Fiber Optics

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The Technology of Fiber Optics

A fiber optic is a cable that is quickly replacing out-dated copper wires. Fiber optics are based on a concept known as total internal reflection. It can transmit video, sound, or data in either analog or digital form. Compared to copper wires it can transmit thousands of times more data and has many general uses ranging from telecommunications, computing, and medicine.
In the summer of 1970, scientists at the Corning Glass Works developed a single mode fiber with a loss of 20 dB/km. This corresponds to over a 99% loss over one km, which may seem useless, but at the time it was a spectacular breakthrough. On October 30, 1986, a fiber across the English Channel became operational. In December 1988, the TAT-8, the first transatlantic fiber cable became fully functional. Currently, the standard losses of fiber are within 0.5 – 0.25 dB/km with a data transfer rate of one trillion bits per second.
The basic setup for a fiber optical system is that first, a transmitter receives an electrical signal, usually from a copper wire. The transmitter drives a current on a light source and the light source launches the optical signal into the fiber. Inside the cable, repeaters often amplify the signal due to slight losses in power. Once the signal is through the cable, a light detector receives and converts it back to an electrical signal to send down another copper wire.
There are five layers in almost all fiber optic cables. The inner most layer is the optical core. This is the light-carrying element typically made of silica or germania with an index of refraction of 1.48. The layer surrounding the central core is the optical cladding made of pure silica and has an index of refraction of 1.46. It is the boundary between these two layers that the light reflects off of, so the light never actually enters the cladding, it just reflects off the boundary. The next layer is the buffer material that shields the...