In this paper, we describe a hybrid nonlinear P-P Bistable Optical Device (BOD), the length of its cavity is controllable. The dynamic equations of the system and the equilibrium splution which shows the optical bistable nature are given. The bis-tability and linear modulation characteristics are discussed. The stability of the equilibrium state and the "critical slowing down" effect of transient behavior are analysed. The experimental demonstrations are in agreement with the theoretical evaluations.