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Abstract In this article, we design a triple-band graphene refractive index sensor with good angle-polarization tolerance, which is composed of graphene elliptic–circular nanodisk resonators periodically arranged on a dielectric substrate. The numerical results indicate that the resonant wavelengths of three modes of graphene resonators show consecutively linear tunability when the refractive index of the surrounding medium varies, and the sensitivity is up to 11. 56 μ m /RIU. The sensing range can be further adjusted by controlling the doping level of graphene. In addition, the proposed graphene sensor maintains polarization insensitivity over a wide angular range (0–60°), showing very good angle-polarization tolerance. This work enables us to achieve a tunable triple-band sensor and provides potential value for label-free biomedical sensing. Highlights • The model can excite three dips that supported by different parts of the structures. • The structures will have optimal sensing performance with the increase of wavelength or proportion. • The sensing range can be adjusted by changing the doping level of graphene. • Sensing characteristics are not affected by angles and polarization. [ABSTRACT FROM AUTHOR]

Simulation based on the finite-difference time-domain (FDTD) has been performed, and theoretical models comprising concentric Ag nanoring-nanodisk of different parameters have been constructed to research their plasmon properties. According to unique electronic properties of concentric nanoring-nanodisk, abundant plasmon properties could be obtained at their interfaces, including dipole, quadrupole, and octupole plasmon resonance modes. Complex field distributions which are induced by concentric nanoring-nanodisk support the possibility to create dark resonance mode. This can lead to Fano-like resonance combining with bright resonance mode by predominantly dipole resonance. A concentric nanoring-nanodisk system has been proved to support Fano-like resonance without symmetry breaking. At the frequency of the Fano resonance, strong localized optical fields can be obtained. Narrow spectral features with high local fields of Fano resonances make it possible to achieve many applications based on surface plasmon property. [ABSTRACT FROM AUTHOR]

Here, we provide a simulation based on finite-difference time-domain (FDTD) way of the properties of surface plasmons on Ag nanoring and study their electric field distribution in order to identify different multiple surface plasmon resonances. We can obtain the symmetric field distribution that parallels to the orientation of direction of incident light. We find their propagation can be controlled. And we discuss some of the parameters that influence the optical response of the Ag nanoring. Adjustment of nanoring radius (inner radius and outer radius) and height can change the absorption intensity and the resonance peaks. The simulation of the field distribution also displays that the location of the field enhancement is specified by the different resonance patterns. Dipole, quadrupole, and octupole plasmon resonance modes can be found in the Ag nanoring at resonance wavelength. This is an important step toward a thorough understanding of plasmon resonance in Ag nanorings. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical simulation based on a finite-difference time-domain method (FDTD) shows that the solar absorber can reach ultra-broadband and high-efficiency by refractory metals titanium (Ti) and titanium nitride (TiN). In the absorption spectrum of double-size cross-shaped absorber, the absorption bandwidth of more than 90% is 1182 nm (415.648–1597.39 nm). Through the analysis of the field distribution, we know the physical mechanism is the combined action of propagating plasmon resonance and local surface plasmon resonance. After that, the paper has a discussion about the influence of different structure parameters, polarization angle and angle of incident light on the absorptivity of the absorber. At last, the absorption spectrum of the absorber under the standard spectrum of solar radiance Air Mass 1.5 (AM1.5) is studied. The absorber we proposed can be used in solar energy absorber, thermal photovoltaics, hot-electron devices and so on. [ABSTRACT FROM AUTHOR]