OPTICAL PICKUP DEVICE AND WAVELENGTH SELECTIVE DIFFRACTION GRATING

摘要

An optical pickup device which has a two-wavelength semiconductor laser (23) which emits a laser beam with a wavelength of 635 nm and a laser beam with a wavelength of 780 nm selectively, a collimator lens (24), a hologram (25) formed on the surface of the collimator lens (24), a polarization glass (22) having an annular polarization region (40) and an object lens (21). The hologram (25) does not diffract the laser beam with the wavelength of 635 nm but diffracts the laser beam with the wavelength of 780 nm outward. As a result, the imaginery light source of the 780 nm laser beam is closer to the collimator lens (24) than the light source of the 635 nm laser beam. Therefore, the object lens (21) focuses the 635 nm laser beam on the recording surface of the transparent substrate (31) of a DVD and focuses the 780 nm laser beam on the recording surface of the transparent substrate (32) of a CD-R. With this constitution, the optical pickup device can reproduce data recorded on both DVD and CD-R whose transparent substrates have thicknesses different from each other. <IMAGE>