Abstract

Analog lightwave transmission at 1.5 μm using cascaded erbium-doped fiber amplifiers (EDFAs) allows cost-effective transport and distribution of video channels to a high number of optical network units (ONUs) in fiber-to-the-curb (FTTC) or fiber-to-the-home (FTTH) systems. However, the high dispersion of standard single-mode fiber at 1.5 μm together with the laser chirp, results in unacceptably high distortion levels. Also, the EDFA gain-slope in combination with the laser chirp increases the distortion. There are three ways known to overcome these problems: (1) Electronic predistortion of the transmitter¹; (2) use an externally modulated transmitter, because in that case there is virtually no chirp²; (3) optical compensation using dispersion-compensating fiber (DCF). The latter has been demonstrated for long-haul systems.³ In this paper we show that with a directly modulated transmitter in a CATV transport and distribution system with cascaded EDFAs similar power budgets and transmission distances can be achieved as in an externally modulated system, without electronic predistortion, by using DCF and carefully designed EDFAs with low gain-slope. Optical compensation with DCF allows for higher network engineering flexibility compared with electronic predistortion, because a transmitter with predistortion can only be tuned for a certain distance. By building the DCF into EDFAs, it is possible to perform the compensation on different network segments, thus allowing different link lengths in a splitted system.

© 1996 Optical Society of America