| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an objective lens capable of suppressing a side lobe at the time of using an optical disk used in a state where the light is condensed with a low NA (numerical aperture). <P>SOLUTION: The objective lens 10 is a single lens, both faces of which are aspherical, and a diffraction lens structure is formed on at least one face 11 of the lens. The diffraction lens structure formed in a center area Rc is designed so that the diffraction efficiency of primary diffraction light may become the largest for two wavelengths. The diffraction lens structure formed in an ambient area Rh is set as follows, the phases of two kinds of luminous flux transmitted through the ambient area and the center area become nearly the same for the wavelength corresponding to a DVD, and the phase of the luminous flux transmitted through a circular band constituting a 1st annular area in the ambient area Rh is different from the phase of the luminous flux transmitted through the center area for the wavelength corresponding to a CD, the phase of the luminous flux transmitted through a circular band constituting a 2nd annular area positioned outside the 1st annular area is made to be nearly the same as the phase of the luminous flux transmitted through the center area Rc. <P>COPYRIGHT: (C)2004,JPO |
