JP2002040267A - Plastic optical fiber and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic optical fiber for high-speed communication having low transmission loss and a broad transmission band by using a kind of sheath resin. SOLUTION: The plastic optical fiber having an excellent compatibilized part at a boundary between a core and a sheath is manufactured by subjecting a core resin and the sheath resin to multicomponent fiber spinning by a double- layer multicomponent fiber spinning die provided with a nozzle having contracting parts 4, 5 at which a nozzle radius gradually reduces from an upstream part to a downstream part.

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 for short-distance high-speed communication and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, various plastic optical fibers have been developed in the field of communication, and there is a demand for a fiber which can transmit at a higher speed, has less light loss due to bending, and is easy to handle.

[0003] JP-A-9-101423, JP-A-9-101423
JP-A-159844 and JP-A-9-243836 disclose that a core resin and two kinds of sheath resins having different refractive indices are melted and supplied to a three-layer composite spinning die, respectively.
A three-layer high-speed plastic optical fiber comprising a sheath layer / second sheath layer is disclosed. The fiber broadens the transmission band of the plastic optical fiber by reducing the difference between the refractive index of the first sheath layer and the refractive index of the core and lowering the numerical aperture of the fiber, and has a higher refractive index than the first sheath layer. By providing the second sheath layer having a low refractive index, light loss due to bending is reduced.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic optical fiber capable of high-speed communication and having a small optical loss due to bending with a simpler structure using only one kind of sheath resin. is there.

[0005]

Means for Solving the Problems A first aspect of the present invention is to form a core composed of a polymethyl methacrylate resin, form a transparent composition when mixed with the polymethyl methacrylate resin, and form a sodium D line Refractive index at 1.38 ~
A plastic having a sheath made of vinylidene fluoride resin of 1.42, having a transmission band per 50 m of 100 MHz or more, measured at an incident NA of 0.65, and having a compatible portion at the interface between the core and the sheath. A method for producing an optical fiber, wherein the polymethyl methacrylate-based resin and the vinylidene fluoride-based resin are supplied to a two-layer composite spinning die in a molten state, and the nozzle diameter is reduced gradually from upstream to downstream. And a composite spinning through a nozzle having two or more portions.

A second aspect of the present invention is to form a core composed of a polymethyl methacrylate resin and a transparent composition when mixed with the polymethyl methacrylate resin,
A sheath made of a vinylidene fluoride resin having a refractive index of 1.38 to 1.42 at a sodium D line, and a transmission band per 50 m measured at an incident NA of 0.65 is 1
00 MHz or more, and a thickness of 0.6 to
A plastic optical fiber having a compatible part of 3.0 μm and manufactured by the manufacturing method of the present invention.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a method of spinning a core resin and a sheath resin by using a nozzle having two or more reduced portions in which the nozzle diameter rapidly decreases in the middle. This is an invention in which a good compatible part is formed at the interface of No. 1 to realize an interface having a refractive index distribution.

The polymethyl methacrylate (PMMA) resin used as the core resin in the present invention is a homopolymer or a copolymer containing 50% by weight or more of methyl methacrylate. Examples of the copolymerizable component include esters of acrylic acid and methacrylic acid with alcohols such as methanol and ethanol.

The polyvinylidene fluoride resin used as the sheath resin in the present invention forms a transparent composition when mixed with the above-mentioned PMMA resin, and contains sodium D
It is a resin having a refractive index of 1.38 to 1.42 in a line. For example, Japanese Patent No. 260242 or Patent No. 25
No. 83523. Specifically, it is a homopolymer or a copolymer containing 50% by weight or more of vinylidene fluoride, or a composition containing 50% by weight or more of vinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoroacetone, Copolymer of fluoride, hexafluoroacetone and trifluoroethylene, copolymer of vinylidene fluoride, hexafluoroacetone and tetrafluoroethylene, copolymer of vinylidene fluoride and hexafluoropropene, vinylidene fluoride and hexafluoropropene And tetrafluoroethylene, an alloy of vinylidene fluoride homopolymer and PMMA resin, and the like.

In the present invention, the core resin and the sheath resin are supplied in a molten state to a two-layer composite spinning die, and the core resin and the sheath resin are supplied to the core / sheath die.
A sheath structure is manufactured. A feature of the present invention is that, in the two-layer composite spinning die, in moving the inside of the nozzle while forming a concentric structure of the core and the sheath, two or more reduced portions where the nozzle diameter is gradually reduced from upstream to downstream are reduced. The use of a nozzle provided. In the present invention, by using a nozzle having such a specific structure, a good compatible portion having a higher refractive index than the sheath resin at the interface between the core and the sheath and having a refractive index distribution is formed, and A transmission band can be obtained.

Here, the compatible portion is defined as a portion between a homogeneous boundary line which can be regarded as a core resin when a cross section of a plastic optical fiber is viewed with a transmission microscope and a boundary line of a sheath resin layer which is uniformly mottled by crystals. This is an intermediate layer in which a core resin and a sheath resin are mixed. In the plastic optical fiber of the present invention, the thickness of the compatible portion is 0.6 to 3.0 μm, and preferably 1.7 to 2.5 μm. It is. The compatible portion can be formed by appropriately selecting the type of the sheath and the resistance structure of the nozzle of the composite spinning die.

FIG. 1 schematically shows a cross-sectional shape of an example of a two-layer composite spinning die used in the present invention. In the figure, 1 is a core resin inlet, 2 is a sheath resin inlet, 3 is a junction, 4 is a first reduced portion, 5 is a second reduced portion, and 6 is a strand outlet.

In the composite spinning die shown in FIG. 1, a core resin is introduced from an upstream core resin inlet 1 and a strand of the core resin is wrapped with a sheath resin at a junction 3 to form a concentric structure of a core and a sheath. For a while, the strand is caused to flow in the region of the same diameter for a while, and then the diameter of the strand is sharply reduced in the first reduced portion 4 and then maintained at the same diameter.
After the diameter of the strand is further sharply reduced by the reducing portion 5, the same diameter is maintained for a while, and the strand is discharged from the strand discharge port 6.

The inside of the nozzle having a plurality of reduced portions is a core
While the sheath of the sheath structure is being extruded,
In the first reduction part 4, the fiber corresponding to the numerical aperture (NA) simply composed of the core and the sheath is mixed with the core resin and the sheath resin at the interface between the core and the sheath, and the fiber is formed at the interface between the core and the sheath. A compatible portion having a higher refractive index than the sheath resin is formed. Further, in the second reduced portion 5, the core resin is further mixed into the compatible portion, and the refractive index of the portion closest to the core increases,
A compatible portion having a refractive index distribution is formed, and as a result, a plastic optical fiber having a very low NA can be obtained.

The nozzle according to the present invention has two or more reduced portions in which the diameter of the nozzle gradually decreases. FIG. 2 shows an enlarged sectional view of the reduced portion. In the reduced portion according to the present invention, the angle of inclination of the nozzle wall, represented by θ in FIG. 2, is preferably 5 to 80 °, more preferably 30 to 60 °.

In the plastic optical fiber of the present invention, the core resin is not mixed at a position about 2 μm outside the boundary between the core and the sheath, so that the sheath resin exhibits a low refractive index inherent to the sheath resin. Unlike a single-layer low NA fiber, a large light loss does not occur, and a light quantity equivalent to a fiber having an NA of about 0.5 can be maintained.

In the above description, a nozzle having two reduced portions has been taken as an example. However, a configuration in which three or more reduced portions are provided may be used. In addition, the inclination angle (θ) of the nozzle wall surface in each reduction section may be the same or different.

The strand spun as described above is stretched about 1.3 to 4 times, and then stretched to 100 to 300 times.
A short annealing treatment at a temperature of ° C. for several seconds is performed to obtain a bare plastic optical fiber. Usually, a protective coating is applied to the outside of the bare wire thus obtained and used as a cable.

The transmission band of the plastic optical fiber of the present invention is much larger than the value expected from the refractive index of the same core resin and sheath resin, and the sheath obtained by the conventional manufacturing method is a fluorinated methacrylate. The resin having a structure NA of 0.10 or a resin made of vinylidene fluoride resin.
It is much larger than about 5 fibers. That is, according to the present invention, a fiber having a transmission band of 100 MHz or more per 50 m measured at an incident NA of 0.65 can be obtained.

[0020]

(Examples) As a core resin, a PMMA resin having a refractive index of 1.492 and a weight average molecular weight of 100,000 at a sodium D line at 20 ° C. was used, and vinylidene fluoride / trifluoroethylene was used as a sheath resin. / 80/14/6 (molar ratio) / hexafluoroacetone, having a refractive index at 20 ° C. of sodium D line at 1.395, 230 ° C., and 3.8 kg melt flow. A resin having an index of 20 g / 10 min was used.

The above two resins were supplied to a two-layer composite spinning die via an extruder and a gear pump such that the volume ratio of core resin / sheath resin became 96/4. The temperature of the composite spinning die was 240 ° C., and as shown in FIG. 1, a nozzle having two reduced portions and a diameter of a strand discharge port of 3000 μm was used.

The strand extruded from the strand discharge port of the composite spinning die was stretched and annealed to obtain a bare plastic optical fiber having a core diameter of 980 μm and a sheath outer diameter of 1000 μm. The thickness of the compatible part measured in a photograph of the cross section of the bare wire taken at a magnification of 20000 with a transmission microscope was 1.9 μm. Further, the bare wire was covered with polyethylene so as to have an outer diameter of 2.2 mm to obtain a cable.

The transmission loss of the obtained plastic optical fiber cable was measured using an LNA 0.1
When measured using a light source of 5,650 nm, 130
The loss was as low as dB / km. In addition, the cable 50
When the transmission band of m was measured by a pulse method using a light source of LNA 0.65 and 650 nm, it was 150 MHz.

Further, take 2 m of the cable, and
Loss was 0.7 dB when connected to a 0.6 LED and wrapped once around a 10 mm radius rod.

Comparative Example A plastic optical fiber cable was manufactured in the same manner as in Example except that a nozzle having only one reduced portion was used. When the transmission band per 50 m of the obtained cable was measured in the same manner as in the example, 70
MHz.

[0026]

As described above, according to the present invention,
Excellent plastic light suitable for short-distance, high-speed communication by achieving a wide transmission band and low transmission loss in a core / sheath structure using one kind of sheath resin, and furthermore, obtaining a fiber with small optical loss due to bending. A fiber is provided.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a cross-sectional structure of an example of a two-layer composite spinning die used in the production method of the present invention.

FIG. 2 is an enlarged sectional view of a reduced portion of a nozzle used in the present invention.

[Explanation of symbols]

 1 Core Resin Inlet 2 Sheath Resin Inlet 3 Confluence 4 First Reduction 5 Second Reduction 6 Strand Outlet

Claims (2)

[Claims] 1. A core composed of a polymethyl methacrylate-based resin and a transparent composition when mixed with the polymethyl methacrylate-based resin, and having a refractive index of 1.38 to 1. A plastic optical fiber having a sheath made of a vinylidene fluoride-based resin which is 42, a transmission band per 50 m of 100 MHz or more, measured at an incident NA of 0.65, and having a compatible portion at the interface between the core and the sheath. The polymethyl methacrylate-based resin and the vinylidene fluoride-based resin are supplied in a molten state to a two-layer composite spinning die, and a reduced portion in which the nozzle diameter is gradually reduced from upstream to downstream is formed. A method for producing a plastic optical fiber, comprising performing composite spinning through a nozzle having two or more locations. 2. A core composed of a polymethyl methacrylate-based resin and a transparent composition when mixed with the polymethyl methacrylate-based resin, and having a refractive index of 1.38-1. And a sheath made of a vinylidene fluoride-based resin of No. 42, a transmission band per 50 m measured at an incident NA of 0.65 is 100 MHz or more, and a thickness of 0.6 to 3.0 at the interface between the core and the sheath. A plastic optical fiber having a compatible part of 0 μm and manufactured by the manufacturing method according to claim 1.