S-band all-Raman amplifiers for 40 x 10 Gb/s transmission over 6 x 100 km of non-zero dispersion fiber

The increasing demand for transmission capacity requires novel amplifiers to make full use of the low-loss spectral window in optical fibers. Raman amplification offers a flexible approach to expand the transmission bandwidth beyond the C and L gain bands of erbium-doped fiber amplifiers. Distributed Raman amplification in the transmission span permits system performance not possible using only discrete amplifiers. Additional Raman amplification in the inter-span dispersion compensating fiber (DCF) allows simultaneous compensation of span dispersion and residual fiber loss. In this paper we report on the performance of S-band Raman amplifiers designed to operate from 1488 nm to 1518 nm. We demonstrate error-free WDM transmission of 40 x 10 Gb/s over 6 x 100 km of a prototype TrueWave(R) fiber. The bit-rate distance product is 240 Tb/s-km, an order of magnitude higher than previously published results for S-band transmission. Two main elements contributed to this result. The first is the design of the S-band amplifiers. The inline Raman amplifiers simultaneously compensated dispersion and 24-dB span loss by using a combination of distributed amplification in the transmission fiber followed by discrete amplification in the DCF. We also designed discrete Raman amplifiers (booster and preamplifier) for use at the terminals. The second important element in this experiment is design of transmission fiber. We used a prototype TrueWave(R) fiber with a zero dispersion wavelength below commercially available non-zero dispersion shifted fiber (1400 nm) that provides sufficient dispersion in the S-band to allow DWDM transmission without incurring penalties from four-wave mixing.