Systems and methods to increase pump conversion efficiency of an optical fiber

A method for increasing optical pump conversion efficiency (PCE) for an optical fiber pumped by a multi-mode pump diode, the optical fiber including a first active region and a second active region, the second active region arranged concentrically to the first active region, the first active region doped with erbium ions without ytterbium ions, and the second active region co-doped with erbium ions and ytterbium ions, the optical fiber further including a cladding layer surrounding the core area, the method comprising:

• receiving, by the optical fiber, optical wavelengths from the multi-mode pump diode;
• absorbing, by the second active region, a spectrum of optical wavelengths;
• absorbing, by the first active region, optical wavelengths in a C-band;
• emitting, by both the first active region and the second active region, optical wavelengths in the L-band, via stimulated emission.

A system for amplifying an L-band signal, the system comprising:

• a source of multimode pumping light;
• a signal-pump combiner optically coupled to the source;
• and
• an optical fiber optically coupled to the source and signal-pump combiner, the optical fiber including a first active region and a second active region, the second active region arranged concentrically to the first active region, the first active region doped with erbium ions without ytterbium ions, and the second active region co-doped with erbium ions and ytterbium ions, the optical fiber further including a cladding layer surrounding the core area.