Goro Fujita

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.

A magneto-optical recording method of magnetic field modulation with pulsed laser irradiation

A new magneto-optical recording method of magnetic field modulation with pulsed laser irradiation has been developed. In this paper, we report the theory of the recording process and the characteristics of the method. This method is appropriate for high power-efficiency and high density edge-recording.

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.

EVALUATION OF A 120 MM SIZED MAGNETO OPTICAL DISK SYSTEM OF OVER 6 GB CAPACITY

We have studied the feasibility of the 120-mm-sized magneto optical disk system which achieves 6-GB user capacity using an optical pickup with a 640-nm wavelength laser and a 0.6-numerical aperture of the objective lens. We have used three technologies: a laser-pulsed magnetic-field modulation recording, a center-aperture-detection type of magnetically-induced super resolution disk with a 0.6-mm-thick single substrate and partial response equalization with maximum likelihood detection. We have evaluated the system-margins of write power, radial tilt, tracking and focusing offset and have confirmed the feasibility of the linear bit density of 0.235 µm/bit in 0.6-µm track pitches.

New approach to high-density recording on a magneto-optical disk

We have studied the influence of the pit shape upon the amplitude characteristics of the optical channel in an MO disk system, and studied three channel codings to determine their suitability for high-density recording. It is confirmed that magnetic field modulation with pulsed laser irradiation has the highest amplitude characteristics and NRZI format is most adequate for the method at the density of 0.6 micrometers /bit to 1.0 micrometers /bit.

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.

New Structure Disk for a Magneto-Optical Composite Head System

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.

Study of Error Propagation due to Dust for Thin-Cover Coat Disk Systems

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 K-value. 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.