Introduction

In 1952 physicist Narinder Singh Kapany, based on studies conducted by english physicist John Tyndall that the light could travel in curve inside a material (in Tyndall's experiment this material was water), could conclude his experiments that led to the invention of the optical fiber. Optical fiber is an excellent transmition medium used by systems that require a high bandwidth, like the telephony systems, videoconference, local networks (LANs), etc.

There are two main advantages on optical fibers over metallic cables. Optical fiber is totally imune to electromagnetic interference, which means that data isn't corrupted during their transmition. The second main advantage is that optical fiber doesn't conduct electrical current, thus no electricity-related issue is found by using optical fibers, like electrical potential difference between devices or problems with lightnings.

As the name implies, optical fibers use light to transmit data. At one end of the cable, a LED (Light Emitting Diode) or a semiconductor laser is used as the light source. LEDs can transmit data up to 300 Mbps and is used on short-distance fibers, while with laser the transfer rate can easily reach the Gbps range and is used in long-distance fibers.

The light used in optical fibers is near the infrared range, so it is invisible to the human eye. Actually optical fibers can use light from different wavelenghts, as you can on the table below. Recently ITU classified the wavelenghts that can be used in optical fibers into "bands". So an optical fiber operating on the O band means that the wavelenght of the light used in the cable is between 1260 and 1360 nm.

Band	Descriptor	Range (nm)
O band	Original	1260 to 1360
E band	Extended	1360 to 1460
S band	Short wavelength	1460 to 1530
C band	Conventional	1530 to 1565
L band	Long wavelength	1565 to 1625
U band	Ultralong wavelength	1625 to 1675

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