Hamza Dely

Transfert de données à haut débit dans le moyen infrarouge à température ambiante à l'aide de dispositifs intrabande ultrarapide: Le développement des dispositifs unipolaires, dont les lasers à cascade quantique (QCL) sont le meilleur exemple, a ouvert des nouvelles possibilités en termes de circuits photoniques dans l’infrarouge moyen (3 μm-12 μm) avec de nombreuses applications à la clé : spectroscopie, LIDAR, communications en espace libre. Le potentiel des dispositifs unipolaires reposant sur le très court temps de vie des transitions intrabandes offrent naturellement de meilleures performances en terme de bande passante à −3 dB (quelques 100GHz) que leurs équivalents infrarouge proche à 1.5 μm largement déployés aujourd’hui et sont, à l’heure actuelle, la meilleure solution pour moduler à très haute fréquence les faisceaux issus de QCL dans le moyen infrarouge aux longueurs d’onde de 10 μm. Ce travail de thèse présente dans un premier temps la physique des dispositifs unipolaires avant d’exposer les résultats de transmission de données à très haut débit sur porteuse dans l’infrarouge moyen obtenus à l’aide de différents systèmes constitués de dispositifs quantiques unipolaires tels que les modulateurs, détecteurs et QCL opérés à température ambiante. En particulier j’ai démontré que le design d’un nouveau type de modulateur externe basé sur l’effet Stark intrabande permet d’envisager une amélioration substantielle des performances de ces systèmes de communication moyen infrarouge au-delà de 100 Gbit · s⁻¹. Le dispositif permet également d’envisager la conception de systèmes de détection cohérente permettant de repousser encore les débits présentés dans cette thèse. Des projets en cours permettront d’intégrer ces dispositifs au sein de circuits photoniques analogues à ceux ayant changé radicalement les télécommunications à 1.5μm ces dix dernières années.

Mid-infrared spectroscopy is a powerful technique for identifying chemical and biological substances, increasing the demand for compact and cost-effective integrated systems. In this context, integrated electro-optic modulators are essential to implement advanced techniques such as synchronous detection or dual-comb spectroscopy. In this paper, we present a waveguide-integrated electro-optic modulator operating in a broad spectral range from 5 to 9 µm wavelength, based on a Schottky diode embedded in a graded silicon germanium waveguide. By using the free-carrier plasma absorption effect, the device achieves an extinction ratio of up to 1.9 dB at a wavelength of 9 µm. Two different methods have been used to evaluate the device speed. In both cases, high-speed operation up to 7 GHz is obtained, while the optical bandwidth is estimated to be around 3 GHz. These results represent a significant step forward in both the development of characterization techniques and in the performance of mid-IR integrated modulators, paving the way for high-performance on-chip spectroscopic systems.

The development of on-chip spectroscopic systems has attracted a lot of attention in recent years. Such systems require broadband mid-infrared sources, resulting in the exploration of mid-infrared supercontinuum generation. This study focuses on reducing the pump peak power to obtain on-chip octave-spanning supercontinua at wavelengths from 4 to 13 μm, leveraging the high nonlinear refractive index and low propagation losses of Ge-rich graded SiGe photonic circuits. Two distinct platforms are explored, one grown in an industrial-scale epitaxy tool and the other using low-energy plasma-enhanced chemical vapor deposition. These silicon-compatible platforms are used to design nonlinear waveguides exhibiting anomalous group velocity dispersion, enabling soliton fission based octave-spanning supercontinuum generation at a record-low peak power of 311 W in this wavelength range. This work paves the way toward chip-based commercially available supercontinuum sources in the mid-infrared.

Phase modulation is demonstrated in a quantum Stark effect modulator designed to operate in the mid-infrared at wavelength around 10 $μ$m. Both phase and amplitude modulation are simultaneously resolved through the measurement of the heterodyne signal arising from the beating of a quantum cascade laser with a highly stabilized frequency comb. The highest measured phase shift is more than 5 degrees with an associated intensity modulation of 5%. The experimental results are in full agreement with our model in which the complex susceptibility is precisely described considering the linear voltage dependent Stark shift of the optical resonance.

Free-space optical communications in the mid-infrared transparency windows (4–5 and 8–14 μm wavelength regions) is emerging as a viable solution for high bitrate data transmission. Unipolar quantum optoelectronics is the technology of choice for data communication in this wavelength region, thanks to the high frequency response of detectors and modulators. In this work, it is demonstrated that the performances of these devices can be substantially enhanced by embedding them into metamaterials. It is also shown that metamaterials have to be engineered differently in detectors than in modulators, as the role of light–matter interaction must be tuned adequately in the two devices. Metamaterial-enhanced performances allow the realization of data transmission with a record rate of 68 Gbit/s, while ensuring robustness and consistency, as it should be for real-world applications. These findings underscore the promising role of metamaterial-enhanced unipolar devices in advancing free-space optical communication systems.

The large mid-infrared (MIR) spectral region, ranging from 2.5 µm to 25 µm, has remained under-exploited in the electromagnetic spectrum, primarily due to the absence of viable transceiver technologies. Notably, the 8–14 µm long-wave infrared (LWIR) atmospheric transmission window is particularly suitable for free-space optical (FSO) communication, owing to its combination of low atmospheric propagation loss and relatively high resilience to turbulence and other atmospheric disturbances. Here, we demonstrate a direct modulation and direct detection LWIR FSO communication system at 9.1 µm wavelength based on unipolar quantum optoelectronic devices with a unprecedented net bitrate exceeding 55 Gbit s⁻¹. A directly modulated distributed feedback quantum cascade laser (DFB-QCL) with high modulation efficiency and improved RF-design was used as a transmitter while two high speed detectors utilizing meta-materials to enhance their responsivity are employed as receivers; a quantum cascade detector (QCD) and a quantum-well infrared photodetector (QWIP). We investigate system tradeoffs and constraints, and indicate pathways forward for this technology beyond 100 Gbit s⁻¹ communication.

This study investigates the potential of long-wave infrared (LWIR) free-space optical (FSO) transmission using multilevel signals to achieve high spectral efficiency. The FSO transmission system includes a directly modulated-quantum cascade laser (DM-QCL) operating at 9.1 µm and a mercury cadmium telluride (MCT) detector. The laser operated at the temperature settings of 15°C and 20°C. The experiment was conducted over a distance of 1 m and in a lab as a controlled environment. We conduct small-signal characterization of the system, including the DM-QCL chip and MCT detector, evaluating the end-to-end response of both components and all associated electrical elements. For large-signal characterization, we employ a range of modulation formats, including non-return-to-zero on-off keying (NRZ-OOK), 4-level pulse amplitude modulation (PAM4), and 6-level PAM (PAM6), with the objective of optimizing both the bit rate and spectral efficiency of the FSO transmission by applying pre- and post-processing equalization. At 15°C, the studied LWIR FSO system achieves net bitrates of 15 Gbps with an NRZ-OOK signal and 16.9 Gbps with PAM4, both below the 6.25% overhead hard decision-forward error correction (6.25%-OH HD-FEC) limit, and 10 Gbps NRZ-OOK below the 2.7% overhead Reed-Solomon RS(528,514) pre-FEC (KR-FEC limit). At 20°C, we obtained net bitrates of 14.1 Gbps with NRZ-OOK, 16.9 Gbps with PAM4, and 16.4 Gbps with PAM6. Furthermore, we evaluate the BER performance as a function of the decision feedback equalization (DFE) tap number to explore the role of equalization in enhancing signal fidelity and reducing errors in FSO transmission. Our findings accentuate the competitive potential of DM-QCL and MCT detector-based FSO transceivers with digital equalization for the next generation of FSO communication systems.

This article presents low-loss mid-infrared waveguides fabricated on a Ge-rich SiGe strain-relaxed buffer grown on an industrial-scale 200 mm wafer, with propagation losses below 0.5 dB/cm for 5-7 µm wavelengths and below 5 dB/cm up to 11 µm. Investigation reveals free-carrier absorption as the primary loss factor for 5-6.5 µm and silicon multiphonon absorption beyond 7 µm wavelength. This result establishes a foundation for a scalable, silicon-compatible mid-infrared platform, enabling the realisation of photonic integrated circuits for various applications in the mid-infrared spectral region, from hazard detection to spectroscopy and military imaging.

Phase modulation is demonstrated in a quantum Stark effect modulator designed to operate in the mid-infrared at wavelength around 10 µm. Both phase and amplitude modulation are simultaneously resolved through the measurement of the heterodyne signal arising from the beating of a quantum cascade laser with a highly stabilized frequency comb. The highest measured phase shift is more than 5 degrees with an associated intensity modulation of 5 %. The experimental results are in full agreement with our model in which the complex susceptibility is precisely described considering the linear voltage dependent Stark shift of the optical resonance.

Lack of critical communication components (external modulators, high-sensitivity detectors, amplifiers) has long hindered the development of high-speed free-space transmission in the 8-12 μm thermal atmospheric window. Unipolar quantum technology has emerged as a game-changer by developing key elements that outperform conventional direct-modulation schemes in terms of performance. In particular, we demonstrated a free-space communication at 30 Gbits/s. High-speed modulation of the 9 μm-wavelength beam from a quantum cascade laser is implemented with a Stark-effect external modulator while fast detection relies on a quantum well infrared photodetector. In between, a multi-pass cell allows increasing the propagation distance to 31 meters.