Patent ID: 7024092

Claim:
A method of adapting an optical rare-earth-doped waveguide having a plurality of transverse propagation modes, such that in use, signal gains of non-fundamental modes of the waveguide are attenuated relative to a signal gain of a fundamental mode of the waveguide; the waveguide having a light-guiding region defined by a refractive index-modifying dopant, and the refractive index-modifying dopant having a thermal diffusion coefficient at temperature T in the waveguide which is greater than a thermal diffusion coefficient of the rare-earth-dopant at temperature T in the waveguide, the method comprising: treating the waveguide such that a concentration profile of the refractive index-modifying dopant becomes broader than a concentration profile of the rare earth dopant; wherein the treatment of the waveguide comprises non-uniformly heating a length of the waveguide at the temperature T for a period of time sufficient to cause relatively greater thermal diffusion of the refractive index modifying dopant than the rare earth dopant such that the concentration profile of the refractive index-modifying dopant becomes broader than the concentration profile of the rare earth dopant; and such that the concentration profile of the refractive index-modifying dopant is broadened non-uniformly along the length of the waveguide.