Design of liquid crystal lens for the compensation of spherical aberration in the Blu-ray optical pickup

Abstract

There are many proposals and studies for the high density optical data storages with a data capacity over 150GB. Multi-layer recording is consider as one of the best candidates for the next generation optical data storage since it can be realized with an addition of a few optical components in the current Blu-ray (BD) optical pickup. Of course, it is required to compensate the spherical aberration between the recording layers in the multi-layer disk. A novel liquid crystal (LC) lens is proposed and designed to compensate the spherical aberration occurred by the difference of substrate thickness. New structure of liquid crystal (LC) lens includes both concave and convex surfaces which can compensate the spherical aberration with a relatively long range. Since previously developed LC panel showed very low tolerance to the shift of objective lens, new design was proposed with a special LC lens structure to improve both characteristics of the shift tolerance and compensation range. The refractive index of LC lens is changed by applying a voltage on the ITO electrodes prepared with a curvature surface. Therefore, a focal point of the transmitted light can be changed with a careful control of applied voltage, resulting in a compensation of the spherical aberration. Several types of LC lens, including spherical and aspherical surfaces, were designed and their performance was simulated theoretically. With an optimized curvature control with the spherical LC lens, the aberration of BD optical pickup can be kept under 0.018λRMS even for the thickness variation of ±25μm.