SYSTEMS AND METHODS TO INCREASE PUMP CONVERSION EFFICIENCY OF AN OPTICAL FIBER

An optical fiber configured to improve the pump conversion efficiency of an L-band fiber amplifier which uses the multimode pump source. By directly absorbing multimode light including 915 nm, an active fiber core region co-doped with both erbium and ytterbium can provide gain to the L-band signals via stimulated emission. The unwanted C-band amplified spontaneous emission (ASE) light generate from this active fiber core region can be absorbed by another active fiber core region doped with erbium, then provides additional gain to the L-band signals. Active regions and cladding can be configured to match a given spatial mode of the optical signal. Signal-pump combiners with end-coupling or side coupling can be used.