Retour au site du LAAS-CNRS

Laboratoire d’analyse et d’architecture des systèmes
Choisir la langue : FR | EN

575documents trouvés

17446
11/12/2017

Reconfigurable grounded vector antenna for 3D electromagnetic direction finding applications

J.DUPLOUY, C.MORLAAS, H.AUBERT, P.POULIGUEN, P.POTIER, C.DJOMA

MINC, ENAC, DGA, Bruz

Revue Scientifique : IEEE Antennas and Wireless Propagation Letters, 4p., Décembre 2017, DOI 10.1109/LAWP.2017.2779878 , N° 17446

Lien : https://hal-enac.archives-ouvertes.fr/hal-01658238

Diffusable

Plus d'informations

Abstract

In this letter, a reconfigurable grounded wideband antenna is proposed in view of vector sensor applications. This antenna combines two orthogonal and colocated semi-circular arrays of Vivaldi antennas mounted over a metallic support. The radiation patterns of two wideband magnetic dipoles and one wideband electric dipole can be synthesized thanks to an appropriate antenna excitation. Measurement results are in good agreement with the simulated results obtained from full-wave electromagnetic simulations. The proposed antenna exhibits stable radiation patterns over a wide impedance bandwidth of 1.69:1, a high radiation efficiency and a good isolation between the antenna input ports. This antenna is a good candidate for wideband 3D direction finding using a vector sensor.

141719
17468
08/12/2017

Conception et analyse de micro-résonateurs opt iques pour la générat ion de peignes de fréquences

C.ARLOTTI

PHOTO

Doctorat : Université de Toulouse III - Paul Sabatier, 8 Décembre 2017, 156p., Président:P.ARGUEL, Rapporteurs: P.FERON, R.OROBTCHOUK, Examinateurs: N.BELABAS, Directeurs de thèse: S.CALVEZ, G.ALMUNEAU , N° 17468

Diffusable

Plus d'informations

Abstract

Whispering-gallery –mode micro-resonators, whether in the form of disks, rings or racetracks, have become the key building blocks of many high-performance photonic components. The embodiments exploiting the III-V semiconductors are particularly attractive for they open the possibility of integrating active and passive sections together and therefore diversify the functionalities on the same photonic chip. Furthermore, the vertical integration of the resonator above its access waveguide(s) makes it possible to distribute the active and passive functions on distinct planes and makes the realization of the components easier by using better-controlled methods. A fabrication technique recently introduced in the team and based on the AlGaAs / AlOx technological platform, allowed us to realize, by means of simple steps, vertically-coupled microdisks. The performance of these components, however, is limited due to their architecture, complicated by their constitutive multilayer stack. The research carried out during this PhD thesis focused on the feasibility of emitting an optical frequency comb from these resonators. For this purpose, the components must be designed so as to present a sufficiently high quality factor while maximizing the power circulating in the cavity in order to be able to trigger the non-linear processes required for the comb generation. For a transverse singlemode component, the intracavity power is maximal when the system operates in critical coupling regime, i.e .when the losses inside the cavity are equal to external losses (or coupling losses). As a first step, we have developed a semi-analytical tool based on a modal expansion in order to carry out a broadband parametric study of the performances of vertically coupled systems. Up to now, this coupling layout has indeed been little studied, both theoretically and practically. Our generic model, based on the coupled mode theory (CMT) and the universal relations governing the spectral properties of coupled micro-resonators, reveals two theoretical conditions for obtaining an achromatic critical-coupling regime when the cavity and its access waveguide are phase-mismatched. We first applied it to the simulation of single-mode racetrack resonators made of Si3N4 / SiO2 since several studies have already demonstrated comb generation using this technological platform. Our work resulted in the design of phase-mismatched and technologically feasible structures with criticalcopuling bandwidths being increased by one order of magnitude compared to the reference case of phase-matched waveguides. We subsequently initiated a numerical evaluation of frequency comb generation, based on the iterative resolution of the non-linear Schrödinger equation taking into account the variations of the spectral and dispersive properties of these racetracks. The generic model has finally been applied to AlGaAs / AlOx microdisks. For this purpose, we have introduced a criterion allowing an unambiguous implementation of CMT in the case of asymmetric couplers having a multi-layer separation zone. The results, in good agreement with experimental data, allowed us to better understand the limitations of the fabricated devices and to propose new structures AlGaAs / AlOx with improved performances. The experimental validation of the proposed designs for both the Si3N4 / SiO2 and AlGaAs / AlOx components is currently in progress.

Résumé

Les micro-résonateurs à modes de galerie, qu’ils soient déclinés sous forme de disques, anneaux ou hippodromes, sont devenus les éléments constitutifs clés de nombreux composants photoniques de haute performance. Les réalisations exploitant les semiconducteurs III-V sont particulièrement attrayantes car elles ouvrent la possibilité d’intégrer conjointement des sections actives et passives et donc de diversifier les fonctionnalités sur une même puce photonique. Au niveau technologique, l’intégration verticale du résonateur au-dessus de ses guides d’accès permet de distribuer les fonctions actives et passives sur des plans distincts et de faciliter la réalisation des composants grâce à des procédés mieux maitrisés. Une technique de fabrication récemment introduite dans l’équipe et basée sur la filière AlGaAs/AlOx a ainsi permis de réaliser, à l’aide d’étapes simples, des micro-disques couplés verticalement à leur guide d’accès. Les performances de ces composants restent toutefois limitées en raison de leur architecture, complexifiée par les empilements multicouches qui les constituent. Les travaux de recherche menés au cours de cette thèse ont porté sur la faisabilité d’émettre un peigne de fréquences optiques à partir de ces résonateurs. Pour cela, les composants doivent être conçus de manière à présenter un facteur de qualité suffisamment élevé tout en maximisant la puissance circulant dans la cavité, afin de pouvoir déclencher les processus non-linéaires à la base de la génération du peigne. Pour un composant monomode transverse, la puissance intracavité est maximale lorsque le système opère en régime de couplage critique, c’est-à-dire lorsque les pertes internes à la cavité sont égales aux pertes externes (ou pertes par couplage). Nous avons donc développé un outil semi-analytique basé sur une expansion modale afin de réaliser une modélisation paramétrique large bande des performances des systèmes couplés verticalement, encore peu étudiés, tant au plan théorique que pratique. Notre modèle générique exploite la théorie des modes couplés (CMT) et les relations universelles régissant les propriétés spectrales des micro-résonateurs couplés. Nous l’avons étendu en étudiant l’influence spectrale de différents paramètres opto-géométriques sur la fonction de transfert de la cavité couplée et avons, en particulier, mis en évidence par une approche variationnelle, deux conditions théoriques permettant d’obtenir un régime critique achromatique lorsque la cavité et son guide d’accès sont désaccordés en phase. Ce modèle à d’abord été appliqué à la simulation de résonateurs en hippodromes exploitant la filière Si3N4/SiO2 car plusieurs études ont déjà démontré la génération de peignes avec cette plateforme technologique. Ces travaux ont abouti au dessin de structures désaccordées en phase et technologiquement réalisables dont la bande passante critique est augmentée d’un ordre de grandeur par rapport au cas plus répandu de guides accordés en phase. Nous avons ensuite initié une évaluation numérique de la génération de peignes de fréquences, basée sur la résolution itérative de l’équation de Schrödinger non-linéaire prenant en compte les variations des propriétés spectrales et dispersives de ces hippodromes. Le modèle générique a enfin été appliqué aux micro-disques AlGaAs/AlOx. Pour cela, nous avons introduit un critère permettant d’utiliser la CMT dans le cas de coupleurs asymétriques présentant une zone de séparation multicouche. Les résultats, en bon accord avec l’expérience, nous ont permis de mieux appréhender les limitations des dispositifs réalisés et de proposer de nouvelles structures pour en améliorer les performances. Le dessin d’une nouvelle structure AlGaAs/AlOx multicouche permettant d’améliorer les facteurs de qualité des résonateurs jusqu’à deux ordres de grandeurs a ainsi été proposé. La validation expérimentale des dessins proposés tant pour la filière Si3N4/SiO2 que AlGaAs/AlOx est en cours.

141873
17462
01/12/2017

Lithographie par nanoimpression pour la fabrication de filtres à réseaux résonants en cavité

S.AUGÉ

PHOTO

Doctorat : 1er Décembre 2017, 192p., Président: P.ARGUEL, Rapporteurs: J.BOUSSEY, Y.JOURLIN, Examinateurs: V.YAM, Directeurs de thèse: O.GAUTHIER LAFAYE, A.MONMAYRANT , N° 17462

Diffusable

Plus d'informations

Abstract

Cavity resonator integrated grating filters (CRIGFs) are a new generation of nanostructured reflective filters. They present a strong interest for many applications. However, their manufacturing is relatively complex: CRIGFs are components structured at small scales compared to the wavelength of interest but on a relatively large area. They are usually made by electron beam lithography technique which presents a sufficient resolution but does not allow parallel patterning and is thereby time consuming for large area components. Furthermore, CRIGFs are often fabricated on insulating wafers which make the e-beam lithography process more complicated. In this PhD, a CRIGF process manufacturing has been implemented through soft mold nanoimprint lithography (SNIL). This high throughput collective technology keeps the benefits of the traditional electron beam lithography while overcoming its limits. Nano-scale patterns can be made by a simple stamping under UV exposure of a soft mold on a polymer resist layer. After stabilizing the process and assessing the technique limits, plenty of CRIGFs have been manufactured. They exhibit optical performances in the near-infrared range equivalent to those manufactured by e-beam lithography. Secondly, it has been demonstrated that the implemented process is generic. We have shown the possibility to overcome the usual design trade-offs by structuring directly the waveguide, before embedding. Moreover, this same process has been shown to be applied in a straightforward way to fabricate CRIGFS in the mid-infrared range using a III-V crystalline material and micrometric sized patterns. Finally, we have demonstrated the great flexibility and sustainability of the process by testing different potential geometries of CRIGFs. Notably, we have designed a CRIGF with a period gradient leading to the first tunable CRIGF ever demonstrated. Lastly, we have evaluated the potential manufacturing of complex CRIGFs with several corrugation levels.

Résumé

Les filtres CRIGFs sont une nouvelle génération de filtres optiques réflectifs nanostructurés qui présentent un très fort intérêt pour de nombreuses applications. Cependant, leur fabrication est relativement complexe : il s’agit de composants structurés à des échelles petites devant la longueur d’onde d’utilisation, mais de surface totale relativement grande. Ils sont usuellement fabriqués en utilisant des procédés de lithographie de type lithographie électronique, qui présente une résolution suffisante mais qui est séquentielle et donc lente pour de telles surfaces de composant. En outre, les CRIGFs sont souvent réalisés sur des substrats isolants, ce qui complexifie encore plus l’utilisation de cette lithographie. Lors de cette thèse, un procédé de fabrication des CRIGFs a été développé à partir de la lithographie par nanoimpression via moule souple (SNIL). Cette technologie collective et à haut rendement contourne les inconvénients et garde les avantages de la traditionnelle lithographie électronique. Elle permet de fabriquer des motifs nanométriques par simple pressage d’un moule souple sur une couche de résine de polymères sous insolation d’ultraviolets. Après avoir stabilisé le procédé et établi les limites de la technologie, de nombreux filtres CRIGFs ont ainsi été créés. Ils présentent des résultats optiques équivalents dans le proche infrarouge (NIR) à ceux fabriqués par lithographie électronique. Dans un deuxième temps, le caractère générique du procédé mis en place a été démontré de plusieurs façons. Premièrement, nous avons montré qu’il était possible à l’aide de celui-ci de dépasser les compromis usuels de conception en structurant directement le guide d’onde, qui sera ensuite ré-encapsulé. Deuxièmement, nous avons montré que ce même procédé pouvait être directement transféré pour réaliser des filtres CRIGF dans la gamme du moyen infrarouge, bien que les filtres soient alors réalisés sur un matériau cristallin III-V et présentent des dimensions micrométriques plutôt que nanométriques. Enfin, nous avons démontré la grande souplesse et stabilité du procédé en l’utilisant pour explorer différentes géométries potentiellement intéressantes de cette nouvelle famille de filtres optiques nanostructurés. Nous avons notamment étudié des CRIGFs comportant un gradient de période qui ont permis pour la première fois d’obtenir un filtre CRIGF accordable. Pour finir, nous nous sommes attachés à étudier le potentiel de réalisation de filtres CRIGFs plus complexes et présentant plusieurs niveaux de corrugation.

Mots-Clés / Keywords
Nanoimpression; filtre à réseaux; lithographie à haute résolution; SNIL; CRIGF; Nanoimprint; Grating filter; High resolution lithography;

141853
17386
01/11/2017

Achromatic critically coupled racetrack resonators

C.ARLOTTI, O.GAUTHIER-LAFAYE, A.MONMAYRANT, S.CALVEZ

PHOTO

Revue Scientifique : Journal of the Optical Society of America. B, Optical physics, Vol.34, N°11, pp.2343-2351, Novembre 2017 , N° 17386

Lien : https://hal.laas.fr/hal-01619015

Diffusable

Plus d'informations

Abstract

In this paper, we investigate the spectral response of whispering-gallery-mode (WGM) resonators coupled to their access waveguide with a view to design their constitutive waveguides to promote critical-coupling over a wide spectral range and thereby facilitate their use for high-sensitivity sensing or nonlinear frequency conversion applications. The carried-out theoretical analysis is based on the universal response functions of singlemode and unidirectional devices. A coupled-mode treatment of the coupling region enables to derive two sets of favorable designs. The identified resonator/access waveguide systems exploit waveguides with mismatched propagation constants forming a coupling section exhibiting either an achromatic beat-length or an achromatic power-transfer coefficient. This generic model is followed by a numerical case study of vertically-coupled Si3N4 racetrack resonators. The conventional (quasi-)phase-matched configuration, treated as a reference case, is shown to display a critical-coupling bandwidth of 23 nm at a wavelength of 1550nm, whereas the proposed new designs demonstrate critical bandwidths larger than 330nm, i.e. exhibit bandwidths enhanced by more than one order of magnitude.

141321
17396
31/10/2017

Electromodulation spectroscopy of strain related shifts and pressure coefficients for heavy-hole, light-hole, and spin-orbit transitions in GaAsBi layers grown on GaAs

F.DYBALA, J.KOPACZEK, E.M.PAVELESCU, C.ROMANITAN, O.LIGOR, A.ARNOULT, C.FONTAINE, R.KUDRAWIEC

Wroclaw University, IMT, TEAM, PHOTO

Rapport LAAS N°17396, Octobre 2017, 24p.

Non diffusable

141373
17401
31/10/2017

Integration of electro-absorption modulator in a vertical-cavity surface-emitting laser

L.MARIGO-LOMBART, S.CALVEZ, A.ARNOULT, A.RUMEAU, C.VIALLON, H.THIENPONT, K.PANAJOTOV, G.ALMUNEAU

PHOTO, TEAM, I2C, MOST, Bruxelles

Rapport LAAS N°17401, Octobre 2017

Lien : https://hal.laas.fr/hal-01614811

Diffusable

Plus d'informations

Abstract

VCSELs became dominant laser sources in many short optical link applications such as datacenter, active cables, etc. Actual standards and commercialized VCSEL are providing 25 Gb/s data rates, but new solutions are expected to settle the next device generation enabling 100 Gb/s. Directly modulated VCSEL have been extensively studied and improved to reach bandwidths in the range of 26-32 GHz [Chalmers, TU Berlin], however at the price of increased applied current and thus reduced device lifetime. Furthermore, the relaxation oscillation limit still subsists with this solution. Thus, splitting the emission and the modulation functions as done with DFB lasers is a very promising alternative [TI-Tech, TU Berlin]. Here, we study the vertical integration of an Electro-Absorption Modulator (EAM) within a VCSEL, where the output light of the VCSEL is modulated through the EAM section. In our original design, we finely optimized the EAM design to maximize the modulation depth by implementing perturbative Quantum Confined Stark Effect (QCSE) calculations, while designing the vertical integration of the EAM without penalty on the VCSEL static performances. We will present the different fabricated vertical structures, as well as the experimental electrical and optical static measurements for those configurations demonstrating a very good agreement with the reflectivity and absorption simulations obtained for both the VCSEL and the EAM-VCSEL structures. Finally, to reach very high frequency modulation we studied the BCB electrical properties up to 110 GHz and investigated coplanar and microstrip lines access to decrease both the parasitic capacitance and the influence of the substrate. 100 words: In this presentation, we describe the operation of Multiple-Quantum-Wells Asymmetric Fabry-Perot modulator, vertically integrated into a VCSEL structure for high-speed modulation. First we optimize the Electro-Absorptive Modulator (EAM) and the EAM-VCSEL structures by utilizing a perturbative quantum-confined Stark-effect and transfer matrix calculations. Then we present experimental reflectivity, LIV curves and photocurrent measurements and demonstrate very good agreement with our modelling results. High frequency measurements of BCB electrical response up to 110 GHz are carried out to estimate the parasitic effects due to the pad configuration and the impact of the substrate.

141379
17336
26/10/2017

Phase noise study based on transfer function in coupled optoelectronic oscillators

R.KHAYATZADEH, V.AUROUX, G.BAILLY, A.FERNANDEZ , O.LLOPIS

MOST, I2C

Manifestation avec acte : International Topical Meeting on Microwave Photonics ( MWP ) 2017 du 23 octobre au 26 octobre 2017, Beijing (Chine), Octobre 2017, 4p. , N° 17336

Lien : https://hal.laas.fr/hal-01587950

Diffusable

Plus d'informations

Abstract

In this paper, the transfer function theory is used to model the phase noise power spectral density in coupled optoelectronic oscillators. A resonator is placed into the model in order to take into account the quality factor (Q) enhancement due to the optical loop. The results of this model are then compared with experimental measurement results. The model is able to describe the phase noise spectrum shape and to give indications on the noise contributors, which helps in improving oscillator's performance.

141077
17383
23/10/2017

Analysis and implementation of a direct phase unwrapping method for displacement measurement using self-mixing interferometry

A.EHTESHAM, U.ZABIT, O.BERNAL, G.RAJA, T.BOSCH

Riphah, OSE, UETTAXILA

Revue Scientifique : IEEE Sensors Journal, 10p., Octobre 2017, DOI 10.1109/JSEN.2017.2758440 , N° 17383

Lien : https://hal.archives-ouvertes.fr/hal-01617743

Diffusable

Plus d'informations

Abstract

Self-Mixing (SM) or optical feedback interferometry has been widely used for displacement and velocity measurement applications. For metric information retrieval with < λ/2 precision, various phase unwrapping methods have been proposed. However, these are computationally heavy and require large number of hardware resources, thereby hindering the development of real-time, embedded solutions for large bandwidth applications. In this regard, a simple and efficient feedback phase retrieval algorithm, called Consecutive Samples based Unwrapping (CSU) is presented. Detailed analysis of its error performance has been conducted as a function of key optical feedback parameters. A theoretical study has also been conducted to explain as to why such good error performance is obtained for such a simple algorithm by establishing a linear relation between the modulated laser power signal and the laser phase in the absence of optical feedback for specific ranges of key optical feedback parameters. We applied CSU on various simulated and experimentally acquired signals using SMI for the retrieval of harmonic and arbitrary displacements and found out that CSU retrieves target displacement with a precision of about λ/10 while consuming much less time and hardware resources. The paper also presents FPGA based hardware design results of CSU and compares its performance with a traditional analytical phase unwrapping method in terms of maximum clock frequency, latency, and on-chip hardware resources. This hardware comparison strongly establishes the advantages of such a fast and computationally light algorithm, readily suitable for large bandwidth, embedded, real-time sensing applications.

141316
17379
20/10/2017

Oxide-confined VCSELs fabricated with a simple self-aligned process flow

L.MARIGO-LOMBART, S.CALVEZ, A.ARNOULT, H.THIENPONT, K.PANAJOTOV, G.ALMUNEAU

PHOTO, TEAM, Bruxelles

Revue Scientifique : Semiconductor Science and Technology, 5p., Octobre 2017, DOI 10.1088/1361-6641/aa90ae , N° 17379

Lien : https://hal.laas.fr/hal-01614784

Diffusable

Plus d'informations

Abstract

We propose a simplified and easier fabrication process flow for the manufacturing of AlOx-confined VCSELs based on combining the oxidation step with a self-aligned process, allowing the mesa etching and two successive lift-off steps based on a single lithography step. The electro-optical confinement achieved by standard lateral oxidation enables a low threshold and a single mode behaviour for the VCSEL. This simplified process can largely improve VCSEL manufacturing by reducing the processing time and costs compared to the standard VCSEL process. Introduction: Vertical-cavity surface-emitting lasers (VCSEL) have become the preferred light sources in many photonic systems, enabling short-link interconnections [1] but also in other emerging mass-market applications like sensing and detection [2]. The large production volume of VCSELs would benefit from a simplification of the manufacturing process flow that may largely increase the cost-effectiveness. Indeed, compared to the LED and LDs, the VCSEL fabrication process flow requires a large number of elementary steps defined by successive inter-aligned photolithography levels. A precision in the micron range is required to ensure the lateral alignment between the optical waveguide and the electrical injection. For these reasons, one of the most important concerns for the VCSEL manufacturers is to improve the production throughput by lowering the fabrication time and cost per wafer. The development of a self-aligned process is of great interest as already demonstrated for the fabrication of high performance HBT transistors or ridge lasers [3,4]. To that extent, Al-Omari [5] used a top metallic contact deposited over a photoresist layer as a hard mask to dry-etch the VCSEL mesa. Chua [6] developed a pseudo-planar approach by opening via holes down to the AlAs layer to carry out the lateral oxidation. This process has subsequently been improved by Strzelecka [7] to increase the device density. Recently, we have shown that air-post VCSELs could be created using an innovative self-aligned process, which combined several masking and lift-off steps defined by a single lithographic step [8]. In this paper, we extend this work and propose a new process flow to fabricate, in a very simple and straightforward way, the widely-used oxide-confined VCSELs. The demonstrated process drastically simplifies the oxide-confined VCSEL fabrication by reducing the total number of lithographic alignment steps from four or more to only one alignment, with the additional advantage of relieving the required tolerances. This process flow, most suitable for 3D imaging and sensing applications, can also be easily implemented for the fabrication of other optoelectronic devices such as modulators, ridge waveguide lasers, detectors, solar cells or any process combining dry etch, passivation and metallization.

141294
17476
14/10/2017

Ultra-low power IR-UWB transceiver for wireless sensors network

B.BENAMROUCHE, A.RUMEAU, D.DRAGOMIRESCU

MINC, I2C

Manifestation avec acte : International Semiconductor Conference ( CAS ) 2017 du 11 octobre au 14 octobre 2017, Sinaia (Roumanie), Octobre 2017, 4p. , N° 17476

Diffusable

Plus d'informations

Abstract

This paper presents a new transceiver for impulse radio ultra-wideband (IR-UWB) systems. This work is related to CHIST-ERA SMARTER project (Smart Multifunctional Architecture and Technology for Energy aware wireless sensoRs) which address autonomous wireless sensors nodes. The ultra low-power transceiver consists of an on-off keying (OOK) modulator/demodulator and a pulse generator. To reduce power consumption a solution based on clock gating technology has been implemented. The clock gating solution allowed us to divide by almost two the power consumption. A first prototype was developed on FPGA to prove the transceiver functionalities. The second prototype is an ASIC in ST Microelectronics 65nm CMOS technology designed using clock gating technology for ultra-low power purpose.

142035
Les informations recueillies font l’objet d’un traitement informatique destiné à des statistiques d'utilisation du formulaire de recherche dans la base de données des publications scientifiques. Les destinataires des données sont : le service de documentation du LAAS.Conformément à la loi « informatique et libertés » du 6 janvier 1978 modifiée en 2004, vous bénéficiez d’un droit d’accès et de rectification aux informations qui vous concernent, que vous pouvez exercer en vous adressant à
Pour recevoir une copie des documents, contacter doc@laas.fr en mentionnant le n° de rapport LAAS et votre adresse postale. Signalez tout problème de dysfonctionnement à sysadmin@laas.fr. http://www.laas.fr/pulman/pulman-isens/web/app.php/