The 30mW Visual Fault Locator (VFL) is a pen-style fiber optic cable tester. It typically features a 2.5mm universal connector compatible with SC, FC, and ST interfaces and has a testing range of 10km. 

Key Features and Usage

• Function: The VFL emits a bright 650nm red laser light into the fiber optic cable. This allows technicians to visually pinpoint fiber breaks, tight bends, poor connections, or cracks by observing where the scattered red light emerges.
• Compatibility: Most models come with a 2.5mm universal adapter for SC, FC, and ST connectors. For users with LC interfaces, a separate 1.25mm FC-LC adapter is generally required.
• Durability: VFL comes with an aluminum alloy or metal body designed to prevent crash and dust damage. 
• Operating Modes: The device can operate in both Continuous Wave (CW) mode for steady light and Pulsed mode to improve fault location visibility in high ambient light conditions and extend battery life.
• Portability: The pen-type design is compact, lightweight, and often includes a pouch or lanyard, making it portable and easy for field testing and maintenance.