Akio Futamata

Optical tunneling effect calculation of a solid immersion lens for use in optical disk memory

A solid immersion lens (SIL) has the advantage of easily decreasing the spot size for high data density in optical recording. To accurately obtain the optical tunneling effect for a high-N.A. SIL, we calculated the optical tunneling beam characteristics, using electromagnetic theory. Tunneling beam spot-size dependence on polarization direction and energy-transfer efficiency are also clearly shown.

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.

Flat Intensity Lens with High Optical Efficiency and Small Spot Size for Use in Optical Disc

The optical system in recordable optical discs must realize both, a smaller spot size for high data capacity, and an increased optical power for a high data transfer rate. We have devised a simple optical element that converts the Gaussian intensity distribution into a flat intensity distribution by refraction without optical power loss or aberrations.

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.