Fiber Optic Power Budget Calculator
Check whether a fiber link works: compare the transmitter power budget against fiber, connector and splice losses to find the margin.
How it works
Power budget = Tx power − Rx sensitivity · Link loss = km × dB/km + connectors × 0.5 + splices × 0.1 · Margin = budget − loss
A fiber link closes only if the light reaching the receiver is stronger than its sensitivity. The power budget is how many decibels you have to spend — transmitter output minus receiver sensitivity — and every element of the link spends some: the fiber itself by length, plus a fixed loss at each connector and splice. Subtracting total loss from the budget gives the margin; engineers like to keep at least 3 dB in hand for ageing, dirt and repairs.
Worked example
A −3 dBm transmitter and a −23 dBm receiver give a 20 dB budget. A 10 km link at 0.35 dB/km loses 3.5 dB in fiber, 1.0 dB across two connectors and 0.1 dB at one splice — 4.6 dB total. The margin is 20 − 4.6 = 15.4 dB, a very healthy link.
Frequently asked questions
How much margin should a link have?
Aim for at least 3 dB above the loss. That headroom absorbs connector dirt, tighter bends, splice repairs and the small drift of transmitter power and receiver sensitivity as equipment ages.
Why do 1310 nm and 1550 nm differ?
Single-mode fiber attenuates less at 1550 nm (about 0.22 dB/km) than at 1310 nm (about 0.35 dB/km), so longer runs typically use 1550 nm. Multimode fiber has much higher loss and is used only for short distances.
What if the margin is negative?
The link will not reliably pass traffic — the received power is below the receiver’s sensitivity. Shorten the run, use lower-loss fiber or wavelength, reduce the number of connectors, or choose optics with more output power or better sensitivity.
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This calculator is for educational purposes. Double-check important results before acting on them.