Optical pick-up apparatus with tracking error detection by detection of amount of light in fan field

Claim 1

An optical pick-up apparatus comprising: a semiconductor laser for emitting a laser beam; a converging optical system projecting the laser beam emitted by said semiconductor laser onto an optical record medium as a spot; a hologram means including a first hologram for diffracting a return laser beam reflected by said optical record medium in a diffracting direction to produce at least one diffracted beam, said hologram means being constructed to give said diffracted beam astigmatism; and a photodetecting means for receiving said diffracted beam emanating from said hologram means to detect a tracking error signal, said photodetecting means including a plurality of light receiving regions which are divided by a division line substantially parallel with the diffracting direction of said hologram means, said tracking error signal being detected on the basis of a distribution of an amount of light in a far field; wherein said photodetecting means further comprises third and fourth photodetectors, and said hologram means further comprises a second hologram for diffracting the laser beam reflected by the optical record medium to produce ±1-order diffracted beams directed to said third and fourth photodetectors and 0-order beam directed to said first hologram, whereby a focusing error signal is derived by processing output signals from said third and fourth photodetectors.