The Study Of Wavefront Coding Technology And Its Application For Tunable Liquid Lens

Wavefront coding technology is a hybird optical/digital technology based on Fourier Optics. By designing a special optical mask to code the system'optical transfer function (OTF) and using digital processes to decode the coded intermediate image, additional capacities not possible with a purely optical system can be achieved. In the ways of lowering cost and enabling digital imaging system to extend the depth of field (DoF) by more than ten times without stopping down the aperture nor declining lateral resolution, it draws great attentions among researchers specialized in optics and computer graphics. Besides extending DoF, this technology is also shows an attractive way for reducing DoF and estimating the out-of-focus appearance of the objects, known as passive ranging. However, in-depth researches on these aspects are not well-defined.In this dissertation, comprehensively theoretical work was carried out to dissert the applications of wavefront coding technology in passive ranging and DoF controlling. Impacts on the alignment error from the mismatch between the coordinates of the cosine mask for passive ranging together with the cubic phase mask for extending DoF and the coordinates of the optical system have been discussed, which demonstrate the necessity of the match between the coordinates of the digital filter and those of the mask function. Fisher Information Matrixes are used to analyze the corresponding accuracy of the passive ranging and the image restoration, and the Cramer-rao bounds are derived with their.OTF respectively. Meanwhile, the accuracy of defocus parameter estimation is studied based on various input spectrum. Additionally, the roles of wavefront coding technology in reduction of DoF are introduced. In order to maximize the reduction effect, required phase function is designed by objective function constructed by Hilbert space angle of the system OTF with different defocus parameters. By representing the phase function for reducing DoF in form of sine series, its corresponding parameters are optimized using the adaptive genetic algorithm (AGA). Obvious reduced DoF can be observed from the simulation results.A liquid tunable focus lens fabricated with a convenient and low-cost process that combined single-point diamond turning (SPDT) with soft lithography using polydimethylsiloxane (PDMS) is also introduced in this dissertation. And a novel proposal by combining the wavefront coding technology with liquid tunable focus lens is also demonstrated. First, an improved model for tunable liquid lens with double cavities is proposed in this paper. Compared to the normal structure combined of a single lens cavity and a single PDMS membrane, the new structure with double cavities promises a safer bonding between the lens cavity and the PDMS membrane. Then we use the liquid tunable focus lens to improve the processes for passive ranging through wavefront coding technolgy based on this structure. The influence of the spherical aberration with the liquid lens, together with the calibration of the focal length of the lens with the mask for passive ranging, is also analyzed there.Finally, as larger focal depth provides the optical system with higher tolerance to the defocus-related aberrations, a novel liquid tunable lens is presented, in which a petal cubic phase plate is integrated into the lens's cavity. With this structure, both focal length tunability and an enhance DOF can be simultaneously achieved in the same liquid lens, it can make the liquid lens a more powerful tool for imaging systems. Optical performances of the hybrid lens are disserted by using the Zemax software. Considering the limit of processing conditions, we take the rotational symmetric quartic function to fabricate the liquid tunable lens with extending DoF phase plate. Experimental results demonstrate that both focal length tunability and extended DOF can be achieved with the proposed liquid lens. It gives appliable example to the application of the wavefront coding technology to the liquid tunable focus lens.