If you’re reading this, it’s likely thanks to an Internet connection. There is a high chance that this connection is made possible by optical fiber. Fiber optics is as ingrained in our daily lives as electric light, and we’re sure you don’t think about everything it takes to light a bulb when you flip a switch. The same goes for optical fiber: there are still secrets to uncover, and one of them is dark fiber, which remains unfamiliar to many.

What is dark fiber?

Dark fiber refers to an infrastructure of optical fiber cables that are laid—whether on land, underground, or under the sea—but are not currently in use. The technical characteristics of dark fiber do not differ fundamentally from those of regular fiber optics. However, they do vary in terms of use, equipment, and configuration. It is called “dark” because no light pulses travel through it, which is the defining feature of optical fiber as a connectivity medium.

Spain has approximately two million kilometres of dark fiber available. This amount is a preventive strategy by players in the tech market, including the government, public administrations, companies, and operators. It is a way to anticipate future connectivity demands. Dark fiber is also used as a backup in case the nature of services changes. Should the market shift in the future—which is almost a certainty—the cost of installing optical fiber from scratch would be very high, and it would lag behind user needs and be unable to meet growing demand .

Uses of dark fiber and why it is less known than optical fiber

Dark fiber is typically used by large operators who lease it to third parties on medium or long-term agreements, usually to other operators or mid-sized companies. It is also an investment by governments and public entities to strengthen connectivity infrastructure.

In other words, dark fiber is not a resource or a term commonly understood by the average end-user, small business owners, or freelancers. This is the main reason why dark fiber, unlike optical fiber, remains somewhat. out of reach for the general public

Differences between optical fiber and dark fiber

The primary difference between dark fiber and fiber optics lies in their operational status, i.e., whether they are “lit” or not. There are no formal characteristics that separate them. The behaviour of dark fiber, once managed by a client for their own use, depends largely on the equipment the client installs and the products and services they aim to offer their clients, once its status changes from dark fiber to “normal” or “lit” optical fiber.

The versatility of optical fiber always depends on the operator. It is the client who installs and manages the necessary equipment, sets bandwidth limits, and decides how this connectivity capacity is shared by end-users. In fact, it is the users who engage with the operator through service contracts.

The technical performance of optical fiber also depends on the operator: its latency and performance are influenced by the usage and demand from the operator’s end-users. Security of the optical fiber and the active and passive measures also depend on the operator, although users must secure their equipment and connections with measures such as passwords.

Dark fiber equals maximum customisation

With dark fiber, it is the operator who purchases or leases specific kilometres of fiber for each case. They are responsible for installing and managing the necessary equipment for its use. The capacity, latency, and behaviour of the dark fiber connection also depend on the client and are fully customisable to their needs, as they are the sole user. This customisation also extends to security measures, which are typically enhanced, and various configuration options for the line.

Since it is a strategic resource for telecommunications operators, the amount of dark fiber purchased or leased, the services provided, and the different methods of exploitation, including services to end clients to recoup investment, are crucial decisions for their stakeholders. Although the initial investment can be high, the customisation capabilities once dark fiber is acquired tend to be greater.