Study on the analysis of the crosstalk and the performance improvement of the liquid lenticular lens array

Abstract

Multi-view technology that forms multiple viewing zones has become a major form of autostereoscopic 3D displays. There are two types of multi-view displays: those with a parallax barrier and those with a lenticular lens. The lenticular lens type has dominated the 3D display market because its high brightness and resolution. However, in this lenticular lens system, the lens array in front of the display has a fixed shape and consequent-ly it is difficult to show 2D images. To convert 3D images to 2D images and vice versa, methods using liquid crystal lenses, liquid tunable lens, and liquid lenticular lenses have been researched. In particular, the liquid len-ticular lens type is relatively simple and operates under high speeds because of the electrowetting phenomenon. The electrowetting phenomenon changes the surface tension by varying electrical potential difference. Water and oil are used because they are immiscible and they form liquid lens. By applying a voltage to water, the fo-cal length of the lens could be tuned as a contact angle of water changes. 3D and 2D images can be observed with a convex and a flat lens state respectively by changing the applied voltage. Liquid lenticular lens array was fabricated through the microelectromechanical system (MEMS) process. To make a chamber, silicon mold was fabricated and nickel electroplating was done. Polymer chamber was made through a hot embossing process. Electrode layer and dielectric layer were deposited through thermal evaporation and chemical vapor deposition (CVD) respectively. Oil and water dosing was done and followed by sealing process. The oil used for dosing consists of a mixture of dodecane and bromonaphthalene with a certain ratio to match the refractive index of the polymer chamber. To operate the liquid lenticular lens, two electrode layers are needed. One electrode was deposited on the polycarbonate chamber and the other elec-trode was deposited on the sealing glass. By applying voltage to two electrode, water moves and oil forms len-ticular lens. However, liquid lenticular lens system causes crosstalk which is a double image and degrades clear 3D images. This undesired phenomenon happens when parts of the image intended to be seen by one eye become visible to the other eye. In this study, methods of reducing the crosstalk are presented and improved perfor-mance was demonstrated. To reduce the crosstalk of the liquid lenticular lens, diopter of the lens which is a main factor for measuring the optical power of a lens and quantifying clear 3D images should be increased and the unnecessary light which does not pass through the liquid lens should be blocked. In the liquid lenticular lens system, diopter can be increased by the chamber material because the difference of the refractive index be-tween D.I. water and oil determines the refraction of the light from the display. Removing the bottom part of the electrode also helps increase the diopter of the liquid lens because the bottom part of the electrode causes the oil to get together easily when the high voltage is applied. The change of the crosstalk according to the diop-ter of the liquid lenticular lens array was presented. Unnecessary light that passes through the top part and the wall part of the chamber was analyzed and the ratio of the unnecessary light from the top and the wall part of the chamber was theoretically calculated. The unnecessary light was blocked using the laminating foil and in-creasing the thickness of the electrode layer. Operation tests were done using the improved liquid lenticular lens array and the reduction of the crosstalk of the lens was demonstrated.