Preventing Coma Aberration by Annular Apodizer for Optical Disk Tilting

This research was carried out to determine the optimum parameters for an optical apodizer, applicable to a pick-up head for higher recording density optical disks. The coma aberration generated by tilting a disk increases the side-lobe intensity of the beam waist spot, and the increased side-lobe portion of the beam waist spot mainly deteriorates crosstalk from an adjacent track. Calculations were made to estimate coma aberration, in which the author adopted the annular radius of the apodizer and the side-lobe intensity of the beam waist spot as parameters. The result, which was confirmed experimentally, is that an annular apodizer whose radius is half the pupil radius effectively prevents coma aberration.