JP2003084132A - Polarization separation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization separation device in which the degree of parallelness between transparent substrates is highly maintained, the adhesion strength is enhanced and peeling is hardly caused. SOLUTION: The polarization separation device 1 has a birefringent grating layer which consists of: layers of a birefringent film 3 having a grating 8 with a periodical rugged pattern formed; and an overcoat layer 4 formed by applying an isotropic material on the grating of the periodical rugged pattern to fill the pattern and on the whole surface of the birefringent film 3 and which is interposed between transparent substrates (2, 6). The device 1 has a space 7 to be filled with an adhesive and formed by removing a part of the birefringent film 3, and the space 7 is filled with an adhesive. The thickness of the overcoat layer 7 from the face in contact with the upper face of the projections of the grating with the periodical rugged pattern of the birefringent film 3 to the face in contact with the transparent substrate 7 in the opposing side to the upper faces of the projections is <=10 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization separation element, and more particularly to a polarization separation element having a birefringence diffraction grating layer.

[0002]

2. Description of the Related Art In recent years, various types of polarizing elements having different diffraction efficiencies depending on the polarization direction have been proposed. Among them, a birefringent diffraction element is used as a thin polarization separating element for pickups for the purpose of downsizing pickups for optical discs. Several grating type polarization separation elements have been proposed.

For example, as a conventional example, in Japanese Patent Laid-Open No. 63-314502, there is an example in which lithium niobate (LiNbO3) which is a birefringent optical crystal material is used as a substrate. According to this, lithium niobate, which is a birefringent optical crystal material, is used as a substrate, proton exchange is performed on this substrate in a periodic pattern, and a dielectric film is loaded on this proton exchange region. In this proton exchange region, the refractive index increases for extraordinary rays and decreases for ordinary rays. Therefore, by canceling the phase difference of the ordinary ray in the proton exchange region with the dielectric film, it is possible to realize a polarizer in which the ordinary ray travels straight and only the extraordinary ray is diffracted. This birefringent diffraction grating type polarizer can be miniaturized and mass-produced and a high degree of polarization separation can be obtained, but there is a problem that it takes time to manufacture. That is, since it was necessary to perform periodic proton exchange with respect to the crystal, it took several hours just to exchange the proton. Further, there are drawbacks such that it takes time to manufacture and the manufacturing cost becomes high because an optical crystal is used for the substrate.

In consideration of this point, in Japanese Patent Laid-Open No. 10-302291 and Japanese Patent Laid-Open No. 2000-75130, as a polarization separating element which can be manufactured at a low cost by a simple process, a compound having a periodic concave-convex grating on a transparent substrate is disclosed. A birefringence diffraction grating type polarization separation element having a structure in which a refraction film and an isotropic overcoat layer are coated or loaded on the refraction film has been proposed. Among them, the one using a polymer birefringent film as a birefringent material has a relatively low material cost, so that mass production is relatively easy.

Further, as shown in the schematic cross-sectional view of the conventional example of FIG. 5, as a structure aiming at improving the flatness of both surfaces of the polarization separation element and the strength of the element in order to obtain better optical characteristics, as shown in FIG. A birefringent film 3 having a periodic concavo-convex lattice formed on a transparent substrate 2 made of plastic or the like is adhered by an adhesive layer 5, and the birefringent film 3 is an isotropic overcoat layer 4
There is proposed a polarization separation element 10 which is covered with the overcoat layer 4 and is bonded to the transparent substrate 2 also as an adhesive layer. The optical element having such a structure has strength as an optical element and has high productivity.

[0006]

However, the polarization splitting element 10 having the above-described structure has two transparent substrates 2.
It was found that peeling was likely to occur at the end of No. 6, and the storage stability (durability) was not sufficient. One of the reasons for the peeling problem is considered to be that internal stress occurs due to environmental changes such as temperature changes because the birefringent film 3 and the transparent substrates 2 and 6 have different contraction rates and thermal expansion rates. To be As a result, peeling occurred from the end portion of the element 10. In general, internal stress is likely to occur on the joint surface of different materials, and warping and accompanying peeling of the adhesive surface are likely to occur. Further, the internal stress easily causes peeling when an impact is applied, and problems such as weak impact resistance have not been solved.

As a countermeasure against this peeling, there has been considered a method of increasing the adhesive strength by increasing the thickness of the overcoat layer 4 and / or the adhesive layer 5 which also serves as an adhesive layer. However, if you simply thicken the adhesive layer or overcoat layer,
Since the influence of the shrinkage of the adhesive itself that occurs during curing of the adhesive becomes large, it becomes very difficult to make the layer thickness uniform, and the parallelism between the transparent substrates cannot be maintained, and the optics of the polarization separation element cannot be maintained. This causes deterioration of characteristics (especially wavefront aberration). Also,
Increasing the thickness of the entire device goes against the original purpose of making the device smaller and thinner. Further, in that case, a large amount of the adhesive to be used is required, which causes a problem that productivity is deteriorated. There is a need for a polarization beam splitting element having a structure in which the overcoat layer 4 is thinned so that the parallelism between transparent substrates can be made good and easy, the adhesive force is enhanced, and peeling does not occur.

[0008]

According to a first aspect of the present invention, a birefringent film having a periodic concavo-convex grating is formed, and an isotropic material is filled and coated on the entire surface of the periodic concavo-convex grating and the birefringent film. In a polarization separation element in which a transparent substrate sandwiches a birefringent diffraction grating layer formed by laminating an overcoat layer
An adhesive filling space formed by removing a part of the birefringent film is provided, and the space is filled with an adhesive, and contacts the upper surface of the convex portion of the periodic concave-convex grating of the birefringent film in the overcoat layer. The polarization separation element is characterized in that the thickness of the surface and the surface of the transparent substrate facing the upper surface of the convex portion in contact with the facing surface is 10 μm or less.

As described above, by providing the adhesive between the transparent substrates sandwiching the adhesive filling space for strengthening the adhesion, it is possible to suppress the occurrence of peeling in the polarization separation element, and at the same time. The thickness (hereinafter referred to as the film thickness of the overcoat layer. The dimension A in FIG. 1) can be set to 10 μm or less, which is thinner than usual, and as a result, the upper and lower transparent substrates are kept in good parallelism. It is possible to provide a good polarization separation element that can be easily controlled, is lighter, smaller, and has high reliability.

According to a second aspect of the invention, the adhesive filling space is
The polarization splitting element according to claim 1, wherein the transparent substrate is provided by being deformed. The adhesiveness can be further enhanced by scraping the transparent substrate. Claim 3
The invention of (1) is the polarization beam splitting element according to claim 1 or 2, wherein the overcoat layer is selected from acrylic and epoxy materials.

The invention of claim 4 is characterized in that the birefringent film on which the periodic concavo-convex grating is formed is a polymer birefringent film. It is an element. The invention of claim 5 is characterized in that the birefringent film on which the periodic concavo-convex grating is formed is a polymer birefringent film in which molecular chains are oriented. It is a polarization separation element. The invention of claim 6 is the polarization beam splitting element according to any one of claims 1 to 5, wherein the polymer birefringent film has the molecular chains oriented by stretching.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As one embodiment of the polarization beam splitting element 1 of the present invention, as shown in the sectional view of FIG. 1, a birefringent film in which a periodic concave-convex grating is formed on a transparent substrate 2. Three
Are adhered by the adhesive layer 5, the birefringent film 3 and the adhesive layer 5 are partially removed, and a portion (adhesion strengthening portion 7) intended to strengthen the adhesive force is provided.

No birefringent film is present in the adhesive strength portion 7,
By providing the adhesive filling space between the upper and lower transparent substrates, the capacity of the adhesive layer substantially existing between the upper and lower transparent substrates (2, 7) can be increased, and the adhesive strength is improved.
With such a structure, the thickness of the overcoat layer (adhesive layer) (2, 6) between the transparent substrate and the birefringent film surface 3 on which the periodic concave-convex lattice is formed without peeling ( It is possible to reduce the dimension A) in FIG.
By reducing the film thickness A in this way, it becomes easy to maintain good parallelism between the upper and lower transparent substrates, and the productivity can be improved.

Here, it is possible to use the same material as the above-mentioned overcoat layer as the adhesive. Thereby, the manufacturing process can be simplified. However, it is possible to use different materials for the adhesive and the overcoat layer. The part for strengthening the above-mentioned adhesion (adhesion strengthening part 7)
In addition to the shape as shown in FIG. 1, the transparent substrate may be shaved as shown in FIGS. 2 and 3 to be deformed. In that case, the adhesive area is increased, so that the adhesive force is further enhanced. Further, by similarly roughening the surface of the adhesion-strengthening portion, the adhesion strength can be similarly enhanced.

The material used for the overcoat layer of the polarization beam splitting element 1 is preferably acryl or epoxy based from the viewpoint of easy control of properties such as viscosity and refractive index, adhesive strength and transparency. Further, in consideration of the shrinkage ratio after curing, an epoxy resin having a low shrinkage ratio is generally more preferable.

Birefringent film 3 used in the polarization splitting element 1
Is a large area and can be mass-produced at low cost,
Polycarbonate (PC), Polyvinyl alcohol (PVA),
A polymer birefringent film made of polymethyl methacrylate (PMMA), polystyrene, polysulfone (PSF), polyether sulfone (PES), polyimide or the like is preferable. Above all, a polymer film in which molecular chains are oriented is preferable, and a stretched organic polymer film is particularly preferable in view of productivity.

[0017]

EXAMPLES Hereinafter, the present invention will be specifically described by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 A polymer birefringent film 3 having a thickness of 100 μm was attached to a transparent substrate 2 having a thickness of 500 μm with an adhesive layer 5 having a thickness of 20 μm using an ultraviolet curable adhesive, and under reduced pressure. After integrating them with each other, irradiate them with ultraviolet rays and
Baking for 0 minutes to completely cure the adhesive layer
(Fig. 4 (a)). After that, a periodic pattern made of metal (□ 3.0 × 3.0 mm / 3.0 μm pitch) is formed on the polymer birefringent film, dry etching is performed using this periodic pattern made of metal as an etching mask, and the metal mask is removed. Then, a periodic concavo-convex grid pattern was formed on the polymer birefringent film (Fig. 4 (b)). Next, the polymer birefringent film and the adhesive layer on the outer periphery of the periodic concavo-convex grating 8 were physically removed by means of a dicing device or the like to create a portion to be an adhesion strengthening portion (Fig. 4 (c)). . Further, an epoxy-based UV-curing resin to be an overcoat layer is bottled on the side of the polymer birefringent film on which the periodic concavo-convex grating 8 is formed, and a transparent substrate having a thickness of 500 μm is placed thereon and pressed to form a concavo-convex grating The inside and the adhesion-strengthened part were filled with an overcoating agent (Fig. 5-d). At this time, the thickness of the overcoat layer is set to 10 μm or less. Then, after irradiating with ultraviolet rays, baking was performed at 100 ° C. for 10 minutes to completely cure, and then cut into □ 5.0 × 5.0 mm by a dicing device to fabricate a polarization separation element having a configuration as shown in FIG. 1 ( Figure 4 (e) and (f)). In this example, the film thickness of the overcoat layer (thickness of the surface of the overcoat layer in contact with the upper surface of the convex portion of the periodic concavo-convex grid and the surface of the opposing transparent substrate in contact with the opposite surface) is 1
It was ~ 3 μm.

(Example 2) A polarization beam splitting element having a structure as shown in FIG. 1 was manufactured by the same manufacturing method as in Example 1 except that an acrylic ultraviolet curing resin was used for the overcoat layer.

(Comparative Example 1) A polarization beam splitting element having a structure as shown in FIG. 5 was manufactured by the same manufacturing method as in Example 1 except that a portion to be an adhesion strengthening portion was not formed.

(Comparative Example 2) A polarization beam splitting element having a structure as shown in FIG. 5 was manufactured by the same manufacturing method as in Example 2 except that the portion to be the adhesion strengthening portion was not formed.

Regarding the above examples and comparative examples, □ 5.
The presence or absence of peeling of the transparent substrate generated during 0 × 5.0 mm dicing was compared. In addition, the appearance was evaluated after fabrication at □ 5.0 x 5.0 mm and after a reliability test (holding at 70 ° C and 95% RH for 200 hours). The thing was marked as ○. Table 1 shows the evaluation results
It was shown to.

[0023]

[Table 1]

[0024]

As described above, the polarized light separating element of the present invention has a portion (adhesion strengthening portion) for the purpose of strengthening the adhesive force of the transparent substrate. It becomes possible to fabricate elements,
Moreover, since the thickness of the overcoat layer between the birefringent film surface on which the periodic concavo-convex grating is formed and the transparent substrate can be configured to be 10 μm or less, the parallelism of the upper and lower transparent substrates can be easily controlled. Thus, it is possible to provide a highly reliable polarization separation element.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a polarization beam splitting element according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of Example 1 of the polarization beam splitting element according to the present invention.

FIG. 3 is a schematic cross-sectional view of a second embodiment of the polarization beam splitting element according to the present invention.

FIG. 4 is a schematic process drawing showing a method for manufacturing a polarization beam splitting element according to the present invention.

FIG. 5 is a schematic cross-sectional view of a polarization separation element according to a conventional example.

[Explanation of symbols]

10 Polarization separation element 2, 6 transparent substrate 3 Birefringent film 4 Overcoat layer 5 Adhesive layer 7 Adhesion strengthening part 8 Periodic uneven grid

Claims (6)

[Claims] 1. A birefringent film formed by laminating a birefringent film having a periodic concavo-convex grating formed thereon, and an overcoat layer obtained by filling and coating an isotropic material on the entire surface of the periodic concavo-convex grating and the birefringent film. In a polarization separation element in which a transparent substrate sandwiches a refraction diffraction grating layer, an adhesive-filled space formed by removing a part of the birefringent film is provided, and the space is filled with an adhesive, and the overcoat layer. The thickness of the surface of the birefringent film in contact with the upper surface of the convex portion of the periodic concavo-convex grating and the surface of the transparent substrate on the side facing the upper surface of the convex portion in contact with the facing surface are 10 μm or less. And a polarization separation element. 2. The polarization beam splitting element according to claim 1, wherein the space filled with the adhesive material is provided by deforming the transparent substrate. 3. The polarization beam splitting element according to claim 1, wherein the overcoat layer is selected from acrylic and epoxy materials. 4. The birefringent film on which the periodic concavo-convex grating is formed is a polymer birefringent film.
4. The polarized light separating element according to any one of 1 to 3. 5. The polarization splitting device according to claim 1, wherein the birefringent film on which the periodic concavo-convex grating is formed is a polymer birefringent film in which molecular chains are oriented. element. 6. The polarization separation element according to claim 1, wherein the polymer birefringent film has a molecular chain oriented by stretching.