JPH0259962B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for forming a light guide path in a transparent substrate made of synthetic resin, which has a refractive index larger than that of the substrate, in a cross section perpendicular to the direction in which light travels. The present invention relates to a method of manufacturing a synthetic resin optical circuit having a refractive index distribution that continuously decreases from the optical axis toward the periphery.

Optical circuits with various optical signal processing functions such as branching, merging, demultiplexing, and multiplexing are extremely useful as peripheral devices for optical communications. When manufacturing a synthetic resin optical circuit as described above, as shown in Fig. ) A transparent gel-like substrate 10 is made by partially polymerizing Ma, and a mask 12 is formed by applying photosensitive resin or the like, leaving grooves 11 that match the planar pattern of the light guide to be formed on the surface of this substrate 10. Then, through this groove 11, a monomer Mb (including a monomer mixture) to form a polymer (including a copolymer) Pb having a refractive index Nb larger than the refractive index Na is diffused and polymerized into the substrate. There is a known method of forming an elongated light guide path 13 in this way.

As another method, as shown in FIG.
4 is made, a mask 15 is applied only to the light guide path portion of this substrate surface, and the mask 15 is overlapped with the substrate 14 from the periphery.
There is also a method of creating the light guide path 16 in the substrate directly under the mask 15 by diffusing a monomer Mb that forms a polymer with a refractive index Nb smaller than that of Na.

However, in the conventional method shown in FIGS. 1 and 2 as described above, masks 12, 15 and gel substrates 10, 1 provided to prevent the diffusion of monomer Mb
Unless the adhesion with 4 is very good, monomeric Mb
This often causes the problem that it is impossible to form a light guide path with a refractive index distribution because it enters between the mask and the gel substrate and diffuses over the entire surface of the gel substrate.

The present invention solves the above-mentioned conventional problems and provides a new synthetic resin that can avoid the problem of adhesion between a mask and a gel substrate when manufacturing a synthetic resin optical circuit in which a light guide path with a refractive index distribution is formed. The purpose of this invention is to provide a method for manufacturing an optical circuit.

That is, the method for producing a synthetic resin optical circuit according to the present invention involves incompletely polymerizing one or more monomers Ma that produces a network polymer Pa having a refractive index of Na to produce a transparent gel-like polymer. One or more monomers forming a substrate and forming a polymer Pb having a refractive index Nb different from that of Na in this transparent gel substrate.
Diffuse and permeate Mb, perform a partial hardening treatment on the surface area of the transparent gel substrate, form a cured part and an uncured part in the surface area in accordance with the pattern of the light guide to be formed, and Mainly removing the uncured portion and the monomer Mb inside the transparent gel substrate corresponding to the uncured portion via the surface of the substrate on which the curing treatment has been performed;
By this, a state is formed in which the monomer Mb remains in the transparent gel substrate in the vicinity of the cured portion even with a concentration gradient that continuously changes,
In this state, the polymerization of the monomers Ma and Mb is completed. Note that the term "polymerization" as used in the present invention includes copolymerization.

As described above, in the present invention, by using the hardened portion formed on the surface of the transparent gel substrate as a so-called mask when removing monomer Mb, monomer Mb is kept in the above-mentioned state. It will remain inside the board. Since this hardened portion is integrated with the transparent gel substrate, the adhesion between the mask and the transparent gel substrate in the conventional example shown in FIGS. 1 and 2 is not a problem. Therefore, a light guide path having a desired refractive index distribution can be formed within the substrate.

In the method according to the present invention, any monomer Ma can be used as long as it forms a transparent network polymer when polymerized, and any double bond that can be cleaved into one molecule to form a crosslink can be used. One or more compounds having two or more may be used. Suitable examples include diallyl phthalate,
diallyl esters such as diallyl isophthalate, diallyl terephthalate, diethylene glycol bisallyl carbonate; triallyl esters such as triallyl trimellitate, triallyl phosphate, triallyl phosphite; allyl methacrylate;
Unsaturated acid allyl esters such as allyl acrylate; divinyl phthalate, divinyl isophthalate,
Mention may be made of vinyl esters such as divinyl terephthalate.

The network polymer Pa of the present invention includes a homopolymer obtained by polymerizing one type of monomer Ma as described above, a copolymer obtained from two or more of these monomers, and a copolymer obtained from two or more of these monomers. Body Ma and styrene,
Contains copolymers with monomers such as methacrylic acid esters and vinyl benzoate. Further, it is assumed that this network polymer Pa has a refractive index of Na.

In the present invention, first, the monomer Ma described above is polymerized to produce a transparent gel-like substrate. monomeric Ma
The polymerization is temporarily stopped when the polymer loses fluidity and becomes a transparent gel, that is, when the polymerization is not completed. If this polymerization is carried out in a mold or frame having a predetermined shape, the gel substrate can be formed at the same time. The resulting gel substrate is then coated with a refractive index different from that of Na.
Diffusion of monomer Mb to produce a polymer with Nb
Let it penetrate.

The monomer Mb used in this process may be one that becomes a linear polymer or a network polymer when polymerized, but it may be one that becomes a linear polymer or a network polymer when polymerized. Preferably, those that can be used to produce a transparent copolymer. As such monomer Mb, styrene, methacrylic ester, acrylic ester, vinyl acetate, vinyl chloride, acrylonitrile, butadiene, or a mixture of two or more of these can be suitably used.

Next, on the surface of the transparent gel substrate on which monomer Mb has been diffused, locally non-uniform polymerization conditions are applied to selectively harden only the surface region. Local heating, light irradiation, electron beam irradiation, etc. can be used as locally non-uniform polymerization conditions, but among these, irradiation with visible light and/or ultraviolet rays is the most convenient method. Will. In addition, if necessary, monomer Ma and/or monomer
A thermal polymerization initiator, a photopolymerization initiator, a photosensitizer, etc. can also be added to Mb.

By curing the surface region by applying locally non-uniform polymerization conditions in this manner, a predetermined pattern is formed by the cured portions and uncured portions. The pattern of cured and uncured parts depends on the shape, size, position, and shape of the light guide path of the optical circuit to be formed.
It is determined depending on the magnitude relationship between Na and Nb.
For example, when Na<Nb, the hardened portion of the surface region corresponds to a portion where the light guide path of the optical circuit is to be formed, and conversely, when Na>Nb, the uncured portion corresponds.

Next, the unpolymerized monomer Mb diffused into the uncured portion and inside the substrate is removed through the patterned surface of the transparent gel substrate. Various methods can be used for removal, such as immersion in a solvent capable of dissolving monomer Mb, vaporization under reduced pressure, and performing the latter after the former. When monomer Mb is removed from the transparent gel substrate using this method, the monomer Mb inside is removed through the part that was cured in the previous step of this process.
It is difficult for Mb to escape, and mainly the uncured portion and the monomer Mb inside thereof escape through the uncured portion. Due to this phenomenon, a concentration distribution of the monomer Mb is generated in the transparent gel substrate in the vicinity of the cured portion. After forming the monomer Mb concentration distribution in the transparent gel substrate in this way, the monomer Mb
By fixing the distribution of Mb, the light guide path of the optical circuit as described above can be formed in the synthetic resin substrate.

Next, the present invention will be described in detail based on embodiments shown in the drawings.

First, as shown in FIG. 3A, a transparent gel substrate 17 is prepared by polymerizing a monomer Ma that produces a network polymer Pa having a refractive index Na in molds 18 and 19. Next, a polymer with a refractive index of Nb is coated on the surface of this transparent gel substrate 17.
The monomer Mb that generates Pb is brought into contact with it in a liquid phase or gas phase, and the monomer Mb is diffused from the entire surface of the transparent gel substrate 17 as shown in FIG. 3A. At this time,
The higher the temperature at which monomer Mb is diffused, the higher the diffusion rate of monomer Mb, but at a temperature lower than the temperature at which monomer Mb polymerizes alone or copolymerizes with monomer Ma Set. Next, as shown in FIG. 3B, a light shielding mask 20 for shielding light is placed on the surface of the transparent gel substrate 17 in which the monomer Mb is diffused, and light is irradiated. The width R1 of the mask 20 is equal to the width R2 of the elongated groove (uncured part) 21 between the hardened parts as shown in FIG.
It is preferable to make the width R3 of the light guide path section 22 considerably smaller than the width R3 shown in FIG. The light emitted is
Ultraviolet rays used for ordinary photocurable resins are preferred. By light irradiation, a hardened portion 23 is formed as shown in FIG. 3C. The thickness of the hardened portion 23 is the same as that of the monomer.
It must be thick enough that Mb does not easily pass through it, but as long as it satisfies this condition, thinner materials are preferable. In the next step, monomer Mb is removed from the groove 21 of width R2 in the cured part 23, but if R2 is not sufficiently smaller than the width R3 of the light guide to be formed, the isoconcentration curve of monomer Mb is parallel to the surface of the transparent gel substrate 17 in this portion, and the cross section does not have a concentric cylindrical shape. As a method for removing monomeric Mb, if monomeric Mb is much more volatile than monomeric Ma, it is sufficient to simply reduce the pressure, but if the volatilities are similar,
A method may be adopted in which the material is immersed in solvents having different solubility. If monomer Ma and monomer Mb are inevitably removed in approximately equal amounts, the concentration distribution of monomer Mb has already been formed within the substrate, so when completing the polymerization, the transparent gel substrate If 17 is kept in contact with the monomer Ma, the monomer Ma
This can compensate for the lack of and alleviate the shrinkage during polymerization. By removing the monomer Mb through the groove 21, the polymerization is completed to fix the concentration distribution of the monomer Mb formed, and then the surface is polished, as shown in FIG. 3D. A transparent synthetic resin optical circuit 24 in which an elongated light guide path portion 22 having a cross section is formed is completed. The width R3 of the light guide path portion 22 is influenced by the width R2 of the groove 21 of the cured portion 23 (=width R1 of the light-shielding mask), the crosslinking density of the transparent gel substrate 17, the monomer Mb removal conditions, etc. In this example, the magnitude relationship between Na and Nb is Na>Nb.

FIG. 4 shows an example in which Na<Nb.
In this example, as in the case of Na>Nb mentioned above,
First, a reticular polymer with a refractive index of Na is formed in the formworks 26 and 27.
A transparent gel substrate 25 is made by partially polymerizing the monomer Ma that generates Pa, and the monomer Mb that generates the polymer Pb with a refractive index Nb is brought into contact with the substrate 25, and the entire surface of the substrate 25 is made to polymerize as shown in FIG. spread from. The temperature at this time is also set at a temperature at which Mb does not polymerize. Next, as shown in FIG. 4B, a transparent gel substrate 24 in which the monomer Mb is diffused is coated with a light-shielding mask 24 that is translucent in a portion corresponding to the light guide path portion and shields light in other portions.
8 and irradiate it with ultraviolet light. The width R4 of the light-transmitting part of the light-shielding mask 28 is equal to the width R4 of the hardened part 29 shown in FIG.
This is approximately equal to the width R6 of the light guide path portion 31 shown in FIG. 4D. Due to ultraviolet irradiation, a linear hardened part 2 is formed as shown in Fig. 4 (c).
9 is formed. It is desirable that this thickness be as thin as possible as long as monomer Mb does not pass through. Next, monomer Mb is removed from the transparent gel substrate 25. Uncured portion 3 on the surface of transparent gel substrate 25
When monomer Mb is removed from 0, a concentration gradient is generated, and monomer Mb moves there from below the hardened portion 29 and from the deep part of the transparent gel substrate 25, and a new concentration gradient is generated. In this way, a monomer with a concentric circular cross section
After forming the Mb concentration distribution, polymerization is completed to fix it, and then the surface is polished, resulting in the formation of an elongated light guide section 31 having a cross section as shown in FIG. 4D. The resin optical circuit 32 is completed. The width R6 of the light guide path portion 31 is approximately equal to the width of the hardened portion 2.
9 (=width R4 of the light-transmitting part of the light-shielding mask).

In the manner described above, it is possible to obtain a flat optical circuit provided with a predetermined light guide path, such as a branching/combining circuit, a branching/combining circuit, a mixing circuit, etc., each having a planar light guide pattern.

Specific Example 1 This specific example 1 follows the method shown in Figure 3. First, 3% by weight of benzoyl peroxide and benzophenone were dissolved in diethylene glycol bisallyl carbonate (CR-39) and poured into a mold. Heat at 80℃ for 90 minutes, and make 50mm x 50mm x 5mm.
A transparent gel substrate was prepared. This was immersed in vinyl benzoate (VB) in which benzoyl peroxide and benzophenone were each dissolved in an amount of 3% by weight,
It was diffused from the surface into the transparent gel substrate. Next, a photomask with 10 black lines of 0.2mm width was placed on the surface of this 50mm x 50mm substrate and exposed to ultraviolet light using an ultra-high pressure mercury lamp. The surface of the gel substrate was cured. This was immersed in acetone to partially elute the monomer, then placed in a desiccator, connected to a vacuum pump, and reduced pressure to volatilize the acetone. This was brought into contact with CR-39 and kept at 80° C. for 15 hours to complete polymerization, and then the portion of CR-39 that was brought into contact with the polymer was removed by polishing. this
The cured body made of CR-39 and VB has a thickness of approximately 1.0 mm.
Ten light guide paths were formed.

Specific Example 2 This specific example 2 follows the method shown in FIG. 4, and first, 3% by weight of benzoyl peroxide is added to diallyl isophthalate (DAIP).
Dissolve 4% by weight of benzophenone, pour this into a mold, and leave it at 80℃ for 3 hours to form a mold of 50mm x 50mm x 5.
A transparent gel substrate of mm size was prepared. 50 of this gel object
Trifluoroethyl methacrylate (3FMA) is brought into contact with a mm x 50 mm surface and diffused from the entire surface, and a photomask with 10 3.0 mm wide slits is placed on it and UV rays from an ultra-high pressure mercury lamp are irradiated. As a result, the surface of the transparent gel substrate in the area corresponding to the slit of the photomask was hardened. Next, this was placed in a desiccator, and a vacuum pump was connected to reduce the pressure, and a portion of 3FMA was removed from the uncured portion. When this was held at 80°C for 15 hours to complete polymerization and then polished, 10 light guide paths with a thickness of about 3.0 mm were formed.

[Brief explanation of drawings]

1 and 2 are cross-sectional views each showing a conventional example of a method for manufacturing a synthetic resin optical circuit, and FIGS. 3 and 4 each show an example of a method for manufacturing a synthetic resin optical circuit according to the present invention. FIG. In addition, in the symbols used in the drawings, 17, 25...
Transparent gel substrate, 20, 28... Light shielding mask, 21,
30...Uncured part, 23,29...Cured part, 22,3
1... Light guide path section, 24, 32... Synthetic resin optical circuit.

Claims (1)

[Claims] 1. A light guide path having a refractive index larger than that of the substrate is formed in a transparent substrate made of synthetic resin, and in this case, the light guide path has an optical axis within a cross section perpendicular to the traveling direction of light. In a method for producing a synthetic resin optical circuit having a refractive index distribution that continuously decreases from the center to the periphery, (a) one or more monomers forming a network polymer Pa having a refractive index of Na; (b) a step of incompletely polymerizing polymer Ma to form a transparent gel-like substrate; (c) performing a partial hardening treatment on the surface area of the transparent gel substrate to form hardened portions and unhardened portions in accordance with the pattern of the light guide path to be formed; (d) forming on the surface area mainly the uncured portion and the inside of the transparent gel substrate corresponding to the uncured portion through the surface of the transparent gel substrate on which the curing treatment has been performed; removing the monomer Mb, thereby creating a state in which the monomer Mb remains in the transparent gel substrate in the vicinity of the cured portion with a concentration gradient that continuously changes; (e) a step of completing the polymerization of the monomers Ma and Mb in the residual state of the monomer Mb.