Abstract

Er-doped fiber amplifiers (EDFAs) are attractive for longdistance optical communication systems, because they can amplify optical signals independently of bit-rate, modulation schemes, number of optical channels and so on. Among these features, the use of IM-DD wavelength- division multiplexed (WDM) technology in the EDFA systems is thought to be a candidate for the deployment of the future multi-destination optical communication networks. Although several experiments show the capability of EDFAs for long distance optical communication systems with IM-DD WDM technique¹ >2.3, the system length was limited to less than 1,500km³ because of the fiber nonlinearity (four wave mixing, FWM). However, the use of optical soliton pulse can remove the effect of FWM, more than 10,000km WDM transmission by using recirculating loop was demonstrated⁴. In this paper, we present the capability of NRZ WDM ultralong distance transmission with the demonstration of 5Gbit/s NRZ 2- channel WDM signals over 4,500km straight-line transmission, together with the discussion of the method to reduce the degradation due to FWM. Description of the Experiments Fig.l shows a schematic diagram of the experimental setup. Two DFB-LDs emitting at 1557nm (channel 1) and 1559nm (channel 2) were used as optical light sources and two electroabsorption (EA) modulators were employed to produce 5Gbit/s 2¹⁵-1 pseudorandom NRZ bit-streams. An extinction ratio of 20dB was obtained at a driving voltage of 3.8V. The two signals were multiplexed with a 3dB fiber coupler. To compensate the insertion loss of the EA modulator modules and the fiber coupler, a booster Er-doped fiber amplifier was used.

© 1993 Optical Society of America