What is the maximum backbone distance for single-mode optical fiber?

What is the maximum backbone distance for single-mode optical fiber?

• A. 10000 meters
• B. 800 meters
• C. 2000 meters
• D. 60000 meters

Answer: (D)

In backbone design, the distance a signal can travel in one span is limited by how much loss the system can tolerate and still be amplified and recovered reliably. For single-mode fiber, attenuation is very low—about 0.2 dB per kilometer at the common 1550 nm window. When you add splices, connectors, and the transmitter/receiver margins, a typical span budget is around 12 dB. With 0.2 dB/km, that translates to roughly 60 kilometers of fiber per span, i.e., about 60,000 meters. Exceeding this requires additional amplification or regeneration, which is why 60,000 meters is considered the practical maximum backbone distance for single-mode fiber. The other distances are typical for shorter, access, or campus links where fewer losses are involved and easier to maintain without extra amplification.

In backbone design, the distance a signal can travel in one span is limited by how much loss the system can tolerate and still be amplified and recovered reliably. For single-mode fiber, attenuation is very low—about 0.2 dB per kilometer at the common 1550 nm window. When you add splices, connectors, and the transmitter/receiver margins, a typical span budget is around 12 dB. With 0.2 dB/km, that translates to roughly 60 kilometers of fiber per span, i.e., about 60,000 meters. Exceeding this requires additional amplification or regeneration, which is why 60,000 meters is considered the practical maximum backbone distance for single-mode fiber.

The other distances are typical for shorter, access, or campus links where fewer losses are involved and easier to maintain without extra amplification.