期刊：
PHYSICAL CHEMISTRY CHEMICAL PHYSICS,2023年25(25):17034-17042 ISSN：1463-9076
通讯作者：
Xiong, CX
作者机构：
[Xiong, Cuixiu; Zhang, Saiwen; Tan, Meng; Wan, Can; Wei, Chengya; Wang, Jie; Xiong, CX] Hunan City Univ, Coll Informat & Elect Engn, All Solid State Energy Storage Mat & Devices Key L, Yiyang 413000, Peoples R China.
通讯机构：
[Xiong, CX ] H;Hunan City Univ, Coll Informat & Elect Engn, All Solid State Energy Storage Mat & Devices Key L, Yiyang 413000, Peoples R China.
摘要：
A fully continuous geometric center symmetric cross-shaped graphene structure is proposed. Each cross-shaped graphene unit cell is composed of a central graphene region and four completely symmetric graphene chips, where each graphene chip acts as both bright and dark modes simultaneously, while the central graphene region always acts as the bright mode. Through destructive interference, the structure can realize the single plasmon-induced transparency (PIT) phenomenon, where the optical responses are independent of the polarization direction of the linearly polarized light due to the symmetry of the structure. Combining numerical simulations with coupled mode theory (CMT) calculations, the modulation of the Fermi energy of graphene to the optical spectra is investigated. The results show that the spectra are blue shifted as the Fermi energy increases, and the absorption of the two absorption peaks is basically equal (48.7%) when the Fermi energy increases to 0.667 eV. Theoretical calculations show that the slow light performance of the designed structure enhances with the increase of Fermi energy, where the maximum group index is high up to 424.73. Furthermore, it is worth noting that the electrode can be made very small due to its fully continuous structure. This work provides guidance in terms of terahertz modulators, tunable absorbers, and slow light devices.
摘要：
We numerically investigate and statistically analyze the impact of medium parameters (modulation depth P, modulation factor omega, and gain/loss strength W (0)) and beam parameters (truncation coefficient a and distribution factor chi (0)) on the propagation characteristics of a cosh-Airy beam in the Gaussian parity-time (PT)-symmetric potential. It is demonstrated that the main lobe of a cosh-Airy beam is captured as a soliton, which varies periodically during propagation. The residual beam self-accelerates along a parabolic trajectory due to the self-healing property. With increment in P, the period of a trapped soliton decreases almost monotonically, while the peak power of a trapped soliton increases monotonically. With the increase in omega or decrease in the absolute value of W (0), the period and peak power of a trapped soliton decrease rapidly and then almost remain unchanged. Moreover, it is indicated that the period of a trapped soliton remains basically unchanged no matter a and chi (0) increase or decrease. The peak power of a trapped soliton increases with increment of a, but the peak power of a trapped soliton stays relatively constant irrespective of variation in chi (0).
摘要：
We propose a simple quasi-continuous monolayer graphene structure and achieve a dynamically tunable triple plasmon-induced transparency (PIT) effect in the proposed structure. Additional analyses indicate that the proposed structure contains a self-constructed bright-dark-dark mode system. A uniform theoretical model is introduced to investigate the spectral response characteristics and slow light-effects in the proposed system, and the theoretical and the simulated results exhibit high consistency. In addition, the influences of the Fermi level and the carrier mobility of graphene on transmission spectra are discussed. It is found that each PIT window exhibits an independent dynamical adjustability owing to the quasi-continuity of the proposed structure. Finally, the slow-light effects are investigated based on the calculation of the group refractive index and phase shift. It is found that the structure displays excellent slow-light effects near the PIT windows with high-group indices, and the maximum group index of each PIT window exceeds 1000 when the carrier mobility of graphene increases to 3.5 m2 V−1 s−1. The proposed structure has potential to be used in multichannel filters, optical switches, modulators, and slow light devices. Additionally, the established theoretical model lays a theoretical basis for research on multimode coupling effects.
期刊：
PHYSICAL CHEMISTRY CHEMICAL PHYSICS,2021年23(6):3949-3962 ISSN：1463-9076
通讯作者：
Li, Hongjian
作者机构：
[Gao, Enduo; Xiong, Cuixiu; Zeng, Biao; Wu, Kuan; Li, Min; Chao, Liu; Ruan, Banxian; Zhang, Baihui; Li, Hongjian] Cent South Univ, Sch Phys & Elect, Changsha 410083, Peoples R China.;[Xiong, Cuixiu] Hunan City Univ, Coll Informat & Elect Engn, All Solid State Energy Storage Mat & Devices Key, Yiyang 413000, Peoples R China.
通讯机构：
[Li, Hongjian] C;Cent South Univ, Sch Phys & Elect, Changsha 410083, Peoples R China.
摘要：
Graphene, a new two-dimensional (2D) material, has attracted considerable attention in recent years because of the metallic characteristics at terahertz frequencies. The phase coupling of multilayer graphene-coupled grating structures is normally used to realize multiple plasmon-induced transparency (PIT) spectral responses. However, the device becomes more complicated with the increase in the number of graphene layers. In this work, we propose a five-step-coupled pyramid-shaped monolayer graphene metamaterial and predict a dynamically controllable PIT with four transparency peaks for the first time in the monolayer graphene metamaterial. A tunable multi-switch and good slow light effect is predicted over the wide PIT window, and the maximum modulation depth is high up to 16.89 dB, which corresponds to 97.95%, while the time delay of the induced transparent window is as high as 0.488 ps, where the corresponding group refractive index is 586. The electric field distributions and quantum level theory are used to explain the physical mechanism of the PIT with four transparency peaks. The coupled mode theory (CMT) is employed to establish the mathematical model of the PIT with four transparency peaks, and the consistency between the simulated and the calculated results is nearly perfect. We believe that the pyramid-shaped monolayer graphene metamaterial could be useful in efficient filters, switches, and slow light devices.
摘要：
A broadband and wide-angled microwave absorber based on resistive-type metamaterial has been proposed and demonstrated in the low-frequency regime of 2-8 GHz. The minimum reflection loss of the absorption peak located at 5.27 GHz is -51.41 dB. Effective bandwidth better than -10 dB reflection loss is able to achieve 2.70 GHz in the range from 3.81 GHz to 6.51 GHz. The underlying physical mechanisms of electromagnetic wave energy attenuation are illustrated in detail by means of surface current, electromagnetic field and power loss density. Furthermore, the influence of structural dimensions on the attenuation properties of the proposed resistive-type metamaterial absorber is also investigated. More importantly, the designed resistive-type metamaterial absorber could operate well with incident angles changing from 0 degrees to 60 degrees under the transverse electric (TE) and transverse magnetic (TM) waves. Research results will be capable of providing guidance for the design and preparation of broadband microwave absorbing materials at low frequencies.
摘要：
We introduce the concept of the photonic crystal (PC) into the waveguide system and propose a metal-dielectric-metal (MDM) waveguide system coupled with three periodic stubs and a multimode cavity. This system can realize multiple ultra-narrow plasmon-induced transparency (PIT) effects with a minimum linewidth of about 4 nm. These PIT peaks exhibit tunable evolution characteristics of two groups. The wavelengths and linewidths of one group of PIT peaks in the transmission spectra only can be changed slightly, while the wavelengths of another group of PIT peaks can be changed significantly by adjusting one of the geometric parameters of the cavity. This research may open up new design ideas for ultra-narrowband multichannel filters and switches.
摘要：
We have proposed a simple metal-dielectric-metal (MDM) waveguide system side-coupled with single-mode and multimode resonators. This proposed structure can achieve a typical dual plasmon-induced transparency (PIT) effect in the transmission spectra. The two PIT peaks exhibit opposite evolution tendencies with the increase in the depth of stubs. A multimode-coupled mode theory (M-CMT), confirmed by simulated results, is originally introduced to investigate the coupling effects of the proposed structure. Compared to the previous reported multichannel filters, the proposed structure includes obvious advantages, such as structural simplicity and ease of fabrication. In addition, the sensing characteristics of the proposed structure based on PIT effects are discussed numerically. The results demonstrate that the proposed structure is suitable for applications in multichannel filters, optical switches, and sensors. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
摘要：
We experimentally study the spatiotemporal evolution of chirped femtosecond laser pulses at a specific spatial position, such as the modulation peak position (MPP), during small-scale self-focusing (SSSF). It is found that the spatial peak intensity at the MPP increases rapidly initially with increment of input power due to the effect of SSSF, however it becomes saturated at the higher power because the finite energy of the beam restraints increasing of the peak intensity at the MPP. The pulse width at the MPP is compressed gradually with rising power owing to the spatiotemporal coupling effect, which will reach the narrowest when the spatial peak intensity at the MPP reaches the maximum. Further, the influence of chirp on the pulse width evolution at the MPP is discussed theoretically. We find that the negative chirp accelerates the pulse width compression because the negative chirp enhances the process of SSSF, but the positive chirp is counterproductive. Our results may provide some helps for propagation and amplification of broadband laser pulses.
摘要：
In this paper, we theoretically and experimentally investigate the initial temporal characterization and the temporal evolution of a picosecond laser pulse by a synchronized femtosecond laser pulse. After theoretically analyzing the measurement principle, we experimentally measure the initial temporal characterization of the picosecond laser pulse. Further, the temporal evolution of the picosecond laser pulse propagating in different lengths of a carbon disulfide (CS2) is measured. We find that the initial temporal shape of the picosecond laser pulse is smooth and clean. As increasing of the CS2 length, the pulse width of the picosecond laser pulse has a trend of slight narrow owing to the spatiotemporal coupling effect.
摘要：
When laser pulses propagate in an inhomogeneous nonlinear medium, we theoretically investigate the evolution of laser pulses by analytically solving the (3 + 1)-dimensional generalized nonlinear Schrodinger equation with variable coefficients and optical lattice. A series of chirped-free and chirped analytic solutions, such as soliton solutions are found and intensities evolution of these analytic solutions are studied in detail. In the absence of optical lattice, we find that the intensities evolution of chirped-free and chirped analytic solutions vary regularly when the diffraction coefficient is the same as the dispersion coefficient. When the diffraction coefficient is different from the dispersion coefficient, the intensities evolution of chirped-free analytic solutions are regular variation, but the intensities evolution of chirped analytic solutions are irregular. In the presence of optical lattice, the intensities evolution of chirped analytic solutions vary regularly because the diffraction coefficient and the dispersion coefficient are always identical. (C) 2017 Elsevier GmbH. All rights reserved.
摘要：
In this paper, the evolution of temporal soliton is investigated analytically when a laser pulse propagates in the inhomogeneous nonlinear medium with a Scarff II parity-time (PT)-symmetric potential. After a detailed analyzing the evolution of the intensity and pulse width (PW) of a temporal soliton, it is find that the chirped-free and chirped temporal soliton are stable when the dispersion coefficient is a periodic modulated function. When the dispersion coefficient are the constant and the exponential decreasing function, the chirped-free temporal soliton is stable, while the chirped temporal soliton is gradually compressed.
