Abstract: A device for coupling a light source and an optical waveguide. The light source has an emissive surface whose dimensions are of the same order of magnitude as or smaller than the cross-sectional dimension of the waveguide. The coupling device comprises a ball lens, which is contact with the light source, and a convergent optical transfer system. The optical transfer system images the input face of the waveguide to the optical center of the ball lens with a magnification of approximately -1. The radiation issuing from any point of the emissive surface of the light source enters the waveguide as parallel rays.