arXiv subjects

Alessandro Ciattoni

Publications and source records attributed to Alessandro Ciattoni.

47 records · Page 3Linked to original sources

arXiv2011

Highly efficient second-harmonic generation from indefinite epsilon-near-zero slabs of subwavelength thickness

We theoretically predict efficient optical second-harmonic generation (SHG) from a few hundred nanometer thick slab consisting of a quadratic nonlinear anisotropic medium whose linear principal permittivities are, at the fundamental wavelength, very small and have different signs (indefinite medium). We show that, by illuminating the slab with a p-polarized fundamental wave (with intensity of a few MW/cm^2), a highly efficient scattering of the second-harmonic field occurs when the conditions of linear complete slab transparency for the fundamental wave are met. The high efficiency of the SHG process, stems from the large non-plasmonic enhancement of the longitudinal field, perpendicular to the slab surface, produced by the very small value of the slab dielectric permittivities. A suitable nano-structured composite is proposed and numerically designed for observing the novel non-phase-matched and highly efficient SHG process from nano-structures.

physics.optics↗

arXiv2011

All-optical active plasmonic devices with memory and power switching functionalities based on epsilon-near-zero nonlinear metamaterials

All-optical active plasmonic devices are of fundamental importance for designing efficient nanophotonic circuits. We theoretically propose and numerically investigate an active plasmonic device made up of a nonlinear epsilon-near-zero metamaterial slab of thickness smaller than 100 nanometers lying on a linear epsilon-near-zero metamaterial substrate. We predict that, in free-space coupling configuration, the device, operating at low-intensity, would display plasmon mediated hysteresis behavior since the phase difference between the reflected and the incident optical waves turns out to be multi-valued and dependent on the history of the excitation process. Such an hysteresis behavior would allow to regard the proposed device as a compact memory unit whose state is accessible by measuring either the mentioned phase difference or the power, which is multi-valued as well, carried by the nonlinear plasmon wave. Since multiple plasmon powers comprise both positive and negative values, the device would also operate as a switch of the plasmon power direction at each jump along an hysteresis loop.

physics.optics↗

arXiv2010

Two-peaked and flat-top perfect bright solitons in epsilon-near-zero nonlinear metamaterials: novel Kerr self-trapping mechanisms

We analytically investigate transverse magnetic (TM) spatial bright solitons, as exact solutions of Maxwell's equations, propagating through nonlinear metamaterials whose linear dielectric permittivity is very close to zero and whose effective nonlinear Kerr parameters can be tailored to achieve values not available in standard materials. Exploiting the fact that, in the considered medium, linear and nonlinear polarization can be comparable at feasible and realistic optical intensities, we identify two novel self-trapping mechanisms able to support two-peaked and flat-top solitons, respectively. Specifically, these two novel mechanisms are based on the occurrence of critical points at which the effective nonlinear permittivity vanishes, the two mechanisms differing in the way the compensation between linear and nonlinear polarization is achieved through the non-standard values of the nonlinear parameters.

physics.optics↗

arXiv2010

Multistability at arbitrary low optical intensities in a metallo-dielectric layered structure

We show that a nonlinear metallo-dielectric layered slab of subwavelength thickness and very small average dielectric permittivity displays optical multistable behavior at arbitrary low optical intensities. This is due to the fact that, in the presence of the small linear permittivity, one of the multiple electromagnetic slab states exists no matter how small is the transmitted optical intensity. We prove that multiple states at ultra-low optical intensities can be reached only by simultaneously operating on the incident optical intensity and incidence angle. By performing full wave simulations, we prove that the predicted phenomenology is feasible and very robust.

physics.optics↗

arXiv2010

Two-parameters electromagnetic hysteresis of a subwavelength nonlinear epsilon-near-zero slab

We consider propagation of transverse magnetic electromagnetic waves through a nonlinear metamaterial slab, of subwavelength thickness and very small average dielectric permittivity, made up of alternating metal and dielectric nonlinear layers. Exploiting the effective-medium approach, we prove that the output field intensity is a multi-valued function of both the input field intensity and incidence angle so that the transmissivity exhibits a novel kind of multi-stability and a pronounced two-parameter hysteresis behavior. The predicted two-parameter hysteresis physically stems from the fact that, since the linear and nonlinear contributions to the overall dielectric response can be comparable, the slab can host more than one electromagnetic configuration compatible with the incident field and the boundary conditions, regardless of the slab thickness. We investigate slab transmission also through full wave simulations proving the robustness of the two-parameter hysteresis beyond the effective-medium approximation.

physics.optics↗

arXiv2010

Transmissivity directional hysteresis of a nonlinear metamaterial slab with very small linear permittivity

We investigate propagation of a transverse magnetic field through a nonlinear metamaterial slab of sub-wavelength thickness and with a very small and negative linear dielectric permittivity. We prove that, for a given input intensity, the output intensity is a multi-valued function of the field incidence angle so that the transmissivity exhibits angular multi-stability and a pronounced directional hysteresis behavior. The predicted directional hysteresis is a consequence of the fact that the linear and nonlinear contributions to the overall dielectric response can be comparable so that the electromagnetic matching conditions at the output slab boundary allow more than one field configurations within the slab to be compatible with the transmitted field.

physics.optics↗

arXiv2008

Tailoring wave nonlinearity through spatial composites

We propose and demonstrate theoretically a method to achieve and design optical nonlinear responses through a light-mediated spatial hybridization of different standard nonlinearities. The mechanism is based on the fact that optical propagation through a spatial composite of different nonlinear media is governed by an effective nonlinear response if the spatial scale of the sequence is much smaller than the light diffraction length. We apply our general approach to the significant case of centrosymmetric photorefractive crystal biased by a periodically modulated external voltage to predict strictly bending-free miniaturized soliton propagation.

physics.optics↗

arXiv2007

Quantum electromagnetic X-waves

We show that two distinct quantum states of the electromagnetic field can be associated to a classical vector X wave or a propagation-invariant solution of Maxwell equations. The difference between the two states is of pure quantum mechanical origin since they are internally entangled and disentangled, respectively and can be generated by different linear or nonlinear processes. Detection and generation of Schrödinger-cat states comprising two entangled X-waves and their possible applications are discussed.

physics.optics↗

arXiv2004

Perfect Optical Solitons: Spatial Kerr Solitons as Exact Solutions of Maxwell's Equations

We prove that spatial Kerr solitons, usually obtained in the frame of nonlinear Schroedinger equation valid in the paraxial approximation, can be found in a generalized form as exact solutions of Maxwell's equations. In particular, they are shown to exist, both in the bright and dark version, as linearly polarized exactly integrable one-dimensional solitons, and to reduce to the standard paraxial form in the limit of small intensities. In the two-dimensional case, they are shown to exist as azimuthally polarized circularly symmetric dark solitons. Both one and two-dimensional dark solitons exhibit a characteristic signature in that their asymptotic intensity cannot exceed a threshold value in correspondence of which their width reaches a minimum subwavelength value.

physics.optics↗

arXiv2004

Azimuthally polarized spatial dark solitons: exact solutions of Maxwell's equations in a Kerr medium

Spatial Kerr solitons, typically associated with the standard paraxial nonlinear Schroedinger equation, are shown to exist to all nonparaxial orders, as exact solutions of Maxwell's equations in the presence of vectorial Kerr effect. More precisely, we prove the existence of azimuthally polarized, spatial, dark soliton solutions of Maxwell's equations, while exact linearly polarized (2+1)-D solitons do not exist. Our ab initio approach predicts the existence of dark solitons up to an upper value of the maximum field amplitude, corresponding to a minimum soliton width of about one fourth of the wavelength.

physics.optics↗

arXiv2000

Anisotropic charge displacement supporting isolated photorefractive optical needles

The strong asymmetry in charge distribution supporting a single non-interacting spatial needle soliton in a paraelectric photorefractive is directly observed by means of electroholographic readout. Whereas in trapping conditions a quasi-circular wave is supported, the underlying double-dipolar structure can be made to support two distinct propagation modes.

physics.optics↗