Calculating the fiber-optic link loss

The fiber-optic link budget must account for all losses at fiber-optic cable splices and connector insertion points. Keep an accurate account of losses at all connectors and splices in the system. Refer to SISNet Repeater Specifications and SISNet Distance Extender Specifications for the link budgets for single mode and multimode fiber at various core diameters. The manufacturer of the components can provide the loss specifications. Many types of cables and connectors with different loss (attenuation) specifications are available.

Example fiber-optic link loss calculation for multimode fiber

The following example shows typical link losses in a multimode, point-to-point fiber-optic link.

• Link budget 11 dB
• Fiber-optic cable (example 2 dB/km) x 2 km max = 4 dB
• TxD connector =.5 dB
• RxD connector =.5 dB
• Patch panel splices 2 x .5 dB = 1 dB
• Fiber-optic cable loss due to aging over time = 3 dB
• Total link losses = 4 + .5 + .5 + 1 + 3 = 9 dB

Margin = 11 dB -9 dB = 2 dB (the margin is greater than zero and falls within the link budget).

Example fiber-optic link loss calculation for single mode fiber

The following example shows typical link losses in a single mode, point-to-point fiber-optic link with a core diameter of 9/125 µm. Refer to SISNet Repeater Specifications and SISNet Distance Extender Specifications for the link budgets for other fiber-optic core diameters.

• Link budget 30 dB
• Fiber-optic cable (example 0.38 dB/km) x 60 km max = 22.8 dB
• TxD connector = 0.6 dB
• RxD connector = 0.6 dB
• Patch panel splices 2 x 0.1 dB = 0.2 dB
• Cable splices 10 x 0.1 dB = 1 dB
• Fiber-optic cable loss due to aging over time = 3 dB
• Total link losses = 22.8 + 0.6 + 0.6 + 0.2 + 1.0 + 3.0 = 28.2 dB

Margin = 30 dB - 28.2 dB = 1.8 dB (the margin is greater than zero and falls within the link budget).