Read/write laser-detector-grating unit (ldgu) with an

Abstract

An apparatus and method for providing tracking and focus error signals for controlling an application of a radiation beam to a data track of an optical storage medium. A data signal, indicative of the data stored on the storage medium, may also be provided. One apparatus in accordance with the present invention includes an optical source to generate a radiation beam; a transparent substrate arranged between the optical source and an optical storage medium; and a grating beam splitter formed on a surface of the substrate and having first, second, third and fourth grating elements for separating a return beam reflected and diffracted from the data track into first, second, third and fourth portions, respectively. In other embodiments, more or less than four grating elements and return beam portions could be used. The portions of the return beam are directed onto a detector array. The first and second grating elements separate the return beam along a plane substantially parallel to a reference plane defined by an optical axis of the radiation beam and a tangent to the data track, and the resulting first and second portions may be used to generate a tracking error signal. The third and fourth grating elements, arranged on opposite sides of and adjacent to the first and second grating elements, separate the return beam along a plane substantially perpendicular to the reference plane, and the resulting third and fourth portions may be used to generate a focus error signal. The optical source, transparent substrate, grating beam splitter and detector array are part of an LDGU contained within a single package.