A polarizer film is used for converting polarized light from a backlight module into light along a first direction. Multiple electrodes are disposed on a transparent substrate. Each electrode extends along a second direction different from the first direction. An alignment of liquid crystal molecules varies according to voltage applied on the electrodes. A retard unit is disposed between the transparent substrate and the polarizer film and used for converting the polarized light into light along a third direction different from the first and second direction. A polarization direction of the emitted light is perpendicular to an alignment of an electrode layer. In this way, an optical axis of the liquid crystal molecules matches the polarization direction of the light from the retard unit when voltage is not applied. So, the maximal lens power is attained with decreasing the cost resulted from the decreased thickness of the liquid crystal layer.