Hi Guys!
Its looks like the most popular question here is How do we do it?
The answer is simpler than you might think, and may cause a lot more questions from you.
We use IM to send the analogue optical signal Intensity Modulation not AM or FM or PWM or...
https://en.wikipedia.org/wiki/Intensity_modulation
when the voltage signal goes up, our light goes up, when the voltage signal goes down our light goes down.
Our wavelength is 660nm but i don't think that's important, the reason we use 660nm is because the bespoke optical fiber we use is most sensitive in that range.
Hope this helps