This chapter looked at a number of the issues that must be considered for a full understanding of the real-world performance of FSO. Weather, link distance, scattering, absorption, turbulence, misaiming, laser wavelength, and data rates all have an impact and must be factored into either a custom calculated link budget or a manufacturer's distance rating.
As future generations of FSO equipment begin to emerge, exciting prospects for even more effective mitigation of issues impacting FSO performance will come about. One example might be low-cost active aiming designs that will allow for low-beam divergence approaching .25 mrad or even less to improve foul weather performance, extend distances up to 10 km or more, and self-aim initially, which would eliminate a tricky part of the installation process. Current 3 and 4 laser systems might be replaced with 8 and 12 laser systems. These potential future enhancements will likely accelerate the deployment of FSO in metropolitan area networks, the subject of our next chapter.
Having discussed some fundamentals of infrared radiation propagation through the atmosphere, this book will start to look at networking issues in the following chapters.