Light source module

A light source module comprising

• at least one light source,
• a first optical waveguide which causes light entering therein from a light inlet end face to emanate from a light outlet end face, and
• an inlet optical system which collects light emitted from the light source and couples it to the light inlet end face of the first optical waveguide, wherein the improvement comprises that the light inlet end face of the first optical waveguide is larger than the light outlet end face thereof in cross-sectional area of the core;
• wherein, when the diameter of light impinging upon the light inlet end face of the first optical waveguide is represented by Dbeam, the numerical aperture of the light at the light inlet end face of the first optical waveguide is represented by NAbeam, the diameter or the length of the longer side of the core of the light inlet end face of the first optical waveguide is represented by Din, the numerical aperture of the core at the light inlet end face of the first optical waveguide is represented by NAin, the diameter or the length of the longer side of the core of the light outlet end face of the first optical waveguide is represented by Dout and the numerical aperture of the core at the light outlet end face of the first optical waveguide is represented by NAout,
• Din×NAin=Dout×NAout, Dbeam<Din and NAbeam<NAin.