Nobuo Nishida

Antireflection effect in ultrahigh spatial-frequency holographic relief gratings

An interpretation model for low reflectivity in ultrahigh spatial-frequency holographic relief gratings is proposed. The model is based on the concept that the grating effective index, caused by grating ultrahigh spatial frequency, is graded in the depth direction and forms an antireflective constitution similar to the multilayer coating. Numerical results show that a sinusoidal grating is antireflective over wide groove depth, wavelength and incident angle ranges, and a grating with nearly triangular section, having a circle arc index distribution, has a very low reflectivity, >10(-4)%. Reflectivity vs groove depth, obtained experimentally for a holographically recorded photoresist grating, agrees fairly well with the numerical results.

A New Associative Memory System Utilizing Holography

A new associative memory utilizing holography is described, which has advantages such as higher density and larger capacity storage, simpler peripheral devices, and reciprocal translation between different kinds of information. The advantages of the holographic associative memory were achieved by use of associative translation function of a hologram and spatial logical operations. Two types of the holographic associative memory are explained; one uses a thin hologram, and the other a thick hologram. In the latter case, the ultimate bit density of 107bits/cm2is expected. A preliminary experiment of the memory system using a thin hologram (10 words x10 interrogation bits x20 information bits) was carried out and confirmed high signal-to-noise ratio in the interrogation and read out operations, associative translation function between different information, and high reliability in the memory operation.

Holographic laser scanners using generalized zone plates

Aberration properties in holographic zone plates for use in laser scanners are investigated. A generalized holographic zone plate is proposed. To generate the zone plate hologram, holographic optical product operations between plural coherent spherical waves, are applied. When spherical waves, N in number, are applied, aberration can be corrected in a scan length magnification equal to or less than N(2). Experimentally, a remarkable aberration correction effect for this hologram generation method is demonstrated for over 50-cm scan length. The configuration and features are described for the developed point-of-sale (POS) scanner employing generalized zone plate holograms.

Holographic disk with high data transfer rate: its application to an audio response memory

This paper describes a memory realized with a high data transfer rate using the holographic parallel-processing function and its application to an audio response system that supplies many audio messages to many terminals simultaneously. Digitalized audio messages are recorded as tiny 1-D Fourier transform holograms on a holographic disk. A hologram recorder and a hologram reader were constructed to test and demonstrate the holographic audio response memory feasibility. Experimental results indicate the potentiality of an audio response system with a 2000-word vocabulary and 250-Mbit/sec bit transfer rate.

Holographic optical elements with optimized phase-transfer functions

To optimize the phase-transfer function of holographic optical elements, a semianalytical method to solve the correction phase is proposed, in which the z-directional cosine of a diffracted light ray is dealt with as an estimated constant. Numerically, the confusion circle radius has been reduced to 1/120 for a holographic laser scanner example by this method, with rapid convergence. It is clarified that, for the generalized holographic zone plate generated with two spherical waves, the hologram phase-transfer function is well optimized for a laser-beam scanner without correction.

Holographic coding plate: a new application of holographic memory.

Detailed description is given of a holographic coding plate that encodes position coordinates of quantized spatial regions on the coding plate. A coding plate fabrication method is described that makes it possible to produce a coding plate of 2(m) x 2(n) quantized regions by a total of (m + n) exposures. Reconstruction of point images and their immobility are discussed in a framework of the first-order approximation. Dancings of the reconstructed point images are explained in terms of the third-order aberrations. Intensity variations of the reconstructed point images due to the volume holographic effect are discussed. Outline of a holographic graphic input device called a Holotablet, which is an example of the application of the holographic coding plate, is described.

High-brightness liquid-crystal light-valve projector using a new polarization converter

A high-brightness liquid crystal light valve (LCLV) projector, in which three amorphous Si TFT-addressed LCLVs are used, has been developed for laroe screen displays. By using a newly developed polarization converter, about twice the brightness has been realized compared to using a conventional sheet polarizer. The polarization converter principle is to efficiently convert an unpolarized light from a light source into a linearly polarized light, used to illuminate a twisted nematic LCLV. The LCLV has 240 x 756 pixels in the 4.3 inch diagonal area. High-brightness full-color images with 120 ft-L brightness have been obtained, when projected onto a 5.0 gain 80 inch diagonal screen using a 300W Xenon arc lamp.

Computer Generated Holographic Optical Elements For Optical Disk Memory Read Write Heads

A new concept optical head, using a holographic optical element has been developed. This holographic element combines three optical functions, beam splitter, focusing error detection and tracking error detection optics functions. A polarizing beam splitter function is also combined for magneto-optical disk head use. These holographic optical elements are computer generated holograms fabricated using electron beam lithography technique. A new optical configuration has been designed for this optical head to remove the influence of wavelength variation in the laser diode used for a light source. The off-set signal in tracking error signal has been reduced by introduction of the holograms which are used only for detecting tacking error. The stable operation and high read out S/N ratio have been obtained by applying this holographic optical element.

The hologram tablet: a new graphic input device

Graphic data tablets are input devices which digitize coordinate positions of topological patterns.

Holographic zone plates for f · θ and collimating lenses

A holographic zone plate generated by subtracting the spherical wave phase is proposed, that is, a hologram generated by using two divergent or convergent spherical waves. This holographic zone plate can correct the increase in focal power in a radial direction in contrast with the interferometric zone plate. Use of this holographic zone plate for f · θ and collimating lenses is analyzed. For an f · θ lens, it is shown that an optimum combination of recording spherical waves exists that satisfies both scan linearity and image field flatness. For a collimating lens for a laser diode, it is shown that aberration can be corrected for different playback wavelengths from that used during recording.