PhD defense Sara Zaminga: Photonic Chaos in Quantum Cascade Lasers: Foundations and Applications in Free-Space Optical Systems
Télécom Paris, 19 place Marguerite Perey F-91120 Palaiseau [getting there], amphi 3 and in videoconferencing
Jury
- Massimo BRAMBILLA, Professor, Politecnico di Bari — Reviewer
- Manijeh RAZEGHI, Professor, Northwestern University — Reviewer
- Paolo BARDELLA, Professor, Politecnico di Torino — Examiner
- Vincent BILLAULT, Research Engineer, Thales — Examiner
- Carlo SIRTORI, Professor, ENS Paris — Examiner
- Beatrice SORRENTE, Research Engineer, ONERA — Examiner
- Sylvie PAOLACCI-RIERA, Research Engineer, Direction Générale de l’Armement — Invited member
- Frédéric GRILLOT, Professor, Télécom Paris — Thesis Director
Abstract
This doctoral thesis explores the use of chaotic light for next-generation free-space optical (FSO) communication systems, focusing on quantum cascade lasers (QCLs) operating in the long-wave infrared (LWIR) atmospheric window. At the core of the study are distributed-feedback (DFB) QCLs, whose unique dynamics are investigated using the Effective Semiconductor Maxwell–Bloch Equations (ESMBEs).
We reveal how physical effects—such as a non-zero linewidth enhancement factor (LEF) and fast spatial hole burning (SHB)—alongside geometrical factors like cavity length and facet coatings, govern both the spectral stability and intrinsic modulation response. These mechanisms are critical to understanding the transition from single-mode to multimode longitudinal emission as the bias current increases.
… we show that photonic chaos emerges through the interplay between internal longitudinal modes and external cavity modes—not from undamped relaxation oscillations, as in interband lasers. The onset of chaos requires feedback strengths nearly two orders of magnitude higher than in diode lasers, consistent with the quasi-Class A nature of QCLs.
Building on this insight, we demonstrate two pioneering applications. First, we realize the first LWIR chaos-based LiDAR system, achieving sub-centimeter precision and meter-range resolution—currently limited by detector bandwidth. Second, we present a chaos-based random number generator (RNG) using DFB QCLs, reaching bit-rates up to 2.5 Gbps—marking a first in this spectral region.
We further examine the resilience of chaotic signals against atmospheric turbulence in the C-band, at 1.55 µm. Using a spatial light modulator to emulate turbulence in the laboratory environment and a self-configurable programmable photonic processor at the receiver end, we recover the degraded chaotic dynamics due to propagation through a turbulent medium, validating the feasibility of turbulence-hardened FSO links.
This work lays the foundation for a new class of LWIR photonic systems that harness deterministic chaos as a resource. By bridging advanced laser physics, nonlinear dynamics, and real-world applications, it paves the way for high-speed, secure, and turbulence-resilient FSO technologies—unlocking new possibilities in remote sensing, telecommunications, and information security.