Just as digital electrical connections use pulses of electricity down a metal cable, fibre optics relies on light pulses down a single fine fibre of glass inside a protective sheath. Electrical signals are turned into light by a laser and focused into the fibre at one end. At the other end, a detector converts the light pulses back to an electrical signal.
A fibre optic cable uses a single 'conductor' and is completely immune to electrical interference, you can run these alongside a mains cable for miles and there will be no interference to the signal. The fibre will not rot or rust and inside the protective sheath is both robust and flexible.
Putting together an optical system is, if anything, simpler than an electrical one, having no cable losses to worry about and access to the entire received spectrum at all points.
Once it is all together it works staggeringly well. Signals of the right level and with no added noise just fall out of the converter box pretty much regardless of what lies between it and the LNB. This makes it perfect for multi-home systems, especially those stretched over large buildings or many buildings. This is where it starts to pay for itself, saving on expensive copper cable, multi-switches, amplifiers, equalisation stages, the higher installation costs, earthing costs and a more pricey design stage.