5 - 0.25 dB/km with a data transfer rate of 1 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 core and cladding. Next is the strength material, which prevents stretch problems when cables are being pulled or moved. Finally the outer jacket protects against abrasions and environmental contaminants and is typically make of a polymer. .
All fiber optic cable can be divided into two categories: singlemode and multimode. The big difference is that singlemode has higher bandwidth. Other aspects are singlemode cables have a smaller core (8 - 10 mm), can travel long distances, use lasers as the light source, and are much more expensive. The wavelengths that the light source transmits are 1310 nm or 1550 nm, which are outside the visible spectrum. Multimode cables have a larger core (60 - 62.5 mm) can only travel 2 km, uses LED's as their light source, and are much cheaper than their counterpart. The wavelengths are 850 nm and 1300 nm, again outside the visible spectrum.