| 摘要 |
The present invention provides an optical head device comprising : a light source for emitting a laser beam ; a polarization beam spritter for receiving the laser beam and dividing first and second linearly polarized beams having first and second polarization directions which are vertical to each other ; an optical transmission system for receiving the first and second polarized beams and respectively transmitting the first and second linearly polarized beams along first and second optical paths which are parallel to each other ; a quarter wavelength plate for receiving the first and second linearly polarized beams and converting the first and second linearly polarized beams into first and second circulatory polarized beams having polarization planes rotating in first and second directions opposite to each other ; and a pair of first and second objective lenses provided for receiving the first and second circulatory polarized beams respectively, the first and second objective lenses having first and second focal lengths which are different from each other, so that any one of the first and second circulatory polarized beams is focused on an optical disk surface and then the first and second circulatory polarized beams are reflected by the optical disk surface and subsequently transmitted through the first and second objective lenses to the quarter wavelength plate whereby the first and second circulatory polarized beams are respectively converted into third and fourth linearly polarized beams having the second and first polarization directions respectively before the third and fourth linearly polarized beams are transmitted through the optical transmission system to the polarization beam spritter whereby the third and fourth linearly polarized beams are transmitted along a common optical path to a single optical detecting system. <IMAGE> |
