Liquid crystal element and optical pickup device having the same

Abstract

A liquid crystal element includes a first transparent electrode (14) and a second transparent electrode (15), which have different concentric split areas (14a-14d) and (15a-15e), each of the split areas (14a-14d) of the first transparent electrode (14) faces two areas out of the split areas (15a-15e) of the second transparent electrode (15), and on the other hand, each of the split area (15a) and the split area (15e) out of the split areas (15a-15e) of the second transparent electrode (15) faces only one area, i.e., the split area (14a) and (14d) of the first transparent electrode (14), and each of the other split areas (15b-15d) faces two areas out of the split areas (14a-14d) of the first transparent electrode (14).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram to show a structure of an optical system of an optical pickup device equipped with a liquid crystal element according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a structure of a liquid crystal element according to the first embodiment.

FIGS. 3A and 3B are top views for explaining a structure of electrode patterns of transparent electrodes of the liquid crystal element according to the first embodiment, and FIG. 3C is a cross sectional view of the same.

FIG. 4 is a graph to show a relationship between the spherical aberration generated in the optical pickup device according to the present embodiment and a phase difference to be generated by the liquid crystal element according to the first embodiment.

FIG. 5A is a top view for explaining a structure of a conventional liquid crystal element, and FIG. 5B is a cross sectional view of the same.

FIGS. 6A and 6B are top views for explaining a structure of an electrode pattern of a transparent electrode of the liquid crystal element according to a second embodiment, and FIG. 6C shows a cross sectional view of the same.

Claims

1. A liquid crystal element comprising liquid crystal and two transparent electrodes including a first transparent electrode and a second transparent electrode sandwiching the liquid crystal, wherein each of the first transparent electrode and the second transparent electrode is divided into a plurality of split areas having different patterns, andthe patterns of the first and the second transparent electrodes are formed in such a manner that the number of phase shift areas that generates a phase difference in a light beam entering the liquid crystal element when predetermined potentials are respectively applied to the split areas is larger than the number of the split areas in each of the first transparent electrode and the second transparent electrode.

2. The liquid crystal element according to claim 1, wherein at least in the portion where the transparent electrode exists, at least one of wires that are drawn out from the split areas of one of the first transparent electrode and the second transparent electrode that has smaller number of the split areas is formed at a position that overlaps a wire that is drawn out from the split area of the other transparent electrode.

3. The liquid crystal element according to claim 1, wherein the split areas formed on the first and the second transparent electrodes are a plurality of concentric areas, each of the split areas of the first transparent electrode faces one or more of the split areas of the second transparent electrode, and at least one of the split areas of the second transparent electrode faces two or more of the split areas of the first transparent electrode.

4. The liquid crystal element according to claim 1, wherein one or more groups of areas out of the split areas have two or more wires that are connected electrically to be the same potential on at least one of the first transparent electrode and the second transparent electrode, and the total number of connection wires that connect the first and the second transparent electrodes to electrodes that are provided externally is less than the number of the phase shift areas.

5. An optical pickup device that is equipped with the liquid crystal element according to claim 1.

6. The liquid crystal element according to claim 2, wherein the split areas formed on the first and the second transparent electrodes are a plurality of concentric areas, each of the split areas of the first transparent electrode faces one or more of the split areas of the second transparent electrode, and at least one of the split areas of the second transparent electrode faces two or more of the split areas of the first transparent electrode.

7. The liquid crystal element according to claim 2, wherein one or more groups of areas out of the split areas have two or more wires that are connected electrically to be the same potential on at least one of the first transparent electrode and the second transparent electrode, and the total number of connection wires that connect the first and the second transparent electrodes to electrodes that are provided externally is less than the number of the phase shift areas.

8. An optical pickup device that is equipped with the liquid crystal element according to claim 2.

9. The liquid crystal element according to claim 3, wherein one or more groups of areas out of the split areas have two or more wires that are connected electrically to be the same potential on at least one of the first transparent electrode and the second transparent electrode, and the total number of connection wires that connect the first and the second transparent electrodes to electrodes that are provided externally is less than the number of the phase shift areas.