JPH11180719A - Production of glass preform for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the producing method of a glass article in which a high concn. additive is uniformly added to a core. SOLUTION: In the production method of the glass article for the optical fiber having the core and a clad, a porous soot body consisting essentially of SiO2 is formed on an inner wall of a glass pipe becoming the clad by a gas phase synthesizing method, and a solution in which particulates of the additive are dispersed is impregnated to the porous soot body, then the material is dried, subjected to heat-clarifying treatment and made into solid.

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 glass preform for an optical fiber, and more particularly to an improvement in an immersion method for adding a silica-based glass fiber preform using a solution.

[0002]

2. Description of the Related Art Conventionally, a vapor phase addition method and a solution impregnation method are known as methods for adding a rare earth element to a quartz fiber. As an example of the gas phase addition method, when synthesizing a coating portion inside a quartz pipe by the MCVD method, together with vapors of glass raw materials SiCl ₄ and GeCl ₄ ,
There is a method in which a rare earth compound is heated at about 00 ° C., the vapor is transferred to a quartz pipe, heated by a burner to vitrify, and the resulting pipe is collapsed and drawn to form a fiber. As an example of the solution impregnation method, V
There is a method of using a core soot created by the AD method or the OVD method. In this method, a rare earth compound is dissolved in alcohol or water, and a soot base material for a core is immersed therein. Next, there is a method in which an alcohol in the soot is evaporated at room temperature, a rare earth compound is deposited in the soot for the core, and sintering and vitrification are performed under various gas atmosphere conditions to obtain an optical fiber preform. JP-A-50-73908). Further, as shown in Japanese Patent Application Laid-Open No. Hei 2-258644, the inner wall of a glass tube for cladding is formed by MCVD.
There is a method of obtaining a preform by depositing an O ₂ -based soot, impregnating it with an additive solution, and then heat-clearing and solidifying.

Further, the inner wall of a glass tube serving as a clad has S
Production of an optical fiber preform comprising forming a glass film containing iO ₂ as a main component and containing a dopant compound such as aluminum or a rare earth element and having a higher refractive index than the glass tube by a sol-gel method and then forming a core by collapsing the glass film. A method has also been proposed (JP-A-5-58664). Similarly, a method is known in which a film to which a rare earth element is added is formed by a sol-gel method, and thereafter, the tube is heated in a metal chloride vapor atmosphere to form a transparent glass (Japanese Patent Laid-Open No. 5-10546).
No. 6).

However, in the above-mentioned known method, the solubility of an additive precursor (for example, an Al salt or a rare earth element chloride) in a solution is limited, which limits the maximum additive. There is a problem. In addition, there is also a problem that a lump of the additive to be immersed is formed in the drying step or the heat treatment step, causing a change in the refractive index distribution or a defect (a cause of crystal formation) of the preform, thereby lowering the yield. This is a phenomenon in which the concentration of a solute increases during drying, crystal nuclei are formed, and crystals of the solute (salt) grow from the nucleus. Particularly, a salt (such as Al) added at a high concentration is dried. It is easy to occur when.

[0005]

For example, in order to apply a rare earth element-doped quartz glass fiber to an optical fiber laser or an optical amplifier fiber, the concentration of the added rare earth element dopant compound has an optimum value. In many cases, there is no problem with the conventional method. However, when a large amount of an element (such as Al) that changes the refractive index is added, the above-mentioned conventional technology does not sufficiently meet this demand. The present invention solves the above-mentioned problems of the prior art, a quartz glass article in which a high concentration of an additive, for example, a dopant compound is uniformly added to a core,
For example, it is an object of the present invention to provide a method for manufacturing a glass preform for an optical fiber.

[0006]

The above objects can be attained by the invention and aspects summarized below. (1) A glass article containing an additive, wherein a porous soot obtained by a gas phase synthesis method is impregnated with a mixed solution in which fine particles of the additive are dispersed, dried, and heated to form a transparent glass. Manufacturing method. (2) In a method of manufacturing a glass preform for an optical fiber having a core and a clad, a porous soot body mainly composed of SiO ₂ is formed on the inner wall of a glass tube to be a clad by a vapor phase synthesis method. A method for producing a glass preform for an optical fiber, characterized by impregnating a mixed solution in which fine particles of an additive are dispersed in a soot body, and then drying, heating, clearing, and solidifying.

(3) Fine particles of the additive are 10 to 100 nm
The method according to the above (1) or (2), having a particle size of: (4) The method according to any one of the above (1) to (3), wherein the concentration of the fine particles in the mixture is 10% by weight or more.

In the above invention (1) or (2), the additive can be added at a higher concentration and more homogeneously than in the immersion method using an ordinary salt solution. According to these methods, it is possible to add a large amount of an element which is conventionally difficult to add, for example, aluminum. The method of the invention (1) is applied not only to the preparation of the core of the glass base material for an optical fiber as in the method of the invention (2), but also to the use of the surface modification by addition to the outermost layer of the clad. You.

In any case, the particle diameter of the additive fine particles is preferably in the range of 10 to 100 nm. A particularly preferred range is from 10 to 40 nm. If the diameter is smaller than 10 nm, there is a problem that the stability of the fine particles is not obtained.
If it exceeds, the refractive index distribution will fluctuate and the preform will have defects (crystal formation causes). The amount of the fine particles is
The content is preferably 10% by weight or more, more preferably 10 to 20% by weight in the mixed solution. If it is less than 10% by weight, the intended purpose of adding the fine particles cannot be achieved.

As additives, aluminum, titanium,
An oxide of germanium, tin, or zinc is used. Generally, water, alcohol, and acid are added to these alkoxides and inorganic salts and hydrolyzed to form fine oxides (hydrates). Alternatively, a colloid can also be formed by dispersing fine particles produced by a gas phase method or the like in a solvent such as water. A solution of the dopant compound is added to the obtained colloidal dispersion. Here, as the dopant compound, a compound such as a rare earth element such as Er, Yb, Nd, or Pr, for example, a salt is used. Thus, a dispersion for immersion is obtained. The dispersion can be stabilized by adding an acid such as sulfuric acid, nitric acid or hydrochloric acid. The concentration of the acid is determined according to the nature of the additive.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to an embodiment. First, a SiO ₂ glass layer containing 15 to 25% by weight of GeO ₂ , for example, is formed on the inner wall of a quartz glass pipe by a gas-phase internal method (MCVD method).
3 layers are laminated. In this case, the glass is sequentially made into a transparent glass, and only the innermost layer is sooted in a porous state. The deposition temperature is 1650 ° C. or higher when the material is made transparent, and 1 μm is required for forming porous soot.
Adjust to a temperature in the range of 550-1600 ° C. Next, a dispersion liquid to be impregnated into the soot phase is prepared as follows.
The above metal alkoxide dissolved in an alcohol such as ethanol, is mixed with dilute aqueous solution of an inorganic acid such as HCl is hydrolyzed, to replace the alcohol with water Al ₂
A colloidal dispersion of a metal oxide such as O ₃ was prepared.
The concentration of the metal oxide is preferably from 10 to 20% by weight. The resulting dispersion, for example, by dissolving the inorganic salts of rare earth elements such as ErCl ₃ · 6H ₂ O to obtain a dispersion containing metal and rare earth elements.

The obtained dispersion is injected and allowed to stand by sealing one end of a quartz glass tube containing the soot body formed above, and when the liquid has permeated the entire soot layer, the residual dispersion is poured out and dried. Removing water, and then heat-clearing the soot body,
Solidify to make a preform. The amount of the metal oxide added to the core of the obtained preform is generally in the range of 0.5 to 10% by weight. No crystals or bubbles are generated in the glass body, and the metal oxide is uniformly dispersed in the core. When the additive is Er, if the above preform is made into a fiber and the optical amplification characteristics are evaluated, an EDF (Er-doped fiber) having excellent amplification characteristics can be obtained. Regarding the dependency of the amplification characteristics of EDF on the concentration of Al added, 1997 IEICE General Conference (C-3-88)
Reports.

According to the present invention, by using a sol in which ultrafine particles (particle diameter of 10 to 100 nm) are dispersed in a liquid, the immersion solute does not substantially cause crystal growth of a salt accompanying drying. It becomes possible to use a high concentration component dispersion. Due to this effect, even when a high concentration is added, glass can be formed without causing aggregation due to crystallization of the additive salt. It is desirable for the uniformity of the additive component that the particle size of the SiO ₂ -based porous material is 500 to 1000 nm and the particle size of the additive fine particles is sufficiently smaller than that. 1 / diameter
It is preferably 10 or less, particularly 10 to 40 mm.

[0014]

The present invention will be described in more detail with reference to the following examples, which are not intended to limit the present invention. (Example 1) Al (O (CH ₃ ) ₂ CH) ₃ [aluminum isoproxide] was used as a starting material. After dissolving aluminum isoproxide in ethanol, a 0.001 N (N) aqueous HCl solution was stirred and mixed, and Al ₂ O ₃ fine particles were formed by a hydrolysis reaction. Thereafter, ethanol was replaced with water to prepare an Al ₂ O ₃ colloidal dispersion. The concentration of Al ₂ O ₃ in the dispersion was 15% by weight.
The ErCl ₃ · 6H ₂ O in the dispersion liquid by dissolving 0.005 N, and the immersion starting dispersion containing Er and Al. The soot body for immersion is composed of two pieces of GeO ₂ inside a quartz glass pipe.
An SiO ₂ glass layer containing 0% by weight is internally vapor-phased (M
After laminating six layers by CVD method, the temperature at the time of deposition was 1550 ° C., and one soot layer having the same composition was formed. In the step of impregnating the soot body with the dispersion, one end of the glass tube containing the deposited soot body is sealed, and the starting dispersion for immersion containing Er and Al is injected from the opposite end and allowed to stand. When the liquid permeated, the residual dispersion liquid was poured out, and water was removed in a dry air flow. Thereafter, the Er / Al-containing soot body was heated to be transparent and solidified to obtain a preform. The amount of Al ₂ O ₃ added at the center of the core of the obtained preform was 20% by weight.
In addition, no crystal or bubbles were generated in the glass body during the heat treatment steps of heat transparency and solidification.

Example 2 A commercially available acid-stable colloidal Al ₂ O ₃ was used for immersion addition. The product is Alfa
2 which is generally available from the company as product number 625443
A 0% by weight alumina colloid solution (HNO ₃ stable type) was used. The ErCl ₃ · 6H ₂ O in the above product was dissolved 0.005 N, and the immersion starting dispersion. The step of impregnating the soot for immersion with the dispersion liquid was performed in the same manner as in Example 1. The amount of Al ₂ O ₃ added at the center of the core of the obtained preform was 30% by weight. In addition, no crystal or bubbles were generated in the glass body during the heat treatment steps of heat transparency and solidification.

(Example 3) Al ₂ O ₃ ultrafine particles were added to 0.0
A dispersion obtained by dispersing 15% by weight in a 001N HNO ₃ aqueous solution was used. Al ₂ O ₃ has a particle diameter of about 0.03 μm manufactured by a gas phase synthesis method, and is commercially available as σ-Al ₂ O ₃ from Degussa and the like.
The ErCl ₃ · 6H ₂ O in the dispersion liquid by dissolving 0.005 N, and the immersion starting dispersion. The step of impregnating the soot for immersion with the dispersion liquid was performed in the same manner as in Example 1. The amount of Al ₂ O ₃ added at the center of the core of the obtained preform was 25% by weight.
Met. In addition, no crystal or bubbles were generated in the glass body during the heat treatment steps of heat transparency and solidification. Al ₂ O
The addition of ₃ is effective in adjusting the refractive index and preventing association of rare earth elements such as Er.

Comparative Example 1 Al_TwoO_ThreeAl as raw material
(NO_Three)_ThreeWas used. The solubility limit in aqueous solution is 77
(G / 100 g water) at this concentration_TwoO_ThreeConversion
The resulting concentration is 10.9% by weight. This Al (NO_Three)
_ThreeErCl to saturated solution_Three・ 6H_Two0.005N dissolved O
Thus, a starting dispersion for immersion was obtained. Dispersion in soot for immersion
The liquid impregnation step was performed in the same manner as in Example 1. Heat clarification,
Crystallization is seen in the glass body during the heat treatment process of solidification,
About half of the total length of the preform cannot be solidified.
Al in the center of the core of the obtained preform_TwoO _ThreeAmount added
Is 10% by weight, and the yield of Al is lower than that of the colloidal dispersion.
It became a low value.

Using the preform obtained in the above example,
Fibers were used to evaluate the optical amplification characteristics. Amplification characteristics
For comparison of evaluation, the conventional immersion method uses Al
_TwoO _ThreeProperties having a concentration of 3 to 5% by weight were also evaluated.
FIG._TwoO_ThreeThe relationship between the density and the bandwidth is shown. Implementation
In Examples 1 to 3, it can be seen that the bandwidth is increased. E
DF has a gain in the 1525-1565 nm band.
Is the band specified in the part of the gain dent around 1537 nm
The entire region as low as 0.5 dB is considered. In that case,
The protruding part of the gain shows the long-period fiber grating after amplification.
Narrow-band fill using fiber or fibre-perot etalons
Can be achieved by combining and removing
You.

[0019] 20 shows a diagram plotting the gain band to the concentration of Al ₂ O ₃ as 2, the bandwidth expanded according concentration of Al ₂ O ₃ is increased, as illustrated in the Examples 1-3
It is understood that a band of 36 to 37 nm can be obtained at 30% by weight.

The steps described above are based on the Er-doped optical fiber.
This is related to improvement of amplifier fiber.
Can be applied to optical fibers for other uses as shown in the following examples.
Can be used. In the core glass of the optical fiber, T
iO_TwoAnd SnO_TwoOxides whose valence is easily changed such as
By adding, the change in valence due to ultraviolet light irradiation
It is possible to change the refractive index. An example of applying this
And the GeO in the core of the optical fiber_TwoTo 240nm band
Irradiation of light causes a change in the refractive index due to a change in absorption, etc.
Thus, various devices can be manufactured. As an example, the sub
Refractive index change in the order of μm in the range of 2 to 40 mm
To create a Bragg grating in the fiber core
Formed and used as a cut-off filter or wavelength splitter / combiner
Wear. TiO_TwoAnd SnO _TwoIs GeO_TwoBasic absorption compared to
Is at a long wavelength, so it is easy for the refractive index to change.
Are known. TiO_TwoIs TiCl_FourLike chloride
Relatively high vapor pressure, refractive index rising early in optical fiber development
It has been widely used as an oxide for use. SnO_TwoIs chloride
Because the vapor pressure of the raw material is low_TwoO_ThreeSame as
As described above, it has been conventionally difficult to add a high concentration.

Example 4 Commercially available alkali-stable roller
Id SnO_TwoWas used for immersion addition. The product is Al
Generally available from fa as product number 39780
15% by weight SnO _TwoA colloid solution was used. In addition,
Sb is added to the liquid dispersion. Keep the above products,
This was used as a starting dispersion for immersion. Dispersion into soot for immersion
The impregnation step was performed in the same manner as in Example 1. The obtained prefor
SnO in the center of the core_TwoThe addition amount was 25% by weight.
Was. In addition, the heat treatment process of heat transparency and solidification
No crystals or bubbles were generated. Obtained Prif
The relative refractive index difference of the core is 2.2%, which is equivalent to a core diameter of 3.5.
μm and a cladding diameter of 125 μm to make an optical fiber.
Was. Using this fiber, an excimer
Laser light as a light source and a 1.55 μm wavelength reflection filter.
Created my bug rating. At this time, the fiber
No hydrogen treatment, but with a grating length of 5 mm
The transmission attenuation was 45 dB. UV-induced refraction at this time
The rate of change is 5.63 × 10^-FourIt was calculated.

Comparative Example 2 For comparison, preforms of SiO ₂ cladding and GeO ₂ / SiO ₂ cladding were prepared by MCVD so that the relative refractive index difference was 2.2%, and this was used as a core diameter. An optical fiber was drawn with a diameter of 3.5 μm and a cladding diameter of 125 μm. Using this fiber, a fiber grating for reflection at a wavelength of 1.55 μm was produced using an excimer laser beam having a wavelength of 247 nm as a light source. When the fiber was not subjected to hydrogen treatment, the transmission attenuation was 15 dB at a grating length of 5 mm. At this time, the amount of change in the ultraviolet-induced refractive index was calculated to be 2.30 × 10 ⁻⁴ . Comparing Example 4 with Comparative Example 2, it can be seen that an ultraviolet-induced refractive index change of about 2.4 times can be produced with the same relative refractive index difference.

TiO ₂ is also available as a product number 40460 from Alfa, which is dispersed in a mixture of 30% by weight of water and polyethylglycol. Addition was possible. T
iO ₂ may be added to the outermost layer of the preform in order to improve the static fatigue characteristics of the fiber by applying a compressive force. This technique can be applied to still another compound. For example, La ₂ O ₃ , Y ₂ O ₃ , Zn
O and In ₂ O _3, like the addition of Al ₂ O _3, it is considered to be effective in expansion of the optical amplification band, and if the decomposition of the salt or oxide is likely to occur, very compared to SiO ₂ It is difficult to add to SiO ₂ because of its high melting point. However, these oxides can also be added using this technique.

Example 5 Ultrafine ZnO particles were added to pure water for 15 minutes.
A dispersion having a weight% dispersion was used. ZnO is metal evaporation,
It has a particle diameter of 0.02 μm center manufactured by the oxidative synthesis method.
Commercially available as O. ErCl to the dispersion liquid ₃ - 6
Of H ₂ O was dissolved 0.005 N, and the immersion starting dispersion. The step of impregnating the soot for immersion with the dispersion liquid was performed in the same manner as in Example 1. Z at the center of the core of the obtained preform
The amount of nO added was 30% by weight. Also, heat transparency,
No crystals and bubbles were generated in the glass body during the heat treatment step of solidification. The relative refractive index difference of the obtained preform is
An optical fiber was drawn at 2% with a core diameter of 4 μm and a clad diameter of 125 μm. Using this fiber, the optical amplification band was measured by Er in the same manner as in Examples 1, 2, and 3. The excitation wavelength is 1.48 μm. When the band was determined from the obtained spectrum in the same manner as in Examples 1, 2, and ₃ , the effect was 37 nm, which was equivalent to that of Al ₂ O ₃ . The addition of Y ₂ O ₃ was also confirmed.

[0025]

According to the present invention, a dispersion (sol) in which ultrafine particles are dispersed in a liquid is used for impregnation of a soot body, so that a high-concentration component dispersion can be used, and salt crystals accompanying drying can be used. Growth is virtually eliminated. Thereby, even if high concentration is added, glass formation can be performed without causing aggregation due to crystallization of the additive salt.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an Al ₂ O ₃ concentration and a bandwidth for comparing an example of the present invention with a conventional example.

FIG. 2 shows Al ₂ O ₃ to clarify the effect of the present invention.
The graph which plotted the gain band at the density | concentration (20-30 weight%).

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Motoki Tsunoi 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (4)

[Claims] 1. A porous soot obtained by a gas phase synthesis method is impregnated with a mixed solution in which fine particles of an additive are dispersed, dried, and then heated to produce a vitrified transparent material. A method for manufacturing a glass article. 2. A method of manufacturing a glass preform for an optical fiber having a core and a clad, comprising forming a porous soot mainly composed of SiO ₂ on an inner wall of a glass tube to be a clad by a gas phase synthesis method. A method for producing a glass preform for an optical fiber, comprising impregnating a mixed solution in which fine particles of an additive are dispersed in a porous soot body, and then drying, heating, clearing, and solidifying. 3. The method according to claim 1, wherein the additive fine particles have a particle size of 10 to 100 nm. 4. The method according to claim 1, wherein the concentration of the fine particles in the mixture is 10% by weight or more.