In this study, a commercial BD (Blu-ray disc) and BD optics (blue laser and NA0.85) were used for multilevel recording. The goal is to double both the present capacity and data transfer rate. To achieve this, it is necessary to overcome severe inter-symbol interference (ISI) from outer cells at a small cell length. In order to suppress ISI, we have developed an advanced data detection method that uses CBDD (Cell Boundary Data Detection) and TCM (Trellis-Coded-Modulation), and have achieved an areal density of 34.6-Gbit/in<sup>2</sup> multilevel recording.
We realized acceptable read/write performances at a track pitch of 320 nm and a bit length of 75 nm, even with an NA of 0.65 and a wavelength of 405 nm, using side-wall-annealing. In addition to this result, we suggested the possibility of a higher linear density; that is, a jitter value of less than 15% was obtained both on land and in groove at a bit length of 60 nm, which corresponds to an areal density of 34 Gbit/in<sup>2</sup>.