| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a constitution for improving temperature characteristic in an optical head system where lights of different wavelengths are focused on the recording surface of an optical recording medium by utilizing the refraction and diffraction of an optical element. <P>SOLUTION: In the optical head system, the height h1 of a beam whose numerical aperture NA is equivalent to 0.6 from an optical axis at the incident surface 51 of a diffraction element 5, the height h4 of the beam from the optical axis at the emitting surface 31 of an objective lens 3, a lens thickness (d) at the center of the objective lens 3, and a focal distance (f) when composing the diffraction operation of the diffraction element 5 and the refraction operation of the objective lens 3 satisfy two following conditional expressions of 0.55<h4/h1<0.85 and 0.5<d/f<0.75. <P>COPYRIGHT: (C)2005,JPO&NCIPI |
