Laboratoire d’analyse et d’architecture des systèmes
C.ARLOTTI, O.GAUTHIER-LAFAYE, A.MONMAYRANT, S.CALVEZ
Revue Scientifique : Journal of the Optical Society of America. B, Optical physics, Vol.34, N°11, pp.2343-2351, Novembre 2017 , N° 17386
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.
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
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.
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.
R.KHAYATZADEH, V.AUROUX, G.BAILLY, A.FERNANDEZ , O.LLOPIS
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
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.
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
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.
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
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  but also in other emerging mass-market applications like sensing and detection . 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  used a top metallic contact deposited over a photoresist layer as a hard mask to dry-etch the VCSEL mesa. Chua  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  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 . 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.
C.ARENAS BUENDIA, J.PHILIPPE, D.HENRY, A.RUMEAU, H.AUBERT, P.PONS
Manifestation avec acte : European Microwave Week ( EuMW ) 2017 du 08 octobre au 13 octobre 2017, Nuremberg (Allemagne), Octobre 2017, 5p. , N° 17268
This communication reports the first experimental results obtained from new type of passive Hydrogen-Pressure Dosimeters for the remote measurement of nuclear radiation. Technological and experimental analyses are performed here to demonstrate the proof-of-concept. Radar measurements of irradiated and non-irradiated passive dosimeters are also reported and confirm the feasibility of the remote reading of such passive sensors. A new design is proposed for minimizing the impact of technological inaccuracies on sensors performances and for facilitating the packaging.
H.AUBERT, D.HENRY, P.PONS
Conférence invitée : IEEE Nanotechnology Materials and Devices Conference ( IEEE NMDC ) 2017 du 02 octobre au 04 octobre 2017, Singapour (Singapour), Octobre 2017, 1p. , N° 17344
The remote measurement of physical or chemical quantities from the wireless reading of active electronic devices with integrated sensors is no more a major issue. Such devices with sensing, identification and communication capabilities can be used as nodes of a network and, more generally, part of the Internet of Things. Passive (batteryless) sensors could be used as sensing nodes in order to ensure unlimited energy autonomy, long-term measurement stability, low-cost of fabrication and operability in harsh or severe environments. However the interrogation range achievable by passive RFID sensors does not exceed 20 meters in harsh and/or highly reflective environments. An alternative solution to RFID sensors technology will be presented at the conference. It consists of applying an active millimeter-wave radar imaging technique to the detection and long-range reading of passive sensors. The use of millimeter-waves frequency for the wireless interrogation of sensors rather than lower frequency offers many advantages, such as, higher electrical length separation distances to objects located around the sensors, higher robustness to multi-paths, smaller sensors and reader antenna sizes, higher frequency bandwidth and compact design for beamforming, multi-beam or beam-steering Radar reader. The first part of the presentation will be devoted to the technology used by the authors and his collaborators at LAAS-CNRS, Toulouse, France, for fabricating miniaturized millimeter-wave passive sensors. Some recent sensors based on MEMS, microfluidic and/or ink-jet printing technologies will be presented. Next an active radar imaging technique will be reported for the long-range reading (up to 50 meters) of these passive millimeter-wave sensors. It consists of performing the beam scanning of the radar main lobe and/or translating the radar for illuminating the scene incorporating the sensors at different angles in order to obtain a 3D radar image. Statistical estimators are then computed from this image for remotely deriving the physical quantity of interest. Very recent results will be reported and discussed at the conference. The technical challenges and possible solutions regarding the fabrication of miniaturized and wireless passive sensors will also be presented.
K.LOUARN, Y.CLAVEAU, A.ARNOULT, C.FONTAINE, J.COLIN, C.CORNILLE, I.MASSIOT, L.MARIGO-LOMBART, F.PIQUEMAL, A.BOUNOUH, N.CAVASSILAS, G.ALMUNEAU
PHOTO, IM2NP, TEAM, LNE, CEA LIST
Manifestation avec acte : Réunion plénière du GDR PULSE ( ) 2017 du 02 octobre au 05 octobre 2017, Paris (France), Octobre 2017, 3p. , N° 17382
Les Jonctions Tunnel (JT) sont des composants très importants pour les cellules solaires multi-jonction, puisqu'elles assurent la connexion électrique en série entre les différentes sous-cellules. Récemment, il a été fabriqué par EPVOM des JTs AlGaAs:C/GaAs:Te et AlGaAs:C/GaInP:Te atteignant des densités de courant pic J pic records de 10 kA/cm² sur substrat GaAs , en remplaçant le dopant N usuel Si par du Te et permettant ainsi d'obtenir les forts niveaux de dopages nécessaires pour augmenter la probabilité d'effet tunnel dans le composant. Nous avons travaillé sur une autre approche pour obtenir des JT de "hautes" performances, et ne nécessitant pas des dopages aussi forts : il s'agit de profiter des offsets de bandes de l'hétérojonction AlGaAsSb/AlGaInAs de type II pour augmenter la probabilité d'effet tunnel.
K.LOUARN, Y.CLAVEAU, A.ARNOULT, C.FONTAINE, J.COLIN, C.CORNILLE, F.PIQUEMAL, A.BOUNOUH, N.CAVASSILAS, G.ALMUNEAU
PHOTO, IM2NP, TEAM, LNE, CEA LIST
Manifestation avec acte : European Photovoltaic Solar Energy Conference and Exhibition ( EU PVSEC ) 2017 du 25 septembre au 29 septembre 2017, Amsterdam (Pays-Bas), Septembre 2017 , N° 17391
Aim and approach-Tunnel Junctions (TJs) are key devices for monolithic Multi-Junction Solar Cells (MJSCs), in which they ensure the series interconnection between the subcells. For GaAs based MJSCs, very low resistive (with peak tunneling current density J peak up to 10 kA/cm²) AlGaAs:C/GaInP:Te or AlGaAs:C/GaAs:Te have been recently developed by MOVPE using Te instead of Si as N-dopant making it possible to get the heavily doping levels needed for tunneling optimization . In this work, we investigate an alternative to this approach. The tunneling probability is increased through the engineering of band-offset thanks to the use of a type II (Al)GaAsSb/(Al)InGaAs staggered heterojunction. Such TJs are suitable for both lattice-matched and metamorphic MJSCs. Scientific innovation and relevance – MBE was used to grow pseudomorphic and metamorphic (Al)GaAsSb/(Al)InGaAs TJs (5% to 10 % In and Sb contents) on GaAs substrate, where Aluminium enables to limit light absorption in the TJ. We have experimentally and theoretically investigated the role of the layer thicknesses on the tunneling mechanisms to propose TJ heterostructure designs suitable for lattice-matched MJSCs and metamorphic MJSCs. Preliminary results and conclusions-For relatively thin [10 to 30 nm] type II TJs, the incorporation of Sb/In in the GaAs TJ is actually degrading the electrical performances, with J peak decreasing from 180 A/cm² for simple GaAs TJ to 70 A/cm² for GaAs 0.95 Sb 0.05 /In 0.05 Ga 0.95 As TJs. On the other hand, thicker 100 nm (Al)GaASb/(Al)InGaAs TJs present the expected tunneling current density increase with J peak close to 1000 A/cm². It worths to note that such thick TJs lead to strain/relaxation issues that could be detrimental for lattice-matched MJSCs but beneficial for metamorphic MJSCs. The origin of this difference in behavior is under investigation both using a semi-classical model  and a Non Equilibrium Green's Function based quantum model . First simulations suggest that it originates from a balance between quantum confinement and type II-related tunneling probability enhancement. Based on these results, we are developing GaAs/InGaAs/GaAsSb/GaAs TJs suitable for lattice-matched MJSCs with preliminary measurements showing a thousand-fold increase of the peak tunneling current. Complementary, we are studying the relaxation mechanisms of (Al)Ga(In)As(Sb) alloys using in-situ MBE stress measurements in order to optimize the growth of metamorphic (Al)GaAsSb/(Al)InGaAs TJs.