JP2000180680A - Signal transmitting multicore plastic optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic optical fiber having a little loss caused by bending, stabilized in connection to a very small spot light source, and efficiency in coupling of light. SOLUTION: In an optical fiber, a large coated fiber 4a having sheath layers 2a, 3a on the periphery of a core 1a having the diameter in the range of 200 μm to 500 μm is arranged in the central part in the section of the fiber, small coated fibers 4b each of which has sheath layers 2b, 3b on the periphery of a small core 1b having the diameter smaller than that of the core 1a of the large coated fiber 4a are arranged on the periphery of the large coated fiber 4a, small coated fibers 4c are concentrically arranged, and therefore, light deviated from the core 1a of the large coated fiber 4a is recovered by the cores 2b of the small coated fibers 4b, and the internal core is protected by the small coated fibers 4c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber used for signal transmission in personal computer communication, control of factory machinery, and optical communication in a moving body.

[0002]

2. Description of the Related Art Plastic optical fibers are usually formed to have a diameter of about 1 mm to maintain mechanical strength and facilitate handling. On the other hand, in order to perform high-speed signal transmission of 100 Mbps or more, the light receiving diameter of the photodiode is often reduced to 0.5 mm or less. Therefore, a large-diameter plastic having a diameter of about 1 mm is used in combination with such a photodiode. When an optical fiber is used, light protrudes from the photodiode, and the coupling loss of light is large. In a multi-core plastic optical fiber, the intensity of light at a light source-side spot is transmitted to the photodiode as it is, so that the light coupling efficiency is higher than that of a large-diameter single-core plastic optical fiber. In particular, since the spot of the LD or LED is bright at the center and dark at the periphery, transmission of light at the center is particularly important.

[0003]

However, the multi-core plastic optical fiber has a problem in the coupling efficiency with the light source. A multi-core plastic optical fiber used for signal transmission in conventional optical communication is obtained by integrating a plurality of cores having a substantially uniform diameter through a sheath layer, and forming a plurality of cores having a small diameter. Light is introduced, and the sheath layer interposed between the cores has a structure that does not transmit light. Therefore, if the spot diameter of the light source is much larger than the core diameter,
It is inevitable that the amount of received light decreases by the area of the sheath layer occupying the fiber cross section, and a loss of about 15% to 30% has usually occurred.

Further, when a light spot such as a transceiver for a quartz optical fiber having a very small light spot is used, the size of the light spot and the distance between the cores, ie, the thickness of the sheath layer cannot be ignored. However, there is a problem in that a small change in the incident position of light results in a change in the amount of received light, and when the light spot has almost entered the sheath layer, the amount of received light becomes extremely small.

An object of the present invention is to solve the above problems and to provide a plastic optical fiber capable of efficiently transmitting and receiving light, and more specifically, to provide a plastic optical fiber irrespective of the size of a light spot of a light source. An object of the present invention is to provide a plastic optical fiber in which a loss of received light is reduced.

[0006]

According to the present invention, a plurality of cores comprising a core made of a transparent resin and a sheath layer made of a resin having a lower refractive index than the core and surrounding the core are integrated. A multi-core plastic optical fiber, wherein a core having a core diameter of 200 μm to 500 μm is arranged at the center of the fiber cross section, and the circumference of the large core is smaller in core diameter than the large core. A multi-core plastic optical fiber for signal transmission characterized by being surrounded by a plurality of small cords and integrated by composite spinning.

In the present invention, preferably, the small core wire is a plastic optical fiber arranged in a double concentric manner around the large core wire, and the sheath layer may have a double structure. It is preferably applied.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The plastic optical fiber of the present invention has a large core wire having a large core diameter disposed in the center of the fiber, and the core diameter is larger than that of the large core wire around the large core wire. The feature is that small small cords are arranged.

The core wire has a diameter of 200 μm to 500 μm.
A sheath layer is provided around a core made of a transparent resin. The sheath layer is formed of a resin having a lower refractive index than the resin constituting the core, and has a thickness of at least one layer and about 1 μm to 10 μm. Form. The diameter of the core of the small core wire is smaller than the diameter of the core of the large core wire, and is preferably 50 μm to 250 μm. A sheath layer similar to the large core wire is provided around the core. In the present invention, in order to reduce light loss due to bending, the above-mentioned sheath layer is formed of the first layer.
It is preferable that a second sheath layer is formed on the outside with a resin having a lower refractive index as a sheath layer, and a two-layer structure is formed.

The cross-sectional area in the diameter direction of the core of the large core wire is preferably 25% to 150%, more preferably 50% to 110% of the light receiving area of the photodiode used. Most preferably, it is ideal to arrange the large conductor at the center of the spot of the light source so that the light receiving surface of the photodiode and the cross section of the core of the large conductor of the fiber just overlap with each other. In consideration of the accuracy of the connector and the like, the above-mentioned area range is preferable in order to cause the light of the highest density portion at the center of the light source to enter the core of the large core line.

When the sectional area of the core is configured to be smaller than the light receiving area of the photodiode within the above-mentioned area range, the loss due to bending can be further reduced. In this case, the small core line in contact with the large core line receives the light deviating from the large core line, and plays a role of sending the light to the photodiode. In this case, although there is a loss on the light receiving surface due to the sheath layer, the light intensity of the spot of the light source in the region of the small core line around the large core line is also weak, so that the influence on the entire received light amount is reduced. Is less.

The small core wire according to the present invention has a role of transmitting light deviating from the large core wire and another role of protecting the large core wire. It is sufficient that at least one layer of the small core wire is arranged around the large core wire, but it may be formed of multiple layers. Preferably, they are arranged in double concentric circles around the major cord. In this case, the inner small core line in contact with the large core line collects light deviating from the large core line, and the outer small core line serves as a protective layer. It is preferable that the small cords are regularly arranged as densely as possible, and the diameter of the core can be set appropriately inside and outside.

FIG. 1 is a cross-sectional view schematically showing the structure of one embodiment of a plastic optical fiber in which a small core wire is arranged in a double concentric manner around the large core wire. In the present embodiment, each core wire has a two-layer structure provided with the above-described second sheath layer. In the figure, 1a-1c is a core, 2a-2c is a first sheath layer, 3a-3c is a second sheath layer, 4a is a large core wire, 4b is a small inner core wire for collecting light, and 4c is a core wire. It is an outer small cord that functions as a protective layer. As described above, by arranging the inner small core wire 4b and the outer small core wire 4c concentrically and evenly, damage to the inner core wire is less likely to occur, and light is efficiently collected by the small core wire 4b. It is preferable because it is performed. FIG. 1 is a schematic view showing the arrangement of the core wires. In an actual fiber cross section, the core has a non-circular cross-sectional shape and is slightly distorted, so that the thickness of the sheath layer is almost uniform. . Therefore, when the core is not a perfect circle, the diameter of the core in the present invention means the average value of the major axis and the minor axis.

In the plastic optical fiber of the present invention, when the area ratio of the core to the cross-sectional area increases, the shape collapses, but the area ratio of the core is 60% to 95%.
Is more preferable, and more preferably 75% to 90%. The total number of cores is preferably 8 to 500. The diameter of the plastic optical fiber of the present invention is intended for 0.4 mm to 1.5 mm, preferably 0.5 mm to 1.2 mm.

Next, the material of each member will be described. The core of each core wire is formed of a transparent resin. Specifically, for example, a plastic such as a polymethyl methacrylate-based resin, a polycarbonate-based resin, or a perfluorinated resin (for example, “CYTOP” of Asahi Glass Co., Ltd.) is used. A known transparent resin can be used as the core resin of the optical fiber. Also,
As the resin forming the sheath layer, a resin having a lower refractive index than the core resin is used.For example, a resin containing a fluoroalkyl methacrylate or a vinylidene fluoride resin, or a mixture of a vinylidene fluoride resin and a methacrylate resin is used. Alloys and the like are used. As described above, the sheath layer may be a single layer or a multilayer structure. In the case of a multilayer, the refractive index of the outer sheath layer is lower than that of the inner sheath layer. As the outer sheath layer in the case of a multilayer structure, a vinylidene fluoride-based resin is preferable in terms of mechanical strength.

[0016] The multi-core plastic optical fiber of the present invention comprises:
It is formed by a composite spinning method using a composite spinning die in which the relative core diameter and core arrangement are determined. That is, the melted core resin and sheath resin are supplied to the composite spinning die and molded at a stretch. The ratio of the area of all the cores and the area of the sheath layer to the cross-sectional area of the plastic optical fiber of the present invention can be determined by the volume ratio of the core resin and the sheath resin supplied to the composite spinning die.

The multi-core plastic optical fiber according to the present invention comprises:
Usually as bare wire, polyethylene, polypropylene, ethylene-vinyl alcohol copolymer, rubber, various thermoplastic elastomers, polyvinyl chloride, cross-linked polyolefin, cross-linked polyvinyl chloride, chlorinated polyethylene compound, polyamide resin, fluoride It is used as a core plastic optical fiber cable coated with a vinylidene resin, a polyester resin, a polyurethane resin, a silicone resin, a thermosetting resin, an ultraviolet curable resin, or the like.

[0018]

EXAMPLE As a core resin, a resin having a refractive index of 1.492, a melt flow index of 230 ° C., a load of 3.8 kg, an orifice diameter of 2 mm and a length of 8 mm was used.
A g / 10 min methyl methacrylate resin was used. The sheath layer has a two-layer structure, and as a first sheath resin constituting the inner first sheath layer, 17% by weight of 17FMA (heptadecafluorodecyl methacrylate), 4% by weight of 4FM (tetrafluoropropyl methacrylate), 6% by weight of 3FM (trifluoroethyl methacrylate) and 74% by weight of MMA (methyl methacrylate) were cast polymerized to give 2% by weight.
A copolymer having a melt flow index of 25 g / 10 minutes at 30 ° C. and a load of 3.8 kg and a refractive index of 1.470 was used. NA is 0.26. The second sheath resin constituting the outer second sheath layer was a copolymer composed of 80 mol% of vinylidene fluoride and 20 mol% of tetrafluoroethylene, and was measured under the same conditions as the first sheath resin. A resin having a melt flow index of 30 g / 10 min was used. The refractive index was 1.402.

As the composite spinning die, one large core wire and eleven small core wires of the first layer are arranged concentrically outside the large core wire, and the outside is further contacted with the small core wire of the first layer. A configuration in which eleven small-core wires of the second layer are arranged concentrically was used. The core diameter of these core wires in the die is
6.2 mm, 2.4 mm, 3, and 8 mm. The core resin, the first sheath resin, and the second sheath resin are supplied to the composite spinning die in a volume ratio of 80: 5: 15, and the strands discharged from the die are converged and stretched twice. Thus, a multi-core plastic optical fiber having a diameter of 1.00 mm and a sheath having two layers was obtained. As shown schematically in FIG. 1, the cross section of this fiber is such that eleven small cores are arranged around a large core and eleven small cores are arranged outside the core. The wire has a first sheath layer and a second sheath layer around the core, and is integrated with the adjacent core wire by the second sheath layer.

The diameter of the core of the core fiber of the obtained fiber is 3
The diameter of the core of the inner cord was 116 μm, and the diameter of the core of the outer cord was 184 μm. This fiber was used as a bare wire and coated with black polyethylene to obtain a multicore plastic optical fiber cable having a diameter of 2.2 mm.

[0021]

As described above, the multi-core plastic optical fiber of the present invention, when using a transmission light source such as an LED or an LD, transmits important central light with a thick core line. Since light is received and the light deviated from the large cord is collected by the small cord, light loss is greatly reduced, and light loss due to bending is also small. Further, even when a light source having a small light spot is used, there is no deviation from the light spot at the time of coupling because the diameter of the core of the large core wire is large, and a reduction in the amount of received light due to the deviation is prevented. Therefore, even if the light source has a large spot diameter or a light source with a very small spot diameter for a quartz optical fiber, efficient light transmission and reception can be performed by stable coupling.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of one embodiment of a multi-core plastic optical fiber of the present invention.

[Explanation of symbols]

 1a-1c Core 2a-2c First sheath layer 3a-3c Second sheath layer 4a Large cord 4b, 4c Small cord

Claims (3)

[Claims] 1. A multi-core plastic optical fiber comprising a plurality of cores made of a core made of a transparent resin and a sheath layer made of a resin having a lower refractive index than the core and surrounding the core. A core wire having a core diameter of 200 μm to 500 μm is arranged at the center of the fiber cross section, and the periphery of the core wire is surrounded by a plurality of small core wires whose core diameter is smaller than that of the large core wire. A multi-core plastic optical fiber for signal transmission characterized by being integrated by spinning. 2. The multi-core plastic optical fiber for signal transmission according to claim 1, wherein said small core wire is arranged in a double concentric manner around said large core wire. 3. The multi-core plastic optical fiber for signal transmission according to claim 1, wherein the sheath layer has a two-layer structure in which the outside is made of a resin having a low refractive index.