PON Optical Power Budget and Reach Calculator (GPON, XGS-PON)
A passive optical network splits one OLT port across many ONTs, and the splitter is usually the biggest loss in the path. This calculator adds splitter, fiber, connector and splice loss, subtracts it from the launch power and shows the margin left against the receiver sensitivity.
Your numbers
Minimum launch power from the optic datasheet
Minimum receive level for the target error rate
Extra loss beyond the ideal 10*log10(N), from the splitter datasheet
Typical value at 1310 nm; use the cable datasheet
Allowance for aging, repairs and temperature
Your results
Planning estimate. Use the transmitter, receiver and splitter datasheet values for your equipment and verify with measured loss on the installed link.
Margin after reserve vs fiber length
Sweeps Fiber length from 0 to 40, holding your other inputs fixed.
Link budget records in your ERP
Optional: a short chat about keeping designed and measured link budgets with your project data.
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How to use it
Enter the minimum transmit power and the receiver sensitivity from the optics datasheets, choose the split ratio, and add your actual fiber length and the number of connectors and splices. Include any design margin your standard requires. The result shows total loss, received power and the remaining margin, and the chart shows how margin falls as the fiber gets longer.
The formulas
An ideal 1:N splitter divides power by N, which is 10 times the base-10 logarithm of N in dB, so 1:32 is about 15.05 dB. Real splitters add excess loss, giving a typical 1:32 value of around 16.5 to 17.5 dB. Fiber loss is length times attenuation. Total loss is the sum of all passive elements. Margin is the transmit power minus total loss minus the receiver sensitivity minus the reserve.
- Splitter loss per stage: 10 * log10(N) + excess loss.
- Cascaded splitters add their losses; sum all stages.
- Class B+ GPON optics are typically specified near 28 dB of path loss; check your optics class.
Common mistakes
Do not use typical power values for the budget; use the minimum transmit power and the worst-case receiver sensitivity. Remember that upstream (1310 nm) and downstream (1490 nm) differ in attenuation and power, so check both directions. Include patch cord connectors at the OLT and ONT, which are easy to forget, and also check the maximum overload level, since a very short link with a low split ratio can saturate the receiver.
Frequently Asked Questions
How much loss does a 1:32 splitter add?
The ideal figure is about 15 dB from 10*log10(32). Real splitters add excess loss, so a typical 1:32 planar splitter is specified around 16.5 to 17.5 dB. Use the datasheet value for the exact part.
What is a typical fiber attenuation for PON?
Standard singlemode fiber is typically 0.35 dB/km at 1310 nm and 0.25 dB/km at 1550 nm in field budgets, with newer cable often better. Use the cable datasheet or the standard limit for your design.
What margin should I design with?
Many designers keep 2 to 3 dB for aging, repairs and temperature. The correct figure depends on your operator policy, so use your own standard rather than a generic number.
Does this work for XGS-PON?
The method is the same. Enter the transmit power and sensitivity for the XGS-PON optics class and use the attenuation at the relevant wavelengths. The optical budget classes differ from GPON, so use the right datasheet values.
Netray can help store design budgets and measured link results against ERP project or service records so differences are visible.
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