A 2.488 Gbit/s FSK field demonstration over a 132 km submarine cable employing an erbium power amplifier

The authors used FSK modulation and optical delay demodulation to demonstrate a sixteen-fold upgrade capability for the UK-Channel Islands No. 7 submarine cable, achieving a line-rate of 2.488 Gbit/s over 132 km nondispersion shifted fibre. Erbium power amplifiers were used to provide a generous operating margin of ≃10 dB and the compact spectrum of FSK modulation overcame the dispersion penalty that would have resulted from direct modulation. Further laboratory measurements have shown that transmission at 5 Gbit/s over 150 km nondispersion shifted fibre, equivalent to 2.5 Gbit/s over 600 km, is possible without any significant dispersion penalty. Numerical simulations broadly substantiate these measurements and further predict that transmission over greater than 1000 km is feasible, given that the fibre loss is overcome through the use of optical amplifiers