Method of making a cladding pumped fiber structure

Fabrication of a cladding-pumped fiber device, the device comprising a core, a contacting pump cladding and a second cladding, the device having a multiple-sided featured interface between the pump cladding and the second cladding, in which the said fabrication comprises the steps of:

• processing a round precursor preform, the precursor preform consisting essentially of a precursor core and a contacting precursor pump cladding to produce a multiple-sided featured processed surface on the precursor pump cladding;
• cladding the said processed surface with a second precursor cladding to produce a final preform;
• and drawing fiber from the said final preform,
• wherein the improvement comprises
• producing the said processed surface by traversing the precursor preform longitudinally by a local heat source along parallel longitudinal paths, thereby forming a series of troughs defining the said processed surface.