Transmission of solitons at 15 GHz and 20 GHz generated by pseudorandom modulation of laser diodes using TDM

Abstract

We have recently shown that pseudorandom sequences of solitons can be generated and transmitted at 5 GHz by direct modulation of laser diodes (LD) when biasing slightly below threshold (C.R. Mirasso and L. Pesquera, IEEE PTL 7. p. 437, 1995). Using this bias current pattern effects are avoided and the fluctuations originated in the LD are reduced. Here we perform numerical simulations to study the transmission of pseudorandom sequences of solitons at 15 GHz and 20 GHz obtained by time division multiplexing (TDM) of 1.55 µm LD modulated at 5GHz and biased slightly below threshold. A narrowband optical filter is used to limit the large bandwidth of the signal produced by the chirping. To reduce soliton interaction the pulses are compressed by using 0.6 km of a normal dispersion fiber (D = −20 ps/nm km). In this way the pulses launched in the fiber have a 10 ps witdh. A large timing jitter is obtained after transmission over transoceanic distances due to the pulse-to-pulse frequency jitter originated in the LD. This jitter is reduced by using guiding filters every 25 km with a bandwidth of 250 GHz. The results in the figure for 15 GHz (left) show that filters are effective to reduce timing jitter. However, in the 20 GHz (right) transmission sequence the interaction leads to errors (see the set ”11” near the end of the sequence). Then more effective soliton control systems (i.e. sliding-frequency filtering) should be used to reduce interaction effects.