JPH044988B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a manufacturing technology for optical fibers used for communication, image transmission, energy transmission, etc. The present invention relates to a method of processing an optical fiber to obtain an optical fiber.

[Prior art]

Optical fibers having a core of quartz glass are increasingly being used in radiation environments such as those found in nuclear power plants.

The reason for this is that the light weight, small diameter, and non-inductive nature of optical fibers are great advantages for communications, and the excellent low loss properties for image guides and light guides.

Particularly in the case of image guides, silica-based optical fibers have the advantage that the increase in loss due to radiation exposure 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 an increase in transmission loss due to radiation irradiation.

Various studies have been conducted to suppress this increase in transmission loss, for example, OH in the core.
For those with many groups, the increase in loss is relatively small.
It is known that the spinning conditions of the optical fiber have a large effect on the increase in loss.

Based on the results of this study, for example,
It was believed that optical fiber containing several hundred ppm of OH groups and spun under optimal conditions could withstand use in the nuclear field, but the increase in transmission due to radiation irradiation was still large, and further improvements in properties were needed. It becomes necessary.

In particular, in the case of optical fibers whose core is quartz glass containing a high concentration of OH groups, there is absorption loss at wavelengths of 0.95 μm and 1.39 μm due to OH groups, and the wavelength
It is said that optical transmission at a wavelength of 1.30 μm is nearly impossible, let alone optical transmission at 0.8 μm.

For this reason, OD group-containing quartz glass is attracting attention because it has the same effect on radiation resistance as OH group, but absorption loss is shifted to longer wavelength bands.

In the case of quartz glass containing OD groups, the wavelength
1.28μm (corresponds to 1.95μm for OH group), wavelength 1.68μm
m (corresponds to 1.24μm), wavelength 1.87μm (corresponds to 1.39μm)
Absorption can be seen in the following cases.

Furthermore, in the case of quartz glass containing OD groups,
It is expected to reduce loss at a wavelength of 0.8 μm.

Methods for manufacturing such OD group-containing quartz optical fibers include a method using D ₂ during soot synthesis by flame hydrolysis reaction, as described in Japanese Patent Application Laid-Open No. 49-9514, and a dry gel ( A known method is to first treat drygel with Cl ₂ and then exchange Cl → OD in a D ₂ O atmosphere.
These methods are industrially undesirable because they use large amounts of expensive D ₂ , D ₂ O, etc. In particular, methods that treat soot in a D ₂ O atmosphere tend to cause devitrification of the glass and do not provide good quality light. Fiber base material is difficult to obtain.

[Purpose of the invention]

In view of the above-mentioned problems, the present invention aims to provide a processing method for obtaining a quartz-based optical fiber containing an OD group with even better radiation resistance.

[Structure of the invention]

In order to achieve the above object, the processing method of the present invention provides an optical fiber containing D ₂ or a D 2 compound in at least one of the stages synchronous with the optical fiber spinning process or the stage in which the optical fiber is _first coated. The optical fiber is characterized by being exposed to an atmosphere to cause the optical fiber to contain OD groups.

[Embodiments of the invention]

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

Incidentally, the optical fiber in the present invention refers to a known optical fiber.
A transparent glass base material for optical fiber manufactured by MCVD method, PCVD method, VAD method, OVD method, sol-gel method, etc., or a base material in which a glass pipe is jacketed on the transparent glass base material as necessary. It refers to the product obtained by heating and stretching, so-called spinning.

Further, the above-mentioned optical fibers include a single-core type having a monocore, a multi-core type having a multi-core, and the like.

The glass that forms the core of the optical fiber is quartz-based, but the cladding is sometimes made of a low refractive index plastic material such as silicone rubber or fluorine-based resin.

By application, the optical fibers mentioned above are made for communications, image guides, and light guides.

It is preferable that the core of the optical fiber be made of pure SiO ₂ because the increase in loss due to radiation irradiation is small.

The content of OH groups in the core is preferably small when used in a long wavelength region 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, the content of OH groups in the core is preferably small. If the material contains a certain amount of OH groups in advance, good results are often obtained in terms of radiation resistance.

Broadband performance is sometimes required for communication optical fibers, and in such cases, the core is made of F, Ge, or P.
The material may be doped quartz having a GI type refractive index distribution doped with quartz or the like.

When the core is the above-mentioned doped quartz, pure SiO ₂ may be used as the silica-based cladding, but if the refractive index of the core is the same or lower than that of SiO ₂ ,
Doped quartz doped with F, B, etc. is used for the cladding.

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 is placed in a D ₂ -containing atmosphere or a D ₂ compound (D ₂ O)-containing atmosphere at least one of the steps synchronous with the optical fiber spinning process or the step in which the optical fiber is provided with a primary coating. exposed, thereby containing an OD group within it.

As described above, the treatment is carried out at a stage synchronized with the optical fiber spinning process, that is, during the spinning tandem line, or at a stage at which the optical fiber is coated with a primary coating, that is, at least a primary coating is applied to the optical fiber, This is carried out at least at one of the stages of winding onto a bobbin or the like or collecting into a bundle.

In the case of an image guide, a transparent glass base material is heated and stretched to a diameter of several millimeters to a few millimeters, and several thousand to tens of thousands of thin rods are drawn together and melted into one piece. Furthermore, the integrated product has a diameter of 0.
The process of heating and drawing fibers from mm to several mm in size is used, and in this type of image guide, as mentioned above, when heating and drawing a thin rod from a transparent glass base material, or by melting and unifying them and then re-drawing them. It is preferable to expose the film to a D ₂ -containing atmosphere or a D ₂ compound (D ₂ O)-containing atmosphere either during heating and stretching or the like.

The steps that are synchronized with the optical fiber spinning process described above include the step of inserting a transparent glass base material for optical fiber into a spinning furnace and spinning an optical fiber from its tip. The process includes the steps from applying the coating to winding it up, but the most efficient step for incorporating OD groups is from the step of spinning the optical fiber in the spinning furnace to just before the primary coating is applied. It will be done. The reason for this is that high-temperature treatment is possible in the spinning furnace by directly utilizing the temperature of the spinning furnace, and in the stage just before the primary coating is applied, the optical fiber itself is still sufficiently high just after spinning. This is because the temperature of the optical fiber itself can be used as the processing temperature.

On the other hand, in the case of processing at a stage where the optical fiber has been primarily coated, the entire winding bobbin is exposed to an atmosphere of D ₂ or D ₂ O, for example. Processing at this stage has the disadvantage that the ambient temperature must be heated externally to the processing temperature, but because the atmospheric conditions can be kept stable, the optical fiber can be uniformly heated to D ₂ along its entire length. Alternatively, it has the advantage of being able to be treated with D ₂ O.

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, the process of spinning the core glass as a core and this It is sufficient that the processing of the present invention is performed during a process synchronized with the core, and that at least only the cores undergo this processing.

Next, the processing temperature will be described.

The processing temperature in an atmosphere containing _D2 (or _D2O ) is
The temperature is 50° C. or higher, and a higher temperature is preferable because the treatment time can be shortened if the treatment temperature is high, for example, in the treatment at a stage synchronized with the spinning process described above.

However, at the stage where the optical fiber is coated with a primary coating,
For coated optical fibers, the processing temperature should be set at 100-250°C to prevent deterioration of the primary coating material.
It is best to keep it at around ℃.

Note that if the treatment temperature is about room temperature, OD groups are hardly generated because D ₂ and the like just enter the optical fiber. Therefore, it is important to keep the processing temperature higher than room temperature.

On the other hand, it is also effective to contact the optical fiber with D ₂ or the like at a relatively low temperature, thereby impregnating the optical fiber with the D ₂ or the like, and then heating the optical fiber to a high temperature.

In this case, the center of the optical fiber can be uniformly impregnated with _D2 , etc., and it can be heated to
It is preferable to carry out OH basic + D ₂ OD group + HD exchange because the OD group concentration in the core becomes higher than the OH group concentration.

The pressure such as D ₂ is not particularly limited, but the higher the pressure, the more advantageous it is that the processing time can be shortened.

It is also known that the loss gradually decreases when the amount of OH groups is 100 ppm or more, preferably about 1000 ppm. Therefore, if such optical fibers are to be obtained, D ₂ (or D ₂ O) should be prepared in advance before treatment.
It is sufficient to contain a large amount of OH groups.

In addition, it may be advantageous if the optical fiber has defects in its molecular structure, and in such cases, it is necessary to heat or stretch the optical fiber preform before the spinning process, for example, before the D ₂ (or D ₂ O) treatment. , a base material with many defects can be created in advance by irradiating it with radiation. D ₂ or
D ₂ O) treatment may be preferable since it results in the D ₂ (or D ₂ O) treatment being applied to optical fibers with structural defects.

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 _SiO2
The glass for the cladding is made by depositing doped quartz doped with B and F on the inner periphery of the quartz tube by the MCVD method. After jacketing the outer periphery of a transparent glass preform, the preform was spun and primary coated to obtain a primary coated optical fiber having a core diameter of 50 μm, an outer diameter of 125 μm, and a silicone rubber coated outer diameter of 400 μm.

This optical fiber has a relative refractive index of 0.75% and a
The OH group content is approximately 0.1 ppm.

Next, the optical fiber with the above primary coating was heated at 200°C.
When treated for 24 hours in an atmosphere containing 1 Kg/cm ² of D ₂ , it contained about 30 ppm of OD groups inside.

After that, the optical fiber is exposed to gamma rays (CO ⁶⁰ ,
10 ⁶ rad/hr), the loss increase after 1 hour was 20 dB/Km (wavelength used: 0.85 μm).

Comparative Example 1 When an optical fiber with a primary coating similar to that in Example 1 was made and irradiated with the same radiation as above without _D2 treatment, the loss increased after 1 hour.
It reached 200dB/Km.

Specific example 2 GeO ₂ −P ₂ O ₅ −SiO ₂ (Δ=1
%) for the core with a GI type refractive index distribution,
A transparent glass base material having a cladding glass consisting of P ₂ O ₅ -F--SiO ₂ was made, and this was spun using a conventional method to obtain a core diameter of 50 μm, a cladding outer diameter of 56 μm,
An optical fiber with a primary coated outer diameter of 125 μm was obtained.

The optical fiber with this primary coating was heated at 100℃ for 1
When treated for 8 hours in an atmosphere containing D ₂ (in air flow) at Kg/cm ² , the loss increase after the treatment was 1.0 dB/Km (using wavelength 1.3 μm).

Next, the optical fiber with the primary coating after the above treatment is
When it was kept in an H ₂ atmosphere (100° C., 1 Kg/cm ² ) for 24 hours and the stability of its transmission characteristics was measured at the same wavelength as above, the loss increase was 0.6 dB/Km.

Comparative Example 2 When an optical fiber with the same primary coating as in Example 2 was made and the same measurements as above were carried out on it without D ₂ treatment, the loss increased by as much as 2.4 dB/Km.

Regarding the absorption peak at a wavelength of 0.95 μm,
In Specific Example 2, the loss increased by 0.3 dB/Km, whereas in Comparative Example 2, the loss increased by 1.3 dB/Km.

In the above embodiments, only the processing of the primary coated optical fiber is shown, but the same effect can be obtained also in the stage synchronized with the spinning process.

〔Effect of the invention〕

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, thereby improving the radiation resistance of the optical fiber and the reliability of its long-term transmission characteristics. This type of optical fiber can be easily manufactured because it is easy to secure and process.

Claims (1)

[Scope of Claims] 1. The optical fiber is exposed to an atmosphere containing D ₂ or a D ₂ compound at at least one of the stages synchronous with the optical fiber spinning process or the stage after the primary coating is applied to the optical fiber. OD to optical fiber
1. A method for treating an optical fiber, characterized by incorporating a group therein. 2. The optical fiber processing method according to claim 1, wherein the D ₂ or D ₂ compound-containing atmosphere has a temperature higher than room temperature.