Electroabsorption and electrorefraction were studied in GaAs/AlGaAs and InP/InAsP multiple quantum well waveguides. Measurements of changes of the absorption coefficient and the refractive index with wavelength and bias voltage were made. Switching ratios of up to 18 dB were obtained for the GaAs/AlGaAs material. The Kramers-Kronig relation was used to calculate the theoretical phase shifts from the absorption coefficient data. / Thesis / Master of Engineering (ME)

In this thesis various subjects at the crossroads of quantummechanics and device physics are treated, spanning from afundamental study on quantum measurements to fabricationtechniques of controlling gates for nanoelectroniccomponents. Electron waveguide components, i.e. electronic componentswith a size such that the wave nature of the electron dominatesthe device characteristics, are treated both experimentally andtheoretically. On the experimental side, evidence of partialballistic transport at room-temperature has been found anddevices controlled by in-plane Pt/GaAs gates have beenfabricated exhibiting an order of magnitude improvedgate-efficiency as compared to an earlier gate-technology. Onthe theoretical side, a novel numerical method forself-consistent simulations of electron waveguide devices hasbeen developed. The method is unique as it incorporates anenergy resolved charge density calculation allowing for e.g.calculations of electron waveguide devices to which a finitebias is applied. The method has then been used in discussionson the influence of space-charge on gate-control of electronwaveguide Y-branch switches. Electron waveguides were also used in a proposal for a novelscheme of carrierinjection in low-dimensional semiconductorlasers, a scheme which altogether by- passes the problem ofslow carrier relaxation in suchstructures. By studying aquantum mechanical two-level system serving as a model forelectroabsorption modulators, the ultimate limits of possiblemodulation rates of such modulators have been assessed andfound to largely be determined by the adiabatic response of thesystem. The possibility of using a microwave field to controlRabi oscillations in two-level systems such that a large numberof states can be engineered has also been explored. A more fundamental study on quantum mechanical measurementshas been done, in which the transition from a classical to aquantum "interaction free" measurement was studied, making aconnection with quantum non-demolition measurements.

External modulators will become key components in fiberoptical communica- tion systems operating at 40Gbit/s andhigher bitrates. Semiconductor electro- absorption (EA)modulators are promising candidates because of their high-speed potential, and their process compatibility with thecorresponding semi- conductor laser light sources. Thetraveling-wave (TW) electrode concept for electro-opticmodulators has been used for a long time in order to resolvethe con°ict between high modulation depth and highmodulation bandwidth. Re- cently, it has been adopted for EAmodulators as well. This thesis presents the work carried out on design,fabrication and analysis of traveling-wave EA modulators(TWEAM) based on InP-InGaAsP. The lengths of TWEAM arecomparable to the lengths of their lumped counterparts. Theexperimental data of this work were analyzed in order show thatthe traveling- wave concept results in better performance evenfor short EA modulators. One key issue is the impedancematching. The low intrinsic characteristic modulator impedancehas to be matched with a corresponding load. In this case, theTW con figuration leads to a much higher bandwidth than for alumped EA modulator with the same length and the same connectedload. An InP process was developed allowing the fabrication ofTWEAM with integrated termination resistors. Experimentalmicrowave properties were ob- tained for different TWEAMgeometries. It is reported on long TWEAM that showstate-of-the-art bandwidth. A 450&#956m long TWEAM reached43GHz, and 67GHz (beyond characterization limit) were indicatedfor a 250&#956m device. The experimental results onmicrowave properties were compared to full-wave, and circuitmodel simulations. The analysis reveals an impedance bandwidthtrade- off for the cross sectional electrode configuration. Results of a new high-impedance design in form of asegmented TWEAM are presented. The devices were processedwithin the frame of this work and record bandwidth performanceis reported. At 50&#937­ impedance a bandwidth in the90GHz region was indicated.

Ultra Wide Band (UWB) is a short-pulse signal which has extremely potential in wireless communication system due to the advantages of high data rate, better immunity to multipath fading, wide bandwidth, and high capability. According to the Federal Communications Commission (F.C.C.), UWB only can be transmitted in short distance of a few to tens of meters due to low power density (-41.3dBm/MHz). However, optical fiber has low loss and cost and wide bandwidth, so it can be achieved in wide area network. In this work, we propose a novel method to generate optical UWB doublet pulse without complicated setup. When electroabsorption modulator (EAM) integrating a taper optical directional coupler (TODC) was applied field, the transmission loss and coupling would change resulting from the absorption coefficient and effective index of active waveguide with the applied field. So, we used a single mode fiber collecting the power after the device, we could get the valley shape transfer function. Using the transfer function of electro-absorption modulator (EAM) integrating TODC we inject a Gaussian pulse into the EAM in the range of valley shape, and it can transform an electrical pulse into optical UWB doublet pulse by acceptable operating point. Therefore, the optical signals could be transmitted in optical fiber so that it can reduce loss of the electro-optic transformation. Experimentally, the full wave at half maximum of doublet pulse, 10dB bandwidth, fractional bandwidth were 75ps, 7.5GHz, 125%, respectively, and power density was less than -41.3dBm/MHz. These were all meeting the F.C.C. standard. In the future, we will use long distant optical fiber to transmitted UWB signal, and compare with different distance. Finally, we will check the UWB signal can be transmitted in optical fiber to achieve wide range signal transmission by bit error rate test.

<p>In this thesis various subjects at the crossroads of quantummechanics and device physics are treated, spanning from afundamental study on quantum measurements to fabricationtechniques of controlling gates for nanoelectroniccomponents.</p><p>Electron waveguide components, i.e. electronic componentswith a size such that the wave nature of the electron dominatesthe device characteristics, are treated both experimentally andtheoretically. On the experimental side, evidence of partialballistic transport at room-temperature has been found anddevices controlled by in-plane Pt/GaAs gates have beenfabricated exhibiting an order of magnitude improvedgate-efficiency as compared to an earlier gate-technology. Onthe theoretical side, a novel numerical method forself-consistent simulations of electron waveguide devices hasbeen developed. The method is unique as it incorporates anenergy resolved charge density calculation allowing for e.g.calculations of electron waveguide devices to which a finitebias is applied. The method has then been used in discussionson the influence of space-charge on gate-control of electronwaveguide Y-branch switches.</p><p>Electron waveguides were also used in a proposal for a novelscheme of carrierinjection in low-dimensional semiconductorlasers, a scheme which altogether by- passes the problem ofslow carrier relaxation in suchstructures. By studying aquantum mechanical two-level system serving as a model forelectroabsorption modulators, the ultimate limits of possiblemodulation rates of such modulators have been assessed andfound to largely be determined by the adiabatic response of thesystem. The possibility of using a microwave field to controlRabi oscillations in two-level systems such that a large numberof states can be engineered has also been explored.</p><p>A more fundamental study on quantum mechanical measurementshas been done, in which the transition from a classical to aquantum "interaction free" measurement was studied, making aconnection with quantum non-demolition measurements.</p>

<p>External modulators will become key components in fiberoptical communica- tion systems operating at 40Gbit/s andhigher bitrates. Semiconductor electro- absorption (EA)modulators are promising candidates because of their high-speed potential, and their process compatibility with thecorresponding semi- conductor laser light sources. Thetraveling-wave (TW) electrode concept for electro-opticmodulators has been used for a long time in order to resolvethe con°ict between high modulation depth and highmodulation bandwidth. Re- cently, it has been adopted for EAmodulators as well.</p><p>This thesis presents the work carried out on design,fabrication and analysis of traveling-wave EA modulators(TWEAM) based on InP-InGaAsP. The lengths of TWEAM arecomparable to the lengths of their lumped counterparts. Theexperimental data of this work were analyzed in order show thatthe traveling- wave concept results in better performance evenfor short EA modulators. One key issue is the impedancematching. The low intrinsic characteristic modulator impedancehas to be matched with a corresponding load. In this case, theTW con figuration leads to a much higher bandwidth than for alumped EA modulator with the same length and the same connectedload.</p><p>An InP process was developed allowing the fabrication ofTWEAM with integrated termination resistors. Experimentalmicrowave properties were ob- tained for different TWEAMgeometries. It is reported on long TWEAM that showstate-of-the-art bandwidth. A 450&#956m long TWEAM reached43GHz, and 67GHz (beyond characterization limit) were indicatedfor a 250&#956m device. The experimental results onmicrowave properties were compared to full-wave, and circuitmodel simulations. The analysis reveals an impedance bandwidthtrade- off for the cross sectional electrode configuration.</p><p>Results of a new high-impedance design in form of asegmented TWEAM are presented. The devices were processedwithin the frame of this work and record bandwidth performanceis reported. At 50&#937­ impedance a bandwidth in the90GHz region was indicated.</p>

Electroabsorption modulators (EAMs) are fundamental components in optical communication systems. Their response is governed by a set of parameters inherent to their internal structure and by the external electrical components used to drive them. The first part of this thesis discusses a new method for the extraction of values for these parameters. The use of EAMs as both optical modulators and photodetectors is exploited for the purpose of parameter extraction. The proposed method allows the estimation of the parameters which govern the internal frequency response of EAMs without any knowledge of the characteristics of the electrical interconnect used to drive them. The procedure also removes the need for an accurately calibrated optical transmitter and receiver pair normally used during the characterization of optoelectronic components. Analytic description and experimental verification are presented. In the second part of this thesis, direct demultiplexing of a 10 Gbit/s channel from a 160 Gbit/s optical time division multiplexing (OTDM) signal using a single lumped, electrically driven EAM is experimentally presented for the first time. Direct demultiplexing is made possible by using an electrical driving signal for the EAM consisting of a sum of in-phase harmonics of the base channel rate. The use of a single EAM as an optical gate is quasi-analytically compared with the common approach of cascading two EAMs when performing 160 Gbit/s to 10 Gbit/s demultiplexing. The analysis reveals that the use of a single EAM is beneficial in terms of lower penalty with respect to degradations in the extinction ratio and width of the pulses used in the OTDM signal. The last part of this thesis introduces an electrical distributed oscillator which works in a regime of oscillation similar to that of mode locked laser (MLL) systems. The oscillator offers the flexibility of producing other waveforms not found in MLLs and has the potential to generate the required electrical driving signal for a single EAM OTDM demultiplexer. Other possible applications of the oscillator include the generation of short pulses for use in radar systems and wireless personal area networks. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2011-06-30 14:41:42.625

[pt] No presente trabalho de tese, se faz uma avaliação de moduladores de amplitude baseados no efeito de electro-absorção. As estruturas usadas para a fabricação dos dispositivos foram estruturas com poços quânticos múltiplos de InAlAs/InGaAs e AlGaAs/GaAs. As estruturas de InAlAs/InGaAs foram projetadas para trabalhar na faixa comercial das telecomunicações (1.55 µm). Por isto a importância de aperfeiçoar os parâmetros de desempenho do dispositivo, tais como Stark shift, chirp, razão de contraste, perda por inserção, entre outros. Um estudo sistemático prévio destas estruturas foi realizado por Pires [Pires,1998]. Ele propõe variar a concentração de gálio na liga para produzir uma leve tensão na estrutura e modificar desta forma as propriedades ópticas do material. O estudo de [Pires,1998] propôs uma faixa de valores para variar a concentração de gálio (entre 46 por cento e 52 por cento) onde pode ser encontrada a melhor condição de operação do dispositivo. Cabe a esta tese aprofundar o estudo nesta faixa de valores, e decidir os parâmetros mais adequados para operação. No referente às estruturas de AlGaAs/GaAs, se toma como partida uma proposta teórica de [Batty et al, 1993], e estudada posteriormente por [Tribuzy, 2001], onde se sugere usar finas camadas de dopagem delta nos poços de GaAs para melhorar o deslocamento Stark em 87% para um campo aplicado de 40 kV/cm. O dispositivo foi desenhado e fabricado, obtendo-se um valor de 78 por cento para o mesmo campo aplicado, resultado relevante, pois é a verificação experimental de uma proposta teórica. / [en] In this thesis work, is made an evaluation of modulators of amplitude based in the electrum-absorption effect. The structures used for the devices were multiple quantum wells of InAlAs/InGaAs and AlGaAs/GaAs. The structures of InAlAs/InGaAs are used to work in the commercial band of the telecommunications (1,55 µm). This is the reason it is important to optimize the parameters of performance of the device, such as the Stark shift, chirp, contrast reason, insertion loss, etc. Previously, a systematic study of these structures was made by [Pires, 1998], the gallium concentration was varied to produce a strain in the structure and to modify the optic properties of the material. In the study of [Pires, 1998] considered the Gallium concentration was varied between 46 percent and 52 percent in which range the best condition to operate the device can be found. This is part of the work here presented. In this thesis this range of values was studied in more detail. For the structures of AlGaAs/GaAs, a theoretical proposal of [Batty et al, 1993] was experimentally investigated. It was suggested a nipi structure to use a fine delta doped in the GaAs wells, this delta doped will improve in 87 percent the Stark shift for a field of 40 KV/cm. The device was simulated and manufactured, obtaining a value of 78 percent for the same field applied, this is a excellent result, because this confirm the theoretical prediction.

La photonique silicium est un domaine de recherche en pleine expansion depuis quelques années. Elle est envisagée comme une solution prometteuse pour le remplacement des interconnexions électriques par des liens optiques. A terme, l’intégration de l’optique et de l’électronique sur les mêmes puces doit permettre une augmentation des performances des circuits intégrés, et ainsi proposer des composants à hautes performances et à bas coût. Dans ce contexte, les travaux menés durant ma thèse ont porté plus spécifiquement sur l’étude de la modulation optique autour de la bande interdite directe et à température ambiante des structures à puits quantiques Ge/SiGe, par effet Stark confiné quantiquement (ESCQ). Des simulations électriques et optiques ont été menées pour concevoir un modulateur fonctionnant à la longueur d’onde de 1.3μm. La fabrication et la caractérisation de ce dispositif a permis de démontrer une modulation efficace autour de 1.3μm avec des taux de modulation atteignant 6 dB avec un dispositif de 50 µm de long. Le second objectif de mon travail a été de concevoir un modulateur intégré sur une plateforme SOI, bénéficiant de structures passives performantes et compactes. La démonstration de l’ESCQ sur une structure à puits quantique Ge/SiGe épitaxiée sur un substrat homogène de 360 nm a ouvert la voie à cette intégration. Des simulations ont été menées pour démontrer la possibilité de réaliser un couplage vertical évanescent entre un guide optique SOI et la structure Ge/SiGe, et pour évaluer les performances de ce dispositif. Un procédé technologique de fabrication a ensuite été défini et toutes les étapes ont été optimisées pour la réalisation du modulateur intégré avec les guides d’onde. Principalement six étapes de lithographies électroniques, et quatre étapes de gravure sont nécessaires. Les résultats préliminaires obtenus avec ces dispositifs sont présentés. Les perspectives de ce travail de thèse concernent la réalisation de circuits intégrés photoniques complexes, intégrant modulateurs, photodétecteurs et structures passives sur le même circuit. / Silicon photonics has generated a great interest for several years, for applications from long-haul optical telecommunication to intra-chip interconnects. The ultimate integration of optics and electronics on the same chip would allow an increase of the integrated circuit performances at low cost. In this context, the work done during my Ph.D is focused on the study of optical modulation around the direct bandgap of Ge/SiGe quantum well structures, at room temperature, by Quantum Confined Stark effect (QCSE). Electrical and optical simulations have been used to design a modulator operating at 1.3μm. Such device has been fabricated and characterized, demonstrating an extinction ratio up to 6 dB using a 50 µm-long structure. The second objective of my work was to design and demonstrate a modulator integrated on SOI waveguide. The demonstration of an efficient QCSE in Ge/SiGe quantum wells grown on the top of a 360nm homogeneous virtual substrate has paved the way for such integration. Simulations were conducted to demonstrate the feasibility of an evanescent vertical coupling between an SOI optical waveguide and a Ge/SiGe active region and to evaluate the performance of this device. A technological process has then been proposed to fabricate the devices. All steps have been optimized for the fabrication of the modulator integrated with the waveguides. Mainly six electronic beam lithography and four etching steps were used. Preliminary experimental results obtained with such component are presented. This work paves the way to the demonstration of complex photonic integrated circuits, including modulators, photodetectors and passive structures on the same chip.

L'augmentation du débit des télécommunications nécessite la réalisation de circuits intégrés utilisant des transistors dont les fréquences de coupure sont de plus en plus élevées. L'évaluation des performances intrinsèques de ces composants fonctionnant aujourd'hui jusqu'à plusieurs centaines de GHz pose un gros problème d'instrumentation. Les capacités des analyseurs de réseaux généralement utilisés pour ces caractérisations sont en effet dépassées.<br /><br />Les méthodes d'échantillonnage électro-optique basées sur l'utilisation d'un laser impulsionnel femtoseconde constituent une méthode alternative de caractérisation hyperfréquences. Ces mesures dont la résolution temporelle peut être inférieure à la picoseconde permettent d'étudier la réponse en fréquence de composants intégrés jusqu'à plus de 1 THz.<br /><br />La méthode d'échantillonnage ultra-rapide que nous proposons est basée sur un effet d'électroabsorption présent dans de nombreux semiconducteurs massifs : l'effet Franz-Keldysh. Cet effet nous permet de sonder optiquement des impulsions électriques ultra-brèves se propageant sur une ligne de transmission déposée sur Arséniure de Gallium (GaAs). Ces impulsions sont également générées par voie optique grâce à un matériau photoconducteur ultra-rapide : le GaAs épitaxié à basse température.<br /><br />La démonstration expérimentale de cette méthode de caractérisation est tout d'abord effectuée en utilisant les propriétés intrinsèques du substrat semiconducteur. Dans un deuxième temps, des améliorations technologiques sont apportées au dispositif expérimental pour permettre une généralisation de la technique de mesure à tout type de substrat. Pour cela, nous avons en particulier mis au point une technique de « lift-off » épitaxial permettant le report des matériaux nécessaires à la mesure sur un circuit ayant déjà subi les étapes technologiques. Ces différentes méthodes de mesure sont ensuite appliquées à la caractérisation de lignes de transmission ou de composants passifs THz. Elles ont permis entre autre la mise en évidence du phénomène de couplage par onde de choc électromagnétique entre deux lignes de transmission coplanaires, ou l'évaluation des paramètres S d'un filtre réjecteur de Bragg intégré sur substrat de quartz jusqu'à 1,2 THz. Enfin, la possibilité d'étudier un transistor bipolaire à hétérojonction à doigt d'émetteur submicronique par cette technique de mesure est envisagée.