JPH0678172B2 - Optical fiber manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an optical fiber having radiation resistance characteristics in which transmission loss does not increase even when receiving radiation.

In recent years, the introduction of optical fiber cables for nuclear reactor control and other various information transmissions has been studied and tested. As described above, the optical fiber used in the nuclear power plant is required to have the radiation resistance property, and therefore its development is being carried out. It is generally known that OH doping is effective for increasing the radiation resistance of optical fibers, but recently, optical fibers doped with OD (D is deuterium) have been reported to be more effective. Has been done. Compared to the OH-doped optical fiber, this optical fiber has an absorption peak shifted to the long wavelength side, and therefore the intrinsic (initial) loss can be reduced. That is, the absorption peak is 0.95 in the optical fiber doped with OH.
On the other hand, the optical fiber doped with OD has an absorption peak of 1.28 μm, and the intrinsic loss at 0.85 μm can be reduced. When a large amount of OH (several hundred to several thousand ppm) is doped into the optical fiber, the intrinsic loss is 0.85μm and 2db / km.
To 10 to 20 db / km, which is not preferable. on the other hand,
Since the optical fiber doped with OD has a slight increase in intrinsic loss as already mentioned, it is preferable to dope OD as much as several hundred to several thousand ppm, but in the prior art, dope this OD heavily. I couldn't.

An object of the present invention is to provide a method of manufacturing an optical fiber having a radiation resistance characteristic by reducing a specific loss by doping a large amount of OD into the optical fiber.

Embodiments of the present invention will be described in detail with reference to the drawings. The drawings show an example of an apparatus for carrying out the method of the present invention. In the illustrated embodiment, the method of the present invention is of high purity obtained by the VAD method. It shows that the soot 10 of the SiO ₂ one-component system is carried out in a furnace 12 for transparent vitrification. In addition, 2 of this soot is SiO ₂ -GeO ₂
It may be a component system. High-purity SiO ₂ soot by VAD method 1
When 0 is set, extremely high quality synthetic quartz glass is obtained.
"Good quality" as used herein means that the impurity concentration is very low and the number of structural defects is small. D (deuterium)
Is an isotope of H, and its chemical properties can be regarded as almost the same as H. H ₂ diffuses in the glass and is captured by structural defects, forming a structure called Si-OH. D also shows the same behavior as H and becomes Si-OD. Therefore, it is understood that the number of structural defects in the glass should be increased in order to dope D into the glass in a large amount. The soot obtained by the VAD method is an aggregate of small glass particles and has a large surface activity. Therefore, D
It is thought that this stage is the largest in the diffusion in the soot.

In view of this, the method of the present invention increases the number of structural defects in the glass particles of the soot by irradiating the soot 10 of SiO ₂ which is the raw material of the optical fiber obtained by the VAD method with radiation or ultraviolet rays. It is designed to capture a large amount of OD groups inside. In the drawing, γ shielded by a lead shield tube 14 in a furnace 12 for vitrifying the SiO ₂ soot 10
The radiation source 16 is arranged, and the γ-rays emitted from the γ-ray source 16 cause a large number of structural defects in the glass particles of the soot 10. Since D and He have been introduced into the furnace core tube 12a in the furnace 12, D is trapped in the structural defects, a Si-OD reaction occurs, and OD groups are introduced into the glass.

In one embodiment of the present invention, D ₂ was introduced into the core tube 12a at a flow rate of 2 liters / minute and He was introduced at a flow rate of 15 liters / minute, and SiO ₂ soot was pulled down into the core tube 12a at a speed of 120 mm / hour. The dose of gamma rays was 10 ^{2 to} 10 ⁴ rad / hour. Suit in this way 10
It was possible to dope D in 1000 ppm or more. When the same procedure as above was performed without γ-ray irradiation, the doping amount of D was 100 ppm or less. The soot 10 becomes transparent by passing through the maximum temperature range (1500 ° C) in the furnace 12, but when it becomes transparent, the introduction of He into the furnace core tube 12a is stopped and only 2 liters of D ₂ are charged. / Min. The reason for stopping the introduction of He is that D of Si-OD is partially scattered by He. It should be noted that the higher the radiation dose, the more structural defects can be generated in the soot glass particles, but if the dose is too high, handling will be a problem for safety, and this aspect must be taken into consideration. It is known that the structural defects generated in the soot disappear within a few minutes to several hours, but when the structural defects are generated as in this example, D ₂ is already sufficiently contained in the glass fine particles. Since it is diffused, Si is
-OD reaction occurs.

Although γ-rays are used in the above embodiment, X-rays or electron beams can be used instead of γ-rays. Further, in the illustrated embodiment, the soot is made transparent immediately after irradiation with the radiation, but D may be introduced after irradiation of the soot with radiation for several hours.
However, as already mentioned, structural defects disappear with time, so the amount that can be doped decreases in this case. In addition to D, D ₂ O may be introduced into the core tube 12a.

According to the present invention, as described above, since a large amount of D or OD can be doped in the optical fiber, there is a practical advantage that the intrinsic loss can be reduced and the radiation resistance can be improved.

[Brief description of drawings]

The drawing is a longitudinal sectional view showing an example of an apparatus for carrying out the method of the present invention. 10 …… SiO ₂ soot, 12 …… furnace, 16 …… radiation source.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuaki Yoshida 6 Yawata Kaigan Dori, Ichihara City, Chiba Prefecture Furukawa Electric Co., Ltd. Chiba Electric Wire Co., Ltd. (72) Inventor Masao Nishimura 6 Hachiman Kaido Dori, Ichihara City, Chiba Prefecture Furukawa Electric Co., Ltd. Chiba Electric Cable Co., Ltd. (72) Inventor Motohiro Nakahara Tokai-mura, Naka-gun, Ibaraki Prefecture 162 Shirahane, Shirahoji, Japan Telegraph and Telephone Public Corporation Ibaraki Telecommunications Research Institute (72) Innovator Nobuo Inagaki Tokai-mura, Naka-gun, Ibaraki Prefecture 162 Shirakuji, Shirane, Ibaraki Electro-Communication Research Laboratories, Nippon Telegraph and Telephone Public Corporation

Claims (2)

[Claims] 1. A method of irradiating a SiO ₂ one-component system or a SiO ₂ -GeO ₂ two-component system soot, which is a raw material for optical fibers obtained by the VAD method, with radiation or ultraviolet rays while increasing the number of defects in glass fine particles. A method for producing an optical fiber, which is obtained by introducing a large amount of OD groups into the soot. 2. A method of manufacturing an optical fiber, wherein the irradiation of the radiation is carried out in a furnace for vitrifying the soot.