Researchers at the University of Electronic Science & Technology of China and Sichuan Normal University (both in Chengdu, China) have experimentally compared two forms of distributed Raman amplification (DRA) for fibers: one relying on random fiber lasers (RFLs) either forward- or backward-pumped, and the other based on the more-conventional bidirectional first- or second-order pumping. All experiments were carried out on 93 km of standard singlemode fiber, with the effective noise figure (ENF) being the parameter of interest.
Bidirectional first-order pumping was done with a 1480 nm pump, while second-order pumping used a 1366 nm pump and two 1454 nm fiber Bragg gratings (FBGs) added to the fiber. The forward (or backward) random laser pumping was similar to the bidirectional second-order pumping, but with the removal of one FBG (or, for backward, the other FBG) to avoid facet feedback while lowering the lasing threshold. Random lasing occurs entirely through random Rayleigh distributed feedback and Raman amplification (no end mirrors are involved). Forward random pumping produced an ENF lower than that of the bidirectional first-order pumping and second-order pumping by 2.3 and 1.3 dB, respectively. Compared to bidirectional pumping, forward and backward random pumping had higher and lower gain, respectively. And, unlike bidirectional pumping, the random-lasing-based amplification was insensitive to variations in ambient temperature between -40 and +40°C. Contact Yun-Jiang Rao at [email protected].
