Akito Iwamoto

Artificial diffuser for Fourier transform hologram recording

A novel artificial diffuser for Fourier transform hologram recording is proposed, and its imaging and spectral properties are analyzed. This new diffuser gives high SNR and resolution characteristics to the holographically reconstructed images and high reliability and redundancy characteristics to the system where holograms are used as information storing media. These characteristics are confirmed by experiments.

Defect-type discriminating optical system

Novel coherent optical defect detecting methods, which can distinguish between opaque defects and transparent defects, are proposed. One of these novel methods makes use of a holographylike polarity reference signal and is suited to automatic detection systems. The other employs two independent light sources, and suitable for visual detection systems. Realizing these novel methods using omnidirectional spatial filters, simple but effective periodic pattern defect-detecting systems are formed, which can be easily accommodated with defect touching-up stages.

Rotation-, shift-, and magnification-insensitive periodic-pattern-defects optical detection system

Defects in rectangular x-y axis decomposable periodic patterns are found to be detected by an omnidirectional (r-theta axis decomposable) spatial filter optical system, where use is made of the spectral difference between periodic patterns and defects. A novel omnidirectional spatial filter, which has bandpass characteristics, is designed to block all the repetitive periodic regular pattern spectra and pass the defect information carrying spectra. According to a computer simulation, the minimum detectable defect size using this optical system is about one-twentieth that of the periodic pattern pitch. This novel optical system is characterized by its ability to detect defects at any location and rotation (shift and rotation immunity of the optical system) and also to be insensitive to object magnification by the frequency domain operation characteristics. This filter application is not limited to 2-D rectangular periodic-pattern-defects detection, but defects in 1-D or skew periodic patterns are also detected by the same filter.

Holographic system for filing and retrieving patents.

A large-capacity high-speed holographic system has been developed for filing and retrieving the patent literature. This machine can store 280,000 pages of the Japanese patents journal (or the U.S. Official Gazette) and any one page can be retrieved within 1 sec. A high-resolution TV camera with 2110 scanning lines and a CRT display terminal with 1055 scanning lines were also developed to clearly represent fine drawings and letters in the patents. The system developed is equipped with a momentary 2.6-Mbyte electric one-frame memory for scanning mode conversion. Any image on the CRT can be printed out on a plain sheet of paper with a laser beam printer.

Holograms produced with double-heterojunction laser illumination

Abstract Off-axis holograms have been constructed with a double-heterojunction (Ga, Al) As-GaAs semiconductor laser, and image reconstruction has been accomplished using a semiconductor and a He-Ne laser. The reconstructed real images were quite clear, and the signal-to-noise ratio of those images was about 10. Experiments suggest that semiconductor lasers can successfully be applied to coherent optics.

Disk-memory pregroove inspection.

An optical inspection system has been developed that detects parameter fluctuations in an optical disk pregroove structure (groove pitch, depth, and width). This optical system was devised using a laser diffraction phenomenon. Groove parameters are measured and calculated from diffracted-light intensity ratios; the groove width is calculated from the second-order diffracted-light intensity ratio to that for the first order. The groove depth is given from the first-order ratio to the zeroth-order light intensity. In addition to this groove parameter inspection, this system is capable of groove defect detection using a spatial filter whose passband is designed to be between the zeroth- and the first-order diffracted-light areas.

Periodic aperture size measurement with submicron accuracy: application to nonuniform detection in color CRT shadow masks

A novel periodic aperture size measurement optical system, which makes use of a coherent light beam/lens 2-D Fourier-transform property, is proposed. Measuring gain and errors is discussed. This optical system is able to produce aperture widths on a 3-D formed surface with the same accuracy as those on a flat surface and is well suited for measuring small aperture size variations in shadow masks for color TV tubes. These variations in shadow masks are considered to cause luminous and color nonuniformities and have been detected heretofore only by visual inspection. The minimum detectable size variation for this new measuring method is ~0.1 microm.