JP2000284131A - Plastic optical fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic optical fiber which allows the reduction of the pressure loss of the plastic optical fiber and a process for producing the same. SOLUTION: The process for producing the plastic optical fiber(POF) by drawing an optical fiber preform includes a stage for preparing plural cylindrical polymers 4 and 5 varying in diameters, a stage for constituting the preform 19 by coaxially arranging the polymers 4 and 5 via a spacing in such a manner that the melt viscosity of the polymers 4 and 5 attains the value within a range enclosed by segments successively connecting point A, B,..., H and A and a stage for obtaining the POF by drawing the preform while reducing the pressure in the spacing of the preform. When the melt viscosity of the adjacent polymers 4 and 5 deviates from the region enclosed by the segments successively connecting the point A, B,..., H and A, air bubbles intrude between the polymers 4 and 5 when the polymers 4 and 5 are brought into contact with each other by collapse or the execution of good drawing is no longer possible.

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 and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a conventional method for producing a plastic optical fiber, for example, there is a method described in Japanese Patent Application Laid-Open No. Sho 60-119509. In this method, first, a certain amount of a polymerizable material is poured into a centrifugal molding cylinder, the cylinder is rotated, and the polymerizable material is polymerized by heating. To stop. Thereafter, polymerizable materials having different compositions are injected into the cylinder, and thereafter, the same operation is repeated to obtain a plastic optical fiber preform in which a plurality of polymer layers having different refractive indexes are laminated in the cylinder. Thereafter, the preform is drawn to obtain a plastic optical fiber.

[0003]

However, in the manufacturing method described in the above-mentioned conventional publication, in the obtained plastic optical fiber preform, white turbidity may occur near an interface between polymers adjacent to each other.
There is a problem that the transmission loss of the plastic optical fiber obtained by drawing the preform increases.

[0004] In view of the above circumstances, an object of the present invention is to provide a plastic optical fiber capable of reducing the transmission loss of the plastic optical fiber and a method of manufacturing the same.

[0005]

The present inventors have studied the method of manufacturing a plastic optical fiber described in the above-mentioned conventional gazette, and as a result, the cause of white turbidity generated near the interface between adjacent polymers is as follows. It has been found that a single polymer domain is formed by the reaction of easily reacting monomers near the interface during polymerization. Here, from the viewpoint of preventing the monomers from reacting during polymerization, the polymer is arranged coaxially with a gap therebetween to form an optical fiber preform, and the preform is drawn by drawing a plastic. It is also conceivable to manufacture optical fibers. However, in this case, fine bubbles may be mixed in the drawing process of the optical fiber preform, or the optical fiber preform may not be drawn well.

Accordingly, the present inventors have conducted intensive studies, and as a result, the polymers are arranged coaxially with a gap therebetween to constitute an optical fiber preform, and the melt viscosity of the adjacent polymers is within a specific range. When the optical fiber preform can be drawn well,
In addition, it has been found that mixing of minute air bubbles can be sufficiently prevented in the process.

That is, a method of manufacturing a plastic optical fiber according to the present invention is a method of manufacturing a plastic optical fiber by drawing an optical fiber preform, wherein a plurality of cylindrical polymers having different diameters are prepared. Step 1 and the melt viscosities of the predetermined polymer and the polymer outside and adjacent to the polymer among the plurality of polymers are all points A, B, C, D and E in FIG. , F, G, H and A, a second step of arranging a plurality of polymers coaxially with a gap therebetween so as to have a value in a region surrounded by a line segment sequentially connecting the optical fiber preform. And a third step of drawing the optical fiber preform while reducing the gap between the optical fiber preforms to obtain a plastic optical fiber.

Further, the plastic optical fiber of the present invention is a plastic optical fiber comprising at least one polymer of a different type with respect to the center polymer, which is laminated coaxially outside the center polymer. The melt viscosity of a predetermined polymer among the center polymer and the outer polymer, and the melt viscosity of the outer polymer adjacent to the polymer are all points A, B, C, D, E, and It is characterized in that it is a value in a region surrounded by a line segment connecting F, G, H and A in order.
The combination of the melt viscosities of adjacent polymers is represented by points A, B,
Outside the region surrounded by the line connecting C, D, E, F, G, H and A sequentially, micro bubbles are generated inside the plastic optical fiber, and the transmission loss of the plastic optical fiber increases.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a plastic optical fiber (hereinafter, referred to as “POF”) of the present invention and a method for manufacturing the same will be described. In all the drawings, the same or equivalent components are denoted by the same reference numerals.

FIG. 1 is a sectional view showing the POF 1. As shown in the figure, the POF 1 is a core 2 disposed at the center.
And a clad 3 laminated coaxially outside the core 2. The core 2 and the clad 3 have the melt viscosities of points A, B, C, D, E, and
A value which is a value in an area surrounded by a line connecting F, G, H and A sequentially is used. In FIG. 2, the horizontal axis represents the melt viscosity of the outer polymer, that is, the clad 3, and the vertical axis represents the melt viscosity of the adjacent inner polymer, that is, the core 2. Melt viscosity at points A to H (x,
y) (x: melt viscosity of clad 3; y: melt viscosity of core 2) are point A (1.4, 1.4) and point B (3.
4,1.4), point C (8.1, 2.2), point D (28,
11), point E (28, 28), point F (15.1, 3
0), point G (8.1, 30) and point H (0.5, 2..
2). Here, from the viewpoint of reducing the transmission loss of the POF 1, the melt viscosities of the core 2 and the clad 3 are all points A, B, C ', D', E, F, G ', H and A in FIG.
Are preferably values in a region surrounded by a line segment that sequentially connects Melt viscosity at points C ', D', G '(x, y)
Respectively represent a point C ′ (8.1, 3.4) and a point D ′ (1
5.1, 8.1) and point G '(2.2, 9).

[0011] The melt viscosity is defined as the weight of a polymer at a drawing temperature of 2.1 mm in diameter and 8 mm in length from an orifice having a load of 216 mm.
It refers to the number of grams extruded at 0 g for 10 minutes and is measured by a melt flow index device.

Next, a method of manufacturing the above-described POF 1 will be described.

FIG. 3 is a sectional view showing a series of manufacturing steps of the POF 1. As shown in FIG. 3A, first, a cylindrical clad portion (cylindrical polymer) 5 and a cylindrical core portion (cylindrical polymer) having an outer diameter smaller than the inner diameter of the clad portion 5 are formed. 4) are prepared (first step). The clad part 5 is to be the clad 3 of the POF 1, and the core part 4 is to be the core 2 of the POF 1. The core part 4 has a higher refractive index than the clad part 5. Each of the core portion 4 and the clad portion 5 has a melt viscosity of points A, B, C,
A value that is a value in an area surrounded by a line segment that sequentially connects D, E, F, G, H, and A is used. In FIG. 2, the melt viscosity of the core 4 is represented by the value on the vertical axis, and the melt viscosity of the clad 5 is represented by the value on the horizontal axis. From the viewpoint of reducing the transmission loss of the POF 1, the melt viscosities of the core portion 4 and the clad portion 5 are all points A, B, C ', D', E, F, G ',
It is preferable that the value be within a region surrounded by a line segment connecting H and A sequentially.

The method for manufacturing the clad portion 5 and the core portion 4 is not particularly limited, and for example, an internal method or an extrusion method can be used. According to the internal method, the core part 4 and the clad part 5 are manufactured as follows.

As shown in FIG. 4, a polymerizable material containing at least one kind of monomer, a polymerization initiator and a chain transfer agent and / or a refractive index adjusting agent is placed in a horizontally arranged cylindrical tube 6 for centrifugal molding. throw into. Next, a cylindrical heater 7 surrounding the cylindrical tube 6 while rotating the cylindrical tube 6 around its central axis D.
The polymerizable material is heated and polymerized to obtain the clad portion 5 inside the cylindrical tube 6. The core part 4 is obtained in the same manner. In FIG. 4, reference numeral 8 denotes a polymerizable material supply port, 9 denotes a cylindrical end opening cover, 10 denotes a rotational force transmitting chuck, 11 denotes a bearing, 1
Reference numeral 2 denotes a bearing fixing base, 13 denotes a rubber elastic ring for closing a cylindrical end opening cover, 14 denotes a polymer material supply pipe cock, 15 denotes a nitrogen gas supply pipe cock, 16 denotes a decompression exhaust pipe cock, and 17 denotes a supply pipe. The polymerization apparatus shown in FIG. 4 has a decompression exhaust pipe cock 16 and can perform polymerization under reduced pressure. However, the polymerization operation does not necessarily need to be performed under reduced pressure and can be performed under atmospheric pressure. Alternatively, it can be performed under pressure. When the polymerization operation is performed under atmospheric pressure or under pressure, the exhaust pipe cock 16 for reducing pressure is not used. The monomer is not particularly limited as long as it is transparent to transmitted light after polymerization. For example, methyl methacrylate (hereinafter, referred to as “MMA”), 2,
2,2-trifluoroethyl methacrylate (hereinafter, referred to as
"3FMA"), 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, 1,1,1,
3,3,3-hexafluoroisopropyl-2-fluoroacrylate and the like are used.

Examples of the polymerization initiator include benzoyl peroxide, acetyl peroxide, azobisisobutyronitrile,
Cumene hydroperoxide, t-butyl peroxide, di-t-butyl peroxide (hereinafter referred to as “PB
D "), 1,1-bis (t-butylperoxy)
3,3,5-trimethylcyclohexane and the like are used, and examples of the chain transfer agent include n-butyl mercaptan (hereinafter, referred to as “nBM”), n-octyl mercaptan, lauryl mercaptan, n-butyl mercaptoacetate, and isooctyl mercaptoacetate. And mercaptan-based chain transfer agents such as methyl mercaptoacetate.

Examples of the refractive index adjuster include phenyl benzoate and benzyl benzoate (n = 1.568, hereinafter,
"BEN"), diphenyl phthalate, butylbenzyl phthalate, dibenzyl terephthalate, n-butyl benzyl phthalate (n = 1.568), triphenyl phosphate, tricresyl phosphate (n = 1.555), phosphorus Tris (2-chloroethyl) acid (n = 1.472), biphenyl (n = 1.587), diphenylmethane (n = 1.
577), diphenyl ether (n = 1.579), diphenyl sulfide (n = 1.6327), benzyl phenyl ether, dibenzyl ether (n = 1.56)
2), dimethyl adipate (n = 1.428), dibutyl adipate, dioctyl adipate, diisopropyl adipate (n = 1.423), di (2-ethylhexyl) adipate, dimethyl sebacate (n = 1. 437
2), dimethyl sebacate (n = 1.4372), dibutyl sebacate, dioctyl sebacate, di (2-ethylhexyl) sebacate, tri-n-butyl phosphate (n
= 1.424), trioctyl phosphate, tris (2-chloroethyl) phosphate, tris (fluoroalkyl) phosphate, dimethyl 1,4-cyclohexanedicarboxylate,
Examples thereof include dimethyl 1,4-cyclohexanone-2,5-dicarboxylate, diglycidyl 1,2-cyclohexanedicarboxylate, diisobutyl sulfide (n = 1.453), and tetramethylene sulfone (n = 1.484).

The melt viscosity of the clad part 5 and the core part 4 is as follows:
The value depends mainly on the type of the monomer, the type of the refractive index adjusting agent to be added to the monomer, and the amount of addition, and can be set to an arbitrary value by appropriately selecting these. next,
As shown in FIG. 3A, the clad part 5 and the core part 4 obtained as described above are held vertically, and are arranged coaxially with a gap 18 therebetween to form an optical fiber preform 19 (No. Step 2).

The upper part of the optical fiber preform 19 is provided with a deaeration port 2.
A concave lid 21 in which 0 is formed is attached, and a decompression device (not shown) is connected to the deaeration port 20. Optical fiber preform 1
The pressure in the gap 9 is reduced by a pressure reducing device. And FIG.
As shown in (b), while reducing the gap between the optical fiber preforms 19, the optical fiber preforms 19 are removed from the lower end by the cylindrical heater 2.
2, the base material 19 is heated, and the clad part 5 and the core part 4 are drawn while being thermally fused to obtain a POF 1 (third step). The drawing temperature is a temperature at which the core part 4 and the clad part 5 can be melted, and varies depending on the composition of the material constituting the clad part 5 and the core part 4, but is usually 150 to 250 ° C. .

When the POF 1 is manufactured as described above, the melt viscosity of the adjacent core 4 and cladding 5 is
The following inconvenience occurs if the area outside the area surrounded by the line connecting points A, B, C, D, E, F, G, H and A in FIG.

That is, when the melt viscosity of the core portion 4 is too low than that of the clad portion 5, as shown in FIG. 5A, when the base material 19 is heated to a temperature at which the clad portion 5 can be drawn, Prior to the clad portion 5, the core portion 4 is melted, and the melted portion extends, hangs down, and comes into contact with the clad portion 5 (see the right side of the central axis C in FIG. 5A). At this time, the air bubbles 23 are caught between the core part 4 and the clad part 5.
Accordingly, the transmission loss of the POF 1 obtained by drawing the base material 19 increases. In particular, when the core 4 melts to a considerable extent prior to the cladding 5 when the base material 19 is heated,
Since the melted portion falls, as a result, the core diameter of the POF 1 becomes non-uniform along the length direction, and good drawing cannot be performed.

Also, the melt viscosity of the clad 5
If it is too low, as shown in FIG.
When the base material 19 is heated to a temperature at which
The viscosity of the clad portion 5 decreases, and the portion extends and hangs. At this time, the pressure in the gap 18 of the base material 19 is reduced, so that the extended clad portion 5 sticks to the core portion 4 and, at this time, bubbles 23 are entrained (see the right side of the central axis C in FIG. 5B). Accordingly, the transmission loss of the POF 1 obtained by drawing the base material 19 increases. In particular, if the clad portion 5 melts to a considerable extent prior to the core portion 4 when the base material 19 is heated, the clad diameter of the POF 1 becomes non-uniform along the length direction, and good drawing cannot be performed.

On the other hand, the adjacent core 4 and cladding 5
2 have points A, B, C, D, E, and
When the value is within a region surrounded by a line connecting F, G, H, and A in order, the optical fiber preform 19 can be drawn well, and the core portion 4 and the clad portion 5 come into contact with each other by collapse. Occasionally, air bubbles do not enter between the core part 4 and the clad part 5 (see the left side of the central axis C in FIGS. 5A and 5B). As a result, the transmission loss of the obtained POF1 can be reduced. Note that the method of manufacturing the POF 1 according to the present invention is not limited to the above-described embodiment. For example, the melt viscosities of the adjacent polymers in the optical fiber preform 19 are all within a region surrounded by a line segment connecting points A, B, C, D, E, F, G, H and A in FIG. Is not limited to one, and may be plural. In this case, the melt viscosity of any of the adjacent polymers is set to a value within a region surrounded by a line connecting points A, B, C, D, E, F, G, H, and A in FIG. To

In the optical fiber preform 19, a columnar core may be arranged inside the innermost core 4.

Hereinafter, the contents of the present invention will be specifically described with reference to examples.

(Examples 1 to 6) Outer diameter 28 mm, inner diameter 24 m
m, cylindrical cladding with a length of 60 cm and an outer diameter of 22 m
m, an inner diameter of 10 mm, and a cylindrical core having a length of 60 cm were separately prepared. As the clad part and the core part, those having a melt viscosity shown in Table 1 for each example were prepared.

[Table 1] The clad was produced as follows. That is,
In a horizontally arranged centrifugal molding cylindrical tube having an inner diameter of 30 mm and a length of 60 cm, a solution having a composition (see Table 2) corresponding to the melt viscosity of the clad portion in each Example of Table 1 was set to 113-1.
Only 18 ml was charged, and both ends were sealed with a cylindrical end opening lid and a rubber elastic ring for sealing the cylindrical end opening lid, respectively.

[Table 2]

Thereafter, the solution was polymerized by being rotated around the central axis at a rotation speed of 1500 rpm while heating from the outside at 100 ° C. for 24 hours with a cylindrical heater surrounding the cylindrical tube for centrifugal molding, thereby obtaining a clad portion. The core was manufactured as follows. That is, the inner diameter 26 arranged horizontally
In a cylindrical tube for centrifugal molding having a length of 60 cm and a length of 60 cm, a composition (Table 2) corresponding to the melt viscosity of the core portion in each Example of Table 1 was prepared.
204) to 215 ml, and both ends thereof were sealed with a cylindrical end opening lid and a rubber elastic ring for sealing the cylindrical end opening lid, respectively. Thereafter, the core was obtained by polymerizing the solution by rotating the cylindrical tube for centrifugal molding at a rotational speed of 1500 rpm around the central axis while heating the cylindrical tube from the outside at 100 ° C. for 24 hours with a cylindrical heater. Next, the clad part and the core part were held vertically and arranged coaxially with a gap therebetween to form an optical fiber preform. A concave lid was fitted to the upper end of the optical fiber preform, and a deaeration port formed in the lid was connected to a decompression device (for example, a vacuum pump). Then, the optical fiber preform was inserted into the cylindrical heater at a speed of 1 mm / min while the gap was depressurized by the decompression device, and the optical fiber preform was drawn while collapsing. Here, the temperature of the cylindrical heater was adjusted to 190 ° C. so that the melt viscosity of the core portion and the clad portion at the surface temperature of the optical fiber preform became the value shown in Table 1. The surface temperature of the optical fiber preform was measured using a radiation thermometer.

As a result, the optical fiber preform was successfully drawn, and the POF of the present invention having an outer diameter of 0.6 mm was obtained. This PO
About F, a white light source (AQ-4303, manufactured by Ando Electric Co., Ltd.)
B) and a spectrum analyzer (AQ-, manufactured by Ando Electric Co., Ltd.)
6315B) was used to measure the transmission loss for 650 nm light. The results are shown in Table 1 and FIGS. The first embodiment corresponds to the point H in FIGS.

In Table 1, when the wire drawing is good and the transmission loss is excellent (200 dB / km or less), "」 ";
Drawing is possible, but transmission loss is inferior (300d
(Less than B / km) is indicated by “△”, and poorly drawn is indicated by “×”. Here, “good drawing” means a state where the wire diameter fluctuation is within ± 20 μm and there is no spike or the like, and “poor drawing” means that the drawing cannot be performed or the wire diameter fluctuation is large and bubbles and spikes frequently occur. State. What is a spike?
A phenomenon in which the outer diameter suddenly increases or decreases,
This is caused by an abrupt change in the outer diameter when these portions are formed into fibers due to scratches on the optical fiber preform or on the surface or uneven portions in the crosslinked state. Note that the above evaluation criteria were similarly applied to Tables 3, 4, 5, and 7 below. FIG. 6 is a graph showing evaluations of Examples 1 to 38 and Comparative Examples 1 to 49,
7 is a graph in which a part of FIG. 6 is enlarged, and FIG. 8 is a graph in which a part near the origin in FIG. 7 is enlarged. (Comparative Examples 1 to
9)

An optical fiber preform was constructed in the same manner as in Example 1 except that the core portion and the clad portion each having a melt viscosity shown in Table 1 for each comparative example were used. A line was drawn.

As a result, as shown in Table 1 and FIG. 6, in Comparative Examples 1, 4, 5, and 8, the drawing was poor. On the other hand, for Comparative Examples 2, 3, 6, 7, and 9, although the wire was drawn, the transmission loss of the POF was measured in the same manner as in Example 1, and the transmission loss was inferior.

(Examples 7 to 14) An optical fiber preform was formed in the same manner as in Example 1 except that cores and claddings having melt viscosities shown in Table 3 were used for each example. With respect to this optical fiber preform, the temperature of the cylindrical heater at the time of drawing was set to 210 ° C., and the melt viscosity of the core portion and the clad portion at the surface temperature of the optical fiber preform was adjusted to a value shown in Table 3, Drawing was performed in the same manner as in Example 1.

[Table 3]

The results are shown in Table 3 and FIG. As shown in Table 3 and FIG. 7, in each case, the wire could be drawn well, and the POF obtained by wire drawing was used in Example 1.
When the transmission loss was measured in the same manner as in the above, all were good. (Comparative Examples 10 to 16)

An optical fiber preform was constructed in the same manner as in Example 7 except that the core part and the clad part each having a melt viscosity shown in Table 3 for each comparative example were used. A line was drawn.

As a result, as shown in Table 3 and FIG. 7, in Comparative Examples 11, 12, 14, and 16, the drawing was poor. On the other hand, in Comparative Examples 10, 13, and 15, although the wire was drawn, the transmission loss of the POF was measured in the same manner as in Example 1, and the transmission loss was inferior.

(Examples 15 to 19) An optical fiber preform was formed in the same manner as in Example 1 except that cores and claddings having a melt viscosity shown in Table 4 were used for each example. The melt viscosity of the core portion and the clad portion at the surface temperature of the optical fiber preform was set at 230 ° C.
And the drawing was performed in the same manner as in Example 1.

[Table 4]

As a result, as shown in Table 4 and FIG. 6, the wire could be drawn well in each case, and the transmission loss of the POF obtained by the wire drawing was measured in the same manner as in Example 1. However, all cases were good.

(Comparative Examples 17 to 26) An optical fiber preform was constructed in the same manner as in Example 15 except that cores and claddings having a melt viscosity shown in Table 4 were used for each comparative example. This optical fiber preform was drawn.

As a result, as shown in Table 4 and FIG. 6, in Comparative Examples 18, 19, 21, 23, 25 and 26, the drawing was poor. On the other hand, Comparative Examples 17, 20, 22, 2
With respect to No. 4, although the wire was drawn, the transmission loss of the POF was measured in the same manner as in Example 1, and it was found that the transmission loss was inferior.

(Examples 20 to 30) The melt viscosities of the core portion and the clad portion at the surface temperature of the optical fiber preform when the temperature of the cylindrical heater at the time of drawing was 210 ° C. were as shown in Table 5. The optical fiber preform was formed in the same manner as in Example 1, and the drawing was performed in the same manner as in Example 1. Table 5 shows the results.

[Table 5]

Further, as shown in FIG. 7 together with the results of Tables 3 and 5, in each case, the wire could be drawn well, and the POF obtained by wire drawing was the same as in Example 1. When the transmission loss was measured by using this method, all the cases were good. In Examples 20, 23, and 26,
This corresponds to points A, B, and C in FIG. Table 6 shows the composition of the solution for producing each of the clad portion and the core portion for Examples 20, 23, and 26.

[Table 6]

(Comparative Examples 27 to 36) An optical fiber preform was constructed in the same manner as in Example 20, except that the core portion and the clad portion each having a melt viscosity shown in Table 5 were used for each comparative example. This optical fiber preform was drawn. Table 5 shows the results.

As shown in FIG. 7 together with the results of Tables 3 and 5, no line could be drawn for Comparative Examples 28 to 35. On the other hand, in Comparative Examples 27 and 36, although the wire was drawn, when the transmission loss of the POF was measured in the same manner as in Example 1, the transmission loss was inferior.

(Examples 31 to 38) The melt viscosity of the core and the clad at the surface temperature of the optical fiber preform when the temperature of the cylindrical heater at the time of drawing was 230 ° C. was as shown in Table 7. The optical fiber preform was formed in the same manner as in Example 1, and the drawing was performed in the same manner as in Example 1. Table 7 shows the results.

[Table 7]

As shown in FIG. 6 together with the results of Tables 4 and 7, in each case, the wire could be drawn well, and the POF obtained by wire drawing was transmitted in the same manner as in Example 1. The loss was measured and found to be good in each case. In Examples 37 and 38, points D and D in FIG.
This corresponds to E. Table 6 shows the composition of the solution for producing each of the clad part and the core part in Examples 37 and 38.

(Comparative Examples 37 to 49) An optical fiber preform was formed in the same manner as in Example 31 except that cores and claddings each having a melt viscosity shown in Table 7 were used for each comparative example. This optical fiber preform was drawn. Table 7 shows the results.

As shown in FIG. 6 together with the results of Tables 4 and 7, the draws of Comparative Examples 37 and 39 to 43 were poor. On the other hand, for Comparative Example 38, although the wire was drawn, the transmission loss of the POF was measured in the same manner as in Example 1, and the transmission loss was inferior.

The above Examples 1 to 38 and Comparative Examples 1 to 49
From the results of the above, when the melt viscosities of the core portion and the clad portion are within the region surrounded by the line segments sequentially connecting the points A, B, C, D, E, F, G, H and A shown in FIG. It was found that the material could be drawn well and the transmission loss could be reduced.

[0048]

As described above, according to the present invention, the optical fiber preform can be drawn well and bubbles can be sufficiently prevented from being mixed in the drawing process, so that the transmission loss of the obtained POF can be reduced. can do.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a plastic optical fiber of the present invention.

FIG. 2 is a diagram showing a relationship between melt viscosities of adjacent polymers.

FIG. 3 is a sectional end view showing a series of manufacturing steps of the method for manufacturing a plastic optical fiber of the present invention.

FIG. 4 is a sectional view showing an apparatus for producing a polymer.

FIG. 5 is a cross-sectional view showing a state in which an optical fiber preform is drawn. The left and right sides of the central axis sequentially connect points A, B,..., H and A in FIG. This shows a case where the image is within a region surrounded by a line segment and a case where the image is outside the region.

FIG. 6 is a graph showing evaluations of Examples 1 to 38 and Comparative Examples 1 to 49.

FIG. 7 is an enlarged graph of a part of FIG. 6; 8 is an enlarged graph of a portion near the origin of FIG.

FIG. 8 is an enlarged graph of a portion near the origin in FIG. 7;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Plastic optical fiber, 2 ... Core, 3 ... Cladding, 4 ... Core part (cylindrical polymer), 5 ... Cladding part (cylindrical polymer), 18 ... Gap, 19 ... Optical fiber preform.

Claims (3)

[Claims] 1. A method for producing a plastic optical fiber by drawing an optical fiber preform to produce a plastic optical fiber, comprising: a first step of preparing a plurality of cylindrical polymers having different diameters; Of the plurality of polymers, the melt viscosity of a predetermined polymer and the melt viscosity of the polymer outside and adjacent to the polymer are all points A, B, C, D, E, F, and G in FIG. , H, and A so that the value is within a region surrounded by a line segment that sequentially connects
A second step of arranging the plurality of polymers coaxially with a gap therebetween to constitute the optical fiber preform; and drawing the optical fiber preform while reducing the gap of the optical fiber preform. A third step of obtaining the plastic optical fiber by using the above method. 2. In the first step, a columnar polymer having a smaller diameter than the polymer disposed on the innermost side is prepared, and in the second step, the innermost cylindrical polymer is provided. The method according to claim 1, wherein the columnar polymer is disposed inside the polymer with a gap therebetween to form the optical fiber preform. 3. A plastic optical fiber in which at least one polymer of a different type with respect to the center polymer is laminated coaxially outside the center polymer, wherein the center polymer and the polymer The melt viscosity of a predetermined polymer among the outer polymers and the melt viscosity of the outer polymer adjacent to the polymer are all points A, B, C, D, E, and
A plastic optical fiber having a value within a region surrounded by a line segment connecting F, G, H, and A sequentially.