If you want to test whether the fiber optic link can operate properly, then you need to calculate the fiber loss, power budget and power margin, which are calculated as follows.

CALCULATION OF FIBER LOSS

In fiber optic cabling, it is often necessary to calculate the maximum loss on a defined length of line. The formula for calculating fiber loss.

TOTAL LINK LOSS (LL) = fiber optic cable attenuation + connector attenuation + fusion splice attenuation [Note: If there are other components (such as attenuators), their attenuation values can be superimposed]

CABLE ATTENUATION (dB) = maximum fiber attenuation coefficient (dB / km) × length (km)

Connector attenuation (dB) = the number of connector pairs × connector loss (dB)

Fusion splice attenuation (dB) = number of fusion splices × fusion loss (dB)

As shown in the above formula, the total link loss is the maximum sum of the worst variables within a section of fiber. It is important to note that the total link loss calculated in this way is only a hypothetical value, as it assumes the possible values of component loss, meaning that the actual loss of the fiber depends on various factors, and the loss value may be higher or lower.

The following is a real-world example to demonstrate how to calculate fiber loss. In the figure below, a single-mode fiber is installed between two buildings with a transmission distance of 10 km and a wavelength of 1310 nm. Also, the fiber has 2 ST connectors and 1 fusion splice head.

CABLE ATTENUATION – According to the standard table above, the maximum attenuation value of outdoor single-mode fiber optic cable with wavelength of 1310nm is 0.5dB / km, so the cable attenuation value is 0.5dB / km x 10km = 5dB.

CONNECTOR ATTENUATION – because 2 ST connectors are used, and the maximum loss of each ST connector is 0.75dB, so 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 SPLICE ATTENUATION – in the TIA/EIA standard specification, the maximum loss of fusion splice is 0.3dB, so the fusion splice attenuation is 0.3dB x 1 = 0.3dB.

This gives a total loss of 5dB + 1.5dB + 0.3dB = 6.8dB for the fiber link. please note that the above calculation is only an assumed value, to get the most accurate loss value, you can use an optical time domain reflectometer OTDR for measurement.