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In this paper, an active tunable terahertz bandwidth absorber based on single-layer graphene is proposed, which consists of a graphene layer, a photo crystal plate, and a gold substrate. When the Fermi energy (E f ) of graphene is 1.5 eV, the absorber shows high absorption in the range of 3.7 THz–8 THz, and the total absorption rate is 96.8%. By exploring the absorption mechanism of the absorber, the absorber shows excellent physical regulation. The absorber also shows good adjustability by changing the E f of graphene. This means that the absorber exhibits excellent tunability by adjusting the physical parameters and E f of the absorber. Meanwhile, the absorber is polarization independent and insensitive to the incident angle. The fine characteristics of the absorber mean that the absorber has superior application value in many fields such as biotechnology and space exploration.

In this paper, a broad band absorber based on a double-ring coupled disk resonator periodic structure, which can work in the visible and mid infrared range, is proposed and investigated. Results show the absorbance is large than 92.4% in the range of 300 nm–4096 nm, and the average absorption is about 97.4% from the visible to mid-infrared bands. Besides, the proposed absorber is wide angle acceptance, background refractive index (RI), and polarization state insensitive. The absorption mechanisms are analyzed and found that it mainly originated from the dielectric lossy property in short-wavelength and gap plasmonic resonances in long-wavelength. It is believed the proposed absorber can find potential applications in the fields of solar cell devices, thermal emitters, and plasmonic imaging.

In this paper, a polarization-insensitive and broadband absorber based on Al 2 O 3 - Ti - Al 2 O 3 rectangular periodic sandwich structure has been studied. Simulations indicate the absorbance remains over 97% at the wavelength from 599 nm to 1912 nm, and the corresponding average absorption is up to 98.5% in this range. Moreover, the broadband absorption is background refractive index and polarization insensitive. The absorption mechanism of the broad-band is studied by impedance-matching theory and finite difference time domain (FDTD) method, which is mainly originated from the cavity plasmonic resonance, surface plasmonic dipolar resonance, and near field plasmonic coupling effect. The proposed broadband absorber is expected to play a role in solar cell, which can be applied in the areas of solar cell design, imaging, and thermal emitters. Moreover, the use of Ti material and Al 2 O 3 instead of noble metals has the advantages of thermal robustness, and lower cost.

In this paper, an ultra-broadband perfect absorber based on a four-layer pyramid metamaterial and a metal insulator metal (MIM) structure has been demonstrated and investigated. Finite-difference time-domain (FDTD) results indicate that the absorption originates from localized surface plasmons and waveguide mode resonance effect. An average absorption of 96.18 % with bandwidth ranging from 308 nm to 2387 nm was achieved, and the average absorption in the entire wave band (200–2800 nm) was approximately 94.64%. The results of the impedance matching theory are consistent with the FDTD simulation. Polarization insensitivity was investigated by studying the absorption characteristic of TE and TM polarizations. The effect of top and bottom materials was investigated and compared in detail. Moreover, by adjusting the geometrical size, the absorption performance can be fine- tuned. In addition, the proposed broadband absorber exhibited excellent absorption stability and environmental refractive index tolerance. Without noble metal materials, the proposed structure can reduce the fabrication costs. We believe that the proposed broadband absorber has potential applications in solar cells, infrared imaging, and thermal emitters.

A monolayer graphene metamaterial composed of a graphene block and four graphene strips, which has the metal-like properties in terahertz frequency range, is proposed to generate an outstanding quadruple plasmon-induced transparency (PIT). Additional analyses show that the forming physical mechanism of the PIT with four transparency windows can be explained by strong destructive interference between the bright mode and the dark mode, and the distributions of electric field intensity and electric field vectors under the irradiation of the incident light. Coupled mode theory and finite-difference time-domain method are employed to study the spectral response characteristics of the proposed structure, and the theoretical and simulated results are in good agreement. It is found that a tunable multi-frequency switch and excellent optical storage can be achieved in the wide PIT window. The maximum modulation depth is up to 99.7%, which corresponds to the maximum extinction ratio of 25.04 dB and the minimum insertion loss of 0.19 dB. In addition, the time delay is as high as 0.919 ps, the corresponding group refractive index is up to 2755. Thus, the proposed structure provides a new method for the design of terahertz multi-frequency switches and slow light devices.

We consider a novel system of two-component atomic Bose-Einstein condensate in a double-well potential. Based on the well-known two-mode approximation, we demonstrate that there are obvious avoided level-crossings when both interspecies and intraspecies interactions of two species are increased. The quantum dynamics of the system exhibits revised oscillating behaviors compared with a single component condensate. We also examine the entanglement of two species. Our numerical calculations show the onset of entanglement can be signed as a violation of Cauchy-Schwarz inequality of second-order cross correlation function. Consequently, we use Von Neumann entropy to quantity the degree of entanglement.