Design of a Slit-Groove Coupler for Unidirectional Excitation of the Guided Surface Plasmon Polaritons Through a Plasmonic Slot Waveguide

In this paper, a plasmonic-photonic nanostructure has been introduced for efficient unidirectional coupling of free-space radiation to surface plasmon polariton (SPP) waves under normal illumination on a subwavelength slit. The structure consists of a conventional metallic slit-groove nanostructure integrated with a plasmonic waveguide to support SPP waves along the desired direction with a remarkable lateral confinement. The unidirectional coupling is achieved by using an integrated plasmonic distributed reflector designed under Bragg condition. This reflector basically distributes part of the light coupled through the slit into the SPP modes of the waveguide. Numerical simulations show that up to 26 % of the normally incident light couples to the transversely localized field of the surface plasmon. In addition, the ratio of mode current density of the surface plasmon, launched in the desired direction, to that in the opposite direction can reach about 23 times. This structure shows a 2.5-fold improvement in coupling efficiency relative to a standard slit-groove structure. Also, the transmission distance for the new nanostructure is shown to be more than 8 times greater than that of the standard nanostructure.     

Near-infrared Plasmonic Far-field Nanofocusing Effects with Elongated Depth of Focus based on Hybrid Au–Dielectric–Ag Subwavelength Structures

In this paper, we propose a new far-field nanofocusing lens with elongated depth of focus (DOF) under near-infrared (NIR) wavelength. The surface plasmons can be excited by using the hybrid metal–insulator–metal (MIM) subwavelength structure under the NIR wavelength. The constructive interference of surface plasmons launched by the subwavelength MIM structure can form a nanoscale focus that is modulated by the novel metal grating from the near field to the far field. The numerical simulations demonstrated that a nanoscale focal spot (in plane focal area 0.177λ ²) with elongated DOF (3.358λ) and long focal length (5.084λ) can be realized with reasonably designing parameters of the lens. By controlling the positions of the inner radii of each slit ring and the grating width, the focal length, focal spot, and DOF can be tuned easily. This design method, which can obtain the nanoscale focal spot and micron DOF in far field under NIR illumination, paved the road for utilizing the NIR plasmonic lens in superresolution optical microscopic imaging, optical trapping, biosensing, and complex wavefront/beam shaper.     

Resonant Broadband Field Enhancement in Cylindrical Plasmonic Structure Surrounded by Perovskite Environment

We demonstrate the optical response of metal nanoparticles and their interaction with organic-inorganic perovskite (methyl ammonia lead halide (CH₃NH₃PbI₃)) environment using discrete dipole approximation (DDA) simulation technique. Important optical properties like absorption, scattering, and electric field calculations for metal nanoparticle using different geometry have been analyzed. The metal nanoparticles embedded in the perovskite media strongly support surface plasmon resonances (SPRs). The plasmonic interaction of metal nanoparticles with perovskite matrix is a strong function of MNP’s shape, size, and surrounding environment that can manipulate the optical properties considerably. The cylindrical shape of MNPs embedded in perovskite environment supports the SPR which is highly tunable to subwavelength range of 400–800 nm. Wide range of particle sizes has been selected for Ag, Au, and Al spherical and cylindrical nanostructures surrounded by perovskite matrix for simulation. The chosen hybrid material and anisotropy of structure together make a complex function for resonance shape and width. Among all MNPs, 70-nm spherical silver nanoparticle (NP) and cylindrical Ag NP having diameter of 50 nm and length of 70 nm (aspect ratio 1.4) generate strong electric field intensity that facilitates increased photon absorption. The plasmonic perovskite interaction plays an important role to improve the absorption of photon inside the thin film perovskite environment that may be applicable to photovoltaics and photonics.

     

Ultra-Subwavelength and Low Loss in V-Shaped Hybrid Plasmonic Waveguide

A new kind of hybrid plasmonic waveguide is proposed, and its propagation properties are investigated using the finite-element method. This waveguide consists of a V-shaped silver nanowire embedded in a low-index dielectric cladding above a semiconductor substrate, which can confine light in the subwavelength region with a long propagation length. The field distribution, the mode effective index, the propagation length, and the normalized mode area of the hybrid mode supported by the waveguide are investigated at the wavelength of 1550 nm, which are dependent on the geometric parameters.     

Spatial Mode Selection by the Phase Modulation of Subwavelength Plasmonic Grating

The extraordinary transmission of the subwavelength gold grating has been investigated by the rigorous coupled-wave analysis and verified by the metal–insulator–metal plasmonic waveguide method. The physical mechanisms of the extraordinary transmission are characterized as the excitation of the surface plasmon polariton modes. The subwavelength grating integrated with the distributed Bragg reflector is proposed to modulate the phase to realize spatial mode selection, which is prospected to be applied for transverse mode selection in the vertical cavity surface-emitting laser.     

Low-Frequency Surface Plasmon Polaritons Guided on a Corrugated Metal Striplines with Subwavelength Periodical Inward Slits

A new type of stripline-based microwave transmission, which has relatively lower crosstalk compared with the conventional striplines, is proposed. The structure is formed by corrugated inward slit that is subwavelength scale on the edge of the stripline via the photolithography techniques. Numerical simulation is used to analyze the transmission and dispersion properties of this new stripline structure, and the results are experimentally verified in the frequency range from 200 MHz to 8 GHz. We found that spoof surface plasmon polaritons are supported on the new stripline structure whose electromagnetic fields are highly localized near the stripline, and hence the coupling is suppressed between the present type of stripline and the conventional stripline. For a structured stripline and a conventional stripline which are parallelly placed and separated by a distance of the stripline width, the crosstalk between them ranges from −17.13 to −64.89 dB, which is much lower than the crosstalk between two coupled conventional striplines. As this new type of stripline has such an important advantage, it would be applicable to high-density microwave circuits or high-speed circuits.     

Discrete Optical Field Manipulation by Ag-Al Bilayer Gratings for Broadband Absorption Enhancement in Thin-Film Solar Cells

Plasmonic gratings have been widely used for light harvesting in thin-film solar cells (TFSCs). However, the detrimental parasitic metal absorption loss limits the actual light absorption in the active layer and reduces the power conversion efficiency. In this paper, it is found that the localized surface plasmon resonance (LSPR) used to increase long-wavelength light absorption has significant field concentration around the bottom corners of metal gratings, but the field distribution for the short-wavelength absorption band localizes around the top corners of gratings. Due to the differences between the spatial field distributions and the related mechanisms of metal loss, discrete optical field manipulation is proposed to suppress the ohmic loss mainly associated with LSPR and the interband transition loss associated with metal materials by using Ag-Al bilayer gratings, where Ag has a small absorption coefficient and Al has a high plasmon frequency. Fifteen to forty percent improvements of photocurrents in TFSCs with Ag-Al bilayer gratings are observed in simulation compared to the ones with single-layer metal gratings. This combined metal nanostructure scheme suppresses the loss issue of metal and extends the application potential of plasmonic light-harvesting techniques.     

Design of Plasmonic Comb-Like Filters Using Loop-Based Resonators

A subwavelength plasmonic comb-like filter is proposed by using dual symmetric slot cavities which are placed between two parallel metal–insulator–metal (MIM) structure waveguides. The structure can be considered as a resonance loop which consists of slot cavity resonators and MIM waveguide resonators. The reflective wavelength range and channel spacing are determined by the lengths of slot cavities and MIM waveguides, respectively. Three, four, and five reflective channels with high reflection are achieved in a small wavelength range. Higher channel count can be available by increasing the length or the real part of effective index of MIM waveguides. Such a device can find applications in various optical systems such as wavelength demultiplexing components.     

High Optical Transmission in a Hybrid Plasmonic-Optical Structure with a Continuous Metal Film

Metals are naturally opaque for electromagnetic (EM) waves below violet frequency due to the Coulomb screening effect. In this letter, we demonstrate high optical transparency of a seamless continuous metal film by sandwiching it in a hybrid plasmonic-optical structure. The proposed structure consists of a plasmonic array and an optical cavity, which exhibits magnetic plasmon (MP) resonance and optical Fabry-Perot (FP) resonance, respectively. An optical transparency of 84% in the near-IR regime is achieved making use of interaction between the plasmonic and optical modes. Furthermore, spectral tunability of the high transparency is demonstrated and robustness under oblique incidence is examined. This work may give insights into plasmonic-optical interactions and may be a potential candidate for transparent electrodes.     

Ferroelectric Hybrid Plasmonic Waveguide for All-Optical Logic Gate Applications

A ferroelectric hybrid plasmonic waveguide, made of a polycrystal lithium niobate waveguide separated from a gold film by a silicon dioxide isolation layer, is fabricated by use of laser molecular beam epitaxy growth, electron beam evaporation, and focused ion beam etching. Strong subwavelength mode confinement and excellent long-range propagation are achieved simultaneously for the hybrid plasmonic mode. An all-optical logic OR gate is also realized based on the ferroelectric hybrid plasmonic waveguide. This may provide a way for the study of all-optical logic gates and integrated photonic circuits.     

Plasmonic Band Gap: Role of the Slit Width in 1D Metallic Grating on Higher Refractive Index Substrate

This paper reports the excitation of surface plasmon polaritons (SPPs) and associated plasmonic band gap (PBG) while using TM plane wave interacting with 1D metallic grating on higher refractive index GaP substrate. A simple method is introduced to estimate the PBG which is crucial for many plasmonic devices. The PBG is estimated by measuring the transmission spectra obtained through the plasmonic grating structures when slit width is varied while periodicity and the thickness of the gold (Au) film remained fixed. The PBG is observed for the grating devices whose slit width is less than one third of the periodicity which is caused by the presence of a higher plasmonic mode. The PBG is absent for the grating device whose slit width is slightly less than half and greater than one third of the periodicity. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Furthermore, such grating offers intermediate scattering to the incident light and the SPP as well which in turn couple more incident energy to the SPPs. Far-field modelling results also support the results obtained through experiment.

     

Multiband Metamaterial Absorber Design Based on Plasmonic Resonances for Solar Energy Harvesting

A new metamaterial absorber is designed and characterized numerically for the harvesting of solar energy. The design is composed of three layers in which the interaction among them gives rise to the plasmonic resonances. The main operation frequency range of the proposed structure is chosen to be the visible regime. However, the design is also analyzed for the infrared and ultraviolet regimes. In order to characterize the absorber, some parametric studies with respect to the dimensions of the structure are carried out. According to the results, it is found that the proposed metamaterial absorber has 98.2 % absorption capability at 445.85 THz and 99.4 % absorption capability between 624 and 658.3 THz. Moreover, the polarization dependency of the structure is examined and it is found that the design operates well as a perfect absorber with polarization independency for the studied frequency range. As a result, the proposed metamaterial absorber can be used for solar energy harvesting as it provides multiple perfect absorption bands in the visible regime.     

Effect of the Number of Zones in a One-Dimensional Plasmonic Zone Plate Lens: Simulation and Experiment

A 1D plasmonic zone plate lens (PZPL) consisting of nano-slits within a metal film introduces a phase delay distribution across the planar device surface by a modulation of the slit widths and positions to achieve light focusing. Using the finite-difference time-domain method, the number of zones is found to be a crucial factor for a well-controlled focal length, i.e. at least three zones are necessary for a PZPL exhibiting a focal length in agreement with the design. This conclusion is confirmed by confocal scanning optical microscopy on PZPLs patterned in an aluminium film. In addition, subwavelength light focusing is demonstrated both theoretically and experimentally in a PZPL. A larger PZPL, i.e. more zones, shows a higher resolution. A full full-width half-maximum of 0.37λ in the focal plane is shown theoretically in a PZPL with seven zones. A comparison between the PZPL and the plasmonic Fresnel zone plate shows that PZPLs have a higher contrast at the focus.     

Ultra-thin Semiconductor/Metal Resonant Superabsorbers

The design of thin-film semiconductor absorbers is a long-sought-after goal of crucial importance for optoelectronic devices. We propose a new strategy that achieves multi-band optical absorption in an ultra-thin semiconductor-insulator-metal nanostructure. The whole thickness of the absorber is just 60 nm, which is less than λ/12. The ultra-thin semiconductor resonators are used as the photonic coupling elements. The plasmonic metal layer with the thickness about 15 nm simultaneously acts as the transmission cancel layer and the plasmon source for resonant coupling with the optical near-field energy. The combined semiconductor resonators and the thin metal film produce strong electromagnetic field coupling and confinement effects, which mainly contribute to the efficient light trapping for the multi-band strong light absorption. The semiconductors such as Si, GaAs, and Ge are confirmed with the capability to show high light absorption via this simple hybrid metal-semiconductor resonant system. These features pave new insight on ultra-thin semiconductor absorbers and hold potential applications for optoelectronics such as nonlinear optics, hot-electron excitation and extraction, and the related devices.

     

Tailoring Absorption in Metal Gratings with Resonant Ultrathin Bridges

We present a theoretical analysis of the effects of short range surface plasmon polariton excitation on subwavelength bridges in metal gratings. We show that localized resonances in thin metal bridges placed within the slit of a free-standing silver grating dramatically modify transmission spectra and boost absorption regardless of the periodicity of the grating. Additionally, the interference of multiple localized resonances makes it possible to tailor the absorption properties of ultrathin gratings, regardless of the apertures’ geometrical size. This tunable, narrow band, enhanced–absorption mechanism triggered by resonant, short-range surface plasmon polaritons may also enhance nonlinear optical processes like harmonic generation, in view of the large third-order susceptibility of metals.     

Broadening of Plasmonic Resonance Due to Electron Collisions with Nanoparticle Boundary: а Quantum Mechanical Consideration

We present a quantum mechanical approach to calculate broadening of plasmonic resonances in metallic nanostructures due to collisions of electrons with the surface of the structure. The approach is applicable if the characteristic size of the structure is much larger than the de Broglie electron wavelength in the metal. The approach can be used in studies of plasmonic properties of both single nanoparticles and arrays of nanoparticles. Energy conservation is insured by a self-consistent solution of Maxwell's equations and our model for the photon absorption at the metal boundaries. Consequences of the model are illustrated for the case of spheroid nanoparticles, and results are in good agreement with earlier theories. In particular, we show that the boundary-collision broadening of the plasmonic resonance in spheroid nanoparticles can depend strongly on the polarization of the impinging light.     

Electro-plasmonic Modal Power Shifting in Metal/Insulator/Semiconductor Structure Tailored as a CMOS-compatible Plasmonic Waveguide

Plasmonics - In this paper, we have proposed a new npn-type design of a CMOS-compatible metal/semiconductor/insulator/metal (MSIM) plasmonic structure, to be used as a different geometry to...     

A Novel Plasmonic Zone Plate Lens Based on Nano-Slits with Refractive Index Modulation

Conventionally, plasmonic lenses introduce a phase delay distribution across their surfaces by modulating the dimensions of nanostructures within a metal film. However, there is very limited modulation of the phase delay due to the small dependence of the mode propagation constant on the structure dimensions. In this paper, a novel design of plasmonic zone plate lenses (PZPL) with both slit width and refractive index modulation is proposed to enable integrating more slits in a fixed lens aperture with the extended phase delay range and, therefore, greatly enhance the performance of the devices. More than three-time enhancement of the light intensity at the focus is achieved compared to the structure with only slit width modulation. Like a conventional immersion system, a PZPL embedded in a dielectric is found to have a further improved focusing performance, where light is focused down to a 0.44λ spot using a PZPL with an aperture of 12λ and a focal length of 6λ. Dispersive light-focusing behaviour is also analysed and the modulation of the focal length by colour has a potential application in stacked image sensors and multi-dimensional optical data storage.     

Multilayer Hybrid Plasmonic Nano Patch Antenna

This is the first report of a hybrid plasmonic nano patch antenna having metal insulator metal (HMIM) multilayer configuration. It is designed in a footprint area of 1.7 × 1.175 μm² to resonate at 1.55 μm wavelength. The proposed antenna is inset fed by an HMIM plasmonic waveguide for achieving proper impedance matching. It is observed, through electromagnetic numerical simulation, that the proposed plasmonic nano patch antenna emits a directional beam with a bandwidth, gain, and efficiency of 0.194 μm, 8.3 dB, and 96% respectively, which are significantly higher than previously reported designs. Since inset-fed antennas are suitable for developing high-gain antenna array, hence further, we examined antenna performance by designing antenna array. The proposed antenna is practically realizable and can be fabricated using standard semiconductor fabrication process. Moreover, it could be used for numerous chip scale applications such as wireless interconnects energy harvesting, photoemission, photo detection, scattering, heat transfer, spectroscopy, and optical sensing.

     

Influence of V-Shaped Metallic Subwavelength Slits with Variant Periods for Superfocusing

In this paper, we discussed the influence of a plasmonic lens with V-shaped metallic subwavelength slits and variant periods on transmission properties. In order to analyze the influence, a finite-difference time-domain numerical algorithm was adopted for computational numerical simulation of the plasmonic structures. The structures are flanked with the penetrated slits through a metal (Ag) film which is coated on a quartz substrate. Our simulation results demonstrated that different cone angles originated from the V-shaped slits generate different influences on the beam propagation. The width variation affects the intensity significantly. The cone angles formed by the V-shaped slits can change the focusing performance. These results are very encouraging for future study of the plasmonic lens-based applications.