Five Orbital-Angular-Momentum Mode-Groups Multiplexed Amplification Based on a Ring-Core Erbium-Doped Fiber

In this work, we experimentally investigated the gain characteristics of a ring-core erbium-doped fiber (RC-EDF) that supports five orbital angular momentum (OAM) mode groups. Through the design and successful fabrication of the erbium-doped fiber, we ensured its capability to support up to five OAM modes. Experimental results indicate that the RC-EDF can simultaneously amplify five OAM mode groups with an average gain exceeding 25 dB, and the mode gain difference across all 20 modes is less than 1 dB.