Michiyoshi Nagashima

New Optical Erasable Medium Using Tellurium Suboxide Thin Film

A suboxide thin film of TeOx ( x is smaller than the stoich.Lometric value ) containing a small amount of additives of such metals and semimetals as Sn and Ge has been found to have the property of showing a reversible change in its optical constants when the film was exposed in turn to two diode laser spots with different sizes, and this property can be utilized for an erasable disc. For recording, a TeOx thin film deposited on a PMMA substrate is irradiated by a diffraction limited laser spot, 0.8 pm in dia., modulated in response to an input electrical signal. This causes a micro-sized area of the film to be suddenly heated and rapidly quenched, resulting in a decrease in optical reflectivity. This recorded bit can be erased at real time by the irradiation of a diffused laser spot to an elliptical shape, 1 x 10 pm, by which the bit recovers its optical properties. An optical head having the two laser beams, one for recording/playback and one for erasing, has been developed. Real time erasing and recording at the same time has been achieved for a video signal. In excess of a million record/erase cycles have been demonstrated with no significant degradation in playback signal quality or erasability. Carrier-to-noise ratio, C/N, was more than 55 dB at 5 MHz, 30 kHz bandwidth.

High density optical disk with V‐shaped grooves

Properties of diffracted light back from an optical disk, which has grooves with a V‐shaped cross‐sectional configuration, are studied by employing scalar diffraction theory. The V‐shaped grooves are spaced bottom to bottom by a presently used track pitch, and all walls of the grooves are capable of storing information. If the optical depth of the V‐shaped groove is one‐fourth of the wavelength of the laser, the 2nd or (−2)nd diffracted light beam contains only the information on a single wall. This property is utilized to double the information density of the optical disk.

Light pulses emitted at microfractures formed by friction between two solid materials

Short-duration light pulses have been observed to be emitted at the moment of microfracture (pit size of 10-20 µm) when two solids are rubbed against each other. When a fused silica sample is scratched by a diamond grain, the observed light pulses have a rise time of less than 10 ns and pulse width of 10-20 ns. A continuous spectrum at 500-800 nm is observed, suggesting 3000° C material part. At 300-400 nm, intense line spectra are observed, which suggests the existence of gaseous *O2 molecules desorbed from SiO2. When the solid fractures, the fractured part heats up to a very high temperature almost instantaneously, and cools down within 10-20 ns.

Diffraction grating lens array

We have proposed a new type of camera module with a thin structure and distance-detection capability. This camera module has a four-lens-array with diffraction gratings (one for blue, one for red, and two for green). The diffraction gratings on the mold are formed mechanically, and the plastic lens array is fabricated by injection molding. The two green images are compared to detect parallax, and parallax-corrected blue, red and green images are then composed to generate a color image. We have developed new design software and molding technologies for the grating lenses. The depth and period of blazed gratings and the shapes of aspheric lenses are optimized; and blue, red and two green aspheric lenses with gratings are molded as a single four-lens-array. The diffraction gratings on both surfaces of each lens act to improve field curvature and realize wide-angle imaging. However, blazed gratings sometimes cause unnecessary diffraction lights that impede the formation ofhigh-resolution images. We have developed a new method to measure necessary first-order diffraction lights and unnecessary diffraction lights separately. Use of this method allows the relationship between molding conditions and necessary/unnecessary diffraction lights to be shown. Unnecessary diffraction lights can be diminished by employing the optimal molding processes, allowing our grating lenses to be used for image capture.

New camera module with thin structure, high resolution and distance-detection capability

Our new type of camera module has a four-lens-array and an imaging sensor. The imaging sensor is divided to four regions, and these four regions are aligned in one-to-one correspondence with the four lenses. Four color filters are placed over the four imaging regions. First region has a blue filter, second has a red, and the other two have green filters, and two regions with green filters are aligned diagonally. Diffraction gratings are formed on aspheric surfaces of the four lenses, and MTF characteristics of these lenses are improved. The four images taken through the different lenses have parallax, but these parallaxes can be calculated by comparison of the two green images. Pixel shifts of blue, red and green images are realized by rotating the four-lens-array slightly with respect to the imaging sensor. After correcting the parallaxes, the green image, the parallax-corrected blue image and the parallax-corrected red image are composed to generate the resultant color image with high resolution. Distances between objects and the four-lens-array are detected by use of the above parallaxes, and measurement error is less than 2.5% for near objects. With above configuration and functions, our camera module has realized smaller height, higher image resolution and distance-detection capability, and will be applied for cellular phones and automobile vehicles.

Measuring longitudinal displacements using laser beam diffraction changes near the focal point

A nanometer displacement probe is created by using a knife edge, a two‐part‐divided photodiode, and high quality lenses. The laser beam, of wavelength 780 nm, is focused on the sample surface, where the image formed of the beam is read by the photodiode through the same optical path. The displacement signal is found to originate from the diffracted image change at the surface. A dynamic range of 2 μm and a minimal resolution of 1 nm for a lens of f=3.6 mm are obtained. The difference current, when normalized by the summation current, becomes a function of displacement and is independent of the sample surface reflectivity. As an application, a piezoceramic piece having a mean roughness of 1.03 μm was used. The frequency characteristics measured by this mechanical displacement method and the conventional electric oscillation measurement method were compared and found to be in good agreement.

Distance detective small camera module

Our new type of camera module is small and thin, and is able to detect the distances of objects as well as their images. The module comprises a four-lens array, one imaging sensor and optical filters. The imaging sensor is divided into four areas, two of which are covered with green filters and the other two with infiared filters. A prototype was fabricated with a focal length of 2.63 mm and a baseline length of 2.59 mm. The two images with the same optical filters have parallax, so the distances of objects can be calculated by comparing the two images. We use infrared images illuminated with infrared LEDs at night, and green images during the daytime. After calibrating the images, we achieved a distance-detection accuracy of within ±2.5% at 1 m in spite of the cameras small baseline length. Consequently, our new distance detection camera module is small and thin, and generates a depth-image of an object as well as its image. Our camera module is thus applicable to vehicles, security systems and three-dimensional imaging.

V-grooved optical disc applied to HDTV signal recording

We have realized a V-grooved optical disc that achieves an increase in recording density over conventional optical discs. This report describes the results of our research : namely its fabrication process and optical read-out method. The features of the V-grooved optical disc system are: 1) high density with narrower track pitch 2) double transfer rate using two-channel simultaneous read-out 3) applicability to read out current CD The V-grooved optical disc is suitable for recording of a baseband HDTV signal because the signal requires a large volume and high transfer rate. 1 . HIGH DENSITY OPTICAL DISCS Optical discs such as Compact Discs (CD) or Video Discs are currently used as information media because they feature large volume high density and easy random access. Recording density reaches 1 bit per 1 um2. However downsizing of disc diameter and applicability to HDTV signals require even higher recording density. Since an optical disc system reads out signals by focusing a laser to the diffraction limit the foremost way to realize higher recording density is minimizing the laser spots focused on the discs shortening of semiconductor laser wavelength and designing of better objective lenses have been the important themes of recent research and development. The wavelength of semiconductor lasers used to read out CD is in the near-infrared around 78Oniu but mass production of G7Onm lasers has just been initiated. Research and development of Il-VI

Laser Nanometer Probe Utilizing Beam Diffraction Pattern Change as a Function of Displacements from the Focal Point.

A laser diode (λ = 780 nm) probe, from which an half-circular beam irradiates in-focus to an objective surface and the diffraction pattern formed on the suface near the focal point is detected by a two-part-divided photo-diode throughout the same optical path, is proposed. The principle of the measurement is discussed by the diffraction pattern change analysis. The response characteristics of the probe prepared are measured; the obtained dynamic ranges are ±1 μm-2 nm for f=3.6 mm, and ±100-0.2 μm forf =23 mm lens. When the output signal, the difference currents of the two parts of the detector, is normarized by the summation of them, it becomes a simple function of displacements inspite of the condition of the material surface; the displacement response curves for a mirror sample, a low reflectivity glass sample and a steel sample having a mean roughness of 1.3 μm, are quite similar.