The NF-904 Visual Fault Locator uses the DFB-LD as the emitting component. Driven by a constant current source, the indicator emits a stable red laser. The NF-904 can be used to inspect fiber failure when connected to an optical interface and be inserted into single mode or multi mode optical fiber. It is an indispensable tool in fiber project constructing, fiber network maintaining, and optical component manufacture and research.