Integral imaging (InI) based light field display method offers a great opportunity to achieve true 3D scene rendering with correct focus cues required for mitigating the well-known vergence-accommodation conflicts. However, one of the main challenges that still needs to be solved is the tradeoff between the spatial resolution and depth resolution. Improving the depth resolution requires the increase of the number of distinct views, which is referred to as the view number, for rendering a 3D scene, while increasing the view number often comes at the cost of the spatial resolution of the scene. In this paper, we describe the design of a time multiplexed InI based light field display that can potentially increase the spatial resolution while maintaining the viewing number and thus depth resolution. By incorporating a high-speed programmable switchable shutter array and synchronizing different elemental image sets rendered on the display with the shutter array in a time-multiplexing fashion, the proposed method can rapidly render a 3D scene from slightly different viewing perspectives. Consequently, the scheme can improve the spatial resolution without compromising the viewing density and eyebox size. By choosing appropriate parameters, the proposed method can render as many as 4 by 4 views with in a 6mm eye box while providing an angular resolution about 1.27 arc mins.
An innovative concept is proposed for an optical element which offers the capability of rapidly switching the optical power of the system among multiple foci. The switchable multifocal element consists of a custom-designed freeform lens offering multiple discrete foci and a programmable high-speed liquid crystal shutter (LCS). The freeform lens is divided into patterned zones, through which multiple distinct foci are produced. The LCS consists of patterned zones corresponding to those zones of the freeform lens, which can be programmably switched on and off. By combining the multi-focal freeform lens and the LCS in a time-multiplexed fashion, a switchable multifocal element with high-speed, large aperture and large range of tunable power was achieved. The multifocal element also meets the other requirement of an ideal tunable optical element such as low-voltage control, robustness, and compactness. A proof-of-concept twofocal head mounted display was designed to demonstrate one application of the new switchable multifocal element. The design can provide a FOV of 40 degrees and angular resolution of 1 arc minutes in visual space in an 8mm by 8mm exit pupil.
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