Amplification of orbital angular momentum modes in an erbium-doped solid-core photonic bandgap fiber

A new kind of erbium-doped solid-core photonic bandgap fiber (ED-SC-PBGF) for amplification of orbital angular momentum (OAM) modes is proposed and investigated. The configurations of annular erbium-doped profile with special design and multi pump modes are used to amplify the signal modes evenly. Using an optimized ED-SC-PBGF pumped with l=1 and 2 modes, differential mode gains of 0.9 dB and gain of more than 20 dB can be achieved for l=1 and 2 OAM signal modes across the full C-band. This OAM-in-fiber amplification techniques would have potential application in ultra-long distance and high capacity OAM optical communication systems and other systems that utilize high power OAM light.