Mechanical analogies for nonlinear light beams in nonlocal nematic liquid crystals

The equations governing nonlinear light beam propagation in nematic liquid crystals form a (2+1)-dimensional system consisting of a nonlinear Schrödinger-type equation for the electric field of the wavepacket and an elliptic equation for the reorientational response of the medium. The latter is "nonlocal" in the sense that it is much wider than the size of the beam. Due to these nonlocal, nonlinear features, there are no known general solutions of the nematic equations; hence, approximate methods have been found convenient to analyze nonlinear beam propagation in such media, particularly the approximation of solitary waves as mechanical particles moving in a potential. We review the use of dynamical equations to analyze solitary wave propagation in nematic liquid crystals through a number of examples involving their trajectory control, including comparisons with experimental results from the literature. Finally, we make a few general remarks on the existence and stability of optically self-localized solutions of the nematic equations

Vortex nematicons in planar cells

We provide experimental evidence that stable vortex-solitons in nematic liquid crystals, termed vortex nematicons, can be generated in planar cells without any external biases, neither electric nor magnetic. We report on nonlinear vortices with extraordinary-wave beams in various undoped samples, pin-pointing how material nonlocality and birefringence aid their stable propagation. Finally, we also demonstrate confinement and waveguiding of an incoherent co-polarized probe signal by the nonlinear vortex

Erratum: Thermo-optic soliton routing in nematic liquid crystals(Optics Letters (2018)43:10(2296-2299)` DOI: 10.1364/OL.43.002296)

We recently reported on controlling optical spatial solitons in nematic liquid crystals through changes of the sample temperature in Ref. [1]. In particular, we demonstrated that both trajectory and confinement of the self-induced waveguides can be altered by exploiting the thermo-optic dependence of the refractive indices and the mechanical constants. After publication, we have noticed misprints in the expression Eq. (3) detailing the walk-off dependence on the refractive indices of the material. The correct formula is (see, e.g., Ref. [2]) In addition, the vertical axes of the photographs in Figs. 1–4 were affected by a scaling error. Here, we provide revised versions of the figures with amended y-axes. Figures 1–4 replace Figs. 1–4 of the previous article in print Ref. [1], respectively. Please note that the captions of all figures are the same as in Ref. [1]. While we apologize for the regrettable oversights, we stress that the error affected only the picture scaling, whereas the graphs Figs. 2(d) and 4(d) did show the correct values. Thus, the indicated scaling changes do not influence either the interpretation of the reported phenomena or the scientific conclusions of the article

Interplay of thermo-optic and reorientational responses in nematicon generation

Employing several nematic liquid crystal mixtures, we investigate how the thermo-optic response of nonlinear birefringent soft-matter affects the propagation of light beams and the features of self-induced waveguides. We address the formation of optical spatial solitons and the control of their trajectories versus temperature, comparing the measurements with the expectations based on a simplified model, showing an excellent agreement. Moreover, in a guest⁻host mixture with an absorbing dye dopant, we study the competition between reorientational and thermal nonlinearities, demonstrating that the two processes can be adjusted independently in order to tune the soliton properties, i.e., trajectory and confinement strength. Our results are an important contribution to better comprehend the role played by material properties on linear and nonlinear beam propagation, as well as their exploitation for signal processing and addressing

Nonlinear competition in nematicon propagation

We investigate the role of competing nonlinear responses in the formation and propagation of bright spatial solitons. We use nematic liquid crystals (NLCs) exhibiting both thermo-optic and reorientational nonlinearities with continuous-wave beams. In a suitably prepared dye-doped sample and dual beam collinear geometry, thermal heating in the visible affects reorientational self-focusing in the near infrared, altering light propagation and self-trapping