By using a special design of electrode pattern and the differential biased circuit, the gradient of the electric field distribution inside the liquid crystal sample cell can be achieved through the adjustment of driving voltage. The characteristics of positive or negative types of lens can be converted by changing the polarity of gradient within the sample cell which posses the homogeneous alignment. The liquid crystal lens with a variable focal length and the tunable types of focusing is demonstrated by utilizing the controllable distribution of electric field. This special design incorporating with the fabrication technology of TFT has a potential to develop a large scale of liquid crystal lens.

It is difficult to fabricate electrode, which have gradient electric field from edge to center by applying voltage. In this study, a gradient refractive index profile can be easily formed. We change the experimental parameter about exposure time of UV light, concentration of PVK film and the Cell gap to investigate the influence on focal length. As the exposure time increase, the differences in conductivity become large from edge to center, which create better index distribution. For high concentration of PVK films, UV light can not effectively improve the conductivity of transmittance zone, which case the worse index distribution. The increasing of cell gap resulting in poor distribution of the refractive index, which cause larger focal length.

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