Patent ID: 7250200

Claim:
A liquid crystal cell comprising a liquid crystal, a constraint, and one or more compensator layers interposed between the liquid crystal and the constraint, each compensator layer containing a transparent amorphous polymeric birefringent material having a) an out-of plane birefringence more negative than −0.005, and a glass transition temperature (Tg) above 180° C., that includes in the backbone a non-visible chromophore containing a vinyl, carbonyl, amide, ester, carbonate, sulfone, azo, or aromatic group, and that does not contain a chromophore off of the backbone, wherein an overall in-plane retardation (Re) of all of the one or more compensator layers is from +20 to −20 nm, and the out-of-plane retardation (Rth) of at least one of the one or more compensator layers is more negative than −20 nm; or b) an out-of plane birefringence more positive than 0.005, a glass transition temperature (Tg) above 160° C., and that contains off the backbone a non-visible chromophore containing a vinyl, carbonyl, amide, ester, carbonate, aromatic, azo or sulfone group, wherein an overall in-plane retardation (Re) of all of the one or more compensator layers is from +20 to −20 nm, and the out-of-plane retardation (Rth) of at least one of the one or more compensator layers is more positive than 20 nm; wherein amorphous means the optical compensator does not produce any sharp diffraction peaks when exposed to X-ray diffraction analysis.