Faster and Longer

Although the fiber optic backbone had been completed, R&D of semiconductor lasers became more active with the goal of longer and faster transmissions. The $1.55 \upmu\mathrm{m}$ band had contributed significantly to longer distances, but required a new challenge, the development of single-mode laser under high-speed modulations. The DFB enabled single mode lasing, however modulation-induced chirping was still a problem for higher speed. Modulation schemes were analyzed theoretically and experimentally to reduce the chirping. This study enabled high-speed transmission up to 10 Gb/s, but also revealed a fundamental trade-off between chirping linewidth and modulation speed. This trade-off, would limit transmission length and bitrate, promoted developments of new devices, including the external feedback laser, the multi-electrode DFB laser, and the EA integrated DFB laser.