Coupling Light from a Laser Diode into a Multimode Fiber

A parabolalike fiber end to couple the light from a high-power laser diode into a multimode fiber is presented. The formula for the coupling efficiency of such a system is given, and numerical evaluation shows that the theoretical coupling efficiency can be as high as 92% without an antireflection coating on the fiberʹs end face. This beam-shaping system can be fabricated easily and has a large alignment tolerance.