Jassem Safioui

Pyroliton: pyroelectric spatial soliton

The concept of optical beam self-trapping in pyroelectric photorefractive medium is presented. We show that the temperature controlled spontaneous polarisation of ferroelectric crystals produces an optical nonlinearity that can lead to formation of 2-D spatial soliton named pyroliton. Experimental demonstrations performed in lithium niobate crystals illustrate that efficient self-trapping occurs either for ordinary or extraordinary polarisation under moderate temperature increase. For instance, a 15 microm diameter pyroliton can be formed with a 10 degree temperature raise.

Polarization and configuration dependence of beam self-focusing in photorefractive LiNbO 3

We present numerical and experimental analyses showing the formation of (2+1)D spatial photorefractive solitons at visible wavelengths in electrically biased lithium niobate crystals for ordinary and extraordinary light polarizations. Similarly sized self-trapped beams are observed for both polarizations, despite the polarization-dependent electro-optic coefficients. The tensorial character of the photovoltaic effect is shown to play a key role. The soliton-induced waveguides are able to properly guide telecommunication wavelengths. Finally, a higher degree of anisotropy is observed for ordinary polarized solitons for specific electro-optic configurations, which reveals the presence of the photorefractive field component perpendicular to the applied field. Experimental results are confirmed by a time-dependent numerical model.

All-optical technique to measure the pyroelectric coefficient in electro-optic crystals

We report an all-optical method to measure the pyroelectric coefficient p of electro-optic crystals. Through this technique, we first acquire the birefringence variation δΔn of the crystal as a function of its temperature T, both in closed and open-circuit conditions, using a Senarmont phase-compensation configuration. Then the pyroelectric field is deduced from the difference between these two measurements, so it leads to the material spontaneous polarization change, whose derivative with respect to the temperature finally gives p. This technique is applied on congruent and stoichiometric lithium niobate.

Light coupling with a nonlinear prism.

We propose the use of a prism with nonlinear optical properties to improve the prism-coupling method. The principle is based on the inscription of an adapted waveguide inside this prism by beam self-trapping to enhance the coupling efficiency and stability. The experimental demonstration is realized with a prism diced from a LiNbO3 wafer to couple light into a resonator.

Pyroelectric Surface-Wave Soliton

Pyroelectric surface-wave solitons are formed at the interface between a nonlinear photorefractive medium and a low index medium. Surface-wave soliton arises from light attraction to the surface and trapping by an asymmetric self-focusing index change.

Beam self-trapping in pyroelectric photorefractive crystals

While most photorefractive (PR) beam self-trapping configurations require application of a high external voltage [1] we instead propose to use PR pyroelectric medium to efficiently trap beams by simple temperature control. This new concept is based on uniform temperature change of a pyroelectric PR crystal which creates an internal electric field that is screened under a local illumination by nonlinear photorefractive effect. Experimental demonstration is performed in the widely available photonic material Lithium niobate (LiNbO3).