JPS58140336A - Manufacture of base material for optical fiber - Google Patents

Abstract

PURPOSE:To provide uniform characteristics to a sintered porous silica body formed by a vapor axial deposition method all over the length by melting the sintered body from the lower part where the silica deposited surface shows a convex shape toward the concave surface under prescribed conditions to uniformalize the ununiform state. CONSTITUTION:A silicon compound or a silicon compound contg. a dopant is subjected to flame oxidation and/or hydrolysis to form a sintered porous doped silica body consisting of fine silica particles. The sintered body is put in a furnace attaining to stationary melting conditions, and it is successively melted from the lower part where the silica deposited surface shows a convex shape toward the concave surface at a constant rate under the same conditions all over the length. By the melting the sintered body is vitrified to give a base material for an optical fiber free from residual bubbles, causing no abnormality in the refractive index and no shift of the deposited layers, and having uniform characteristics all over the length.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a base material for optical fibers, and more particularly, to an industrially advantageous transparent vitrification method for a porous glass sintered body produced by a pneumatic crystal attachment method. .

For the production of optical fiber base materials, silicon tetrachloride (8
1C14) and a dopant for controlling the glass refractive index, such as G o CI
4, P OCl B, BBr, etc. are burned in an oxyhydrogen flame to generate fine particles at t/9, and these are blown onto a rotating refractory target, such as the lower end of a quartz rod, to form porous glass. The porous silica sintered body is sequentially deposited as a sintered body and grown into a columnar shape while being pulled up in the upper axial direction.The porous silica sintered body is then introduced from the bottom of the high-temperature heating furnace and melted sequentially from the top of the sintered body. There is a known method for producing a transparent glass base material.

However, this porous sintered body itself has a low density and contains a large amount of gas, and this means that the lower the density, the lower the thermal conductivity, the lower the strength, and the more fragile it is. Therefore, when this material is heated in a high-temperature heating furnace, the melting and shrinkage ratio in this amorphous sintered body changes due to the asymmetry of heat transfer due to the furnace structure, heat radiation, convection, etc. When it melts from the top, even a slight deviation in its shrinkage speed causes it to shrink and bend asymmetrically, causing the entire sintered body to tilt downward, as shown in Figure 81, and to move away from the point where it received concentrated stress. There are many accidents where this breaks or hits the inner wall of the furnace and is destroyed. In addition, rupture and destruction of the sintered body may occur if there is little clearance between the inner wall of the heating furnace and the sintered body, or if the sintered body has density changes due to changes in the production conditions at the start of production or due to changes in conditions. It is also known that this occurs in most cases when the shape is asymmetric. Therefore, this V9
Another method is to reduce the temperature increase rate for heating the force-sintered body, for example, to slowly raise the temperature so that the temperature difference between the surface and the center of the body is 10°C or less. However, since it takes 2 to 4 hours just to heat the silica sintered body to the melting temperature, the production efficiency is disadvantageously reduced. This also includes a method in which the silica sintered body is held stationary in a fixed furnace and the entire body is heated and melted, but in this case, the heating part of the furnace is heated to the entire surface of the heater. Since the silica sintered body is islanded from approximately the center, the silica sintered body inevitably has a temperature distribution and has a thermal history along its entire length. As a result, the reaction rate between G e Os and P as a dopant and the reactant, their movement, and desorption become non-uniform, making it difficult to use for the purpose of transparent optical fiber. The recording material is in the same dehydrated state over its entire length,
The disadvantage is that they have the same refractive index and are far apart.

Next, when producing a role for transparent optical fiber by melting this νS1III compact, the silica sintered compact is deposited so that the silica deposited surface is concave upward as shown in Figure 2. Therefore, G.0. Refractive index distribution 1M doped with , poai, etc. As shown in Figure 813 of a tyW force sintered body, when the liquefied sintered body is melted from the concave upper part, the internal gas and Mobile germanium, phosphorus, etc. do not move, and they move far toward the center of the sintered body through the low-density layer sandwiched between the two layers.
This becomes a diagram showing abnormalities in gas and refractive index. and,
In particular, when performing moving melting of a LiCa sintered body with a refractive index distribution, this dissolution also proceeds from the center of the ν9i1 sintered body, so the gas between the deposited layers flows from the center as shown in Figure 4. Concentrate 1j15I in the position where you left it! This causes anomalies to occur in concentric circles.

In addition, the density of the porous silica sintered body made by this vapor phase axial attachment method is different between the center and the outer dovetail, so when it is melted, the U-shaped opening on the stacked surface is different. Since the fiber is closed from the same direction, the I11 plane of the fiber will be misaligned as shown in Figure S. These abnormalities will affect the transmission characteristics of the optical fiber made from the target optical fiber base material, especially in the transmission band. It was highlighted that honesty = deterioration.

The present invention relates to a method for manufacturing an optical fiber base material from a sintered silica body that solves these disadvantages. It is characterized by sequentially melting and vitrifying the entire length under the same conditions at a constant speed in a furnace that has reached steady melting conditions.

To explain this, 1. As a result of various studies on the method of manufacturing optical fiber base materials from porous silica sintered bodies manufactured by the vapor phase axial method, the present inventors found that various dopants may be added as needed. Porous glue sintered bodies obtained by flame oxidation and/or hydrolysis of silicon compounds or by depositing tsuka fine powder become curved bodies with downward convex parts. Since the vertical cross section of the force field stack forming the body is concave in all layers, during this melting and vitrification, the layers are moved from the convex part at the end to the U-shaped concave part of each deposited layer. In addition to highlighting that the above-mentioned disadvantages can be solved by heating and melting this V9 force sintered body, the melting and heating of this V9 force sintered body is introduced from this convex part into a heating furnace that has been set in advance as a steady melting condition, and its entire length is If the silica sintered bodies are sequentially melted under the same conditions, the silica sintered body will not be deformed or destroyed, and the refractive index and residual bubbles will not occur, even if there is the disadvantage of asymmetric heat transfer due to heat radiation and convection. The present invention was completed by confirming that it was possible to obtain an optical fiber base material with no abnormalities or deviations in the deposited layer and with uniform characteristics over the entire length.

The porous silica sintered body for carrying out the method of the present invention is
Various silicon compounds or silicon compounds containing dopants are burned in an oxyhydrogen flame, and then blown onto a rotating quartz rod as a refractory target.
It can be produced by the so-called vapor phase sintering method, in which silica particles are deposited and the quartz rods are successively pulled upward to form a rod-shaped silica sintered body. The porous silica sintered body obtained by this method is pure white because it is an aggregate of amorphous silica containing a large amount of gas, and its shape depends on the spread of the oxyhydrogen flame, temperature distribution, and the target surface. The direction of spraying silica on
Although it varies depending on various conditions such as the strength of the force,
In either case, the amount deposited at the center of the shaft is greater than that at the periphery, and the amount of heat is also greater, resulting in a convex body with higher density and dopant concentration at the center. However, the shape of each deposited layer constituting this silica sintered body is a downwardly convex curved shape that is uniformly similar to the bottom of the deposit, and no matter which direction the vertical cutting direction is taken, it becomes a U-shape. . Although we have explained the vapor phase axial method for obtaining silica sintered bodies, this is not limited to this method, and other methods for obtaining porous V9 sintered bodies by laminating multiple layers of silica have been described. It may be created using any method.

The method of the present invention involves sequentially melting the porous ν force sintered body having a downwardly convex portion obtained as described above from the direction in which the &9 force deposited surface shows a convex shape toward the concave surface. This is made into a transparent glass-like material, and the heating furnace may be of either an internal heating type or an external heating type, and may also be of a heating type using a heating coil according to the floating zone m51m method. Further, during this heating and melting, a known method for removing OHI in the sintered body by introducing a salt gas into the furnace may be used in combination. However, in this heating melting process, the heating furnace is preheated before the silica sintered body is introduced, so that the temperature inside the furnace reaches a predetermined steady state, and the gas flow and dehydrating agent inside also reach a steady state. Until then, the silica sintered body must not be introduced here, and it must be kept at a temperature that will not cause a dehydration reaction or release of the dopant contained therein.

In the method of the present invention, the above-described sintered silica is introduced into the heating furnace that has reached a steady state in this way, and is melted and vitrified over its entire length under constant conditions. As described in 4 above, the silica sintered body is
iI must be sequentially dissolved from the direction in which the deposited surface exhibits a convex shape toward its concave surface. To do this, as shown in @6, a v-force sintered body is inserted from the upper part of the furnace and lowered, and the body is strangled, dehydrated, shrunk, and melted. When the silica sintered body is melted in this way, the silica deposited surface is opened in a 0-shape, which melts from the center of the convex portion at the lower end of the ν force sintered body. Air, water, and doping agents such as volatile substances such as volatile Go and O are sequentially extruded through this layer. Since it is carried out in almost the same horizontal plane, there is no trapping of gas. In addition, this shrinkage is performed sequentially along the U5Pg of the deposition surface, so no deviation occurs due to this.In addition, in this method, the entire length is melted so that the same heat history is achieved, so there is no unevenness in the furnace. are equalized, and continuum 5: typical changes in characteristics in the length direction are suppressed.

Therefore, according to this method, the disadvantages caused by the air contained in the silica sintered body can be eliminated, and the non-uniform movement and desorption of the dopant can also be eliminated, so that the desired result can be achieved. There is no fear of breaking or breaking the base material for optical fiber, the silica deposit layer is normally distributed without any disturbance, and the dopant wM refractive index distribution and core erosion are substantially uniform. It can be easily obtained as a standard (see Figure 8).

With the method of the present invention, the melting speed of silica sintered body Ift is 10 to 20 times that of the conventionally known method.
It is possible to perform the process at speeds of 1/min, and this also applies to high NA-fibers with dopant Y multipupils, single-mode fibers with ground layers t'ft1l, step-type distributions, and large diameter fibers. It can also be applied to vitrification of mold mother pots, etc.

According to this, it is possible to homogenize any of those materials, and this also eliminates the vapor phase axial method, which was conventionally required to prevent deformation and breakage during heating and melting. Obtained silica sintered body +7) Densityffl'0.15
It was also recognized that F/ccf1.60.03 g7acr=1te can be lowered.

Next, we will give two practical examples of the method of the present invention.Example 1 Silicon tetrachloride 1: @ large refractive index 1% 3 Gemanium tetrachloride (Gaol) and phosphoric acid trichloride (Pool
,) Flame hydrolyze the mixed gas added with VF11 in a hydrogen flame and spray it onto a rotating quartz rod to deposit fine silica powder.
, the average glazing density is 0. Five cylindrical porous doped G9 force field bodies with t3*o and 01#/cc were created under the same conditions.

Next, the I:H gas and 0.21/min 01 in the furnace were flowed to produce transparent vitrification. A base material for an optical fiber was made by inserting the glue sintered body under the following conditions. When optical fibers were made from this and the transmission loss was measured, the results shown in the following No. 111 were obtained for each sample ≦ 2. It was done.

(Processing conditions) 1) A sintered body was introduced from the bottom of the furnace at a speed of 1 m/min and pulled upward.

2) Place the sintered body in the heating section of the furnace with <79 force, raise the temperature from room temperature to 1600°C for 3 hours, and melt from the side 3) Silica sintered body Y Furnace 7J] #I% part 2.Pull it up to J: and keep it in a position where its end contracts slightly during temperature rise, and after the inside of the furnace reaches a steady state, raise it to the arc inside the furnace;
[4) The lower end of the silica sintered body does not shrink at all even when the temperature is rising. When the sintered silica body is pulled up and the furnace reaches a steady state at tl[l:4] Then, it was melted in the furnace (drawing F at a constant speed and melting 5) by increasing the drawing speed lfv in 4) above (experimental results). Doped silica sintered body vHe gas t'151! The inside of this silica sintered body i1! C so that the temperature is 1650℃
In this case, the sintered body is introduced from the F side of the melting furnace, and the f
The conventional method is to insert the silica sintered body from the hole in the Y furnace and melt it from the convex bottom of the silica sintered body first. When this vitrification was carried out by the method of the present invention, the direction and moving speed were as shown in Table 2 C = g
The following results were obtained.

142fi Example 3 Il! in the same manner as Example 1. Diameter 70&lφ, length 350
Deception, average density! I made two pieces of 0.09±0.1N/cc doped porous silica sintered body Y, this is vlI! How to raise genus 6 in example number 2 (however, since magic 6 is severely deformed, start with 47 conditions, and then move to 46 after stabilizing)
the method of! After melting and vitrifying using the pull-down method of 48 and 48, the fibers are spun into fibers, and the transmission characteristics of these 1 to 0.84 μm are measured at wavelength C: Therefore, the frequency sweep in the transmission band is When compared with $3
The results shown in fi were obtained.

In other words, the transmission characteristics of glass fibers are affected by the degree of internal irregularities, but fibers made from glass melted by the method of the present invention (%8) have fewer internal irregularities. Comparative example Koshita/i66
It was vitrified and made into a fiber using the method of

113 Actual example 4 Silicon tetrachloride gas 'i'1. As III material, diameter 65φ, length 200m, average apparent density 0.04 by vapor phase axis method.
A 1/l-low-polarity sintered silica was made, and this was 11650.
When melted using the 4-hill method at a temperature of 1:4 °C, it was deformed and could not be made into a normal glass 1:4, but this silica sintered body was pulled up to a temperature of 1:4 and then melted using the 4-hill method. As a result, no deformation occurred even at both speeds of 201117 minutes.
A transparent base material for optical fibers can be obtained, and this temperature I
When the temperature was raised to 1,750° C. and the first-stage pull-down method was applied, vitrification of 6= was possible at a rate of 50 parrots/min.

[Brief explanation of drawings]

Fig. 1 is a schematic vertical cross-sectional view showing the fractured state of a silica sintered body according to conventional method-2, Fig. 2 is a schematic vertical cross-sectional view showing the horizontal cross-section of the silica sintered body, and Fig. 3 is a schematic vertical cross-sectional view showing the fractured state of the silica sintered body according to conventional method C; Longitudinal cross-sectional schematic diagram showing how to form an optical fiber base material by force sintering and its melting 6 % #! Figure 4 is a schematic vertical cross-sectional view showing the movement of gas and dopant during dissolution in the conventional silica sintered body. Figure 5 shows the resulting disturbance in the silica deposition during use of the optical fiber. Schematic longitudinal section, Figures 6 and 7
8 and 8 are schematic vertical cross-sectional views showing the melted state of the silica sintered body according to the present invention and the state of silica deposited on the optical fiber base material CX, and FIG. A mirror photo of a longitudinal section of the optical fiber base material, No. 1
Figure 0 is a photograph of a longitudinal section of the optical eyeper base material obtained by the method of the present invention. Patent owner I1 Horo Chemical Industry! Figure 9 Figure 10 Procedure correction calculation (method) % formula %) 2. Name of the invention Method for manufacturing base material for optical fiber 3.1 Relationship with Yamamasa 11 and 7 people, Patent 6 -Name of person (206) Shin-Etsu Chemical Wire Company 4,
Reason! , 11- Location: 〒1 (IJ East I+, Tokyo Chuo 1, (this article A
：Town 4 "Jth No. 9 4jlL'l 1JJAlklk(
27d) 085A, os59J, h11 Masaji) Tsukiie Il! ! l direction (Figures 9-10)

Claims (1)

[Claims] An optical fiber motherboard in which a silicon compound or a silicon compound containing a dopant is oxidized and/or hydrolyzed to produce a porous glass sintered body made of Relica particles, which is then turned into transparent glass in a high-temperature heating furnace. In the method for producing the material, a porous glass sintered body is oriented from the convex direction of the sintered surface to the concave surface, and is heated at a constant speed over its entire length under the same conditions in a furnace that has reached steady melting conditions. A method for producing a base material for optical fiber, characterized by sequential melting and vitrification.