Design and evaluation of high speed DBR lasers for analog and digital transmission

The directly modulated laser is a simple and reliable source for high speed optical transmission of information. It is especially useful in medium to short distance digital links (e.g. metropolitan and local area networks) where the excess pulse dispersion due to laser chirp is not a critical issue. The linear current to light conversion makes it also interesting for transmission of analogue signals over fiber (CATV and microwave links). In both cases a high bandwidth is needed in order to maximize the transmission capacity and retain good distortion characteristics. For single section DFB lasers with low electrical parasitics, the bandwidth is mainly determined by the differential gain of the active material. There has been little progress in improving this material parameter lately beyond what was achieved with the introduction of strained quantum wells. A theoretical and experimental investigation of another approach to further improve the modulation bandwidth, namely by utilizing the dispersive feedback from a detuned Bragg grating in a DBR laser.