Planar lens and method for fabricating the same

Abstract

A planar lens capable of compensating for chromatic aberration and which is easy to manufacture and enables easy assembling of optical pickups and a method for fabricating the planar lens are provided. The planar lens includes a transparent substrate with a lens cavity in a surface of the transparent substrate, and a lens element formed in the lens cavity with a first refracting surface in contact with the bottom of the lens cavity and a second diffracting surface having a diffraction grating opposite to the first refracting surface.

Description

BACKGROUND OF THE INVENTION [0001] This application claims priority from Korean Patent Application No. 2002-70662, filed on Nov. 14, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. [0002] 1. Field of the Invention [0003] The present invention relates to a planar lens and a method for fabricating the same, and more particularly, to an easy-to-fabricate planar objective lens capable of compensation of chromatic aberration, as an essential part of an optical pickup that is used in an optical disc drive (ODD) to write information in and / or reproduce information from an optical disc, such as a compact disc (CD) or a digital versatile disc (DVD), and an easy method for fabricating the planar microlens. [0004] 2. Description of the Related Art [0005] Objective lenses are used to write information in an optical disc by focusing a laser beam emitted from a semiconductor laser used as a light source on a recording ...

AI Technical Summary

Benefits of technology

[0016] The present invention provides a planar objective lens that is easy to manufacture, enables easy assembling of optical pickups, and has good optical performance, and a method for fabricating the planar objective lens.

Problems solved by technology

However, this mold processing method is limited as to processing a curved mold surface corresponding to a spherical or aspheric lens surface.

However, it is difficult to machine a concave mold for lenses under about 1 millimeter in diameter with the mechanical mold machining method, because cutting tools and the curvature of diamond wheels therefore are limited.

However, it is more difficult to manufacture and assemble smaller optical elements, especially with microlenses having a diameter of 1 mm or less because of difficulties in mold machining therefor, as described above.

Even though such microlenses of 1 mm or less in diameter can be manufactured, it is difficult to handle such a small microlens and to assemble an optical pickup with the microlens.

General objective lenses have two opposing surfaces that are spherical or aspheric and which protrude closer to an optical disc, compared to other adjacent optical elements, so they are likely to be abraded or damaged when collided with the optical disc.

In this microlens array manufacturing method by plasma etching, it is difficult to uniformly deposit the photoresist to a sufficient thickness for an objective lens of appropriate thickness so that the sag height of the resulting microlens is limited.

In addition, since the hemispheric photoresist pattern formed by reflowing is directly transferred into a glass substrate, the method cannot be applied for general aspheric lenses excluding spherical lenses.

This method is suitable to manufacture single microlens but not for an array of multiple lenses.

Also, the thin film deposition technique, i.e., sputtering, used in the method takes a long duration for a lens layer having an appropriate thickness.

Furthermore, it is also time consuming to polish the deposited high refractive index material lens layer.

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