In the dynamic field of quantum photonics, our research explores the promising convergence with interband cascade lasers (ICLs), focusing on their applications in free-space communications and quantum photonics. The pressing need for space-to-ground high-speed transmission in the global broadband network development aligns seamlessly with the unique advantages of mid-infrared wavelengths. From minimal atmospheric attenuation to eye-safe operation and resilience against bad weather conditions, mid-infrared wavelengths are expected to provide a robust foundation for these systems. Our work shows that the utilization of interband cascade technology is very much promising for high-speed transmission at a wavelength of 4.2 μm. The low power consumption of both the laser and the detector, combined with a substantial modulation bandwidth and good output power, positions this technology as an ideal solution for free-space optical communications hence enabling multigigabit data rate operations. Concurrently, our research also explores the potential of harnessing squeezed light using high quantum efficiency ICLs. Through a stochastic model approach, we demonstrate that these midinfrared semiconductor devices can exhibit significant amplitude squeezing across a broad bandwidth of several gigahertz when powered by low-noise constant current sources. These collective efforts pave the way for accelerated advancements in mid-infrared ICLs, encompassing both quantum photonics and future free-space laser communication systems include novel quantum key distribution protocols.
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.
Mid-Wave Infrared (MIR) free-space optical communication offers multiple advantages, such as improved transmission capacity through the atmosphere and immunity to electromagnetic interference. In addition, MIR transmission between 8-12 microns provides stealth for the communication signal thanks to the random thermal blackbody radiation having a strong background at these wavelengths, hence greatly reducing the probability of adversaries intercepting a MIR laser signal. Quantum Cascade Lasers (QCL) are optical sources of choice to target this wavelength domain. They are unipolar semiconductor lasers from which stimulated emission is obtained via electronic transitions between discrete energy states inside the conduction band. This work reports on a full unipolar quantum optoelectronics communication system based on a 9-micron QCL and on a Stark-effect modulator. Two different receivers are considered for high-speed detection, namely an uncooled Quantum Cascade Detector (QCD) and a nitrogen-cooled Quantum Well Infrared Photodetector (QWIP). We evaluate the maximum data rate of our link in a back-to-back (B2B) configuration before adding a multi-pass Herriott cell so as to increase the transmission length of the light path up to 31 meters. By using pulse shaping, pre- and post-processing, we reach a record bitrate both two-level (OOK) and four-level (PAM-4) modulation scheme for a 31-meter propagation link and a Bit Error Rate (BER) compatible with standard error-correction codes. Overall, we believe that our unipolar quantum system is of paramount importance for the development of cost-effective, reliable and versatile free-space optics data links.
Interband cascade lasers (ICLs) constitute a new class of semiconductor lasers allowing lasing emission in the 3– 7 μm wavelength region. Their structure presents similarities and differences with respect to both standard bipolar semiconductor lasers and quantum cascade lasers (QCLs). In contrast to QCLs, the stimulated emission of ICLs relies on the interband transition of type-II quantum wells while the carrier-to-photon lifetime ratio is similar to conventional bipolar lasers. ICLs can be classified into class-B laser systems like common quantum well lasers, and they exhibit a multi-GHz relaxation oscillation frequency that is related to the maximum modulation/chaos bandwidth achievable by these lasers. Moreover, ICLs take advantage of a cascading mechanism over repeated active regions, which allows us to boost the quantum efficiency and, thus, the emitted optical power. On top of that, the power consumption of ICLs is one or two orders of magnitude lower than their QCL counterparts whereas high-power of few hundreds of milliWatts can be achieved. Here, we report some recent results on the dynamic and nonlinear properties of ICLs. In particular, we demonstrate the generation of fully-developed chaos under external optical feedback. We show that ICLs exhibit some peculiar intensity noise features with a clear relaxation oscillation frequency. Together, these properties are of paramount importance for developing long-reach secure free-space communication, random bit generator, and remote chaotic LiDAR systems. Lastly, we also predict that ICLs are preferable devices for amplitude-noise squeezing because large amplitude noise reduction is attainable through inherent high quantum efficiency and short photon and electron lifetimes.
Free-space optical communication is a very promising alternative to fiber communication systems, in terms of ease of deployment and costs. Midinfrared light has several features of utter relevance for free-space applications: low absorption when propagating in the atmosphere even under adverse conditions, robustness of the wavefront during long-distance propagation, and absence of regulations and restrictions for this range of wavelengths. A proof-of-concept of high-speed transmission taking advantage of intersubband devices has recently been demonstrated, but this effort was limited by the short-distance optical path (up to 1 m). In this work, we study the possibility of building a long-range link using unipolar quantum optoelectronics. Two different detectors are used: an uncooled quantum cascade detector and a nitrogen-cooled quantum well-infrared photodetector. We evaluate the maximum data rate of our link in a back-to-back configuration before adding a Herriott cell to increase the length of the light path up to 31 m. By using pulse shaping, pre- and post-processing, we reach a record bitrate of 30 Gbit s − 1 for both two-level (OOK) and four-level (PAM-4) modulation schemes for a 31-m propagation link and a bit error rate compatible with error-correction codes.
The challenge of Unipolar Quantum Optoelectronics (UQO) is to bring reliable technology in the mid-infrared and terahertz domains with dozens of GHz bandwidth and room-temperature operation. The semiconductor devices based on this novel technology rely on two-dimensional electronic states localized in the conduction band, which implies that electrons are the only charge carriers involved. Though UQO technology has been proven useful for emission (quantum cascade lasers) and detection (quantum cascade detectors), it is still underdeveloped for other applications, like high-speed modulation. In this paper, we will review our recent results with a full transmission system UQO in the 8 to 14 µm atmospheric window, composed of a quantum cascade (QC) laser, an external modulator and a QC detector, all optimized for operation at 33 THz optical wavelength. Dynamics down to a few dozens of picoseconds are observed, which allow us demonstrating data rate transmission of 10 Gbps without any signal processing. In addition, the paper aims at discussing further applications of UQO in particular for radio over free-space. The basic principle for producing microwave carriers is based on an optical heterodyne beating technique taking advantage of the high-bandwidth potential of QC detectors. Then, the microwave signal is transmitted through a point-to-point wireless link by using radiofrequency antennas. With UQO, microwave signals of dozens of GHz can be achieved. To sum, this paper highlights the importance of using UQO devices operating at a few dozens of THz optical wavelength for both free-space optics and microwave photonics targeting 100 GHz radiofrequencies.
Quantum cascade lasers (QCLs) are relevant optical sources for free-space communication because they can emit in the long-wave infrared (LWIR) domain, i.e. in the 8-12 µm region. The advantage of this optical domain is that it combines a high atmosphere transmission1 with a reduced distortion for propagating beams,2 thus the superiority of LWIR lasers in comparison with existing near-infrared systems is very dependent on link availability.3 Furthermore, QCLs are characterized by the absence of relaxation oscillation resonance.4 This peculiarity could imply a very large modulation bandwidth, even if QCL structures still need to be optimized to avoid parasitic effects.5 Recent experimental efforts have highlighted the potential of QCL-based free-space communication systems6–8 and the current 4 Gbits/s record rate is expected to be outperformed in the near future with bandwidth-enhanced structures.9 This work describes a free-space live video broadcasting with a room-temperature QCL emitting at 8.1 µm. The video file is encoded in uncompressed high-definition format (1280 pixels x 720 pixels) and this corresponds to a data rate of 1.485 Gbits/s with on-off keying scheme. This high-speed electrical signal is directly injected in the QCL via the AC port of a bias tee. The modulated optical signal from the QCL is retrieved with a Mercury-Cadmium-Telluride detector and the resulting electrical signal is sent to a TV monitor where the video can be watched in live. The current findings demonstrate the versatility of a communication system with QCLs and this paves the way for real-field applications
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