Patent ID: 7068572

Claim:
An information reproducing apparatus, comprising: a laser beam source; an objective lens for condensing a beam from said laser beam source on an optical disk; variable focusing means for moving a focal position of an optical spot condensed by said objective lens; tracking means for making the optical spot track a recording track of said optical disk; spherical aberration adding means for adding a variable spherical aberration to light condensed by said objective lens; coma aberration adding means for adding a variable coma aberration to light condensed by said objective lens; a light detector for detecting reflected light from the optical disk; an operation circuit for generating a reproducing signal, a focal shift signal and a tracking shift signal from a detection signal of said light detector; and servo-control means for controlling the variable focusing means, the tracking means, the spherical aberration adding means and the coma aberration adding means, wherein said information reproducing apparatus further comprises: a detected light dividing device for dividing a light flux in the vicinity of an optical axis of said reflected light into a plurality of partial light fluxes to make incident onto the light detector, and dividing the light flux in a peripheral portion of said reflected light into a plurality of partial light fluxes to make incident onto said light detector, wherein said operation circuit generates: a first focal shift signal and a first tracking shift signal based on the detection signal of the partial light fluxes derived from said light flux in the vicinity of the optical axis, a second focal shift signal and a second tracking shift signal based on the detection signal of the partial light fluxes derived from said light flux of the peripheral portion, a spherical aberration signal in accordance with a difference signal between said first and second focal shift signals, and a focal shift signal in accordance with a sum signal; and a coma aberration signal in accordance with a difference signal between the first and second tracking shift signals, and a tracking shift signal in accordance with a sum signal, and wherein said servo-control means controls said variable focusing means in accordance with said −focal shift signal, said tracking means in accordance with the tracking shift signal, said spherical aberration adding means in accordance with said spherical aberration signal, and said coma aberration adding means in accordance with the coma aberration signal.