1. An optical Fiber used to couple and condition Light from an optical Source into an optical fiber. Often the launch fiber is used to create an equilibrium Modal Distribution in multi-mode fiber. Also referred to as Launching Fiber. 2. A fiber optic Cable used in conjunction with a source to excite the Modes of another Fiber Optic Cable in a particular way. Launching Fiber optic Cables are most often used in test systems to improve the precision of measurements.