Satoshi Sugaya

RETROREFLECTING ELLIPSOMETER FOR MEASURING THE BIREFRINGENCE OF OPTICAL DISK SUBSTRATES

A retroreflecting ellipsometer has been constructed for measuring the birefringence of optical disk substrates. In contrast to conventional ellipsometers with two mechanical arms, this system has only one arm along which both the incident and reflected beams travel. This construction eliminates the mechanical limitations of conventional ellipsometers, thereby permitting normal incidence on the sample. In addition, the single arm is adjustable in two dimensions, with the polar incident angle, θ(inc), varying from 0° to 70°, and the azimuthal incident angle, Φ(inc), varying from 0° to 360°. The condition of normal incidence permits accurate measurement of in-plane birefringence. The adjustability of both θ(inc) and Φ(inc) is necessary for the measurement of possible tilts of the index ellipsoid, and also for the variation of birefringence through the substrate thickness. Measurement results showing the useful features of the equipment are presented. The optics of the hemispherical assembly used for retroreflection as well as for the elimination of undesirable refractions are also studied by use of the ZEMAX lens design program.

Magnetooptic recording readout performance improvement

This paper describes magnetooptical (MO) readout and recording performance improvement that increase the MO disk drive performance. In regard to readout performance, a <60-dB readout carrier-to-noise ratio is achieved for an MO disk with a polycarbonate substrate. Also, in regard to recording performance, a new MO head is presented that achieves high optical transmission efficiency (~57%) without sacrificing the readout performance. As a result, disk rotation speed can be increased, and the data transfer rate can be improved.

Magnetic field modulation overwrite characteristics for magneto-optical disks using an active head-to-disk spacing control method

A magnetic field modulation overwrite technique has been developed for magneto-optical (MO) disks using an active head-to-disk spacing control method, that detects the distance between the magnetic head and the recording layer and holds it constant. This method achieves magnetic field modulation overwrite for MO disks, that solves headcrash problem, makes it easy to remove disks and provides constant recording characteristics, even for large axial deflection disks.