High density rewritable recording and readout characteristics with a solid immersion lens (SIL)-based near-field
recording (NFR) are investigated. Substrates for high density are prepared using a phase transition mastering
technique. Cover-layers with different refractive index for different effective numerical apertures in the SIL optics
are coated on rewritable NFR discs for cover-layer incident near-field recording configuration. Two different
effective numerical apertures are chosen between 1.45 and 1.85 to cope with about 70 GB and more than 100 GB
per disc, respectively. The performance readout signals is investigated and compared in terms of increasing
recording densities with reducing track pitch.
We present advanced methods to improve the performance of the near field system. Using the RF signal, the near field
system can detect a tilt error and find the best tilt condition for more wide range. The 2-step approach process can
shorten the pull-in time and decrease the possibility of a collision.
An improved concept of the advanced SIL and its compensation OL of composite effective NA over 1.7 has
been designed and manufactured to achieve wider assembling tolerances, higher data capacities and better signal quality.
Very clear readout signals were measured from a 25 GB BD-like ROM media with 3 um cover layer and the applying
feasibility of the advanced SIL system in near field optical storage was confirmed. With this novel advanced SIL system
and multilayer media concept, total capacity over 500 GB per disc was expected to be accomplished.
Gap servo systems based on one of near field technologies are generally using the 1-beam push pull method to generate servo signal and this causes the optical DC offset problem in servo signal. In this paper, we presented new method of track error generation using the proposed GELP signal for the gap servo near field optical storage systems. By using the GELP signal and 2-divided photo-detector for the gap error signal detection, test result shows the optical DC offset in track error signal generated from lens movement could be eliminated.