High Speed Lasers Based Fiber Optic Systems

The transmitter in a high speed fiber optic system typically consists of a semiconductor laser that is either directly or externally modulated. Although, the small signal modulation bandwidth in semiconductor lasers have exceeded 30 GHz (Fig. 1), external modulation is the preferred method for systems operating at 10 GBit/s and beyond. This has to do with the detrimental effects of laser wavelength chirp under modulation which tends to limit the transmission distance in silica fiber [1]. In long distance fiber transmission using directly modulated lasers at 10 GBit/s, the dispersion limit has also been overcome by techniques [2,3] other than traditional dispersion compensation.