JP2002174804A - Small-sized liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the deterioration of surface precision of a small-sized liquid crystal element due to the swelling of seal under high temperature and humidity environment. SOLUTION: This liquid crystal element which is related to an optical pickup provided with a laser beam source, an objective lens and a small-sized liquid crystal element for correcting aberration is arranged on the laser beam axis, has a cell of <=6 mm×6 mm and is formed in such a manner that the cell gap at the center part under a normal temperature environment becomes 0.075-0.1 μm thicker than the cell gap at the end part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small liquid crystal element used for correcting aberration of an optical pickup.

[0002]

2. Description of the Related Art The following optical pickup is disclosed in Japanese Patent Application Laid-Open No. 9-128785 as a device using a small liquid crystal element for aberration correction. This will be described below with reference to FIG.

According to the above invention, a liquid crystal element is used to
There is disclosed a compatible type optical pickup which corrects coma aberration, spherical aberration, aberration due to relative displacement between an objective lens and a liquid crystal element, and can be used for both DVD5 and CD5. The contents are as follows. In an optical pickup provided with a laser light source 1 and an objective lens 4, a liquid crystal element 3 for aberration correction is arranged on the optical axis of a laser beam B, and a transparent electrode of the liquid crystal element 3 is cross-checked. And the voltage applied to each divided portion is variably controlled by the liquid crystal element control circuit 9, and the aberration is corrected by changing the refractive index of each divided portion.

[0004]

However, in the conventional small liquid crystal device described above, when the device is left in a high-temperature and high-humidity environment and then returned to a normal temperature and normal humidity environment, the surface accuracy of the liquid crystal device decreases. There was a problem.

Here, in view of such a problem, the inventor of the present invention has
An analysis experiment was performed. According to the result, the seal of the small liquid crystal element swells when left in a high-temperature and high-humidity environment for a long time. In addition, it was found that once the seal was swollen, it did not return immediately even when returned to a normal temperature and normal humidity environment.

Further, as a result of the swelling of the seal, the cell gap at the end near the seal becomes thick. Here, since the volume of the liquid crystal in the cell is constant, the cell gap at the center is naturally reduced, so that the surface accuracy is reduced. Specifically, the difference between the thickness of the cell gap at the end and the center is 0.
Due to the generation of about 15 μm to 0.2 μm, the surface accuracy is reduced.

It is an object of the present invention to improve a decrease in surface accuracy of a small liquid crystal device due to swelling of a seal under high temperature and high humidity.

[0008]

(1) To achieve the above object, an optical pickup comprising a laser light source and an objective lens, which is a small-sized aberration-correcting liquid crystal element arranged on a laser optical axis; A small liquid crystal element characterized in that the small liquid crystal element is formed so that the central part of the cell gap is thick. (2) The small liquid crystal element is characterized in that the cell gap is formed so that the cell gap gradually increases from the end to the center. (3) The central part of the cell gap is 0.0
Provided is a small liquid crystal element which is formed to have a thickness of 75 μm to 0.1 μm. (4) The small liquid crystal element is characterized in that the central part of the cell gap is formed by a sealed liquid crystal pressure under a normal temperature environment. (5) The small liquid crystal element has a size of 6 mm × 6 mm or less.

[0009]

FIG. 2 is a sectional view showing a small-sized liquid crystal device at normal temperature according to the present invention. The cell portion of the small liquid crystal element has a shape of 6 mm × 6 mm. (See Fig. 3)

In FIG. 1, reference numeral 21 denotes a glass substrate which is disposed to face the glass substrate 21. A transparent electrode 22 made of ITO (tin-added indium oxide) and an alignment film 2 are formed on the glass substrate 21.
3 are formed in order. And the glass substrate 21
The glass substrate 21 is adhered via a seal 24 disposed around the periphery. In the present embodiment, a thermosetting one-part epoxy seal is used as the material of the seal 24.

In the seal 24, a not-shown spacer in the seal is provided, and the glass substrate 21 surrounded by the seal is provided.
Although not shown, a gap is formed between the two glass substrates by disposing an in-cell spacer (not shown). The liquid crystal 25 is sealed in this gap to form a liquid crystal layer.

Here, the cell gap, which is the thickness of the liquid crystal layer, is measured in a high-temperature and high-humidity environment (for example, 85 ° C., 85% humidity, 5
In order to alleviate the deterioration of the surface accuracy due to the change in the gap due to the expansion of the seal due to the swelling of the seal after returning to room temperature after being left at room temperature (00 hours).

Therefore, the experimental results (0.15 μm to 0.2 μm) under the normal temperature and normal humidity environment described in the above-mentioned technical subject.
(0.075 μm to 0.1 μm) is provided so that the gap at the center becomes thicker. More specifically, it is better that the thickness of the gap is gradually increased from the end (near the seal) toward the center.

In the present embodiment, the gap is 0.1 μm thicker at the center than at the end (near the seal). Specifically, the gap at the center portion is made thicker than the end portion (near the seal) by about 0.1 μm due to the liquid crystal pressure at the time of sealing.

Here, in the case of a 6 mm × 6 mm cell optical element, that is, a small liquid crystal element, the surface accuracy is 0.1 μm or less when the gap at the center is thicker than at the end (near the seal). (Λ = 632.8 nm). This surface accuracy sufficiently satisfies the accuracy required for the optical element.

Further, when the small liquid crystal element is left under high temperature and high humidity and deformed in a direction in which the center portion becomes thinner by about 0.2 μm than the end portion (near the seal), first, Center (near the seal)
Since the thickness is set to about 1 μm, the thickness of the central part is about 0.1 μm thinner than the end (near the seal).
In this case, the surface accuracy is λ / 10 or less. Therefore, the surface accuracy of this liquid crystal element is λ / 10 or less even when the liquid crystal element is left at normal temperature and normal humidity after being left under high temperature and high humidity. Therefore, the precision required for the optical element is sufficiently satisfied.

[0017]

As is apparent from the above description, an optical pickup comprising a laser light source and an objective lens for achieving the above object is a small-sized aberration correcting liquid crystal element arranged on the laser optical axis. Further, it is possible to provide a small liquid crystal element formed such that the central part of the cell gap of the small liquid crystal element is thickened.

Further, in the small liquid crystal device of the present invention, the cell gap is formed so as to gradually increase in thickness from the end to the center, and the center of the cell gap is 0.075 μm or more from the end. Since the center portion is set to be thicker by being formed so as to be 0.1 μm thick, the center portion is thinner by about 0.1 μm than the end portion (near the seal). The surface accuracy at this time is λ /
10 or less.

Further, the small liquid crystal element is operated under a normal temperature environment.
When the center of the cell gap is formed by the pressure of the sealed liquid crystal, it is left under high temperature and high humidity, and the center is thinner by about 0.2 μm than the end (near the seal). First, in the liquid crystal element of the present invention, first, the center portion is 0.1 μm thicker than the end portion (near the seal).
About thick, so the end (near the seal)
As a result, the thickness at the central portion becomes thinner by about 0.1 μm. In this case, the surface accuracy is λ / 10 or less. Therefore, the surface accuracy of this liquid crystal element is λ / 10 or less even when the liquid crystal element is left at normal temperature and normal humidity after being left under high temperature and high humidity. Therefore, the precision required for the optical element is sufficiently satisfied.

The small liquid crystal element of the present invention has a size of 6 mm ×
By being characterized by being 6 mm or less, it has become possible to provide a small-sized liquid crystal element for aberration correction with high accuracy, which is used in an optical system and is particularly arranged on the laser optical axis.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a conventional technique.

FIG. 2 is a conceptual diagram showing an embodiment of the present invention.

FIG. 3 is a conceptual diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 3 Liquid crystal element 4 Objective lens 21 Glass substrate 22 Electrode 23 Alignment film 24 Seal 25 Liquid crystal

Claims (5)

[Claims] 1. An optical pickup comprising a laser light source and an objective lens, wherein the small liquid crystal element for aberration correction is arranged on the laser optical axis, and a central part of a cell gap of the small liquid crystal element is thickened. A small liquid crystal element characterized by being formed on a substrate. 2. The small liquid crystal element according to claim 1, wherein the small liquid crystal element is formed such that a cell gap gradually increases from an end to a center. 3. The small-sized liquid crystal device according to claim 1, wherein a central portion of the cell gap is formed to be 0.075 μm to 0.1 μm thicker than the end portion. 4. The liquid crystal device according to claim 1, wherein the small liquid crystal element is formed under a normal temperature environment by a liquid crystal pressure in which a central portion of a cell gap is sealed. Small liquid crystal element. 5. The small liquid crystal device according to claim 1, wherein the size of the small liquid crystal device is 6 mm × 6 mm or less.