Vector modulation of split-contact DFB lasers

Multisection DFB lasers are currently of interest both for coherent FSK systems, which require a wide electrical tuning range and a large flat FM response, and for high bit rate direct detection systems which require wide bandwidth, low chirp AM response. In this paper the authors report a method of assessing and displaying the FM and AM response of two and three section lasers when the modulating signal is applied in different proportions to all the sections. With such vector modulation, an improvement in the magnitude of the FM response could be obtained, together with a decrease in the residual AM. As expected, the FM response of these devices under vector modulation did not reflect their static tuning contours