JPH0287105A - Production of light guide - Google Patents

Abstract

PURPOSE:To produce the high-performance light guide at a low cost by previously forming a resin layer of a low refractive index to serve as a clad to core forming parts, subjecting a thermoplastic sheet to thermal press forming to form grooves for cores, the inside surfaces of which are enclosed by the resin layer of the low refractive indexz, and embedding a resin of a high refractive index to serve as cores into the grooves for cores. CONSTITUTION:The resin layer 2 of the low refractive index to serve as the clads is formed on the surface of the thermoplastic sheet 1. The thermoplastic sheet 1 constitutes the substrate (base material) to support the cores 6 to be formed afterward. The thermoplastic sheet 1 (composite sheet 11) is then subjected to hot press forming. The press hot press forming is executed by using metallic molds 3, 4 heated to the softening temp. of the resin of the thermoplastic sheet 1 to form the grooves 5, the inside surfaces of which are enclosed by the clad layers 2. The cores 6 are formed in the formed grooves 5 for cores. The example, a liquid curing type high refractive index resin is cast into the grooves 5 and is cured. The high-performance light guide is produced in this way at a low cost.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing an optical waveguide.

[Conventional technology]

An optical waveguide includes a core and a cladding provided outside the core, and the core is made of a material having a higher refractive index than the cladding. Thereby, the light (incident light) that has entered the core of the optical waveguide undergoes repeated total optical reflection at the interface between the core and the cladding, and is confined in the core and transmitted. The larger the difference in refractive index between the core and the cladding, the more difficult it is for light guided within the core to leak out of the core even if the light reception angle becomes large (even if the incident angle becomes small). For this reason, it is preferable that the difference in refractive index between the core and the cladding is large.

Conventionally, optical waveguides have been mainly produced by the following method (1) or (2).

■ A method in which a molded product with a groove in which the core is formed is made by injection molding, etc., this molded product is used as a cladding, and a core is formed in the groove using a resin with a higher refractive index than the cladding.

■ By curing the core part of the resin sheet impregnated with hardening material with light and volatilizing the part of the resin sheet other than the core part by vacuum evaporation, the core and the parts other than the core are cured. A method of forming an optical waveguide by creating a difference in refractive index.

In order to create a difference in refractive index between the craft and the core, it is generally necessary to use a material with a low refractive index for the land. For example, it is preferable to use a material with a refractive index of 1.48 or less. Examples of the low refractive index resin include fluororesin and silicone resin.

[Problem to be solved by the invention]

However, since fluororesins and silicone resins are difficult to mold, it is difficult to obtain grooved molded products using these resins in the method (2) above. On the other hand, polymethyl methacrylate (P), which is easier to mold than these resins,
Since MMA) has a refractive index of 1.49, there is a problem that the difference between the refractive index and the core is small, and leakage during transmission is large.

Furthermore, since method (1) above uses photolithography technology, it requires many steps and increases manufacturing costs.

Furthermore, since the difference in refractive index between the cladding and the core is the difference in refractive index between the monomer and its photocured product, which is very small, there is also the problem of large leakage during transmission.

In other words, in conventional optical waveguide manufacturing methods, if a material that passes through the substrate is selected as the cladding material, the refractive index will not be lower enough than that of the core, resulting in large propagation loss. There were problems such as lack of formability when used as a substrate, and high-performance optical waveguides could not be obtained.

Therefore, it is an object of the present invention to provide a method for producing an optical waveguide that can produce a high-performance optical waveguide at low cost.

[Means to solve the problem]

In order to solve the above problems, the method for manufacturing an optical waveguide according to the present invention includes forming a low refractive index resin layer that will become a cladding on at least the core forming portion of the surface of a thermoplastic resin sheet that will be a substrate, and A thermoplastic resin sheet is hot press-molded to form a core groove whose inner surface is surrounded by the low refractive index resin layer, and a high refractive index resin serving as the core is embedded in the core groove. do.

[For production]

The method for manufacturing an optical waveguide according to the present invention is such that the substrate that supports the core and the cladding are made of different resins, so that the substrate has physical properties that pass through the substrate, such as mechanical strength and heat and moisture resistance. It is possible to use a material having physical properties suitable for the cladding, such as a material having a low refractive index, for the cladding. Therefore, it is possible to create a high-performance optical waveguide with low propagation loss.

Moreover, in this invention, the groove for the core is created using hot press molding, so it is possible to use injection molding to create a grooved substrate and form the core in the groove to obtain an optical waveguide, or photolithography to expose the groove. The cost is lower than the method of creating an optical waveguide by developing and then vacuum-evaporating the uncured monomer.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings showing embodiments thereof.

Figures 1 (a) to (lit) show an outline of one embodiment of the method for manufacturing an optical waveguide according to the present invention in the order of steps. A low refractive index resin layer (hereinafter referred to as "clad layer") 2 serving as a craft is formed on the surface of the resin sheet 1. The thermoplastic resin sheet 1 becomes a substrate (base material) that supports the core 6 that will be formed later.

Thermoplastic resin sheet I-1 on which cladding layer 2 has been formed
(Composite sheet 11) is hot press molded (Fig. 1 (C)
). The hot press molding is performed using a mold 3°4 heated to a temperature higher than the softening temperature of the resin of the thermoplastic resin sheet l, and a core groove 5 whose inner surface is surrounded by the cladding layer 2 is formed (first
Figure (C1, (d)). Mold 3 placed on the cladding layer 2 side
A convex portion 31 having a shape corresponding to the core groove 5 is formed in a portion facing the core forming portion.

A core 6 is formed in the formed core groove 5 (see FIG. 1(e)
)), for example, a method in which a liquid curable high refractive index resin is cast into the groove 5 and cured, or a method in which a thermoplastic resin is molded into :a5 is used.

It is also possible to form the core 6 and use it as the optical waveguide 7, but
In order to improve the flatness of the surface of the core 6, polishing is performed as necessary, as shown in FIG. 2(a) or (b). This polishing can be done by simply scraping off the core material that overflows from the groove 5 (Fig. 2 (a)), or by scraping away the cladding layer 2 formed on the surface side of the substrate 1 to expose the surface of the substrate 1. (Figure 2('b)). Furthermore, if necessary, a low refractive index resin layer serving as a cladding may be formed on the surface of the core by coating or the like. Also,
A protective film may be formed as necessary to prevent the core surface from being scratched. The protective film may also serve as a cladding on the core surface.

The resin layer of the thermoplastic resin sheet 1 is not particularly limited, but includes, for example, polycarbonate, polyacetal, and polyphenylene sulfide. Polyphenylene oxide (
Also called "polyphenylene ether." Below rPPOJ
So-called engineering plastics such as polyether, polysulfone, and polyethersulfone, PMMA, etc. are used, but they have a high strength, heat resistance,
The thermoplastic resin sheet 1, which is preferably made of the engineering plastic from the viewpoint of dimensional stability, may be made by a commonly used method, and the method of forming it is not particularly limited. The thickness of the thermoplastic resin sheet 1 is not particularly limited, but is preferably 0.5 mm or more. If it is thinner than 0.5 m, the strength will be weak and there is a possibility that it will not be able to support the core. Note that the thermoplastic resin sheet 1 is not limited to what is called a sheet, but also includes what is called a so-called plate.

The cladding layer 2 may be formed on the entire surface of the thermoplastic resin sheet 1, but it is sufficient if it is formed at least on a portion where a core is to be formed (a core forming portion). The resin used for the cladding layer 2 is not particularly limited as long as it has a refractive index lower than that of the core, but from a practical standpoint,
Preferably, the refractive index is 1.48 or less. refractive index is 1
．． If it is larger than 48, the refractive index difference with the core is insufficient,
Propagation loss may become large. Examples of the resin used for the cladding layer 2 include, but are not limited to, fluororesins and silicone resins. Cladding layer 2
is formed, for example, by a method of applying (coating) the resin to the thermoplastic resin sheet 1 and solidifying (including curing). The thickness of the cladding layer 2 is not particularly limited, but is between 5 and 50 mm. It is preferable to set it to m. If it is thinner than 5n, the function as a cladding is insufficient, and the propagation loss of light may become large; if it is thicker than 50 μl, hot press molding may become difficult.

The conditions for hot press molding of the composite sheet 11 are not particularly limited as long as the temperature is higher than the softening temperature of the resin of the thermoplastic resin sheet 1 and the pressure is sufficient to form the core i5.

The resin used for the core 6 includes a resin having a refractive index higher than that of the low refractive index resin of the cladding layer 2, preferably 0.05 or more, more preferably 0.10 or more. For example, epoxy resin with a refractive index of 1.55 or more, (meth)
Acrylic resin or the like is used for the core 6.

Note that this invention is not limited to the embodiments described above.
For example, at least one core may be formed in one optical waveguide.

According to this invention, strong materials with good moldability such as engineering plastics can be used for the substrate, and low refractive index resins with poor moldability (for example, fluorine resins and silicone resins) can also be coated. Because it can be easily molded, optical waveguides are much easier to fabricate than conventional methods.

More specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the specific examples below.

Example 1 - Using a polycarbonate plate with a thickness of 2 fi as the thermoplastic resin sheet 1, an optical waveguide 7 was fabricated by the method shown in FIGS. 1(a) to (81).

That is, the entire surface of the polycarbonate plate is coated with fluorine-based resin paint (trademark Lumiflon LF manufactured by Asahi Glass Co., Ltd.).
100) was applied and cured at 100° C. for 2 hours to form a cladding layer 2 with a thickness of 10 pm. Next, a mold 3 in which a convex portion 31 having a shape corresponding to the core groove 5 is formed in the core forming portion is arranged so that the convex portion 31 faces the cladding layer 2, and hot press molding is performed at 170°C. Figure 1(d)
A composite sheet 11 with grooves as shown in Fig. 1 was produced. An epoxy acrylate-based ultraviolet curable resin composition was cast into the grooves 5 of this composite sheet 11 and cured with ultraviolet rays in a nitrogen atmosphere using a SOOW ultra-high pressure mercury lamp for 10 minutes. A linear core 6 of Sa40 Dragon was formed.

The epoxy acrylate ultraviolet curable resin composition contains 60 parts by weight of an epoxy acrylate ultraviolet curable resin (trademark UE8200 manufactured by Dainippon Ink & Chemicals Co., Ltd.), 40 parts by weight of benzyl acrylate, and benzoin dimethyl ether as a photopolymerization initiator. 2M parts were mixed.

Example 2 - The same procedure as Example 1 was carried out until forming the linear core opening,
Furthermore, the surface side with the core is polished to a surface roughness of 0.1.
μm or less, and then apply the Lumiflon LF100 on top of it and dry it in the same manner as above.
It was cured to form a cladding layer and an optical waveguide was obtained.

Example 3 An optical waveguide was obtained in the same manner as in Example 1, except that polyacecool resin was used instead of polycarbonate and the temperature of hot press molding was 200°C.

Example 4 In Example 1, modified P was used instead of polycarbonate.
An optical waveguide was obtained in the same manner as in Example 1, except that PO (trademark Noryl, manufactured by GE) was used and the temperature of hot press molding was 200°C.

Example 5 The procedure was the same as in Example 1, except that a thermosetting epoxy resin composition was used instead of the epoxy acrylate-based ultraviolet curable resin composition, and the composition was cured at 130"C for 4 hours. An optical waveguide was obtained.

The thermosetting epoxy resin composition used here contained 50 parts by weight of bisphenol A epoxy resin (trademark Epicoat 828 manufactured by Yuka Shell Epoxy Co., Ltd.), 50 parts by weight of methylhexahydrophthalic anhydride as a curing agent, and diazabicycloundecene octylate (trademark Ucat S manufactured by San Abbott Co., Ltd.) as a curing accelerator.
A 102) Amounts were mixed and used.

Comparative Example: An acrylic plate with a thickness of 2 mm (
PMMA), without coating the surface with a low refractive index resin, heat press molding was performed at a temperature of 170°C to form a core groove in the same manner as in Example 1, and a core was formed in the same manner as in Example 1. , an optical waveguide was obtained.

The optical propagation loss of each of the optical waveguides of Examples and Comparative Examples was examined under the same conditions, and the results are shown in Table 1. Table 1 shows the refractive index of the core, the outline of the core material, the refractive index of the cladding, the outline of the cladding material, and
An overview of the substrate material, the thickness of the kraft, the thickness of the substrate, whether or not the core surface is polished, and the material of the surface cladding layer are also shown.

As can be seen from Table 1, in each of the optical waveguides of the Examples, a low refractive index material passed through the cladding was used for the cladding, and a material with good formability passed through the substrate was used for the substrate. , it has high performance with low propagation loss. The optical waveguide of the comparative example had a high propagation loss because a material suitable for the cladding could not be used.

〔Effect of the invention〕

Since the method for manufacturing an optical waveguide according to the present invention is as described above, a high-performance optical waveguide can be manufactured at low cost.

[Brief explanation of drawings]

FIGS. 1(a) to (el) are cross-sectional views schematically showing an example of the method for manufacturing an optical waveguide according to the present invention in the order of steps; FIG.
is a cross-sectional view of an optical waveguide obtained in another example, and FIG. 2(b) is a cross-sectional view of an optical waveguide obtained in yet another example. ■...Thermoplastic resin sheet 2...Clad rfi
5... Core groove 6... Core? , 17.27...
・Optical waveguide

Claims (1)

[Claims] 1. In a method for manufacturing an optical waveguide in which a core through which light is transmitted is embedded in a substrate, at least the core forming portion of the surface of the thermoplastic resin sheet serving as the substrate,
A low refractive index resin layer serving as a cladding is formed, and the thermoplastic resin sheet is hot press molded to form a core groove whose inner surface is surrounded by the low refractive index resin layer. A method for producing an optical waveguide characterized by embedding a high refractive index resin as a core in a groove.