Fiber Span Calculator

Calculate maximum unamplified fiber span distance for optical links.

Transmitter

Typical SFP: -5 to +5 dBm

Receiver

Typical SFP: -18 to -34 dBm
Maximum input before damage

Fiber Parameters

Connection Losses

Reserve for aging and repairs (3-6 dB typical)

Common SFP Specifications

SFP Type TX Power RX Sens. Max Dist.
1G-SX (850nm)-9 to -3 dBm-17 dBm550m (OM3)
1G-LX (1310nm)-9 to -3 dBm-20 dBm10 km
1G-ZX (1550nm)0 to +5 dBm-24 dBm80 km
10G-SR (850nm)-7 to -1 dBm-9.9 dBm400m (OM4)
10G-LR (1310nm)-8 to +0.5 dBm-14.4 dBm10 km
10G-ER (1550nm)-4 to +4 dBm-15.8 dBm40 km

Fiber Span Design

Power Budget Formula

Max Span = (Power Budget - Fixed Losses - Margin) / Fiber Attenuation
Power Budget = TX Power - RX Sensitivity

The span is limited by the available power budget after accounting for connector losses, splice losses, and system margin.

Design Considerations

  • Include 3 dB margin minimum for aging
  • Account for future splice additions
  • Verify receiver overload for short links
  • Consider dispersion limits for high-speed links
  • Use OTDR to verify actual losses