Dark Fiber
Unlit fiber infrastructure for organizations that need total control
Overview
Dark fiber refers to unused fiber-optic cable that has been installed but is not currently carrying data. Rather than buying a managed internet service, organizations lease the raw fiber strands and light them with their own networking equipment. This gives the lessee complete control over the connection's capacity, protocols, and encryption without any shared infrastructure. Dark fiber is primarily used by enterprises, data centers, universities, hospitals, and government agencies that require maximum bandwidth, security, and customization.
Typical Speeds
10 Gbps - 100 Gbps
download
Avg. Monthly Cost
$1,000 - $10,000+
per month
Availability
Metro areas with existing fiber routes
coverage
How It Works
When a fiber-optic network is constructed, providers typically install more strands than they immediately need, anticipating future demand. These unlit, or dark, strands can be leased to third parties. The lessee installs optical transceivers and networking equipment at each end of the fiber run. By controlling the equipment, they determine the wavelengths, protocols, and data rates used on the fiber. Using Dense Wavelength Division Multiplexing (DWDM), a single fiber strand can carry 80 or more separate channels of data simultaneously, each at speeds of 100 Gbps or more. This means a single dark fiber pair can theoretically carry 16+ Tbps of data. The fiber itself is passive, requiring no power or maintenance beyond the physical cable. All intelligence and capacity are determined by the equipment attached to each end.
Speed Ranges
Typical Download
10 Gbps - 100 Gbps
Typical Upload
10 Gbps - 100 Gbps
Max Download
Tbps (with DWDM)
Max Upload
Tbps (with DWDM)
Pros
- Virtually unlimited bandwidth, scalable by upgrading endpoint equipment
- Complete control over protocols, encryption, and traffic management
- No shared infrastructure means predictable, guaranteed performance
- Long-term cost advantage for high-bandwidth organizations
- Physical layer security, as the fiber is dedicated to your use
- Future-proof: no technology upgrades needed on the fiber itself
Cons
- Significant upfront investment in optical and networking equipment
- Requires in-house or contracted network engineering expertise
- Only available where existing fiber routes already pass your locations
- Long-term lease commitments, typically 3-20 years
- Maintenance responsibility for end equipment falls on the lessee
- Not practical for small businesses or residential use
Best For
- Data center interconnects requiring massive, low-latency bandwidth
- Universities and research institutions transferring large datasets
- Healthcare networks connecting hospitals and clinics with HIPAA-compliant infrastructure
- Financial institutions needing ultra-low-latency trading infrastructure
- Government and military networks requiring physical security and isolation
- Large enterprises connecting campus buildings or branch offices
Availability
Dark fiber is available primarily in metropolitan areas and along major fiber routes that connect cities. Providers like Zayo, Crown Castle, and Lumen (CenturyLink) maintain extensive dark fiber networks across the U.S. Municipal fiber networks and utility companies also lease dark fiber in some markets. Availability is concentrated in areas with high commercial density. Extending dark fiber to a new location typically requires a construction build-out, which can cost tens of thousands of dollars depending on distance. Organizations interested in dark fiber should contact providers for a site survey and feasibility assessment.
Compared to Other Technologies
Dark fiber is fundamentally different from consumer-grade internet services. While a residential fiber connection delivers 1-10 Gbps managed by your ISP, dark fiber gives you a raw physical medium that you control entirely. The closest comparison is dedicated fiber (DIA), but even DIA is a managed service with set speed tiers. Dark fiber has no inherent speed limit, as capacity is determined by the equipment you attach. The trade-off is complexity and cost: you need networking expertise to operate it, and monthly lease costs start at four figures. For organizations that need it, dark fiber is the most powerful and flexible connectivity option available.
Frequently Asked Questions
Who uses dark fiber?
Dark fiber is used by large enterprises, data centers, universities, healthcare systems, financial institutions, cloud providers, and government agencies. Any organization that needs to move massive amounts of data between locations with guaranteed performance and security is a candidate. Tech companies like Google, Amazon, and Microsoft lease or own vast amounts of dark fiber to connect their data centers.
How much does dark fiber cost?
Costs vary widely based on distance, location, and market. A short metro dark fiber connection (under 10 miles) might cost $1,000-$3,000 per month on a multi-year lease. Longer runs or routes requiring new construction can cost $5,000-$10,000+ monthly, plus construction fees that may run into six figures. Despite the high cost, organizations with sustained high-bandwidth needs often find dark fiber more economical than purchasing equivalent managed bandwidth over time.
What is the advantage of dark fiber over managed fiber services?
Control and scalability. With a managed fiber service, you are limited to the speed tier you purchase, and the provider controls the equipment and configuration. With dark fiber, you choose your own equipment and can upgrade capacity by simply swapping transceivers. There are no monthly bandwidth charges beyond the fiber lease. You also get physical-layer security, as no other traffic ever touches your fiber strands. For organizations that outgrow managed services or need custom network configurations, dark fiber provides unmatched flexibility.
Dark Fiber Providers
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