Design and behaviour of laser modules for Gbit/s rates

Transmitter modules for high bit rates are investigated in order to obtain more efficient use of the capacity of an optical fiber in long-haul communication systems. The modules contain a combination of two lenses for optical coupling, which allows an optical isolator to be built in. The modules operate at 1.3 mu m and 1.55 mu m. To avoid dispersion-limitation at such high transmission rates and at the required fiber length of about 50 km, a laser with a single-mode spectrum in dynamic operations is required. In addition to that the chirp width at 1.55 mu m must be small. The spectral and temporal behavior of the modules, including sidemode suppression, chirp, and relative intensity noise, is examined and compared with that of the system obtained. The influence of optical feedback on chirp and noise is shown.<>