US Patent 7995433 Optical head apparatus and optical disc apparatus

In an optical head apparatus and an optical disc apparatus which can reduce influence of interlayer stray light on a differential push-pull signal without making the configuration complicated, Uy=Ty×N1 is satisfied, where Ty denotes a length in the y-direction of one period of an interference fringe which is formed on the photodetector 9 by reflected light of the zero-order diffracted light by an information recording surface other than the access-target information recording surface, reflected light of the positive-first-order diffracted light by the information recording surface other than the access-target information recording surface, and reflected light of the negative-first-order diffracted light by the information recording surface other than the access-target information recording surface, N1 denotes a positive integer, and Uy denotes each length in the y-direction of the divisional light-receiving elements 9e, 9f, 9g, and 9h. Furthermore, Vy=(Ty/2)×{N2−(½)} is satisfied, where N2 denotes a positive integer and Vy denotes a distance to a division line of the divisional light-receiving elements 9g and 9h and a distance to a division line of the divisional light-receiving elements 9e and 9f, from a center of a main-beam light-receiving unit 9M.