Method and apparatus for detecting a track and focus errors in an

Abstract

A method and apparatus for detecting a track and focus errors in an optical head comprises a step of dividing light beam which is reflected from a recording medium into at least a first, second, and third light beams belonging to first, second and third cross sectional regions thereof, and means therefor. The first region is expressed in its cross sectional position by the equations, ##EQU1## the second region is expressed in its cross sectional position by the equations, ##EQU2## the third region is excluded from said first and second regions and expressed in its cross sectional position by the equations, ##EQU3## where P is a pitch of pits or pregrooves of the recording medium, .lambda. is a wavelength of the light beam, .delta. is a value which is from equal to or more than zero to equal to or less than a maximum moving distance of the object lens in a direction of a track error, d is a diameter of the light beam which is reflected, X is an axis which is parallel to a track error direction to intersect the light axis of said light beam which is reflected, and Y is an axis which is orthogonal to the X to intersect said light axis. The track error is detected in accordance with the light beams of the first and second regions, and the focus error is detected in accordance with the light beam of the third region.