The invention relates to a method for microstructuring an optical waveguide having a first cross-sectional region with a first refractive index, a second cross-sectional region with a second refractive index, and a boundary region in the transition from the first to the second cross-sectional region, in which the optical waveguide is exposed to laser radiation in the form of at least one ultra-short single pulse or a sequence of pulses with a defined energy input, whereby the radiant exposure takes place in such a manner that a modification of at least one optical property of the optical waveguide takes place at at least one defined portion of the boundary region.