Shaping of the end of a multimode optical fiber for efficient coupling light from a laser diode

An entrance surface of a multimode optical fiber with the highest efficienc y of coupling radiation from a laser diode is considered. The geometry of t he surface is designed with the purpose of keeping a refracted ray inside t he fiber with simultaneous minimization of the reflection coefficient in ea ch point of the surface. As a good approximation to the ideal surface, the composite entrance surface of a cylinder-wedge shape is proposed. It has cl early improved the coupling efficiency as compared with that of the purely cylindrical surface. Analysis of the entrance surfaces is based on their tr ansmission coefficients, depending on the incident ray direction. (C) 1999 Optical Society of America.