S

Before UV

illumination After 90

min of UV

exposure

After 120

min of UV

exposure

N. Karimi*, A. Alberucci, M. Virkki, A. Priimägi, M. Kauranen and G. Assanto Faculty of Natural Science, Tampere University of Technology, FI-33101 Tampere, Finland

* E-mail: nazanin.karimi@tut.fi

Quenching nematicon fluctuations via photo-stabilization

Temporal fluctuations of the nematicon trajectories in the observation plane yz in a time window of 4.5 s

References

1) G. Assanto and M. Peccianti, “Spatial solitons in nematic liquid crystals”, IEEE J. Quantum Electron. 39, pp. 13‐21, 2003

2) M. Peccianti and G. Assanto, “Nematicons”, Phys. Rep. 516, pp. 147-208, 2012

3) Y. Aihara, M. Kinoshita, J. Wang, J.-I. Mamiya, A. Priimagi and A. Shishido, “Polymer Stabilization Enhances the Orientational Optical

Nonlinearity of Oligothiophene-Doped nematic liquid crystals”, Adv. Opt. Mater. 1, pp. 787-791, 2013

Abstract

Nematic liquid crystals (NLC) have been extensively employed to generate stable three-dimensional light-induced

waveguides (nematicons) at mW power levels, exploiting all-optical reorientation of the liquid crystal molecules for

self-trapping. At large powers, these spatial solitons are subject to dynamic instabilities due to the interplay between

nonlinear response, thermal agitation, and anchoring at the boundaries. Such instabilities manifest as trajectory

fluctuations in time, the larger the power, the stronger the fluctuations are. Here, we report on our preliminary results

on reducing nematicon transverse fluctuations through photo-induced polymerization in a doped NLC. These results

are promising towards the realization of a soft-matter platform for light-defined guided-wave elements.

Intensity evolution of 3 mW near-IR ordinary and extraordinary-polarized beams propagating in the NLC cell

Top and side view of a planar cell filled up with NLCs

z

y

x

input

interface

z

x

y

beam

3 mm

θ0

beam 100 μm

Reorientational nonlinearity Molecular reorientation

in the nematic phase n||

n

n ^

Nematic phase

θ

Soliton formation

E E z

y y

z Δn

I

Linear diffraction

y y

z z

s k

n

0

s : Poynting vector

k : wave vector

n : optic axis

: walk-off angle

NLC material:

4-Cyano-4’-pentylbiphenyl (5CB),

doped with

6-(4-Cyano-biphenyl-4’-yloxy)hexyl

acrylate (A4CB)

The aperture of the trajectory cone nearly

halved in angle after 120 min UV

exposure, as compared to the case before

illumination.

No penalty on the nonlinear response was

observed.

This improvement can be attributed to

higher viscosity of LC material through

partial polymerization.

Ordinary-polarized Extraordinary-polarized