Post-Doctoral Research Visit F/M Postdoctoral project - Advanced modelling of nonlinear metasurfaces for efficient and ultra-compact short-wavelength infrared radiation

The Inria center at Université Côte d'Azur includes 42 research teams and 9 support services. The center’s staff (about 500 people) is made up of scientists of different nationalities, engineers, technicians and administrative staff. The teams are mainly located on the university campuses of Sophia Antipolis and Nice as well as Montpellier, in close collaboration with research and higher education laboratories and establishments (Université Côte d'Azur, CNRS, INRAE, INSERM ...), but also with the regional economic players.

With a presence in the fields of computational neuroscience and biology, data science and modeling, software engineering and certification, as well as collaborative robotics, the Inria Centre at Université Côte d'Azur  is a major player in terms of scientific excellence through its results and collaborations at both European and international levels.

Atlantis is  a joint project-team  between Inria and  the Jean-Alexandre Dieudonné Mathematics Laboratory at  Université Côte d'Azur. The team  gathers applied mathematicians and  computational scientists who are collaboratively undertaking  research activities aiming at the design, analysis, development and  application of innovative numerical methods for systems of  partial differential equations (PDEs) modelling nanoscale light-matter interaction problems. In this context, the team is  developing  the   DIOGENeS  [https://diogenes.inria.fr/]  software suite,  which  implements  several Discontinuous  Galerkin  (DG)  type methods tailored to the systems  of time- and frequency-domain Maxwell equations  possibly coupled  to  differential  equations modeling  the behaviour of propagation  media at optical frequencies.  DIOGENeS is a unique  numerical   framework  leveraging   the  capabilities   of  DG techniques  for  the simulation  of  multiscale  problems relevant  to nanophotonics and nanoplasmonics.

This postdoctoral project  will be conducted in close collaboration with scientific academic partners in the context of the recently started NO-RESTRAIN project funded by ANR (French National Research Agency): (1) MPQ – Paris Cité with NLMS fabrication; (2) PHELIQS – CEA - Grenoble University for the characterization of the fabricated designs.

In the last decade metasurfaces (MSs), i.e. 2D arrays of optical nanoantennas with subwavelength size and separation [1] have revolutionized the field of linear optics with the promise to replace bulky and difficult-to-align optical components with ultrathin and flat devices like metagratings, metalenses (MLs) and metaholograms, which can also implement new functionalities in terms of aberrations correction and arbitrary wavefront shaping.

The field of flat optics also showed its potential in the nonlinear regime [2] mostly with the huge of III-V semiconductors in two spectral ranges: mid-infrared based on the resonant of quantum-well inter sub band transitions and short wavelength infrared (SWIR) (based on non-resonant structures). In the latter domain, to date, the most studied phenomenon has been second harmonic generation (SHG), which has proven very useful to assess the potential of nonlinear metasurfaces (NLMSs) for nonlinear conversion. However, sum frequency generation (SFG) looks much more promising to go beyond academic interest and develop potentially useful optoelectronic devices. The main reason for it is that the two SFG inputs can have different powers and wavelengths.

Therefore: (a) a weak signal can be mixed with a strong pump and, as a result, one can increase the frequency conversion efficiency by increasing the pump intensity up to signal depletion or radiation damage; (b) the independent tuning of signal and pump wavelengths enables significant spectral agility.

The main goal of the present postdoctoral position is to model, design, and optimize an efficient and ultra- compact upconverter of SWIR radiation into the silicon absorption band. We start first with the two-steps modelling design in which the modeling involves three linear simulations in the frequency domain: one for the pump and signal inputs, and another for the generated nonlinear field, with the latter arising from the overlap of the nonlinear polarization and the nonlinear field distribution. In most of the cases the two-step approach is sufficient to provide a qualitative response of the nonlinear interaction. However, in circumstances where the time dynamics comes into play and/or there is broad spectrum excitation, two-step approaches are no longer appropriate, and one must simulate the full nonlinearity inside Maxwell’s equations, which could be computationally costly. An alternative approach is to couple the linear Maxwell’s equations to nonlinear ordinary differential equations describing the physical mechanism of the problem.

We will rely on our advanced numerical methodology introduced to design highly efficient NLMS. The first component of this methodology is a general modelling approach for the numerical characterization of metasurfaces by solving the full system of 3D time-domain Maxwell equations, which is referred to as the Discontinuous Galerkin Time-Domain (DGTD) method. This DGTD full-wave solver is implemented in the DIOGENeS software suite, which has been developed at INRIA since 2015 [3]. The second component of our modelling methodology is a numerical optimization method. We will rely on the Efficient Global Optimization (EGO) method, an adaptive statistical learning approach based on Gaussian Process (GP) models. The numerical methodology developed at INRIA has been used to optimize various linear metasurface configurations [4-7].

References

1. W. Chen et al., Flat optics with dispersion-engineered metasurfaces, Nature Review Material, vol. 5, 604 (2020)
2. C. De Angelis, G. Leo, D. Neshev, Nonlinear Meta-Optics, CRC Press - Taylor & Francis (2020)

3. DIOGENeS: A DG-based software suite for nano-optics https://diogenes.inria.fr/
4. Isnard et al., Advancing Wavefront Shaping with Resonant Nonlocal Metasurfaces: Beyond the Limitations of Lookup Tables, Scientific Reports 14, 1555 (2024).
5. Elsawy et al., Multiobjective statistical learning optimization of RGB metalens, ACS Photonics, vol. 8, 2498 (2021)
6. Elsawy, et al., Optimization of metasurfaces under geometrical uncertainty using statistical learning, Optics Express, vol. 29, 29887 (2021).
7. Elsawy et al., Universal Active Metasurfaces for Ultimate Wavefront Molding by Manipulating the Reflection Singularities, Laser Photonics Review, vol. 17, 2200880 (2023)

Required knowledge and skills:

• Theory and methodology: computational electromagnetics, finite element methods for PDEs, numerical optimization
• Sound knowledge of nanophotonics, metasurface, metamaterial

Software development skills : Python and Fortran 2003, parallel programming with MPI and OpenMP.

Relational skills : team worker (verbal communication, active listening, motivation and commitment).

Other valued appreciated : good level of spoken and written english.

• Subsidized meals
• Partial reimbursement of public transport costs
• Leave: 7 weeks of annual leave + 10 extra days off due to RTT (statutory reduction in working hours) + possibility of exceptional leave (sick children, moving home, etc.)
• Possibility of teleworking and flexible organization of working hours
• Professional equipment available (videoconferencing, loan of computer equipment, etc.)
• Social, cultural and sports events and activities
• Access to vocational training
• Contribution to mutual insurance (subject to conditions)

Gross Salary : 2788 € per month