JPS5888704A - Manufacture of multiple optical fiber - Google Patents

Abstract

PURPOSE:To prevent bubbling among quartz type optical fiber elements, by bundling >=1,000 of them, and causing prescribed liquid materials to intervene among them, and drawing them. CONSTITUTION:A bundle of at least >=1,000 quartz type optical fiber elements 1a is inserted into a dummy glass tube 5, connected by melting, and put into a reaction tube 6 made of quartz glass. A mixture of the vapor of a glass-forming oxide, such as oxide of B, P, Ge, or Sb; a glass-modifying oxide, such as Bi, Sn, or Tl oxide; and an intermediate oxide, such as Ti, Cd, or Pb oxide; and a carrier gas are introduced into the reactor kept at 800 deg.C through a feed tube 7 to deposit them as intervening materials to the surface of each fiber element 1a, and the bundle is drawn at 1,950-2,100 deg.C. In drawing, the intervening materials are liquefied, and bubbling among the fibers are prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel manufacturing method for optical multiple fibers formed by fusing together a large number of quartz glass-based original fibers.
Regarding this.

Silica glass-based multiple fibers are expected to be used in a variety of fields as a means of easily transmitting images, and are particularly useful in applications such as melting furnaces, nuclear reactors, etc. due to their excellent heat resistance and radiation resistance. It is a rich means of observing the inside of things such as

Multiple fibers are produced by stacking a large number of glass-based optical fiber cables and heating them at a high temperature from one end to draw them.
It is manufactured by fusing the fibers together, and if necessary, bundling a large number of the thus obtained multi-full fibers together and carrying out the same bag-pulling process as described above.

By the way, due to the above-mentioned line drawing, there is a problem that air bubbles remain between each nire element 1 and reduce the image transmission performance of the obtained multiple fiber. We have developed a technique for drawing wire with the presence of a liquid Pa'14, and have succeeded in solving the above problem using this technique.

When multiple fibers are used as a single image transmission body, if the number of optical fiber strands is small, the transmitted image becomes unclear, so it is necessary to have at least 1000 strands.

In order to manufacture a multi-chill fiber of z 6' + "o 'o o," for example, a bundle of 33 optical fibers is used to create a multi-chill fiber with 53 optical fibers by pongee-pulling. Next, the thus obtained multiple fiber 3
All you have to do is draw a line between the three bundles. However, since the strands in the multiple fiber thus obtained are fused and aggregated in a honeycomb shape with 33 strands as a small unit, there is a problem that this honeycomb is unpleasant to the eyes.

By the way, according to the inventors' subsequent research, an outer diameter of 1
When the number of thin optical fibers with no droplet droplets required for image transmission, that is, at least 1000, are bundled and drawn with a specific intervening substance interposed between the strands, no air bubbles remain between the strands. Moreover, multiple fibers without the above-mentioned honeycomb-like aggregation can be obtained. The present invention is based on the above-mentioned new findings 1.
It was developed by Komo, and its gist is to bundle at least 1,000 thin quartz glass optical fibers with an outer diameter of 1 mm and set the drawing temperature between the strands. The wire bundle is drawn in the presence of a liquid intervening substance, and the intervening substance is at least one selected from the group consisting of glass-forming oxides, glass-modifying oxides, and intermediate oxides. It is characterized by:

FIG. 1 schematically shows the drawing process of the optical multiple fiber manufacturing method according to the present invention.
The following is a diagram showing an outline of the method of the present invention and a possible mechanism for preventing the generation of air bubbles between optical fiber strands (referred to as single ζ strands). I will explain about it.

In FIG. 1, a large number of strands 1 are heated uniformly from the periphery by a heating means 3 such as an electric furnace in a state 1 in which an intervening substance 2 is present between them to form the strands 1. The glass is heated to a high temperature above the softening point of quartz glass and drawn in the direction of the arrow. By this drawing, the fibers 1 that are adjacent to each other are fused to each other, and the fibers 1 are fused as a whole into one aggregate, and as a result, one multiple fiber 4 is manufactured. In the present invention, the wire drawing W& means the temperature reached when the strand 1 is heated for drawing in the steady state of the drawing process, and the heating means during drawing,
For example, the temperature of the heat zone of an electric furnace can be considered to be the same temperature.

Before explaining the mechanism for preventing the generation of air bubbles based on the presence of intervening substances, I will briefly explain the mechanism of air bubble generation in the conventional method that does not allow the presence of intervening substances. Either the laminated wire is heated at one end in a state where it is tightly bent to the maximum, and the individual wires are not necessarily uniform in outer diameter, cross-sectional shape, straightness, etc., and there is a Due to slight variations, in the bundled state before heating wire drawing, there are parts where the front surfaces of adjacent strands are in contact with each other and parts where they are not, resulting in a wary state. When heated for pulling, the surfaces that had been in contact with each other rapidly fused together, resulting in
A void is left between the strands, and the void expands to form a void due to the high temperature during wire drawing.

On the other hand, if the intervening substance 2 exists between the strands, it is thought that the following air bubbles are prevented from forming in the strands.

That is, the intervening substance used in the present invention exists as a liquid between the strands that are being drawn.

Now, when a liquid intervening substance is present in the curve of the strands, the intervening substance not only prevents local early fusion of the strands to some extent, but also has a lubricating effect inherent to the liquid and a attracting effect due to surface tension. Even if there is an abnormality in the parallel alignment due to local bending of the strands before fusion, the strands that have been softened at the time of fusion or in the previous stage are aligned in parallel.
9 & function, and at the same time fill the gaps between the strands.

Due to the above-mentioned effects, the voids between the strands are not blocked during the drawing process, and the generation of voids is thus prevented.

The wire may consist of a core of pure silica glass and a cladding of silica glass containing a dopant, a core of quartz glass containing a dopant and a cladding of pure silica glass, or a wire consisting of a core of quartz glass containing a dopant and a cladding of pure silica glass, or a wire with a 1-punto core and a cladding of pure silica glass. It is a quartz glass type material, such as one made of quartz glass containing quartz glass. Of course, each strand may have a boat layer on the outside of the cladding layer. The strands before being drawn are thin, with an outer diameter of less than 1 mm, but with an outer diameter of several tens of μm to several hundred μm, especially 50 μm.
If the diameter is about m to 800 μm, it is within J range.

In the present invention, first, a wire bundle having an intervening substance between the wires is created, and the number of intermediates included in this bundle is as follows:
at least 1000, but preferably 5,000
Approximately 0 to 50,000 wires is suitable, and if the drawing furnace is large, the number may be more than 0 to 50,000 wires.

Next, the substance used as the intervening substance in the present invention and the method for intervening the intervening substance will be explained. Note that before intervening an intervening substance between the strands, impurities with a melting point that cannot be used as an intervening substance in the present invention are removed from the surface of the strands. If an intervening substance is interposed without removing such impurities, the above may not occur. Therefore, in the IC of the present invention, before entering the intervening step, each surface of the strand is treated with a method commonly used in the manufacture of optical fibers. It is desirable to use a conventional cleaning method, for example, a method of cleaning with a hydrofluoric acid aqueous solution and distilled water without applying ultrasonic waves.

The intervening substance used in the present invention is a glass-forming oxide, a glass-modifying oxide, or an intermediate oxide, and is capable of becoming a liquid at the drawing temperature defined above.

In 1 above, the glass-forming oxide is one that can form a stable glass network by itself, and truly satisfies the well-known glass-forming conditions of Zacharias (7). For example, see "Glass Engineering Handbook" edited by Haka Moritani, 10th edition, Chokoku Shoten, Tokyo, 1973, p. 5).

Generally, the strength of single bonds in glass-forming oxides (the value calculated by dividing the dissociation energy of the oxide by the coordination number) is approximately 80 ca.
It is on e11. On the other hand, the lath-decorated oxide is a substance that does not have the ability to form glass by itself, but when mixed into the glass network, it exists stably and can change the properties of the glass. (See pages 5-6). Generally, the strength of single bonds in glass-modified oxides is approximately 10-6.
There are 0 kcae.

Further, the intermediate oxide has properties intermediate between the glass-forming oxide and the glass-modifying oxide, and the strength of its single bond is generally about 60 to 80 kca/1 (as described in the above literature). (See page 6).

The reason for using a glass-forming oxide, a glass-modifying oxide, or an intermediate oxide as an intervening substance in the present invention is that it has a lower melt viscosity in the drawing width than quartz glass constituting the wire, and quartz glass This is because it exhibits good wettability to the wires and has the effect of favorably fusing the strands together.

Among the above-mentioned oxides, compounds of elements belonging to groups II to V of the periodic table are preferable as intervening substances from the above viewpoint.

The melt viscosity of biu□, which constitutes the wire, or the quartz-based glass containing biu□ as a main component is much higher than the melt viscosity of silicides of other elements. In other words, at a drawing temperature of 1, the melt viscosity of the intervening substance of the present invention made of the above-mentioned oxide is significantly lower than the viscosity of the strand during the softening and deformation process. Due to this large viscosity difference, the above-mentioned alignment effect is achieved as a liquid. An intervening material having a viscosity of a wire drawing temperature void is preferred. If the viscosity of the intervening substance at the drawing temperature is excessive, the above-mentioned lubricating effect, attraction effect due to surface tension, or void filling effect will generally be poor, thereby preventing the generation of air bubbles between the strands during drawing. The ability to do so becomes scarce. Although the viscosity of inclusions that is too low is not as problematic as the one on the left, it still tends to have a poor ability to prevent the formation of voids. In addition,
5i02 is known as a glass-forming oxide, but when used alone, it has a melt viscosity comparable to that of the wire constituent material, so
S40. alone cannot be used as an intervening substance in the present invention. However, as described later, it can be used in combination with other inorganic compounds to lower the melt viscosity.

Since the gap between the strands being drawn is narrow and the surface area for intervening substances to evaporate is small, even relatively low boiling point or volatile substances remain in a liquid state during drawing. However, substances with an excessively low boiling point or high volatility may evaporate during drawing, making it impossible to achieve the purpose of the present invention. Therefore, the intervening substance used in the present invention should have a boiling point of 1200°C or higher or the same level as that. Those with low volatility are preferably used.

Preferred examples of intervening substances used in the present invention include oxides of elements such as B, P, Ge, and sb, which belong to glass-forming oxides, Bi, Sn, etc. that add IQ to glass-modified oxides,
10,000 in oxides and intermediate oxides of elements such as 1g, 'f
Examples include oxides of elements such as 'i, Cd, and Pb. Specific (This is B2O3, P2O5, GeO3, 5b
2U, Bi2O3,S n02. Ir2O3,'
f°iu□.

and dO11'bO. These oxides may be used alone or in combination of two or more.

Particularly preferred is t5ρ3.1)bOl”120a
, 5b2OB, T i02, and G e 02. Many inorganic substances are Siu. It has the effect of lowering the bath melt viscosity. As mentioned above, Sr 02 is not used alone, but it can be used as an inorganic material other than Sr 02.
A species or a mixture of two or more species (hereinafter referred to as a mixed intervening substance) can be used as a liquid inclusion having a melt viscosity of 10 poise or less at the drawing temperature, and is also a preferred intervening substance.

Examples of inorganic substances used in admixture with i02 include, for example, the glass-forming oxides defined in the above-mentioned document;
Glass-modified oxides or intermediate oxides include oxides such as b, 1), Ge, Sb%Bi, etc.
, Sn, Te, '1:'i, Cd, Pb,
111 compounds of elements such as Ag and Ma, 15208, P
2O5, Gem2.5b208, B I 20 a, S
nO2, Te2o3, T r 02, CdO, P bo
, AI, Ot, BaO, etc. A preferred example of other inorganic substances is fluorine. 3 to 1000 parts by weight, preferably 10 to 5 parts by weight before adding Sr021
00 parts by weight.

Mixed intervening substance preferably used in the present invention C, B
2O8, '110°, P2O6, Ge1, B12o8,
A mixture of at least one member selected from the group consisting of Ae2o8 and PbO and SiO3, furthermore B2O3,1'
+02, Bi20B, and a mixture of 5iu2 and at least 1N selected from the group consisting of PbO, especially 5iu
2 and 5i02 + 00 weight per part 5-500 parts by weight of 82()B t2-100 weight ill (1,)'
rj (J2) is a tocaranal mixture. These mixed intervening substances are mixed with the strand l at the drawing temperature. Wettability,
It has excellent coexistence, and as a result, the wires can be fused together more uniformly, and the cross-sectional shape of the wires is less likely to change shape during the drawing process, resulting in improved image resolution and image transmission ability. Or even better multiple fibers can be obtained.

In the present invention, the intervening substance may be in a solid state such as powder at a stage before drawing. When using a powdered intervening substance to intervene between the wires, the most preferred method is to sink a predetermined number of wires into a deposit of the powder and bundle the wires within the deposit. Alternatively, a fine powder intervening substance is forcibly poured into the gap between pre-bundled wire bundles from one end of the wire bundle together with a suitable carrier gas such as N, 0, air, etc.

Further, the solid intervening substance may be used as a solution or dispersion in a suitable solvent or in a molten state by heating.

In that case, the interposition can be carried out by immersing the wire bundle in a solution or dispersion or in a melt, or by pouring the solution, dispersion, or melt into one end of the wire bundle.

In accordance with the second aspect of the present invention, only a small amount of intervening material is required between the wires, and the area of the intervening material attached to the surface of the wire is calculated as follows: For example, about 0.1 to 1% of the cross-sectional area of the wire is sufficient. When the intervening substance is used in the form of a solution or dispersion, it is preferable to heat the wire bundle to remove the solvent and dispersant before entering the winning process.

A preferred method for interposing an intervening substance between the strands is a method using a precursor of the intervening substance. The term "precursor" as used herein refers to a substance that generates the above-mentioned intervening substances between the strands by decomposition, oxidation, or other chemical reactions, and by heating during or in the preliminary stage of drawing, such as intervening substances. Many salts of acids and nucleic acids of the elements constituting the element, or carbonates, nitrates, sulfates, halides, hydroxides, organic acid salts, and chelate compounds of the elements can be used as precursors. For example, if the intervening substance is B2O3, then boron acid is HBBOB.
, boron chloride B, CeB, etc. can be used as a precursor. 1 (3B08 decomposes when heated to about 190°C to produce 13208, and when BCe8 is heated to about 700°C in the presence of 0° gas, 13 seaa and 0° react to form M As another example, when the intervening material is a mixed intervening material of SiO3 and B2O3, S+ CB4 and BCg8 are used as precursors, and the precursors are heated at about 800°C in the coexistence of 02. When heated to , a mixture of SiO3 and )08 is produced.

Specific precursors other than the above 0 include BHg (7)
7 Hon, Bz-2F, BdF2, BF3, B1-
12CI, halogenated porans such as BHC12, BHg1, cibocines such as B2H6, B(UCt(a)
Alcokylated boron such as 3, 'T' + F4, '1
．． '+Ce4, TiBr4'z,! l” 0) HaO
Saponification f! I n, k! phosphine such as -48,
PH2F, PHF2, PF3, IIH2Ce, PHC
e2, PCl3, PH213r, 1'H13r2f
z Tonohalogenated phosphine POCIB, 1'0B
Phosphorus oxyhalide such as r3, <pno”, rc42
)B , (i)I”Jce2)4, (i'Ncp2)s
, (t'l'Jce2)6, (PNC12)7,
Phosphonitrile chloride such as GeM, germane such as GeHB F, Get(2F2, Get(Fa,
GeF4, GeHaCe, Getl2(,,
i12, GeM(-e B, Ge Ce4, GeHf3
r, halogenated germane such as GeHBr8, GeHBr8, GeBr4, or AeCe8.5bce8
．． 5bCe5, CdCe2, 'rlC1, B + G
12.81 CiB a, 5nCe2.5nCe4, P
A halide such as bCe2 is preferably used.

Examples of precursors of S'U2 other than those mentioned above include, for example, S
+ Silane such as H4, 5it (8F, SiH2F
2.5iHF8.5ip4.5iH8tr:6,5i
H2C12,5ince8.5iH8Br.

SiH1(r 5iHBr 5iBr SiHI
, 22'8' such as 5it-1212
41 3 Halogenated silane etc. can be used. Among these, perhalides, particularly SiC%, are preferred.

Before the above, when the lily pad is heated to a high temperature, for example, 500° C. or higher, particularly 800° C. or higher, in the coexistence of an oxygen element, such as oxygen gas, it forms an oxide as an intervening substance.

General 1. Many of the precursors are in the V state of liquid or gas at a lower temperature than the intervening substance itself, or are easily obtained as a solution dissolved in water or other solvents. The fact that the intervening substance can be present in the form of a liquid such as a gas, liquid, or solution between unloaded wires allows the intervening substance to adhere uniformly to the surface of each strand compared to when powder is used. .

Uniformity of the intervening substance on the surface of the valley wire (4) is effective in achieving the object of the present invention, so in the present invention, it is possible to easily use the liquid as a means for intervening the intervening substance. The use of precursors is highly preferred.

When using a gaseous precursor, the temperature of the wire bundle is maintained at a low temperature below the boiling point of the precursor, and the precursor gas or precursor gas is The precursor gaff may be vertically assembled on the unloaded surface by flowing the precursor gaff continuously from one end of the bundle into the gap between the strands together with a carrier gas such as air. Or, conversely, the bundle of strands is held at a temperature at which the precursor gas reacts to produce inclusions a, and the precursor gas is used to generate the reactions necessary to generate the inclusions as needed. It may also be made to flow together with a gas in a reservoir to react and generate an intervening substance while passing over the surface of the wire, and to deposit the generated intervening substance on the surface of the wire.

In addition, the precursor is about 0.01 parts per 111 parts of the carrier gas +oo volume at a temperature such as 800°C to 1500°C that flows together with the carrier gas, particularly the boron gas, in the form of a gaseous gas, in other words, produces oxides. ~200 volume I
L is preferably about 05 to 100, especially about 1 to
Preferably, the mixture is mixed at a ratio of 50 parts. First, if a mixed gas of a precursor and a carrier gas can be transferred at a low temperature, it will be easier to maintain the temperature of the mixed gas transfer pipe. Preferably, the material has a vapor pressure of at least 10 tmnH9 at 300°C.

Figure 2 shows a specific method for depositing the intervening substance produced by reacting the precursor gas on the surface of the strand.
This is a drawing to explain C.

Figure 2 (here, a section m1 from a large number of strands (1a)
- It is housed in a reaction tube (6) made of an LJ-shaped quartz glass tube or the like. (6a) is a protrusion provided on the inner wall of the reaction tube (6), and the protrusion (6a) allows the wire bundle i to
l+ is held at the center of the reaction tube. Attach the gas supply pipe (7) to the end of the bundle +l+ on the opposite side to the side where the dummy glass tube (5) is attached, with the bundle (1) firmly inserted into the supply pipe (70), The end of the supply tube (7) into which the tube was inserted is airtightly fixed to the reaction tube (61) via a heat-resistant ring (8) made of fluorocarbon resin or the like.

On the opposite side of the reaction tube (61) to which the gas supply pipe (7) is attached, an exhaust chamber (9) is attached to the reaction tube (6) and an airtight plug via a heat-resistant stopper (10) made of fluororesin or the like. .Reverse rc+'W with the supply pipe (7) and exhaust pipe (9) as rotation axes.
+61 and the bundle fl+ installed inside it are rotated (does not need to be rotated) at a speed of several to several tens of r, p, m, and the reaction tube (parallel to 61) is A burner that moves back and forth to
Heating is performed to a temperature ζ necessary to cause a reaction that produces intervening substances. It goes without saying that the burner (11) may be replaced by other heating means such as a fixed direct-air furnace. The heating temperature may vary depending on the reaction temperature of the precursor gas used, or may vary depending on the reaction temperature of the precursor gas used.
Preferably it is at least about 500°C, especially at least about 800°C. Note that if the heating temperature is too high, evaporation of the generated oxide and deformation of the element may occur.
Preferably, the temperature is 0°C or lower, particularly 1500°C or lower. Generally, the most suitable heating temperature is 900-1200
It is ℃.

Thus, when a mixed gas of the precursor and carrier gas is supplied to the reaction tube (611) through the supply pipe +51, most of the mixed gas passes through the gap between the four wires forming the bundle +11. The reaction occurs in the part 1 kept at a high temperature by the moving burner (11), and the intervening substances and products are removed through the dummy glass tube (6) and the exhaust pipe (
9) Exhaust the air from the outside.

When using a precursor gas, a mixed gas of the precursor gas and carrier gas is added at a flow rate of about 50 to 2000 rrLe/min.
By supplying for about 0 minutes to 10 hours, a sufficient amount of the intervening substance can be deposited on the surface of the wire.

In general, it is better to gradually deposit a required amount of intervening substances little by little than to deposit them rapidly, so that the deposited layer thickness will be more uniform. It is preferable to supply it for about an hour.

In order to more stably produce multiple fibers with no voids and image performance, we first deposit an intervening substance with a low melting degree on the surface of the strand, and then (as mentioned above) It is preferable to use a two-step process in which a layer of a mixed intervening material containing S+02 with excellent coexistence is deposited.

Preferred intervening substances having a low melt viscosity are those having a viscosity at the drawing temperature of 10 poise or less, Tatoe, B2O3, Sb2θ8, ■/20, 3.8120
B etc. Note that a three-step process may be performed in which an intervening material layer having a low melt viscosity similar to that in the first step is deposited on top of the mixed intervening material layer.

In the 1st and 6th stages (expressed as an area ratio to the cross-sectional area of the wire, it is sufficient that the adhesion end of the intervening substance is about 0.001 to 0.1% of the cross-sectional area of the wire; on the other hand, in the second stage m of the mixed intervening substance is expressed in the same ratio as above, and is 01~
It is about 1%.

In the flea cage of the present invention, a plurality of methods for intervening the intervening substance described above may be combined. The preferred combination is
A method using an aqueous solution of a precursor such as F481303 and a mixture of a precursor gas and a carrier gas (S
1ce4+ BCe8+02). In the combination of such different types of intervening methods, if the precursor is a fluid, the intervening methods for each intervening substance may be applied in any order, or may be applied alternately and repeatedly.

Since the amount of the intervening substance used in the present invention is small, even if it remains between the fused strands after drawing, it will not adversely affect the image transmission characteristics of the multiple fiber in actual printing. .

The intervening substance used in the present invention generally has a refractive index different from that of the glass material constituting the core of the optical fiber in the strand.
．． Except for the intervening material containing F, the refractive index of the intervening material is SiO
It is larger than that of 2. When an intervening material whose refractive index is higher than that of SiO□ remains at the interface of the strand with a certain thickness even after drawing, the inclusion layer exhibits an optically favorable effect. For example, when an intervening layer having a higher refractive index than quartz glass remains on the optical fiber layer, the remaining layer acts as a light-shielding layer.

In the present invention, it is preferable to include a light-absorbing substance in the intervening substance, so that even if there is an optical signal leaking from each optical element leg in the multiple fiber, it is absorbed and the adjacent optical fiber is absorbed. Unloaded (this will prevent it from entering).

7J') Examples of such light-absorbing substances include wavelengths (004
Substances that exhibit no characteristic absorption in the visible range from μm to 0.7 μm include Fe, Ni, (0, Mn, and Cr).

Examples include substances containing elements such as Cu, such as oxides thereof. The light-absorbing substance exhibits a significant light-absorbing effect even if it is present in the intervening substance in an amount of about 0.001.

The bundle of strands with intervening substances interposed by the method of each building was taken out from the reaction tube (61), or when the reaction tube was made of quartz glass, it was placed in one reaction tube (6). The whole reaction tube is then subjected to a drawing step. This drawing can be carried out under the same method and temperature conditions as the drawing of the base material in the production of silica glass optical fibers. That is, the above-mentioned wire or One end of the reaction tube containing the bundle was heated to 1900 ~
All you have to do is heat it to 2200 degrees Celsius and stretch it out.

When the reaction tube is drawn, multiple fibers having a skin layer of quartz glass on the outer periphery of multiple bundles of wires fused together are obtained. It is appropriate that the outer diameter of the drawn multiple fiber is about 0.5 to 5 mm, and the outer diameter of each strand contained therein is about 10 to 50 μm.

If the drawing temperature is too low, the melt viscosity of the silica glass will be too high, which will inhibit good fusion between the wires, while if the drawing temperature is too high, the evaporation or sublimation of the quartz glass will be significant. It is preferable to carry out the heating in a range of approximately ℃.

During the transition from the step of intervening the intervening material to the wire drawing step, even if the intervening material adhering to the surface of the strand in a liquid state solidifies, there is no problem with providing it separately.

When a solution or molten precursor is used, or when a gaseous precursor is used, and the intervening substance is still attached to the surface of the wire in the form of a precursor before drawing. It is preferable to heat the wire bundle to a commercial temperature in advance to cause a necessary reaction in the precursor to generate an intervening substance before drawing.

BEST MODE FOR CARRYING OUT THE INVENTION Next, the method of the present invention will be explained in more detail with reference to Examples and Comparative Examples.

Examples 1 to 12, Comparative Example 1 A cladding layer with a thickness of 55 μm made of quartz glass doped with B2O3 and Fl on the outside of a core portion made of pure quartz glass with an outer diameter of 300 μm, and a cladding layer with a thickness of 15 μm on top of the cladding layer made of quartz glass doped with B2O3 and Fl. 8,000 wires with an outer diameter of 400 μm and a length of 400+, each having a quartz glass port layer, were washed in 20 volumes of fluoridated water solution and then in distilled water using ultrasonic waves, and then bundled in distilled water. Ta. Then, the wire bundle was made into an inner diameter of 48
III11, housed approximately in the middle of a synthetic quartz pipe with an outer diameter of 51 mm and a length of 800 mm, close one end of the pipe, and while drawing a vacuum from the other end, both ends of the wire bundle are fused to the wall of the pipe, and then The closed end was opened again. The synthetic quartz pipe containing the wire bundle thus obtained was subjected to the 1st to 5th stages of treatment shown in Table 1 in an electric furnace maintained at 1000°C. In the case of Comparative Example 1, only 02 gas was supplied.

After this, a synthetic quartz pipe, also known as Soto, was drawn at 2000° C. to obtain a multiple fiber with an outer diameter of 1.4 mm and eaooo optical fibers. When the cross section of this multiple fiber was inspected using an optical microscope with a magnification of 50 times, it was found that a very large number of air bubbles remained between the fused strands in the case of Comparative Example 1, and in the case of Examples 1 to 12. In all cases, there were very few or no remaining voids.

Example 13.14 Outer diameter 2 made of pure silica glass doped with GeL
An outer diameter of 280 pm, with a 4071 m thick cladding layer made of pure silica glass on the outside of a 0.0011 m core;
The 12,000 strands on the length 50 side were subjected to the same treatment as in Example 1 (Sister Example 13) or the same treatment as in Example 8 (
Example 14) was carried out and a multiple fiber with 12,000 strands was obtained by bag drawing at 52,000°C.

Example 15 Instead of the precursor gas treatment in Example 1, a synthetic quartz pipe containing a bundle of strands was kept at 90°C for 20 days.
Heavy equipment - Boric acid lined up (200 ppm Co (+N08
), and a water bath solution in which the synthetic quartz pipe was immersed and then pulled up from the water bath solution, and placed in an electric furnace maintained at 1000°C to form a mixture of 13□08 and CoO on the surface of the wire. A multiple fiber with an outer diameter of 1.4 mm was manufactured, differing from Practical Example 1 only in that it produced .

When the front surface of each of the multiple fibers produced in Examples 13 to 15 was inspected using an optical microscope (with a trowel) at a magnification of 50 times, no air bubbles were observed at the interface of the fused strands in any case.

[Brief explanation of the drawing]

FIG. 1 is a detailed explanatory diagram of the present invention, in which 1a is an optical fiber element, 2 is an intervening substance, 3 is a heating means for drawing the wire, and FIG. 2 is a diagram showing the optical fiber element. 1 is an explanatory diagram of an example of a method for interposing an intervening substance in the gap between a bundle of wires, in which 1 is a bundle of the wires, 6 is a reaction tube, 11 is a burner, and 7 is a method for reacting a gas that is a raw material for generating an intervening substance. This is a reservoir tube for feeding into the tube 6. Patent applicant: Dainichi Nippon Electric Cable Co., Ltd. Representative Director Yukio Aoyama-3:

Claims (1)

[Claims] Outer diameter S mrn At least 1000 virgin silica glass optical fibers are bundled together, and the strands are heated at a drawing temperature (in which a liquid intervening substance is present) between the core strands. 1. A method for producing an optical multiple fiber, which comprises drawing a bundle, and wherein the intervening substance comprises at least one persimmon selected from the group consisting of glass-forming oxides, glass-modifying oxides, and intermediate oxides.