Object lens producing device and producing method

Abstract

An objective lens unit manufacturing apparatus for manufacturing an objective lens unit, with a numerical aperture not less than 0.7, made up by a plurality of lenses, includes a positioning mechanism (31) for positioning one lens (2) in a cylindrically-shaped lens holder (3) of a synthetic resin material, using another lens (1), already mounted and secured to the lens holder, as a reference, and for securing the one lens to the lens holder, for setting relative positions of the one and the other lenses.

Description

TECHNICAL FIELD [0001] This invention relates to a method and apparatus for producing an objective lens unit made up by a plural number of objective lenses and which may be used with advantage for an optical pickup used in turn for writing information signals on a optical recording medium and for reading out information signals recorded thereon. BACKGROUND ART [0002] Up to now, an optical recording medium, exemplified by an optical disc, has been used as a recording medium for information signals. An optical pickup device is used for writing or reading out information signals on or from an optical recording medium. The optical pickup device includes a semiconductor laser, as a light source for radiating a light beam to be illuminated on the optical recording medium, and an objective lens unit for condensing the light beam radiated from the semiconductor laser for illuminating the light beam to a signal recording surface of the optical recording medium. [0003] In the optical pickup d...

AI Technical Summary

Benefits of technology

The present invention provides a method and apparatus for producing a novel objective lens unit, which overcomes the deficiencies of conventional techniques. The objective lens unit has a numerical aperture not less than 0.7 and is made up by multiple lenses, in which the relative positions of the lenses can be adjusted to high accuracy and in which spherical aberration can be suppressed. The method involves positioning one lens in a cylindrically-shaped lens holder of a synthetic resin material, using another lens already mounted and secured to the lens holder as a reference, and securing the one lens to the lens holder by setting the relative positions of the lenses. The method also involves causing a light beam to be incident on the lenses, reflecting the light beam, and detecting focusing error signals with respect to the reflecting member to adjust the distance between the lenses based on the amount of spherical aberration. The objective lens unit manufacturing apparatus includes a lens holder with lens inserting sections for controlling the offset of the lenses and a reflecting member for detecting focusing error signals. The other lens used as a reference is the lens remote from the optical recording medium, with the surface of its outer rim used as a reference surface for positioning the one lens. The parallelism between the reference surface and the positioning member is measured using laser light, and the lenses are attracted under a pneumatic pressure differential for abutting the reference surface against the positioning member. The invention provides a more efficient and effective method for producing objective lens units with improved performance.

Problems solved by technology

In light of for example mold release properties, it is extremely difficult to form the objective lens unit having a non-spherical surface of a large curvature using a metal die.

Moreover, with an objective lens unit having a non-spherical surface of a larger curvature and a larger numerical aperture (NA), the light beam radiated from the light source cannot be condensed accurately on the signal recording surface even on occurrence of perturbations resulting from the slightest tilt relative to the optical axis.

With these methods, the phenomena observed are not changed independently for respective adjustment parameters, such that adjustment is extremely time-consuming due to many looped procedures required for achieving the final performance.

The lens secured in position in this manner in the lens holder with an adhesive is likely to undergo misregistration due to environmental changes, such as increasing temperature or humidity.

It is however extremely difficult to have the two lenses mounted within the lens holder as this high degree of accuracy is maintained.

Additionally, depending on the mounting environment, fine dust and dirt on the order of 1 μm tend to be intruded into a space between the step within the lens holder and the lens to render it difficult to maintain parallelism between the two lenses.

Although the spherical aberration of the lenses being adjusted may be measured using an interferometer, a complicated apparatus is needed, while the production cost is increased.

Images