Surface Plasmon Polariton Beam Research Articles

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.

Arbitrary orthogonal polarization-dependent directional launching of Bessel-like surface plasmon polariton beams

Nondiffracting Bessel-like SPP beams, with the unique features of effectively suppressing the diffraction of the beam, have great application prospects in the fields of on-chip interconnection circuit, optical tweezers, and micromanipulation. In practical applications, active manipulation of nondiffracting Bessel-like SPP beams is essential. Here, we proposed two kinds of nondiffracting Bessel-like SPP beam unidirectional devices controlled by arbitrarily orthogonally polarized incidence light, which can generate and manipulate zeroth-order or first-order Bessel-like SPP beams, respectively. The results show that, by changing the distance between two pairs of slit couplers with different resonance responses, the nondiffracting Bessel-like SPP beams can be directionally excited at arbitrarily polarized incidence, and the excitation direction of the nondiffracting Bessel-like SPP beams will reverse under the corresponding orthogonally polarized incidence. The proposed devices provide promising opportunities for constructing polarization-based dynamic manipulation plasmonic devices of nondiffracting SPP beams and have potential applications in on-chip interconnection circuits.

Circularly Polarized Spoof Surface Plasmon Polariton Beam Splitter Based on Transmissive Spin‐Decoupled Metasurface

Circularly polarized (CP) spoof surface plasmon polariton (SSPP) functional metadevices, especially those with spin decoupling and hybrid modes, play an important role in modern photonics applications. However, currently available SSPP functional metadevices have the defect of restricted functionalities and single‐working modes for a given polarization, as it is a great challenge to simultaneously support SSPPs with hybrid modes and different wavefronts. Herein, a general strategy is proposed for designing CP SSPP functional metadevices with spin decoupling and hybrid modes based on transmissive spin‐decoupled metasurfaces and angle‐insensitive anisotropic SSPP eigenmode plates (EMPs). The metasurface can simultaneously and independently control the resonant and geometrical phases of the CP waves, and the SSPP EMP satisfies the hybrid‐mode (both transverse magnetic [TM] and transverse electric [TE] modes) momentum matching with high angular/momentum stability of the propagating SSPPs. For verification, a CP SSPP beam splitter is designed, fabricated, and experimentally demonstrated, which can convert incident right‐handed (R) and left‐handed (L) CP plane waves to CP hybrid‐mode SSPP deflected beams and decoupled beams, respectively. The work paves the way for the realization of CP SSPP multifunctional‐integration metadevices with hybrid modes and other functionalities, which can find extensive applications in different frequency domains.

Direct observation of longitudinal aberrated wavefields

Rather than focusing on a focal spot, aberrated wavefields spread out over a region. As a wave phenomenon, optical aberrations are analyzed in terms of waves propagating in the 3D space. In this work, we report the observation of 2D longitudinal aberrated wavefields. This observation can be visualized by mapping the intensity distributions of surface plasmon polaritons (SPPs) that propagate on a metal/air interface using leakage radiation microscopy. The orientation of the SPP beam is tweaked by tilting and translating the system to mimic aberrated beams, presenting known Seidel terms: defocus, spherical, coma, and tilt aberration. This approach allows the examination of the longitudinal evolution of aberrated beams in a visual and rapid manner, in contrast to more complicated post-processing reconstructions.

Active control of surface plasmon polaritons with phase change materials

Active control of surface plasmon polaritons (SPPs) is highly desired for nanophotonics. Here we employ a phase change material Ge2Sb2Te5 (GST) to actively manipulate the propagating direction of SPPs at the telecom wavelength. By utilizing the phase transition-induced refractive index change of GST, coupled with interference effects, a nanoantenna pair containing GST is designed to realize switchable one-way launching of SPPs. Devices based on the nanoantenna pairs are proposed to manipulate SPPs, including the direction tuning of SPP beams, switchable SPP focusing, and switchable cosine–Gauss SPP beam generating. Our design can be employed in compact optical circuits and photonics integration.

Ultrafast spatiotemporal control of the femtosecond Bessel surface plasmon polariton by a chirped laser pulse

Nondiffracting Bessel surface plasmon polariton (SPP) beam, which has unique properties of non-divergence, self-healing and straight trajectory, is potential to the fields of on-chip interconnect circuits and near-field optical trapping. However, it remains a significant challenge to achieve the spatiotemporal manipulation of nondiffracting Bessel SPP pulse in nanometer spatial and femtosecond temporal scale. Here, we propose a novel method of ultrafast spatiotemporal control of Bessel SPP pulses at the nano-femtosecond spatial–temporal scale. This on-chip plasmonic device can achieve the wavelength-based manipulation of the Bessel SPP beam with a high extinction ratio. The Bessel SPP pulse that develops in the femtosecond time scale in this device is presented. Importantly, we also demonstrate a solution for ultrafast spatiotemporal control of Bessel SPP pulses on the femtosecond time scale by controlling the chirp of the incident ultrafast laser pulse. Additionally, a higher coupling efficiency of the Bessel SPP into the waveguide than that of a plane SPP is demonstrated. The sequential coupling to the dielectric waveguides with femtosecond interval of Bessel SPP pulses is also achieved. This work offers great promise in applications such as high-speed, highly integrated nanophotonic devices, on-chip interconnect circuits and ultrafast beam shaping.

Simulation of On-Chip Broadband Photon Spin Router Base on Nondiffracting Surface Plasmon Beam Launching

The development of a photonic device based on a non-diffracting surface plasmon polariton (SPP) beam can effectively improve the anti-interference ability. Furthermore, an easily adjustable on-chip routing device is highly desirable and extremely important in practical optical communication applications. However, no non-diffracting SPP-beam-based spin routing devices with high tunability in multiple degrees of freedom have been reported. In this study, we theoretically designed a simple micro-nano structure to realize a highly adjustable non-diffracting SPP-beam-based spin router using Finite-Difference Time-Domain (FDTD) simulation. The simulation results show that the structure enables spin-controlled nondiffracting SPP-beam directional launching. The launching direction of the nondiffracting SPP beam can be dynamically rotated counterclockwise or clockwise by changing the incident angle. Hence, the routing SPP beam can be coupled to different output waveguides to provide dynamic tunability. Moreover, this device shows good broadband response ability. This work may motivate the design and fabrication of future practical photon routing devices.

Topological Bloch–Zener oscillations in non-Hermitian graphene plasmonic waveguide arrays

We investigate the topological Bloch–Zener oscillations for surface plasmon polaritons (SPPs) propagating in a Su–Schrieffer–Heeger plasmonic system, which composed of graphene dimer arrays with a potential gradient. The topological trivial and non-trivial band gaps are achieved to investigate the topological effect to plasmonic Bloch oscillations. The topological transition from trivial phase to non-trivial one through the exceptional point is realized by alternating the gain and loss in the graphene waveguide arrays. Zener tunneling of the SPP beam was observed in the parity-time (PT) symmetric region, which was prohibited in the PT-symmetric broken region. The numerical calculations demonstrated reasonable agreements with theoretical tight-binding model. Furthermore, a single dynamically stable zero-energy edge state was also found in these non-Hermitian plasmonic waveguide arrays.

Investigation of a dual-hole structure-based broadband femtosecond nondiffracting SPP beam emitter by photoemission electron microscopy

Nondiffracting surface plasmon polariton (SPP) beam, which has unique self-healing and non-divergence properties, can be a good candidate in the next-generation on-chip devices and has attracted considerable attention. Here, a simple and broadband coupled femtosecond nondiffracting SPP beam emitter based on a dual-hole structure has been demonstrated and characterized by photoemission electron microscopy (PEEM). The PEEM experiments show that, compared with the usual one-color PEEM, the two-color PEEM scheme offers a clear image of the nondiffracting SPP by effectively reducing the influence of the light-SPP interference field. As a result, the parameters of the nondiffracting SPP beam, such as the divergence angle, waist width, and propagation distance, are experimentally determined. The PEEM images of the nondiffracting SPP are well reproduced by the finite-difference time-domain (FDTD) method. This work plays a vital role in the further study of, e.g., high spatial and temporal characterization of the dynamic evolution of nondiffracting SPP beam.

Efficient and wavelength-dependent directional launching of a nondiffracting surface plasmon polariton beam device

The high-efficiency excitation and dynamic manipulation of the nondiffracting surface plasmon polariton (SPP) beam are important prerequisites for practical applications including the next-generation on-chip devices, near field optical trapping, and micromanipulation. Here we proposed two kinds of high-efficiency coupling and wavelength-dependent nondiffracting SPP beam unidirectional devices, which can generate and manipulate Bessel-like SPP beam or SPP Bottle beam, respectively. Different from the conventional groove or ridge structure that equally split SPP power to propagate from the boundary to both sides, the compact coupling element directs all of the SPP power of the matched wavelength to one side, resulting in higher collecting efficiency. Besides, as the wavelength of the incident light is changed, the generated Bessel-like SPP beam or SPP Bottle beam can be directionally excited on one side of the device. The design of the proposed devices provides a new means for constructing plasmonic devices with wavelength-dependent dynamic manipulation of nondiffracting SPP beams and has potential applications in on-chip interconnect circuits and near-field optical trapping.

Multi-Directional Plasmonic Splitter and Polarization Analyzer Based on the Catenary Metasurface

Owing to the unique properties of strongly confined and enhanced electric fields, surface plasmon polaritons (SPPs) provide a new platform for the realization of ultracompact plasmonic circuits. However, there are challenges in coupling light into SPPs efficiently and subsequently routing SPPs. Here, we propose a multi-directional SPP splitter and polarization analyzer based on the catenary metasurface. Based on the abundant electromagnetic modes and geometric phase modulation principle of catenary structure, the device has realized high-efficiency beam splitting for four different polarization states (x-polarization, y-polarization, LCP, and RCP). The central wavelength of the device is 632 nm and the operation bandwidth can reach 70 nm (585–655 nm). Based on the phenomenon of SPP beam splitting, we present a prototype of a polarization analyzer, which can detect the polarization state of incident light by adding photodetector with light intensity logic threshold in four directions. Moreover, by combining this device with dynamic polarization modulation techniques, it is possible to be served as a router or switch in integrated photonic circuits.

Spoof surface plasmon polariton beam splitters integrated with broadband rejection filtering function

In this paper, a new kind of spoof surface plasmon polariton (SSPP) beam splitter integrated with band-rejection filtering functions is presented. Firstly, the mechanism of single-band rejection phenomena of the SSPP transmission lines (TLs) with and without T-shaped decorations are revealed through dispersion analyses. Based on the single-band rejection filter, multi-band rejection filters are further designed by introducing different intervals between the symmetric T-shaped decorations. Furthermore, we construct a compact Y-shaped beam splitter integrated with a broadband band-rejection filtering function using the SSPP TLs, which consists of an SSPP TL with rectangular grooves and two filtering branch SSPP TLs. Multiple band-rejection integrated beam splitters can also be realized by incorporating different intervals between the T-shaped decorations. The integration of the SSPP beam splitter and band-rejection filter offers compact areas, lower insertion loss and controllable passband features. It is strongly believed that that the proposed idea will raise promising possibilities in the integration of multiple microwave functions in the same component, e.g. filtering antennas, filtering switches, multifunctional radiofrequency (RF) passive and active components capable of performing several RF analog signal-processing functions in the same circuit volume, and so on.

Broadband terahertz surface plasmon-polaritons beam splitter

In this paper, we propose a novel design of broadband terahertz (THz) surface plasmon-polaritons (SPPs) beam splitter, which obtains 50%-50% energy splitting on input and output SPPs waveguides. The conventional THz SPPs beam splitter is a component of the two parallel THz SPPs waveguides coupler, which can only operate at the single frequency. To make the device more universal, we employ the quantum engineering technique, called fractional stimulated Raman adiabatic passage (f-STIRAP) to design the 50%-50% beam splitter with good performance on broadband.

Non-Reciprocal, Robust Surface Plasmon Polaritons on Gyrotropic Interfaces

Unidirectional surface plasmon polaritons (SPPs) at the interface between a gyrotropic medium and a simple medium are studied in a newly-recognized frequency regime wherein the SPPs form narrow, beam-like patterns due to hyperbolic dispersion. The SPP beams are steerable by controlling parameters such as the cyclotron frequency (external bias) or the frequency of operation. The bulk band structure along different propagation directions is examined to ascertain a common bandgap, valid for all propagation directions, which the SPPs cross. The case of a finite-thickness gyrotropic slab is also considered, for which we present the Green function and examine the thickness and loss level required to maintain a unidirectional SPP.

In-plane interferometry of terahertz surface plasmon polaritons

The paper is devoted to the development of interferometric schemes for determining the complex refractive index κ = κ′+i·κ″ κ of surface plasmon-polaritons (SPPs) of the terahertz (THz) spectral range. As the value of κ depends on the dielectric constant εm of the metal surface guiding the SPPs it can be used for determining ϵm in the far infrared what other optical methods fail to do due to high reflectivity of metals. We discuss two types of THz SPP interferometers in which the interference pattern is formed as a result of the interaction of SPP beams themselves rather than bulk waves produced by these beams. The first type of interferometers are static devices that enable one to investigate fast processes on the metal surface, while the second type are dynamic ones that make it possible to realize Fourier spectroscopy of the metal surface and its transition layer at THz frequencies. Devices of the both types produce interferograms enabling one to determine the real and the imaginary parts of κ. The results of experiments on the interaction of THz SPPs with flat mirrors and beam – splitting plates, the key elements of the THz SPP interferometers, are presented.

Generation of Flat Top Surface Plasmon Polariton Beams by Near Field Holography.

Controlling the shape and trajectory of the surface plasmon polariton (SPP) beams is the key to all SPP-based applications. In this paper, a novel plasmonic device that can generate in-plane flat top SPP beams is designed by near field holography. The relationship between the transverse profile intensity of the generated flat top SPP beams and the structural parameters of the designed device is analyzed. The results of this paper can provide the possibility for further practical application utilizing flat top SPP beams.

Photonic Hook Plasmons: A New Curved Surface Wave

AbstractToday the surface plasmon‐polariton (SPP) waves propagating along the curve trajectory are the only plasmonic beams of the Airy family. Herein, a new class of curved surface plasmon wave, the photonic hook plasmon (PHP), is introduced. The PHP is created using the in‐plane focusing of the SPP wave through an asymmetric dielectric particle. This is fundamentally simpler than the generation of the SPP Airy‐family beams. The PHP propagates along a wavelength‐scaled curved trajectory with radius less than the SPP wavelength, which represents the smallest radius of curvature ever recorded for an SPP beam, and can exist despite the strong energy dissipation at metal surface.

Nonlocal and Nonlinear Surface Plasmon Polaritons and Optical Spatial Solitons Induced by the Thermocapillary Effect.

We study the propagation of surface plasmon polaritons (SPPs) on a metal surface which hosts a thin film of a liquid dielectric. The Ohmic losses that are inherently present due to the coupling of SPPs to conductors' electron plasma, induce temperature gradients and fluid deformation driven by the thermocapillary effect, which lead to a nonlinear and nonlocal change of the effective dielectric constant. The latter extends beyond the regions of highest optical intensity and constitutes a novel thermally self-induced mechanism that affects the propagation of the SPPs. We derive the nonlinear and nonlocal Schrödinger equation that describes propagation of low intensity SPP beams, and show analytically and numerically that it supports a novel optical spatial soliton excitation.

Dielectric meta-walls for surface plasmon focusing and Bessel beam generation

Freely tailoring the wavefronts of surface plasmon polaritons (SPPs) is a central goal in plasmonics, but the conventional approaches exhibit low efficiencies and/or require bulky devices. Here, we propose to utilize ultrathin dielectric meta-walls placed vertically on a plasmonic metal to efficiently reshape the wavefront of a launched SPP beam. Based on such a strategy, we experimentally demonstrate two effects in the microwave regime, namely focusing and Bessel beam generations of spoof SPPs. Near-field scanning measurements are in excellent agreement with full wave simulations. This work can stimulate research in many applications related to SPP manipulations, such as enhanced nonlinear effect, nano-particle trapping, and so on.

Dynamic tailoring of surface plasmon polaritons through incident angle modulation

Dynamic tailoring of the propagating surface plasmon polaritons (SPPs) through incident angle modulation is proposed and numerically demonstrated. The generation and tailoring mechanism of the SPPs are discussed. The relationship formula between the incident angle and the generated SPP wave vector direction is theoretically derived. The correctness of the formula is verified with three different approaches using finite difference time domain method. Using this formula, the generated SPP wave vector direction can be precisely modulated by changing the incident angle. The precise modulation results of two dimensional Bessel-like SPP beam and SPP bottle beam array are given. The results can deepen the understanding of the generation and modulation mechanism of the SPPs.