JPH0455282Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical diffraction grating, and more particularly to an improvement in an optical diffraction grating that can be molded with high precision using synthetic resin.

[Conventional technology]

Generally, an optical diffraction grating is made up of a large number of fine optical diffraction grooves formed in parallel on one side of a flat glass or plastic substrate. Used to detect tracking error signals.

Conventionally, this optical diffraction grating has been manufactured by the method shown in FIGS. 13A to 13D.

That is, an organic material is uniformly applied to one side of a substrate 1 such as plastic to a thickness of about 1 μm and solidified to form an organic material layer 3 (FIG. 13A), and a resist is used to form a predetermined fine pattern on this organic material layer 3. A grid pattern 5 is formed by baking (FIG. 13B), and the part of the organic layer 3 where the grid pattern 5 is not formed is dissolved and removed using a solvent that does not dissolve the resist, and the grid pattern 5 is also removed. (1st
3C), an optical diffraction grating E having grating grooves 7 as shown in FIG. 13D was formed by leaving a portion of the organic layer 3 corresponding to the grating pattern 5.

As shown in FIG. 14, this optical diffraction grating E is supported inside a ring-shaped housing 9 and manufactured as a product.

[The problem that the idea attempts to solve]

As described above, the method of forming the lattice pattern 5 on the substrate 1 through the organic material layer 3 and partially dissolving and removing the organic material layer 3 with a solvent requires manufacturing time and makes it difficult to simplify the manufacturing equipment. However, the cost tends to be high, and there is a limit to the miniaturization of the product.

On the other hand, if the optical diffraction grating E can be manufactured by injection molding from a synthetic resin, the manufacturing process will be simplified and costs can be significantly reduced, and the manufacturing equipment will also be simplified.

However, the optical grating E has a depth of 0.3 μm and a width of 20 μm.
It is necessary to form the lattice grooves 7 with an accuracy of ±0.1 μm, but when injection molding is performed using molten resin, the molten resin tends to solidify with a certain molecular orientation.

As a result, molecular orientation distortion occurs during solidification, which tends to cause twisting and distortion in the optical diffraction grating, and it also becomes susceptible to the effects of external heat and humidity, reducing dimensional accuracy. It has been difficult to form an optical diffraction grating.

The present invention was developed under these circumstances, and it is easy to form highly accurate grating grooves even by injection molding with synthetic resin, and it is possible to create an optical diffraction grating made of synthetic resin with practical precision. This is what we provide.

[Means to solve the problem]

In order to achieve this purpose, the present invention includes a main body of an optical diffraction grating having a large number of optical diffraction grooves.
A thicker flange is integrally injection molded with the optical diffraction grating body from transparent synthetic resin.

[Effect]

In the present invention equipped with such a means, if the molten synthetic resin is injected into the mold using the flange part as an injection gate and injection molding is performed, the molten synthetic resin flows into the flange part and then into the optical diffraction grating main body part. Molded synthetic resin tends to become non-oriented in the optical diffraction grating body.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are a sectional view and a plan view showing an embodiment of an optical diffraction grating according to the present invention.

In both figures, the thickness of approximately 1.0 mm is made of transparent synthetic resin, e.g. polymethyl methacrylate (PMMA).
On one side of the disc-shaped optical diffraction grating main body 11, there is a grating groove 13 having a concave cross section with a depth of 0.3 μm and a width of about 20 μm.
are formed in large numbers in parallel.

Around the optical diffraction grating body 11, a flange 15 approximately twice the thickness of the optical diffraction grating body 11 is integrally molded in a ring shape from the same material as the optical diffraction grating body 11 by injection molding. E is formed.

In addition to polymethyl methacrylate (PMMA), transparent synthetic resins include thermoplastic polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), and thermosetting polydiethylene glycol bisallyl carbonate (CR- 39)
etc. can be used. However, polymethyl methacrylate (PMMA) is preferred from the viewpoints of transparency, lightness, ease of processing, impact resistance, etc.

In such an optical diffraction grating E, the flange 15 around the optical grating body 11 is connected to the optical grating body 11.
Since it is thicker, when manufacturing it by injection molding with a mold, the molten synthetic resin flows into the flange part and then the optical diffraction grating body 11 is molded.
In the optical diffraction grating body 11, the dissolved synthetic resin tends to become non-oriented. These relationships will become clearer through the manufacturing method described below.

Although the external shape of the optical diffraction grating body 11 of the present invention described above is circular, the shape of the optical diffraction grating body 11 is not limited to this, and can be arbitrarily selected such as a rectangle. The shape of the integrally formed flange 15 is also not limited to the ring shape as shown in FIG.

For example, as shown in FIG. 3, an oval-shaped flange 17 having a larger diameter than the optical diffraction grating body 11 may be used.
Flange 15,1 thicker than optical diffraction grating body 11
7 may be integrally provided around the optical diffraction grating body 11.

Next, an example of a method for manufacturing such an optical diffraction grating will be described.

First, as shown in Figure 4, iron alloy, copper alloy,
A processed layer 21 of, for example, nickel or aluminum is formed on one surface (upper surface in FIG. 4) of a disk-shaped core substrate 19 made of a metal compound such as an aluminum alloy.
Form uniformly with a thickness of 10 μm or more using vapor deposition or electroless plating.

Next, a lattice groove 13 is formed in the processed layer 21 with a depth of 0.3 μm and a width using a cutting tool 23 such as a diamond cutter.
Core 2 is formed by forming many in parallel with a pitch of 20μm and a pitch of 20μm.
5 (Figures 5 and 6).

This core 25 contributes to the shaping of the optical diffraction grating body 11 of the optical diffraction grating E, and the dimensions, formation pitch, etc. of the grating grooves 13 are arbitrarily selected depending on the application.

Then, as shown in FIG. 7, the core 25 is placed at the tip of a cylindrical core support 31 that stands up from the movable platen 29 of the injection molding machine 27, and the fixed platen is placed opposite the movable platen 29. 33
Another column 37 is placed at the tip of the cylindrical core support 35 which is erected from the top.

Note that the core 37 has a disk shape with the same diameter as the core 25, and is made of, for example, nickel or aluminum.

Each core support 31, 35 is surrounded by a longer mold base 39, 41, and the core 2
5 and 37 are surrounded by mold bases 39 and 41 and fixed within the recess.

Furthermore, each mold base 39, 41 has a space around the core 25, 37, and when the tips of these mold bases 39, 41 come into contact, a ring-shaped space is formed around the core 25, 37. A void 43 is formed. Further, a gap is also formed between the cores 25 and 37. In addition, the seventh
Reference numeral 45 in the figure is an injection gate through which molten resin is injected.

Then, the movable side platen 29 of these injection molding machines 27 is brought close to the fixed side platen 33, and the tips of these mold bases 39, 41 are brought into contact with each other, for example.
The optical diffraction grating E is manufactured by injecting molten synthetic resin at a temperature of about 220° C. at a predetermined pressure through the injection gate 45 and solidifying it.

Generally, when molten synthetic resin is injected into an injection mold, the molten synthetic resin is swept away from the injection gate 45 through the cavity 47 of the mold, as shown in FIGS. It is filled into the cavity 47 while being pushed back.

Therefore, molecular orientation is likely to occur within the cavity 47, and the shrinkage rate is different between the molecular orientation direction and the direction perpendicular to this, resulting in molecular orientation distortion and birefringence, particularly near the ends of the optical grating body 11. easy.

On the other hand, in the manufacturing method described above, the 10th
As shown in the figure and the schematic diagram of FIG. It is washed away and filled.

Therefore, within the cavity 49, molecular orientations in various directions coexist, and a non-molecular orientation state of the dissolved synthetic resin is formed, making it difficult for molecular orientation distortion to occur, and suppressing birefringence near the ends of the optical grating body 11. In addition, uniform transmission characteristics can be obtained throughout.

As described above, in the present invention, the flange 15 has an important meaning in the molecular orientation of the molten synthetic resin, but in order to make the molten synthetic resin non-molecularly oriented in the optical diffraction grating main body 11 portion, the molten synthetic resin must be placed in the mold. It is preferable that the entire circumference is filled from the portion corresponding to the flange 15 to the portion corresponding to the optical diffraction grating body 11.

Therefore, by making the flange 15 thicker than the optical diffraction grating main body 11, a non-molecular orientation state can be easily achieved, but more specifically, it is better to make the surface area of the flange 15 larger than the surface area of the optical diffraction grating main body 11.

The present inventor proposed that the flange 1 in the configuration shown in FIG.
5 is made thicker than the optical diffraction grating body 11,
When we measured the deformation of the grating grooves 13 by changing their surface area ratio, we found that the deformation was observed as shown in Fig. 12.
It has been found that in order to suppress the surface area to 0.1 μm or less, the surface area of the flange 15 should be selected to be approximately 1.5 times larger than that of the optical diffraction grating body 11.

In particular, the thickness and surface area of the flange 15 should be selected to be approximately 1.5 times or more larger than that of the optical diffraction grating body 11.

Note that the shape of the cores 25 and 37 described above is not limited to a flat plate shape, and if a curved core is used, the optical diffraction grating E including the optical diffraction grating main body 11 having a curved surface can be manufactured.

[Effect of idea]

As explained above, in the optical diffraction grating of the present invention, a thicker flange is integrally injection molded with the optical diffraction grating body using transparent synthetic resin around the periphery of the optical diffraction grating body. If it is transformed into an injection gate, the molten synthetic resin tends to become non-oriented in the optical diffraction grating body.

Therefore, twisting and distortion are less likely to occur in the optical diffraction grating body, and the flanges absorb deformation of the optical diffraction grating body due to external heat and humidity, so the molding precision of the grating grooves is greatly improved. Even when molded, practical products can be provided.

Furthermore, since it is possible to use a normal injection mold, it can be carried out with a simple manufacturing device.

Although there is currently a technology for forming optical lenses using synthetic resin, the present invention is useful in the field of optical diffraction gratings.

[Brief explanation of the drawing]

1 and 2 are a sectional view and a plan view showing one embodiment of the optical diffraction grating according to the present invention, and FIG. 3 is a plan view showing another embodiment of the optical diffraction grating according to the present invention.
Figures 4 to 7 are process diagrams showing an example of the method for manufacturing the optical diffraction grating shown in Figure 1, and Figures 8 to 11 are process diagrams showing the synthesis in the mold during the solidification process of the synthetic resin shown in Figure 7. Fig. 12 is a diagram illustrating the resin filling process, Fig. 12 is a characteristic diagram showing the relationship between the distortion of the grating grooves and the area ratio of the optical grating body to the flange in the optical diffraction grating of the present invention, and Figs. FIG. 14, which is a process diagram showing a method for manufacturing an optical diffraction grating, is a sectional view showing a conventional optical diffraction grating as a product. DESCRIPTION OF SYMBOLS 1... Substrate, 3... Organic layer, 5... Lattice pattern, 7, 13... Lattice groove, 9... Housing,
11... Optical diffraction grating body, 15, 17... Flange, 19... Core substrate, 21... Processing layer, 23...
...cutting tool, 25,37...core, 27...injection molding machine, 29,33...platen, 31,35...
... Core support, 39, 41 ... Mold base, 4
5... Injection gate, 47, 49... Cavity,
E... Optical diffraction grating.

Claims (1)

[Claims for Utility Model Registration] An optical diffraction grating comprising: an optical diffraction grating body having a large number of optical diffraction grooves; and a flange formed thicker around the optical diffraction grating body, An optical diffraction grating characterized in that the optical diffraction grating main body and the flange are integrally injection molded from a transparent synthetic resin.