IT Technology: Signal Loss Calculation for Fiber

For multimode fiber, the loss is about 3 dB per km for 850 nm sources, 1 dB per km for 1300 nm. (3.5 and 1.5 dB/km max per EIA/TIA 568) This roughly translates into a loss of 0.1 dB per 100 feet (30 m) for 850 nm, 0.1 dB per 300 feet(100 m) for 1300 nm.
For singlemode fiber, the loss is about 0.5 dB per km for 1310 nm sources, 0.4 dB per km for 1550 nm. (1.0 dB/km for premises/0.5 dB/km at either wavelength for outside plant max per EIA/TIA 568)This roughly translates into a loss of 0.1 dB per 600 (200m) feet for 1310 nm, 0.1 dB per 750 feet (250m) for 1300 nm.


So for the estimated loss of a cable plant, calculate the approximate loss as:
(0.5 dB X # connectors) + (0.2 dB X# splices) + (fiber attenuation X the total length of cable)

A basic guideline for loss measurements is to estimate the loss using these approximate values:
Connector loss: 0.5 dB per mated pair
Splice loss: 0.2 dB per splice
Fiber loss:
Multimode: 3 dB/km @ 850 nm, 1 dB/km @ 1300 nm
Singlemode: 0.4 dB/km @ 1300 nm, 0.3 dB/km @ 1550 nm
For example: a 1.5 km multimode link with 3 connections @ 850 nm:
Loss = (1.5 km X 3 dB/km) + (3 conn X 0.5 dB)
Loss = 4.5 dB + 1.5 dB = 6 dB