Abstract
As an approach to the recording/reproducing system of the record capacity of 25GB on a thin cover layered(=0.1mm thickness)of phase change optical disk with a 405nm GaN laser and a high NA(=0.85)objective lens, we have been working on the PRML technology, especially, paying attention to the combination with run length limited modulation code. Focusing on the correlation between the measured MTF character and the PR character, we did theoretical simulations and actual experiments. As a simulation result, it is found that PR(3, 4, 4, 3)ML was the most suitable for a D8-15 modulation code system and PR(1, 2, 2, 1)ML for a(1, 7)modulation code system. The actual recording/reproducing experiment results show that the PRML improves the reproducing stress margin significantly in comparison with conventional level-slicing method in both D8-15 and(1, 7)modulation code systems. The BER after PRML in both modulation code systems was almost equal, i.e.about 1e-5. These experimental results have made it clear that record capacity of 25GB would be realized if PRML is used in either case applying(1, 7)modulation code system or D8-15 modulation code system.
