Dark Fiber (“dark fiber”) is a continuously installed fiber optic connection between two locations, where only the unlit (i.e., unused) fiber itself is provided. The provider thus supplies only the physical infrastructure, not the active transmission technology or a preconfigured data service. From the defined handover points, responsibility for operation, illumination, and use lies entirely with the customer.
The term “dark” means that initially no light signal is transmitted over the fiber. Only when the customer connects their own active network equipment such as transceivers, multiplexers, or optical transmission systems is the fiber “lit” and used for data transmission. This gives the customer full control over bandwidth, protocols, and network design.
Dark fiber connections are primarily used by enterprises, data center operators, telecommunications providers, and public institutions that require high bandwidth, low latency, or maximum network sovereignty. Common scenarios include site interconnection for large companies, data center interconnection, or building proprietary carrier networks.
A key advantage of dark fiber is its high flexibility. Customers can choose the transmission technology themselves and increase capacity by replacing the active equipment without having to install new lines. In addition, dark fiber enables very high data security and low latency, as no third-party active network technology is present in the transmission path.
