A higher power version of the fiber tracer called a visual fault locator (VFL, visual fault finder) uses a visible laser that can also find faults. The red laser light is powerful enough for continuity checking or to trace fibers for several kilometers, identify splices in splice trays and show breaks in fibers or high loss connectors. You can actually see the loss of light at a fiber break by the bright red light from the VFL through the jacket of many yellow or orange simplex cables (excepting black or gray jackets, of course.) It’s most important use is finding faults in short cables or near the connector where OTDRs cannot find them.
You can also use this gadget to visually verify and optimize mechanical splices or prepolished-splice type fiber optic connectors. By visually minimizing the light lost you can get the lowest loss splice. In fact- don’t even think of doing one of those prepolished-splice type connectors without one. No other method will assure you of high yield with those connectors.
A note on VFL eye safety. VFLs use visible light. You will find it uncomfortable to look at the output of a fiber illuminated by a VFL. That’s good, because the power level is high and you should not be looking at it. When tracing fibers, look from the side of the fiber to see if light is present.
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