In fiber optic cable installation, accurate measurement and calculation of attenuation in optical fiber is a very important step to verify network integrity and ensure network performance. Optical fiber will cause obvious signal loss (i.e. optical fiber loss) due to optical absorption and scattering, which will affect the reliability of optical transmission network. How to calculate optical fiber loss?

Standard for optical fiber loss

The Telecommunications Industry Association (TIA) and the Electronic Industries Alliance (EIA) jointly formulated the EIA / TIA standard, which specifies the performance and transmission requirements of optical cables and connectors. Now it is widely accepted and used in the optical fiber industry. EIA / TIA standard specifies that the maximum attenuation is one of the most important parameters in optical fiber loss measurement.

In fact, the maximum attenuation is the attenuation coefficient of the optical cable, in dB / km. The following figure shows the maximum attenuation of different types of optical cables in EIA / TIA-568.

How to calculate fiber loss

If you want to check whether the optical fiber link can operate normally, you need to calculate the optical fiber loss, power budget and power margin. The calculation method is as follows. In optical fiber network, it is often necessary to calculate the maximum loss on a certain length of cabling.

Total link loss (LL) = optical cable attenuation + connector attenuation + fusion attenuation (if there are other components (such as attenuators), their attenuation values can be superimposed)

Maximum Loss

As shown in the above formula, the total link loss is the maximum sum of the worst variables in a section of optical fiber. It should be noted that the total link loss calculated in this way is only an assumed value, because it assumes the possible value of component loss, that is, the actual loss of optical fiber depends on various factors, and the loss value may be higher or lower.

Optical cable attenuation (DB) = maximum optical fiber attenuation coefficient (dB/km) × Length (km)

Connector attenuation (DB) = number of connectors × Connector loss (DB)

Fusion attenuation (DB) = number of fusion splice × Fusion splice loss (DB)

Attenuation Calculate

The following is a practical example to demonstrate how to calculate the fiber loss. Suppose there is a single mode fiber optic cable is installed between two buildings, with a transmission distance of 10km and a wavelength of 1310nm. At the same time, the optical fiber has 2 ST connectors and 1 fusion joint.

Optical cable attenuation – according to the above standard table, the maximum attenuation value of outdoor single-mode optical cable with wavelength of 1310nm is 0.5dB/km, so the attenuation value of optical cable is 0.5dB/km × 10km=5dB.

Connector attenuation – because 2 ST connectors are used and the maximum loss of each ST connector is 0.75dB, the connector attenuation is 0.75dB × 2=1.5dB. In the actual calculation, the insertion loss of the connector can refer to the specification value provided by the supplier.

Fusion attenuation – the TIA / EIA standard specifies that the maximum loss of fusion is 0.3dB, so the fusion attenuation is 0.3dBx1 = 0.3dB.

It can be concluded that the total loss of the optical fiber link is 5dB + 1.5dB + 0.3dB = 6.8dB.

Summary

Because the fiber network has great advantages in meeting people’s demand for high bandwidth, the application range of optical fiber is becoming wider and wider. It is necessary for the selection of high-quality fiber optic cable and components to ensure the accuracy of network performance.