Visual Fault Locator, a red visible laser, usually 635 to 650 nm, coupled into a fiber through a universal ferrule adapter. Light escaping at a break, a tight bend or a cracked connector glows through jackets and boots, so faults within a few kilometers can be seen directly. It is also the fastest way to check continuity and identify which fiber is which across a panel.
Put the VFL on port 7 and walk the jumpers, wherever that cord glows red is where it's broken.
Bend-insensitive fiber and black jackets hide a VFL's glow, so a VFL that shows nothing has not proven the cable is clean.
Also heard as
- visual fault locator
- red light
Related terms
Red light
Installer slang for a visual fault locator and the red laser it puts into the fiber.
Macrobend
A bend in a fiber tight enough to see, which lets light escape the core and causes loss.
Fiber identifier
A clip-on tester that detects light in a fiber through a gentle bend, without cutting it or interrupting traffic.
OTDR
Optical Time Domain Reflectometer: a tester that maps a fiber's loss and events by timing light reflected back along it.