A handheld device that clamps a fiber or jumper into a small controlled bend and senses the light leaking out. It shows whether a fiber carries traffic, which direction the light is moving and whether a test tone, commonly 270 Hz, 1 kHz or 2 kHz, is present from a source at the far end. It is the standard way to confirm a fiber is dark before cutting or splicing into it.
Clip the fiber identifier on before you cut anything, if it shows traffic on that buffer tube we stop.
Clamping the identifier causes a momentary bend loss, so on a link with little margin it can cause errors: keep the clip short.
Also heard as
- live fiber identifier
- LFI
Related terms
Lit
Describes a fiber that is carrying live traffic from active equipment, as opposed to dark.
Macrobend
A bend in a fiber tight enough to see, which lets light escape the core and causes loss.
VFL
Visual Fault Locator: a bright red laser pen that shows breaks, bends and bad connectors as visible glowing points.
Dark fiber
Installed fiber with no transmission equipment attached, either spare or leased bare to a customer who lights it.