Optical pickup apparatus, optical disc apparatus, and track recognition signal detection method

摘要

A primary spot and a secondary spot are formed on an optical disc 101. The primary spot is used for recording and reproduction. The secondary spot is positioned apart from the primary spot. The secondary spot differs from the primary spot in a distance from an objective lens. This distance (defocus amount) Def satisfies a range: 0.4 x Def0 ≤ Def ≤ 1.7 x Def0. It is assumed that a light source wavelength is lambda , a track pitch of the optical disc 101 is Tp, and a numerical aperture of the objective lens is NA and that Def0 = Ä0.178 lambda /ä1-cos(sin<-1>NA)üÜ.Ää1-( lambda /(Tp.NA))ü+2.35Ü.