Write and erase mechanism of surface controlled bistable nematic pixel

Recently a new nematic bistable pixel, using simple monostable planar ancho rings, has been proposed [4-6]. This pixel can be switched between two text ures, having the same boundary conditions but different optical properties: one texture (U) is undistorted, whereas the other one (T) is characterized by the presence of a half-turn twist. The U --> T switching was obtained b y abruptly dropping the driving electric field. A slow decrease of the driv ing electric field favors the T --> U transition. The electric field fall r ate discriminates the kind of coupling between the boundary surfaces; hydro dynamic or elastic. Here we show the same behavior of this system by using square electric field pulses. We present experimental results concerning th e critical values (amplitude and duration) of the driving signals, for whic h the elastic and the hydrodynamic effects are balanced and we measure thei r optimized values. Our results are in reasonable agreement with the theore tical predictions obtained by a simplified model.