In the paper, the beam propagation method is used to analyze the characteristics and the applications of nonlinear optical waveguide structures. The nonlinear optical waveguide is a medium whose refractive index changes with the electric field intensity. Based on the mode theory, the propagating envelop of optical light waves in the three-layers nonlinear waveguide with the nonlinear cladding, the nonlinear substrate and the linear guiding film can be solved. Not only the dispersion relation curve is described, but also the affection of input power to the electric field distribution is observed. In the application of nonlinear optical waveguide structure, the three-layers nonlinear waveguide structure and the local nonlinear Mach-Zehnder waveguide interferometer structure will be discussed: In the three-layers nonlinear waveguide structure, by launching the symmetric and antisymmetric modes, various characteristics of spatial optical solitons will be observed. Based on the interaction property between spatial optical solitons, a new all-optical 1¡ÑN switching device will be proposed; In the local nonlinear Mach-Zehnder waveguide interferometer structure, by fixing the input signal power and changing the control power, output signal beam will show the switching property. Besides, by changing the local nonlinear distributions, the nonlinear Mach-Zehnder interferometer will show various logic functions. The numerical results show that the proposed structures could function as all-optical switch devices and all-optical logic gates.

<p>Free Space Optics (FSO) has received a great deal of attention lately both in the military and civilian information society due to its potentially high capacity, rapid deployment, portability and high security from deception and jamming. The main issue is that severe weather can have a detrimental impact on the performance, which may result in an inadequate availability. </p><p>This report contains a feasibility study for an all-optical free-space link intended for short-range communication (200-500 m). Laboratory tests have been performed to evaluate the link design. Field tests were made to investigate availability and error performance under the influence of different weather conditions. Atmospheric impact due to turbulence related effects have been studied in detail. The most crucial part of the link design turned out to be the receiver optics and several design solutions were investigated. The main advantage of an all-optical design, compared to commercially available electrooptical FSO-systems, is the potentially lower cost.</p>

In this thesis, we demonstrate a new type of resonant, nonlinear, light-matter interaction facilitated by the unique electromagnetic vacuum density-of-state (DOS) structure of Photonic Band Gap (PBG) materials. Strong light localization inside PBG waveguides allows extremely strong coupling between laser fields and embedded two-level quantum dots (QD). The resulting Mollow splitting is large enough to traverse the precipitous DOS jump created by a waveguide mode cutoff. This allows the QD Bloch vector to sense the non-smoothness of the vacuum structure and evolve in novel ways that are forbidden in free space. These unusual strong-coupling effects are described using a "vacuum structure term" of the Bloch equation, combined with field-dependent relaxation rates experienced by the QD Bloch vector. This leads to alternation between coherent evolution and enhanced relaxation. As a result, dynamic high-contrast switching of QD populations can be realized with a single beam of picosecond pulses. During enhanced relaxation to a slightly inverted steady state at the pulse peak, the Bloch vector rapidly switches from anti-parallel to parallel alignment with the pulse torque vector. This then leads to a highly inverted state through subsequent coherent "adiabatic following" near the pulse tail, providing a robust mechanism for picosecond, femto-Joule all-optical switching. The simultaneous input of a second, weaker (signal) driving beam at a different frequency on top of the stronger (holding) beam enables rich modulation effects and unprecedented coherent control over the QD population. This occurs through resonant coupling of the signal pulse with the Mollow sideband transitions created by the holding pulse, leading to either augmentation or negation of the final QD population achieved by the holding pulse alone. This effect is applied to ultrafast all-optical logic AND, OR and NOT gates in the presence of significant (0.1 THz) nonradiative dephasing and (about 1%) inhomogeneous broadening. Further numerical studies of pulse evolutions inside the proposed devices demonstrate satisfactory population contrast within a PBG waveguide length of about 10 micro meter. These results provide the building blocks for low-power, ultrafast, multi-wavelength channel, on-chip, all-optical computing.

In this thesis, we demonstrate a new type of resonant, nonlinear, light-matter interaction facilitated by the unique electromagnetic vacuum density-of-state (DOS) structure of Photonic Band Gap (PBG) materials. Strong light localization inside PBG waveguides allows extremely strong coupling between laser fields and embedded two-level quantum dots (QD). The resulting Mollow splitting is large enough to traverse the precipitous DOS jump created by a waveguide mode cutoff. This allows the QD Bloch vector to sense the non-smoothness of the vacuum structure and evolve in novel ways that are forbidden in free space. These unusual strong-coupling effects are described using a "vacuum structure term" of the Bloch equation, combined with field-dependent relaxation rates experienced by the QD Bloch vector. This leads to alternation between coherent evolution and enhanced relaxation. As a result, dynamic high-contrast switching of QD populations can be realized with a single beam of picosecond pulses. During enhanced relaxation to a slightly inverted steady state at the pulse peak, the Bloch vector rapidly switches from anti-parallel to parallel alignment with the pulse torque vector. This then leads to a highly inverted state through subsequent coherent "adiabatic following" near the pulse tail, providing a robust mechanism for picosecond, femto-Joule all-optical switching. The simultaneous input of a second, weaker (signal) driving beam at a different frequency on top of the stronger (holding) beam enables rich modulation effects and unprecedented coherent control over the QD population. This occurs through resonant coupling of the signal pulse with the Mollow sideband transitions created by the holding pulse, leading to either augmentation or negation of the final QD population achieved by the holding pulse alone. This effect is applied to ultrafast all-optical logic AND, OR and NOT gates in the presence of significant (0.1 THz) nonradiative dephasing and (about 1%) inhomogeneous broadening. Further numerical studies of pulse evolutions inside the proposed devices demonstrate satisfactory population contrast within a PBG waveguide length of about 10 micro meter. These results provide the building blocks for low-power, ultrafast, multi-wavelength channel, on-chip, all-optical computing.

This thesis evaluates the performance of service differentiation with different class of services namely protection, reservation and the best effort services on the NxN meshed torus and the ring topology, which are established as survivable all&amp / #8208 / optical WDM networks. Blocking probabilities are measured as performance criteria and the effects of different number of wavelengths, different type of services and different topology size with wavelength selective lightpath allocation schemes are investigated by simulations with respect to increasing load on the topologies.

Le contrôle de l’aimantation sans application de champ magnétique externe est un domaine de recherche en plein essor, étant prometteur pour les applications technologiques d’enregistrement magnétique et de spintronique. En 2007, Stanciu et al. ont découvert la possibilité de retourner l’aimantation dans un film fait d’alliage ferrimagnétique de GdFeCo en utilisant des impulsions laser femtoseconde. Longtemps cantonné aux alliages de GdFeCo, ce retournement tout-optique s’avère un phénomène plus général, puisqu’il a été mesuré plus récemment dans une large variété de matériaux ferrimagnétiques et ferromagnétiques. Cette découverte a ainsi ouvert la voie à l’intégration de l’écriture tout-optique dans l’industrie des mémoires magnétiques. Néanmoins, l’ensemble des modèles théoriques expliquant le retournement tout-optique dans le GdFeCo ne semblent pas s’appliquer aux autres matériaux magnétiques, mettant ainsi en question l’unicité de l’origine microscopique de ce phénomène. Au cours de cette thèse, nous avons étudié la réponse aux impulsions laser femtoseconde des alliages ferrimagnétiques et des multicouches ferromagnétiques, dans l'objectif d'élucider divers aspects du mécanisme du retournement optique. Nous avons élucidé expérimentalement les paramètres magnétiques gouvernant le retournement tout-optique. Nous avons montré que l’observation du retournement tout-optique nécessite des domaines magnétiques plus grands que la taille du faisceau laser pendant le processus de refroidissement, un critère qui est commun à la fois aux matériaux ferrimagnétiques et ferromagnétiques. En outre, nous nous sommes intéressés à l’intégration du retournement tout-optique dans des dispositifs de spintronique. Grâce à une caractérisation temporelle de l’aimantation dans des croix de Hall via l’effet Hall extraordinaire, nous avons distingué entre deux types de mécanismes du retournement optique. Le premier type est un retournement purement thermique obtenu avec une impulsion unique dans les alliages ferrimagnétiques de GdFeCo, tandis que le deuxième type est un retournement cumulative et à deux régimes dans les alliages ferrimagnétiques de TbCo et les multicouches ferromagnétiques de Co/Pt. Ce dernier consiste en une formation indépendante de l’hélicité de multidomaines magnétiques suivie d'une ré-aimantation dépendante de l'hélicité sur plusieurs dizaines de millisecondes. / The control of magnetization without external magnetic fields is an emergent field of research due to the prospect of impacting many technological applications such as magnetic recording and spintronics. In 2007, Stanciu et al. discovered an intriguing new possibility to switch magnetization in a ferrimagnetic GdFeCo alloy film using femtosecond laser pulses. This all-optical switching of magnetization had long been restricted to GdFeCo alloys, though it turned out to be a more general phenomenon for a variety of ferromagnetic and ferromagnetic materials. This discovery paved the way for an integration of the all-optical writing in storage industries. Nevertheless, the theoretical models explaining the switching in GdFeCo alloys films do not appear to apply in the other materials, thus questioning the uniqueness of the microscopic origin of all-optical switching. In this thesis, we have investigated the response of femtosecond laser pulses in ferrimagnetic alloys and ferromagnetic multilayers to the action of femtosecond laser pulses, in order to elucidate several aspects of the all-optical switching mechanism. We have experimentally studied the magnetic parameters governing the all-optical switching. We showed that the observation of all-optical switching requires magnetic domains larger than the laser spot size during the cooling process; such a criterion is common for both ferrimagnets and ferromagnets. Furthermore, we have investigated the integration of all-optical switching in spintronic devices via the anomalous Hall effect. Through a time-dependent electrical investigation of the magnetization in Hall crosses, we distinguished between two types of all-optical switching mechanisms. The first type is the single-pulse helicity-independent switching in ferrimagnetic GdFeCo alloy films as shown in previous studies, whereas the second is a two regimes helicity-dependent switching in both ferrimagnetic TbCo alloys and ferromagnetic Co/Pt multilayers. The latter consists in a step-like helicity-independent multiple-domain formation followed by a helicity-dependent remagnetization on several tens of milliseconds.

Depuis une quinzaine d’années, de nombreuses solutions différentes ont été proposés afin de modifier l’aimantations de matériaux sans aucun champ magnétique extérieur appliqué. La manipulation d’aimantation à moindre coût énergétique, de préférence à des échelles de temps ultracourtes, est devenu un enjeu fondamental avec des implications pour les technologies d’enregistrement magnétique et de nouvelles sortes de stockage. Sur ce chemin, le type d’interaction découverte par Stanciu et al. ouvre la voie à l’utilisation de la lumière comme moyen d’exciter et de sonder directement les matériaux magnétiques. La description des théories et modèles existants dans ce domaine permet de nous rendre attentif sur les différents paramètres impliqués par l’interaction des lasers ultrarapides et matériaux magnétiques. L’entrelacement spécifique des impulsions de chaleur et de moment angulaire propre aux lasers ultrarapides est mise en avant afin de discuter de leur rôle dans les phénomènes observés. Le délai des interactions responsables de l’état final de l’aimantation est abordé et notamment la manière dont celle-ci ont un impact sur la façon dont le système se stabilise après une excitation laser. En outre, nous nous sommes intéressés à la relation entre les paramètres matériels et l’état final de l’aimantation obtenue avec un laser ultrarapide. Grâce aux nombreuses classes de matériaux magnétiques existantes les paramètres magnétiques peuvent être ajustés dans une grande gamme de valeurs et de manière entièrement contrôlés. Notre installation d’imagerie magnétique est alors capable de sonder les caractéristiques optiques et la stabilité des domaines après l’excitation. Nous avons finalement démontré que le retournement optique dépendent de l’hélicité peut être observée non seulement dans un grand nombre de couches minces d’alliages de terre rare-métaux de transition (RE-TM) mais aussi dans une variété beaucoup plus large de matériaux, y compris les multicouches et hétérostructures de RE-TM. Nous montrons en outre que les hétérostructures ferrimagnétiques dépourvues de terres rares présentent également un retournement optique. Nous avons en plus développé le contrôle optique de multicouches ferromagnétiques dont des films granulaires actuellement explorés pour l’enregistrement magnétique ultra-haute densité de demain. Notre découverte montre que la manipulation de l’aimantation dans des matériaux magnétiques est un phénomène beaucoup plus général que précédemment suspecté et peut avoir un impact majeur sur l’enregistrement magnétique et le stockage de l’information grâce à l’intégration nouvelle de ce type de contrôle optique dans des bits ferromagnétiques / The possibilities of modifying magnetization without applied magnetic fields have attracted growing attention over the past fifteen years. The low-power manipulation of magnetization, preferably at ultrashort timescales, has become a fundamental challenge with implications for future magnetic information memory and storage technologies. In particular the interplay of laser and magnetism recently discovered by Stanciu et al. opens up new way for light to be used as an excitation and a probe of magnetic materials. A description of the current models and frameworks developed in the field requires a careful look at the different parameters involved through the interaction of ultrafast lasers and magnetic materials. The specific and complex interplay between heat and angular momentum transfer is highlighted in order to discuss the role of each of them in the phenomena observed. The timescales of the different interactions responsible for the final state of magnetization are presented and will impact the way the system recovery after a laser excitation. Besides we were interested in exploring the relation between the material parameters such as anisotropy, ordering temperature and exchange coupling on the final state of magnetization obtained with a laser. Indeed thanks to the many different magnetism classes existing the magnetic parameters can be tuned widely and in a controlled manner. Our imaging setup then is able to probe the optical characteristics and domain stability after the laser excitation. We finally demonstrated that all-optical helicity-dependent switching (AO-HDS) can be observed not only in selected rare earth-transition metal (RE-TM) alloy films but also in a much broader variety of materials, including RE-TM alloys, multilayers and heterostructures. We further show that RE-free Co-Ir-based synthetic ferrimagnetic heterostructures designed to mimic the magnetic properties of RE-TM alloys also exhibit AO-HDS. We further developed the optical control of ferromagnetic materials ranging from magnetic thin films to multilayers and even granular films being explored for ultra-high-density magnetic recording. Our finding shows that optical control of magnetic materials is a much more general phenomenon than previously assumed and may have a major impact on data memory and storage industries through the integration of optical control of ferromagnetic bits

The aim of this research is to investigate the performance of a bi-stable device using a single active element and to design a higher order all optical binary delta-sigma modulator (BΔΣM). A Delta sigma modulator has two important components that require enhancement to achieve robust modulation. The first component is the integrator which accumulates the error and at the same time leaks it. Here, the integrator is a single ring laser consisting of a semiconductor optical amplifier (SOA) and a filter to allow the light frequency of interest into the ring. The other component is the bi-stable device (called Schmitt trigger) that switches either ON (1) or OFF (0). There are different novel approaches to developing a bi-stable circuit. First, the coupled two ring lasers where each ring suppresses each other. Second, a novel idea that considered as a bi-stable device with single active element to achieve reduced power and reduce cost. This type of circuit is merged ring lasers with using single SOA. This system is modeled and its bistability hysteretic characteristics is investigated. The first bi-stable device is used to construct an all optical BΔΣM with 1st, 2nd and 3rd -order approaches. It performs better when the SOA bulk device is replaced by multi-quantum well (MQW) SOA.

The growing use of the internet and the wide variety of applications which run on it puts a considerable demand for high bandwidth networks. All optical core networks are one such possible networks which cater to the demand of high bandwidths.Since the all optical routers use the fiber delay lines as optical buffers, it is impossible to build optical buffers of such high capacity.The present day solutions for optical buffers are fiber delay lines(FDL) which are nothing but long optical fiber lines which are convoluted and folded in order to provide the necessary delay in transmission resulting in a small buffer which can store packets and thus can be used as a buffer.If we consider the example of a single TCP source sending an infinite amount of data with packets of constant size with the flow passing through a single router. If we make an assumption that the sender's access link is much faster than the receiver's bottleneck link of capacity, it will cause packets to be queued at the router.We propose a mechanism to pace traffic in the network based on the queue length of the buffer in the output port. The underlying principle delays the transmission of the packet depending on the instantaneous queue length of the buffer.A prototype of such a model was simulated in network simulator and the performance metrics were measured.

All-optical synchronization and its application in advanced optical communications have been investigated in this dissertation. Dynamics of all-optical timing synchronization (clock recovery) using multi-section gain-coupled distributed-feedback (MS-GC DFB) lasers are discussed. A record speed of 180-GHz timing synchronization has been demonstrated using this device. An all-optical carrier synchronization (phase and polarization recovery) scheme from PSK (phase shift keying) data is proposed and demonstrated for the first time. As an application of all-optical synchronization, the characterization of advanced modulation formats using a linear optical sampling technique was studied. The full characterization of 10-Gb/s RZ-BPSK (return-to-zero binary PSK) data has been demonstrated. Fast lockup and walk-off of the all-optical timing synchronization process on the order of nanoseconds were measured in both simulation and experiment. Phase stability of the recovered clock from a pseudo-random bit sequence signal can be achieved by limiting the detuning between the frequency of free-running self-pulsation and the input bit rate. The simulation results show that all-optical clock recovery using TS-DFB lasers can maintain a better than 5 % clock phase stability for large variations in power, bit rate and optical carrier frequency of the input data and therefore is suitable for applications in ultrafast optical packet switching. All-optical timing synchronization of 180-Gb/s data streams has been demonstrated using a MS-GC DFB laser. The recovered clock has a jitter of less than 410 fs over a dynamic range of 7 dB. All-optical carrier synchronization from phase modulated data utilizes a phase sensitive oscillator (PSO), which used a phase sensitive amplifier (PSA) as a gain block. Furthermore, all-optical carrier synchronization from 10-Gb/s BPSK data was demonstrated in experiment. The PSA is configured as a nonlinear optical loop mirror (NOLM). A discrete linear system analysis was carried out to understand the stability of the PSO. Complex envelope measurement using coherent linear optical sampling with mode-locked sources is investigated. It is shown that reliable measurement of the phase requires that one of the optical modes of the sampling pulses be locked to the optical carrier of the data signal to be measured. Carrier-envelope offset (CEO) is found to have a negligible effect on the measurement. Measurement errors of the intensity profile and phase depend on the pulsewidth and chirp of the sampling pulses as well as the detuning between the carrier frequencies of the data signal and the center frequency of the sampling source. Characterization of the 10-Gb/s RZ-BPSK signal was demonstrated using the coherent detection technique. Measurements of the optical intensity profile, chirp and constellation diagram were demonstrated. A CW local oscillator was used and electrical sampling was performed using a sampling scope. A novel feedback scheme was used to stabilize homodyne detection.