Long haul modems

In the 1960s, Bell began to digitize the telephone system, and developed early high-speed radio modems for this purpose. Once digital long-haul networks were in place, they were leased for every other purpose.
Optic fiber manufacturing was perfected in the 1980s, and optic modems were first invented for these early systems. The first systems simply used light emitting diodes and PIN diodes. Faster modulation was quickly adopted for long-haul networks. In the 1990s, multispectral optical modems were adopted as well.