Abstract: An optical encoder has a light source and a diffracted light interference device including at least first and second diffraction gratings confronting each other, producing diffracted light beams in specific orders by passing light emitted from the light source through the first and second diffraction gratings, and making the diffracted light beams in the specific orders, which have passed through the diffraction gratings, interfere with each other to produce on-axis interference light beams in which the sum of the orders of the diffraction at the diffraction gratings is zero and off-axis interference light beams in which the sum of the orders of the diffraction is not zero. A phase device is adjusting the phases of the on-axis interference light beams and the off-axis interference light beams emitted from plural portions of the diffracted light interference device. A plurality of light sensors receive and detect the on-axis interference light beams and the off-axis interference light beams device.

Abstract: An optical encoder includes: a light source; a first grating plate having a first diffraction grating for diffracting a light beam emitted from the light source; a second grating plate having a second diffraction grating for further diffracting the light beam diffracted by the first diffraction grating; a reflector for reflecting the light beam from the second grating plate so as to allow the light beam to reenter the second grating plate; and a light-receiving portion for receiving the light beam reflected by the reflector and successively diffracted by the second and first grating plates, wherein a diffraction angle of plus and minus first-order diffracted light beams of the first diffraction grating is substantially equal to that of the plus and minus first-order diffracted light beams of the second diffraction grating, and the light-receiving portion generates an electric signal in accordance with the amount of the plus and minus first-order diffracted light beams of the first diffraction grating.

Abstract: A Fourier transform optical apparatus for optically Fourier transforming an input image includes a spatial light modulator for displaying an input image, a light source for irradiating the input image on the spatial light modulator, a first convex lens and a first concave lens arranged near the spatial light modulator and a second convex lens arranged at the composite focal plane of the first convex lens and first concave lens. The respective focal lengths of these three lenses are determined to satisfy conditions such that a light ray passing an intersection of the spatial light modulator and an optical axis of the Fourier transform optical apparatus becomes a light ray parallel to the optical axis after passing the second convex lens and a light ray incident to the first convex lens in parallel to the optical axis is focused at the composite focal point of the first convex lens, first concave lens and the second convex lens.

Abstract: In an optical information processor, phase-type spatial modulation of light is achieved by placing a twisted nematic liquid crystal cell between two polarizers, such that a direction of alignment of liquid crystal molecules at an input side of the liquid crystal cell is parallel to a transmission access of a first one of the polarizers, and such that a direction of alignment liquid crystal molecules at an output side of the liquid crystal cell is parallel to a transmission access of a second one of the polarizers. Also, phase modulation which is substantially free from amplitude variations can be realized by placing two twisted nematic liquid crystal cells between two polarizers.

Abstract: There is disclosed a method for measuring retardation .DELTA.nd of a liquid crystal cell in which a linearly polarized light beam is impinged upon a liquid crystal cell, the liquid crystal cell is rotated in a plane perpendicular to an optical axis of a measuring optical system so that the transmission through the liquid crystal cell for the light beam having a polarization parallel to that of the incident light beam becomes maximal, the wavelength of the incident light beam is varied to detect at least one wavelength .lambda..sub.s at which the transmission has an extreme and, finally, .DELTA.nd is calculated from .DELTA.nd=.lambda..sub.s .sqroot.m.sup.2 -(1/4) for the case of m-th minimal transmission or from .DELTA.nd=.lambda..sub.s .sqroot.m.sup.2 +m for the case of m-th maximal transmission.

Abstract: A Fourier transform lens assembly suited for use in an optical information processor includes a first lens group having a positive power, a second lens group having a negative power disposed on one side of the first lens group, and a third lens group having a positive power disposed on the side opposite to the first lens group with respect to the second lens group. The distance between a front focal plane and a back focal plane of the Fourier transform lens assembly is less than two times a focal length of the Fourier transform lens assembly.

Abstract: An input image of an object is optically Fourier-transformed and after coordinate-transforming the Fourier-transformed input image optically to obtain a rotation-invariant and scale-invariant image, the resultant image is pattern-matched with a computer generated hologram of a reference image. The coordinate-transformation of the Fourier-transformed input image is made using an optical phase filter represented as a computer generated hologram.

Abstract: An input image of an object is optically Fourier-transformed and after coordinate-transforming the Fourier-transformed input image optically to obtain a rotation-invariant and scale-invariant image, the resultant image is pattern-matched with a computer generated hologram of a reference image. The coordinate-transformation of the Fourier-transformed input image is made using an optical phase filter represented as a computer generated hologram.

Abstract: A Fourier transform lens assembly suited for use in an optical information processor includes a first lens group having a positive power, a second lens group having a negative power disposed on one side of the first lens group, and a third lens group having a positive power disposed on the side opposite to the first lens group with respect to the second lens group. The distance between a front focal plane and a back focal plane of the Fourier transform lens assembly is less than two times a focal length of the Fourier transform lens assembly.

Abstract: A visual recognition apparatus for use in, for example, a robot requires an optical information processor for performing image processing or image recognition. The optical information processor includes a first spatial light modulator for displaying an input image, a first lens having a front focal plane on which the first spatial light modulator is positioned, a second spatial light modulator for displaying at least one optical filter, a second lens having a front focal plane on which the second spatial light modulator is positioned, and a third lens having a front focal plane on which a rear focal plane of the second lens lies. The optical information processor also includes a beam splitter for combining together light transmitted through the first lens with light transmitted through the third lens, and a fourth lens having a front focal plane on which both a rear focal plane of the first lens and a rear focal plane of the third lens generally lie.

Abstract: A vision recognizing method includes a logarithmic polar coordinate transforming method including the steps of storing an input image f1(x, y); optically generating complex amplitude information f1(x, y)A(x, y)T(x, y) by multiplying the information of the input image by the product of phase information A(x, y) for performing a logarithmic polar coordinate transformation and amplitude information T(x, y), an amplitude of which changes according to distance between each point composing the amplitude information and origin of logarithmic polar coordinate; and Fourier-transforming the complex amplitude information f1(x, y)A(x, y)T(x, y). An optical information processing apparatus is used to carry out the method and includes a combination of lenses and liquid crystal displays.

Abstract: An optical encoder is used for detecting the position, speed, acceleration etc. of a moving or rotating object. The optical encoder includes a light source, a collimator lens for collimating a light emitted from the light source, a transparent lens plate having an array of lenses formed therein at regular intervals, and a light detector located on a focal plane of the lenses lying on the side opposite to the collimator lens with respect to the lens plate.

Abstract: New methods for producing computer generated holograms to be used for a liquid crystal spacial light modulator having a plurality of pixels, wherein the amplitude component of a coherent wave disturbance is corrected by taking into account the phase distortion due to the twist of liquid crystal molecules of the liquid crystal spacial light modulator.