Fiber Loss Budget
Calculate total optical fiber loss budget from distance, splices and connectors.
About Fiber Loss Budget
An optical link budget compares how much power the transmitter provides (relative to the receiver's minimum usable power) against how much power is actually lost along the path. Total loss sums fiber attenuation (length × dB/km), connector loss (a fixed loss per connector pair, typically 0.3-0.75 dB), and splice loss (typically 0.05-0.3 dB per fusion splice). The link margin — available power budget minus total loss — must be positive, and ideally has a few dB of safety margin, for the link to work reliably over its lifetime accounting for aging and minor future changes.
Formulas
Total link loss
total_loss = (fiber_length × loss_per_km) + (connectors × connector_loss) + (splices × splice_loss)
- d
- Fiber length in km
- \alpha
- Fiber attenuation in dB/km
- n_c, L_c
- Connector count and loss each
- n_s, L_s
- Splice count and loss each
Link margin
margin = (tx_power − rx_sensitivity) − total_loss
Worked example
With the default values below, Fiber Loss Budget returns Link Margin of 15.80. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Transmitter Poweraccepts -10–10 dBm
- 0 dBm
- Receiver Sensitivityaccepts -35–-10 dBm
- -24 dBm
- Fiber Lengthminimum 0 km
- 20 km
- Fiber Attenuationminimum 0 dB/km
- 0.35 dB/km
- Number of Connectorsminimum 0
- 2
- Loss per Connectorminimum 0 dB
- 0.5 dB
- Number of Splicesminimum 0
- 2
- Loss per Spliceminimum 0 dB
- 0.1 dB
Results
- Link Margin
- 15.80 dB
- Total Loss
- 8.20 dB
- Available Power Budget
- 24.00 dB
- Fiber Attenuation Loss
- 7.00 dB
- Connector Loss
- 1.00 dB
- Splice Loss
- 0.20 dB
Step by step
- 1Values used
- 2Total link loss
- 3Link margin
- 4Link Margin= 15.80 dB
- 5Total Loss= 8.20 dB
- 6Available Power Budget= 24.00 dB
- 7Fiber Attenuation Loss= 7.00 dB
- 8Connector Loss= 1.00 dB
- 9Splice Loss= 0.20 dB
Assumptions and limits
- The result is derived only from the 8 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
What link margin is considered safe?
A margin of at least 3 dB is a common minimum design target, providing headroom for fiber aging, additional splices added later, temperature effects, and component tolerances. Critical long-haul links often target 6 dB or more.
Why does 1550nm fiber have lower attenuation than 1310nm?
Silica fiber has a natural attenuation minimum around the 1550nm wavelength window (roughly 0.2-0.25 dB/km) compared to about 0.35 dB/km at 1310nm, due to the physics of Rayleigh scattering and absorption in glass — which is why long-haul systems favor 1550nm.
Why do splices lose less power than connectors?
A fusion splice permanently melts two fiber ends together into a continuous glass path with minimal reflection or misalignment, typically losing only 0.05-0.1 dB. A connector involves a mechanical, reconnectable interface with inherent small air gaps or alignment imperfections, typically losing 0.3-0.75 dB.
What happens if the link margin is negative?
The receiver won't get enough optical power to reliably detect the signal, causing high bit error rates, intermittent link drops, or complete link failure. You'd need to shorten the fiber run, reduce splices/connectors, use lower-loss components, boost transmitter power, or use a more sensitive receiver.