Exploring Mid-IR FSO Communications with Unipolar Quantum Optoelectronics

Free space optical (FSO) communication is considered a critical part of future ICT infrastructure, particularly in non-terrestrial communication segments. In this context, the ability to achieve fast and reliable FSO propagation through long-distance atmospheric channels is the most important factor in choosing technological solutions. One property of optics directly related to this factor is the choice of wavelength. It has been identified that the mid-infrared (mid-IR) regime, which includes two atmospheric transmission windows—the mid-wave IR (MWIR, 3-5 μm) and the long-wave IR (LWIR, 8-12 μm)—can potentially offer a promising solution for achieving such performance. Additionally, viable semiconductor sources and detectors that support high-speed and efficient signal transmission are also considered critical to generating sufficient critical mass to advance the application of mid-IR FSO. Unipolar quantum optoelectronics, including quantum cascade lasers (QCL), Stark modulators, quantum cascade detectors (QCD), and quantum-well IR photodetectors (QWIP), among other components, emerge as potential candidates to build such FSO subsystems and systems. We present our recent efforts in conducting subsystem and system-level studies with different variants of these unipolar quantum optoelectronics and demonstrate the potential for feasible transmitter and receiver performance in a laboratory environment. We also discuss the key challenges and considerations of such technologies towards practical development. Finally, we summarize recent research and development efforts worldwide in advancing this highly promising direction.