Surface Plasmon Polariton Waves Research Articles

Novel Highly Efficient Buried Gratings for Selective Coupling of SPP Waves onto Single Interfaces

Diffraction gratings have always been used to effectively couple optical radiation within integrated waveguides. This is also valid for plasmonic structures that support Surface Plasmon Polariton (SPP) waves. Traditional gratings usually excite SPP waves at the interface where they are located or, for thin metal nanostrips, at both interfaces. But reducing the thickness of the metal layer in the presence of a grating has the handicap of increasing the tunnelling of light towards the substrate, which means higher losses and reduced coupling efficiency. In this paper, we design and optimize novel gratings buried within the metallic thin films for selective coupling of SPP waves onto individual interfaces. Compared with traditional superficial gratings, the novel buried ones demonstrate higher efficiency and much lower residual tunnelling of light through the coupling structures.

Ultrathin tunable UWB metasurface absorber design by exciting plasmonic modes in bilayer graphene stack

This work presents a graphene-based ultra-wideband (UWB) tunable metasurface absorber (MSA) consisting of top patterned graphene (Gpat) and bottom continuous graphene (Gcont) separated by a 2 μm thick silicon dioxide (SiO2) substrate. An absorptivity (Af) ≥ 90 % from 0.1 to 14 THz (fractional bandwidth = 197.2 %) has been achieved in three steps: (i) Fabry-Perot cavity mode has been generated near 0.1 THz using bilayer graphene stack, (ii) multiple plasmonic modes have been excited by engraving resonant slots on Gpat and (iii) plasmonic coupling strength has been enhanced between Gpat and Gcont by adjusting SiO2 substrate's thickness. The excited plasmonic modes show high absorption due to the generation of localized surface plasmon polariton (LSPP) waves. The fourfold symmetry in design nullifies the effect of the polarization angle (ϕ). Interestingly, the orthogonal modes' excitation helps to achieve similar Af response under both transverse electric and transverse magnetic polarizations for incidence angle (θ) up to 60°. Further, an effective DC biasing mechanism has been devised to tune the chemical potential (μc) of the interconnected Gcont, which ensures common DC bias between unit cells. A DC voltage from 0 to 10.2 V can vary μc (Bottom) from 0 to 1 eV to provide frequency tunability.

Vertical coupling to photonic crystal waveguide using chiral plasmonic lenses

Manipulating surface plasmon polariton waves for the development of micro-nano devices has been widely studied in recent years. Two-dimensional artificial photonic crystals have bandstructure characteristics like semiconductors. However, the requirement for light to be incident along the structural periodic direction poses a challenge in coupling light into the photonic crystal, thereby impeding its integrations and applications. In this work, we proposed coupling vertically incident left-circularly polarized light into a photonic crystal waveguide using a chiral plasmonic lens. Linearly-polarized light can also generate surface plasmon polariton waves and couple them into photonic crystal waveguides, but the intensity is lower. In contrast, right-circularly polarized light propagates in the opposite direction and exhibits minimal propagation into the photonic crystal waveguide. The results indicate that the proposed structure can operate broadband within the wavelength range of 620–670 nm. This method provides a simple and easily integrated coupling method for photonic crystal devices.

Multi-Mode Long-Wavelength GaAs/AlGaAs Quantum Well Infrared Photodetectors for Circular Polarization Detection

We present an integrated device combining a double L-shaped chiral metasurface with long-wavelength GaAs/AlGaAs quantum well infrared photodetectors (QWIPs), achieving a circular polarized extinction ratio (CPER) as high as 45 in the long-wavelength infrared range of 7–9 μm. The unit of the chiral metasurface array consists of two structurally identical L-shaped gold structures with central symmetry. The CPER of the double L-shaped QWIPs is 14 times higher than that of a single L-shaped QWIP. The device operates in three modes within the detection band: the microcavity mode, the surface plasmon polariton (SPP) mode, and the hybrid mode. The double L-shaped chiral structure selects and reflects a small portion of left-handed circularly polarized light (LCP), while the majority enters the device and excites SPP modes with the bottom gold grating layer, leading to an absorption enhancement. In contrast, right-handed circularly polarized light (RCP) is mostly reflected with limited excitation of SPP waves. QWIPs exhibit a peak absorption of 0.8 and a coupling efficiency of 2700% in the active region of the quantum well due to the combined effects of the microcavity and SPP modes, in which the SPP mode plays a dominant role. The proposed device maintains high circular polarization discrimination capability under large incident angles and can be applied in spectral imaging.

Electrically tunable virtual image Luneburg lens using graphene.

Virtual image lenses play essential roles in various optical devices and applications, including vision correction, photography, and scientific instruments. Here, we introduce an approach for creating virtual image Luneburg lenses (LL) on graphene. Remarkably, the graphene plasmonic lens (GPL) exhibits electrically tunable virtual focusing capabilities. The design principle of the tunability is based on the nonlinear relationship between surface plasmon polariton (SPP) wave mode index and chemical potential of graphene. By controlling the gate voltage of graphene, we can achieve continuous tuning of virtual focus. A ray-tracing technique is employed to determine the required gate voltages for various virtual focal lengths. The proposed GPL facilitates adjustable virtual focusing, promising advancements in highly adaptive and transformative nanophotonic devices.

Atom localization by damping spectrum of surface plasmon polariton waves

The damping spectrum of surface plasmon polaritons (SPPs) is significantly enhanced for atom localization in regions beneath λ/20×λ/20. By changing the phases and directions of control fields, two and single localization peaks are observed in the SPP damping spectrum. Circular and elliptical localization peaks are predominantly controlled in the λ2 areal region of −π≤kx≤π and −π≤ky≤π. Additionally, craters and sharp peaks resembling localization can be modified and controlled within the two-dimensional space of λ2 with a resolution smaller than λ2/400. These modifications may be advantageous to the trapping of neutral atoms, nanolithography, and plasmonics technology.

Enhanced THz Circular-Polarization Detection in Miniaturized Chips with Chiral Antennas

Recent advancements in terahertz (THz) wave technology have highlighted the criticality of circular-polarization detection, fostering the development of more compact, efficient on-chip THz circular-polarization detectors. In response to this technological imperative, we presented a chiral-antenna-integrated GaAs/AlGaAs quantum well (QW) THz detector. The chiral antenna selectively couples the incident light of a specific circular-polarization state into a surface-plasmon polariton wave that enhances the absorptance of the QWs by a factor of 12 relative to a standard 45° faceted device, and reflects a significant amount of the incident light of the orthogonal circular-polarization state. The circular-polarization selectivity is further enhanced by the QWs with a strong intrinsic anisotropy, resulting in a circular-polarization extinction ratio (CPER) as high as 26 at 6.52 THz. In addition, the operation band of the device can be adjusted by tuning the structural parameters of the chiral structure. Moreover, the device preserves a high performance for oblique incidence within a range of ±5°, and the device architecture is compatible with a focal plane array. This report communicates a promising approach for the development of miniaturized on-chip THz circular-polarization detectors.

Coherent Control of Angular Interrogation of Sensitivity of the Surface Plasmon Polariton Waves at the Interface of Metal and Dielectric Medium

Coherent Control of Angular Interrogation of Sensitivity of the Surface Plasmon Polariton Waves at the Interface of Metal and Dielectric Medium

The demultiplexing and broadband focusing on a gold nanoarray of in-plane propagating surface plasmons

An analytical approach is presented to comprehensively describe a meticulously designed gold nanoarray situated on a silicon waveguide(length (L) and width(W) are 12 µm and 3 µm). The incorporation of a glass substrate with an L and W of 12 µm is proposed as a means to achieve broadband focusing. At the same time, a demultiplexing element utilizing surface plasmon polariton (SPP) waves is introduced, employing a novel phase modulation method that uses in-plane diffraction processes. The analytical calculations are focused on the sublattice arrays, which are currently under investigation to enhance the performance of demultiplexers and confocal SPP beams. The suggested method exhibits various functionalities that make it a promising approach. Its planar construction ensures a streamlined and integrated design, and the absence of SPP coupling processes adds to its practicality for implementation in photonic integrations. By leveraging the unique properties of the gold nanoarray on the silicon waveguide, combined with the glass substrate for broadband focusing and the novel phase modulation method for demultiplexing SPP waves, this approach holds great potential for advancing the field of photonics.

Manipulation of surface plasmon polariton fields excitation at quantum-size slit in a dielectric and graphene interface

The dispersion relation of surface plasmon polaritons is controlled and modified at the interface of atomic and Graphene medium. The beats patterns and moire fringes spacing are modified from vectorial character of the waves and parameters of the driving fields coupled with system energy levels. The beats patterns are investigated with the influence of control fields and its parameters. It is reported that the phase shifts Φ1,2 are the strong functions of the probe detuning and distance x along the interface. The light and surface plasmon polariton waves polarization is a strong oscillation function of both the position and time variation as well as driving fields parameters. The maximum value of phase sensitivity SΦ1 is 600 and SΦ2 is 400 radian per unit change of refractive index of the atomic medium at x=20λ. This work is particularly useful for surface plasmon resonance sensors technology.

Surface plasmon resonance based sensor using one-dimensional photonic crystal

A surface plasmon resonance (SPR) based sensor is presented for the optical sensing that employs one-dimensional photonic crystal (1DPC). An interface of a metal and 1DPC is utilized to excite the surface plasmon-polariton (SPP) waves using prism-coupling. The 1DPC is made up of a bilayer structure of two different dielectric materials. The excited SPP waves are utilized to sense a small change in the refractive index of the dielectric material. A very simple and compact design is proposed for the optical sensing of the dielectric material. A p-polarized plane wave is incident from the metal side and the change in the refractive index of the dielectric material is observed by computing the corresponding change in the incidence angle of excitation of the SPP wave. Absorptance peaks are shifting with a small change in the refractive index of the dielectric materials. It is observed that by changing the refractive index of the prism sensitivity changes with an inverse relation. The power density of the proposed sensor is limited to the metal and 1DPC interface which is the manifestation of the excitation of the SPP wave at that interface. Better results of sensitivity are achieved using this simple design of metal and 1DPC.

Coherent manipulation of intensity interrogation of sensitivity of the surface plasmon polariton waves at the dielectric and silver metal interface

AbstractIn this manuscript, Intensity interrogation of sensitivity of the surface plasmon polariton waves (SPPs) is coherently manipulated, at the interface of four‐level dielectric medium and silver metal using prism geometry. Sensitivity of SPPs with respect to refractive index is written as . A useful control in sensitivity is reported with probe and control fields detuning, Rabi frequency and decay rate. Sensitivity is a function of probe field detuning and control field Rabi frequency. The maximum sensitivity is reported to with probe field detuning and control field Rabi frequency, while minimum sensitivity is investigated to with control field phase and control field Rabi frequency. The sensitivity in this manuscript shows useful application in biosensor and photovoltaic devices.

Self-assembled gold nanoribbons via surface plasmon polaritons: The role of femtosecond laser

Plasmonic nanostructures have emerged as a critical component in broad fields ranging from optical modulation to biosensing and energy harvesting. Here, an ultrathin titanium (Ti) film (8 nm) is introduced between the gold (Au) film and fused silica (SiO2) substrate to facilitate energy deposition of the surface plasmon polariton (SPP) waves excited at the Ti/SiO2 interface under 1030 nm fs laser irradiation. The femtosecond laser-SPPs patterning results in the formation of Au nanoribbons with a width of about 270 nm and a spatial period of about 700 nm. Notably, centimeter-scale, self-assembled nanoribbons of high uniformity are achieved within several minutes. The localized surface plasmon resonance (LSPR) induced absorption peak is measured at the near-infrared band, confirming the high quality of the fabricated plasmonic nanostructures. Our findings suggest that the femtosecond laser-SPPs patterning technique represents a promising approach for the rapid and cost-effective production of large-scale plasmonic nanostructures.

Manipulation of sensitivity of the surface plasmon polariton waves at the interface of high magneto-optical medium and silver metal using angular interrogation

In this manuscript, sensitivity of the surface plasmon polariton waves (SPPs) using angular interrogation is coherently manipulated at the interface of four level high magneto-optical medium and silver metal using prism geometry. The control and probe fields detuning, Rabi frequency and decay rate manipulated significantly the angular interrogation of sensitivity of the surface plasmon polariton waves. The permittivity ϵd and permeability μd of the high magneto-optical medium play an important role in the manipulation of the sensitivity. The sensitivity is a function of control field detuning. The maximum sensitivity is reported to 800 deg/RIU with control field detuning. The minimum sensitivity is investigated to 6 deg/RIU with probe field detuning and Rabi frequency of control field. The reported results have useful applications in data storage and chemical sensing technologies.

Ultrafast Dynamics of Extraordinary Optical Transmission through Two-Slit Plasmonic Antenna.

We have theoretically investigated the spatial-temporal dynamics of extraordinary optical transmission (EOT) through a two-slit plasmonic antenna under femtosecond laser dual-beam irradiation. The dynamic interference of the crossed femtosecond laser dual-beam with the transiently excited surface plasmon polariton waves are proposed to characterize the particular spatial-temporal evolutions of EOT. It is revealed that the dynamic EOT can be flexibly switched with tunable symmetry through the respective slit of a two-slit plasmonic antenna by manipulating the phase correlation of the crossed femtosecond laser dual-beam. This is explained as tunable interference dynamics by phase control of surface plasmon polariton waves, allowing the dynamic modulation of EOT at optimized oblique incidences of dual-beams. Furthermore, we have obtained the unobserved traits of symmetry-broken transient spectra of EOT from the respective up- and down-slit of the antenna under crossed femtosecond laser dual-beam irradiation. This study can provide fundamental insights into the ultrafast dynamics of EOT in two-slit plasmonic antennas, which can be helpful to advance a wide range of applications, such as ultrafast plasmonic switch, ultrahigh resolution imaging, the transient amplification of non-linear effects, etc.

Sensitivity of the Surface Plasmon Polariton Waves at the Interface of Metal and Dielectric Medium Using Doppler Broadening Effect

Sensitivity of the Surface Plasmon Polariton Waves at the Interface of Metal and Dielectric Medium Using Doppler Broadening Effect

Ultra-broadband interconnection between two SPP nanostrips by a photorefractive soliton waveguide.

We propose a very efficient approach to interconnect together two metallic nanostrips supporting the propagation of surface plasmon polariton (SPP) waves by fabricating a photorefractive soliton guide. By designing a multilayer geometry for plasmon systems, it is possible to control the diffraction of light at the end of the metallic nanostrip, reducing its angular dispersion and directing it towards the second nanostrip. Between the two, a photorefractive crystal allows the self-confinement of light, creating a waveguide that can be used both by the light that wrote it and by other wavelengths sent as signals. These signals can be recoupled in the form of SPP waves in the second nanostrip with an efficiency of about 40% for a broad band of wavelengths.

Scattering Amplitude of Surface Plasmon Polariton Excited by a Finite Grating.

Unusual optical properties of laser-ablated metal surfaces arise from the excitation of local plasmon resonances in nano- and microstructures produced by laser-processing and from the mutual interaction of those structures through surface plasmon polariton (SPP) waves. This interaction provides a synergistic effect, which can make the optical properties of the composite nanostructure drastically different from the properties of its elements. At the same time, the prediction and analysis of these properties are hampered by the complexity of the analytical solution to the problem of SPP excitation by surface objects of arbitrary configuration. Such a problem can be reduced to a simpler one if one considers the geometry of a structured surface as a superposition of harmonic Fourier components. Therefore, the analytical solution to the problem of surface plasmon polariton excitation through the scattering of light by a sinusoidally perturbed plasmonic metal/vacuum boundary becomes very important. In this work, we show that this problem can be solved using a well-known method for calculating guided-mode amplitudes in the presence of current sources, which is used widely in the waveguide theory. The calculations are carried out for the simplest 2D cases of (1) a sinusoidal current of finite length and (2) a finite-length sinusoidal corrugation on a plasmonic metal surface illuminated by a normally incident plane wave. The analytical solution is compared with the results of numerical simulations. It is shown that, in the first case, the analytical and numerical solutions agree almost perfectly. In the second case, the analytical solution correctly predicts the optimum height of the corrugation xopt, providing the maximum SPP excitation efficiency. At the same time, the analytical and numerical values of the SPP amplitude agree very well when the corrugation height x turns out to be x≪xopt or x≫xopt (at least up to 3xopt); at x=xopt, the mismatch of those does not exceed 25%. The limitations of the analytical model leading to such a mismatch are discussed. We believe that the presented approach is useful for modeling various phenomena associated with SPP excitation.

The effect of nanoelectrodes number and length on enhancing the THz photomixer performance

Abstract: Despite the distinct features of the continuous wave (CW) Terahertz (THz) emitter using photomixing technique, it suffers from the relatively low radiation output power. Therefore, one of effective ways to improve the photomixer emitter performance was using nanodimensions electrodes inside the optical active region of the device. Due to the nanodimension sizes and good electrical conductivity of silver nanowires (Ag-NWs), they have been exploited as THz emitter electrodes. The excited surface plasmon polariton waves (SPPs) on the surface of nanowire enhances the incident excitation signal. Therefore, the photomixer based Ag-NW compared to conventional one significantly exhibits higher THz output signal. In this work, the effect of Ag-NWs dimensions and number on the incident optical field is investigated by utilizing the Computer Simulation Technology (CST) Studio Suite. The simulation results show that increasing Ag-NWs length to SPP propagation length ratio plays a significant role on the incident field increment due to its effect on reducing the SPP propagation losses. The increment of Ag-NWs number and length in the nanoelectrodes based photomixer can contribute to increase the electric field in the active region by 1.5 times at the longer excitation wavelength (850 nm). As a result of this increment, the THz output power and the conversion efficiency are expected to be enhanced by a factor of five

The plasmon–polariton scattering by random-impedance surface defects: The interplay between localization and outflow

We study the scattering of TM-polarized surface plasmon-polariton (SPP) by the finite section of flat metal–vacuum interface with a random impedance. We analyze the solution to the integral equation that connect the scattered field and the incident plasmon–polariton, and is valid for any strength of the scattering and dissipative characteristics of the conducting half-space. We show that the norm of the intermode scattering operator as a measure of scattering strength is not only determined by the parameters of the random impedance (the variance, correlation radius, the length of the heterogeneous section of the interface), but also crucially depends on the metal conductivity. For a small norm of the integral operator, the incident surface plasmon polariton radiates effectively into vacuum, resulting in excitation of quasi-isotropic Norton-type waves above the conducting surface. The intensity of the leaking field is expressed in terms of the pair correlation function of the impedance, whose dependence on wave numbers of incident and scattered waves demonstrates the possibility to observe a phenomenon similar to Wood’s anomalies of wave scattering by periodic gratings. Under strong scattering regime, the radiation into the upper half-space is highly suppressed and the SPP wave is mainly backscattered from the heterogeneous surface segment. For the lossless conducting half-space, the surface plasmon–polariton becomes unstable for arbitrarily small fluctuations of the conductor polarizability. The mirroring should also take place at small norm of the scattering operator, yet in this case it is related to Anderson’s localization of the SPP within the disordered section.