Request an intervention

Tools · Calculator

Optical link budget calculator.

One link, its loss budget, the optical class of the equipment. Optical link budget, loss budget and optical power budget are three names for this same calculation. The default values come from the standards and from the operational notes on this site: replace them with the data of your cable and your components.

First-approximation tool: detailed design requires the real data of the cable, the components and the equipment.

The calculator needs JavaScript.

Without JavaScript the formula and the table of typical values remain: the arithmetic takes a minute by hand.

Budget = (L × α) + (Ns × Ls) + (Nc × Lc) + Lsp + M

The link

The real length of the installed fibre, including slack in the chambers and risers: not the straight-line distance.

Wavelength

Changing window resets the attenuation coefficient to the matching typical value.

Typical values for an ITU-T G.652.D single-mode fibre: 0.35 dB/km at 1310 nm and 0.25 dB/km at 1550 nm. Detailed design uses the datasheet figure of the cable actually installed.

The components

Every splice in the chain, including those planned for future repairs.

A well-made fusion splice loses 0.02-0.05 dB; a serious specification sets a design threshold of ≤ 0.1 dB as a bidirectional average. A mechanical splice loses 0.1-0.3 dB.

Every patch counts: the jumpers at both ends are the item most often forgotten.

A clean, well-aligned UPC connector measures 0.2-0.3 dB. ANSI/TIA-568.3-D allows up to 0.75 dB per pair: that is a standard limit, not a design target.

Maximum insertion losses from clause 6.6 of ITU-T G.671, WR1 window, normal reach. Two cascaded stages add up and weigh more than a single stage of the same overall ratio.

Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.

The design

Design practice reserves 2-3 dB for fibre ageing, extreme temperatures and future repairs not foreseen at design time.

GPON B+ 28 dB and C+ 32 dB (ITU-T G.984.2); XGS-PON E1 33 dB (ITU-T G.9807.1). The other XGS-PON classes — N1 29 dB, N2 31 dB, E2 35 dB — can be entered with “Custom”.

The link budget

Cable attenuation
—
Splice loss
—
Connector loss
—
Splitter loss
—
Design margin
—
Total
—

First-approximation tool: detailed design requires the real data of the cable, the components and the equipment.

The formula

Budget = (L × α) + (Ns × Ls) + (Nc × Lc) + Lsp + M

  • L — link length in km; α — cable attenuation in dB/km.
  • Ns, Ls — number of fusion splices and loss per splice in dB.
  • Nc, Lc — number of connector pairs and loss per pair in dB.
  • Lsp — splitter insertion loss in dB, zero on a point-to-point link.
  • M — design margin in dB.
  • The link holds if the budget calculated this way stays below the optical class of the equipment.

The default values, and where they come from

Every value preloaded in the calculator is listed here with its source. They are standard and design references, not guarantees of outcome: the thresholds of an individual project are fixed on the real route.

Item Default value Standard or source
Cable attenuation at 1310 nm 0.35 dB/km ITU-T G.652.D single-mode fibre, typical value taken from the note on the optical budget.
Cable attenuation at 1550 nm 0.25 dB/km ITU-T G.652.D single-mode fibre, typical value taken from the note on the optical budget.
Fusion splice 0.05 dB Range 0.02-0.05 dB; specification threshold ≤ 0.1 dB as a bidirectional average.
Connector pair 0.30 dB Clean UPC 0.2-0.3 dB; maximum 0.75 dB allowed by ANSI/TIA-568.3-D.
1:2 splitter 3.9 dB Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.
1:4 splitter 7.4 dB Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.
1:8 splitter 10.6 dB Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.
1:16 splitter 14.1 dB Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.
1:32 splitter 17.5 dB Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.
1:64 splitter 20.9 dB Maximum insertion loss, ITU-T G.671 clause 6.6, WR1 window, normal reach.
Design margin 3 dB Design practice of 2-3 dB for ageing, temperature and future repairs.
GPON B+ class 28 dB GPON class optical budget, ITU-T G.984.2.
GPON C+ class 32 dB GPON class optical budget, ITU-T G.984.2.
XGS-PON E1 class 33 dB XGS-PON class optical budget, ITU-T G.9807.1.

How to read this calculation

The number that matters is the total: if it exceeds the budget of the optical class, the link does not work worse, it does not respond. It is a binary threshold, and it is the same one that testing measures in the field.

The design margin is not a loss item: it is the room reserved today for the repair splice, the ageing and the temperatures of five years from now. A design handed over with zero residual margin is compliant on paper and fragile in real life.

On a PON network the splitter is the heaviest item, and on its own it decides the optical class: the calculation is worth redoing before choosing the split ratio, not after the cable is laid.

The result stays an estimate: it holds as long as the values entered match the datasheet of the cable and of the components that will actually be installed, and it has to be verified with an insertion-loss measurement at testing.

The notes behind the values

How Do You Calculate the Optical Budget of a Fibre Link? How many dB does a PON splitter lose? The ITU-T G.671 thresholds GPON or XGS-PON: Symmetrical 10-Gigabit Fibre Has Arrived — Is Your Site Ready?

The service

ODN/PON design and optical budget

First-approximation tool: detailed design requires the real data of the cable, the components and the equipment.

The first step

A site survey. Then the numbers.

Tell us the environment and the need; we tell you times, methods and costs. Before we start, not after.

30 minutes video call or site survey €150 free July promotion
Request an intervention

We reply within one business day. Survey and quote are free.