Quantum Key Distribution Link Margin Calculator
Translate launch power, optical loss, and detector sensitivity into a deterministic link margin for a quantum key distribution hop.
Engineering aid only. Validate assumptions with optical test sets and security proofs before field deployment.
Examples
- 1.25 mW launch, 32 dB loss, -65 dBm sensitivity, 3 dB penalty ⇒ Received power -33.04 dBm and link margin 31.96 dB.
- 0.5 mW launch, 40 dB loss, -70 dBm sensitivity, penalty left blank (defaults 3 dB) ⇒ Received power -40.01 dBm and margin 29.99 dB.
FAQ
What goes into channel loss?
Sum splice and connector loss, fiber attenuation, pointing loss for free-space segments, and any wavelength-selective filters to avoid underestimating attenuation.
How conservative should the implementation penalty be?
Laboratory demonstrations often observe 1–2 dB, but fielded QKD links can see 3–5 dB. Use the higher end when temperature swings or platform motion are significant.
Is positive margin enough for secure key rates?
A positive margin is necessary but not sufficient. Secret key rate also depends on quantum bit error rate and detector dark counts; use this calculator to ensure photons arrive within the detector's dynamic range before modeling protocol throughput.
Additional Information
- Result unit: received power and link margin in dBm/dB; positive margin indicates secure key throughput headroom.
- Implementation penalty defaults to 3 dB to reflect typical filter, pointing, and timing penalties in field deployments.
- Launch power is converted to dBm using 10·log10(mW); channel loss and penalties subtract directly in decibels.