Objective lens for optical recording media and optical pickup apparatus using the same
AssigneeFuji Photo Optical Co., Ltd.
InventorToshiaki Katsuma
Life of this patent
Estimating the term…
Abstract
An objective lens for converging two wavelengths of light to their predetermined positions is constituted by two or three lenses. Respective materials for forming adjacent lenses are chosen such that the respective refractive indices of adjacent lenses substantially equal each other with respect to only one of the two wavelengths of light, whereas the form of each lens surface is configured so as to suppress aberration in the objective lens as a whole.
Claims10
An objective lens, consisting of two lenses disposed in a luminous flux, for carrying out focusing on two optical recording media having different thicknesses from each other,
- wherein said two lenses are constituted by respective materials different from each other;
- wherein said two lenses satisfy the following conditional expressions (1) and (2) respectively with respect to wavelengths λ1 and λ2 of light:
- N1(λ1)≅N2(λ1) (1)
- N1(λ2)≠N2(λ2) (2)
- where
- N1(λ1) is the refractive index of the first lens with respect to wavelength λ1 of light;
- N1(λ2) is the refractive index of the first lens with respect to wavelength λ2 of light;
- N2(λ1) is the refractive index of the second lens with respect to wavelength λ1 of light;
- and
- N2(λ2) is the refractive index of the second lens with respect to wavelength λ2 of light;
- wherein approximately equal to in equation (1) is defined as values equal to or less than 0.00057;
- wherein each lens surface has a form configured so as to suppress aberration in said objective lens as a whole, and
- wherein said wavelength λ1 is used for one optical media and said wavelength λ2 is used for another optical media.
An objective lens, consisting of three lenses disposed in a luminous flux, for carrying out focusing on two optical recording media having different thicknesses from each other,
- wherein at least adjacent lenses in said three lenses are constituted by respective materials different from each other;
- wherein said three lenses satisfy the following conditional expressions (3) and (4) respectively with respect to wavelengths λ1 and λ2 of light:
- N1(λ1)≅N2(λ1) and N2(λ1)≅N3(λ1) (3)
- N1(λ2)≠N2(λ2) and N2(λ2)≠N3(λ2) (4)
- where
- N1(λ1) is the refractive index of the first lens with respect to wavelength λ1 of light;
- N1(λ2) is the refractive index of the first lens with respect to wavelength λ2 of light;
- N2(λ1) is the refractive index of the second lens with respect to wavelength λ1 of light;
- N2(λ2) is the refractive index of the second lens with respect to wavelength λ2 of light;
- N3(λ1) is the refractive index of the third lens with respect to wavelength λ1 of light;
- and
- N3(λ2) is the refractive index of the third lens with respect to wavelength λ2 of light;
- wherein approximately equal to in equation (3) is defined as values equal to or less than 0.00057;
- wherein each lens surface has a form configured so as to suppress aberration in said objective lens as a whole, and
- wherein said wavelength λ1 is used for one optical media and said wavelength λ2 is used for another optical media.
Dependencies are inferred from the claim text.