| 摘要 |
An optical pickup includes a first optical source producing a first optical beam having a wavelength lambda 1 , a second optical source producing a second optical beam having a wavelength lambda 2 (lambda 1<lambda2 ), and a single objective lens focusing any of the first and second optical beams to an optical recording medium, the first optical beam is incident to the objective lens as a parallel beam and the second optical beam is incident to the objective lens as a divergent optical, wherein an aperture is provided at a front side of the objective lens with offset from a principal point at the front side by a distance t given by an equation <?in-line-formulae description="In-line Formulae" end="lead"?>t=L-NA 1. f/tan(asin(NA 2 obj)),<?in-line-formulae description="In-line Formulae" end="tail"?> wherein f represents a focal distance of the objective lens, NA 1 represents the numerical aperture at the side of the image surface when the first optical source is turned on, NA 2 obj represents the numerical aperture at the front side when the second optical source is turned on, and L represents the object distance at the time when the second optical source is turned on.
|
