KR100619342B1 - Method of manufacturing optical fiber in mcvd - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber, and more particularly, to a method for manufacturing an optical fiber containing low hydroxyl ions, which can increase productivity by setting a low deposition volume of a clad layer.

To this end, the present invention uses an anhydrous heat source such as an electric resistance furnace as the moving heat source used in the MCVD process, and the deposition volume of the core layer of the core of the optical fiber base material is 1/3 or more and 1 / of the deposition volume of the clad layer. It is characterized by setting to 1.2 or less.

In the case of the optical fiber manufactured by the method of the present invention, absorption loss by OH-group is 0.340 dB / km or less at 1.31 μm, 0.400 dB / km or less at 1.38 μm, and 0.200 dB / km or less at 1.55 μm.

Optical fiber, absorption loss, deposition volume

Description

Optical fiber manufacturing method {METHOD OF MANUFACTURING OPTICAL FIBER IN MCVD}

The following drawings attached to this specification are illustrative of preferred embodiments of the present invention, and together with the detailed description of the invention to serve to further understand the technical spirit of the present invention, the present invention is a matter described in such drawings It should not be construed as limited to

1 is a schematic diagram of a crystal chemical vapor deposition (MCVD) apparatus according to the present invention.

FIG. 2A is a view for explaining a process of depositing a cladding layer on an inner wall of a quartz tube using the apparatus of FIG. 1.

FIG. 2B is a view for explaining a process of depositing a core layer on an inner wall of a quartz tube on which a clad layer is deposited using the apparatus of FIG. 1.

3 is a cross-sectional view of the optical fiber hollow base material manufactured through FIGS. 2A and 2B.

4 is a longitudinal cross-sectional view of an optical fiber base rod manufactured by closing the hollow base material of FIG. 3 through a condensation process.

5 is a device for overcladding an optical fiber base rod using a large diameter quartz tube.

6 is a schematic configuration diagram of an apparatus for cutting an optical fiber using an over clad preform.

7 is a graph showing the absorption loss according to the wavelength of the optical fiber core layer by comparing the conventional method with the method of the present invention.

8 is a flowchart illustrating a method of manufacturing an optical fiber according to the present invention.

<Description of main parts of drawing>

              40: core 30: clad

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber, and more particularly, to a method for manufacturing an optical fiber containing low hydroxyl ions, which can increase productivity by setting a low deposition volume of a clad layer.

In optical fiber manufacturing, the final substrate is suspended vertically and moved into the edge at a controlled speed. The base material is softened in the furnace and freely withdrawn from the molten end of the base material by a capstan located at the base of the cutting column. The present invention relates to such a base material and an optical fiber drawn from the base material and a method of manufacturing the same.

The optical fiber base material is a cylindrical solid rod having a refractive index profile suitable for guiding light. The amount of optical fiber drawn out from this base material is directly proportional to the size of the base material. Therefore, using a larger base material can significantly reduce the manufacturing cost of the optical fiber.

Various processes for manufacturing the optical fiber base material have been proposed. In particular, Modified Chemical Deposition (MCVD) is known which forms the refractive index of the base material by depositing glass particles on the inner wall of the quartz tube.

This MCVD method has a disadvantage in that the size of the optical fiber base material is limited due to the low glass deposition rate. During the MCVD process the glass soot is deposited on the inner surface of the quartz tube and sintered at the same time. At this time, an acid and a hydrogen burner are used a lot as a heating source.

Multiple thin layers of cladding material are deposited first, followed by multiple thin layers of core material. The diameter of the deposited core is represented by d and the diameter of the deposited clad is represented by d.

In order to form an ideal refractive index profile, only the core material should be deposited on the inner wall of the quartz tube. In this state, the ratio of cladding / core (D / d) is 1.00. In this case, however, the absorption loss due to hydroxyl ions (OH-) in the signal transmission region (especially 1383 nm) of the optical fiber cannot be effectively lowered.

Therefore, conventionally, an optical fiber in which a cladding layer is disposed before the core layer is formed on the inner wall of the quartz tube and the cladding / core (D / d) ratio is set to at least 7.5 has been reported. However, when the cladding layer relatively thicker than the core layer is disposed in this way, the absorption loss due to hydroxyl ions (OH-) can be significantly lowered, but the number of deposited layers is increased, resulting in a problem of low productivity.

Korean Patent Laid-Open Publication No. 1999-7119 proposes a method for manufacturing a single mode optical fiber having an outer diameter ratio (D / d) of clad to core of 7.5 or less, and Korean Patent Laid-Open Publication No. 2000-11715 discloses that a deposited core material is weak. A method of fabricating an optical fiber having a diameter larger than 5 mm and an outer diameter in which the deposited cladding material is less than about 15 mm is proposed.

One of the reasons for the increase in the concentration of hydroxyl ions in the core layer of the optical fiber is that the hydroxyl ions or the hydrogen component formed on the surface of the quartz tube diffuse into the core layer due to the acid and hydrogen burners. Therefore, the adoption of an anhydrous heat source (for example, a plasma torch or a heating furnace) that does not generate hydroxyl ions or hydrogen components is considered.

As such, when an anhydrous heat source other than an acid or hydrogen burner is used as the heat source of the MCVD process, it is necessary to properly adjust the ratio of the deposition amount of the clad layer to the deposition amount of the core layer in consideration of the manufacturing time and productivity of the optical fiber base material. There is. That is, compared to acid and hydrogen burners, the anhydrous heat source generates less hydroxyl ions or hydrogen components penetrating the core layer, so that the deposition volume of the clad layer can be set lower.

In the MCVD process, thick deposition of the cladding layer is intended to prevent diffusion of hydroxyl ions or hydrogen components from the outside air (especially the heat source) to the core layer. This has been pointed out as a cause of lowering the manufacturing efficiency and productivity of the MCVD process.

Accordingly, the present inventors propose a method of maintaining an absorption loss by adopting an anhydrous heat source such as a heating furnace and reducing the deposition volume of the clad layer to increase the manufacturing efficiency and productivity of the MCVD process.

That is, the present invention is characterized by providing an optical fiber manufacturing method having a low absorption loss, high manufacturing efficiency and productivity. To this end, the present inventors provide a deposition volume ratio of the core layer and the clad layer that can increase productivity while maintaining optical characteristics such as absorption loss.

Optical fiber manufacturing method according to an aspect of the present invention

Depositing a cladding layer having a deposition volume V _clad by heating the tube using an anhydrous heat source while introducing the cladding forming material into a quartz tube having a low hydroxide ion (OH−) level; Depositing a core layer having a deposition volume V _core by heating the tube using an anhydrous heat source while injecting a core forming material into an inner surface of the tube on which the clad layer is deposited; (At this time, the core layer and the cladding layer are deposited to have a deposition volume (V _core ) of at least 1/3 of the deposition volume (V _clad ) of the cladding layer.)

Disintegrating the quartz tube in which the core layer and the clad layer are formed to generate a base rod; Disposing the base rod in a quartz tube having an inner diameter larger than an outer diameter of the base rod; Exposing the quartz tube and the base rod to a moving heat source for overcladding; And pulling the optical fiber core wire from the overclad optical fiber base material.

The absorption loss of the fabricated fiber should be less than 0.340dB / km at 1.31㎛, 0.200dB / km at 1.55㎛ and 0.400dB / km at 1.38㎛.

Preferably, the optical fiber manufacturing method of the present invention is characterized in that the core layer is deposited to have a deposition volume (V _core ) of 1 / 1.2 or less with respect to the deposition volume (V _clad ) of the _clad layer.

Moreover, another one aspect of this invention relates to the optical fiber base material manufactured by the manufacturing method mentioned above, and the optical fiber edge-lined from this base material.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the common or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

The optical fiber manufacturing method of the preferred embodiment according to the present invention comprises (1) a process of producing a hollow base material, (2) a process of forming a base rod by collapsing the hollow base material, and (3) using a large diameter quartz tube. And a step of overcladding the base rod, and (4) a step of drawing the optical fiber from the overclad optical fiber base material.

<MCVD apparatus>

1 illustrates a device for heating a quartz tube to produce a base rod by an MCVD process.

The MCVD apparatus of the present invention comprises a shelf 1 having a tail stock 10 and a head stock 8 for supporting the quartz tube 2 in a rotatable manner. One end of the quartz tube 2 is connected to the first dummy tube 4 by a weld joint 4a, and the other end is the second dummy tube by a weld joint 6a. 6). The first dummy tube 4 and the second dummy tube 6 are supported by the main shaft 8 and the tail stock 10, respectively.

Reactant containing impurities such as germanium and the reaction gas (3) containing oxygen is introduced into the tube (2) through the gas inlet pipe of the headstock (8), and then the outside through the exhaust pipe of the tailstock (10) To be discharged. The reaction gas introduced into the tube 2 is heated by the heat source 5 that moves while heating the outer circumferential surface of the quartz tube 2. As the heat source 5, an anhydrous heat source such as a plasma torch or a heating furnace is employed. In particular, in the case of the present invention, it is preferable to adopt an electric resistance furnace using graphite as a heating element as this heat source.

<Manufacture of optical fiber base rod>

1. Cladding layer forming step (see Fig. 2a)

A quartz tube having a low hydroxyl ion (OH-) concentration is selected, preferably a quartz tube having a hydroxyl ion concentration of 0.5 ppm or less (see S100 in FIG. 8). 8) and the quartz tube using the heat source 5 while blowing a mixture gas of soot forming gas (SiCl ₄ , GeCl ₄ , POCl ₃ ) and oxygen gas into the tube while rotating while supporting the tailstock 10. The temperature inside is heated to 1700 ° C or higher.

The soot forming gas introduced in the direction of the arrow in FIG. 2A generates soot 30a while oxidizing by heat conducted from the surface of the quartz tube 2, which moves to a relatively low temperature region within the tube. By the thermophoretic phenomenon is deposited on the inner wall of the tube.

As such, the quartz tube 2 having at least one layer of clad soot particles 30a deposited on the inner wall thereof is moved by moving the heat source 5 in the direction of the arrow in FIG. 2A after the deposition process is completed, as shown in the drawing. The soot 30a deposited on the inner wall is sintered and vitrified to form the sintered layer 30b.

When the deposition and sintering process is performed, a cladding layer 30 is formed, and the process is continuously repeated until the cladding layer has a desired thickness (see S200 of FIG. 8).

2. Core layer forming step (see Fig. 2b)

The temperature in the quartz tube is changed to 1700 ° C using the heat source 5 while blowing a mixture gas of soot forming gas (SiCl ₄ , GeCl ₄ ) and oxygen gas into the quartz tube 2 having the clad layer 30 formed thereon. Heating above.

The soot forming gas introduced into the quartz tube generates a soot 41a by oxidizing by heat conducted from the surface of the quartz tube 2, and the soot 41a moves to a relatively low temperature region within the tube. It is deposited on the cladding layer 30 by the thermophoretic phenomenon.

As described above, a hollow preform in which the cladding layer 30 and the core layer 40 are deposited on the inner wall 10 of the quartz tube by performing the cladding layer forming process and the core layer forming process is performed as shown in FIG. 3. Can be formed.

At this time, the cladding layer 40 of the hollow base material may have a relatively low deposition volume with respect to the deposition volume of the core layer 30, unlike the prior art. This is because the heat source used for performing the deposition process is an anhydrous heat source, not an acid or hydrogen burner. That is, in the case of the present invention, the clad layer 30 and the core layer 40 are deposited such that the deposition volume of the core layer is 1/3 or more and 1 / 1.2 or less with respect to the deposition volume of the clad layer.

If the deposition volume of the core layer 40 with respect to the cladding layer 30 is 1 / 1.2 or more, the thickness of the deposition cladding layer becomes too low to achieve a desired absorption loss, and if less than 1/3 Since the number of deposited layers of the cladding layer is increased, the production time and productivity of the hollow base material are deteriorated. (See S300 of FIG. 8)

The hollow base material thus prepared is formed into an optical fiber preform rod having a shape as shown in FIG. 4 by a known collapsing process.

At this time, the diameter (d) of the core layer 40 of the base rod is preferably 6mm or more, and the diameter (D) of the clad layer 30 of the base rod is the deposition volume ratio of the clad layer and the core layer (1/3). ~ 1 / 1.2). Reference numeral 2 in FIG. 4 is a closed quartz tube to form the outermost cladding layer 2 of the optical fiber base rod (see S400 of FIG. 8).

The cladding layer forming step, core layer forming step, and condensation step are continuous processes using the same equipment and the same heat source.

In the present invention, the shape of the heat source 5 used in the cladding layer forming process, the core layer forming process, and the condensation process may be variously modified. For example, various heating means such as a plasma torch and an electric resistance furnace may be employed. have.

<Overcladding>

The base rod manufactured through the condensation process is overclad through the apparatus shown in FIG. 5 to form a large diameter optical fiber base material.

A quartz tube 33 having an inner diameter larger than the outer diameter of the mother rod 77 is prepared to accommodate the mother rod 77 therein. As the quartz tube 33 forms the outermost clad layer of the optical fiber to be drawn, the quartz tube 33 should have corresponding optical or geometrical characteristics.

Quartz facing the one end of the base rod 77 in a state in which the base rod 77 is inserted into the quartz tube 33 so that the length axis of the prepared base rod 77 and the length axis of the quartz tube 33 coincide with each other. The other end 33 of the tube is joined to the lower handle tubes 11 and 31, respectively, and fixed to the vertical shelf 15 by using the upper chuck 12 and the lower chuck 32, respectively. For this reason, the base rod 77 and the quartz tube 33 are vertically supported with respect to the longitudinal axis in the state coupled with each other.

As such, the moving heat source (for example, the electric resistance path) 44 is moved to the upper end of the quartz tube 33 with the base rod 77 interposed in the quartz tube 33 to be positioned near the initial joint. The outer circumferential surface of the quartz tube 33 is heated while rotating the base rod 77 and the quartz tube 33 at predetermined speeds about their longitudinal axes, respectively.

When the outer circumferential surface of the quartz tube 33 is heated by the moving heat source 40 while the purging gas (not shown in the drawing) is supplied, a portion of the quartz tube 33 in which a hot zone is formed (that is, an initial stage) The initial junction is closed as the junction collapses.

When the initial joint is formed, a negative pressure is applied to the quartz tube 33, and the base tube 77 and the quartz tube 33 are completely heated by heating the quartz tube 33 while moving the moving heat source 40 downward along the length axis. (See S500 of FIG. 8).

In FIG. 5, reference numeral 11 denotes an upper handle tube, 12 an upper chuck, 14 a guide rod, 15 a vertical shelf, 31 a lower handle tube, 32 a lower chuck, 45 a tube, 50 a vacuum pump, and 60 a carriage. , 70 denotes a power supply unit.

<Optical fiber cutting edge>

The final preform formed through the overcladding process is drawn out to a fine diameter optical fiber by the edge line device of FIG. 6.

The final preform 35 is heated in the edge line 110, melted and drawn out to the fine diameter optical fiber 115. The drawn optical fiber 115 is coated with a protective coating on its outer circumferential surface by the device 130 after its diameter is measured in the device 120. The optical fiber 115 coated with the protective coating layer is wound on a bobbin (not shown) through the center measuring device 140 and the outer diameter measuring device 150. Power for drawing the optical fiber from the edge line 110 is provided from the capstan at 160 (see S600 in FIG. 8).

The optical loss of the optical fiber produced by the method of the present invention is shown in FIG.

Figure 7 shows the optical loss in the 1100nm to 1700nm region occurring in the optical fiber core, the dotted line shows a conventional optical fiber, the solid line is made of the optical loss produced by the improved method according to the present invention It is shown.

In the case of the optical fiber manufactured by the method of the present invention, the absorption loss by the OH-group was significantly reduced to 0.340 dB / km or less at 1.31 μm, 0.400 dB / km or less at 1.38 μm, and 0.200 dB / km or less at 1.55 μm.

As mentioned above, although this invention was demonstrated by the limited embodiment and drawing, this invention is not limited by this and is within the equal range of a common technical idea in the technical field to which this invention belongs, and a claim to be described below. Of course, various modifications and variations are possible.

The optical fiber manufactured according to the method of the present invention has an excellent absorption loss at 1,100 nm to 1,700 nm, which is an operating wavelength band, compared to the conventional optical fiber. In addition, since the deposition volume of the clad layer relative to the deposition volume of the core layer can be set lower than that of the conventional optical fiber, the manufacturing efficiency and productivity of the optical fiber are high.

Claims (7)

An optical fiber manufacturing method using a crystal chemical vapor deposition (MCVD), Depositing a clad layer having a deposition volume V _clad by heating the tube using an anhydrous heat source while introducing a cladding forming material into the quartz tube; Depositing a core layer having a deposition volume V _core by heating the tube using an anhydrous heat source while injecting a core forming material into an inner surface of the tube on which the clad layer is deposited; At this time, the core layer and the cladding layer are deposited to have a deposition volume (V _core ) of at least 1/3 of the deposition volume (V _clad ) of the cladding layer; Disintegrating the quartz tube in which the core layer and the clad layer are formed to generate a base rod; Disposing the base rod in a quartz tube having an inner diameter larger than an outer diameter of the base rod; Exposing the quartz tube and the base rod to a moving heat source for overcladding; Drawing an optical fiber core wire from the overclad optical fiber base material; The absorption loss of the optical fiber thus produced is 0.340dB / km or less at 1.31㎛, 0.200dB / km or less at 1.55㎛, 0.400dB / km or less at 1.38㎛. The method of claim 1, And the anhydrous heat source is an electric resistance furnace using graphite as a heating element. The method of claim 1, And depositing the core layer such that the diameter of the central core layer of the base rod is 6 mm or more. The method of claim 1, The OH ion concentration of the quartz tube is 0.5ppm or less manufacturing method. The method of claim 1, And depositing a core layer so as to have a deposition volume (V _core ) of 1 / 1.2 or less with respect to the deposition volume (V _clad ) of the _clad layer. An optical fiber base material manufactured according to the method of claim 1. An optical fiber edged from the optical fiber base material of claim 6.

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