on one side of the disc.
Due to such high density recording on a DVD, the spot diameter of the laser beam, which reads pit information from a DVD, is set to a value fairly smaller than that of a laser beam used to read information from a CD. The spot diameter of the laser beam is proportional to the wavelength xcex of the laser being used and is inversely proportional to the numerical aperture of the objective lens. Accordingly, a laser beam can have a small spot diameter if the wavelength of the laser light source is short and the numerical aperture of the objective lens is large.
Moreover, it is desired that a DVD player reproduce a CD in addition to a DVD since a DVD and aon the transparent electrodes functions as a xc2xc-wavelength plate during CD reproduction.
In a conventional optical system, such as the one described in the foregoing description, a laser beam from a laser source is guided to a recorded surface of a disc through a polarized beam splitter and a liquid crystal panel that functions as a xc2xc-wavelength plate. This beam is reflected from the disc and passes through the polarized beam splitter and the liquid crystal panel. The reflected beam is polarized 90-degrees with respect to the incident laser beam as a result of passing through the liquid crystal panel twice. Then, the reflected beam is guided to a photo detector, which is positioned in a different direction from the light source, by the polarized beam splitter. However, some