JPH0933735A - Plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a plastic optical fiber having a core-clad structure and having heat resistance and low transmission loss characteristics which are comparable to a polymethacrylate by constituting the core of a polymer comprising a specified structural unit. SOLUTION: This fiber has such a core-clad structure that the core consists of a polymer comprising a structural unit expressed by formula. The core material having this structural unit can be obtd. by polymn. of α-methylene-y- butylolactone derives having this structure. In formula, R1 , R2 are preferably substituents having <=12 carbon number because when the structure has a larger bulk, the heat resistance and the polymn. degree decrease. The alkyl groups to be introduced into R1 , R2 are expressed by structural formula Cn H2n+1 (n<12) and may have a straight or branched structure. Further, R1 and R2 may be coupled to form a six-member structure of a cyclohexyl group. The polymn. method is not limited but block polymn. is preferable from the viewpoint of decreasing the loss of the optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical fiber usable as an optical information communication medium.

[0002]

2. Description of the Related Art Optical transmission is widely used as a communication medium by taking advantage of its large capacity and being completely unaffected by electromagnetic noise. Practical optical transmitters are roughly classified into quartz type and plastic type depending on their materials. Further, it can be classified into a single mode type and a multimode type according to the mode of the transmission mode. Furthermore, there are a step index type (hereinafter referred to as “SI type”) and a continuous graded index type (hereinafter referred to as “GI type”) in which the refractive index change along the radial direction of the cross section is discontinuous from the refractive index distribution pattern. It may be classified into.

Commercially available silica-based single mode fibers are characterized by overwhelmingly low loss and wide band. Taking advantage of this feature, it is used for long-distance, large-capacity communication trunk lines. The plastic type is SI type plastic optical fiber (hereinafter "SI
Type POF "is commercially available and has a large diameter (500 to 1000
Its greatest feature is that it has excellent flexibility while having a high numerical aperture (NA ≈ 0.5).

The silica type single mode fiber has an extremely wide band, but at the same time, the core diameter serving as the light receiving surface is extremely small (about 10 μm) and the difference in the refractive index between the core and the clad is small, so that the positional relationship with the light source and the incident angle are small. Since the allowable range is narrow, it takes a lot of effort to perform alignment (position and angle adjustment) operations when connecting with peripheral devices. Further, since the material is quartz, it is difficult to process the end face, which is a connecting portion with the light emitting / receiving element.

In addition, even if the silica type GI type fiber has a larger diameter and a higher numerical aperture than the silica type single mode fiber, the SI type
Compared to POF, it has a smaller aperture and numerical aperture. Further, since the material is quartz, it is necessary to perform an operation such as polishing of the end face of the fiber such as the coupling portion. To compensate for such drawbacks, plastic clad quartz core fibers using quartz as the core material and plastic as the clad material are also commercially available, but the difficulty of end face treatment is unavoidable and the flexibility is also sufficiently improved. Not a thing.

From these viewpoints, the advantages of the plastic optical fibers currently on the market are that they have a large diameter, are flexible and easy to handle, have a wide tolerance range of coupling alignment, and are easy to connect. There is a point that an optical device is unnecessary.

Then, SI type POF makes use of the above-mentioned feature,
Applications for short-distance communication such as data link and sensors are spreading. In the future, it is expected to be a low-cost information transmission line for short distances with many connection points such as facility networks such as LAN between devices inside and outside the floor for FA and OA, and terminal wiring in the subscriber network (FTTH). In addition, since it is excellent in flexibility, it is less likely to be damaged, broken or deteriorated even in a vibrating environment. In this respect as well, it is far superior to the quartz system and can be used for signal transmission lines such as networks in moving bodies such as automobiles, trains and airplanes. Is also being applied.

Since ordinary plastic optical fibers have a low transmission loss and have no problem in mechanical properties and weather resistance, those using polymethylmethacrylate as a core material are predominant. Since the upper limit temperature of the optical fiber with poly (methyl methacrylate) as the core is limited to the glass transition point Tg of this material, even if a coating with high heat resistance is applied, it is limited to at most 105 ° C. However, the heat resistance is insufficient in the above-mentioned communication in the mobile body and in the outdoor use.

As a method of improving the heat resistance of the plastic optical fiber, there are mainly a method of increasing the Tg of the core material and a method of applying a heat resistant coating. As for the former which raises the Tg of the core material, 1) Polycarbonate having a high glass transition point as a polymer alone is used as the core material (JP-A-61-2627).
No. 06), 2) an olefin-based copolymer containing a polycyclic olefin-based monomer is used as a core material (JP-A-61-2).
11315 gazette), 3) using a copolymer of a methyl methacrylate monomer and another high Tg monomer as a core material, and using an aromatic maleimide as a comonomer (Japanese Patent Publication No. 5-82405, Tokufair 5-
82406), and aliphatic maleimides (JP-A-63-63).
80205), alicyclic methacrylates (JP-A-6-206)
No. 1-260205).

[0010]

However, the above-mentioned 1
And 2) are sufficient in terms of size and stability of mechanical properties at high temperature, but have larger transmission loss characteristics than polymethylmethacrylate-based optical fibers, and their aging changes at high temperatures. It has the drawback of being large. See also 3)
Although the one using an aliphatic maleimide has good characteristics in terms of transmission loss, heat resistance and balance of mechanical properties, the transmission loss is lower than that of a plastic optical fiber using polymethylmethacrylate alone as a core material. The problem is that the transmission distance is largely limited to short distances.

Further, when considering use in a moving body such as an automobile, it is expected that the number of bent portions will increase because the cables need to be laid out in a limited space. Generally, bending the fiber increases the transmission loss, which is disadvantageous in that the transmission loss of the fiber itself is large, and the method of improving the heat resistance by sacrificing the transmission loss as in the examples 1) to 3) Not enough.

The object of the present invention is to solve these problems,
An object of the present invention is to provide a plastic optical fiber having excellent low transmission loss characteristics comparable to polymethylmethacrylate and heat resistance.

[0013]

The gist of the present invention resides in a plastic optical fiber having a core / clad structure in which a core is composed of a polymer composed of structural units represented by the following general formula (1).

[0014]

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The inventors of the present invention have made earnest studies to develop a plastic optical fiber having improved heat resistance and sufficiently low transmission loss. As a result, a polymer having the structural unit represented by the general formula (1) has sufficient heat resistance. It has been found that it is the most suitable as the core material of the optical fiber having the characteristics and transmission loss characteristics.

The core material having the structural unit represented by the general formula (1) used in the present invention can be obtained by polymerizing the α-methylene-γ-butyrolactone derivative represented by the following general formula (2).

[0017]

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Regarding R1 and R2 in the formula, when the structure becomes bulky, the heat resistance and the polymerizability are lowered, so that the number of carbon atoms is 12
The following substituents are preferred. The alkyl group which can be introduced by R1 and R2 has a structural formula of C _n H _{2n + 1} (n ≦ 12)
And can have a linear structure or a branched structure. Further, a 6-membered ring structure of cyclohexyl group may be formed by the R1 and R2 groups.

The core material of the present invention is obtained by polymerizing one kind of the monomer having the structural unit represented by the general formula (2), or by copolymerizing two or more kinds of the monomers having these structural units. It is a thing.

The polymerization mode for obtaining such a core material is not particularly limited, but bulk polymerization is preferable from the viewpoint of reducing the loss of the optical fiber. The polymerization initiator is not particularly limited as long as it does not adversely affect side reactions or coloring during polymerization. It can be appropriately selected depending on the polymerization mode, the polymerization temperature, the polymerization rate, and the polymerization time, and a plurality of types of polymerization initiators can be used together. Examples thereof include azo compounds such as azobisisobutyronitrile and peroxide compounds such as benzoyl peroxide.

A chain transfer agent may be used for the purpose of controlling the molecular weight during polymerization. The chain transfer agent is not particularly limited as long as it does not adversely affect side reactions or coloring during polymerization, and can be appropriately selected for the target molecular weight, and a plurality of kinds of chain transfer agents can be used together. good.
Examples of chain transfer agents include primary, secondary, and tertiary mercaptans such as n-butyl mercaptan, isobutyl mercaptan, and t-butyl mercaptan, thioglycolic acid, and esters thereof.

The material of the clad layer is not particularly limited as long as it is a polymer having a refractive index smaller than that of the material used for the core. Fluorinated methacrylate polymers or copolymers, copolymers of fluorinated methacrylate and methacrylate, vinylidene fluoride-tetrafluoroethylene copolymers, α-fluoromethacrylate resins to take advantage of the high numerical aperture of plastic optical fibers ,
Alternatively, it is preferable to use a mixture thereof. From the viewpoint of improving heat resistance, an α-fluoromethacrylate resin having a high Tg is preferable.

The thickness of the clad portion is preferably 1 μm or more in order to make the leaked light too negligible to increase the transmission loss of the entire optical fiber when it is too thin.

In the plastic optical fiber having the core / clad structure of the present invention, the core and the clad polymer are melted and extruded from the composite nozzle by the composite spinning method, and the clad polymer solution is applied to the fibrous shaped core polymer. After that, it can be produced by a coating method for removing the solvent.

A protective layer may be coated on the outer peripheral portion of the clad layer for the purpose of improving heat resistance, moisture resistance and chemical resistance.

[0026]

EXAMPLES The present invention will be specifically described below based on examples.

Example 1 25 parts of diethyl oxalate was added to 100 parts of anhydrous tetrahydrofuran in which 10 parts of sodium ethoxide was dispersed, and γ-butyrolactone was added dropwise at 15 ° C. or below.
It was left for 16 hours. Next, formaldehyde was blown into the reaction solution, the solvent was distilled off, and then extraction with ether was performed. The extracted ether phase was mixed with saturated aqueous sodium carbonate solution and stirred for 1 hour. Then, the solvent was distilled off, and the residue was attached to a Vigreux tube and distilled under reduced pressure to obtain α-methylene-γ.
-Butyrolactone was obtained.

Α-methylene-γ synthesized in this way
-Butyrolactone was added with 20 ppm of di-t-butylperoxide as an initiator and 0.1 wt% of octyl mercaptan as a chain transfer agent, and bulk polymerization was performed to produce a core material polymer.

As a clad material, a polymer of α-fluoroacrylic acid trifluoroethyl / α-fluoroacrylic acid methyl (85/15 molar ratio) was used.

These polymers were spun using a screw type extruder from a two-layer concentric circular composite nozzle to produce a plastic optical fiber having a core / clad structure with a fiber diameter of 1000 μm and a core diameter of 980 μm.

The optical transmission loss of this plastic optical fiber was 220 dB / km (measurement method: 50 m-5 m cutback method, wavelength: 650 nm, incident NA = 0.1). When this fiber was heat-treated at 125 ° C. for 1000 hours, the increase in optical transmission loss was maintained at 20 dB / km or less, and good heat resistance was exhibited.

Example 2 50 parts of 37% aqueous formalin solution, methyl acrylate 7
0 parts and 30 parts of 1,4-diazabicyclo- [2,2,2] -octane were dissolved in 200 parts of 1,2-dimethoxyethane and stirred at room temperature for 50 hours, and then the organic phase was separated from the reaction solution. , Α-hydroxymethyl methyl acrylate were obtained. This methyl α-hydroxymethyl acrylate was diluted with 6 volumes of anhydrous ether, and 20 parts of tribromide was added dropwise to this solution in an ice bath, and the mixture was stirred at room temperature for 3 hours for reaction. After the reaction was completed, water was added and the organic phase was separated to obtain methyl α-bromomethylacrylate.

A solution prepared by diluting this methyl α-bromomethyl acrylate with 3 times the amount of anhydrous tetrahydrofuran was added with 7 parts of zinc, 25 parts of acetone and 10 parts of anhydrous tetrahydrofuran.
It was added dropwise to 0 part of the mixed solution. After completion of dropping, the mixture was stirred for 3 hours, poured into a 10% hydrochloric acid aqueous solution, the organic phase was washed well with water, dehydrated over sodium sulfate, and evaporated under reduced pressure to obtain α-.
Methylene-4,4-dimethyl-γ-butyrolactone was obtained.

This α-methylene-4,4-dimethyl-γ
-Butyrolactone was used as the core material and the other conditions were the same as in Example 1 except that the fiber diameter was 1000 μm,
A plastic optical fiber having a core-clad structure with a core diameter of 980 μm was prepared.

The optical transmission loss of this plastic optical fiber was 230 dB / km (measurement method: 50 m-5 m cutback method, wavelength: 650 nm, incident NA = 0.1). When this fiber was heat-treated at 125 ° C. for 1000 hours, the increase in optical transmission loss was maintained at 25 dB / km or less, and good heat resistance was exhibited.

Comparative Example 1 Polycarbonate resin Iupilon of Mitsubishi Gas Chemical Co., Inc. was used as a core material, and a clad material was a polymer of α-trifluoroethyl acrylate / methyl α-fluoroacrylate (molar ratio 85/15). Using. These polymers were spun from a two-layer concentric circular composite nozzle in the same manner as in Example 1 using a screw type extruder, and the fiber diameter was measured;
A plastic optical fiber with a core-clad structure having a thickness of 1000 μm and a core diameter of 980 μm was manufactured.

The optical transmission loss of this plastic optical fiber was 280 dB / km (measurement method: 50 m-5 m cutback method, wavelength: 650 nm, incident NA = 0.1). When this optical fiber was heat-treated at 125 ° C. for 1000 hours, the optical transmission loss increased by 40 dB / km.

[0038]

As described above, the plastic optical fiber of the present invention has excellent performance such as low optical transmission loss and high heat resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Kamo 20-1 Miyuki-cho, Otake-shi, Hiroshima Mitsubishi Rayon Co., Ltd. Central Research Laboratory (72) Inventor Kikue Irie 20-1 Miyuki-cho, Otake-shi, Hiroshima Central Research Laboratory, Mitsubishi Rayon Co., Ltd.

Claims (1)

[Claims] 1. A plastic optical fiber having a core / clad structure in which a core is composed of a polymer composed of structural units represented by the following general formula (1). Embedded image