Whenever you need to install or troubleshoot fiber cables, visual fault locator (VFL) is an easy and essential tool for quickly positioning the problem areas. As a fiber optic tester, VFL is used to trace optic fibers, check fiber continuity and find fiber breaks, damaged connectors, defective splices, tight bends in optical cables. Two basic types of VFL are pen shape VFL and hand held VFL. Pen shape VFL is very small with a pocket size to be carried anywhere. Hand held VFL has a range of connector bulkheads styles from universals to specific connector types. This article will lead you to know more information about VFL.
Importance of VFL
VFL can pinpoint the exact fiber damage location, therefore technicians are able to diagnose and solve the problem in a timely manner which efficiently avoids further fiber damage. VFL is also used for conducting continuity tests and performing fiber identification. With the help of VFL, specialists can easily isolate high losses and faults in optical fiber cables. As we all know, a good cabling system is the pledge of a good data center. In order to maintain the perfect functioning of fiber optic cables, VFL is an indispensable tool to be applied for the routine trouble shooting.
How VFL Works?
The invisible light signals are typically transmitted at 1300 nm to 1650 nm wavelengths over fiber optic cables. Different from the way that OTDR (optical time-domain reflectometer) locates the faults by measuring the time of the incidence and the amplitude of the reflected pulses sent to the fiber optic cable, VFL uses powerful visible light at the wavelengths between 360 nm to 670 nm to visually and quickly locate the faults in the cables. When the visible light leaks out at a certain point of optical cable, it shows that the VFL has reached a fault. It is also easy to see light leaking through the plastic cable jackets under the right illumination of VFL. Generally, a VFL can work at the distance between 2 km to 5 km.
How to Use VFL?
Using VFL is not a difficult task. Just follow the steps to know the operation procedure:
- Step one, remove the plastic connector covers from both ends of the fiber cable.
- Step two, connect the VFL to one end of the fiber cable.
- Step three, press the tester button and observe whether light emanates from the other end of the fiber. This gives a simple indication of the continuity of the fiber link.
- Step four, repeat the above steps with other fiber cables to see if visual light is leaking out from a faulty splice. This may illustrate an easy way of carrying out visual fault locating on bad splices or joints.
- Step five, disconnect all equipment, put the plastic covers back to the connector ends and return everything to the state it was.
- Point one, do not look directly into the VFL’s output.
- Point two, cover the VFL’s output with the dust cap when it is not in use.
- Point three, VFL is not recommended to be used on dark colored or armored cables.
VFL is an equipment for fiber testing, troubleshooting and measurement. It is ideal for locating a large number of defects that are hidden in an OTDR “blind-spot” or “dead-zone”. Fiber breaks, faulty connectors, sharp bends, bad splices and other similar faults can be visually located by VFL’s visual light injected into a fiber. VFL can boost productivity in the field by providing fast detection, precise fault location and ORL (optical return loss) measurements. If you don’t have it, better get one for your project.
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.
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.