JPH0312340A - Radiation resistant optical fiber - Google Patents

Abstract

PURPOSE:To reduce transmission loss due to radiation at low temp. by forming a guartz clad on a specified pure quartz core. CONSTITUTION:A core material made of pure quartz having <=10ppm hydroxyl group content and <=1ppm chlorine content is put in a clad material made of a washed and dried guartz glass tube and they are heated to 500-1,600 deg.C. A compd. contg. at least one among C, N, O, S and Se and at least one kind of halogen but not contg. H2 and having a fluid state at room temp. is fed into the gap between the core and clad materials in a vapor phase and the core and clad materials are melted by further heating and spun to obtain a radiation resistant optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radiation-resistant optical fiber with improved transmission loss due to radiation at low temperatures.

[Conventional technology]

In recent years, a wide variety of optical fibers have been put into practical use in many fields. Generally, optical fibers exhibit unique transmission loss characteristics. This transmission loss is particularly noticeable in certain wavelength bands, so when using optical fibers, it is important to avoid absorption bands as much as possible and operate in a low-loss region.

In particular, when an optical fiber is exposed to radiation (α, β, T-rays, etc.), a new wavelength loss band may be generated or the absorption loss in the original loss band may be further increased.

By the way, it is known that in an optical fiber having a core made of pure quartz, chlorine impurities in the core increase loss due to radiation. This is because when elemental chlorine is present in pure silica glass, it is thought that the elemental chlorine may cause some defects in the glass, and the defects may be promoted by radiation irradiation.

Regarding hydroxyl groups in the core, it has been said that optical fibers containing a large amount of hydroxyl groups have less increase in loss due to radiation. However, as the content increases, the inherent loss (loss when not irradiated) increases, especially 1
．． Since it is difficult to use it in the 3 μm band, it is usually not used in this band.

[Problem to be solved by the invention]

Various attempts have been made to exploit the above-mentioned characteristics of optical fibers and to develop optical fibers with excellent radiation resistance by reducing the chlorine and hydroxyl group content in the core as much as possible.

In particular, from now on, it is thought that optical fibers will be used more often in environments where the temperature is lower and the temperature changes are more pronounced (and where there is greater risk of exposure to radiation), such as in aircraft, communication satellites, space stations, etc. However, there is room for improvement in the transmission characteristics of current optical fibers at low temperatures.

Therefore, an object of the present invention is to provide a radiation-resistant optical fiber in which increase in transmission loss due to radiation irradiation at low temperatures is suppressed as much as possible.

[Means to solve the problem]

As a result of intensive research to achieve the above object, the present inventors have developed an optical fiber manufactured using the MRT method (details will be described later), in which the optical fiber has a core made of pure quartz and a It has been discovered that the above object can be achieved by having a cladding made of quartz provided, the hydroxyl content of the core is 10 ppm or less, and the chlorine base [1 of the core is IPPm or less], and the present invention has been completed. I ended up doing it.

That is, the optical fiber of the present invention uses the MRT method and has a core with a hydroxyl group content and a chlorine content below a specific value, thereby significantly improving radiation resistance at low temperatures.

However, the low temperature referred to in the present invention refers to room temperature (10 to
(approximately 30°C) to approximately -55°C or less 1. In particular, this refers to temperatures below about -80°C, and the optical fiber of the present invention has excellent radiation resistance even at this low temperature, particularly in the temperature range around -80°C.

The MRT method, which is a manufacturing method for the optical fiber of the present invention, is a type of rod-in-tube method, and is a method for manufacturing the optical fiber of the present invention.
It is an abbreviation for n-Tube method. The outline of this method is to insert the core material into the cladding material, heat it, weld the core material and cladding material, and then spin the material. C, N in the gap
, OlS, Se, and at least one halogen, and does not contain hydrogen and is a compound that forms a fluid at room temperature. method (Japanese Unexamined Patent Publication No. 55-7
(See Publication No. 1636).

In the present invention, the quartz glass used as the core material is glass-like and highly pure 5iOz, and the hydroxyl group content and chlorine content of the core are 1 loppm or less, respectively.
It is sufficient if it is less than ppm.

Therefore, the hydroxyl group content contained in the core is 10 ppm.
The following is sufficient, but preferably 0, 1 p p
m or less, particularly preferably OPPm.

Similarly, the chlorine content in the core may be 1.1) pm or less, preferably 0.1 ppm or less, especially O
Preferably it is ppm.

Note that a normal cladding is sufficient as long as it is made of quartz.

Next, an example of manufacturing an optical fiber using the MRT method will be briefly described. However, the MRT method can basically be carried out in a manner similar to the mouth-in-tube method, and the following is an overview focusing on the characteristic manufacturing process.

First, the hydroxyl group and chlorine contents are each 10 ppm, I
A pure quartz glass rod of PPm or less is mechanically polished to form a core material with a diameter of, for example, about 10 mm, which is washed in the order of trichlorethylene, methanol, pure water, 10% HF, and pure water, and then dried in a vacuum dryer. . On the other hand, B and F
The cladding material, which is made of a quartz glass tube doped with an appropriate amount of Heat to a temperature in the range of 500 to 1600°C. In the state before welding of the core material and the cladding material heated to the required temperature, CC1, along with N is flowed into the gap between the core material and the cladding material, and the temperature is further increased.
By welding the core material to the cladding material and spinning this, an optical fiber with excellent radiation resistance at low temperatures can be obtained.

The radiation-resistant optical fiber of the present invention is a fiber having a core and a cladding made of the above-mentioned materials.
It is sufficient if it is manufactured by the T method and has the same structure as a conventional optical fiber in other respects. That is, for example, a plastic jacket made of silicone resin, thermoplastic resin, or the like is provided on the crund to prevent water from entering, similar to a normal optical fiber.

〔Example〕

Next, in order to clarify how advantageous the optical fiber of the present invention is in terms of transmission loss at low temperatures (particularly in the temperature range around -80°C), examples and experimental examples will be described. .

Example 1 As an example, using pure quartz as the core material, the above MRT
Optical fibers were prepared using core materials having hydroxyl group and chlorine contents as shown in Table I based on production examples using the method.

The amount of B and F doped into the cladding is adjusted so that the relative refractive index difference between the core and the cladding is 1%, and the refractive index distribution is of a step index type. In addition, a synthetic quartz pipe was used for the support layer.

Comparative Examples 1 to 3 As comparative examples, optical fibers similarly produced using the MRT method were prepared. However, the hydroxyl group content and chlorine content of the core are as shown in Table I.

Note that the optical fibers obtained in the above Examples and Comparative Examples are as follows:
The core diameter/optical fiber diameter is 50/125 μm.

Experimental Example 1 As an experimental example, each of the above optical fibers was irradiated with gamma rays using cobalt-60 as a radiation source at a dose rate of 10'R/H (roentgen/hour) for 1 hour, and the transmission loss during and after the irradiation was measured. The results are shown in Table I.

However, the conditions during irradiation are as follows: 50 m long optical fibers are arranged in a bundle with a diameter of about 30 cm in a constant temperature chamber installed in the irradiation chamber, and the temperature of the optical fibers is kept at -80°C using liquid nitrogen.
It was kept at °C. The measurement conditions were to use an LED that emits wavelengths in the 0.85 μm band and 1.3 μm band as the light source;
The optical power was set to -20 dBm and -30 dBm.

(Margin) [Effects of the Invention] As explained above, the optical fiber of the present invention has a core with a hydroxyl group content of 10 ppm or less, and a core with a chlorine content of 10 ppm or less.
fi is 1 ppm or less, and since it is manufactured by the MRT method, it can be irradiated with radiation at low temperatures (particularly in the temperature range around -80°C), as is clear from the examples and experimental examples. The generation of new wavelength absorption bands and the increase in loss in the characteristic wavelength absorption bands (particularly 0.85 μm and 1.3 μm absorption bands) are suppressed as much as possible, and the transmission loss for radiation at low temperatures is extremely small.

Therefore, the optical fiber of the present invention is most advantageous in terms of radiation resistance at low temperatures.

Claims (1)

[Claims] It has a core made of pure quartz and a cladding made of quartz provided on the core, and the hydroxyl group content of the core is 10 ppm.
A radiation-resistant optical fiber characterized in that the optical fiber has a chlorine content of 1 ppm or less in the core, and is produced by an MRT method.