CW pumped Raman preamplifier in a 45 km-long fibre transmission system operating at 1.5 μm and 1 Gbit/s

We describe direct Raman amplification by a CW pump of a distributed feedback semiconductor laser operating in the 1.5 μm low-loss region of a single-mode optical fibre, and at powers comparable to the spontaneous Raman scattering from the pump. A direct measure of the increase in receiver sensitivity from bit-error-rate measurements show an enhancement in the signal-to-noise ratio at these low signal powers.