All-Dielectric Metamaterials for Metadevices : Negative Index and Near-Zero Index Materials
see attached file
Probing valley Hall currents in graphene
The first isolation of graphene, one atom thick layer of carbon atoms arrange in hexagons, in 2005 attracted a lot of attention given its remarkable characteristics: high carriers mobility, ambipolar behavior, great mechanical strength. Not long after this, other 2D layered materials were found to have also remarkable characteristics and host a large number of phenomena of condensed matter physics. A great technological achievement of our days is the stack of these 2D layers to form van der Waals (vdW) heterostructures [Nat. Nanotech 5, 722] and therefore combine the properties of each material to design materials with new properties [Nature 499, 419].
Contrary to conventional 2D materials, grown by molecular beam epitaxy, the layered vdW structures can be make of any combination of 2D materials, given that there are not restrictions of lattice parameter. Other degree of freedom of these heterostructures is the relative angular alignment between its layers, which can dramatically alter its fundamental properties. A remarkable example of this, predicted for certain vdW heterostructures, is the emergence of phases of matter where charge carriers flow without dissipation. In heterostructures of graphene crystallographically aligned with boron nitride (insulator isomorph to graphene), such a phase has been predicted. However, due to the scarcity of experimental tools to control the layer alignment the observations available remain inconclusive [Science 346, 448; Science adv. 4, eaaq0194].
In this experimental internship (with possibility to be extended to a PhD thesis), we propose to use a new technique to control the angular alignment between layers in a vdW heterostructure [Science 361, 690] to investigate the generation and control of electrical signals related to this phases of matter in graphene. The successful candidates will participate actively in sample fabrication (assembly of vdW heterostructures, angular control of layers using an AFM, e-beam lithography) and electronic transport measurements at low temperatures. Experience in micro and nano fabrication process is not required since the students will have the necessary training at the lab.
Hybrid nanostructures for nonlinear parametric processes
The control of light propagation at the nanoscale is one of the major subjects of present research. By enabling the confinement of the light in volumes as small as few cubic half-wavelength, photonic nanostructures allowed the demonstration of very interesting devices such as efficient single photon sources, low threshold nanolasers and low energy activation all optical gates.
Since a few years, our team at LPN has been particularly interested in exploiting the enhancement of the light-matter interaction using photonic crystals in order to obtain large nonlinear effects with reduced powers. The nonlinear effects under study, such as Kerr effect or second harmonic generation, enable a range of possibilities such as the control of light by light, light amplification or the generation of new frequencies.
In the proposed project, the candidate will focus her/his work on the study of second and third order nonlinear processes within semiconductor micro/nanostructures. The idea will be to use the unique dispersive properties of, e.g. photonic crystals, in order to obtain integrated parametric amplifier or frequency combs sources. As the use of only one type of material can be a limitation, heterogeneous integration of different materials will be implemented as a novel approach with the idea to exploit each class of material at its best.
The candidate will be involved in the modelling and the simulation of the structures under investigation, in the nanofabrication of the samples and in the sophisticated optical experiments necessary to observe the nonlinear behaviours.
The work can be pursued during a PhD thesis within the framework of the european Training Network H2020 - MOCCA.
Hybrid III-V semiconductor on SOI optoelectronic devices
Photonic devices play a crucial role in the domain of information and communication technology, due to their ability to bring efficient solutions to data transmission and processing.Tremendous development, through optical fibres backed by related devices and circuits composed of light sources, optical amplifiers, wavelength multiplexers, photodetectors, etc, have greatly revolutionized communication in general. As a necessary evolution, attention is now being directed to optical datacom and computercom with an emphasis on the conception of power efficient ultracompact optoelectronic components. In photonics, the challenges which we face today, swirls around providing together the necessary active and passive functionalities fully integrated into a chip. These functionalities are, among others, light emission and amplification, filtering, wavelength routing ((de)multiplexing), detection or switching. Because all of these functionalities have to comply with ultra-compactness and low-loss circuitry while maintaining low cost production in CMOS fabs, few materials can pretend to fit in. In this context, Silicon on insulator (SOI) photonics, enhanced by III-V semiconductors is a key technology combining the best of both materials leading to a highly versatile hybrid photonics platform which opens the way to large scale photonic integration. During the last years, in my research team, we have taken forward this domain to the nanophotonic world by demonstrating III-V on SOI active devices based on planar photonic crystals (PhCs) to address the issues of compactness and power efficiency. Indeed, planar PhCs which consist of wavelength scale arrangements of holes (typ. radius~100nm), drilled into a semiconductor thin slab enable a quasi-extensive control of the electromagnetic field confinement and propagation. They have demonstrated over the last decade their capacity to shelter extremely efficient nonlinear interactions exploitable for low threshold laser emission , all-optical switching , etc… The proposed project aims at building a new panel of hybrid III-V on SOI optical devices with performance beyond the state of the art in terms of footprint, power efficiency and speed, to meet the stringent requirements for on-chip optical interconnects. The targeted components will be electrically driven nanolaser, an optical amplifier and a memory.
The student will be required to focus on the design, fabrication, and experimental aspects withcontinuous feedbacks “loops” between all these different aspects. This multi-task work is possible with the remarkable facilities and resources of C2N.
The work can be pursued during a PhD thesis within the framework of the ERC project HYPNOTIC.
Analog computing with brain-inspired micropillar lasers
Artificial neural networks, which are at the heart of recent progress in analog computation and machine learning, are becoming increasingly important for our future digital societies. We propose to study coupled spiking photonic nodes in order to implement simple photonic artificial neural networks. Each node is materialized by a micropillar laser with integrated saturable absorber, whose neuromimetic properties have already been explored in the team.
In neurons, information is coded with spikes (electrical pulses) which are excited in an all-or-none fashion provided input stimuli to the neuron soma exceed a given threshold. This generic property is called excitability and has been demonstrated in micropillar lasers. Though, the optical spikes emitted by these latter are more than one millions times shorter in duration than biological action potentials. Hence, photonic neurons could in principle be interesting to build ultrafast artificial neural networks. The computing capability of optical neurons are enforced by the property of temporal summation also already demonstrated by us in micropillar lasers, and which provides universal computation capability.
The internship will consist in participating to the research lead in the group on the implementation of brain-inspired, photonic analog computing. The work consists majorily of optical experiments, with modelling and technology in the C2N clean-room.
Pulse train interaction and control in a microcavity laser with delayed optical feedback S. Terrien, B. Krauskopf, N. G. Broderick, R. Braive, G. Beaudoin, I. Sagnes, S. Barbay, Opt. Lett. 43, 3013 (2018)
Spike latency and response properties of an excitable micropillar laser F. Selmi, R. Braive, G. Beaudoin, I. Sagnes, R. Kuszelewicz, T. Erneux, S. Barbay, Phys. Rev. E 94, 042219 (2016)
Temporal summation in a neuromimetic micropillar laser F. Selmi, R. Braive, G. Beaudoin, I. Sagnes, R. Kuszelewicz, S. Barbay, Opt. Lett. 40, 5690 (2015)
Relative Refractory Period in an Excitable Semiconductor Laser F. Selmi, R. Braive, G. Beaudoin, I. Sagnes, R. Kuszelewicz, S. Barbay, Phys. Rev. Lett. 112, 183902 (2014)
F. Selmi, Thèse de doctorat, Réponse excitable et propriétés neuromimétiques de micropiliers lasers à absorbant saturable, 2015.
website : https://toniq.c2n.universite-paris-saclay.fr/fr/activites/smila/neuromimetic-photonics/