| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical head device having an alleviated asymmetry of an FE signal and an optimized focusing sensitivity. <P>SOLUTION: The optical head device includes a hologram element. The hologram element has a four division regions separated by a straight line extending along a radial direction and a straight line extending along a tangential direction, i.e., a first diffraction region, a second diffraction region adjacent to the first diffraction region in the radial direction, a fourth diffraction region located diagonally opposite to the first diffraction region, and a third diffraction region located diagonally opposite to the second diffraction region. The first diffraction region has first coma, and causes a portion of reflected light to be incident to a first detection region. The second diffraction region has the first coma, and causes a portion of the reflected light to be incident to a second detection region. The third diffraction region has second coma whose polarity is opposite to that of the first coma, and causes a portion of the reflected light to be incident to a third detection region. The fourth diffraction region has the second coma, and causes a portion of the reflected light to be incident to a fourth detection region. <P>COPYRIGHT: (C)2011,JPO&INPIT |
