The third- and fourth-order orbital angular momentum multiplexed amplification with ultra-low differential mode gain

TL;DR

This paper demonstrates the design and fabrication of a ring-core erbium-doped fiber supporting up to the fourth-order OAM modes, achieving high average gain and ultra-low differential mode gain for mode multiplexed amplification.

Contribution

It introduces a novel two-layer erbium-doped ring-core fiber supporting high-order OAM modes with low differential gain for improved mode multiplexed amplification.

Findings

Average gain >19dB for four OAM modes covering C-band

Differential mode gain less than 1dB

Conjugate OAM modes have nearly identical gain under various pump powers

Abstract

In this Letter, a ring-core erbium-doped fiber (RC-EDF), with two-layer erbium-doped structure, supporting up to the fourth-order orbital angular momentum (OAM) mode is designed and fabricated for OAM mode multiplexed amplification. Using the RC-EDF, the third- and fourth-order OAM modes amplification with ultra-low differential mode gain (DMG) is demonstrated by observing both the modal intensity and phase distribution and measuring the modal gain under the fundamental mode core-pumping. The measured average gain of four modes (l=+3, -3, +4, -4) multiplexed amplification is higher than 19dB cover the C-band and the DMG is less than 1dB. Additionally, the gain of two conjugate OAM modes are almost the same under different pump power no matter they are amplified simultaneously or separately.