It is some years since I seriously worked on optical communications. My main "thing" was over the horizon, so called non-line-of-sight (NLOS) beaconing. I was surprised that with very simple, homemade gear I could get well over the horizon, with no clouds to help. If my poor health had not got in the way, I am sure far greater ranges would have been possible. The record (in Australia I think) is an incredible distance.
I only had one speech contact over 11km line of sight and that was with G4HJW. All my gear was made in the back of the garage and it was very simple. The optics used low cost PVC drain pipes and the lenses were made from magnifying glasses obtained from a local Poundland store. The electrical gear was very simple and low cost. It was not worth making PCBs. Test gear is very simple. Optical experiments are low cost and fun.
My main G3XBM website has much more on my gear and experiments including NLOS tests.
See https://sites.google.com/view/g3xbm4/home/optical-nanowaves/line-of-sight .