OPTICAL SYSTEM FOR COUPLING LIGHT SOURCE

PURPOSE:To execute easily a polish-working and an assembly, and to execute a mass-production at a low cost by arranging two self-focusing type lenses consisting of a cylindrical transparent body having a specified refractive index n(r) in a distance of (r) from the center, in the optical axis direction, and making a numerical aperture of a light source side of an optical system larger than a numerical aperture of an emitting side. CONSTITUTION:An optical system 1 is constituted by placing two self-focusing type lenses 2, 3 so that the axes are made to coincide and each end face is made to adhere tightly. The self-focusing type lenses 2, 3 consist of a transparent cylindrical body of glass, synthetic resin, etc., and all end faces of both the lenses 2, 3 form a plane vertical to the optical axis. Also, as for both the lenses 2, 3, a refractive index n(r) in a distance of (r) from the optical axis has a refractive index distribution as shown in the equation. Particulars of the lens are selected so that numerical apertures NA1, NA2 of both the lenses 2, 3 become a relation of NA1>NA2. Also, with regard to a biquadratic term coefficient h4 in the equation of the lenses 2, 3, h4 of the first lens 2 of the light source side is made smaller than h4 of the second lens 3.