Insuring the integrity of fiber cable installations is crutial and this is done through accurate measuring and testing of fiber loss. Signal loss in fiber can result in unreliable and inconsistent transmissions.

Defining Fiber Losses

Fiber loss is also known as fiber optic attenuation or attenuation loss. Attenuation loss is measured by the amount of light lost between the input and output. A number of things can cause fiber loss and include; material absorbtion, fiber bending and connector loss.

Losses can be categorised into two basic groups. Intrinsic Loss and Extrinsic Loss. Intrinsic Loss refers to any loss that takes place due to things such as absorption loss, dispersion loss and scattering caused by the defects, Extrinsic Loss are caused by factors such as splicing loss, connector loss, and bending loss.

Standards for Fiber Loss

Standard regarding fiber loss have been developed by the Telecommunications Industry Association (TIA) and Electronic Industries Alliance (EIA) that specify performance and transmission requirements for fiber optic cables and connectors which are widely accepted throughout the industry. 

The maximum attenuation is actually the attenuation coefficient of fiber optic cable, which is expressed in dB/km. It is one of the most important parameters for fiber loss measurement. The maximum attenuation for different types of fiber optic cables (as defined by the TIA/EIA) are shown in the table below:

How to Calculate Losses in Fiber Optic Cable

For the various types of loss there are various fiber loss formulae that can be used, they are as follows;

The Total Link Loss = Cable Attenuation + Connector Loss + Splice Loss

Cable Attenuation (dB) = Maximum Cable Attenuation Coefficient (dB/km) × Length (km)

Connector Loss (dB) = Number of Connector Pairs × Connector Loss Allowance (dB)

Splice Loss (dB) = Number of Splices × Splice Loss Allowance (dB)

These formulae show that the total loss is the sum of the worst variables within the various fiber segments. (Please note that the loss calculated in this way is an estimation as there various factors that influence the results.)