Observation of Optical Spatial Solitons in a Highly Nonlocal Medium

We report on the observation and quantitative assessment of self-trapped pulsating beams in a highly nonlocal nonlinear regime. The experiments were conducted in nematic liquid crystals and allow a meaningful comparison with the prediction of a scalar theory in the perturbative limit, while addressing the need for beyond-paraxial analytical treatments.

Figure 1

(a) Experimental setup: a $75\mu \mathrm{m}$ thick (along $x$) planarly aligned nematic LC cell is voltage biased via thin-film electrodes. A light beam impinges from the left and propagates along $z$. A CCD camera with a microscope monitors the beam evolution along $y$ and $z$ by acquiring images of the scattered light from the top. (b) The photo of a typical pulsating soliton. (c) Plot of relative error $e=(\mathrm{\text{measured}}-\mathrm{\text{actual}})/(\mathrm{\text{actual}})$ in evaluating the beam waist from the scattered light, as modeled by a Gaussian blur. The cell thickness is much larger than the beam, justifying the radial symmetry assumption.

Figure 2

Measured SW waist versus propagation distance for various excitation powers $P_{in}$.

Figure 3

Observation of accessible solitons: (a) maximum waist versus power; (b) inverse square of waist vs power; (c) period vs power (error bars are negligibly small); (d) inverse square of waist vs period. The solid lines are best fits from the theory.