There’s a good chance that somewhere beneath the street outside your office, there is at least one strand of optical fiber among hundreds or even thousands within a fiber optic cable that hasn’t yet transmitted data. Engineers call it “dark fiber,” which is installed fiber waiting in conduit often alongside power lines, water mains, and gas pipes. While “dark” may sound negative or even obsolete, it should be thought of as primed for switching on or imagined as a blank canvas holding incredible opportunity.
Fiber optic cables transmit data as pulses of light through thin strands of glass, carrying vast amounts of data across long distances faster and more reliably than copper wire. Fiber is undoubtedly the backbone of the modern internet. Your data from internet searches, transactions, and video calls – even the data enabling your reading of this blog – almost certainly travels through fiber. While optical fiber is critical for broadband and data communication, very few people realize what else this extra capacity could be doing.
These unused fibers were primarily installed for excess capacity, ready in case demand increased or new lines were needed. A single fiber optic cable route can contain hundreds of individual fibers, some deployed, some inactive. However, with a few attachments, these unused fibers could become something much more.
Instead of transmitting cable, internet, or phone data like their companion strands, these dark fiber strands can be utilized to instead detect vibrations, temperature changes, and physical strain along its entire length in real time. A single strand can then provide situational data on the remaining strands, the cable itself, the conduit, and even the surrounding environment, including other co-located utilities. The fiber line essentially becomes a real-time continuous sensor stretching for miles.
Put simply, the same cable that carries your internet can, with the right equipment, tell you about digging activity nearby, that a section of power line is running hot, or something is applying pressure to a conduit it shouldn’t be touching. An average internet customer or homeowner may find this to be a neat application, but it is the industrial and commercial owners and operators of buried infrastructure that should take note. As much as 50 million miles of buried pipelines, cables, and wires exist under the surface of the United States. These public and private lines are often co-located with conduits and fiber optic cable. These are the lines that stand to gain new resilience and cost saving applications by turning on the dark fibers.
This technology, called Distributed Fiber Optic Sensing (DFOS), has been commercially deployed and validated across multiple continents in many diverse applications but remains a relatively unknown part of the national conversation on infrastructure protection.
Driven by the surge in demand for AI infrastructure and federal broadband investment, the United States is in the middle of the largest fiber deployment in history. The power demand for data centers is projected to double by 2030. Recent studies have suggested a $1.4 trillion investment needed in the power utility industry over the next 5 years. These facilities all depend on a largely unmonitored web of buried infrastructure, an estimated 50 million miles in the U.S. alone. When something goes wrong (buried infrastructure damages cost tens of billions of dollars annually in the U.S. alone), operators are forced to respond reactively.
DFOS closes that gap by creating a layer of continuous awareness that currently doesn’t exist. This added awareness enables continuous monitoring across thousands of miles of critical infrastructure, detecting construction activity, thermal anomalies, intrusions, and ground movement before they escalate into outages, breaches, or fires. DFOS technology activates the already-existing infrastructure capacity from fiber lines and uses it to protect the buried infrastructure we depend on.
Examples of this technology enhancing resilience and safety are increasing. Texas811’s Guardian Program is already using DFOS to catch excavation activity in real time and dispatching crews before damage occurs. Internationally, South Korea’s national electric utility deployed DFOS on a critical 500kV transmission corridor to protect against construction disturbances. The NSA has already mandated physical fiber monitoring across the U.S. government and defense networks for the same reasons that apply to commercial data centers.
Infrastructure doesn’t have to be fragile just because it’s underground and out of sight. The tools that could make it more resilient are already in the ground, underutilized. Once fiber conduit is buried, retrofitting becomes significantly more expensive than incorporating these capabilities from the start. The companies, utilities, and policymakers planning out the next decade of American infrastructure have a narrow window to incorporate DFOS into the design, rather than treating it as an expensive afterthought.
The capability is already there. The question is whether we are smart enough to utilize it.
Written by Lilly Petruzzi, AI and Data Policy Fellow
The Alliance for Innovation and Infrastructure (Aii) is an independent, national research and educational organization working to advance innovation across industry and public policy. The only nationwide public policy think tank dedicated to infrastructure, Aii explores the intersection of economics, law, and public policy in the areas of climate, damage prevention, eminent domain, energy, infrastructure, innovation, technology, and transportation.