Correction of Substrate Vertical Birefringence Using Patterned Wave Plate

Abstract

In an optical disk system in which an optical head with a polarizing optics is employed and light is focused through a substrate of the disk, the read/write characteristics of the system are degraded by the birefringence of the substrate. A polycarbonate substrate has both an in-plane birefringence and a vertical birefringence. The birefringence of the polycarbonate substrate is measured and its influence is estimated by a numerical calculation. It is understood that the in-plane birefringence simply decreases light intensity at the photodetector, while the vertical birefringence not only decreases light intensity at the photodetector but also increases a focused spot diameter on the disk and decreases the resolution of a radio frequency (RF) signal. A method of correcting the vertical birefringence using a newly developed patterned wave plate is proposed to improve the read/write characteristics of an optical disk system. Increases in the light intensity and resolution using a patterned wave plate are confirmed experimentally.