Category Archives: Fiber Optic Testers

Visually Locating Fiber Loss With VFL

As fiber links support higher speed network bandwidths with increasingly stringent requirements, it is becoming all the more important to ensure that your backbone links meet tightening loss standards. As network applications grow and expand, the need for higher data transmission capacity continues to grow as well. To guarantee reliable and efficient network connectivity and data transfer, the testing tool holds a key position in reducing the time spent identifying and locating the fiber loss. In this article, we will introduce an useful tool—visual fault locator (VFL) to achieve quicker, easier and more efficient fiber loss identification.

Introduction to VFL

VFL, also known as visual fault locator, serves as a fiber optic testing device that is widely used 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. Designed with FC, SC and ST universal adapter, this fiber fault locator can be used without any other additional fiber adapters to locate fault up to 10 km in fiber cable. Featured by compact size, low weight and red laser output, the VFL is widely adopted to visually locate loss locations on fiber links and can also be employed to confirm fiber continuity.

Generally, there exist two types of commonly used VFLs : pen shape visual fault locator and hand-held visual fault locator, the following picture shows the outlook of them.

Visual fault locator

How Does VFL Work?

Since the light involved in transmitting signals over fiber optic is usually at 1300nm to 1650nm wavelength which is invisible to human, we can barely see it with our naked eyes. However, by injecting powerful visible light at 360nm to 670nm wavelength to the fiber, VFL helps to visually and directly locate the faults in fiber optic cable. This visible light keeps traveling along the core until it reaches a fault, then it leaks out, which can be seen through plastic coating and jackets. Thus, we can visually locate loss locations be it a macrobend, faulty connectors or a poor splice. In addition, VFL also helps to cover the range where optical time-domain reflectometers (OTDRs) are not useful because of the dead zone of the OTDR.

Fiber testing

Application of VFL

VFL is an ideal tool for locating 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 VFL. Visual fault locator can boost productivity in the field by providing fast detection, precise fault location, distance, loss, and ORL measurements.

Reference Guide to Use VFL

Network environments sometimes are too complicated for technicians to find the fault location, which makes visual fault locator a vital and indispensable tool for fixing the problem timely and precisely. 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. Here we offer you step-by-step procedures on how to use a VFL.

  • Step 1: Remove the plastic connector covers from both ends of the test fiber cable.
  • Step 2: Connect the fiber optic visual fault locator to 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 3: 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 4: Disconnect all equipment, put the plastic covers back on the connector ends and return everything to the state it was before you started the practical, so the next group can carry out the practical in full.


What should be addressed is that during the testing process, you should never look into the output of VFL directly. After finishing the whole procedure, and remember to cover the VFL’s output with the dust cap.


Visual fault locator provides us a simple and convenient way to quickly locate faults in fiber optic cable, which is proved to be time saving and economical as well. Besides, it also alleviates the problems and pressures when dealing with massive fiber optic cabling system. Hope this article would help you get a better understanding of visual fault locator.

A Kind Of Fiber Test Equipment – Visual Fault Locators In Fiberstore

FiberStore offers many kinds of fiber optic testing equipment. For example,common used fiber optic test equipment included fiber optic power meter, fiber optic light source, fiber multimeter, optical time domain reflectometer (OTDR) and fiber fault locator. In this article,I will detail the Visual Fault Locators.

Visual Fault Locators:

Fiber optic fault locator is a small size and simple test equipment used to locate the optical fiber linking faults, there are several models with different output power. Fiber optic fault locator can detect the bend point or break point of the fiber glass. It is widely used in telecommunications, CATV and fiber optic projects.

Visual fault locator (also called laser fault locator or 650nm fault locator) is a handheld device using 650nm or 635nm visible laser source that emits a bright beam of laser light into a fiber, allowing the user to visually detect a fiber fault for up to 5 km.

Laser Fault Locators provide the capability to trace fiber routes for end-to-end continuity. Locate breaks within the deadzone of an OTDR, bad splices, potential fiber problems caused by imperfections as well as microbends and macrobends. These devices also can be used as fiber identifiers. They can operate on multimode or singlemode fibers independent of the transmission wavelength. Visible beams make results easily noticeable. Laser fault locators are excellent instruments for locating fiber faults and other anomalies where the pulse width of the laser used in OTDRs won’t allow measurements to be made. Applications include LAN, WAN, fiber data links, telephone and CATV.

With these fault locators you can easily isolate high losses and faults in optical fiber cables. The bright beam of 650nm or 635nm red light in a fiber allows you to see a break as a glowing or blinking red light. Two versions are available: one with a universal port for 2.5mm ferrule connectors (FC, SC, ST, E2000, DIN), and one which includes an adapter that allows use with 1.25mm ferrule connectors as well (LC, MU).

Handheld Optical Visual Fault Locator BML201 650n 10mw with 2.5mm Universal Adapter(10km)

Features of FOFS’s line of Visual Fault Locator(Laser Fault Locator):

  •     Both CW and pulsed mode are available
  •     Lightweight (handheld and pen shape available)
  •     Long continuous operation time
  •     Cost effective solution

Besides the Visual Fault Locators,FiberStore also offer a full range of fluke test equipment.From industrial electronic installation, maintenance and service, to precision measurement and quality control, Fluke tools help keep business and industry around the globe up and running. Typical customers and users include technicians, engineers, medical-device manufacturers, and computer network professionals – people who stake their reputations on their tools, and use tools to help extend their personal power and abilities.

Note:When selecting optical fiber test equipment, in addition to want to consider the function and quality of equipment, and some is you should pay attention to:For example, the working wavelength (typical is 1310nm, 1550nm and 850nm), fiber light source type, fiber optic glass type (single mode or multimode), fiber connection interface (like FC, SC) and the system capacity and possible loss range.Fiber optic test equipment working environment is also the factor you should consider, whether you are going to use the fiber test equipment indoor or outdoor, the equipment working temperature, power supply, battery life.