Hiroshi Uchiyama

Volumetric Optical Recording Using a 400 nm All-Semiconductor Picosecond Laser

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.

Recording Capacity Enhancement of Micro-Reflector Recording

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.

Direct Servo Error Signal Detection Method from Recorded Micro-Reflectors

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.

Drive system and readout characteristics of micro-reflector optical disc

This paper reviews the analyses and the experimental results of Micro-reflector optical disc system. In Micro-reflector optical disc, data are recorded on multiple virtual planes in a monolithic holographic medium. We have demonstrated the possibility of huge capacity from our analyses of readout characteristics of the Micro-reflector. In addition, we have developed the five-axis servo control system in order to achieve precise control of two counter-propagating light spots in recording media. Using this system, we succeeded in four-layer recording/readout.

Wear mechanisms of Co-Cr sputter deposited magnetic tapes in helical scan video tape recorders

The wear mechanisms of Co-Cr sputter-deposited tapes for perpendicular magnetic recording by rotary video heads in the still mode of video tape recorders were investigated by using two kinds of experimental apparatus. One is a rotary-head-type friction tester in which the surface of the rotating head can be observed continuously by a microscope with a stroboscope synchronized with the head rotation; the other is a scratch tester in which the scratched surface of a tape specimen can be observed in situ through the transparent hemispheric slider. It was found that the wear debris of the Co-Cr layer transfers onto the head surface, forms the asperities on the head, and scars the tape surface, with the increasing amount of head tracing. A carbon protective layer can prevent the Co-Cr layer from transferring onto the head and being subsequently scarred. However, the carbon protective layer may be peeled by the rotating head when the frictional force increases up to the interfacial shearing strength between the carbon layer and the Co-Cr layer. >

Dynamic Recording of 200 Gbytes in Three-Dimensional Optical Disk by a 405 nm Wavelength Picosecond Laser

We present experimental results of our volumetric optical data storage system. To achieve volumetric recording over a wide depth range of 250 µm 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.

Volumetric Optical Recording with Void Marks Using an All-Semiconductor Picosecond Laser

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.

Magnetic anisotropy derived from interparticle interactions in CoPtCr/SiO2 granular thin film longitudinal media

The magnetic anisotropy derived from interparticle interactions in a CoPtCr/SiO2 granular thin film longitudinal medium has been experimentally studied. In order to clarify the effect of magnetostatic interactions between particles in the medium, the angular dependence of the interaction fields has been investigated. The interaction fields in the medium were obtained from the remanent magnetization curves measured in several directions in the plane normal to the medium plane by compensating for the demagnetizing fields at each measurement direction. It has been shown that the interparticle interactions in the medium exhibit clear anisotropy, which is related to the magnetostatic interactions. As a result, the intrinsic magnetic anisotropy of the medium has been quantitatively separated into two contributions, the magnetic interaction anisotropy between particles and the anisotropy of each particle. The magnetic anisotropy caused by the interparticle interactions in the medium plays an important role in th...