How Does Fibre Optic Loss Occur?

Data transmission through fibre optic cable has many advantages over other transmission media such as copper cable or radio. Compared with other transmission media, fibre optic cable is lighter, smaller and more flexible with faster speed over long distance. However, there are some factors influencing the performance of fibre optic cable. Fibre optic loss is an important factor to be considered when selecting and installing cables. This article will introduce detailed information about fibre optic loss.

When a beam of light carrying signals travels through the core of fibre optic cable, the light will become weaker. That means the signals will be weaker. This phenomenon is called fibre optic loss or attenuation. The decrease in power level is described in dB. To transmit optical signals smoothly and safely, fibre optic loss must be decreased. Fibre optic loss is caused by internal reasons and external causes, which are also known as intrinsic fibre core attenuation and extrinsic fibre attenuation.


Intrinsic Fibre Core Attenuation

Internal fibre optic loss, also usually called intrinsic attenuation, is caused by the fibre optic cable itself. There are two causes of intrinsic attenuation. One is light absorption and the other one is scattering.

Light absorption is a major reason of fibre optic loss during optical transmission. Light is absorbed in the fibre by the materials of fibre optic cable. So light absorption is also known as material absorption. The lost power actually transferred into other forms of energy like heat because of molecular resonance and wavelength impurities. Atomic structure lies in any pure material and they absorb selective wavelengths of radiation. More over, we can’t find total pure materials in the market. So manufacturers use germanium and other materials with pure silica to optimise the fibre optic core performance.

The scattering of light is caused by molecular level irregularities in the glass structure. The light scatters in all direction. Some of them keeps traveling in the forward direction. And the light not scattered in the forward direction will be lost in the fibre optic link. Thus, to reduce fibre optic loss caused by scattering, the fibre optic core should be almost perfect and the fibre optic coating and extrusion should be carefully controlled.

Extrinsic Fibre Attenuation

Extrinsic fibre attenuation is also an important factor influencing the performance of fibre optic cable. It’s usually caused by improper handling of fibre optic cable including bend loss and splicing loss.

Bend loss is generally caused by fibre optic bend. There are two kinds of bending: micro bending and macro bending. Macro bending refers to a large bend in the fibre (with more than a 2 mm radius). To reduce fibre optic loss, you should better notice the followings:

  • Fibre core deviate from the axis;
  • Manufacturing defects;
  • Mechanical constraints during the fibre laying process;
  • Environmental variations like the change of temperature, humidity or pressure.


Fibre optic splicing is another cause of extrinsic fibre attenuation. It’s very common to splice fibre optic cable. So the splicing loss can’t be avoided but can be reduced with proper handling ways. For example, you can choose high quality fibre optic connectors and fusion splicing machine.

There are many factors causing fibre optic loss. To reduce the intrinsic fibre core attenuation, you should select good quality fibre optic cable. To reduce extrinsic fibre attenuation, you should better need proper handling and skills.