Patent ID: 6961291

Claim:
An auto-focus system of an optical access unit for reading and writing data from and to a first information layer and a second information layer of an optical storage medium, the system comprising: an astigmatic lens which creates a first set of line images and a second set of line images, wherein the first set of line images comprises at least one line image for refracting light rays from the first information layer, and wherein the second set of line images comprises at least one line image for refracting light rays from the second information layer, and a confocal aperture placed at a first focal line image from the first set of line images created by the astigmatic lens, wherein the confocal aperture blocks the light rays reflected from the second information layer but not the light rays reflected from the first information layer when accessing the first information layer, and wherein the confocal aperture blocks the light rays reflected from the first information layer but not the light rays reflected from the second information layer when accessing the second information layer.