112 orbital angular momentum modes amplification based on a 7RC-EDF with low differential mode gain.

We demonstrate 112 orbital angular momentum (OAM) modes amplification based on a designed and fabricated 7-ring-core erbium-doped fiber (7RC-EDF). The differential mode gain (DMG) of all the intra-core OAM modes in 7RC-EDF is effectively reduced. The DMG of intra-core modes can be suppressed by the high overlap between the signal modes and pump fundamental mode resulting from the designed structures of the ring core assisted by a trench. The differential gain of the inter-core can be controlled by the power of the core-pump configuration as well. With an experimentally optimized scheme of the pump power of each core, a record low-DMG of 2.8 dB among the 112 OAM modes (16-OAM-mode per core in the 7-core) is achieved at a wavelength of 1550 nm. The obtained favorable performance of the 112 OAM modes based on 7RC-EDF indicates it may promote a long-haul high-density OAM modes multiplexed transmission.