Abstract

Recently several groups^1,2 have reported error free soliton transmission over more than 9,000 km at Gb/s rates. When solitons are generated by gain-switched lasers, the pulses are severely chirped and a narrow-band optical filter must be used.¹ It has been observed³ a large pulse spreading for distances greater than a few thousand kilometers when using a DFB laser and a bias current (C_b) above threshold. We have recently shown⁴ that this pulse spreading is due to the pulse-to-pulse frequency jitter originated in the laser diode (LD). In this work the effect of C_b on soliton generation and transmission is studied. We numerically obtain that when the laser is biased slightly below threshold pulse spreading is strongly reduced for any frequency of modulation in the GHz range. With this bias current we can generate solitons under both periodic modulation (PM) and pseudorandom word modulation (PRWM). When the laser is biased above threshold it is not possible to generate solitons under PRWM for frequencies >2 GHz due to pattern effects.

© 1994 IEEE