Bit Rate Dependence of Chirp Penalty for 1.55 mu m DFB Lasers.

In this manuscript we give both experimental and theoretical results that show the dispersion penalty caused by chirp in a DFB laser system is approximately proportional to the square of the bit rate. Using a variable bit rate regenerator we measured the chirp induced dispersion penalty for a 120`km fiber span over 300 MB/s to 1.4 GB/s. A computer simulation of the experiment gave good agreement to the measured data. Our results indicate that a long-haul system using the current CMBH laser and conventional fiber operating at 1.2 GB/s might be viable provided we are willing to allow dispersion penalties in the 1`dB range at the beginning of life. However, extrapolating our results to 2.5 GB/s shows that the dispersion penalties would be unacceptable using the current laser. Therefore, a 2.5 GB/s 1.55 mu m direct detection systems using conventional fiber would require a new low chirp laser.