Commercialization & System Generations (1970s–2000)

Once low-loss fiber and semiconductor lasers existed, the next challenge was to turn laboratory demonstrations into reliable, economically competitive telecommunications systems. Progress unfolded in successive “generations” defined by wavelength, fiber type, and amplification technology.

First Field Trials and Early Systems (1975–1980)

In April 1977 AT&T installed an experimental fiber-optic transmission system in Chicago’s downtown Loop. Three weeks later General Telephone and Electronics (GTE) carried the first live telephone traffic over fiber in Long Beach, California, at 6 Mbit/s. Similar trials followed in the United Kingdom, Japan, and elsewhere.

These first-generation systems typically operated near 850 nm using multimode fiber and gallium-aluminum-arsenide lasers or LEDs. Bit rates were in the range of tens of megabits per second and repeater spacing was limited to a few kilometers by fiber loss and dispersion.

Single-Mode Fiber and the 1.3 µm Window

Multimode fiber suffered from intermodal dispersion that limited bandwidth-distance product. In the early 1980s the industry shifted rapidly to single-mode fiber operating at approximately 1.3 µm, where silica fiber has both low loss and near-zero chromatic dispersion. Long-distance carriers such as MCI and AT&T began deploying single-mode systems capable of hundreds of megabits per second over tens of kilometers without regeneration.

Submarine Cables and TAT-8

The first commercial submarine fiber-optic systems appeared in the mid-1980s. In December 1988 TAT-8, the first transatlantic fiber-optic cable, entered service between the United States, the United Kingdom, and France. It used single-mode fiber and 1.3 µm technology with regenerative repeaters. Subsequent cables quickly increased capacity and began incorporating the next major breakthrough: optical amplification.

The Erbium-Doped Fiber Amplifier

In the mid-to-late 1980s research groups led by David Payne at the University of Southampton and Emmanuel Desurvire at Bell Labs developed the erbium-doped fiber amplifier (EDFA). An EDFA amplifies optical signals directly in the 1.55 µm wavelength band—the region of lowest loss in silica fiber—without converting them to electrical form. This invention eliminated the need for frequent electronic regenerators on long routes and made wavelength-division multiplexing practical, because a single amplifier could boost many wavelength channels simultaneously.

Wavelength-Division Multiplexing and the Capacity Explosion

Commercial dense wavelength-division multiplexing (DWDM) systems appeared in the mid-1990s. By transmitting dozens (later hundreds) of independent wavelength channels on a single fiber, operators multiplied capacity far beyond what electronic time-division multiplexing alone could achieve. Submarine systems such as TAT-12/13 (1996) were among the first to exploit optical amplifiers and multiple wavelengths.

The combination of low-loss fiber, EDFAs, and WDM produced an unprecedented growth in transmission capacity that underpinned the rapid expansion of the internet in the late 1990s and beyond. Although the telecom boom of that era was followed by a sharp market correction, the underlying optical technology continued to advance.