Effect of Wood's anomalies on the profile of extraordinary transmission spectra through metal periodic arrays of rectangular subwavelength holes with different aspect ratio

Highly Transparent and Polarization-Maintained Terahertz Plasmonic Metamaterials Based on Metal-Wire-Woven Hole Arrays: Fundamentals and Characterization of Transmission Spectral Peaks

Metal-hole-supported terahertz (THz) waves through the structure of a metal-wire-woven hole array (MWW-HA) present high-frequency-passed transmittance spectra of one plasmonic metamaterial with artificial plasmonic frequencies, which are inversely proportional to metal-hole widths. For the transmitted THz waves of MWW-HA, transverse-electric (TE) and transverse-magnetic (TM) waveguide modes mix within a symmetric metal-hole boundary. THz resonance waves transversely crossing the holes of MWW-HA are experimentally characterized with spectral peaks in the frequency range of 0.1–2 THz that are correlated with aperture sizes, unit-cell-hole widths, metal-wire thicknesses, and wire-bending angles. The metal-hole-transported resonance waves of MWW-HA are dominated by TE waveguide modes instead of TM ones because a hole width of MWW-HA is approximate to the half wavelength of a resonance wave. The round metal edges of the woven metal wires can minimize the effective optical length of a thick metal hole to transmit THz resonance waves, thereby resulting the smallest rotation angle of linear polarization and high transmittance up to 0.94. An MWW-HA structure is therefore reliable for supporting metal-hole resonance waves with low resistance, whereas a metal-slab-perforated hole array cannot achieve the same result.

Sharp resonances in terahertz free-standing three-dimensional metallic woven meshes

Free-standing structures that do not require any holder or substrate show high levels of flexibility and stretchability and hence are well-suited for THz applications. In this work, a free-standing three-dimensional metallic woven mesh is experimentally and numerically investigated at terahertz frequencies. Such mesh fabricated by weaving techniques exhibits sharp Fano-like resonances, which has not been found in previous studies. Investigation results indicate that the high Q resonances originate from the bending effect in bent wires, which can be termed as Wood's anomalies. The resonance field longitudinally covers the input and output end faces of the woven mesh, thereby obtaining a large field volume. These properties in this kind of meshes are well suited for wave manipulation and biomolecular sensing in the terahertz regime.

Terahertz composite plasmonic slabs based on double-layer metallic gratings

One composite plasmonic slab with a broad bandgap (40%) is experimentally and numerically demonstrated in the terahertz (THz) region. The composite slab consists of double-layer metallic gratings and a dielectric film, which supports two resonant modes. Electric field vectors and charge distributions proved that the low-frequency resonant mode originates from the symmetric plasmonic mode, while the high-frequency resonant mode is induced by the hybrid mode of plasmonic and dielectric modes. Compared with the double-layer metallic grating, the inserted dielectric film significantly enhances the transmission of the transverse magnetic (TM) waves and induces Fano resonances. The near-field coupling between metal gratings and dielectric film can be manipulated by changing the thickness and the refractive index of dielectric films. We further demonstrated that the plasmonic bandgap can be manipulated by tuning the grating width. These results suggest that this composite plasmonic slab is promising in terahertz integrated components development such as a filter, polarizer, or sensor.

Linewidth reduction effect of a cavity-coupled dual-passband plasmonic filter

We propose a novel cavity-coupled MIM nano-hole array structure that exhibits a tunable dual passband in the near-infrared regime. When compared with the traditional single metal film, the designed structure provides a coupling effect between Gspp and SPP to significantly reduce the linewidths of the two transmission peaks. We also reveal the physical origin of the positive and negative influence of the cavity effect on the transmission of high-frequency and low-frequency peaks. This work supplies a new modulation theory for plasmonic devices based on the EOT phenomenon and has a wide application prospect in the fields of infrared sensor, plasmonic filter, and hyperspectral imaging.

Continuously Tunable, Polarization Controlled, Colour Palette Produced from Nanoscale Plasmonic Pixels

Colour filters based on nano-apertures in thin metallic films have been widely studied due to their extraordinary optical transmission and small size. These properties make them prime candidates for use in high-resolution colour displays and high accuracy bio-sensors. The inclusion of polarization sensitive plasmonic features in such devices allow additional control over the electromagnetic field distribution, critical for investigations of polarization induced phenomena. Here we demonstrate that cross-shaped nano-apertures can be used for polarization controlled color tuning in the visible range and apply fundamental theoretical models to interpret key features of the transmitted spectrum. Full color transmission was achieved by fine-tuning the periodicity of the apertures, whilst keeping the geometry of individual apertures constant. We demonstrate this effect for both transverse electric and magnetic fields. Furthermore we have been able to demonstrate the same polarization sensitivity even for nano-size, sub-wavelength sets of arrays, which is paramount for ultra-high resolution compact colour displays.

Plasmonic metasurface for simultaneous detection of polarization and spectrum

We present a new plasmonic metasurface for simultaneous detection of polarization and spectrum of incident light. The demonstrated metasurface is a rationally designed cluster of artificial atoms that are engineered to exhibit polarization and wavelength-selective optical transmission. The fundamental building block of this structure is periodically coupled subwavelength aperture arrays with different orientations and lattice constants. When integrated with pixelated photodetectors, the metasurface can be used to measure the polarization and spectral information of an optical input. In this Letter, simultaneous detection of the polarization and spectrum of polarized light was experimentally demonstrated by analyzing the transmitted intensity distribution through the metasurface. The demonstrated metasurface offers great potential for many applications, such as polarimetric multispectral imaging and polarization-division multiplexing in optical communications.

Slow-light effect via Rayleigh anomaly and the effect of finite gratings

In this Letter, we investigate the slow-light effect of subwavelength diffraction gratings via the Rayleigh anomaly using a fully analytical approach without needing to consider specific grating structures. Our results show that the local group velocity of the transmitted light can be significantly reduced due to the optical vortex, which can inspire a new mechanism to enhance light-matter interactions for optical sensing and photodetection. However, the slow-light effect will diminish as the transmitted light propagates farther from the grating surface, and the slowdown factor decreases as the grating size shrinks.

On-fiber plasmonic interferometer for multi-parameter sensing

We demonstrate a novel miniature multi-parameter sensing device based on a plasmonic interferometer fabricated on a fiber facet in the optical communication wavelength range. This device enables the coupling between surface plasmon resonance and plasmonic interference in the structure, which are the two essential mechanisms for multi-parameter sensing. We experimentally show that these two mechanisms have distinctive responses to temperature and refractive index, rendering the device the capability of simultaneous temperature and refractive index measurement on an ultra-miniature form factor. A high refractive index sensitivity of 220 nm per refractive index unit (RIU) and a high temperature sensitivity of -60 pm/ °C is achieved with our device.

Periodicity-induced symmetry breaking in a Fano lattice: hybridization and tight-binding regimes

We investigate experimentally and theoretically the role of periodicity on the optical response of dolmen plasmonic arrays that exhibit a Fano line shape. Contrary to previous works on single nanostructures, this study deals with the in-plane near-field coupling between adjacent unit cells. By making an analogy to the electronic properties of atoms in the tight-binding model, specific behaviors of photonic states are investigated numerically as a function of the structural asymmetry for different coupling directions. These predictions are verified experimentally with dark-field measurements on nanostructure arrays which exhibit high tunability and fine control of their spectral features as a function of the lattice constants. These effects, originated from symmetry-breaking and selective excitation of the subradiant mode, provide additional degree of freedom for tuning the spectral response and can be used for the sensitive detection of local perturbations. This study provides a general understanding of the near-field interactions in Fano resonant lattices that can be used for the design of plasmonic nanostructures and planar metamaterials.

Design and fabrication of birefringent nano-grating structure for circularly polarized light emission

Three different nano-grating structures are designed as phase retarders that can transform linearly polarized light to circularly polarized emission for the wavelengths of 488 nm, 532 nm and 632.8 nm, respectively. Gold based nano-grating structures with various periods are fabricated by utilizing laser interference lithography. The ellipticity of all circularly polarized emission can reach around 90% such that the structure has great potential in the applications of three-dimensional (3D) display. The effects of the slit width and metal thickness modulations are simulated by rigorous coupled wave analysis (RCWA) method. Besides, the field intensity and phase of the transmitted TM and TE waves are also simulated to understand their polarization characteristics.

Polarization anisotropic transmission through metallic Sierpinski-Carpet aperture array

Extraordinary optical transmission through rectangular Sierpinski -Carpet aperture array on an Ag film has been observed. Attributed to the fractal-featured rectangle array, it exhibits polarization dependence and dual-band transmission simultaneously. In addition, the incident angle invariance transmission displays within a certain angle range, which is quite different from ordinary rectangles. This report provides a way to achieve the polarization-manipulated multi-band transmission in infrared region.

Plasmonic light harvesting for multicolor infrared thermal detection

Here we combined experiments and theory to study the optical properties of a plasmonic cavity consisting of a perforated metal film and a flat metal sheet separated by a semiconductor spacer. Three different types of optical modes are clearly identified-the propagating and localized surface plasmons on the perforated metal film and the Fabry-Perot modes inside the cavity. Interactions among them lead to a series of hybridized eigenmodes exhibiting excellent spectral tunability and spatially distinct field distributions, making the system particularly suitable for multicolor infrared light detections. As an example, we design a two-color detector protocol with calculated photon absorption efficiencies enhanced by more than 20 times at both colors, reaching ~42.8% at f1 = 20.0THz (15μm in wavelength) and ~46.2% at f2 = 29.5THz (~10.2μm) for a 1μm total thickness of sandwiched quantum wells.

An optimized surface plasmon photovoltaic structure using energy transfer between discrete nano-particles

Surface plasmon enhancement has been proposed as a way to achieve higher absorption for thin-film photovoltaics, where surface plasmon polariton(SPP) and localized surface plasmon (LSP) are shown to provide dense near field and far field light scattering. Here it is shown that controlled far-field light scattering can be achieved using successive coupling between surface plasmonic (SP) nano-particles. Through genetic algorithm (GA) optimization, energy transfer between discrete nano-particles (ETDNP) is identified, which enhances solar cell efficiency. The optimized energy transfer structure acts like lumped-element transmission line and can properly alter the direction of photon flow. Increased in-plane component of wavevector is thus achieved and photon path length is extended. In addition, Wood-Rayleigh anomaly, at which transmission minimum occurs, is avoided through GA optimization. Optimized energy transfer structure provides 46.95% improvement over baseline planar cell. It achieves larger angular scattering capability compared to conventional surface plasmon polariton back reflector structure and index-guided structure due to SP energy transfer through mode coupling. Via SP mediated energy transfer, an alternative way to control the light flow inside thin-film is proposed, which can be more efficient than conventional index-guided mode using total internal reflection (TIR).

Localized shape resonance on silver film perforated by H-shaped and more complex shaped hole arrays

The experimental results of light transmission through periodic array of H-shaped hole and more complicated hole which is a combination of multiple U shape are demonstrated. The observations indicate that the localized shape resonance in the longest resonant length of unfolded U-shaped part of the hole always appears. However, localized modes resonant in smaller U-shaped length don't always appear. Localized mode with non-U-shaped resonant path cannot be seen in our sample. In addition, localized mode with different order and resonant path can be excited by different polarized light.

Light transmission through nanostructured metallic films: coupling between surface waves and localized resonances

We present an experimental and computational investigation of the optical properties of thin metallic films periodically perforated with nanometric apertures and show that high transmission through such a structure is attributable to the localized surface plasmon (LSP) resonances of the aperture. The periodicity-related optical phenomena, including Wood's anomaly and surface plasmon polariton (SPP) excitation, interfere with LSPs and generate Fano resonances with asymmetric spectral profiles. The transmission maximum of the Fano profile is related to the constructive interference between the LSP field and diffracted light propagating along the surface; the transmission minimum of the Fano profile is caused by the destructive interference between LSPs and SPPs. The study confirms the negative role of SPP in transmission through the structure.

Midwave thermal infrared detection using semiconductor selective absorption

The performance of thermal detectors is derived for devices incorporating materials with non-uniform spectral absorption. A detector designed to have low absorption in the primary thermal emission band at a given temperature will have a background-limited radiation noise well below that of a blackbody absorber, which is the condition typically assessed for ultimate thermal detector performance. Specific examples of mid-wave infrared (ʎ ∼ 3-5 μm) devices are described using lead selenide as a primary absorber with optical cavity layers that maximize coupling. An analysis of all significant noise sources is presented for two example room-temperature devices designed to have detectivities up to 4.37 × 10(10) cm Hz(1/2) W(-1), which is a factor 3.1 greater than the traditional blackbody limit. An alternative method of fabricating spectrally selective devices by patterning a plasmonic structure in silver is also considered.