Vis-link 5mW 5km fiber visual fault locator (VFL) is a pen-style, portable tool used to detect breaks, bends, cracks, or poor connections in single-mode or multi-mode fiber optic cables. It uses a bright red 650nm laser to create a visible glow where light escapes, often offering continuous (CW) or pulsed modes for easier detection, typically through a 2.5mm universal adapter