Voltage-driven beam bistability in a reorientational uniaxial dielectric

Abstract

We report on voltage controlled bistability of optical beams propagating in a nonlocal reorientational uniaxial dielectric, namely, nematic liquid crystals. In the nonlinear regime where spatial solitons can be generated, two stable states are accessible to a beam of given power in a finite interval of applied voltages, one state corresponding to linear diffraction and the other to self-confinement. We observe such a first-order transition and the associated hysteresis in a configuration when both the beam and the voltage reorientate the molecules beyond a threshold.

Self-confined light waves in nematic liquid crystals

“…Since the evolution of spatial solitary waves is essentially governed by their main wavevector, nematicons propagating across a graded-index or abrupt dielectric interface are subject to standard or anomalous refraction (depending on the angle of incidence and the orientation of the optic axis) [81,82,83], as well as total internal reflection and lateral beam displacement [84,85]. They also exhibit confinement bistability in cavityless geometries versus beam power [86,87,88], applied voltage [89] and angle of incidence [90] and are able to form multicolour, vector and cluster states [55,91,92,93,94,95]. Finally, reorientational solitons can coexist/compete with either electronic [65,96,97] or thermal responses in NLC [30,31,32,98,99,100,101], yielding novel features in suitably doped materials [67,102,103,104,105].…”

“…for −L ≤ y ≤ L was assumed, so that at y = ±L the electric field essentially vanishes. Hence, the background orientation resulting from this bias can, in principle, be calculated from the director equation (89) with u = 0. However, the resulting equation is a form of the parabolic cylinder equation [154], not useful to evaluate the integrals in the momentum equation (95).…”

Bistable Beam Propagation in Liquid Crystals

“…As shown in Fig. 7(a), we investigated the propagation of a P = 2 mW beam for various applied voltages: selfconfinement occurred when all-optical and electric responses sufficed to overcome the FT [37]. This was observed above V = 1 V, when the beam width gradually reduced until it resulted into a spatial soliton.…”

“…In this Paper we address, both experimentally and theoretically, OB between wave-propagation states corresponding to beam diffraction and spatial solitons, respectively, in an optically nonlinear as well as electro-optic reorientational medium, namely nematic liquid crystals (NLC), where either the optical power or the bias voltage can control light localization and its evolution/switching between different states. With respect to our previous works [36], [37], here we generalize the approach of Ref. [38] developing a general theory based upon the Green function, and accounting for the simultaneous presence of voltage and optical fields.…”

Optically-driven switching of a planar nematic liquid crystal cell with parallel rubbing

“…In liquid crystals such nonlinearities are already noticeable for milliwatt powers of an optical beam [2]. Optical reorientation in liquid crystals is commonly used for the generation of spatial optical solitons [3][4][5][6].…”