OPTICAL PICKUP DEVICE

摘要

An optical pickup device includes: a semiconductor laser (1) selectively generating a laser beam (25) with a wavelength of 635 nm and a laser beam (27) with a wavelength of 780 nm: and an optical device (5) having a central region (5b) in which a hologram (20) is formed and a peripheral region (5a) in which a diffraction grating (21) is formed. Optical device (5) is arranged immediately below an objective lens (7). Central region (5b) allows transmission of the laser beam with the wavelength of 635 nm without any diffraction, but increases the diameter of the laser beam with the wavelength of 780 nm by diffraction. On the other hand, peripheral region (5a) allows transmission of the laser beam with the wavelength of 635 nm without any diffraction, but substantially shields the laser beam with the wavelength of 780 nm by diffraction. Thus, all of laser beam (25) with the wavelength 635 nm is transmitted through objective lens (7) and focused on a signal recording surface (9a) of a DVD (26). The periphery of laser beam (27) with the wavelength of 780 nm is significantly diffracted by peripheral region (5a) of optical device (5) and only the central portion of laser beam (27) enters objective lens (7) while increasing its diameter. Thus, laser beam (27) with the wavelength of 780 nm is focused on a signal recording surface (99a) of a CD-R or a CD-ROM (31). Therefore, the optical pickup device is capable of compatibly reproducing the DVD, CD-R and CD-ROM.