Optical link budget calculator
Add up transmitter power, fibre and connector losses, penalties and receiver sensitivity to see the link margin and the reach it allows.
Analog, RF, photonics and packagingFree to useHow it worksSourcesWhere it helps
Fills the inputs below with typical figures. Replace any of them with your own.
- Link margin, worst case
- 0.20 dB
- -7.90 dBm at the receiver against -8.10 dBm needed
- Link margin, typical
- 4.40 dB
- -3.70 dBm at the receiver
- Channel loss
- 6.10 dB
- Worst case; typical 4.20 dB
- Power at the receiver, worst case
- -7.90 dBm
- 0.162 mW, on OMA
- Maximum reach, worst case
- 10.5 km
- Typical 22.57 km
- Total budget
- 7.30 dB
- Minimum launch power minus sensitivity
Check these
- Less than 1 dB of worst-case margin is left (0.20 dB). Measurement uncertainty, cleaning and re-mating can use that up.
Available: 7.30 dB between the minimum launch power and the sensitivity. Typical loss is written after each bar.
- Fibre4.00 dBtypical 3.50 dB
- Connectors1.50 dBtypical 0.60 dB
- Splices0.60 dBtypical 0.10 dB
- Dispersion and other penalties1.00 dBtypical 1.00 dB
Show the data as a table
| Item | Loss (dB) |
|---|---|
| Fibre | 4.00 dB |
| Connectors | 1.50 dB |
| Splices | 0.60 dB |
| Dispersion and other penalties | 1.00 dB |
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| Element | What was counted | Worst-case loss | Typical loss | Power after it, worst case | Power after it, typical |
|---|---|---|---|---|---|
| Launch power (minimum, typical) | OMA | -0.80 dBm | 1.50 dBm | ||
| Fibre | 10 km at 0.4 dB/km (typical 0.35) | 4.00 dB | 3.50 dB | -4.80 dBm | -2.00 dBm |
| Connectors | 2 at 0.75 dB (typical 0.3) | 1.50 dB | 0.60 dB | -6.30 dBm | -2.60 dBm |
| Splices | 2 at 0.3 dB (typical 0.05) | 0.60 dB | 0.10 dB | -6.90 dBm | -2.70 dBm |
| Dispersion and other penalties | 1 dB | 1.00 dB | 1.00 dB | -7.90 dBm | -3.70 dBm |
| Ageing and safety allowance | 0 dB | 0.00 dB | 0.00 dB | -7.90 dBm | -3.70 dBm |
- Received power, worst case (solid line, circles)
- Received power, typical (dashed line, squares)
- Needed at the receiver (dotted line, triangles)
Show the data as a table
| Fibre length (km) | Received power, worst case | Received power, typical | Needed at the receiver |
|---|---|---|---|
| 0 | -3.9 | -0.2 | -8.1 |
| 1.09 | -4.34 | -0.583 | -8.1 |
| 2.19 | -4.78 | -0.966 | -8.1 |
| 3.28 | -5.21 | -1.35 | -8.1 |
| 4.37 | -5.65 | -1.73 | -8.1 |
| 5.47 | -6.09 | -2.11 | -8.1 |
| 6.56 | -6.53 | -2.5 | -8.1 |
| 7.66 | -6.96 | -2.88 | -8.1 |
| 8.75 | -7.4 | -3.26 | -8.1 |
| 9.84 | -7.84 | -3.65 | -8.1 |
| 10.9 | -8.27 | -4.03 | -8.1 |
| 12 | -8.71 | -4.41 | -8.1 |
| 13.1 | -9.15 | -4.79 | -8.1 |
| Connectors | Worst-case margin | Worst-case reach |
|---|---|---|
| 0 | 1.70 dB | 14.25 km |
| 2 | 0.20 dB | 10.5 km |
| 4 | -1.30 dB | 6.75 km |
| 6 | -2.80 dB | 3 km |
| 8 | -4.30 dB | 0 m |
The connector table runs 0, 2, 4, 6, 8 connectors with every other input as entered above.
How it works
An optical link budget adds up what the transmitter puts into the fibre, takes off every loss and penalty on the way, and compares what is left with what the receiver needs. This tool gives the power at the receiver, the margin in the worst and typical cases, and the longest fibre the budget allows, for single-mode and multimode links, pluggable optics, co-packaged optics and passive optical networks.
- Put the powers on one scale. Launch power and receiver sensitivity are quoted either as average power or as optical modulation amplitude (OMA, the difference between the one and zero levels). The extinction ratio r is the ratio of the one level to the zero level in linear terms. The tool converts the launch power onto the basis of the sensitivity, so both sides are compared like for like. Milliwatts and dBm are converted both ways.
P(dBm) = 10 x log10(P(mW)); r = 10^(extinction ratio dB / 10); OMA = 2 x average power x (r − 1) / (r + 1) - Add up the channel loss. The fibre loss is its attenuation per kilometre times the length. Connectors and splices are their count times the loss of one. Any other component, such as a splitter, a multiplexer or a coupler on a package, is a row with a count and a loss. Each loss is run twice: once with the worst-case figures (published maxima) and once with typical ones. A loss given as the percentage of light transmitted is converted to dB.
channel loss = attenuation x length + connectors x loss each + splices x loss each + sum of (count x loss) for the other components; loss (dB) = −10 x log10(transmission) - Penalties, allowance and the BER. Dispersion, transmitter and other penalties are taken off as dB (a fixed part plus an optional part that grows with length). The ageing and safety allowance is a further reserve. A receiver sensitivity is quoted at a stated bit error ratio. If you need a lower BER, a thermal-noise-limited receiver needs optical power in proportion to the Q factor, so the sensitivity moves by the ratio of the two Q factors.
BER = 0.5 x erfc(Q / sqrt(2)); sensitivity change (dB) = 10 x log10(Q at target BER / Q at quoted BER) - Received power and margin. The worst case uses the minimum launch power and the maximum losses; the typical case uses the typical launch power and the typical losses. The margin is how far the received power sits above what the receiver needs. A positive worst-case margin means the link is built to hold across the stated tolerances.
received power = launch power − channel loss − penalties; link margin = received power − (sensitivity + BER change + allowance); total budget = minimum launch power − sensitivity - Maximum reach. Reach is the length at which the margin falls to zero. The fixed losses (connectors, splices, other components, the fixed penalty, the allowance and the BER change) are taken off the budget first, and what is left is divided by the loss per kilometre. Where dispersion or modal bandwidth limits the reach before power does, the reach from power alone is an upper bound.
reach (km) = (launch power − sensitivity − BER change − allowance − fixed losses − fixed penalty) / (attenuation + penalty per km) - Receiver overload check. A link can fail by too much light as well as too little. With the maximum launch power and the typical (lowest) loss, the power at the receiver is compared with the receiver's maximum input.
maximum received power = maximum launch power − typical channel loss
Assumptions
- All losses are loss of power in dB and add; reflections, interferometric noise and mode partition noise are covered only by the penalty you enter.
- The worst case combines the minimum launch power with every loss at its maximum at the same time, which is deliberately cautious; the typical case shows what a link normally measures.
- Dispersion and other penalties are the figures you enter; the tool does not calculate chromatic or modal dispersion.
- The BER adjustment assumes a thermal-noise-limited receiver with a constant noise level, so required power is proportional to Q.
- The preset power levels and losses are editorial figures for a typical case, taken from the sources named; replace them with your transceiver and cable data.
Limits and warnings
- Multimode reach is limited by modal bandwidth as well as by power; the tool gives the power-limited reach only.
- PAM4 and forward-error-corrected receivers do not follow the simple Q rule for BER changes; use the vendor's sensitivity at your BER.
- Wavelength-dependent loss across a WDM grid, polarisation-dependent loss and temperature dependence of the laser are not modelled; fold them into the component rows or the penalty.
- Optical amplifiers, dispersion compensation and coherent receivers need an optical signal-to-noise budget, which is outside this tool.
- Standard clause values used in the presets come from task force working documents; the published clause is the authority for a conformance claim.
Sources
The methods and default figures rest on these public sources. The wording here is our own; read the source for its full text.
- IEEE Std 802.3 Ethernet: Clause 88 (100GBASE-LR4 PMD), Clause 95 (100GBASE-SR4 PMD) and Clause 124 (400GBASE-DR4 PMD), IEEE Standards Association, 2022. Cited by name, part and clause; the method here is written in our own words. Clause numbers confirmed from the task force documents below (Table 88-7 and 88-8, Table 95-7 and 95-8, Table 124-6 and 124-7).
- A comment on Table 88-7 and 88-8 in Draft 1.0 (100GBASE-LR4 level diagram) (opens in a new tab), H. Oomori, C. Cole, K. Mori and M. Shishikura; IEEE 802.3ba Task Force, November 2008. Launch OMA of −0.8 to 4.0 dBm, OMA sensitivity of −8.1 dBm, 6.3 dB channel insertion loss and 2.2 dB allocation for penalties.
- 100GBASE-xR4 Discussion (opens in a new tab), P. Anslow; IEEE P802.3ba Task Force, July 2008. The 100GBASE-LR4 power budget table agreed for the first draft.
- Improved optical power specs for 200GBASE-DR4 and 400GBASE-DR4 (opens in a new tab), P. Dawe; IEEE P802.3bs Task Force, September 2017. Draft Table 124-6 and 124-7 for 400GBASE-DR4: OMAouter minimum, TDECQ and receiver sensitivity, before and after the proposed change.
- MMF ad hoc working document, 100GBASE-SR4 draft tables (P802.3bm Draft 3.0a extract) (opens in a new tab), J. King; IEEE P802.3bm 40 Gb/s and 100 Gb/s Fiber Optic Task Force, July 2014. Launch power, OM3 and OM4 channel insertion loss and the 3.5 dB/km cabled fibre figure at 850 nm.
- Characteristics of a single-mode optical fibre and cable (Recommendation G.652) (opens in a new tab), ITU-T, August 2024 edition. The recommendation is cited by name. The attenuation maxima used for the single-mode presets (0.4 and 0.3 dB/km for the C and D variants) are as published in fibre vendor data sheets and a fibre comparison article; the recommendation text itself was not opened, so check the figure for your variant.
- Gigabit-capable passive optical networks (GPON): Physical media dependent (PMD) layer specification (Recommendation G.984.2) (opens in a new tab), ITU-T, August 2019. The class B+ optics are in Annex A. The class budget numbers used here are taken from the vendor note below, not from the recommendation text.
- Introduction to Optical Link Budget Between OLT and ONU (opens in a new tab), TP-Link Omada Network Support (vendor application note), 16 December 2025. The link budget sum, class B+ and C+ launch power and sensitivity, splitter, connector and fibre losses and the 3 dB ageing allowance.
- Calculating Fiber Optic Loss Budgets (opens in a new tab), The Fiber Optic Association, Inc., 2004 to 2018. Typical and maximum attenuation by wavelength, connector and splice losses and the method of subtracting the link loss and a margin from the dynamic range.
- Fiber-Optic Communication Systems, 4th edition (chapter 4, optical receivers), G. P. Agrawal; John Wiley and Sons, 2010. The relation between bit error ratio and the Q factor and the receiver sensitivity at a given BER. Edition details confirmed from the publisher's catalogue data; the equation numbers were not checked.
Where it helps
The lifecycle stages this tool serves: 2 stages in 1 lifecycle.
More analog, rf, photonics and packaging tools
Method notev1Formula, ranges, sources and limits
Adds up launch power, fibre, connector, splice and component losses and penalties against receiver sensitivity to give the power at the receiver, the worst-case and typical link margin and the reach the budget allows.
Formula
P(dBm) = 10 x log10(P(mW)); r = 10^(extinction ratio dB / 10); OMA = 2 x average power x (r − 1) / (r + 1); channel loss = attenuation x length + connectors x loss each + splices x loss each + sum of (count x loss) for the other components; loss (dB) = −10 x log10(transmission); BER = 0.5 x erfc(Q / sqrt(2)); sensitivity change (dB) = 10 x log10(Q at target BER / Q at quoted BER); received power = launch power − channel loss − penalties; link margin = received power − (sensitivity + BER change + allowance); total budget = minimum launch power − sensitivity; reach (km) = (launch power − sensitivity − BER change − allowance − fixed losses − fixed penalty) / (attenuation + penalty per km); maximum received power = maximum launch power − typical channel loss
| Input | Unit | Range it holds for | Comes from |
|---|---|---|---|
| Power unit | choice | dbm, mw | Your figure |
| Launch power quoted as | choice | average, oma | Your figure |
| Sensitivity quoted as | choice | average, oma | Your figure |
| Minimum launch power | dBm or mW | -40 to 40 | Your figure |
| Typical launch power | dBm or mW | -40 to 40 | Your figure |
| Extinction ratio | dB | 0.1 to 40 | Your figure |
| Receiver sensitivity | dBm or mW | -50 to 20 | Your figure |
| Length unit | choice | km, m | Your figure |
| Fibre length | km or m | from 0 | Your figure |
| Worst-case fibre attenuation | dB/km | 0 to 10 | Your figure |
| Typical fibre attenuation | dB/km | 0 to 10 | Your figure |
| Connectors | count | 0 to 100 | Your figure |
| Worst-case loss per connector | dB | 0 to 5 | Your figure |
| Typical loss per connector | dB | 0 to 5 | Your figure |
| Splices | count | 0 to 200 | Your figure |
| Worst-case loss per splice | dB | 0 to 3 | Your figure |
| Typical loss per splice | dB | 0 to 3 | Your figure |
| Loss unit | choice | db, pct | Your figure |
| Fixed penalties | dB | 0 to 20 | Your figure |
| Penalty that grows with length | dB/km | 0 to 10 | Your figure |
| Ageing and safety allowance | dB | 0 to 20 | Your figure |
| BER the sensitivity is quoted at | ratio | 1e-18 to 0.4 | Your figure |
| BER you need | ratio | 1e-18 to 0.4 | Your figure |
Outputs: Channel loss, worst case (dB); Power at the receiver, worst case (dBm); Link margin, worst case (dB); Link margin, typical (dB); Maximum reach, worst case (km).
Assumptions
- All losses are loss of power in dB and add; reflections, interferometric noise and mode partition noise are covered only by the penalty you enter.
- The worst case combines the minimum launch power with every loss at its maximum at the same time, which is deliberately cautious; the typical case shows what a link normally measures.
- Dispersion and other penalties are the figures you enter; the tool does not calculate chromatic or modal dispersion.
- The BER adjustment assumes a thermal-noise-limited receiver with a constant noise level, so required power is proportional to Q.
- The preset power levels and losses are editorial figures for a typical case, taken from the sources named; replace them with your transceiver and cable data.
Uncertainty: The arithmetic is exact. The result is as good as the launch powers, sensitivities, losses and penalties entered; a worst-case stack-up is cautious, and a measured link usually lands between the typical and worst-case figures. Expect the preset figures to differ from a given product by a few tenths of a dB.
Known limits
- Multimode reach is limited by modal bandwidth as well as by power; the tool gives the power-limited reach only.
- PAM4 and forward-error-corrected receivers do not follow the simple Q rule for BER changes; use the vendor's sensitivity at your BER.
- Wavelength-dependent loss across a WDM grid, polarisation-dependent loss and temperature dependence of the laser are not modelled; fold them into the component rows or the penalty.
- Optical amplifiers, dispersion compensation and coherent receivers need an optical signal-to-noise budget, which is outside this tool.
- Standard clause values used in the presets come from task force working documents; the published clause is the authority for a conformance claim.
Where the method comes from
Follows The Fiber Optic Association, Calculating Fiber Optic Loss Budgets (2004 to 2018) (opens in a new tab). The platform's version departs from it as follows.
- Launch power, sensitivity and penalties are entered directly, with average power and OMA converted through the extinction ratio Why: The guide works from a single dynamic range; high-speed Ethernet optics quote OMA and penalties separately.
- Worst-case and typical figures are run side by side, with a reach worked back from the margin Why: A stack-up that only shows one case hides whether the link holds at the tolerance limits.
- The sensitivity can be moved to a different bit error ratio through the Q factor Why: Sensitivity is quoted at one BER; a design often needs another.
Reference example, checked by test: Worked example in this method note: one lane of 100GBASE-LR4 over 10 km with the preset figures (minimum launch OMA of −0.8 dBm, OMA sensitivity of −8.1 dBm, 0.4 dB/km worst case, two 0.75 dB connectors, two 0.3 dB splices and a 1 dB penalty), hand-worked in the tool's unit test. Channel loss, worst case 6.1; Power at the receiver, worst case -7.9; Link margin, worst case 0.2; Link margin, typical 4.4; Maximum reach, worst case 10.5.
Versions
- v1 (2026-10-25): First version, built from the tool idea.
Terms on this page
- Optical link budget
- The accounting of transmitted power against every loss and penalty along a link, including fibre attenuation, connectors and dispersion, to confirm enough power reaches the receiver with margin.
- Co-packaged optics
- An approach that places optical engines inside the same package as a switch or accelerator ASIC, replacing long electrical traces to a front-panel module with a short in-package link.
- Extinction ratio
- The ratio of optical power in a logic one to that in a logic zero, usually quoted in dB.
- dBm
- An absolute power level expressed logarithmically against a 1 mW reference, so 0 dBm is 1 mW and 30 dBm is 1 W.
- Insertion loss
- The signal power lost by inserting a component such as a filter, switch or connector into a path, measured in decibels.
- dB
- A logarithmic ratio unit, ten times the log of a power ratio or twenty times the log of a voltage ratio.
- BER
- The fraction of received bits that are wrong, measured over a defined observation window.
- Q factor
- The ratio of energy stored to energy dissipated per cycle in a resonant element, setting how narrow and low-loss a resonance is.
- Bandwidth
- In meeting jargon, a person's or team's available working capacity rather than any data rate.
- Transceiver
- An integrated device combining the transmit and receive signal chains for a communication link, typically including LNA, mixers, filters, VGAs, synthesiser and data converters.
- PAM4
- Signalling with four voltage levels carrying two bits per symbol, halving the Nyquist frequency for a given bit rate at the cost of roughly 9.5 dB of signal-to-noise ratio and three stacked eyes to...
- Tiger team
- A small hand-picked cross-functional group pulled off normal duties to solve one hard problem quickly, with direct access to management and to resource.
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