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How To Check Your Fiber Link In Two Minutes With A Visual Fault Locator

Mar 12, 2008
What are fiber optic visual fault locators?

Fiber optic visual fault locators are also called visual fault finders. They are low cost, battery powered fiber test tools to find fiber imperfections, fiber breaks (fiber cutting), microbends and macrobends in fiber optic cable links.

Visual fault locators come in a pen shape or handheld style with a fiber optic connector adapter to accept different connectors such as FC, ST, SC, LC or even MTRJ.

How do they work?

Visual fault locators inject a highly visual red color laser light into optical fiber cables. The red light can be switched between continuous mode (continuous wave) or pulse mode with a 1~2 Hz frequency and 60ms duration.

The light source is usually a high power, extra long life, class 2 laser diode at 635nm. Other available wavelengths are 650nm and 670nm.

The fault locator injects light into fiber cables through a built-in connector adapter. Two types of connector adapters are available: 2.5mm and 1.25mm in diameter. The 2.5mm version accepts FC, SC and ST connectors and the 1.25mm version accepts LC and MU connectors.

The fiber installation technician can then look at the length of the fiber cable and where glowing or blinking light is seen, a break, microbending or macrobending exists.

The tool can be used as a stand-alone first-line basic troubleshooting tool or in conjunction with an OTDR to pinpoint faults. It can also be used as a continuity tester.

The construction of a laser fault locator

Laser fault locator is a simple and reliable tool. It consists of laser light source, pulse modulation circuit board, light coupling lens and fiber optic connector adapter.


Fiber optic visual fault locators are regularly used for testing and finding breaks in LANs, FDDI, ATM, fiber data links and loops, telephones, ships and other vessels.

Its industry applications include fiber optic networks, telecoms network and CATV network maintenance.

Manufacturer brand names and their corresponding quality

Wilcom, Fluke, Noyes, Greenlee, Ideal, Wavetek all supply high quality visual fault locators. Our preference is Wilcom's products since they have been in this market the longest time and their products are generally very high quality.

Understanding the specifications

1. 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.

2. Wavelength

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

3. 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).

4. 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.

5. 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.

6. Battery

Usually two AAA alkalescence batteries
About the Author
Find out even more about fiber optic visual fault finder , fiber optic visual fault locator , optical fiber identifier on Fiber Optics For Sale Co's web site. FOFS is one of the largest suppliers of fiber optic cabling products.
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