An erbium doped fibre repeater/preamplifier in a 100 km intensity modulated direct detection 2.5 Gb/s system

The potential of rare-earth doped, single-mode fibre to provide travelling wave amplification in the third telecommunications window is now well established. Indeed interest in these devices has proliferated to such an extent that Er³⁺-doped fibre amplifiers are now undergoing optical transmission system tests. Multiamplifier systems, high gain devices, and coherent systems have all featured in recent publications. The authors report the use of a diode pumped Er³⁺ fibre amplifier in a 2.5 Gb/s, 100 km, direct detection system experiment. The amplifiers performance as both an in-line optical repeater and an optical preamplifier was investigated. In a repeater configuration an overall system improvement of 8.6 dB was observed whilst, when in a preamplifier format, an improvement in receiver sensitivity of 6.9 dB was achieved. These figures are shown to be consistent with simple theoretical noise considerations