Patent ID: 7724633
Filing Date: 2010-05-25
Classification: G11B

Abstract:
1. An aberration correcting apparatus used for an optical pickup which can focus a first light beam for a first optical disc on the first optical disc and a second light beam for a second optical disc on the second optical disc by using an objective lens, said aberration correcting apparatus comprising: a liquid crystal optical element which is disposed to cross a unified optical axis and which comprises a liquid crystal, the unified optical axis being obtained by matching an optical axis of the first light beam with an optical axis of the second light beam; two electrode layers which are provided for said liquid crystal optical element and which face each other with the liquid crystal therebetween; a first electrode which is formed in any one of said two electrode layers and which is located on a point P, if it is assumed that each of the electrode layers and the unified optical axis cross at the point P, a circle whose central point is the point P and whose diameter is substantially equal to an effective diameter D a plurality of second electrodes which are formed in any one of said two electrode layers and which are located so as to surround said first electrode; a plurality of third electrodes which are formed in any one of said two electrode layers, which partially overlap a circumference of the circle C a non-application area which is located between said first electrode and said third electrodes when each of said two electrode layers, which are superimposed, is observed in the unified optical axis, which is substantially annular, and which does not change a state of voltage application to the liquid crystal depending on voltage application to said first electrode and said third electrodes; a first voltage application controlling device for controlling voltage application to said first electrode and said second electrodes in order to correct spherical aberration with regard to the first optical disc; a second voltage application controlling device for controlling the voltage application to said third electrodes in order to correct astigmatism aberration with regard to the first optical disc; and a third voltage application controlling device for controlling voltage application to said first electrode and said third electrodes in order to correct spherical aberration with regard to the second optical disc.