Micro-reflector recording is a potential candidate for sub-terabyte optical storage systems. In this paper, the latest progress on increasing storage capacity and on improving recording transfer rate of micro-reflector recording is presented. With our dynamic tester, we successfully recorded ten signal layers dynamically in a monolithic recording material. For every signal layer, moderate bit error rate was obtained by employing readout signal processing. Our experimental results indicate the potential for increasing recording transfer rate and recording density.

We have demonstrated volumetric optical recording using an all-semiconductor picosecond laser, which generated optical pulses with a duration of 3 ps and a maximum peak power of 100 W at a wavelength of 404 nm and a repetition frequency of 1 GHz. This pulsed laser system efficiently induced multiphoton absorption in the recording media due to its high peak power and high repetition rate. The recording marks were formed as submicrometer voids inside a single thick recording layer by multiphoton absorption. A clear readout signal was obtained from the recorded marks.

We discussed data error propagation due to dust on disk surfaces in cases of various cover coat thicknesses and dust sizes. We proposed a system durability gauge K-value and discussed abilities of error correction codings (ECCs) by using a measured Kvalue. A measured dust particle distribution was shown, and error propagation was calculated for thin-cover cases with different K-values. We found that 0.6-1.2 mm cover coat disk systems are free of errors due to dust and a thin-cover coat disk is not always worse. In the thin-cover coat systems, it is particularly necessary to increase K-value and to optimize ECC schemes.

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We demonstrated volumetric optical recording with void marks in a bulk recording medium using a newly developed all-semiconductor picosecond laser. The laser is compact and has an ultrahigh peak power, which is necessary for practical application of the volumetric optical recording system. We confirmed the laser to be able to record void marks effectively on our recording media. The laser was implemented to our optical drive system as a light source and as much as 30 layer void-mark recording was carried out on the 200-µm-thick bulk recording medium. The total recording capacity was 97 Gbyte and the bit error rates (bERs) were measured to be on the order of 10-4 for most of the layers. We believe that this was a significant step to realize a practical volumetric optical recording system.

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A new structure disk was developed for a magneto-optical (MO) composite head system. The new disk has a thin readout substrate under and a high magnetic permeability layer over the MO layer. The effect of the high magnetic permeability layer was confirmed experimentally and agreed well with theoretical results. The normal component of the magnetic field at the MO layer is enhanced 1.6 times by the high magnetic permeability layer.

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