Fiber optics

Fiber optics is the technology of guiding light along thin strands of glass or plastic called optical fibers. Light entering one end of a fiber is kept inside by reflection and travels to the other end, where it can carry information as pulses. Optical fibers are used in communication networks, in medical instruments and in sensors, and the Royal Swedish Academy of Sciences noted in 2009 that they carry almost all telephony and data traffic.

History of fiber optics

Short, simple optical fibers have been used in medicine since the 1930s, when bundles of thin glass rods allowed doctors to look inside the stomach. Long-distance use was held back by the glass itself. According to the Nobel Prize committee, the fibers available in the 1960s could carry light only about 20 meters.

In 1966 Charles K. Kao calculated how to transmit light over long distances through optical glass fibers. He found that a fiber of the purest glass could carry light signals over 100 kilometers. His enthusiasm inspired other researchers, and the first ultrapure fiber was made four years later, in 1970. Kao received a share of the 2009 Nobel Prize in Physics for these achievements.

The Institute of Electrical and Electronics Engineers (IEEE) recognizes the 1970 work of Corning scientists Robert Maurer, Peter Schultz and Donald Keck. Engineers from the British Post Office had asked Corning for help with a fiber whose total attenuation, or loss of signal strength, would be about 20 decibels per kilometer, while the best bulk optical glasses of the day lost approximately 1,000 decibels per kilometer. The Corning team produced a fiber with 17 decibels per kilometer. By 2011, according to the IEEE history page, more than 1.6 billion kilometers of optical fiber had been installed around the globe.

How fiber optics works

An optical fiber relies on a property of light called total internal reflection. When light traveling in a material with a high refractive index meets a material with a lower index at a shallow angle, it is reflected back instead of escaping. In a fiber, a central glass core has a higher refractive index than its surroundings, so a ray of light bounces along the inside of the fiber and moves forward.

The Nobel Prize committee gives typical dimensions: the whole fiber is about 125 micrometers across, and the core is typically about 10 micrometers wide, which is less than a single hair. Infrared light with a wavelength of 1.55 micrometers suffers the lowest loss and is used today for optical communication. Choosing a low-loss wavelength is as important as the purity of the glass.

A complete link needs more than a fiber. A light source, provided by semiconductor technology, turns electrical signals into light pulses, a detector turns them back into electrical signals, and an extended network of transmitters, receivers, amplifiers and switches ties the links together. The Nobel committee stressed that the telecommunications revolution rested on the work of thousands of scientists and inventors worldwide.

Types of optical fiber

Fibers are commonly classed by how many light paths, or modes, they allow. Single-mode fibers have a very narrow core, about 10 micrometers in typical long-distance designs, so light follows essentially one path and signals can travel far with little distortion. Multimode fibers have wider cores that allow many paths, which makes them easier to connect but limits distance, so they are used mainly within buildings and campuses.

Materials differ too. Glass fibers dominate telecommunications because of their low loss, while plastic fibers are cheaper and more flexible and are used for short links. Fibers are packaged into cables with protective layers and strength members, so that thousands of kilometers can be installed on land, in ducts or on the seabed.

Applications of fiber optics

The leading application is communication. Low-loss glass fibers support global broadband, and they form the long-distance backbone that links cities and continents. The full communication system is covered in the entry on fiber-optic communication, and the capacity advantage is explained under bandwidth. Even wireless services such as Wi-Fi typically reach the wider internet through a fiber link behind the access point.

Medicine remains an important use. Bundles of fibers carry light into the body so that a physician can see inside a patient, the descendant of the 1930s experiments the Nobel committee describes. Fibers are also used in sensors that detect changes in temperature, strain or pressure along a cable, and in lighting and decoration, where light is guided to places a lamp cannot fit.

Advantages and disadvantages of fiber optics

The IEEE history page states that only optical fiber provides the bandwidth required for high-speed transmission of voice, data and video at modern volumes. Light signals in glass are also immune to electrical interference that disturbs copper wires, and they lose little strength over distance, so fewer repeaters are needed along a route.

The disadvantages are practical. Fibers must be joined with precision, because small misalignments lose light. Glass can break if bent too sharply or handled roughly. Installing new cable is costly, especially in the final connection to homes, and the equipment at each end requires power. These costs explain why many networks mix fiber with other media.

Fiber optics vs. copper cable

Copper wire carries electrical signals and is cheap and familiar, but its signals weaken faster and are more vulnerable to interference, which limits both distance and speed. Fiber carries light, which supports far higher data rates over much longer distances. Copper can also deliver electrical power to connected devices, which glass cannot do, so the two are often used together in a network.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed November 4, 2026Researched and drafted with AI assistanceReport an issue