High gain distributed Raman amplifier for orbital angular momentum mode-division multiplexing and wavelength-division multiplexing in 104-km ring-core fiber over the C+L band

Mode-division multiplexing (MDM) and wavelength-division multiplexing (WDM) are regarded as effective solutions for enhancing the communication capacity of fiber-optic transmission system. To extend the transmission distance, a suitable amplification technique is required to amplify the signal light, with distributed Raman amplifier (DRA) offering a high-flat gain. In this paper, we experimentally demonstrate the transmission of 3 orbital angular momentum (OAM) mode-division multiplexing and 9 wavelength-division multiplexing ranging from 1530 nm to 1610 nm over 104-km self-designed ring-core fiber (RCF) with the assistance of DRA. The homemade all-fiber mode selective couplers (MSCs) are able to (de)multiplex OAM modes (OAM01, OAM11, OAM21) efficiently in long-distance MDM+WDM fiber-optic transmission system. The OAM-DRA provides high gain (with the on-off gain greater than 10 dB) as well as flat gain (with a differential wavelength gain less than 0.88 dB and a differential mode gain less than 0.28 dB) over the C+L band.