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Visual Fault Locator Tutorial

June 26, 2014
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Visual Fault Locator Tutorial

What Is Visual Fault Locator?

Visual Fault Locator (identifier), or VFL/VFI, is a visible red laser designed to inject visible light energy into an optical fiber. Sharp bends, breaks, faulty connectors and other faults will "leak" red light allowing technicians to visually spot the defects.

Fiber visual fault locator, also called laser fault locator, is a 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. Designed with a FC,SC,ST universal adapter, this fiber fault locator is used without any other type of additional adapters ,it can locates fault up to 10km in fiber cable,with compact in size, light in weight, red laser output. Fiber visual fault locator include the pen type ,the Handheld type,and Portable visual fiber fault locator.Here is a video of visual fault locator solution, illustrating how to use and select VFL properly.

Difference Between VFL and Fiber Continuity Tester

The most important difference is their light source. A fiber continuity tester typically uses a red or green color high intensity LED while a laser visual fault locator uses red color semiconductor (635-650nm) laser. The optical output power of the laser is typically 1mW or less. Because of the high optical output power, you should never view the output of the VFL directly.

Fiberstore VFL

Visible lasers produce a more powerful light and can provide more information to the technician than a LED light. By coupling the fiber link to a visible laser, problems with connectors, breaks in the fiber near connectors or splices, and some bend radius violations can be located.

On the other hand, LED powered fiber continuity tester can only verify that light can travel through the fiber link and no more information is obtained. Fiber continuity tester simply yields a "no go" result. If the light isn't visible at the other end of the fiber link, then the fiber is unusable in its present state and requires further testing and repair.

Working Principal of Visual Fault Locator

The VFL fills the core of the optical fiber with light from the laser. The light from the laser escapes the optical fiber at a break or macrobend. The light escaping from the optical fiber will typically illuminate the buffer surrounding the optical fiber. Macrobends are not always visible through the jacket but are typically visible through the buffer. Breaks may be visible through the jacket of the fiber optic cable depending on jacket color, thickness, number of optical fibers in the cable, and amount of strength member.

Types of Visual Fault Locators

The Visual Fault Locator is available in different shapes and sizes. Some may look like a pen, others may be built into an optical time domain reflectometer (OTDR), and some may look like a small test equipment box. There are two types of VFLs: contact and non-contact. With a contact VFL, the optical fiber under test will make contact with the VFL. However, with a non-contact VFL the optical fiber under test will not touch the VFL.

Pen-shape VFL
Model Number: FS1565E

Specifications:F-P LD laser sourceCW and MOD modeFC SC and ST interfaceCrash-proof and dust-proof design for laser headHigh reliability power outputBattery Operating Time: 20 minutesLaser case ground design prevents ESD damageNanotechnology multi-static protectionPen-shaped design, portable and easy to useOperating Temperature(℃): 10~+60℃Storage Temperature(℃): -40~+85℃Shell Material: Aluminum alloy

Pen-shape VFLfrom Fiberstore

Handheld VFL
Model Number: BML201

Specifications:Provide two different output power and different dynamic distance: BML200(>1mW) and BML201 (>10mW)Fast locate the broken pointThe universal fiber adapter can be connected with all 2.5mm adapters, e.g. FC, SC or ST2Hz glint or continuous outputBattery low indicationEnergy save mode: about 10 minutes no operation will cause the device automatic power offFull energy can support above 12 hours operationAC/DC Adapter: Input: 100-240V AC 50/60Hz Output: 5VDCStorage Temperature: -20 -- +60 ℃, 90%RHOperating Temperature: -10 -- +50 ℃, 90%RHPower Supply: 2 * AA batteries or AC/DC adapterSize: 160mm * 75mm * 32mmWeight: About 170g

Handheld Visual Fault Locator from Fiberstore

VFL Important Parameters

Fiber distance: The fiber distance spec tells the longest fiber length where you can still see the leakage light without difficulty. This spec is determined by the laser light power. The industry standard spec is 10km for multimode fibers and 5km for single mode fibers.

Wavelength: Wavelength is not a critical spec. 635nm, 650nm and 670nm will all work just fine.

Output power: Output power is an important spec for visual fault locators. The higher output power, the longer fiber distance it can support. This spec is usually 0.5mW coupled to single mode fibers and 2mW to free space (which means no fiber coupling, just the light output from the tester's connector adapter).

Fiber mode: All visual fault locators can work with both single mode and multimode fibers. Since multimode fiber has a 50um or 62.5um core, which is much bigger than single mode fiber's 9um core, more light power can be coupled in to multimode fibers. That translates to longer fiber distance for multimode fibers which is usually 10km. For single mode fiber, however, fiber distance is only 5km.

Modulation frequency (CW and 2Hz): Human eyes are much more sensitive to a blinking light than to a steady light. So visual fault locators provides two operating modes: continuous wave and pulse light. In most cases, fiber optic installation technicians prefer the pulse light mode which turns the laser source on and off in 2Hz or 1Hz frequency.

Battery: Usually two AAA alkalescence batteries

VFP Maintenance Tips

Tip One: Clean both ends of the VFL after 50 matings or sooner if performance diminishes.

Tip Two: Clean ST connector ferrule end face with a lint-free wipe (FWP-C) soaked with alcohol (reagent grade isopropyl alcohol, with a minimum 90% concentration).

Tip Three: Clean the split sleeve with an alcohol soaked cleaning swab (FSWB-C). Replace the split sleeve onto fiber ferrule and screw housing into place securely.

Tip Four: Clean FVFL output by unscrewing housing and removing split sleeve. Be careful not to lose the small spacer ring around the ferrule.

VFL Using Instructions

The first thing you will need to do is clean the connector endface and inspect it with a microscope. If the endface finish is acceptable, the VFL can be connected to a fiber connector should not be viewed directly during this testing.After connecting the fiber visual fault locator to the opti-crimp connector ferrule (with the included patch cord), turn the VFL “on”. Notice the red glow in the connector ferrule.While carefully inserting the cleaved field fiber into the connector using constant light pressure, notice the red glow diminish as the cleaved field fiber approaches the prepolished fiber stub in the connector. The insertion mark on the fiber will also approach the end of the connector ferrule.To turn on the VFL, press and hold the ON/OFF button for approx. 2-3 seconds. The green LED will illuminate to indicate that the unit is on. The green LED will blink if the batteries require replacing.To toggle between continuous and pulsed modes, use the 2Hz button. In continuous mode the red LED will be off and in the 2Hz mode the red LED will be on.Should be kept away from water, dust, static electricity, and environments of extreme temperature.Exercise care when handling the VFL.Remove the batteries for prolonged periods of storage.Never look into the path of the Laser Beam.Never look into the end of a fiber that may have any fiber visual fault locator, or any other laser, coupled to it.Never launch visual fault locator into active equipment or microscope. Make sure that the end opposite the Visual Fault locator is not connected to any electronics or active equipment during termination.


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