Abstract

High-bit rate (40 Gbit/s) transmission systems have attracted much attention recently for application in very-short-reach (VSR) optical links. 40-Gbit/s serial transmission systems can provide more flexible and low-cost configuration than that of parallel and wavelength division multiplexing (WDM) systems. A transmission distance for VSR optical links of around 2 km using a single mode fiber (SMF) has been proposed.¹ For this purpose, cost-effective transmitter and receiver design is desirable. 40 Gbit/s LiNbO₃ Mach-Zehnder modulators and electroabsorption modulators are now commercially available, but they are expensive and require a high-power CW source. On the other hand, direct modula tion of lasers provides compact and cost-effective transmitters. Although a 10-Gb/s transponder module with a distributed feedback (DFB) laser is now commercially available, no direct modulation at 40 Gbit/s has yet been reported. This is because the modulation bandwidth of conventional lasers is limited to around 20 GHz. This restriction, however, is not fundamental. According to recent advanced technologies, 40-Gbit/s direct modulation is possible for DFB lasers.

© 2002 Optical Society of America