A new modulation code and new signal reproduction processes for a high-density optical disk system are proposed. With these new techniques, the capacity of the optical disk system can be 30% higher than the present digital versatile disk (DVD) system. An evaluation in terms of the bit error rate by both simulation and hardware experiments is also shown.

A method to observe sonoluminescing bubble motion has been studied. By a single flash of a stroboscope much shorter than the acoustic cycle, a charge coupled device (CCD) camera captures an instantaneous image of the bubble, which includes the dancing condition. Changing the flash timing of the stroboscope slowly made it possible to observe periodical expansion and contraction of the bubble. It is clarified that the bubble size and the phase at the time the bubble collapses changes according to the amplitude of sound pressure.

A new physical format using groove recording and new signal processing techniques is discussed. The signal reproduction of shallow pre-embossed pits was confirmed with a technique utilizing tangential push-pull (TPP) and a compatible partial response (PR) equalizing system. An evaluation in terms of the bit error rate by hardware experiments is demonstrated.

The noise reduced disc and the advanced signal reproduction system with the asymmetry compensatory function enhance the disc capacity up to 19.8 GBytes per DVD size.The noise was reduced by applying Aluminum based multi-component alloy for the reflective layer, moreover all the loops in the system accurately function even under the signal asymmetric condition by using the newly developed Error Feedback type PRML. The error rate characteristics versus disc tilts suggest that the ROM disc system has sufficient performance for the practical use.

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