New Focusing Error Detection Method using a Tilted Holographic Optical Element

Abstract

Recently, optical units, which integrate an optical disk pickup (excluding the objective lens) in a hybrid system using a holographic optical element (HOE), have been actively investigated with a view to practical use. A small holographic optical unit (HOU) enables the optical pickup to be downsized and lighter in weight. However, the downsizing of the HOU is restricted by the number of terminals which connect the respective photo-diode (PD) elements (generally more than 4-section PDs) and the laser diode (LD) with external circuits.