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Routing of anisotropic spatial solitons and modulational instability in liquid crystals

Abstract

In certain materials, the spontaneous spreading of a laser beam (owing to diffraction) can be compensated for by the interplay of optical intensity and material nonlinearity. The resulting non-diffracting beams are called ‘spatial solitons’ (refs 1–3), and they have been observed in various bulk media4,5,6. In nematic liquid crystals7,8,9, solitons can be produced at milliwatt power levels10,11,12 and have been investigated for both practical applications13 and as a means of exploring fundamental aspects of light interactions with soft matter14,15. Spatial solitons effectively operate as waveguides, and so can be considered as a means of channelling optical information along the self-sustaining filament. But actual steering of these solitons within the medium has proved more problematic, being limited to tilts of just a fraction of a degree16,17,18,19,20. Here we report the results of an experimental and theoretical investigation of voltage-controlled ‘walk-off’ and steering of self-localized light in nematic liquid crystals. We find not only that the propagation direction of individual spatial solitons can be tuned by several degrees, but also that an array of direction-tunable solitons can be generated by modulation instability21,22,23,24,25. Such control capabilities might find application in reconfigurable optical interconnects, optical tweezers and optical surgical techniques.

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Figure 1: Sketch of the sample.
Figure 2: Spatial soliton voltage routing.
Figure 3: Spatial soliton trajectories and walk-off.
Figure 4: Observation of anisotropic modulational instability and generation of multiple spatial solitons for two different biases.

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Acknowledgements

We thank A. Alberucci, G. Coschignano and A. Fratalocchi for support in the laboratory.

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Correspondence to Gaetano Assanto.

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The authors declare that they have no competing financial interests.

Supplementary information

Supplementary Video 1

This movie shows the voltage-controlled steering of a spatial soliton acquired by the CCD camera. (MPG 2383 kb)

Supplementary material Word file

The file contains 4 supplementary figures, and equations. Supplementary figures 1-3 report additional experimental results. Supplementary figure 4 shows the coefficients of the theoretical model. Supplementary equations concern a brief outline of the derivation of the model and the determination of the director angle profile. (DOC 434 kb)

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Peccianti, M., Conti, C., Assanto, G. et al. Routing of anisotropic spatial solitons and modulational instability in liquid crystals. Nature 432, 733–737 (2004). https://doi.org/10.1038/nature03101

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