Asymmetric long-period-grating based dual-concentric-core Few Mode Erbium Doped Fiber Amplifier for Space Division Multiplexing

This article proposes an original concept of a dual-concentric-core few-mode erbium doped fiber (EDF) for amplification of the LP11 and LP21 mode groups of a few mode fiber (FMF) at 1530-nm wavelength with controlled differential modal gain (DMG). The proposed EDF consists of a central core and a ring core. The ring core is doped with Er3+ ions and participates in amplification. The mode groups of line FMF excite the corresponding central core modes of the EDF, which are converted into suitable ring-core modes using asymmetric long period gratings (ALPGs). After amplification, the ring modes are converted back using ALPGs into the central core modes, which are subsequently injected into the line FMF. Two important features of the proposed scheme which help in achieving any desired DMG value are (i) nearly equal overlap of the pump mode(s) with different ring modes and (ii) independent choice of amplifier length for different signal mode groups. It should be useful for optical fiber communication system employing space-division multiplexing (SDM).