Third-order hybrid Raman amplifier with 102-nm wideband high gain and ultralow noise figure for 18 × 112 Gbps WDM IM-DD transmission

Abstract

Broadband optical amplifiers are essential for fully utilizing the low-loss transmission window of single-mode fiber (SMF), thereby enabling ultra-wideband and high-capacity optical transmission. In this work, we experimentally demonstrate a third-order hybrid Raman amplifier (HRA) that consists of a third-order distributed Raman amplifier (DRA) cascaded with a lumped Raman amplifier (LRA). The proposed HRA is implemented over a 101.5-km SMF EX2000 and a 15.7-km dispersion-compensating fiber, achieving a 102-nm (1524–1626 nm) amplification bandwidth that covers the full C and L bands. The HRA provides a maximum on-off gain of 33.7 dB and an average on-off gain of 30.4 dB. The average effective noise figure (NF) is −5.3 dB, and the lowest effective NF is −7.6 dB, indicating that the HRA takes full advantage of the ultralow effective NF of the DRA and the high gain provided by the LRA. Using pure Raman amplification, we demonstrate intensity-modulation direct-detection (IM-DD) transmission over 18 wavelength-division multiplexing (WDM) channels at two data rates. The 56 Gbps$/\lambda$ PAM-4 signals meet the 7 % overhead hard-decision forward error correction (HD-FEC) threshold, while the 112 Gbps$/\lambda$ PAM-4 signals satisfy the 20 % overhead soft-decision forward error correction (SD-FEC) threshold.