What is Visual Fault Locator?

The Visual Fault Locator (VFL), like the continuity tester, is an essential instrument in any fiber optic tool kit. The VFL is not one of the cheapest instruments in your toolbox.


It will help you to easily discover optical fiber breakage or macro bends, as well as a bad fusion splice in multimode or single-mode optical fiber.

The VFL enables the operator to view the optical fiber break. The optical fiber may break in places other than fiber optic cables. Inside the connector or connector ferrule, the optical fiber may break. A microscope cannot see the optical fiber unless it is damaged at the end face of the connection.

Typically, students join wires that appear wonderful under a microscope but fail continuity testing. When this happens, the most difficult element is detecting which connector contains the optical fiber break. In the absence of a VFL in the classroom, students would have to cut the cable in half and use a continuity tester to locate the faulty connection.

In the same way, the visual fault locator can be used to assess the continuity of an optical cable. When utilizing a continuity tester, the first step is to clean and visually verify the connector’s end face before inserting it into the continuity tester. After cleaning and inspecting the connector, make sure the continuity tester is working properly. Turn on the continuity tester and make sure it is emitting light.

How to Use

The first step is to clean the connector end face and check it under a microscope.

If the end face finish is acceptable, the VFL can be attached to a fiber connector. During this testing, the VFL should not be viewed directly.

The VFL directs laser light into the core of the optical fiber. The laser’s light exits the optical fiber at a break or macro bend.

Typically, the light emitted by the optical fiber will illuminate the buffer that surrounds the optical fiber.

Macro bends are sometimes visible through the jacket, although they are usually visible through the buffer.

Depending on the jacket color, thickness, number of optical fibers in the cable, and amount of strength member, breaks may be seen through the jacket of the fiber optic cable.

Visual Defect Locator

A macro bend in an optical cable can also be located using the visual defect locator.

Macro bends, on the other hand, do not allow nearly as much light to pass through the buffer and jacket as a break in the optical fiber.

Locating a macro bend using the VFL may necessitate dimming the scene. On an OTDR (optical time-domain reflectometer) trace, the macro bends and high loss fusion splices look the same. A high-loss fusion splice can be identified using the VFL.