Optoelectronic switch and continuosly tunable filter based on a liquid crystal waveguide.

In this paper the possibility of using ferroelectric liquid crystals in active waveguide devices is explored through the analysis of an integrated electro-optic switch and a continuously tunable filter. The design and the analysis of two electro-optical devices, based on a Bragg grating integrated in a glass waveguide having liquid crystal as cover, are presented. The integrated optics structure allows to change the reflectivity of the Bragg mirror by means of electro-optic effects of smectic liquid crystals. The integrated fast electro-optic switch is based on electro-optic properties of smectic C* in the Surface Stabilised liquid crystal structure and on the selective properties of integrated Bragg grating. It presents the output directly in the frequency domain, overcoming the typical problems of intensity dependent devices, without requiring external electronic circuit. Moreover the possibility to realise a novel continuously tunable integrated filter, combining the linear electro-optic effect of smectic A* and the selective property of Bragg grating, has been explored. The proposed filter is characterised by a narrow bandwidth, desired feature for WDM technique. The principal advantages of such device include fast tuning speed, wide tuning range, low power consumption and low cost.