Split-element liquid crystal tunable optical filter

Claim 2

A liquid crystal split-element optical filter comprising one or more stages optically coupled in series wherein at least one stage comprises: a first polarizer; a second polarizer oriented parallel or perpendicular to said first polarizer; a center retarder unit positioned between said first and second polarizers, and comprising one or more retarders and having a composite retardance oriented parallel or perpendicular to said first polarizer; a first split-element retarder unit, positioned between said first polarizer and said center retarder unit, and comprising a first split-element retarder, oriented at ±π/4 with respect to said first polarizer; and a second split-element retarder unit, positioned between said center retarder unit and said second polarizer, and comprising a second split-element retarder of equal retardance to said first split-element retarder and oriented at ±π/4 with respect to said first polarizer; wherein at least one of said retarder units comprises a first liquid crystal retarder, said first liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation and a second orientation.

Claim 3

The split-element filter of claim 1 wherein said center retarder unit has a composite retardance of a half-wave oriented parallel to said first polarizer, and wherein said first split-element retarder is oriented perpendicular to said second split-element retarder.

Claim 4

The split-element filter of claim 2 wherein said center retarder unit is approximately achromatic.

Claim 5

The split-element filter of claim 2 wherein said center retarder unit comprises a fixed half-wave retarder oriented parallel to said first polarizer.

Claim 6

The split-element filter of claim 2 wherein said first split-element retarder is a first fixed split-element retarder and wherein said first split-element retarder unit further comprises said first liquid crystal retarder, positioned between said first fixed split-element retarder and said first polarizer, said first liquid crystal retarder having said first orientation parallel to said first polarizer and said second orientation parallel to said first fixed split-element retarder.

Claim 7

The split-element filter of claim 5 wherein said first liquid crystal retarder is a SmC* liquid crystal retarder.

Claim 8

The split-element filter of claim 5 wherein said first liquid crystal retarder is a half-wave retarder.

Claim 9

The split-element filter of claim 5 wherein said second split-element retarder is a second fixed split-element retarder and wherein said second split-element retarder unit further comprises a second liquid crystal retarder, positioned between said second fixed split-element retarder and said second polarizer, said second liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation parallel to said second polarizer and a second orientation parallel to said second fixed split-element retarder.

Claim 10

The split-element filter of claim 8 wherein said first and second liquid crystal retarders are SmC* liquid crystal retarders.

Claim 11

The split-element filter of claim 8 wherein said first and second liquid crystal retarders are quarter-wave retarders.

Claim 12

The split-element filter of claim 2 wherein said first split-element retarder is a first fixed split-element retarder and wherein said first split-element retarder unit further comprises said first liquid crystal retarder, positioned between said first fixed split-element retarder and said center retarder unit, said first liquid crystal retarder having said first orientation parallel to said first polarizer and said second orientation parallel to said first fixed split-element retarder, and wherein said second split-element retarder is a second fixed split-element retarder and wherein said second split-element retarder unit further comprises a second liquid crystal retarder, positioned between said second fixed split-element retarder and said center retarder unit, said second liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation perpendicular to said first polarizer and a second orientation parallel to said second fixed split-element retarder.

Claim 13

The split-element filter of claim 11 wherein said first and second liquid crystal retarders are quarter-wave retarders.

Claim 14

The split-element filter of claim 11 wherein said first split-element retarder unit further comprises a third liquid crystal retarder, positioned between said first fixed split-element retarder and said first polarizer, said third liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation parallel to said first polarizer and a second orientation parallel to said first fixed split-element retarder, and wherein said second split-element retarder unit further comprises a fourth liquid crystal retarder, positioned between said second fixed split-element retarder and said second polarizer, said fourth liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation parallel to said second polarizer and a second orientation parallel to said second fixed split-element retarder.

Claim 15

The split-element filter of claim 2 wherein said first split-element retarder is a first fixed split-element retarder and wherein said first split-element retarder unit further comprises a passive quarter-wave retarder, positioned between said first polarizer and said first fixed split-element retarder, with optic axis oriented parallel or perpendicular to said first polarizer, and said first liquid crystal retarder positioned between said first polarizer and said passive quarter-wave retarder, said first liquid crystal retarder having a half-wave retardance and having said optic axis continuously rotatable between said first and second orientations.

Claim 16

The split-element filter of claim 14 wherein said first liquid crystal retarder is a SmA* liquid crystal retarder.

Claim 17

The split-element filter of claim 2 comprising a quarter-half-quarter compound retarder positioned between said first and second split-element retarders, said quarter-half-quarter compound retarder comprising a first passive quarter-wave retarder oriented parallel or perpendicular to said first polarizer, a second passive quarter-wave retarder oriented parallel or perpendicular to said first polarizer, and said first liquid crystal retarder positioned between said first and second passive quarter-wave retarders, said first liquid crystal retarder having a half-wave retardance and having said optic axis continuously rotatable between said first and second orientations.

Claim 18

The split-element filter of claim 16 wherein the composite retardance of said quarter-half-quarter compound retarder is equal to the composite retardance of the combination of a first variable retarder oriented at ±π/4 with respect to said first polarizer, a second variable retarder, of equal retardance to said first variable retarder, oriented at ±π/4 with respect to said first polarizer, and a fixed half-wave retarder, positioned between said first and second variable retarders, and oriented parallel to said first polarizer.

Claim 19

The split-element filter of claim 16 wherein said second passive quarter-wave retarder is oriented perpendicular to said first passive quarter-wave retarder.

Claim 20

The split-element filter of claim 18 wherein said first liquid crystal retarder is a SmA* liquid crystal retarder.

Claim 21

The split-element filter of claim 16 wherein said quarter-half-quarter compound retarder further comprises a second liquid crystal retarder, positioned between said first and second passive quarter-wave retarders, said second liquid crystal retarder having a half-wave retardance and having a rotatable optic axis, and wherein said second passive quarter-wave retarder is oriented parallel to said first passive quarter-wave retarder.

Claim 22

The split-element filter of claim 20 wherein said first liquid crystal retarder is a SmA* liquid crystal retarder.

Claim 23

The split-element filter of claim 21 wherein said second liquid crystal retarder is a SmA* liquid crystal retarder.

Claim 24

The split-element filter of claim 1 wherein said center retarder unit comprises a fixed center retarder oriented parallel or perpendicular to said first polarizer, and said first liquid crystal retarder, said first liquid crystal retarder having said first orientation perpendicular to said fixed center retarder and said second orientation parallel to said fixed center retarder.

Claim 25

The split-element filter of claim 23 wherein said first liquid crystal retarder is a SmC* liquid crystal retarder.

Claim 26

The split-element filter of claim 23 wherein said first liquid crystal retarder is a quarter-wave retarder.

Claim 27

The split-element filter of claim 1 wherein said center retarder unit comprises a fixed center retarder oriented parallel or perpendicular to said first polarizer, and wherein said first split-element retarder is a first fixed split-element retarder and wherein said first split-element retarder unit further comprises said first liquid crystal retarder, positioned between said first fixed split-element retarder and said fixed center retarder, said first liquid crystal retarder having said first orientation parallel to said center retarder and said second orientation parallel to said first fixed split-element retarder, and wherein said second split-element retarder is a second fixed split-element retarder and wherein said second split-element retarder unit further comprises a second liquid crystal retarder, positioned between said second fixed split-element retarder and said center retarder, said second liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation parallel or perpendicular to said center retarder and a second orientation parallel to said second fixed split-element retarder.

Claim 28

The split-element filter of claim 26 wherein said first and second liquid crystal retarders are SmC* liquid crystal retarders.

Claim 29

The split-element filter of claim 1 wherein said center retarder unit comprises a fixed center retarder oriented parallel or perpendicular to said first polarizer, and wherein said first split-element retarder is a first fixed retarder and wherein said first split-element retarder unit further comprises said first liquid crystal retarder, positioned between said first fixed split-element retarder and said first polarizer, said first liquid crystal retarder having said first orientation parallel to said first polarizer and said second orientation parallel to said first fixed split-element retarder, and wherein second split-element retarder is a second fixed split-element retarder and wherein said second split-element retarder unit further comprises a second liquid crystal retarder, positioned between said second fixed split-element retarder and said second polarizer, said second liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation parallel to said second polarizer and a second orientation parallel to said second fixed split-element retarder.

Claim 30

The split-element filter of claim 28 wherein said first and second liquid crystal retarders are SmC* liquid crystal retarders.

Claim 31

The split-element filter of claim 1 wherein said center retarder unit comprises a first passive quarter-wave retarder oriented at ±π/4 to said first polarizer, a second passive quarter-wave retarder oriented parallel or perpendicular to said first passive quarter-wave retarder, and said first liquid crystal retarder positioned between said first and second passive quarter-wave retarders, said first liquid crystal retarder having a half-wave retardance and having said optic axis continuously rotatable between said first and second orientations, said center retarder unit further comprising a fixed center retarder positioned between said first split-element retarder unit and said first passive quarter-wave retarder, and oriented parallel or perpendicular to said first polarizer.

Claim 32

The split-element filter of claim 30 wherein said first liquid crystal retarder is a SmA* liquid crystal retarder.

Claim 33

The split-element filter of claim 1 wherein said center retarder unit comprises a fixed center retarder oriented parallel or perpendicular to said first polarizer, and wherein said first split-element retarder is a first fixed split-element retarder and wherein said first split-element retarder unit further comprises a first passive quarter-wave retarder, positioned between said first polarizer and said first fixed split-element retarder, with optic axis oriented parallel or perpendicular to said first polarizer, and said first liquid crystal retarder positioned between said first polarizer and said first passive quarter-wave retarder, said first liquid crystal retarder having a half-wave retardance and having said optic axis continuously rotatable between said first and second orientations, and wherein said second split-element retarder is a second fixed split-element retarder and wherein said second split-element retarder unit further comprises a second passive quarter-wave retarder, positioned between said second polarizer and said second fixed split-element retarder, with optic axis oriented parallel or perpendicular to said first polarizer, and a second liquid crystal retarder having a half-wave retardance and having a continuously rotatable optic axis, positioned between said second polarizer and said second passive quarter-wave retarder.

Claim 34

The split-element filter of claim 32 wherein said first and second liquid crystal retarders are SmA* liquid crystal retarders.

Claim 35

The split-element filter of claim 1 wherein said center retarder unit comprises a first center-split-element retarder oriented parallel or perpendicular to said first polarizer, a second center-split-element retarder, of equal retardance to said first center-split-element retarder, oriented parallel or perpendicular to said first polarizer and a center-center retarder, positioned between said first and second center-split-element retarders, and oriented at ±π/4 to said first polarizer.

Claim 36

The split-element filter of claim 34 wherein said center-center retarder is a half-wave retarder, and wherein said second center-split-element retarder is oriented perpendicular to said first center-split-element retarder.

Claim 37

The split-element filter of claim 1 wherein the retardances of said center retarder unit and of said first and second split-element retarders are in a Lyot progression.

Claim 38

The split-element filter of claim 1 wherein said second split-element retarder is oriented parallel to said first split-element retarder, and wherein the composite retardance of said center retarder unit is mλ, an integral number m of full-waves at a design wavelength λ, and wherein the retardance of each of said first and second split-element retarders is (2 n m+1/4)λ, where n is a whole number.

Claim 39

The split-element filter of claim 1 further comprising a third polarizer, oriented at a fixed angle with respect to said first polarizer and positioned on the opposite side of said second polarizer from said second split-element retarder unit, and further comprising a second-stage retarder positioned between said second polarizer and said third polarizer.

Claim 40

A double split-element optical filter comprising one or more stages optically coupled in series wherein at least one stage comprises: a first polarizer; a second polarizer, oriented parallel or perpendicular to said first polarizer; a center retarder oriented at ±π/4 to said first polarizer, and positioned between said first and second polarizers; a first inner-split-element retarder, oriented parallel or perpendicular to said first polarizer, and positioned between said first polarizer and said center retarder; a second inner-split-element retarder, of equal retardance to said first inner-split-element retarder, oriented parallel or perpendicular to said first polarizer, and positioned between said center retarder and said second polarizer; a first outer-split-element retarder, oriented at ±π/4 with respect to said first polarizer, and positioned between said first polarizer and said first inner-split-element retarder; and a second outer-split-element retarder, of equal retardance to said first outer-split-element retarder, oriented at ±π/4 with respect to said first polarizer and positioned between said second inner-split-element retarder and said second polarizer.

Claim 41

A double split-element optical filter comprising one or more stages optically coupled in series wherein at least one stage comprises: a first polarizer; a second polarizer, oriented parallel or perpendicular to said first polarizer; a center retarder oriented at ±π/4 to said first polarizer, and positioned between said first and second polarizers; a first inner-split-element retarder, oriented parallel or perpendicular to said first polarizer, and positioned between said first polarizer and said center retarder; a second inner-split-element retarder, of equal retardance to said first inner-split-element retarder, oriented parallel or perpendicular to said first polarizer, and positioned between said center retarder and said second polarizer; a first outer-split-element retarder, oriented at ±π/4 with respect to said first polarizer, and positioned between said first polarizer and said first inner-split-element retarder; and a second outer-split-element retarder, of equal retardance to said first outer-split-element retarder, oriented at ±π/4 with respect to said first polarizer and positioned between said second inner-split-element retarder and said second polarizer.

Claim 42

The double split-element filter of claim 39 wherein the retardance of said center retarder is (m+1/4)λ, where m is an integer and λ is a design wavelength.

Claim 43

The double split-element filter of claim 40 wherein the retardance of each of said first and second inner-split-element retarders is (2 n m+1/2)λ, where n is a whole number.

Claim 44

The double split-element filter of claim 41 wherein the retardance of each of said first and second outer-split-element retarders is (2 p m+1/8)λ, where p is a whole number.

Claim 45

The double split-element filter of claim 39 wherein said first and second inner-split-element retarders are oriented parallel to each other and wherein said first and second outer-split-element retarders are oriented perpendicular to each other.

Claim 46

The double split-element filter of claim 39 wherein said first and second inner-split-element retarders are oriented perpendicular to each other and wherein said first and second outer-split-element retarders are oriented perpendicular to each other.

Claim 47

The double split-element filter of claim 39 wherein said first and second inner-split-element retarders are oriented parallel to each other and wherein said first and second outer-split-element retarders are oriented parallel to each other and are perpendicular to said center retarder.

Claim 48

The double split-element filter of claim 39 wherein at least one of said retarders is a variable retarder.

Claim 49

The double split-element filter of claim 46 wherein said variable retarder is a liquid crystal variable retarder.

Claim 50

The double split-element filter of claim 47 wherein said liquid crystal variable retarder is a nematic liquid crystal variable retarder.

Claim 51

The double split-element filter of claim 39 wherein at least one of said retarders comprises a fixed retarder and further comprises a smectic liquid crystal retarder with rotatable optic axis.

Claim 52

A reflection-mode split-element filter comprising: a polarizer; a reflector; a center retarder unit positioned between said polarizer and said reflector, and comprising one or more retarders and having a composite retardance oriented parallel or perpendicular to said polarizer; and a split-element retarder unit, positioned between said polarizer and said center retarder unit, and comprising a split-element retarder, oriented at ±π/4 with respect to said polarizer; wherein at least one of said retarder units comprises a liquid crystal retarder, said liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first and a second orientation.

Claim 53

A reflection-mode split-element filter comprising: a polarizer; a reflector; a center retarder unit positioned between said polarizer and said reflector, and comprising one or more retarders and having a composite retardance oriented parallel or perpendicular to said polarizer; and a split-element retarder unit, positioned between said polarizer and said center retarder unit, and comprising a split-element retarder, oriented at ±π/4 with respect to said polarizer; wherein at least one of said retarder units comprises a liquid crystal retarder, said liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first and a second orientation.

Claim 54

A liquid crystal split-element optical filter comprising one or more stages optically coupled in series wherein at least one stage comprises: a first polarizer; a second polarizer oriented parallel or perpendicular to said first polarizer; a center retarder unit positioned between said first and second polarizers, and comprising one or more retarders and having a composite retardance oriented parallel or perpendicular to said first polarizer; a first split-element retarder unit, positioned between said first polarizer and said center retarder unit, and comprising a first split-element retarder, oriented at ±π/4 with respect to said first polarizer; a second split-element retarder unit, positioned between said center retarder unit and said second polarizer, and comprising a second split-element retarder of equal retardance to said first split-element retarder and oriented at ±π/4 with respect to said first polarizer; and a liquid crystal means, positioned between said second split-element retarder unit and said second polarizer, for adding a half-wave of retardance and thereby reversing the locations of transmission maxima and minima; wherein at least one of said retarder units comprises a first liquid crystal retarder, said first liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation and a second orientation.

Claim 55

A liquid crystal split-element optical filter comprising one or more stages optically coupled in series wherein at least one stage comprises: a first polarizer; a second polarizer oriented parallel or perpendicular to said first polarizer; a center retarder unit positioned between said first and second polarizers, and comprising one or more retarders and having a composite retardance oriented parallel or perpendicular to said first polarizer; a first split-element retarder unit, positioned between said first polarizer and said center retarder unit, and comprising a first split-element retarder, oriented at ±π/4 with respect to said first polarizer; a second split-element retarder unit, positioned between said center retarder unit and said second polarizer, and comprising a second split-element retarder of equal retardance to said first split-element retarder and oriented at ±π/4 with respect to said first polarizer; and a liquid crystal means, positioned between said second split-element retarder unit and said second polarizer, for adding a half-wave of retardance and thereby reversing the locations of transmission maxima and minima; wherein at least one of said retarder units comprises a first liquid crystal retarder, said first liquid crystal retarder having a fixed retardance and having an optic axis rotatable between a first orientation and a second orientation.