Radial Tilt Detection Using Push–Pull Signals

Abstract

A high-density optical disk system uses an objective lens with a high numerical aperture (NA) and a light source with a short wavelength (λ). However, the coma aberration caused by a relative radial tilt between the objective lens and an optical disk increases in proportion to NA3/λ. Therefore, the reliability of the optical disk system can be improved by detecting and compensating the radial tilt because the coma aberration deteriorates the read and write performance. This paper describes a radial tilt detection method that is based on analysis of the intensity distribution of reflected light from the optical disk. This method can be performed with high accuracy even at the boundary area of recorded and unrecorded tracks, and with an objective lens displacement. Furthermore, a tracking error signal detection method that can be used with the tilt detection method simultaneously is described. Its performance was confirmed experimentally using the optical pickup for a Blu-ray Disc (BD).