t limitation 560Mbit/s realised with 2 X 280Mbit/s channels. The loss and on the section length. For example with conventional fibre of dispersion requirements were satisfied by operating single mode at 16ps/km.nm dispersion and a 0.2nm chirp the 1db dispersion pen- 1300nm with a chromatic dispersion of less that 2ps/km.nm, a alty corresponds to 32km. Again the system is dispersion limited but Fabry-Perot laser and a InGaAsP p-i-n detector followed by an this time not exclusively due to dispersion but also to the interaction integrated Si transimpedance receiver. The receiver sensitivity was of laser dynamics (chirp) with dispersion. With a DSF the 1dB -31dBm, -2dBm optical power and with 6dB total margin the dispersion penalty corresponds to 173km. available section loss was 23dB including the splice losses. With The dispersion penalty for (LD (2) where is half the 0.45dB/km loss the section length was 50km. period of the laser relaxation oscillations, is given by Equation The system was commissioned in 1988 and its success encour- 53.76, and for LD (2) by Equation 53.77. aged the installation of other systems such as the Trans Pacific Cable TPC-3 (2x 280Mbit/s; 1988) the California to Hawaii HAW- (53.76) Penalty 1 Mbit/s; 1988), the Private Transatlantic Cable PTAP-1 (2 420 Mbit/s; 1989), the North Pacific Cable NPC (3 X 565 Mbit/s; 1990) and the TAT-9 system (2 X 560 Mbit/s; 1991). TAT-9 is the (53.77) Penalty most complex of the submarine systems designed. At the American end there are two spurs. One from Canada (220 km) and one from the USA (1320 km). They combine in an undersea branching multi- For example assume that = 80ps. Then with = 0.15nm the plexer/demultiplexer. Then there are 4600km across the North At- maximum LD (2) product is 0.533ns/nm. For LD (2) = 0.5 the lantic to another undersea multiplexer/demultiplexer out of which penalty is 5.53 at 2.4Gbit/s. there are three spurs. One to UK (530km), one to France (302km) The obvious solution to the chirp problem with directly modulated and one to Spai