What is Dark Fiber?

• A. Unused optical fiber that can be leased or rented for long fiber runs
• B. Fiber currently in use by networks
• C. Fiber with enhanced shielding
• D. Submarine fiber only

Answer: (A)

Dark fiber is unlit optical fiber that has already been laid but isn’t carrying signals yet. The “dark” name comes from the fact there’s no light being transmitted on it. Companies or networks can lease or rent this fiber and then install their own transceivers and equipment to light it themselves, making long-distance or private connections tailored to their needs. This gives more control over routing, capacity, and latency, and can be cost-effective for very high-bandwidth, custom networks.

This differs from fiber that’s already in use by networks, which is lit fiber and comes with the service and devices provided by the carrier. The idea of enhanced shielding isn’t a standard description of fiber optics, and submarine fiber isn’t restricted to being dark—submarine links can also be lit.