| 摘要 |
PROBLEM TO BE SOLVED: To balance on-axis characteristics for one optical information recording medium and off-axis characteristics for the other medium by forming plural divided faces concentric to the optical axis on one face of an objective lens and forming one divided face satisfying specified conditions. SOLUTION: Plural divided faces are formed concentric to an optical axis on one face of an objective lens 1. This structure is formed to balance the spherical aberration generated by the difference in the thickness t1 and t2 of transparent substrates 21. When a DVD is used, beams passing through a first divided face and third divided face form a spot light, while when a CD is used, the beams passing through the first divided face and second divided face form the spot light on an information recording face 22. The unsatisfactory quantity SC1 for sinusoidal conditions of the light beams passing through the first and third divided faces when a DVD is used is specified to 0.06>=SC1/f1>=0.002, wherein f1 is the focal length of the objective lens 1 for the thickness t1 of the transparent substrate. Thereby, both of the performance of the spot light on a DVD using on-axis light and the performance of the spot light on a CD using off-axis light can be obtd. |
