Optical fiber

An optical fiber is a thin, flexible strand made of glass or plastic.

These fibers function by transmitting light from one end to the other. They are essential for fiber-optic communication, which allows data to move at much higher speeds than traditional electrical cables. Because light signals travel through them with very little loss, they can cover much longer distances. Furthermore, optical fibers are immune to electromagnetic interference. This makes them more reliable than metal wires in many environments.

The mechanism that keeps light inside the fiber is called total internal reflection. An optical fiber consists of a central core surrounded by a transparent cladding. The cladding is a material with a lower index of refraction than the core. This difference in refraction causes light to bounce off the boundary between the core and the cladding. As a result, the fiber acts as a waveguide, directing the light along its length.

There are two main types of optical fibers based on how they carry light. Multi-mode fibers have a wider core diameter. They support many different propagation paths, or transverse modes, of light. These are typically used for short-distance communication or for transmitting high power. In contrast, single-mode fibers (SMF) have a much smaller core. They support only a single mode of light. Because of this, single-mode fibers are used for most communication links longer than 2 kilometers.

The history of light guidance began in the early 1840s in Paris. Daniel Colladon and Jacques Babinet first demonstrated light guiding through refraction. In 1870, John Tyndall wrote about total internal reflection in a book about light. By the late 19th century, doctors used glass rods to illuminate body cavities. In the 1950s, scientists like Bram van Heel and Harold Hopkins developed bundles of fibers to transmit images. In 1956, researchers at the University of Michigan patented the first practical gastroscope. This device used fibers to see inside the human body.

A major breakthrough occurred in 1965. Charles K. Kao and George A. Hockham proposed that light loss, or attenuation, was caused by impurities. They suggested that using high-purity silica glass could make fibers practical for communication. This theory was correct and earned Kao the Nobel Prize in Physics in 2009. In 1970, researchers at Corning Glass Works achieved a crucial attenuation limit. They did this by doping silica glass with titanium. Later, they used germanium dioxide as a core dopant to improve performance.

Manufacturing improvements helped make this technology widespread. Initially, high-quality fibers could only be made at two meters per second. In 1983, chemical engineer Thomas Mensah joined Corning and increased this speed to over 50 meters per second. This made optical fiber cables much cheaper than copper ones. In 1968, NASA even used fiber optics in television cameras sent to the moon. These cameras were so important that their use was classified as confidential at the time.

Today, optical fibers have many vital connections to modern technology. They are used in computer networking to achieve data rates of 10 or 40 Gbit/s. Through wavelength-division multiplexing (WDM), a single fiber can carry many independent channels of light. Fibers also serve as advanced sensors. They can measure strain, temperature, and pressure by analyzing changes in the light. Some sensors are so small they can be inserted into blood vessels via a hypodermic needle.