JP2002318320A - Method for splicing glass fibers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for splicing two glass fibers different in glass transition point TG. SOLUTION: In this glass fiber splicing method, a glass fiber 1 having TG=T1 and a glass fiber 2 having TG=T2 <T1 and an outer diameter D2 are butted on each other at the end face to be connected so that their axes are aligned; heating is performed in the manner that the fiber 1 has the highest temperature at the part 1 μm or more away from the end face and that the fiber 2 is softened and deformed at the end face; and the ratio Dd /D2 of the maximum diameter Dd of the deformed end face to the outer diameter D2 in the glass fiber having a glass transition point of T2 is regulated to >=1.02 and <=1.1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for connecting two glass fibers having different glass transition points.

[0002]

2. Description of the Related Art For the purpose of application to optical amplifiers in optical communication systems, the development of rare earth element-containing glass fibers comprising a core glass and a cladding glass, wherein the core glass contains a rare earth element and has an optical amplification function has been promoted. ing. In particular, glass fibers in which the rare earth element is Er (erbium) have been actively developed.

On the other hand, in order to cope with diversification of communication services expected in the future, a wavelength division multiplexing optical communication system (WDM) for expanding transmission capacity has been proposed. In WDM, as the number of wavelength multiplexing channels increases, the transmission capacity increases. Therefore, 1.2-
There is a need for an optical amplifying medium that can amplify light having a wavelength of 1.7 μm in a wide band. The rare earth element-containing glass fiber is considered to be applied to, for example, the above-mentioned applications.

[0004] As a rare earth element-containing optical amplification glass fiber, an Er-containing quartz glass fiber is widely known. However, for light having a wavelength of 1.2 to 1.7 μm, Er
The wavelength width at which gain can be obtained with the contained silica-based glass fiber is narrow, 1.530 to 1.565 μm in the C band, that is, about 35 nm, and 1.575 to 1.607 in the L band.
μm, that is, about 32 nm.

As an optical amplifying medium for solving this problem, Japanese Patent Application Laid-Open No. H11-317561 discloses Bi in molar%.
₂ O ₃ : 20-80 mol%, B ₂ O ₃ : 15-80 mol%,
A light amplification glass (E) in which Er is added to a matrix glass made of CeO ₂ or the like by 0.01 to 10% by mass percentage.
r-containing Bi ₂ O ₃ -based glass). The wavelength widths at which the gain can be obtained in Examples 1 to 10 of the optical amplification glass exemplified in the publication are all 100 nm or more, and Er is used.
It is at least 2.5 times the contained quartz glass.

[0006]

SUMMARY OF THE INVENTION
When considering an optical amplifier using an i ₂ O ₃ -based glass fiber as an optical amplification medium, the Er-containing Bi ₂ O ₃ -based glass fiber includes:
The problem is how to connect with a silica glass fiber widely used as a communication glass fiber. That is, there is a problem how to realize a connection that is small in reflection or loss of signal light on the connection surface (hereinafter, referred to as connection loss) and has excellent durability.

As a method for connecting two glass fibers, a fusion method as shown in FIG. 4 is known. That is, 2
The end faces of the glass fibers 51 and 52 to be connected are abutted with each other, and a contact portion 54 between the end faces and the end face is provided near the outside of the contact portion and an electrode 5 opposed to the contact portion is disposed therebetween.
Heating by the discharge generated between 3 and 53,
The end faces of the glass fibers of the book are fused. Here, the contact portion 54 is located on a straight line connecting the opposing electrodes 53, 53.

However, the glass transition point _TG differs between the Er-containing Bi ₂ O ₃ -based glass fiber and the quartz-based glass fiber, and it is difficult to connect the glass fibers by the above fusion method. That is, the _TG of Er-containing Bi ₂ O ₃ -based glass fiber is typically below 600 ° C., while the _TG of silica-based glass fiber is typically above 1000 ° C. When discharge is performed as shown in FIG. 4 so that the end faces can be fused, remarkable softening flow or volatilization occurs at the end faces of the Er-containing Bi ₂ O ₃ -based glass fiber, and the connection loss cannot be reduced. An object of the present invention is to provide a method of connecting glass fibers that solves the above-mentioned problem relating to the connection of two glass fibers having different T _G.

[0009]

SUMMARY OF THE INVENTION The present invention comprises a glass fiber glass transition point of T _1, each of the glass fiber having an outer diameter D ₂ glass transition point of T ₂ <T ₁ A T ₂ butting the end faces to be connected of the glass fibers of the two such axes matching, such as the temperature of the portion where the glass transition point of the glass fiber is T _1, or more far 1μm from said end face is the highest subjected to heat, and to a method of connecting glass fibers of the two as the end face portion of the glass fiber glass transition point of T ₂ is deformed by softening, the glass transition point is at T ₂ A glass fiber connecting method is provided wherein the ratio D _d / D ₂ of the maximum diameter D _d to D ₂ of the deformed end face portion of the glass fiber is 1.02 or more and 1.1 or less (first invention).

Also, the axes of the glass fiber having a glass transition point of T ₁ and the glass fiber having a glass transition point of T ₂ and an outer diameter of D ₂ satisfying T ₂ <T ₁ coincide with each other. The end faces to be connected of the two glass fibers are abutted with each other, and the glass transition point of the glass fiber is T ₁ .
The _two glass pieces are heated so that the temperature at the portion 1 μm or more away from the end face is the highest, and the end face portion of the glass fiber whose glass transition point is T ₂ is softened and deformed. a method of connecting the fiber, the ratio L _d / D ₂ of the length L _d and D ₂ of the end face portion of the glass transition point is the deformation of the glass fiber is T ₂ 0.24
Provided is a glass fiber connection method of not less than 0.4 and not more than 0.4 (second invention).

The present inventor has found that when two glass fibers having different glass transition points are fused and connected, the strength of the connecting portion is limited by limiting the deformation of the connecting portion of the connected glass fibers to a certain range. To a possible level, and
The inventors have found that the connection loss can be reduced, and have reached the present invention.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The glass fiber of the present invention may have a core / cladding structure or may not have a core / cladding structure. Hereinafter, connection of a glass fiber having a core / cladding structure will be described.

In the present invention, the glass transition point _TG of the glass fiber having a core / cladding structure is the glass transition point of the core glass or the glass transition point of the clad glass. When the glass transition points of the core glasses of the two glass fibers to be connected are the same and the glass transition points of the clad glass are different, _TG is the glass transition point of the clad glass. When the glass transition points of the clad glass of the two glass fibers to be connected are the same and the glass transition points of the core glass are different, _TG is the glass transition point of the core glass. When the glass transition points of both the core glass and the clad glass of the two glass fibers to be connected are different, _TG is the glass transition point of the core glass.

[0014] Typical values for T _G is the silica glass fiber _{(SF) 1000~1200 ℃, Bi 2} O 3 based glass fiber (BF) at 300 to 600 ° C., more typically three hundred and sixty to six hundred ° C. It is.

The glass transition point T ₁ of two glass fibers
And T the difference ₂ (T ₁ -T ₂₎ but is positive, typically at 400 ° C. or higher, more typically 500 ° C. or higher.

A glass fiber having a glass transition point of T ₁ (hereinafter referred to as a high melting point glass fiber) has a core diameter d ₁ and a cladding diameter D ₁ , and a glass fiber having a glass transition point of T ₂ (hereinafter referred to as a low melting point glass fiber). . the core diameter d ₂ and the cladding diameter D ₂ of) described below. In addition,
d ₁ , D ₁ , d ₂ , and D ₂ are values at the end face of the glass fiber to be connected.

Each of d ₁ and d ₂ is typically 1 to
20 μm. When BF is used as the low-melting glass fiber, d ₂ is typically 1 to 15 μm. When light propagates from the high melting point glass fiber side to the low melting point glass fiber side, it is preferable that (d ₁ −d ₂ ) ≧ −5 μm. When light propagates from the low melting point glass fiber side to the high melting point glass fiber side, (d ₂ −d ₁ ) ≧ −5 μm
It is preferable that (D ₁ -d ₂ ) is -5 to +5 μm
It is particularly preferred that Outside this range, a restriction on the direction of light propagation may be required.

D ₁ and D ₂ are typically both 40
２００200 μm. When used in an optical communication system, D ₁ and D ₂ are typically both 120-13
0 μm. Further, (D ₁ -D ₂ ) is preferably set to −3 to +3 μm.

When the present invention is used for connecting a glass fiber used in a WDM, the glass fiber is usually used in a single mode, and the high-melting glass fiber and the low-melting glass fiber each have a mode field diameter of 1 to 20 μm. And the difference between the two is preferably 1 μm or less. More preferably, the difference is zero.

In this case, the core glass refractive index n _1CR and the cladding glass refractive index n 1 of the high melting point glass fiber are used.
_The relative refractive index difference Δn ₁ = [n _1CR −n _1CL ] / 2n _1CR calculated from _1CL (n _1CL is typically 1.5 ± 0.1) is preferably 0.2 to 4%, Preferably 0.5 to 1.8
%, The core glass refractive index n of the low melting glass fiber
_Relative refractive index difference Δn calculated from _2CR and cladding glass refractive index n _2CL (n _2CR is typically 2.04 ± 0.1)
₂ = [ _{n2CR- n2CL} ] / _2n2CR is preferably 3% or less, more preferably 1% or less, particularly preferably 0.5%.
And preferably 0.1% or more, more preferably 0.3% or more.

In the above case, the numerical aperture of the high-melting glass fiber NA ₁ = [n _1CR ² −n _1CL ² ] ^0.5 and the numerical aperture of the low-melting glass fiber NA ₂ = [n _2CR ² −n _2CL ^2]. ]
^0.5 is preferably 0.10 to 0.42, more preferably 0.15 to 0.29, respectively. (NA ₁ -N
When A ₂ ) is -0.05 to +0.05, (d ₁ -d
₂ ) is preferably −1.5 to +1.5 μm,
When (NA ₁ −NA ₂ ) is from −0.01 to +0.01, (d ₁ −d ₂ ) is preferably from −0.3 to +0.3 μm.

Next, in the first invention and the second invention,
The requirement regarding the deformation of the connecting portion of the connected glass fiber will be described with reference to FIG. FIG. 1 shows a photograph of a connected portion of a connected glass fiber taken with a microscope while irradiating light from the side, and sketching the photograph. 1 the refractory glass fiber, the second low-melting glass fiber, A is a fusion surface end surface and a low melting the end face of the glass fiber 2 having a high melting point glass fiber 1 is produced fused, D ₁ is the high-melting glass fiber 1 cladding The diameter (outer diameter) and D ₂ are the cladding diameter (outer diameter) of the low-melting glass fiber 2. S1 and S2 are both brighter than the other parts. It is considered that S1 and S2 are bright due to the light condensing action of the glass fibers 1 and 2 respectively.

On the other hand, the portion sandwiched between S1 and S2 belongs to an end surface portion deformed due to the fusion of the end surfaces (hereinafter, referred to as a deformed portion). It is considered that the light condensing action does not occur in the deformed portion, and therefore, it is darker than S1 and S2.

In the first invention, the maximum diameter D of the deformed portion
_d and the ratio D _d / of the cladding diameter D ₂ of the low-melting glass fiber 2
D ₂ is from 1.02 to 1.1. If it is less than 1.02, the strength of the connecting portion is low, and even if a reinforcing material is attached to the connecting portion, the problem of strength remains. Preferably it is 1.04 or more. 1.
If it exceeds 1, the connection loss increases. Preferably it is 1.08 or less.

In the second invention, the length L _{d of the} deformed portion is
And the ratio L _d / D of the cladding diameter D ₂ of the low melting point glass fiber 2
₂ is 0.24 to 0.4. If it is less than 0.24, the strength of the connecting portion is small, and even if a reinforcing material is attached to the connecting portion, the problem of strength remains. Preferably it is 0.26 or more, more preferably 0.28 or more. If it exceeds 0.4, the connection loss increases. Preferably 0.36 or less, more preferably 0.3
4 or less.

In the first invention, as in the second invention, L
It is preferred _d / D ₂ is from 0.24 to 0.4.

Next, a method of softening and deforming the end face portion of a glass fiber to be connected will be described with reference to FIG. 2 by taking as an example a case in which a discharge generated between opposing electrodes is used for heating. In FIG. 2, 1 is a high melting point glass fiber, 2
Is a low-melting glass fiber, 1A and 2A are abutted end faces of the high-melting glass fiber 1 and the low-melting glass fiber 2, respectively, and 3 is a discharge heating electrode. FIG.
(A) is a front view and (b) is a side view.

First, the high-melting glass fiber 1 and the low-melting glass fiber 2 are butted so that the axes of the high-melting glass fiber 1 and the low-melting glass fiber 2 coincide. When the present invention is applied to an optical amplifier or the like of an optical communication system, “the axes are coincident” here typically means
It means that the axis deviation of the core of each of the high melting point glass fiber 1 and the low melting point glass fiber 2 is less than 0.5 μm.

The end faces of the high-melting glass fiber 1 and the low-melting glass fiber 2 to be abutted are preferably flat. By doing so, the end surfaces of the high melting point glass fiber 1 and the low melting point glass fiber 2 can be in contact with each other over the entire surface. FIG.
The angle between the end face and the axis of each glass fiber is 90 °
The angle α in the present invention is 90
It is not limited to °, but preferably α is less than 90 °. 90
In the case of °, the reflection of light caused by the difference in the refractive index between the high-melting glass fiber 1 and the low-melting glass fiber 2 is increased on the fusion surface formed by fusing the end surface 1A and the end surface 2A, and as a result, much light is returned. Become. When the glass fiber connected according to the present invention is applied to a laser device, the feedback light may destabilize laser oscillation or may increase an unnecessary signal (spurious). It is more preferably at most 87 °. Α is preferably 60 ° or more. If the angle is less than 60 °, it may be difficult to process the end face, and problems such as a decrease in flatness of the end face may occur. It is preferably at least 75 °, more preferably at least 80 °.

Next, the high melting point glass fiber 1 is brought into contact with a portion where the straight line connecting the tips Y and Y of the discharge heating electrodes 3 and 3 intersects, that is, a portion C where the straight line XX and the line segment YY intersect in FIG. The butted high-melting glass fiber 1 and low-melting glass fiber 2 are set such that the distance x from the end surface 1A becomes 1 μm or more. Note that FIG.
Is the case where the axis of the high melting point glass fiber 1 is coincident with the straight line XX, the axis is on the line segment YY connecting the discharge heating electrodes 3, 3, and the axis is orthogonal to the line segment YY. And C is the middle point of YY.

FIG. 2 shows that α is 90 as described above.
°, but when α is different from 90 °, the x
Is “the center of the end face 1A”, that is, “the end face 1A and the straight line XX
Of intersection ”and C.

Next, a voltage is applied between the discharge heating electrodes 3 and 3 to generate a discharge so that a portion 1 μm or more away from the butted end face 1 A of the high melting point glass fiber 1 has the highest temperature. Heat. Said "the hottest"
2 means that the temperature is the highest when viewed in the axial direction.
In the above, the "highest temperature" portion on the axis is C. If the distance between the highest temperature portion C and the butted end face 1A is less than 1 μm, that is, x <1 μm, a remarkable softening flow or volatilization occurs at the end face of the low-melting glass fiber, and the butted ends are brought together. The end faces cannot be fused or connection loss increases. x is preferably 1
It is at least 0 μm, more preferably at least 100 μm, particularly preferably at least 250 μm. Also, x is typically 5
mm or less, more typically 1 mm or less.

C located at the center of the discharge region has the highest temperature as described above. On the other hand, when x.gtoreq.1 .mu.m, the butted end face 2A of the low-melting glass fiber is set.
Is located at the non-central portion of the discharge region where the discharge energy density is lower than the central portion of the discharge region, and its temperature is lower than the temperature at C. As a result, both the remarkable softening flow and volatilization at the end face 2A are reduced. The abutted end face 1A and the abutted end face 2A can be fused without occurrence.

In the present invention, in order to perform the end face fusion more appropriately, the force for abutting the end faces is adjusted so that the low melting glass fiber is moved toward the high melting glass fiber side during the end face fusion, or the high melting glass fiber is moved. To the low melting glass fiber side. This moving amount y is preferably 50 μm or less. If it exceeds 50 μm, the deformation of the fusion end face becomes remarkable, and the butted end faces may not be fused or the connection loss may increase. More preferably 1
0 μm or less, particularly preferably 3 μm or less, most preferably 2 μm or less.

The fusion is performed by a distance x (≧ 1 μm), a distance L ₁ between the tips Y of the discharge heating electrodes 3, 3, a discharge current I, a discharge time t, a number of discharges n, a discharge pause time t ′, This is performed by appropriately adjusting the movement amount y and the like.

FIG. 3 is a view for explaining another method for softening and deforming the end face portion of the glass fiber to be connected by using a discharge generated between the electrodes facing each other.
(A) is a front view, (b) is a side view. In this method, the axis of the high-melting glass fiber 1 does not intersect with the line YY connecting the tips Y of the electrodes 3 for discharge heating. Others are the same as the method A shown in FIG. Note that, in FIG. 3, the display of the straight line XX, the distance x, and the highest temperature portion C of the high melting point glass fiber 1 shown in FIG. 2 are omitted.

In the method A described with reference to FIG. 2, the high melting point glass fiber 1 is heated by the central portion of the discharge region, which is considered to have the highest discharge energy density. However, the method described with reference to FIG. B), the high-melting glass fiber 1 is heated by the non-center portion of the discharge region, which is considered to have a lower discharge energy density.

In the method B, a distance L ₂ (a distance between a straight line YY ′ drawn perpendicularly to the axis of the high-melting glass fiber 1 from the tip Y of the discharge heating electrode 3 and the tip Y of the other discharge heating electrode 3. > 0 mm). In the method B, the distance z (> 0 mm) between the highest temperature part C ′ at the center of the discharge region and the straight line YY ′ is preferably 1 μm or more. In method B, there are more parameters for optimizing the fusion than in method A, and it is considered that more appropriate fusion can be performed. However, in the method B, the heating becomes non-uniform than in the method A, and there is a possibility that it is difficult to optimize the fusion.

The high melting point glass fiber has a _TG of 1,000 to
1200 ° C., T _G of the low-melting glass fiber 300-6
If at 00 ° C., Method A for optimizing the fusion
Alternatively, preferred ranges of the above-listed parameters in method B are described below. It is preferable that the distance L ₁ is 0.5 to 20 mm. The discharge current I is preferably 1 to 100 mA.

The number of discharges n is preferably 1000 or less,
More preferably, it is 100 or less. The discharge time t for one discharge is preferably 0.001 to 1 second, more preferably 0.001 to 0.1 second, and particularly preferably 0.01 to 0.1 second.
1 to 0.1 seconds. When n ≧ 2, the discharge pause time t ′
Is preferably 0.001 to 1 second, more preferably 0.1 to 1 second.
001 to 0.5 seconds, particularly preferably 0.01 to 0.1 seconds. The moving amount y is preferably 3 μm or less, more preferably 2 μm or less.

When the distance L ₁ is 0.5 to 0.7 mm, the distance x is preferably 5 μm or more, more preferably 10 μm.
That is all.

When L ₁ is more than 0.7 mm and not more than 20 mm, the distance x is preferably not less than 100 μm. If it is less than 100 μm, remarkable softening flow or volatilization may occur at the end face of the low-melting glass fiber. More preferably 200 μm or more, particularly preferably 2 μm or more.
It is 50 μm or more. Further, x is preferably not more than 500 μm. If it exceeds 500 μm, the temperature of the butted end faces of the high-melting glass fiber or the low-melting glass fiber may be too low to fuse the butted end faces. It is more preferably 400 μm or less, particularly preferably 300 μm or less.

[0043] In method A, 0.5 to 2 mm and the electrode tip distance L _1, the discharge current I 10~30mA, the product nt of discharge number n and the discharge time t for a single discharge 0.
It is particularly preferable that 1 to 0.2 second and y be 1 to 3 μm.

In the method B, the distance L ₂ is 0.001 m
m and preferably 1 mm or less.

As described above, the present invention has been described by taking as an example the case where a discharge generated between opposing electrodes is used for heating. However, the present invention is not limited to this, and another heating method may be used. For example, heating by a laser, heating by a hydrogen burner, heating by an electric heater, and the like can be given.

[0046] The T _G is SF as glass fiber is 1000 to 1200 ° C., the T _G is 300 to 600
BF is exemplified as a glass fiber having a temperature of ° C. The SiO ₂ content of SF is preferably 90 mol% or more.

Bi of BF_TwoO_ThreeContent is 20-80 mol%
It is preferred that Bi of BF _TwoO_ThreeOther ingredients
For example, B_TwoO_Three, Al_TwoO_Three, SiO_Two, Ga
_TwoO_Three, TeO_Two, CeO_Two, Er_TwoO_Three, Tm_TwoO_Three, Yb_Two
O_ThreeAnd the like. To add optical amplification function to BF
BF must contain Er or Tm
Is preferred.

When BF containing Er is used as the optical amplification glass fiber, the core glass is composed of a matrix glass having a Bi ₂ O ₃ content of 20 to 80 mol% and containing Er of 0.01 to 10 in terms of mass percentage. % Is preferable. The matrix glass preferably contains one of B ₂ O ₃ and SiO ₂ .

[0049]

DESCRIPTION OF THE PREFERRED EMBODIMENTS T _G is 1010 ° C., the end face to be connected is perpendicular to the axis and flat, the core diameter at the end face is 3.6 μm, the cladding diameter is 125 μm, and the cladding glass refractive index is 1.50. , NA is 0.2 and length is 1
000 mm quartz glass fiber SF1 (SiO ₂ content = 97 mol%), _TG is 470 ° C., the end face to be connected is perpendicular and flat to the axis, and the core diameter at the end face is 3. 6 [mu] m, a cladding diameter of 125 [mu] m, the core glass refractive index 2.04, an NA of 0.2, the length was prepared Bi ₂ O ₃ based glass fiber BF1 of 200mm (α = 90 °).

The core glass of the BF1 is Bi ₂ O ₃ : 4
3 mol%, Al ₂ O ₃ : 3.5 mol%, SiO ₂ : 32 mol%, Ga ₂ O ₃ : 18 mol%, TeO ₂ : 3.5 mol%
Is a glass in which Er is added to a matrix glass of 0.7% by mass percentage. Further, the cladding glass, Bi ₂ O _3: 43 _{mol%, Al 2 O 3: 7} .
5 mol%, SiO ₂ : 32 mol%, Ga ₂ O ₃ : 14 mol%, TeO ₂ : 3.5 mol%.

The end faces of the two glass fibers to be connected were butted so that the axes of the two fibers coincided with each other, and the end faces were fused by Method A under the following interelectrode discharge conditions. That is, x: 280 μm, L ₁ : 1.0 m
m, I: 20 mA, n: 13 times, t: 0.01 second,
t ′: 0.03 seconds, y: 3 μm. As the discharge electrode, a tungsten electrode having a diameter of 1 mm at the bottom of the conical portion at the tip and a height of 1.2 mm at the conical portion was used.

The connecting portion of the two glass fibers thus connected is photographed using a microscope while irradiating light from the side surface thereof, and the maximum diameter D _d and length L _{d of the} deformed portion are obtained.
Was measured. D _d is 133.8 μm, L _d is 41.3 μm
Met. Since D ₂ is 125 μm, D _d / D ₂ is 1.07 and L _d / D ₂ is 0.33.

[0053] 1.5 of the connected glass fiber
When the connection loss for light having a wavelength of 5 μm was measured,
0.3 dB. Note that the connection loss is preferably 1 dB or less, and more preferably 0.5 dB or less.

When the strength of the connected glass fiber was measured, the strength was 0.8 GPa.
The strength is preferably at least 0.08 GPa, more preferably at least 0.16 GPa. 0.08 GP
If it is less than a, practical strength may not be obtained even if a reinforcing material is attached to the connection part.

[0055]

According to the present invention, the end faces of two glass fibers having different glass transition points can be fused well, and the connection loss can be reduced. Also, by attaching a reinforcing material to the connection portion, the connection portion strength can be obtained to the extent that practical strength can be obtained.

An optical amplifier incorporating a silica glass fiber and a glass fiber in which Er is added to the core and a Bi ₂ O ₃ glass fiber having an optical amplification function and connected by the method of the present invention is used as the optical amplifier. Since the connection between the fiber and the silica glass fiber for communication is easy, the fiber can be widely used in a conventional optical communication system using the silica glass fiber.

[Brief description of the drawings]

FIG. 1 is a sketch of a photograph of a glass fiber connection portion taken with a microscope while irradiating light from the side surface thereof.

[FIG. 2] The end face of the glass fiber to be connected is softened.
It is a figure showing the method of changing.

FIG. 3 softens the end face of the glass fiber to be connected;
It is a figure showing another method of changing.

FIG. 4 is a diagram showing a conventional method of connecting glass fibers.

[Explanation of symbols]

 1, 51: High-melting glass fiber 1A: Butted end face of high-melting glass fiber 2, 52: Low-melting glass fiber 2A: Butted end face of low-melting glass fiber 3, 53: Electrode for discharge heating 54: Contact portion A: Fusion surface

Claims (8)

[Claims] _1. A glass fiber having a glass transition point of T ₁ and an outer diameter D ₂ having a glass transition point of T ₂ and T ₂ <T _1.
So that the respective axes of the glass fibers coincide with each other.
The end faces of the glass fibers to be connected are abutted to each other, and the glass fiber having a glass transition point T ₁ is heated so that the temperature of a portion separated from the end face by 1 μm or more becomes the highest, and the glass transition point there a method of an end face portion of the glass fiber is T ₂ connects the two glass fibers so as to deform softened, the glass transition point of the end face portion which is the deformation of the glass fiber is T ₂ A glass fiber connection method in which the ratio D _d / D _{2 of the} maximum diameter D _d to D ₂ is 1.02 or more and 1.1 or less. _2. The ratio L _d / D ₂ of the length L _d to D ₂ of the deformed end face portion of the glass fiber having a glass transition point of T ₂ is not less than 0.24 and not more than 0.4. The glass fiber connection method according to 1. 3. A glass fiber having a glass transition point of T ₁ and a glass fiber having a glass transition point of T ₂ and an outer diameter of D ₂ satisfying T ₂ <T ₁ so that the axes thereof coincide with each other. The end faces of the glass fibers to be connected are abutted to each other, and the glass fiber having a glass transition point T ₁ is heated so that the temperature of a portion separated from the end face by 1 μm or more becomes the highest, and the glass transition point there a method of an end face portion of the glass fiber is T ₂ connects the two glass fibers so as to deform softened, the glass transition point of the end face portion which is the deformation of the glass fiber is T ₂ glass fiber connection method ratio L _d / D ₂ of the length L _d and D ₂ is 0.24 to 0.4. 4. The heating is performed such that the temperature of a portion of the glass fiber having a glass transition point of T ₁ which is at least 100 μm away from the end face is the highest.
4. The glass fiber connection method according to 2 or 3. 5. The glass fiber connecting method according to claim 1, wherein each of the two glass fibers to be connected is a glass fiber having a core / cladding structure. 6. The glass fiber connecting method according to claim 1, wherein the difference between T ₁ and T ₂ is 400 ° C. or more. 7. The glass fiber connecting method according to claim ₁ , wherein T ₁ is 1000 to 1200 ° C. 8. The method according to claim 1, wherein T ₂ is 300 to 600 ° C.
8. The glass fiber connection method according to any one of items 7.