Research on fabrication method for tunable liquid lenticular lens arrays with shifted viewing zones

Abstract

Multi-view display system is a promising method for three-dimensional image realization. The system produces three-dimensional images by localizing several viewing zones. This provides motion parallax to a certain angle of viewing zone as the observer moves inside the area. As the number of viewing zones increases, the multi-view system provides more smooth motion parallax. However, the limitation is that the resolution become lower simultaneously. In this paper, a fabrication of liquid-filled tunable lenticular lens array is proposed for an idea of increasing viewing zones without resolution loss. The liquid lenticular lens array operates by using electro-wetting principle which modifies the surface tension of liquids on a solid surface using a voltage. By applying certain voltages, the structural shape of the liquid in a chamber can become a lenticular lens shape from initial state. In addition, the left and right electrodes of the proposed liquid lenticular lens are separated so that different voltages can be applied to each side. This results in shifted viewing zones as the optical axis of the liquid lens is tilted. Therefore, the number of viewing zones can be doubled by switching optical axes of the liquid lenticular lens array quickly. The liquid-filled lenticular lens array consists of two different types of liquids and a chamber. The master mold of the chamber is fabricated by wet-etching process on a <100> silicon wafer by KOH solution to make a trapezoidal-shaped chamber. The liquid lens with slanted side walls have an advantage of achieving high dioptric power. After electroplating process to make a nickel mold, the chamber structure is replicated in poly methyl methacrylate (PMMA) by hot embossing. Shadow evaporation is used to deposit gold separately on each side of sidewalls, and additional patterning processes including metal transfer micro-molding method are conducted for the electrode separation patterning. The proposed liquid lenticular lens array operates as three states of convex lenticular lens array. Left and right directional tilted states, and a normal state without tilting effect are those. The tilting angle of each tilted states is ±4°. At the tilted states, the measured positions of viewing zones are shifted by ±4° horizontally. Therefore, the entire field of view is increased by 8 degrees. Furthermore, as combining the shifted viewing zones at the same time, the number of viewing zones generated by the proposed liquid lenticular lens array can be expected to be increased in three times with time-multiplexing process.