The mid-infrared (2–20 𝜇𝑚) is of great interest for spectroscopy and optical communications, thanks to its characteristic molecular absorptions and its two atmospheric transparency windows (3–5 𝜇𝑚 and 8–12 𝜇𝑚). Advances in materials and epitaxial growth are driving the development of mid-IR photonic integrated circuits (PICs), offering the prospect to realize compact, robust, and energy-efficient systems for portable spectroscopy and real-time detection applications. The research on mid-IR PICs focuses on reducing propagation losses of dielectric waveguides. In addition, efforts are devoted to develop high-𝑄 resonators, versatile passive devices useful for filtering, wavelength division multiplexing and Kerr frequency comb generation (as demonstrated in the near infrared region). Furthermore, efficient and ultrafast integrated mid-IR modulators need developments, especially in the long-wave infrared region. They allow for an improved functionality of photonic integrated circuits, enabling electro-optic comb generation, synchronous detection, and high-speed data transmission for optical communications. The choice of a PIC platform depends heavily on the transparency of its constituent materials: III–V semiconductors are particularly attractive due to their low optical losses and their ability to monolithically integrate active and passive components. In this context, we investigated the performance of III–V passive devices, notably low-loss waveguides and high-Q resonators. In addition, we fabricated ultrafast amplitude modulators operating in the 8–12 μm band, which exploit intersubband transitions in asymmetric coupled quantum wells to achieve modulation.

Jury members:

• Giacomo Scalari. Rapporteur & Examinateur. Professeur, ETH Zurich
• Laurent Cerutti.  Rapporteur & Examinateur. Maitre de conferences. IES, Université de Montpellier
• Delphine Marris-Morini. Examinatrice. Professeure, Univeristé Paris Saclay
• Christelle Monat. Examinatrice. Professeure, ECL Lyon
• Roland Teissier. Directeur de recherce CNRS. IES, Montpellier

Thesis investigates the emission and nonlinear optical properties of single-walled carbon nanotubes (SWCNTs) integrated with silicon-based photonic nanostructures. The research focuses on the integration of carbon nanotubes with silicon photonics platforms to realize active and nonlinear optical functionalities for future integrated photonic systems. The thesis reviews the synthesis, deposition, optical characterization, and device-level integration of SWCNTs, with particular emphasis on photoluminescence enhancement and nonlinear optical effects.

Members of jury :

• Zhipei Sun Professor, Aalto University
• Etienne Gaufrès CNRS Researcher, LP2N
• Samuel Serna Associate Professor, Bridgewater State University
• Alfredo De Rossi Research Engineer, Thales TRT
• Arianna Filoramo Research Engineer, CEA Saclay
• Nicolas Dubreil Professor, LP2N

Figure 1. (a) Photoluminescence enhancement setup (b) Schematic of fabricated device (c) SEM image of dielectrophoresis deposited carbon nanotubes

Ultrafast lasers revolutionized photonics by providing high peak intensities and pulse durations in the picosecond to femtosecond ranges. Passive mode-locking is the leading technique for generating short pulses, relying on saturable absorbers—nonlinear optical elements with intensity-dependent absorption. While semiconductor saturable absorber mirrors (SESAMs) are well-established for visible and near-infrared frequencies, a compact mid-infrared equivalent is lacking at longer wavelengths (λ > 3 µm). This thesis work proposes a novel mid-infrared SESAM concept based on the strong light-matter coupling between intersubband transitions in III-V semiconductor quantum wells and the resonant mode of metal-metal microcavities. Leveraging the strong field confinement in these structures, the saturation intensity of the intersubband transition is lowered to 10–20 kW cm−2, a level accessible by quantum (or interband) cascade lasers. We implemented a predictive tool based on coupled-mode theory to design the main figures-of-merit of a SESAM, such as modulation depth, non-saturable losses, low-intensity reflectivity and saturation intensity, exploiting both the sample geometry and the active region material. Time-domain pump–probe measurements revealed ultrafast decay times for these SESAMs of approximately 2 ps. These findings open the route towards applications with broad-gain laser sources such as mid-infrared fiber lasers, aiming to demonstrate self-starting passive mode-locking.

Members of jury :

• Maria AMANTI, Rapporteur & Examinatrice, Maîtresse de conference (HDR), MPQ Paris

• Sukhdeep DHILLON, Rapporteur & Examinateur, Directeur de recherche (HDR), LPENS Paris

• Aloyse DEGIRON, Examinateur, Directeur de recherche (HDR), MPQ Paris

• Virginie TRINITÉ, Examinatrice, Docteure Thales Palaiseau

Fig. The intersubband transition of a III-V semiconductor quantum well is embedded in an array of metal-metal microcavity resonators. The optical response of the sample is measured under low intensity - showing the appearance of intersubband polaritons in strong coupling - and high intensity - showing the absorption saturation of the intersubband transition. Pumping at the upper polariton frequency, the reflectivity of the device is measured varying the intensity of a quantum cascade laser. The result is the optical response of a semiconductor saturable absorber mirror (SESAM) tunable in the whole mid-infrared.