Development of a multi-criteria comparison tool for electrochemical stationary storage systems
Use of stationary storage systems is now essential to keep pace with changes in the electricity grid and the growing integration of intermittent renewable energies such as solar and wind power. The choice of a storage solution is based on a number of criteria, including performance, lifetime, environmental impact, safety, regulatory constraints and, of course, economics.
The laboratory possesses comparative data on these different criteria, via experimental studies and feedback on existing systems. In addition, an initial software tool has been developed to assess environmental impact using LCA (Life Cycle Assessment). The aim of this thesis work is to integrate these different components into a broader comparison tool with a multi-criteria approach, targeting specific case studies and a limited number of storage technologies that have reached sufficient maturity for the available data to be reliable.
High yield strength austenitic stainless steels for nuclear applications: numerical design and experimental study
The PhD thesis is part of a project that aims at designing new austenitic stainless steels grades for nuclear applications, which are specifically suitable to in-service conditions encountered by the components and to the manufacturing process. More precisely, the subject deals with bolt steels achieved by controlled nitriding of powders which are then densified by hot isostatic pressing. Indeed, current bolt steel grades may suffer from stress corrosion cracking, while nitriding allows to increase the chromium content, which is beneficial from that point of view.
The study will start by the definition of specifications and associated criteria, then CALPHAD calculations in the Fe-Cr-Ni-Mo-X-N-C system will be done to define promising compositions. Then, selected compositions will be supplied as powders. The behaviour of powders during nitriding will be studied and modelled. Samples will be nitrided, densified and heat treated. One grade will be then selected and fully characterised: mechanical properties and deformation mechanisms, corrosion behaviour. One important objective is to demonstrate the advantages of the new grade compared to the industrial solution.
Space-time Modulated Electromagnetic Metasurfaces for Multi-functional Energy-Efficient Wireless Systems
Next-generation (XG) wireless systems envision an unprecedented network densification and the efficient use of the near-millimeter-wave (mmW) spectrum. Disruptive concepts are required to minimize the number of antenna systems and their power consumption. Reconfigurable intelligent surfaces (RISs) can provide high-gain beam-forming using simple devices (e.g. p-i-n diodes) to control their scattering properties of their unit-cells. However, the efficiency of an RIS and the wireless functions it can simultaneously realize, are bound by its inherent linearity and reciprocity.
Space-time modulated metasurfaces (STMMs) have recently emerged as a beam-forming solution overcoming fundamental limits of linear time-invariant systems. Leveraging an additional time-variation of the unit-cell response, with respect to RISs, an STMM can tailor at the same time angular and frequency spectra of the radiated fields, without using multiple active circuits as in current systems.
Most models for the design of STMMs are oversimplified and consider 1-D modulations in quasi-static temporal regime. The impact of spatial discretization and phase quantization is overlooked. The few reported prototypes are often electrically small, with a coarse (half-a-wavelength) period. Most demonstrators operate in reflection, below 17 GHz and enable only a 1-bit phase resolution. Independent far-field beam-steering at several frequencies has been proved in a single scan plane.
This Ph.D. thesis aims at modelling, designing and demonstrating electrically large and multi-functional transmissive STMM antennas with enhanced phase resolution and beam-forming capabilities. Efficient numerical models will enable the computation of the fields scattered by a STMM in far- and near-field regions, for arbitrary spatial and time modulation periods. Holographic and compressive sensing techniques will be proposed to jointly optimize the metasurface phase profile and the time-modulation waveforms, enabling harmonic beam-shaping. A thorough study of the effect of phase resolution, STMM period and time-modulation frequency on the performance, power consumption and complexity of the control electronics will be provided.
A transmissive STMM prototype based on p-i-n diodes and enabling a 2-bit phase resolution will be realized for the first time, building on the group background on space-modulated electronically reconfigurable flat lens antennas. It will work in a frequency range suited to terrestrial and satellite networks (17-31 GHz). Multiple antenna functionalities will be experimentally characterized using the same prototype, such as: (i) simultaneous and non-reciprocal 2-D beam-forming at different harmonics of the time-modulating signals, in either far-field or near-field region; (ii) pattern shaping at the fundamental frequency, using optimized time-sequences to increase the effective phase resolution.
The fundamental and experimental contributions of this research will broaden the physical insight on time-modulated metasurfaces and increase the maturity of this technology for energy-efficient smart antennas with applications to wireless networks and integrated communication and sensing systems. An intense dissemination activity in high-impact scientific journals of electrical engineering and applied physics is expected, given the novelty of the topic and the growing interest it triggers in several communities.
Study of new photodiode architecture for IR imagers
In the field of high-performance infrared detection, CEA-LETI plays a leading role in the development of the HgCdTe material, which today offers such performance that it is integrated into the James Webb Space Telescope (JWST) and allows the observation and study of deep space with unparalleled precision to date. However, we believe that it is still possible to make a significant step forward in terms of detection performance. Indeed, it seems that a fully depleted structure, called a PiN photodiode, could further reduce the dark current (and thus reduce noise and gain sensitivity at low photonic flux) compared to the non-fully depleted structures currently used. This architecture would represent the ultimate photodiode and would allow either a further increase in performance at a given operating temperature or a significant increase in the operating temperature of the detector, with the potential to open new fields of application by greatly simplifying cryogenics.
Your role in this thesis work will be to contribute to the development of the ultimate photodiode for very high-performance infrared detection, characterize and simulate the PiN photodiodes in HgCdTe technology manufactured on our photonic platform.
Candidate Profile:
You hold a Master's degree in optoelectronics and/or semiconductor material physics and are passionate about applied research.
The main technical skills required are: semiconductor component physics, optoelectronics, data processing, numerical simulations, interest in experimental work to carry out characterizations in a cryogenic environment but also theoretical work to carry out numerical simulations.
The PhD student will be integrated into a multidisciplinary team ranging from the growth of II-VI materials to electro-optical characterization, including microelectronics manufacturing processes in clean rooms and the packaging issues of such objects operating at low temperature.
3D interferometric imaging system with reception module in integrated optics
3D sensing by capturing depth images, is a key function in numerous emerging applications such as augmented reality, robotics and telemedicine. The laboratory has developed an innovative 3D sensing micro-optical prototype, using a frequency modulated Lidar technology with simultaneous illumination of the whole scene. The next step is the miniaturization of the setup with integrated optics. A first PhD is ongoing in the laboratory, focusing on the integration of the illumination module.
The proposed PhD will target the definition of an integrated optics architecture for the reception module. The main objective is to realize the beam recombination with integrated optics, using waveguides and grating couplers, to enable the heterodyne mixing of light back-scattered by the scene with the local oscillator. The candidate will design these integrated optical components in connection with the refractive optical system, simulate the propagation of the beams and interference using Lumericaland Zemaxsoftwares, contribute to device realization in clean room, perform the optical characterization of the components, and experimentally validate the proof of concept of depth imaging with the miniaturized prototype.
Depending on the progress of the developments, the PhD will include the development of a module combining the illumination and reception functions in a single component. Several patents, publications and presentations in international conferences are expected in the framework of this PhD.
development of capacitive IIIV-Silicon modulators for emerging applications in silicon photonics
The proposed thesis work consists in developing phase modulators based on the integration of IIIV-Silicon hybrid capacitors in silicon waveguides, at a wavelength of 1.55µm to meet the emerging demands of photonics (optical computing on chip, LIDAR). Unlike telecom/datacom applications, which have enabled the emergence of integrated silicon photonics, these new application fields involve circuits that require a very large number of phase modulators. All-silicon modulators based on PN junctions, which have optical losses of several dB and centimeter sizes, are a bottleneck to the emergence of these applications.
IIIV-Si hybrid capacitors can allow, thanks to the electro-optical properties of IIIV materials, to reduce the size of silicon modulators by an order of magnitude and improve their energy efficiency (reduction of optical losses). First functional modulators have been designed, fabricated and tested. The first step will be to study in details their performance (losses, efficiency, speed, hysteresis) and to understand their limitations, using the available photonic simulation tools and electrical characterization methods (C(V), interface charge density, DLTS, etc.). In particular, this will involve better understanding the impact of the manufacturing process on the electro-optical properties. In a second step, the doctoral student will propose improvements to the designs and manufacturing processes (in collaboration with our microfabrication specialists), and will validate them experimentally using hybrid capacities and modulators integrating these capacities.
improving effiiciency and directivity in color conversion µLEDs with metasurfaces
In the field of augmented reality, the development of full color µLEDs matrices is a critical step towards miniaturizing and simplifying the optical system. Current pixel architectures in microLEDs displays are based on color conversion. Short wavelength emission from a first active material is absorbed by a second active layer to be re-emitted at longer wavelength. In current architectures, re-emission follows a lambertian profile making them unsuitable for AR/VR applications.
Recent work by the Charles Fabry laboratory - Institut d’Optique, as part of E. Bailly's thesis, has demonstrated that combining metasurfaces with color converters can enable shaping the radiation pattern. The primary goal of this thesis is to apply this innovative method by integrating it with blue GaN µLEDs developed at CEA-LETI.
Throughout this thesis, the student will first design the devices using optical simulations, aiming to optimize them for both efficiency and directional angular radiation pattern. Following this, the student will fabricate the devices in the clean room at LETI and perform opto-electrical characterization.
The initial design phase will primarily take place at the Quantum Nanophotonics and Plasmonics team of Charles Fabry laboratory - Institut d’Optique, in Saclay, under the supervision of the thesis director. The student will then move to CEA-LETI in Grenoble for the fabrication, characterization and comparison with simulation results.
The selected student will benefit from the extensive expertise in nano-photonics and simulation at the Charles Fabry laboratory, as well as the technological, simulation, and characterization expertise in µLEDs at CEA-LETI.
The Quantum Nanophotonics and Plasmonics at Institut d’Optique team investigates the physics and engineering of spontaneous light emission (fluorescence, incandescence, electroluminescence), at different scales (quantum regime with single photon and single atoms, collective effects, photon condensates, condensed matter systems…).
The LITE (Emissive Technologies Integration Laboratory) at CEA-LETI focuses on manufacturing microemitting devices (µLED, OLED, LCD) in a silicon microelectronics foundry-type environment. This includes, for example improving µdisplays performances, made above ASICs, while reducing the pixel size, or demonstrating new use cases of these light sources in the field of biomedical optical sensors.
Attention-based Binarized Visual Encoder for LLM-driven Visual Question Answering
In the context of smart image sensors, there is an increasing demand to go beyond simple inferences such as classification or object detection, to add more complex applications enabling a semantic understanding of the scene. Among these applications, Visual Question Answering (VQA) enables AI systems to answer questions by analyzing images. This project aims to develop an efficient VQA system combining a visual encoder based on Binary Neural Networks (BNN) with a compact language model (tiny LLM). Although LLMs are still far from a complete hardware implementation, this project represents a significant step in this direction by using a BNN to analyze the context and relationship between objects of the scene. This encoder processes images with low resource consumption, allowing real-time deployment on edge devices. Attention mechanisms can be taken into consideration to extract the semantic information necessary for scene understanding. The language model used can be stored locally and adjusted jointly with the BNN to generate precise and contextually relevant answers.
This project offers an opportunity for candidates interested in Tiny Deep Learning and LLMs. It proposes a broad field of research for significant contributions and interesting results for concrete applications. The work will consist of developing a robust BNN topology for semantic scene analysis under certain hardware constraints (memory and computation) and integrating and jointly optimizing the BNN encoder with the LLM, while ensuring a coherent and performant VQA system across different types of inquiries.
Development of micro-optic strcture for uncooled infrared imaging sensor
In this thesis, we aim to incorporate a low-resolution angular sorting function capable of discerning the primary direction of incident infrared flux. This information is crucial for enhancing image processing algorithms, thereby facilitating faster automatic focusing, improved image segmentation, and more accurate depth estimation.
To achieve this functionality, a micro-optics network at pixel level must be designed and realised. At present, we are considering two competitive approaches: refractive microlenses and meta-surfaces. As a PhD student, your responsibilities will include:
?- Establishing the preliminary specifications for these microlenses
?- Designing the micro-optics using numerical simulation and predicting their performance
?- Overseeing the manufacturing of these micro-optics in a clean room environment
?- Characterising the micro-optics on a dedicated laser bench and performing a proof of concept by coupling them with an infrared imager
You will be fully integrated into the Laboratory of Thermal and THz Imaging of the CEA Leti which develops, realizes, and characterizes imaging technologies based on micro-bolometers.