| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide such an optical pickup device which suppresses an aberration even if the optical axes of an objective lens and another optical system are misaligned. <P>SOLUTION: The optical pickup device records or reproduces information signals by irradiating a rotating optical disk with light along its tracks and has a light source, a beam expander for changing the parallelism of the light emitted from the light source, and the objective lens 33 for condensing the light emitted from the beam expander and irradiating the optical disk with this light along its tracks. The beam expander consists of a concave lens 31 and a Fresnel lens 32. The focal length f<SB>n</SB>of the Fresnel lens 32 exists in the range satisfying the equation f<SB>1</SB><f<SB>n</SB><f<SB>2</SB>when a designed lower limit wavelength and designed upper limit wavelength are respectively defined as λ<SB>1</SB>and λ<SB>2</SB>, the focal length and partial dispersion of the objective lens 33 respectively as f<SB>0</SB>and ν<SB>0</SB>, and the difference between the focal lengths corresponding to the wavelengths λ<SB>1</SB>and λ<SB>2</SB>is defined as Δ. In the equation, f<SB>1</SB>=((λ<SB>2</SB>/λ<SB>1</SB>)-1)f<SB>0</SB>ν<SB>0</SB>, f<SB>2</SB>=(1-(λ<SB>2</SB>/λ<SB>1</SB>))b, b=-f<SB>0</SB>(f<SB>0</SB>+Δ)/Δ. <P>COPYRIGHT: (C)2003,JPO |
