Impact of DFB-LD FM response distortion, in amplitude and phase, on FSK coherent systems

The influence of amplitude and phase distortions of the FM response of DFB (distributed feedback) lasers on coherent FSK (frequency shift keying) transmission systems has been investigated. It was found that pattern effects are mainly due to phase distortions, while the IF (intermediate frequency) spectrum broadening is due to both amplitude and phase distortions. Possible remedies are described, including device selection, line coding, and phase and/or amplitude equalization of the FM response. A comparison between observed spectra and computer analysis has been performed, showing a good agreement. Transmission experiments at 140 Mb/s have been carried out, showing the predicted effects on the eye diagram.<
>