How do you use a visual fault locator to identify and locate fiber breaks in FTTP networks?

1 What is a VFL and how does it work?

A VFL is a handheld tool that looks like a pen or a flashlight. It has a connector that fits into the fiber port of an optical network terminal (ONT), a splitter, or a patch panel. When you turn on the VFL, it sends a continuous or pulsed red light through the fiber core. The light travels along the fiber until it reaches a break or a bend, where it escapes from the fiber and becomes visible to the naked eye. By following the light, you can pinpoint the exact location of the fault and mark it for repair.

2 How to prepare for using a VFL?

Before using a VFL, you need to take some safety precautions and prepare the equipment and the environment. First, you need to wear protective eyewear and avoid looking directly into the fiber or the VFL output, as the light can damage your eyes. Second, you need to clean the fiber connectors and ports with lint-free wipes and alcohol to remove any dust or dirt that can affect the light transmission. Third, you need to turn off any active equipment or sources of light that can interfere with the VFL signal or cause confusion. Fourth, you need to have a fiber map or a schematic diagram of the network to identify the possible routes and locations of the fiber cables.

3 How to use a VFL to test an ONT?

An ONT is a device that converts the optical signal from the fiber cable into an electrical signal for the end-user devices. To test an ONT with a VFL, you need to disconnect the fiber cable from the ONT and connect the VFL to the fiber port. Then, you need to turn on the VFL and observe the light coming out of the other end of the fiber cable. If the light is bright and steady, it means that the fiber cable is intact and the problem is with the ONT or the devices connected to it. If the light is dim or flickering, it means that there is a break or a bend somewhere along the fiber cable.

4 How to use a VFL to test a splitter?

A splitter is a device that splits the optical signal from one fiber cable into multiple fibers for different customers. To test a splitter with a VFL, you need to disconnect the fiber cable from the splitter and connect the VFL to the fiber port. Then, you need to turn on the VFL and observe the light coming out of each of the output fibers from the splitter. If the light is bright and steady on all fibers, it means that the splitter and the fibers are working properly. If the light is dim or flickering on some fibers, it means that there is a break or a bend on those fibers.

5 How to use a VFL to test a patch panel?

A patch panel is a device that connects different fiber cables in a network. To test a patch panel with a VFL, you need to disconnect the fiber cable from the patch panel and connect the VFL to the fiber port. Then, you need to turn on the VFL and observe the light coming out of the corresponding fiber port on the other side of the patch panel. If the light is bright and steady, it means that the patch panel and the fiber cable are functioning well. If the light is dim or flickering, it means that there is a break or a bend on the fiber cable.

6 How to repair a fiber break?

Once you have identified and located the fiber break with the VFL, you need to repair it as soon as possible to restore the service. The most common method of repairing a fiber break is to splice the two ends of the fiber together using a fusion splicer, a device that melts and fuses the fiber cores with an electric arc. To splice a fiber break, you need to cut the fiber cable at the break point, strip off the protective coating, cleave the fiber ends, align them in the fusion splicer, and initiate the splicing process. After splicing, you need to protect the splice with a heat-shrink tube or a splice tray, and test the fiber cable again with a VFL or an optical power meter.

7 Here’s what else to consider

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