Hi all,,
Both are optical and wireless communication. And Yes. FSO is a subset of OWC.
However, the application areas seem to differ.
In FSO, The main source of penalty is the atmospheric attenuation. However, OWC can be used for large distances where the atmospheric attenuation is not the major source of penalties, but the pointing angle is. e.g. satellite communications.
I am posting alink. you could go through this. :http://staging.optiwave.com/resources/applications-resources/optical-system-free-space-optics-fso/
Best Wishes
Naazira Badar