Dark fiber is a lease of the physical strands, unlit. No carrier equipment, no per-megabit billing, no service on it at all until you put your own optics on both ends.
What changes when you light it yourself
On a normal circuit you buy capacity and pay more for more of it. On dark fiber you buy the path, and capacity becomes a function of the equipment you attach. Upgrading from 10G to 100G can mean changing optics rather than renegotiating a contract.
You also get complete control of what runs over it — your own encryption, your own protocols, no carrier in the middle of your traffic.
What you take on
Everything the carrier used to do:
- Optics and transport equipment at both ends, and the capital to buy them.
- Engineering staff who can design, monitor and troubleshoot an optical path.
- Operational responsibility. There is no SLA on the light, because you are the one lighting it.
Who it suits
Organisations with sustained, large, predictable capacity needs and the in-house capability to run transport: hospitals and health systems, universities, trading firms where microseconds are money, carriers and service providers, and enterprises connecting their own data centres.
Who it does not suit
If you do not have — or do not want — network engineering staff, dark fiber converts a solved problem into your problem. A managed wavelength gives you most of the deterministic-performance benefit while leaving the optical layer someone else's job. That is the right answer far more often than dark fiber is.
The honest test
If reading the section above about optics and monitoring felt like a description of your team's ordinary work, dark fiber may be excellent value. If it felt like a list of new hires, it is not.
