Patent ID: 6084840
Filing Date: 2000-07-04
Classification: G11B

Abstract:
An optical pickup comprising:a light source;an objective lens for converging incident light from the light source onto a recording medium, wherein the objective lens is arranged to be movable in radial and vertical directions of the recording medium;a holographic optical element for changing a traveling path of the incident light, the holographic optical element being positioned along an optical path between the light source and the recording medium, the holographic optical element having first and second diffraction plates which are divided along a first boundary line and have different diffraction patterns;a photodetector having first and second divided plates which are divided along a second boundary line which is perpendicular to the radial and vertical directions of the recording medium, wherein the first and second divided plates receive light passed through the first and second diffraction plates after the light is reflected from the recording medium; anda differential amplifier for differentially amplifying electrical signals photoelectrically converted by the first and second divided plates;wherein the first boundary line of the holographic optical element is arranged at a predetermined angle with respect to the radial direction of the recording medium, such that the amount of light received by the first and second divided plates is equal to each other when the center of the objective lens is properly located on the optical path, and the amount of light received by the first and second divided plates is different from each other when the center of the objective lens is deviated from the optical path.