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Tunability is a core issue for the operation of all-optical photonic devices and circuits. Highly resolved wavelength selectivity and precisely defined dispersion must be actively tuned and stabilized to be practically useful. Further, if the nonlinear response itself can be tuned then a new range of all optical switching devices may be realized. This project has attacked this challenging task both theoretically and experimentally.
We achieved dramatic reduction of the threshold power for nonlinear effects via infiltration of liquid-crystal defects into periodic structures. By placing the liquid crystal defect layer asymmetrically inside the periodic structure, we observed a nonreciprocal response. We succeeded in reversing this by using a pair of defects, one of them a nonlinear liquid crystal defect layer, and varying the input wavelength, resulting in reversible optical diode operation.
In further work we have demonstrated that a one-dimensional photonic crystal with a homeotropic nematic liquid crystal defect behaves as a polarization-sensitive nonlinear all-optical device. In further studies of liquid infiltrated photonic crystal fibres we succeeded in switching of the nonlinear behaviour of the structures from focusing to defocusing by taking advantage of the precise temperature tunability of the liquid infiltrated fibres.
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