A method for trimming an effective refractive index of optical waveguiding structures made for example in a high refractive index contrast material system. By compaction of cladding material in a compaction area next to patterns or ridges that are formed in the core material for realizing an optical waveguiding structure, the effective index of refraction of the optical waveguiding structure can be trimmed. Thus, the operating wavelength of an optical component comprising such an optical waveguiding structure can be trimmed. An optical waveguide structure thus obtained is also disclosed.