Field curvature reduction for optical system

Abstract

An optical head (1) for scanning an optical record carrier (2) is provided with a compensator (16) for compensating the field curvature aberration of the objective system (18) caused by operation of the optical head at a different field angles. A surface of the compensator (16) comprises a phase structure in the form of annular areas (52, 53, 54, 55, 56), the areas forming a non-periodic pattern of optical paths of different lengths. The optical paths change as a function of field angle and form a field angle-dependent wavefront deviation that compensates field curvature of the optical head.

Description

technical field [0001] The invention relates to an optical head for scanning an optical record carrier with an information layer, said optical head comprising a radiation source for generating a radiation beam; an optical system for converging the radiation beam to a focal point on the information layer, said optical system imparting a field angle dependent first wavefront deviation to the radiation beam; and a compensator for imparting a second wavefront deviation to the radiation beam to compensate for the first wavefront deviation. The invention also relates to an optical device comprising an optical system imparting a field-angle-dependent first wavefront deviation to a radiation beam passing through the optical device and a compensator arranged to compensate for the First wave front deviation. Background of the invention [0002] A multi-track head scans several tracks simultaneously on the information layer of the optical record carrier. This is achieved by focusing,...

AI Technical Summary

Problems solved by technology

While it results in significantly reduced field curvature, a drawback of placing the element close to the focal plane is that it becomes sensitive to dust and other contamination

Although such blazed kino holograms can be engineered to produce 100% efficiency in a particular diffraction order, practical gratings have never achieved such high efficiencies

This reduction in the optical path efficiency of the optical head is disadvantageous in optical recorders, which require large amounts of radiant energy for writing information on or reading information from the record carrier at high speed

Another drawback of these periodic grating structures is that they generally contain a large number of zones, making them difficult to fabricate

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