Alteration of imaging properties of an optical pickup's objective lens by a nonrotationally symmetric coating

One can control the aberrations of an optical readout system by varying the width of a strip of antire-flection coatings deposited upon plastic object ive lenses. It is found that one can control the magnitude of the third-ord er astigmatism of the system by changing the coating width. This process ha s the advantage that it does not significantly cause other kinds of aberrat ion such as coma and spherical aberrations to deteriorate. When these nonro tational symmetrically (NRS) coated lenses are used for off-axis operations such as tracking movements in optical drives, the change in the magnitude of the astigmatism (Delta AS) that is generated can be made smaller than th ose of symmetrically coated or noncoated lenses. As much as a 73% decrease in Delta AS was observed experimentally with a NRS-coated lens. Including t he birefringence of the plastic material in the analysis yields a low and c onstant level of astigmatism generated by shifting of the objective lens. ( C) 2000 Optical Society of America OCIS codes: 220.3630, 220.1250, 310.1620 .