Masaharu Moritsugu

Optimization of magneto-optic head

We have optimized the beam splitter in a magneto-optic system for improving a signal amplitude and carrier-to-noise ratio. We calculated the optimum conditions using the Jones matrix and taking the optics and media characteristics into account. We obtained a good readout signal.

New Optical Head for Magneto-optic Library Units

We have developed a magneto-optical head to provide both fast access and large memory capacities for optical library systems. It features a pair of optical heads which face each other on opposite sides of the disk, and a new tracking method which enables a wide tracking range. The bias coil to generate the magnetic field is mounted around the objective lens of each optical head. The two opposing bias coils can generate an interlocking magnetic field of more than 250 Oe. We call this bias-coil driving method the push-pull driving. The power consumption needed for a 250 Oe field is only 2 W. A new tracking method makes it possible to use a stepping motor for coarse access. Two stepping motors are used not only for on-media access but also for media-to-media access, which help to miniaturize the drive. A good magneto-optical readout signal was obtained. Its carrier-to-noise ratio is more than 50 dB for a mark length of I gm. We confirmed that this signal level is sufficient for recording on magneto-optical disks.

Jitter Characteristics of Mark Edge Recording on MO Disks

Edge shift and jitter characteristics have been examined using both conventional disks and an overwritable disk with three exchange-coupled layers. Edge jitter consists of random jitter, edge shifts dependent on data patterns (thermal interference), and edge shifts independent of data patterns (fluctuations of temperature or light spot control). Write compensation is an effective means of correcting shifts depending on data patterns. The shifts which are independent of data patterns can be rendered negligible in comparison with random jitter by using an edge detection method in which the leading and trailing edges are detected independently. The results were the same for the overwritable disk. The possibility of applying edge recording in magnetooptic disk systems was thus confirmed.

Clock generation circuit of a sampled servo optical disk drive

The clock generation circuit we developed for a 5.25-in sampled servo format optical disk drive is linked to the spindle motor control system. In has fast pull-in characteristics and a highly accurate disk rotational control system without need for a special rotary encoder.