Directly-Modulated MWIR FSO Communication With High-Speed Uni-Traveling Carrier Photodiode

The mid-infrared (MIR) free-space optical (FSO) transmission systems based on quantum cascade laser (QCL) have attracted substantial attention. Nevertheless, a major limitation persists at the receiver side, which remains dominated by mercury cadmium telluride (MCT) detectors due to the lack of competitive alternatives. This prevalent reliance is particularly problematic in the mid-wave infrared (MWIR) band, where MCT detectors are fundamentally constrained by limited modulation bandwidth and cooling requirements. This study explores the potential of MWIR FSO transmission that leverages an MWIR uni-traveling carrier photodiode (UTC-PD) to attain high-speed communication. We present an experimental demonstration of an MWIR FSO link at 4.65 μm, combining a directly-modulated (DM) QCL with an uncooled UTC-PD detector based on InAs/InAsSb type-II superlattices. A transmission data rate of up to 14 Gb/s over a 31-m optical path length (OPL) is successfully achieved, demonstrating superior performance compared to a benchmark commercial MCT. Our findings suggest that the UTC-PD-based MIR FSO receiver offers a promising solution towards the next generation of optical wireless communication networks.