High-performance plasmonic oblique sensors for the detection of ions

Theoretical study of extremely narrow plasmonic surface lattice resonances observed by MIM nanogratings under normal incidence in asymmetric environments

Nanoarray structures can support plasmonic surface lattice resonances (SLRs) with extremely narrow linewidths and huge electric field enhancement features, which are attractive applications in nanolasers, biochemical sensors, and nonlinear optics. However, current nanoarray structures located in an asymmetric dielectric environment with a refractive index contrast of 1.00/1.52 of the superstrate/substrate excite much poorer SLRs under normal incidence, which largely limits their application range. In this work, we report extremely narrow SLRs supported by one-dimensional metal-insulator-metal nanograting in asymmetric dielectric environments. The simulation results show that an SLRs with linewidth of 3.26 nm and quality factor of 233.2 can be excited under normal incidence. This high-quality SLRs is attributed to the interference formation between the out-of-plane dipole resonance mode and the out-of-plane quadrupole resonance mode. We also show that the resonance wavelength and quality factor can be tuned by changing the structure geometry and period, and we calculate the normal incidence SLRs quality factor to be up to 248 in 1.33/1.52 and 250 in 1.45/1.52. We expect the SLRs of this work to find potential applications in asymmetric dielectric environments.

A review of dielectric optical metasurfaces for spatial differentiation and edge detection

Dielectric metasurfaces-based planar optical spatial differentiator and edge detection have recently been proposed to play an important role in the parallel and fast image processing technology. With the development of dielectric metasurfaces of different geometries and resonance mechanisms, diverse on-chip spatial differentiators have been proposed by tailoring the dispersion characteristics of subwavelength structures. This review focuses on the basic principles and characteristic parameters of dielectric metasurfaces as first- and second-order spatial differentiators realized via the Green's function approach. The spatial bandwidth and polarization dependence are emphasized as key properties by comparing the optical transfer functions of metasurfaces for different incident wavevectors and polarizations. To present the operational capabilities of a two-dimensional spatial differentiator in image information acquisition, edge detection is described to illustrate the practicability of the device. As an application example, experimental demonstrations of edge detection for different biological cells and a flower mold are discussed, in which a spatial differentiator and objective lens or camera are integrated in three optical pathway configurations. The realization of spatial differentiators and edge detection with dielectric metasurfaces provides new opportunities for ultrafast information identification in biological imaging and machine vision.

Ultra-broadband solar absorbers for high-efficiency thermophotovoltaics

Metamaterial absorbers have attracted great attention over the past few years and exhibited a promising prospect in solar energy harvesting and solar thermophotovoltaics (STPVs). In this work, we introduce a solar absorber scheme, which enables efficient solar irradiance harvesting, superb thermal robustness and high solar thermal energy conversion for STPV systems. The optimum structure demonstrates an average absorbance of 97.85% at the spectral region from 200 nm to 2980 nm, indicating the near-unity absorption in the main energy range of the solar radiance. The solar-thermal conversion efficiencies surpassing 90% are achieved over an ultra-wide temperature range (100-800 °C). Meanwhile, the analysis indicates that this metamaterial has strong tolerance for fabrication errors. By utilizing the simple two-dimensional (2D) titanium (Ti) gratings, this design is able to get beyond the limit of costly and sophisticated nanomanufacturing techniques. These impressive features can hold the system with wide applications in metamaterial and other optoelectronic devices.

Narrowband Light Reflection Resonances from Waveguide Modes for High-Quality Sensors

Designing various nanostructures to achieve narrowband light reflection resonances is desirable for optical sensing applications. In this work, we theoretically demonstrate two narrowband light reflection resonances resulting from the excitations of the zero-order transverse magnetic (TM) and transverse electric (TE) waveguide modes, in a waveguide structure consisting of an Au sphere array on an indium tin oxide (ITO) spacer on a silica (SiO₂) substrate. The positions of the light reflection resonances can be tuned easily, by varying the array periods of gold (Au) spheres or by changing the thickness of the ITO film. More importantly, the light reflection resonances have a very narrow bandwidth, the full width at half maximum (FWHM) of which can be reduced to only several nanometers for the zero-order TM and TE waveguide modes. The conventionally defined performance parameters of sensors, sensitivity (S) and figure of merit (FOM), have quite high values of about 80 nm/RIU and 32, respectively, in the visible wavelength range.