Coherent interlayer cross talk and stray-light intensity of multilayer read-only-memory (ROM) optical disks are investigated. From results of scalar diffraction analyses, we conclude that layer separations above 10 microm are preferred in a system using a 0.85 numerical aperture objective lens in terms of signal quality and stability in focusing control. Disk structures are optimized to prevent signal deterioration resulting from multiple reflections, and appropriate detectors are determined to maintain acceptable stray-light intensity. In the experiment, quadrilayer and octalayer high-density ROM disks are prepared by stacking UV-curable films onto polycarbonate substrates. Data-to-clock jitters of < or = 7% demonstrate the feasibility of multilayer disk storage up to 200 Gbytes.

Following [6] relating the matrix string theory to the light-cone superstring field theory, we write down two supercharges in the matrix string theory explicitly. After checking the supersymmetry algebra at the leading order, we proceed to discuss higherorder contact terms.

We developed a high density near field optical recording disc system with a solid immersion lens and two laser sources. In order to realize the near field optical recording, we used a phase change recording media and a molded polycarbonate substrate. The near field optical pick-up consists of a solid immersion lens with numerical aperture of 1.84. The clear eye pattern of 90.2 GB capacity (160nm track pitch and 62 nm per bit) was observed. The jitter using a limit equalizer was 10.0 % without cross-talk. The bit error rate using an adaptive PRML with 8 taps was 3.7e-6 without cross-talk. We confirmed that the near field optical disc system is a promising technology for a next generation high density optical disc system.

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Key technologies for near-field recording/readout systems using a solid immersion lens (SIL) are summarized in this paper. Our system employing a SIL of 1.84 numerical aperture (NA) and a laser diode (LD) of 405 nm wavelength has realized the capacity of a 112 GB in a 12 cm diameter phase-change disc along with a write-power margin of ±11.2% and a data transfer rate of 36 Mbps. Such a larger-capacity data storage system should provide a high data transfer rate. A preliminary result of 1.84 NA dual-channel near-field recording/readout using a monolithic dual-beam LD with 412 nm wavelength is presented.

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We have succeeded in writing and reading a random pattern on a polycarbonate disk at relatively high transfer rate with a near field writable system. For the purpose, we have modified a head actuator and improved a servo system.

Micro-reflector data storage is a practical candidate for post Blu-ray optical memory. It is based on bit-wise recording in a monolithic recording medium with a reference layer. In our conventional drive system, the objective lens position is controlled by servo error signals obtained from the reference layer. However, this servo system is not sufficiently robust against recording medium tilt and decentering because the servo error signals are not directly obtained from recorded marks. Here, we present a novel direct three-dimensional servo method to resolve this problem. In this servo method, the objective lens position is controlled by servo error signals directly obtained from recorded marks, or micro-reflectors. We verified the validity of the novel servo method by simulations. Furthemore, we demonstrated the improvement of the envelope and the jitter of a RF signal by the novel servo method experimentally.