Advanced Beam Detection for Free-Space Optics Operating in the Mid-Infrared Spectra

The article addresses the challenges of beam position tracking in Free-Space Optical Communication (<i>FSOC</i>) systems. A review of available photodetector technologies is presented, highlighting their operating principles and applications in optical links. The analysis indicates that most current monitoring devices function with the visible and near- or short-infrared ranges. However, due to the propagation characteristics of radiation in terrestrial environments, the mid-wave infrared (<i>MWIR</i>) region offers particularly promising opportunities. To the end, the work introduces a novel detector module based on an <i>MWIR</i> quadrant detector capable of simultaneously performing two essential tasks: monitoring beam position and receiving transmitted data. Such an integrated approach has the potential to significantly simplify the design of mobile <i>FSOC</i> systems, especially those requiring accurate transceivers' tracking. The concept was validated through laboratory experiments on an <i>MWIR</i> link model, where both the signal bandwidth and position transfer function of the quadrant detector were examined.