| 摘要 |
A coupling lens for chromatic aberration correction is placed between a light source and an objective lens for focusing light beams with a plurality of wavelengths on an information recording surface of an optical recording medium, and at least one surface of the coupling lens includes a plurality of annular zones having a step concentric with an optical axis. The coupling lens is designed so that when a wavelength lambda<SUB>1</SUB>=380 to 430 nm and a height of the step is d=m<SUB>1</SUB>lambda<SUB>1</SUB>/(n<SUB>1</SUB>-1) where m<SUB>1 </SUB>is an actual number and n<SUB>1 </SUB>is a refractive index of the coupling lens at the wavelength lambda<SUB>1</SUB>, 9.9<=M<SUB>1</SUB><=10.1 is satisfied.
|
