Quantum Dot Lasers as Comb Sources
- Dumont, Mario
- Advisor(s): Bowers, John
Abstract
Quantum dot (QD) lasers have found a broad range of applications owing to their unique gain properties, with an atom-like density of states. This has given them the ability to reach the highest CW lasing temperature recorded, allows for reflection insensitive operation enabling deployment without isolators, and producing defect tolerant lasers, which provides a pathway to III-V lasers directly grown on silicon photonic-integrated-circuits. It has also enabled a new generation of semiconductor mode locked lasers (MLLs), which have applications in the formation of optical frequency combs for DWDM light sources.
Using QD-MLLs, combs with extremely broad bandwidth and uniform power distribution are generated, which allows a single device to transmit greater than 10 Tb/s. In this dissertation, the tools to analyze the performance of these device are explained in detail. A focus is given on energy efficiency because the next generation of photonics demands stringent size, cost, power budgets. Remarkably, the energy efficiency with which individual comb lines are generated can match the efficiency performance of commercial DFB lasers. This was made possible by improvements in the growth, fabrication and design of the laser, which allowed the comb line efficiency to reach 10%. The laser dynamics that allowed the formation of ultra-flat combs were also studied. These devices produce a mode locking state known as frequency modulated (FM) combs. The QD gain properties were studied to understand how they produce FM combs, and how the bandwidth of combs can be tuned in a device to match the system requirements. DWDM systems using these combs are also discussed. A ultra-compact and energy-efficient system using silicon photonics is discussed, which uses 20 comb lines to transmit 1 Tb/s of data. And a coherent communication system using two QD-MLLs as the transmitter and receiver local oscillator are presented, which was capable of transmitting 12.1 Tb/s of data.