High-speed frequency modulation and switching of tunable distributed feedback lasers with two active segments

The author extends the analysis of high-speed frequency modulation in DFB lasers with two active segments. The strong FM response in such lasers is very different, in both magnitude and phase, for the red- and blue-shifted static tuning regimes. The author introduces the frequency step-response function to characterize in the time domain the dynamics of laser frequency switching from one value to another. This time domain picture shows clearly the effects of magnitude and phase variation of the FM response on the switching behavior of the laser. He defines the frequency switching speed of the laser and observes a tradeoff relation between this speed and the magnitude of the FM response, as characterized by the magnitude-speed product. The results indicate that with optimum laser parameters and operating conditions, the frequency switching rate, and thus also the frequency shift keying (FSK) modulation rate, can be extended to the multigigahertz range (>8 GHz)