169 research outputs found
Nonlinear photonics in mid-infrared quantum cascade lasers
No full textLes lasers à cascade quantique émettant dans le moyen-infrarouge sont des lasers semi-conducteurs unipolaires qui sont devenus des sources couramment utilisées pour des applications telles que la spectroscopie de gaz, les communications en espace libre ou les contre-mesures optiques. Appliquer une perturbation externe, typiquement une contre-réaction optique ou de l’injection optique, entraîne une forte modification des propriétés d’émission du laser à cascade quantique. La contre-réaction optique influe sur les propriétés statiques du laser Fabry-Perot ou à contre-réaction répartie, conduisant à une augmentation de la puissance, à une diminution du seuil, à une modification du spectre optique qui peut devenir monomode ou multimode, et à une amélioration de la qualité de faisceau dans les lasers à ruban large fortement multimode transverses. Cela induit également un comportement dynamique différent, et un laser à cascade quantique soumis à de la contre-réaction peut osciller périodiquement ou même devenir chaotique : ce travail présente la toute première observation d'instabilités optiques dans le moyen-infrarouge. De plus, une étude numérique de l’injection optique montre que les lasers à cascade quantique peuvent se verrouiller optiquement sur une plage de plusieurs gigahertz, sur laquelle leur stabilité devrait être accrue et leur bande passante de modulation significativement augmentée. Une dynamique prometteuse apparaît également en dehors de la zone de verrouillage, avec l’apparition d’oscillations périodiques à une fréquence accordable ainsi que des événements isolés de forte intensité. Un laser à cascade quantique soumis à un contrôle externe peut donc être une source très performante pour les applications moyen-infrarouges usuelles, mais pourrait aussi en adresser de nouvelles, telles que des oscillateurs photoniques accordables, des générateurs d’événements rares, des LIDAR chaotiques, des communications sécurisées par chaos ou des contre-mesures imprévisibles.Mid-infrared quantum cascade lasers are unipolar semiconductor lasers, which have become widely used sources for applications such as gas spectroscopy, free-space communications or optical countermeasures. Applying external per-turbations such as optical feedback or optical injection leads to a strong modification of the quantum cascade laser prop-erties. Optical feedback impacts the static properties of mid-infrared Fabry-Perot and distributed feedback quantum cas-cade lasers, inducing power increase, threshold reduction, modification of the optical spectrum, which can become either single- or multimode, and enhanced beam quality of broad-area transverse multimode lasers. It also leads to a different dynamical behavior, and a quantum cascade laser subject to optical feedback can oscillate periodically or even become chaotic: this work provides the very first analysis of optical instabilities in the mid-infrared range. A numerical study of optical injection furthermore proves that quantum cascade lasers can injection-lock over a few gigahertz, where they should experience enhanced stability and especially improved modulation bandwidth. Furthermore, some promising dynamics appear outside the locking range with periodic oscillations at a tunable frequency or high-intensity events. A quantum cascade laser under external control could therefore be a source with enhanced properties for the usual mid-infrared applications, but could also address new applications such as tunable photonic oscillators, extreme events gen-erators, chaotic LIDAR, chaos-based secured communications or unpredictable countermeasure
Lasers à cascades quantiques moyen-infrarouges pour les communications sécurisées par chaos
No full textLes lasers à cascades quantiques (LCQs) sont des lasers semiconducteurs émettant dans le moyen-infrarouge. Ce domaine optique est bien connu pour ses propriétés d'absorption pour de nombreuses molécules et les lasers à cascades quantiques ont déjà fait leurs preuves en spectroscopie. Des expériences de communication en espace libre ont également vu le jour à ces longueurs d'onde et l'objectif de cette thèse était d'explorer plus en détail ce champ d'applications en réalisant une communication sécurisée reposant sur le chaos optique. La thèse avait pour but de préciser de manière expérimentale les conditions optimales (température, courant de pompe, longueur de cavité externe...) pour obtenir du chaos optique afin de l'utiliser dans des applications futures. Durant cette thèse, une transmission sécurisée a été réalisée avec deux LCQs grâce au principe de synchronisation du chaos, ce qui est une première. Cela permet d'entrevoir tout le potentiel offert par ces lasers en terme de communication au moyen-infrarouge, où la transparence de l'atmosphère donne un net avantage aux LCQs comparés aux diodes laser conventionnelles émettant dans le proche infrarouge. En parallèle de ces expériences sur les communications sécurisées, d'autres phénomènes non-linéaires ont également été observés en fonction des conditions d'opération. Ainsi, le phénomène d'entrainement, connu pour les diodes laser, a pu être démontré expérimentalement. Lors d'une réinjection avec rotation de polarisation, il a été possible de voir que le LCQ était capable d'émettre une onde carrée dont la période et le rapport cyclique pouvaient être modifiés en fonction des paramètres du montage. Enfin, la présence d'événements extrêmes, commune à d'autres systèmes optiques et même d'autres systèmes physiques, a également pu être observée, ce qui pourrait être un frein à un système de communication utilisant des LCQs car les événements extrêmes ont tendance à perturber le signal du laser et ainsi à brouiller le message envoyé. L'ensemble de ces résultats expérimentaux a permis une meilleure compréhension des dynamiques non-linéaires présentes dans un LCQ et contribueront à étendre les champs d'application pour ce type de laser moyen-infrarouge qui reste pour le moment restreint à la spectroscopie et aux contre-mesures optiques mais dont le potentiel est très élevé.The mid-infrared domain is a promising optical domain because it holds two transparency atmospheric windows, as well as the fingerprint of many chemical compounds. Quantum cascade lasers (QCLs) are one of the available sources in this domain and have already been proven useful for spectroscopic applications and free-space communications. The purpose of that dissertation is to go one step further by implementing a secure free-space communication relying on optical chaos and consequently, to give an accurate cartography of non-linear phenomena in quantum cascade lasers. Initial efforts about free-space secure chaotic transmission have been carried out during this Ph.D. thesis with two chaos-synchronized QCLs, which is a pioneer result paving the way for mid-infrared private communications. In order to have a global picture about the non-linear dynamics in QCLs under external optical feedback, we tuned many experimental parameters and this allowed us studying new phenomena in QCLs. We thus found similarities between QCLs and laser diodes when the chaotic dropouts are synchronized with an external modulation, known as the entrainment phenomenon. A cross-polarization reinjection technique led to square-wave emission in the output of the QCL. Eventually, we studied the triggering of rogue waves in QCLs. Rogue waves are a quite common phenomenon in optics (among other domains in science) but they have never been triggered on-demand in semiconductor lasers under external optical feedback before. Further studies will try to avoid such phenomenon in the output of a QCL under external optical feedback since it can disturb the message to be transmitted in a secure communication. All these experimental results allowed a better understanding of the non-linear dynamics of QCLs and will extend the potential applications of this kind of semiconductor lasers, which have currently been restricted to molecular spectroscopy and optical countermeasure systems
Recommended from our members
Heritage and Housing: The Impact of Historical Designation in Miami’s Urban Development.
No full textThis thesis looks at the role of historical designation in gentrification in the three
boundary neighborhoods of Little Havana, Overtown, and Allapattah in Miami’s urban
core. The pace of development in Miami has resulted in rapid and uneven displacement
of historically marginalized and under-resourced communities. These displacements are
accompanied by the loss of cultural heritage. The study also outlines Miami's history of
racial segregation and unequal access to economic resources. The author hypothesizes
that race is a more statistically significant predictor of gentrification than other factors,
although historical designation and community engagement may mitigate these negative
impacts. Through multivariate regression (MVR) and Structural Equation Modeling
(SEM), the thesis explores the influence of historical designation, race, economic factors,
and political power on urban development outcomes.
Using data from sources such as the U.S. Census Bureau, the study applies MVR
to identify critical variables influencing neighborhood transformation; SEM confirms the
interrelationships between these variables. The analysis shows neighborhoods with strong
“Power of Place” may be more resilient to gentrification, though predominantly Black
areas remain at higher risk than Hispanic ones, even when historically designated. The
conclusion emphasizes the need for policies that combine historical preservation with
affordable housing strategies, advocating for urban growth that honors cultural heritage
while promoting equity. The author calls for further research on leveraging historical
designation to protect vulnerable communities from gentrification’s adverse effects
Accurate modelling of quantum well infrared photodetectors by FDTD
No full textA Finite Difference Time Domain approach is used to design and optimize QWIPs optoelectronic devices. Results showing the influence of some parameters on the performance of these devices are presented and discussed
QCL - Optical-Feedback Cavity Enhanced Absorption Spectroscopy For The Analysis Of Atmospheric 13CO2/12CO2 In Ice-Core Gas Bubbles
No full textInternational audienceIn the context of a globally warming climate it is crucial to study the climate variability in the past and to understand the underlying mechanisms. The composition of gas stored in bubbles in polar ice presents a paleo-climate archive that provides a powerful means to study the exact mechanisms involved in the ~40% increase in the atmospheric CO2 concentration between glacial and interglacial climates. It is particularly important to understand such natural coupling between climate and the carbon cycle, as it will partly determine what natural feedback can be expected on the atmospheric CO2 concentration in a future warmer world. The source of the CO2 released into the atmosphere during previous deglaciations can be constrained from isotopic measurements by the fact that the different CO2 reservoirs (terrestrial biosphere, oceans) and associated mechanisms (biological or physical) have different isotopic signatures. Unfortunately, such isotope studies have been seriously hampered by the experimental difficulty of extracting the CO2 without contamination or fractionation, and measuring the isotope signal off-line on an isotope ratio mass spectrometer (IRMS). Here we present an alternative method that leverages the extreme sensitivity afforded by Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) in the Mid-Infrared [1]. This region of the spectrum is accessed by a custom-developed Quantum Cascade Laser operating near 4.35 µm. The feedback to the laser of light that has been spectrally filtered by a high-finesse, V-shaped enhancement cavity has the effect of spectrally narrowing the laser emission and to auto-lock the laser frequency to one of the cavity's longitudinal modes, with clear advantages in terms of acquisition time and signal-to-noise ratio of the measurement. The line strengths in this region are about 5 orders of magnitude higher than in the more easily accessible NIR region near 1.6 µm and about 1000 times higher than at 2 µm. The instrument is temperature stabilization at the mK-level. Together with a small cavity volume of ~20 mL, this enables the analysis of nmol-sized samples with high precision (< 0.05‰) in a fraction of the time required by the conventional IRMS-based technique. We will show preliminary results obtained on synthetic samples. [1] Maisons G., Gorrotxategi Carbajo P., Carras M., Romanini D.: Optical-feedback cavity-enhanced absorption spectroscopy with a quantum cascade laser, Opt. Lett., 35, 3607, 2010. [2] Morville J., Kassi S., Chenevier M., and Romanini D.: Fast, low-noise, mode-by-mode, cavity-enhanced absorption spectroscopy by diode-laser self-locking, Appl. Phys., B 80, 1027-1038, 2005
QCL - Optical-Feedback Cavity Enhanced Absorption Spectroscopy For The Analysis Of Atmospheric 13CO2/12CO2 In Ice-Core Gas Bubbles
No full textInternational audienceIn the context of a globally warming climate it is crucial to study the climate variability in the past and to understand the underlying mechanisms. The composition of gas stored in bubbles in polar ice presents a paleo-climate archive that provides a powerful means to study the exact mechanisms involved in the ~40% increase in the atmospheric CO2 concentration between glacial and interglacial climates. It is particularly important to understand such natural coupling between climate and the carbon cycle, as it will partly determine what natural feedback can be expected on the atmospheric CO2 concentration in a future warmer world. The source of the CO2 released into the atmosphere during previous deglaciations can be constrained from isotopic measurements by the fact that the different CO2 reservoirs (terrestrial biosphere, oceans) and associated mechanisms (biological or physical) have different isotopic signatures. Unfortunately, such isotope studies have been seriously hampered by the experimental difficulty of extracting the CO2 without contamination or fractionation, and measuring the isotope signal off-line on an isotope ratio mass spectrometer (IRMS). Here we present an alternative method that leverages the extreme sensitivity afforded by Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) in the Mid-Infrared [1]. This region of the spectrum is accessed by a custom-developed Quantum Cascade Laser operating near 4.35 µm. The feedback to the laser of light that has been spectrally filtered by a high-finesse, V-shaped enhancement cavity has the effect of spectrally narrowing the laser emission and to auto-lock the laser frequency to one of the cavity's longitudinal modes, with clear advantages in terms of acquisition time and signal-to-noise ratio of the measurement. The line strengths in this region are about 5 orders of magnitude higher than in the more easily accessible NIR region near 1.6 µm and about 1000 times higher than at 2 µm. The instrument is temperature stabilization at the mK-level. Together with a small cavity volume of ~20 mL, this enables the analysis of nmol-sized samples with high precision (< 0.05‰) in a fraction of the time required by the conventional IRMS-based technique. We will show preliminary results obtained on synthetic samples. [1] Maisons G., Gorrotxategi Carbajo P., Carras M., Romanini D.: Optical-feedback cavity-enhanced absorption spectroscopy with a quantum cascade laser, Opt. Lett., 35, 3607, 2010. [2] Morville J., Kassi S., Chenevier M., and Romanini D.: Fast, low-noise, mode-by-mode, cavity-enhanced absorption spectroscopy by diode-laser self-locking, Appl. Phys., B 80, 1027-1038, 2005
Optimisation électronique et électromagnétique de détecteurs quantiques dans l'infrarouge
No full textPARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF
- …
