PhD defense

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    (in french)

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Alisier PARIS

    Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau

    PhD defense

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    (in french)

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Pierre BONNET

    Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau

    PhD defense

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    (in french)

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Émile SIVRÉ

    Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau

    PhD defense

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    (in french)

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Sokhna Mery NGOM

    Centre de Nanosciences et de Nanotechnologies et ONERA, C2N, Palaiseau

    PhD defense

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    (in french)

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Dorian OSER

    Centre de Nanosciences et de Nanotechnologies et ONERA, C2N, Palaiseau

    PhD defense

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    (in french)

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Ludivine EMERIC

    Centre de Nanosciences et de Nanotechnologies et ONERA, C2N, ONERA, Palaiseau

    PhD defense

    Jury members :

    Agnès Maître Institut des NanoSciences de Paris, Rapporteur

    Nicolas Bonod Institut Fresnel, Rapporteur

    Jean-Jacques Greffet Laboratoire Charles Fabry, Institut d’Optique, Examinateur

    Yannick De Wilde Institut Langevin, Examinateur

    Elizabeth Boer-Duchemin Institut des Sciences Moléculaires d’Orsay, Examinatrice

    Jean-Luc Pelouard C2N, Directeur de thèse

    Claire Deeb Almae Technologies & C2N, Co-directrice de thèse

    Riad Haïdar ONERA, Invité

    The great concentration of light-matter interaction inside optical nanoresonators achieving a strong confinement of electromagnetic field in a nanometric space paves the way toward innovative applications in the infrared domain, in optics, optoelectronics, chemistry or biology. Resonators constituted of a stack of metal, insulator and metal allow to achieve stronger confinement for thinner insulator gap. However, in case of a gap thinner than a few nanometers, electrons have a non-negligible probability to pass from a metal to the other by tunneling effect. Questioning electrons description in classical theory, this quantum effect has been highlighted and studied in various kinds of nanogap optical antennas: between an AFM tip and a substrate, between two nanoparticles, inside a metallic constriction…

    In this thesis, we have used a MIM nanoresonator: stacking solid layers allows a good control of its geometry and its evolution over time. This structure has two roles: accessing quantitatively the underlying physics and testing its potential application. Nanofabrication processes have been specifically developed and validated by optical and electrical characterizations of nanoresonators. In the quantum domain, measured reflectivity spectra cannot be explained by a widespread approach introducing an electrical conduction inside the insulator. Furthermore, the measured shift under an electrical bias is weak (δλ/(λV2) ≈ 3×10-2V-2) and opposite to literature predictions. These results highlight unexplained behaviors and paves the way to new researches about nanogap optical antennas.

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    Metasurfaces for bioimaging

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Antu GORTARI

    Centre de Nanosciences et de Nanotechnologies et ONERA, C2N, Palaiseau

    PhD defense

    Alejandro GIACOMOTTI, Chargé de Recherche, Center Nanosciences Et Nanotechnologies - CNRS, Directeur de thèse

    Gilles  TESSIER, Professeur des Universités, Université Paris Descartes, Institut de la Vision, Rapporteur

    Anne  SENTENAC, Directeur de Recherche, Institut Fresnel, Rapporteur

    Stéphanie  PITRE-CHAMPAGNAT, Chargé de Recherche, Imagerie par Resonance Magnetique Medicale et Multi-Modalites, Université Paris-Saclay, Examinateur

    Joerg  ENDERLEIN, Professeur des Universités, Georg August University of Göttingen III. Physical Institute Biophysics / Complex Systems, Examinateur

    Patrice  GENEVET, Directeur de Recherche, CRHEA, Examinateur

    Nathalie  WESTBROOK, Professeur des Universités, Institut d’Optique, Examinateur

    Sophie  BOUCHOULE, Directeur de Recherche, Center Nanosciences Et Nanotechnologies - CNRS, CoDirecteur de thèse

    In recent years there has been a significant effort to push electromagnetic metasurfaces with the ability to abruptly change light properties into visible wavelengths. These advancements have opened a new range of possibilities to reshape light using ultra-thin optical devices and there is one field that is starting to gather attention: bioimaging. One technique particularly well suited for the study of molecules near a cell membrane is Total Internal Reflection Fluorescence (TIRF) microscopy, which relies on an evanescence field created by light being totally internally reflected within a glass substrate due to its high incidence angle. As of today, TIRF is generally implemented using bulky high-NA, small field of view oil objectives.

    In this project we present the realization of metasurface-based TIRF microscopy substrates consisting of periodic 2D arrays of asymmetric structures fabricated in titanium dioxide on borosilicate glass. These patterns, as small as 48nm, were optimized through rigorous coupled-wave analysis to couple 50-90% of the incoming normally incident light into the first diffraction order, which outputs at an angle that suffices total internal reflection in water and eliminates the requirement for high NA objectives or prisms to achieve TIRF. Being able to utilize lower-magnification air objectives and having a large evanescence field area provide unique TIRF conditions not accessible by traditional methods. Additionally, these structures are compatible with soft UV nanoimprint lithography, for cost-effective scale production, to give TIRF’s high contrast, low photodamage and low photobleaching capabilities to inexpensive wide-field microscopes

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    Subwavelength engineering of silicon waveguides and cavities for nonlinear photonics

    Center for Optical and Electromagnetic Research,, Conference room, Zijingang Campus,Zhejiang University, Hangzhou, China

    Jianhao ZHANG

    Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau

    PhD defense

    Eric CASSAN, Professeur, Université Paris-Sud, Directeur de thèse

    Régis BARILLE, Professeur, Universite Angers/CNRS UMR 6200, Rapporteur

    Béatrice DAGENS, Professeur, Université Paris Sud/CNRS UMR 9001, Examinateur

    Xinliang ZHANG, Professeur, Huazhong University of Science and Technology, Examinateur

    Liu LIU, Professeur South China Normal University, Rapporteur

    Jianjun HE, Professeur, Zhejiang University, Examinateur

    Second-order Pockels and the third-order Kerr effects are among the important effects exploited for light modulation and light generation in integrated photonic platforms. To take advantage of these nonlinearities in silicon photonics, especially due to the lack of second order effect in bulk Si, the use of subwavelength optical structures is explored. In this context, this thesis work has focused on two main aspects, including: 1) Exploration of a novel photonic cavity scheme to take benefit of the electro-optical Pockels effect in strained Si structures for the realization of ultra-fast lower-consumption compact silicon modulators; 2) Exploration of a new family of waveguides leading to an automatic satisfaction of energy/momentum conservation for the purpose of Kerr frequency comb generation in integrated photonic platforms.
    For improving the performances of integrated silicon resonant optical modulators, we have developed a novel Fano cavity resonator enabled by sub-wavelength engineering, leading simultaneously to high extinction ratio (23 dB) with a small Q factor of only 5600, and characterized by an ultra-low power consumption of less than 5 fj/bit when relying on the free carrier plasma dispersion effect. We have further extended the method to design a strained silicon Fano modulation structure which performances traditionally suffer from the weak amplitude of the exploited strain-induced Pockels effect and from considerable microwave losses due to large footprint components. By means of the proposed ultra-compact subwavelength structured Fano resonator, around 200-fold/60-fold (Q factor of 32000/5600) improvement on the modulation extinction ratio with the same driven voltage was theoretically predicted.
    For improving the exploitation of silicon Kerr nonlinearities, we have proposed a novel family of graded index optical waveguides intending to automatically fulfill the energy and momentum conservation laws of four-wave mixing processes. The design of the waveguide section is based on a principle inherited from quantum wells of wave mechanics and concepts inherited from subwavelength structures for the practical realization of the rather particular index profiles. Standing on these specific waveguides in term of light dispersion, we have applied them to the modeling of frequency micro-combs (e.g. frequency combs generated using micro-ring resonators and a CW light source) by solving the nonlinear relevant equations (Lugiato-Lefever) to dynamically analyze the soliton comb spectrum generation process in various configurations. On top of this model, the specifically automatically phase-matched sub-wavelength-enabled graded-index waveguides were considered to trim and extend the bandwidth of silicon soliton frequency combs, demonstrating enlarged bandwidth and improved spectrum design flexibility with respect to previous works.
    Overall, one of the dominant features of our study was to contribute to showing that sub-long wavelength photonic structures could provide concrete solutions to problems useful for the realization of on-chip non-linear functions. Subwavelength/nano structures not only benefit to passive photonic circuits which have been intensively developed in the past ten years, but also show strong potentials in the realization of active functions. This subwavelength toolbox is decisive in practice for the concrete achievement of the objectives pursued.

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    Integrated nano-optomechanics in photonic crystals

    Centre de Nanosciences et de Nanotechnologies, Amphithéâtre, Palaiseau

    Rui ZHU

    Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau

    PhD defense

    Jury members:

    Isabelle ROBERT-PHILIP, Directrice de Recherche, Université de Montpellier, Directeur de thèse

    Marc FAUCHER, Chargé de Recherche, IEMN, Rapporteur

    Nicolas LE THOMAS, Professeur, Ghent University - IMEC, Rapporteur

    Xavier CHECOURY, Professeur, Université Paris Sud, Examinateur

    Maria-Pilar BERNAL-ARTAJONA, Directeur de Recherche, FEMTO-ST, Examinateur

    High purity reference oscillators are currently used in a wide variety of frequency control and timing applications including radar, GPS, space... Current trends in such fiels call for miniaturized architectures with direct signal generation in the frequency range of interest, around few GHz. Recently, novel optomechanically-enhanced architectures have emerged with this purpose. Such optomechanically-driven oscillators not only generate microwave signals directly in the GHz frequency range with possibly low phase noise but also are amenable to a high degree of integration on single chip settings. This PhD work falls within this scope. The optomechanically-driven oscillator under study consists of suspended photonic crystal cavities coupled to integrated silicon-on-insulator waveguides in a three-dimensional architecture. These cavities harbor highly-confined optical modes around 1,55 µm and mechanical modes in the GHz and most importantly, feature a high phonon-photon spatial overlap, all resulting in an enhanced optomechanical coupling. This enhanced optomechanical coupling strength is here probed optically on photonic crystal structures with optimized design. These cavities are hosted in III-V semiconductor materials whose piezoelectricity enable us to integrate additional tools for probing and controlling mechanical vibrations via capacitive, piezoelectric or acoustic driving. This full control over the mechanical modes and optomechanical interaction, paves the way towards the implementation of integrated injection locking circuits of feedback loops for reducing the phase noise of the oscillator.

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    III-V/Silicon tandem solar cells grown with molecular beam epitaxy

    Institut Photovoltaïque d'Ile de France (IPVF), Amphithéâtre, Palaiseau

    Amadeo MICHAUD

    Centre de Nanosciences et de Nanotechnologies, C2N, Palaiseau

    PhD defense

    Jury members :

    M Alain Le Corre, FOTONS, Rapporteur

    M James Connolly, IPVF, Rapporteur

    M Andrea Gauzzi, IMPMC, Examinateur

    M Wilfried Favre, INES, Examinateur

    M Jean Christophe Harmand, C2N, Directeur de thèse

    Mme Jara Fernandez Martin, TOTAL,Directrice de thèse 

    Abstract :

    Terrestrial photovoltaic is dominated by Silicon based devices. For this type of solar cells, the theory predicts an efficiency limit of 29%. With photovoltaic modules showing 26.6% efficiency already, Silicon-based modules is a mature technology and harvest almost their full potential. In this work, we intend to explore another path toward the enhancement of photovoltaic conversion efficiency. Tandem solar cells that consist in stacking sub-cells, allow overcoming the Si efficiency limit. Since solar cells made of III-V semiconductors are good complements to Silicon solar cells, theory predicts that efficiency above 40% is attainable when combining those types of cells. This work focuses on the elaboration of a performant III-V solar cell, compatible for a tandem use.

    The first stage of the PhD was to build expertise on phosphide alloys epitaxy with MBE. The influence of the growth conditions on GaInP properties were studied. Then GaInP single junction solar cells were fabricated. The different layers composing the cells were optimized.

    P-GaInP is presented as a potential limit of solar cell performance. Indeed, a small diffusion length of the generated carriers was evidenced in this material. A practical solution was proposed and implemented: we designed a cell combining GaInP and AlGaAs in a heterojunction cell. An efficiency of 18.7% was obtained using this structure.