Reiji Tamura

High-Speed Write/Read Techniques for Blu-ray Write-Once Discs

We have been developing high-speed write/read techniques for Blu-ray discs. We carried out 1–12× write/read tests on a phase-change Blu-ray write-once disc using an improved tester, an adaptive partial-response maximum-likelihood (PRML) technique, and a new write adjustment method. Sufficiently good limit equalizer jitter values of less than 6.5% were obtained under all write-speed conditions. Good bit error rates of less than 10-6 and fair power margins of more than ±10% were obtained under all write/read speed conditions.

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%).

Crosstalk Cancellation for 50-GB/Layer Optical Recording

We have developed write/read technologies for post-Blu-ray Disc (BD) with a capacity of 50 GB/layer. In this report, the authors propose a crosstalk cancellation method that minimizes the error between the crosstalk canceled signal and the target signal that is generated from the binary output of an adaptive-partial response maximum likelihood (PRML) decoder. The experimental results obtained using our method show that the bit error rate is reduced to 1/100. A high-density recoding of 50 GB/layer was demonstrated using our method.

Read/Write Technology for 50 GB/layer at 100 Mbps

We developed read/write technology for high-density optical data storage of 50 GB/layer at a data transfer rate of 108 Mbps. We demonstrated the writing and reading capabilities of a 50 GB/layer optical disk recording system at 36 Mbps with a sufficient power margin, using a three-beam crosstalk canceller with optical response equalizers, using a phase-change write-once disk. Bit error rates were below 1×10-4 at 108 Mbps. Experimental results showed that the technology realizes writing and reading densities two times higher and data transfer rates three times higher than those of Blu-ray with a simple optical component such as Blu-ray.

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.

Progress of Phase-Change Single-Beam Overwrite Technology

Studies on relationships between single beam overwrite characteristics and physical and chemical properties of the phase change recording media and their mechanisms are reviewed. Improvements in overwrite characteristics based on these studies, especially improvements in carrier to noise ratio(C/N) and the life of recorded dots by the addition of one of the transition metal elements or Tt are also reported. The maximum C/N was 61dB and the estimated life of the recorded dots is longer than 100 years at 60°C.

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.

Recording Characteristics And Reliability Of Novel Writable-cd Using A Au-Sn Alloy Single Layer

Over the past few years, some studies have been made on write-once type writableCD1)-3). This writable-CD has attracted a great deal of interest due to compatibility with conventional CD. This has been realized by means of double layered structure, dye recording layer and Au reflective layer. This has, however, disadvantages of degradation of dye layer by sun light irradiation and rapid drop of reflectance with a little decrease of wavelength. To solve these problems, we introduce novel writable-CD using Au-Sn alloy. This has advantages of single layered simple structure, low toxicity and high tolerance to sun light.

Analysis of Reproduced Waveform in Phase-Change Single-Beam Overwrite

Reproduced wave forms for the mark-center-detection and the mark-edge-detection recording methods are analysed for a phase-change optical disk with a Ge–Sb–Te–Co recording film which certifies a high C/N and single-beam overwrites of more than 105 times. The result showing that the disk has high-density recording capability. Signal demodulation for the mark-edge-detection recording method is possible at a small error-generation probability when the recording laser power is in the range of 60% to 140% of the most preferable power level and the erase ratio is greater than 25 dB.