JPH08110420A - Plastic optical fiber - Google Patents

Abstract

PURPOSE: To provide a plastic optical fiber used for short-distance optical communication. CONSTITUTION: This plastic optical fiber 11 is produced by heating and fusing a preform 10 consisting of a core having high refractive index and a plastic clad having lower refractive index than the core, and spinning into a fiber having a specified outer diameter. By using a material which is solid at <=70 deg.C as the dopant to be added to the core, a plastic optical fiber with little transmission loss can be drawn while suppressing shrinkage after thermal deterioration.

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 used for short distance optical communication.

[0002]

2. Description of the Related Art An optical fiber having both a core and a clad made of plastic is used as a short-distance optical transmission line in which transmission loss is not a problem between electronic devices for transmitting and receiving optical signals, as compared with glass fiber. It is widely used due to its ease of use and low cost, and is particularly important in the concept of next-generation communication networks such as LAN and ISDN.

Conventionally, a step index (SI) type optical fiber having a refractive index distribution as shown in FIG. 2 has been put into practical use. However, this fiber has a small transmission capacity and is used for communication. The graded index (G
It is necessary to use type I) optical fiber.

A conventional method for producing a plastic optical fiber is, for example, Japanese Patent Laid-Open No. 12460/1992.
As disclosed in Japanese Patent Laid-Open No. 2 (1994), there is used a method in which a core material is spun into a predetermined diameter and a clad material is coated on the core material. This method is used for manufacturing a GI type plastic optical fiber. However, there is a problem that the coating process must be performed in multiple steps, and the manufacturing process is complicated.

Therefore, if a GI type preform is synthesized, heated and melted to form a fiber, the number of manufacturing steps can be reduced, and various optical fibers having different outer diameters can be manufactured.

[0006]

However, in the method of inserting the GI preform into the drawing furnace and drawing the wire,
When the drawing tension is high, the polymer of the clad material is oriented, so that there is a problem that after drawing, when the drawing environment receives heat in the laying environment, the polymer shrinks.

In view of the above problems, it is an object of the present invention to provide a plastic optical fiber which suppresses fluctuations in outer diameter due to heat after being made into a fiber and can guarantee long-term reliability as a plastic optical fiber.

[0008]

A plastic optical fiber according to the present invention which achieves the above object is a plastic optical fiber comprising a core having a high refractive index and a clad having a refractive index lower than that of the plastic optical fiber. It is characterized in that the dopant added to the core is solid at a temperature of 70 ° C. or lower. In addition, the molecular weight of the dopant is 10
It may be 00 or less. Further, the refractive index distribution of the fiber may be of a graded index (GI) type.

The contents of the present invention will be described below.

FIG. 1 schematically shows a plastic optical fiber drawing apparatus for carrying out the drawing of the plastic optical fiber of the present invention. As shown in the figure, a heater 2 and a furnace core tube 3 are provided in the furnace body 1, and an optical fiber resin base material (preform) 10 is provided from an upper opening 1 a of the furnace body 1.
Is inserted, the drawn plastic optical fiber 11 is drawn out from the lower opening 1b, and then the outer diameter measuring device 4 measures the outer diameter of the plastic optical fiber 11 before it is wound by the winding device 5.

In the present invention, the dopant added to the core constituting the resin base material (preform) 10 for optical fiber is a material which is solid at 70 ° C. or lower. This is because when the optical fiber is drawn, the optical fiber 11 is stretched in the longitudinal direction, so that the polymer constituting the clad is oriented, and the oriented fiber is taken up by the reel. As a result, when the polymer receives heat, it shrinks in an attempt to return to its original state. As a result, the optical fiber itself contracts, and along with this, strain is applied in the longitudinal direction of the optical fiber, causing structural irregularity and increasing transmission loss. Therefore, as shown in Examples described later, the dopant added to the core is made of a material that is solid at 70 ° C. or lower, so that the mobility of the dopant is suppressed and diffusion is suppressed. Here, the reason why the dopant is solid at 70 ° C. or lower is in consideration of the laying environment of the plastic optical fiber. Also, if the molecular weight of the dopant is large, the compatibility with the polymer deteriorates,
The molecular weight is preferably 1,000 or less. Further, a dopant having a small absorption in the visible light region is preferable in view of transmission loss.

Here, the dopant added to the core is 70
℃ The material is solid below, for example, diphenyl phthalate _{(C 6 H 4 (COOC 6} H 5) 2; mp 70-7
3 ° C.), triphenylphosphine _{((C 6 H 5) 3} P;
Melting point 80.5 ° C.) and dibenzyl phosphate ((C
₆ H ₅ CH ₂ O) ₂ PHO ₂ ; melting point 78-79 ° C.), 4,
4′-dibromobenzyl (melting point: 224-226 ° C.),
4,4'-dibromobiphenyl (melting point; 167-170)
C.), 2,4'-dibromoacetophenone (melting point; 10
8 to 110 ° C.), 3 ′, 4′-dichloroacetophenone (melting point; 72 to 74 ° C.), 3,4-dichloroaniline (melting point; 70 to 72.5 ° C.), 2,4-dibromoaniline (melting point; 78 ˜80 ° C.), 2,6-dibromoaniline (melting point; 80 to 82 ° C.), 1,4-dibromobenzene (melting point; 87 to 89 ° C.) and the like.

The plastic optical fiber preform used in the present invention shows a GI type refractive index distribution, uses polymethylmethacrylate (PMMA) having good light transmittance as a clad material, and has a high refractive index compound in the core. The preform is not limited in length and outer diameter. Here, examples of the compound having a high refractive index include benzyl-n-butyl phthalate (refractive index: 1.575) and 1-methoxyphenyl-1-.
Phenylethane (refractive index: 1.571), benzyl benzoate (refractive index: 1.568), bromobenzene (refractive index: 1.557), o-dichlorobenzene (refractive index:
1.551), m-dichlorobenzene (refractive index: 1.5
43), 1,2′-dibromoethane (refractive index: 1.53
8), 3-phenyl-1-propanol (refractive index: 1.
532) etc. can be illustrated. Further, a conventional liquid refractive index adjusting material as a dopant and a solid material at 70 ° C. or lower can be used together. The compounding ratio in this case can be 5 to 50% by weight of the dopant with respect to the polymer, but when a large amount of the dopant is compounded, the mechanical properties of the resulting fiber deteriorate,
It is desirable to add up to about 20% by weight. In particular, the liquid refractive index adjusting material and the material that is solid at 70 ° C. or lower can be mixed in any proportion, but if the proportion of the solid material is high, the heat resistance of the optical fiber can be expected. On the contrary, when the ratio of the liquid refractive index adjusting material is high, the loss can be suppressed low. Also,
As the material of the preform, in addition to the polymethylmethacrylate (PMMA), polycarbonate (PC),
And monofunctional (meth) acrylates, fluorinated alkyl (meth) acrylates, polyfunctional (meth) acrylates, polyfunctional (meth) acrylates, acrylic acid, methacrylic acid, styrene, chlorostyrene, etc. Examples thereof include transparent copolymers of a monomer and methyl methacrylate, but are not limited thereto.

[0014]

The preferred embodiments of the present invention will be described below.

(Example 1) Using PMMA for the cladding,
Diphenylphthalic acid (C ₆H
_Four(COOC₆H_Five)₂A melting point of 70 to 73 ° C.)
And a plastic optical fiber having a GI type refractive index distribution
A preform for ba was prepared. The temperature inside the furnace core tube is 220 ° C
Insert the preform into the drawing furnace set to
To 650 μm and draw at a linear velocity of 2 m / min.
went.

The transmission loss of the obtained GI type plastic optical fiber was measured and found to be 220 d at a wavelength of 650 nm.
B / km. Next, after degrading this fiber at 70 ° C. for one day, the shrinkage residual ratio and the transmission loss were measured and found to be 99% and 210 dB / km, respectively, and the fluctuations were small.

(Example 2) Using PMMA for the cladding,
Triphenylphosphine (((
C ₆ H ₅ ) ₃ P; melting point 80.5 ° C.) was doped to prepare a preform for a plastic optical fiber having a GI type refractive index distribution. Insert the preform into a drawing furnace with the temperature inside the furnace core tube set to 220 ° C, and set the center value of the outer diameter to 650 μm.
Was set, and drawing was performed at a linear velocity of 2 m / min.

The transmission loss of the obtained GI type plastic optical fiber was measured and found to be 230 d at a wavelength of 650 nm.
B / km. Next, after the fiber was deteriorated at 70 ° C. for 1 day, the shrinkage residual ratio and the transmission loss were measured to be 97% and 240 dB / km, respectively, and the fluctuations were small.

(Example 3) PMMA was used for the cladding,
Dibenzyl phosphate (((
C ₆ H ₅ CH ₂ O) ₂ PHO ₂ ; melting point 80.5 ° C.) was doped to prepare a preform for a plastic optical fiber having a GI type refractive index profile. The temperature inside the furnace core tube is 220
The preform was inserted into the drawing furnace set at 0 ° C., the center value of the outer diameter was set at 650 μm, and drawing was performed at a drawing speed of 2 m / min.

The transmission loss of the obtained GI type plastic optical fiber was measured and found to be 250 d at a wavelength of 650 nm.
B / km. Next, after degrading this fiber at 70 ° C. for 1 day, the shrinkage residual ratio and the transmission loss were measured and found to be 98% and 240 dB / km, respectively, and their fluctuations were small.

Comparative Example 1 PMMA was used for the cladding,
PMMA was doped with diphenyl sulfide (liquid at room temperature) into the core to prepare a preform for a plastic optical fiber having a GI type refractive index distribution. Insert the preform into a drawing furnace with the temperature inside the furnace core tube set to 220 ° C, set the center value of the outer diameter to 650 μm, and draw at a linear velocity of 2 m / m.
The line was drawn in.

The transmission loss of the obtained GI type plastic optical fiber was measured and found to be 230 d at a wavelength of 650 nm.
B / km. Next, after the fiber was deteriorated at 70 ° C. for 1 day, the shrinkage residual ratio and the transmission loss were measured to be 80% and 450 dB / km, respectively, and the fluctuations were large.

(Comparative Example 2) PMMA was used for the cladding,
PMMA was doped with diphenylmethane (liquid at room temperature) in the core to prepare a preform for a plastic optical fiber having a GI type refractive index distribution. Insert the preform into a drawing furnace with the temperature inside the furnace core tube set to 220 ° C, set the center value of the outer diameter to 650 μm, and draw at a linear velocity of 2 m / m.
The line was drawn in.

The transmission loss of the obtained GI type plastic optical fiber was measured and found to be 250 d at a wavelength of 650 nm.
B / km. Next, after the fiber was deteriorated at 70 ° C. for 1 day, the shrinkage residual ratio and the transmission loss were measured and found to be 75% and 500 dB / km, respectively, and the fluctuations were large.

(Comparative Example 3) PMMA was used for the clad,
Bromobenzene for PMMA in the core (liquid at room temperature)
To prepare a preform for a plastic optical fiber having a GI type refractive index distribution. The preform was inserted into a drawing furnace in which the temperature inside the furnace core tube was set to 220 ° C., the center value of the outer diameter was set to 650 μm, and drawing was performed at a drawing speed of 2 m / min.

The transmission loss of the obtained GI type plastic optical fiber was measured and found to be 220 d at a wavelength of 650 nm.
B / km. Next, after degrading this fiber at 70 ° C. for 1 day, the shrinkage residual ratio and the transmission loss were measured and found to be 70% and 600 dB / km, respectively, and the fluctuations were large.

In the drawing method of the plastic optical fiber of this embodiment, since the solid material at 70 ° C. or lower is used as the dopant for the core forming the fiber, the shrinkage after the heat deterioration is suppressed, and the transmission loss is reduced. It is possible to reduce the rise. As a result, long-term reliability when the optical fiber is installed can be guaranteed.

[0028]

As described above, according to the plastic optical fiber of the present invention, the solid core material at 70 ° C. or lower is used as the dopant for the core of the fiber, so that the shrinkage after thermal deterioration is suppressed. As a result, it is possible to reduce the increase in transmission loss.

[Brief description of drawings]

FIG. 1 is a schematic view of a drawing apparatus for carrying out drawing of an optical fiber according to the present invention.

FIG. 2 is a refractive index profile of a step index (SI) type optical fiber.

FIG. 3 is a refractive index distribution diagram of a graded index (GI) type optical fiber.

[Explanation of symbols]

 1 Furnace Main Body 2 Heater 3 Furnace Core Tube 4 Outer Diameter Measuring Device 5 Winding Device 10 Preform 11 Optical Fiber

Front Page Continuation (72) Inventor Yasuhiro Koike 23, 534, Kaeocho, Midori Ward, Yokohama City, Kanagawa Prefecture

Claims (3)

[Claims] 1. A plastic optical fiber comprising a core having a high refractive index and a clad having a refractive index lower than that of plastic, wherein the dopant added to the core is solid at a temperature of 70 ° C. or lower. Plastic optical fiber. 2. The plastic optical fiber according to claim 1, wherein the molecular weight of the dopant is 1000 or less. 3. The refractive index profile of the fiber is of the graded index (GI) type.
The described plastic optical fiber.