International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / This paper presents the results of installing a distributed feedback (DFB) laser transmitter and the appropriate optical receiver in an operational site. Frequencies from 1435 to 2400 megahertz are transported intact from a remote site to a local site. From the theoretical calculations, 10 dB of dynamic range may need to be recovered by the use of an automatic gain circuit. The actual device is a delight, needing no additional circuitry to meet specifications. Predictions of performance were made from calculations. The installed system was measured for 1 dB compression point and for figure of merit.

With the rapid development of fiber access networks, data centers, 5th generation cellular networks, and many more, there is an increasing demand for cost effective light sources possessing specification including high frequency modulation efficiency, low noise figure, and high data rate up to 40 Gb/s or even 100 Gb/s. Semiconductor lasers are considered the most attractive candidate in such applications for their low cost, high energy efficiency, and compact size. The focus of this thesis is the development of novel designs of semiconductor DFB lasers for device performance improvement with the help of numerical simulation tools. The governing equations used in the simulation of DFB lasers are briefly explained, which covers the calculation of optical field, carrier transport, material gain, and thermal diffusion. The TWM based on these governing equations are adopted for the numerical laser solver used in the following chapters for device performance simulation. Three novel DFB structures are then proposed in the thesis to achieve different specifications. The first proposed structure is a three-electrode DFB laser which can be directly frequency modulated. Numerical simulation shows that a high frequency modulation efficiency of 26GHz/mA from 0 to 100GHz and 17GHz/mA from 100GHZ to 200GHz can be achieved, respectively. Large-signal simulation of the waveform and eye-diagram of a frequency shift-keying (FSK) signal generated by the laser is also performed by converting it to an amplitude shift-keying (ASK) signal through an optical slope filter. The second proposed structure is a DFB laser with asymmetric λ/8 phase-shifted grating designed to flatten the relaxation oscillation peak through longitudinal spatial hole burning (LSHB) effect. Optimization of the phase-shift position to be 25% (in terms of the total length of the cavity) away from the high reflective (HR)-coated facet leads to reduced power leakage thus a higher quality factor of the cavity. The combined effect provides an improved RIN figure for the proposed DFB laser. The third proposed structure is a DFB laser with periodic current blocking grating. This novel grating is designed to improve the modulation bandwidth of DFB lasers by exploiting the enhancement of net differential gain. The effectiveness of the design is verified numerically, and excellent 3dB bandwidth enhancement are found for both uniform grating and λ/4 phase-shifted grating structures. / Thesis / Doctor of Philosophy (PhD) / Semiconductor lasers are by far the most ubiquitous of all lasers, with their applications ranging from communication to manufacturing and from cooling of atoms to sensing of minor movement. And as the fabrication technique of semiconductor laser mature, numerical simulation tools now play the critical role in laser development. This thesis focuses on the design and simulation of novel structures for distributed-feedback (DFB) lasers to improve the performance of such devices, including the frequency tuning efficiency, relative intensity noise (RIN), and modulation bandwidth. The proposed new structures and the underlying ideas led to them are thoroughly explained in the thesis. The device performances are also investigated numerically by applying traveling wave method (TWM). Simulation results are presented and discussed to provide design guidelines for the proposed structures.

Les futurs systèmes de communication utiliseront des porteuses de fréquences d'ondes millimétriques (mm) (30 GHz - 300 GHz) et au-delà pour surmonter la saturation des différentes bandes de fréquence et atteindre des débits élevés. Les systèmes radio sur fibre (RoF) ont attiré l'attention grâce à leur faible coût et à la faible atténuation des fibres. Dans le cadre de cette thèse, différentes configurations et plusieurs conceptions de lasers ont été proposées pour la génération de fréquences radio par voie optique. L’amélioration du processus de fabrication de laser développé au laboratoire a permis d’obtenir des sources monomodes émettant autour du pic d'erbium (1534 nm) jusqu'à des puissances optiques de sortie de 41 mW avec une efficacité de 9,8%. Leurs largeurs de raie optiques ont été mesurée égales à 2 kHz et leur bruit d’intensité relatif (RIN) égal à -145 dB/Hz après 50 MHz. Avec ces lasers, des signaux électriques à des fréquences millimétriques de largeur de raie de quelques kHz ont été générés. Trois configurations hétérodynes ont été proposées pour améliorer la stabilité thermique des signaux générés afin de répondre aux normes IEEE. Des lasers co-intégrés ont été de plus fabriqués pour générer des porteuses comprises entre 5GHz et 165GHz. Une étude comparative a montré que les comportements des porteuses ainsi générées étaient indépendants de la fréquence produite. Enfin, les conceptions de structures intégrant coupleur, adaptation de modes et de plusieurs lasers sur verre pompés par une unique source ont été étudiées. En utilisant les porteuses générées par ces dernières réalisations, des transmissions de données ont été accomplies répondant aux normes requises. / Future communication systems will use millimeter-wave (mm) (30 GHz - 300 GHz) frequency carriers and beyond to overcome the saturation of different frequency bands and achieve high data rates. Radio-over-Fiber (RoF) systems have gained attention thanks to their low cost and low fiber attenuation. In this thesis, different configurations and several laser designs have been proposed for radio frequency generation by photonic based technique. The Improvement of the laser fabrication process developed in the laboratory resulted in single-mode sources emitting around the erbium peak (1534 nm) up to 41 mW optical output power with 9.8% efficiency. Their optical linewidths were measured equal to 2 kHz and their relative intensity noise (RIN) equal to -145 dB/Hz after 50 MHz. Using these lasers, electrical signals at millimeter frequencies having linewidths of few kHz have been generated Three heterodyning configurations have been proposed to improve the thermal stability of the generated signals in order to meet the IEEE standards. Co-integrated lasers have been further manufactured to generate carriers between 5GHz and 165GHz. A comparative study showed that the behaviors of the carriers thus generated were independent of the produced frequency. Finally, the designs of structures integrating coupler, tapers and several lasers on glass pumped by a single source were studied. By using the carriers generated by these latest implementations, data transmissions have been accomplished meeting the required standards.

Universiẗat, Diss., 2003--Heidelberg.

The duty-cycle randomness (DCR) lying the Bragg grating of the distributed feedback (DFB) lasers introduced by the fabrication process is inevitable even with the state-of-the-art technologies such as the electron beam lithography and dry or wet etching. This thesis investigates the impact of grating DCR on DFB laser performance through numerical simulations. The result reveals that such a randomness causes a reduction on the side mode suppression ratio (SMSR), and deteriorates the noise characteristics, i.e., broadens the linewidth and increases the relative intensity noise (RIN). With the grating DCR, the effective grating coupling coefficient decreases as evidenced by the reduced Bragg stopband width. However, the longitudinal spatial hole burning (LSHB) effect in the DFB lasers can somewhat be diminished by the grating DCR. The seriousness of these effects depends on different grating structures and their coupling strengths. Our simulation shows that a degradation of 17dB can be brought to the SMSR of the uniform grating DFB lasers with their duty-cycles taking a deviation of ±25% in a uniformly distributed random fashion. It also broadens the linewidth of the quarter-wavelength phase-shifted DFB lasers by more than 2.5 folds. The impact of this effect on the RIN is moderate – less than 2%. All the performance deteriorations can partially be attributed to the effective reduction of the grating coupling coefficient around 20% by such a DCR. / Thesis / Master of Applied Science (MASc)

No description available.

Les besoins actuels des systèmes de télécommunications et des capteurs optiques poussent à réaliser des circuits intégrés optiques présentant toujours plus de fonctions sur un même substrat. Atteindre un tel niveau d'intégration est difficile, car les matériaux et les procédés technologiques employés pour implémenter les différentes fonctions optiques ne sont pas toujours compatibles entre eux. Cette thèse s'inscrit dans la problématique de l'intégration des fonctions optiques actives (émission, amplification) et passives (multiplexage, filtrage, etc.) sur substrat passif et reporte la réalisation d'un laser DFB hybride tridimensionnel par échange d'ions sur verre passif et report de plaque d'un verre actif codopé Er3+:Yb3+. Ce laser est constitué d'un guide canal de Bragg, sélectivement enterré dans le substrat passif, et chargé par un guide plan, réalisé dans le verre actif (dopé avec une concentration massique de 2,3% en Er2O3 et 3,6% en Yb2O3). Il est caractérisé par une émission monomode de (420±15) µW à 1534 nm, pour (390±20) mW de puissance de pompe injectée. Ce dispositif ouvre ainsi la voie vers l'intégration de fonctions actives, localisées à la surface du substrat passif, avec des fonctions passives, réalisées en exploitant le volume et la surface du même substrat. / The current needs of optical telecommunications and sensors require developing integrated optical circuits providing different and heterogeneous functions on the same substrate. The main issue is the incompatibility between the manufacturing processes of these optical functions. This work deals with the integration of active (emission, amplification) and passive (multiplexing, filtering, etc.) functions on a passive glass substrate. Its aim is to develop a DFB three-dimensional hybrid laser by ion-exchange in passive glass. This laser is made of a Bragg channel waveguide, selectively buried in the passive glass substrate, loaded by a plane waveguide, defined at the surface of an Er3+:Yb3+ codoped active glass wafer. It emits a (420±15) µW laser signal at 1534 nm for (390±20) mW injected pump power. Hence this device opens the way towards the integration of active functions, located at the surface of the passive glass substrate, with passive ones, spreading at its surface and in its volume.

De nombreux capteurs optiques, tels que les LIDARS, nécessitent des sources laser à la fois puissantes et spectralement fines. Dans ce contexte, l'objectif de ce projet est la réalisation de sources laser impulsionnelles intégrées, dont les caractéristiques spectrale et temporelle atteignent la limite théorique prédite par la théorie de Fourier. Pour ce faire, nous proposons une structure laser de type DFB avec un fonctionnement déclenché. La technologie de l'échange d'ions est retenue pour réaliser des guides d'onde amplificateurs dans un verre phosphate dopé ytterbium. La cavité DFB est ensuite constituée par gravure d'un réseau de Bragg à la surface des guides amplificateurs. Le comportement impulsionnel est obtenu par dépôt, sur la structure précédente, d'une couche mince d'acétate de cellulose dopée avec l'absorbant saturable BDN. Cette structure nous a permis d'obtenir des lasers impulsionnels monomodes longitudinaux dont les caractéristiques spectrales atteignent la limite de Fourier. Une étude en concentration d'absorbant saturable du superstrat montrent une variation de la durée des impulsions de 2,5 ns à 100 ns avec des puissances crêtes respectives de 30 W et 14 W. Nous parvenons donc à des spectres de largeur à mi-hauteur de valeur 9 MHz. Ces résultats ouvrent la voie à la réalisation de sources laser compactes pour les lidars embarqués. / Various optical sensors, such as LIDARs, need laser sources both powerful and narrow-linewidth. In this context, the aim of this project is the realization of integrated pulsed laser sources with a Fourier Transform Limited (FTL) spectrum. To do so, we propose a passively Q-switched DFB laser structure. Ion-exchange technology is used to realize amplifier waveguides on Ytterbium-doped phosphate glass. The DFB cavity is made by dry etching of a Bragg grating on the waveguides surface. The Q-Switched behavior is obtained by depositing a BDN-doped cellulose acetate coating layer, acting as a saturable absorber. This structure allowed us obtaining FTL single-frequency pulsed lasers. When studying the impact of BDN concentration, we observe pulses ranging from 2,5 ns with 40 W peak power, to 100 ns with 14 W peak power. Thus, our device FWHM linewidth goes down to 9 MHz. These results pave the way for the realisation of compact laser sources for embedded lidar systems.

The main aim of the thesis is a frequency stabilization of the DFB semiconductor laser diodes. The temperature stability of the laser diode chip, the stability and the noise of the injection current and the backward reflections are the crucial parameters which affects the frequency stability. These influences are described and the resolution is proposed. The theory of the external methods of the frequency stabilization and the comparison of these methods is presented. One method was choosed and this method was realized for 760 and 1540 nm wavelength laser diodes. In this method was used the frequency stabilization based on the linear absorption to the spectral lines of the gases. The diploma work is closed by the measured results of the frequency stability of the used laser diodes and by the comparison of level of stability achieved by the other methods.