Patent attributes
An echelon type diffraction structure 5a is formed on the flat optical surface of a lens 5, thereby ensuring easy designing and easy production of a diffraction structure as a microstructure. Further, the light of wavelength λ1 is applied to the diffraction structure 5a in a tilted position with respect to the optical axis of the lens 5 so that the first order diffracted light produced by the diffraction structure 5a travels along or parallel to the optical axis of the lens 5, with the result that improved light transmittance can be maintained. Further, a lens 7b is arranged between a light emitting device 7a and lens 5. Thus, the flat optical surface of the lens 5 is arranged on the side of the end face 1a of an optical fiber 1, thereby reducing the deterioration in aberration more effectively.
