41-nm 3-dB gain-band optical amplifier using an Er-doped core and Sm-doped inner-cladding fiber without external filters

A new fiber structure optical fiber amplifier was reported where the core was doped with erbium (Er) and the inner-cladding was doped with samarium (Sm). Feasibility of gain control by evanescent wave interaction with an absorbing material in the inner-cladding was experimentally demonstrated. The optical amplifier using the proposed fiber resulted in the gain variation between gain peak and valley less than 2.5 dB without using external gain equalizing filters.