Post-Doc

                              Mid-IR photonic integrated circuits

 

Mid-infrared (mid-IR) spectroscopy is a nearly universal way to identify chemical and biological substances, as most of the molecules have their vibrational and rotational resonances in the mid-IR wavelength range. The development of mid-IR photonic circuits on silicon chips has recently gained a lot of attention, as it could offer high performance, low cost, compact, low weight and power consumption photonic circuits. Among the different materials available in silicon photonics, germanium (Ge) and silicon-germanium (SiGe) alloys with a high Ge concentration are particularly interesting because of the wide transparency window of Ge extending up to 15 µm.
In this context, we aim at demonstrating breakthrough in the field of mid IR photonic integrated circuits based on Ge-rich SiGe materials. The main achievements obtained in the recent years are described below:
- It has been demonstrated that a Ge-rich graded SiGe platform relying on a graded SiGe layer epitaxially grown on Si substrate, presents definitive advantage in terms of mid-IR photonics platform, as a single waveguide can be used with low propagation losses in an unprecedent wavelength range, up to 11 wavelengths, for both TE and TM polarization [1].
-  A whole set of passive devices has then been demonstrated: (i) Optical spectrometers working in a wide mid-infrared spectral range have been developed using a classical Fourier-transform approach [2], leading to the first on-chip spectrometer working from 5 to 8.5 µm wavelength. (ii) a new spectrometer has then been proposed to overcome the tradeoff between bandwidth and resolution of classical approaches. To this end, the spatial heterodyning of Mach Zehnder arrays is combined with optical path tuning by thermo-optic effect. A mid-infrared SiGe spectrometer was then demonstrated with a resolution better than 15 cm−1 and a bandwidth of 603 cm−1 near 7.7 μm wavelength with a 10 MZI array [3]. Finally resonators have been investigated in different configurations, based on racetrack devices and Bragg grating based Fabry-Perot cavities corresponding to the first integrated resonators reaching 8 µm wavelength [4,5]
- Active devices is a challenge to achieve a complete mid-IR photonics platform. As a preliminary step towards the implementation of a high-performance integrated modulator in the mid-IR regime, all-optical modulation has been demonstrated [6]. This first experimental demonstration of optical modulation in a mid-IR PIC, carried out in long wave infrared (LWIR) regime confirms theoretical free-carrier electro-absorption predictions paves the way for efficient electrically driven optical modulators. On another side on-chip broadband light sources are of significant interest for compact sensing devices. In that regard, supercontinuum generation offers a mean to efficiently perform coherent light conversion over an ultrawide spectral range, in a single and compact device. On-chip two-octave supercontinuum generation in the mid-infrared wavelength, ranging from 3 to 13 μm and covering almost the full transparency window of germanium has been demonstrated recently [7]. Such an ultrawide spectrum is achieved thanks to the unique features of Ge-rich graded SiGe waveguides, which allow second-order dispersion tailoring and low propagation losses over a wide wavelength range. This results also rely on the use of a Ge-rich approach which benefits from a large Kerr coefficient and tight confinement, thus, enhancing the nonlinear processes.

As a next step we would like to develop active devices in the mid-IR, that can have a strong impact for all applications. Both electro-optic and non-linear devices are targeted. Furthermore the combination of Quantum Cascade Lasers (QCL) with Silicon-Germanium (SiGe)-based mid-IR photonic integrated circuits (PIC) benefiting from both on-chip optoelectronic devices and optical non-linear functionalities will be targeted.

 The research activity will include:
- theoretical study and electro/optical simulations (linear and non-linear devices)
- clean room fabrication
- experimental characterizations using mid-IR optical bench existing in the group
     
The repartition between the three aspects can be tuned as a function of the Post-Doc researcher skills and motivation. The post-doc researcher will be actively involved in the current activity of the group, collaborating with PhD students, and researchers of different research backgrounds and nationalities. The work is done in the framework of a collaboration with L-Ness lab (Politecnico di Milano) and IES (Université de Montpellier).

 

 

References :

[1]  M. Montesinos-Ballester, V. Vakarin, Q. Liu, X. Le Roux, J. Frigerio, A. Ballabio, A. Barzaghi, C. Alonso-Ramos, L. Vivien, G. Isella, D. Marris-Morini, “Ge-rich graded SiGe waveguides and interferometers from 5 to 11 μm wavelength range”, Optics Express, 28 (9), 12771 (2020). https://doi.org/10.1364/OE.391464
[2] Q. Liu, J.M. Ramirez, V. Vakarin, X. Le Roux, C. Alonso-Ramos, J. Frigerio, A. Ballabio, E. Talamas Simola, D. Bouville, L. Vivien, G. Isella, D. Marris-Morini, “Integrated broadband dual-polarization Ge-rich SiGe mid-infrared Fourier-Transform spectrometer”, Optics Letters, 43 (20), 5021-5024 (2018). https://doi.org/10.1364/OL.43.005021,  https://hal.archives-ouvertes.fr/hal-01891844v1
[3] M. Montesinos-Ballester, Q. Liu, V. Vakarin, J M. Ramirez, C. Alonso-Ramos, X. Le Roux, J. Frigerio, A. Ballabio, E. Talamas, L. Vivien, G. Isella, D. Marris-Morini, “On-chip Fourier-transform spectrometer based on spatial heterodyning tuned by thermooptic effect,” Scientific Reports, 9, 14633 (2019) https://doi.org/10.1038/s41598-019-50947-x
[4] J-M. Ramirez, Q. Liu, V. Vakarin, X. Le Roux, J. Frigerio, A. Ballabio, C. Alonso Ramos, E. Talamas Simola, L. Vivien, G. Isella, D. Marris-Morini, “Broadband integrated racetrack ring resonators for long-wave infrared photonics”, Optics Letters, 44 (2), 407 (2019). https://doi.org/10.1364/OL.44.000407 , https://hal.archives-ouvertes.fr/hal-01983394
[5] Q. Liu, J M. Ramirez, V. Vakarin, X. Le Roux, J. Frigerio, A. Ballabio, E. Talamas Simola, C. Alonso Ramos, D. Benedikovic, D. Bouville, L. Vivien, G. Isella, D. Marris-Morini, “On-chip Bragg grating waveguides and Fabry-Perot resonators for long-wave infrared operation up to 8.4 μm”, Optics Express 26 (26), 34366 (2018). https://doi.org/10.1364/OE.26.034366
[6] M. Montesinos-Ballester, V. Vakarin, J M. Ramirez, Q. Liu, C. Alonso-Ramos, X. Le Roux, J. Frigerio, A. Ballabio, A. Barzaghi, L. Deniel, D. Bouville, L. Vivien, G. Isella, and D. Marris-Morini « Optical modulation in Ge-rich SiGe waveguides in the mid-IR wavelength range up to 11 μm”, Communications Materials, 1, 6 (2020) https://doi.org/10.1038/s43246-019-0003-8
[7] M. Montesinos-Ballester, C. Lafforgue, J. Frigerio, A. Ballabio, V. Vakarin, Q. Liu, J. M. Ramirez, X. Le Roux, D. Bouville, A. Barzaghi, C. Alonso-Ramos, L. Vivien, G. Isella, and D. Marris-Morini, On-Chip Mid-Infrared Supercontinuum Generation from 3 to 13 μm Wavelength ACS Photonics (2020), https://dx.doi.org/10.1021/acsphotonics.0c01232

 

Post-Doc

A postdoc position (24 months with possibility of extension) has opened to carry out experimental research on Quantum Fluids of Light at the Center for Nanoscience and Nanotechnology (C2N, Université Paris-Saclay, France), in the context of the ERC starting grant project ARQADIA: “Artificial quantum materials with photons: many-body physics and topology” led by Sylvain Ravets. The general objective of the project is to study out-of-equilibrium strongly correlated phases of light in nanofabricated photonic quantum materials. The research will be conducted in the “polariton quantum fluids” team at C2N (http://www.polaritonquantumfluid.fr), in tight collaboration with Sylvain Ravets and Jacqueline Bloch.Quantum fluids of light emerge in semiconductor microcavities, where both light and electronic excitations (excitons) can be confined to very small volumes. The resulting strong light-matter coupling gives rise to hybrid light-matter quasi-particles named cavity polaritons. Polaritons propagate like photons but interact with their environment via their matter part. Contrary to conservative systems, like cold atoms, cavity polaritons are intrinsically dissipative and can thus be used to naturally implement quantum simulations of driven-dissipative systems. Furthermore, multi-photon entanglement can be imprinted directly on photons leaking out of the system, thus realizing new sources of quantum light.At the core of the present project are state of the art lattices of coupled resonators, which will be realized in the C2N clean room, fully equipped for nano-technological processing. Such lattices enable on demand tailoring of the polariton dispersion in order to control the polariton dynamics. One important challenge will be to induce photon-photon interactions that are strong enough to generate quantum correlations betweenpolaritons. Several ideas will be explored to obtainnew cavity structures with improved optical properties, and featuringactive materialswith optimized polariton interactions. The physical properties of these synthetic materials will be probed by advanced optical and quantum optical spectroscopy at cryogenic temperature. The quantum nature of the generated states will be revealed by measuring spatio-temporal correlations between photons escaping polariton lattices. This will be realized for different dimensionalities (1D, 2D), and various geometries of the lattice, in particular those featuring topologically non-trivial band structures obtained by breaking time-reversal symmetry under intense externally applied magnetic fields. The platform will offer a unique opportunity to study the interplay between nonlinearities and topology in open systems.The recruited postdoc will be involved in thedesign and fabrication of the cavity samples, the experimental study of the out of equilibrium dynamics, as well as theoretical modelling via simulations. He/she will actively participate in weekly research group meetings and will be involved in the co-supervision of PhD students working on other projectsrelated to topology ornonlinear optics. The candidate should be a highly motivated researcher with independent and creative thinking. Strong skills in experimental physics are required, together with solid knowledge in photonics, solid state and quantum physics. Candidates should have a significant publication track record, and a recently obtained PhD diploma.Candidates are requested to send the following documents to S. Ravets (sylvain.ravets@c2n.upsaclay.fr) and/or J. Bloch (jacqueline.bloch@c2n.upsaclay.fr):-Detailed CV (pdf)-Motivation letter (pdf) -Candidates are kindly requested to ask to two reference researchersto send recommendations letters.

Post-Doc

Neuromorphic photonics aims at combining the neuron-like properties of specific devices with photonics technologies for novel concepts of computing. We have developed at the C2N a neuromimetic micropillar laser which behaves as a optical neuron: whenever it is excited above a given threshold, it emits a spike and returns back to a quiet state. The emitted spike is the optical equivalent of the electric action potential in biological neurons, but is a million times shorter in duration. This may open new avenues for neuromorphic computing.
One interesting configuration is when the micropillar lasers are coupled side-by-side (evanescently). In that case, a spike excited on one end of a chain can propagate through the chain without attenuation: this is called saltatory propagation. This  propagation mode is especially interesting since the speed of the spike can be controlled externally. Also, when two spikes are
counter-propagating and collide, unlike linear waves which would simply interfere and cross, they both disappear. Based on these mechanisms, logical gates can be build, and also on-chip pattern recognition circuits which can recognize simple patterns of spike timings [1].
The aim of the postdoc will be to study these phenomena. First the candidate will study the propagation of the spikes in simple structures. Then they will study the collision of spikes to form logical gates.
The fabrication of the samples will take place at the C2N clean-room facility. The host team laboratory is fully equipped with optics and fast acquisition instruments. The postdoc will be supervised by Sylvain Barbay, Research Director at CNRS and will be funded by the FunComp European project for a duration of 12 months.
The candidate is expected to have completed their PhD and to have some background in nonlinear photonics and/or neuromorphic photonics and/or nanofabrication. The work will consist in participating to the fabrication, and taking in charge the modeling and experimental activities as well as participating to the dissemination of results. Salary will be inline with CNRS policy and past experience.

[1] Photonic computing with single and coupled spiking micropillar lasers V. A. Pammi, K.
Alfaro-Bittner, M. G. Clerc, S. Barbay, IEEE J. Sel. Top. Quantum Electron. 26, 1500307
(2020).

For more information: https://toniq.c2n.universite-paris-saclay.fr/fr/activites/smila/neuromimetic-
photonics/