Papers by Alessandro Ciattoni
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
Optical parametric amplification (OPA) is a second-order nonlinear optical process whereby a sign... more Optical parametric amplification (OPA) is a second-order nonlinear optical process whereby a signal field is amplified by a pump while generating an idler field, and allows the generation of broadly tunable coherent radiation for many photonic applications, e.g. spontaneous parametric down-conversion [1] for entangled photon pair generation. Here we demonstrate single-pass OPA at the ultimate thickness limit in monolayer transition-metal dichalcogenides [2] . The absence of dispersion-induced phase mismatch, thanks to the vanishing thickness of the nonlinear medium, bypasses phase-matching requirements and achieves ultrabroad amplification bandwidths ( Fig. 1a-b ), with a linear dependence of the amplification gain with pump and signal powers ( Fig. 1c ).
Scientific Reports, 2016
Periodic patterns of photo-excited carriers on a semiconductor surface profoundly modifies its ef... more Periodic patterns of photo-excited carriers on a semiconductor surface profoundly modifies its effective permittivity, creating a stationary all-optical quasi-metallic metamaterial. Intriguingly, one can tailor its artificial birefringence to modulate with unprecedented degrees of freedom both the amplitude and phase of a quantum cascade laser (QCL) subject to optical feedback from such an anisotropic reflector. Here, we conceive and devise a reconfigurable photo-designed Terahertz (THz) modulator and exploit it in a proof-of-concept experiment to control the emission properties of THz QCLs. Photo-exciting sub-wavelength metastructures on silicon, we induce polarization-dependent changes in the intra-cavity THz field, that can be probed by monitoring the voltage across the QCL terminals. This inherently flexible approach promises groundbreaking impact on THz photonics applications, including THz phase modulators, fast switches, and active hyperbolic media.
Physical Review B, 2015
We develop, from first principles, a general and compact formalism for predicting the electromagn... more We develop, from first principles, a general and compact formalism for predicting the electromagnetic response of a metamaterial with non-magnetic inclusions in the long wavelength limit, including spatial dispersion up to the second order. Specifically, by resorting to a suitable multiscale technique, we show that medium effective permittivity tensor and the first and second order tensors describing spatial dispersion can be evaluated by averaging suitable spatially rapidly-varying fields each satysifing electrostatic-like equations within the metamaterial unit cell. For metamaterials with negligible second-order spatial dispersion, we exploit the equivalence of first-order spatial dispersion and reciprocal bianisotropic electromagnetic response to deduce a simple expression for the metamaterial chirality tensor. Such an expression allows us to systematically analyze the effect of the composite spatial symmetry properties on electromagnetic chirality. We find that even if a metamaterial is geometrically achiral, i.e. it is indistinguishable from its mirror image, it shows pseudo-chiral-omega electromagnetic chirality if the rotation needed to restore the dielectric profile after the reflection is either a 0 • or 90 • rotation around an axis orthogonal to the reflection plane. These two symmetric situations encompass two-dimensional and one-dimensional metamaterials with chiral response. As an example admitting full analytical description, we discuss one-dimensional metamaterials whose single chirality parameter is shown to be directly related to the metamaterial dielectric profile by quadratures.
Physical Review A, 2015
We investigate the nonlinear optical features of a graphene sheet embedded in an active cavity an... more We investigate the nonlinear optical features of a graphene sheet embedded in an active cavity and we show that, when tuned near its lasing threshold, the cavity is able to isolate the spatially localized graphene nonlinearity thus producing a very strong nonlinear device response with multivalued features. As opposed to standard situations where the small thickness of the graphene sheet hampers its remarkable nonlinear optical properties to be exploited, in our scheme the strong nonlinear optical regime is mainly triggered by the very intrinsic planar localization of graphene nonlinearity. The proposed strategy for exploiting graphene nonlinearity through its unleashing could open novel routes for conceiving ultra-efficient nonlinear photonic devices.
Laser-Induced Damage in Optical Materials: 2002 and 7th International Workshop on Laser Beam and Optics Characterization, 2003
ABSTRACT
Journal of Physics D: Applied Physics, 2015
We investigate the nonlinear optical features of a graphene sheet embedded in an active cavity an... more We investigate the nonlinear optical features of a graphene sheet embedded in an active cavity and we show that, when tuned near its lasing threshold, the cavity is able to isolate the spatially localized graphene nonlinearity thus producing a very strong nonlinear device response with multivalued features. As opposed to standard situations where the small thickness of the graphene sheet hampers its remarkable nonlinear optical properties to be exploited, in our scheme the strong nonlinear optical regime is mainly triggered by the very intrinsic planar localization of graphene nonlinearity. The proposed strategy for exploiting graphene nonlinearity through its unleashing could open novel routes for conceiving ultra-efficient nonlinear photonic devices.
Lecture Notes in Electrical Engineering, 2015
ABSTRACT
Conference on Lasers and Electro-Optics 2010, 2010
ABSTRACT We consider specific metamaterials hosting a novel extreme nonlinear regime where the li... more ABSTRACT We consider specific metamaterials hosting a novel extreme nonlinear regime where the linear and nonlinear dielectric responses are comparable, a regime supporting peculiar beams whose power flow direction reverses its sign along the transverse profile.
Optics Express, 2009
We demonstrate the electro-activation of funnel waveguides through the quadratic electro-optic ef... more We demonstrate the electro-activation of funnel waveguides through the quadratic electro-optic effect in paraelectric potassiumlithium-tantalate-niobate. This allows us to achieve electro-optic intensity modulation in a single optical beam, a 1x2 switch, and finally the electrically controlled morphing of a single waveguide into a 1x2 and a 1x4 divider.
Optics Express, 2002
We derive the analytical expression of the Stokes parameters corresponding to a Gaussian beam pro... more We derive the analytical expression of the Stokes parameters corresponding to a Gaussian beam propagating along the optical axis of a uniaxial crystal, pointing the simultaneous effects of anisotropy and diffraction out. The theoretical results are compared with experimental measurements at the output of a calcite crystal, showing a good agreement.
Physical Review E, 2004
A vector propagation scheme for describing electromagnetic nondiffracting beams (X waves͒ is intr... more A vector propagation scheme for describing electromagnetic nondiffracting beams (X waves͒ is introduced. In particular we show that, from the knowledge of the transverse field components on a given transverse plane and at a fixed instant, it is possible to predict the whole electric field everywhere which in particular allows us to investigate the imaging properties of nondiffracting beam. Furthermore, we show that the longitudinal field component crucially depends on the pulse velocity and that it can be neglected only if the velocity is slightly greater than c. The proposed formalism is tested by means of two examples, the vector fundamental and Gaussian X waves which admit analytical treatment. As an application of the propagation scheme, we derive in closed form the expressions for the field propagator showing that its transverse component formally coincides with one of the scalar fundamental X wave.
Physical Review A, 2008
We analytically investigate solitons counterpropagating in a longitudinally modulated Kerr medium... more We analytically investigate solitons counterpropagating in a longitudinally modulated Kerr medium by means of the Hirota bilinear approach. We show that Hirota solvability ͑partial integrability of the system͒ physically corresponds to the exact mutual cancellation of the effects of all the underlying nonlinear gratings. This cancellation is achieved in two different situation: either through a suitable choice of the field profile or by means of a peculiar tailoring of the nonlinear modulation. In the first situation we obtain both bright and dark one-soliton solutions whose intensity ratio between forward and backward propagating beams is set by the nonlinear modulation. In the second situation, we derive two-soliton solutions obtained by nonlinearly dressing two independent linear grating eigenmodes sharing the same propagation constant.
Physical Review A, 2012
We theoretically predict efficient optical second-harmonic generation (SHG) from a micrometer-thi... more We theoretically predict efficient optical second-harmonic generation (SHG) from a micrometer-thick slab consisting of a quadratic nonlinear anisotropic medium whose linear principal permittivities have, at the fundamental wavelength, real parts of different signs (indefinite permittivity) and magnitude smaller than 1. We show that, by illuminating the slab with a p-polarized fundamental wave (with intensity of a few MW/cm 2), highly efficient scattering of the second-harmonic field occurs in conditions at which the slab is linearly fully transparent for the fundamental wave. The high efficiency of the SHG process stems from the enhancement of the longitudinal field, perpendicular to the slab surface, produced by the very small value of the slab dielectric permittivities. We investigate the role played by medium losses, showing that, even in the strong-absorption regime, the described process yields a second-harmonic field which is much stronger than that produced by a standard (not indefinite) nonlinear slab.
Optics Letters, 2006
Transverse instabilities are shown to accompany counterpropagation of optical beams through refle... more Transverse instabilities are shown to accompany counterpropagation of optical beams through reflection gratings in Kerr media. The instability threshold of continuous waves is analytically derived, and it is shown that the presence of the grating broadens and narrows the stability region of plane waves in focusing and defocusing media, respectively. Furthermore, counterpropagating soliton stability is numerically investigated and compared with the transverse modulation instability analysis, revealing an underlying physical link.
Optics Letters, 2001
The strong asymmetry in charge distribution supporting a single non-interacting spatial needle so... more 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.
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Papers by Alessandro Ciattoni