Optical pickup apparatus and liquid crystal optical element

Abstract

The present invention is directed to the provision of an optical pickup apparatus in which a liquid crystal optical element constructed by combining an aberration correcting liquid crystal panel and a λ/4 liquid crystal panel in an integral fashion is mounted in a tilted position. More particularly, the invention provides a liquid crystal optical element comprising a first liquid crystal layer for correcting aberration, a second liquid crystal layer functioning as an nλ/4 plate and combined in an integral fashion with the first liquid crystal layer, a transparent electrode for generating a potential difference on the second liquid crystal layer in order to control an amount of phase difference for the light beam passing through the second liquid crystal layer, and a driver for driving the transparent electrode so as to generate a potential difference that is the lowest among a plurality of potential differences that cause the second liquid crystal layer to function as an nλ/4 plate. The invention also provides an optical pickup apparatus incorporating such a liquid crystal optical element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein:

FIG. 1 is a schematic diagram showing the configuration of an optical apparatus 1 which includes an optical pickup apparatus and a liquid crystal optical element according to the present invention;

FIG. 2( a) is a cross-sectional view of the liquid crystal optical element 100, and FIG. 2(b) is a plan view of the liquid crystal optical element 100 as viewed from the light exit side;

FIG. 3 is a schematic cross-sectional view for explaining the structure of the liquid crystal optical element 100;

FIG. 4( a) is a diagram showing an arrangement in which the Z-axis of the liquid crystal optical element 100 is oriented parallel to the optical axis (the optical element is not tilted), and FIG. 4(b) is a diagram showing an arrangement in which the liquid crystal optical element 100 is tilted by an angle a as shown in FIG. 2;

FIG. 5( a) is a diagram showing a spherical aberration correcting transparent electrode pattern formed as a first transparent electrode 151, FIG. 5(b) is a diagram showing an example of the voltage applied to the transparent electrode pattern of the first transparent electrode 151, and FIG. 5(c) is a diagram showing an example of spherical aberration as improved by the transparent electrode pattern of the first transparent electrode 151;

FIG. 6 is a diagram showing one example of the electrode pattern of a second transparent electrode;

FIG. 7 is a diagram showing the relationship between the amount of phase difference and the potential difference applied to a second liquid crystal layer 120 when a 650-nm light source was used;

FIG. 8 is a diagram showing the relationship between ellipticity and incidence angle when the 650-nm light source was used and when the second liquid crystal layer 120 was caused to function as the 3λ/4 plate;

FIG. 9 is a diagram showing the relationship between ellipticity and incidence angle when the 650-nm light source was used and when the second liquid crystal layer 120 was caused to function as the 5λ/4 plate;

FIG. 10 is a diagram showing the relationship between ellipticity and incidence angle when the 650-nm light source was used and when the second liquid crystal layer 120 was caused to function as the 7λ/4 plate;

FIG. 11 is a diagram for explaining the behavior of a homogenously aligned liquid crystal layer in the presence of an applied potential difference;

FIG. 12 is a diagram showing the relationship between the amount of phase difference and the voltage applied to an alternative second liquid crystal layer 201 when the 650-nm light source was used;

FIG. 13 is a diagram showing the relationship between ellipticity and incidence angle when the 650-nm light source was used and when the alternative second liquid crystal layer 201 was caused to function as the 3λ/4 plate;

FIG. 14 is a diagram showing the relationship between ellipticity and incidence angle when the 650-nm light source was used and when the alternative second liquid crystal layer 201 was caused to function as the 5λ/4 plate;

FIG. 15 is a diagram showing the relationship between the amount of phase difference and the voltage applied to the second liquid crystal layer 120 when a 780-nm light source was used;

FIG. 16 is a diagram showing the relationship between ellipticity and incidence angle when the 780-nm light source was used and when the second liquid crystal layer 120 was caused to function as the 3λ/4 plate;

FIG. 17 is a diagram showing the relationship between ellipticity and incidence angle when the 780-nm light source was used and when the second liquid crystal layer 120 was caused to function as the 5λ/4 plate;

FIG. 18 is a diagram showing the relationship between the amount of phase difference and the voltage applied to the alternative second liquid crystal layer 201 when the 780-nm light source was used;

FIG. 19 is a diagram showing the relationship between ellipticity and incidence angle when the 780-nm light source was used and when the alternative second liquid crystal layer 201 was caused to function as the 3λ/4 plate;

FIG. 20 is a diagram showing the relationship between ellipticity and incidence angle when the 780-nm light source was used and when the alternative second liquid crystal layer 201 was caused to function as the 5λ/4 plate;

FIG. 21 is a diagram showing the relationship between the amount of phase difference and the voltage applied to a further alternative second liquid crystal layer 211 when the 650-nm light source was used;

FIG. 22 is a diagram for explaining the behavior of a vertically aligned liquid crystal layer in the presence of an applied potential difference;

FIG. 23( a) is a diagram showing a coma correcting transparent electrode pattern formed as the first transparent electrode 151, FIG. 23(b) is a diagram showing an example of the voltage applied to the transparent electrode pattern of the first transparent electrode 151, and FIG. 23(c) is a diagram showing an example of coma as improved by the transparent electrode pattern of the first transparent electrode 151;

FIG. 24( a) is a diagram showing an astigmatism correcting transparent electrode pattern formed as the first transparent electrode 151, FIG. 24(b) is a diagram showing an example of the voltage applied in the Y-axis direction of the transparent electrode pattern of the first transparent electrode 151, and FIG. 24(c) is a diagram showing an example of astigmatism in the Y-axis direction as improved by the transparent electrode pattern of the first transparent electrode 151; and

FIG. 25( a) is a diagram showing the astigmatism correcting transparent electrode pattern formed as the first transparent electrode 151, FIG. 25(b) is a diagram showing an example of the voltage applied in the X-axis direction of the transparent electrode pattern of the first transparent electrode 151, and FIG. 25(c) is a diagram showing an example of astigmatism in the X-axis direction as improved by the transparent electrode pattern of the first transparent electrode 151.

Claims

1. An optical pickup apparatus comprising: a light source for emitting a light beam;a liquid crystal optical element having a first liquid crystal layer for correcting aberration and a second liquid crystal layer functioning as an nλ/4 plate in an integral fashion, and disposed at an angle relative to an optical axis of said light beam;a transparent electrode for generating a potential difference on said second liquid crystal layer in order to control an amount of phase difference for said light beam passing through said second liquid crystal layer;an objective lens for focusing the light beam passed through said liquid crystal optical element; anda driver for driving said transparent electrode so as to generate a potential difference that is the lowest among a plurality of potential differences that cause said second liquid crystal layer to function as an nλ/4 plate.

2. The optical pickup apparatus according to claim 1, wherein the angle that a rubbing direction of said first liquid crystal layer makes with a rubbing direction of said second liquid crystal layer is approximately 45 degrees.

3. The optical pickup apparatus according to claim 2, wherein said liquid crystal optical element is tilted in a direction that matches the rubbing direction of said first liquid crystal layer.

4. The optical pickup apparatus according to claim 1, wherein said first liquid crystal layer corrects coma, spherical aberration, or astigmatism.

5. The optical pickup apparatus according to claim 1, wherein said first liquid crystal layer and said second liquid crystal layer are provided alternately between three transparent substrates in said liquid crystal optical element.

6. An optical pickup apparatus comprising: a light source for emitting a light beam;a liquid crystal optical element having a first liquid crystal layer for correcting aberration and a homogeneously aligned second liquid crystal layer functioning as an nλ/4 plate in an integral fashion, and is disposed at an angle relative to an optical axis of said light beam;a transparent electrode for generating a potential difference on said second liquid crystal layer in order to control an amount of phase difference for said light beam passing through said second liquid crystal layer;an objective lens for focusing the light beam passed through said liquid crystal optical element; anda driver for driving said transparent electrode so as to generate a potential difference corresponding to the amount of phase difference that achieves the highest order n among a plurality of amounts of phase difference that cause said second liquid crystal layer to function as an nλ/4 plate.

7. The optical pickup apparatus according to claim 6, wherein the angle that a rubbing direction of said first liquid crystal layer makes with a rubbing direction of said second liquid crystal layer is approximately 45 degrees.

8. The optical pickup apparatus according to claim 7, wherein said liquid crystal optical element is tilted in a direction that matches the rubbing direction of said first liquid crystal layer.

9. The optical pickup apparatus according to claim 6, wherein said first liquid crystal layer corrects coma, spherical aberration, or astigmatism.

10. The optical pickup apparatus according to claim 6, wherein said first liquid crystal layer and said second liquid crystal layer are provided alternately between three transparent substrates in said liquid crystal optical element.

11. An optical pickup apparatus comprising: a light source for emitting a light beam;a liquid crystal optical element having a first liquid crystal layer for correcting aberration and a vertically aligned second liquid crystal layer functioning as an nλ/4 plate in an integral fashion, and is disposed at an angle relative to an optical axis of said light beam;a transparent electrode for generating a potential difference on said second liquid crystal layer in order to control an amount of phase difference for said light beam passing through said second liquid crystal layer;an objective lens for focusing the light beam passed through said liquid crystal optical element; anda driver for driving said transparent electrode so as to generate a potential difference corresponding to the amount of phase difference that achieves the lowest order n among a plurality of amounts of phase difference that cause said second liquid crystal layer to function as an nλ/4 plate.

12. The optical pickup apparatus according to claim 11, wherein the angle that a rubbing direction of said first liquid crystal layer makes with a rubbing direction of said second liquid crystal layer is approximately 45 degrees.

13. The optical pickup apparatus according to claim 12, wherein said liquid crystal optical element is tilted in a direction that matches the rubbing direction of said first liquid crystal layer.

14. The optical pickup apparatus according to claim 11, wherein said first liquid crystal layer corrects coma, spherical aberration, or astigmatism.

15. The optical pickup apparatus according to claim 11, wherein said first liquid crystal layer and said second liquid crystal layer are provided alternately between three transparent substrates in said liquid crystal optical element.

16. A liquid crystal optical element disposed at an angle relative to an optical axis, comprising: a first liquid crystal layer for correcting aberration;a second liquid crystal layer functioning as an nλ/4 plate and combined in an integral fashion with said first liquid crystal layer;a transparent electrode for generating a potential difference on said second liquid crystal layer in order to control an amount of phase difference for said light beam passing through said second liquid crystal layer; anda driver for driving said transparent electrode so as to generate a potential difference that is the lowest among a plurality of potential differences that cause said second liquid crystal layer to function as an nλ/4 plate.

17. The liquid crystal optical element according to claim 16, wherein the angle that a rubbing direction of said first liquid crystal layer makes with a rubbing direction of said second liquid crystal layer is approximately 45 degrees.

18. The liquid crystal optical element according to claim 17, wherein said liquid crystal optical element is tilted in a direction that matches the rubbing direction of said first liquid crystal layer.

19. The liquid crystal optical element according to claim 16, wherein said first liquid crystal layer corrects coma, spherical aberration, or astigmatism.

20. The liquid crystal optical element according to claim 16, wherein said first liquid crystal layer and said second liquid crystal layer are provided alternately between three transparent substrates.

21. A liquid crystal optical element disposed at an angle relative to an optical axis, comprising: a first liquid crystal layer for correcting aberration;a homogeneously aligned second liquid crystal layer functioning as an nλ/4 plate and combined in an integral fashion with said first liquid crystal layer;a transparent electrode for generating a potential difference on said second liquid crystal layer in order to control an amount of phase difference for said light beam passing through said second liquid crystal layer; anda driver for driving said transparent electrode so as to generate a potential difference corresponding to the amount of phase difference that achieves the highest order n among a plurality of amounts of phase difference that cause said second liquid crystal layer to function as an nλ/4 plate.

22. The liquid crystal optical element according to claim 21, wherein the angle that a rubbing direction of said first liquid crystal layer makes with a rubbing direction of said second liquid crystal layer is approximately 45 degrees.

23. The liquid crystal optical element according to claim 22, wherein said liquid crystal optical element is tilted in a direction that matches the rubbing direction of said first liquid crystal layer.

24. The liquid crystal optical element according to claim 21, wherein said first liquid crystal layer corrects coma, spherical aberration, or astigmatism.

25. The liquid crystal optical element according to claim 21, wherein said first liquid crystal layer and said second liquid crystal layer are provided alternately between three transparent substrates.

26. A liquid crystal optical element disposed at an angle relative to an optical axis, comprising: a first liquid crystal layer for correcting aberration;a vertically aligned second liquid crystal layer functioning as an nλ/4 plate and combined in an integral fashion with said first liquid crystal layer;a transparent electrode for generating a potential difference on said second liquid crystal layer in order to control an amount of phase difference for said light beam passing through said second liquid crystal layer; anda driver for driving said transparent electrode so as to generate a potential difference corresponding to the amount of phase difference that achieves the lowest order n among a plurality of amounts of phase difference that cause said second liquid crystal layer to function as an nλ/4 plate.

27. The liquid crystal optical element according to claim 26, wherein the angle that a rubbing direction of said first liquid crystal layer makes with a rubbing direction of said second liquid crystal layer is approximately 45 degrees.

28. The liquid crystal optical element according to claim 27, wherein said liquid crystal optical element is tilted in a direction that matches the rubbing direction of said first liquid crystal layer.

29. The liquid crystal optical element according to claim 26, wherein said first liquid crystal layer corrects coma, spherical aberration, or astigmatism.

30. The liquid crystal optical element according to claim 26, wherein said first liquid crystal layer and said second liquid crystal layer are provided alternately between three transparent substrates.