Broadband quantum-dot frequency-modulated comb laser

Frequency-modulated (FM) laser combs, which offer a periodic quasi-continuous-wave output and a flat-topped optical spectrum, are emerging as a promising solution for wavelength-division multiplexing applications, precision metrology, and ultrafast optical ranging. The generation of FM combs relies on spatial hole burning, group velocity dispersion (GVD), Kerr nonlinearity, and four-wave mixing (FWM). While FM combs have been widely observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a low-dispersion FP cavity can be a challenge in platforms where the waveguide dispersion is mainly determined by the material. Here we report a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the FM comb can be generated independently. The high FWM efficiency of -5 dB allows the QD laser to generate an FM comb efficiently. We also demonstrate that the Kerr nonlinearity can be practically engineered to improve the FM comb bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that our QD platform can deliver is as large as 2.2 THz. This study gives novel insights into the improvement of FM combs and paves the way for small-footprint, electrically-pumped, and energy-efficient frequency combs for silicon photonic integrated circuits (PICs)

Unveiling the dynamical diversity of quantum dot lasers subject to optoelectronic feedback

This paper investigates experimentally and numerically the nonlinear dynamics of an epitaxial quantum dot laser on silicon subjected to optoelectronic feedback. Experimental results showcase a diverse range of dynamics, encompassing square wave patterns, quasi-chaotic states, and mixed waveforms exhibiting fast and slow oscillations. These measurements unequivocally demonstrate that quantum dot lasers on silicon readily and stably generate a more extensive repertoire of nonlinear dynamics compared to quantum well lasers. This pronounced sensitivity of quantum dot lasers to optoelectronic feedback represents a notable departure from their inherent insensitivity to optical feedback arising from reflections. Moreover, based on the Ikeda-like model, our simulations illustrate that the inherent characteristics of quantum dot lasers on silicon enable rapid and diverse dynamic transformations in response to optoelectronic feedback. The emergence of these exotic dynamics paves the way for further applications like integrated optical clocks, optical logic, and optical computing

Subspace tracking for independent phase noise source separation in frequency combs

Advanced digital signal processing techniques in combination with ultra-wideband balanced coherent detection have enabled a new generation of ultra-high speed fiber-optic communication systems, by moving most of the processing functionalities into digital domain. In this paper, we demonstrate how digital signal processing techniques, in combination with ultra-wideband balanced coherent detection can enable optical frequency comb noise characterization techniques with novel functionalities. We propose a measurement method based on subspace tracking, in combination with multi-heterodyne coherent detection, for independent phase noise sources identification, separation and measurement. Our proposed measurement technique offers several benefits. First, it enables the separation of the total phase noise associated with a particular comb-line or -lines into multiple independent phase noise terms associated with different noise sources. Second, it facilitates the determination of the scaling of each independent phase noise term with comb-line number. Our measurement technique can be used to: identify the most dominant source of phase noise; gain a better understanding of the physics behind the phase noise accumulation process; and confirm, already existing, and enable better phase noise models. In general, our measurement technique provides new insights into noise behavior of optical frequency combs

Lasers à îlots quantiques sur silicium : propriétés non-linéaires, dynamique et applications

La photonique sur silicium est une technologie prometteuse pour les systèmes de communication à haut débit, les interconnexions optiques à courte portée et pour le déploiement des technologies quantiques. La croissance de matériaux III-V sur silicium constitue également une solution idéale pour la prochaine génération de circuits photoniques intégrés (PIC). Dans ce contexte, les lasers à îlots quantiques (QD) utilisant des atomes semi-conducteurs comme milieu de gain sont des candidats très prometteurs en raison de leur compacité, de leur grande stabilité thermique et d’une tolérance accrue aux défauts structuraux. L'objectif de cette thèse est d'étudier les propriétés non-linéaires et les dynamiques des lasers QD sur Si en vue des applications susmentionnées. La première partie se polarise sur les lasers QD directement épitaxiés sur Si en présence de contre-réaction optique (EOF). Dans le régime de cavité courte, les résultats rapportent des tolérances élevées aux réflexions parasites ce qui rend possible l’intégration de ces sources sur des PIC dépourvus d’isolateur optique. Par ailleurs, la réduction du facteur d’élargissement spectral est un déterminant fondamental permettant d'atteindre cet objectif. La deuxième partie analyse les propriétés statiques et dynamiques d'un laser QD à rétroaction optique distribuée (DFB) pour des applications sans isolateur et sans Peltier. Pour ce faire, la conception du laser intègre un désaccord entre le pic de gain et le pic d’émission DFB contrôlable par la variation de température. Par conséquent, les performances du laser sont substantiellement améliorées avec l'augmentation de la température. La troisième partie du manuscrit aborde les lasers QD sur Si pour la génération de peigne de fréquences optiques (OFC). Les techniques de contrôles externes comme la contre-réaction et l'injection optique sont utilisées pour régénérer les performances notamment le bruit de phase, la gigue temporelle et la bande passante d'émission du peigne. La dernière partie s'articule autour des non-linéarités optiques dans les lasers QD sur Si notamment sous l'angle du mélange à quatre ondes (FWM). L'étude montre que l'efficacité FWM du laser QD est supérieure de plus d'un ordre de grandeur à celle d'un laser à puits quantiques prouvant ainsi que les milieux QD sont très efficaces pour obtenir des peignes de fréquence de grande qualité et de l’auto blocage de mode. Ce travail démontre l'importance des solutions lasers QD en particulier pour les technologies photoniques intégrées sur Si.Silicon photonics is promising for high-speed communication systems, short-reach optical interconnects, and quantum technologies. Direct epitaxial growth of III-V materials on silicon is also an ideal solution for the next generation of photonic integrated circuits (PICs). In this context, quantum-dots (QD) lasers with atom-like density of states are promising to serve as the on-chip laser sources, owing to their high thermal stability and strong tolerance for the defects that arise during the epitaxial growth. The purpose of this dissertation is to investigate the nonlinear properties and dynamics of QD lasers on Si for PIC applications. The first part of this thesis investigates the dynamics of epitaxial QD lasers on Si subject to external optical feedback (EOF). In the short-cavity regime, the QD laser exhibits strong robustness against parasitic reflections hence giving further insights for developing isolator-free PICs. In particular, a near-zero linewidth enhancement factor is crucial to achieve this goal. The second part is devoted to studying the static properties and dynamics of a single-frequency QD distributed feedback (DFB) laser for uncooled and isolator-free applications. The design of a temperature-controlled mismatch between the optical gain peak and the DFB wavelength contributes to improving the laser performance with the increase of temperature. The third part of this dissertation investigates the QD-based optical frequency comb (OFC). External control techniques including EOF and optical injection are used to optimize the noise properties, reduce the timing-jitter, and increase the frequency comb bandwidth. In the last part, an investigation of the optical nonlinearities of the QD laser on Si is carried out by the four-wave mixing (FWM) effect. This study demonstrates that the FWM efficiency of QD laser is more than one order of magnitude higher than that of a commercial quantum-well laser, which gives insights for developing self-mode-locked OFCs based on QD. All these results allow for a better understanding of the nonlinear dynamics of QD lasers and pave the way for developing high-performance classical and quantum PICs on Si

Lasers à îlots quantiques sur silicium : propriétés non-linéaires, dynamique et applications

Silicon photonics is promising for high-speed communication systems, short-reach optical interconnects, and quantum technologies. Direct epitaxial growth of III-V materials on silicon is also an ideal solution for the next generation of photonic integrated circuits (PICs). In this context, quantum-dots (QD) lasers with atom-like density of states are promising to serve as the on-chip laser sources, owing to their high thermal stability and strong tolerance for the defects that arise during the epitaxial growth. The purpose of this dissertation is to investigate the nonlinear properties and dynamics of QD lasers on Si for PIC applications. The first part of this thesis investigates the dynamics of epitaxial QD lasers on Si subject to external optical feedback (EOF). In the short-cavity regime, the QD laser exhibits strong robustness against parasitic reflections hence giving further insights for developing isolator-free PICs. In particular, a near-zero linewidth enhancement factor is crucial to achieve this goal. The second part is devoted to studying the static properties and dynamics of a single-frequency QD distributed feedback (DFB) laser for uncooled and isolator-free applications. The design of a temperature-controlled mismatch between the optical gain peak and the DFB wavelength contributes to improving the laser performance with the increase of temperature. The third part of this dissertation investigates the QD-based optical frequency comb (OFC). External control techniques including EOF and optical injection are used to optimize the noise properties, reduce the timing-jitter, and increase the frequency comb bandwidth. In the last part, an investigation of the optical nonlinearities of the QD laser on Si is carried out by the four-wave mixing (FWM) effect. This study demonstrates that the FWM efficiency of QD laser is more than one order of magnitude higher than that of a commercial quantum-well laser, which gives insights for developing self-mode-locked OFCs based on QD. All these results allow for a better understanding of the nonlinear dynamics of QD lasers and pave the way for developing high-performance classical and quantum PICs on Si.La photonique sur silicium est une technologie prometteuse pour les systèmes de communication à haut débit, les interconnexions optiques à courte portée et pour le déploiement des technologies quantiques. La croissance de matériaux III-V sur silicium constitue également une solution idéale pour la prochaine génération de circuits photoniques intégrés (PIC). Dans ce contexte, les lasers à îlots quantiques (QD) utilisant des atomes semi-conducteurs comme milieu de gain sont des candidats très prometteurs en raison de leur compacité, de leur grande stabilité thermique et d’une tolérance accrue aux défauts structuraux. L'objectif de cette thèse est d'étudier les propriétés non-linéaires et les dynamiques des lasers QD sur Si en vue des applications susmentionnées. La première partie se polarise sur les lasers QD directement épitaxiés sur Si en présence de contre-réaction optique (EOF). Dans le régime de cavité courte, les résultats rapportent des tolérances élevées aux réflexions parasites ce qui rend possible l’intégration de ces sources sur des PIC dépourvus d’isolateur optique. Par ailleurs, la réduction du facteur d’élargissement spectral est un déterminant fondamental permettant d'atteindre cet objectif. La deuxième partie analyse les propriétés statiques et dynamiques d'un laser QD à rétroaction optique distribuée (DFB) pour des applications sans isolateur et sans Peltier. Pour ce faire, la conception du laser intègre un désaccord entre le pic de gain et le pic d’émission DFB contrôlable par la variation de température. Par conséquent, les performances du laser sont substantiellement améliorées avec l'augmentation de la température. La troisième partie du manuscrit aborde les lasers QD sur Si pour la génération de peigne de fréquences optiques (OFC). Les techniques de contrôles externes comme la contre-réaction et l'injection optique sont utilisées pour régénérer les performances notamment le bruit de phase, la gigue temporelle et la bande passante d'émission du peigne. La dernière partie s'articule autour des non-linéarités optiques dans les lasers QD sur Si notamment sous l'angle du mélange à quatre ondes (FWM). L'étude montre que l'efficacité FWM du laser QD est supérieure de plus d'un ordre de grandeur à celle d'un laser à puits quantiques prouvant ainsi que les milieux QD sont très efficaces pour obtenir des peignes de fréquence de grande qualité et de l’auto blocage de mode. Ce travail démontre l'importance des solutions lasers QD en particulier pour les technologies photoniques intégrées sur Si

Multimode Physics in the Mode Locking of Semiconductor Quantum Dot Lasers

Quantum dot lasers are an attractive option for light sources in silicon photonic integrated circuits. Thanks to the three-dimensional charge carrier confinement in quantum dots, high material gain, low noise and large temperature stability can be achieved. This paper discusses, both theoretically and experimentally, the advantages of silicon-based quantum dot lasers for passive mode-locking applications. Using a frequency domain approach, i.e., with the laser electric field described in terms of a superposition of passive cavity eigenmodes, a precise quantitative description of the conditions for frequency comb and pulse train formation is supported, along with a concise explanation of the progression to mode locking via Adler’s equation. The path to transform-limited performance is discussed and compared to the experimental beat-note spectrum and mode-locked pulse generation. A theory/experiment comparison is also used to extract the experimental group velocity dispersion, which is a key obstacle to transform-limited performance. Finally, the linewidth enhancement contribution to the group velocity dispersion is investigated. For passively mode-locked quantum dot lasers directly grown on silicon, our experimental and theoretical investigations provide a self-consistent accounting of the multimode interactions giving rise to the locking mechanism, gain saturation, mode competition and carrier-induced refractive index

SocialDrought: A Social and News Media Driven Dataset and Analytical Platform towards Understanding Societal Impact of Drought

Drought poses significant challenges to sustainability across various sectors in our society, leading to substantial consequences on agriculture, environments, ecosystems, public health, and socioeconomic stability. While prior work has studied the impacts of drought using professionally measured data sources, the societal perspectives of drought impacts remain largely under-explored. In this work, we present SocialDrought, a novel and comprehensive dataset to facilitate research on the societal impacts of drought. In particular, SocialDrought consists of three major components: 1) over 1.5 million social media posts, 2) over 1,400 news articles collected and verified by domain experts, and 3) over 31,000 meteorological records from the U.S. Drought Monitor about drought severity. In addition, we also introduce an online analytical platform that enables interactive and real-time data exploration to gain timely insights into the societal impacts of drought. Our interdisciplinary dataset integrates both conventional meteorological data and unconventional social and news media data to provide a holistic understanding of drought impacts. SocialDrought opens new opportunities to study the societal impacts of drought through the lens of social and news media

Broadband quantum-dot frequency-modulated comb laser.

Frequency-modulated (FM) laser combs, which offer a quasi-continuous-wave output and a flat-topped optical spectrum, are emerging as a promising solution for wavelength-division multiplexing applications, precision metrology, and ultrafast optical ranging. The generation of FM combs relies on spatial hole burning, group velocity dispersion, Kerr nonlinearity, and four-wave mixing (FWM). While FM combs have been widely observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a low-dispersion FP cavity can be a challenge in platforms where the waveguide dispersion is mainly determined by the material. Here we report a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the FM comb can be generated independently. The high FWM efficiency of -5 dB allows the QD laser to generate FM comb efficiently. We also demonstrate that the Kerr nonlinearity can be practically engineered to improve the FM comb bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that our QD platform can deliver is as large as 2.2 THz. This study gives novel insights into the improvement of FM combs and paves the way for small-footprint, electrically pumped, and energy-efficient frequency combs for silicon photonic integrated circuits (PICs)

Dynamic and nonlinear properties of epitaxial quantum dot lasers on silicon for isolator-free integration

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