Eugenio DelRe

Electro-optic beam manipulation through photorefractive needles

We demonstrate electro-optic spatial two-dimensional mode switching in a bulk sample of potassium lithium tantalate niobate. Spatial confinement, mode coupling, and electro-optic functionality are mediated by two photorefractive needle solitons of opposite electroholographic charges embedded together in their anisotropic lobular structure.

Anisotropic charge displacement supporting isolated photorefractive optical needles

Strong asymmetry in the charge distribution supporting a single noninteracting 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.

Pairing space-charge field conditions with self-guiding for the attainment of circular symmetry in photorefractive solitons

By means of a comparative study, we identify a specific physical mechanism that leads to circular-symmetric two-dimensional photorefractive solitons, and determine the conditions for their observation. For a given photorefractive crystal, this allows the control of the transition from an elliptical soliton-supporting regime to a round soliton-supporting one. This indicates a basic recipe to generate electro-optic devices in three-dimensional crystals compatible with single-mode fiber.

Shock Waves in Disordered Media

We experimentally investigate the interplay between spatial shock waves and the degree of disorder during nonlinear optical propagation in a thermal defocusing medium. We characterize the way the shock point is affected by the amount of disorder and scales with wave amplitude. Evidence for the existence of a phase diagram in terms of nonlinearity and amount of randomness is reported. The results are in quantitative agreement with a theoretical approach based on the hydrodynamic approximation.

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.

Equalizing disordered ferroelectrics for diffraction cancellation

We show how the cross-over effect of dipolar glasses can be used to observe diffraction cancellation in composite ferroelectric samples independently of composition. We are able to selectively frustrate the dielectric anomaly of different compositionally disordered photorefractive ferroelectrics to achieve scale-free optical propagation at one same temperature.

Optical nonlinearity and existence conditions for quasi-steady-state photorefractive solitons

Generalizing soliton description using spatiotemporal wave variables, we identify and experimentally validate the nonlinearity supporting quasi-steady-state solitons in biased photorefractive crystals for the one-dimensional case, the transient counterpart of the explicit one-dimensional screening soliton theory. The approach leads to a non-Kerr-like spatially local exponential nonlinearity and explicitly provides soliton existence conditions. These find quantitative agreement with a series of experiments in potassium lithium tantalate niobate and reproduce previously described transient behavior.

Approach to space-charge field description in photorefractive crystals

Recent analytical results in the frame of photorefractive spatial-soliton propagation are exploited to derive a novel scheme for the investigation of space-charge field formation in photorefractive crystals. The procedure is specialized to describe a two-wave mixing configuration. To test our predictions, we have performed an experiment in a sample of BaTiO3.

Measurement of scaling laws for shock waves in thermal nonlocal media

We are able to detect the details of spatial optical collisionless wave breaking through the high aperture imaging of a beam suffering shock in a fluorescent nonlinear nonlocal thermal medium. This allows us to directly measure how nonlocality and nonlinearity affect the point of shock formation and compare results with numerical simulations.

Subwavelength optical spatial solitons and three-dimensional localization in disordered ferroelectrics: Toward metamaterials of nonlinear origin

We predict the existence of a class of multidimensional light localizations in out-of-equilibrium ferroelectric crystals. In two dimensions, the nondiffracting beams form at an arbitrary low-power level and propagate even when their width is well below the optical wavelength. In three dimensions, a subwavelength light bullet is found. The effects emerge when compositionally disordered crystals are brought to their metastable glassy state, and leading to the suppression of evanescent waves, they can have a profound impact on super-resolved imaging and ultradense optical storage, resembling metamaterials in many ways.