphene-based photonic crystals

In this work, we demonstrate the existence of TE polarized surface Bloch modes localized at the boundary of semi-infinite graphene-based photonic crystal and homogeneous dielectric. Imposing an alternate low-high doping level on graphene layers along the multilayer, it is possible to open bandgaps where mode localization can be achieved for TE polarization. The surface modes reported here exist in the low terahertz regime with a corresponding long decaying length and close to allowed band. Due to the tunable gap characteristics of the periodic structure proposed, an on-off switch for TE polarized surface Bloch modes can be achieved. We proved that TE polarized surface mode excitation can be achieved by attenuated total reflection technique in the Otto configuration, making them suitable for experimental probing. Fermi levels considered in this work lie in the range 0.2eV<μ<0.8eV, which is experimentally achievable in electrical gated configurations.

Slow light performance enhancement of graphene-based photonic crystal waveguide

We propose a graphene-based photonic crystal (PC) slow light waveguide, which is realized by creating periodical air holes in a silicon layer to achieve spatially varying chemical potentials of graphene. The structure is optimized around 30 THz, and a large group index of 166.6 is obtained, with a very low propagation loss of −2.1 dB/um. The corresponding normalized delay-bandwidth product reaches as high as 4.00. Furthermore, the slow light performance can be dynamically tuned by changing a bias voltage. The center frequency of the slow light waveguide can be tuned between 19.1 THz and 27.4 THz. Our results suggest that graphene-based PC structures are very promising for slow light devices.

Controlling TE surface waves by self-defocusing cap layer in graphene-based photonic crystal

We have analytically studied the localized TE surface waves (SWs) in a one-dimensional graphene-based photonic crystal that is capped by a self-defocusing nonlinear layer. Our method is based on the first integral of the nonlinear Helmholtz wave equation. We have investigated the possibility of controlling the dispersion behavior inside the graphene-induced photonic bandgap (GIBG) via two controllable parameters: the intensity of the electromagnetic field at the surface of the nonlinear cap layer and the chemical potential of the graphene. The results showed that the frequency of the SWs inside the GIBG can be controlled by adjusting the intensity of the electromagnetic field and the chemical potential. We also compared the dispersion of the surface modes in GIBG with Bragg bandgap by changing the intensity of field at the surface of the nonlinear cap layer. It was found that the relative frequency variation of the surface modes inside the GIBG is more than the Bragg bandgap.

On transmittance and localization of the electromagnetic wave in two-dimensional graphene-based photonic crystals

Two-dimensional graphene-based photonic crystal (GPC) formed by a periodic array of the homogeneous dielectric cylinders etched in the alternating graphene and dielectric layers and its inverse counterpart are considered. The transmittance of the photonic crystal is obtained. The waveguide due to the localization of the electromagnetic wave on the lattice defect that breaks the translational symmetry of the GPC of two different topologies is studied. The different topologies of GPC are characterized by different photonic band structures with different widths of photonic band gaps (PBG) and provide different frequencies for the localized electromagnetic wave due to the defect. The frequencies of the localized mode for both type of the GPC, located inside the lowest PBG, are in the range of THz or tens of THz depending on the topology of the GPC. It is shown that the photonic band gap always can be tuned by changing the chemical potential of graphene to provide formation of the localized photonic mode due to the defect. The technological advantages of the GPC, as well as the opportunity to tune the PBG and the frequency of the localized electromagnetic wave in the terahertz region of spectrum for the GPC are discussed.

Confinement of Bloch surface waves in a graphene-based one-dimensional photonic crystal and sensing applications**Project supported by the National Natural Science Foundation of China (Grant Nos. 61203211 and 41675154), the Six Major Talent Peak Expert of Jiangsu Province, China (Grant No. 2015-XXRJ-014), and the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20141483).

Bloch surface waves (BSWs) are excited in one-dimensional photonic crystals (PhCs) terminated by a graphene monolayer under the Kretschmann configuration. The field distribution and reflectance spectra are numerically calculated by the transverse magnetic method under transfer-matrix polarization, while the sensitivity is analyzed and compared with those of the surface plasmon resonance sensing method. It is found that the intensity of magnetic field is considerably enhanced in the region of the terminated layer of the multilayer stacks, and that BSW resonance appears only in the interface of the graphene and solution. Influences of the graphene layers and the thickness of a unit cell in PhCs on the reflectance are studied as well. In particular, by analyzing the performance of BSW sensors with the graphene monolayer, the wavelength sensitivity of the proposed sensor is 1040 nm/RIU whereas the angular sensitivity is 25.1°/RIU. In addition, the maximum of figure of merit can reach as high as 3000 RIU−1. Thus, by integrating graphene in a simple Kretschmann structure, one can obtain an enhancement of the light–graphene interaction, which is prospective for creating label-free, low-cost and high-sensitivity optical biosensors.

Tunable surface waves in nonlinear graphene-based one-dimensional-photonic crystal

The nonlinear TE surface waves guided by an interface of a semi-infinite Kerr-type dielectric medium and a one-dimensional graphene-based photonic crystal have been investigated using the transfer-matrix method. It is shown that increasing the intensity of the incident beam drastically changes dispersion behavior inside the graphene-induced photonic band gap as a result of nonlinearity. Also regarding the simulation results, it reveals that the peculiar dispersion that is governed by a nonlinear structure appeared to be tuned by graphene conductivity via an external electric field. Applying such an electric field makes it possible to easily tune the nonlinear surface waves at the desired frequency only by adjusting the chemical potential of the graphene. Also, it is shown that for application purposes, the results of studies can be applied to the case in which graphene nanolayers are embedded by identical dielectric constant, i.e., zero permittivity contrast of dielectric.

Photonic Bandgap Properties of One-Dimensional Graphene-Based Photonic Crystals with a Single Dielectric

The transfer matrix method was used to investigate the photonic bandgap properties of one-dimensional graphene-based photonic crystal (GPC) with a single dielectric medium. The first layer of the unit cell of the GPC consists of a traditional dielectric medium and the second is the same dielectric medium wherein graphene sheets are embedded. Numerical calculation results show that the width of the low frequency bandgap decreases as the period of the GPC, the permittivity of the dielectric, the thickness of the dielectric layer, the filling factor of the dielectric layer, and the period of the graphene-dielectric multilayer medium structure increase and increases as the thickness of the graphene-dielectric multilayer medium structure increases. The influence of the above parameters on the Bragg bandgap is different from their effects on the low frequency bandgap. Due to the graphene conductivity could be tuned by varying the chemical potential, so GPC is a tunable PC and may have many potential applications in photonics.