Linewidth Enhancement Factor in InAs/GaAs Quantum Dot Lasers and Its Implication in Isolator-Free and Narrow Linewidth Applications

Abstract

The linewidth enhancement factor (α H ) is an important parameter for semiconductor lasers. In this paper, we investigate, both theoretically and experimentally, the key parameters that affect α H of InAs/GaAs quantum dot lasers. Both dot uniformity and doping density are found to be critical in achieving small α H in quantum dot lasers. The prospects for quantum dot lasers in isolator-free and narrow linewidth applications are also discussed.

Optical Injection Locking: From Principle to Applications

“…Should the α becomes zero, the equation 2degenerates to an equation independent of carrier number N , and will result in a symmetric locking range. Recent advance in quantum dot lasers shows that low or zero α can be achieved [45], providing new opportunities to the field of OIL dynamics.…”

“…quantum dots) requires new scientific understanding on the OIL laser dynamics. For example, the low/negative linewidth enhancement factor available with the quantum dot material could significantly reduce the modulation chirp and provide symmetric locking region [45]. New laser designs involving silicon photonics have demonstrated new features such as an extended photon lifetime for significant reduction of the intrinsic laser linewidth [127].…”

Recent Progress of Quantum Dot Lasers Monolithically Integrated on Si Platform

“…The employment of QDs also provides better dynamic properties, such as low relative intensity noise (RIN) and linewidth enhancement factor (LEF), compared with the QW structure [63,64]. In the optical communication system, a low RIN is desired to improve the data transmission rate and distance with a high signal-to-noise ratio (SNR) and low bit-error-rate (BER).…”

Feedback Sensitivity of DBR-Type Laser Diodes

“…Several recent publications (e.g., [4] and [5]) have described laser diodes with zero or near-zero (effective) linewidth enhancement factor  and coherence collapse in these laser diodes was shown to occur at significantly elevated feedback levels. In [4], quantum dot material was used with very small material -factor, while in [5] the effective -factor was reduced for carefully designed DFB (Distributed Feedback), DBR (Distributed Bragg Reflector) and DR (Distributed Reflector) lasers. The influence of the feedback on linewidth (as well as on tuning) is however expressed by the feedback coefficient C, which so far has been mainly discussed for single section laser diodes (as in [6]).…”

“…There are basically 2 measures to quantify the feedback sensitivity of a laser diode. A first measure is the feedback level at which the coherence collapse occurs, a feedback level which has been shown [3] to depend on the effective linewidth enhancement factor eff as (1+ eff 2 )/eff 4 . However, external feedback can have a detrimental effect on the laser linewidth even at feedback levels much below the level where coherence collapse occurs.…”