The photoinduced optical non-linear effect in nematic liquid crystals is analyzed. On this basis, an optical-optical device is obtained based on the principle of liquid crystal displays. First, the beam propagation in a simple model which is obtained based on liquid crystal displays is given by Jones matrix. Secondly, the external voltage is replaced by an oblique incidence control beam to reorientate the molecule of the liquid crystals. Base on this principle, the phase and power of the out-put beam is modulated by the control beam. Finally, the influence of temperature on optical-optical control devices is investigated based on the temperature characteristics of 5CB liquid crystal. Numerically results indicate that the phase difference of out-put light increases monotonically with the raise of the control beam intensity, so the power of the out-put beam appears periodic oscillation with the increases of the control beam intensity. The out-put beam intensity of the signal beam can be linear modulated by the adjustment of the control beam intensity when the control beam intensity changes from 0.5(MW·m-2) to 1.1(MW·m-2). It is found that the power of the out-put beam shows periodic oscillation with the increases of the temperature when the control light intensity is fixed. This discovery shows a available scheme for the achievement of optical device.