Cladding-pumped Er-doped fiber with absorbing inclusions for suppression of high-order modes

a novel method of higher order modes suppression in a large mode area double clad Er-doped fiber is proposed and demonstrated. For this aim absorbing inclusions (Tm-doped rods) were inserted into the first cladding of the Er- doped fiber to achieve a resonant coupling between high order modes and modes located in the inclusions.