Dark Fiber, Sourced on Your Side of the Table
Dark fiber is unlit fiber you lease or buy the right to use, and light with your own equipment. It gives you capacity you control for years. TREU finds the routes, competes the providers and negotiates the terms with your legal team, then manages the agreement for as long as it runs.
Book a conversationWhat Dark Fiber Is, and When It Makes Sense
A dark fiber agreement gives you dedicated strands of fiber between locations. No provider equipment sits on them. You choose the optics, the capacity and the encryption, and you add bandwidth by changing equipment, not by signing a new order. You pay for the fiber itself, either through an indefeasible right of use (IRU), usually with an annual maintenance fee, or through a multi-year lease that usually includes maintenance.
When it makes sense
- Connecting your own data centers, colocation sites or campus buildings with high and growing traffic.
- Workloads that need low, predictable latency or full control of encryption, such as trading, financial or secure government networks.
- Resilience that depends on routes you can see and verify, not a provider's promise of diversity.
- Bandwidth needs where lit services, priced over the full term, cost more than fiber plus your own equipment.
When it does not
In our judgment, dark fiber is the wrong buy when:
- Your sites are far from existing fiber routes, and construction would dominate the cost.
- Your bandwidth needs are modest and steady.
- You do not want to own and run optical equipment. A managed wavelength or Ethernet service will often fit better.
If one of these applies to you and the answer is not dark fiber, that is our recommendation.
Dark fiber, wavelengths or Ethernet
| Dark fiber | Wavelength service | Ethernet or dedicated internet | |
|---|---|---|---|
| Who runs the equipment | You | The provider | The provider |
| How you add capacity | Upgrade your optics | Order a new or larger wavelength | Order a higher bandwidth tier |
| How you pay | IRU plus annual maintenance, or a multi-year lease | Recurring, priced by capacity | Recurring, priced by circuit and bandwidth |
| Best fit | High, growing traffic between your own sites | High capacity without running optical equipment | Most branch and internet connectivity |
Technical Considerations
Dark fiber gives you control of the optical layer, so the design decisions are yours. These are the ones that decide whether a route works on day one and keeps working.
Distance and loss
Every route has a loss budget: the fiber's loss over its length, plus every splice and connector. Your optics must cover that total with margin to spare. Loss also differs by wavelength, so a route that works at one wavelength may not work at another. We have the provider show the measured loss, so your optics are sized against it, not the distance on a map.
Optics and reach
Standard 10 gigabit optics are specified for about 10 or 40 kilometers of single-mode fiber. Coherent 400 gigabit optics built to the industry 400ZR agreement reach up to 120 kilometers on amplified links, and much less without amplification. Some long-reach optics are specific to one equipment maker, so mixing brands across a route needs testing first.
More capacity on the same strands
Wavelength division multiplexing (CWDM or DWDM) carries several channels on one fiber pair. It multiplies what each strand can carry, and it adds filters that must be planned and patched to the right ports.
Building entry and laterals
The fiber still has to reach your equipment: conduit into the building, riser space, landlord approval and a clear handoff point. Fiber in the building does not mean a provider can serve your floor. For real resilience, the two routes should enter on different sides of the building.
Verifying route diversity
Route maps are a start, not proof. Providers lease fiber from one another, separate routes can meet at the same bridge or crossing, and records are not always accurate. We have providers show where routes converge and how they enter each building, and write diversity into the contract.
Acceptance testing
Test every strand before you accept it: OTDR traces in both directions at the wavelengths you will use, end-to-end loss with a calibrated light source and power meter, and dispersion measurements on long or high-speed routes. Keep the reports. They are your baseline when something changes.
Running it
Once the fiber is lit, the optical equipment, its monitoring and its spares are yours, and the provider repairs the cable. Agree before you sign who watches the light levels and who calls whom when they drop.
What It Solves for IT and Finance
For IT and network leaders: capacity you control
- Add bandwidth on your schedule, without re-quoting a circuit or waiting on a provider order.
- Choose your own equipment, protocols and encryption end to end.
- Verify route diversity before you sign and write it into the contract, instead of finding out after an outage.
- Fiber providers handled by TREU, with the terms and renewal dates on every route on our calendar, not your team's.
For finance: cost you can plan around
- A cost that stays largely flat as bandwidth grows: more capacity costs you equipment, not a new circuit price.
- An upfront IRU and a lease, modeled side by side over the full term, so finance can choose how it carries the cost. How either is treated on your books is a question for your accountants; we provide the numbers they need.
- Maintenance fees, escalators and renewal terms agreed before signature, not discovered at renewal.
Dark Fiber, Stage by Stage
See how we work-
Supplier identification
We map your sites, circuits, contracts and bandwidth plans, then find the providers with fiber on or near your routes, wherever your sites are. That includes the regional, utility and municipal networks that national carriers may not show you.
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Buying cycle
We decide with you whether dark fiber, wavelengths or a mix fits best, set the routes and diversity you need, and model an IRU against a lease over the full term. We compare routes, construction costs and terms side by side, and negotiate with your legal team.
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Implementation oversight and accountability
We hold the provider to its construction, permit and splicing dates, and to the acceptance tests and test results it agreed to.
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Client and supplier lifecycle management
We track annual fees, relocation terms and the renewal date, and start renegotiating early, for as long as the agreement runs.
What to Watch For in a Dark Fiber Contract
Dark fiber agreements run for years, and most of the cost is set at signature. These are the terms we negotiate hardest.
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The actual route.
Ask for route maps in the contract, not a sales diagram. Two "diverse" routes that share a bridge, a conduit or a building entrance are one route when it fails.
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Construction and laterals.
Who pays to build the last segment into your building, what happens if construction runs over, and when the clock on your term starts.
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Acceptance testing and payment.
Agreed loss and splice thresholds, the tests the provider runs, and your remedy if the fiber does not pass. Billing should start at acceptance, and an IRU payment is often split between signature and acceptance.
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Repair commitments.
Dark fiber service levels often focus on how fast a cut is repaired rather than on uptime, and some add an availability target. Look at response and repair times, how they are measured, and whether the credits are worth claiming.
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Maintenance fees and escalators.
What the annual fee covers, how much it can rise, and whether it can be renegotiated at renewal.
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Relocations.
When road or utility work forces the fiber to move, who pays and how much notice you get.
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Maintenance windows.
Notice periods for planned work, the windows it must fall in, and any limit you need on how often it happens.
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Assignment and change of control.
What happens to your agreement if the provider is sold or sells the route.
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End of term.
Renewal rights, the price at renewal, and what happens to your use of the strands when the term ends.
This list is a starting point for your review. TREU is not a law firm. Your counsel gives the legal advice.
Questions Buyers Ask About Dark Fiber
What is dark fiber?
Dark fiber is optical fiber that has been installed but is not lit by the provider. You lease, or buy the right to use, dedicated strands and connect your own equipment at each end, so you control the capacity, the protocols and the encryption.
What is the difference between dark fiber and lit fiber?
With lit fiber, the provider runs the equipment and sells you a service, such as a wavelength or an Ethernet circuit, at a set bandwidth. With dark fiber, you run the equipment, and you can raise capacity by upgrading your optics instead of ordering a new service.
How much does dark fiber cost?
It depends on the route length, whether fiber already exists or must be built, the number of strands, the term, and whether you lease or buy an IRU. An IRU usually combines a large upfront payment with an annual maintenance fee. A lease is usually a recurring charge that includes maintenance. Because pricing varies widely by route, the reliable way to know is to compete the providers that serve your locations, which is what TREU does.
What is a dark fiber IRU?
An IRU, or indefeasible right of use, is a long-term right to use specific fiber strands. Terms most often run 20 years or more, often with renewal options, and some providers offer shorter ones. Most of the cost is paid upfront, with an annual fee for maintenance. The provider usually keeps ownership of the cable, though some IRUs transfer it at the end of the term. A lease is the shorter alternative, often three to five years, with maintenance usually included in the recurring charge. The right choice depends on how long you will need the route and how finance wants to carry the cost.
How long does it take to get dark fiber?
It depends on the route and how much must be built. Where fiber already runs to both locations, delivery is mostly splicing and testing, and typically takes a few weeks to about four months. Where a short lateral must be built into a building, expect weeks to months more. A new route can take several months or longer, depending on the route, permits, rights of way and building access. TREU asks providers for a committed delivery date before you sign and holds them to it.