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Ferroelectric liquid crystal tunable filters and color generation

  • US 5,132,826 A
  • Filed: 05/11/1990
  • Issued: 07/21/1992
  • Est. Priority Date: 10/30/1989
  • Status: Expired due to Term
First Claim
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1. A tunable optical filter comprising one or more stages positioned in series along a light propagation axis wherein a stage comprises:

  • an entrance polarizer which defines a plane of polarization of light entering said filter stage and an exit polarizer which is oriented in a fixed position with respect to said entrance polarizer;

    at least one birefringent element and at least one ferroelectric liquid crystal cell positioned in series along said light propagation axis between said polarizers wherein said birefringent element is positioned between said exit polarizer and said ferroelectric liquid crystal cell; and

    means for applying an electric field to said ferroelectric liquid crystal cell such that said cell is thereby switched between an unswitched state and a switched state;

    wherein said polarizers, said ferroelectric liquid crystal cell and said birefringent element are oriented with respect to each other and the plane of polarization of entering light such that, when said electric field is applied to switch said ferroelectric liquid crystal cell between said unswitched and said switched state, the output of said filter is thereby tuned between a first transmission spectrum defined by the transmission characteristics of said birefringent element and a second transmission spectrum defined by the combined transmission characteristics of said birefringent element and said ferroelectric liquid crystal cell in the switched state; and

    wherein, when said filter contains more than one stage, the exit polarizer of a stage is the entrance polarizer for the next successive stage positioned in series along said light propagation axis of said filter.

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