Optical pick-up for DVD

The optical pick-up for DVD with CD compatibility is discussed. DVD players or DVD-ROM drives are strongly required to have the conpatibility with conventional CD for the comrcialization of DVD. However, the difference of the substrate thickness between DVD and CD causes the different spherical aberration and prevents the laser beam from being focused into a diffraction limt spot size with only one objective lens. Several types of optical pick-ups for overcoming this problg and the twin lens type optical pick-up which is one of these solutions, are introduced.