1 Liquid Crystals & Photonics group, ELIS Department, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium, ilias. manolis@ elis. UGent. be 2 Department of Electronic Engineering, University of Rome “La Sapienza”, via Eudossiana 18, 00184, Rome, Italy 3CNR-Institute for Microelectronics and Microsystems-Section of Rome, via del Fosso del Cavaliere 100, 00133, Rome, Italy