Enhanced Performances of Quantum Dot Lasers Operating at 1.3 m
ABSTRACT Due to their delta-like density of states, quantum dots (QDs) were expected to improve laser device performances with respect to quantum wells (QWs). Nevertheless, some important drawbacks limit this technology. For instance, QD laser still suffers from a low value of the modal gain, due to the low areal density of QDs, and inhomogeneous broadening, especially when multistacked layers are used. In this paper, we demonstrate that a linear increase of the QD modal gain with the QD layers number, as typically achieved in multi-QW lasers, is possible by a careful control of the Stranski-Krastanov QDs growth and QDs stacking optimization. A low-transparency current density of 10 A/cm2 per QD layer and a modal gain of 6 cm-1 per QD layer were achieved from laser structures containing up to seven QD layers. We demonstrate 10-Gb/s direct modulation (until a temperature of 50 degC) and high T 0 (110 K) from a single-mode device containing six QD layers.
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ABSTRACT: Single colloidal quantum dots (QDs) are increasingly exploited as triggered sources of single photons. This review reports on recent results on single photon sources (SPS) based on colloidal quantum dots, whose size, shape and optical properties can be finely tuned by wet chemistry approach. First, we address the optical properties of different colloidal nanocrystals, such as dots, rods and dot in rods and their use as single photon sources will be discussed. Then, we describe different techniques for isolation and positioning single QDs, a major issue for fabrication of single photon sources, and various approaches for the embedding single nanocrystals inside microcavities. The insertion of single colloidal QDs in quantum confined optical systems allows one to improve their overall optical properties and performances in terms of efficiency, directionality, life time, and polarization control. Finally, electrical pumping of colloidal nanocrystals light emitting devices and of NC-based single photon sources is reviewed.Opto-Electronics Review 01/2010; 18(1):1-9. · 0.92 Impact Factor
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ABSTRACT: The ultra-fast gain dynamics in quantum-dot semiconductor optical amplifiers (QD-SOAs) have been studied for different types of Auger-assisted relaxation processes. The ultra-fast gain recovery time and gain compression are studied for p-type doped and un-doped QD-SOAs using rate equation model. Our calculations show that the ultra-fast gain dynamics is governed by electron-electron Auger-assisted process for un-doped QD-SOA and by electron-hole Auger-assisted process for p-type doped (N<sub>A</sub>=1.25times10<sup>18</sup> cm<sup>-3</sup>) QD-SOA. We find that the ultra-fast gain recovery time for un-doped QD-SOA is comparable with that of p-type doped QD-SOA when both electron hole and electron-electron processes present in the active region. We find that the percentage of ultra-fast gain compression in un-doped QD-SOA is limited to ~ 72%. While for p-type doped (N<sub>A</sub>=1.25times10<sup>18</sup> cm<sup>-3</sup>) QD-SOA, we find that the percentage of ultra-fast gain compression increases as the applied current increases where it can reach >95% at very high applied current.Journal of Lightwave Technology 08/2009; · 2.56 Impact Factor