A visible fault locator is a fiber optic laser light tester that can be used to find problems and check continuity over lengths of only a few Km. It can also be used along with an OTDR tester to find a fault with greater accuracy. Fiber optic cable. Fluke Networks has a wide range of Fiber Optic testing products to help certify that power losses are within standards and to troubleshoot broken and high loss links on single-mode and multimode fiber all with ease-of-use, accuracy, and durability. Get pass/fail results in seconds. A clip-on identifier is not strictly a fault locator, but is. Fiber optics is a technology that utilizes thin strands of glass or plastic, called optical fibers, to transmit data in the form of light pulses.