Topological photonics is a rapidly expanding field of research. By combining light states within materials (bulk) and at interfaces (boundaries), it aims to create photonic modes that become robust against fabrication imperfections and mitigate the intrinsic limitations of classical systems. In particular, active systems based on coupled micro- or nanolasers can produce robust laser states, which falls within the research domain of topological lasers [1-2]. However, these systems face several challenges that make their practical use difficult.
Notably, the so-called zero modes protected by symmetry or by the topology of the lattice, are located at the center of photonic bandgaps and feature out-of-phase oscillation (dark modes). Consequently, their free-space radiation efficiency is very low and they are typically confined at boundaries (edge-states).
In this PhD project, we propose to develop a new type of topological laser based on a chain of coupled optical nanocavities in a photonic crystal, offering solutions to these issues. Specifically, we will exploit a unique property of our platform: the sign inversion of evanescent coupling between two adjacent coupled nanolasers [3]. In addition, spatial distributions of gain by means of spatial modulators (SLMs) will leverage bulk topological modes. Dr. A. Giacomotti, a researcher at LP2N, has been involved in the development of coupled optical nanocavities in the context of nanolasers [3-4]. This research is part of the French ANR PRC project "WHEEL" ("A new generation of interacting resonators: non-Hermitian and time-modulated coupling"), which A. Giacomotti leads.

Objectives- The recruited candidate will be responsible for both numerical simulations and experimental studies of coupled nanolaser arrays in III-V semiconductor photonic crystals (InP with InGaAsP quantum wells). The goal is to create a laser chain of the Su-Schrieffer-Heeger type with 9 to 10 coupled cavities, achieving in-phase topological zero modes through the coupling sign-inversion technique, which is possible with our PhC technology [3].
In this case, the modes could be protected either by non-Hermitian symmetries (e.g., chiral symmetry) or by the topology of the lattice, while remaining bright (high emission efficiency) and bulk –in contrast to edge-modes.

Keywords- Active nanophotonics, semiconductors, nanolasers, topological lasers, non-Hermitian photonics.

Work Description- This PhD work will be carried out in the “Photonic Systems” group at the LP2N lab in Bordeaux.
The PhD funding is for 3 years, ideally starting on October 1st 2025. Nanofabrication will be carried out in collaboration with the C2N clean-room in Palaiseau, France (missions Bordeaux-Palaiseau will be arranged).
The involved tasks at LP2N are:
• Numerical simulations and nanophotonic design
• Optical characterization (photoluminescence spectra, imaging)
• Nanolaser emission characterization (optical & RF spectra, mode intensity dynamics)
• Laser beam control using spatial light modulators (SLM)

[1] Y. Ota, K. Takata, T. Ozawa, A. Amo, Z. Jia, B. Kante, B., ... and S. Iwamoto, Nanophotonics 9, 547 (2020).
[2] M. Parto, S. Wittek, H. Hodaei,... and M. Khajavikhan, Physical review letters 120, 113901 (2018).
[3] M. Hedir, K. Ji, J. A. Levenson, R. El-Ganainy, L. Ge, and A. M. Yacomotti, “Probing non-Hermitian zero modes in a nanophotonic trimer: from non-uniform to twisted coupling”, PRA 110, 043515 (2024).
[4] K. Ji, Q. Zhong, L. Ge, G. Beaudoin, I. Sagnes, F. Raineri, R. El-Ganainy, and A. M. Yacomotti, “Tracking exceptional points above the lasing threshold,” Nature Communications 14 (2023).