Although researchers have successfully designed optical-quality plastics, the nonlinear optical properties of plastic tend to fade over time. Therefore, many researchers have dismissed plastics as impractical for use in fiber optic devices and light sources. That may change soon. Scientists at Molecular OptoElectronics Corp. of Watervliet, N.Y., have found a way to engineer polymers with optical properties four times as stable as previously possible. The discovery is based on a chemical property known as chirality, a molecular form, where two seemingly identical molecules really are mirror images. The two may react differently, and by identifying chirality, researchers have developed materials with precisely engineered qualities. By inserting a chiral twist in molecules such as polycarbonates, they could fabricate more optically stable substances.