Noriyoshi Shida

Multilayer Optical Read-Only-Memory Disk Applicable to Blu-ray Disc Standard Using a Photopolymer Sheet with a Recording Capacity of 100 GB

We have been investigating a multilayer optical disk applicable to Blu-ray Disc (BD) standard using a photopolymer (2P) sheet in order to realize a recording capacity of 100 GB on a 12-cm-diameter disk. We had already developed a 2P sheet utilizing the multilayer disk. In this study, we developed a BD-type quad-layer disk using the 2P sheet, and investigated readout signals from each layer. The jitter values of layer 0 (L0), layer 1 (L1), layer 2 (L2) and layer 3 (L3) in the quad-layer disk were 6.5%, 7.1%, 7.3% and 6.6%, respectively. According to the analysis of the components of jitter values, the main factor behind the deterioration of jitter values is the crosstalk from adjacent layers. However, the jitter value of each layer was sufficient to reproduce the recorded data. From these results, we proved the feasibility of realizing the BD-type multilayer read-only-memory (ROM) disk with the recording capacity of 100 GB.

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.

Superlarge-capacity optical disk with multilayer structure fabricated using a photopolymer sheet

We have been studying a multilayer disk in order to realize a 12-cm-diameter optical disk with the recording capacity of 100 GB or more. We tried to fabricate a multilayer disk using a photopolymer sheet. We developed a new sheet, and confirmed the performance of this sheet. A single layer disk made using this sheet had a value of 5.3%, and a 25 GB capacity. Then we fabricated a dual layer disk. The thickness variations from the disk surface to each recording layer were ±0.6 µm and ±0.7 µm. These results indicated the possibility of realizing a multilayer disk for a high-numerical-aperture (high-NA) system. We will evaluate the signals reproduced from the multilayer disk in the next step.

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.

Super high density optical disc by using multi-layer structure

To realize a super high density optical disc, the authors made basic researches into a space layer by using a photopolymer sheet owing to the uniformity of each space layer thickness. Then a prototype disc was manufactured. Thickness variation on each sheet was within 1.3 /spl mu/m. The transcription characteristic was verified. The data-to-clock jitter of the disc was measured. The recording capacity was 27.4 GB on a 12 cm disc. The capacity of each layer was 13.7 GB. As a result of these basic researches, we realized a super high density optical disc by using multi-layer structure, it is very important to utilize a photopolymer sheet for the space layer. It then will be possible to realize the recording capacity of 50 GB or over on a 12 cm disc having a four layered structure.

Improvement of the photo-polymer sheet for the multi-layer disk with the high NA objective lens and blue-violet laser

In ODS2000, we reported experimental results for the triple-layer disk using the photo-polymer (2P) sheet (N. Shida et al, ODS 2000 Tech. Dig., pp. 27-29, 2000). The subjects of the 2P sheet were the high transmittance, low variation of thickness and duplicate performance. Therefore, we developed a new 2P sheet which has sufficiently high transmittance of over 95% and sufficiently small thickness variation of less than /spl plusmn/0.5 /spl mu/m to realize the multi-layer read-only disk. We evaluated the duplicate performance of an improved 2P sheet as the layer 0 (L0) in a dual-layer read-only disk. The disk had 25 Gbyte capacity on each information layer. We measured the jitter value of a sample disk using the reproduction system with a numerical aperture (NA) of 0.85 and a blue-violet laser and the limit equalizer (Y. Tomita, Jpn. J. Appl. Phys. vol. 40, pp. 1716-1722, 2001). As a result, the jitter values were 8.0% on L0 and 7.8% on layer 1 (L1).

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.