Improving the Modulation Bandwidth in Semiconductor Lasers by Passive Feedback

We explore the concept of passive-feedback lasers (PFLs) for direct signal modulation at 40 Gb/s. Based on numerical simulation and bifurcation analysis, we explain the main mechanisms in these devices that are crucial for modulation at high speed. The predicted effects are demonstrated experimentally by means of correspondingly designed devices. In particular, a significant improvement of the modulation bandwidth at low-injection currents can be demonstrated