What Are Visual Locators and How Do They Help the Industry?


The biggest problems that arise from optical fiber networks are the troubles with connecting them. This is why we look for efficient methods which will help us better troubleshoot problem areas in the cables. One such product is a Visual Fault Locator.

A Visual Fault Locator is a very important part of the installation and maintenance kit of fiber optic cables. It can help us identify breaks, bends or wear of the fiber glass used in single mode or multi mode optical fiber cables. The light used in optical fiber cables is infrared light so it’s impossible to see where the losses in the cables are happening with the naked eye. This is where VFLs come into the picture as they use light from a powerful laser source which we can use to see where the high losses are taking place in an optical fiber cable.

Fiber Continuity Testers vs. VFLs

The main difference between fiber continuity testers and visual fault locators are the kind of light source they use. Fiber continuity testers use visible LEDs (mainly red or green) whereas visual fault locators use a high power red laser diode (635-670nm). The fiber continuity testers are the more basic ones as they can only help us find out if there is a problem with the fiber by identifying whether light will pass through the entire cable or not. If the light passes through the cables it works well and if not, it requires a more detailed analysis.

Whereas VFLs give us a more detailed analysis by helping us pin-point the exact location the losses are happening because of bad connections or bends, and we don’t have to trouble ourselves with any other equipment for further diagnosis.

The Principle On Which Visual Fault Locators Work

A high power red laser diode is used to send light through the core of the optical fiber cable which can travel for some distance and help us trace the light as it passes through the cables and spot any high losses in them. VFLs have a main application for short distance cables ranging up to a few kilometers and this is why they can be used as a part of OTDRs in regions of OTDR dead zones.

Types of Visual Fault Locators

Visual fault locators come in different shapes and sizes. There are two types based on how they function, namely contact and non-contact. In case of a contact VFL, the optical fiber we are testing comes in direct physical contact with the VFL and in case of a non-contact VFL, the optical fiber we are testing does not come in direct contact with the VFL. For commercial purposes, there are 3 main types of Visual Fault Locators:

  • Pen-style visual fault locator: This is pocket sized and can be carried around easily. This is a kind of contact VFL.
  • Hand-held visual fault locator: This is a type of contact VFL and comes in different connector types, ranging from specific connector types to universal.
  • Portable visual fiber fault locator: This is a non-contact VFL and is used to identify faults and losses in optical fiber cables especially in short range cables like LAN, ATM, FDDI, and telecommunication networks.

Important Parameters of VFLs

Some important parameters by which VFL performance can be measured which are:

  • Output power- The output power is a very important factor for VFL performance. VFLs can work for longer distances with higher output power.
  • Fiber distance – This is the maximum distance in the optical fiber cables till which we can see losses or problem areas without much problem. This is determined by the power of the laser diode. Normal VFLs have a 5km range for industrial single mode fibers and 10km range for multi mode fibers.
  • Wavelength – The wavelength of the VFLs work just fine in the range of 635nm – 670nm.
  • Modulation frequency – The eye is better able to pick up on a blinking light which is why technicians prefer VFLs with a blinking light rather than a steady one as it helps them diagnose the defects in cables better.

Learned All You Need About Visual Fault Locators?

A Visual Fault locator is an ideal instrument for installation, testing and maintenance of fiber optic cables because it can be used to locate a lot of defects that can occur in optical fiber cables like breaks, cracks, or bends in regions of bad fusion splices. Since the light passing through fiber optic cables is infrared, a visual fault locator is a great tool to help us see the areas which need improvement through our own eyes. A VFL begins its process by emitting light via a powerful red laser through the core of the optical fiber cable. When light passes through the cable, it illuminates the region surrounding the cable(buffer) in regions where there are any anomalies such as breaks, cracks or connector bends, due to radiation of the visible red light. This can work perfectly when used as a part of an OTDR as OTDRs have some blind spots or dead-zones during which we don’t get readings and since VFLs can help us see where our defects are, that solves many problems. Using VFLs can prove to be very useful and boost productivity because it provides quick and easy detection of the damage and helps us find the exact location where the problem lies so technicians can diagnose, troubleshoot and fix the problem in record time.

Looking for Visual Fault Locators? We have a large selection of VFLs in our store!


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