D. Pierangeli

Observation of an intrinsic nonlinearity in the electro-optic response of freezing relaxors ferroelectrics

We demonstrate an electro-optic response that is linear in the amplitude but independent of the sign of the applied electric field. The symmetry-preserving linear electro-optic effect emerges at low applied electric fields in freezing nanodisordered KNTN above the dielectric peak temperature, deep into the nominal paraelectric phase. Strong temperature dependence allows us to attribute the phenomenon to an anomalously reduced thermal agitation in the reorientational response of the underlying polar-nanoregions.

Super-crystals in composite ferroelectrics

As atoms and molecules condense to form solids, a crystalline state can emerge with its highly ordered geometry and subnanometric lattice constant. In some physical systems, such as ferroelectric perovskites, a perfect crystalline structure forms even when the condensing substances are non-stoichiometric. The resulting solids have compositional disorder and complex macroscopic properties, such as giant susceptibilities and non-ergodicity. Here, we observe the spontaneous formation of a cubic structure in composite ferroelectric potassium–lithium–tantalate–niobate with micrometric lattice constant, 104 times larger than that of the underlying perovskite lattice. The 3D effect is observed in specifically designed samples in which the substitutional mixture varies periodically along one specific crystal axis. Laser propagation indicates a coherent polarization super-crystal that produces an optical X-ray diffractometry, an ordered mesoscopic state of matter with important implications for critical phenomena and applications in miniaturized 3D optical technologies.

Aging solitons in photorefractive dipolar glasses

We study experimentally the aging of optical spatial solitons in a dipolar glass hosted by a nanodisordered sample of photorefractive potassium-sodium-tantalate-niobate (KNTN). As the system ages, the waves erratically explore varying strengths of the nonlinear response, causing them to break up and scatter. We show that this process can still lead to solitons, but in a generalized form for which the changing response is compensated by changing the normalized wave size and intensity so as to maintain fixed the optical waveform.

Intrinsic negative mass from nonlinearity

We propose and provide experimental evidence of a mechanism able to support negative intrinsic effective mass. The idea is to use a shape-sensitive nonlinearity to change the sign of the mass in the leading linear propagation equation. Intrinsic negative-mass dynamics is reported for light beams in a ferroelectric crystal substrate, where the diffusive photorefractive nonlinearity leads to a negative-mass Schrödinger equation. The signature of inverted dynamics is the observation of beams repelled from strongly guiding integrated waveguides irrespective of wavelength and intensity and suggests shape-sensitive nonlinearity as a basic mechanism leading to intrinsic negative mass.

Observation of polarization-maintaining light propagation in depoled compositionally disordered ferroelectrics

We investigate the evolution of the state of polarization of light propagating through bulk depoled composite ferroelectrics below the Curie temperature. In contrast to standard depoled ferroelectrics, where random birefringence causes depolarization and scattering, light is observed to suffer varying degrees of depolarization and remains fully polarized when linearly polarized along the crystal principal axes. The effect is found to be supported by the formation of polarized speckles organized into a spatial lattice and occurs as the ferroelectric settles into a spontaneous super-crystal, a three-dimensional coherent mosaic of ferroelectric clusters. The polarization lattices gradually disappear as the ferroelectric state reduces to a disordered distribution of polar nanoregions above the critical point.

Anti-diffracting beams through the diffusive optical nonlinearity

Anti-diffraction is a theoretically predicted nonlinear optical phenomenon that occurs when a light beam spontaneously focalizes independently of its intensity. We observe anti-diffracting beams supported by the peak-intensity-independent diffusive nonlinearity that are able to shrink below their diffraction-limited size in photorefractive lithium-enriched potassium-tantalate-niobate (KTN:Li).

Miniaturized electro-optic infrared beam-manipulator based on 3D photorefractive funnels

We demonstrate tunable electro-optic guiding, shaping, and switching of beams in the near infrared spectrum ( 980 nm), typical of VCSEL technology, using biomimetic 3D funnel waveguides miniaturized into a sample of potassium–lithium–tantalate–niobate. The switchable waveguides are written using the slow photorefractive build-up of a 3D volume space-charge field caused by a diffracting continuous wave low intensity λ = 532 nm beam, and electro-optic functionality is supported by the quadratic electro-optic effect of the high-symmetry paraelectric phase.

Observation of replica symmetry breaking in disordered nonlinear wave propagation

A landmark of statistical mechanics, spin-glass theory describes critical phenomena in disordered systems that range from condensed matter to biophysics and social dynamics. The most fascinating concept is the breaking of replica symmetry: identical copies of the randomly interacting system that manifest completely different dynamics. Replica symmetry breaking has been predicted in nonlinear wave propagation, including Bose-Einstein condensates and optics, but it has never been observed. Here, we report the experimental evidence of replica symmetry breaking in optical wave propagation, a phenomenon that emerges from the interplay of disorder and nonlinearity. When mode interaction dominates light dynamics in a disordered optical waveguide, different experimental realizations are found to have an anomalous overlap intensity distribution that signals a transition to an optical glassy phase. The findings demonstrate that nonlinear propagation can manifest features typical of spin-glasses and provide a novel platform for testing so-far unexplored fundamental physical theories for complex systems.Replica symmetry breaking describes identical copies of a randomly interacting system exhibiting different dynamics. Here, Pierangeli et al. observe this critical phenomenon in the optical wave propagation inside a disordered nonlinear waveguide.

Photorefractive solitons in an out-of-equilibrium disordered ferroelectric

We study two-dimensional soliton beams in disordered ferroelectrics. Super-cooling accelerates photorefractive response and changes steady-state anisotropy. Effects are attributed to the anomalous polarization response of polar-nano-regions.