Disclosed are planar waveguides comprising substantially polarization-independent Bragg gratings. A preferred embodiment of the invention comprises a Si body with a silica lower cladding layer thereon, and a phosphorus P-doped silica core on the lower cladding. Appropriate periodic recessed features are etched into the core, and phophorus P- and B-doped silica upper cladding is deposited over the core. The dopant concentrations are adjusted such that the refractive index difference between core and upper cladding is small (0.35-1.45.times.10.sup.-2), and such that the flow temperature of the upper cladding material is lower than that of the core material. In another preferred embodiment a thin layer of Si.sub.3 N.sub.x (x.about.4) is conformally deposited over the core after the grating etch, and the upper cladding material is deposited onto the Si.sub.3 N.sub.x layer. Bragg devices according to the invention are advantageously used in Integrated Optical Circuits (IOCs), e.g. in IOCs used in WDM optical communication systems.