Tetsuya Imai

25 Gbyte Read-Only Memory Disk by Injection-Compression Molding Process

We studied the feasibility of fabricating a disk replica at a recording capacity of 25 Gbytes by a conventional injection molding process. This work is the first attempt at fabricating a disk replica using a stamper recorded by an electron beam recorder. The bottom jitter value of the injection-molded disk was 9.3% when using a conventional equalizer and 6.5% when using an additional limit equalizer. These values were highly similar to those of the photo-polymer (2P) disk. The residual error on the axial tracking of the injection-molded disks was smaller than that of the 2P disk, and the residual error on the radial tracking was almost the same as that of the 2P disk.

Bd-type write-once disk with pollutant-free material and starch substrate

We realized an inorganic write-once disk for an optical recording system of the Blu-ray disk format. We developed a new Al alloy for the reflective layer and a Nb-compound oxide nitride material for the dielectric layer. By adopting these materials for the reflective layer and the dielectric layer of our write-once disk, we achieved complete exclusion of toxic substances specified in the pollutant release and transfer register (PRTR) law. That is, this disk did not contain any substances specified in the PRTR law. We confirmed this disk to be compatible with 1× to 2× recording at the user capacity of 25.0 GB. The bottom jitter values of both 1× and 2× were less than 6.0%. In addition, we developed another kind of substrate, which was made of a natural polymer derived from corn starch. The bottom jitter value was 6.0% at the user capacity of 25.0 GB with the limit equalizer.

System Stability against Fingerprints on Blu-ray Disc System

To realize a cartridge-free Blu-ray disc system, we investigated the behavior of a servo system with fingerprint contamination, and the correlations between the system stability and shapes of fingerprints. As a result, we found that the primary factors of servo failure were not only reflectivity changes but also wavefront aberration caused by the presence of fingerprints. Useful parameters for detecting serious fingerprint contamination were focus and tracking servo error signals standardized by the focus sum signal and the ratio of the width to pitch of fingerprints. Finally, we fabricated test disks with artificial fingerprints to design drive systems for the cartridge-free Blu-ray disc system.

Mechanism of Radial Skew Generation of an Optical Disk

It is important to control radial skew in order to realize a high-density optical disk. However, the causes of the radial skew had not been made clear. In this paper we will describe the causes. We also developed a new method to analysis for the radial skew. By using this method, we found that the temperature difference between a static cavity surface and a moving cavity surface caused the radial skew, which fluctuated on a radius. We also found that a mechanical ejector pushout, and the temperature difference between sprue parts and cutter parts caused the central skew component of the disk. At the same time, we were also able to realize that the radial skew was caused by the stumper came from the thermal resistance between the stumper and the cavity.