Patent ID: 7990834

Claim:
An optical pickup device having a laser as a source of light emitting light in turn branched via an optical branching element into at least three beams of light including a main beam and two sub beams in turn condensed via an objective lens on an optical recording medium at a guide groove and reflected by said optical recording medium to provide three reflections of light in turn received by different detectors, each divided into two regions, respectively, to obtain a differential signal from said detectors to generate a tracking error signal from said differential signal, wherein: said optical branching element is a diffraction grating divided into at least three regions including a first region, a second region and a third region located intermediate between said first and second regions, said first, second and third regions have a periodical structure with their respective phases different from each other, said periodical structure has grating grooves in a direction determined depending on said phase of said second region and so as to be inclined relative to a direction that is perpendicular to said guide groove of said optical recording medium; and if relative to said first region said second regions has a phase difference a in degrees, on said optical recording medium said main beam and said sub beams have a distance L therebetween, and said optical recording medium has said guide groove with a pitch M, then said optical branching element has said periodical structure with said grating grooves in a direction that is inclined relative to said direction perpendicular to said guide groove of said optical recording medium by an angle θ=((180−α)/360)tan −1 (M/L).