Objective lens for optical pick-up head of optical disk drive

DETAILED DESCRIPTION It is therefore the principle object of the present invention to provide an objective lens for optical pick-up head of optical disk drive devices capable of simplifying the focus switching mechanism.
It is another object of the present invention to provide an objective lens for optical pick-up head of optical disk drive devices suitable for easy and low cost manufacturing.
It is yet another object of the present invention to provide an objective lens for optical pick-up head of optical disk drive devices featuring substantially zero energy loss for achieving dual-focusing utilizing one single lens or a combination of two simple lenses.
The present invention achieves the above identified objects by providing an objective lens for an optical disk drive device.
The objective lens comprises four portions each having a aspherical surface for focusing a light beam of a designated wavelength to a designated focal point.
The first portion has a first aspherical surface that focuses the light beam to a first focal point.
The second portion has a second aspherical surface that focuses the light beam to a second focal point.
The third portion has a third aspherical surface featuring the same surface curvature characteristics and aspherical coefficients as that of the first aspherical surface and focuses the light beam to the first focal point.
And, the fourth portion has a fourth aspherical surface featuring the same surface curvature characteristics and aspherical coefficients as that of the second aspherical surface and focuses the light beam to the second focal point.
The objective lens can be made as a single-piece lens that suffers no energy loss for either focusing.