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Fiber optic power budget

Add up fiber, connector, splice and splitter losses to see whether the light reaches the receiver with room to spare, how much margin is left and how far the link can go.

Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.

Check
Transmitter and receiver

For GPON the page checks both directions at minimum transmitter power: downstream at 1490 nm (OLT → ONU) and upstream at 1310 nm (ONU → OLT).

Fiber
Connections and splitters

Count every mated connector pair (patch panel, splice closure, wall outlet). TIA-568.3-D allows up to 0.75 dB per pair and 0.3 dB per splice; good connectors measure 0.3 to 0.5 dB and fusion splices about 0.1 dB.

Criterion

Safety: never look into the end of a live fiber or connector, even with a magnifier or an unfiltered microscope. Light at 1310 to 1550 nm is invisible and can damage the retina (IEC 60825-2).

—Link margin in the worst direction
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Optical power along the link

From transmitter to receiver in the critical direction: fiber loses gradually; connectors, splices and splitters in steps. Dashed lines are the sensitivity and the sensitivity plus margin.

Tap the chart to see the values.

Margin versus link length

Same connections and splitters, changing only the distance. Where the line crosses the required margin is the maximum reach.

Tap the chart to see the values.

The report gathers this page's inputs, results, equations, assumptions and references, with fields for project, engineer and revision. In the print dialog, choose Save as PDF.

Method, assumptions and references

Equations used

Total loss = α · L + n_c · a_c + n_s · a_s + Σ splitter loss + other
Received power = P_tx,min − total loss; margin = P_rx − sensitivity
Maximum reach = (P_tx,min − sensitivity − fixed losses − required margin) ÷ α
PLC splitters (typical maximum): 1:2 3.8; 1:4 7.3; 1:8 10.5; 1:16 13.7; 1:32 17.1; 1:64 20.5 dB (ideal 10 · log N)

Assumptions and limits

  • Standard maximum cabled attenuation: G.652.D 0.40 dB/km (1310 and 1490 nm) and 0.30 dB/km (1550 nm); TIA-568.3-D single-mode 0.5 dB/km outside plant and 1.0 dB/km inside plant; multimode OM3/OM4 3.5 dB/km (850 nm) and 1.5 dB/km (1300 nm). Typical manufacturer values are lower.
  • GPON (ITU-T G.984.2, Amendment 2): B+ with OLT at +1.5 dBm and ONU at −27 dBm downstream, ONU at +0.5 dBm and OLT at −28 dBm upstream; C+ with +3/−30 dBm and +0.5/−32 dBm. Minimum transmitter power is used (worst case).
  • Chromatic dispersion, power penalties, reflections and multimode modal bandwidth are not included. Confirm with loss testing (OLTS) and OTDR after installation.

Standards and technical documents

  • ITU-T G.652 (11/2016): Characteristics of a single-mode optical fibre and cable
  • ITU-T G.657 (11/2016): Bending-loss insensitive single-mode optical fibre and cable
  • ITU-T G.984.2: Gigabit-capable passive optical networks (GPON): Physical media dependent (PMD) layer specification, incl. Amendment 2
  • ANSI/TIA-568.3-D: Optical Fiber Cabling and Components Standard
  • ISO/IEC 11801-1:2017: Information technology — Generic cabling for customer premises
  • ISO/IEC 14763-3: Testing of optical fibre cabling
  • Telcordia GR-1209-CORE: Generic requirements for passive optical components
  • IEC 60825-2: Safety of laser products — Safety of optical fibre communication systems

U.S. regulations

  • NFPA 70 (NEC) Article 770: optical fiber cables
  • OSHA 29 CFR 1910.268: telecommunications
  • ANSI Z136.2: safe use of optical fiber communication systems utilizing laser diode and LED sources

Frequently asked questions

How do I calculate a fiber optic power budget?

Add fiber attenuation (length × dB/km), connector, splice and splitter losses and subtract them from the minimum transmitter power. Over 6 mi of G.652.D at 1490 nm (3.9 dB), with 4 connector pairs at 0.5 dB, 6 splices at 0.1 dB and a 1:32 splitter (17.1 dB), the loss is 23.6 dB.

How much loss does a 1:32 splitter add?

Ideal loss is 10 · log 32 = 15 dB. Commercial PLC splitters are rated at about 17 dB because of excess loss and internal connections. A 1:64 is above 20 dB.

What is the difference between GPON class B+ and C+?

Class B+ accepts up to 28 dB of optical distribution network loss and C+ up to 32 dB. The extra 4 dB allows larger splits or longer distances, with more expensive OLT optics.

What safety margin should I use?

For access networks, 3 to 5 dB. It covers repair splices, laser aging and dirty connectors. A repair splice costs about 0.1 dB; a dirty connector can cost more than 1 dB.