Which statement best defines Dark Fiber?

• A. Unused optical fiber that can be leased or rented for long fiber runs
• B. Active fiber used by networks
• C. Fiber designed for indoor use
• D. Undersea fiber

Answer: (A)

Dark fiber refers to optical fiber that has been laid and owned or leased by a carrier but is not currently carrying any light signals. It’s literally “unlit” fiber—no data is being transmitted until a customer lights it with their own equipment. This is why it’s something a business can lease and then light and manage themselves to build a private, scalable link. The term emphasizes the state of the fiber as idle infrastructure that can be activated by the user.

That’s why the best description is unused optical fiber that can be leased or rented for long fiber runs. The other statements describe fiber that is actively in use, or focus on where the fiber is deployed or its physical design, rather than its lighting state.