(en anglais) Astronomy meets photonics: a unique potential for the next decadeC2N, Amphitheater, Palaiseau
New discoveries in astronomy rely primarily on the astronomers' ability to develop and exploit new technologies to process and analyze the very few distant stellar photons collected by telescopes. On the other side photonics has demonstrated, through numerous applications, a strong potential to route and manipulate light, which can be seen as an appealing alternative to classical free space optics. For the last ten years, "astrophotonics" has brought together these two fields and tried to improve on the versatility, robustness and simplification of, otherwise, increasingly complex and bulky instruments onboard the 10m or future 40m telescopes.
In this talk, I will focus on the recent achievements of "photonics for astronomy" mainly in the infrared part of the spectrum. I will review some of the major constrains in observational astrophysics that we are facing when developing new astronomical instrumentation and attempt to give a perspective, based on examples applicable to techniques such as interferometry and coronography, for future synergies that may profoundly impact optical and infrared instrumentation for ground- and space-based astronomy in the upcoming decade.
Keywords: high-angular resolution astronomy, infrared instrumentation, astrophotonics
(en anglais) Advanced numerical methodology for designing passive and active nanophotonic devicesC2N, Amphitheater, Palaiseau
In this presentation, I am excited to share with you our cutting-edge optimization approach
for multiobjective metasurface setups. Our method is based on statistical learning, which
utilizes surrogate modeling to predict the behavior of new designs during the optimization
process [1-2]. This approach allows us to rapidly converge to the global set of optimal
solutions while reducing the number of solver calls and iterations compared to traditional
global evolutionary strategies.
We put our optimization approach to the test by optimizing a 3D achromatic metalens with a
numerical aperture greater than 0.5. Our results were remarkable, achieving focusing
efficiencies of almost 50% for three colors (red, green, blue). This achievement sets a new
record for RGB metalens of this kind, and it was accomplished using simple cylindrical
nanopillar geometries that are easier to fabricate than complex freeform geometries .
Additionally, we developed a adopted our novel optimization method to consider the
fabrication imperfections relying on the metamodel context .
In the second part of my presentation, I will discuss our innovative design strategy to achieve
full phase modulation of light reflected from an arbitrary active metasurface with near-unity
efficiency . We adopted our advanced optimization method and considered the near-field
coupling between strongly resonant pixels and the nonlocal response to maximize the active
beam steering performance. This breakthrough technology has exciting applications in
imaging microscopy, high-resolution image projection, optical communication, and 3D light
detection and ranging (LiDAR).
Overall, our cutting-edge optimization approach together with our innovative design
strategies represent significant breakthroughs in the field of metasurface setups, with the
potential to transform a wide range of applications.
 M. Elsawy, et al, «Global optimization of metasurface designs using statistical learning methods», Scientific
Reports, Vol. 9, No. 17918, (2019).
 M. Elsawy, et. al, Multiobjective statistical learning optimization of RGB metalens, ACS Photonics, Vol. 8,No. 8,
pp. 2498–2508 (2021).
 M. Elsawy, et. al, Optimization of metasurfaces under geometrical uncertainty using statistical learning,
Optics Express 29(19), 29887–29898 (2021).
 M. Elsawy, et. al, Universal Active Metasurfaces for Ultimate Wavefront Molding by Manipulating the
Reflection Singularities. Laser Photonics Rev, 2200880, (2023)
keywords: Nanophotonics designs, Multiobjective optimization, Active metasurface, RGB Metalens, Geometrical imperfections
Mahmoud Elsawy is an experienced researcher with a demonstrated history of working in the field of electromagnetic modeling for linear and nonlinear Photonic devices. He received his PhD from the University of Aix-Marseille, France, in 2017, specializing in optics, photonics, and image processing. The topic of his PhD thesis was dedicated to the development of computational models for the design of realistic integrated nonlinear plasmonic waveguides. He spent a year as a postdoctoral researcher at the Institut Fresnel in Marseille, France. After a postdoc at Inria Sophia Antipolis, France, in the field of numerical optimization of nanophotonics, he became a permanent member of the Atlantis project team in December 2020 as an Inria Starting Faculty Position (ISFP) His research activities focus on the modeling and design of innovative passive and programmable metasurface devices.
(en anglais) High performance silicon and silicon metamaterials for integrated photonicsC2N, Amphitheater, Palaiseau
Silicon based photonics has been under great scrutiny in recent years due to their potential for making highly compact monolithic integration of multifunctional electronic and photonic devices on the same substrate. The most popular platform is the high index contrast silicon-on-insulator (SOI) system. The high refractive index contrast between the silica cladding and the silicon waveguide core facilitates the confinement and guiding of light in structures within submicron or nanometer dimensions. In addition, the mature silicon microfabrication technology establishes a firm foundation for making low-cost and compact integrated photonic devices. A wide range of active and passive optical devices has been realized on the SOI platform. The applications of these devices can be found in high-speed communications, health industry, chemical and biological analysis, environmental monitoring, optical interconnects, and renewable energy. This talk will focus on the research work by Dr. Ye’s group at Carleton University, ranging from fundamental metamaterial design using subwavelength gratings, polarization rotators and splitters, polarization-insensitive and broadband grating couplers, mode-division multiplexers, multimode couplers, spectral filters, nano-grating antennas, to optical phased arrays.
keywords : Silicon photonics, subwavelength gratings, polarization control, optical antennas, micro-rings/disks
Dr. Winnie Ye is a Fellow of the Engineering Institute of Canada (EIC) and a Full Professor in the Department of Electronics at Carleton University. She was also a Canada Research Chair (Tier II) in Nano-scale IC Design for Reliable Opto-Electronics and Sensors from 2009 to 2021. Her expertise is in silicon photonics and its applications in telecommunications, data communication, biophotonics, and renewable energy. Dr. Ye received her B.Eng., M.A.Sc. and Ph.D degree in Electrical and Computer Engineering from Carleton University and the University of Toronto, respectively. Dr. Ye returned to Carleton as a faculty member in 2009.
(en anglais) Bright Fluorescent Polymeric Nanomaterials for Biosensing and BioimagingC2N, Amphitheater, Palaiseau
Dye-loaded fluorescent polymeric nanoparticles (NPs) appear as an attractive alternative to inorganic NPs, such as quantum dots (QDots). Confining large number of dyes with bulky counterions within small polymeric nanoparticles makes the latter particularly bright and enable phenomenon of giant light-harvesting. Functionalization of these NPs with DNA yields FRET-based color switching nanoprobes for nucleic acids with single-molecule sensitivity and compatibility with RGB camera of a smartphone, important for cancer diagnostics. We also found that the energy transfer between two NPs connected by DNA duplexes does not follow canonical Förster law, allowing efficient long-range FRET at distances up to 20 nm, important for construction of ultrasensitive biosensors. When applied to cells, the small size of NPs was found essential for their free diffusion in cytosol and detection of intracellular RNA. At the animal level, the high brightness of NPs enabled single-particle tracking in the mice brain and visualization of crossing the blood-brain barrier. The developed small dye-loaded polymeric NPs open the route to ultrabright tools for sensing and tracking of biomolecules in biology and medicine.
Andrey Klymchenko obtained his PhD degree in 2003 from Kyiv National University. Then, he worked as post-doctoral fellow in the University of Strasbourg and Catholic University of Leuven. Then, he joined CNRS in 2006, received CNRS Bronze Medal in 2010 and was promoted to Director of Research in 2014. In 2015, he obtained ERC consolidator grant BrightSens. In 2021, he received Prix du Dr et de Mme Henri LABBE from French Academy of Sciences and he was elected a member of Academia Europaea. He is a leader of “Nanochemistry and Bioimaging” group and a co-founder of a start-up BrightSens Diagnostics. He is a co-author of over 250 peer-reviewed articles and 12 patents.
(en anglais) Europeanisation of my PhD Project with the EUGLOH European Alliance : A reallistic Picture ?C2N - Centre de Nanosciences et de Nanotechnologies, , Palaiseau
(en anglais) C2N PhD student seminarC2N, Amphitheatre, Palaiseau
- Xin Zheng (C2N Photonics Department) - GRadien INdex (GRIN) optics in silicon photonics
- Junbum Park (C2N Nanoelectronics Department) - Full Band Monte Carlo simulation of 2D h-BN nanostructure for phonon transport based on ab initio calculation
- Kamel-Eddine Harabi (C2N Nanoelectronics Department) - Memristor Based Artificial Intelligence Accelerators using
In/Near Memory Computing Paradigm
- Cléophanie Brochard (C2N Materials Department) - Heat transport in Van der Waals heterostructures
(en anglais) The squeeze laser and its applicationsC2N - Centre de Nanosciences et de Nanotechnologies, , Palaiseau
An increased number of laser-based measurements in metrology are performed at the quantum-noise limit. One potential approach to enhance the signal-to-noise ratio in quantum-noise limited measurements is to increase the power of the light used. However, this straightforward approach comes with its own set of challenges and limitations. It can lead to thermal deformations in the optical beam path or even the destruction of the measurement sample and requires improved laser safety measures. To overcome these limitations, squeezed light emerged as a valuable solution. Squeezed light directly reduces the quantum noise, enabling enhanced precision in measurements without the need for excessively high light power. For example, as of 2019, all gravitational-wave observatories worldwide use squeezed vacuum states. In the talk, we will explain the concepts behind squeeze lasers in more detail and showcase how they effectively reduce quantum noise in measurements. Applications and recent advancements will also be discussed.
Photo : State-of the art squeeze laser developed at Uni Hamburg.
(en anglais) Superconductor-semiconductor quantum dot systems in nanowires – from in situ fabrication to entanglementC2N, Amphitheatre, Palaiseau
Hybrid nanomaterials are attractive for research on several types of gate-tunable quantum devices, e.g. superconducting qubits (gatemons), Andreev spin qubits, cryogenic switches, quantum limited amplifiers and for fundamental studies of bound states in superconductors and quantum dots . Superconductor-semiconductor nanowires have been established as an essential platform in this research.
We firstly discuss the excitations and correlations arising in short chains of coupled quantum dots and superconducting islands in Al/InAs nanowires . We then take a look beneath the surface of these devices, addressing advances in materials science where epitaxial growth, in situ fabrication and implementation of various superconductors have expanded the available parameter space for hybrid devices [3,4]. We will finally focus on opportunities arising from growth of multiple coupled nanowires .
 E. Prada et al., From Andreev to Majorana bound states in hybrid superconductor-semiconductor nanowires, Nature Rev. Phys. 2, 575 (2020)
 J.C. Estrada Saldana et al., Excitations in a superconducting Coulombic energy gap, Nature Comm. 13, 2243 (2022); Two Bogoliubov quasiparticles entangled by a spin, arxiv:2203.00104
 T. Kanne et al., Epitaxial Pb on InAs nanowires for quantum devices, Nature Nano. 16, 767 (2021)
 D. Carrad et al., Shadow Epitaxy for In Situ Growth of Generic Semiconductor-Superconductor Hybrids, Adv. Mat. 32, 1908411 (2020)
 T. Kanne et al., Double nanowires for hybrid quantum devices, Adv. Func. Mat. 32, 2107926 (2021)
Jesper Nygård is professor in experimental physics at the Niels Bohr Institute, Copenhagen where he was cofounder of the Center for Quantum Devices, and former head of the Nano-science Center. His research interests bridge growth of the semiconductor-superconductor hybrid materials by molecular beam epitaxy, electronic devices based on nanowires, and quantum transport. He currently resides in Grenoble where he holds a visiting chair of excellence at LANEF, Institut Néel, CNRS, and CEA (2022-25).
(en anglais) Nonlinear metasurfaces based on intersubband polaritonsC2N, Amphitheatre, Palaiseau
Intersubband transitions in n-doped coupled semiconductor quantum wells allow one to quantum-engineer materials with highly nonlinear optical response. The intersubband transitions in these materials are limited, however, to (mostly) electric field polarized perpendicular to the semiconductor heterostructure layers, which reduces their usefulness for free-space optics applications. This limitation can be removed and the already giant nonlinear optical response can be further enhanced if the intersubband transitions are coupled to electromagnetic modes of optical nanoresonators fabricated in semiconductor heterostructures to form intersubband polaritonic metasurfaces. In this presentation, I will present our latest results on developing intersubband polaritonic metasurfaces with record-high second- and third-order nonlinear optical responses. In particular, we will present metasurfaces designed for efficient mid-infrared second harmonic and difference-frequency generation with controllable phases of the nonlinear optical response and metasurfaces designed for saturable absorption and power limiting.
(en anglais) Tuning Properties of Magnetic Tunnel Junctions for High Density STT-MRAMC2N, Amphitheater, Palaiseau
The magnetic tunnel junction (MTJ), a device comprised of two ferromagnetic electrodes with a thin (about 1 nm) insulating tunnel barrier in between, was first proposed in a Ph.D. thesis by Michel Jullière in 1975 and reached widespread commercialization nearly 30 years later as the read sensor in hard disk drives. MTJs became essential for data storage in consumer laptop and desktop computers, early-generation iPods, and now in data centers that store the information in “the Cloud.” The application of MTJs has expanded even further, becoming the storage element in non-volatile memory, first in toggle magnetic random access memory (MRAM) used in automotive applications and outer space, and now in the production of spin-transfer torque MRAM as a replacement for embedded flash memory. As computing capabilities advance and drive demand for high-performance memory, innovation in MTJs continues in order to deliver faster, high-density MRAM that can support last-level cache, in-memory computing, and artificial intelligence.
In this talk, I will describe the seminal discoveries that enabled MTJs for pervasive use in hard disk drives, MRAM, and magnetic sensors. As the demand for faster and higher density memory persists, still more breakthroughs are needed for MTJs contained in device pillars (or bits) just tens of nanometers in diameter. These advances require tuning of material properties at the atomic scale as well as across arrays of millions of bits in a memory chip. I will describe the magnetic properties of MTJs that are essential for high-performance MRAM and how to engineer these properties to deliver high spin-transfer torque efficiency and high data retention. In addition, I will describe the fabrication and individual addressing of MRAM bits in a 50nm full pitch array, as a step toward achieving high-density MRAM.
Tiffany S. Santos received S.B. and Ph.D. degrees in materials science and engineering from MIT. She is the Director of Non-Volatile Memory Materials Research at Western Digital, in San Jose, California where she leads a team working on materials for magnetic random access memory technology and other exploratory projects. She first joined the company in 2011, when it was previously known as Hitachi Global Storage Technologies, to work on research of granular FePt media for heat-assisted magnetic recording. Prior to working in industry, she was a Distinguished Post-Doctoral Fellow, and later an Assistant Scientist, at the Center for Nanoscale Materials of Argonne National Laboratory where she studied emergent phenomena at the interfaces of complex oxide heterostuctures. In 2009, she was awarded the L’Oréal USA Fellowship for Women in Science. In 2022, she became a Distinguished Lecturer of the IEEE Magnetics Society. She is General Chair of the 2025 MMM Conference to be held in Palm Beach, Florida.