Designed surface modes propagating along hyperbolic metamaterials

2013

We report on surface-wave propagation (SWP) that occurs in semi-infinite hyperbolic metamaterials whose optical axis is set in the interface plane. In practice it is implemented by a multi-layered metal-dielectric nanostructure that is cut normally to the layers. Our theoretical analysis shows that various conditions can be designed enabling distinct regimes of SWP. We concluded that hybridization of SWP polarization leads to tighter confinement near the interface as compared with conventional surface plasmon polaritons. By using the finite-element method (FEM), we demonstrate that the fields are enhanced on the walls of metallic films, and thus minimizing significantly its presence inside …

Spectral anomalies in focused waves of different Fresnel numbers

2004

Light propagation induces remarkable changes in the spectrum of focused diffracted beams. We show that spectral changes take place in the vicinity of phase singularities in the focal region of spatially coherent, polychromatic spherical waves of different Fresnel numbers. Instead of the Debye formulation, we use the Kirchhoff integral to evaluate the focal field accurately. We find that as a result of a decrease in the Fresnel number, some cylindrical spectral switches are geometrically transformed into conical spectral switches.

Engineered surface waves in hyperbolic metamaterials

2013

We analyzed surface-wave propagation that takes place at the boundary between a semi-infinite dielectric and a multilayered metamaterial, the latter with indefinite permittivity and cut normally to the layers. Known hyperbolization of the dispersion curve is discussed within distinct spectral regimes, including the role of the surrounding material. Hybridization of surface waves enable tighter confinement near the interface in comparison with pure-TM surface-plasmon polaritons. We demonstrate that the effective-medium approach deviates severely in practical implementations. By using the finite-element method, we predict the existence of long-range oblique surface waves. This research was fu…

Cantor-like fractal photonic crystal waveguides

2005

Abstract We propose a new class of one-dimensional (1D) photonic waveguides: the fractal photonic crystal waveguides (FPCWs). These structures are photonic crystal waveguides (PCWs) etched with fratal distribution of grooves such as Cantor bars. The transmission properties of the FPCWs are investigated and compared with those of the conventional 1D PCWs. It is shown that the FPCW transmission spectrum has self-similarity properties associated with the fractal distribution of grooves. Furthermore, FPCWs exhibit sharp localized transmissions peaks that are approximately equidistant inside the photonic band gap.

Spectral anomalies in supercontinuum focused waves

2006

The diffraction-induced spectral anomalies in the focal plane of an apertured spherical wave with supercontinuum flat-top power spectrum are investigated. Coherent broadband radiation (also incoherent white light) demonstrates a strong blue shift in the vicinity of the optical axis, and discrete spectral gaps with overall red shift arise out of this central region. Unlike narrow-band light, the spectral switch effect fades away with ultra-broad spectra.

Three-dimensional superresolution by annular binary filters

1999

We present a new family of annular binary filters for improving the three-dimensional resolving power of optical systems. The filters, whose most important feature is their simplicity, permit to achieve a significant reduction, both in the transverse and in the axial direction, of the central lobe width of the irradiance point spread function of the system. The filters can be used for applications such as optical data storage or confocal scanning microscopy.

Tunable optical sectioning in confocal microscopy by use of symmetrical defocusing and apodization

2008

We present two novel optical methods to achieve a significative improvement in the optical-sectioning capacity of confocal scanning microscopes. The techniques, whose real power is the simplicity with which they can be implemented, consist of a suitable combination of symmetrical defocusing with two different manners of apodizing both parts of the confocal architecture. It is shown that the proposed techniques are useful in both the bright-field and the fluorescence modes and for reflection and transmission geometries.

Free-space delay lines and resonances with ultraslow pulsed Bessel beams

2008

We investigate the ultraslow motion of polychromatic Bessel beams in unbounded, nondispersive media. Control over the group velocity is exercised by means of the angular dispersion of pulsed Bessel beams of invariant transverse spatial frequency, which spontaneously emerge from near-field generators. Temporal dynamics in transients and resonances over homogeneous delay lines (dielectric slabs) are also examined.

Ultrafast beam shaping with high-numerical-aperture microscope objectives

2009

Ultrafast diffraction results in spatiotemporal un-coupling of the wave field, inducing spectral anomalies and pulse stretching. Localized compensation may be achieved via angular dispersion driven by diffractive optical elements (DOEs). We report on an DOEs-based beam shaper of ultrashort optical pulses with high spatiotemporal resolution. Inspection of the validity of our approach is performed in the single-cycle regime.

Coupled plasmonic graphene wires: theoretical study including complex frequencies and field distributions of bright and dark surface plasmons

2020

Theoretical research on localized surface plasmons (LSPs) supported by a structure formed by two parallel dielectric wires with a circular cross section wrapped with a graphene sheet has an impact in the practical realm. Here, LSPs are represented in the form of an infinite series of cylindrical multipole partial waves linked to each of the graphene wires. To obtain the kinematics (complex eigenfrequencies) and dynamic characteristics (field distributions) of the LSPs, we consider the analytic extension to the complex plane of the solution to the boundary value problem. The lower frequency LSP group is formed by four branches, two of them corresponding to bright modes and the others to dark…

Lasing condition for trapped modes in subwavelength--wired PT--symmetric resonators

2021

The ability to control the laser modes within a subwavelength resonator is of key relevance in modern optoelectronics. This work deals with the theoretical research on optical properties of a PT-symmetric nano-scaled dimer formed by two dielectric wires, one is with loss and the other with gain, wrapped with graphene sheets. We show the existence of two non-radiating trapped modes which transform into radiating modes by increasing the gain–loss parameter. Moreover, these modes reach the lasing condition for suitable values of this parameter, a fact that makes these modes achieve an ultra high quality factor that is manifested on the response of the structure when it is excited by a plane wa…

Controlling the Carrier-Envelope Phase of Few-Cycle Laser Beams in Dispersive Media

2011

During the last decade it has been practicable to achieve a full control of the temporal evolution of the wave field of ultrashort mode-locked laser beams (1). Advances in femtosecond laser technology and nonlinear optics have made possible to tailor the phase and magnitude of the electric field leading to a wide range of new applications in science. Many physical phenomena are dependent directly on the electric field rather than the pulse envelope such as electron emission from ionized atoms (2) and metal surfaces (3), or carrier-wave Rabi-flopping (4). Moreover, attosecond physics is for all practical purposes accessible by using femtosecond pulses with controlled carrier-envelope (CE) ph…

Axial behavior of diffractive lenses under Gaussian illumination: complex-argument spectral analysis

1999

We present a general procedure to analyze the axial-irradiance distribution generated by an unlimited diffractive lens under coherent, Gaussian illumination. The resulting on-axis diffraction pattern, which is evaluated in terms of the power complex spectrum of the Fresnel-zone transmittance, explicitly depends on the truncation parameter that we define, which evaluates the effective number of zones illuminated by the Gaussian beam. Depending on the value of this parameter, different kinds of axial behavior are observed. In particular, for moderate values a multiple-focal-shift phenomenon appears, and a simple formula for its evaluation is presented. Additionally, for low values of the trun…

Inverse focal shift: A new effect in truncated cylindrical waves

1999

We report on a general analytical procedure to analyse the axial focusing properties of uniform cylindrical waves truncated by a rectangular window. The resulting on-axis diffraction pattern explicitly depends on the square of the window height-to-width ratio. Depending on the value of this parameter, different kinds of axial behaviour are observed. In particular, it is found that for low values of this parameter and low Fresnel number, instead of the expected focal-shift effect, an inverse focal-shift phenomenon can appear, i.e. the maximum of the axial-irradiance distribution is displaced further away from the window.

Numerical and experimental investigation of short Au nanorods

2014

The plasmonic properties of Au nanorods (NRs) have been investigated theoretically and experimentally, a system that is of high current interest in relation to various nanophotonics applications. The non-aligned NRs arrays were formed by a seed-mediated growth method that relies on the reduction of metal salt by a weak reduction agent in the presence of preformed metallic seed nanoparticles. We applied the finite-element method to calculations of absorption spectra from gold NRs supported in an aqueous solution. Comparison to experimentally measured spectra is found in a good agreement.

Scattering of electromagnetic waves from a graphene-coated thin cylinder of left-handed metamaterial

2017

Abstract In this paper, we explored the scattering behavior of thin cylinders made of a left-handed material (LHM) and coated by a monoatomic graphene layer. A spectral tunability of the resonance peaks is evidenced by altering the chemical potential of the graphene coating, a fact that occurs at any state of polarization of the incident plane wave in opposition to the case of scatterers of dielectric core. On the contrary, no invisibility condition can be satisfied for dielectric environments. A singular performance is also found for cylinders with permittivity and permeability near zero. Practical implementations of our results can be carried out in sensing and wave manipulation driven by…

Analytical formula for calculating the focal shift in apodized systems

1998

We report a quite simple analytical formula for the evaluation of the focal shift in apodized systems, with or without rotational invariance. Specifically it is shown that the magnitude of the focal shift is determined by the product of the Fresnel number of the focusing geometry and the standard deviation of a mapped version of the azimuthal average of the pupil transmittance. To illustrate our approach, several examples are examined.

Dielectric metalenses with engineered point spread function

2017

High-index silicon nanoblocks support excitation of both electric and magnetic resonance modes at telecommunication wavelengths. At frequencies where both electric and magnetic resonance modes are excited simultaneously, changing the geometrical dimensions of the silicon cubes creates a 2π full span over the phase of the transmitted light in different amplitude ranges. We take advantage of the additional power-flux modulation of the scattered signal to focus the incident light with desired full width at half maximum (FWHM) and side lobe levels (SLLs) in both the lateral and axial directions. By implementing proper amplitude filters within the telecommunication working wavelength (1.55 μm), …

Optimization of multilayered nanotubes for maximal scattering cancellation

2016

An optimization for multilayered nanotubes that minimizes the scattering efficiency for a given polarization is derived. The cylindrical nanocavities have a radially periodic distribution, and the marginal layers that play a crucial role particularly in the presence of nonlocalities are disposed to reduce the scattering efficiency up to two orders of magnitude in comparison with previous proposals. The predominant causes leading to such invisibility effect are critically discussed. A transfer-matrix formalism is additionally developed for the fast estimation of the scattering efficiency of the nanostructures.

Single-Polarization Double Refraction in Plasmonic Crystals: Considerations on Energy Flow

2014

We examined the optical properties of nanolayered metal-dielectric lattices. At subwavelength regimes, the periodic array of metallic nanofilms demonstrates nonlocality-induced double refraction, conventional positive and as well as negative. In particular, we report on energy-flow considerations concerning both refractive behaviors concurrently. Numerical simulations provide transmittance of individual beams in Ag-TiO2 metamaterials under different configurations. In regimes of the effective-medium theory predicting elliptic dispersion, negative refraction may be stronger than the expected positive refraction. This research was funded by the Spanish Ministry of Economy and Competitiveness …

Angular spectrum of diffracted wave fields with apochromatic correction.

2008

We report on compensation of diffraction-induced angular dispersion of ultrashort pulses up to a second order. A strategy for chromatic correction profits from high dispersion of kinoform-type zone plates. Ultraflat dispersion curves rely on a saddle point that may be tuned at a prescribed wavelength. Validity of our approach may reach the few-cycles regime.

Flexible design of multifocal metalenses based on autofocused Airy beams

2018

Extreme miniaturization of on-demand optical devices such as ultrathin lenses is currently leading to significant advancements in manufacturing novel materials and nanotechnologies. Flexibility and tunability of engineered layouts enable efficient integration of complex photonic modules. In this regard, here we propose an autofocused Airy (AFA)-based metalens that operates, depending on the molded phase profile, as a multifocal focusing lens, which to the best of our knowledge has not been reported before. To do this, we call attention to the fact that the two conjugate focal points of an AFA beam can be brought into real space by applying a proper convex lens phase profile. Considering ful…

Nonlocal dispersion anomalies of Dyakonov-like surface waves at hyperbolic media interfaces

2016

Dyakonov-like surface waves (DSWs) propagating obliquely on an anisotropic nanostructure have been theoretically proved in a few cases including 2D photonic crystals and metal-insulator (MI) layered metamaterials. Up to now, the long-wavelength approximation has been employed in order to obtain effective parameters to be introduced in the Dyakonov equation, which is largely restricted to material inhomogeneities of a few nanometers when including metallic elements. Here, we explore DSWs propagating obliquely at the interface between an insulator and a hyperbolic metamaterial, the latter consisting of a 1D MI bandgap grating using realistic slab sizes. We found unexpected favorable condition…

X-wave bullets with negative group velocity in vacuum.

2006

Propagation-invariant, X waves with negative group velocity are reported. Beam aperturing allows for a comprehensive analysis concerning the causality of the optical signal and forerunner formation.

Generation of accelerating beams using nano-scale metallic circular gratings

2014

Spatially accelerating beams that are solutions to the Maxwell equations may propagate along incomplete circular trajectories, after which diffraction broadening takes over and the beams spread out. In this paper we report on numerical simulations that show the conversion of a high-numerical-aperture focused beam into a nonparaxial shape-preserving accelerating beam having a beam-width near the diffraction limit. Beam shaping is induced by a diffractive optical element that consists of a non-planar sub-wavelength grating enabling a Bessel signature.

Plasmon-driven Bessel beams

2012

We report on subwavelength diffraction-free beams with grazing propagation in metal-dielectric devices. The nondiffracting beams are resonantly transmitted through the nanostructured medium leading to light confinement and wave amplification around the beam axis.

Dyadic Green's function for the electrically biased graphene-based multilayered spherical structures

2020

Abstract Dyadic Green's function for a multilayered spherical structure with alternating graphene-dielectric shells is extracted in this paper. To this end, the unknown expansion coefficients of the scattering superposition method are obtained by considering graphene local surface currents at the interface of two adjacent layers. To validate the formulas, the procedure of Mie scattering analysis employing our formulas is clarified and the extinction efficiencies of various graphene-based nanoparticles are computed. The possibility of using the proposed structure in the design of multi-band optical absorbers is discussed in detail. Moreover, a closed-form formula for obtaining the Purcell fa…

Plasmon-driven nondiffracting surface beaming

2011

We introduce diffraction-free plasmonic waves in metal-dielectric surfaces which are the analogue to nondiffracting Bessel beams in free space. By interfering multiple converging plane waves with controlled phase matching, we generate a subwavelength transverse spot located at the boundaries of a 1D plasmonic lattice. The diffraction-free beam is resonantly transmitted through the stratiform medium leading not only to light confinement but also to wave enhancement assisted by surface plasmons polaritons. To conclude, we briefly analyze other types of localized surface modes which were proposed recently.

Gaussian imaging transformation for the paraxial Debye formulation of the focal region in a low-Fresnel-number optical system

2000

The Debye formulation of focused fields has been systematically used to evaluate, for example, the point-spread function of an optical imaging system. According to this approximation, the focal wave field exhibits some symmetries about the geometrical focus. However, certain discrepancies arise when the Fresnel number, as viewed from focus, is close to unity. In that case, we should use the Kirchhoff formulation to evaluate accurately the three-dimensional amplitude distribution of the field in the focal region. We make some important remarks regarding both diffraction theories. In the end we demonstrate that, in the paraxial regime, given a defocused transverse pattern in the Debye approxi…

Diffraction-free beams in thin films

2009

The propagation and transmission of Bessel beams through nano-layered structures has been discussed recently. Within this framework we recognize the formation of unguided diffraction-free waves with the spot size approaching and occasionally surpassing the limit of a wavelength when a Bessel beam of any order n is launched onto a thin material slab with grazing incidence. On the basis of the plane-wave representation of cylindrical waves, a simple model is introduced providing an exact description of the transverse pattern of this type of diffraction-suppressed localized wave. Potential applications in surface science are put forward for consideration. Ministerio de Ciencia e Innovación (MI…

Subwavelength surface waves with zero diffraction

2011

We identified nanostructured devices sustaining out-of-plane nondiffracting beams with near-grazing propagation and a transverse beamwidth clearly surpassing the diffraction limit of half a wavelength. This type of device consists of a planar multilayered metal-dielectric structure with a finite number of films deposited on a solid transparent substrate. We assumed that the nondiffracting beam is launched from the substrate. The construction of the subwavelength diffraction-free beam is attended by plane waves which are resonantly transmitted through the stratified medium. Therefore, light confinement and wave amplification occurs simultaneously. We performed an optimization process concern…

Uniaxial epsilon-near-zero metamaterials: from superlensing to double refraction

2014

We investigated optical properties of nanostructured metal-dielectric multilayered lattices under the conditions of epsilon-near-zero (ENZ), a concept derived from the effective-medium approach (EMA). We theoretically found that the periodic array of metallic nanolayers may exhibit either superlensing driven by broadband canalization from point emitters or single-polarization double refraction, and conventional positive as well as negative, even at subwavelength regimes. For the latter case, we formulated a modified EMA, and subsequently a generalized refraction law, that describes both refractive behaviors concurrently. The modal coupling of plasmonic lattice resonances, and nonlocality in…

A broadband multifocal metalens in the terahertz frequency range

2016

Abstract Metasurfaces, the 2D form of metamaterials with their ability in phase, amplitude and polarization manipulation are widely used in designing optical devices. Efforts to find proper photonic components in the terahertz (THz) range of frequency lead us to adopt metasurfaces as their constituent elements. Here, we conceived a broadband THz lens with an adjustable number and arrangement of focal points. To have a full control over the lens functionality, we used a metasurface with the capability of simultaneously modulating the amplitude and phase of the incident wave. C-shaped ring resonators (CSRRs) with different geometry and orientation capable of simultaneously manipulating phase …

Three-dimensional point spread function of multilayered flat lenses and its application to extreme subwavelength resolution

2011

The three-dimensional (3D) point spread function (PSF) of multilayered flat lenses was proposed in order to characterize the diffractive behavior of these subwavelength image formers. We computed the polarization-dependent scalar 3D PSF for a wide range of slab widths and for different dissipative metamaterials. In terms similar to the Rayleigh criterion we determined unambiguously the limit of resolution featuring this type of image-forming device. We investigated the significant reduction of the limit of resolution by increasing the number of layers, which may drop nearly 1 order of magnitude. However, this super-resolving effect is obtained in detriment of reducing the depth of field. Li…

Subwavelength Bessel beams in wire media

2013

Recent progress is emerging on nondiffracting subwavelength fields propagating in complex plasmonic nanostructures. In this paper, we present a thorough discussion on diffraction-free localized solutions of Maxwell’s equations in a periodic structure composed of nanowires. This self-focusing mechanism differs from others previously reported, which lie on regimes with ultraflat spatial dispersion. By means of the Maxwell–Garnett model, we provide a general analytical expression of the electromagnetic fields that can propagate along the direction of the cylinder’s axis, keeping its transverse waveform unaltered. Numerical simulations based on the finite element method support our analytical a…

Plano-concave microlenses with epsilon-near-zero surface-relief coatings for efficient shaping of nonparaxial optical beams

2017

Abstract Epsilon-near-zero (ENZ) materials, including artificial metamaterials, have been advanced to mold laser beams and antenna-mediated radiated waves. Here we propose an efficient method to control Ohmic losses inherent to natural ENZ materials by the assembly of subwavelength structures in a nonperiodic matrix constituting an ENZ metacoating. Implemented over plano-concave transparent substrates whose radius can be of only a few wavelengths, ENZ surface-relief elements demonstrate to adequately shape a plane wave into highly localized fields. Furthermore, our proposal provides an energy efficiency even higher than an ideally-lossless all-ENZ plano-concave lens. Our procedure is satisf…

White-light-modified Talbot array illuminator with a variable density of light spots.

2008

A flexible array illuminator, comprising only two conventional optical elements, with a variable density of bright white-light spots is presented. The key to our method is to obtain with a single diffractive lens an achromatic version of different fractional Talbot images, produced by free-space propagation, of the amplitude distribution at the back focal plane of a periodic refractive microlens array under a broadband point-source illumination. Some experimental results of our optical procedure are also shown.

Nondiffracting Bessel plasmons.

2011

We report on the existence of nondiffracting Bessel surface plasmon polaritons (SPPs), advancing at either superluminal or subluminal phase velocities. These wave fields feature deep subwavelength FWHM, but are supported by high-order homogeneous SPPs of a metal/dielectric (MD) superlattice. The beam axis can be relocated to any MD interface, by interfering multiple converging SPPs with controlled phase matching. Dissipative effects in metals lead to a diffraction-free regime that is limited by the energy attenuation length. However, the ultra-localization of the diffracted wave field might still be maintained by more than one order of magnitude. This research was funded by the Spanish Mini…

Novel prospects in hyperbolic metamaterials: Dyakonov-like surface waves

2014

Gouy wave modes: undistorted pulse focalization in a dispersive medium.

2007

Gouy wave modes are linear waves with finite energy that propagate without distortion at any phase and group velocity through a focal region in a dispersive medium. These features make them potentially useful for the onset and control of nonlinear interactions.

Energy flow canalization of evanescent cylindrical-vector beams

2013

We analyzed ultra-confined vector beams with radial and azimuthal polarizations which are critically self-governed inside plasmonic metamaterials. We succeeded in the separation of polarization singularities in the fields at the nanoscale. The examined metamaterials are suitable for long-range transport of subwavelength Bessel beams without discernible blurring. These results open the door to develop integrated devices for applications such as the manipulation of polarization and angular momentum of surface-plasmon excitations.

Highly Anisotropic Wave Propagation in All-Dielectric Active Waveguides

2018

In this communication, we integrate an active planar waveguide on a birefringent substrate to show experimental evidence of a selective propagation of the spontaneous emission into the propagating. An anisotropic response with significantly-reduced directional excitation along the optic axis as compared with its perpendicular direction is observed. We additionally provide a theoretical modal analysis of the planar microstructure, which is in good agreement with our experimental results.

Subwavelength beams with polarization singularities in plasmonic metamaterials

2014

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. This research was funded by the Spanish Ministry of Economy and Competitiveness under the project TEC2011-29120-C05-01.

Dyakonov surface waves in lossy metamaterials

2015

We analyze the existence of localized waves in the vicinities of the interface between two dielectrics, provided one of them is uniaxial and lossy. We found two families of surface waves, one of them approaching the well-known Dyakonov surface waves (DSWs). In addition, a new family of wave fields exists which are tightly bound to the interface. Although its appearance is clearly associated with the dissipative character of the anisotropic material, the characteristic propagation length of such surface waves might surpass the working wavelength by nearly two orders of magnitude. This research was funded by the Spanish Ministry of Economy and Competitiveness under the Project TEC2013-50416-E…

Amplitude modulation technique for designing metalenses with apodized and enhanced resolution focal spots

2017

Abstract In this paper we show that engineering both phase and amplitude of the scattered light can be employed in designing metalenses with either higher resolution or apodized focal spots. C-shaped split-ring micro-resonators (CSRRs) with different geometrical parameters are selected to have a full control of amplitude and phase. While phase engineering is necessary for light focusing, amplitude modulation of the scattered wave can be applied to characterize the focal point properties such as resolution gain and sidelobe level. We show that both axial and transverse resolution improvement or apodization is possible in the far-field region by applying proper amplitude function. Amplitude m…

Analytical characterization of spectral anomalies in polychromatic apertured beams

2006

Abstract The power spectrum of polychromatic apertured spherical waves changes strongly in the vicinity of phase singularities. A spectral shift effect is observed and, in some cases, a spectral switch occurs together with a broadening of the power spectrum. Low-order moments of the power spectrum are evaluated in points of the focal volume with spectral anomalies. First-order analytical expressions are proposed for the evaluation of the relative spectral shift and the relative spectral broadening in the transverse focal plane and along the optical axis. The influence of the fractional bandwidth and the selected singularity order is considered.

Three-dimensional field distribution in the focal region of low-Fresnel-number axicons.

2006

Three-dimensional intensity and phase distributions generated by microaxicons are evaluated in the low-Fresnel-number regime. Apertured and nonapertured conical wavefronts may generate transverse patterns with notable deviations from the expected nondiffracting Bessel beam. First-order analytical expressions are proposed for the evaluation of the wave field produced by axicons of different Fresnel number in the focal region.

Bloch surface waves engineering in one-dimensional photonic crystals with a chiral cap layer

2019

We investigate the localization properties of surface waves created at the interface between a truncated 1D photonic crystal and homogeneous medium in the presence of a chiral cap layer using the transfer matrix method. The numerical results show that the interface can support surface waves with both transverse electric and transverse magnetic polarizations. We demonstrate that the surface waves can be engineered by varying the chirality parameter of the cap layer, which plays an important role in controlling and localization of surface states. It is shown that the effect of a chirality parameter on surface waves with transverse electric polarization is more remarkable compared with surface…

Plasmonic stratified devices for superlensing in the self-focusing regime

2012

We show that diffraction-management of subwavelength scattered fields assisted by metallodielectric heterostructures leads to superresolving imaging. An accurate design of a passive multilayered compound provides nearly aberration-free images with subwavelength resolution out of the canalization regime even using optical paths longer than a wavelength.

Isotropic compensation of diffraction-driven angular dispersion

2007

We report on an optical arrangement capable of compensating angular dispersion of paraxial wave fields developed by diffractive optical elements (DOEs). Schematically, the system is a beam expander in which two phase-only zone plates have been inserted, remaining afocal the coupled system. The DOE, which induces a continuous set of dispersive tilted plane waves, is placed at a specific position within the proposed setup providing an output spectrum with achromatic angular deviation. A directional matching between phase fronts and pulse fronts of output wave packets is demonstrated.

Diffraction-managed superlensing using plasmonic lattices

2012

Abstract We show that subwavelength diffracted wave fields may be managed inside multilayered plasmonic devices to achieve ultra-resolving lensing. For that purpose we first transform both homogeneous waves and a broad band of evanescent waves into propagating Bloch modes by means of a metal/dielectric (MD) superlattice. Beam spreading is subsequently compensated by means of negative refraction in a plasmon-induced anisotropic medium that is cemented behind. A precise design of the superlens doublet may lead to nearly aberration-free images with subwavelength resolution in spite of using optical paths longer than a wavelength.

Propagation of Dyakonon Wave-Packets at the Boundary of Metallodielectric Lattices

2013

We rigorously analyze the propagation of localized surface waves that takes place at the boundary between a semi-infinite layered metal-dielectric (MD) nanostructure cut normally to the layers and a isotropic medium. It is demonstrated that Dyakonov-like surface waves (also coined dyakonons) with hybrid polarization may propagate in a wide angular range. As a consequence, dyakonon-based wave-packets (DWPs) may feature sub-wavelength beamwidths. Due to the hyperbolic-dispersion regime in plasmonic crystals, supported DWPs are still in the canalization regime. The apparent quadratic beam spreading, however, is driven by dissipation effects in metal. This work was supported by the Spanish Mini…

Some considerations on the transmissivity of trirefringent metamaterials

2016

Nonlocal effects in metal–dielectric (MD) periodic nanostructures may typically be observed when the plasmonic particles and gaps are on the scale of a few tens of nanometers, enabling under certain conditions (succinctly for epsilon near zero) a collimated beam to split into three refracted signals. We developed a method for precisely evaluating the categorized transmissivity in an air/trirefringent metamaterial interface, which uses a fast one-dimensional Fourier transform and finite element solvers of Maxwell’s equations. In periodic arrays of MD nanofilms, it is proved a tunable transmissivity switch of the multirefracted beams under varying angle of incidence and wavelength, while keep…

Considerations on the electromagnetic flow in Airy beams based on the Gouy phase

2012

We reexamine the Gouy phase in ballistic Airy beams (AiBs). A physical interpretation of our analysis is derived in terms of the local phase velocity and the Poynting vector streamlines. Recent experiments employing AiBs are consistent with our results. We provide an approach which potentially applies to any finite-energy paraxial wave field that lacks a beam axis. This research was funded by the Spanish Ministry of Economy and Competitiveness under the project TEC2009-11635.

Focal squeeze in axicons

2005

The on-axis irradiance distribution of a truncated conical wavefront is evaluated in terms of the Fresnel number of the focusing geometry. In agreement with geometrical optics, a focal line of increasing intensity is generated for extremely high Fresnel numbers. Otherwise clear deviations may be observed for the position of the maximum irradiance along the optical axis. A remarkable focal squeeze appears and, for decreasing Fresnel numbers, this effect manifests stronger. An analytical formula is provided for the fast evaluation of the focal squeeze.

Surface waves in plasmonic anisotropie media

2012

We investigate the spatial dispersion of hybrid-polarized surface waves excited at the boundary of a semi-infinite layered metal-dielectric nanostructure. We put emphasis in the case that the thickness of a metal layer becomes of the order of the metal skin depth. We demonstrate that the use of the so-called effective medium approximation (EMA) is not justified, in general. For that purpose, we compare the results using the EMA model and numerical simulations based on the finite-element method. We include an analysis of the influence of metallic losses.

Dyakonons in hyperbolic metamaterials

2013

We have analyzed surface-wave propagation that takes place at the boundary between an isotropic medium and a semi-infinite metal-dielectric periodic medium cut normally to the layers. In the range of frequencies where the periodic medium shows hyperbolic space dispersion, hybridization of surface waves (dyakonons) occurs. At low to moderate frequencies, dyakonons enable tighter confinement near the interface in comparison with pure SPPs. On the other hand, a distinct regime governs dispersion of dyakonons at higher frequencies. Full Text: PDF References Z. Ruan, M. Qiu, "Slow electromagnetic wave guided in subwavelength region along one-dimensional periodically structured metal surface", Ap…

Effective Fresnel-number concept for evaluating the relative focal shift in focused beams

1998

We report on an analytical formulation, based on the concept of effective Fresnel number, to evaluate in a simple way the relative focal shift of rotationally nonsymmetric scalar fields that have geometrical focus and moderate Fresnel number. To illustrate our approach, certain previously known results and also some new focusing setups are analytically examined.

Metalenses with high-NA, enhanced resolution and apodization

2017

Dielectric microlenses employed in imaging and focusing for optoelectronics are currently prospects to be substituted by metalenses showing an extraordinary optical performance within notably reduced volumes. Here we present some proposals to achieve an enhanced resolution in metallodielectric metasurface-based lenses established on either efficient arrangements with high numerical aperture or spatial filtering enabling to surpass the limit of resolution derived by the Rayleigh criterion.

Metacoatings for wavelength-scale, high-numerical-aperture plano–concave focusing lenses

2016

We design plano–concave silicon lenses with coupled gradient-index plasmonic metacoatings for ultrawide apertured focusing utilizing a reduced region of ∼20λ2. The anomalous refraction induced in the planar input side of the lens and in the boundary of the wavelength-scale focal region boosts the curvature of the emerging wavefront, thus significantly enhancing the resolution of the tightly focused optical wave. The formation of a light tongue with dimensions approaching those of the concave opening is here evidenced. This scheme is expected to have potential applications in optical trapping and detection.

Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI3 Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials

2020

Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled. These results can be of i…

Temporal effects in ultrashort pulsed beams focused by planar diffracting elements

2006

The pulse envelope of an ultrashort pulsed beam is evaluated on the focal points of a Fresnel zone plate. The description of the field dynamics is given in terms of a diffraction-induced pulse train. Within these terms we follow an analytical procedure to characterize the temporal broadening observed at the principal focus, which is significant if the number of Fresnel zones exceeds the number of cycles in the pulse. For Gaussian-type envelopes, the focal field may be accurately expressed in a simple closed form. This expression has a flat-top shape at the principal focus and other odd-order foci, and a two-peak envelope in the case of a low-integer even-order focus. Finally, extremely high…

Diffraction-free beams with elliptic Bessel envelope in periodic media

2007

We report on discrete, nondiffracting, paraxial beams with a Bessel spatial envelope in 1D periodic structures of dielectric media. Anisotropy of the envelope profile is demonstrated to behave in the same manner as extraordinary waves in uniaxial crystals.

Focal shift in optical waves with off-axis focus

2003

We present a formulation for a suitable description of the focal shift in optical waves that have an off-axis focus. This shift that is primarily produced along the chief axis is given in terms of the focal distance and depends only on a parameter that is named as the generalized Fresnel number. Any non-uniform, either truncated and non-apertured optical beam with off-axis focus may be considered.

Dyakonov-like surface waves in the THz regime

2016

Abstract Here we examine Dyakonov-like surface waves (DSWs) in the THz regime traveling along the plane interface between a non-conducting isotropic medium and a low-loss graphene-based uniaxial metamaterial with the optic axis (OA) oriented along with the interface. New insights concerning the propagation characteristics of DSWs are given by analyzing the dispersion relation in such configuration, that is evaluated using the effective medium theory. The range of angles with respect to the OA which is determined for the in-plane wave vector can be conveniently tuned with extremely flexibility in opposition with DSWs excited in natural anisotropic media. The properties discussed here are of …

Asymmetric transmission of transverse magnetic or radially polarized THZ waves through sub-wavelength gratings

2015

We have developed a metallic double circular grating with sub-wavelength slits which blocks radially polarized light incident from one of its sides and acts as a focusing diffractive element in the other direction. The proposed grating has been optimized for the sub-THz frequency range. Unidirectional transmission through the grating has been demonstrated experimentally at 0.1 THz. We have also developed a planar metallic double grating with sub-wavelength slits which blocks light with a transverse magnetic polarization incident from one of the grating sides and transmits radiation incident from the opposite direction into the +1 and −1 diffraction orders. These gratings which could be used…

Ultrafast diffraction of tightly focused waves with spatiotemporal stabilization

2008

Experimental studies of ultrafast beam shaping have come about from the need to compensate diffraction-induced dispersive effects in femtosecond laser beams. From a theoretical point of view, chromatic matching of diffracted spherical waves in the vicinity of the geometrical focus is attained by applying conveniently dispersive boundary conditions in the far-field zone, a subject thoroughly analyzed in the paraxial regime. For applications demanding high spatial resolution, however, high-numerical-aperture microscope objectives may be employed instead and would lead to nonparaxiality of the focal wavefields. These circumstances have motivated our investigation. Concretely we report on prere…

Spatial modulation of the electromagnetic energy transfer by excitation of graphene waveguide surface plasmons

2019

We theoretically study the electromagnetic energy transfer between donor and acceptor molecules near a graphene waveguide (WG). The surface plasmons (SPs) supported by the structure provide decay channels which lead to an improvement in the energy transfer rate when the donor and acceptor are localized on the same side or even on opposite sides of the WG. The modification of the energy transfer rate compared to its value in absence of the WG are calculated by deforming the integration path into a suitable path in the complex plane. Our results show that this modification is dramatically enhanced when the symmetric and antisymmetric SPs are excited. Notable effects on the spatial dependence …

Accelerating wide-angle converging waves in the near field

2014

We show that a wide-angle converging wave may be transformed into a shape-preserving accelerating beam having a beam-width near the diffraction limit. For that purpose, we followed a strategy that is particularly conceived for the acceleration of nonparaxial laser beams, in contrast to the well-known method by Siviloglou et al (2007 Phys. Rev. Lett. 99 213901). The concept of optical near-field shaping is applied to the design of non-flat ultra-narrow diffractive optical elements. The engineered curvilinear caustic can be set up by the beam emerging from a dynamic assembly of elementary gratings, the latter enabling to modify the effective refractive index of the metamaterial as it is arran…

Multi-frequency super-scattering from sub-wavelength graphene-coated nanotubes

2019

A cylindrical multilayered structure with three coupled graphene shells is shown to behave as a dual-band super-scatterer at mid-infrared frequencies. Under the 2D plasmonic nature of graphene material, multiple scattering resonances are attained in the deep subwavelength regime using an isotropic material. In the proposed structure, we efficiently exploit the existing three plasmonic resonances in each scattering channel. These resonances are tailored by dispersion engineering, which is simply displayed through the Bohr model applied to the associated planar structure. For the super-scatterer design, it is essential that the resonances of multiple channels coincide in a single frequency. H…

Tunable scattering cancellation of light using anisotropic cylindrical cavities

2016

Engineered core-shell cylinders are good candidates for applications in invisibility and cloaking.In particular, hyperbolic nanotubes demonstrate tunable ultra-low scattering cross section in the visible spectral range. In this work we investigate the limits of validity of the condition for invisibility, which was shown to rely on reaching an epsilon near zero in one of the components of the effective permittivity tensor of the anisotropic metamaterial cavity. For incident light polarized perpendicularly to the scatterer axis, critical deviations are found in low-birefringent arrangements and also with high-index cores. We demonstrate that the ability of anisotropic metallodielectric nanoca…

Paraxial waves in the far-field region

2002

Summary By investigating the changes suffered by a paraxial beam propagating in the near-field and in the far-field regions, it has been found a set of wave equations valid for points gradually closer to the near field. A relevant expression for the validity of the far-field approximation is given from the paraxial Helmholtz equation. It is pointed out that the well-known Fresnel number associated with every transverse diffraction pattern can be interpreted as a magnitude that measures the relative standard deviation of the Fraunhofer pattern and a first-order field, thus reporting on an integral expression suitable for a general case. Finally, the Rayleigh range of the optical beam is dedu…

Broadband focused waves with compensated spatial dispersion: transverse versus axial balance.

2007

We determine the constraints an ABCD optical system must verify to achieve, at the focal region, broadband waves with compensated spatial dispersion either along the optical axis, called on-axis isodiffracting fields, or in the lateral direction, here named in-plane isodiffracting beams. An optical configuration is identified for generating both types of achromatic broadband focused wave fields. An experimental verification is also provided.

Tunable invisibility cloaking by using isolated graphene-coated nanowires and dimers

2017

AbstractWe investigate, both theoretically and numerically, a graphene-coated nano-cylinder illuminated by a plane electromagnetic wave in the far-infrared range of frequencies. We have derived an analytical formula that enables fast evaluation of the spectral window with a substantial reduction in scattering efficiency for a sufficiently thin cylinder. This polarization-dependent effect leads to tunable resonant invisibility that can be achieved via modification of graphene chemical potential monitored by the gate voltage. A multi-frequency cloaking mechanism based on dimer coated nanowires is also discussed in detail.

Asymmetric apodization in confocal scanning systems.

2008

A new class of superresolution pairs of pupil filters for three-dimensional, two-pupil confocal imaging is proposed. A distinctive feature of these filters is the asymmetry of their impulse response. For synthesizing the amplitude transmittance of such filters the Fourier transform properties of Hermitian functions are employed. It is shown that, with simple phase-only filters that belong to the class in question, either axial or unidirectional lateral superresolution is achieved.

Practical formula for the evaluation of high-order multiphoton absorption in thin nonlinear media

2009

We present an analytical formula for the fast and accurate evaluation of nonlinear absorption in materials exhibiting an admixture of different multiphoton processes. This approach is specifically addressed for its use in thin films when the slowly varying envelope approximation applies. The contribution of absorptions of distinct order is conveniently averaged in order to use well-known expressions for a single multiphoton process. In the latter case, therefore, our simple expression is reduced toward the exact solution.

Metamaterial coatings for subwavelength-resolution imaging

2011

Coating lenses are membranes made of materials exhibiting negative index of refraction and deposited on other media with high dielectric constant e 3 . Unfortunately far-field imaging suffers from centrosymmetric aberrations. We propose a simple procedure to compensate partially deviations from ray-tracing perfect imaging in asymmetric metamaterial lenses. We also show that, under some circumstances, coating superlens may recover subwavelength information transmitted in a relative spatial spectrum ranging from 1 to √e 3 .

Ultrathin high-index metasurfaces for shaping focused beams

2015

The volume size of a converging wave, which plays a relevant role in image resolution, is governed by the wavelength of the radiation and the numerical aperture (NA) of the wavefront. We designed an ultrathin (λ/8 width) curved metasurface that is able to transform a focused field into a high-NA optical architecture, thus boosting the transverse and (mainly) on-axis resolution. The elements of the metasurface are metal-insulator subwavelength gratings exhibiting extreme anisotropy with ultrahigh index of refraction for TM polarization. Our results can be applied to nanolithography and optical microscopy. Spanish Ministry of Economy and Competitiveness (MEC) (TEC2013-50416-EXP).

Three-dimensional point spread function and generalized amplitude transfer function of near-field flat lenses.

2010

We derive a nonsingular, polarization-dependent, 3D impulse response that provides unambiguously the wave field scattered by a negative-refractive-index layered lens and distributed in its image volume. By means of a 3D Fourier transform, we introduce the generalized amplitude transfer function in order to gain a deep insight into the resolution power of the optical element. In the near-field regime, fine details containing some depth information may be transmitted through the lens. We show that metamaterials with moderate absorption are appropriate for subwavelength resolution keeping a limited degree of depth discrimination.

Highly localized accelerating beams using nano-scale metallic gratings

2015

Spatially accelerating beams are non-diffracting beams whose intensity is localized along curvilinear trajectories, also incomplete circular trajectories, before diffraction broadening governs their propagation. In this paper we report on numerical simulations showing the conversion of a high-numerical-aperture focused beam into a nonparaxial shape-preserving accelerating beam having a beam-width near the diffraction limit. Beam shaping is induced near the focal region by a diffractive optical element that consists of a non-planar subwavelength grating enabling a Bessel signature. This research was funded by the Spanish Ministry of Economy and Competitiveness under the project TEC2011-29120…

Metasurfaces for colour printing

2014

We present a theoretical analysis and experimental evidences of metasurfaces based on particle resonators that achieve bright-field colour prints. We created pixels that support individual colours, miniaturized and juxtaposed at the optical diffraction limit. Different strategies are followed to offer the flexibility of using both transmitting and epi (reflective) white light sources. We discuss their potential applications in large-volume colour printing via nanoimprint lithography.

Variations of OCT measurements corrected for the magnification effect according to axial length and refractive error in children

2018

Purpose: The aim of this paper was to examine the distribution of macular, retinal nerve fiber layer (RNFL) thickness and optic disc parameters of myopic and hyperopic eyes in comparison with emmetropic control eyes and to investigate their variation according to axial length (AL) and spherical equivalent (SE) in healthy children. Methods: This study included 293 pairs of eyes of 293 children (145 boys and 148 girls), ranging in age from 6 to 17 years. Subjects were divided according to SE in control (emmetropia, 99 children), myopia (100 children) and hyperopia (94 children) groups and according to axial AL in 68 short ([Formula: see text]22.00[Formula: see text]mm, 68), medium (from [For…

Nonparaxial shape-preserving Airy beams with Bessel signature

2014

Spatially accelerating beams that are solutions to Maxwell equations may propagate along incomplete circular trajectories. Taking these truncated Bessel fields to the paraxial limit, some authors have sustained that it has recovered the known Airy beams (AiBs). Based on the angular spectrum representation of optical fields, we demonstrated that the paraxial approximation rigorously leads to off-axis focused beams instead of finite-energy AiBs. The latter will arise under the umbrella of a nonparaxial approach following elliptical trajectories in place of parabolas. The analytical expression of such a shape-preserving wave field under Gaussian apodization is disclosed by using third-order no…

Multi-frequency near-field enhancement with graphene-coated nano-disk homo-dimers.

2019

In this paper, a 3D sub-wavelength graphene-coated nano-disk dimer (GDD) is proposed for multi-frequency giant near-field enhancement. We observed that the dual-band operation originates from the excitation of hybridized localized surface plasmons on top and bottom faces of the disks along with the mutual coupling from the adjacent particle. Due to the sub-wavelength nature of the disks, the excited localized surface plasmons on the sidewalls are weak but they still can affect the dual operating bands. On the other hand, the strength and resonance frequency of the enhanced fields can be simply modulated by tuning the relative distances of 2D graphene disks on top and bottom faces. Adjustabl…

Conditions for achieving invisibility of hyperbolic multilayered nanotubes

2016

Invisibility of nanotubes has recently been demonstrated in highly anisotropic metamaterials in the transition regime from hyperbolic to elliptic dispersion [Sci. Rep. 5 (2015) 16027]. In such study, the characterization of a realistic multilayered metamaterial was carried out by means of an effective medium approach providing average components of the permittivity tensor and wave fields. Here, the edge effects of the metal-dielectric stratified nanotube for different combinations were thoroughly analyzed. We show how the boundary layers, which in principle remain fully irrelevant in the estimation of the effective permittivity of the nanotube, however play a critical role in the scattering…

Dyakonov-like surface waves in semi-infinite metal-dielectric lattices

2012

We demonstrated the existence of Dyakonov-like surface waves propagating at the boundary between a metal-insulator lattice and an isotropic dielectric. A range of propagation angles substantially greater than that for conventional birefringent materials is obtained, and with reasonably small losses.

Left-handed metamaterial coatings for subwavelength-resolution imaging

2012

We report on a procedure to improve the resolution of far-field imaging by using a neighboring high-index medium that is coated with a left-handed metamaterial. The resulting plot can also exhibit an enhanced transmission by considering proper conditions to retract backscattering. Based on negative refraction, geometrical aberrations are considered in detail since they may cause a great impact in this sort of diffraction-unlimited imaging by reducing its resolution power. We employ a standard aberration analysis to refine the asymmetric configuration of metamaterial superlenses. We demonstrate that low-order centrosymmetric aberrations can be fully corrected for a given object plane. For su…

Diffraction-free propagation of subwavelength light beams in layered media

2010

Self-collimation of tightly localized laser beams demonstrated in periodic media relies on a perfect-matched rephasing of the Fourier constituents of the wavefield induced by a plane isofrequency curve. An alternate way paved for the achievement of such a phase matching condition developed a suitable spatial filtering in order to select those frequencies experiencing the same phase velocity projected over a given orientation. In principle this procedure is valid for complex structured metamaterials. However, a great majority of studies have focused on free-space propagation leading to the well-known Bessel beams. This paper is devoted to the analysis of this sort of nondiffracting beams tra…

Unconventional, efficient and flexible bifocal lens design by metalens and AFA beam combination

2019

In the field of metasurface-based light focusing, both convex metalenses with parabolic phase profile and autofocused Airy (AFA) beams play essential roles. AFA beam generation as a combination of two convergent mirrored Airy beams leaves the space between the two launched Airy profiles inefficient with zero amplitude transmission and constant phase distribution. In this paper, we propose using this inutile space as an independent metalens. We show that coincidence of the focal spot of the metalens to that of the AFA beam will increase the focusing intensity more than 24 percent at its focal point. It is shown that using the nonoperative space between the two launched Airy beams as an indep…

Accurate expansion of cylindrical paraxial waves for its straightforward implementation in electromagnetic scattering

2017

Abstract The evaluation of vector wave fields can be accurately performed by means of diffraction integrals, differential equations and also series expansions. In this paper, a Bessel series expansion which basis relies on the exact solution of the Helmholtz equation in cylindrical coordinates is theoretically developed for the straightforward yet accurate description of low-numerical-aperture focal waves. The validity of this approach is confirmed by explicit application to Gaussian beams and apertured focused fields in the paraxial regime. Finally we discuss how our procedure can be favorably implemented in scattering problems.

Focal waveforms with tunable carrier frequency using dispersive aperturing

2008

We introduce the concept of dispersive aperturing involving a beam truncation by hard-edge apertures where diameter of the processed beam changes upon frequency. Applied to focused waves, this procedure transforms power spectra at the focal point (and the surroundings). Waveforms at focus conserve pulse duration but carrier frequency may be altered substantially. In principle, some degrees of freedom allow carrier-frequency tuning at convenience.

Substantial enlargement of angular existence range for Dyakonov-like surface waves at semi-infinite metal-dielectric superlattice

2012

We investigated surface waves guided by the boundary of a semi-infinite layered metal-dielectric nanostructure cut normally to the layers and a semi-infinite dielectric material. Using the Floquet-Bloch formalism, we found that Dyakonov-like surface waves with hybrid polarization can propagate in dramatically enhanced angular range compared to conventional birefringent materials. Our numerical simulations for an Ag-GaAs stack in contact with glass show a low to moderate influence of losses. This research was funded by the Qatar National Research Fund under the project NPRP 09-462-1-074, by the Spanish Ministry of Economy and Competitiveness under the project TEC2009-11635, and by the Serbia…

Controlling the carrier-envelope phase of few-cycle focused laser beams with a dispersive beam expander

2008

We report on a procedure to focalize few-cycle laser pulses in dispersive media with controlled waveform. Stationarity of the carrier-envelope phase for extended depth of focus is attained by shaping the spatial dispersion of the ultrashort beam. An adjustable group velocity is locally tuned in order to match a prescribed phase velocity at focus. A hybrid diffractive-refractive lens system is proposed to drive the wavefield to an immersion microscope objective under convenient broadband modulation. Numerical simulations demonstrate robustness over positioning of this dispersive beam expander.

Debye representation of dispersive focused waves

2006

We report on a matrix-based diffraction integral that evaluates the focal field of any diffraction-limited axisymmetric complex system. This diffraction formula is a generalization of the Debye integral applied to apertured focused beams, which may be accommodated to broadband problems. Longitudinal chromatic aberration may limit the convenience of the Debye formulation and, additionally, spatial boundaries of validity around the focal point are provided. Fresnel number is reformulated in order to guarantee that the focal region is entirely into the region of validity of the Debye approximation when the Fresnel number of the focusing geometry largely exceeds unity. We have applied the matri…

Oblique surface waves at an interface between a metal–dielectric superlattice and an isotropic dielectric

2012

We investigate the existence and dispersion characteristics of surface waves that propagate at an interface between a metal–dielectric superlattice and an isotropic dielectric. Within the long-wavelength limit, when the effective-medium (EM) approximation is valid, the superlattice behaves like a uniaxial plasmonic crystal with the main optical axes perpendicular to the metal–dielectric interfaces. We demonstrate that if such a semi-infinite plasmonic crystal is cut normally to the layer interfaces and brought into contact with a semi-infinite dielectric, a new type of surface mode can appear. Such modes can propagate obliquely to the optical axes if favorable conditions regarding the thick…

Diffraction-managed superlensing using metallodielectric heterostructures

2012

We show that subwavelength diffracted wave fields may be managed inside multilayered plasmonic devices to achieve ultra-resolving lensing. For that purpose we first transform both homogeneous waves and a broad band of evanescent waves into propagating Bloch modes by means of a metal/dielectric (MD) superlattice. Beam spreading is subsequently compensated by means of negative refraction in a plasmon-induced anisotropic effective-medium that is cemented behind. A precise design of the superlens doublet may lead to nearly aberration-free images with subwavelength resolution in spite of using optical paths longer than a wavelength. This research was funded by the Spanish Ministry of Economy and…