High-gain integrated in-line few-mode amplifier enabling 3840-km long-haul transmission

An integrated few-mode erbium-doped fiber amplifier (FM-EDFA) with high modal gain is suitable for the in-line amplification in mode-division multiplexing transmission (MDM) systems. We first experimentally demonstrate a dual-stage integrated FM-EDFA supporting three linear polarization modes. Consisting of integrated passive components with low insertion losses, the FM-EDFA has a similar structure and performance to widely used commercial single-mode EDFAs. The averaged modal gain of 25 dB, the differential modal gain (DMG) of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mo form="prefix">&lt;</mml:mo> <mml:mn>1.1</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> , and noise figures of 5–7 dB are simultaneously achieved. In addition, the DMG of the 3M-EDF itself is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mn>0.3</mml:mn> <mml:mtext> </mml:mtext> <mml:mi>dB</mml:mi> </mml:mrow> </mml:math> . Moreover, an MDM transmission experiment with the in-line few-mode amplification by our proposed FM-EDFA over a 3840-km few-mode fiber link for a 28-Gbaud quadrature phase-shift keying (QPSK) signal is demonstrated.