Which two wavelengths are used when measuring single-mode fiber spans?

Which two wavelengths are used when measuring single-mode fiber spans?

• A. 1310 nm and 1550 nm
• B. 850 nm and 1300 nm
• C. 1550 nm and 1625 nm
• D. 1310 nm and 1490 nm

Answer: (A)

Two wavelengths used for measuring SMF spans are 1310 nm and 1550 nm. These lie in the silica fiber’s standard low-loss windows and are widely supported by test equipment, making measurements reliable and comparable across labs. The 1310 nm region has near-zero dispersion, which helps with predictable, straightforward measurements over shorter spans. The 1550 nm region offers the lowest attenuation, allowing accurate testing of longer spans. Measuring at both wavelengths also helps reveal wavelength-dependent loss or issues with connectors and splices that wouldn’t show up at a single wavelength. Other pairs, like 850 nm and 1300 nm or 1490 nm and 1625 nm, aren’t the standard for SMF span measurements.

Two wavelengths used for measuring SMF spans are 1310 nm and 1550 nm. These lie in the silica fiber’s standard low-loss windows and are widely supported by test equipment, making measurements reliable and comparable across labs. The 1310 nm region has near-zero dispersion, which helps with predictable, straightforward measurements over shorter spans. The 1550 nm region offers the lowest attenuation, allowing accurate testing of longer spans. Measuring at both wavelengths also helps reveal wavelength-dependent loss or issues with connectors and splices that wouldn’t show up at a single wavelength. Other pairs, like 850 nm and 1300 nm or 1490 nm and 1625 nm, aren’t the standard for SMF span measurements.