Ultra-Long-Span U-Band Transmission Enabled by Incoherently Pumped Raman Amplification

We demonstrate U-band Raman amplification in non-zero dispersion shifted fibre, exploiting the amplified spontaneous emission of an erbium-doped fibre amplifier as a broad-bandwidth, incoherent pump for low-noise amplification. By doing so, we achieve a high overall gain of ∼22 dB over a 3-dB bandwidth of ∼2.6 THz and obtain noise figures better than 4.3 dB and 5 dB in a 40 km-long, discrete amplifier configuration, in forward pumped and backward pumped scenarios, respectively. The performance of the U-band Raman amplification is also studied through transmission of a coherent signal over a 285-km point-to-point link. This work represents, at the time of writing, the longest-reach single-span U-band transmission demonstrated.