from the very entertaining: Birth of the Laser Printer
"The problem is, the bits are all coming out a kilometer away, and the printer’s down here at the other end, so how do we get the data to this thing?
So, we sat down one time and said, "So why don’t we make an optical link?" Because we looked at doing microwave, but those were only three megahertz, and you’ve got to get enough FCC permission to do that, even then. So the interesting thing is there are no communications regulations on through-the-air optical communications. As long as the beam power doesn’t destroy things. [Laughter] We built something called a SLOT POLOS , which is the PARC On-Line Office System, Jeanie certainly would probably remember that, so SLOT POLOS On-Line Optical Link. And how do you do this?
Well, I went to my friends Edmund again -- I’ll get free catalogs for the rest of my life [laughter] -- and basically bought four astronomical telescopes. These are just simple Newtonian reflectors. And put two in a box at the 3180 building, on the roof, and two on the roof of Building 34. I put a photomultiplier at the focus of one, and a laser at the focus of the other, and we had a full-duplex optical link running at 30 megabits a second. We used helium-neon for two reasons. First of all, relatively inexpensive -- accousto-optic modulators to turn it on and off. And by using visible light, there was only one risk: fog was a bad thing, because you couldn’t see through fog. On the other hand, if you used infrared, you couldn’t go through rain but you could go through fog. So, made a back-of-the-envelope judgment that rain was probably going to be more prevalent than fog, and went with the visible. It was a good choice, because I think we were only down one day due to fog, in the one year that this system was up."
That's my 2 copper cents worth.
Cents (at least US$) are made of Zinc.
Chemist who falls in acid will be tripping for weeks.