ABSTRACT
The rapid increase in network traffics has made high capacity optical communication systems including short reach systems crucial. For this purpose, high speed semiconductor lasers have been developed. Direct modulation of semiconductor lasers has been used for simple configuration of transmitter modules, while the frequency chirp is caused with intensity modulation. The direct modulation characteristics of semiconductor lasers can be examined by using rate equations. There are certain limitations for the modulation bandwidth with increasing the output power of semiconductor lasers. They are: thermal heating, damping due to nonlinear gain, and parasitic capacitance. Kenichi Iga investigated the limit of modulation speed of semiconductor lasers for various modulation of parameters such as the laser gain coefficient, recombination lifetime of carriers, and the cavity Q values in comparison with the conventional direct modulation scheme. The maximum modulation frequency for the gain and Q value modulation is enhanced to be ten times larger than the relaxation oscillation frequency.
