Tag Archives: Visual Fault Locator

Visual Fault Locator Overview

Whether install new fiber links or troubleshooting an existing network, the faster you can locate a problem, the faster you can fix it. To locate the faults in fiber optic cables in a short time, various fiber optic testers are being invited to locate the faults of the fiber optic cable, like OTDR (optical time-domain reflectometer). However, OTDR has dead zone during the testing. Another simple and useful tester which can work in an OTDR dead zone is usually being used to work as an accessory of OTDR. It is known as VFL (visual fault locator) which can also work alone to locate the faults in fiber optic cable in a time saving manner in some situations.

What Is VFL?

Visual fault locator is now one of the most commonly used fiber optic testing devices to trace optical fibers, check fiber continuity and find faults such as breaks, bad splices and tight, sharp bends in fiber optic cable. The most popular visual fault locators are pen shape VFL and hand-held VFL, which are showed in the following picture respectively.

pen shape VFL and hand-held VFL

How VFL Works

The light used for transmit signals over fiber optic is usually at 1300 to 1650nm wavelength which is invisible to naked eyes. Unlike OTDR which measures the time of the incidence and the amplitude of the reflected pulses sent to the fiber optic cable to locate the faults, VFL uses powerful visible light at the 360 to 670nm wavelength injecting to a fiber to visually and directly locate the faults in fiber optic cable. The visible light travels along the core until it reaches a fault, where it leaks out. Light leaking through the fault can be seen through plastic coating and jackets under suitable illumination. This is how VFL locates the faults in fiber optic cable.

Visual fault locators radiate in continuous wave (CW) or pulse modes. The glint of the light source in VFL is usually at 1 or 2 Hz, kHz range is also being provided in today’s market. The output power is generally at 1 mW or less. The working distance of a VFL is usually in the range of 2 to 5 km.

How to Use VFL

VFL is very easy to use. The steps to use a VFL are provided as following:

  • Step One: remove the plastic connector covers from both ends of the test fiber cable.
  • Step Two: connect the fiber optic visual fault locator one end of the fiber. Press the tester button and observe that light emanates from the other end of the fiber. This gives a simple indication of the continuity of the fiber link.
  • Step Three: repeat with several other fibers. Check for light that can be seen leaking from a faulty splice. This may illustrate an easy way of carrying out visual fault finding on bad splices or joints.
  • Step Four: disconnect all equipment, put the plastic covers back on the connector ends and return everything to the state it was in before you started the practical so that the next group can carry out the practical in full.


Notes during the using of a VFL:

  • 1.Never look directly into the VFL’s output.
  • 2.Cover the VFL’s output with the dust cap when the VFL is not in use.
  • 3.Not recommended for use on dark colored or armored cables.

Using simple but useful technical principle, visual fault locator individually can provide an economic and time saving solution to locator faults in fiber optic cables in some cases. While working as an accessory of OTDR, VFL, together with OTDR, can provide the fiber technician the best solution to locate fiber faults.

Introduction of Visual Fault Locator

Many of the problems encountered in troubleshooting fiber optic networks are related to making proper connections. Since the light used in fiber optic systems is infrared (IR) light, which is beyond the range of the human eye, one cannot see it. In order to solve these problems, you need a visual fault locator. Visual fault locator(VFL) is a kind of device which is able to locate the breakpoint, bending or cracking of the fiber glass. It can also locate the fault of OTDR dead–zone and make fiber identification from one end to the other end. This text will give you a brief introduction of visual fault locator.

Working Principle

A powerful visible light from a red diode laser is injected into the fiber, so not only fibers  can be traced, but also high loss points can be made visible. Most applications center on short cables to connect to the fiber optic trunk cables, such as those used in premises cabling or telco central offices. The VFL works best on short cables, up to a few kilometers, thus, it covers the range where optical time-domain reflectometers (OTDRs) are not useful because of the dead zone of the OTDR.

Types of Visual Fault Locator

Visual fault locators generally include the pen type, handheld type and portable visual fiber fault locator.

Pen-style visual fault locator, as showed in the picture below, with a pocket-size, can be carried anywhere easily.

pen type VFL

Hand-held visual fault locator, as the following picture shows, is offered in a range of connector bulkheads styles, from universals to specific connector types.

Handheld VFL

Portable visual fiber fault locator is used to identify fiber and locate faults of single-mode or multi-mode fiber, it is a helpful assistant for finding fault in dead zone of OTDR, it is also a basic maintenance tool for fiber network, LAN, ATM fiber system and telecom network system. The appearance of a portable visual fiber fault locator is showed the following picture.

Portable Visual Fault Locator

Application of Visual Fault Locator

Visual fault locator is a kind of test equipment for testing, troubleshooting and measurement. The VFL 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 “blind-spot” or “dead-zone”. Fiber breaks, faulty connector, sharp bends, bad splices and similar faults can be visually located by light radiated outside the fiber when the light is injected into a fiber. Visual fault locator can boost productivity in the field by providing fast detection, precise fault location, distance, loss, and ORL measurements.

Importance of Visual Fault Locator

The complex network integrated by optical fiber, connector and jumper makes you difficult to find the fault location. So the visual fault locator is an essential tool that quickly and easily locates problem areas in fiber cables. By pinpointing the exact location of fiber damage, technicians can diagnose, troubleshoot and fix the problem timely and efficiently. The VFL is also used for conducting continuous tests and performing fiber identification. With visual fault locator, you can easily isolate high losses and faults in optical fiber cables.

Fiberstore Solution

In terms of its types, applications, importance we can know the VFL is an ideal tool for locating a large number of defects that occur at connection and around fiber cabinets which are hidden in an OTDRs “blind-spot” or “dead-zone”. Fiberstore can not only supply visual fault locators, but also offer a new kind of Fiber laser tester, fiber optic pen, fiber laser pen. If you have any requirements, please contact us at sales@fs.com or live chat with us.