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Photonic switches are becoming key components in advanced optical networks because of the large variety of applications that they can perform. One of the key advantages of photonic switches is that they redirect or convert light without having to make any optical to electronic conversions and vice versa, thus allowing networking functions to be lowered into the optical layer. InP-based switches are particularly attractive because of their small size, low electrical power consumption, and compatibility with integration of laser sources, photo-detectors, and electronic components. In this dissertation the development of integrated InP photonic switches using an area-selective zinc diffusion process has been investigated. The zinc diffusion process is implemented using a semi-sealed open-tube diffusion technique. The process has proven to be highly controllable and reproducible by carefully monitoring of the diffusion parameters. Using this technique, isolated p-n junctions exhibiting good I-V characteristics and breakdown voltages greater than 10 V can be selectively defined across a semiconductor wafer. A series of Mach-Zehnder interferometric (MZI) switches/modulators have been designed and fabricated. Monolithic integration of 1x2 and 2x2 MZI switches has been demonstrated. The diffusion process circumvents the need for isolation trenches, and hence optical losses can be significantly reduced. An efficient optical beam steering device based on InGaAsP multiple quantum wells is also demonstrated. The degree of lateral current spreading is easily regulated by controlling the zinc depth, allowing optimization of the injected currents. Beam steering over a 21 microns lateral distance with electrical current values as low as 12.5 mA are demonstrated. Using this principle, a reconfigurable 1x3 switch has been implemented with crosstalk levels better than -17 dB over a 50 nm wavelength range. At these low electrical current levels, uncooled and d.c. bias operation is made feasible. The use of multimode interference (MMI) structures as active devices have also been investigated. These devices operate by selective refractive index perturbation on very specific areas within the MMI structure, and this is again realized using zinc diffusion. Several variants such as a compact MMI modulator that is as short as 350 µm, a robust 2x2 photonic switch and a tunable MMI coupler have been demonstrated.

Ce travail de thèse porte sur la synthèse organo-métallique de nanoparticules (NPs) semi-conductrices colloïdales de phosphures d’indium (InP), de zinc (Zn3P2) et de structures cœur/coquille obtenues par la croissance d’une couche de sulfure de zinc (ZnS) à la surface des NPs. Les objectifs consistent à comprendre et maîtriser la synthèse dans le but de décaler les longueurs d’onde d’absorption et d’émission vers le proche infra-rouge, domaine spectral intéressant pour l’imagerie biomédicale.Le premier chapitre présente l’état de l’art sur les nanocristaux (NCx) d’InP et d’InP/ZnS. Un bref rappel sur les propriétés physico-chimiques des NCx semi-conducteurs est présenté et différentes synthèses sont décrites. Une attention toute particulière a été portée sur la taille des NCx, le décalage de l’émission de fluorescence vers les plus grandes longueurs d’onde et l’optimisation des rendements quantiques. Les potentialités offertes par ces objets soit pour les diodes électroluminescentes (LED) blanches soit pour l’imagerie biomédicale montrent l’intérêt d’utiliser les NCx de type InP/ZnS plutôt que d’autres matériaux à base d’éléments toxiques (Cd, Pb, …).Le deuxième chapitre porte sur une synthèse à partir des carboxylates d’indium connue de la littérature. Le but est alors de caractériser la structure des NPs pour comprendre le déroulement de la synthèse et de l’enrobage. Des mesures par résonance magnétique nucléaire (RMN) en phase solide et spectroscopie photo-électronique par rayons X (XPS) révèlent l’oxydation des NPs d’InP. La couche d’oxyde qui se forme durant la synthèse des NPs d’InP s’épaissit lors de l’enrobage. Cette oxydation provient d’un couplage décarboxylant des acides carboxyliques à haute température en présence des NPs. Elle serait à l’origine de l’inhibition de croissance des objets, ce qui limiterait les gammes de longueurs d’onde atteignables.Le troisième chapitre concerne une nouvelle synthèse à partir d’amidinate d’indium au lieu des carboxylates d’indium. L’intérêt de cette approche est la possibilité d’abaisser considérablement la température de réaction (150°C au lieu de 280°C) et ainsi d’éviter la réaction secondaire de décarboxylation. Un enrobage à basse température (150°C) est aussi mis en place. La synthèse induit également une oxydation de la surface des NPs d’InP. Un nouveau couplage a lieu entre les ligands, l’acide palmitique et l’hexadécylamine, et donne de nouvelles conditions oxydantes. Le jeu sur les ratios des ligands montre qu’en bouleversant le milieu réactionnel, les NPs d’InP ne présentent pas de réponse en luminescence concluante. La synthèse et l’enrobage sont alors réalisés sous atmosphère de dihydrogène (H2) en réacteur Fisher-Porter dans le but de contrer ces conditions oxydantes. La synthèse et l’enrobage donnent des tailles de NPs de l’ordre de 3,4 nm (condition nécessaire pour s’approcher d’une émission dans l'infra-rouge) et un rendement quantique de 18-20 %, résultats encore jamais atteints lors de cette thèse.Le dernier chapitre est consacré à une étude exploratoire sur les NPs de Zn3P2. Le phosphure de zinc est un matériau prometteur du fait de l’abondance de ses constituants non toxiques et des longueurs d’onde potentiellement accessibles. Différents paramètres de synthèse sont étudiés et les propriétés structurales et optiques sont caractérisées. Des résultats préliminaires sur l’enrobage montrent des difficultés liées à la stabilité des NPs de Zn3P2. L’utilisation de l’oxyde de trioctylphosphine (TOPO) semble permettre la passivation de ces NPs à l’air et en travaillant sous H2 une meilleure stabilité est envisageable / Résumé de la thèse en anglais : This PhD investigation focuses on organometallic synthesis of indium phosphide (InP), zinc phosphide (Zn3P2) colloidal semiconductor nanoparticles (NPs) and core/shell structures which were obtained by the growth of a layer of zinc sulfide (ZnS) on the surface. The objectives are to understand and control the synthesis in order to shift the absorption and emission wavelengths to the near infra-red range, interesting for biomedical imaging.The first chapter presents the state of the art on the InP and InP/ZnS nanocrystals (NCx). A brief recall on the physical and chemical properties of semiconductor NCx is presented and various syntheses are described. Particular attention was paid to the size of NCx, the shift of the fluorescence emission to higher wavelengths and the optimization of quantum yields. The potential of these objects for white light emitting diodes (LED) or biomedical imaging shows the value added of using InP/ZnS NCx rather than other materials based on toxic elements such as cadmium, lead elements…The second chapter focuses on a synthesis from indium carboxylates known in the literature. The goal is to characterize the structure of NPs to understand the procedure of the synthesis and the coating. Measurements by Nuclear Magnetic Resonance (NMR) in solid state and Photoelectronic X-ray spectroscopy (XPS) revealed the oxidation of InP of the NPs. This oxide layer increases during the coating. This originates from a decarboxylating coupling of carboxylic acids at high temperature in the presence of NPs. This oxidation is believed to inhibit the growth of the object, which restricts the attainable range of wavelengths.The third chapter provides a novel synthesis from indium amidinate instead of indium carboxylate. The advantage of this approach is the potential to lower significantly the reaction temperature (150°C instead of 280°C) and to avoid secondary decarboxylation reaction. A coating with ZnS at low temperature (150°C) is also developed. The synthesis of InP NPs also causes an oxidation of the surface. A coupling takes place again between the ligands, palmitic acid and hexadecylamine providing new oxidizing conditions. The study of different ratios of ligands shows that when the reaction medium is modified, the InP NPs do not exhibit a conclusive luminescence response. Synthesis and coating are carried out under an atmosphere of hydrogen (H2) in Fisher-Porter reactor in order to counter these oxidizing conditions. NPs with diameters of the order of 3,4 nm (a necessary condition to approach the infra-red emission) and a quantum yield of 18-20% are thus obtained. These had never been observed before during this thesis.The last chapter is devoted to an exploratory study on Zn3P2 NPs. Zinc phosphide is a promising material because of non-toxic and abundant constituents, and potential access to near infra-red wavelengths. Different synthesis parameters are studied and the structural and optical properties are characterized. Preliminary results on the coating show instabilities of the Zn3P2 NPs. The use of trioctylphoshine oxide (TOPO) appears to allow the passivation of the NPs in the air and a better stability is possible under an atmosphere of H2

Photonic crystals (PhCs) are structures periodic in thedielectric constant. They exhibit a photonic bandgap, i.e., arange of wavelengths for which light propagation is forbidden.Engineering of defects in the PhC lattice offers new ways toconfine and guide light. PhCs have been manufactured usingsemiconductors and other material technologies. This thesisfocuses on two-dimensional PhCs etched in InP-based materials.Only recently, such structures were identified as promisingcandidates for the realization of novel and advanced functionsfor optical communication applications. The primary focus was on fabrication and characterization ofPhC structures in the InP/GaInAsP/InP material system. Thedemands on fabrication are very high: holes as small as100-300nm in diameter have to be etched at least as deep as 2µm. Thus, different etch processes had to be explored andspecifically developed for InP. We have implemented an etchingprocess based on Ar/Cl2chemically assisted ion beam etching (CAIBE), thatrepresents the state of the art PhC etching in InP. Different building blocks were manufactured using thisprocess. A transmission loss of 10dB/mm for a PhC waveguide, areflection of 96.5% for a 4-row mirror and a record qualityfactor of 310 for a 1D cavity were achieved for this materialsystem. With an etch depth of 4.5 µm, optical loss wasfound to be close to the intrinsic limit. PhC-based opticalfilters were demonstrated using (a) a Fabry-Pérot cavityinserted in a PhC waveguide and (b) a contra-directionalcoupler. Lag effect in CAIBE was utilized positively to realizehigh quality PhC taper sections. Using a PhC taper, a couplingefficiency of 70% was demonstrated from a standard ridgewaveguide to a single line defect PhC waveguide. During the course of this work, InP membrane technology wasdeveloped and a Fabry-Pérot cavity with a quality factorof 3200 was demonstrated. Keywords:photonic crystals, photonic bandgap materials,indium phosphide, dry etching, chemically assisted ion beametching, reactive ion etching, electron beam lithography,photonic integrated circuits, optical waveguides, resonantcavities, optical filtering, finite difference time domain,plane wave expansion.

Photonic crystals (PhCs) are periodic dielectric structures that exhibit a photonic bandgap, i.e., a range of wavelength for which light propagation is forbidden. The special band structure related dispersion properties offer a realm of novel functionalities and interesting physical phenomena. PhCs have been manufactured using semiconductors and other material technologies. However, InP-based materials are the main choice for active devices at optical communication wavelengths. This thesis focuses on two-dimensional PhCs in the InP/GaInAsP/InP material system and addresses their fabrication technology and their physical properties covering both material issues and light propagation aspects. Ar/Cl2 chemically assisted ion beam etching was used to etch the photonic crystals. The etching characteristics including feature size dependent etching phenomena were experimentally determined and the underlying etching mechanisms are explained. For the etched PhC holes, aspect ratios around 20 were achieved, with a maximum etch depth of 5 microns for a hole diameter of 300 nm. Optical losses in photonic crystal devices were addressed both in terms of vertical confinement and hole shape and depth. The work also demonstrated that dry etching has a major impact on the properties of the photonic crystal material. The surface Fermi level at the etched hole sidewalls was found to be pinned at 0.12 eV below the conduction band minimum. This is shown to have important consequences on carrier transport. It is also found that, for an InGaAsP quantum well, the surface recombination velocity increases (non-linearly) by more than one order of magnitude as the etch duration is increased, providing evidence for accumulation of sidewall damage. A model based on sputtering theory is developed to qualitatively explain the development of damage. The physics of dispersive phenomena in PhC structures is investigated experimentally and theoretically. Negative refraction was experimentally demonstrated at optical wavelengths, and applied for light focusing. Fourier optics was used to experimentally explore the issue of coupling to Bloch modes inside the PhC slab and to experimentally determine the curvature of the band structure. Finally, dispersive phenomena were used in coupled-cavity waveguides to achieve a slow light regime with a group index of more than 180 and a group velocity dispersion up to 10^7 times that of a conventional fiber. / QC 20100712

<p>Photonic crystals (PhCs) are structures periodic in thedielectric constant. They exhibit a photonic bandgap, i.e., arange of wavelengths for which light propagation is forbidden.Engineering of defects in the PhC lattice offers new ways toconfine and guide light. PhCs have been manufactured usingsemiconductors and other material technologies. This thesisfocuses on two-dimensional PhCs etched in InP-based materials.Only recently, such structures were identified as promisingcandidates for the realization of novel and advanced functionsfor optical communication applications.</p><p>The primary focus was on fabrication and characterization ofPhC structures in the InP/GaInAsP/InP material system. Thedemands on fabrication are very high: holes as small as100-300nm in diameter have to be etched at least as deep as 2µm. Thus, different etch processes had to be explored andspecifically developed for InP. We have implemented an etchingprocess based on Ar/Cl₂chemically assisted ion beam etching (CAIBE), thatrepresents the state of the art PhC etching in InP.</p><p>Different building blocks were manufactured using thisprocess. A transmission loss of 10dB/mm for a PhC waveguide, areflection of 96.5% for a 4-row mirror and a record qualityfactor of 310 for a 1D cavity were achieved for this materialsystem. With an etch depth of 4.5 µm, optical loss wasfound to be close to the intrinsic limit. PhC-based opticalfilters were demonstrated using (a) a Fabry-Pérot cavityinserted in a PhC waveguide and (b) a contra-directionalcoupler. Lag effect in CAIBE was utilized positively to realizehigh quality PhC taper sections. Using a PhC taper, a couplingefficiency of 70% was demonstrated from a standard ridgewaveguide to a single line defect PhC waveguide.</p><p>During the course of this work, InP membrane technology wasdeveloped and a Fabry-Pérot cavity with a quality factorof 3200 was demonstrated.</p><p><b>Keywords:</b>photonic crystals, photonic bandgap materials,indium phosphide, dry etching, chemically assisted ion beametching, reactive ion etching, electron beam lithography,photonic integrated circuits, optical waveguides, resonantcavities, optical filtering, finite difference time domain,plane wave expansion.</p>

Semiconductor quantum dots (QDs) are well established as sub-Poissonian sources of entangled photon pairs. To improve the utility of a QD light source, it would be advantageous to extend their emission further into the near infrared, into the low absorption wavelength windows utilised in long-haul optical telecommunication. Initial experiments succeeded in interfering O-band (1260—1360 nm) photons from an InAs/GaAs QD with dissimilar photons from a laser, an important mechanism for quantum teleportation. Interference visibilities as high as 60 ± 6 % were recorded, surpassing the 50 % threshold imposed by classical electrodynamics. Later, polarisation-entanglement of a similar QD was observed, with pairs of telecom-wavelength photons from the radiative cascade of the biexciton state exhibiting fidelities of 92.0 ± 0.2 % to the Bell state. Subsequently, an O-band telecom-wavelength quantum relay was realised. Again using an InAs/GaAs QD device, this represents the first implementation of a sub-Poissonian telecom-wavelength quantum relay, to the best knowledge of the author. The relay proved capable of implementing the famous four-state BB84 protocol, with a mean teleportation fidelity as high as 94.5 ± 2.2 %, which would contribute 0.385 secure bits per teleported qubit. After characterisation by way of quantum process tomography, the performance of the relay was also evaluated to be capable of implementing a six-state QKD protocol. In an effort to further extend the emitted light from a QD into the telecom C-band (1530—1565 nm), alternative material systems were investigated. InAs QDs on a substrate of InP were shown to emit much more readily in the fibre-telecom O- and C-bands than their InAs/GaAs counterparts, largely due to the reduced lattice mismatch between the QD and substrate for InAs/InP (~3 %) compared to InAs/GaAs (~7 %). Additionally, to minimize the fine structure splitting (FSS) of the exciton level, which deteriorates the observed polarisation-entanglement, a new mode of dot growth was investigated. Known as droplet epitaxy (D-E), QDs grown in this mode showed a fourfold reduction in the FSS compared to dots grown in the Stranski-Krastanow mode. This improvement would allow observation of polarisation-entanglement in the telecom C-band. In subsequent work performed by colleagues at the Toshiba Cambridge Research Labs, these D-E QDs were embedded in a p-i-n doped optical cavity, processed with electrical contacts, and found to emit entangled pairs of photons under electrical excitation. The work of this thesis provides considerable technological advances to the field of entangled-light sources, that in the near future may allow for deterministic quantum repeaters operating at megahertz rates, and in the further future could facilitate the distribution of coherent multipartite states across a distributed quantum network.

Orientador: Fernando Iikawa / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-21T01:34:49Z (GMT). No. of bitstreams: 1 Girardi_TiagoIllipronti_M.pdf: 2091533 bytes, checksum: 1e5e58f3f5149c97c47c1bf44b7aa186 (MD5) Previous issue date: 2012 / Resumo: Neste trabalho, estudamos o efeito de diferentes condições de interface de InP/GaAs nas propriedades ópticas de pontos quânticos auto-organizados, crescidos por epitaxia de feixe químico, no modo Stranskii-Krastanov. Espera-se que os pontos quânticos de InP/GaAs apresentem alinhamento de bandas do tipo II, e somente os elétrons ficam confinados, enquanto os buracos ficam localizados nas camadas de GaAs em volta do ponto quântico, atraídos pelo elétron. No entanto, devido ao efeito de mistura de átomos nas interfaces o perfil de potencial nas interfaces pode ser alterado significativamente, afetando, com isso, as propriedades ópticas dos pontos quânticos. Foram estudadas amostras com as seguintes condições de interface entre a camada de InP e as camadas de GaAs: inclusão ou não de uma camada de InGaP em uma ou nas duas interfaces. O InGaP gera uma barreira para ambos os tipos de portadores de carga em uma junção tanto com o GaAs como InP e evita a difusa de As das camadas de GaAs para a de InP. Através de medidas de fotoluminescência resolvida no tempo, observamos a variação do tempo de decaimento da emissão óptica associada aos pontos quânticos de acordo com as diferentes condições de interface. Foi observado um tempo curto de decaimento em amostras sem a inclusão de InGaP e com a inclusão apenas na interface superior, enquanto foi observado um tempo longo quando incluímos camadas de InGaP em ambas as interfaces. O tempo de decaimento curto é incompatível com o alinhamento de bandas do tipo II, que deveria separar espacialmente o elétron do buraco. A partir desses resultados e estudos anteriores a esse trabalho, pudemos concluir que o tempo curto se deve à mistura de átomos nas regiões de ambas as interfaces, gerando ligas que localizam os portadores próximos um ao outro. O tempo longo na amostra contendo InGaP nas duas interfaces é atribuído à separação espacial do elétron e do buraco. O efeito de mistura de átomos nas interfaces, neste caso, não forma uma liga na interface que localize os dois tipos de portadores próximos um ao outro. Isso pode ser uma alternativa de preparação de pontos quânticos de InP/GaAs onde se mantém separados espacialmente o elétron e o buraco / Abstract: We studied the effect of different interface conditions on the optical properties of InP/GaAs self-assembled quantum dots grown by chemical beam epitaxy in the Stranskii-Krastanov mode. InP/GaAs quantum dots is expected to present type II band alignment, and only electrons are confined, whereas the holes are localized in the GaAs layers around the quantum dot, attracted by the electron. However, due to the atomic intermixing effect in the interface the potential profile can be strongly changed, affecting the optical properties of the quantum dots. We studied samples with the following conditions at the interfaces between the InP layer and GaAs layers: the inclusion, or the lack of, a InGaP layer at one of or both interfaces. InGaP generates a barrier for both types of carriers in a junction with GaAs and InP, and avoid the diffusion of As from the GaAs layers to the InP one. Using time-resolved photo-luminescence, we observed a change of the optical emission decay times associated to the quantum dots as the interface condition is changed. We observed a short decay lifetime in samples without InGaP layers and with the inclusion in the top interface only, whereas we observed a long decay time when we included InGaP layers in both interfaces. The short decay lifetime is incompatible with the type II band alignment, where the electron and the hole should be spatially separated. Using these and other previous results, we concluded that the short decay lifetime is due to the atomic intermixing in both interfaces regions, forming alloys that localize the carriers near each other. The long lifetime observed for sample containing InGaP in both interfaces is attributed to the large electron-hole spatial separation. In this case intermixing effects at the interfaces do not form a potential well to localize the carries near each other / Mestrado / Física / Mestre em Física

La théorie, la conception, l'optimisation et la caractérisation d'amplificateurs distribués en technologie TBDH InP 0,7 µm, pour les systèmes de communications optiques à 100 Gbit/s, sont présentés. Nous montrons comment l'exploitation adaptée du concept d'amplificateur distribué avec une technologie de transistors bipolaires à produit vitesse-amplitude élevé a permis la réalisation d'un driver de modulateur électro-optique fournissant une amplitude différentielle d'attaque de 6,2 et 5,9 Vpp, à 100 et 112 Gbit/s, respectivement, avec une qualité de signal élevée. Ce circuit établit ainsi le record de produit vitesse-amplitude à 660 Gbit/s.V sur tranche et 575 Gbit/s.V en module hyperfréquence. Dans le cadre du projet Européen POLYSYS, il a été associé à un laser accordable et un modulateur pour la réalisation d'un module transmetteur optoélectronique compact, démontrant des performances avançant l'état de l'art des communications optiques courtes distances à 100 Gbit/s. / The theory, design, optimisation and characterisation of distributed amplifiers in 0.7-µm InP DHBT technology, for 100-Gbit/s optical communication systems, are presented. We show how the appropriate implementation of the distributed amplifier concept in a bipolar transistors technology with high swing-speed product has enabled the realisation of an electro-optic modulator driver with 6.2- and 5.9-Vpp differential driving amplitude at 100 and 112 Gb/s, respectively, with a high signal quality. This circuit thus establishes the swing-speed product record at 660 Gb/s.V on wafer and at 575 Gb/s.V in a microwave module. In the frame of the European project POLYSYS, it has been co-packaged with a tunable laser and a modulator to realise a compact optoelectronic transmitter module, which has demonstrated performances advancing the state of the art of short reach 100-Gb/s optical communications.

This dissertation documents works on two projects, which are broadly related to photonic integration using III-V semiconductor platform for fiber-based optical communication. Our principal project aims to demonstrate continuous variable quantum key distribution (CV-QKD) with InP-based photonic integrated cir cuit at the 1550 nanometer of optical wavelength. CV QKD protocols, in which the key is encoded in the quadrature variables of light, has generated immense interest over the years because of its compatibility with the existing telecom infrastructure. In this thesis, we have proposed a design of a photonic inte grated circuit potentially capable of realizing this protocol with coherent states of light. From the practical perspective, we have basically designed an optical transmitter and an optical receiver capable of carrying out coherent communi cation via the optical fiber. Initially, we established a mathematical model of the transceiver system based on the optical transfer matrix of the foundry spe cific (Fraunhofer Heinrich Hertz Institute-Germany) building blocks. We have shown that our chip design is versatile in the sense that it can support multiple modulation schemes. Based on the mathematical model, we estimated the link budget to assess the feasibility of on-chip implementation of our protocol. Then we ran a circuit level simulation using the process design kit provided by our foundry to put our analysis on a better footing. The encouraging result from this step prompted us to generate the mask layout for our transceiver chips, which we eventually submitted to the foundry. The other project in the thesis grew out of a collaboration with one of our industry partners. The goal of the project is to enhance the performance of a distributed feedback laser emitting at the 1310 nanometer of optical wavelength by optimizing its design. To that end, we first derived the expression for transmission and reflection spectrum for the laser cavity. Those expressions contained parameters which needed to be obtained from the transverse and the longitudinal mode analysis of the laser. We performed the transverse mode analysis and the longitudinal mode analysis with commercially available numerical solvers. Those mode profiles critically depend on the grating physical parameters. Therefore by tweaking grating dimensions one can control the transmission characteristics of the laser.