JP2001133655A - Heat treatment method foe glass fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat treatment method for a glass fiber, which improves the mechanical strength in the heated portion of the glass fiber, after the regulation of characteristics by a heat treatment is carried out. SOLUTION: A glass part 11 of the optical fiber exposed in a glass exposing portion 10 of the coated optical fiber 1, and a multicore burner 21 for heat treating the optical fiber 11 are installed within a gas purging box 20 in the heat treatment to the optical fiber of a glassfiber consisting of SiO2-based glass. The concentrations of H2O and O2 in the heat treatment atmosphere in the gas-purging box 20 and the flame from the multicore burner 21 are both specified to be 1% or lower. As a result, generation and diffusion of OH groups during the heat treatment or the generation of the defects by the dissolution, etc., of O2 are lessened, by which the degradation in the mechanical strength of the optical fiber is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for adjusting characteristics of glass fibers such as optical fibers.

[0002]

2. Description of the Related Art In a process such as fusion splicing of an optical fiber, a heat treatment may be performed to change a mode field diameter (MFD) of the optical fiber or various optical characteristics. Heating the optical fiber diffuses the dopant of the core, which can increase or adjust the mode field diameter.

For example, when connecting optical fibers having different mode field diameters, the glass portion of the optical fiber in the vicinity of the fusion spliced portion is heated using a burner or the like after fusion splicing. Enlarging the mode field diameters is performed (for example, see Japanese Patent No. 280435).
No. 5). At this time, the connection state between the mode fields is improved, for example, the mode field diameter continuously changes near the fusion splicing part, and the splice loss at the fusion splicing part in optical transmission can be reduced. it can.

In particular, with the recent increase in WDM transmission capacity, (1) reduction of non-linear effects due to an increase in the mode field diameter in an optical fiber portion where a signal light having a strong signal light power is transmitted. , (2) reduction of the chromatic dispersion slope for increasing the number of wavelength multiplexing, and (3) reduction of the total dispersion of the optical fiber.
It is difficult to satisfy all of these characteristics with a single optical fiber. On the other hand, an attempt has been made to configure an optical transmission line satisfying the above-described conditions by connecting a plurality of optical fibers having different structures and characteristics such as a mode field diameter in a cascade. In such a case,
It is important to reduce the connection loss by expanding the mode field in the above-described heat treatment.

[0005]

When the above-mentioned heat treatment is performed on the connection portion after the fusion splicing of the optical fiber, there is a problem that the strength of the optical fiber at the heated portion is reduced. That is, performing the heat treatment on the exposed glass part of the optical fiber causes a problem that a defect is caused on the glass surface of the optical fiber due to a trauma or a change in a chemical bonding state. The occurrence of this defect
It lowers the mechanical strength of the optical fiber after connection, which may cause the optical fiber to break.

At this time, the breaking strength of the optical fiber at the connection portion is, for example, about several 100 MPa (fiber diameter of 125 μm).
To about several hundred g). On the other hand, when using an optical component such as a fiber connector that completely fixes the fiber portion, or when fixing with a reinforcing member, the fixing method can compensate for the breaking strength reduced by the heat treatment. It is possible.

However, when an optical fiber connecting portion is formed in a fiber cable as a transmission line, the mechanical strength of the optical fiber cannot be sufficiently compensated. Therefore, in order to ensure long-term reliability with respect to the tension applied to the cable, it is necessary to improve the breaking strength of the connection portion of the optical fiber itself. The same applies to the adjustment of the optical characteristics by heating the optical fiber, which is performed in addition to the processing step of expanding the mode field diameter after fusion splicing. Further, the above-mentioned decrease in mechanical strength due to the heat treatment is not limited to the adjustment of the optical characteristics of the optical fiber, but also occurs in the heat treatment step for adjusting the characteristics of the glass fiber including the optical fiber. .

The present invention has been made in view of the above problems, and has been made in consideration of the above-mentioned problems, and has been made in view of the fact that the heat treatment of glass fibers for improving the mechanical strength in the heated portion of the glass fibers after the characteristics have been adjusted by the heat treatment. The aim is to provide a method.

[0009]

Means for Solving the Problems To achieve such an object
In order to heat the glass fiber according to the present invention,
Heat treatment of glass fiber by flame
A heat treatment method for adjusting characteristics, wherein the atmosphere of the heat treatment is
H in air and in the flame used for heat treatment _TwoO and
O_TwoCharacterized by having a concentration of less than 1%
You.

The inventor of the present application focused on the influence of H ₂ O (water vapor) and O ₂ (oxygen) existing around the glass fiber during the heat treatment on the decrease in the mechanical strength of the glass fiber due to the heat treatment. That is, for example, in the case of glass fiber such as an optical fiber made of SiO ₂ glass, as a cause of the defect, Si-
O-Si bond is formed by reaction with H ₂ O molecule or the like.
It is considered that OH groups are generated as -OH, and the generated OH groups diffuse into the glass by heating.
Excessive O ₂ also causes a decrease in the mechanical strength of the glass due to melting into the glass. In addition, similarly, glass fibers made of glass other than SiO ₂ glass also have defects due to the influence of H ₂ O and O ₂ existing in the periphery.

On the other hand, in the above-mentioned heat treatment method, the concentrations of H ₂ O and O ₂ in the atmosphere and the flame at the time of heat treatment of the glass fiber are each set to less than 1%. As a result, it is possible to prevent a decrease in the mechanical strength of the glass fiber due to generation of defects on the glass surface, such as suppression of generation and diffusion of OH groups during the heat treatment.

Further, the above-mentioned flame is a flame using CO and O ₂ . By using a gas containing no H ₂ (hydrogen) as a gas species for generating a flame, the concentration of H ₂ O in the flame can be reduced.
At this time, the gas is made so that the concentration of O ₂ becomes less than 1% after the reaction.

Further, C for O ₂ in this flame
It is preferable that the mixing ratio of O is larger than 2 (CO / O ₂ > 2). At this time, since a gas containing more CO than the mixing ratio 2 required for the reaction of CO and O ₂ is obtained, the concentration of H ₂ O is reduced as described above, and at the same time, the gas is completely reacted with the flame. O ₂ can be eliminated.

Further, the heat treatment atmosphere is an inert gas atmosphere. Since the inert gas atmosphere contains substantially no water vapor, it is suitable for reducing the concentration of H ₂ O. Also, the O ₂ concentration is similarly reduced. As the above-mentioned inert gas atmosphere, for example, N ₂ , He,
It is preferable to include at least one gas of Ar and Ne.

Further, the glass fiber is an optical fiber made of SiO ₂ glass, and the characteristics to be adjusted are as follows.
The optical characteristics of the optical fiber may be characterized.
At this time, an optical fiber whose optical characteristics are adjusted and a decrease in mechanical strength is suppressed is obtained. Also,
As for the glass fibers having other structures or compositions, the concentrations of H ₂ O and O ₂ were 1% as described above.
By setting it to be less than that, similarly, a decrease in mechanical strength due to the heat treatment can be suppressed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the glass fiber heat treatment method according to the present invention will be described below in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

FIG. 1 is a front sectional view schematically showing an optical fiber heat treatment method according to an embodiment of the present invention. Note that each of the cross-sectional views described below regarding the heat treatment is a cross-section of a plane including the center line of the optical fiber to be processed.

An optical fiber shown as an object of a heat treatment in FIG. 1 is a coated optical fiber in which a coating 12 made of a synthetic resin or the like is formed on the outer periphery of a glass portion 11 of the optical fiber (hereinafter, simply referred to as the optical fiber 11). It is one. The portion where the heat treatment is performed is the glass exposed portion 10 from which the coating 12 is removed and the optical fiber 11 is exposed.

The optical fiber in such a state is, for example, 2
It is obtained at the time of fusion splicing of an optical fiber. In the fusion splicing of optical fibers, after removing the coating over a predetermined length at the tip portion of each optical fiber to be connected, the connection surfaces of the tip portions where the glass part of the optical fiber is exposed are connected by arc discharge or the like. Fusion splicing. In the connection of the optical fiber, the state of the optical fiber after the fusion splicing and before the recoating corresponds to the coated optical fiber 1 having the glass exposed portion 10 shown in FIG.

In the heat treatment method for an optical fiber shown in FIG. 1, the optical fiber is heated using a flame by a burner. As the burner in the present embodiment, a multi-core burner 21 supplied with gas from a single burner gas supply pipe 21a and having a plurality of gas outlets 21b for generating a flame is used. A plurality of gas injection ports 21b provided in the multi-core burner 21, in FIG. 1, five gas injection ports 21b are arranged at substantially equal intervals on a straight line extending in a predetermined direction. The multi-core burner 21 is installed with respect to the gas purge box 20 such that a portion including each gas ejection port 21b is located inside the gas purge box 20.

The coated optical fiber 1 to be subjected to the heat treatment is applied to the exposed glass portion 10 in a state where its axial direction is substantially coincident with a predetermined straight line which is parallel to and opposed to the straight line in which the gas outlets 21b are arranged. The exposed portion of the optical fiber 11 to be subjected to the heat treatment is set in the gas purge box 20 so as to be within a position range where the portion can be heated by the flame generated at the gas outlet 21b. For example, in the heat treatment for adjusting the mode field diameter after the fusion splicing of the optical fiber, the heat treatment is performed on a predetermined range including the fusion spliced portion.

A gas supply pipe 21a for the multi-core burner 21
A predetermined gas is supplied from the
When the flame is generated in b, the flame heats the optical fiber 11 of the glass exposed portion 10 by the flame. The conditions of the heat treatment vary depending on the optical characteristics to be adjusted, the structure of the optical fiber, and the like. For example, the heating temperature is about 1200 ° C. to 1500 ° C., and the heating time is about 1 minute to 20 minutes.

In this embodiment, the coated optical fiber 1
And the multi-core burner 21 (excluding the lower part of the gas supply pipe 21a) as a heat treatment device,
As described above, it is installed inside the gas purge box 20. By employing a configuration in which the heat treatment is performed in a container whose atmosphere can be adjusted, such as a gas purge box, the atmosphere around the optical fiber when performing the heat treatment can be effectively adjusted.

The gas forming the atmosphere in the gas purge box 20 is supplied from a gas supply port 22 provided in the gas purge box 20 and exhausted from an exhaust port 23. By the gas supplied from the gas supply port 22 and the gas generated from the flame supplied from the multi-core burner 21 and the exhaust of the gas from the exhaust port 23, a constant heat treatment atmosphere is maintained in the gas purge box 20. You.

The heat treatment atmosphere supplied from the gas supply port 22 and the flame from the multi-core burner 21 used for the heat treatment have a H ₂ O and O ₂ concentration of less than 1% in the atmosphere and the flame. It is to be.

Specifically, the heat treatment atmosphere in the gas purge box 20 may be a rare gas such as He, Ar, Ne, or N2.
An inert gas atmosphere such as ₂ is preferable. Further, an inert gas atmosphere other than the above, or a gas other than the inert gas that satisfies the above conditions for the concentration of H ₂ O and O ₂ may be used as the atmosphere.

As for the flame from the multi-core burner 21, it is preferable to use a mixed gas composed of CO and O ₂ as the flame generating gas supplied from the burner gas supply pipe 21a. Further, it is preferable to set the mixing ratio of CO to O ₂ in this gas to be larger than ₂ in order to reduce the O ₂ concentration after the reaction.

H ₂ in the atmosphere of the heat treatment and in the flame
The effect of the above-described optical fiber heat treatment method in which the concentrations of O and O ₂ are each less than 1% will be described.

In the process of processing an optical fiber, when the vicinity of the fusion spliced portion of an optical fiber having a different mode field diameter is heated to adjust the mode field diameter to reduce the connection loss, the light made of SiO ₂ glass is used. In some cases, the optical properties are adjusted by heating the fiber. At this time, the mechanical strength of the optical fiber in the heated glass portion is reduced.

It is considered that the defects that occur on the glass surface during the heat treatment and lower the strength of the optical fiber are mainly caused by OH groups (hydroxyl groups) and excess O ₂ . In the heat treatment process performed on the glass part with the glass part of the optical fiber exposed, such as when the resin coating is removed, the glass surface directly touches the atmosphere of the outside air, and And dust will adhere.

When the glass part of the optical fiber is heated in this state, the SiO ₂ glass Si—O
Changed to Si-OH bonds -Si reacts with such H ₂ O molecules, resulting in OH group has expired bond Si-O-Si. Furthermore, the OH group diffuses into the optical fiber by heating, so that a defect due to the OH group grows. As a result, the breaking strength of the optical fiber after the heat treatment decreases. Excessive O ₂ present on the glass surface also forms oxygen-excess defects due to dissolution in the glass and the like, and similarly causes a decrease in mechanical strength of the glass.
Such a decrease in strength also occurs in glass fibers having a composition or structure other than those described above.

On the other hand, in the above-described embodiment, the concentrations of H ₂ O and O ₂ contained in the atmosphere and the flame during the heat treatment are both less than 1%. As a result, H ₂ O and O ₂
Can be reduced on the glass surface,
The occurrence of defects due to the generation and diffusion of OH groups and the dissolution of O _{2 on} the glass surface during the heat treatment of the optical fiber is suppressed, and a decrease in the breaking strength of the optical fiber or, in general, the glass fiber is prevented.

In the heat treatment, it is preferable to use a container whose atmosphere can be adjusted, such as a gas purge box. It is preferable to use an inert gas atmosphere as a heat treatment atmosphere in the gas purge box. Since the inert gas atmosphere does not substantially contain water vapor, the H ₂ O concentration can be reliably reduced. The same applies to the reduction of the O ₂ concentration. As the inert gas, He, Ar, N
A rare gas such as e or N ₂ can be used. Further, a mixture of an inert gas and another gas or a material other than the inert gas, which satisfies the above-described conditions for the concentrations of H ₂ O and O ₂ may be used as the heat treatment atmosphere.

Further, regarding the flame used for the heat treatment,
A flame using CO and O ₂ is preferable. CO
The mixed gas composed of O ₂ and O ₂ is a gas species that does not contain H ₂ , whereby it is possible to make the flame almost free of H ₂ O. In particular, the oxygen - as compared with the case of using hydrogen flame or hydrocarbon flame, can be reduced as much as possible of H ₂ O concentration in the flame.

In the case of this gas composition, the H ₂ O and O ₂ concentrations are simultaneously reduced by setting the mixing ratio so that the O ₂ concentration in the flame after the reaction is less than 1%. Can be. In particular, it is preferable to make the mixing ratio of CO to O ₂ larger than 2 (CO / O ₂ > 2). At this time, since O ₂ is completely eliminated in a state where the reaction has been completed by the flame, it is possible to make a state where neither H ₂ O nor O ₂ exists in the flame.

FIG. 2 is a graph showing the breaking strength of the optical fiber after the heat treatment. Here, the horizontal axis represents the breaking strength (GPa) of the optical fiber, and the vertical axis represents the cumulative breaking probability (%), and each data point obtained by the measurement indicates what percentage of the optical fiber breaks at the breaking strength. Is shown. Data measurement was performed using ten optical fibers for each condition.

Of the respective data, the breaking data A indicated by a black circle indicates the breaking strength of the optical fiber in the initial state where the heat treatment is not performed. On the other hand, the breaking data B, C, and D indicated by white circles indicate the breaking strength after the heat treatment.

Here, the breaking data B and C of the conventional example are subjected to a heat treatment as shown in FIG. That is, the optical fiber 11 is heated using the two burners 31 and 32 disposed so as to face each other with the optical fiber 11 of the exposed glass portion 10 interposed therebetween. These burners 3
1, 32 are directions in which the installed optical fiber 11 extends,
In FIG. 3, the optical fiber 11 is movable in the left-right direction in the figure, whereby the entire portion of the optical fiber 11 that needs to be heated is heated. The optical fiber 11 and the burner 3
Nos. 1 and 32 are not installed in the gas purge box.

On the other hand, the breaking data D according to the present invention is subjected to a heat treatment according to the embodiment shown in FIG. In the fracture data B, C, and D, the heating process is performed under substantially the same heating conditions by applying the heating conditions described above with respect to the heating process shown in FIG.

The breaking data B is based on a conventional heat treatment method in which the concentrations of H ₂ O and O ₂ in the atmosphere of the heat treatment and the flame are not less than 1%, respectively. I have. Burner 3
A mixed gas of C ₃ H ₈ and O ₂ is used for the flames from 1, 32. On the other hand, in the fracture data C, the heat treatment is performed under the same atmospheric conditions as the fracture data B, but a mixed gas of CO and O ₂ is used for the flames from the burners 31 and 32. The fracture data D is based on the example of the present invention using the heat treatment method of the above-described embodiment. In the fracture data D, Ar gas, which is an inert gas, is used as the atmosphere of the heat treatment, and the flame from the multi-core burner 21 has CO and O _{2 having} a mixture ratio of CO / O ₂ slightly larger than _2.
Is used.

At this time, according to the breaking data A of the initial fiber, while a breaking strength of about 5 GPa was obtained,
After the heat treatment, in the fracture data B of the conventional example 1 in which the heat treatment was performed using the air atmosphere and the C ₃ H ₈ —O ₂ flame, the fracture strength was much lower than 1 GPa. Also,
Also in the fracture data C of the conventional example 2 using the CO-O ₂ flame, although the fracture strength is slightly improved, 1G
It is slightly lower than Pa. On the other hand, according to the fracture data D according to the embodiment of the present invention, although the fracture strength is lower than that of the initial fiber, the H ₂ in the atmosphere of the heat treatment and the flame is reduced.
It can be seen that when the concentrations of O and O ₂ are each less than 1%, the breaking strength is maintained at 1 GPa or more, and the decrease in the mechanical strength of the optical fiber due to the heat treatment is greatly suppressed. The 50% breaking strength of the breaking data B, C, and D is about 0.3 GPa for the breaking data B, about 0.8 GPa for the breaking data C, and about 1.8 for the breaking data D according to the present invention.
GPa.

Here, the optical fiber is also heated at the time of fusion splicing of the optical fiber, but the heating at the fusion splicing is performed for a sufficiently short time as compared with the heat treatment for adjusting the optical characteristics such as the mode field diameter. It is. Accordingly, the average breaking strength is about 2-3 GPa (fiber diameter 1
(About 3 kg at 25 μm). In contrast, in the case of heating for adjusting optical characteristics,
Since the heat treatment time is relatively long, the control of the concentration of H ₂ O and O ₂ in the atmosphere and the flame as described above is effective for suppressing a decrease in strength. The use of a chlorine-hydrogen flame during fusion splicing to suppress a decrease in rupture strength due to OH groups has been reported in Elec. Lett.
981) pp.812-813.

The glass fiber heat treatment method according to the present invention is not limited to the above-described embodiment, and various modifications and changes can be made to the configuration of the treatment apparatus used and the treatment conditions.

For example, the burner used for the heat treatment is not limited to the multi-core burner shown in FIG. 1, but may be other types such as a single-core burner movably installed or a burner arranged oppositely. May be used. Further, as the gas for generating the flame, other than the above-mentioned CO—O ₂ mixed gas, any other gas that satisfies the conditions regarding the concentration of H ₂ O and O ₂ may be used.

Further, in the above-described embodiment, Si
Although the adjustment of the optical characteristics by the heat treatment on the optical fiber made of O ₂ -based glass has been described, the adjustment of the characteristics by the heat treatment on the glass fiber having another form or composition is also performed with respect to the atmosphere and the flame at the time of the heat treatment. By applying the above conditions of the H ₂ O and O ₂ concentrations, the decrease in mechanical strength due to the heat treatment can be similarly suppressed.

[0046]

The glass fiber heat treatment method according to the present invention has the following effects as described in detail above. That is, in the heat treatment for the glass fiber such as the optical fiber made of SiO ₂ glass, the concentration of H ₂ O and O ₂ in the atmosphere and the flame used for the atmosphere and the flame used for the heat treatment are set to 1 respectively. %. As a result, generation and diffusion of OH groups causing defects generated during the heat treatment, O ₂
Can be reduced, and therefore, a decrease in the mechanical strength of the glass fiber due to the heat treatment is suppressed.

As the heat treatment for the glass fiber, there is a heat treatment for adjusting the optical characteristics of the optical fiber.
For example, after fusion splicing of optical fibers having different mode field diameters, a heat treatment is performed on the glass portion of the optical fiber for the purpose of adjusting the mode field diameter. In recent years, the necessity of such an optical fiber connection has been increasing in order to configure a transmission line satisfying some characteristic conditions required for an optical transmission line. On the other hand, by applying the above-described heat treatment method, an optical fiber transmission line in which the connection loss at the connection portion is reduced and the breaking strength after the cable is formed is improved.

Also, in processing steps other than the connection of the optical fiber, it is conceivable that the optical characteristics such as the mode field diameter must be similarly adjusted by heating, and the above-described heat treatment method is applied to those steps. This makes it possible to increase the mechanical strength of the optical fiber transmission line or the optical fiber component after the heat treatment. further,
Similarly, for the property adjustment of glass fibers other than optical fibers by heat treatment, the mechanical strength of the glass fibers after heat treatment can be similarly improved.

[Brief description of the drawings]

FIG. 1 is a front sectional view schematically showing a heat treatment method for an optical fiber which is an embodiment of a heat treatment method for a glass fiber.

FIG. 2 is a graph showing the breaking strength of an optical fiber after a heat treatment.

FIG. 3 is a front cross-sectional view schematically showing a heat treatment method for an optical fiber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Coated optical fiber, 10 ... Exposed glass part, 11 ... Glass part of optical fiber, 12 ... Coating, 20 ... Gas purge box, 21 ... Multi-core burner, 21a ... Gas supply pipe for burner,
21b: gas ejection port, 22: gas supply port, 23: exhaust port.

Continued on the front page (72) Inventor Tomomi Sano 1-term Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa F-term in Sumitomo Electric Industries, Ltd. Yokohama Works 2H036 MA11

Claims (5)

[Claims] 1. A heat treatment method for performing a heat treatment on a glass fiber with a flame to adjust the characteristics thereof, wherein H ₂ O and O are contained in an atmosphere of the heat treatment and in a flame used for the heat treatment. _2. A heat treatment method for glass fibers, wherein the concentration of each of the _two is less than 1%. 2. The heat treatment method for glass fibers according to claim 1, wherein the flame is a flame using CO and O ₂ . 3. The method according to claim _2, wherein the mixing ratio of CO to O _{2 in the} flame is larger than 2. 4. The method according to claim 1, wherein the atmosphere is an inert gas atmosphere. 5. The glass fiber according to claim 1, wherein the glass fiber is an optical fiber made of SiO ₂ glass, and the characteristic to be adjusted is an optical characteristic of the optical fiber. Heat treatment method.