A Brief History of Fiber-Optic Communications
This section discusses the
history of fiber optics, from the optical semaphore telegraph to the invention of
the first clad glass fiber invented by Abraham Van Heel. Today more than 80 percent
of the world’s long-distance voice and data traffic is carried over optical-fiber cables.
Dinesh Chand Sanwal
S/O Bhuwan Chand Sanwal
Optical communication systems date back to the 1790s, to the optical semaphore telegraph invented by French inventor Claude Chappe. In 1880, Alexander Graham Bell patented an optical telephone system, which he called the Photophone.
However, his earlier invention, the telephone, was more practical and took tangible shape. The Photophone remained an experimental invention and never materialized. During the 1920s, John Logie Baird in England and Clarence W. Hansell in the United States patented the idea of using arrays of hollow pipes or transparent rods to transmit images for television or facsimile systems.
In 1954, Dutch scientist Abraham Van Heel and British scientist Harold H. Hopkins
separately wrote papers on imaging bundles. Hopkins reported on imaging bundles of
unclad fibers, whereas Van Heel reported on simple bundles of clad fibers. Van Heel covered a bare fiber with a transparent cladding of a lower refractive index. This protected the fiber reflection surface from outside distortion and greatly reduced interference between fibers.
Abraham Van Heel is also notable for another contribution. Stimulated by a conversation
with the American optical physicist Brian O’Brien, Van Heel made the crucial innovation
of cladding fiber-optic cables. All earlier fibers developed were bare and lacked any form of
cladding, with total internal reflection occurring at a glass-air interface. Abraham Van Heel covered a bare fiber or glass or plastic with a transparent cladding of lower refractive index.This protected the total reflection surface from contamination and greatly reduced cross talk between fibers. By 1960, glass-clad fibers had attenuation of about 1 decibel (dB) per meter, fine for medical imaging, but much too high for communications. In 1961, Elias
Snitzer of American Optical published a theoretical description of a fiber with a core so
small it could carry light with only one waveguide mode. Snitzer’s proposal was acceptable
for a medical instrument looking inside the human, but the fiber had a light loss of 1 dB per meter. Communication devices needed to operate over much longer distances and required a light loss of no more than 10 or 20 dB per kilometer.
By 1964, a critical and theoretical specification was identified by Dr. Charles K. Kao for
long-range communication devices, the 10 or 20 dB of light loss per kilometer standard.
Dr. Kao also illustrated the need for a purer form of glass to help reduce light loss.
In the summer of 1970, one team of researchers began experimenting with fused silica, a
material capable of extreme purity with a high melting point and a low refractive index.
Corning Glass researchers Robert Maurer, Donald Keck, and Peter Schultz invented fiber-optic wire or “optical waveguide fibers” (patent no. 3,711,262), which was capable of carrying 65,000 times more information than copper wire, through which information carried by a pattern of light waves could be decoded at a destination even a thousand miles away. The team had solved the decibel-loss problem presented by Dr. Kao.
The team had developed an SMF with loss of 17 dB/km at 633 nm by doping titanium into the fiber core. By June of 1972, Robert Maurer, Donald Keck, and Peter Schultz invented multimode germanium-doped fiber with a loss of 4 dB per kilometer and much greater strength than titanium-doped fiber. By 1973, John MacChesney developed a modified chemical vapor-deposition process for fiber manufacture at Bell Labs. This process spearheaded the commercial manufacture of fiber-optic cable.
In April 1977, General Telephone and Electronics tested and deployed the world’s first live
telephone traffic through a fiber-optic system running at 6 Mbps, in Long Beach, California. They were soon followed by Bell in May 1977, with an optical telephone communication system installed in the downtown Chicago area, covering a distance of 1.5 miles (2.4 kilometers). Each optical-fiber pair carried the equivalent of 672 voice channels and was equivalent to a DS3 circuit. Today more than 80 percent of the world’s long distance voice and data traffic is carried over optical-fiber cables.
Dinesh Chand Sanwal
S/o Bhuwan Chand Sanwal