How Fiber‑Optic Cables Are Protected and Repaired After Being Cut

Even the most robust network can be disrupted when a fiber‑optic cable is accidentally cut, as happened when a construction excavator severed a line serving Tencent’s services.

To prevent large‑scale outages, telecom operators employ two primary protection mechanisms: 1+1 redundancy , which adds a standby fiber alongside the primary line and automatically switches traffic when a fault is detected, and ring self‑healing , where the network forms a closed loop that reroutes traffic in the opposite direction if a segment fails.

When a cut occurs, a dedicated team of “communication heroes” is alerted 24/7. They rush to the site equipped with a 24‑hour‑on phone, OTDR (optical time‑domain reflectometer), fiber‑splicing machine, power meter, and safety gear.

At the site, the OTDR is used to locate the exact break point by analyzing reflected light curves; the distance shown on the curve corresponds to the fault location. Once identified, the repair follows the principle “restore service first, repair later” by using any spare fibers in the cable to quickly re‑establish connectivity.

The actual splicing process is meticulous: technicians strip the outer protective jacket, clean the exposed fibers, remove the coating, cleave the fiber ends, and then fuse them in a splicing machine. After a successful splice, a heat‑shrink tube is applied, fibers are organized in a splice box, sealed with gel, and the enclosure is secured.

Because fiber strands are thinner than a human hair, the operation demands great physical stamina and precision; improper splicing can cause high loss and degrade signal quality, especially in harsh environments such as deserts, underground ducts, or severe weather.

Despite the difficulty, these field engineers keep the backbone of the internet running, ensuring that users experience uninterrupted service even after a cable is cut.