JP3960896B2 - Optical fiber manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber manufacturing method, and more particularly to an efficient optical fiber manufacturing method in which long-term stability of optical transmission characteristics in a wavelength band of 1380 to 1400 nm is ensured.
[0002]
[Prior art]
In an optical communication system, infrared light having a wavelength of 800 to 900 nm or a wavelength of 1300 to 1600 nm is usually used. Recently, a trend to effectively use light having a wavelength of 1300 to 1600 nm is being advanced.
A problem in the latter wavelength band is that absorption occurs in the optical fiber used, resulting in an increase in transmission loss.
[0003]
It is known that this absorption is caused by OH groups generated inside the optical fiber.
For example, even when an optical fiber is manufactured using high-purity silica, an OH group of less than about 0.1 ppm is usually generated in the optical fiber.
In addition, even if an optical fiber with few OH groups is used after drawing, if it is laid and actually used, it will be exposed to ambient hydrogen under the ambient temperature, and the hydrogen will diffuse into the optical fiber. Thus, it is known that OH groups are generated, and transmission loss at wavelengths of 1300 to 1600 nm, particularly at wavelengths of 1380 to 1600 nm, increases with time. This time-dependent change in transmission loss caused by the presence of hydrogen is usually referred to as “hydrogen time-dependent loss”.
[0004]
Such an effect of hydrogen diffusion is observed even through the cladding when optical fibers are bundled as a communication cable. This hydrogen diffusion has already been observed at room temperature even when exposed to an atmosphere of a trace amount of hydrogen of about 0.01% for several days. For example, at a wavelength of 1383 nm, 0.02 dB / km to 0.12 dB / km loss is allowed.
[0005]
By the way, it is considered that hydrogen is generated based on the corrosion phenomenon caused by different metals present in the optical cable and surrounding moisture, and is generated when the silicone resin constituting the coating is heated. And in the case of the optical fiber laid in seawater or the air | atmosphere, there exists a problem that hydrogen aging loss is especially large.
To deal with such a problem, a D ₂ treatment has been proposed in which exposure to a deuterium (D ₂ ) atmosphere prior to actual use of an optical fiber and then, for example, it is left in the air (for example, Patent Document 1). reference).
[0006]
In this method, by reacting D ₂ with structural defects or OH groups present in the optical fiber after drawing, and leaving it for a predetermined time, the generation factor of OH groups during actual use is eliminated in advance. The purpose is to prevent an increase in transmission loss due to the generation of the group.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-148450
[Problems to be solved by the invention]
However, in the case of the D ₂ treatment described in Patent Document 1 described above, the time for performing the D ₂ treatment is very long, and the D ₂ treatment diffuses into the optical fiber and remains unreacted with the OH group. There is a problem that the time for leaving the D ₂ molecule to escape out of the optical fiber is very long. For this reason, the above prior art has low production efficiency in actual industrial production and is not necessarily a satisfactory method for practical use.
[0009]
The present invention is to solve the above problems of the conventional D ₂ process, by carrying out the D ₂ treatment quickly and efficiently, to provide a method of manufacturing an optical fiber long-term stability of transmission characteristics is ensured Objective.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, after exposing an optical fiber immediately after being drawn and wound on a bobbin in a gas atmosphere containing deuterium gas, the deuterium gas in the optical fiber is released. A method for manufacturing an optical fiber is provided, wherein the optical fiber is wound back to another bobbin while applying tensile tension before the end.
[0011]
At that time, the tensile tension is preferably a tensile tension corresponding to 0.5 to 2% in terms of an elongation value of the optical fiber, and when the optical fiber is unwound, the optical fiber is desired in the longitudinal direction. It is preferable to cut and divide into lengths.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, first, an optical fiber coated by drawing an optical fiber preform is wound around a bobbin by a conventional method, and then D ₂ treatment is performed immediately.
Specifically, the bobbin immediately after winding the optical fiber is housed in a sealed container, and a gas containing D ₂ is enclosed therein, and is left as it is for a predetermined time. The
[0013]
As the atmospheric gas, for example, air or a mixed gas of inert gas (He, Ar, N _2, etc.) and D ₂ is used, and in this case, a gas containing 0.01 to 100% of D ₂ is preferable. A mixed gas containing nearly 100% D ₂ can suppress an increase in transmission loss even in a short-time treatment, and is preferable in terms of treatment efficiency.
If the treatment time is less than 1 hour, the effect of the D ₂ treatment is not sufficiently exerted, and if it exceeds 10 hours, the effect reaches saturation, and the production efficiency is naturally reduced. That's fine. It is preferable that the time is around 2 hours.
[0014]
If the temperature during the D ₂ treatment is too low, the reaction of the D ₂ treatment is slow, and conversely, if it is too high, the treatment time can be shortened, but on the other hand, the coating may be deteriorated. The temperature during the treatment is preferably controlled within a range of 25 ± 3 ° C.
Immediately after the D ₂ treatment, the treated optical fiber is rewound onto another bobbin. At this time, it is necessary to apply a tensile tension to the optical fiber.
[0015]
That is, the present invention is characterized in that the conventional step of leaving for a long time after the D ₂ treatment for degassing free D ₂ molecules is omitted.
This rewinding can be carried out in air-controlled air or in a nitrogen atmosphere.
By applying a tensile tension to the optical fiber, a load is applied to the coating, and the temperature of the optical fiber core (glass) slightly increases due to the bending and frictional energy of the coating. Also, tensile tension is applied to the optical fiber core (glass), and the D ₂ concentration on the surface of the optical fiber core is zero or very low, so that residual D ₂ molecules inside the core can easily escape to the outside. The time required for degassing is shortened.
[0016]
The tensile tension applied at this time is set so that the elongation of the optical fiber is 0.5 to 2.5%. When tension is applied such that the elongation is less than 0.5%, the above-mentioned effect cannot be obtained. When tension is applied such that the elongation is greater than 2.5%, the coating may be damaged. Because there is.
Further, at the time of rewinding, if the optical fiber is cut to a desired length such as the length at the time of shipment, it is efficient because it is not necessary to newly provide a cutting process.
[0017]
【Example】
An optical fiber was manufactured by drawing an optical fiber preform manufactured by a conventional method, and this was wound around a bobbin. An example of a transmission loss spectrum diagram of this optical fiber is shown in FIG.
In the figure, the peak A ₀ appearing near the wavelength of 1380 nm is a transmission loss due to the OH group.
[0018]
Next, the bobbin was placed in a sealed container, filled with 100% D _{2 and} 0% N ₂ gas, and left at 25 ° C. for 2 hours for D ₂ treatment.
After the D ₂ treatment under the above conditions, the transmission loss was measured after being left for 72 hours. The results are shown in FIG.
As is clear from the transmission loss spectrum diagram of FIG. 2, a new peak A ₁ is observed near the wavelength of 1420 nm, and a new broad peak A ₂ is also observed near the wavelength of 1500 nm. The former A ₁ is an increase in loss due to the occurrence of absorption loss due to the D ₂ molecule itself diffused in the optical fiber, and the latter A ₂ has an OD group bonded to a structural defect before the D ₂ treatment, This is based on the occurrence of absorption loss due to the OD group.
[0019]
The bobbin optical fiber was then rewound onto another bobbin in the atmosphere. At this time, tensile tension was applied to the optical fiber so that the elongation was 1.1%, and the optical fiber was cut and separated every 25.26 km.
Then, the transmission loss at a wavelength of 1420 nm after the start of the D ₂ process is measured over time, and the transmission loss before the D ₂ process (value at 1420 nm in FIG. 1) is subtracted from the measured value at each time point. The relationship between the amount of change and the elapsed time after the D ₂ treatment was examined, and this is shown by-♦-in FIG.
[0020]
For comparison, the optical fiber after D ₂ treatment is left in the atmosphere as it is without rewinding to another bobbin. In this case, the amount of change in transmission loss and the elapsed time after D ₂ treatment I investigated the relationship. The result was shown by -x- mark of FIG.
As is apparent from FIG. 3, in the optical fiber manufactured by the example method, free D ₂ molecules exhibiting absorption loss near the wavelength of 1420 nm escape in a shorter time than in the case of the optical fiber manufactured by the comparative example method. You can see that
[0021]
【The invention's effect】
As apparent from the above description, according to the present invention, when attempting to produce an optical fiber with reduced hydrogen aging loss by D ₂ treatment, without left for a long time after D ₂ processing as in the prior art Can also achieve the purpose. This is an effect that the present invention brings about the rewinding by cutting and dividing immediately after applying the tensile tension after the D ₂ treatment.
[0022]
Therefore, according to the method of the present invention, an optical fiber that does not increase transmission loss can be produced in a short time, and a long-time leaving step is not required. Therefore, a large number of bobbins that wind up the cut and divided optical fiber can be formed. It is not necessary to stay for a long time, and it is important to contribute to the practical use of D ₂ treatment.
[Brief description of the drawings]
FIG. 1 is an example of a transmission loss spectrum diagram of an optical fiber before D ₂ treatment.
FIG. 2 is an example of a transmission loss spectrum diagram of an optical fiber after D ₂ treatment.
[3] the difference in transmission loss at D ₂ before and after processing wavelength 1420 nm, which is a graph showing the relationship between the elapsed time after D ₂ treatment initiation.

Claims (2)

In an optical fiber manufacturing method,
Winding the drawn optical fiber around a first bobbin;
A deuterium treatment step of exposing the optical fiber wound around the first bobbin to a deuterium gas atmosphere; and
A step of rewinding the optical fiber after the deuterium treatment from the first bobbin to the second bobbin while applying tensile tension immediately.
The method for producing an optical fiber, wherein the tensile tension is a tensile tension corresponding to 0.5 to 2% in terms of an elongation value of the optical fiber.   The optical fiber manufacturing method according to claim 1, wherein when the optical fiber is wound, the optical fiber is cut into a desired length in the longitudinal direction and divided.

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