Guided wave all-optical devices based on liquid crystals

In the present work, we will review our recent work on guided wave photonic devices using liquid crystals for optical switching and filtering signals at wavelengths of C-band (1530-1565 nm) used in fiber optic systems [1]. Such devices are based either on liquid crystal core waveguides or phase gratings made of composite materials using liquid crystals and polymers. We will show how nonlinear optical effects in nematic liquid crystals can be exploited to obtain light modulation and all-optical switching of signals by using an optical control. A POLICRYPS (POlymer LIquid CRYstal Polymer Slices) phase grating, made of a methyl-red doped nematic liquid crystal alternated to polymer slices, as an overlayer on top of an ion-exchanged waveguide is used to obtain a tunable optical filter. The filter is optically driven a green light signal by exploiting the trans-cis photo-isomerization of methyl-red molecules which brake the homogeneous alignment of nematic liquid crystals in the POLICRYPS, inducing a phase change in the grating and tuning the filter optical response. Both experimental and theoretical findings will be presented. References: [1] D. C. Zografopoulos, R. Asquini, E. E. Kriezis, A. d'Alessandro, R. Beccherelli, Guided-wave liquid crystal photonics. Lab on a chip 12, 3598, (2012) [2] A. d’Alessandro, R. Asquini, M. Trotta, G. Gilardi, R. Beccherelli, I. C. Khoo, All-optical intensity modulation of near infrared light in a liquid crystal channel waveguide, Appl. Phys. Let., 97, 093302, (2010). [3] G. Gilardi, L. de Sio, R. Beccherelli, R. Asquini, A. d'Alessandro and C. Umeton, Observation of tuneable optical filtering in photosensitive composite structures containing liquid crystals, Opt. Let. 36, 24, 4755 (2011).