FOCAL ERROR DETECTING DEVICE

摘要

PURPOSE:To cancel the focal offset by the flaw on the surface of an optical recording medium by providing a quartered light receiving means symmetrically with an optical axis along a track far-field pattern. CONSTITUTION:Two light receiving means 40 are provided so that the respective may become symmetrical by interposing an optical axis and the means 53 adding the phase difference of the output signals of respectively two pairs of light receiving elements 40a-b, 40c-d is provided. The phase difference by the flaw on the surface of an optical recording medium can be offset without sacrificing the detection sensibility of the phase difference by a focal error. The focal error detecting device using a focal error detecting method by a phase difference method and yet causing no offset on the focal error signal by the flaw on the surface of the optical recording medium can thus be obtd.