Compatible Objective Lens for Blu-ray Disc and Degital Versatile Disc Using Diffractive Optical Element and Phase-Step Element which Corrects both Chromatic and Spherical Aberrations

Abstract

A compatible lens with a diffractive optical element that overcomes differences in disk thickness and longitudinal chromatic aberration and phase steps that eliminate chromatic spherical aberrations are proposed. Both blue and red parallel incident rays can be converged on both disks; therefore, the servo and readout signals can be detected by a single common photodetector. A compatible optical head, which can write Blu-ray Discs (BDs) and degital versatile discs (DVDs) with only one objective lens assembly and one photodetector, can be achieved. We show the convergence of the blue and red parallel incident rays and signal readout using the compatible objective lens.