Hideyoshi Yamaoka

Influence of birefringence on the signal quality of magnetooptic disks using polycarbonate substrates

Magnetooptic (MO) disks using polycarbonate (PC) substrates were investigated. Birefringences of the PC disk substrates molded with different methods were measured. Signal qualities for MO disks with the PC disk substrates were also measured and the effect of the birefringence on the signal quality was estimated.

An Etched Glass Master and a Photomask for an Optical Disk Substrate

Abstract A new manufacturing process of a preformatted glass disk substrate and a photomask for producing the glass substrate was studied. In the substrate, the depth in the pit area differs from that in the track area. In the photomask, the pit area has different transmissivity from the track area. In this new process, latent preformatted patterns are formed in photoresist with either a laser cutting method or a contact printing method, and a new etching method comprising the first etching, the first ashing, the second etching and the second ashing is carried out. The mass production of the optical disk glass substrate can be realized with this new process. This technique can also be applied to forming an etched glass master for fabricating a polycarbonate disk substrate.

CHARACTERISTICS OF A SUPER RESOLUTION MAGNETO-OPTICAL DISK USING AN IN-PLANE MAGNETIZATION FILM

A super resolution magneto - optical (MO) disk with the medium of a GdFeCo readout layer and a DyFeCo recordingla yer was in vestigated. The readout la yer wasdesig nedsoas to show in - plane magnetization at room temperature and perpendicular magnetization above lOOV for high readout resolution. Readout signal quality was measuredatseverallinearvelocities. The ve-lo city dependence was little in the range from 5 to l0m/s; the maximum car-rier to noise ratio (CNR) at each velocitiesisnearlyequal. The per-formance of high densityrecording was studied with a 680nm wavelength optical head. The CNR and thecrosstalk were 45dB and -40dB respectively at 0.55dm mark leng th and 0.8um track pitch.

Recording characteristics of a magneto-optical super-resolution disk

To reduce recording magnetic field of a magneto-optical super-resolution disk which uses an in-plane magnetization readout layer, we developed a new disk structure. By preparing a DyFeCo intermediate layer between the readout layer and the recording layer, the recording magnetic field was greatly reduced and then both super-resolution readout and mark-edge recording by a magnetic field modulation method were achieved. By using the new triple-layered disk for super-resolution readout, a carrier to noise ratio of 45 dB at a 0.4 micrometers mark length was obtained and the recording magnetic field became 15 kA/m.

Magneto-Optical Disk By Contact Printing Method

This paper describes magneto-optical disk employing the contact printing method for a glass substrate. This method brings high productivity to a disk preparation process and high dynamic performance.