JP2002296604A - Liquid crystal optical element and optical pick-up device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide liquid crystal optical element which is minimized in the degradation of the properties for light transmission of liquid crystal optical element caused by the generation of bubbles. SOLUTION: The liquid crystal optical element is composed of two sheets of substrates with electrodes, etc., being laminated in a pre-determined gap with a seal in between and equipped with an optically effective irradiation region. It is characterized by having the seal in a specific pattern outside the effective irradiation region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Japanese Patent Laid-Open No. 9-128785 discloses a liquid crystal optical element used for correcting aberrations of an optical pickup device.
Japanese Patent Application Laid-Open Publication No. 2002-133873 discloses that a liquid crystal optical element is used to correct coma aberration, spherical aberration, aberration due to a relative displacement between an objective lens and a liquid crystal optical element, and the like, so that it can be used for both DVD and CD. An optical pickup device of the type is disclosed. FIG. 4 is a diagram showing a configuration of an optical pickup device described in the publication. The contents are as follows. In an optical pickup device having a laser light source 51 and an objective lens 54, a liquid crystal optical element 53 for aberration correction is arranged on the optical axis of the laser beam B, and the transparent electrode of the liquid crystal optical element 53 is The liquid crystal optical element control circuit 59 variably controls the voltage applied to each of the divided portions, and corrects the aberration by changing the refractive index of each of the divided portions.

In general, a plurality of liquid crystal optical elements are formed on a large substrate in consideration of mass productivity, and finally divided into individual liquid crystal optical elements. Produced by the method. Hereinafter, the related art will be described with reference to the drawings.

FIG. 5 is a plan view of the large-sized substrate provided with a plurality of liquid crystal optical elements 25 before the liquid crystal is injected in the step of manufacturing the above liquid crystal optical element. As shown in FIG. 5, a first alignment mark 21 and a second alignment mark 22 necessary for alignment are provided at the four corners of the large-sized substrate using the same material as an electrode described later.

FIG. 6 is a sectional view showing an AA section in FIG. As shown in FIG. 6, a liquid crystal optical element according to the related art has a first substrate 30 and a second substrate 31, in which a first electrode 3 made of indium tin oxide (hereinafter referred to as ITO) is provided.
2 and a second electrode 33, and the first electrode 32 and the second
A first alignment film 35 and a second alignment film 36 for aligning the liquid crystal are provided on the upper surface of the electrode 33, and the first alignment film 35 and the second alignment film 36 And a cell spacer 37 for maintaining a gap (hereinafter referred to as a “cell gap”) at a predetermined dimension, a cell gap at a predetermined interval, and a liquid crystal between the first substrate 30 and the second substrate 31. And a seal 24 for sealing between them.
Then, liquid crystal is injected into a space 34 surrounded by the seal as described later.

FIG. 7 is a plan view showing the shape of the seal of a liquid crystal optical element according to the prior art. In FIG. 7, the shape of the seal 41 is rectangular except for an injection hole portion for injecting liquid crystal, and both the outer shape and the inner shape have a uniform line width. Also, each side of the rectangular shape outside the seal 41 is linearly arranged along the scribe line 42.

In FIG. 7, an area 43 indicates an effective irradiation range of the laser beam when the liquid crystal optical element is used in the optical pickup device shown in FIG. It has an elliptical shape.

Next, a manufacturing method for obtaining the above liquid crystal optical element will be described. The cleaned first substrate 30 and second
Substrates 31 are each formed by sputtering using ITO.
Is formed with a thickness of 200 nm. Thereafter, an exposure process and a development process are performed using a predetermined photomask, and the first electrode 32 and the second
Electrode 33, the first alignment mark 21 and the second
And the alignment mark 22 are formed.

Thereafter, the first substrate 30 and the second substrate 31
, And a first alignment film 35 and a second alignment film 3 made of polyimide resin are formed on the first electrode 32 and the second electrode 33.
6 is formed by a printing method, and a heat treatment is performed using a clean oven. Thereafter, the surfaces of the first substrate 30 and the second substrate 31 are rubbed with a roll wrapped with a cotton cloth,
An alignment treatment is performed by a rubbing method.

After that, a sealing material obtained by mixing a thermosetting epoxy resin with a spacer (not shown) made of glass fiber which fits a predetermined cell gap is screen-printed around the display of the first substrate 30. Is formed. Further, a solution obtained by dispersing an in-cell spacer 37 made of plastic beads matching a predetermined cell gap size in a mixed solution of alcohol and pure water is applied to the second substrate 31.
Spray.

Here, the reason why the spacer in the seal is made of glass fiber and the spacer in the cell is made of plastic beads will be described. Since the cell gap in a liquid crystal optical element greatly affects optical characteristics, it is necessary to control the cell gap strictly. In addition, since the intracellular spacer is present in an optically significant portion, it is desirable that the optical spacer has as little optical influence as possible. Therefore, plastic beads are used for the spacer in the cell so that the optical gap is small and the cell gap can be easily adjusted to a predetermined value.

However, since it is difficult to maintain the cell gap against external force only by using the spacer in the cell, it is necessary to stabilize the cell gap by inserting a spacer in the seal. Since the spacer in the seal exists in an optically insignificant part, a columnar fiber is used mainly for enhancing the maintenance of the cell gap. As is clear from FIG. 6, the gap at the portion supported by the seal 24 is not the same as the cell gap (gap between the alignment films 35 and 36). Is used.

In any case, as a whole, the cell gap is maintained by the support of both the in-cell spacer and the in-seal spacer, but the accuracy of the spacer diameter is generally better in the in-cell spacer.

After the above-mentioned arrangement of the sealing material and the dispersion of the spacers in the cells, the first and second substrates 30 and 30 are aligned using the first alignment mark 21 and the second alignment mark 22. 31 are superimposed, and a plurality of points around the superimposed first substrate 30 and second substrate 31 are temporarily fixed with an ultraviolet curing adhesive.

Thereafter, the first substrate 30 and the second substrate 31 thus superimposed are set on a seal hardening jig,
The sealing material is cured by performing heat treatment in a firing furnace while applying pressure at a predetermined pressure.

After that, the first substrate 30 and the second substrate 31
Is cut into strips by a scribe step and a break step to obtain a strip-shaped substrate including a plurality of liquid crystal optical elements (hereinafter referred to as a “strip”). The steps of injecting the liquid crystal and sealing the injection hole are performed on the strip.

Here, the scribing step and the breaking step will be described. In the cutting step of the glass substrate, first, a cutter wheel made of diamond is rotated along a portion of the glass substrate to be cut to form a scribe line (scribe step). Next, the glass surface opposite to the surface on which the scribe line was formed was hit with a squeegee made of urethane rubber or the like to apply bending stress to the glass substrate, or the glass substrate itself was rolled by a roller or the like to generate the scribe line. The glass substrate is cut by further progressing the crack in the direction perpendicular to the substrate surface (break step).

FIG. 8 shows a pressure jig for sealing a liquid crystal optical element after a liquid crystal injecting step (description is omitted).
Reference numeral 12 denotes a pressure plate, which is provided with convex portions 13 for individually pressing the outside of the liquid crystal optical element 5 of the strip 10 on both sides thereof. Here, the material of the pressing plate 12 is aluminum, stainless steel, or the like. The projection 13 is made of rubber. The strips 10 and the pressure plates 12 are alternately superposed.

FIG. 9 is an explanatory view showing a case where the strip is sealed by a method called outer pressure sealing using the pressing jig shown in FIG. 8, and FIG. FIG. 4B is a perspective view showing a state, FIG. 4B is a cross-sectional view showing a place where an external force is applied to the strip 10, and FIG.

In FIG. 9, 1 is an upper substrate, 2 is a lower substrate,
Reference numeral 3 denotes a sealant, 4 denotes liquid crystal injected into the liquid crystal optical element 5, 17 denotes a liquid crystal injection port, and 18 denotes a sealing agent.

The sealing is performed by the following steps. With the liquid crystal 4 injected into the strip 10, a sealing agent 18 such as a photocurable resin is applied to the vicinity of the liquid crystal injection port 17 (see FIG. 9A).

Next, an external pressure P is partially applied to portions 1b and 2b of the upper substrate 1 and the lower substrate 2 outside the portion where the liquid crystal 4 of the liquid crystal optical element 5 is injected. At this time, FIG.
As shown by the dotted line in (c), the upper substrate 1 and the lower substrate 2 are deformed into a concave shape at the portions 1b and 2b outside the portion of the liquid crystal optical element 5 into which the liquid crystal 4 is injected by bending deformation. The portion where the liquid crystal 4 is injected is deformed in a convex shape. For this reason, the volume of the liquid crystal optical element 5 increases, and the pressure inside the liquid crystal optical element 5 becomes lower than the outside air.
Enters the liquid crystal injection port 17. When the sealing agent 18 has entered, the pressure inside the liquid crystal optical element 5 approaches the pressure of the outside air.

Next, with the external pressure P still applied, the sealing agent 18 is cured by light irradiation, heat, or the like to seal the hole.

Next, by removing the external pressure P, the sealing step is completed. At this time, the convex liquid crystal optical element 5
Presses the liquid crystal 4 inside to return to the original state. For this reason, the pressure in the liquid crystal optical element 5 increases from the time of sealing, and becomes sufficiently higher than the outside air.

After the above sealing step is completed, an isotropic treatment is performed, and the portions 1 b, 2
The strip 10 is cut at b, and cut into individual liquid crystal optical elements 5. The isotropic treatment is performed for the purpose of properly aligning the liquid crystal molecules, in which the liquid crystal optical element is heated once, all the liquid crystals are heated to the isotropic phase temperature, and then gradually cooled to the operating temperature. It is.

The surfaces of the individually separated liquid crystal optical elements 5 are also convex, and the pressure inside the liquid crystal optical elements 5 is maintained sufficiently high due to the restoring force. The gas dissolved in the sealing agent 18 and the like is prevented from being vaporized to form bubbles, and the generation of bubbles in the liquid crystal optical element is effectively prevented.

[0027]

As described above, in the conventional liquid crystal optical element, in order to maintain the cell gap, a spacer in the cell is provided inside the liquid crystal optical element, and a spacer in the seal is provided inside the seal. . However, since there is a spacer in the cell inside the liquid crystal optical element, the transmittance of the laser light incident on the liquid crystal optical element having an optically effective irradiation area is affected by the diffraction and scattering of light by the contour of the spacer in the cell. However, there is a problem that the transmittance is reduced.

If the spacer in the cell is eliminated in order to solve the above-mentioned problem, there is a new problem that it becomes difficult to maintain the cell gap.

Further, when the liquid crystal injection hole is sealed, if the sealing agent is wrapped around the spacer in the cell, the thermal expansion coefficient of the spacer agent is different from that of the sealing agent. When it is added, a void is formed around the spacer in the cell in the sealing agent, and bubbles are easily generated. When air bubbles are generated, the transmission characteristics of the liquid crystal optical element change, and desired characteristics cannot be obtained as a light valve or a display element, and there is a serious problem that reliability is reduced.

Further, in the sealing step at the time of manufacturing the liquid crystal optical element, if the pressure applied to the outer portion of the portion into which the liquid crystal is injected is insufficient, the convex restoring force does not become sufficiently large. Since the pressure inside the cell is not sufficiently increased, there is a problem that bubbles are easily generated.

[0031]

As a result of various studies, the present inventor has concluded that these problems are related to the shape of the seal. That is, if the width of the seal is small, the seal acts only as a fulcrum, so the convex restoring force generated on the substrate is only the restoring force of the substrate itself,
The pressure inside the cell is not sufficiently increased, and bubbles are easily generated. Also, when the seal acts as a fulcrum, the action of maintaining the cell gap is reduced, and the spacer in the cell is required to maintain the cell gap, resulting in a decrease in the optical characteristics as described above. become. Further, if the distance between the opposing seals inside the seal is long, the convex restoring force is weakened, and air bubbles are also likely to be generated.

In order to solve these problems, a means used by the present invention is to add a sealing material to a portion other than the optically effective irradiation area of the liquid crystal optical element, where the sealing material was not provided conventionally. In this way, the fulcrum effect of the seal is reduced, thereby eliminating the spacer in the cell to improve the optical characteristics of the liquid crystal optical element, and the convex restoring force generated on the substrate reduces the restoration of the substrate itself. The purpose is to add the restoring force of the seal itself to the force to sufficiently increase the pressure inside the cell and more effectively prevent the generation of bubbles.

As another means, in addition to the above-mentioned means, the spacer in the seal is formed in a bead shape, or a mixture of a fiber-shaped spacer and a bead-shaped spacer is provided. By providing a highly accurate bead-shaped spacer in the seal, the accuracy of the cell gap is not reduced.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION In a liquid crystal optical element in which two substrates on which electrodes are formed are bonded together with a predetermined gap through a seal, a first embodiment of the present invention relates to By making the outer shape different from the inner shape, the supporting area of the seal is increased, and the distance between the seals, that is, the distance between the fulcrums is substantially shortened. In this case, it is desirable to make the inner shape of the seal substantially similar to the outer peripheral shape of the effective irradiation area. Often the shape is substantially circular. The outer shape of the seal is desirably substantially rectangular.

The inner shape of the seal may be a shape having a plurality of convex portions substantially along the outer peripheral shape of the effective irradiation area. When the outer peripheral shape of the effective irradiation area is substantially circular, the inner shape of the seal may be such that the convex portions are provided at four inner corners of a substantially rectangular shape. The inner shape of the seal may be circular, and the outer shape may be substantially circular with four convex portions.

In a second embodiment of the present invention, a sub-support portion is provided outside or inside the seal separately from the seal. It is desirable that the sub-support portion is made of the same material as the seal. The auxiliary support may have a continuous shape or may be separated into a plurality. In any case, it is desirable that the shape of the seal or the sub-supporting portion adjacent to the outer periphery of the effective irradiation region is such that it is along the outer periphery of the effective irradiation region.

When the outer peripheral shape of the effective irradiation area is substantially circular, the sub-supporting portions can be provided at four inner corners of a seal having a rectangular inner shape. The outer shape of the seal may be circular, and the sub-supporting portion may be provided outside the seal. The outer shape may be substantially circular with four convex portions.

According to a third embodiment of the present invention, both the outer shape and the inner shape of the seal are substantially similar to the outer peripheral shape of an optically effective irradiation area where light is applied to the liquid crystal optical element. It is. As described above, the outer peripheral shape is often substantially circular. This embodiment has the following features.

When the outer shape of the seal is linear,
Since the distance between the scribe line 42 and the outer periphery of the seal 41 in FIG. 7 can be kept constant, the stress applied in the break process is evenly applied to the scribe line 42, and the linearity of the cut side when the break occurs Can be improved.
However, in the third embodiment, the scribe line 42
Since the distance between the seal and the outer periphery of the seal 41 is not constant,
The stress applied in the break step is not evenly applied to the scribe line 42, and has a disadvantage that the linearity of the cut side may be reduced in some cases.

However, according to the third embodiment, the distance from the center of the liquid crystal optical element to the inner and outer circumferences of the seal in the outer peripheral direction is relatively uniform, so that the optical characteristics are improved. There is an advantage that the entire element is uniform.

The present invention employing the above embodiment can be applied to various liquid crystal optical elements. For example, even if one of the electrodes of the liquid crystal display element is a single electrode, or one of the electrodes, The electrode may be divided into a plurality, or both the electrodes may be divided into a plurality. (Embodiment) FIG. 1 is a plan view showing a seal shape of a liquid crystal optical element showing a first embodiment of the present invention. In FIG. 1, the outer shape of the seal 61 is substantially rectangular, and the inner shape is a shape along the outer periphery of the effective irradiation area 62 (which will be described as a substantially circular shape in the following embodiments).

When FIG. 1 is compared with FIG. 7, it is clear that the liquid crystal optical element according to the present invention can have a larger seal area. Thus, the number of spacers in the seal involved in supporting the substrate can be increased, so that the cell gap can be maintained even if the spacers in the cell are eliminated. In this embodiment, the case where the inner shape of the seal is circular is shown, but other shapes may be used as long as a desired number of spacers in the seal can be secured.

FIG. 3A is a schematic cross-sectional view of the liquid crystal optical element having the shape shown in FIG. 1 when cut along A1-A1, and shows the seal and the deformation of the glass substrate when external pressure is applied. It shows the situation. FIG. 3B is a schematic cross-sectional view when the liquid crystal optical element having the shape shown in FIG. 1 is cut along B1-B1, and shows the state of the seal and the deformation of the glass substrate when external pressure is applied. ing.

In the section taken along line A1-A1 in FIG. 1, the glass substrate is largely deformed into a convex shape as shown in FIG. On the other hand, in the B1-B1 cross section, the glass substrate is deformed into the shape shown in FIG. This is Figure 3
It is considered that (b) is due to the fact that the seal area is larger and the facing distance of the seal is shorter. In other words, if the seal area is large, the number of spacers in the seal that supports the substrate also increases, making it difficult for the seal to be crushed by stress, and also increasing the resistance to the force of the substrate to warp outward. It is considered that the force that hinders deformation is a great result.

That is, when the liquid crystal optical element of this embodiment is subjected to the above-mentioned external pressure, a large central convex deformation occurs at the center of the liquid crystal optical element, but a large deformation occurs at a distance from the central part. Absent. If the outer pressurization is removed in such a state, a large restoring force is generated in the central convex portion at the central portion. Therefore, when liquid crystal is actually injected and sealed, a large internal pressure is applied inside the liquid crystal optical element,
The prevention of bubble generation is effectively performed.

According to this embodiment, there is provided an extremely reliable liquid crystal optical element in which the transmittance of laser light is improved by about 1 to 2%, and there is no generation of bubbles and no change in characteristics such as light transmission characteristics. You can do it.

FIG. 2 shows another embodiment of the present invention. FIG.
In FIG. 7, the seal 61 is formed in a predetermined pattern outside the effective irradiation area 62, and both the outer shape and the inner shape are substantially rectangular. Further, it has a shape in which circular sub-support portions 63 are arranged at four corners. The sub-supporting portion may be any as long as it can maintain the cell gap. For example, a flat plate spacer having a specified thickness can be used.

In this manner, the cell gap can be maintained at a predetermined value without the spacer in the cell, so that the transmittance of the liquid crystal optical element can be prevented from lowering. It is possible to improve reliability such as preventing the generation of bubbles due to thermal stress at the time of hole formation.

The auxiliary support may be made of the same material as the seal 61. In this case, since the in-seal spacer is also present inside the sub-support portion 63, the number of in-seal spacers that contribute to supporting the cell gap is larger than in the conventional liquid crystal optical element, and the same as in the above case. The effect of can be obtained.

In FIG. 2, the sub support 63 is provided with a seal 61.
However, it may be connected to the seal 61 as shown by a thick dotted line in FIG. In this case, when the sub-support portion 63 is made of the same material as the seal 61, the seal 61
Can be considered to have been deformed to have a convex portion inside.

FIG. 10 is a plan view showing another three embodiments of the present invention. In all the embodiments shown in FIG. 10, both the outer shape and the inner shape of the seal 61 are effective irradiation areas 62.
3 shows a case that is substantially similar to the outer peripheral shape of FIG.

FIG. 10A shows an example in which a sub-support 63 is provided outside the seal 61. FIG. 10B shows an example in which the sub-support portions 63 provided outside the seal 61 are continuously provided without being separated from each other to form one sub-support portion.
Naturally, a sub-support portion having such a shape may be provided inside the seal. Further, as indicated by a thick dotted line, the sub-supporting portion may be connected to the seal.

FIG. 10C shows that both the outer shape and the inner shape of the seal 61 are substantially similar to the outer shape of the effective irradiation area 62, and no auxiliary support is provided. However, even in this case, since the facing distance of the seal 61 is short on average, the cell gap can be easily maintained even without the intra-cell spacer. Further, if the width of the seal 61 is increased as shown in FIG. 10C, the same effect as in the other embodiments can be obtained.

In the embodiment shown in FIGS. 10B and 10C, the structure viewed from the center of the liquid crystal optical element toward the outer periphery is substantially uniform over the entire circumference, so that optical non-uniformity is reduced. It can be said that the structure is more preferable as an optical element.

[0055]

As is clear from the above description, according to the liquid crystal optical element of the present invention, the spacer in the cell is eliminated by devising the shape of the seal, the transmissivity is high, and the effect of preventing the generation of bubbles is obtained. It is possible to provide a small and highly reliable liquid crystal optical element. The liquid crystal optical element of the present invention is particularly suitable for use in a small device such as an optical pickup device.

[Brief description of the drawings]

FIG. 1 is a diagram showing a seal shape according to a first embodiment of the present invention.

FIG. 2 is a view showing the shapes of a seal and a sub-support according to another embodiment of the present invention.

FIG. 3 is a schematic sectional view illustrating an embodiment according to the present invention.

FIG. 4 is a schematic diagram for explaining a conventional technique.

FIG. 5 is a diagram for explaining a conventional technique.

FIG. 6 is a diagram for explaining a conventional technique.

FIG. 7 is a diagram showing a seal shape according to the related art.

FIG. 8 is a diagram showing a method of manufacturing a liquid crystal optical element according to the related art.

FIG. 9 is a view illustrating a method of manufacturing a liquid crystal optical element according to the related art.

FIG. 10 is a view showing a shape of a seal and a sub-support portion according to another embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 30 first substrate 31 second substrate 32 first electrode 33 second electrode 35 first alignment film 36 second alignment film 37 spacer in cell 51 laser light source 53 liquid crystal optical element 54 objective lens 59 liquid crystal optical element Control circuit 61 Seal 62 Effective irradiation area

Claims (19)

[Claims] 1. A liquid crystal optical element comprising two substrates on which electrodes are formed and bonded with a predetermined gap through a seal, wherein the outer shape and the inner shape of the seal are different. Liquid crystal optical element. 2. The liquid crystal optical element according to claim 1, wherein the inner shape of the seal is substantially circular. 3. The liquid crystal optical element according to claim 1, wherein the inner shape of the seal is a substantially rectangular shape having projections at four corners. 4. The liquid crystal optical element according to claim 1, wherein the outer shape of the seal is a substantially circular shape having four convex portions. 5. A liquid crystal optical element in which two substrates on which electrodes are formed are stuck with a predetermined gap through a seal, and a sub-support is provided inside or outside the seal. Liquid crystal optical element. 6. The liquid crystal optical element according to claim 5, wherein the sub-support portion is made of the same material as the seal. 7. The seal according to claim 5, wherein an inner shape of the seal is substantially rectangular, and the sub-supporting portions are provided at four inner corners of the seal. Liquid crystal optical element. 8. The liquid crystal optical device according to claim 5, wherein the outer shape of the seal is substantially circular, and the sub-support portion is provided outside the seal. element. 9. The liquid crystal optical element according to claim 8, wherein the inner shape of the seal is substantially circular. 10. The liquid crystal optical element according to claim 1, wherein an outer shape of the seal is substantially rectangular. 11. A liquid crystal optical element in which two substrates on which electrodes are formed are stuck together with a predetermined gap through a seal, and the inner shape of the seal is irradiated with light to the liquid crystal optical element. A liquid crystal optical element having a shape substantially similar to the outer peripheral shape of an optically effective irradiation area. 12. The liquid crystal optical element according to claim 11, wherein the outer shape of the seal is substantially similar to the outer peripheral shape of the effective irradiation area. 13. A liquid crystal optical element in which two substrates on which electrodes are formed are adhered with a predetermined gap through a seal, wherein the inner shape and the outer shape of the seal are substantially circular. Liquid crystal optical element. 14. The liquid crystal optical element according to claim 1, wherein at least one of the electrodes of the substrate is a single electrode. 15. The liquid crystal optical element according to claim 1, wherein at least one of the electrodes of the substrate is divided into a plurality of electrodes. 16. The liquid crystal optical element according to claim 1, wherein both the electrodes of the substrate are divided into a plurality of electrodes. 17. The liquid crystal optical element according to claim 1, wherein the seal has at least a circular bead-shaped spacer inside. 18. An optical pickup device using the liquid crystal optical element according to claim 1. Description: 19. The optical pickup device according to claim 18, wherein an optically effective irradiation area of the liquid crystal optical element is set inside the seal or the sub-support portion.