JPH06298542A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To prevent a preform for glass from release, dropping and disperse of concentration of the preform by preparing the preform for glass so that a porous glass layer has prescribed bulk density. CONSTITUTION:SiCl4, GeCl4, etc., which are raw materials are introduced together with an inert gas and O2 gas from one end of a glass pipe obtained by boring a rod-like glass preform obtained by VAD method while rotating the glass pipe and the raw materials are moved while heating the pipe surface to deposit a porous glass layer having 0.2g/cm<3> to 0.8g/cm<3> bulk density. As necessary, a solution containing one or more kinds of compounds (e.g. ErCl3) of element selected from Er, Nd, Yb, Tm, Pr, La, Al and P in a solvent consisting of water or ethanol are added to this porous glass layer and permeated into the porous glass layer. Then, the resultant porous glass layer is vitrified by heating and this glass pipe is collapsed to produce the objective preform for optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a base material for an optical fiber, and more specifically, an optical fiber doped with various additives such as a rare earth element-doped optical fiber used in a rare earth element-doped optical fiber amplifier. The present invention relates to a method suitable as a method for manufacturing a base material.

[0002]

2. Description of the Related Art As a method for producing a base material for an optical fiber doped with a rare earth element, reference 1 [JETownsend, SBPoole, DNPay
ne "Solution-doping technique for fabrication of
rare-earth doped optical fibers ", IEE Electronics
Letters, vol.26, No.7, pp329 to 331 (1987)], the solution impregnation method is applied to the MCVD method which is a typical method for producing a preform for optical fibers. Normal M
In the CVD method, as shown in FIG. 1, glass raw materials (for example, SiCl ₄ , GeCl ₄ , BC) are placed inside the starting quartz pipe.
(1 ₃ , POCl _3, etc.), oxygen (O ₂ ) gas, and an inert gas while flowing the starting quartz pipe by an external heat source typified by an oxyhydrogen burner to oxidize the glass raw material in the pipe. By doing so, glass fine particles are generated. The glass fine particles are deposited on the inner surface of the pipe on the downstream side of the heat source to form a porous glass layer. The porous glass layer deposited by reciprocating the heating source is heated to form a transparent glass film. In the method of Reference 1, at this time, the temperature of the heating source is adjusted to an extent that glass fine particles can be generated, but it is insufficient for making the porous glass layer transparent, and after the porous glass layer is deposited on the inner surface of the pipe, A solution in which a chloride of a rare earth element is dissolved is poured into the pipe, the porous glass layer is impregnated with the solution, dried, the solvent is distilled off, and the transparent glass layer is again heated to make the glass layer transparent. A rare earth element is added to. Then, the pipe is heated and solidified. Since rare earth elements are generally added to the core region of an optical fiber, as described in Reference 1, a cladding layer is formed on the inner surface of a starting quartz pipe by a conventional MCVD method.
After being deposited by the method, a porous glass layer is generally formed as the core layer by the above-mentioned means and solution impregnation is performed.

[0003]

Conventionally, when a rare earth element-doped optical fiber preform is manufactured by such a method, the porous glass layer is peeled off from the inner surface of the pipe during solution impregnation, drying, or transparent vitrification. However, there is a problem that it is difficult to add a desired amount because the amount of the rare earth element added varies greatly. For such a problem, conventionally, by adjusting the heating conditions at the time of forming the porous glass layer and the supply amount of the raw material gas for the porous glass layer, or the heating conditions at the time of drying and making transparent by trial and error. I was dealing with it. However, even if stable manufacturing conditions were found once, if the fiber structure and the like were changed, similar trial and error had to be repeated, which was extremely inefficient.

[0004]

[Means for Solving the Problems] The inventors of the present invention have conducted extensive studies on the relationship between the above problems and various factors in the optical fiber preform manufacturing process, and the bulk density of the porous glass layer is very important. Yes, this is 0.2 g / cm ^{3 to} 0.8
The inventors have found that the desired amount of the rare earth element can be stably added to the glass regardless of the composition of the glass by adjusting g / cm ³ . That is, the present invention, after depositing a porous glass layer containing quartz glass as a main component on the inner surface of the glass pipe, permeate the porous glass layer with a solution containing an additive to the porous glass layer,
Then, in the method for producing a glass preform for heating the porous glass layer to make it transparent glass and solidifying the glass pipe, the bulk density of the porous glass layer is 0.2 g /
It is characterized in that it is set to cm ^{3 to} 0.8 g / cm ³ . As an additive to the above-mentioned porous glass layer, particularly preferably E
A solution containing one or more compounds of an element selected from r, Nd, Yb, Tm, Pr, La, Al and P, and the solvent containing the additive to the porous glass layer is water or ethanol. Is particularly preferred. When the rod-shaped glass base material obtained by the VAD method is pierced into a pipe shape as the glass pipe, the contamination of OH and impurities that hinder the transmission of light is extremely small.
According to the method D, a large base material can be obtained, and thus glass pipes having various wall thicknesses can be used, which is desirable.

[0005]

The solution impregnation of the porous glass layer will be described with reference to FIG. As shown in FIG. 5, when the bulk density is high, that is, when the deposition in the crevice is small, the amount of solution intrusion is small and the addition amount tends to be small. Tends to be large. It is considered that this causes variations in the added amount (concentration).
Also, drying, heating, peeling of the porous glass layer at the time of transparency,
Regarding the falling off, when the bulk density is relatively small, the adhesion between the glass particles (soot) and the inner surface of the pipe is small, and the mutual adhesion of the glass particles is small, so when the glass particles shrink due to drying or heating. It is considered that the soot is peeled off or comes off.

Therefore, a porous glass layer having various bulk densities is internally attached to the inner surface of the pipe to prepare an optical fiber preform, and the fiber is drawn. As a result, the bulk density is 0.2 g / cm.
It was found that when the amount was ^{3 to} 0.8 g / cm ³ , the desired rare earth element could be added without peeling or dropping of the porous glass layer. In this region of bulk density, the amount of rare earth element added can be estimated by the following equation (1).

[Equation 1]

The deposition of the porous glass layer in the present invention will be specifically described. As shown in FIG. 1, while rotating the glass pipe, the porous glass layer is introduced from one end together with a carrier gas such as inert gas and O ₂ gas. Raw material of SiCl
₄ , GeCl ₄ , BCl ₃ , POCl _3, etc. are introduced,
While heating the glass pipe surface with an oxyhydrogen burner, move the burner in the longitudinal direction of the glass pipe at a constant speed,
A porous glass layer is deposited on the inner surface of the glass pipe. The bulk density of the porous glass layer is determined by the amount of raw material input (SiCl ₄ ,
It depends on the vapor pressure of GeCl ₃ etc. and the flow rate of carrier gas), the thermal power of the oxyhydrogen burner, and its moving speed. By changing these conditions, a porous glass layer with various bulk densities is deposited. Can be made. In order to permeate the solution containing the additive into the porous glass layer, for example, after pouring the solution into the pipe, the excess solution is discarded, but the method is not limited thereto. As the additive, a compound of an element to be added to the porous glass layer, such as chloride or oxide, specifically, Er (ErCl ₃ or the like), Nd (NdCl ₃ or the like),
Yb (such as YbCl _3), Tm (such as TmCl _3), P
r (PrCl ₃ etc.), La (LaCl ₃ etc.), Al
Examples include compounds of rare earth elements such as [Al (NO ₃ ), etc.], P (P ₂ O ₅ , H ₃ PO _4, etc.), and other elements. As the solvent to which the additive is added, for example, water,
Alcohols such as ethanol can dissolve the added element-containing compounds such as chlorides and salts sufficiently, and most of them volatilize by natural drying, and in addition, they can be easily and thoroughly removed by reactive gas such as Cl ₂ Is.

[0008]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. [Example 1] A rod-shaped SiO ₂ glass base material obtained by the VAD method was perforated to a length of 200 mm and an outer diameter of 25 m.
Several pipes having m and an inner diameter of 12 mm were prepared.
With the configuration shown in FIG. 1, while rotating the glass pipe, N ₂ gas, O ₂ gas as inert gas, and SiCl ₄ and GeCl ₄ as raw materials for the porous glass layer were introduced from one end, and the pipe surface was oxyhydrogen burner. While heating, the burner was moved in the longitudinal direction of the pipe at a constant speed, and several pipes were prepared by depositing a porous glass layer on the inner surface of the pipe. Several pipes having different bulk densities of the porous glass layers were produced by changing the raw material input amounts (SiCl ₄ , GeCl ₃ vapor pressure and carrier gas flow rate), the heating power of the oxyhydrogen burner, and the moving speed. Furthermore, ethanol (C ₂ H
₅ OH) to _{Al (NO 3) 3 · 9H} 2 concentration O 0.35 mol / l, ErCl ₃ · 6H ₂ O to 5 × 10 ^-3
The solution dissolved at a concentration of mol / liter was poured into each glass pipe, and the solution was permeated into the porous glass layer.
After that, remove the excess solution remaining in each glass pipe,
While flowing a gas such as O ₂ or Cl ₂ into each glass pipe, the porous glass layer was heated to be transparent, and the glass pipe was solidified to obtain an optical fiber preform. Each of the obtained base materials was cut into slices, and the concentration of Er in the core portion produced by the deposition shown in FIG. 2 was analyzed by the ICP-MS method (inductively coupled high frequency plasma mass spectrometry). The results are summarized in Fig. 3. In FIG. 3, ● indicates that the composition of the porous glass layer is 90 mol% SiO ₂ -10 mol% GeO ₂ , and ○ indicates S.
iO ₂ 80 mol% -GeO ₂ 20 mol%, Δ is SiO ₂
What was 100 mol% is shown. From the result of Figure 3,
Er in the range of the bulk density of 0.20 to 0.78 g / cm ³
It is considered that Er is volatilized and that the concentration is lower than the result obtained by calculation from the above-mentioned bulk density because Er is volatilized at the time of heat transparency and solidification of the pipe. Further, in A and B indicated by X in the figure, peeling occurred regardless of the composition of the glass. Bulk density 0.20 g / c
In the region of less than m ³ , the porous glass layer is peeled off, and in the region of more than 0.8 g / cm ³ , the volume of the fine glass particles at the time of solution permeation is small, and heating transparency
Almost no addition due to volatilization of Er during solidification.

[Embodiment 2] In the same manner as in Embodiment 1,
Made a glass pipe with a porous glass layer deposited on the surface
It was The bulk density of the porous glass layer is 0.3 g / cm.
³And Water (H ₂O) or ethanol (C₂H_FiveO
ErCl in H)₃・ 6H₂5 x 5 x 10 O^-3Mol / li
Toll concentration, Al (NO₃)₃・ 9H₂O in various concentrations
The porous glass layer is infiltrated with the
Solidify by the same method as in Example 1, and change the Al concentration in the core
It analyzed by the ICP-MS method. The results are shown in FIGS. 3 and 4.
The Er concentration was 1000 ppm, which was the same as the result of Example 1.
there were. In Fig. 4, ○ indicates that the solvent of the impregnation solution is ethanol.
, ● is H₂Represents O. As shown in FIG.
The concentration in the glass increased with the concentration in the solution.
In addition, Al (NO₃)₃・ 9H₂O is dissolved in ethanol
It has a low degree of resolution, and in the concentration range of 1 mol / liter or more,
Al precipitation occurred after drying, so if the concentration is higher than this, the solvent
Water (H₂O) was used.

As described above, a rare earth element is added to quartz glass by infiltrating the porous glass layer deposited on the inner surface of the glass pipe with a solution containing a rare earth element, heating the material for transparency, and conducting a pipe solid compound. In the element addition method, peeling of the porous glass layer and variations in the addition concentration, which have been problems in the past, were detected by adjusting the bulk density of the porous glass layer to 0.
It could be solved by a ^{20g / cm 3 ~0.8g / cm 3} .

[0011]

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of an MCVD method.

FIG. 2 is a cross-sectional view of a solidified base material for heating for explaining a portion where the amount of rare earth element addition in the example of the present invention was measured.

FIG. 3 shows the bulk density (g / g) of the porous glass layer on the inner surface of the pipe.
³ is a graph part showing the relationship between cm ³ ) and Er addition concentration (ppm).

FIG. 4 shows the bulk density (g / g) of the porous glass layer on the inner surface of the pipe.
³ is a graph part showing the relationship between (cm ³ ) and Al addition concentration (ppm).

FIG. 5 is a schematic diagram illustrating a mechanism of adding a rare earth element by impregnating a porous glass layer with a solution.

Claims (4)

[Claims] 1. A porous glass layer containing quartz glass as a main component is deposited on the inner surface of a glass pipe, and then a solution containing an additive to the porous glass layer is permeated into the porous glass layer, Then, in the method for producing a glass preform for heating the porous glass layer to make it transparent glass and solidifying the glass pipe, the bulk density of the porous glass layer is 0.2 g / cm ^{3 to} 0.8 g. / Cm ^{3 The} method for producing a preform for optical fibers, characterized in that 2. The additive to the porous glass layer is Er,
2. The method for producing an optical fiber preform according to claim 1, which is one or more kinds of compounds of an element selected from Nd, Yb, Tm, Pr, La, Al and P. 3. The method for producing an optical fiber preform according to claim 1, wherein the solvent of the solution containing the additive for the porous glass layer is water or ethanol. 4. The method for producing a glass base material for an optical fiber according to claim 1, wherein a rod-shaped glass base material obtained by a VAD method is drilled to form a pipe shape as the glass pipe. .