E. DelRe

One-dimensional steady-state photorefractive spatial solitons in centrosymmetric paraelectric potassium lithium tantalate niobate

We report the first observation of spatial one-dimensional photorefractive screening solitons in centrosymmetric media and compare the experimental results with recent theoretical predictions. We find good qualitative agreement with theory.

Soliton electro-optic effects in paraelectrics

The combination of charge separation induced by the formation of a single photorefractive screening soliton and an applied external bias field in a paraelectric is shown to lead to a family of useful electro-optic guiding patterns and properties.

Self-focusing and self-trapping in unbiased centrosymmetric photorefractive media

We predict self-focusing and self-trapping of optical beams propagating in unbiased centrosymmetric photorefractive crystals in the near-transition paraelectric phase, where the nonlinear response is proportional to the square of the diffusion space-charge field.

Wiggling and bending-free micron-sized solitons in periodically biased photorefractives

Considering nonlinear optical propagation through photore-fractive crystals in which the bias voltage is periodically modulated along the propagation direction, we are able to identify the conditions in which a beam forms a soliton in a straight line down to micron-sized widths. The effect, which is numerically investigated considering the full (3+1)D spatio-temporal light-matter dynamics, emerges when the period of modulation of the bias is smaller than the beam diffraction length. In conditions in which the two scales are comparable, the soliton follows a characteristic wiggling trajectory, oscillating in response to the oscillating bias. The finding indicates a method to achieve highly miniaturized soliton-based photonic applications that do not require specific off-axis alignment.

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.

Electro-activation and electro-morphing of photorefractive funnel waveguides

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.

Beam shaping and effective guiding in the bulk of photorefractive crystals through linear beam dynamics

The authors demonstrate a technique to optically imprint through linear beam propagation an index pattern in the bulk of a photorefractive crystal capable of beam reshaping and waveguiding. The procedure is based on the separation into two distinct phases of the photosensitive and refractive response, so that light is in all cases undergoing only linear propagation. When saturation in the response becomes dominant, the scheme is able to achieve both one-dimensional and two-dimensional waveguiding. The result allows the straightforward writing of multiwaveguide circuits, where traditional schemes based on spatial solitons are in practice burdened by nonlinearity.

NONLINEAR OPTICAL PROPAGATION PHENOMENA IN NEAR-TRANSITION CENTROSYMMETRIC PHOTOREFRACTIVE CRYSTALS

We relate on a series of optical nonlinear propagation phenomena, mediated by photorefraction, present in ferroelectric crystals heated above the Curie point, in proximity of the critical regime. In particular, we discuss centrosymmetric screening solitons, diffusion-driven anisotropic nonlinear diffraction, ellipticity locking, diffusion-driven solitons, and spatial beam head-on collisions.

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.

Collisions and inhomogeneous forces between solitons of different dimensionality

We exploit nonlinear propagation in photorefractive crystals to observe the phenomenology associated with the collision and interaction of solitons of different tranverse dimensions: a self-trapped stripe and a round soliton. Along with evidence of particlelike behavior, our results indicate the emergence of a new phenomenology related to the hybrid-dimensional system.