Visual Fault Locator for Troubleshooting Fiber Optic Networks

In order to ensure proper cable connections, it is necessary to use fiber optic testers to troubleshoot fiber optic networks regularly. There are various fiber optic testers invited to locate the faults in fiber patch cables in a short time, like visual fault locator (VFL), which is a device able to locate the breakpoint, bending or cracking of the fiber glass. It can also locate the fault of OTDR (optical time-domain reflectometer) and can make fiber identification from one end to the other end. To better understand visual fault locator, this article will introduce it in details.

The Importance of Visual Fault Locator

Whether installing new fiber links or troubleshooting an existing network, the faster you can locate a problem, the faster you can fix it. Visual fault locator is an essential tool that can pinpoint the exact location of fiber damage making it easier for technicians to diagnose, troubleshoot and fix the problems efficiently. Nowadays, visual fault locator is one of the most commonly used fiber optic testing devices to trace optical fibers, check fiber continuity and find faults. Generally, there are two types of visual fault locators: pen shape VFL and hand-held VFL (shown in the following picture).


Working Principle of Visual Fault Locator

As we all know, the light used in fiber optic system is infrared (IR) light (usually at 1300 to 1650 nm wavelength) which is beyond the range of the human eye. VFL uses a powerful visible light (at the 360 to 670 nm wavelength) from a red diode laser injecting into the fiber, so not only fibers can be traced, but also high loss points can be made visible. The visible light will leak out when it reaches a fault. The light leaking through the fault can be seen through plastic coating and jackets under suitable illumination. The VFL works best on short cables, up to a few kilometers, and it covers the range where OTDRs are not useful.

Using and Choosing Tips for Visual Fault Locator

Although visual fault locator is a simple tool, there are still many factors which should be taken into consideration when you choose and use it. The following part lists some aspects:

  • Focus on the launching power and launching range when choosing a VFL. The launching power is the lowest power that the visual fault locator needs, and the launching range is the distance that the VFL can detect. For example, the launching power of a BML-206-10 pen shape VFL is 10mW, which can detect the distance up to 8 km to 10 km.
  • The stability is the most important part of a visual fault locator. Without a stable light source, it cannot work well and please leave it alone.
  • When using the visual fault locator, view the VFL’s light indirectly by holding a white card or paper in front of the VFL output or the fiber connector emitting the light. Although momentary exposure to the VFL’s output will not damage your eyes, direct and long-term exposure is potentially hazardous.
  • Cover the VFL’s output with dust cap when it is not in use.
  • VFL is not recommended for use on dark-colored or armored cables, since the VFL’s light may not be visible through thick or dark-colored cable sheaths or connector dust caps.

With ease of use, visual fault locator is an ideal tool for locating a large number of defects that occur at connection and around fiber cabinets which are hidden in an OTDR’s “blind spot” or “dead zone”. As a professional manufacturer and supplier of fiber optic cabling products, Fiberstore provides a series of fiber optic testers (like VFL, OTDR) and fiber optic tools (like network cable testers).


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