Naomasa Nakamura

Dual-layer rewritable phase-change recording media for HD DVD system

We have investigated the recording characteristics of the dual-layer phase-change recording media for a system that uses the blue-violet laser (wavelength of 405 nm), with the numerical aperture of 0.65 and light incidence on 0.6-mm-thick substrate having the land and groove format (HD DVD). In order to achieve higher storage density for its beam spot size, a number of technologies have been incorporated into the media, such as the bismuth-substituted pseudobinary GeSbTe alloy recording film and hafnium oxide-based interface layer material. The feasibility of the user capacity of 36 GB has been successfully demonstrated.

Advanced phase change media for blue laser recording of 18 GB capacity for 0.65 numerical aperture and 30 GB capacity for 0.85 numerical aperture

We attempted to improve phase change media to achieve larger capacity for systems with blue lasers using numerical apertures (NA) of both 0.85 and 0.65. It was found that the Bi-added GeTe-rich pseudo-binary composition promised high erase ratio even when we did not use any interface layers on a recording layer. The use of an absorption control layer (ACL) was also attempted to suppress the cross erase (XE). It was found that the ACL was very effective in suppressing the XE. The advanced phase change media that used the above novel technologies showed good analog performance. The advanced media also showed bER of less than 1.0×10-4, promising 18 GB capacity for an NA of 0.65 and 30 GB capacity for an NA of 0.85.

Transition Mechanism of WOx Available for Optical Disc by Laser Irradiation

WOx thin films are one of the candidates for the recording layer of write-once optical discs and the inorganic photoresist material used in heat-mode mastering. We have investigated the transformation mechanism of WOx during laser irradiation. As a result, we observed changes in the volume and crystallinity of WOx film. We conclude from various analyses that the solubility of WOx film in alkali solution may sensitively depend on the atomic ordering determined by deposition conditions or laser exposure conditions.

Dual-layer phase-change recording media for system with NA of 0.65 and light incidence on 0.6-mm-thick substrate

We have investigated the recording characteristics of the dual-layer phase change recording media for the sysetm with the NA of 0.65, the wavelength of 405 nm, and the light incidence on 0.6-mm-thick substrate having the land and groove format. For both L0 and L1 of the dual-layer disc, we have adopted bismuth substituted pseudo-binary GeSbTe alloy film as the recording layer and a novel interface layer material in order to improve overwriting characteristics. Bit error rate measurements have successfully demonstrated the feasibility of the user capacity of 36GB and confirmed 30GB with tilt margins.

Experimental study of 28-GB optical disk using a blue laser

The possibility of an optical disk capacity of 28GB/side is studied. The read-write characteristics of a phase-change optical disk are examined using a thin cover layer, a blue laser diode, high NA objective lens and the PRML method. The wide tilt margins of high-density recording are achieved.

Advanced phase change medium of over 30 GB capacity for blue laser and high-NA objective lens

Advanced phase change medium of over 30GB data capacity has been proposed and the recording characteristics of the medium have been described. The medium has L-H polarity, Bi-substituted GeTe-rich pseudo-binary alloy film as the recording layer, and thin metal absorption control layer. The recording measurement was carried out by using a blue laser light source with the wavelength of 405nm and an objective lens with NA of 0.85. Both CNR and ER have been improved by the use of the Bi-substituted GeTe-rich composition. XE has been reduced by the use of the absorption control layer. The bER measurement demonstrated its capability for over 30GB data capacity.

Phase-change recording media of 20-GB capacity for system with 0.6-mm-thick substrate

We have developed phase change media of 20GB user data capacity for the next generation optical recording system using a blue-violet laser diode with the wavelength of 405nm. An objective lens with the numerical aperture of 0.65 has been used along with mm-thick substrates on which the laser is incident. We have employed the land and groove recording. A transparent film with high thermal conductivity has been adopted at the light incident side of the recording layer in order to improve the carrier to noise ratio and the erase ratio as well as to reduce the cross-erase. Bottom channel bit error rate of less than 1×10-6 has been obtained and its wide tilt margins have successfully demonstrated the strong feasibility for the next generation rewritable system.

High-density recording for greater than 1-GByte capacity using a 90-mm phase-change optical disk

The mark edge recording characteristics of a new thermally balanced phase-change optical disk operating at a wavelength of 690 nm have been studied, especially from the viewpoint of designing an optical disk drive. As a recording method, the multi-pulse write compensation method with constant duration of the read power level immediately after every multi-pulse, called the off-pulse, was applied. A high carrier-to-noise ratio (CNR) of 54 dB, a high erasability of 35 dB, and an overwrite power margin from -15% to +5% were obtained for a bit length of 0.5 micrometers and a track pitch of 1.0 micrometers at 14.7 m/s linear velocity. These results mean that it is possible to design an optical disk drive providing a capacity of 1.1 GBytes using a 90 mm double-sided disk. Further, it has been found that the off-pulse plays a very important role in controlling the precision of mark edge recording.

High-speed HD DVD-R disc with organic dye

High speed HD DVD-R disc with low-to-high polarity organic dye was developed. For development of organic dye, Type A and Type B having different properties in sensitivity and read stability were examined. 4x speed recording is possible with both Type A and Type B. Furthermore, in type B, the sufficient signal characteristics were obtained at 5x speed recording for single layer disc and 2x speed recording for dual layer disc.

Experimental study of 30 GB/side rewritable optical disk using a blue-laser diode

The read-write characteristics of a land and groove disk have been examined using a blue-laser diode, high NA objective lens and the PRML method. The wide tilt and defocus margins have been obtained and no deterioration by CW has been observed at a data bit length of 0.0987 /spl mu/m and a track pitch of 0.29 /spl mu/m. These experimental results certify the feasibility of a rewritable optical disk with a capacity of 30 GB/side.