Objective lens and optical pickup system

Abstract

There is provided an optical pickup system which includes a first light source emitting first light having a wavelength lambda 1, a second light source emitting second light having a wavelength lambda 2 longer than the wavelength lambda 1, a third light source emitting third light having a wavelength lambda 3 longer than the wavelength lambda 2, and an objective lens focusing the first light on an information recording surface of a first optical recording medium, focusing the second light on an information recording surface of a second optical recording medium, and focusing the third light on an information recording surface of a third optical recording medium. In the optical pickup system, at least one lens surface of the objective lens is divided into a plurality of concentric sections with an optical axis, having a step at each boundary between the sections, each of the sections has a different aspherical shape and m 1 >m 2 >0 and -0.060<=m 3 <=-0.020 are satisfied where an imaging magnification at the first light is m 1, an imaging magnification at the second light is m 2, and an imaging magnification at the third light is m 3 in the objective lens. This enables a decrease in aberration at the first light and the second light and an increase in object distance at the third light. Further, this step enables the shared use of a photodetector for detecting the first light and a photodetector for detecting the second light.

Description

technical field [0001] The invention relates to an objective lens and an optical system of an optical pick-up. In particular, it relates to an objective lens and an optical pickup optical system of an interchangeable recording and reproducing device that uses a plurality of types of monochromatic light and is used in a multi-wavelength optical system that is compatible with various optical recording media. Background technique [0002] In recent years, high-density optical discs (Blu-ray, HD-DVD) using blue lasers have begun to be used. The recording density of an optical disk depends on the diameter of the spot of light collected on the information recording surface. When λ is the wavelength of light emitted from the light source and NA is the image-side numerical aperture of the objective lens, the spot diameter is proportional to λ / NA. Therefore, the increase in the density of the optical disc can be realized by shortening the wavelength of the laser light for the optic...

AI Technical Summary

Problems solved by technology

However, depending on the difference in optical path length from each light source to the collimator lens, the incident light to the objective lens is either divergent or converging. Therefore, when the objective lens is displaced vertically with respect to the optical axis by tracking, aberrations occur.

In Patent Document 1, since the light incident on the collimator lens from a light source corresponding to a CD is assumed to diverge, aberration occurs due to the displacement of the objective lens relative to the optical axis during tracking.

[0008] In addition, in the method of causing the diffraction effect by using a hologram element, the problem of a decrease in the diffraction efficiency arises

Especially in the compatibility between HD-DVD, DVD, and CD, since the wavelength band used is wide (400nm~800nm), it is difficult to ensure the diffraction efficiency of each HD-DVD, DVD, and CD

Therefore, there is a problem that high light utilization efficiency cannot be obtained for all HD-DVD, DVD, and CD.

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