Holographic member for a real-time clock in a raster output scanner
First Claim
Patent Images
1. An optical element for directing a portion of a light beam from a fixed source toward first and second fixed external locations, comprising:
- an elongated member;
a first grating, adapted to receive light from the fixed source and form an interference pattern forming a light wave toward the first fixed external location, the first grating having a variable pitch dependent on the angular position of an area of the first grating relative to the first fixed external location; and
a second grating, adapted to receive light from the fixed source and form an interference pattern forming a light wave toward the second fixed external location, the second grating having a variable pitch dependent on the angular position of an area of the first grating relative to the second fixed external location;
the first and second gratings being arranged in an interleaved fashion along the member, whereby a light beam spot moving along the member will cause an interference pattern forming a light wave to be directed alternately to the first external location and the second external location.
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Abstract
A grating having holographic properties is employed in a pixel clock for a raster-output scanner. A pilot beam, off-axis from the writing beam creating a latent image on the photoreceptor, is focused on the grating. The grating is adapted to direct a portion of the pilot beam to a photodetector in a fixed point location. The holographic properties of the grating ensure that a wave associated with a reflected interference pattern is always directed at the photodetector throughout the scan path of the pilot beam.
57 Citations
10 Claims
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1. An optical element for directing a portion of a light beam from a fixed source toward first and second fixed external locations, comprising:
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an elongated member; a first grating, adapted to receive light from the fixed source and form an interference pattern forming a light wave toward the first fixed external location, the first grating having a variable pitch dependent on the angular position of an area of the first grating relative to the first fixed external location; and a second grating, adapted to receive light from the fixed source and form an interference pattern forming a light wave toward the second fixed external location, the second grating having a variable pitch dependent on the angular position of an area of the first grating relative to the second fixed external location; the first and second gratings being arranged in an interleaved fashion along the member, whereby a light beam spot moving along the member will cause an interference pattern forming a light wave to be directed alternately to the first external location and the second external location.
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2. A raster output system of the type having a writing beam modulated in accordance with image data and reflected from a reflecting surface and caused to scan across a photosensitive surface, and a pilot beam reflected from substantially the same location of the reflecting surface as the writing beam at a given time, the improvement comprising:
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encoder means having an optical pattern thereon, the optical pattern adapted to interact with the reflected pilot beam scanning across the optical pattern to create an optical signal indicative of the behavior of the writing beam relative to the photosensitive surface; and light collection means for directing light associated with the optical signal toward a fixed point, the light collection means including diffraction means for directing an interference pattern forming a light wave toward the fixed point in response to the pilot beam interacting with the light collection means. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10)
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Specification