1. Field of the Invention
The present invention relates to an object lens used with an optical pickup for recording and/or playing information signals to and/or from three different types of optical discs, the optical pickup, and an optical disc device using the optical pickup.
2. Description of the Related Art
As of recent, there has been proposed, as a next-generation optical disc format, an optical disc capable of high density recording, wherein signals are recorded and played using an optical beam of blue-violet semiconductor laser beam having a wavelength around 405 nm (hereafter referred to as “high density recording optical disc”). This high density recording optical disc is being proposed with a structure wherein the cover layer for protecting the signal recording layer is thin, 0.1 mm for example.
In providing an optical pickup compatible with such high density recording optical discs, compatibility with CDs (Compact Discs) using a wavelength around 785 nm and DVDs (Digital Versatile Discs) using a wavelength around 655 nm, according to the related art, is desirable. That is to say, there is demand for an optical pickup and optical disc device having compatibility among optical discs of multiple formats with different disc structures and accordingly different laser specifications.
There has been related art which realizes recoding or playing of information signals to/from three types of optical discs of different formats, such as that shown in FIG. 60, for example. This arrangement involves having two types of object lenses and two types of optical systems, one corresponding to DVD and CD, and the other to high density recording optical discs, with the object lenses being switched over according to the wavelength being used.
An optical pickup 430 shown in FIG. 60 realizes recording and/or playing to and/or from optical discs of different types, by having two types of object lenses, object lens 433 and object lens 434. The optical pickup 430 has a light source unit 432, such as a laser diode or the like, including an emitting unit for emitting an optical beam of a wavelength around 785 nm for optical discs such as CDs and an emitting unit for emitting an optical beam of a wavelength around 655 nm for optical discs such as DVDs, a light source unit 431, such as a laser diode or the like, including an emitting unit for emitting an optical beam of a wavelength around 405 nm for high density recording optical discs, an object lens 434 for optical discs such as DVDs and CDs, and an object lens 433 for high density recording optical discs. The optical pickup also has collimator lenses 442A and 442B, quarter-wave plates 443A and 443B, redirecting mirrors 444A and 444B, beam splitters 437 and 438, gratings 439 and 440, a photosensor 445, a multi-lens 446, and so forth.
An optical beam of a wavelength around 785 nm emitted from the light source 432 is transmitted through the beam splitter 437 and beam splitter 438, and is input to the object lens 434. The object lens 434 condenses the beam onto the signal recording face of the optical disc having a protective layer (cover layer) 1.1 mm thick.
In the same way, the optical beam of a wavelength around 655 nm emitted from the light source 432 is input to the object lens 434 via exactly the same optical path, and is condensed onto the signal recording face of the optical disc having a protective layer 0.6 mm thick. Return light of a wavelength of 785 nm and of a wavelength of 655 nm reflected off of the signal recording face of the optical disc passes through the beam splitter 438, and is detected by the photosensor 445 having a photodetector or the like.
An optical beam of a wavelength around 405 nm emitted from the light source 431 is reflected at the beam splitter 437, and is input to the object lens 433 via the beam splitter 438. The object lens 433 condenses the beam onto the signal recording face of the optical disc having a protective layer 0.1 mm thick. Return light of a wavelength of 405 nm reflected off of the signal recording face of the optical disc is detected at the photosensor 445 via the beam splitter 438.
Thus, the optical pickup shown in FIG. 60 realizes recording and/or playing of three different types of optical discs by having two types of object lenses, the object lens 434 for DVDs and CDs, and the object lens 433 for high density recording optical discs, thereby realizing compatibility between multiple types of optical discs.