Abstract: There is disclosed an optical substrate having a surface and a cladding on said surface, the cladding comprising a polysiloxane polymer, a thickness of at least 1.5 ?m, and a refractive index of less than 1.45, measured at 632 nm.

Abstract: A layered structure comprising a substrate layer; and a layer of a siloxane polymer on the substrate layer, the layered structure being capable of being bent about a mandrel having a radius of curvature without breaking. The layer of the siloxane polymer has a thickness of 1 to 50 ?m, in particular about 5 to 20 ?m, and it is obtained by depositing on the substrate a composition comprising at least three different silane monomers, including at least one bi-silane; at least one of the silane monomers having an active group capable of achieving cross-linking to adjacent siloxane polymer; at least partially hydrolyzing the silane monomers to form siloxane polymer chains; and cross-linking the siloxane polymer chains so as to achieve a cross-linked siloxane polymer layer on the substrate.