JPH0558664A - Optical fiber base material manufacturing method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for manufacturing an optical fiber preform that can be used, for example, for manufacturing a fiber for an optical fiber laser and an optical amplifier. According to the present invention, there is provided a method for producing an optical fiber preform having a core and a cladding, the core of which is doped with a dopant compound, wherein the inner wall of the glass tube to be the cladding contains the dopant compound containing Si oxygen as a main component. After forming a glass film with a higher refractive index than the tube by the sol-gel method,
It is characterized by forming a core by collapsing. The addition of compounds of rare earth elements as dopant compounds is a particularly preferred embodiment of the invention. According to the present invention, a dopant such as a rare earth element can be uniformly added to the core at a high concentration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a base material for an optical fiber used for an optical fiber laser, an optical amplifier fiber and the like.

[0002]

2. Description of the Related Art Conventionally, rare earth elements have been added to silica-based fibers.
Gas phase addition method and solution impregnation method are known as addition methods.
It As an example of the vapor phase addition method, a quartz pad is formed by the MCVD method.
When synthesizing the coating on the inside of the ip
Is SiCl_FourAnd GeCl _FourWith steam of 1
The rare earth compound is heated at around 000 ° C, and this vapor is converted into quartz.
Transfer to a pipe and heat with a burner to vitrify.
Draw the pipe obtained by collapsing and drawing
There is a method to make fiber.

As an example of the solution impregnation method, there is a method of using a soot for core prepared by the VAD method. In this method, the rare earth compound is dissolved in alcohol, and the soot base material for core is immersed in this. Next, the alcohol in the soot is evaporated at room temperature to deposit the rare earth compound in the soot for the core, and the sintering is performed under normal helium gas atmosphere conditions,
Transparent glass is formed to obtain an optical fiber preform.

[0004]

In order to apply the rare earth element-doped quartz glass fiber to an optical fiber laser or an optical amplifier fiber, it is desirable that the concentration of the dopant compound such as the rare earth element added is high. However,
In the conventional method, vitrification requires a high temperature of 1500 ° C. or higher, so even if an attempt is made to add it at a high concentration, the rare earth element is crystallized in the glass, and there is a problem that a uniformly added glass cannot be obtained. An object of the present invention is to solve the above problems and to provide a method for producing an optical fiber preform in which a high concentration of a rare earth element is uniformly added to a core.

[0005]

As a means for solving the above problems, the present inventors have formed a glass film doped with a rare earth element at a high concentration by using the sol-gel method, and use this as the optical fiber preform. I came up with the idea of applying it to the creation method of. That is, the present invention is a method of manufacturing an optical fiber preform having a core and a clad, in which the dopant compound is doped into the core, in which SiO 2 is formed on the inner wall of the glass tube to be the clad.
Provided is a method for producing an optical fiber preform characterized by forming a glass film containing a dopant compound containing ₂ as a main component and having a higher refractive index than the glass tube by a sol-gel method, and then forming a core by collapsing. .. In a particularly preferred embodiment of the present invention, silicon alkoxide,
SiO is formed by uniformly coating the inner wall of a glass tube with a sol-gel solution prepared by adding water, alcohol and acid to one or more metal alkoxides selected from titanium alkoxide, germanium alkoxide and aluminum alkoxide and further dissolving the dopant compound. It can be mentioned that a glass film containing ₂ as a main component and a dopant compound and having a higher refractive index than the glass tube is formed. It is also a particularly preferred embodiment that the dopant compound is a compound of a rare earth element.

[0006]

As a method for doping glass with a rare earth element, the vapor phase method and the solution impregnation method are known as described above. In these methods, a vapor of a rare earth element or a solution of a rare earth element is diffused in a porous body of silica glass synthesized by a vapor phase method to make the porous body into a transparent vitreous material. Need. The rare earth element added in the glass is uniformly dispersed in the case of a low concentration, but is easily crystallized in an attempt to add it in a high concentration. This tendency is more remarkable at higher temperatures, making it difficult to manufacture high-concentration added glass. By the way, as a method for synthesizing glass, the sol-gel method has a characteristic that glass is obtained by a relatively low temperature process of about 1000 ° C. using a silicon alkoxide as a glass raw material. According to this method, it is possible to synthesize glass doped with a rare earth element at a much higher concentration than the conventional method. Therefore, the inventors of the present invention have considered the application of this sol-gel method to the formation of the core portion to which the rare earth element is added, and have reached the present invention.

According to the present invention, as an optical fiber preform composed of a core and a cladding, a coating film doped with a rare earth element is formed on the inner surface of a glass tube serving as a cladding by a sol-gel method. This film is made into a transparent glass and a glass tube is collapsed. At this time, it is desirable to flow a mixed gas of chlorine gas and oxygen gas in the tube. By flowing chlorine gas, the water content of the coating film can be removed and a glass with low transmission loss can be obtained. Further, by flowing the oxygen gas, vaporization of the rare earth element in the glass can be prevented and stable doping can be performed at a high concentration. As described above, the optical fiber preform manufactured according to the present invention has a core / clad, and has a portion in which the rare earth element is doped at a high concentration in the core. It goes without saying that the outer diameter ratio of the core and the clad can be adjusted arbitrarily.

The present invention will be described more specifically. As the metal of the metal alkoxide used in the hydrolyzed solution of the sol-gel method according to the present invention, various metal alkoxides can be used, and particularly preferable examples include silicon, germanium, aluminum and the like, and methoxides and ethoxides thereof. , Propoxide, butoxide and the like are mentioned as preferable alkoxides. Examples of the alcohol used in the sol-gel method of the present invention include methanol, ethanol, isopropyl alcohol, butanol and the like. An acid or an alkali can be added as a catalyst. For example, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid or the like can be used as the acid, and ammonia water or the like can be used as the alkali. The composition ratio of the sol-gel solution (hydrolysis solution) may be in the range usually used in this kind of technical field, for example, the ratio of alcohol to water is about 0.5 to 5 times the molar ratio, and Generally, the amount of water to be added is about 2 to 5 times the molar ratio of the metal alkoxide, and the amount of acid as a catalyst is about 1 to 5 in pH. Examples of the dopant compound of the present invention include lanthanoid rare earths, and Er, Nd, Pr and the like are particularly preferable. These rare earth elements may be added to the sol-gel solution in the form of chloride, nitrate or the like.

[0009] the glass tube to Kuratsudo in the present invention may be those having a lower refractive index than the core, SiO ₂
When coating the film, a glass tube doped with fluorine is used, and when coating a film with an increased refractive index doped with titanium, germanium or the like, a tube made of either fluorine-doped glass or silica glass may be used.
As a method of attaching the sol-gel solution to the inner wall of the glass tube to be the cladding, there is a dip coating method, such as immersing the glass tube in the sol-gel solution and pulling it up at a constant speed, or filling the glass tube with the sol-gel solution and pulling it out at a constant speed. And coat. After the adhesion, it is dried and gelled by a technique known in this field, for example, at a temperature of 15
After drying at about 0 ° C, there is a method of heating at about 1000 ° C. As described above, a glass film containing SiO ₂ as a main component and a dopant compound as a main component and having a higher refractive index than the glass tube can be formed. Then, for example, a temperature of 1500 to 180
Although a glass rod is obtained by sintering at 0 ° C. and solidifying, it is preferable to flow a mixed gas of chlorine and oxygen as described above at the time of transparent vitrification of this film and collapse of the glass tube. The oxygen gas concentration in the mixed gas is preferably 10 to 60%. As a result, a glass base material including the core and the cladding to which the dopant compound is uniformly added is obtained.

[0010]

【Example】

Example 1 A core solution is prepared by the sol-gel method. Silicon ethoxide 50 ml, 1N hydrochloric acid 20 ml and ethanol 20 ml
1.6 g of erbium chloride was dissolved in the mixed solution. A glass rod doped with fluorine so as to have a refractive index lower than that of pure silica by 0.34% was produced by the VAD method, and a hole having a diameter of 4 mm was formed at the center. The outer diameter of this glass rod was 20 mm. This glass tube was immersed in the sol-gel solution and pulled up at a speed of 100 mm / min to coat the inner surface of the tube. The film thickness at this time was 2 μm. Next, in this glass tube, 50cc of chlorine,
While flowing 50 cc of oxygen, the glass tube was heated with an oxyhydrogen burner to vitrify the coating film, and the glass tube was collapsed to obtain an optical fiber preform. When this base material was drawn, the cladding diameter was 125 μm and the core diameter was 10 μm.
Fiber was obtained and analyzed by EPMA,
It was confirmed that the entire core was doped with 5% by weight of Er. Further, when the fluorescence lifetime was measured, it was 12 mse.
c. Thus, a value equivalent to the fluorescence lifetime when Er was uniformly dispersed was obtained.

Example 2 Silicon ethoxide 50 ml, titanium isopropoxide 0.86 ml, 1N hydrochloric acid 20 ml and ethanol 20 ml
Were mixed and 1.6 g of erbium chloride was dissolved to prepare a coating solution. A 4 mm hole was directly drilled in a pure silica rod prepared by the VAD method. The outer diameter of the glass rod was 20 mm. The opening was filled with the sol-gel solution, and a valve previously attached to the lower part of the glass tube was opened to withdraw at a constant speed for coating. The film thickness was 2 μm. Thereafter, the same treatment as in Example 1 was carried out to obtain an optical fiber preform. When this base material was drawn, a fiber with a clad diameter of 125 μm and a core diameter of 10 μm was obtained, and it was confirmed by EPMA that 5 wt% Er was doped in the entire core, and the fluorescence lifetime was 12 mse.
c. Met. Also, when the refractive index of the core was measured,
It was found to be 0.35% higher than the clad of pure silica.

[0012]

As described above, according to the present invention, an optical fiber preform having a high concentration of a dopant compound added to the core can be obtained. Therefore, a highly efficient fiber laser and an optical amplifier with a high gain can be obtained. It is possible to produce a fiber for use.

Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location G02B 6/00 356 A 7036-2K

Claims (3)

[Claims] 1. A method for producing an optical fiber preform having a core and a clad, the core of which is doped with a dopant compound, wherein the inner wall of the clad glass tube contains a dopant compound containing SiO ₂ as a main component. A method for producing an optical fiber preform, comprising forming a glass film having a higher refractive index than that of a sol-gel method and then performing collapsing to form a core. 2. A sol-gel solution prepared by adding water, alcohol and acid to at least one metal alkoxide selected from silicon alkoxide, titanium alkoxide, germanium alkoxide and aluminum alkoxide, and further dissolving a dopant compound therein. The method for producing an optical fiber preform according to claim 1, wherein a glass film containing a doping compound containing SiO ₂ as a main component and having a higher refractive index than the glass tube is formed by uniformly coating the glass tube. 3. The method of manufacturing an optical fiber preform according to claim 1, wherein the dopant compound is a compound of a rare earth element.