A fiber laser pen is a handheld visual fault locator (VFL) used in fiber optics to detect breaks, bends, and other faults by emitting a bright red laser light. The light escapes at the fault location, providing a clear visual marker for technicians to identify and fix issues in optical fibers and networks. These pens are portable, battery-powered, and compatible with various connectors, making them essential for field testing and maintenance in telecommunications and networking.