JPH01259305A - Multiple fiber consisting of quartz glass system - Google Patents

Abstract

PURPOSE:To obtain the multiple fibers which are excellent in radiation resistance, brightness of transmitted images, light leakage characteristic, and flexibility by respectively specifying the core occupying rate of unit optical fibers, the average outside diameter of cores and the thickness of clad layers. CONSTITUTION:The multiple fibers 1 consisting of a quartz glass system are formed by welding 1,000-20,000 pieces of the unit optical fibers 1' to each other. The respective fibers 1' consist of the cores 2 consisting of high-purity quartz glass and the clad layers 3 consisting of doped quartz glass and the clad layers are welded to each other. The core occupying rate is specified to 40-70%, the average outside diameter D of the cores to 5-20mum and the thickness Tc of the clad layers to a 1.375-0.025D<=Tc<=1.0+0.05D thickness range. The multiple fibers which are excellent in the radiation resistance, the brightness of the transmitted images, the light leakage characteristics, and the flexibility are thereby obtd. and are effectively used for the image scope of a nuclear reactor, etc.

Description

[Detailed Description of the Invention] The present invention is characterized by excellent radiation resistance in the light region.
Therefore, the present invention relates to a multiple fiber suitable as an image transmission body for industrial image scopes.

BACKGROUND OF THE INVENTION In recent years, image scopes have been widely used in places where there is a possibility of being exposed to radiation, such as in nuclear reactors, nuclear ships, and artificial satellites.

As image transmitting bodies for image scopes, 21111, which are quartz glass-based multiple fibers and multi-component glass-based multiple fibers, are known. In comparison, it has excellent radiation resistance, so it is used exclusively for observation in the radiation field described above.

However, due to recent remarkable advances in various technologies, silica glass-based multiple fibers have been developed that are excellent in radiation resistance, brightness of transmitted images, light leakage (crosstalk), and flexibility. is required.

According to the detailed research conducted by the present inventors, even silica glass-based multiple fibers have different characteristics, depending on the structure of the core and crat layers. It fluctuates greatly. Therefore, the object of the present invention is to provide a silica glass-based multiple fiber that can meet all of the above requirements and is suitable as an image transmission body for industrial image scopes used for observation in radiation fields and at high temperatures. It is about providing.

As a means to solve the above-mentioned problems, the present invention provides a cladding layer made of doped quartz glass on a pure silica glass core and a 1ooo~2 of a quartz glass optical fiber having a support +i made of quartz glass with a drawing temperature of at least 1800°C depending on the history.
It has a structure in which 0,000 optical fibers are fused together, and in each of the mutually fused optical fibers, the core has a space factor of 40 to 70.
An object of the present invention is to provide a silica glass-based multiple fiber having an average outer diameter of 5 to 20 μm in terms of %, and a cladding layer 1゛c having a thickness satisfying f2fi+. It is something to do.

1.375 − 0.025D ≦T c ≦1.0
+0.05D ・ ・(Conventionally, doped on a pure silica glass core) 'A quartz glass-based light having a silica glass cladding layer and, if necessary, a silica glass support layer thereon. For multiple fibers having a structure in which a large number of fibers are fused together, the thickness Tc of the cladding layer should be at least a certain value, especially 1.0 + 0.
It was thought that it would be preferable to set it to 05D or higher, but
The sound of the present invention is based on this recognition, and unexpectedly, a silica glass-based multiple fiber that satisfies the following conditions (1) to (4) at the same time has a cladding layer thickness Tc of l.
, 0 + 0.05D or more -F, it was found that it exhibited excellent performance that satisfied the various requirements described above.

(11) The number of optical fibers included in the multiple fiber is 1,000 to 20,000, (2) the core space factor of each optical fiber is 40 to 70%, (3) the core of each optical fiber is Average outer diameter is 5~20μ■
and +41 8 optical fiber crut layer is
It must have a Jγ value Tc that satisfies the following.

By satisfying all of the above configurations, a silica glass-based multiple fiber having excellent radiation resistance, brightness of transmitted images, light leakage properties, and nJ IQ properties can be obtained.

FIGS. 1 and 2 are cross-sectional views of multiple fibers according to an embodiment of the present invention.

In the embodiment of FIG. 1, multiple core Iha 1 is:
It has a structure in which 1,000 to 20,000 unit optical fibers L are fused together, and each unit optical fiber L has a core 2 made of high-purity quartz glass and a cladding made of doped silica glass. The cladding layers 3 of adjacent unit optical fibers 1° are fused together.

In the embodiment of FIG. 2, the multiple fibers l are
1000 to 20 of unit optical fibers 1' having a support layer 4 made of silica glass on top of the crand layer 3
000, and has a structure in which the support layers 4 are fused together. In FIGS. 1 and 2, 5 is a skin layer provided on the outermost side of the multiple fibers. Further, the refractive index difference (80) between the core 2 and the cladding layer 3 is preferably at least 0.00B, particularly about 0.01-0.015.

The multiple fiber 1 having the structure shown in FIG.
The core 2 and the clad [ 3, 211 structure, and then drawn to obtain a preform of unit optical fiber 1°, and then bundle the required number of preforms to obtain 1.800 to 2,200′.
It can be manufactured by heating it to a temperature of c to soften it, and drawing it to a predetermined thickness, for example, 0.1 to 5 m, or 0.2 to 21 in l.

The multiple fiber l having the structure shown in Fig. 2 is
It can be manufactured in the same manner as above using a three-layer horizontally dipping base material obtained by the in-tube method or the like. The thickness of the support layer 4 is 0.01=1. Approximately +1m is appropriate.

The cladding layer 3 is made of silica glass containing, for example, B and/or F as a dopant. Such doped quartz glass is, for example, BCI, , l
3F3.5iC1, and /lu gas mixture with oxygen, I3
The well-known chemical vapor deposition (CVL) method uses a mixed gas of c 13 , Si Fa, and oxygen, or a mixed gas of B F x or I'3C13, 81Cl a, and oxygen as raw materials. ). Among the raw material mixture gases mentioned above, BF
It is a mixed gas of z, 5iC14 and 02.

The embodiment shown in FIG. 2 has a support layer 4, but if the constituent material of the support layer 4 is quartz glass containing a large amount of impurities, it may have an adverse effect on radiation resistance. Therefore, the constituent material 4A of the support layer 4 should be quartz glass having a drawing temperature of at least 1800°C, such as natural quartz glass or synthetic quartz glass, especially with a purity of 99% by weight.
Of the above, high purity synthetic quartz glass with a purity of 99.9% or more is particularly preferred. The above drawing temperature means that a pipe with an inner diameter of 23 mm and an outer diameter of 26 u made using the quartz glass to be tested is heated and softened, and a reduced pipe with an inner diameter of 2.3 m and an outer diameter of 2.6 mm is drawn at a rate of 0.5 m/min. It is defined as the lowest temperature at which the glandular tension becomes 500 g or less. Examples of the quartz glass having the above-mentioned high drawing temperature include natural quartz glass and synthetic quartz glass, preferably synthetic quartz glass, particularly high-purity quartz glass having a purity of 99.99% by weight or more.

In addition, when manufacturing multiple optical fibers, for example, a quartz glass pipe is filled with optical fibers and then drawn, and a skin corresponding to the pipe is added to the outer periphery of the group of optical fibers that are fused together. It is preferable that the layer 5 is fused in terms of flexibility and resistance to bending of the resulting multiple optical fiber.

As mentioned above, in the present invention, the following ill to (4)
) It is necessary to satisfy all the requirements.

10 The number of optical fibers included in the multiple fiber is 1000 to 20000, (2)
The core space factor of each optical fiber is 40 to 70%, (3) The average outer diameter of the core of each optical fiber is 5 to 20 μ-
and (4) the crand layer of each optical fiber has a thickness T c that satisfies the above formula il+.

1.375-0.025D≦Tc≦1.0 + 0.0
51)...(1) In the present invention, the thickness of the cladding layer of each optical fiber included in the multiple fiber 'C
thinner than the conventionally recognized range, and -17
In order to ensure the brightness of the transmitted image and the flexibility of the multiple fibers by increasing the space factor of the above-mentioned fibers, the radiation resistance, brightness of the transmitted image, light leakage characteristics, and flexibility are also excellent. The requirements of ill ~ (4) are now mandatory,
If the upper and lower limits of each requirement are exceeded, it will be difficult to achieve the object of the present invention. On the other hand, if the requirements are as follows, favorable results for the -layer can be obtained. That is, O) The number of optical fibers included in the multiple fiber is 2000-18000, especially 3000-150.
(2) The core space factor of each optical fiber is 40 to 60%, especially 45 to 60%, (3) The average outer diameter of the core of each optical fiber is 7 to 15 μm, (4) The cladding layer of each optical fiber has a thickness Tc that satisfies the following formula (2), especially the following formula (3).

1.354-0.021D≦Tc≦1.025+
0.045D ・-(211,339-0,018D≦
Tc≦1.045 + 0.041D ・−(31 In the present invention, the thickness of the cladding layer 2 and the support layer 3 of each optical fiber may generally be the average value of each layer, but the thickness of the cladding layer 2 If most of the support layer 3 has a hexagonal shape, the thickness of each side (if fused with the corresponding layer of an adjacent optical fiber, half the total thickness of the fused portion) ).

In the present invention, it is preferable that the optical fibers present within a radius of at least 80% from the center of the cross-section of the multiple fibers are arranged in a regularly aligned structure with each other M@. To explain this condition, as mentioned above, the multiple fiber of the present invention is manufactured by drawing a large number of bundles of optical fiber preforms.
If there is a large variation in the outer diameter between materials, or if the heating temperature or drawing speed during drawing is uneven, the arrangement of each optical fiber will be irregular due to the random numbering that occurs during drawing. As a result, the cladding layer becomes thinner in some areas, resulting in many areas where the cores are abnormally close to each other, or even a large number of air bubbles remaining between the fused optical fibers. The occurrence of such irregularly arranged portions, portions where the cores are abnormally close to each other, or a large number of bubbles may cause a decrease in the radiation resistance of the multiple fiber. Therefore, in the present invention, the optical fibers existing within a radius of at least 80% from the center of the cross section of multiple fibers are stacked in a stacked manner as regularly as possible (of course, the optical fibers are localized within the radius of 80%). Moreover, it is preferable that the cores are arranged and fused (although it is acceptable even if the cores are irregularly arranged, the cores are abnormally close to each other, or there are air bubbles, as long as the scratching is slight).

The present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 10, Comparative Examples 1 to 6 Table 1 shows that a large number of optical fibers with a two-layer structure consisting of a pure silica glass core and a cladding layer of doped silica glass were densely packed into a quartz glass tube and heated to 2200°C. Table 2 shows the structure and properties of various multiple fibers obtained by drawing the pure silica glass core and doped silica glass cladding layer.

A large number of optical fibers with a three-layer structure consisting of a quartz glass support jl are densely packed into a quartz glass tube,
The structure and characteristics of various multiple fibers obtained by drawing at ℃ are shown.

Note that the characteristics of the multiple fibers were evaluated by the methods shown below.

Radiation resistance: As shown in Figure 3, the evaluation test was conducted using a CobOT radiation source with a length of 3 at a predetermined dose rate (2xlO'R/H).
A 10 m length of the 0 m multiple fiber test sample was bundled into a coil shape (--) and γ-ray irradiation was performed at a dose of 2 x 10'H, and both ends of the multiple fiber l were taken out through a shield Wi, 9. Light from a white light source (50 W) was input, and the light emitted from the other end was measured with a monochromator/photometer and recorded on a recorder.

Irradiation is performed in the air, except during measurement. The multi-optical fiber was removed from the light source to prevent the effects of photobleaching.

Multiple fiber loss (a(dB/+m,,a
L480nm) was measured by the CUT BAC method. In addition, images were observed using the irradiated multiple fibers for test drawings of nine standard Kodanoku colors.

Brightness of the transmitted image: Light leakage characteristics of the transmitted image expressed as a comparative value with the multiple fiber total transmitted light amount (30 m) shown as a reference example in Table 2 set as 1: Fluorescence with high brightness in the multiple fiber test sample The lights were directly observed and qualitatively evaluated in three ranks based on the degree of flare and blurring of the image.

Flexible tQ property: The number of breakages was measured when a 180φ bend screening test was performed using a 30 m long multiple fiber test sample.

“Below is the margin]

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of multiple fibers according to embodiments of the present invention. FIG. 3 is an explanation of a method for testing the radiation resistance of multiple fibers in the atmosphere using 0060 gamma rays as a radiation source. 1: Multiple fiber cable: Unit optical fiber 2: Core 3: Cladding layer 4: Support layer Patent applicant Mitsubishi Cable Industries, Ltd.

Claims (1)

[Scope of Claims] 1. A silica glass-based light having a cladding layer made of doped silica glass on a pure silica glass core and, if necessary, a support layer made of silica glass having a drawing temperature of at least 1800°C. 1000~20 of fiber
It has a structure in which 000 optical fibers are fused together, and the core has a space factor of 40 to 70% in each fused optical fiber.
, the average outer diameter D is 5 to 20 μm, and the cladding layer T
c is a silica glass-based multiple fiber characterized by having a thickness that satisfies the following formula. 1.375-0.025D≦Tc≦1.0+0.05D