Daisuke Koreeda

Design of an objective lens for optical disc systems employing a blue laser by scalar diffraction simulation

We have designed a compatible objective lens for HD DVD/DVD/CD drives utilizing a multiple diffractive structure. In this case, if priority has been given to a high HD DVD diffraction efficiency, the CD diffraction efficiency is reduced. Therefore, plenty of noise light is generated at the entrance pupil diameter of a CD inner area which may cause a false signal in the focus error (FE) signal during CD playback. Furthermore, the quality of the spot and the side-lobe intensity gets worse due to the light at the entrance pupil diameter of a CD outer area, and hence, may cause recording and playback problems. To solve these problems, we improved the objective lens applying a scalar diffraction simulation. We separated the position of the false signal far away from the regular signal in the FE signal, and suppress the amplitude of the false signal much smaller than the regular signal in FE signal during CD playback to achieve the reliable focus servo. In addition, we managed to improve the spot and the side-lobe quality to a practical level during CD playback with providing an aperture filtering function on the objective lens.