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Diffractive optical device including grating elements with different grating periods and duty ratios

  • US 5,742,433 A
  • Filed: 04/04/1996
  • Issued: 04/21/1998
  • Est. Priority Date: 10/18/1993
  • Status: Expired due to Term
First Claim
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1. A diffractive optical device, comprising:

  • a substrate for allowing transmission therethrough of light to be diffracted; and

    a grating section located on the substrate and including a plurality of grating elements arranged in a disposition plane in a continuous grating pattern which collects light incident at an offset angle with respect to a direction normal to the disposition plane, said continous grating pattern having a plurality of grating periods within the continuous grating pattern, wherein the smallest grating period is greater than 1/2 n of the wavelength of said light where n is the refractive index of the substrate, said plurality of grating elements including;

    a first plurality of grating elements having a first duty ratio, the first plurality of grating elements having a first grating period which results in a first diffraction efficiency with said light being incident at said offset angle, anda second plurality of grating elements having a second duty ratio different from the first duty ratio, said second plurality of grating elements having a second grating period which results in a second diffraction efficiency with said light being incident at said offset angle,said first plurality of grating elements arranged such that said first grating period is smaller than said second grating period.

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