Yoshito Tsunoda

Diode laser direct modulation heterodyne interferometer

A new type of heterodyne interferometer was made through direct modulation of a diode laser wavelength. A measurement accuracy of better than lambda/50 and repeatability of lambda/100 were obtained. This interferometer shows promise for use in testing wavefront aberrations, especially in optical disk systems.

Compact magnetooptical disk for coded data storage

A compact magnetooptical disk having 500 times the capacity of a 13.34-cm (5.25-in.) floppy disk has been developed for use in coded data storage applications. Low error rates are attained by the use of advanced highly sensitive polarization detection optics and high-quality recording media. Progress in these fields has been based on noise analysis of readout signals. The disk drive can write and erase data by sectors and can also play current write-once-type optical disks. This disk/disk drive unit promises to lead to enhanced storage capacity and to support the current drive to enhance office automation and other information systems.

Optical Digital Data Storage Technologies With Semiconductor Laser Nead

A laboratory model optical disk file memory for digital data storage is developed. User storage capacity is 2GBytes per disk and data transfer rate is 350KBytes/sec. Average seek time is 150msec. Several new technologies supporting the device are also described in detail.

High density image-storage holograms by a random phase sampling method.

The random phase sampling method that has been proposed to make high quality and high storage density holograms capable of storing image information is described and discussed from the aspect of the quantitative characteristics of its reconstructed image. The method enables the uniform distribution of light energy over the hologram area made on the exact Fourier transformed plane. The details of the characteristics of the method are investigated, especially with respect to the luminance tone linearity, the signal-to-noise ratio, and the resolution to give good agreement with the results of a calculation. In the experiment, reconstructed images with high quality were obtained from holograms of 2-mm diam, which were made by 10(6) sampling and random phase shifting. By using the random phase sampling medthod, an image retrievel model system storing twenty kinds information was developed. This system holds promise of being used in various practical applications such as holographic ultramicrofilm system or a holographic videopackage system.

Holographic video disk: an alternative approach to optical video disks

Optical video disks employing time sequential coding are superior to mechanical video disks because of their noncontact reproducing capability. One drawback in the optical systems is the necessity of precise focusing and tracking adjustments. To solve this problem, an alternative approach, using a holographic technique that makes it possible to store a frame of information in a specified area redundantly, is proposed. A design concept and experiments relating to the breakthroughs are described. A combination of random phase sampling holography and coherently superimposing holography makes it possible to store color-encoded images sufficient for about a 30-min motion picture on a disk of 300 mm in diameter. A sound recording technique suitable for the holographic video disk, constituting one-dimensional hologram-type, pulse-coded-modulation signals, is proposed.

High storage density optical disks using pit-edge recording on PbTeSe thin film

Pit-edge recording, where, the leading and trailing edges of the pit correspond to code-data 1, can achieve about one and a half times more bit density than that of pit-position recording. Using pit-edge recording with an effective write-read compensation scheme, we have achieved high linear density of 0.63 microm/bit on a PbTeSe ablative type optical disk. The write compensation is able to cancel pit expansion caused by thermal diffusion and surface tension of the recording film. We also confirmed the possibility of 0.50-microm/bit recording with an advanced compensation scheme on a PbTeSe optical disk. The corresponding user data capacity is ~1 Gbyte/side on a 130-mm diam optical disk.

Sn-Te-Se Phase Change Recording Film For Optical Disks

Sn-Te-Se amorphous-crystalline phase change recording film is analyzed on write/erase cyclability, erasing speed, and activation energy of crystallization. The Sn-Te-Se thin film, sandwiched by two SiO2 thin film layers, is deposited on an organic-thick-film coated glass substrate. Then, another organic thick film is coated onto these layers. For these samples, the maximum erasure(crystallization) speed by laser beam irradiation and other write/erase characteristics are measured. Information can be written and erased more than 106 times. The crystallization activation energy is also measured and found to be about 2.3eV. The life of the amorphous state is estimated to be about 10 years at 40°C. These experimental results show that Sn-Te-Se thin film is promising as a reversible phase change recording film.

Use of heterostructure diode lasers in video disk systems

The application of heterostructure lasers to video disk systems is described. The buried heterostructure diode laser is used as a light source of the optical pickup for the optical video disks. This pickup enables video signals to be reproduced with a SNR of more than 40 dB. These lasers can be not only used as a light source to read out the signal from the disk but also as a detector of the reflected light.

Compact Magneto-Optical Disk for Coded Data Storage

A compact magneto-optical disk drive compatible with current optical disk systems is reported. A tracking detection system enabling use with add-on (non-erasable) optical disks was adopted. High-speed accessing was accomplished by constructing the head from both stationary and moving mechanisms. Noise analyses showed that for large analyzer angles ¿<inf>A</inf>, N<inf>disk</inf> ≫ N<inf>laser</inf> ≫ N<inf>shot</inf>, but when the SN ratio was maximum at ¿<inf>A</inf> ~ 10°, the three noise levels were roughly equal.

Semiconductor Laser Pickup for Optical Video Disk Player

Almost five years have passed since the concept of the optical video disk system was first presented, and several kinds of systems have been developed these few years. 1,2,3,4 Recently, the standardization of these confused optical video disks was made and optical video disk player systems have already reached the stage of commercial development.5 Optical video disk systems offer several advantages to mechanical and capacitive video disk systems. High image quality, still and slow motion picture capability are some of its chief attractions. Unfortunately, large, complicated, and expensive optical pickups still remain a problem. Part of the difficulties is the use of the He-Ne laser as a light source. Although the He-Ne laser is one of the most stable and compact gas laser among several commercial available lasers, its size, over 200mm length and 30mm in diameter, is still too large for a compact optical pickup. Moreover, high voltage power supply of over 1.5KV are not desirable for home use systems. In addition, the optical system used in the pickup is quite complex because separate laser beams are used to detect the auto-focusing signal, the tracking signal, and the video signal. These factors make for a very expensive overall cost in labor for manufacturing and maintenance.