This work demonstrates that mid-infrared quantum cascade lasers operating under external optical feedback can output a chaotic dynamics through low-frequency fluctuations close to 77 K. Results also show that the birth of chaotic dynamics is not limited to near-threshold pumping levels. In addition, when the semiconductor material is cooled down from room temperature to 77 K, it is found that the laser destabilization takes place at a lower feedback ratio which proves that quantum cascade lasers are sensitive to temperatures, likely due to changes in the upper state lifetime. These examinations are meaningful for chaotic operation of quantum cascade lasers in secure atmospheric transmission lines and optical countermeasure systems.

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 optics data transmission with bitrate in excess of 10 Gbit s −1 is demonstrated at 9 µm wavelength by using a unipolar quantum optoelectronic system at room temperature, composed of a quantum cascade laser, a modulator, and a quantum cascade detector. The large frequency bandwidth of the system is set by the detector and the modulator that are both high frequency devices, while the laser emits in continuous wave. The amplitude modulator relies on the Stark shift of an absorbing optical transition in and out of the laser frequency. This device is designed to avoid charge displacement, and therefore it is characterized by an intrinsically large bandwidth and very low electrical power consumption. This demonstration of high-bitrate data transmission sets unipolar quantum devices as the most performing platform for the development of optoelectronic systems operating at very high frequency in the mid-infrared for several applications, such as digital communications and high-resolution spectroscopy.

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.

Mid-infrared quantum cascade lasers operating under external optical feedback and external periodic bias forcing are shown to exhibit a deterministic chaotic pattern composed of frequencies which are linked to the one of the forcing. Results also show that both the amplitude and the frequency of the forcing play a key role in the number of retrieved spikes per modulation period. These findings are of paramount importance for chaotic operation of quantum cascade lasers in applications such as optical countermeasure systems and secure atmospheric transmission lines, as well as for simulating neuronal systems and the communication between neurons due to sudden bursts.

This study investigates chaotic and spiking dynamics of mid-infrared quantum cascade lasers operating under external optical feedback and emitting at 5.5 µm and 9 µm. 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 lowfrequency 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 µm-5 µm and 8.5 µm-11 µm.

Space-to-ground high-speed transmission is of utmost importance for the development of a worldwide broadband network. Mid-infrared wavelengths offer numerous advantages for building such a system, spanning from low atmospheric attenuation to eye-safe operation and resistance to inclement weather conditions. We demonstrate a full interband cascade system for high-speed transmission around a wavelength of 4.18 µm. The low-power consumption of both the laser and the detector in combination with a large modulation bandwidth and sufficient output power makes this technology ideal for a free-space optical communication application. Our proof-of-concept experiment employs a radio-frequency optimized Fabry–Perot interband cascade laser and an interband cascade infrared photodetector based on a type-II InAs/GaSb superlattice. The bandwidth of the system is evaluated to be around 1.5 GHz. It allows us to achieve data rates of 12 Gbit/s with an on–off keying scheme and 14 Gbit/s with a 4-level pulse amplitude modulation scheme. The quality of the transmission is enhanced by conventional pre- and post-processing in order to be compatible with standard error-code correction.

Quantum cascade lasers (QCLs) are optical sources exploiting radiative intersubband transitions within the conduction band of semiconductor heterostructures. 1 The opportunity given by the broad span of wavelengths that QCLs can achieve, from mid-infrared to terahertz, leads to a wide number of applications such as absorption spectroscopy, optical countermeasures and free-space communications requiring stable single-mode operation with a narrow linewidth and high output power. 2 One of the parameters of paramount importance for studying the high-speed and nonlinear dynamical properties of QCLs is the linewidth enhancement factor (LEF). The LEF quantifies the coupling between the gain and the refractive index of the QCL or, in a similar manner, the coupling between the phase and the amplitude of the electrical field. 3 Prior work focused on experimental studies of the LEF for pump currents above threshold but without exceeding 12% of the threshold current at 283K 4 and 56% of the threshold current at 82K. 5 In this work, we use the Hakki-Paoli method 6 to retrieve the LEF for current biases below threshold. We complement our findings using the self-mixing interferometry technique 5 to obtain LEFs for current biases up to more than 100% of the threshold current. These insets are meaningful to understand the behavior of QCLs, which exhibit a strongly temperature sensitive chaotic bubble when subject to external optical feedback. 7