Interactions of accessible solitons with interfaces in anisotropic media: the case of uniaxial nematic liquid crystals

Abstract

We investigate, both theoretically and experimentally, spatial soliton interaction with dielectric interfaces in a strongly anisotropic medium with nonlocality, such as nematic liquid crystals. We throw light on the role of refractive index gradients as well as optic axis variations in both voltage-and self-driven angular steering of non-local solitons. We specifically address and then employ in experiments a suitably designed electrode geometry in a liquid crystalline cell in order to define and tune a graded dielectric interface by exploiting the electrooptic response of the material through the in-plane reorientation of the optic axis in two distinct regions. We study both refraction and total internal reflection as well as voltage controlled steering of spatial solitons.

Power-controlled transition from standard to negative refraction in reorientational soft matter

“…% 0:2 in the visible spectrum), with walk-off (angular departure of Poynting vector from wavevector) as large as E7°, thus enhancing the role of anisotropy at dielectric interfaces 30,31 ; moreover, they are transparent from infrared to ultraviolet, with losses mainly due to Rayleigh scattering 23,24 ; finally, their response is such that a non-perturbative nonlinear regime can be experimentally accessed in the context of classical optics 32 .…”

Interactions of Self-Localised Optical Wavepackets in Reorientational Soft Matter

“…Nematicons can be similarly refracted at interfaces that delineate NLC regions with different background orientations of the optic axis, resulting in unequal refractive indices. However, in spite of their particle-like behaviour resembling plane waves with a principal wavevector, since nematicons are extended nonlinear wavepackets in a nonlinear medium, their refraction and reflection can depart from those of linear light beams [74].…”

Nematicons and Their Electro-Optic Control: Light Localization and Signal Readdressing via Reorientation in Liquid Crystals

“…The nematicon trajectories for input wavevectors k || ẑ were computed via Equation (4) and are shown in Figure 9d,e , assuming the input beam is launched in region 1 corresponding to y > 0 (in region 2 y < 0). We note that, due to the initial walk-off, nematicons interact with the interface, even when the wavevector, k , is parallel to ẑ , allowing larger overall deflections as compared to an isotropic material [ 35 ]. The interface attracts and repels the soliton when V 1 < V 2 and V 1 > V 2 , respectively, with the output nematicon position and angle depending on both the bias difference Δ V = V 1 –V 2 and the absolute value |V 1 | (or |V 2 | ), due to the medium anisotropy [ 35 ].…”

“…Increasing V 2 , the angle of refraction increases ( Figure 10a–c ). Conversely, when V 2 = 0, the angle of incidence changes with V 1 , due to walk-off; in this case, the Poynting vector after the transition can point towards negative y , due to significant walk-off, resulting in nematicon transmission through the interface, even under TIR conditions for the wavevector; for instance, Figure 10d ( V 1 = 0.9 V) displays an outgoing nematicon that propagates nearly parallel to the interface [ 35 ]. For V 1 > 0.9 V, the soliton undergoes TIR; see Figure 10e,f .…”

“…Corresponding graphs of ( e ) nematicon trajectory in yz and ( f ) its slope. Noteworthy, non-specular reflection can be observed, due to the optical anisotropy [ 35 , 36 ].…”