Tetsuhiro Sakamoto

Design of Domain Wall Displacement Detection Disk with Groove Recording for High Density and Wide Recording Power Tolerance

Domain wall displacement detection (DWDD) magneto-optical (MO) recording is the most useful method for achieving high linear density recording without using a higher numerical aperture (NA) objective lenses. Securing a wide recording power tolerance is very important to realize a high density optical storage system. From this point of view, we designed the DWDD disk with groove recording using blue laser and NA 0.60 optics. We optimized the heat sink structure and the displacement layer for groove recording, and we could improve the bit error rate with a track pitch of 0.44 µm and a high linear density of 0.07 µm/bit, which corresponds to 21 Gbit/inch2. Additionally, we developed groove substrates using reactive ion etching (RIE) and O2 plasma treatment. We found that the land shape was very important for the recording power tolerance, and we could obtain a wide recording power tolerance with a bit length of 0.09 µm. We confirmed that we could achieve higher density by using a narrower track pitch while maintaining sufficient recording power tolerance.

Recording power tolerance of magneto-optical media on RIE-formed substrate using NA 0.85 and 407-nm optics

To realize high density magneto-optical recording, it is important to suppress the disk noise. As we have reported, UV irradiation before sputtering films on the substrate could suppress the disk noise. But UV irradiation changed the shape of land and groove. We found that it caused poor recording power tolerance, because cross-talk could not be canceled using the phase compensation method. We developed a substrate formed by using a RIE process. Using this RIE-formed substrate, we could suppress the disk noise without UV-irradiation and improve the recording power tolerance.

System tolerance of 64-mm-diameter magneto-optical disks with a 4.7-Gigabyte capacity

We observed sufficiently wide detection tolerances in a magneto-optical (MO) drive system based on the domain-wall-displacement detection (DWDD) method. Those DWDD disks had a capacity of 4.7 Giga-byte on 64 mm diameter substrates optimized for land and groove (L/G) recording. Addressing was performed with the assistance of a one-side-wobbled groove. We investigated two types of DWDD disks i.e. the anneal-less type and the sidewall-annealed type.

High-density magneto-optical disk using domain wall displacement detection

Domain wall displacement detection (DWDD) is the promising method for achieving very high-density magneto-optical disk. The resolving power can be expanded far beyond the optical limit which is determined by the light wavelength and the numerical aperture of the objective lens. Some technologies have been introduced to ensure the smooth wall motion which is the key to the high performance of DWDD. Very smooth surface is obtained by pretreatment of the substrate or by reactive ion etching process on a glass master. Reverse disk rotation for readout is effective in reducing the jitter because the front line for starting position of the wall displacement curves to the same direction as recorded crescent domains. A possibility of an areal density of 20 Gb/in2 has been shown for the DWDD media using a blue-violet laser diode and a numerical aperture of 0.6.

Domain wall displacement detection (DWDD) with land-groove recording for achieving 30 Gbit/inch/sup 2/

The authors previously studied domain wall displacement detection (DWDD) (T. Shiratori et al, J. Mag. Soc. Jpn., vol. 22, supp. no. S2, pp. 47-50, 1998) with land-groove recording and reported successful recording at 20 Gbit/inch/sup 2/ areal density (T. Sakamoto et al, Tech. Dig. ODS 2001, MD8, pp. 73-75, 2001). The technical approach for huge capacity with DWDD is decided according to the method for shortening the track pitch. When groove or land-recording is chosen, it is difficult to prepare quality substrates for good signals and to obtain stable tracking. When land-groove recording is chosen, the most difficult problem is to obtain a sufficiently wide recording power margin. The authors studied DWDD in more detail and clarified the necessary conditions for improvement of DWDD using the reverse rotation readout method. In this paper, we show and explain some interesting experimental results of laser power margins in the case of land-groove recording. The results raise the possibility of 30 Gbit/inch/sup 2/ DWDD and some ideas are discussed at the end of this paper.

Domain Wall Displacement Detection Mini Disc with Land/Groove Recording Applied to Mini Disc Systems

We confirmed a wide tolerance and capability of over 2.0 GB/64 mm, equivalent to 14 times the capacity of Mini Disc (MD) using a combination of domain wall displacement detection (DWDD) and land/groove recording and by optimizing groove geometry and surface treatment.

15 Gbit/inch/sup 2/ areal density optical disk using the DWDD medium with blue LD recording

We developed a new layer structure of domain wall displacement detection (DWDD) optimized for a blue laser diode (LD) and confirmed that acceptable characteristics could be obtained. We tested readout and recording with a blue LD on this DWDD disk and confirmed that the jitter did not exceed 15% for bit lengths longer than 0.125 /spl mu/m at the track pitch of 0.35 /spl mu/m. In consideration of the experimental results, we could confirm that a DWDD disk with blue LD readout and recording could be available with an areal density of 15 Gbit/inch/sup 2/ with a jitter criterion of 15%.