KR100271517B1 - Confinement method of dopants in optical fiber core - Google Patents

Abstract

PURPOSE: A method of dopant confinement against an optical fiber core is provided to be capable of confining dopant and sub additives of high density against the optical fiber core by performing a soot core deposition step after a collapse step. CONSTITUTION: First, in a sintered core deposition step, a substrate tube is heated to deposit particles on an inner wall of the tube while SiCl4 and O2 simultaneously flows in the substrate tube. Then, in a collapse step, the substrate tube is heated by the temperature over a glass softening point. Next, in a soot core layer deposition step, the substrate tube is heated under the temperature at which the sintering process isn't occurred while SiCl4 flows in the substrate, thereby depositing SiCl4 on the inner wall of the sintered core.

Description

How to constrain the dopant to the fiber core

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates generally to optically amplified optical fiber (Erbium Doped Fiber (EDF)) to which rare earth elements have been added and to a method of manufacturing the same. The present invention relates to a method of effectively adding a rare earth element (erbium and the like) and an auxiliary additive (particularly aluminum) to all or a part of the method, and a method of effectively compensating a refractive index dip at a core center.

Generally, there are various methods of adding rare earth elements to the optical fiber core, but they can be largely divided into a solution doping method and a vapor phase doping method.

In the liquid phase method, rare earth elements (Er, Yb, La, Nd, Pr, etc.) and minor additives (Al, etc.) are dissolved in a solvent (water, ethanol, etc.) and deposited on a porous optical fiber core, followed by vitrification at high temperature. To produce an optical fiber base material. This method has the advantage of producing a rare-earth-doped optical fiber without significantly changing the conventional single-mode optical fiber manufacturing method, but modified chemical vapor deposition of the reaction tube in the manufacturing method for erbium doping Vapor Deposition (MCVD) There is a disadvantage that it must be removed from the lathe and soaked in the rare earth-added solution and then mounted on the lathe again. Therefore, it can be contaminated with impurities such as moisture and take much time compared with other manufacturing methods due to detachment of the reaction tube.

2 illustrates a conventional method of adding a dopant by a liquid phase method among methods of adding a dopant to a core of an optical fiber. Referring to FIGS. 1A, 1B, and 2, this conventional rare earth element-added optical fiber base material manufacturing method will be described. When the optical fiber core layer is deposited, all pores or portions of the optical fiber core are not completely sintered, and a lot of pores are produced. After forming a soot core layer 14 containing (step 21), a solution in which the dopants and co-dopants are dissolved in the soot core layer 14 After absorbing (step 22), it is dried and sintered to add the dopant and the additive (step 23).

Referring to FIG. 1A, a process of manufacturing an optical fiber doped with rare earth element erbium (Er) and an auxiliary additive aluminum (Al) by MCVD method will be described in more detail. The additive fiber base material manufacturing method forms an optical fiber inner clad layer 12 inside a reaction tube 11 and deposits an optical fiber soot core layer 14 (step 21). A solution containing rare earth elements (erbium) and a minor additive (aluminum) dissolved in the quartz glass tube powder thus formed is allowed to infiltrate the soot core layer 14 evenly (step 22), and then the non-penetrating solution is removed. And the soot core layer is dried with dry N ₂ gas (step 23). The dried reaction tube 11 is heated to a temperature of about 1800 ° C. or more to sinter the soot core layer 14 (step 23), and then heated to a high temperature of about 2000 ° C. to form a central hole 15. ) To reduce the hole to some extent, and then form a glass rod through a sealing step 24 to completely remove the hole at a temperature of 2000 ° C. or higher. As a result, a base material of a rare earth element-added optical fiber is made, and the base material is drawn while heating in an electric furnace at about 2000 ° C. to make an optical fiber.

However, in the conventional rare earth element-added optical fiber base material manufacturing method, since the fiber core layer is formed and then subjected to a high temperature collapsing step 24 over 2000 ° C., germanium (Ge) from GeO ₂ to GeO and O ₂ as shown in As it is decomposed and volatilized, it acts to reduce the refractive index of the center of the optical fiber core.

[Equation 1]

2 GeO ₂ (s)-GeO (g) + O ₂ (g)

In particular, the soot core layer 21 is porous and has a large surface area to promote volatilization of germanium, thereby lowering the refractive index of the core layer and having a step index profile distribution in the form of a step. It acts as a factor that makes it difficult to control the refractive index distribution of the required rare earth element-added optical fiber.

In addition, the conventional method serves to promote the diffusion of aluminum used as an additive. In general, aluminum added in the optical fiber core is known to diffuse easily at high temperatures of 1600 ° C or higher. That is, the aluminum added to the core layer is diffused from the center of the core to the inner cladding layer 12 when subjected to the collapsing step 24 which is heated at a high temperature of 2000 ° C. or higher. Diffusion into clad layer 12 expands the core and impairs the circularity of the core.

This aluminum diffusion phenomenon of the conventional method also serves to promote the diffusion of the erbium (Er) element. That is, erbium is confined to aluminum and diffuses like aluminum, thereby lowering erbium concentration at the core center. This is a significant disadvantage in the manufacturing process, where the elemental erbium and aluminum must be constrained to the core center.

SUMMARY OF THE INVENTION The present invention has been made in view of the conventional problems as described above, and an object thereof is to produce a rare earth element-added optical fiber that constrains a high concentration of dopants and subadditives to an optical fiber core.

Another object of the present invention is to prepare an optical fiber base material in which a rare earth element and an additive (particularly, aluminum) are added at a high concentration in the center of the core in the manufacture of the rare earth element-added optical fiber, and the diffusion of aluminum is prevented to make the refractive index distribution close to the step shape To provide a way.

1A is a diagram for illustrating a method of manufacturing an optical fiber core layer according to the present invention, and FIG. 1B is a side cross-sectional view of the optical fiber core according to the present invention.

2 illustrates a method of adding a dopant to an optical fiber core by a liquid phase method according to the prior art.

3 illustrates a method of adding a dopant to an optical fiber core in accordance with the present invention.

* Explanation of symbols for main parts of the drawings

11: reaction tube 12: inner clad layer

13: sintered core layer 14: soot core layer

15: hall

In order to achieve the above object, the present invention is a method for restraining the dopant when the dopant is added to the core of the rare earth element-added optical fiber, by heating the reaction tube while flowing the reactant into the reaction tube and deposited on the inner wall of the reaction tube Sintered core layer deposition step of sintering; A collapsing step of heating the reaction tube having the sintered core layer deposited on an inner wall to a high temperature above the softening point of glass; And a soot core layer deposition step of depositing a porous soot core layer on the inner wall of the sintered core layer at a low temperature where sintering does not occur; A soot core layer deposition step is performed after the collabs step and a sintered core layer deposition step is performed before the collabs process.

The above objects, features, and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Referring to Figure 3, a method of adding a dopant to an optical fiber core in accordance with the present invention is illustrated.

In a preferred embodiment according to the present invention, an inner clad layer deposition process is first performed by depositing an inner clad layer 12 on an inner wall of a reaction tube 11 made of quartz glass ( Not shown). In this step, the temperature of the bubbler (bubbler) containing the halogenated SiCl ₄ , POCl ₃ is fixed to 25 ± 1 ℃ and reactants (eg, SiCl ₄ , POCl ₃ ) using oxygen (O ₂ ) as the transport gas ) Is controlled by a mass flow controller (MFC). Other reactants (He, O ₂ , Freon, etc.) are supplied in the direct reaction zone because they exist in a high pressure gas state. In addition, the reaction tube 11 is heated while reciprocating the main burner several times to form the inner clad layer 12 to a desired thickness.

In a preferred embodiment of the inner clad layer deposition step according to the present invention, the inner clad layer is reciprocated at least 15 times by adding SiCl ₄ = 500 sccm, POCl ₃ = 90 sccm, 0 ₂ = 500 sccm and C ₂ F ₆ = 10 sccm to reciprocate the main burner. (12) is deposited. At this time, the deposition temperature is increased by 2 ° C for each pass of the main burner based on 1840 ° C to correct the temperature drop due to deposition.

The internal clad layer deposition step is followed by a sintered core deposition process 31, in which sintered core layer deposition step 31 flows SiCl ₄ and GeCl ₄ simultaneously with O _2, and burner temperature. The main burner is moved while heating to about 1950 ° C., and these reactants (SiCl ₄ , GeCl ₄ , O _2, etc.) react with each other to completely sinter the fine particles, which are transparent to the inner wall of the reaction tube 11. Deposit. In the sintered core layer deposition step 31, the number of depositions of the sintered core layer is controlled to adjust the core cofinement ratio (the radius a of the region doped with erbium and the additive) and the sintered core region b. Radius ratio (a / b)) can be easily adjusted. The amount of reactant added in this step depends on the refractive index required.

The subsequent collapse process 32 is a step in which the reaction tube is heated to a high temperature above the softening point of the glass and gradually sinks by the surface tension of the quartz glass while maintaining the circularity of the holes 15. In the conventional Collabs step 32, the inner hole 15 is reduced by heating the reaction tube 11 to a temperature of about 2000 ° C. or higher, during which germanium is doped in the optical fiber core layer in a GeO ₂ (s) state. As shown in this formula (1), it decompose | dissolves into GeO (g) and volatilizes. Therefore, a core dip phenomenon in which the refractive index of the center of the optical fiber core falls is generated. In addition, when performing the collapsing step 32 after the solution doping process 35, which will be described below, as in the conventional method, the dopant may be volatilized with the volatilization of germanium, and the inner clad layer through diffusion. Go to (12) to reduce the dopant concentration at the core center.

However, since the collapsing step 32 according to the present invention is performed after the sintered core layer deposition step 31, the sintered core layer 13 deposited on the sintered core layer deposition step 31 is carried out. Diffusion of the dopant doped by the cladding layer 12 is suppressed. In addition, since the collapsing step 32 of the present invention is performed before the soot core layer deposition process 34 and the solution doping step 35, which will be described later, the optical fiber core constraint ratio can be easily adjusted. By reducing the total amount of heat applied after solution doping, the dopant (doped Er or Al) may be suppressed from being volatilized by the high temperature or diffused into the inner clad layer 12, thereby maintaining a high dopant concentration at the core center.

In a preferred embodiment of the Collabs step 32 according to the invention, the pressure inside the reaction tube 11 is taken into account, taking into account the sealing process 37 and the core restraint ratio described below at a heating temperature of 2000 ° C. or higher. And the number of passes of the main burner are adjusted to make a hole 15 of appropriate size.

The following core etching process 33 is a step for removing by fluorine etching a portion where germanium is volatilized and the refractive index is lowered after the collapsing step 32. In a preferred embodiment of the core etching step 33 according to the present invention, the fluorine compounds C ₂ F ₆ and O ₂ are flowed and heated to a temperature of 1570 ° C. to remove portions of which the internal refractive index is reduced. At this time, GeCl ₄ is also flowed together to increase the refractive index compensation effect.

Next, the soot core layer deposition step 34 is performed by flowing a reactant (SiCl ₄ , GeCl _4, etc.) into the reaction tube 11, and at an inner temperature of the sintered core layer 13 at a low temperature at which no sintering occurs. It is a step of depositing on. The soot core layer deposition step 34 according to the present invention can be performed after the collapsing step 32 to optimize core restraint. That is, by performing the soot core layer deposition step 34 after the collabs step 32, the soot core layer 14 is deposited in the inner hole 15 of the smaller reaction tube to deposit a relatively appropriate amount of the soot core layer 14. It can be deposited, so it is easy to adjust the core constraint ratio.

As in the conventional method, the soot core layer deposition step 34 before the collabs step 32 results in a large surface area deposited due to the large inner diameter of the reaction tube 11 on which the soot core layer 14 is deposited. There is a limit to reducing the cross-sectional area of the core layer 14, and in general, the rare earth element-added optical fiber has a small core size, so that if the core is large in the primary base material, the over cladding (or jaws) overlying the inner cladding layer 12 is required. Ket) step had to be performed. However, according to the present invention as described above, the soot core layer deposition step 34 is performed after the collapsing step 32 so that the amount of deposition of the core is the size of the glass tube hole 15 after the collapsing step 32. Can be adjusted to reduce over cladding steps.

In a preferred embodiment of the soot core layer deposition step 34 according to the present invention, the amount of SiCl ₄ and GeCl ₄ is appropriately adjusted according to the core confinement ratio, while flowing into the reaction tube 11. The deposited soot core layer 14 is deposited at a relatively low temperature so as not to sinter. The soot core layer 14 is then made porous, to facilitate penetration of the doping solution into the core.

The subsequent solution doping step 35 is a step in which a dopant is added to the reaction tube 11 in which the soot core layer 14 is deposited, in which the dopant (Er, Al, etc.) is dissolved at a predetermined concentration. The solution doping step 35 according to the invention is carried out after the collapsing step 32, since the inner hole 15 of the tube to be doped is small, so that even a small amount of doping solution can be sufficiently doped The amount of solution used can be greatly reduced. In the solution doping step 35, the dopant is doped by the thickness of the soot core layer 14 and the diffusion to the inner clad layer 12 is suppressed by the sintered core layer 13.

In a preferred embodiment of the solution doping step 35 according to the present invention, after dissolving ErCl ₃ 6H ₂ O and AlCl ₃ in ethanol, the soot core layer deposition step 34 is completed. It is placed in the reaction tube 11 to allow sufficient penetration of the solution into the porous soot core layer 14.

The next dehydration process 36 is performed to remove the solvent contained in the soot core layer 34. The drying step 36 minimizes loss factors such as residual doping solvent and moisture, and removes low-boiling organic matter carbonized at the glass processing temperature, and is an important step to improve the loss of the optical fiber.

In a preferred embodiment of the drying step 36 according to the invention, the main burner is heated to about 900 ° C. while reciprocating several times, or flowing dry nitrogen to remove the solvent remaining in the soot core layer 14, and He And a gas such as Cl ₂ is flowed into the reaction tube 11 to completely remove moisture remaining in the soot core layer 14.

After the drying step 36 is finished, a sintering process 36 is performed in which the reaction tube 11 is heated to high temperature to vitrify the soot core layer 34. In this step, since the soot core layer 14 is composed of a porous soot layer to facilitate the doping solution to penetrate into the core, relatively large volatilization of germanium constituting the soot core layer 14 occurs. At this time, by flowing an appropriate amount of GeCl ₄ , the formation of GeO (g) can be suppressed to prevent the decrease in the refractive index, and volatilization of the dopant due to volatilization of germanium (Ge) can be suppressed.

In one preferred embodiment of the sintering step 36 according to the present invention, after the drying step 36 is finished, the reaction tube 11 is heated to a temperature of 1900 ° C. or more to completely vitrify the porous soot core layer 14 to be transparent. And a suitable amount of GeCl ₄ is flowed to compensate for the core dip during the sintering step 36.

Finally, the tube sealing process 37 is a step of heating the reaction tube 11 to a high temperature to completely remove the inner hole of the reaction tube 11. In this step, the production of GeO (g) is accelerated since the operation is performed at a high temperature of 2000 ° C. or higher. In the present invention, GeCl ₄ is prevented by flowing GeCl ₄ during the tube sealing step 37 to prevent the formation of GeO (g). The refractive index distribution can be obtained.

In a preferred embodiment of the sealing step 37 according to the invention, the reaction is carried out with moving the main burner at a slower speed in the collapsing step 32 at the same temperature as in the collapsing step 32 according to the invention. The tube 11 is heated to completely remove the inner hole 15 to form a glass rod-shaped optical fiber base material, and flow GeCl ₄ to compensate for the core dip.

According to the method according to the present invention, the soot core layer deposition step 34, which is easy to add dopant, can be performed after the collapsing step 32 to confine the dopant in the center of the optical fiber core, and the sintered core layer deposition step 31 ) And the soot core layer deposition step 34 and the solution doping step 35 may be performed after the collabs step 32 to prevent diffusion of the dopant by high temperatures, The core etching step 33 may be performed after the step 32 to obtain a stepped refractive index distribution, and the GeCl ₄ gas may be flowed during the core etching step 33, the sintering step 36, and the tube sealing step 37. Compensate for core dips.

In addition, a preferred embodiment of the present invention is disclosed for the purpose of illustration, those skilled in the art will be able to make various modifications, changes, additions, etc. within the spirit and scope of the present invention, such modifications and modifications belong to the following claims You will have to look.

Claims (15)

In a method for confining a dopant when a dopant is added to a core of a rare earth element-added optical fiber, SiCl ₄ and O ₂ are simultaneously flown into a reaction tube made of quartz glass. Heating the reaction tube, and sintered core deposition in which the particles generated by the reaction are sintered and deposited on the inner wall of the reaction tube; A collapsing step of heating the reaction tube having the sintered core layer deposited on an inner wall to a high temperature above the softening point of glass; And a soot core layer deposition step of heating the reaction tube at a low temperature at which no sintering occurs while flowing SiCl ₄ into the reaction tube after the collapsing step and depositing it on the inner wall of the sintered core layer. Constraining the dopant to the optical fiber core comprising a. The method of claim 1, wherein depositing the sintered core layer deposits GeCl ₄ gas with SiCl ₄ . The method of claim 1, wherein the soot core layer deposition step comprises flowing GeCl4 gas with SiCl4. The method of claim 1, further comprising a core etching step of removing a portion of the inner surface of the reaction tube whose refractive index is lowered by heating the C ₂ F ₆ and O ₂ after the Cullebs step. And confining the dopant to the optical fiber core. The method of claim 4, wherein the core etching step is performed by heating at a temperature of about 1570 ° C. 6. 5. The method of claim 4, wherein said core etching step is performed while flowing a GeCl ₄ gas. A method for constraining the dopant when a dopant is added to a core of a rare earth element-added optical fiber, wherein the reaction tube is heated and reacted while flowing SiCl ₄ simultaneously with O ₂ into a reaction tube made of quartz glass. A sintered core layer deposition step of depositing the sintered particles onto the inner wall of the reaction tube; A collapsing step of heating the reaction tube having the sintered core layer deposited on an inner wall to a high temperature above the softening point of glass; After the collapsing step, a core etching step of heating and removing a portion having a low curvature of the inner surface of the reaction tube while flowing C ₂ F ₆ and O ₂ ; A soot core layer deposition step of depositing the inner wall of the sintered core layer by heating at a low temperature at which sintering does not occur while flowing SiCl ₄ into the reaction tube after the collapsing step; A solution doping step of adding a dopant by adding a solution in which a dopant is dissolved at a predetermined concentration into the reaction tube on which the soot core layer is deposited; A drying step of heating the reaction tube to remove a solvent contained in the soot core layer; A sintering step of sintering the soot core layer by heating the reaction tube to a high temperature; And a sealing step of heating the reaction tube to a high temperature to remove the holes remaining in the reaction tube. Constraining the dopant to the optical fiber core comprising a. The method of claim 7, wherein GeCl ₄ gas is flowed in the core etching step. 8. The method of claim 7, wherein the dopant is confined to the optical fiber core by flowing GeCl ₄ gas in the sintering step. The method of claim 7, wherein GeCl ₄ gas is flowed in the sealing step. 10. The method of claim 7, wherein the drying step comprises flowing dry nitrogen into the reaction tube to remove the solvent contained in the soot core layer. 8. The method of claim 7, wherein the core etching step is performed by heating at a temperature of about 1570 ° C. 8. The method of claim 7, wherein said drying step is performed by heating at a temperature of about 900 < 0 > C. 8. The method of claim 7, wherein the step of depositing the sintered core layer deposits GeCl ₄ gas with SiCl ₄ . 8. The method of claim 7, wherein the soot core layer deposition step comprises flowing GeCl ₄ gas with SiCl ₄ .