Optical Power Budget Calculator

Work out whether a fiber span will actually close: transmit power, fiber attenuation, splices, connectors and splitters against receiver sensitivity, with the remaining margin.

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The most negative power the optic can still decode.
PON only - see the GPON splitter calculator.
Try:

Result

Total budget
23 dB
TX power minus RX sensitivity
Total path loss
7.6 dB
Remaining margin
15.4 dB
Power at receiver
-7.6 dBm
Verdict
Link closes with healthy margin
Maximum distance at this design
56 km

Loss breakdown

ElementCalculationLoss (dB)
Fiber 12 km @ 1310 nm12 × 0.35 dB/km4.2
Fusion splices (4)4 × 0.10 dB0.4
Connector pairs (4)4 × 0.50 dB2
Splitteras entered0
Ageing / repair penaltyas entered1
Totalsum7.6

Budget consumption

Path loss used7.6 dB of 23 dB
Good margin
Healthy design margin. Record the as-built receive level at turn-up so future drift can be measured against it rather than guessed at.

About Optical Power Budget Calculator

A fiber link closes when the light arriving at the receiver is above its sensitivity threshold - with enough margin left for the fiber to age, for a digger to cost you a repair splice, and for a connector to get dirty. This adds up every loss element and tells you what is left.

The loss elements

Attenuation dominates over distance: roughly 0.35 dB/km at 1310 nm, 0.22 dB/km at 1550 nm, and around 3 dB/km for multimode at 850 nm. Fusion splices cost about 0.1 dB each, mated connector pairs about 0.5 dB, and a mechanical splice around 0.3 dB. On a short link, connectors and patch panels are the budget - not the fiber.

Margin, and why 3 dB

Margin absorbs what the design cannot predict: connector contamination, a repair splice or two over the life of the cable, temperature effects and transmitter ageing. Three decibels is the common minimum, and it is worth remembering that 3 dB is half the power - margin disappears faster than it looks on a spreadsheet.

Common use cases

  • Deciding whether a route needs a higher-power optic before you buy it.
  • Checking a PON design closes at the worst-case ONU after the splitter.
  • Explaining to a contractor why six patch panels in a path is a problem.

Edge cases and gotchas

  • Receiver overload matters too: on a short span with a long-reach optic, too much light saturates the receiver. Add an attenuator when the arriving power exceeds the maximum input.
  • Multimode attenuation is roughly ten times single-mode; do not reuse single-mode coefficients.
  • Splitter loss is not exactly 3 dB per split - real components include excess loss, which the GPON calculator accounts for.

Frequently asked questions

What margin should I design for?
3 dB minimum, 5 dB where the route is hard to access or likely to be dug up. PON deployments typically design to the class limit with a similar allowance.
My receive level is fine but errors are climbing - why?
Check for receiver overload on short links, dispersion on long 10G spans, and reflectance from a poor connector. Power level alone does not describe signal quality.