| 摘要 |
Provided is an objective lens for selectively focusing each of light beams having three wavelengths λ1, λ2, and λ3 on a signal recording surface of a corresponding optical disc, the wavelengths λ1, λ2, and λ3 satisfying at least a relationship λ1<λ2<λ3, the objective lens including a diffraction section disposed on an entry-side surface thereof, the diffraction section including a first region disposed in an innermost radius portion, a second region disposed outside the first region, and a third region disposed outside the second region, the first to third regions being formed so that an aperture of the light beams are appropriately limited, the first region including a staircase-like diffractive structure having a certain number of levels configured so that diffracted light of a predetermined order has the highest diffraction efficiency and optical-path-difference phase amounts for the levels of the diffractive structure has a certain relationship. |
