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Semiconductor nanostructures with low dimensionality like quantum dots and quantum dashes are one of the best attractive and heuristic solutions for achieving high performance photonic devices. When one or more spatial dimensions of the nanocrystal approach the de Broglie wavelength, nanoscale size effects create a spatial quantization of carriers leading to a complete discretization of energy levels along with additional quantum phenomena like entangled-photon generation or squeezed states of light among others. This article reviews our recent findings and prospects on nanostructure based light emitters where active region is made with quantum-dot and quantum-dash nanostructures. Many applications ranging from silicon-based integrated technologies to quantum information systems rely on the utilization of such laser sources. Here, we link the material and fundamental properties with the device physics. For this purpose, spectral linewidth, polarization anisotropy, optical nonlinearities as well as microwave, dynamic and nonlinear properties are closely examined. The paper focuses on photonic devices grown on native substrates (InP and GaAs) as well as those heterogeneously and epitaxially grown on silicon substrate. This research pipelines the most exciting recent innovation developed around light emitters using nanostructures as gain media and highlights the importance of nanotechnologies on industry and society especially for shaping the future information and communication society., Quantum dot are one of the best practical examples of nanotechnologies. Owing to the discrete energy levels, quantum dot lasers output unique features like thermal stability, feedback insensitivity and spectral purity.

We demonstrate the detection of speech signals and footsteps through a novel polarization-multiplexed coded differential-phase OTDR (optical time domain reflectometry) interrogation of standard telecom fibers in different configurations. We assess the sensitivity to audio signals by measuring the induced phase variation with respect to the sound pressure level of the perturbation, and manage to detect acoustic signals with high reliability. Further experiments are performed using an installed fiber cable showing the ability to track footsteps in an indoor scenario. These experiments pave the way for numerous applications of Distributed Acoustic Sensing (DAS) where a high sensitivity is required.

Optical communications networks include basic components such as EDFAs and WSSs that present a polarization gain imbalance. The gain imbalance at the component output depends on the incident state-of-polarization. This well-known phenomenon called Polarization Dependent Loss (PDL) is revisited in this article and systematically analyzed within the framework of communications theory and practical achievable information rates. The rate impairment induced by PDL is discussed on an optical channel with distributed PDL and on a simplified equivalent lumped PDL channel. We have previously designed the New Spatially Balanced (NSB) signaling, an optimal 4D modulation based on this simplified model. We explore in this article its performance through numerical simulations and experimentally over a transmission in a recirculating loop with in-line PDL. Experimental measurements confirm an accurate channel modeling and significant information rate gains brought by NSB that results in SNR gains of the order of 0.4 dB at a practical transmission outage.

Photonic integrated circuits (PICs) have enabled numerous high performance, energy efficient, and compact technologies for optical communications, sensing, and metrology. One of the biggest challenges in scaling PICs comes from the parasitic reflections that feed light back into the laser source. These reflections increase noise and may cause laser destabilization. To avoid parasitic reflections, expensive and bulky optical isolators have been placed between the laser and the rest of the PIC leading to large increases in device footprint for on-chip integration schemes and significant increases in packaging complexity and cost for lasers co-packaged with passive PICs. This review article reports new findings on epitaxial quantum dot lasers on silicon and studies both theoretically and experimentally the connection between the material properties and the ultra-low reflection sensitivity that is achieved. Our results show that such quantum dot lasers on silicon exhibit much lower linewidth enhancement factors than any quantum well lasers. Together with the large damping factor, we show that the quantum dot gain medium is fundamentally dependent on dot uniformity, but through careful optimization, even epitaxial lasers on silicon can operate without an optical isolator, which is of paramount importance for the future high-speed silicon photonic systems.

A convolutional neural network is proposed to mitigate fiber transmission effects, achieving a five-fold reduction in trainable parameters compared to alternative equalizers, and 3.5 dB improvement in MSE compared to DBP with comparable complexity., 2 pages, 3 figures. Submitted to the OSA Advanced Photonics Congress 2021. Presented in Signal Processing in Photonic Communications (SPPCom) 2021. From the session: Neural Networks Applications for Photonic Systems (SpM5C)

International audience; This study deals with the communication capabilities of two kinds of semiconductor lasers emitting in one of the atmosphere transparency windows, around 4 µm. One of these two lasers is a quantum cascade laser and the other one is an interband cascade laser. With the quantum cascade laser, a subsequent attenuation is added to the optical path in order to mimic the attenuation of free-space transmission of several kilometers. Direct electrical modulation is used to transmit the message and two-level formats, non-return-to-zero and return-to-zero, are used and compared in terms of maximum transmission data rate. The sensitivity to optical feedback is also analyzed, as well as the evolution of the error rate when reducing the optical power at the level of the detector. This work provides a novel insight into the development of future secure free-space optical communication links based on midinfrared semiconductor lasers and sheds the light on improvements required to achieve multi-Gbits/s communication with off-the-shelf components. Index Terms-Quantum cascade laser, interband cascade laser, mid-infrared photonics, free-space communication. I. INTRODUCTION T HE development of semiconductor laser technology was considerably boosted with inventing quantum cascade lasers (QCLs) in early 90s [1] and interband cascade lasers (ICLs) shortly afterwards [2]. At the early stages of QCLs, free-space optical transmissions were envisioned [3] alongside Manuscript

Mid-infrared free-space optical communication has a large potential for high speed communication due to its immunity to electromagnetic interference. However, data security against eavesdroppers is among the obstacles for private free-space communication. Here, we show that two uni-directionally coupled quantum cascade lasers operating in the chaotic regime and the synchronization between them allow for the extraction of the information that has been camouflaged in the chaotic emission. This building block represents a key tool to implement a high degree of privacy directly on the physical layer. We realize a proof-of-concept communication at a wavelength of 5.7 μm with a message encryption at a bit rate of 0.5 Mbit/s. Our demonstration of private free-space communication between a transmitter and receiver opens strategies for physical encryption and decryption of a digital message., Free-space communication in the mid-IR domain has many potential applications, but security is still challenging. Here, the authors use chaos synchronization in a QCL-based free-space link as a way to increase privacy of such transmissions.

We propose a method to estimate the amplitude of an unexpected power loss which, leveraging on a calibration, enables the real-time monitoring of a network link. It is based on an existing fiber-longitudinal power profile evaluation technique. The reliability of the method is assessed experimentally. When the anomaly is located at 0 km from the beginning of the span, the estimation bias is smaller than 0.2 dB for losses up to 10 dB. When the anomaly is located at 25 km from the beginning of the span, the same estimation bias is observed but for losses up to 5 dB. In both cases, the standard deviation of the estimation is smaller than 0.2 dB.

We introduce dual-polarization probing codes based on two circularly shifted frequency sweep signals enabling perfect channel estimation. This is achieved with a probing length equal to at least twice the fiber round-trip propagation time., Conference paper (27th International Conference on Optical Fiber Sensors), 4 pages, 7 figures

We introduce a coherent-MIMO Δϕ-OTDR based sensing technique that uses digital frequency division multiplexing of probing codes in order to mitigate the coherent fading issue in Δϕ-OTDR. Orthogonal frequency division multiplexing (OFDM) is used to probe the optical channel on several electrical subcarriers, and their responses are then combined according to specific reliability criterion to enhance the overall sensing sensitivity. This allows for a decrease of the noise floor in sensing measurements on standard single mode fiber (SSMF) and the mitigation of false alarms. Coherent MIMO-OFDM enables sensing over telecom fibers with a measured sensitivity level below 21 p ε / H z along 1.3km fiber over a mechanical bandwidth of 760Hz. Enhancements in the dynamic range for detection of mechanical excitation are presented with a gain over 18dB as compared to single-carrier probing.

International audience

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Distributed optical fiber sensors using Brillouin scattering have already demonstrated their ability to measure changes in strain and temperature over long distance. However, the simultaneous sensitivity of the Brillouin scattering to these two parameters is a real disadvantage during the instrumentation and monitoring of structures, such as for civil engineering, oil industry applications (i.e. instrumentation of pipelines or wells) or electrical power cables monitoring. In this article, we present a new instrument enabling independently measurement of temperature or strain using a unique fiber in a single measurement. This method, which we will call B-OTDR DSTS for “Distributed Strain and Temperature Sensing”, is based on the measurement of frequency (as a standard BOTDR) but also intensity of Brillouin scattering. However, as the measurement of the latter requires an accurate measurement of power levels along the fiber, it is necessary to correct the losses by a Rayleigh OTDR measurement. The architecture of the BOTDR-DSTS allows simultaneous measurement of the Brillouin and Rayleigh backscatters. We will detail the validation results of this new device and show the interest of such a measurement on the instrumentation of a cable into a 2 km deep observation well.

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Brillouin optical time‐domain reflectometry (BOTDR) has the advantage of requiring access to only one end of the sensing fibre, which is an important property for some applications. The coherent detection of spontaneous Brillouin scattering allows high sensitivity of temperature/strain measurements, close to one of the well‐known Brillouin optical time‐domain analyser‐based solutions. In‐line amplification based on bidirectional erbium‐doped fibre amplification (EDFA) modules can improve sensing distance and temperature accuracy. This study demonstrates a distributed sensing over 150 km with 5‐m spatial resolution and a temperature error of less than 2°C in 10 min without requiring specific BOTDR adaptation. A record performance of 0.7°C in 60 min has been also obtained, which corresponds to the best performance obtained in reflectometer configuration at this distance.

International audience; We present a complete characterization of reflective electroabsorption modulators (EAMs) monolithically integrated with semiconductor optical amplifiers (SOAs), components that are capable of operating beyond 50 Gb/s in the C-band. The devices are based on GaInAsP multiple quantum wells on InP substrate, leveraging semi-insulating buried heterostructure waveguide definition and butt-joint integration technologies. Different device configurations, based on 80-μm and 150-μm long EAMs, are fabricated and characterized in both static and dynamic modes. The frequency response of the 80-μm long EAM is still flat at 26.5 GHz (setup upper limit) whereas the 150-μm long EAM exhibits a 3-dB cutoff bandwidth of 23 GHz. A zero-chirp is achieved for EAM reverse bias voltages between −1.2 V and −1.5 V depending on the wavelength. Under large-signal modulation, the frequency chirp induced by the shorter EAM is almost half that of the longer EAM, with their respective peak values being +1.5/−2 GHz and +3.2/−3.7 GHz (rising/falling edges) at 1545 nm (−1.3 V bias, 2.6 V voltage swing). We obtained high dynamic extinction ratios of ~14.5 dB and ~8 dB from the longer and the shorter EAMs, respectively, when they are operated at 25 Gb/s using non-return-to-zero coding. Finally, we achieved 12 km and 16 km colorless transmissions in the C-band (between 1530 nm and 1545 nm) over a standard single-mode fiber without equalization using the 150-μm and the 80-μm EAMs, respectively, with 4.5 dB and 2.5 dB dispersion penalties at a bit error rate of 10E−3.

We report on the first experimental chaos synchronization in mid-infrared quantum cascade lasers and subsequently perform private free-space transmission at a bit-rate of 0.5 Mbits/s. The quality of the privacy is assessed with eye diagrams, both at the legitimate receiver side and illegitimate receiver side.

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International audience

International audience; Cet article présente une méthode de captation de vibrations à partir de fibre optiques, inspirée des télécommunications optiquesà très haut débit et longue distance. Nous y détaillons le principe du cohérent-MIMO : un capteurà diversité de polarisation avec source laser cohérente, qui permet la captation de phénomènes mécaniques large bande.

International audience; Nous proposons une adaptation de la méthode de mesure du champ lointain pour obtenir une caractérisation résolue spectralement notamment pour des diodes semi- conductrices en régime d’émission spontanée amplifiée. Nous décrivons en détail la méthode de mesure mise en place et présentons les résultats obtenus dans le cas d’une diode à hétérostructure.

International audience; Nous proposons une méthode pour estimer l'amplitude d'une chute de puissance dans un réseau fibré en utilisant un estimateur de profils longitudinaux de puissance basé sur l'analyse de signal reçu. Celle-ci s'appuie notamment sur une calibration et un formalisme simple. Nous analysons expérimentalement la précision de l'estimation en fonction de la distance à l'amplificateur précédent.

We semianalytically and numerically investigate the static and dynamical characteristics of quantum-dot (QD) lasers directly grown on silicon by considering the Shockley-Read-Hall (SRH) recombination. The static characteristics are studied through small-signal analysis, including the ${\ensuremath{\alpha}}_{H}$ factor, damping factor, and modulation dynamics. In addition, the feedback dynamics are analyzed through improved corpuscular rate equations based on the classical Lang-Kobayashi (LK) model with time series, bifurcation diagrams, and phase portraits. We find that a smaller ${\ensuremath{\alpha}}_{H}$ factor but larger damping factor are obtained by decreasing the nonradiative recombination lifetime. On top of that, in both the short- and long-external-cavity regimes, any decrease of the SRH recombination lifetime obliterates significantly chaotic regions and shifts the first Hopf bifurcation point to higher feedback values. Overall, this work provides insights into the understanding of QD laser physics, hence highlighting the influence of the SRH lifetime on the reflection sensitivity of epitaxial QD lasers on silicon. These results are qualitatively consistent with recent experiments and are therefore helpful for designing feedback-resistant lasers for future photonic integrated circuits operating without optical isolation.

Silicon-based epitaxial quantum dot (QD) lasers with strong tolerance for back-reflections have paved the way for developing isolator-free photonics integrated circuits (PICs). This remarkable feature is attributed to the peculiar benefits of QDs, including a large material gain, a strong damping, and a small linewidth enhancement factor [1] . The laser performance can also be optimized by applying p-modulation doping in the active region [1] . In a previous study, the sensitivity of epitaxial QD lasers on silicon subject to short- and long-delay optical feedback were performed [2] . On the top of that, a further investigation of the feedback dynamics on the intra- and inter-chip scale is of significant importance for photonic integration applications.

International audience; We demonstrate the performance of a novel multi-carrier MIMO fiber sensing interrogator based on OFDM approach. Over an installed telecom fiber cable, coherent fading is mitigated by means of a purely digital subcarrier combiner.

This study investigates chaotic and spiking dynamics of mid-infrared quantum cascade lasers operating under external optical feedback and emitting at 5.5 $\mu {\text{m}}$ and 9 $\mu {\text{m}}$ . In order to deepen the understanding, the route to chaos is experimentally studied in the case of continuous-wave and current modulation operation. The non-linear dynamics are analyzed with bifurcation diagrams. While for quasi-continuous wave operation, chaos is found to be more complex, pure continuous wave pumping always leads to the generation of a regular spiking induced low-frequency fluctuations dynamics. In the latter, results show that by combining external optical feedback with periodic forcing and further induced current modulation allows a better control of the chaotic dropouts. This work provides a novel insight into the development of future secure free-space communications based on quantum cascade lasers or unpredictable optical countermeasure systems operating within the two transparency atmospheric windows hence between 3 $\mu {\text{m}}$ –5 $\mu {\text{m}}$ and 8.5 $\mu {\text{m}}$ –11 $\mu {\text{m}}$ .

International audience; We experimentally display temporal chaotic waveforms in the mid-infrared domain with two different types of semiconductor lasers. The generated high-dimensional non-linear dynamics are of prime interest for private communications and physical random number generation.

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Quantum cascade lasers (QCLs) are optical sources exploiting radiative intersubband transitions within the conduction band of semiconductor heterostructures.1 Mid-infrared QCLs have been thoroughly considered for applications such as spectroscopy,2 free-space communications3 and countermeasure systems.4 Under self-optical feedback, QCLs have been proven to operate in several non-linear dynamic regimes,5 including low-frequency fluctuations and deterministic chaos, which are suitable for private communications taking advantage of both chaos masking and background stealth. However, the previous experiments focused on distributed feedback (DFB) quantum cascade lasers emitting at 5.7 µm, which is not an optimized wavelength for free-space applications. Indeed the atmosphere is characterized by two transparency windows between 3-4 µm and 8-12 µm, which are called bandpass L and bandpass N, respectively.6 Furthermore, the 5.7 µm lasers were studied at the chip level, which means that end users must own the dedicated mounts, connectors and mid-infrared optics in order to take advantage of these quantum cascade sources. This work extends our knowledge by exploring the non- linear dynamics of a packaged Fabry-Perot (FP) QCL emitting at 4 µm. The advantage of the FP configuration is an increased output-power compared to DFB sources, though the FP configuration is not well-known yet.7 Moreover, this laser comes in a handy environment with embedded focusing optics and high-heat load (HHL) packaging for plug-and-play operation. Consequently, the current findings pave the way for off-the-shelf private s at mid-infrared wavelength where high-power and compact turnkey systems are required.

The sensitivity of a hybrid distributed feedback semiconductor (DFB) laser heterogeneously integrated onto silicon (Si) is extensively characterized in the presence of external optical feedback at different bias and temperature conditions. The unique modal engineering approach of the device allows the light generated in the III-V material to be stored in the low-loss Si region to significantly enhance the quality (Q) factor of the cavity resonator. This design leads to an increased temperature tolerance of the laser without impacting the transmission efficiency even under the most severe feedback conditions. At a temperature of T = 35◦C, the laser continuous to unveil optimal performance and exhibits feedback insensitivity when externally modulated at 10 Gbps transmission over a 10 km fiber coil. The study presented here demonstrates the ability of a high-Q laser to achieve floor-free transmission at different operating conditions with a power penalty degradation no greater than 1.5 dB. The prolonged transition to the coherence collapse regime at a much higher reflection level evidenced by this device when compared to its III-V counterparts in addition to its ability to withstand perturbations associated with temperature variations and unintentional back-reflections delivers a step forward towards isolator-free applications. This work suggest that this type of semiconductor lasers can serve as a promising solution for the development of compact and reliable photonic integrated circuits (PICs).

This work reports on an investigation of the dynamics of $1.3\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\text{m}$ epitaxial quantum dot (QD) lasers on silicon subject to delayed optical feedback. Operating the device under different feedback conditions, we experimentally identify various dynamical states of periodic oscillations. In the long-cavity feedback regime, the device remains chaos-free up to $\ensuremath{\approx}70% (\ensuremath{-}1.55\phantom{\rule{0.16em}{0ex}}\mathrm{dB})$ feedback strength. This remarkable result is in agreement with prior studies and is attributed to the particular design and properties of the QD-based active region. Shortening the external cavity length to the short-cavity regime being on the scale of photonics integrated circuits (PICs), the onset of periodic oscillations only takes place under extremely high feedback strength, which is much higher than those in PICs. The devices studied exhibit strong resistance to chip-scale back reflections in absence of any unstable oscillation. Our results also demonstrate that p doping is an efficient technique to further improve the feedback tolerance. These results point out the potential of QD lasers as an on-chip light source not requiring an optical isolator and gives insights for developing ultrastable silicon transmitters for PIC applications.

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Differential phase optical time-domain reflectometry is subject to Rayleigh fading, which locally impedes proper phase extraction. We introduce in this Letter a reliability metric derived from the measured Jones matrix estimates of the fiber sensor to discriminate between true perturbations and false alarms caused by Rayleigh backscatter fading points. The proposed soft-decision metric is also of interest for further post-processing stages exploiting artificial intelligence based classifiers.

International audience; We experimentally present a 10-Gb/s Fiber Wireless IFoF/V-band uplink of four625Mbaud 16QAM signals with a linear, high-power monolithically integrated reflective electroabsorptionmodulator with semiconductor optical amplifier for 5G mmWave fronthaul networks.

This work reports on a high-efficiency InAs/GaAs distributed feedback quantum dot laser. The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static, dynamic, and nonlinear intrinsic properties to all improve with temperature, including the lasing efficiency, the modulation dynamics, the linewidth enhancement factor, and consequently the reflection insensitivity. Results reported show an optimum operating temperature at 75°C, highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.

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A unique feature of quantum cascade lasers relies on the ultrafast carrier relaxation lifetime that occurs on a picosecond time scale. Furthermore, the very sharp electronic transitions among the conduction-band states (subbands) lead to specific selection rules, which in theory exclude the TE-polarized light emission. Under cross-polarization reinjection, we stimulate the polarization switching dynamics in such an intersubband device. The mid-infrared modulation signal is phase-shifted between the TM mode and the TE mode, with a typical microsecond time scale different from pure time-delay dynamics. We also prove that both the frequency and the duty cycle of the modulated pattern can be slightly tuned by varying the characteristics of the reinjected light. These results reveal the possibility of favoring the TE polarization in a quantum cascade laser and generating a square-wave modulation with cross-polarization reinjection.

The realization of high-frequency unipolar quantum optoelectronic devices enables the demonstration of high bitrate free space data transmission in the second atmospheric window. Data-bits are written onto the laser emission using a large bandwidth amplitude modulator that operates by shifting the absorption of an optical transition in and out of the laser frequency.

International audience; We experimentally realize a free-space transmission over one meter with roomtemperature quantum cascade lasers and interband cascade lasers. With direct electrical modulation and raw analysis, the data-rate of the real-time transmission outperforms similar reported schemes.

International audience; We propose a method to experimentally demonstrate contextuality with a family of tests for qudits. The experiment we propose uses a qudit encoded in the path of a single photon and its temporal degrees of freedom. We consider the impact of noise on the effectiveness of these tests, taking the approach of ontologically faithful non-contextuality. In this approach, imperfections in the experimental set up must be taken into account in any faithful ontological (classical) model, which limits how much the statistics can deviate within different contexts. In this way we bound the precision of the experimental setup under which ontologically faithful non-contextual models can be refuted. We further consider the noise tolerance through different types of decoherence models on different types of encodings of qudits. We quantify the effect of the decoherence on the required precision for the experimental setup in order to demonstrate contextuality in this broader sense.

International audience; We demonstrate experimentally that mid-infrared quantum cascade lasers (QCLs) operating under external optical feedback exhibit extreme pulses. These events can be triggered by adding small amplitude periodic modulation, with the highest success rate for the case of a pulse-up excitation. These findings broaden the potential applications for QCLs, which have already been proven to be a semiconductor laser of interest for spectroscopic applications and countermeasure systems. The ability to trigger extreme events paves the way for optical neuron-like systems where information propagates as a result of high intensity bursts.

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We demonstrate an all-optical square modulation in a room-temperature quantum cascade laser with cross-polarization reinjection. The duty cycle of the pattern is controlled by varying the components of the polarization, paving the way for integrated photonic memories and direct modulation of light at mid-infrared wavelength.

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This work investigates the dynamics of two-state quantum dot lasers through semi-analytically solving a set of rate equations. Simulations reveal that the occurrence of excited state lasing reduces the damping factor and relaxation oscillation frequency of the laser while increases the linewidth enhancement factor associated to the ground state transition. These results are in good agreement with the experimental observation showing that the quantum dot laser becomes more sensitive to external optical feedback at excited state lasing threshold. This work brings novel insights in the understanding of quantum dot laser physics that are useful for designing feedback resistant lasers in photonic integrated technologies.

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This work experimentally investigates the impact of p-doping on the relative intensity noise (RIN) properties and subsequently on the modulation properties of semiconductor quantum dot (QD) lasers epitaxially grown on silicon. Owing to the low threading dislocation density and the p-modulation doped GaAs barrier layer in the active region, the RIN level is found very stable with temperature with a minimum value of − 150 d B / H z . The dynamical features extracted from the RIN spectra show that p-doping between zero and 20 holes/dot strongly modifies the modulation properties and gain nonlinearities through increased internal losses in the active region and thereby hinders the maximum achievable bandwidth. Overall, this Letter is important for designing future high-speed and low-noise QD devices integrated in future photonic integrated circuits.