JP4361439B2 - Optical fiber processing method - Google Patents

Description

  The present invention relates to an optical fiber processing method.

  In general, an optical fiber is manufactured by melting and drawing an optical fiber preform made of quartz glass. Specifically, the optical fiber preform is melted at a high temperature of, for example, about 2000 ° C., the fused quartz glass is drawn out from the tip thereof into a thread shape, and this is cooled rapidly with a cooling cylinder or the like, and then the surface is An optical fiber is obtained by coating with a surface protecting resin.

  In general, in the optical fiber manufacturing process, the fused quartz glass is rapidly cooled to generate a non-bridging oxygen center hole (hereinafter also abbreviated as “NBOHC”). It is known to do. In the optical fiber manufacturing process, it is possible to promote NBOHC recombination and reduce NBOHC by slowing the cooling rate of the fused quartz glass. However, with this method, it is impossible to completely eliminate NBOHC from the optical fiber.

  NBOHC remaining in the optical fiber is combined with hydrogen remaining in the optical fiber or hydrogen generated from the surface protecting resin to generate a Si—OH bond. When a hydroxyl group (-OH) is generated, absorption loss due to a hydroxyl group in the vicinity of a wavelength of 1383 nm increases, and the transmission characteristics of the optical fiber deteriorate.

Conventionally, as a method for suppressing an increase in absorption loss due to a hydroxyl group in the vicinity of a wavelength of 1383 nm, a quartz glass that forms an optical fiber by winding the optical fiber around a bobbin and exposing it to a gas atmosphere containing deuterium in this state. A method has been proposed in which NBOHC and deuterium (D ₂ ) are reacted to form a deuterated hydroxyl group (—OD) (see, for example, Patent Document 1 and Patent Document 2).

 NBOHC easily reacts with deuterium at room temperature to form a deuterated hydroxyl group, and the light absorption of the deuterated hydroxyl group is 1.87 μm, so the transmission band of optical communication is not affected. Therefore, Patent Document 1 and Patent Document 2 propose a method of exposing an optical fiber to an atmosphere of a gas containing deuterium at a temperature of 40 ° C. or less to suppress a change in the concentration of hydrogen contained in the optical fiber over time. ing.

In the method of reacting NBOHC with deuterium (D ₂ ) to form deuterated hydroxyl group (-OD), considering the manufacturing cost, the exposure time of the optical fiber is shortened and a gas containing low concentration deuterium is used. It is desirable to use and process.
For example, it is disclosed that the exposure time for exposing an optical fiber to a gas atmosphere containing deuterium requires 1 day to 2 weeks in Patent Document 1 and 1 week in Patent Document 2.

 In addition, the optical fiber is usually exposed to an atmosphere of a gas containing deuterium while being wound around a bobbin or the like, but the gas containing deuterium hardly spreads to the vicinity of the bobbin winding core. NBOHC in the optical fiber is easily bonded to deuterium to form a deuterated hydroxyl group. Therefore, the reaction using NBOHC as a heavy hydroxyl group is greatly affected by the contact frequency between NBOHC and a gas containing deuterium. Therefore, among the optical fibers wound around the bobbin, the optical fiber located in the vicinity of the bobbin core, that is, in the lower layer is difficult to come into contact with the gas containing deuterium. As a result, the reaction between NBOHC and deuterium proceeds. hard.

 For example, even if an optical fiber wound on a bobbin or the like is exposed to a mixed gas having a deuterium concentration of 1% for 24 hours by the methods disclosed in Patent Documents 1 and 2, the vicinity of the bobbin core, that is, NBOHC could not be eliminated in the optical fiber located in the lower layer. Therefore, in order to eliminate NBOHC over the entire area of the optical fiber wound around a bobbin or the like, it is necessary to use a gas containing a high concentration of deuterium and to increase the exposure time.

Further, in order to expose the optical fiber to an atmosphere of a gas containing deuterium, an optical fiber wound around a bobbin or the like is arranged in the reaction tank, and a gas containing deuterium is supplied into the reaction tank. Thereafter, the reaction vessel is sealed for a predetermined time. Conventionally, after performing a process for reducing NBOHC in an optical fiber, the gas containing deuterium is exhausted without being reused, and the gas containing deuterium is expensive, so the manufacturing cost is very high. There was a problem of becoming higher.
JP 2002-148450 A JP 2003-137580 A

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber processing method capable of eliminating NBOHC over the entire area of an optical fiber wound around a bobbin.

In order to solve the above-mentioned problems, the present invention provides an optical fiber comprising: a step A for winding an optical fiber around a bobbin; and a step B for exposing the optical fiber wound around the bobbin to a gas atmosphere containing deuterium. In the processing method, in step A, when the outer diameter of the optical fiber is d and the interval at which the optical fiber is wound around the bobbin is S , the optical fiber is wound so as to satisfy the relational expression S ≧ 2d. Provided is an optical fiber processing method in which an optical fiber is wound around a bobbin so as to satisfy a relational expression of 0.2N ≦ T ≦ 2.0N, where T (N) is a tension .

  According to the present invention, in the step of winding the optical fiber around the bobbin, if the outer diameter of the optical fiber is d and the interval at which the optical fiber is wound around the bobbin is S, the optical fiber satisfies the relational expression S ≧ 2d. Even if the optical fiber is wound around the bobbin by supplying a gas containing deuterium into the reaction vessel in which the optical fiber wound around the bobbin is disposed, The gas containing deuterium passes through the gap between the wound optical fibers and quickly reaches the vicinity of the bobbin core. As a result, the contact efficiency between the optical fiber located near the bobbin winding core, that is, the lower layer, and the gas containing deuterium is improved.

  According to the present invention, in the step of winding the optical fiber around the bobbin, the optical fiber satisfies the relational expression of 0.2N ≦ T ≦ 2.0N, where T (N) is the winding tension of the optical fiber. Even if the optical fiber is wound around the bobbin with a constant tension, the gas containing deuterium passes through the gap between the wound optical fibers and quickly winds the bobbin. It reaches around the core. As a result, the contact efficiency between the optical fiber located near the bobbin winding core, that is, the lower layer, and the gas containing deuterium is improved.

  Therefore, according to the present invention, even when a gas containing a low concentration of deuterium is used and the optical fiber is exposed to the atmosphere of the gas containing the low concentration of deuterium, the entire time of the optical fiber is reduced. NBOHC can be extinguished. As a result, productivity can be improved and manufacturing costs can be reduced.

  Hereinafter, an optical fiber processing method embodying the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an example of an optical fiber processing apparatus used in the optical fiber processing method according to the present invention.
In FIG. 1, 10 is an optical fiber processing device, 11 is a reaction tank, 12 is a gas introduction port, 13 is a gas introduction opening / closing valve, 14 is a gas supply pipe, 15 is an exhaust port, and 16 is an exhaust opening / closing valve. , 17 is an exhaust pump, 18 is a differential pressure gauge, 20 is an optical fiber, and 21 is a bobbin.

The reaction tank 11 is a container provided with a sealable space in which the optical fiber 20 can be accommodated, and has a pressure resistance and a sealing property that can withstand a vacuum state of about 0.1 kPa and a pressure state of normal pressure to 250 kPa or less. Have
A gas supply pipe 14 is connected to a gas introduction port 12 provided in the reaction layer 11 via a gas introduction opening / closing valve 13. A gas containing deuterium can be supplied into the reaction tank 11 from the gas supply pipe 14.

  Here, the gas containing deuterium is a deuterium gas alone or a mixed gas containing deuterium gas.

  An exhaust port 15 provided in the reaction tank 11 is connected to an exhaust pump 17 such as a vacuum pump through an exhaust opening / closing valve 16. A gas containing deuterium in the reaction tank 11 can be exhausted from the exhaust pump 17.

  The reaction tank 11 is provided with a differential pressure gauge 18 so that the pressure in the reaction tank 11 can be measured. Based on the measured value by the differential pressure gauge 18, the gas supply opening / closing valve 13 is opened and closed, and the supply amount of gas containing deuterium from a gas supply source (not shown) connected to the gas supply pipe 14 is adjusted, The inside of the reaction tank 11 can be set to an atmosphere of a gas containing deuterium at a predetermined pressure. Further, the exhaust pump 17 is started and stopped based on the measured value by the differential pressure gauge 18 so that the inside of the reaction tank 11 can be in a reduced pressure atmosphere of a predetermined pressure.

  Furthermore, the reaction tank 11 is provided with temperature adjusting means (not shown) such as a heater and a cooling mechanism, a thermometer (not shown), and a temperature adjusting unit (not shown), and thereby the internal temperature is adjusted. Thus, the inside of the reaction vessel 11 can be brought to a constant temperature state of 40 ° C. or lower.

  The reaction tank 11 is equipped with an electromagnetic valve or the like that can adjust the gas flow rate instead of the on-off valve 13, and can adjust the supply amount of gas containing deuterium supplied into the reaction tank 11. May be.

Next, with reference to FIG. 1, one Embodiment of the processing method of the optical fiber which concerns on this invention is described.
In the optical fiber processing method of this embodiment, first, an optical fiber 20 having a predetermined length is wound around a bobbin 21 (step A).

  In this step A, when the outer diameter of the optical fiber 20 is d (mm) and the interval at which the optical fiber 20 is wound around the bobbin 21 is S (mm), the optical fiber 20 is satisfied so as to satisfy the relation S ≧ 2d. Winding on the bobbin 21.

  In S <2d, among the optical fibers 20 wound around the bobbin 21, the optical fiber 20 located in the vicinity of the core of the bobbin 21, that is, in the lower layer, is difficult to come into contact with the gas containing deuterium. Reaction with hydrogen is difficult to proceed.

  Further, in this step A, when the tension for winding the optical fiber 20 around the bobbin 21 is T (N), the optical fiber 20 is wound around the bobbin 21 so as to satisfy the relational expression 0.2N ≦ T ≦ 2.0N. You may take it.

  When T <0.2N, the tension T for winding the optical fiber 20 around the bobbin 21 is too weak, the winding bulk density of the optical fiber 20 is reduced, and the winding length is shortened, which is not suitable for production. On the other hand, when T> 2.0N, the glass density of the optical fiber 20 is increased and the diffusion of deuterium is inhibited. As a result, the reaction between NBOHC and deuterium does not proceed easily, and the disappearance of NBOHC is slow. Become.

  Next, the optical fiber 20 wound around the bobbin 21 is exposed to a gas atmosphere containing deuterium to perform a process of reducing NBOHC in the optical fiber 20 (step B).

In this process B, first, the optical fiber 20 wound around the bobbin 21 is placed in the reaction vessel 11 of the processing apparatus 10.
Next, after the exhaust pump 17 is actuated, the exhaust open / close valve 16 is opened, the air in the reaction tank 11 is exhausted, and the pressure in the reaction tank 11, that is, the space containing the optical fiber 20, is reduced to a reduced pressure atmosphere. The optical fiber 20 is exposed to a reduced pressure atmosphere.

Next, after closing the exhaust opening / closing valve 16, the temperature in the reaction vessel 11 is adjusted to 40 ° C. or less by a temperature adjusting means (not shown), a thermometer (not shown), or a temperature adjusting unit (not shown). Of constant temperature.
Next, the gas introduction opening / closing valve 13 is opened, and a gas containing deuterium is supplied to the reduced pressure atmosphere in the reaction tank 11.

  Then, a gas containing deuterium is supplied until the inside of the reaction vessel 11 reaches a predetermined pressure, and the space containing the optical fiber 20 in the reaction vessel 11 is replaced with a gas containing deuterium. The on-off valve 13 is closed to seal the inside of the reaction tank 11, and in this reaction tank 11, the optical fiber 20 is exposed to a gas atmosphere containing deuterium.

By this step B, the optical fiber 20 is exposed to an atmosphere of a gas containing deuterium, and NBOHC in quartz glass forming the optical fiber 20 and deuterium (D ₂ ) are reacted to form a deuterated hydroxyl group (—OD). As a result, the formation of a hydroxyl group (—OH) can be prevented. Thereby, the absorption wavelength band of the optical fiber 20 can be moved from the 1.38 μm band that is the absorption wavelength band of the hydroxyl group to the 1.87 μm band that is the absorption wavelength band of the heavy hydroxyl group, that is, other than the optical communication wavelength band. it can. Therefore, it is possible to suppress the deterioration of the transmission characteristics of the optical fiber 20 due to the absorption loss due to the hydroxyl group in the quartz glass.

  In this embodiment, when the outer diameter of the optical fiber 20 is d (mm) and the interval at which the optical fiber 20 is wound around the bobbin 21 is S (mm) in the above step A, the relational expression S ≧ 2d is obtained. If the tension for winding the optical fiber 20 around the bobbin 21 or T (N) is T (N), the relational expression 0.2N ≦ T ≦ 2.0N is satisfied. In the optical fiber processing method of the present invention, the outer diameter of the optical fiber 20 is d (mm) and the optical fiber 20 is wound around the bobbin 21 in the process A. If the interval to be taken is S (mm), the relationship of S ≧ 2d is satisfied, and if the tension for winding the optical fiber 20 around the bobbin 21 is T (N), the relationship is 0.2N ≦ T ≦ 2.0N I satisfy the formula In the optical fiber 20 may be wound on a bobbin 21.

  In this embodiment, the optical fiber 20 is wound around the bobbin 21 at regular intervals so as to satisfy the relational expression S ≧ 2d, or the relational expression 0.2N ≦ T ≦ 2.0N is satisfied. The optical fiber 20 is wound around the bobbin 21 with a constant tension, and after the inside of the reaction tank 11 in which the optical fiber 20 is disposed is made a reduced pressure atmosphere, a gas containing deuterium is supplied into the reaction tank 11. Thus, even in the state where the optical fiber 20 is wound around the bobbin 21, the gas containing deuterium whose diffusion rate is increased in the reaction tank 11 passes through the gap between the wound optical fibers 20 and quickly. It reaches to the vicinity of the core of the bobbin 21. As a result, the contact efficiency between the optical fiber 20 located near the core of the bobbin 21, that is, the lower layer, and the gas containing deuterium is improved.

Since NBOHC is easily bonded to deuterium to form a deuterated hydroxyl group, the reaction in which NBOHC and deuterium are combined to form a deuterated hydroxyl group (reaction that eliminates NBOHC) is greatly dependent on the contact frequency between NBOHC and deuterium gas. to be influenced.
According to the present invention, as described above, in the optical fiber 20 near the winding core of the bobbin 21, the contact frequency (contact efficiency) between the optical fiber 20 and the gas containing deuterium can be increased. Thus, the reaction rate between NBOHC and deuterium can be increased over the entire area of the optical fiber 20 wound up by 21. Therefore, NBOHC is extinguished over the entire area of the optical fiber 20 even when the gas containing the low concentration deuterium is used and the time for exposing the optical fiber 20 to the atmosphere of the gas containing the low concentration deuterium is shortened. be able to.

  The optical fiber that can be processed by the optical fiber processing method of the present invention is not particularly limited. According to the optical fiber processing method of the present invention, any optical fiber can be processed as long as it is an optical fiber containing quartz glass as a constituent material.

  Hereinafter, the present invention will be described more specifically with experimental examples, but the present invention is not limited to the following experimental examples.

(Experimental example 1)
An optical fiber having an outer diameter of 250 μm was wound around a bobbin so that the winding height was 30 mm. At this time, the interval at which the optical fiber was wound around the bobbin was varied between 0.4 mm and 0.9 mm, and several types of bobbins having different optical fiber winding intervals were produced.
Each bobbin was placed in a reaction tank of an optical fiber processing apparatus as shown in FIG. 1, and the pressure in the reaction tank was reduced to 1 kPa (absolute pressure). Thereafter, a gas containing deuterium was supplied into the reaction vessel so that the partial pressure of deuterium became 1.0 kPa or 2.0 kPa, and the reaction vessel was sealed at 95 kPa. In this state, the optical fiber was exposed to a gas atmosphere containing deuterium for 7 hours in the reaction vessel.
After being exposed to a gas atmosphere containing deuterium for 7 hours, the optical fiber is removed from the reaction vessel, and the outermost optical fiber (existing on the surface) of the optical fibers wound on the bobbin, the lowermost optical fiber, The amount of NBOHC remaining was converted from the absorption loss at 0.63 μm, which is the NBOHC absorption wavelength range, and the time for NBOHC to disappear was measured. FIG. 2 shows the relationship between the NBOHC extinction delay time calculated from the difference between the NBOHC disappearance time of the outermost optical fiber and the NBOHC disappearance time of the lowermost optical fiber and the optical fiber winding interval. Show.
From the results shown in FIG. 2, when an optical fiber having an outer diameter of 250 μm is treated with deuterium regardless of the partial pressure of deuterium, the optical fiber winding interval is 0.5 mm or more if the optical fiber winding interval is 0.5 mm or more. It was found that there was no effect on the deuterium treatment.

(Experimental example 2)
An optical fiber having an outer diameter of 250 μm having the same characteristics as the optical fiber used in Example 1 was wound around a bobbin so that the winding height was 30 mm. At this time, the interval at which the optical fiber was wound around the bobbin was varied between 0.4 mm and 0.9 mm, and several types of bobbins having different optical fiber winding intervals were produced.
Each bobbin is placed in a reaction tank of an optical fiber processing apparatus as shown in FIG. 1, and the partial pressure of deuterium is 1.0 kPa or 2.0 kPa without reducing the pressure in the reaction tank. A gas containing deuterium was supplied into the reaction tank, the pressure in the reaction tank was set to 95 kPa, and the reaction tank was sealed. In this state, the optical fiber was exposed to a gas atmosphere containing deuterium for 24 hours in the reaction vessel.
After being exposed to an atmosphere of a gas containing deuterium for 24 hours, the optical fiber is taken out of the reaction vessel, and the optical fiber in the outermost layer (existing on the surface) of the optical fibers wound around the bobbin, The amount of NBOHC remaining was converted from the absorption loss at 0.63 μm, which is the NBOHC absorption wavelength range, and the time for NBOHC to disappear was measured. FIG. 3 shows the relationship between the NBOHC extinction delay time calculated from the difference between the time when the NBOHC in the outermost optical fiber disappears and the time when the NBOHC in the lowermost optical fiber disappears, and the optical fiber winding interval. Show.
From the results shown in FIG. 3, when an optical fiber having an outer diameter of 250 μm is treated with deuterium regardless of the partial pressure of deuterium, if the winding distance of the optical fiber is 0.5 mm or more, the winding distance of the optical fiber It was found that there was no effect on the deuterium treatment.

(Experimental example 3)
An optical fiber having an outer diameter of 175 μm and an optical fiber having an outer diameter of 500 μm were wound around a bobbin so that the winding height was 30 mm. At this time, the interval at which the optical fiber was wound around the bobbin was changed, and several types of bobbins having different winding intervals were produced for each optical fiber.
Each bobbin was placed in a reaction tank of an optical fiber processing apparatus as shown in FIG. 1, and the pressure in the reaction tank was reduced to 1 kPa (absolute pressure). Thereafter, a gas containing deuterium was supplied into the reaction vessel so that the partial pressure of deuterium became 1.0 kPa, and the reaction vessel was sealed at 95 kPa. In this state, the optical fiber was exposed to a gas atmosphere containing deuterium for 7 hours in the reaction vessel.
After being exposed to a gas atmosphere containing deuterium for 7 hours, the optical fiber is removed from the reaction vessel, and the outermost optical fiber (existing on the surface) of the optical fibers wound on the bobbin, the lowermost optical fiber, The amount of NBOHC remaining was converted from the absorption loss at 0.63 μm, which is the NBOHC absorption wavelength range, and the time for NBOHC to disappear was measured. The NBOHC extinction delay time calculated from the difference between the time when the NBOHC in the outermost optical fiber disappears and the time when the NBOHC in the lowermost optical fiber disappears, and the winding interval (S) of the optical fiber are calculated as follows. The value divided by the outer diameter (d) is shown in FIG.
From the results of FIG. 4, it was found that if the S / d is 2 or more, regardless of the outer diameter of the optical fiber, the winding interval of the optical fiber has no effect on the deuterium treatment.

(Experimental example 4)
An optical fiber having an outer diameter of 250 μm was wound around a bobbin such that the winding interval was 0.6 μm and the winding height was 30 mm. At this time, the tension for winding the optical fiber around the bobbin was changed, and several types of bobbins having different winding tensions were produced.
Each bobbin was placed in a reaction tank of an optical fiber processing apparatus as shown in FIG. 1, and the pressure in the reaction tank was reduced to 1 kPa (absolute pressure). Thereafter, a gas containing deuterium was supplied into the reaction vessel so that the partial pressure of deuterium became 1.0 kPa, and the reaction vessel was sealed at 95 kPa. In this state, the optical fiber was exposed to a gas atmosphere containing deuterium for 7 hours in the reaction vessel.
After being exposed to a gas atmosphere containing deuterium for 7 hours, the optical fiber is removed from the reaction vessel, and the outermost optical fiber (existing on the surface) of the optical fibers wound on the bobbin, the lowermost optical fiber, The amount of NBOHC remaining was converted from the absorption loss at 0.63 μm, which is the NBOHC absorption wavelength range, and the time for NBOHC to disappear was measured. FIG. 5 shows the relationship between the NBOHC extinction delay time calculated from the difference between the NBOHC disappearance time of the outermost optical fiber and the NBOHC disappearance time of the lowermost optical fiber and the winding tension of the optical fiber. Show.
From the results of FIG. 5, it was found that the winding tension had no effect on the deuterium treatment when the winding tension was 2.0 N or less. However, if the winding tension is less than 0.2 N, it is considered that the tension is too low and the winding state of the optical fiber on the bobbin is deteriorated, and the winding length is shortened.

It is a schematic block diagram which shows an example of the processing apparatus of the optical fiber used with the processing method of the optical fiber which concerns on this invention. In Experimental example 1, it is a graph which shows the relationship between the extinction delay time of NBOHC, and the winding interval of an optical fiber. In Experimental example 2, it is a graph which shows the relationship between the extinction delay time of NBOHC, and the winding interval of an optical fiber. In Experimental example 3, it is a graph which shows the relationship between the extinction delay time of NBOHC, and the value which remove | divided the winding interval (S) of the optical fiber by the outer diameter (d) of the optical fiber. In Experimental Example 4, the NBOHC extinction delay time calculated from the difference between the time when the NBOHC of the outermost optical fiber of the optical fiber wound around the bobbin disappears and the time when the NBOHC of the lowermost optical fiber disappears It is a graph which shows the relationship with the winding tension | tensile_strength of an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Optical fiber processing apparatus, 11 ... Reaction tank, 12 ... Gas introduction port, 13 ... Gas introduction opening / closing valve, 14 ... Gas supply piping, 15 ... Exhaust port , 16 ... Open / close valve for exhaust, 17 ... Pump for exhaust, 18 ... Differential pressure gauge, 20 ... Optical fiber, 21 ... Bobbin.

Claims (1)

An optical fiber processing method comprising: a step A for winding an optical fiber on a bobbin; and a step B for exposing the optical fiber wound on the bobbin to an atmosphere of a gas containing deuterium,
In step A, when the outer diameter of the optical fiber is d and the interval at which the optical fiber is wound around the bobbin is S, the tension that winds the optical fiber is T (N) so that the relational expression S ≧ 2d is satisfied. Then, the optical fiber is wound around a bobbin so as to satisfy the relational expression of 0.2N ≦ T ≦ 2.0N.

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