JP2534994B2 - Polymer optical waveguide and method for manufacturing the same - Google Patents

Description

The present invention relates to a method for producing a polymer optical waveguide, and more particularly to branching of large-diameter optical fibers such as plastic optical fibers.
The present invention relates to a method for producing a polymer optical waveguide which is suitable for use in bonding and for forming a fine pattern.

[Conventional technology]

Optical waveguides are extremely useful for easily branching / coupling optical fibers. Among them, polymer optical waveguides are expected to be versatile in terms of good workability and easy handling. However, these polymer optical waveguides are mainly manufactured by irradiation with light such as ultraviolet rays in order to form a fine pattern. In this case, the diameter of the waveguide is limited to several hundreds μm at the maximum, and therefore it is only used for branching and coupling of the glass optical fiber. On the other hand, as an optical waveguide for a plastic optical fiber, the simplest method is to make a waveguide core from a plastic material having a high refractive index and then embed it in a low refractive index material. However, although it is possible to form a waveguide diameter up to several millimeters by this method, it is extremely difficult to form a fine pattern due to deformation and contraction during molding.
In order to solve this problem, a mask having a fine pattern is formed on a transparent gel substrate, and a high or low refractive index monomer is diffused in and out to form an optical waveguide having a refractive index distribution. It is being manufactured. In order to maintain a fine pattern in forming the refractive index distribution, the adhesiveness between the mask and the gel substrate is particularly problematic, and a method for improving this point is disclosed in JP-A-59-69706 and JP-A-59-69706. 204803
Has been proposed in the issue.

[Problems to be solved by the invention]

In the above-mentioned conventional technique, a hardened portion and an uncured portion are formed in the surface area of the gel substrate as a waveguide pattern, or a protruding portion or a sharp dent portion integrated with the substrate is provided. In order to form a refractive index distribution by removing or impregnating a monomer having a refractive index different from that of the gel substrate from only one direction of the substrate as shown in FIG. 4 (b), FIG. As described above, there is a problem that the substrate is easily deformed and it is difficult to form a fine pattern. Furthermore, the dimensions of the waveguide pattern formed by the hardened portion and the uncured portion formed on the surface of the substrate or the dimensions of the waveguide pattern formed by the protrusions and depressions integrated with the substrate are the dimensions of the waveguide portion actually formed in the substrate. There is also a problem that it is difficult to control the manufacturing process of the waveguide.

It is an object of the present invention to provide a method for producing a polymer optical waveguide, which can easily form a waveguide diameter up to several mm while maintaining a fine pattern required for the optical waveguide.

[Means for solving problems]

The method for producing a polymer optical waveguide according to the present invention comprises (a) a transparent gel obtained by partially polymerizing _one or more monomers M ₁ which form a polymer P ₁ having a refractive index of N _1. Forming a synthetic resin substrate having a shape of (b), (b) creating a portion where the polymerization reaction has been selectively advanced on the surface and inside of the transparent gel substrate by light irradiation through a mask, and selectively proceeding the polymerization reaction A step of forming an optical waveguide pattern with the above-mentioned portion, (c) one or two kinds of polymer P ₂ having a refractive index N ₂ lower than the refractive index N ₁ from both surfaces of the transparent gel substrate on which the optical waveguide pattern is formed.
A step of diffusing / permeating at least one kind of monomer M ₂ into the inside to form a concentration gradient, (d) a transparent gel substrate having the concentration gradient formed by diffusing / permeating the above-mentioned monomer M ₂ into the inside, Monomer
Or to complete the polymerization of the monomer M ₁ and M ₂ C. in M _2, or a transparent synthetic resin film or a synthetic resin plate having a low refractive index than the transparent gel substrate on both sides or around the transparent gel substrate A step of completing the polymerization of the monomers M ₁ and M _{2 while} keeping them in close contact with each other.

As the one or more monomers M ₁ for producing the transparent gel-like synthetic resin substrate in the present invention, any one can be used as long as it becomes a transparent network polymer having a high refractive index when polymerized. It is possible to use, and it is possible to use a compound having two or more double bonds in one molecule as at least one kind of monomer. Examples thereof include diallyl phthalate, diallyl isophthalate, diallyl terephthalate and other diallyl esters; vinyl ester such as divinyl phthalate, divinyl isophthalate and divinyl terephthalate. Further, a low refractive index polyfunctional monomer such as diethylene glycol bisallyl carbonate or diethylene glycol dimethacrylate may be mixed with a high refractive index monofunctional monomer such as benzyl methacrylate, phenyl methacrylate or styrene. . Further, a monomer capable of forming a network polymer by ionic crosslinking may be used. Examples of monomers capable of forming such ionic crosslinks include metal-containing transparent monomers disclosed in Japanese Patent Application No. 59-36053. In the case of forming a waveguide pattern by irradiating light among the above monomers, a metal-containing transparent monomer is particularly preferable because it can be patterned sharply in a short time.

In the present invention, the monomer M ₁ is partially polymerized to prepare a transparent gel-like substrate. The thickness of this substrate is selected depending on the shape of the waveguide to be manufactured, but if the thickness is 10 mm or more, it becomes difficult to control the impregnation process, and therefore it is preferably less than that value. This polymer is in an incompletely polymerized state,
It is a transparent gel that loses fluidity.

In the present invention, various methods are conceivable for forming the waveguide pattern to the surface and the inside of the transparent gel substrate, such as local heating with heat rays such as infrared rays and light irradiation with ultraviolet rays, electron beams, X-rays, lasers and the like. However, because of the ease of forming a fine pattern and the ease of handling, a mask is placed on the gel substrate as shown in FIG. 1 and light irradiation is performed to selectively reach the inside of the gel substrate. A method of forming a portion where the polymerization reaction has proceeded and a portion where the polymerization reaction has not proceeded is suitable. If the transparent gel substrate is thick, the transmission distance is limited by irradiation with light such as ultraviolet rays. In that case, therefore, it is also possible to apply a mask to both surfaces of the substrate and perform light irradiation from both surfaces. Also, if necessary,
Addition of not only a thermal polymerization initiator but also a photopolymerization initiator, a photosensitizer, etc. to the monomer M ₁ and / or the monomer M ₂ for more effective selective polymerization reaction. You can also

In the present invention, in order to form an optical waveguide in a transparent gel substrate, a concentration gradient is obtained by impregnating a monomer that forms a polymer with a low refractive index from at least both sides of a transparent gel substrate on which an optical waveguide pattern is formed. Is used to form a refractive index distribution. Other methods of forming the refractive index distribution include extracting and diffusing unreacted high refractive index monomer to the outside, or impregnating the gel substrate with a low refractive index monomer in advance. , There is a method of removing some to the outside,
In this case, if the substrate becomes thick, the removal of the monomer in the central portion becomes uncontrollable, and it becomes difficult to form a desired refractive index distribution. Therefore, in the present invention, the method of impregnating the low refractive index monomer, which is the easiest to form the refractive index distribution, is adopted.

The low-refractive-index weight body M ₂ used here may be either a linear polymer or a reticulated polymer when polymerized, but it may be a copolymer with the monomer M ₁ . Those which polymerize to give transparent polymers are preferred. As an example,
There are ordinary acrylic acid ester, methacrylic acid ester or acrylic acid, methacrylic acid, etc.
One kind or two or more kinds are used.

In the present invention, the above-mentioned monomer M ₂ is impregnated and permeated into the gel substrate at room temperature or under heating. When the impregnation is carried out under heating, the impregnation speed becomes fast, so that the optical waveguide can be formed quickly, but the temperature is preferably 80 ° C. or lower because the gel substrate is also hardened. The refractive index distribution of the optical waveguide portion manufactured by the present invention does not need to have a perfect parabolic curve as shown in FIG. 3 (a), but as shown in FIG. 3 (b). Even a curve having a high refractive index flat portion in the central portion and a peripheral portion having a refractive index distribution can sufficiently exhibit the function.
Therefore, the impregnation condition can be appropriately selected according to the shape of the optical waveguide.

In this way, the transparent gel substrate formed with the concentration gradient of the monomer M ₂ is a low refractive index monomer for impregnation upon to complete the polymerization of the monomer M ₁ and the monomer M ₂ M _In order to prevent volatilization of ₂ and deformation of the substrate, complete the polymerization in the monomer M ₂ , or
Alternatively, a transparent synthetic resin plate or synthetic resin film having a low refractive index is adhered to both sides or the periphery of the substrate to complete the polymerization. Further, the transparent synthetic resin plate or synthetic resin film used here can also serve as a reinforcing plate for facilitating cutting and polishing of the end face of the optical waveguide. In the present invention, the synthetic resin plate or the synthetic resin film adhered to both sides or the periphery of the substrate needs to be a material having a lower refractive index than the substrate in order to reinforce the clad effect of the waveguide.

As such a resin plate or resin film, a low refractive index acrylic plate, a polydiethylene glycol bisallyl carbonate plate, a thin plate made from a polymer of fluorinated acrylic ester or methacrylic ester, a film or other low refractive index There are thin films and films made of a copolymer. There are various methods for adhering a low refractive index plastic plate or film to a substrate. For example, mechanical pressure bonding with a spring-type clip and thermal polymerization or photopolymerization of the unreacted monomer Upon polymerization, the plastic plate or film adheres to the transparent substrate. At this time, a glass plate, a metal plate or another plastic plate may be newly inserted into the upper and lower surfaces of the plastic so that pressure is evenly applied, and pressure bonding may be performed. The glass plate, metal plate or plastic plate used here can be removed after the completion of the polymerization of the monomers M ₁ and M ₂ , but it is of course possible to use them in close contact.

[Work]

In the present invention, to form an optical waveguide pattern on a transparent gel substrate not only on the surfaces of both sides of the substrate but also on the inside is to uniformly impregnate / diffuse the low refractive index monomer from both sides of the substrate to the inside. Therefore, it is possible to prevent the generation of strain and stress caused by the uneven concentration distribution on both surfaces of the substrate. As a result, the gel substrate is less likely to be deformed, and the waveguide pattern can be accurately maintained. Further, in the present invention, since the low refractive index monomer is impregnated and diffused from both sides of the transparent gel substrate, the optical waveguide portion is formed in a circular shape or a shape close to a circular shape in the substantially central portion of the transparent gel substrate. . for that reason,
In the gel substrate after impregnation / diffusion, during the process of completing the polymerization of unreacted monomers, the deformation of the substrate or the deformation of the shape of the optical waveguide part due to the difference in copolymerization reactivity ratio or polymerization shrinkage is reduced. be able to. Further, in the present invention, since the low refractive index portion corresponding to the cladding of the optical waveguide can be formed simultaneously in the vertical and horizontal directions, a post process such as forming a new cladding portion becomes unnecessary.

In the present invention, forming the waveguide pattern up to the inside of the gel substrate also has an advantage that the actually manufactured waveguide diameter can be manufactured with substantially the same size as the mask pattern diameter.

〔Example〕

 Hereinafter, the present invention will be described with reference to examples and drawings.

Example 1 The method of Example 1 is shown in FIG. Acrylic acid 0.12
18 mol, 0.0656 mol of cinnamic acid are dissolved in 70 ml of benzene,
0.0423 mol of barium hydroxide monohydrate (Ba (OH) ₂ .H ₂ O) was gradually reacted at room temperature. After adding 25 parts of vinyltoluene and 25 parts of glycidyl methacrylate so that the composition becomes 50 parts by weight (hereinafter abbreviated as "parts"), water and benzene, which are reaction by-products, are distilled off under reduced pressure to obtain a metal-containing transparent single amount. Got the body 0.2 parts of dimyristyl peroxydicarbonate and 0.5 parts of benzoin ethyl ether were dissolved in 100 parts of this monomer, and the mixture was poured into a glass plate which was released from the silicon, and the temperature was kept at 60 ° C.
It was left for a period of time to prepare a 40 × 20 × 2 mm transparent gel substrate.
On top of this gel substrate, leaving two 1 mm wide and 40 mm long parts on the glass substrate, put the mask shown in Fig. 1 with chrome vapor-deposited on all the latter parts, and use a high pressure mercury lamp for 3 minutes to UV light. It was exposed. It was possible to visually determine that the UV-irradiated portion was polymerized to the inside of the gel substrate. Then, the transparent substrate was immersed in a solution of 75 parts of glycidyl methacrylate containing 25 parts of dimyristyl peroxydicarbonate and 25 parts of acrylic acid, and allowed to stand at room temperature for 2 hours. Then, the transparent substrate was taken out and the thickness was 2 mm. 2 sheets of polydiethylene glycol bisallyl carbonate (1), and a glass plate having a thickness of 2 mm on the outer side of the sheet was fixed by pressure with a spring type clip. Then, this substrate was heat-cured at 70 ° C. for 3 hours and at 80 ° C. for 3 hours, and then the glass plate was removed to obtain a transparent plate having a sandwich structure ((e) in FIG. 1).

When the end face of the obtained transparent plate was cut and polished, it was found that two transparent optical waveguides having a diameter of about 1 mm were present in the central portion of the transparent substrate depending on the portion irradiated with ultraviolet rays.
This cross section was cut into a thickness of 1 mm, and the maximum refractive index difference was measured with an interference microscope (Zeiss Interfaco), and it was 0.023. Further, the refractive index distribution of the waveguide had almost the same curve as in (a) of FIG. Further, the optical loss of this optical waveguide was 0.2 dB / cm with He-Ne laser light.
From the above, it can be seen that this transparent plate forms an optical waveguide as shown in FIG.

Example 2 The method of this Example 2 is the same as the method shown in FIG. 0.1218 mol of acrylic acid and 0.0656 mol of cinnamic acid were dissolved in 70 ml of benzene, and barium hydroxide monohydrate (Ba (OH)
₍₂ · H ₂ O) 0.0423 mol was gradually reacted at room temperature. After adding 25 parts of chlorostyrene and 25 parts of glycidyl methacrylate so that the composition would be 50 parts, water and benzene were distilled off under reduced pressure to obtain a metal-containing transparent monomer. This monomer 100
0.2 part of dimyristyl peroxydicarbonate, 0.5 part of benzoin ethyl ether and 0.1 part of n-dodecyl mercaptan were dissolved in 40 parts of the solution, and 40 × 2 was prepared in the same manner as in Example 1.
A 0 × 2 mm transparent gel substrate was prepared. A glass mask similar to that of Example 1 was placed on this gel substrate, and UV exposure was performed for 5 minutes using a high pressure mercury lamp. In this substrate, it was confirmed that the UV-irradiated portion was polymerized to the inside according to the pattern. Then, the transparent substrate was immersed in a solution of 42 parts of glycidyl methacrylate containing 0.2 part of dimyristyl peroxydicarbonate, 16 parts of acrylic acid, and 42 parts of trifluoroethylmethacrylate, and allowed to stand at room temperature for 5 hours, and then transparent. Take out the substrate, 2mm thick polymethylmethacrylate plate and 3m thick outside
It was crimped and fixed by a spring type clip through a glass plate of m.
Then, after heat-curing this substrate at 70 ° C. for 3 hours and 80 ° C. for 3 hours, the glass plate was removed to obtain a sandwich structure plate.

The end faces were cut and polished in the same manner as in Example 1, and the maximum refractive index difference and the optical loss were obtained. About 1 mm in the center of the obtained transparent plate
There are two nearly circular optical waveguides, and the maximum refractive index difference is
It was 0.047. The refractive index distribution of the waveguide showed the same curve as in (b) of FIG. Furthermore, the optical loss of this optical waveguide was 0.34 dB / cm with He-Ne laser light. Example 3 The method of this Example 3 is shown in FIG. A glass mask as shown in FIG. 2 (a) was placed on the transparent gel substrate obtained in Example 1, and UV exposure was performed for 3 minutes using a high pressure mercury lamp. The glass mask used here is one in which two portions having a width of 1 mm and a length of 40 mm and a peripheral portion width of 1 mm are left on the glass substrate, and the remaining portions are all chromium-deposited.

Then, the transparent substrate was immersed in a solution of 40 parts of glycidyl methacrylate containing 0.3 part of dimyristyl peroxydicarbonate, 5 parts of acrylic acid, and 55 parts of 2-hydroxyethyl methacrylate, and allowed to stand at room temperature for 2 hours. It was left as it was at 60 ° C. for 3 hours and at 80 ° C. for 2 hours. Since the gel substrate was completely cured together with the low refractive index monomer, the end face portion of the optical waveguide was cut out and polished, and two approximately circular circles with a diameter of about 1 mm were formed in the center of the transparent substrate. It was found that the above optical waveguide exists ((d) in FIG. 2). The maximum refractive index of this optical waveguide was 0.021, and the optical loss was 0.31 dB / cm with He-Ne laser light.

Example 4 The method of this Example 4 is the same as the method shown in FIG. Dissolve 3 parts of lauroyl peroxide and 1 part of benzoin ethyl ether in 100 parts of diallyl isophthalate, pour into a glass plate released from silicon and leave at 70 ° C for 5 hours to give a transparent gel substrate of 40 x 20 x 2 mm. It was made. A glass mask similar to that used in Example 3 was placed on the gel substrate, and UV exposure was performed for 30 minutes using a high pressure mercury lamp. Then, the transparent substrate is immersed in trifluoroethyl methacrylate containing 2 parts of lauroyl peroxide,
After leaving it at 3 ° C for 3 hours, it was left as it was at 70 ° C for 6 hours and 90 ° C for 2 hours. The diallyl isophthalate gel substrate was completely cured together with trifluoroethyl methacrylate, so cut out the end face of the optical waveguide,
After polishing, the center of the transparent substrate had a diameter of 2
It was found that there is a book optical waveguide. However, the cross section of this optical waveguide showed an inverted triangular shape rather than a circular shape. This cross section was cut into a thickness of 1 mm, and the maximum refractive index difference was measured and found to be 0.051. Furthermore, the optical loss of this optical waveguide was 1.2 dB / cm with He-Ne laser light.

〔The invention's effect〕

According to the present invention, it is possible to obtain a polymer optical waveguide in which a waveguide diameter can be easily formed up to several mm while maintaining a fine pattern for the optical waveguide. Therefore, a large-diameter optical fiber such as a plastic optical fiber can be branched and coupled more easily, and thus is extremely useful as an optical component in the field of optical communication and optical information processing.

[Brief description of drawings]

1 and 2 are cross-sectional views showing an example of a polymer optical waveguide manufactured by the present invention and a manufacturing method, and FIG. 3 is a refractive index distribution of a polymer optical waveguide manufactured by the present invention. And FIG. 4 is a cross-sectional view showing a conventional method. 1 ... Transparent gel substrate, 2 ... Mask, 3 ... Selective polymerized portion, 4 ... Low refractive index monomer for impregnation, 5 ... Low refractive index transparent plastic plate, 6 ... Glass Plate, 7 ... Optical waveguide part, 8 ... Transparent polymer with low refractive index.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiaki Okabe 4026 Kujimachi, Hitachi City Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Kiyoyoshi Tanno 4026 Kujicho, Hitachi Hitachi Ltd. Hitachi Research Co., Ltd. In-house (72) Hiroshi Terao 4026 Kujimachi, Hitachi City Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Noriaki Takeya 4026 Kujimachi, Hitachi City Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Masato Shimura 4026, Kujimachi, Hitachi, Ltd., Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Hideki Asano 4026, Kujimachi, Hitachi, Ltd., Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor, Tomiya Abe, Kuji, Hitachi 4026, Machi, Hitachi, Ltd., Hitachi Research Laboratory (56) References JP-A-50-151164 (JP, A) JP-A-59-59421 (J , A) JP Akira 60-208701 (JP, A) JP Akira 59-71830 (JP, A)

Claims (2)

(57) [Claims] _{1. A method} for producing a polymer P ₁ having a refractive index of N ₁ (a) 1
A step of partially polymerizing _one or more kinds of monomers M ₁ to form a transparent gel-like synthetic resin substrate, and (b) irradiating light through a mask onto the surface and inside of the transparent gel substrate. A step of forming a portion where a polymerization reaction is selectively advanced and forming an optical waveguide pattern by the portion where the polymerization reaction is selectively advanced, (c) refraction from both sides of the transparent gel substrate on which the optical waveguide pattern is formed, Polymer P _{2 with} refractive index N ₂ lower than index N ₁
That diffuses one or more monomers M ₂ that generate
Permeating to form a concentration gradient, (d) the monomer
The transparent gel substrate provided with the concentration gradient of M ₂ is diffused and permeated into the inside, or to complete the polymerization of the monomer M ₁ and M ₂ in the monomer M _2, or than the transparent gel substrate Also comprises a step of completing the polymerization of the monomers M ₁ and M _{2 while} keeping a transparent synthetic resin film or synthetic resin plate having a low refractive index in close contact with both sides or the periphery of the transparent gel substrate. Polymer optical waveguide manufacturing method. 2. The method for producing a polymer optical waveguide according to claim 1, wherein the transparent synthetic resin serving as the substrate contains metal ions.