Scientific Direction
Transfer of knowledge to industry
Scientific Direction
Département d'Optronique (LETI)
Laboratoire Architecture Systèmes Photoniques
01-11-2020
SL-DRT-20-0522
Photonics, Imaging and displays (.pdf)
Gamma imaging is a technique widely used in medical imaging (molecular imaging, nuclear medicine) and security (transportation, industry). CdZnTe semiconducting detectors usage is currently emerging for SPECT (Single Photon Emission Computed Tomography, using gamma-cameras) and portable gamma imaging. Indeed, they enable performance improvements in speed, sensitivity and image quality. These detectors operate at room temperature and are sensitive to five physical parameters of the interaction: deposited energy E, interaction time T and the 3-dimensional position XYZ. These parameters are estimated by real-time analysis of anode electronics signals. However, the link between electrical signals and physical parameters is not fully known, as material physical properties are not uniform inside detector. The goal of this Ph.D. internship is to overcome these limits by using machine learning techniques to model actual detector response. Recent multi-layered deep learning technique enable to build and train complex and flexible system models, and to overcome our lack of knowledge about detector physics. The identification of internal physical parameters of the detector would allow to optimize estimation of interaction location, time and energy. This will lead to a better image quality and then capability to detect small and weak objects, enabling better diagnoses and lower false alarm rate. The student may have a background in applied mathematics (machine learning) and/or instrumentation physics. He/she need to have taste for multi-disciplinary research, mixing experimental physics and data science.
Département d'Optronique (LETI)
Laboratoire Architecture Systèmes Photoniques
01-09-2020
SL-DRT-20-0690
Photonics, Imaging and displays (.pdf)
The photonic systems architecture laboratory is part of the CEA LETI optronics department. We have a solid expertise in the development of new detection modules including a semiconductor or scintillator detector combined with readout electronics for X-ray or gamma imaging in the fields of medical imaging or security control. The objective of this thesis is to study the traps levels and densities in the bandgap of a new perovskite-based semiconductor material for direct X-ray detection developed for medical radiography. Its use as photoconductive devices in matrix imagers should improve the spatial resolution of images and increase the signal, thus reducing the dose given to the patient, or even providing access to new information on tissue composition. To reach this goal, the student, physicist and experimenter, will develop specific test bench to identify and characterize these electronic traps in the volume of crystals and at the interfaces of the devices. He will determine the nature of the defects of the thick crystalline layers developed by a doctoral student at CEA LITEN. The student will model the effect of these trap levels on the performance of the devices. In parallel, the student will study the origin of the current of darkness in perovskite devices. These results will be correlated with experimental measurements made by a doctoral student from CEA LETI. Finally, he will provide feedback on the development of crystals and devices in order to minimize the traps density and improve their overall performance.
Département d'Optronique (LETI)
Laboratoire des Capteurs Optiques
01-10-2020
SL-DRT-20-0776
Photonics, Imaging and displays (.pdf)
Integrated laser sources compatible with microelectronic technologies is currently one of the main challenges for silicon photonics. CEA is part of the few laboratory that demonstrated mid-infrared optically pumped lasing in GeSn micro-cavities. Our aim is to go towards lasing at room temperature in fully relaxed or tensile-strained heterostructures and quantum wells made of germanium tin alloys. Defect reduction in the gain zone and carrier confinement optimisation in order to reach high gain is the major issue of this study. We would indeed like to minimize the lasing threshold and obtain continuous emission lasers. We also target a decrease the concentration of tin in germanium by focusing strain to further increase the crystalline quality of quantum wells and heterostructures and still reach direct band gap in the structures. Objectives of the research will be (i) to reduce crystalline defects in the gain zone, (ii) to find efficient geometries to confine electrons and holes, (iii) to apply tensile strain to germanium tin crystals, (iv) to evaluate the electrical gain dependence with different strains and doping levels, (v) to characterise the optoelectronic properties of epitaxial materials, (vi) to design and fabricate laser cavities with strong optical confinement in order to reach tunable continuous germanium lasers compatible with the current microelectronic technologies for environmental detection.
Département d'Optronique (LETI)
Laboratoire d'Intégration Photonique sur Silicium
01-09-2020
SL-DRT-20-0798
Photonics, Imaging and displays (.pdf)
The use of silicon photonics has been identified as a mean to overcome interconnect limitations and efficiency, but also as a versatile platform able to address the new problematics encountered in Lidar and quantum photonics applications. However, the possibility to have high-speed pure phase optical modulation has not been addressed yet on this platform. Silicon, as a centrosymmetric material does not exhibits second order non-linearities. Nevertheless, it has been theoretically and experimentally demonstrated that by applying a mechanical strain, its centrosymmetric can be broken, leading to the exhibition of second order non-linearities. Recent proofs of concept have been demonstrated with a modulation at 20GHz based on the use of silicon nitride stress layers deposited by PECVD on top of silicon. The objectives of the PhD will be to enhance the Pockels effect in silicon waveguides by a factor of 10 to 100, in order to reach performances close to LiNbO3. This research activity will include : Fine theoretical study of the involved processes and how to control them, and also electro-optic simulations in order to evaluate the performances of such devices and optimize the overlap between the strain field and the optical mode in the waveguide; The design and fabrication of optical phase modulators optimized to maximize the Pockels effect in the waveguide; DC and RF characterization of optoelectronics devices bas on second order non-linearities.
Département d'Optronique (LETI)
Laboratoire des Composants Emissifs
01-09-2020
SL-DRT-20-0813
Photonics, Imaging and displays (.pdf)
GaN-based microLEDs are on the verge to revolutionize the display world, on one hand providing ultra-high brightness microdisplays for augmented reality applications, on the other hand paving the way for large area displays with unrivaled image quality. Blue-emitting LEDs based on nitride semiconductors exhibit good efficiency, however it is not the case for green and red ones, for which external quantum efficiency does not exceed a few percent. The main reasons are related to the existing growth techniques, which induce high polarization field and high level of crystalline defects. We propose a novel GaN growth technique which will allow to fabricate microleds with improved efficiency both in blue, green and red. The objective of the thesis is first to investigate and improve the growth conditions in order to obtain GaN Led epilayers for blue, green and red emission with better crystalline quality. The objective is also to fabricate and characterize GaN microleds in order to verify the improvement at the device level.
Département d'Optronique (LETI)
Laboratoire Architecture Systèmes Photoniques
01-10-2020
SL-DRT-20-0837
Photonics, Imaging and displays (.pdf)
CEA Tech Leti is involved for several years in the development of an original concept of optical device for Augmented Reality applications. This retinal projection display concept is based on advanced technological process: SiN waveguide photonics and holographic printers. The PhD is dedicated to the first technology and concern the design of addressing waveguide architecture. It will be done in continuity of a former ending PhD on the design of dense waveguide networks in the visible range. This network, that has to interact with pixelated holograms, has to be addressed by an array of optical emitters. The PhD student will simulate and develop the waveguide multi-level architecture needed to link the emitters (LED, VCESL, laser array) to the waveguides network. He will also follow the technological steps in the clean room and bring the device characterization. The Phd will end by the conception and realization of a prototype demonstrating the interaction between an optical emitter array and a digital hologram through a waveguide network.
Département d'Optronique (LETI)
Laboratoire d'Imagerie thermique et THz
01-10-2020
SL-DRT-20-0845
Photonics, Imaging and displays (.pdf)
The Terahertz (THz, 300 GHz-3 THz) frequency band triggers a high interest in numerous application domains (imaging, spectrometry, industrial inspection and test, surveillance, instrumentation) thanks to the good propagation properties through non-conductive materials, the presence of resonance frequencies typical of numerous molecules, the potential for high spatial resolution, and their non-ionizing properties. CEA-LETI is a world-leading research laboratory in THz technologies and developed several THz detectors and imaging circuits, both cooled and uncooled, for imaging applications. Since 2018, a THz imager developed and manufactured at CEA-LETI is available commercially in the THz camera from i2S (www.i2s.fr/en). The objective of this PhD thesis is to investigate and develop a new THz detector technology with a significant breakthrough in terms of sensitivity enabling passive imaging applications. The PhD student will work in a team gathering all the expertise, instrumentation and facilities required in this project. He/she will take part in all the activities involved in the development of these new detectors, in particular system studies, design and simulation (thermal, mechanical, electromechanical), fabrication, and characterization.
Département d'Optronique (LETI)
Laboratoire d'Imagerie thermique et THz
01-09-2020
SL-DRT-20-0856
Photonics, Imaging and displays (.pdf)
Uncooled thermal detectors absorb the infrared flux for wavelengths from 7µm to 14µm. This corresponds to an atmospheric transmission window and to the maximum emission of a blackbody at 300K, which enables the detection of temperature variations of less than 100mK. The operating principle of microbolometers is based on the temperature measurement of a suspended membrane absorbing the infrared flux. The thermal transducer is the sensitive element of the microbolomètre, which determines its signal-to-noise ratio and therefore the performance of the bolometric pixel. In recent years, the miniaturization of microbolometer technologies has led to pixel size reduction down to 12 µm and has been accompanied by a reduction of manufacturing costs. However the current technology reaches its limits in a way that it becomes extremely difficult to pursue the pixel size reduction. The thesis topic is the study of a breakthrough technology for microbolometers. Unlike conventional detectors, which use thermistor for the thermal transduction, the proposed research topic will examine an original technology based on vertical diodes. The subject will focus on characterizing and modeling the performance of such a device.
Département d'Optronique (LETI)
Laboratoire d'Intégration Photonique sur Silicium
01-10-2020
SL-DRT-20-0859
Photonics, Imaging and displays (.pdf)
Quantum information processing turns out to be a major challenge for our society with the development of quantum computers, able to solve complex problems much more rapidly than a classical computer, and of quantum communications providing absolute security for information transfer. The development of integrated technologies is essential for the future large-scale deployment of compact and low-cost quantum information systems. CEA-Leti has been developing for several years a silicon photonics platform, providing integrated components and circuits for various applications such as telecom/datacom, lidars and more recently quantum communications. The objective of this PhD is in a first step to design, fabricate in the Leti clean room and characterize a new generation of advanced superconducting quantum detectors on Silicon able to detect single photons with above 90% efficiency. In a second step, these detectors will be integrated into secure quantum communication circuits. This PhD will benefit from collaborations with academic laboratories in France and in Europe.
Département d'Optronique (LETI)
Laboratoire Architecture Systèmes Photoniques
01-10-2020
SL-DRT-20-0876
Photonics, Imaging and displays (.pdf)
3D sensing by capturing depth images, is a key function in numerous emerging applications such as facial recognition, augmented reality, robotics or drones. CEA targets the development of an innovative 3D sensing module, inspired from Lidar, and including various innovative components, from the coherent optical source to the photo-detector. The proposed PhD will focus on the definition of an integrated optics architecture coupled to an optical imaging system, optical simulation with internal code or commercial software, fabrication in micro-electronic clean-room, electro-optical characterization of individual components, computing of algorithms for signal or image processing, and demonstration of the whole system, for its miniaturization and integration for example in mobile devices such as a smartphone. The work will be performed in close collaboration with a research team that will develop in parallel a first version of the system in free space. A transfer to the industry is targeted in the end.
Département d'Optronique (LETI)
Laboratoire d'Intégration Photonique sur Silicium
01-10-2020
SL-DRT-20-0877
Photonics, Imaging and displays (.pdf)
The main activities of this proposed PhD thesis will consist in the realization of silicon photonics structures for the improvement of Quantum Key Distribution (QKD) protocols. The final goals will tackle both main strategies currently employed for QKD, decoy state QKD and entanglement based QKD. Ultralow loss silicon photonics devices will be used to obtain functionalities that would be impossible or cumbersome using non integrated setups and for the convenience and reliability of operation that come from integration. Entanglement is a fundamental resource in quantum information and at the base of the most demanding protocols including device independent quantum cryptography. Room temperature, silicon integrated sources of entangled photon pairs are extremely important for the widespread adoption of quantum communication, yet despite many demonstrations in the past ten years a complete turn-key silicon source of entangled photon pairs is still lacking. In this second objective we will demonstrate such a source by integrating laser pump, source of photon pairs, and filtering and demultiplexing stages all on the same chip.
Département d'Optronique (LETI)
Laboratoire d'Imagerie thermique et THz
01-10-2020
SL-DRT-20-0893
Photonics, Imaging and displays (.pdf)
Uncooled infrared focal plane array (U-IRFPA) microbolometer technology has opened the field of thermal imaging to various novel applications, such as automotive driving assistance, building automation, leisure, smartphone. These new applications are expected to grow rapidly to reach a large volume market. Firstly developed at CEA-LETI, microbolometer technology was then transferred to LYNRED (LYNRED by SOFRADIR & ULIS, www.lynred.com) in charge of its industrialization. However, the freshly expressed new commercial needs require an improvement of the technology based on some breakthrough developments, in particular to reduce the pixel pitch to 5µm, i.e. the ultimate size sets by the IR radiation diffraction. It is the framework of this doctoral study, which aims at developing a novel class of microbolometers, by the mean of a thermal micro-transducer based on a MOS technology on FD-SOI silicon thin film, whose performance is expected as a breakthrough with respect to thermistor-based current technology. Research work will cover both the architectural design of a new integrated IR sensor on silicon, its technological prototyping (on the Leti's 200mm silicon platform) and the finale evaluation of its performance. Basically, it means both design and achievement of a disruptive sensor which differs from a classical unitary MOS-FET transistor as it could features for example an active sensor made of several different devices, or even a smart sensor adjusting itself its sensor properties in standalone. At the end of the 3 years, the student will have led to an in-depth evaluation of the feasibility of this technology for uncooled IR imaging.
Département d'Optronique (LETI)
Laboratoire des Capteurs Optiques
01-10-2020
SL-DRT-20-0900
Photonics, Imaging and displays (.pdf)
Currently the challenge is to develop automation and non-invasive measurements to enhance early identification or diagnosis. The optical technologies are the label free methods to detect and identify the chemical composition of sample. Infrared spectroscopy is a widespread and reliable method to obtain a spectral fingerprint of sample based on absorption of mir-IR light. An optical platform has been developed to measure the absorption of light through the sample, combining quantum cascade laser (QCL) and bolometer matrix. The objective of the thesis is to explore the potential of Mid-IR digital holography in order to obtain information on the phase of the sample. The thesis will aim to choose the best optical configuration of interferometer and the implement it in conventional optics. After processing the images and extracting the information, a second task will be perform this function on an integrated optical component
