Dark Fiber
What It Is, What It Costs, IRUs vs Leases, Dark Fiber Providers and Dark Fiber vs Lit Fiber
Dark fiber gives you your own fiber strands between sites, with as much bandwidth as your equipment can light. We find who has strands on your route and negotiate the lease or IRU, alongside your data center space.
Price My Dark Fiber RouteDark fiber is the most private, most scalable way to connect two sites, and AI has turned it into one of the most sought-after assets in digital infrastructure. Hyperscalers accounted for 57 percent of all metro dark fiber installations in the United States between 2020 and 2024, and the largest fiber networks are being bought and extended to keep up. This guide covers what dark fiber is, how it works, dark fiber vs lit fiber, what it costs, how IRUs work, and how to find dark fiber providers on your route. For every connection type side by side, see data center connectivity.
Sources: lease ranges from ITG; IRU terms and hyperscaler share from Compute Law; Zayo network per Fierce Network. As of October 2026.
Coverage is route by route. We find the carriers, regional networks and utilities with fiber between your exact sites.
Monthly lease against upfront IRU over the life of the asset, with maintenance and escalators included.
Route diversity, building laterals, repair times, relocation clauses and escalators settled before you sign.
The provider you choose pays us. Your rate is not marked up, and you’ll hear back within 24 hours.
Dark Fiber at a Glance
| Dark fiber | Lit fiber (wavelength or private line) | |
|---|---|---|
| What you get | Fiber strands you light yourself | A managed circuit at a set speed |
| Bandwidth | Whatever your optics support; upgrade by changing equipment | The speed you buy; upgrade by ordering more |
| Who runs the equipment | You | The carrier |
| Pricing | Lease per route or upfront IRU | Monthly per circuit, by speed and distance |
| Typical term | 5 years leased to 20 or more on an IRU | 1 to 5 years |
| Best for | Large, growing bandwidth between fixed sites | Moderate bandwidth without an optical team |
Send both addresses, the bandwidth you need now and in three years, and your timeline. You’ll hear back within 24 hours with who has fiber on the route.
What Is Dark Fiber?
The dark fiber meaning, or dark fiber definition, is simple: fiber-optic strands that are installed but unlit, leased to a customer who supplies the equipment that lights them. The term dates from the build-out of the 1990s, when carriers laid far more fiber than they needed and leased the spare strands. You will also see it spelled dark fibre, the British spelling of the same thing.
How it works
Fiber is leased in pairs, one strand to send and one to receive. You install optical equipment at each end, and the light carries your data.
How capacity grows
With DWDM optics, one pair can carry dozens of wavelengths of 100 Gbps or more. More capacity means new equipment, not a new contract.
Why companies choose it
Control, privacy and cost at scale: no carrier equipment on the path, no per-circuit pricing, and capacity that grows with you.
Dark Fiber vs Lit Fiber
Lit fiber is fiber a carrier has already lit and sells as a service: a wavelength, an Ethernet private line, metro Ethernet or dedicated internet. The carrier runs the equipment and you buy a set speed. Dark fiber flips that: you run the equipment and the speed is up to you.
Choose dark fiber when
You need 100 Gbps or more between fixed sites, bandwidth will keep growing, you want full control of the path, and you have, or can hire, an optical networking team.
Choose lit fiber when
You need under about 10 Gbps, want the carrier to run and repair the equipment, or need the connection quickly without building anything.
For wavelengths, private lines and the other managed options, see data center connectivity.
Dark Fiber Networks: Metro and Long Haul
| Metro dark fiber | Long-haul dark fiber | |
|---|---|---|
| Distance | Within a city, usually under about 50 miles | Between cities and data center markets |
| Typical use | Data centers, offices and exchanges in one metro | Linking regions, AI campuses and cloud regions |
| Typical lease | About $1,000 to $5,000 a month per route | Higher; often $5,000 to $25,000 or more a month |
| Equipment | Optics at each end | Optics plus regeneration and amplification along the route |
Lease ranges from ITG. Actual pricing depends on the route, competition and term.
Most providers publish a dark fiber map of their network, but maps show where fiber runs, not whether spare strands are available on your exact path. That takes a route-specific request, which is where checking several networks at once saves weeks.
Dark Fiber for Data Centers and AI
AI has become the main force in the dark fiber market. AI data centers move enormous volumes of data between campuses, cloud regions and internet exchanges, and they buy fiber in bulk and on long terms. The networks are consolidating and expanding to meet it:
Zayo and Crown Castle
Zayo closed its $4.25 billion purchase of Crown Castle’s fiber business on May 1, 2026, adding about 90,000 route miles and bringing its North American network to about 224,000 miles.
New long-haul routes
Zayo has announced plans for 5,000 new long-haul route miles by 2030 for AI demand, with 28 routes funded or underway.
Hyperscale contracts
Lumen reports nearly $9 billion in AI and cloud connectivity contracts, and fiber makers now offer cables with 3,456 strands or more.
Sources: Fierce Network; DCD; Compute Law.
Planning an AI deployment? See AI and GPU colocation and wholesale colocation.
Dark Fiber Pricing and Cost
Dark fiber pricing is usually quoted per strand per mile per month, or as a total monthly price for a route. Pairs cost twice a single strand, rings and diverse paths cost more, and building laterals add to the total. Utility rate cards are one of the few places prices are published, which makes them a useful benchmark.
MCA calculation from the published NES dark fiber rate card, before its 20 percent ring discount. Commercial carrier pricing varies widely by market. Free to cite with a link to this page.
What else you pay for
Optics at each end, usually $2,000 to $8,000 per transceiver set for a basic metro pair; building laterals; and colocation or cross-connects where the fiber lands.
Escalators
Monthly leases often include annual increases of CPI or 2 to 4 percent. Fix them in the contract.
Total cost of ownership
A basic metro pair with optics, engineering and commissioning often runs $15,000 to $30,000 upfront plus $1,000 to $3,000 a month.
Sources: ITG; DGTL Infra.
Dark Fiber Lease vs IRU: Indefeasible Right of Use Explained
An indefeasible right of use, or IRU, is a long-term right to use specific fiber strands that the provider cannot take back during the term. Most IRU fiber deals run 15 to 20 years, and AI data centers are signing 20 to 30. The buyer pays most of the price upfront, then annual maintenance, and usually records it as a long-term asset rather than a monthly expense.
| Dark fiber lease | IRU | |
|---|---|---|
| Payment | Monthly | Mostly upfront, plus annual maintenance |
| Typical term | About 5 years or less | 15 to 20 years, often 20 to 30 for AI |
| Total cost over a long term | Higher | Usually lower |
| Accounting | Operating expense | Usually a capital asset |
| Best for | Shorter or uncertain needs, preserving cash | Long-term, strategic routes |
IRU terms per Compute Law and ITG. Confirm accounting treatment with your auditor.
Dark Fiber Providers
Dark fiber providers range from national networks to city utilities, and coverage is route by route, so the provider that suits one path may have nothing on another. Most sell dark fiber services as a monthly lease or an IRU, often with optional maintenance, monitoring and building laterals.
National carriers
Zayo, Lumen, AT&T and Verizon run large metro and long-haul networks and lease dark fiber between major markets.
Regional fiber companies
Regional networks often have the densest fiber in their metros and can be the most flexible on laterals and pricing.
Utilities and cities
Some electric utilities and municipalities lease spare fiber at published rates, which can be competitive on local routes.
Data center campuses
Operators run fiber between their own buildings on a campus, often as campus cross-connects rather than dark fiber.
How to Buy Dark Fiber
Route and diversity
The exact path, how it avoids shared conduits with your other connections, and the distance, which sets latency.
Laterals and building entry
Who builds the last stretch into each building, how long it takes, and what it costs.
Repair commitments
How fast cuts are repaired, who you call, and what credits apply if they miss.
Term, escalators and relocation
Annual increases, what happens if the fiber must be moved, and your options at the end of the term.
How We Find Dark Fiber
You send the route
Both addresses, bandwidth now and in three years, lease or IRU, and your timeline. You’ll hear back within 24 hours.
We check who has fiber
Carriers, regional networks and utilities with strands on your path, with laterals and diversity checked.
We negotiate and you sign
Price, escalators, repair commitments and term settled before you sign. The provider you choose pays us.
Fiber reach and cost decide whether a site works. Developers, landowners and investors get a fixed-fee site and fiber study, and data center due diligence on acquisitions. Engagements are paid and start in the mid five figures; see data center consulting.
Frequently Asked Questions
What is dark fiber?
Fiber-optic cable leased without equipment attached. You connect your own optical equipment at each end to light it, so you control the bandwidth and can upgrade it by changing equipment rather than contracts.
Why is it called dark fiber?
Because no light travels through the fiber until the customer connects its own equipment. Fiber that a carrier has already lit and sells as a service is called lit fiber.
What is the difference between dark fiber and lit fiber?
Dark fiber is bare strands you light and run yourself. Lit fiber is a managed service on a carrier's fiber, sold as a wavelength, Ethernet private line or internet connection at a set speed. Dark fiber suits large, growing bandwidth; lit fiber suits moderate needs without an optical team.
How much does dark fiber cost?
Metro dark fiber commonly leases for about $1,000 to $5,000 a month per route, with long-haul routes costing more. An IRU can cost $50,000 to $500,000 or more upfront plus annual maintenance, and optics and engineering add roughly $15,000 to $30,000 for a basic metro pair.
What is an indefeasible right of use?
An IRU is a long-term right to use specific fiber strands, usually for 15 to 20 years and often 20 to 30 for AI data centers. The buyer pays mostly upfront plus annual maintenance, and the right cannot be revoked during the term.
Is an IRU better than a lease?
An IRU usually costs less over a long term and locks in capacity, but needs capital upfront. A lease keeps cash free and suits shorter or uncertain needs. The decision usually turns on how long you will need the route and how you treat capital spending.
Who are the main dark fiber providers?
National carriers such as Zayo, Lumen, AT&T and Verizon, regional fiber companies, and some utilities and cities that lease spare fiber. Coverage is route by route, so the right provider depends on who has fiber between your sites.
Can I use dark fiber for internet?
Dark fiber is not an internet service on its own. Dark fiber internet usually means lighting your own fiber to reach an internet exchange or a transit provider in a carrier hotel, which can give very high bandwidth at a lower cost per gigabit for large users.
Who uses dark fiber?
Hyperscalers and AI companies connecting data centers, banks and trading firms linking sites, large enterprises joining offices and data centers, carriers, universities and health systems.
Can I get dark fiber to my building?
Only if a provider has fiber nearby and can build a lateral into your building. Laterals and building entry often add cost and time, so checking routes early matters.
How much bandwidth can dark fiber carry?
As much as the equipment at each end supports. A single fiber pair can carry many wavelengths of 100 Gbps or more using DWDM optics, so capacity grows by upgrading equipment.
Why is AI increasing demand for dark fiber?
AI data centers move enormous amounts of data between campuses, cloud regions and exchanges. Hyperscalers accounted for 57 percent of US metro dark fiber installations from 2020 to 2024, and carriers are building new long-haul routes to keep up.
What should a dark fiber contract include?
The exact route and diversity, building laterals, repair time commitments, maintenance fees, price escalators, relocation rules if the fiber must move, and what happens at the end of the term.
Do you charge for finding dark fiber?
No. The provider you choose pays us from its channel budget, and your rate is not marked up. You'll hear back within 24 hours.
Price Your Dark Fiber Route
Tell us the two sites, the bandwidth you need and whether you prefer a lease or an IRU. You’ll hear back within 24 hours. No cost, no obligation, and the provider you choose pays us.
Once you have contacted a provider directly, it usually will not work through an advisor on your deal.
Connectivity: data center connectivity, hybrid cloud colocation, cloud repatriation and disaster recovery colocation.
Data centers: wholesale colocation, colocation pricing, data center lease and data center cost.
AI and GPU: AI and GPU colocation, GPU rental and powered land.
Fiber-heavy markets: NYC metro carrier hotels, Northern Virginia, Chicago, Dallas and Texas.
Planning: data center relocation, data center consulting, data center due diligence and how a data center broker works.
