Friday, November 02, 2007

TDK Prototypes Holographic Material w/ Enhanced Recording Capability of 76 Gbits/inch2TDK Prototypes Holographic Material w/ Enhanced Recording Capability of 76 Gbits/inch2

TDK Corp prototyped a material with enhanced recording capability intended for holographic media and presented the results of recording/playback using this material.

The material has a high M# of 41.8/mm. The M# indicates the overwriting capability of holographic media. As the M# gets higher, the degree of data multiplexing can be increased more easily, resulting in a higher recording density. The shrinkage percentage is 0.29%.

According to the company, when the data was written on the prototype material by coaxial holographic recording, it was confirmed that the material can provide a recording density of 76 Gbits/inch2. Sony Corp undertook the data recording.

The achievement was presented at ISOM'07, an international conference on optical memory held in Singapore from Oct 21 to 25, 2007, as well as at other events.

TDK improved the M# by increasing the difference in refractive index between the portion that turns into polymer by the monomer multiplexing at the time of recording interference fringes and the binder portion except the polymer. The intensity of diffracted light at the time of playback increases as the difference in refractive index becomes greater, thereby resulting in satisfactory reproduction signals even when the data is overwritten.

Increasing the difference in refractive index

Source : Click here

In order to increase the difference in refractive index, TDK enhanced the refractive index of the binder by mixing it with a transition metal having a high refractive index. However, if the metal component is singly mixed, the material becomes clouded and cannot be used for recording due to the degradation of compatibility between the binder and monomer. To prevent the deterioration of compatibility, the company combined the binder with an organic group.

TDK also produced two other recording materials. One has an M# enhanced to 63.5/mm while maintaining a shrinkage percentage of 0.29%. The other has a shrinkage percentage reduced to 0.08% while retaining a comparable M# of 45.6/mm.

Both materials were achieved by the improvement of monomers used. In general, it is difficult to maintain a high M# and low shrinkage percentage at the same time because when the proportion of monomer is increased to improve the M#, the proportion of binder, which reduces shrinkage, decreases, and thus increasing the shrinkage percentage.

The higher the shrinkage percent is, the harder it becomes to record interference fringes. On the other hand, the M# decreases when the shrinkage percentage is reduced.

The company plans to actually record data on the new materials, and focus on the development of recording materials having even higher M# and lower shrinkage percentage.

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