Patent ID: 6130872
Filing Date: 2000-10-10
Classification: G11B

Abstract:
An optical pickup apparatus for reading recorded information from an optical recording medium, said optical pickup apparatus including and optical system which comprises:light intensity detection means having quartered light receiving surfaces;two semiconductor lasers for emitting light beams of different wavelengths;an objective lens for directing each of said light beams onto an optical recording medium to form a light spot on a recording surface; andfirst and second holographic optical elements located between said quartered light receiving surfaces and said objective lens,wherein one of said two semiconductor lasers is arranged to direct the light beam to said first and second holographic optical elements in a manner that a main axis of said light beam is normal to said first and second holographic optical elements, and the other one of said two semiconductor lasers is arranged at a position that its light beam incident into said first and second holographic optical elements emerges therefrom at right angles; andwherein said first holographic optical element eliminates coma aberration and spherical aberration of a light beam of a first wavelength from said one of said semiconductor lasers, reflected by said recording surface, thereby generating a predetermined amount of astigmatism, andsaid second holographic optical element eliminates coma aberration and spherical aberration of a light beam of a second wavelength from the other one of said semiconductor lasers, reflected by said recording surface, thereby generating a predetermined amount of astigmatism.