JPH10268146A - Plastic optical fiber and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide a plastic fiber capable of preventing light leakage without requiring a light-collecting component in connection with a light source and a light receiving portion, and a method of manufacturing the same. SOLUTION: In a refractive index distribution type optical fiber having a matrix of a non-crystalline fluorine-containing polymer having substantially no C—H bond, a diameter or a cross-sectional shape of a light transmitting portion at an end of the fiber is the fiber end. The plastic optical fiber is different from the diameter or cross-sectional shape of the light transmitting part of the other fiber 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 easily connecting a light source or a light receiving section to an optical fiber and connecting the optical fibers to each other, and a method for manufacturing the same.

[0002]

2. Description of the Related Art An optical fiber (hereinafter referred to as an optical fiber strand unless otherwise specified in the present invention, and may be simply abbreviated as a fiber) is an inorganic fiber having excellent light transmission properties over a wide wavelength range. Glass-based optical fibers are known, but optical fibers using plastic as a base material have been developed and put into practical use because they are not only poor in workability and are easily broken when bent, but also expensive. This plastic optical fiber has a core layer based on a polymer such as polymethyl methacrylate, polycarbonate, or polystyrene having good light transmission properties, and a polymer such as a fluorine-containing polymer having a lower refractive index and a substantially transparent refractive index. And a cladding layer having a base material as a basic structural unit. Also, Japanese Patent Application Laid-Open No. 2-244007 proposes using a fluorine-containing resin for the core and the clad.

[0003] A graded index (GI) optical fiber is known as an optical fiber along with a graded index optical fiber comprising a core and a clad. The refractive index distribution of a graded index optical fiber is one in which the refractive index decreases in a curve close to a parabola from the center toward the radial direction (for details, see the following document). As a graded index plastic optical fiber, for example, “Chemical and Industrial” No. 45
Vol. 7 (1992) 1261-1264;
No. 173026, WO94 / 04949, WO94
/ 15005 and the like are known.

According to Japanese Patent Application Laid-Open No. Hei 8-5848,
2. Description of the Related Art A refractive index distribution type optical fiber having a matrix of a non-crystalline fluorine-containing polymer having substantially no C—H bond is known. This optical fiber has a low optical transmission loss and a wide transmission band in a wide transmission wavelength range.

[0005] The product forms of these optical fibers include (1) an optical fiber cord in which an optical fiber is covered with a coating material, (2) a bundle fiber also serving as an optical fiber cord, and (3) a bundle fiber and a tension member. Optical fiber cables and the like in combination.

[0006]

As described above, the plastic optical fiber has characteristics that are not present in the inorganic glass-based optical fiber. However, it is required that the plastic fiber be easily connected to each other or to another optical device or optical element. I was

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is the following inventions (1) to (3).

(1) A plastic optical fiber characterized in that a diameter or a cross-sectional shape of a light transmitting portion of at least one end of the plastic optical fiber is different from a diameter or a cross-sectional shape of a light transmitting portion of a fiber portion other than the fiber end. .

(2) By changing the relative speed of the movement and drawing of the preform when drawing the plastic optical fiber by drawing the base material, or by extruding and drawing the fiber when obtaining the plastic optical fiber by extruding and drawing. By changing the relative speed, a portion where the diameter or cross-sectional shape of the light transmitting portion of the fiber is changed is formed, and by cutting this changed portion, the diameter or cross-sectional shape of the light transmitting portion at the end of the fiber is changed. A method for producing a plastic optical fiber, comprising obtaining a fiber having a diameter or a cross-sectional shape different from that of a light transmitting portion of a fiber portion other than an end portion.

(3) By contacting the fiber end with the shaping jig while at least one of the plastic optical fiber end and the shaping jig is heated, and changing the diameter or the cross-sectional shape of the light transmitting portion of the fiber. A method for producing a plastic optical fiber, comprising obtaining a fiber in which the diameter or cross-sectional shape of the light transmitting portion of the fiber end is different from the diameter or cross sectional shape of the light transmitting portion of the fiber portion other than the fiber end.

The fiber of the present invention may be a graded index optical fiber or a graded index optical fiber. Further, the light transmitting portion may be made of a non-fluorinated plastic material or may be made of a fluorine-based plastic material. A non-fluorinated plastic material such as a combination of a core made of a non-fluorinated plastic material and a clad made of a fluoroplastic material is used. A combination of a plastic material and a fluoroplastic material may be used.

Examples of the fluorine-based plastic material include polymers of fluorine-containing monomers such as polyfluoroalkyl acrylate and polyfluoroalkyl methacrylate, and other fluorine-based plastic materials. A particularly preferred fluorine-based plastic material is a non-crystalline fluorine-containing polymer having substantially no C—H bond. More preferably, it is a non-crystalline fluoropolymer having substantially no C—H bond and having a ring structure in the main chain.

The end of the fiber according to the present invention is a portion where the diameter of the light transmitting portion or the cross-sectional shape of the light transmitting portion starts to change from the light transmitting portion of the other fiber portion from the front end portion in the fiber length direction. Means up to the area.
Further, the light transmitting portion means a portion occupied by the core portion in the graded index optical fiber, and a portion occupied by 5% or more of the maximum intensity in the intensity distribution of light emitted from the fiber in the radial direction of the fiber in the graded index optical fiber.

In the fiber of the present invention, the diameter or cross-sectional shape of the light transmitting portion of at least one end of the fiber is different from the diameter or cross sectional shape of the light transmitting portion of the fiber portion other than the fiber end.

For example, when the fiber is opposed to a light source having a diameter approximately equal to or larger than the diameter of the light transmitting portion of the fiber, the diameter of the light transmitting portion at the fiber end is changed to the light transmitting portion of the fiber other than the fiber end. It is preferable that the diameter is larger than the diameter of the portion and the diameter of the light transmitting portion at the fiber end is larger than the diameter of the light source. Thereby, the connection between the light source and the fiber can be performed while preventing light leakage without using a light-collecting component. When the light emitted from the fiber is received by the light receiving portion having a small diameter, the diameter of the light transmitting portion at the end of the fiber is preferably smaller than the diameter of the light transmitting portion of the fiber other than the end of the fiber. As a result, the emitted light can be easily focused and centered, and light leakage at the time of connection can be prevented.

Further, by making the cross-sectional shape of the fiber end facing the light source or the light-receiving portion the same or similar to the cross-sectional shape of the light source or the light-receiving portion, light leakage at the time of connection can be similarly prevented.

When the diameter of the light transmitting portion is increased toward the fiber tip, the diameter at the fiber tip is 1.5 to 5 times the diameter of the light transmitting portion of the fiber other than the fiber end. Rates are usually employed. When reducing the diameter of the light transmitting portion toward the fiber tip, the diameter at the fiber tip is 1/1 / the diameter of the light transmitting portion of the fiber other than the fiber end.
A reduction ratio of 5 to 2/3 times is usually adopted. The diameter of the fiber part other than the fiber end is usually 20-500μ
m is adopted.

The length of the fiber end in the present invention is:
Although it varies depending on the enlargement ratio, reduction ratio, and the like, it is usually 0.5 to 50 cm, preferably 3 to 30 cm. The total length of the fiber of the present invention is usually 50 to 200.
m is adopted. For shorter fibers, the length of the fiber end should be in the above range and 1% of the total fiber length.
/ 10 or less is preferable.

The above-mentioned refractive index distribution type optical fiber is composed of a matrix resin having a refractive index difference and a diffusion material, and the diffusion material is distributed in the matrix resin along a specific direction with a concentration gradient. Is preferred. Since it has a low transmission loss and a high transmission band in a wide transmission region band, a fluoropolymer having substantially no C—H bond is used as a matrix resin, and a low molecular weight substantially C-
A refractive index distribution type optical fiber made of a fluorine-based plastic material using a fluorine-based compound having no H bond as a diffusing substance is more preferable.

In this case, the number average molecular weight of the fluorinated polymer is preferably 10,000 to 5,000,000, preferably 5 to 5,000,000.
0.00-1,000,000 is more preferable. The number average molecular weight of the low molecular weight fluorine compound is 300 to 1
000 is preferred, and 300 to 5,000 is more preferred. Such a refractive index distribution type optical fiber is known from JP-A-8-5848 and the like.

In the fiber of the present invention, the diameter of the light transmitting portion at the fiber end or the cross-sectional shape of the light transmitting portion is defined as
As a method of making the diameter different from the diameter of the light transmitting portion or the cross-sectional shape of the light transmitting portion in other parts, a method in which fiber portions having different diameters or shapes are formed without joining, and a fiber having a different diameter or shape are used. A method in which portions are formed by bonding is used. It is preferable to use a method of forming without joining for reasons such as high productivity.

The following methods (1) to (4) can be used as a method of forming the film without joining.

(1) A method of changing the relative speed between the movement of the base material and the drawing when the fiber is obtained by drawing the base material.

(2) A method in which the fiber is obtained by extrusion and drawing by changing the relative speed of fiber extrusion and drawing.

(3) A method in which after heating the fiber end in advance, the fiber end is brought into contact with a shaping jig to change the diameter of the light transmitting portion of the optical fiber or the sectional shape of the light transmitting portion.

(4) After heating the shaping jig in advance,
A method in which the end of the optical fiber is brought into contact with a shaping jig to change the diameter of the light transmitting portion or the sectional shape of the light transmitting portion of the optical fiber.

In the above method (1), the moving speed of the base material is the speed at which the base material plasticized in the heating furnace is discharged out of the heating furnace, and the drawing speed is the speed outside the heating furnace. This is the speed at which the discharged fiber is pulled by a take-up device such as a take-up roll.

By reducing the speed of drawing relative to the speed of movement of the preform, the diameter of the fiber can be increased. In addition, the diameter of the fiber can be reduced by increasing the drawing speed with respect to the moving speed of the base material.

Therefore, by reducing the drawing speed with respect to the moving speed of the base material and continuously increasing the drawing speed, a fiber having a diameter which is larger than that of the other fiber portions by a predetermined length of the continuous fiber can be obtained. By cutting the fiber portion having the increased diameter, a fiber is obtained in which the diameter of the light transmitting portion at the fiber end is larger than the diameter of the light transmitting portion of the other fiber portion.

On the other hand, by increasing the drawing speed with respect to the moving speed of the base material and continuously decreasing the drawing speed, a fiber having a diameter smaller than that of the other fiber portions by a predetermined length of the continuous fiber can be obtained. By cutting the fiber portion having the reduced diameter, a fiber in which the diameter of the light transmitting portion at the fiber end is smaller than the diameter of the light transmitting portion of the other fiber portion can be obtained.

In the above method (2), the fiber extrusion speed and the drawing speed correspond to the moving speed of the base material and the drawing speed in the method (1), respectively. By changing the relative speed of the optical fiber, a fiber in which the diameter of the light transmitting portion at the fiber end is different from the diameter of the light transmitting portion of the other fiber portion can be obtained in the same manner as in the method (1).

In the above methods (3) and (4),
The shaping jig is for changing the shape of the fiber end portion plasticized by heating. Usually, the shape of the fiber end can be changed by bringing the fiber end plasticized by heating into contact with the shaping jig.

A preferred example of the shaping jig is a mold (see FIGS. 8 to 10) capable of forming a cavity having the same shape as the end of the fiber after the shape change. If the cross-sectional area of the fiber end is larger than the cross-sectional area of the other fiber portions, the mold uses a split mold.

Another preferable example of the shaping jig is a pressing roller (FIG. 5) for pressing plasticized fiber to obtain a cross section from a circular cross section to an elliptical cross section when the fiber is obtained by extrusion molding or drawing of a base material. Or a shaping roller (see FIG. 10) for heating and plasticizing the molded fiber and pressing the plasticized fiber to compress the fiber into a circular cross section to an elliptical cross section. Another example of a shaping jig is a gripper for drawing a plasticized fiber (see FIG. 11).
It is.

In the above methods (3) and (4), both the heating of the fiber end and the heating of the shaping jig may be performed in advance. Further, the heating may be performed after the fiber end is brought into contact with the shaping jig without heating in advance.

The optical fiber is replaced with the above-mentioned (1) to (4)
After being deformed by such a method as described above, a coating layer may be provided on this strand, but usually, the optical fiber cord is formed by the above-mentioned (1) to (4).
As a result, the diameter of the light transmitting portion at the end of the fiber or the cross-sectional shape of the light transmitting portion is different from the diameter of the light transmitting portion of the other portion or the cross sectional shape of the light transmitting portion. Things.

In the present invention, the non-crystalline fluorine-containing polymer having substantially no C—H bond and having a ring structure in the main chain includes a fluorine-containing aliphatic ring structure and a fluorine-containing imide. A fluorinated polymer having a ring structure, a fluorinated triazine ring structure or a fluorinated aromatic ring structure is preferred. Among the fluorinated polymers having a fluorinated aliphatic ring structure, those having a fluorinated aliphatic ether ring structure are more preferred.

The fluorinated polymer having a fluorinated aliphatic ring structure is more likely to be subjected to heat stretching or melting described later than a fluorinated polymer having a fluorinated imide ring structure, a fluorinated triazine ring structure or a fluorinated aromatic ring structure. This is a more preferable polymer because the polymer molecules are less likely to be oriented during fiber formation by spinning, and as a result, light is not scattered.

As the polymer having a fluorinated aliphatic ring structure, a polymer obtained by polymerizing a monomer having a fluorinated ring structure, or a fluorinated monomer having at least two polymerizable double bonds is subjected to cyclopolymerization. The polymer having a fluorinated aliphatic ring structure in the main chain obtained by the above method is preferred.

A polymer having a fluorinated alicyclic structure in the main chain obtained by polymerizing a monomer having a fluorinated alicyclic structure is known from JP-B-63-18964. That is, perfluoro (2,2-dimethyl-
A monomer having a fluorinated aliphatic ring structure such as 1,3-dioxole) is homopolymerized, and this monomer is converted into a radical polymerizable monomer such as tetrafluoroethylene, chlorotrifluoroethylene, or perfluoro (methyl vinyl ether). By copolymerizing with the above, a polymer having a fluorinated aliphatic ring structure in the main chain is obtained.

A polymer having a fluorinated aliphatic ring structure in the main chain obtained by cyclopolymerization of a fluorinated monomer having at least two polymerizable double bonds is disclosed in
238111 and JP-A-63-238115. That is, by subjecting a monomer such as perfluoro (allyl vinyl ether) or perfluoro (butenyl vinyl ether) to cyclopolymerization, or by subjecting such a monomer to tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), or the like. By copolymerizing with a radical polymerizable monomer, a polymer having a fluorinated aliphatic ring structure in the main chain can be obtained.

Further, perfluoro (2,2-dimethyl-
Monomers having a fluorinated aliphatic ring structure such as 1,3-dioxole) and perfluoro (allyl vinyl ether)
A polymer having a fluorinated aliphatic ring structure in the main chain can also be obtained by copolymerizing a fluorinated monomer having at least two polymerizable double bonds such as fluorinated or perfluoro (butenyl vinyl ether).

Specific examples of the polymer having a fluorinated aliphatic ring structure include those having a repeating unit selected from the following formulas (I) to (IV). In addition, the fluorine atom in these polymers having a fluorinated aliphatic ring structure may be partially substituted with a chlorine atom in order to increase the refractive index.

[0044]

Embedded image

[In the above formulas (I) to (IV), p is 0 to 5, q is 0 to 4, r is 0 to 1, p + q + r is 1 to 5.
6, s, t, and u are 0 to 5, respectively, and s + t + u is 1 to 5.
6, R is F or CF ₃ , R ¹ is F or CF ₃ , R ² is F
Or CF ₃ , X ¹ is F or Cl, X ² is F or Cl
It is. As the polymer having a fluorinated aliphatic ring structure, a polymer having a ring structure in the main chain is suitable, but a polymer containing 20 mol% or more, preferably 40 mol% or more of polymer units having a ring structure is preferred. It is preferable in terms of transparency, mechanical properties, and the like.

[0046]

Embodiments of the present invention will be described below with reference to the drawings. The fibers in FIGS. 1 to 12 are strands of a gradient index optical fiber obtained using an amorphous fluoropolymer having no C—H bond and a diffusing substance having no C—H bond. FIG. 2 shows a layout of a light source and a fiber in a conventional coupling system. When an LED (light emission diode) having an emission wavelength of 650 nm is used as the light source 1, the LED emits surface light with a width of about 300 μm. It was necessary to collect the light through 3. Therefore, an expensive lens group is required, and it is necessary to secure a space between the light source and the fiber,
Further, a mechanism for accurately holding the lens group at a predetermined position is required. Further, the incident angle of the light condensed by the lens becomes larger than the emission angle of the light source, and the amount of light leaking from inside the fiber to the outside increases.

FIG. 1 shows a layout in the case of using the fiber 4 having a different cross section according to the present invention. For an LED that emits surface light with a width of about 300 μm, the core diameter at the fiber end is 1
By increasing the diameter from 25 μm to 400 μm, it became possible to connect the light source to the fiber without interposing a light-collecting component such as a lens. In addition, it was possible to prevent light from leaking from the inside of the fiber to the outside.

FIG. 3 shows another embodiment of the fiber 5 having a different cross section according to the present invention. When light is guided to a light receiving element having a narrow receiving width of 50 μm, it may be necessary to accurately guide light to the center of the fiber core, contrary to the embodiment of FIG. At that time, the core diameter at the fiber end is 125μ.
By reducing the diameter from m to 50 μm and placing the light receiving element 30 near the fiber emission end, it was possible to guide the light emitted from the fiber to the light receiving element 30 without leakage.

Further, in order to make the outgoing light incident on an LD having an elliptical radiation shape without leakage, an example of a different cross-section fiber 6 in which the cross-sectional shape of the end of the fiber is processed into a similar elliptical shape is shown. The results are shown in FIG.

Next, a method for changing the end of the fiber into the shape described above will be described. FIG. 5 shows an example of an apparatus for producing the fiber of the present invention. A base material 7 having a diameter distribution of 20 mm and having a diameter distribution of 20 mm is plasticized in a heating furnace 8, drawn by a take-up roll 9 at a speed of 20 m / min, and has an outer diameter of 250 μm and a core diameter of 125 μm. Fiber was obtained. The diameter of the fiber is measured by a laser-type length measuring machine 10 and the data is sent to an arithmetic processing unit 11 so that the rotation speed of the take-up roll can be precisely adjusted so that the fiber diameter can be controlled to a constant size. ing. After drawing a predetermined amount, the drawing speed is linearly reduced from 20 m / min to 2 m per minute in the range of 1.0 second, and continuously linearized from 2 m to 20 m per minute in the range of 1.0 second. Increased. As a result, the diameter of the fiber is from 250 μm to 8 in the range of the fiber length of 30 cm.
To a fiber length of 30 μm,
fiber diameter from 800 μm to 250 cm
A fiber changed to μm was obtained. As shown in FIG. 6, the different cross section of the fiber is cut at the center by a cutter 12 provided in front of the winding drum.
A fiber 13 having an enlarged fiber end was manufactured.

Further, using the same fiber manufacturing apparatus as above,
Take-up roll 9 at a speed of 20 m / min.
A refractive index distribution type fiber having a core diameter of 0 μm and a core diameter of 125 μm was drawn, a predetermined amount was drawn, and then a pressure roll 14 provided below the take-up roll 9 was operated, and the fiber was sandwiched between the fibers for a period of 0.5 second. . As a result, a fiber having a different cross section having an elliptical cross section was obtained within a fiber length range of 15 cm. As shown in FIG.
The different cross section of this fiber was cut at the center by a cutter 12 provided in front of the winding drum to produce a fiber 15 having an oval fiber end.

Next, a description will be given of a method of processing the cross section of the fiber end portion in a separate step. FIG. 8 is a schematic view of a method for expanding a fiber end according to the present invention. Diameter 300
A fiber having a core diameter of 150 μm and a core diameter of 150 μm was inserted into an end shaping jig 16 heated to 140 ° C. by an internal heater (a), and the fiber was pressed for 10 seconds while the inside of the jig was kept in a reduced pressure state ( b). Thereafter, the reduced pressure inside the jig was released, and the jig was split into two pieces and the fiber was taken out (c). As a result, a fiber having an outer diameter of 600 μm at the end and an expanded core diameter of 300 μm was obtained. The same processing was also possible by pressing the fiber held by a jig 17 as shown in FIG. 9 against a plate 18 heated to 140 ° C.

FIG. 10 is a schematic diagram of a method of changing the fiber end from a circle to an ellipse. After preheating a fiber having a diameter of 300 μm and a core diameter of 150 μm to 140 ° C.,
A fiber is sandwiched between the shaping rollers 19 and 2 kg /
A pressure of cm ² was applied. As a result, an elliptical fiber having a long outer diameter of 500 μm and a short outer diameter of 200 μm was obtained.

FIG. 11 is a schematic view of a method for narrowing the fiber end. 10 mm of the end of the fiber having a diameter of 500 μm and a core diameter of 250 μm is preheated to 180 ° C. in advance (a), sandwiched by a stretching jig 20 and stretched 20 mm (b), air-cooled as it is, The part was excised (c). As a result, the outer diameter of the end is 125μ.
m, a fiber whose core diameter was reduced to 62.5 μm was obtained.

Next, a description will be given of a method of performing different cross-section processing of the fiber end by attaching another component in another step. FIG.
As shown in FIG. 2, one of the diameters previously formed by the above-described drawing apparatus is 500 μm, and the other is 250 μm.
Only the small-diameter side 23 of the chip 22 of
Heat to 40 ° C and cut fiber end by 5mm at 200 ° C
The tip 22 was pressed against the fiber (a). As a result, as shown in FIG. 12 (b), a fiber of a different cross section with an enlarged fiber end was obtained.

[0056]

According to the present invention, when a fiber is connected to a light source or a light receiving portion of an optical device or the like, the fiber end section is selected in accordance with the cross-sectional shape of the fiber, and the fiber is connected without a lens or the like. Allows you to connect with
In addition, when light is introduced into a light receiving element having a small diameter, centering can be easily performed, and light leakage can be prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a connection layout with a light source using a fiber having a different cross section according to the present invention.

FIG. 2 is an explanatory view of a conventional connection layout between a light source and a fiber.

FIG. 3 is an explanatory view of a connection layout between another embodiment of the fiber of different cross section of the present invention and a light receiving element.

FIG. 4 is an explanatory view of a connection layout between still another embodiment of the fiber of different cross section of the present invention and a light source, wherein a is a layout;
b is the LD light distribution shape of the BB line section in a, and c is the optical fiber shape of the BB line section.

FIG. 5 is an explanatory view of an apparatus for producing a fiber of the present invention.

FIG. 6 is an explanatory diagram of a fiber end portion 13 of an enlarged different cross section manufactured by the same device.

FIG. 7 is an explanatory view of a fiber end portion 15 having a reduced cross section of the same.

FIG. 8 is an explanatory view of a method of enlarging a fiber end according to the present invention, wherein a is a step of inserting the fiber into a heated jig, b is a step of pressing the fiber while reducing the pressure inside the jig after insertion, c. FIG. 4 is an explanatory view of a process of opening a jig and taking out a fiber.

FIG. 9 is an illustration of another method of enlarging the fiber end of the present invention.

FIG. 10 is an explanatory diagram of a method of changing a cross section of a fiber end from a circle to an ellipse.

FIG. 11 is an explanatory view of a method of narrowing the end of a fiber;
FIG. 4 is a diagram illustrating a step of preheating a fiber end, a step of bending by sandwiching a jig with a jig, and a step of cutting a part of the end with a cutter.

FIG. 12 is an explanatory view of a method of attaching a separately formed end of a different cross section to a fiber end, in which a is a step of pressing a heated end of a different cross section to a heated end of a fiber, and b is an enlarged different cross section. Forming an end;

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Moto Imai 4-1-1, Kamidadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Koji Oganezawa 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Asahi Glass (72) Inventor Takashi Tsukamoto 1150 Hazawa-cho, Kanagawa-ku, Yokohama, Kanagawa Prefecture

Claims (7)

[Claims] 1. A plastic optical fiber, wherein a diameter or a cross-sectional shape of a light transmitting portion of at least one end of the plastic optical fiber is different from a diameter or a cross-sectional shape of a light transmitting portion of a fiber portion other than the fiber end. 2. A fiber end formed by molding.
A plastic optical fiber according to claim 1. 3. The plastic optical fiber according to claim 1, wherein a fiber end portion is formed by joining a member that can be a fiber end portion and a fiber tip portion. 4. The plastic optical fiber according to claim 1, wherein the plastic optical fiber is a refractive index distribution type optical fiber having a matrix of a non-crystalline fluoropolymer having substantially no C—H bond. . 5. A plastic optical fiber obtained by drawing a preform by changing the relative speed of the movement and drawing of the preform, or by obtaining a plastic optical fiber by extrusion and drawing, the relative distance between the extrusion and the drawing of the fiber. By changing the speed, a portion where the diameter or cross-sectional shape of the light transmitting portion of the fiber is changed is formed, and by cutting this changed portion, the diameter or cross-sectional shape of the light transmitting portion at the fiber end is changed to the fiber end. A method for producing a plastic optical fiber, comprising obtaining a fiber having a diameter or a cross-sectional shape different from that of a light transmitting portion of a fiber portion other than a portion. 6. The diameter or cross section of the light transmitting portion of the fiber is changed by contacting the fiber end with the shaping jig while at least one of the plastic optical fiber end and the shaping jig is heated. A method for producing a plastic optical fiber, comprising obtaining a fiber in which a diameter or a cross-sectional shape of a light transmitting portion of a fiber end is different from a diameter or a cross-sectional shape of a light transmitting portion of a fiber portion other than the fiber end. 7. The method according to claim 5, wherein the optical fiber is a refractive index distribution type optical fiber having a matrix of a non-crystalline fluoropolymer having substantially no C—H bond.