Developing a quality assessment method for evaluating focusing quality of an LC lens used in an optical pickup

Abstract

The liquid crystal (LC) lens with multi-ring electrodes for cameras in cell phones is designed in this study based on theoretical analysis, simulations and optimization. This study starts with the calculations to show that a substantial size reduction of a lens module can be offered by an insertion of LC lens. As compared to conventional cameras, the lens module in phone cameras particularly requires shorter focal length (around 8cm) and larger aperture (greater than 3 mm). The currently available LC lenses, however, fails to provide both the above capabilities. To remedy the problem, the method to design a large-aperture LC lens with multi-ring electrodes is developed in this study, and a new quality-assessment method is developed to evaluate the designed multi-ring LC lens via point spread function (PSF) and modulation transfer function (MTF). The number and widths of the ring-type electrodes are further optimized to reach certain required levels of PSF and MTF for the LC lens. This is achieved by designating a finite number of ring electrodes first and then assigning the width of each electrode proportional to the slope of the required applied voltage along the radius of the LC lens. Optimization results show that the three-ring LC lens with ring widths particularly designed reached satisfactory MTF of 65% for 5 and 48% for 7 line pairs per millimeter, which are not increased significantly even with the ring number increased to seven.