A planar optical device is formed on a substrate (12) and comprising an array of waveguide cores (14) and a cladding layer (16) formed contiguously with the cores. At least one of the array of waveguide cores (14) and the cladding layer (16) is an inorganic-organic hybrid material that comprises an extended matrix containing silicon and oxygen atoms with at least a fraction of the silicon being directly bonded to substituted or unsubstituted hydrocarbon atoms. In accordance with other embodiments of the invention, a method of forming an array of cores comprises the steps of preparing a core composition precursor material; partially hydrolyzing and polymerizing the material; forming an array of waveguide cores under conditions effective to form an inorganic-organic hybrid material that comprises an extended matrix containing silicon and oxygen atoms with at least a fraction of the silicon being directly bonded to substituted or unsubstituted hydrocarbon atoms.