Ce travail de thèse concerne la réalisation d’une source VECSEL bi-fréquence émettant à 1550 nm pour les capteurs à fibres optiques à base de l’effet Brillouin. Nous présentons la conception et la réalisation de la source VECSEL bi-fréquence. Nous comparons les spécifications de notre source réalisée avec ceux recommandés pour la source utilisée avec les capteurs de Brillouin. Dans un premier temps, nous avons testé les structures VECSELs fabriquées au laboratoire LPN-CNRS dans le but de sélectionner la structure la plus performante pour notre cavité finale. La structure sélectionnée fournit une puissance de sortie ~200 mW avec un schéma d’évacuation de chaleur à travers le miroir de Bragg. Il est nécessaire de générer un décalage fréquentiel autour de 11 GHz, pour cela, dans un second temps, nous avons calculé l’accordabilité du décalage fréquentiel par plusieurs façons (la rotation de la lame biréfringente, la variation de la longueur de cavité et la variation de la température du cristal biréfringent). Nous avons trouvé qu’une accordabilité grossière (de l’ordre du GHz) peut-être assurée avec la rotation de la lame biréfringente alors qu’une accordabilité plus fine (de l’ordre de MHz) peut-être assurée avec la variation de la température du cristal ainsi que la variation de la longueur de cavité. Dans un troisième temps, nous avons démontré la possibilité de réaliser une émission bi-fréquence avec nos structures semi conductrices, néanmoins l’émission obtenue était instable. Après l’optimisation de la table optique l’émission obtenue observée sur un analyseur de spectre optique (avec une résolution de 1 GHz) était stable. Un meilleur contrôle de la stabilité de l’émission bi-fréquence est assuré avec la focalisation du diamètre du spot de pompage. Pour obtenir de faibles diamètres du spot de pompage, nous avons utilisé une diode laser de pompage monomode qui permet de pomper le mode fondamental de cavité. Les puissances de sorties ont été examinées. Nous avons remarqué qu’une puissance de sortie de 50 mW peut être obtenue en optimisant la réflectivité du miroir de sortie ainsi que la fonction de filtre et l’ISL de l’étalon Fabry-Pérot. Dans un quatrième temps nous avons examiné la stabilité de l’émission bi-fréquence avec une résolution ~ 1 GHz pour de différentes valeurs de recouvrement spatial entre les modes de cavité. Une émission bi-fréquence stable était observée avec un coefficient de recouvrement spatial allant jusqu’à 70%. Une examination de la stabilité avec une résolution de l’ordre de kHz était réalisée. Nous avons observé une largeur de raie de 200 kHz. Pour estimer la dérive du battement fréquentiel sur des temps longs, nous avons examiné l’évolution de l’enveloppe fréquentielle sur des intervalles temporels d’une minute. Une dérive de 0.8 MHz/minute était observée / In this thesis, we focus on the development of a dual-frequency VECSEL source operating at 1550 nm for Brillouin based optical fiber sensors. We present the design and the realization of this dual-frequency source. We compare the obtained results to the recommended specifications for Brillouin fiber sensors. In a first step, we have examined the output power of VECSEL structures fabricated in the LPN-CNRS labs. The selected structure ensure an output power of ~200mW using a downward heat dissipation scheme. For our application, it is crucial to ensure a frequency difference between the two cavity modes close to 11 GHz. For this reason, in a second step, we have calculated the frequency difference tunability with several ways (rotation of the birefringent crystal, temperature variation of the birefringent crystal and cavity length variation). A large tunability (GHz order) is ensured when the birefringent crystal is rotated. A weak tunability (MHz order) is ensured by varying the cavity length and the crystal temperature. In a third step, we have demonstrated the realization of a dual-frequency VECSEL at 1550 nm; however, the obtained laser emission was unstable. By optimizing our optical table, the observed dual frequency emission was stable (using a resolution ~1 GHz). A better control of the laser emission stability is ensured by a better focalization of the pump spot diameter. For this reason we have used a single mode laser diode as a pump source. This type of source ensures the pumping of the fundamental cavity modes only. By examining the influence of intra cavity elements on output powers, we have concluded that, an output power around 50 mW can be obtained using an output coupler of 99% reflectivity and a Fabry-Perot etalon with FSR= 15 nm and filter function close to 0.56 nm at 99.5% transmission. In a fourth step, we have examined the stability of the dual-frequency emission with a resolution ~1 GHz for different values of the coupling constant coefficient. A stable dual-frequency emission is obtained with a coupling coefficient between the modes up to 70 %. By investigating the stability with a kHz resolution we have obtained a FHWM close to 200 kHz.To estimate the jitter of the beat frequency obtained we have examined the evolution of the frequency envelope over a minute. A jitter of 0.8 MHz/minute was observed

The extraction of high power with high beam quality from semiconductor lasers has long been a goal of semiconductor laser research. Optically pumped vertical-external-cavity surface-emitting lasers (VECSELs) have already shown the potential for their high power high brightness operation. In addition, the macroscopic nature of the external cavity in these lasers makes intracavity nonlinear frequency conversion quite convenient. High-power high-brightness VECSELs with wavelength flexibility enlarge their applica-tions. The drawbacks of the VECSELs are their poor spectral characteristics, thermal-induced wavelength shift and a few-nm-wide linewidth.The objective of this dissertation is to investigate tunable high-power high-brightness VECSELs with spectral and polarization control. The low gain and microcavity reson-ance of the VECSEL are the major challenges for developing tunable high-power VECSELs with large tunability. To overcome these challenges, the V-shaped cavity, where the anti-reflection coated VECSEL chip serves as a folding mirror, and an extremely low-loss (at tuned wavelength) intracavity birefringent filter at Brewster's angle are employed to achieved the high gain, low-loss wavelength selectivity and the elimination of microcavity. This cavity results in multi-watt TEM00 VECSELs with a wavelength tuning range of 20~30 nm about 975 nm. Also the longitudinal mode discrimination introduced by birefringent filter makes the linewidth narrow down to 0.5 nm. After the tunable linearly polarized fundamental beam is achieved, the tunable blue-green VECSELs are demonstrated by using type I intracavity second-harmonic generation. The spectral control of VECSELs makes it possible to apply them as an efficient pump source for Er/Yb codoped single-mode fiber laser and to realize the spectral beam combining for multi-wavelength high- brightness power scaling.In this dissertation, theory, design, fabrication and characterization are presented. Rigorous microscopic many-body theory of the quantum well gain, based on semiconductor Bloch equations and k.p theory, is introduced. The closed loop design tool based on this theory is not only used to design the VECSEL structure, but also used as a precise on-wafer diagnostics tool by the experiment/theory comparison of the photo-luminescence. The characterization of the wafer shows that the modeling is in good agreement with the measured results.The VECSEL high power high brightness performance relies on the fabrication of the chip. The fabrication method of the VECSEL chip, which provides the optically smooth surface and good heat dissipation, is presented. The anti-reflection coating on the chip surface can significantly improve the slope efficiency of VECSEL when high reflectivity output coupler is used. Over 12-W VECSEL cw output power with 43 % slope efficiency is demonstrated at 0 oC. A beam quality factor (M^2 factor) of 1.75 is obtained at 11 W output power.

Optically pumped semiconductor vertical external cavity surface emitting lasers (VECSEL) were first demonstrated in the mid 1990's. Due to the unique design properties of extended cavity lasers VECSELs have been able to provide tunable, high-output powers while maintaining excellent beam quality. These features offer a wide range of possible applications in areas such as medicine, spectroscopy, defense, imaging, communications and entertainment. Nowadays, newly developed VECSELs, cover the spectral regions from red (600 nm) to around 5 µm. By taking the advantage of the open cavity design, the emission can be further expanded to UV or THz regions by the means of intracavity nonlinear frequency generation. The objective of this dissertation is to investigate and extend the capabilities of high-power VECSELs by utilizing novel nonlinear conversion techniques. Optically pumped VECSELs based on GaAs semiconductor heterostructures have been demonstrated to provide exceptionally high output powers covering the 900 to 1200 nm spectral region with diffraction limited beam quality. The free space cavity design allows for access to the high intracavity circulating powers where high efficiency nonlinear frequency conversions and wavelength tuning can be obtained. As an introduction, this dissertation consists of a brief history of the development of VECSELs as well as wafer design, chip fabrication and resonator cavity design for optimal frequency conversion. Specifically, the different types of laser cavities such as: linear cavity, V-shaped cavity and patented T-shaped cavity are described, since their optimization is crucial for transverse mode quality, stability, tunability and efficient frequency conversion. All types of nonlinear conversions such as second harmonic, sum frequency and difference frequency generation are discussed in extensive detail. The theoretical simulation and the development of the high-power, tunable blue and green VECSEL by the means of type I second harmonic generation in a V- cavity is presented. Tens of watts of output power for both blue and green wavelengths prove the viability for VECSELs to replace the other types of lasers currently used for applications in laser light shows, for Ti:Sapphire pumping, and for medical applications such as laser skin resurfacing. The novel, recently patented, two-chip T-cavity configuration allowing for spatial overlap of two, separate VECSEL cavities is described in detail. This type of setup is further used to demonstrate type II sum frequency generation to green with multi-watt output, and the full potential of the T-cavity is utilized by achieving type II difference frequency generation to the mid-IR spectral region. The tunable output around 5.4 µm with over 10 mW power is showcased. In the same manner the first attempts to generate THz radiation are discussed. Finally, a slightly modified T-cavity VECSEL is used to reach the UV spectral regions thanks to type I fourth harmonic generation. Over 100 mW at around 265 nm is obtained in a setup which utilizes no stabilization techniques. The dissertation demonstrates the flexibility of the VECSEL in achieving broad spectral coverage and thus its potential for a wide range of applications.

Ever since the first laser demonstration in 1960, applications for laser systems have increased to include diverse fields such as: national defense, biology and medicine, entertainment, imaging, and communications. In order to serve the growing demand, a wide range of laser types including solid-state, semiconductor, gas, and dye lasers have been developed. For most applications it is critical to have lasers with both high optical power and excellent beam quality. This has traditionally been difficult to simultaneously achieve in semiconductor lasers. In the mid 1990's, the advent of an optically pumped semiconductor vertical-external-cavity surface-emitting laser (VECSEL) led to the demonstration of high (multi-watt) output power with near diffraction limited (TEM00) beam quality. Since that time VECSELs covering large wavelength regions have been developed. It is the objective of this dissertation to investigate and explore novel cavity designs which can lead to increased functionality in high power, high brightness VECSELs. Optically pumped VECSELs have previously demonstrated their potential for high power, high brightness operation. In addition, the "open" cavity design of this type of laser makes intracavity nonlinear frequency conversion, linewidth narrowing, and spectral tuning very efficient. By altering the external cavity design it is possible to add additional functionality to this already flexible design. In this dissertation, the history, theory, design, and fabrication are first presented as VECSEL performance relies heavily on the design and fabrication of the chip. Basic cavities such as the linear cavity and v-shaped cavity will be discussed, including the role they play in wavelength tuning, transverse mode profile, and mode stability. The development of a VECSEL for use as a sodium guide star laser is presented including the theory and simulation of intracavity frequency generation in a modified v-cavity. The results show agreement with theory and the measurement of the sodium D1 and D2 lines are demonstrated. A discussion of gain coupled VECSELs in which a single pump area accommodates two laser cavities is demonstrated and a description of mode competition and the importance of spontaneous emission in determining the lasing condition is discussed. Finally the T-cavity configuration is presented. This configuration allows for the spatial overlap of two VECSEL cavities operating with orthogonal polarizations. Independent tuning of each cavity is presented as well as the quality of the beam overlap and demonstration of Type II intracavity sum frequency generation. Future applications to this configuration are discussed in the generation of high power, high brightness lasers operating from the UV to far-infrared and even terahertz regimes.

Vertical External Cavity Surface Emitting Lasers (VECSELs) have become well established in recent years for their design flexibility and promising power scalability. Recent efforts in VECSEL development have focused heavily on expanding the medium into the ultrafast regime of modelocked operation. Presented in this thesis is a detailed discussion regarding the development of ultrafast VECSEL devices. Achievements in continuous wave (CW) operation will be highlighted, followed by several chapters detailing the engineering challenges and design solutions which enable modelocked operation of VECSELs in the ultrafast regime, including the design of the saturable absorbers used to enforce modelocking, management of the net group delay dispersion (GDD) inside the cavity, and the design of the active region to support pulse durations on the order of 100 fs. Work involving specific applications - VECSELs emitting on multiple wavelengths simultaneously and the use of VECSEL seed oscillators for amplification and spectral broadening - will also be presented. Key experimental results will include a novel multi-fold cavity design that produced record-setting peak powers of 6.3 kW from a modelocked VECSEL, an octave-spanning supercontinuum with an average power of 2 W generated using a VECSEL seed and a 2-stage Yb fiber amplifier, and two separate experiments where a VECSEL was made to emit on multiple wavelengths simultaneously in modelocked and highly stable CW operation, respectively. Further, many diagnostic and characterization measurements will be presented, most notably the in-situ probing of a VECSEL gain medium during stable modelocked operation with temporal resolution on the order of 100 fs, but also including characterization of the relaxation rates in different saturable absorber designs and the effectiveness of different methods for managing the net GDD of a device.

We present a novel Vertical External Cavity Surface Emitting Laser (VECSEL) cavity design which makes use of multiple interactions with the gain region under different angles of incidence in a single round trip. This design allows for optimization of the net, round-trip Group Delay Dispersion (GDD) by shifting the GDD of the gain via cavity fold angle while still maintaining the high gain of resonant structures. The effectiveness of this scheme is demonstrated with femtosecond-regime pulses from a resonant structure and record pulse energies for the VECSEL gain medium. In addition, we show that the interference pattern of the intracavity mode within the active region, resulting from the double-angle multifold, is advantageous for operating the laser in CW on multiple wavelengths simultaneously. Power, noise, and mode competition characterization is presented.

L’objectif général de ce projet de thèse est le développement industriel de source lasers accordables de haute cohérence à base de technologies III-V dans les gammes spectrales 0.95-1.1µm, et 2-2.5µm. Ce travail est le fruit d'un partenariat entre les laboratoires IES et C2N, avec la société INNOPTICS spécialisée dans l'intégration de composant opto-électronique.Il s'agit ici de tirer profit des nombreux avantages des composants VeCSELs (Vertical external Cavity Surface Emitting Laser) pour atteindre une combinaison des performances cohérence - puissance - accordabilité - compacité, inaccessible avec les technologies laser commerciales d'aujourd'hui. Pour atteindre cet objectif le travail est scindé en deux grandes parties :- L'étude physique de la dynamique non linéaire d'un laser VECSEL en régime continu et en présence de dispersion de phase. Nous montrons l'existence d'une dynamique déterministe du champ laser qui donne naissance à un régime multimode longitudinal non stationnaire régulier ou à un régime mono-fréquence stable. Ce résultat permet alors la conception de source de haute cohérence à forte puissance sans élément intracavité sélectif en longueur d'ondes.- Le développement de nouvelles sources monofréquences compact largement accordables bas bruit avec une largeur de raie étroite. Cette partie comporte l’étude physique des composants, depuis l’optimisation du milieu à gain jusqu'à l'émission laser en terme de cohérence spatiale et temporelle, ainsi qu'un travail sur l'environnement du laser (mécanique et thermique optimisée pour la stabilité de la fréquence laser). / The main goal of this thesis is the industrial development of highly coherent tunable laser sources based on III-V technologies in the 0.95-1.1μm and 2-2.5μm spectral ranges.This work is the result of a partnership between the IES and C2N laboratory together with the company INNOPTICS, specialized in the packaging of optoelectronics devices.We take advantage of the Vertical External Cavity Surface Emitting Laser (VECSEL) technology to achieve a combination of coherence - power -tunability -compactness, overcoming the performances of today's commercial laser technologies. To achieve this goal the work is divided into two main parts:- The physical study of the non-linear dynamics of a VECSEL laser in continuous wave operation and in the presence of cavity phase dispersion. We show the existence of a deterministic dynamics of the laser field that gives rise to a regular non-stationary longitudinal multimode regime or a stable single-frequency regime. This result then makes it possible to design a source of high coherence with high power without any intracavity wavelength selective element.- The development of new low noise compact single frequency sources with a narrow linewidth. This part involves the physical study of the components, from optimization of the gain medium to the laser emission in terms of spatial and temporal coherence, as well as a work on the environment of the laser (optimization of the thermal mechanical properties of the packaging for the stability of the laser frequency).

Ce travail de thèse porte sur la conception, la réalisation et l'étude physique de sources lasers de haute cohérence et de forte puissance émettant dans le proche et le moyen infrarouge. Nous nous intéressons plus particulièrement aux lasers à semiconducteur émettant par la surface en cavité externe verticale (VECSEL), l'objectif étant d'obtenir un fonctionnement laser monofréquence accordables et robustes, de forte puissance à température ambiante et en régime continu dans la gamme spectrale 2-3µm et autour de 1µm, avec des dispositifs pompés optiquement ou électriquement. Nous traitons de la conception et de la caractérisation des VECSEL, depuis l'optimisation du milieu à gain jusqu'à l'élaboration et la caractérisation de prototypes laser fonctionnels, et nous effectuons une étude approfondie des propriétés physiques de l'émission laser en terme de cohérence spatiale et temporelle. / This thesis focuses on the design, realization and physical study of high power and highly coherent laser sources emitting in the near and mid-infrared. We are particularly interested in vertical external cavity surface emitting laser (VECSEL), the aim being to obtain a robust and tunable single frequency operation with high power at room temperature in continuous wave and in the spectral range of 2-3µm and around 1µm, with optically or electrically pumped devices . We discuss the design and characterization of VECSEL, from optimization of the gain medium to the development and characterization of a functional laser prototype, and we conduct a thorough study of the physical properties of the laser emission in terms of spatial and temporal coherence.

Cette thèse porte sur la conception, la réalisation et l'étude expérimentale d'une source laser bifréquence de haute cohérence émettant à 1 µm en vue d'obtenir par photomélange un émetteur THz. Nous nous intéressons plus particulièrement aux lasers à semiconducteur émettant par la surface en cavité externe verticale (VeCSEL), l'objectif étant d'obtenir un fonctionnement laser bifréquence robuste en régime continu, basé sur la coexistence simultanée de deux modes transverses de Laguerre-Gauss. La sélection de seulement deux modes transverses est réalisée grâce à des masques de pertes insérés intracavité dans le plan transverses. Les caractéristiques du laser bifréquence, telles que l'équilibre entre les puissances des deux modes, le caractère monofréquence de chacun des deux modes, l'accordabilité de l'écart de fréquence, la simultanéité de l'émission et la cohérence du battement THz obtenu, sont étudiées. Enfin, la génération THz par photomélange est effectuée grâce au VeCSEL bifréquence et à une photodiode UTC commerciale. / This work focuses on the design, realization and experimental study of highly coherent dual-frequency laser sources emitting at 1 µm for THz radiation generation by photomixing. We are particularly interested in vertical-external-cavity surface-emitting laser (VeCSEL), the aim being to obtain a robust dual-frequency continuous wave operation, based on simultaneous coexistence of two Laguerre-Gaussian transverse modes. We design intracavity transverse selective losses mask to select only the two Laguerre-Gaussian modes. The stable and simultaneous dual-frequency operation, the beat-frequency tunability range and the temporal coherence was specifically studied. We demonstrated THz emission by seeding a uni-travelling-carrier photodiode by an optically-pumped dual-frequency vertical-external-cavity surface-emitting.

Since its first successful demonstration more than five decades ago [1], laser technology experienced a huge leap forward in terms of technological innovations and the understanding of underlying physical principles of operation. There were many efforts made by those in both the scientific and commercial communities who envisioned the potential of lasers. As a result, the laser now is a powerful scientific tool in many disciplines. It is widely used not only in physics, but also in chemistry, biology, medicine, engineering, environmental sciences, arts and their interdisciplinary fields. Moreover, it now has a vast number of applications in industry and everyday life whether it is light and matter interaction, communication and IT, healthcare and many other uses of this light source. By the same time, photonics comprises a market of multi-billion EUR value [2].At every stage of development, different laser parameters were engineered to suit those to specific application with some other parameters usually being sacrificed. Together with this, things like compactness and cost were always an issue to consider. A huge impact to the field of photonics was made by the development of semiconductor based structures that could be used as a light amplifying medium. Semiconductor lasers not only allowed the miniaturization of many devices, but also provided new opportunities for laser scientists due to ability to engineer their bandgap properties and to confine the carriers in different dimensions.The development of vertical external cavity surface emitting lasers (VECSELs), which are also known as optically pumped semiconductor lasers (OPSLs) or semiconductor disk lasers (SDLs) realized an important feature in semiconductor based lasers – high multi- Watt output power was combined with diffraction limited output beam profile.This work is devoted to the development of semiconductor disk lasers based on novel quantum dot (QD) structures. QD structures were embedded in this type of laser recently and allowed a number of advantages compared with the widely used quantum well (QW) structure. These included new spectral region coverage at 1-1.3 µm, enhanced wavelength tuneability and ultrafast carrier dynamics, which potentially will improve mode locked operation. QDs were also used as a base for semiconductor saturable absorbers in modelocking experiments.During the time of these studies, QD SDLs at new spectral regions and record output power were demonstrated. Power scaling up to 6 W was achieved for 1040 nm, 2.25 W for 1180 nm and 1.6 W for 1260 nm devices. Excited state transition in QDs was shown to be more efficient for high power QD SDLs as compared with ground state transition. New spectral regions were covered by QD SDLs using frequency doubling into the visible region with green, orange and red light emission with output powers of 2 W, 2.5 W and 0.34 W respectively. The broad gain bandwidth of the quantum dot material was explored and wavelength tuneability up to 60 nm around 1040 nm, 69 nm around 1180 nm, and 25 nm around 1260 nm was demonstrated.A QD based saturable absorber was used to mode-lock the quantum well SDL, resulting in the first such type of laser with sub-picosecond pulse widths. Pulses with duration of 870 fs at a repetition rate of 896 MHz and wavelength of 1028.5 nm were demonstrated. Pulses were 1.14 times Fourier limited and an average output power of 46 mW was achieved. Finally, quantum well based VECSELs with electrical pumping schemes were tested. The devices were first tested in the cw configuration. Highest output powers up to 60 mW were achieved from such devices. Devices were then tested in mode-locking experiments. Pulsed operation was observed and the measurements indicated 270 ps width pulses with 8 mW average output power at 1.9 GHz repetition rate. All devices operated at 980 nm.This thesis consists of six chapters. In the introductory part of this work, QD based SDLs and their development and applications will be reviewed together with their operational principles. Chapter two will describe the growth, fabrication and preparation of SDL samples. Continuous wave and mode-locked operation results will be presented in chapters three and four. Electrically pumped devices will be presented in chapter five along with experimental results. Conclusions and future prospects will be given at the end of this work. The list of publications which were generated during the studies is included at the beginning of this work.The work presented in thesis was done under the FAST-DOT project. This is a European FP 7 project targeted at the development of compact and low-cost novel quantum dot based laser sources for biophotonic applications.