A laser beam with an annular or ring shaped intensity distribution, such as a TEM.sub.01 * beam, is scanned across the surface of a photosensitive thin film to directly produce changes of refractive index in selected regions of the film. This method is suitable for producing channel waveguides for planar lightwave circuits, where the refractive index profile (solid curve) of such a waveguide is more uniform than the prior art refractive index profile (dashed curve) produced by a TEM.sub.00 laser beam, and has a reduced bend loss.