Plasmonic effect using a cross-hair can convey strongly localized surface plasmon modes among the separated composite nanostructures. Compared to its counterpart without the cross-hair, this characteristic has the remarkable merit of enhancing absorptance at resonance and can make the structure carry out a dual-band plasmonic perfect absorber (PPA). In this paper, we propose and design a novel dual-band PPA with a gathering of four metal-shell nanorods using a cross-hair operating at visible and near-infrared regions. Two absorptance peaks at 1050 nm and 750 nm with maximal absorptance of 99.59% and 99.89% for modes 1 and 2, respectively, are detected. High sensitivity of 1200 nm refractive unit (1/RIU), figure of merit of 26.67 and Q factor of 23.33 are acquired, which are very remarkable compared with the other PPAs. In addition, the absorptance in mode 1 is about nine times compared to its counterpart without the cross-hair. The proposed structure gives a novel inspiration for the design of a tunable dual-band PPA, which can be exploited for plasmonic sensor and other nanophotonic devices.

https://www.mdpi.com/2079-4991/10/3/493/pdf

Perfect Dual-Band Absorber Based on Plasmonic Effect with the Cross-Hair/Nanorod Combination

Surface plasmon resonance sensor based on photonic crystal fiber with indium tin oxide film

Multi-band, tunable, high figure of merit, high sensitivity single-layer patterned graphene—Perfect absorber based on surface plasmon resonance

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength. The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method. Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure. Subsequently, one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte. After optimizing the grating geometric variables of the structure, the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit (nm/RIU) and the figure of merit of 409 RIU−1. The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.

A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure*

A tunable terahertz (THz) narrowband absorber in view of bulk Dirac semimetal (BDS) is designed in this paper. The tunable terahertz absorber's basic unit comprises BDS, intermediate medium, and metal substrate. The BDS has good surface conductivity and the Fermi energy of that is flexible tunable, and the good surface conductivity might make controlled by Fermi energy. The absorption characteristics of the designed absorber are simulated by the finite integral time domain technique. The calculation results show that the designed absorber achieves ideal absorption in 139.97 μm, 163.52 μm, 247.76 μm bands, and the absorption rate is more than 0.96, which realizes ideal narrowband absorption and dynamic tuning. We find that the absorption peaks are flexible and adjustable by changing the Fermi energy of BDS, and the frequency adjustability of the absorber is analyzed. In addition, the effects of different structural parameters on the absorption efficiency and the absorption performance at different incident angles are studied. These results show that, compared with traditional metamaterials, Dirac semimetallic absorbing materials can tune the resonant frequency more effectively, even without reconstructing the structure, which has great application value in many fields, and provide a new reference for future research.

Terahertz tunable three band narrowband perfect absorber based on Dirac semimetal

In this work, we present an efficient polarization conversion device via using a hollow graphene metasurface. The platform can simultaneously realize a series of excellent performances, including the broadband x-to-y cross polarization conversion (CPC) function with near unity polarization conversion ratio (PCR), dual-frequency linear-to-circular polarization conversion (LTC-PC) function, and highly sensitive polarization conversion function manipulation under wide oblique incidence angle range. For instance, the proposed device obtains an x-to-y CPC function with the bandwidth up to 1.83 THz (χPCR ≥98.8%). Moreover, the x-to-y CPC function can be switched to LTC-PC function via artificially tuning the Fermi energy of graphene. The maximal frequency shift sensitivity (S) of polarization conversion function reaches 23.09 THz/eV, suggesting a frequency shift of 2.309 THz for the LTC-PC function when the chemical potential is changed by 0.1 eV. Based on these superior performances, the polarization converter can hold potential applications in integrated and compact devices, such as polarization sensor, switches and other optical polarization control components.

Multi-functional polarization conversion manipulation via graphene-based metasurface reflectors.

We propose a high-quality multispectral plasmonic sensor by coating a dielectric grating on the semiconductor-metal-semiconductor stacks. Ultra-narrow plasmonic resonances with the minimum bandwidth of 8 nm are insensitive to the polarization of incident light. The ultra-narrow multi-band phenomenon can be ascribed to the synergy of guided mode resonances, cavity modes and surface plasmon polaritons. The sensor displays superior refractive index sensitivity (404.295 nm/RIU) and figure of merit (50.3) and can also be used to detect the protein layer in sub-nanometer thickness. These offer new perspectives for achieving ultra-compact efficient sensors and filters.

https://iopscience.iop.org/article/10.7567/1882-0786/ab24af/pdf

Grating-assisted ultra-narrow multispectral plasmonic resonances for sensing application

We theoretically present a tunable dual-band perfect absorber in the visible and near-infrared regions for sensing applications. The absorber consists of a periodic metal-dielectric-metal shell-core nanorod array and a thick metal film separated by a periodic dielectric nanorod array. Two narrow perfect absorption bands (98.2% and 99.7%) are achieved due to the synergy of localized surface plasmons (LSPs), propagating surface plasmons (PSPs) and lattice resonances. The two narrow bands both are sensitive to the refractive index change and the maximum sensitivity is 783.705 nm/RIU (RIU is the refractive index unit). These enable the structure to have great potential in the fields of perfect absorbers, plasmonic sensors, and filters.

Tunable dual-band plasmonic perfect absorber and its sensing applications

The invention provides a tunable dual-band perfect absorber for visible-near infrared bands. The absorber comprises a metal base layer, a medium nanorod structure array layer and a metal-medium-metalcore/shell nanorod structure array layer. The absorber has two perfect absorption peaks at the 749 nanometer of a visible light band and the 1749 nanometer of a near infrared band, the absorption exceeds 98%, and the two perfect absorption peaks are insensitive to the angles and polarization states of incident light. The absorber has high-sensitivity optical sensing performance and the sensing sensitivity for environmental refractive index change detection is as high as 783.705 manometer/RIU, so that the absorber exceeds the traditional absorbers in the aspect of performance.

Tunable dual-band perfect absorber for visible-near infrared bands

The invention provides a polarization-independent ultra-narrow multiband tunable perfect absorber, and belongs to the field of metamaterials. The absorber comprises a metal layer, a dielectric layer and a periodic metal nanostructure array layer; the metal layer as a reflection layer is arranged on a bottom layer; the dielectric layer is positioned between the metal layer and the periodic metal nanostructure array layer; and the periodic metal nanostructure array layer is formed by periodically arranging metal cylinders with air holes etched in the middles. According to the absorber, ultra-narrow multiband perfect absorption can be realized, and the perfect absorption is insensitive to polarization state change under normal incident light. The maximum absorption of the absorber reaches 99.9%; the maximum bandwidth does not exceed 30 nm; and the sensing sensitivity reaches 325 nm/RIU.

Liu Ye

Papers

Multi-functional polarization conversion manipulation via graphene-based metasurface reflectors.

Grating-assisted ultra-narrow multispectral plasmonic resonances for sensing application

Tunable dual-band plasmonic perfect absorber and its sensing applications

Tunable dual-band perfect absorber for visible-near infrared bands

Polarization-independent ultra-narrow multiband tunable perfect absorber