Nobuhiro Tokushuku

High C/N Recording in Sb2Se3/Bi Write-Once Disk

The read-out signal in an alloying disk, which has a large phase difference of the reflection coefficient between nonrecorded and recorded states, was analyzed by taking into account the effects of grooves. It was found that the read-out signal can be enhanced by interference between light reflected from a groove and recording media. A 60-dB CN (carrier-to-noise) ratio was obtained by applying this idea to the Sb2Se3/Bi alloying disk. NTSC (National Television System Committee) direct FM signal recording was confirmed by using this disk. It can be read by a modified Laser Disc player system.

Optimization of Crystallization Characteristics for Phase-Change Optical Disk with Ag–Ge–Sb–Te Recording Film

A Ag–Ge–Sb–Te recording film was developed, and its chemical composition was optimized to minumize overwrite jitter. The cause of the jitter was investigated by measuring the crystallization ratios and by transmission electron microscopy. It was found that the overwrite jitter increased with a shortage of Ge or Ag because the crystallization speed increased when these elements were added, while it increased with an excess of Ge or Ag because the crystallization speed decreased when these elements were added. A model based on the atomic bond distance and the strength of interatomic interactions in the crystal was devised. The model can be used to explain the mechanism by which a slight change in the chemical composition of recording films changes the crystallization speed. It was confirmed that the proposed disk with recording film having a small amount of Ag had the minimum overwrite jitter (under 10%).

Mechanism of mark deformation in phase-change media tested in an accelerated environment

Increased jitter caused by recording marks becoming deformed in an accelerated environmental test was investigated and a model where the change in the speed of crystallization is affected by passive oxidation on the amorphous surface of the recording layer was devised. The model clarified the mechanism by which deformation in the marks caused increased jitter in the accelerated environmental test. Adding nitrogen into the gas when sputtering the protective layer adjacent to the recording film was investigated. It was confirmed that a prototype disk with this protective layer has decreased jitter after a 500 h accelerated test and superior power margins.

New Erasable Optical Media Using Sb-Se-Bi Alloy Film

Antimony-Selenium alloy film with Bismuth has good characteristics for erasable optical disk media. The mechanism of the reversible change is phase transition between amorphous and crystalline states. It is confirmed by small-angle X-ray diffraction analysis that Se-Bi component plays an important role in this reversible change. The minimum erase time is 1 μs. The film has high transition temperature and activation energy of crystallization. It has a long life span of written spots in amorphous state. Recording film of Sb-Se-Bi alloy is formed on 20 cm 0 PMMA substrate and is covered with protective films. The disk samples are written and erased at a speed of 1800 rpm, using an optical head with two diode laser beams. Carrier-to-Noise ratio is more than 55 dB at 5 MHz, 30 KHz bandwidth. The newly developed disk realized high performance and durability for the use of an erasable video file system.

Improvement of Overwrite Jitter of a Phase-Change Optical Disk with Al-Alloy Double-Reflective-Layer Structure

To obtain minimum overwrite jitter after 104 overwrites, the cause of degradation of readout waveforms after 104 overwrites was investigated by transmittance electron microscopy (TEM). To decrease the temperature of the recording film at the track center during recording, an Al-alloy double-reflective-layer structure is proposed. Two relationships, one between the thermal conductivity of the first reflective layer and the temperature of the recording film during recording and the other between the thermal conductivity and the readout waveforms after overwrites of more than 105 times, were investigated using thermal simulation and a digital versatile disk (DVD) disk tester. The optimized disk has a minimum overwrite jitter after 105 overwrites at a linear velocity of 6 m/s.

High density write-once optical disk for HDTV

We have developed a high density write-once optical disk by utilizing the reflection plane shift recording method and a 670nm short-wavelength laser diode. A high CNR of 60dB at 12.5MHz has been obtained, which is enough to record and play back MUSE encoded HDTV signals on a disk. A 42 dB SNR of the HDTV signal recorded has been obtained. Recording and playing back a digital ATV signal was also carried out on the write-once disk. It was demonstrated that a 32QAM-FM modulated ATV signal could be recorded on the disk.

RECORDING MECHANISM OF HIGH CN RATIO Sb-Se/Bi WRITE-ONCE OPTICAL DISC

Sb-Se/Bi films for write-once optical disks have been investigated and it was determined that the recording mechanism of Sb-Se/Bi film was interdiffusion and crystallization. Interdiffusion occurred below 200 C and Bi- Se crystals were produced within the interdiffused Sb-Se-Bi alloy layer. The peak concentration of Bi and Sb were exchanged between the as-deposited and after-annealed state. Sb-Sei films have a remaricably fast recording time of 30 ns at 9.7 mW laser power with a high CN ratio of over 60 dB at 8 MHz recording frequency. According to the Arrhenius equation, media life is presumed to be about 159 years at 25 C.

High density write-once optical disk for high definition television

The authors have developed a high density write-once optical disk using the reflection plane shift recording method. A high carrier-to-noise ratio (60 dB at 12.5 MHz) was obtained by using a 670-nm wavelength laser diode, which is enough to realize high-definition pictures of good quality. A high SNR (42 dB) of recorded HDTV (high-definition television) MUSE signals was obtained. This disk has format compatibility to Hi-Vision VD (video disk). It can also accommodate compressed digital HDTV signals. >