OPTICAL PICKUP USING OPTICAL PHASE PLATE

PROBLEM TO BE SOLVED: To make two disks interchangiable by shifting the phase of light traveling from an optical part adjusting means to an objective lens and using either of first light or second light depending upon a used optical recording medium. SOLUTION: A collimator lens 34 collimates an incident light beam from a second beam splitter 33 to make it parallel with an optical axis perpendicular to the surface of a variable diaphragm 35 and the collimated beam is made to transmit through in a manner of wavelength selection. A phase plate part 36 is used for making a light spot size small so as to perform recording/ reproducing in a CD-R disk 9. The phase plate part 36 makes the light having the wavelength of 780nm traveling from the variable diaphragm 35 to the objective lens 37 shift the phase by 180 deg., and the light of 650nm by 360 deg.. Consequently, the light of 780nm shifted by 180 deg. actually passes through an aperture with super-high resolution compared with the case the phase plate part 36 is not used, the light spot size on the information recording surface of the CD-R disk 9 is made small and the spherical aberration is removed.