JP3194213B2 - Manufacturing method of optical amplification fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a fiber for optical amplification, and more particularly to a method for manufacturing a fluoride optical fiber for optical amplification with low loss and high efficiency.

[0002]

2. Description of the Related Art Fluoride optical fibers are attracting attention as a good host medium for lasers and optical fiber amplifiers because fluoride glass has a low phonon energy. In particular, a rare-earth-doped fluoride optical fiber in which rare-earth ions are added to a core is a medium that can obtain a high optical amplification gain in a wavelength region used for optical communication. Among these rare earth ions, Pr is an ion capable of amplifying light of 1.3 μm, which is a main wavelength band used for communication, and P
An optical amplifier using a fluoride optical fiber doped with r has been manufactured. An optical fiber used for a high-efficiency optical fiber amplifier needs to have a sufficiently high light intensity in the core, and therefore needs to have a large relative refractive index difference and a small core diameter. Further, it is necessary that the loss of the fiber is as small as possible.

In order to reduce the diameter of the core, thermal processing of the glass is repeated several times in the fiber manufacturing process. The surface of the glass base material or jacket tube is polished prior to thermal processing, but OH groups or water molecules penetrate into the flaws created by polishing on the surface. Occurs. This crystal causes a structural irregular scattering loss of the fiber or a significant decrease in the strength of the fiber.

[0004] As a solution to this problem, after polishing the surface of the base material or jacket tube, the surface of the glass is made of ZrOC.
How to remove scratches caused by the etching was polished in hydrochloric acid solution of l ₂ it has been used. However, this method has the drawback that if the concentration of the solution is not selected, the hydrolysis of the surface proceeds or the surface becomes rough. Even if the surface is smoothed by etching, crystallization occurs during the drawing process unless the adsorbed OH groups or water molecules are removed.
As a method for preventing this, a method of performing a heat treatment in a gas containing fluorine or a method of introducing a gas containing fluorine into a drawing atmosphere has been used. In this case, it is necessary to heat to a high temperature in order to sufficiently advance the fluorination, and there is a drawback that a remarkable effect cannot be obtained below the crystallization temperature of the glass. As a solution to this, there is a method of using HF having a high activity against fluorination from a low temperature as a fluorinating agent. However, since HF has a property of easily associating with water molecules by hydrogen bonding, commercially available HF is used.
It contains 30 ppm or more of water as an impurity. The free energy of the hydrolysis reaction of the fluoride glass surface by water is large, and even if a very small amount of water is present, the surface hydrolysis reaction occurs and crystallization proceeds, so that the fluorinating agent must be removed unless the water in the HF is removed. Does not work effectively. As described above, since the contamination of water in HF is caused by its high chemical affinity, there is no means capable of effectively removing water.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing an optical fiber for optical amplification having a low loss and a high strength, which solves the above problems and disadvantages.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned drawbacks, a method for manufacturing an optical amplifying fiber according to the present invention comprises:
Work to stretch the optical fiber preform made of fluoride glass
For optical amplification including a step of drawing and / or drawing.
In the method for producing iba , prior to drawing or drawing, the surface of a glass tube used as a base material and / or a jacket tube is made of 0.005 to 0.1 mol / l of ZrO.
Etching with a 0.005 to 0.2 mol / l HCl aqueous solution containing Cl ₂ ,
Base material and / or jacket tube, F ₂ in HF
HF and F containing at least one molar ratio based on the water content of
It is characterized in that heat treatment is performed in a gas containing ₂ .

Further, in the present invention, when the optical fiber preform and / or the jacket tube after the etching by the above method are heat-treated in a gas containing HF and F ₂ ,
The heating temperature is 50 ° C. or more and 300 ° C. or less.

In the present invention, a base material or a jacket tube having a smooth surface can be manufactured by using a concentration of an etching solution which does not cause hydrolysis or roughening of the surface. By removing the adsorbed OH groups and water molecules with a fluorinating agent, it becomes possible to produce a high-quality optical amplification fiber without crystallization. In particular, by adding an appropriate amount of F ₂ to HF, the water in HF can be changed to HF and O ₂ , and the fluorination reaction on the surface can effectively proceed.

Therefore, according to the present invention, it is possible to stably produce an optical amplification fiber having low loss and high strength.

Next, the present invention will be described in detail with reference to examples.

[0011]

The present invention will be described below with reference to examples.
The present invention is not limited thereby.

[0012]

Example 1 As a representative of ZrF ₄ -based fluoride glass, 4
8ZrF ₄ -23BaF ₂ -2.5LaF ₃ -2YF _3-
4.5AlF ₃ using a glass rod of the composition of -20NaF (mol%). 220-400-6 using water-resistant abrasive paper
The surface was polished in the order of 00-800-1000-1500-4000. In polishing No. 4000, the surface appears slightly cloudy due to polishing scratches. The polished glass rod was immersed in a hydrochloric acid solution of ZrOCl ₂ and etched for 10 minutes while stirring the solution with a stirrer.
After etching, the rod was washed with water and dried with ethanol, and the surface state was observed with a scanning electron microscope. Table 1 shows the results.

As is evident from Table 1, in a region where the concentration of the hydrochloric acid solution of ZrOCl ₂ is high, the etching of the surface proceeds, but the surface is roughened by about 5 to 50 μm.
This indicates that selective etching of a specific component proceeds. On the other hand, on the low concentration side, the polishing scratches were not sufficiently removed, and as a result of etching for further 10 minutes,
Fine precipitates adhered to the surface and became cloudy. As a result of the analysis, this attached substance was composed of Zr and O, and because the concentration of the etching solution was low, the hydrolysis proceeded faster than the etching. The region where the surface roughness is 0.1 μm or less by electron microscope observation is defined as a concentration of 0.005 to 0.1 mol / l of ZrOCl _{2 in} a hydrochloric acid solution.
rOCl ₂ , ranging from 0.005 to 0.2 mol / l HCl.

Based on these results, 56
ZrF ₄ -20BaF ₂ -8PbF ₂ -2.5LaF ₃ -2
YF ₃ -4.5AlF ₃ -7LiF, 50HfF ₄ -15.7BaF ₂ -3.3CaF _2- as cladding glass
2.5LaF ₃ -2.0YF ₃ -4.5AlF ₃ -5.5
Fibers were made using NaF-16.5KF. At this time, the fiber was prepared by inserting a preform prepared by a suction method into a jacket tube, stretching it, and then inserting it again into the jacket tube and drawing to produce a single mode fiber. UV-cured alkylate resin was used as the fiber coating material. At this time, the surface of the base material, the surface of the jacket tube, and the surface of the drawn base material were all treated with the etching solution shown in Table 1 for 10 minutes.
Etched for minutes.

Table 1 shows the measured results of the loss of the prepared fiber at 1.2 μm and the tensile strength of the fiber. What is the transmission loss and strength? 0.1 dB in a region where the surface roughness observed by an electron microscope is 0.1 μm or less.
/ M or less and 700 MPa or more. These values are the loss required to realize a practical gain factor of 0.2 dB / mW, the strength required from the viewpoint of practical handling and reliability, and these can be realized from the results in Table 1. The concentration of the etchant is 0.005 to 0.1mo
1 / l ZrOCl ₂ , 0.005 to 0.2 mol / l
Is clearly in the range of HCl.

In this embodiment, ZrF ₄ is used as the glass.
Although one kind of glass composition of a fluoride glass having ZrF ₄ as a main component was used, a glass having a high strength can be produced by using the etching solution of the present invention with any glass as long as the glass has ZrF ₄ as a main component. did it. Furthermore, the same effect as in the present embodiment was obtained for glass containing HfF _4, InF ₃ , or CdF ₂ as a main component.

By using the concentration range of the etching solution of the present invention, an optical fiber with low loss and high reliability was manufactured.

[0018]

The surfaces of the fluoride glass base material and the jacket tube whose surfaces were etched as described above were heat-treated in an HF gas stream. Table 2 shows the processing conditions, the tensile strength of the produced fiber, and the loss at 1.2 μm. In the HF used for this heat treatment, 20 ppm of water is mixed in as impurities. For this reason, a trace amount of F ₂ was added as a water removing agent, as a removing agent for water generated by the reaction between the oxide on the glass surface and HF, and as a fluorinating agent for the glass surface. As is clear from Table 2, H
Strength and loss of the fiber sharply improved by the addition of an equivalent amount or more of F ₂ with respect to water content in F.

FIG. 1 shows the measurement results of gas components at 100 ° C. Water to it can be seen that the water the gas increases the amount of F ₂ is rapidly decreased. For this reason, the water generated when the oxide on the base material surface is fluorinated with HF can be changed to HF by F ₂ , and the partial pressure of water in the atmosphere can be kept low. As a result, the water generated by the fluorination reaction can be kept below the equilibrium partial pressure, and oxygen impurities on the surface of the glass can be effectively removed. Further, as is clear from Table 2, when the temperature of the heat treatment is in the range of 50 ° C to 300 ° C, 700M
A fiber having a tensile strength of Pa or more and a transmission loss at 1.2 μm of 0.05 dB / mW or less was produced. At temperatures below 50 ° C in this temperature range, HF and F ₂ used as fluorinating agents are not sufficiently activated, and the fluorination rate is not sufficient. At temperatures above 300 ° C, crystallization of the fluoride glass itself occurs, resulting in strength and loss. The characteristics deteriorate. Therefore, in order to effectively bring out practical characteristics, the heat treatment temperature of the base material or the jacket tube needs to be in the range of 50 ° C to 300 ° C.

As a result, it has been clarified that a high-strength, low-loss fiber for optical amplification can be produced by heat treatment in a mixed gas stream of HF and F ₂ .

[0022]

[0023]

[0024]

Example 2 The glass used for fabricating the fiber was InF ₃
The surface treatment was performed in the same manner as in Example 2 except that the same etching liquid as in Example 1 was used except that the main component was. Table 3 shows the results. As is clear from the table, ZrF
Fiber strength and loss were also improved in glass containing InF ₃ as a main component as in glass containing ₄ as a main component. Therefore, it has been clarified that the concentration of the etching solution and the treatment in a mixed gas of HF and F ₂ are effective methods for producing a high-strength and low-loss optical amplification fiber.

[0025]

[0026]

Example 3 The glass used for producing the fiber was HfF ₄
The surface treatment was performed in the same manner as in Example 2 except that the same etching liquid as in Example 1 was used except that the main component was. Table 4 shows the results. As is clear from the table, ZrF
_As with the glass containing _four main components, the strength and loss of the fiber were improved in the glass containing HfF ₄ as the main component. Therefore, the concentration of the etching solution and the treatment in a mixed gas of HF and F ₂ are effective methods for producing a high-strength and low-loss optical amplification fiber even when a glass mainly containing HfF ₄ is used. It became clear that it was.

[0027]

[0028]

[0029]

Embodiment 4 The glass used for producing the fiber is CdF ₂
The surface treatment was performed in the same manner as in Example 2 except that the same etching liquid as in Example 1 was used except that the main component was. Table 5 shows the results. As is clear from the table, ZrF
₄ strength and loss of fiber also in glass mainly composed of glass as well as CdF ₂ mainly composed of is improved. Therefore, the concentration of the etching solution and the treatment in the mixed gas of HF and F ₂ are effective methods for producing a high-strength and low-loss fiber for optical amplification even using a glass containing CdF ₂ as a main component. It became clear that it was.

[0030]

[0031]

[0032]

As described above, according to the present invention, a low loss and high strength of an optical fiber can be realized.
As a result, high reliability, which is essential for practical use,
An optical amplifier with high characteristics can be easily configured. Therefore, by doping light-emitting ions such as Pr, Nd, and Er, it is possible to increase the efficiency and reliability of optical amplification at various wavelengths, so that the cost and performance of the optical communication system can be reduced. There is.

[Brief description of the drawings]

FIG. 1 shows measured HF and F in Example 2 of the present invention.
Shows the F ₂ dependent moisture concentration in the atmosphere including _2.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasutake Oishi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Yoshiki Nishida 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Kenji Kobayashi 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Shoichi Sudo 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-4-16524 (JP, A) JP-A-3-103338 (JP, A) JP-A-6-1634 (JP, A) W. SCHNEIDER et al. 'Fluoride glass etching method of preparation of infra-red fiber with with tensile strength,' Electronics Letters, Vol. 22, No. 18, p. 949-950, (1986) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03B 37/012

Claims (2)

(57) [Claims] 1. A method of manufacturing a fiber for optical amplification, comprising a step of drawing and / or a step of drawing a base material for an optical fiber made of a fluoride glass, as a base material and / or a jacket tube prior to drawing or drawing. The surface of the glass tube to be used is 0.005 to 0.1 mol /
0.005 to 0.2 mol / l containing 1 ZrOCl ₂
Etch with an aqueous solution of HCl .
The optical fiber preform and / or jacket tube is
₂ in a molar ratio of 1 or more to the water content in HF
A method for producing a fiber for optical amplification, comprising performing heat treatment in a gas containing HF and F ₂ . 2. The method according to claim 1, wherein the heating temperature of the base material and the jacket tube in the gas containing HF and F ₂ is 50 ° C. or more and 300 ° C. or less. .