| High-speed laser sources are critical components in optical communications systems and are presently the subject of intense research efforts. We present a comprehensive study of different modulation schemes. First, modulation schemes on a single semiconductor laser are investigated and compared for the first time. They include electrical modulation, optical modulation, and electrical modulation of an injection-locked laser. Electrical modulation on a single semiconductor is commonly used in the real system at bit rates below 10 Gbit/s and has drawbacks such as chirping and low bandwidth. To improve the high-speed performance of a single laser, we intensively study the injection locking technique. It is shown that this technique greatly reduces chirping, improves modulation bandwidth, and is very useful for ultra-high-speed communication systems. Ours is the first experiment focusing on bandwidth enhancement of the high-speed modulation and relative intensity noise (RIN) spectra of a side-mode injection-locked FP laser system. Second, we investigate integrated electroabsorption modulator-lasers. They are more compact and have very good high-speed performance. We study injection locking using these integrated devices, presenting a novel data acquisition method by directly measuring the modulator section photocurrent. The optical coupling effect in an integrated device is also investigated and is an important issue when an amplifier is integrated. We also measure external modulation to cover major modulation methods in optical transmitters. Finally several issues for optical transmitters are addressed, such as bandwidth, chirping, output power, and integration. |
