Hideo Ando

Preventing Coma Aberration by Annular Apodizer for Optical Disk Tilting

This research was carried out to determine the optimum parameters for an optical apodizer, applicable to a pick-up head for higher recording density optical disks. The coma aberration generated by tilting a disk increases the side-lobe intensity of the beam waist spot, and the increased side-lobe portion of the beam waist spot mainly deteriorates crosstalk from an adjacent track. Calculations were made to estimate coma aberration, in which the author adopted the annular radius of the apodizer and the side-lobe intensity of the beam waist spot as parameters. The result, which was confirmed experimentally, is that an annular apodizer whose radius is half the pupil radius effectively prevents coma aberration.

Full-Height Magneto-Optic Rewritable Disk Drive

1 , 2 A magneto optic (MO) rewritable disk drive has been put to practical use. The ISO standardization activity on a 130 mm rewritable disk is in its final stage and it will be standardized in 1989. An MO disk drive must he equipped with bias magnetic field generating functions in addition to the same characteristics as that of a write once read many (WORM) disk drive. The key factor for the broad acceptance of MO disk drives by users is that they conform to the ISO standard and that the drive size is of such a widely adopted size as that of a magnetic disk drive.

Focusing Error Detection by the Double-Edge Method

Conventional methods of focusing error detection have their respective disadvantages. To eliminate such difficulties, we have developed a new focusing error detection method. We have devised a unique principle for detection, by simulating the effect of each optical parameter on the focusing error detection characteristics, and evaluating the characteristics of the newly established optical head. This error detection method is influenced less by the tracking error signal, and it is also possible to obtain a tracking error signal from the same photodetector.