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.

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 present experimental results of our volumetric optical data storage system. To achieve volumetric recording over a wide depth range of 250 m in a recording medium, we developed a relay lens system for compensating for the spherical aberration of a high-numerical-aperture (0.85) objective lens. The disk employs a single monolithic recording layer and a reference layer for servo control. A 405-nm-wavelength titanium:sapphire laser that exhibits 2 ps pulse duration and a more than 2 kW peak power is used for recording. We adopted void formation and mark position as recording principles. We have experimentally demonstrated 34-layer dynamic recording, corresponding to a capacity of 200 Gbytes. #

Several important hologram reconstruction parameters of shift multiplexing with a randomly phase encoded reference beam were investigated as functions of the reference beam average speckle size at the medium. Those are shift selectivity, reference beam defocus margin, and medium tilt margin. It was confirmed that these parameters are linearly dependent on the average speckle size in certain directions. The exception was the in-track direction medium tilt margin which is dominated by the Bragg matching condition. We found that smaller average speckle size is preferable in view of achieving higher recording density, while larger average speckle size is desirable in view of having wider playback margins. Based on the experimental results, the multiplexing of 300 holograms per unit area was demonstrated with a polymer medium with sufficiently low bit error rates.