Kenichi Shimomai

Low-cost ultrahigh areal density optical disc system towards 400 Gbyte/disc

We introduce a new 400 Gbyte disc system, which has twice as much areal density as BDXL™ does, retaining the use of the conventional optical head and disc technology. Our proposal is based on the application of code modulations with enlarged minimum run length (d) and land/groove (L/G) geometry to increase linear recording density and track density by 1.5 and 1.33 times, respectively. Also, saw tooth wobble (STW) was introduced for a multilayered L/G disc system to suppress readout signal fluctuations. Here, we demonstrated that the linear recording density increased to 45.5 Gbyte/layer by applying d = 3 to a commercially available BDXL™. Also, we checked that crosstalk, which is a major concern in an L/G disc with a track pitch of 240 nm, was suppressed to below −30 dB by choosing the proper groove depth. Moreover, the investigation of the effect of track width modulation on the write/read performance demonstrated that an adverse influence can be suppressed by employing STW.

A high transmittance optical recording material with long-term reliability for super-multilayer discs

As a means of increasing data capacity, the multilayer optical disc is a promising approach. Because the recording layers in multilayer optical discs must have a high transmittance, they are commonly made of transparent oxide films. Moreover, the recording layer must have sufficient long-term reliability for data archival. In this work, a recording material with high transmittance and long-term reliability for use in super-multilayer discs was investigated. This paper clarifies the recording mechanism of GeBi oxide material and proposes a suitable material design that satisfies the abovementioned characteristics. Furthermore, experimental results of recording on super-multilayer discs based on GeBi oxide recording material are presented.

Advanced organic dye for high-speed, high-density optical media

Advances in organic dye progress are indispensable for high-speed, high-density recording of recordable Blu-ray Disc™ (BD-R) low-to-high (LTH) discs without a low elastic modulus layer. The optimal physical properties of the organic dyes, i.e., a low decomposition calorific value, a low decomposition temperature, and a large n-value, were determined, and a dye with these properties was synthesized. A BD-R disc using the dye conformed to the BD-R LTH standard at 8× recording and ever higher speeds should be possible. Furthermore, the possibility of 33 GB/layer high-density recording was suggested.

Dual-Layer Recordable Digital Versatile Disc Having Protruded Land Pre Pit in L1 Layer Fabricated by Inverse Stack Method

The dual-layer recordable digital versatile disc (DVD-R DL) fabricated by an inverse stack method has not been released in the market because of unstable land pre pit (LPP) addressing in an L1 layer due to its peculiar disc structure. We have developed a DVD-R DL disc that has the novel shape of the protruded LPP in the L1 layer fabricated by an inverse stack method. The height of the protruded LPP is larger than the land height of the L1 substrate to restrain extensions in the radial direction of recording marks. We have confirmed that the protruded LPP disc satisfies the specifications of DVD-R DL and enables stable LPP addressing.