High density phase-change recording beyond 2.6 GByte

We review the current status of high density phase-change optical recording at red wavelengths. A user bit capacity of 3.0 GByte has been realized on a 120 mm rewritable disk by using in-grove recording and a simple and reliable wobbled groove format. The headerless format shows excellent data and address integrity during cyclability tests and it has a high degree of compatibility with read-only DVD. In order to extend disk capacity even further, both radial and tangential densities must be increased. In increasing the radial density, land/groove recording appears mere promising than in-groove recording because optical cross-talk between neighbouring tracks can be largely cancelled. 8 reduction of the track pitch in land/groove recording below 0.74 mu m results in thermal cross-talk leading to partial erasure of data in the adjacent tracks. The minimum bit length which gives acceptable recording tolerances in both land and groove tracks is 0.32 mu m. With the combination of a track pitch of 0.74 mu m and a bit length of 0.32 mu m, an areal density of 2.7 Gbit/in(2) and a user capacity of 3.5 GByte should be possible in land/groove recording.