Objective lens element

摘要

An objective lens element having excellent compatibility with optical discs having different base material thicknesses is provided. The objective lens element has optically functional surfaces on an incident side and an exit side. At least either one of the optically functional surfaces on the incident side and the exit side includes a diffraction portion which satisfies at least either one of the following formulas (1) and (2):
θ1×θ2<0 (“×” represents multiplication)  (1),(sin θ2)/λ2=−(sin θ1)/λ1  (2),
where
θ1 is the diffraction angle of a light beam having a diffraction order providing the maximum diffraction efficiency at the wavelength λ1, andθ2 is the diffraction angle of a light beam having a diffraction order providing the maximum diffraction efficiency at the wavelength λ2.

主权项

1. An objective lens element having optically functional surfaces on an incident side and an exit side, the objective lens element converging a first incident light beam of wavelength λ1 through a base plate having a thickness t1 to form a spot, and converging a second incident light beam of wavelength λ2 longer than the wavelength λ1 through a base plate having a thickness t2 larger than the thickness t1 to form a spot, wherein:
at least either one of the optically functional surfaces on the incident side and the exit side includes a diffraction portion that satisfies the following formula (1)
Φ2<Φ02<Φ01<Φ1  (1),where
Φ1 is the power of a surface including the diffraction portion and acting on a light beam having a diffraction order providing the maximum diffraction efficiency at the wavelength λ1 (Φ1≠0), Φ2 is the power of the surface including the diffraction portion and acting on a light beam having a diffraction order providing the maximum diffraction efficiency at the wavelength λ2 (Φ2≠0), Φ01 is the power of a base refractive surface obtained by removing the diffraction portion from Φ1, and Φ02 is the power of the base refractive surface obtained by removing the diffraction portion from Φ2.