International Symposium on Optical Memory and Optical Data Storage Topical Meeting

We report the first integrated optical bead device using a blue-violet LD (laser diode), which is a key device for realizing a small and thin-shaped Blu-ray Disc drive. While integrating seven optical parts into one device, by adopting a molded compound lens with high transmissivity to the blue-violet wavelength, the small size of 11 mm /spl times/ 6 mm /spl times/ 4.1 mm has been realized. At this time, we have played back a Blu-ray Disc media using this small optical bead device and have achieved a good jitter value of 7.3%.

Presents the table of contents for Post deadline session papers.

The ever-increasing demand for higher capacities driven by data intensive applications such as high-quality video has been met through steady increase of the areal bit density of the optical media. Very recently, the so-called Blu-ray Disc (BD) standard was announced, offering a capacity of up to 27 Gbytes per 12 cm disk. The BD format is designed as a groove-only format, which allows easier ROM, R and dual layer disk standard extension since no prepit headers are required. Another approach to increasing the effective storage capacity is quite unique for optical memories: multi-layer recording. Thin phase-change layers are one of the most promising recording materials (T. Akiyama et al, Jpn. J. Appl. Phys. vol. 40, pp. 1598, 2001; E.R. Meinders et al, Proc. SPIE vol. 4342, p. 64, 2001). However, due to high absorption, the number of recording layers is currently limited to two layers only. In this paper we discuss the required technologies to realize a dual-layer BD type system. This includes primarily the dual-layer phase-change disk technology, beam shaping to enhance the light efficiency of the optical head unit and spherical aberration control to compensate cover layer thickness variations.

Showed the feasibility of 4.7-GB DVD-RAM media for 5/spl times/ recording. In order to maintain compatibility with current 2/spl times/ drives, we reduced jitter in both 2/spl times/ and 5/spl times/ recording. The most important design concept is to control the crystal growth velocity and crystal nucleation frequency: the former should be reduced and the latter increased. To control these values, we prepared a medium having a Ge-Sb-Te recording film and a nucleation promoting film. It showed jitter lower than 10% in both 2/spl times/ and 5/spl times/ recording.

Write-once media has been used as storage media for medical data, official documents in order to prevent tampering. In addition, write-once media, such as CD-R or DVD-R are the most popular storage media for the computer in the world by reason of the interchangeability with the ROM disc. On the other hand, in order to obtain much larger capacity, DVR-blue system (/spl lambda/ = 405 nm, NA = 0.85) has been proposed. Many storage media, such as rewritable discs, write-once discs, ROM discs have been developed to apply this system. We have already reported high speed rewritable disc for this system. We have developed write-once disc for this system, too. And we have achieved wide data recording rate in the range of 35 Mbps to 140 Mbps on a disc with inorganic recording material. In this report, we show the read and write characteristics of the write-once disc with inorganic write-once material.

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).

Two approaches have been proposed for achieving 25-50 Gbyte capacity on one side of a 120 mm disc: using a two-element high numerical-aperture (NA) objective and using a dual-layered disc. One of the problems with these approaches is that an error in the cover-layer thickness of only a few microns can lead to serious spherical aberration. (SA). This is a particularly serious problem in dual-layered discs due to the distance between the two recording layers. Another problem is the narrow working distance (WD) of the two-element objective lens, which can result in the lens crashing onto the disc. To overcome these problems, we previously described accurate detection of and dynamic compensation for SA (Jpn. J. Appl. Phys., 40, 2001, and Proc. of SPIE, 4342, 2002) and a single-element high NA objective with a wide WD (Tech. Dig. of ISOM, 2001). In this paper, we review our related previous work and describe the latest advances.

High-speed and high-density recording using blue laser appears to be the main stream for the next generation of phase-change optical disks. Sb-rich phase-change recording materials present one option as a medium for high-speed recording. We have estimated the crystal growth rate (CGR) of two variants of the GeSbTe recording material, for 100 Mbps recording (type 1) and Sb-rich material for 300 Mbps recording (type 2), by comparing the simulation and experimental results. We studied the characteristics of the materials in writing and erasing for high-speed recording. We applied our phase-change simulator (PCS) to search for the relationship between the linear velocity of the rotating disk and the formation of amorphous material in the recording layer. In this study, we used the optical system with NA = 0.85, /spl lambda/ = 405 nm and disks with 320 nm track pitch.

Developed a dual-stage tracking mechanism using a MEMS tracking mirror and used /spl mu/-analysis and synthesis to design a controller satisfying multiple desired specifications. The efficiency of the proposed method was demonstrated by an experiment having tracking errors of less than 10 nm. We expect the MEMS tracking mirror to contribute to the creation of high-density optical disk drives.

Kỹ thuật ghi quang thay đổi pha đã phát triển rất nhanh trong vài năm qua. Các kỹ thuật ghi phức tạp hơn đang được nghiên cứu để áp dụng vào ghi thay đổi pha, bao gồm ghi nhiều mức và ghi nhiều lớp (H.D. Shieh et al, 2001; L. Shi et al, 2000; T. Akiyama et al, 2001). Chúng yêu cầu kiểm soát chính xác công suất laser và thời gian xung để đạt được hiệu suất đĩa tối ưu (ghi và xóa). Do đó, cần có sự hiểu biết tốt hơn về động học của quá trình kết tinh của vật liệu ghi. Đã có nhiều nỗ lực được dành cho việc mô phỏng quá trình kết tinh trong ghi quang thay đổi pha. Mansuripur et al (Applied Optics, vol. 39, no. 35, pp. 6695-6701) đã nghiên cứu các hiệu ứng nucleation nhất thời, Sheila et al (Proc. SPIE, vol. 4090, pp. 116-121) đã mô hình hóa sự dao động do bản chất thống kê của sự nucleation và tăng trưởng tinh thể. Cả hai mô phỏng của họ đều dựa trên mô hình kết tinh 2D. Tuy nhiên, để hiểu một số hiện tượng kết tinh, như ảnh hưởng của độ dày lớp ghi và ảnh hưởng của bề mặt lớp điện môi (nucleation không đồng nhất), chúng ta phải nghiên cứu kết tinh trong các lớp mỏng ở ba chiều. Trong bài báo này, chúng tôi thiết lập một mô hình isothermal để giải thích các ảnh hưởng của độ dày lớp ghi. Dựa trên mô hình isothermal, chúng tôi phát triển một phương pháp để mô phỏng quá trình kết tinh của vật liệu ghi thay đổi pha trong 3D.