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Nematicons and their electro-optic control: light localization and signal readdressing via reorientation in liquid crystals.

Piccardi A, Alberucci A, Assanto G - Int J Mol Sci (2013)

Bottom Line: Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies.Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing.Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing.

View Article: PubMed Central - PubMed

Affiliation: Nonlinear Optics and OptoElectronics Lab (NooEL), University of Rome "Roma Tre", Via della Vasca Navale 84, Rome 00146, Italy. assanto@uniroma3.it.

ABSTRACT
Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely "nematicons". Nematicons can guide other light signals and interact with inhomogeneities and other beams. Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing. Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing.

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(a) Photographs of frequency-controlled nematicon steering; (b)Walk-off versus bias frequency for various rms (root mean square) voltage values. The lines intersect when, at the crossover frequency, the dielectric anisotropy is zero and, therefore, there is no electric reorientation; (c) Relative beam width (w0 is the initial waist) versus frequency. The frequency-dependent reorientation also affects the nonlinearity, which vanishes at the crossover value.
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f13-ijms-14-19932: (a) Photographs of frequency-controlled nematicon steering; (b)Walk-off versus bias frequency for various rms (root mean square) voltage values. The lines intersect when, at the crossover frequency, the dielectric anisotropy is zero and, therefore, there is no electric reorientation; (c) Relative beam width (w0 is the initial waist) versus frequency. The frequency-dependent reorientation also affects the nonlinearity, which vanishes at the crossover value.

Mentions: For V = 2.5, 3.5 and 6 V, we varied the frequency, f, from f = 1 kHz to f = 100 kHz and measured the soliton walk-off δ(f), as graphed in Figure 13b. Starting from the value at low frequency, the walk-off decreased until 0º at f = fc for all three voltages; then, it changed sign for f > fc, i.e., when the electric torque changed sign. Moreover, as is visible from the acquired images in Figure 13a and from the graph of the waist versus f in Figure 13c, the nonlinear response strongly depended on f, with the beam loosing confinement for f = fc, where the anisotropy, and thus, n2, according to Equation (3), became negligible. Using this dependence of the optic axis reorientation from frequency, we could maximize the steering exclusively due to walk-off variations up to Δδ ≈ 13º, with a deflection twice larger than in standard NLC (see Figure 8).


Nematicons and their electro-optic control: light localization and signal readdressing via reorientation in liquid crystals.

Piccardi A, Alberucci A, Assanto G - Int J Mol Sci (2013)

(a) Photographs of frequency-controlled nematicon steering; (b)Walk-off versus bias frequency for various rms (root mean square) voltage values. The lines intersect when, at the crossover frequency, the dielectric anisotropy is zero and, therefore, there is no electric reorientation; (c) Relative beam width (w0 is the initial waist) versus frequency. The frequency-dependent reorientation also affects the nonlinearity, which vanishes at the crossover value.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3821595&req=5

f13-ijms-14-19932: (a) Photographs of frequency-controlled nematicon steering; (b)Walk-off versus bias frequency for various rms (root mean square) voltage values. The lines intersect when, at the crossover frequency, the dielectric anisotropy is zero and, therefore, there is no electric reorientation; (c) Relative beam width (w0 is the initial waist) versus frequency. The frequency-dependent reorientation also affects the nonlinearity, which vanishes at the crossover value.
Mentions: For V = 2.5, 3.5 and 6 V, we varied the frequency, f, from f = 1 kHz to f = 100 kHz and measured the soliton walk-off δ(f), as graphed in Figure 13b. Starting from the value at low frequency, the walk-off decreased until 0º at f = fc for all three voltages; then, it changed sign for f > fc, i.e., when the electric torque changed sign. Moreover, as is visible from the acquired images in Figure 13a and from the graph of the waist versus f in Figure 13c, the nonlinear response strongly depended on f, with the beam loosing confinement for f = fc, where the anisotropy, and thus, n2, according to Equation (3), became negligible. Using this dependence of the optic axis reorientation from frequency, we could maximize the steering exclusively due to walk-off variations up to Δδ ≈ 13º, with a deflection twice larger than in standard NLC (see Figure 8).

Bottom Line: Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies.Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing.Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing.

View Article: PubMed Central - PubMed

Affiliation: Nonlinear Optics and OptoElectronics Lab (NooEL), University of Rome "Roma Tre", Via della Vasca Navale 84, Rome 00146, Italy. assanto@uniroma3.it.

ABSTRACT
Liquid crystals in the nematic phase exhibit substantial reorientation when the molecules are driven by electric fields of any frequencies. Exploiting such a response at optical frequencies, self-focusing supports transverse localization of light and the propagation of self-confined beams and waveguides, namely "nematicons". Nematicons can guide other light signals and interact with inhomogeneities and other beams. Moreover, they can be effectively deviated by using the electro-optic response of the medium, leading to several strategies for voltage-controlled reconfiguration of light-induced guided-wave circuits and signal readdressing. Hereby, we outline the main features of nematicons and review the outstanding progress achieved in the last twelve years on beam self-trapping and electro-optic readdressing.

Show MeSH