Ferroelectric liquid crystal tunable filters and color generation
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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Abstract
Discretely and continuously tunable filers emplying FLC cells are provided. Exemplary discretely tunable filters employ bistable smectic C* FLC cells. Exemplary continuously tunable filters employ smectic A* FLC cells. Single or multiple stage filters are provided. Blocking filters useful for color generation are also provided. The FLC filters provided can be temporally multiplexed.
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Citations
40 Claims
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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:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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35. A blocking filter which comprises N stages positioned along a light propagation axis wherein N [=3 or more along a light propagation axis] is three or more;
- wherein a stage comprises;
an entrance polarizer and an exit polarizer which are oriented either parallel or perpendicular to one another wherein the entrance polarizer determines the plane of polarization of light entering said stage; a ferroelectric liquid crystal cell positioned between said polarizers such that in its unswitched state the plane defined by the optic axis of said cell and said light propagation axis is parallel to said plane of polarization of entering light;
wherein the thickness of said cell and the orientation of said polarizers are chosen such that when said ferroelectric liquid crystal is in the switched state said filter transmits a desired wavelength band while blocking an undesired wavelength band; andmeans 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 the exit polarizer of a stage in the entrance polarizer for the next successive state, said N stage filter thereby comprising N ferroelectric liquid crystal cells; and wherein said N ferroelectric liquid crystal cells in said different stages are synchronously switched in pairs of two by application of said electric field such that when each pair of cells is switched the filter transmits a selected wavelength band while blocking at least two undesired wavelength bands. - View Dependent Claims (36, 37, 38, 39, 40)
- wherein a stage comprises;
Specification