Monolithic passively mode-locked colliding pulse semiconductor lasers generating pico- to sub-picosecond terahertz optical pulse trains are promising sources for future applications in ultra-high speed data transmission systems and optical measurements. However, in the absence of external synchronization, these passively mode-locked lasers suffer from large amplitude and timing jitter instabilities resulting in broad comb linewidths, which precludes many applications in the field of coherent communications and signal processing where a much narrower frequency line set is needed. In this dissertation, a novel quantum dot based coupled cavity laser is presented, where for the first time, four-wave mixing (FWM) in the monolithically integrated saturable absorber is used to injection lock a monolithic colliding pulse mode-locked (CPM) laser with a mode-locked high-Q ring laser. Starting with a passively mode-locked master ring laser, a stable 30 GHz optical pulse train is generated with more than 10 dB reduction in the RF noise level at 20 MHz offset and close to 3-times reduction in the average optical linewidth of the injection locked CPM slave laser. The FWM process is subsequently verified experimentally and conclusively shown to be the primary mechanism responsible for the observed injection locking. Other linear scattering effects are found to be negligible, as predicted in the orthogonal waveguide configuration. The novel injection locking technique is further exploited by employing optical hybrid mode-locking and increasing the Q of the master ring cavity, to realize an improved stabilization architecture. Dramatic reduction is shown with more than 14-times reduction in the photodetected beat linewidth and almost 5-times reduction in the optical linewidth of the injection locked slave laser with generation of close to transform limited pulses at ~ 30 GHz. These results demonstrate the effectiveness of the novel injection locking technique for an all-on-chip stability transfer and provides a new way of stabilizing monolithic optical pulse sources for applications in future high speed optical networks.

This dissertation explores various aspects and potential of optical pulse generation based on active, passive, and hybrid mode-locked quantum dot semiconductor lasers with target applications such as optical interconnect and high speed signal processing. Design guidelines are developed for the single mode operation with suppressed reflection from waveguide discontinuities. The device fabrication procedure is explained, followed by characteristics of FP laser, SOA, and monolithic two-section devices. Short pulse generation from an external cavity mode-locked QD two-section diode laser is studied. High quality, sub-picosecond (960 fs), high peak power (1.2 W) pulse trains are obtained. The sign and magnitude of pulse chirp were measured for the first time. The role of the self-phase modulation and the linewidth enhancement factor in QD mode-locked lasers is addressed. The noise performance of two-section mode-locked lasers and a SOA-based ring laser was investigated. Significant reduction of the timing jitter under hybrid mode-locked operation was achieved owing to more than one order of magnitude reduction of the linewidth in QD gain media. Ultralow phase noise performance (integrated timing jitter of a few fs at a 10 GHz repetition rate) was demonstrated from an actively mode-locked unidirectional ring laser. These results show that quantum dot mode-locked lasers are strong competitors to conventional semiconductor lasers in noise performance. Finally we demonstrated an opto-electronic oscillator (OEO) and coupled opto-electronic oscillators (COEO) which have the potential for both high purity microwave and low noise optical pulse generation. The phase noise of the COEO is measured by the photonic delay line frequency discriminator method. Based on this study we discuss the prospects of the COEO as a low noise optical pulse source.

Thulium (Tm)-doped ultrafast fiber lasers with emission wavelengths around 2 μm are desirable sources for scientific, industrial, medical, and environmental applications and flexible testbeds for investigating nonlinear pulse dynamics. Although exceptional research attention has been drawn by Tm-doped ultrafast fiber lasers in recent years, their designs and dynamics are significantly less explored compared to other fiber laser systems. Despite the broad emission spectrum of Tm-doped fibers, power scaling of Tm-doped ultrafast fiber lasers has been limited at shorter wavelengths of their emission spectrum (<1920 nm) due to challenges including signal re-absorption. However, compact, high-energy ultrafast sources at these less-exploited wavelengths can enable various applications including nonlinear microscopy. Further, due to the challenges of implementing real-time characterization around 2 μm, transient nonlinear pulse dynamics have rarely been reported from Tm-doped ultrafast fiber lasers. Resolving these dynamics can not only provide insights into new laser designs but also guide the generation of novel pulse profiles which can benefit a wide range of applications depending on their parameters. This dissertation focuses on developing various novel Tm-doped ultrafast fiber laser systems with unprecedented performance: High-energy operation is demonstrated at less-exploited wavelengths and unique waveforms are generated with their nonlinear dynamics investigated in real-time. First, a high-energy (394-nJ) Tm-doped chirped-pulse-amplification fiber laser system is designed and optimized for operation at the wavelength of 1900 nm and supports the generation of 950-nm ultrashort (390-fs) pulses via frequency-doubling. The system represents the highest pulse-energy (138 nJ) in the femtosecond regime for any fiber-based systems around this wavelength to date, which can be highly attractive for two-photon microscopy with spatiotemporal-multiplexing. To gain deeper insights into the operation of ultrafast Tm-doped fiber lasers, various new nonlinear dynamics are investigated by a home-built real-time characterization setup based on dispersive Fourier transform for 2 μm pulses: A new mode-locking regime is demonstrated which can deliver both up-chirped and close-to-chirp-free dissipative pulses with a 10-fold difference in their pulse energies/durations, providing a versatile source that can switch between different pulse profiles. Following that, soliton molecules with unique partial spectral modulation patterns are synthesized based on two dissimilar pulses from the same cavity, which represent an interesting analogy to ‘heteronuclear’ chemical molecules and hold great potential for optical information processing. Further, mode-locking evolution between dissimilar coherent pulses are studied in Tm-doped ultrafast fiber lasers. Finally, combining both high-energy operation and novel waveform-generation, we present a Tm-doped fiber laser source delivering amplified (~ 200 nJ) noise-like pulses without requiring any feedback mechanism. / 2025-09-10T00:00:00Z

In dieser Arbeit werden einige Probleme im Zusammenhang mit der Erzeugung ultrakurzer Pulse in modengekoppelten Lasern unter Verwendung analytischer und numerischer Methoden theoretisch untersucht. Weiterhin werden einige Resultate über die Strahlung resonanter Medien, welche durch einen ultrakurzen Überlichtgeschwindigkeits-Lichtpuls angeregt werden, dargestellt. / In this thesis current problems related to the generation of short optical pulses in mode-locked lasers are considered in a theoretical context. We use numerical and analytical methods to study these problems. Additionally, the problem of resonant medium radiation excited by ultrashort light pulse propagating at superluminal velocity is investigated.

Les travaux de recherche, rapportés dans ce manuscrit, portent sur l’étude d’un laser à fibre en forme de huit et le développement de sources à 1.6 µm. En premier temps, nous avons étudié la dynamique impulsionnelle d’un laser à fibre micro-structurée en forme de huit. L’objectif est de montrer l’impact des propriétés de la fibre micro-structurée sur le comportement impulsionnel du laser. Nous avons également étudié le phénomène d’hystérésis dans cette cavité. Nos résultats numériques ont permis de démontrer l’universalité de ce phénomène dans les cavités lasers. Autrement, il est indépendant de la technique de verrouillage de modes. En second lieu, nous avons développé une source laser émettant à 1.6 µm à partir d’un amplificateur fonctionnant dans la bande C. La méthode que nous avons explorée est basée sur la gestion des pertes linéaires. L’émission, en continu et en verrouillage de modes, a été démontrée dans deux configurations différentes. Enfin et en se basant sur ce concept, nous avons rapporté des sources accordables sur une large fenêtre spectrale. Nous avons également étudié différentes formes des régimes harmoniques autour de 1.6 µm. / During our research, we are interested in studying of the figure of eight fiber laser based on the microstructured optical fiber and developing a 1.61 µm mode locked fiber laser from a C-band double-clad Er : Yb doped fiber amplifier. In the first step and based on a theoretical model, we have investigated the multi-pulse emission of a microstructured figure-of eight fiber laser operating in passive mode-locking. The proposed laser is mode locked by the nonlinear amplifying loop mirror (NALM). We further study the hysteresis dependence and the number of pulses in steady state as a function of both the small signal gain and the nonlinear coefficient of microstructured fiber. Our results demonstrate that the nonlinear coefficient of microstructured fiber plays a key role in the formation of multi-soliton. In the second step and based on the control of the linear losses of the cavity, we demonstrate the possibility to achieve filter less laser emission above 1.6 μm, from a C-band double-clad Er: Yb doped fiber amplifier, using a figure-of-eight geometry and a unidirectional ring cavity. We also reported a widely tunable mode locked fiber laser and harmonic mode locking of twin and third pulse around 1.61 µm.

Rational harmonic mode-locking (RHML) fiber lasers generating picoseconds pulsewidth at high-repetition-rate have emerged as a key component for the high-bit-rate optical time-division multiplexing (OTDM) communication system. In this research, we have discovered higher order RHML semiconductor optical amplifier fiber laser (SOAFL) has the degradation on mode-locking capacity, and an output pulse-train with un-equalized peak amplitudes. Therefore, the main focus of the dissertation is focused on the pulse quality analysis and improvement of RHML-SOAFL via optical pulse injection. First, we observed the degradation on mode-locked mechanism of the dark-optical-comb injection mode-locked semiconductor optical amplifier fiber laser (SOAFL) at RHML order increases to >8. Such a less pronounced RHML mechanism at higher orders is mainly attributed to the weak mode-locking strength at high RHML orders as compared to continuous-wave (CW) lasing mechanism, which has been quantified by reduction of spectral linewidth and pulse-shortening force, and the ratio of DC/pulse amplitude enhancement for discriminating 1st to 20th-order RHML capability. To overcome the un-equalized RHML peak intensity, optical injection induced gain modulation of a SOA are demonstrated to equalize the peak intensity of 5-GHz and 40-GHz RHML-SOAFL by using 1-GHz inverse-optical-pulse and a reshaped 10-GHz gain-switching FPLD pulse injection, respectively. The optical injection mode-locking models are constructed to simulate the compensation of uneven amplitudes between adjacent RHML pulse peaks before and after pulse-amplitude equalization. The optimized RHML pulse exhibits a signal-to-noise suppression ratio of 45-dB, and the clock amplitude jitter below the threshold limitation of 10%. On the other hand, to avoid the mode-locked degradation on RHML, a 2nd-order fractional Talbot effect induced frequency-doubling of 10-GHz optical pulse-train is demonstrated to backward inject a SOAFL for 40-GHz RHML. In comparison with the SOAFL pulse-train repeated at 40-GHz generated by the 4th-order purely RHML process, the optimized 2nd-order fractional Talbot effect in combination with the 2nd-order RHML mechanism significantly enhances the modulation-depth of RHML, thus improving the on/off extinction ratio of the 40-GHz SOAFL pulse-train. Such a new scheme also provides a more stable 40-GHz RHML pulse-train from the SOAFL with its timing jitter reduce. Finally, we established a SHG-FROG to distinguish linear and nonlinear chirp of 10-GHz soliton HML-SOAFL, and further extracted intra-cavity linear dispersion via simulation of Schrodinger equation. After the procedure, the linear chirp almost dominates chirp characteristics for optical pulse injection HML-SOAFL system.

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Cette thèse s’est concentrée sur l’étude des lasers à blocage de modes destinés à la fenêtre de télécommunication de 1,55 µm et à base de bâtonnets quantiques dont la croissance a été réalisée sur des substrats d’InP. Un des principaux objectifs de ce travail de thèse a consisté à apporter de nouveaux éléments permettant de mieux appréhender les aspects physiques sous-tendant le mécanisme du ML dans ces dispositifs. En effet, une meilleure compréhension du comportement intrinsèque de ces dispositifs et la façon dont ils sont affectés par des facteurs externes, qui pourraient être présents dans les conditions réelles d’utilisation, est cruciale pour leur intégration dans des technologies futures. Un deuxième objectif majeur de ce travail a consisté à démontrer le potentiel d’exploitation de ces dispositifs dans différents scenarii d’applications / This PhD thesis focuses on the study of mode locked laser diodes based on novel optimized InAs Quantum Dash structures grown on InP substrates. It covers several important modelling aspects, the clean room processing of single and two section shallow ridge waveguide lasers, characterization of the fabricated devices and the evaluation of their performance in different application scenarios. Systematic characterization experiments and subsequent analyses have allowed to gain a much deeper comprehension of the physical mechanisms related to the mode locking regime in these devices, thus far not completely understood. This has allowed to better control most of the main physical phenomena limiting device performance, resulting in first demonstrations of record peak power, sub-picosecond pulse, low radio frequency linewidth and high repetition frequency mode locked lasers grown on InP substrates, opening the way to a vast number of potential applications in the 1.55 µm telecommunication window

Optische Frequenzkämme (OFC) haben eine Vielzahl von Anwendungen in den angewandten Wissenschaften und der Grundlagenforschung, die auf der Bestimmung von absoluten Frequenzen und Frequenzdifferenzen beruhen, revolutioniert. Für letzteres wird nur die Stabilisierung des spektralen Abstandes der individuellen Kammlinien des OFCs benötigt, was erlaubt, den OFCG auf die Anwendung anzupassen und die Systemkomplexität zu reduzieren. Eine solche Anwendung ist der Quantentest der Universalität des Freien Falls (UFF) im Rahmen der Experimentserie QUANTUS. Mit diesem Test soll der Freie Fall zweier atomarer Spezies, Rubidium (Rb) und Kalium (K), in Mikrogravitation vergleichen werden. Das Ziel dieser Doktorarbeit war die Entwicklung eines hochkompakten, robusten, und weltraum-tauglichen diodenlaser-basierten OFCG mit einem modengekoppelten optischen Spektrum im Wellenlängenbereich um 780 nm. Es wurde ein diodenlaser-basierter OFCG entwickelt, der mit einer spektrale Bandbreite von mehr als 16 nm bei 20 dBc, einer optischen Leistung der Kammlinien > 650 nW (bei 20 dBc), einer Pulswiederholrate von 3.4 GHz, und einer RF-Linienbreite der frei-laufenden Pulswiederholrate < 10 kHz die Anforderungen übertrifft. Um ein Proof-of-Concept Demonstratormodul zu realisieren, wurde der diodenlaser-basierte OFCG in eine weltraum-taugliche Technologieplattform, die für die Anwendung in zukünftigen QUANTUS-Experimenten entwickelt wurde, hybrid-integriert. Der Nachweis einer ausreichend hohen RF-Stabilität des OFCGs wurde durch Stabilisierung der Pulswiederholrate auf eine externe RF Referenz erbracht. Dies ermöglichte eine stabilisierte Pulswiederholrate mit einer RF-Linienbreite von weniger als 1.4 Hz (auflösungsbegrenzt), was die die Anforderung übertrifft. Der entwickelte diodenlaser-basierten OFCG ist wichtiger Schritt in Richtung eines verbesserten Vergleichs des Freien Falls von Rb- und K-Quantengasen innerhalb der QUANTUS-Experimente in Mikrogravitation. / Optical frequency combs (OFC) have revolutionized various applications in applied and fundamental sciences that rely on the determination of absolute optical frequencies and frequency differences. The latter requires only stabilization of the spectral distance between the individual comb lines of the OFC, allowing to tailor and reduce system complexity of the OFC generator (OFCG). One such application is the quantum test of the universality of free fall within the QUANTUS experimental series. Within the test, the rate of free fall of two atomic species, Rb and K, in micro-gravity will be compared. The aim of this thesis was the development of a highly compact, robust, and space-suitable diode laser-based OFCG with a mode-locked optical spectrum in the wavelength range around 780 nm. A diode laser-based OFCG was developed, which exceeds the requirements with a spectral bandwidth > 16 nm at 20 dBc, a comb line optical power > 650 nW (at 20 dBc), a pulse repetition rate of 3.4 GHz, and an RF linewidth of the free-running pulse repetition rate < 10 kHz. To realize a proof-of-concept demonstrator module, the diode laser-based OFCG was hybrid-integrated into a space-suitable technology platform that has been developed for future QUANTUS experiments. Proof of sufficient RF stability of the OFCG was provided by stabilizing the pulse repetition rate to an external RF reference. This resulted in a stabilized pulse repetition rate with an RF linewidth smaller than 1.4 Hz (resolution limited), thus exceeding the requirement. The developed diode laser-based OFCG represents an important step towards an improved comparison of the rate of free fall of Rb and K quantum gases within the QUANTUS experiments in micro-gravity.