Plasmonic Beam Research Articles

Generation of ultra-wideband achromatic Airy plasmons on a graphene surface.

Tunable ultra-wideband achromatic plasmonic Airy beams are demonstrated on graphene surfaces. Surface plasmonic polaritons are excited using diffractive gratings. The phase and amplitude of plasmonic waves on the graphene surface are determined by the relative position between the grating arrays and the duty ratio of the grating unit cell, respectively. The transverse acceleration and nondiffraction properties of plasmonic waves are observed. The achromatic Airy plasmons with identical acceleration trajectory at different excited frequencies can be achieved by tuning dynamically the Fermi energy of graphene without reoptimizing the grating structures. The proposed devices may find applications in photonics integrations and surface optical manipulation.

Creation of multiple on-axis foci and ultra-long focal depth for SPPs.

We present the design of a plasmonic lens (PL) which is composed of pixelated nano-grooves on a gold film for the coupling and focusing of surface plasmon polaritons (SPPs) into multiple focal spots on the optical axis. The pixelated grooves are arranged along the y-axis and the x-position of each groove is optimized by the simulated annealing algorithm. PLs that implement two and three on-axis foci are presented and the designed structures have been validated with FDTD simulations. We also successfully constructed a long-focal-depth PL with a longitudinal FWHM of the focus that reached 25 plasmonic wavelengths, while its transverse field profile is maintained over 15 µm distance. The presented design method constitutes a new basis for plasmonic beam engineering, and the proposed particular SPP focal fields have potential applications in multiple imaging, particle manipulating, and plasmonic on-chip signal transmission.

Indefinite Plasmonic Beam Engineering by In-plane Holography.

Recent advances in controlling the optical phase at the sub-wavelength scale by meta-structures offer unprecedented possibilities in the beam engineering, holograms, and even invisible cloaks. In despite of developments of plasmonic beam engineering for definite beams, here, we proposed a new holographic strategy by in-plane diffraction process to access indefinite plasmonic beams, where a counterintuitive oscillating beam was achieved at a free metal surface that is against the common recognition of light traveling. Beyond the conventional hologram, our approach emphasizes on the phase correlation on the target, and casts an in-depth insight into the beam formation as a kind of long depth-of-field object. Moreover, in contrast to previous plasmonic holography with space light as references, our approach is totally fulfilled in a planar dimension that offers a thoroughly compact manipulation of the plasmonic near-field and suggests new possibilities in nanophotonic designs.

Plasmonic Airy Beam Generation by Both Phase and Amplitude Modulation with Metasurfaces

The Airy beam represent the only possible nondiffracting wave packets in 1D planar systems with curved trajectory, which has attracted considerable research interest due to its nondiffracting, self‐healing properties, and unique self‐bending behavior in the absence of any external potential. Because of the complexity of the Airy function and generation structure, an Airy beam with both phase and amplitude modulation is hard to realize. Here, a simplified metasurface composed of orthogonal nanorods is proposed, which can generate plasmonic Airy beams with both phase and amplitude modulation. By changing the configuration of the nanorods, the phase and amplitude can be simultaneously modulated. The bending degree of the generated Airy beam can be easily controlled by changing the number of nanorods. The proposed controllable Airy beam with both phase and amplitude modulation overcomes certain limitations of the customary Airy beam and can aid in the development of more accurate applications of the Airy beam in microfields.

Single-plasmon interferences

Surface plasmon polaritons are electromagnetic waves coupled to collective electron oscillations propagating along metal-dielectric interfaces, exhibiting a bosonic character. Recent experiments involving surface plasmons guided by wires or stripes allowed the reproduction of quantum optics effects, such as antibunching with a single surface plasmon state, coalescence with a two-plasmon state, conservation of squeezing, or entanglement through plasmonic channels. We report the first direct demonstration of the wave-particle duality for a single surface plasmon freely propagating along a planar metal-air interface. We develop a platform that enables two complementary experiments, one revealing the particle behavior of the single-plasmon state through antibunching, and the other one where the interferences prove its wave nature. This result opens up new ways to exploit quantum conversion effects between different bosonic species as shown here with photons and polaritons.

Curved Surface Plasmon Polariton Excitation With Shaped Beam by Fifth-Power Phase Mask

We experimentally demonstrate a novel and simple method for the excitation of a curved surface plasmon polariton on a silver nanofilm. We generated an Airy-like shaped beam in the Fourier plane by using a fifth-power phase mask imposed on a spatial light modulator to excite surface plasmon polariton on the silver nanofilm consisting of silver nanoparticles. The intensity distribution of the surface plasmon polariton trajectories was recorded by the leakage radiation microscope, which indicates that a plasmonic polynomial beam is produced on the silver nanofilm. This method provides relatively commercial and dynamic manipulation of a curved surface plasmon polariton on a noble metallic nanofilm.

Beam Collimation Using an Anisotropic Metamaterial Slab Without Any Nanometer-Sized Aperture

Plasmonic beam collimation effect has been thoroughly investigated based on the well-known nanometer-scale bull’s eye structure formed by complex and high-cost fabrication processes. In this work, we report our effort for attaining beam collimation using an anisotropic metamaterial (AMM) slab that consists of a stack of alternating metal/dielectric layers and an integrated top metal grating. The results show that AMM slab allows creating the beam collimation effect similar to that of the bull’s eye structure, an enabling technology for practical application due to its simple architecture and cost benefits. The excitation of surface plasmons at the AMM/air interface is derived. The structure of the AMM slab and its impact on beaming performance were analyzed using the effective medium theory and finite element method.

Boundary effects in finite size plasmonic crystals: focusing and routing of plasmonic beams for optical communications

Plasmonic crystals, which consist of periodic arrangements of surface features at a metal–dielectric interface, allow the manipulation of optical information in the form of surface plasmon polaritons. Here we investigate the excitation and propagation of plasmonic beams in and around finite size plasmonic crystals at telecom wavelengths, highlighting the effects of the crystal boundary shape and illumination conditions. Significant differences in broad plasmonic beam generation by crystals of different shapes are demonstrated, while for narrow beams, the propagation from a crystal onto the smooth metal film is less sensitive to the crystal boundary shape. We show that by controlling the boundary shape, the size and the excitation beam parameters, directional control of propagating plasmonic modes and their behaviour such as angular beam splitting, focusing power and beam width can be efficiently achieved. This provides a promising route for robust and alignment-independent integration of plasmonic crystals with optical communication components.

Propagation of grating-coupled surface plasmon polaritons and cosine–Gauss beam generation

When a surface plasmon polariton (SPP) is excited through a metallic grating in the conical mounting configuration, it propagates along a direction nonparallel to the grating Bragg vector. We will derive, under any possible coupling condition, the propagation direction as a function of experimental parameters, with particular attention to its relation with the azimuthal rotation angle. We will identify the conditions to achieve the maximum angular deflection with respect to the grating vector, also in relation to the grating geometry. Moreover, we will investigate the special configuration in which two SPP modes propagating toward different directions are simultaneously excited by the same light beam, suggesting to exploit this configuration to generate nondiffractive plasmonic beams (cosine–Gauss beams). The analytical treatment is supported by simulations with Chandezon’s method.

Plasmonic Polarization Beam Splitter Based on Dual-Core Photonic Crystal Fiber

In this paper, two kinds of novel plasmonic polarization beam splitters based on dual-core photonic crystal fiber (DC-PCF) have been designed and analyzed through the full-vector finite element method. The metallic gold is used as the surface plasmon resonance (SPR) active metal. The coupling characteristics of the designed DC-PCF can be enhanced by the resonant coupling between the second-order surface plasmon polariton (SPP) mode and the core-guided modes. A gold layer in the designed DC-PCF is introduced to achieve an perfect splitting performance and an ultra-bandwidth compared to the designed DC-PCF with gold wire. Numerical results show the ultra-bandwidth of core A and B of the polarization beam splitter with gold layer can reach 210 and 220 nm, as the extinction ratio better than -20 dB, covering the E, S, C, and L optical communication bands. The extinction ratios of core A and B can reach to -84 and -46 dB at the wavelength of 1.55 μm, respectively, and the length of splitter is 0.542 mm.

Polarization controlled coupling and shaping of surface plasmon polaritons by nanoantenna arrays.

We demonstrate experimentally the use of ordered arrays of nanoantennas for polarization controlled plasmonic beam shaping and excitation. Rod- and cross-shaped nanoantennas are used as local point-like sources of surface plasmon polaritons, and the desired phase of the generated plasmonic beam is set directly through their spatial arrangement. The polarization selectivity of the optical nanoantennas allows us to further control the excitation, enabling the realization of a variety of complex and functional plasmonic beam shaping elements. We demonstrate this concept by generating plasmonic self-accelerating beams, plasmonic bottle beams, and switchable dual-focii plasmonic lenses. The freedom in the design and arrangement of these nanoantennas enables us to specifically tailor and control the shapes, wavelengths, and coupling efficiencies of complex plasmonic beams.

Corrections to “Low Loss, High Extinction Ration and Ultra-Compact Plasmonic Polarization Beam Splitter” [Apr 1 2014 660-663

The title of the above paper <xref ref-type="bibr" rid="ref1" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">[1]</xref> was published with an error. The word “Ration” is not correct. The correct title is as follows:

Optical singularities in plasmonic fields near single subwavelength holes

We identify phase and polarization singularities in near-field measurements and theoretical modeling of the electric near-field distributions that result from the scattering of surface plasmon polaritons from single subwavelength holes in optically thick gold films. We discuss properties of the singularities, such as their topological charge or the field amplitudes at their locations. We show that it is possible to tune the in-plane field amplitude at the positions of the polarization singularities by three orders of magnitude simply by varying the hole or incident plasmon beam size.

An Improved Design Formula for the Plasmonic Directional Beaming of Light

An improved formula is suggested for the estimation of the diffraction angles of surface plasmon polaritons via dielectric or metal-dielectric ridge gratings. We propose on-axis and off-axis directional beaming structures designed by this formula and prove their appropriateness using rigorous numerical calculations. A plasmonic beam focusing structure is also proposed.

Coupled Airy breathers.

The dynamics of two component-coupled vectorial Airy beams is investigated. In the linear propagation regime, a complete analytic solution describes the breather-like propagation of two components that feature nondiffracting self-accelerating Airy behavior. The superposition of two beams with different input properties opens the possibility of designing more complex nondiffracting propagation scenarios. In the strongly nonlinear regime, the dynamics remain qualitatively robust as is revealed by direct numerical simulations. Because of the Kerr effect, the two beams emit solitonic breathers whose coupling period is compatible with the remaining Airy-like beams. The results of this study are relevant for the description of photonic and plasmonic beams that propagate in coupled planar waveguides, as well as for birefrigent or multiwavelength beams.

Rapidly accelerating Mathieu and Weber surface plasmon beams.

We report the generation of two types of self-accelerating surface plasmon beams which are solutions of the nonparaxial Helmholtz equation in two dimensions. These beams preserve their shape while propagating along either elliptic (Mathieu beam) or parabolic (Weber beam) trajectories. We show that owing to the nonparaxial nature of the Weber beam, it maintains its shape over a much larger distance along the parabolic trajectory, with respect to the corresponding solution of the paraxial equation-the Airy beam. Dynamic control of the trajectory is realized by translating the position of the illuminating free-space beam. Finally, the ability of these beams to self-heal after blocking obstacles is demonstrated as well.

Subwavelength beams with polarization singularities in plasmonic metamaterials

We investigated the diffraction behavior of plasmonic Bessel beams propagating in metal-dielectric stratified materials and wire media. Our results reveal various regimes in which polarization singularities are selectively maintained. This polarization-pass effect can be controlled by appropriately setting the filling factor of the metallic inclusions and its internal periodic distribution. These results may have implications in the development of devices at the nanoscale level for manipulation of polarization and angular momentum of cylindrical vector beams.

Highly sensitive beam steering with plasmonic antenna.

In this work, we design and study a highly sensitive beam steering device that integrates a spiral plasmonic antenna with a subwavelength metallic waveguide. The short effective wavelength of the surface plasmon polaritons (SPPs) mode supported by the metallic waveguide is exploited to dramatically miniaturize the device and improve the sensitivity of the beam steering. Through introducing a tiny displacement of feed point with respect to the geometrical center of the spiral plasmonic antenna, the direction of the radiation can be steered at considerably high angles. Simulation results show that steering angles of 8°, 17° and 34° are obtainable for a displacement of 50 nm, 100 nm and 200 nm, respectively. Benefiting from the reduced device size and the shorter SPP wavelength, the beam steering sensitivity of the beam steering is improved by 10-fold compared with the case reported previously. This miniature plasmonic beam steering device may find many potential applications in quantum optical information processing and integrated photonic circuits.

Dynamic plasmonic beam shaping by vector beams with arbitrary locally linear polarization states

Vector beams, which have space-variant state of polarization (SOP) comparing with scalar beams with spatially homogeneous SOP, are used to manipulate surface plasmon polarizations (SPPs). We find that the excitation, orientation, and distribution of the focused SPPs excited in a high numerical aperture microscopic configuration highly depend on the space-variant polarization of the incident vector beam. When it comes to vector beam with axial symmetry, multi-foci of SPPs with the same size and uniform intensity can be obtained, and the number of foci is depending on the polarization order n. Those properties can be of great value in biological sensor and plasmonic tweezers applications.

Shaping plasmonic light beams with near-field plasmonic holograms

We introduce a new class of plasmonic holograms for the near field. These holograms provide complete control of the amplitude and phase of surface plasmon polaritons (SPPs), thereby enabling the generation of any desired plasmonic light beam. The scheme is based on a two-dimensional near-field plasmonic hologram, which couples the SPP from free space into the metal&#x2013;dielectric interface, and also sets the attributes of the plasmonic beam. We demonstrate the concept for a wide variety of plasmonic beams with different qualities&#x2014;in particular, &#x201C;self-similar&#x201D; Hermite&#x2013;Gauss beams, &#x201C;nondiffracting&#x201D; cosine-Gauss beams, and &#x201C;self-accelerating&#x201D; Airy beams.