JPH0915432A - Plastic optical fiber for optical sensor - Google Patents

Abstract

PURPOSE: To make the light loss less when cores are bent and to enhance reliability by setting the dimensional of the respective cores at a size of a specific range and specifying the area of the cores at the section and the area of a sheath to a ratio of a specific range. CONSTITUTION: The diameter of the respective cores 1 is 50 to 200μm. Seven or more pieces of the core fibers are discretely partitioned and are integrated by packing a resin of the sheath 2 having the refractive index lower by 0.005 to 0.25 than the refractive index of the resin of the cores 1, by which the ratio of the area of the cores 1 at the section and the area of the sheath 2 is specified to 40:60 to 98:2. Namely, the light loss by bending of the optical fiber increases if the diameter of the cores 1 is larger than 200μm. The transmission loss increases if the diameter of the respective cores 1 is smaller than 50μm. The number of the cores 1 is specified to >=7 pieces at which the arrangement of the cores 1 stabilizes from the need for making the section uniform. The structure is formed by integrating the many cores 1 and the sheath resin enclosing the cores. The light loss is more excellent than heretofore even if the optical fiber having the diameter of the section of about 1mm is bent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for optical fiber type photoelectric sensors and has a small transmission loss and good environmental resistance.
Moreover, the present invention relates to a plastic optical fiber and its cable in which the transmission loss is small even when the optical fiber is bent, that is, the bending loss is small.

[0002]

2. Description of the Related Art A plastic optical fiber used in a conventional optical fiber sensor is an optical fiber in which a sheath is concentrically coated around a core, and the diameter of the core is usually 0.5 to 1.
It is 5 mm, and even in a special case, it is about 0.25 mm. Such a plastic optical fiber has a single core and
It is generally used one by one, and in some cases, a plurality of bundles may be used. In addition, JP-A-5-401
According to Japanese Patent Laid-Open No. 80, a multi-core optical fiber sensor unit having a core diameter of 5 μm to 50 μm and composed of at least 500 or more core resin islands is disclosed.

[0003]

In the case of a single-core plastic optical fiber that has been put into practical use, there is a problem that bending loss is large when bent with a small bending radius.
Further, in the above-mentioned multi-core optical fiber sensor unit, since the core diameter is as small as 50 μm or less, there is a problem in reliability in long-term use at high temperature.

[0004]

In order to solve these problems, the present inventors have made various investigations, and as a result, have made the diameters of the individual cores within a specific range, and have a cross-sectional core area and sheath area. It was found that a plastic optical fiber having an excellent feature that the light loss when bent is small and the reliability is high can be provided by setting the ratio within the specific range of (3), and thus completed the present invention.

That is, according to the present invention: the diameter of each core is 50 μm or more and 200 μm or less, and 7 or more of the core fibers are separately partitioned, and 0.005 or more and 0.25 or less depending on the refractive index of the resin of the core. To provide a multicore plastic optical fiber for an optical sensor having a ratio of the area of the core to the area of the cross section of 40:60 to 98: 2 when the resin of the sheath having a low refractive index is filled together. It is also characterized in that the ratio of the area of the core to the area of the sheath is 90:10 to 98/2. In addition, the refractive index of the sheath resin is 0.04 more than the refractive index of the core resin.
It is also characterized by low points. Also provided is a multi-core plastic optical fiber cable in which a protective coating layer is provided on the multi-core plastic optical fiber for an optical sensor described above.

Hereinafter, the present invention will be described in detail. In the present invention, various transparent resins can be used as the core material. As a particularly preferable resin, a known methylmethacrylate resin can be used. For example, a methyl methacrylate homopolymer or a copolymer containing 50% by weight or more of methyl methacrylate, and acrylic acid esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate as copolymerizable components, There are methacrylic acid esters such as ethyl methacrylate, propyl methacrylate, and cyclohexyl methacrylate, maleimides, acrylic acid, methacrylic acid, maleic anhydride, styrene, etc. A polymerized copolymer can be mentioned.
Methyl methacrylate-based resin has high transparency and thus can be transmitted over a long distance.

Styrene resins can be used as other preferable resins. For example, a styrene homopolymer, an acrylonitrile-styrene copolymer, a styrene-methylmethacrylate copolymer, a styrene-maleic anhydride copolymer, a styrene-six-membered cyclic anhydride copolymer, etc. Examples thereof include copolymers obtained by copolymerizing more than one kind of other components. Styrene-based resins have low hygroscopicity, so they are not easily affected by water.

As another preferable resin, a polycarbonate resin can be used. For example, aliphatic polycarbonate and aromatic polycarbonate, and copolymers of these with dioxy compounds such as 4,4-dioxyphenyl ether, ethylene glycol, p-xylene glycol and 1,6-hexanediol, Hetero bond copolymers having an ester bond in addition to the carbonate bond are also included. Polycarbonate resins have the features of high heat resistance and low hygroscopicity.

As another preferred resin, an amorphous polyolefin resin can be used. For example, "Arton" manufactured by Nippon Synthetic Rubber Co., Ltd., "A" manufactured by Mitsui Oil Co., Ltd.
There are resins such as "PO" and "ZEONEX" manufactured by Nippon Zeon Co., Ltd. Amorphous polyolefin resin has excellent heat resistance.

As the sheath resin, a resin having a refractive index lower than that of the core resin by 0.005 or more and 0.25 or less, preferably by 0.04 or more is used. The sheath resin is not particularly limited as long as it satisfies this condition. Examples of the sheath resin include methacrylic resin and / or acrylate resin and / or vinylidene fluoride resin.

For example, a methacrylic monomer such as fluorinated methacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate or butyl methacrylate, or an acrylate monomer such as fluorinated acrylate, methyl acrylate, ethyl acrylate, propyl acrylate or butyl acrylate is a main raw material monomer. And a vinylidene fluoride copolymer, a blend of a vinylidene fluoride copolymer and a methylmethacrylate resin, and the like. The refractive index of the inner sheath resin is 0.005 or more and 0.25 or more than the refractive index of the core material.
A resin that can be adjusted to have a low refractive index, preferably 0.04 or more, can be used.

For example, fluorinated methacrylate monomers include trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, heptadecafluorodecyl methacrylate, octafluoropropentyl methacrylate and the like, and fluorinated acrylate monomers include trifluoroethyl methacrylate. Examples include fluoroethyl acrylate, tetrafluoropropyl acrylate and octafluoropentyl acrylate.

Further, if desired, this copolymer composition 1
Per 100 parts by weight of methacrylic acid, o-methylphenylmaleimide, maleimide,
It is also possible to introduce components such as maleic anhydride, styrene, acrylic acid, and a methacrylic acid six-membered cyclized product. Specifically, for example, a copolymer of heptadecafluorodecyl methacrylate and methyl methacrylate, a copolymer of tetrafluoropropyl methacrylate and methyl methacrylate, a copolymer of trifluoroethyl methacrylate and methyl methacrylate, pentafluoropropyl. A copolymer of methacrylate and methyl methacrylate,
Heptadecafluorodecyl methacrylate / tetrafluoropropyl methacrylate / methyl methacrylate copolymer, heptadecafluorodecyl methacrylate / trifluoroethyl methacrylate / methyl methacrylate copolymer, heptadecafluorodecyl methacrylate / trifluoroethyl methacrylate / tetra Examples thereof include copolymers of fluoropropyl methacrylate and methyl methacrylate.

The composition ratio of each monomer may be appropriately adjusted and determined so that the refractive index of the sheath resin is lower than the refractive index of the core material by 0.005 or more. Among these, heat resistance,
Considering the balance of transparency and mechanical properties, it is preferable to use a copolymer of heptadecafluorodecyl methacrylate, trifluoroethyl methacrylate, tetrafluoropropyl methacrylate and methyl methacrylate.

The vinylidene fluoride resin includes vinylidene fluoride resin and vinylidene fluoride and other components such as tetrafluoroethylene, trifluoroethylene, hexafluoropropylene, hexafluoroacetone and at least one component. There are copolymers. The sheath resin does not necessarily need to contain a component containing fluorine. However, the refractive index of the sheath resin needs to be lower than the refractive index of the core material by 0.005 or more and 0.25 or less. Preferably 0.0
It is desirable that it is lower than 4 and lower than 0.25.

If the refractive index difference with the core material is less than 0.005, the refractive index of the core material is too close, and the amount of light taken into the plastic optical fiber becomes too small.
The detection sensitivity of the optical sensor deteriorates. Further, if the difference in the refractive index from the core material exceeds 0.25, the crystallinity of the sheath resin increases and the transmission loss deteriorates. The refractive index is 23 using the Abbe refractometer.
The value measured using a sodium D line as a light source in a thermostatic chamber at ℃ is used.

The melt index of the core material is 0.5.
It is preferably g / 10 minutes or more and 10 g / 10 minutes or less. The melt index of the sheath material is larger than the melt index of the core material, and is preferably 5 g / 10 minutes or more and 60 g / 10 minutes or less. This melt index is measured according to ASTM-1238 under the conditions of a test temperature of 230 ° C., a load of 3.8 kg, and a die inner diameter of 2.0955 mm.

When the melt index of the sheath resin is too small, the wire diameter varies greatly due to the large frictional resistance with the wall surface of the die, and the fiber cannot be molded. On the other hand, if it is too large, only the sheath will flow first, and this too cannot be molded into a fiber having a constant wire diameter.

The multicore plastic optical fiber of the present invention comprises:
Its cross section is generally substantially circular and its diameter is about 0.1 mm to 3 mm, usually 0.5 mm to
It is about 1.0 mm. Here, the diameter of each core is 50μ
It is not less than m and not more than 200 μm. The diameter of each core is 200
If it is larger than μm, the optical loss due to bending of the optical fiber becomes large. When the diameter of each core is smaller than 50 μm, transmission loss increases and noise may occur when a laser is used as a light source.

Since it is necessary to make the cross section as uniform as possible, the number of cores is set to 7 or more so that the arrangement of the cores is stable.
It is preferably 500 or less. In a multi-core plastic optical fiber having such a structure, a large number of cores and a sheath resin surrounding it are firmly integrated,
Even if this multi-core plastic optical fiber having a cross-sectional diameter of about 1 mm is bent into a small size, the optical loss is far superior to that of commercially available plastic optical fibers.

The method for producing a multi-core plastic optical fiber according to the present invention uses a special nozzle and two extruders under a clean environment with almost no dust and dust, and a core material and a sheath material in a molten state. And is preferably performed by a composite spinning method in which a multicore plastic optical fiber having a sea-island structure is molded.
That is, the core material and the sheath material are supplied to the composite spinning die in a molten state, first, the core material is supplied almost evenly to a die plate having seven or more holes, and subsequently, the core material is guided by a guide of a thin tube. Let it flow down. Next, the molten sheath material is supplied around all the thin tubes in which the core material flows, and is spun into a structure in which the core serves as an island and the sheath serves as the sea. Then, it is stretched 1.3 times to 3.
The multi-core plastic optical fiber of the present invention is obtained by orienting the molecules to 0 times and improving the mechanical properties.

The cores are preferably arranged in a close packing structure. However, when the number of cores is relatively small, the cores arranged on the outermost periphery are made uniform in order to make the influence of the subsequent coating uniform. It is preferable that they are on the same circumference. For example, a 7-core plastic optical fiber in which one core wire is surrounded by 6 core wires in a circular shape, and a 19-core plastic optical fiber in which the outer circumference is surrounded by 12 core wires in a circular shape is further added. A 37-core, 61-core, 91-core, etc. plastic optical fiber which is sequentially surrounded by a circle is preferable.

The multicore plastic optical fiber of the present invention comprises:
Since it is mainly used for photoelectric sensors, the resolution as an image fiber does not matter, but the ratio of the area of the core to the area of the sheath in the cross section of the multi-core plastic optical fiber is 4
It is 0 to 60 to 98 to 2. When the core ratio is smaller than 40:60, the amount of transmitted light becomes smaller. If the sheath ratio is smaller than 98: 2, the transmission loss cannot be maintained.

When it is desired to increase the amount of transmitted light, the amount of the sheath should be small within the range where the transmission loss value is maintained, and the ratio of the area of the core to the area of the sheath in the cross section of the multicore plastic optical fiber is 90:10. To 98 to 2 are preferred.

The multicore plastic optical fiber thus produced is coated with a resin composition for coating to further improve heat resistance and mechanical properties, and is actually used as a multicore plastic optical fiber cable. Preferably. A known resin composition can be used as the resin composition for protective coating. For example, polyethylene, polypropylene, ethylene-vinyl alcohol copolymer, rubber, various thermoplastic elastomers, polyvinyl chloride, crosslinked polyolefin, crosslinked polyvinyl chloride, chlorinated polyethylene compound, polyamide resin, fluororesin, polyester resin, polyurethane resin , A silicone resin, a thermosetting resin, an ultraviolet curable resin and the like, and a mixture of these resins.

As reinforcing fibers, aramid fibers, polyacetal fibers, ultra high molecular weight polyethylene fibers, metal fibers, etc. may be interposed. The thickness of the coating layer may be appropriately determined according to the actual conditions of use. It is also possible to stack several layers.

As a method for coating the plastic optical fiber with these protective coating resin compositions, a method in which the plastic optical fiber is produced by a composite spinning method and then the outer side thereof is coated with a heat-melted coating material is adopted. Preferably. For example, the method of coating is to coat the plastic optical fiber with molten resin using a crosshead die to provide wire coating.

The multicore plastic optical fiber for an optical sensor and the cable thereof according to the present invention, having the above-mentioned structure, has a characteristic that the amount of light is small and the transmission loss is small even if the fiber is bent slightly. Even with a conventional bundle fiber in which thin optical fibers are bundled, the optical loss when bent can be reduced, but since the thin individual optical fibers of the bundle fiber are disjointed, there is a problem in fixing at the terminal.

However, since the core wire of the multicore plastic optical fiber of the present invention is fixed by the sheath resin, unlike the bundle fiber, it can be handled as an optical fiber having one core in appearance and can be used as a connector or the like. The terminal fixing method can be fixed by caulking the covering or adhering with an adhesive, and the constituent cores do not retract or jump out.

[0030]

EXAMPLES Hereinafter, the present invention will be described with reference to examples in order to further clarify the present invention, but the scope of the present invention is not limited to these examples. [Measurement method] Melt index: Using a melt indexer manufactured by Toyo Seiki, in accordance with ASTM-1238, a test temperature of 23
The measurement was performed at 0 ° C., a load of 3.8 kg, and a die inner diameter of 2.0955 mm. Refractive index: Measured using an Atago Abbe refractometer type 1 and using a sodium D line in a thermostatic chamber at 23 ° C. Transmission loss: Measured by the cutback method of 52 m-2 m. A monochromatic light with a wavelength of 650 nm or 670 nm is used as the light source, and the incident opening angle is 0.15 radian.

Example 1 A methyl methacrylate resin having a melt flow index of 2 g / 10 minutes and a refractive index of 1.492 as a core resin, and a melt flow index of 30 g / 10 minutes and a refractive index of 1.405 as a sheath resin. The vinylidene fluoride resin was used. Refractive index difference is 0.08
It was 7. The methyl methacrylate resin, which is the core material, was melted by an extruder for core material and supplied to a die plate having 217 holes. Next, the sheath resin is supplied to a die plate having 217 holes so that the core material is filled around the core material, and all the core wires are filled and closely attached to each other by attaching a cap squeezed and converged. A multicore plastic optical fiber having a substantially circular cross section was obtained.

At this time, the volume ratio of the core resin to the sheath resin was set to 80/20. The average diameter of one core of this multicore plastic optical fiber was about 60 μm, and the total diameter was 1.0 mm. The transmission loss of this multicore plastic optical fiber was 0.24 dB / m at a wavelength of 650 nm as measured by the 52 m-2 m cutback method. Further, this multicore plastic optical fiber was coated with low density polyethylene to obtain a multicore plastic optical fiber cable having an outer diameter of 2.2 mm. The transmission loss of this multi-core plastic optical fiber cable is 52m-2m
It was 0.24 dB / m at a wavelength of 650 nm as measured by the cutback method, which was the same as before the coating.

Next, the bending characteristics of this multicore plastic optical fiber cable were measured. L with center wavelength of 657 nm
The ED was used as the light source. This multi-core plastic optical fiber cable is cut into a length of 3 m, and the central part has a radius of 10
When the amount of transmitted light when wound around a cylinder of mm once is measured, it holds 99% or more of that when not bent,
There was almost no bending loss. This multi-core plastic optical fiber cable was subjected to a heat resistance test at a humidity of 60 ° C. and 95% RH. After 1000 hours, 0.1 dB /
Only a loss increase of about m was observed and the stability was high.

(Example 2) The same core resin, sheath resin and protective coating material as in Example 1 were used. The same die plate with 217 holes as in Example 1 was used. The difference from Example 1 is that the volume ratio of the core resin to the sheath resin is 95: 5. The average diameter of one core of this multicore plastic optical fiber was about 66 μm, and the total diameter was 1.0 mm. Since the ratio of the sheath was small, the shape of each core was almost regular hexagon.
The transmission loss of this multi-core plastic optical fiber is 52m.
It was 0.18 dB / m at a wavelength of 650 nm as measured by the -2m cutback method.

Further, this multicore plastic optical fiber was coated with low density polyethylene to obtain a multicore plastic optical fiber cable having an outer diameter of 2.2 mm. The transmission loss of this multi-core plastic optical fiber cable is 52m-
It was 0.18 dB / m at a wavelength of 650 nm as measured by a 2 m cutback method, which was the same as before coating.

Next, the bending characteristics of this multicore plastic optical fiber cable were measured. L with center wavelength of 657 nm
The ED was used as the light source. This multi-core plastic optical fiber cable is cut into a length of 3 m, and the central part has a radius of 10
When the amount of transmitted light when it was wound around a cylinder of mm once was measured, it was 99% when it was not bent, and there was almost no bending loss. When this multicore plastic optical fiber cable was subjected to a heat resistance test at a humidity of 60 ° C. and 95% RH, a loss increase of about 0.1 dB / m was observed after 1000 hours, and the stability was high.

(Example 3) The same core resin, sheath resin and protective coating material as in Example 1 were used. The methyl methacrylate resin, which is the core material, was melted by an extruder for core material and supplied to a die plate having 37 holes. Next, the sheath resin is supplied to a die plate having 37 holes so that the core material is filled around the core material, and all the core wires are filled and closely attached to each other by attaching a squeezed cap and converging. A multicore plastic optical fiber having a substantially circular cross section was obtained.

The volume ratio of the core resin to the sheath resin at this time was set to be 91: 9. The average diameter of one core of this multicore plastic optical fiber was about 160 μm, and the total diameter was 1.0 mm. The transmission loss of this multicore plastic optical fiber was 0.17 dB / m at a wavelength of 650 nm as measured by the 52 m-2 m cutback method.

Further, this multicore plastic optical fiber was coated with low density polyethylene to obtain a multicore plastic optical fiber cable having an outer diameter of 2.2 mm. The transmission loss of this multicore plastic optical fiber cable is 52m-
It was 0.17 dB / m at a wavelength of 650 nm as measured by a 2 m cutback method, which was the same as before coating. Next, the bending characteristics of this multicore plastic optical fiber cable were measured. An LED having a center wavelength of 657 nm was used as a light source. This multi-core plastic optical fiber cable was cut into a length of 3 m, and the amount of transmitted light was measured when the center part was wrapped around a cylinder with a radius of 10 mm once. Was almost never. When this multicore plastic optical fiber cable was subjected to a heat resistance test at a humidity of 60 ° C. and 95% RH, a loss increase of about 0.1 dB / m was observed after 1000 hours, and the stability was high.

Example 4 A polycarbonate resin having a melt index of 4.5 and a refractive index of 1.586 was used as a core resin, and a melt index of 30 was used as a sheath resin.
A vinylidene fluoride resin having a refractive index of 1.392 was used. The difference in refractive index was 0.194. The core material polycarbonate resin was melted by an extruder for core material and supplied to a die plate having 217 holes. Next, the sheath resin is supplied to a die plate having 217 holes so that the core material is filled around the core material, and all the core wires are filled and closely attached to each other by attaching a cap squeezed and converged. A multicore plastic optical fiber having a substantially circular cross section was obtained.

The volume ratio of the core resin to the sheath resin at this time was set to be 91: 9. The average diameter of one core of this multicore plastic optical fiber was about 64 μm, and the total diameter was 1.0 mm. The transmission loss of this multicore plastic optical fiber was 0.8 dB / m at a wavelength of 670 nm as measured by the 52m-2m cutback method.

Further, this multicore plastic optical fiber was coated with low density polyethylene to obtain a multicore plastic optical fiber cable having an outer diameter of 2.2 mm. The transmission loss of this multi-core plastic optical fiber cable is 52m-
It was 0.8 dB / m at a wavelength of 670 nm as measured by a 2 m cutback method, which was the same as before coating. Although the transmission loss was larger than that in Example 1, the difference in refractive index was large. Therefore, in the case of the LED light source, the amount of received light was large, and the optical power at a length of 2 m was about 1.5 dB larger than that in Example 1.

Next, the bending characteristics of this multicore plastic optical fiber cable were measured. L with center wavelength of 657 nm
The ED was used as the light source. This multi-core plastic optical fiber cable is cut into a length of 3 m, and the central part has a radius of 10
When the amount of transmitted light when wound around a cylinder of mm once is measured, it holds 99% or more of that when not bent,
There was almost no bending loss. This multi-core plastic optical fiber cable was subjected to a heat resistance test at a humidity of 60 ° C. and 95% RH. After 1000 hours, 0.1 dB /
Only a loss increase of about m was observed and the stability was high.

Comparative Example 1 The same core resin, sheath resin and protective coating material as in Example 1 were used. A core of a methyl methacrylate resin and a sheath of the above-mentioned resin are spun into a single-core plastic optical fiber having a core diameter of 0.98 mm and an outer diameter of 1.0 mm. After coating, a plastic optical fiber cable having an outer diameter of 2.2 mm was obtained.

Next, the bending characteristics of this plastic optical fiber cable were measured. LED with center wavelength of 657 nm
Was used as the light source. When this single-core plastic optical fiber cable was cut into a length of 3 m and the central portion was wound around a cylinder having a radius of 5 mm once, the amount of transmitted light was measured, and only 61% of that when not bent was retained.

Comparative Example 2 The same core resin, sheath resin and protective coating material as in Example 1 were used. Melt the methyl methacrylate resin, which is the core material, with an extruder for core material,
It was supplied to a die plate having 0 holes. Next, the sheath resin is supplied to a die plate having 3500 holes so that the core material is filled around the core material, and all core wires are filled and tightly adhered so that all core wires are converged and converged. A multicore plastic optical fiber having a substantially circular cross section was obtained.

At this time, the volume ratio of the core resin to the sheath resin was set to 80/20. The average diameter of one core of this multicore plastic optical fiber was about 15 μm, and the total diameter was 1.0 mm. The transmission loss of this multi-core plastic optical fiber was 1.0 dB / m at a wavelength of 650 nm as measured by the 52m-2m cutback method.

Further, this multicore plastic optical fiber was coated with low density polyethylene to obtain a multicore plastic optical fiber cable having an outer diameter of 2.2 mm. The transmission loss of this multi-core plastic optical fiber cable is 52m-
It was 1.0 dB / m at a wavelength of 650 nm as measured by a 2 m cutback method, which was the same as before coating. Next, the bending characteristics of this multicore plastic optical fiber cable were measured. An LED having a center wavelength of 657 nm was used as a light source. This multi-core plastic optical fiber cable was cut into a length of 3 m, and the amount of transmitted light was measured when the center part was wrapped around a cylinder with a radius of 10 mm once. As a result, 99% or more of that without bending was retained. There was almost no loss. When this multicore plastic optical fiber cable was subjected to a heat resistance test at a humidity of 60 ° C. and 95% RH, a deterioration of 0.4 dB / m was observed after 1000 hours.

[0049]

According to the present invention, it is possible to obtain a multi-core plastic optical fiber for an optical sensor, which has a small transmission loss, good environmental resistance, and a small increase in the transmission loss even when the optical fiber is bent, that is, a small bending loss. The multi-core plastic optical fiber for an optical sensor obtained by the present invention has a transmission loss of 52 m-2 m, a cut-back method, and a light source of wavelength 650.
nm or 670 nm monochromatic light is used and the incident aperture angle is 0.
It is less than 1.0 dB / m when measured at 15 radians.

Furthermore, when a heat resistance test of this multi-core plastic optical fiber cable was performed at a humidity of 60 ° C. and 95% RH, a change of less than 0.4 dB / m was observed after 1,000 hours, and the resistance was high. Good environmental characteristics. In addition, bending loss uses an LED with a center wavelength of 657 nm as a light source,
Cut this multi-core plastic optical fiber to a length of 3 m,
When the transmitted light was measured when the central part was wrapped around a cylinder having a radius of 10 mm once, 90% or more of the light when not bent was retained, showing an extremely good value.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of a multicore plastic optical fiber of the present invention.

FIG. 2 is a schematic view showing a cross section of a multicore plastic optical fiber cable of the present invention.

[Explanation of symbols]

 1 core 2 sheath 3 protective coating layer

Claims (4)

[Claims] 1. The diameter of each core is not less than 50 μm and not more than 200 μm.
m or less, and 7 or more of the core fibers are separately partitioned,
The sheath resin having a refractive index lower than the refractive index of the core resin by 0.005 or more and 0.25 or less is filled and collected, and the ratio of the core area to the sheath area of the cross section is 40:60 to 98: 2. A multi-core plastic optical fiber for an optical sensor. 2. The ratio of the area of the core to the area of the sheath is 90:10.
The multi-core plastic optical fiber for an optical sensor according to claim 1, wherein the multi-core plastic optical fiber is from 98 to 2. 3. The multicore plastic optical fiber for an optical sensor according to claim 1, wherein the refractive index of the resin of the sheath is lower than the refractive index of the resin of the core by 0.04 or more. 4. A multicore plastic optical fiber cable in which a protective coating layer is provided on the multicore plastic optical fiber for an optical sensor according to claim 1.