JPS6090852A - Treatment of glass for optical fiber - Google Patents

Abstract

PURPOSE:To improve the radiation resistance of quartz glass for an optical fiber by exposing the glass to an atmosphere contg. D2 or a D2 compound to introduce OD groups. CONSTITUTION:Glass for an optical fiber such as a molded body of quartz glass soot forming a porous glass base material for an optical fiber, a molded body of quartz glass forming a transparent glass base material for an optical fiber or a molded body of glass forming an optical fiber is exposed to an atmosphere contg. D2 or a D2 compound to introduce OD groups into the glass. Thus, an optical fiber enduring a radiation environment in a nuclear power plant is obtd.

Description

[Detailed Description of the Invention] The present invention relates to a manufacturing technology for optical fibers used for communication, image transmission, energy transmission, etc., and it is possible to obtain optical fibers that have high long-term reliability in the long wavelength region and excellent radiation resistance. The present invention relates to a glass processing method.

As one of the fields in which optical fibers made of quartz glass are being applied, applications under radiation environments such as inside nuclear power plants are rapidly increasing.

The reason for this is that optical fibers are lightweight for communication purposes;
This is because the small diameter, non-inductive property, and excellent low loss properties are major advantages in the case of image guides and light guides.

Particularly in the case of image guides, silica-based optical fibers have the advantage that loss increase due to radiation irradiation is extremely small compared to multi-component glasses that have been widely used in the past, and their practical use is rapidly expanding.

However, in a high-energy radiation environment such as gamma rays, neutron beams, X-rays, and electron beams, even silica-based optical fibers cannot avoid increased transmission loss due to radiation.

Various studies have been conducted to suppress this increase in transmission loss. For example, fibers with a large number of OH groups in the core have a relatively small increase in loss, and optical fiber spinning conditions have been found to influence the amount of increase in loss. It is known that this can have a major impact.

Based on the results of these studies, it was thought that an optical fiber containing several hundred ppr1 OH groups in its core and spun under optimal conditions would be able to withstand use in the nuclear field. The increase in loss is still large, and in the case of optical fibers with a core made of quartz glass containing a particularly high concentration of OH groups, there is absorption loss at wavelengths of 0.95 μm and 1.39 μm due to OH groups.
Optical transmission at a wavelength of 0.8μm as well as at a wavelength of 1.30μm
Optical transmission at m is nearly impossible! /) It is being done.

For this reason, OD group-containing silica glasses are attracting attention, although they have the same effect as OH groups in terms of radiation resistance, but their absorption loss is shifted to longer wavelength bands.

In the case of quartz glass containing OD groups, wavelength x, 28μ
m (corresponding to 1.95 fim with OH group), wavelength 1.6
8μm (corresponds to 1.24μm), wavelength 1.87μm
Absorption is observed at (j:It, corresponding to 39 pm).

Furthermore, in the case of quartz glass containing OD groups, the wavelength is 0.
Low loss is expected at 8 μm.

Methods for manufacturing such OD group-containing quartz optical fibers include a method using soot synthesis using a flame hydrolysis reaction, as described in JP-A No. 49-9514, and a method using dry gel (produced by a sol-gel method). Methods such as first treating dryget with C and then exchanging Ct → OD in a DIO atmosphere are known, but these methods are expensive* and require large quantities of DtO, so they are not industrially preferred. In particular, a method in which soot is treated in a DtO atmosphere tends to cause devitrification of the glass, making it difficult to obtain a high-quality optical fiber base material.

The present invention aims to provide a novel processing method for obtaining quartz-based optical fiber glass containing OD groups that has even better radiation resistance.

The processing method of the present invention is to process quartz-based optical fiber/glass into D.
2 or D! The glass is characterized by containing OD groups in the glass by exposing it to a compound-containing atmosphere.

Hereinafter, specific examples of the method of the present invention will be described.

↓fi o++ +r k) 1. -) A quartz-based glass soot molded body composed of a porous glass base material for a fiber and a transparent glass base material for an optical core. This is a general term that includes quartz-based glass molded bodies, glass molded bodies that make up optical fibers, etc., and does not include glass raw materials in the gas phase or liquid phase.

Regarding the above-mentioned optical fiber glass, when it is a porous glass base material, it is made by a known VAD method, OVD method, sol-gel method, etc., and the transparent glass base material is a porous glass base material made by each of these methods. The optical fiber can be obtained by transparently vitrifying it, or by the well-known MCVD method or PCVD method, and furthermore, the optical fiber can be obtained by heating and stretching a transparent glass base material.

Further, when the optical fiber glass is in the above-mentioned base material stage, the glass vibrator may be jacketed as necessary.

The optical fiber glass as a final product is the above-mentioned optical fiber, which includes a single core type having a monocore, a multicore type having a multicore, and the like.

The glass that makes up the core of optical fiber is quartz-based.
In addition to quartz, the cladding may also be made of a low refractive index plastic material such as silicone rubber or fluorine resin.

In terms of uses, the above-mentioned optical fibers are made for communications, image guides, and light guides.

It is preferable that the core of the optical fiber is pure Stow, since the increase in loss due to radiation irradiation is small.

The OH group content in the core is preferably small when used in a long wavelength range such as 1.3 μm or 1.55 μm, but
When used in a short wavelength region such as 0.85 μm or in a visible light region such as an image guide, good results are often obtained in terms of radiation resistance if the core contains a certain amount of OH groups in advance.

Optical fibers for communication may require broadband performance, and in such cases, the core may be doped quartz having a Gl-type refractive index distribution doped with FtGe5P or the like.

When the core is the above-mentioned doped quartz, the quartz-based cladding may be pure 5ins, but if the refractive index of the core is 5ins
, the cladding is F, B.
Doped quartz is used.

Of course, the optical fiber may be of the SI type, and may be either a single mode transmission type or a multimode transmission type.

The above-mentioned optical fiber glass is exposed to an atmosphere containing % Ih, or alternatively, to an atmosphere containing a compound (DzO), thereby causing the glass to contain OD groups.

As can be understood from the above description, the processing at this time includes a stage for the porous glass base material, a stage for the transparent glass base material, a stage for the optical fiber, and a stage synchronized with the optical fiber spinning process.
It is carried out in any one stage, in any two or more stages, or in all stages.

In addition, if the core glass is made before the cladding glass or in a separate process from the cladding glass, or if the cladding is made of plastic,
Sometimes only the core glass is subjected to the above treatment.

A preferred processing step is when the optical fiber glass is a porous glass matrix, since this facilitates the diffusion of Dt (or 0).

In the case of an image guide, the transparent glass base material has a diameter of 1,111 to 0. Thousands to tens of thousands of thin rods obtained by this process are drawn together and melted into one piece, and the integrated product is then heated and drawn to a diameter of 0. It takes a process of heating and drawing several to several ■ fibers, and in this image guide, when making the above thin rod, after making the thin rod and before melting and integrating it, It is also preferable to carry out the above treatment.

The processing temperature in an atmosphere containing D, (or 0) is 50
℃ or higher, and a higher temperature is preferable because the processing time can be shortened.

At the optical fiber stage, the processing temperature is preferably about 100 to 250°C to prevent deterioration of the primary coating material.
A treatment temperature of about 00 to 1600°C is selected.

In addition, when processing a transparent glass base material, it is possible to process it at a temperature that allows it to be stretched (for example, 2000 to 2100°C), and when processing a porous glass base material, it is possible to process it at a temperature that allows it to be sintered. is preferred.

In the present invention, the optical fiber glass is DI (or DI
When processing by exposing to an atmosphere containing O), for example, if the processing temperature is room temperature, Dt and the like will simply enter the optical fiber glass and OD groups will be difficult to generate.

Therefore, it is important to set the processing temperature higher than room temperature.

Contact with optical fiber glass D2 etc. at a relatively low temperature,
It is also effective to impregnate the optical fiber glass with 1) and then heat the glass to a high temperature.

In this case, it goes all the way to the center of the optical fiber glass.

etc. can be uniformly impregnated, so by heating it, for example, O
H group + D,;! It is preferable to perform OD group + HD exchange because the OD group concentration in the core becomes higher than the OH group concentration.

The pressure such as Dt is not particularly limited, but the higher the pressure, the more advantageous the processing time can be obtained.

D. When processing optical fiber glass with a high concentration of OH groups in an atmosphere containing O
When the reaction of H groups occurs, the concentration of OD groups and 10H groups decreases from near the outer surface to the inside of the optical fiber glass.

In the case of a porous glass base material, if it is directly subjected to D2 treatment, the OD group content will increase, but it will also contain OH groups, and absorption loss due to OH groups may be inconvenient.

At this time, the porous glass base material is treated with nitrogen, such as Cz.
+, after dehydration by treatment in the presence of halogen gas or halogen compound gas such as Ft,
! O) It is good to treat it, so that there is no OH group but OD
A grouped optical fiber glass is obtained.

This dehydration treatment uses a ct of ~5 vat% or less or a He atmosphere containing a chlorine compound.

On the contrary, the OH group is 100 ppm or more, preferably halo00p
The loss gradually decreases when it reaches about pm.

In such a case, the porous glass base material before the Dt (or DxO) treatment is made to contain multiple OH groups.

In addition, it may be advantageous if the optical fiber glass has a molecular structural defect, and in such cases Dt (or D
t0) The above-mentioned defects are increased by heating and stretching the transparent glass base material before treatment or irradiating it with radiation.

Next, specific examples of the present invention and comparative examples thereof will be explained.

Specific example 1 A porous glass base material for the core made of pure SiO was produced by the VAD method, and made into transparent glass by a conventional method, while doped quartz doped with B and F was applied to the outer periphery of a quartz tube by the MCVD method. This quartz tube is deposited to make a cladding glass, and this quartz tube is jacketed around the outer periphery of the transparent glass base material for the core, and then the base material is spun and primary coated to form a core with a diameter of 50 μm and an outer diameter of 125 μm. An optical fiber with a diameter of 400 μm was obtained.

This optical fiber has a relative refractive index of 0.75% and an OH in the core.
The group content is about 0.1 ppm.

Next, the optical fiber was treated at 200° C. for 24 hours in an atmosphere containing 1 h/lri, and the optical fiber contained approximately 301) Pm f) OD base material.

After that, the above optical fiber is connected to a T-line (Co”, 10'rad
/hr), the loss increase after 1 hour was 20
dB/Km (used wavelength 0.85 ttm)
.

Comparative Example 1 An optical fiber similar to that of Example 1 was made, and when it was irradiated with radiation in the same manner as above without any treatment, the loss increase after 1 hour was as much as 200 dB/km.

Specific Example 2 After dehydration treatment by heating at 900°C in a He gas stream for 3 hours, D? The treatment was carried out for 3 hours in a containing atmosphere (airflow).

Thereafter, the atmosphere was changed to He, and the base material was turned into transparent glass at 1380°C.

A quartz tube with glass for cladding similar to that in the specific example was jacketed around the outer periphery of the transparent glass base material for the core containing OD groups as described above, and an optical fiber was obtained in the same manner as in specific example 1.

The OD groups in this optical fiber reached so ppm, but the OH groups were less than 1 ppm.

Furthermore, when the optical fiber of Specific Example 2 was irradiated with radiation in the same manner as in Specific Example 1, the loss increase after 1 hour was 18
dB/Km (wavelength used: 085 μm).

The above matters have been described from the viewpoint of radiation resistance of the optical fiber, but since the optical fiber treated by the method of the present invention has stable transmission characteristics over a long period of time, this point will also be explained.

That is, under certain special circumstances, hydrogen may be present around the optical fiber, for example, when water is injected into a place where dissimilar metals are present, or under heating when the optical fiber has a certain kind of coating material. Hl is generated, and this hydrogen diffuses into the optical fiber, causing increased loss.

For optical fiber glass treated as in the present invention, H7
The increase in loss caused by transmission is extremely small, and its transmission characteristics have long-term stability.

Specific examples and comparative examples regarding this are shown below.

Specific example 3 Ge0t Psis S 1ot(
Core glass with GI type refractive index distribution of 621%) and s
A transparent glass base material having a Norad glass made of Os-FSiOx was made, and this was spun using a conventional method to obtain a core diameter of 50 μm1 and a cladding outer diameter of 56 μm1.
An optical fiber with an outer diameter of 125 μm was obtained.

When this optical fiber was treated for 8 hours at 100° C. in an atmosphere containing h/cttl glue (in an air flow), the loss increase after the treatment was as follows. OdB/Km (wavelength used: 13 μm).

Next, the optical fiber after the above treatment is placed in an H2 atmosphere (100
C, I Ky/ca ) for 24 hours, and the stability of its transmission characteristics was measured at the same wavelength as above, and the loss increase was o6 dB/Km.

Comparative Example 2 When the same optical fiber as in Example 2 was made and the same measurements as above were performed on it without D2 treatment, the loss increase was as much as 2.4 dB/-.

Regarding the absorption peak at a wavelength of 0.95 μm, specific example 3 had an increase in loss of 0.3 dB/Km, whereas comparative example 2 had an increase of 1. The loss increased by +n in a dB/.

Furthermore, it can be said that there is a slight difference in the stability of the transmission characteristics between Specific 813 and Comparative Example 2 at a wavelength of 1.3 μm, but at a wavelength of 0.8 μm, the stability of Specific Example 2 greatly exceeds that of Comparative Example 2. Ta.

Specific example 4 VAD method Niyori, Ge0t-F SiO* (621%
) with a Gl-type distribution and pure Si
A porous glass base material having a porous glass for cladding made of Ox was prepared, and this was made transparent and vitrified by a conventional method and spun to obtain an optical fiber having a core diameter of 50 μm and an outer diameter of 125 μm.

When this optical fiber was fabricated and treated in the same manner as in Example 3 and tested for hydrogen resistance in the same manner as in Example 3, the loss increase was OdB/Km.

Comparative Example 3 An optical fiber similar to that of Specific Example 4 was made, and the hydrogen resistance test described above was conducted without D2 treatment.
The loss increase was 0.24 dB/I[m.

As explained above, when using the treatment method of the present invention, it is possible to sufficiently and effectively incorporate OD groups into the optical fiber glass, thereby improving the radiation resistance of the optical fiber glass and the reliability of its long-term transmission characteristics. etc., and is sufficiently easy to process, so that optical fiber glass processing can be carried out easily.

Patent applicant's agent Patent attorney Makoto Ito Procedural amendment (method) 1. Indication of the case Japanese Patent Application No. 58-1979452 Title of the invention Process for processing optical fiber glass 3, person making the amendment Relationship to the case Patent applicant Furukawa Electric Co., Ltd. 4, person making the amendment 100 6 Full text of the specification subject to the amendment , 7゜Contents of amendment to power of attorney Submit a separate copy of the document, power of attorney, and the full text of the typewritten specification (no changes to the contents).

that's all

Claims (1)

[Scope of Claims] (1) A method for processing optical fiber glass, which comprises exposing quartz-based optical fiber glass to a Dt or compound-containing atmosphere to cause the glass to contain OD groups. (2) The method for treating optical fiber glass according to claim 1, which comprises exposing the optical fiber glass constituting the porous glass preform for optical fibers to a predetermined atmosphere. (3) A method for processing optical fiber glass according to claim 1, in which optical fiber glass constituting a transparent glass base material for optical fiber is exposed to a predetermined atmosphere. (4) A method for processing optical fiber glass according to claim 1, which comprises exposing the optical fiber glass constituting the optical fiber to a predetermined atmosphere. 1. The method for treating optical fiber glass according to claim 2]j1, wherein the optical fiber glass is exposed to a predetermined atmosphere in a predetermined atmosphere by exposing the optical fiber glass to a predetermined atmosphere. (6) A method for treating optical fiber glass according to any one of claims 1 to 5, wherein the Dt or compound-containing atmosphere has a temperature higher than room temperature.