Shuichi Ichiura

High density digital videodisc using 635 nm laser diode

By developing a high resolution pick-up using a red laser diode with a wavelength of 635 nm and by examining the disc parameters, we have developed a CD-ROM which has a recording density four times that of existing CDs. The track pitch of this CD-ROM is 0.85 /spl mu/m and the recording linear velocity is 0.7 m/s. With these disc parameters, a storage capacity of 2.2 GB was obtained. We recorded digital motion pictures with a data transfer rate of 4 Mbps onto the disc and succeeded in the realization of a high quality digital videodisc with one hour of playback time. >

Fabrication of Laser Beam Axis Compensator by Photonic Crystal Technique for Optical Pickup Units

A laser beam axis compensator was fabricated for an optical pickup unit with blue and red lasers. The device consisted of multiwavelength wave plates and a double-refractive-index material. The wave plates were realized by a photonic crystal technique. By measuring the beam profiles of the blue and red lasers, the device was confirmed to function as a laser axis compensator. Under 110 µm laser beam axis shift setting conditions, readout signal patterns from an optical disc were measured.

Phase-change optical disc of 20-GB capacity using NRZI+, Turbo coding with blue laser

Recently, there has been much research on high-density recording of phase change optical disc using blue laser. In most research, RLL (Run Length Limited) modulation such as (1,7) RLL and EFM (Eight to Fourteen Modulation) modulation is used for high-density recording and channel clock regenerating. NRZI (Non Return to Zero Inverse) modulation has a wider window width than other modulation methods. This is a superior characteristic for achieving a high-density recording system of optical disc. We introduced NRZI+ modulation to suppress the low frequency components. And we obtained a result of a bER (bit Error Rate) of less than 1×10-4 at a bit length of 0.13μm using Turbo coding with an objective lens of NA 0.7 and a blue laser of 405 nm wavelength. This result shows that a recording capacity of 20 GB is feasible using NRZI modulation.

2.5-inch quadruple-density CD-ROM using visible laser diode

We have achieved a 2.5 inch (64 mm) quadruple density CD-ROM by developing a high resolution pick-up with our newly-developed visible laser diode whose wavelength is 635 nm, and also developing a disk cutting machine using a Kr ion laser with a wavelength of 407 nm.