KR20050118564A - Manufacturing method for single mode optical fiber having low oh attenuation at 1383nm wavelength - Google Patents

Abstract

The present invention relates to a method for producing a base material for single mode optical fibers having a low loss at a 1383 nm wavelength band. The present invention can be used as a single-mode transmission optical fiber in the entire wavelength range including 1340 ~ 1460nm wavelength was considered to be impossible to use due to high loss by completely removing the OH group to produce a low-frequency single-mode base material The present invention relates to a method of manufacturing a base material for a single mode optical fiber so as to have a low water peak. In particular, the core and clad composition ratio (D / d) of the core rod in the process of depositing the porous glass fine particles in the prepared seed rod in the conventional VAD method is characterized in that 5.0 to 5.4.

According to the present invention, an optical fiber base material that can be used at any wavelength in the wavelength range of 1280 to 1620 nm can be produced efficiently and at low cost.

In addition, the present invention is a very useful invention that can provide an optical fiber having a low OH group loss of less than 0.30dB / km at 1383nm wavelength because it is manufactured by D / d = 5.0 ~ 5.4.

Description

Manufacturing Method for Single Mode Optical Fiber Having Low OH Attenuation at 1383nm Wavelength

The present invention relates to a method for producing a base material for single mode optical fibers having a low loss in the 1383 nm wavelength band. More specifically, the present invention includes a wavelength of 1340 to 1460 nm, which was considered to be a wavelength region that cannot be used because of high loss by completely removing the hydroxyl group (hereinafter referred to as "OH group") to produce a low-frequency single-mode base material. The present invention relates to a method for manufacturing a base material for a single mode optical fiber having a low water peak so as to be used as a single mode optical fiber for the entire wavelength region.

Conventionally, a method of manufacturing a base material of a glass material by using a VAD method (Vapor-Axial Deposition Method) of a single mode optical fiber is carried out by flame hydrolysis reaction of glass material (SiO ₂ + GeO ₂ ) and clad (SiO _{2 +} CF _{4 The} porous glass fine particles having the composition of the present invention are deposited on the prepared glass rod to form core soot deposits with a diameter ratio of 3.5 to 7 of the core and the clad (hereinafter, referred to as a glass rod, seed rod), and the state deposited thereon is called a "core soot deposit".

The core soot deposit is heated to a temperature of 1250 ° C. to 1350 ° C. in a furnace containing chlorine (Cl ₂ ) gas (600 cc / min ≦ chlorine flow rate ≦ 1000 cc / min) and helium gas to remove OH groups. Dehydration step; A step of transparent vitrification of the core oot deposits from which the OH groups have been removed by heating to an appropriate temperature of 1450 ° C. or higher under a helium atmosphere;

Heat-extending the vitrified core soot deposits with a designed outer diameter on a drawing shelf with oxygen and a hydrogen burner to make glass rods for a constant outer diameter; Performing a hydrohydrolysis reaction on the outer circumferential portion of the glass rod for cores to deposit a sealica suit (hereinafter referred to as "clad suit" or "secondary clad"); The clad soot deposits were vacuum sintered in a helium gas atmosphere while gradually increasing the temperature from 1000 ° C. to 1600 ° C. to produce a single mode optical fiber base material.

Conventional fiber is manufactured by VAD method and the ratio of core and clad (hereinafter referred to as "D / d") is about 3.5 ~ 7.0. It has been produced at 4.5 degrees. D / d = 4.0 ~ 4.5, diffusion from outside to unreacted Si-O bonding structure inside core rod during core rod manufacturing or secondary clad manufacturing (diffusion distance SQRT {L} = 4Dt, where D is the diffusion coefficient t reacts with the incoming hydrogen ions over time, resulting in high OH loss at around 1383 nm. Even after the optical fiber was manufactured, it could not be used as a transmission optical fiber in the wavelength region of 1340nm ~ 1460nm.

In the conventional single mode optical fiber manufacturing method, a large absorption peak is generated by the OH group in the 1383 nm wavelength band, and a loss occurs near the 1383 nm wavelength.

Accordingly, an object of the present invention is to provide a method of manufacturing an optical fiber that can be used in the entire wavelength range of 1280nm-1620nm by minimizing OH group absorption loss in the 1340nm-1460nm wavelength region. Fabrication of single mode optical fibers with low OH absorption loss at 1383 nm by VAD method has been described in several literatures (e.g., VAD Single mode Fiber with 0.2dB / km Loss, Electronics letters 22nd January, published by S. Tomaru et al. 1981 Vol. 17 NO.2 pp 92-93). Here, the main contents were successfully manufactured by the VAD method up to D / d = 3.5-7.0 by the VAD method, and ultra-low loss VAD single mode optical fiber was manufactured by the D / d = 6.5-7.5.

On the other hand, according to the Republic of Korea Patent Publication No. 1999-007119 (published: January 25, 1999, Applicant: Lucent Technologies) "optical fiber low loss at 1385 nm and its manufacturing method", D / d = 2.0 ~ 7.5 and hollow cylindrical Disclosed is a manufacturing technique of an optical fiber having a low loss at 1385 nm by manufacturing a preform using a tube. Here, as the D / d increases, the deposition efficiency and manufacturing time increase, and thus the manufacturing cost increases. When the D / d is too small, the OH group absorption loss increases. Therefore, it is desirable to manufacture optical fibers having low OH group loss efficiently at low manufacturing cost.

It is an object of the present invention to provide a method for manufacturing a base material for a single mode optical fiber having low OH group loss with efficient D / d at low manufacturing cost by improving the problems of the prior art.

That is, the loss of the 1340-1460nm wavelength band is lower than the 1310nm wavelength band generally used in the current optical transmission system, which makes it possible to expand the usable band of 100 nm or more compared to the conventional single mode optical fiber, and to use any wavelength in the 1280-1620nm wavelength band. It is an object of the present invention to provide a method for producing a base material for single mode optical fibers having a low water peak.

The present invention for achieving the object of the present invention by flame hydrolysis reaction of the glass raw material by depositing SiO ₂ + GeO _{2 on} the core, SiO ₂ + fluorine compound on the clad porous glass fine particles to the prepared seed rod And a dehydration process of removing the OH groups from the furnace core of Cl ₂ (or SiCl ₄ ) gas and metal chlorides, and depositing the core oot deposits deposited on the seed rod. A step of transparent vitrification by sintering the core butt deposits at an appropriate temperature, a process of drawing the vitrified core suit deposits to a designed outer diameter to make a core glass rod, and an outer peripheral portion of the core glass rods In the method of manufacturing the base material of the optical fiber by the conventional VAD method, which further comprises a step of subjecting the hydrolysis reaction to flame hydrolysis reaction and depositing the sealica soot and sintering the clad soot deposit.

Depositing D / d = 4.8 to ˜5.5 in the process of depositing the porous glass fine particles on the seed rod; In the dehydration step of removing the OH group, the core soot deposit deposited on the seed rod is removed while heating to a dehydration temperature of 1150 ° C. ± 30 ° C. in a furnace in a helium gas atmosphere; In the process of always transparent vitrification, the above OH group-removed core soot deposits are sintered at a sintering temperature of 1500 ° C. ± 30 ° C. in a helium atmosphere; In the process of making the glass rod for the core, the soot sediment is stretched vertically in the carbon-resistance furnace with the designed outer diameter and then stretched to the target elongation in a shelf using oxygen and hydrogen burners; The method further includes the step of sintering the clad soot deposits in a vacuum and helium atmosphere, and drawing the single mode having a low loss at a 1383 nm wavelength band where water absorption loss is 0.30 dB / km or less in the 1383 nm ± 3 nm wavelength range. It is characterized by manufacturing an optical fiber base material. In the process of depositing the glass fiber on the seed rod is characterized in that it has a D / d = 4.8 ~ 5.5. In the process of making the glass rod for core further comprises etching (etching) the surface with a mixture of distilled water and hydrofluoric acid, the ratio of the hydrofluoric acid mixture in the etching process is preferably 0.5% to 10%.

An embodiment of the present invention will be described below with reference to the drawings. 1 is a schematic view showing the D / d and the refractive index profile of the core diameter (d) and the clad diameter (D) of the core rod of the optical fiber manufacturing method of the present invention, Figure 2 is a schematic diagram showing a manufacturing process of the present invention.

Figure 3 is a block diagram showing a manufacturing process of the present invention, Figure 4 is a loss graph for each optical fiber wavelength, Figure 5 is a graph of the OH group loss change in the 1383nm wavelength region according to D / d.

3 is a block diagram showing a manufacturing process of the present invention. In the order of claim 1, the manufacturing process of the present invention comprises the steps of depositing porous glass fine particles on a prepared seed rod by depositing SiO ₂ + GeO _{2 on} the core and SiO ₂ + fluorine on the cladding by flame hydrolysis of the glass raw material; A dehydration step of removing OH groups from the core soot deposits deposited on the seed rod in a furnace containing Cl ₂ (or SiCl ₄ ) gas and He gas; A step of transparent vitrification by sintering the core soot deposits from which the OH groups have been removed at a suitable temperature in a He atmosphere; Drawing the vitrified core soot deposited body to a designed outer diameter to make a glass rod for core (core rod); Optionally, etching the surface of the core glass rod with distilled water and hydrofluoric acid mixture;

Depositing clad suits by subjecting the hydrolysis reaction to the outer peripheral portion of the glass rod for cores again; It progresses to the process of sintering the said clad soot deposit body. In addition, the vitrified core soot sediment is stretched to the designed outer diameter characterized in that the process of extracting the vitrified base material as a thin single-mode optical fiber in the process of making a glass rod for the core.

Table 1 below shows the change of OH group loss in the 1383nm wavelength region of the optical fiber according to the diameter ratio (D / d) of the core of the core rod and the cladding. FIG. 5 is a graph showing changes in OH group loss in the 1383 nm wavelength region according to D / d. FIG.

D / d 1383nm OH Loss (dB / km) 4.5 0.33 4.8 0.31 5.0 0.29 5.2 0.28 5.4 0.27 5.8 0.27 6.2 0.27 6.6 0.27 7.0 0.27

In Table 1, it can be seen that it is preferable to prepare a core chute base material between D / d = 5.0 to 5.4 in order to manufacture the optical fiber having the most effective and economically low OH group loss. However, even though D / d = 5.8 ~ 7.0, the loss is low as 0.27 ㏈ / km, but it is difficult to use because it is uneconomical in this part. Therefore, between D / d = 5.0 and 5.4, economical and low loss.

The following Table 2 compares the technical differences that appear in the manufacturing process of the present invention and the prior art for the low loss single mode optical fiber manufacturing method by the VAD method. Comparison between the prior art and the present invention based on the manufacturing process of FIG. 2 with reference to the core diameter (d) of the core rod and the D / d and the refractive index of the clad diameter (D) of the optical fiber of the present invention shown in FIG. do.

FIG. 4 is a graph showing a loss-by-wavelength loss of a general single mode optical fiber and an optical fiber having low OH absorption loss in a 1383 nm wavelength region. FIG. According to FIG. 4, since a single peak optical fiber has an OH peak at 1383 ± 3 nm, it cannot be used as a transmission wavelength. Fibers with low OH absorption loss in the 1383nm wavelength region can be used as transmission wavelengths at 1383 ± 3nm wavelength because the OH peak is removed.

Prior art Invention 1. Preparation of core suit 1. Preparation of core suit 1) Composition-Core: SiO ₂ + GeO ₂ -Clad: SiO ₂ 2) D / d (core / clad): 3.5 to 7.0 1) Composition-core: SiO ₂ + GeO ₂ -clad: SiO ₂ + fluorine compound 2) D / d (core / clad): 4.8∼5.5 2. Primary dewatering Cl ₂ + He gas atmosphere 2. Primary dewatering Cl ₂ (or SiCl ₄ ) + He Gas Atmosphere Temperature: 1140 ℃ ± 30 3. Primary vitrification (sintering) He gas atmosphere 3. Primary vitrification (sintering) He gas atmosphere degree: 1500 degrees Celsius ± 50 4. Manufacturing glass rod for core 4. Manufacturing glass rod for core 1) Primary drawing: Carbon resisting vertical furnace 2) Secondary drawing: H2 + O2 flame mill 5. HF Etching 0.5 to 10% (Fluoride / Water) 5. Manufacture of suits for clad 6. Manufacture of suits for clad VAD method or Collabs method 6. Second dewatering Cl ₂ + He gas atmosphere 7. Second vitrification He gas atmosphere 7. Second vitrification  Vacuum + He gas atmosphere 8. Singlemode Fiber Drawing (Drawing) 8. Singlemode Fiber Drawing (Drawing) 9.1383 ± 3nm OH Loss  ≥0.35dB / km 9.1383 ± 3nm OH Loss  ≤0.30dB / km

As described above, according to the present invention, the loss in the 1340 ~ 1460nm wavelength band is lower than the 1310nm wavelength band generally used in the current optical transmission system, it is possible to expand the usable band of 100nm or more than conventional single-mode optical fiber.

According to the present invention, it is possible to provide a single mode optical fiber that can be used in any wavelength in the wavelength range of 1280 to 1620 nm.

In addition, in many applications, it is possible to provide a method for manufacturing a base material for a single mode optical fiber having low cost and low peak of OH group. In addition, the present invention can provide an optical fiber having a low OH group loss of less than 0.30dB / km at a wavelength of 1383 nm, since the D / d = 5.0 ~ 5.4 can be effectively manufactured in a low cost structure in manufacturing the core rod by the VAD method Is a very useful invention.

1 is a schematic diagram showing the D / d and refractive index profiles of the core diameter (d) and the cladding diameter (D) of the core rod of the optical fiber manufacturing method of the present invention,

2 is a schematic view showing a manufacturing process of the present invention,

3 is a block diagram showing a manufacturing process of the present invention;

4 is a loss graph for each optical fiber wavelength,

5 is a graph showing the change of OH group loss in the 1383 nm wavelength region according to D / d.

<Brief description of the main parts of the drawing>

1 core suit 2 core part

3: cladding part 4: clad burner (SiCl ₄ + CF ₄ )

5: burner for core (SiCl ₄ + GeCl ₄ )

Claims (5)

Flame-hydrolyzing the glass raw material to deposit SiO ₂ + GeO _{2 on} the core and SiO ₂ + fluorine compound on the clad to deposit porous glass fine particles on the prepared seed rod. And a dehydration process of removing the OH groups from the furnace core of Cl ₂ (or SiCl ₄ ) gas and metal chlorides, and depositing the core oot deposits deposited on the seed rod. A step of transparent vitrification by sintering the core butt deposits at an appropriate temperature, a process of drawing the vitrified core suit deposits to a designed outer diameter to make a core glass rod, and an outer peripheral portion of the core glass rods In the method of manufacturing the base material of the optical fiber by the conventional VAD method, which further comprises a step of subjecting the hydrolysis reaction to flame hydrolysis reaction and depositing the sealica soot and sintering the clad soot deposit. Depositing such that the diameter ratio (D / d) of the core and the clad is 4.8 to 5.5 in the process of depositing the porous glass fine particles on the seed rod; In the dehydration step of removing the OH group, the core soot deposit deposited on the seed rod is removed while heating to a dehydration temperature of 1150 ° C. ± 30 ° C. in a furnace in a helium gas atmosphere; In the process of transparent vitrification, the above OH group-removed core soot deposits were sintered at a sintering temperature of 1500 ° C. ± 30 ° C. in a helium atmosphere; In the process of making the glass bar for cores, the soot sediment is stretched vertically in a carbon-resistance furnace with a designed outer diameter, and then stretched from the shelf to the target elongation using oxygen and hydrogen burners; A method of manufacturing a single mode optical fiber base material having a low loss at a 1383 nm wavelength band, further comprising the step of sintering the clad soot deposit in a vacuum and helium atmosphere. The method of claim 1, wherein the porous glass fine particles to the prepared seed rod The core and clad composition ratio (D / d) of the core rod in the deposition process is a method for producing a single mode optical fiber base material having a low loss at 1383 nm wavelength band, characterized in that 5.0 to 5.4. The method of claim 1, wherein the OH-based absorption loss in the 1383nm ± 3nm wavelength region through the step of melting the preform, cooling, coating, curing, winding step in the drawing process of thinning the vitrified clad soot deposit with a thin optical fiber A method of manufacturing a base material for a single mode optical fiber having a low loss in a 1383 nm wavelength band, characterized by being 0.30 dB / km or less. According to claim 1, wherein the core soot deposits are prepared with a core and cladding diameter ratio (D / d) of 3.5 to 4.0. A method of manufacturing a base material for a single mode optical fiber having a low loss in a 1383 nm wavelength band, wherein the OH group absorption loss is 0.30 dB / km or less in the wavelength region. 5. The method of claim 4, wherein the collapsing method is performed by stretching the core stretched body manufactured in claim 1 to the designed stretched nerve and collapsing the core stretched body into the glass tube for cladding in a vertical carbon resistance furnace. A method for producing a base material for single mode optical fibers having a low loss at a 1383 nm wavelength band.