MXPA00012582A - Optical fiber preform having oh barrier and manufacturing method thereof - Google Patents

Abstract

An optical fiber preform having a substrate tube, a cladding layer and a core layer further includes a first barrier layer deposited by a material having a low OH diffusion coefficient between the substrate tube and the cladding layer, wherein the first barrier layer is for substantially preventing OH contained in the substrate tube from being diffused into the cladding layer. The optical fiber preform further includes a second barrier layer formed by depositing a material having a low OH diffusion coefficient between the cladding layer and core layer, for substantially preventing OH which has been diffused into the cladding layer from the substrate tube from being diffused further into the core layer. Outer and inner OH barriers containing no P2O5 are deposited between the substrate tube and the cladding layer and between the cladding layer and the core layer in a deposition process, such that OH can be effectively prevented from being diffused from the substrate tube to the core layer in a core deposition process, a collapsing process or a closing process.

Description

PREFORM OF OPTIC FIBER WITH BARRIER FOR THE OH AND METHOD FOR ITS MANUFACTURE FIELD OF THE TECHNIQUE The present invention relates to a general preform of optical fiber, and more particularly, to an optical fiber preform to minimize the diffusion of OH from the substrate tube to the center of an optical fiber, and its manufacturing method.

ANTECEDENTS OF THE TECHNIQUE A simple mode optical fiber is made by depositing a coating layer and a central layer. In a DC-SM type (single cladding mode pressed), a coating layer is deposited by means of Si02 doping with P205, Ge02, and F to decrease the deposition temperature and the refractive index, a central layer for the Light transmission is deposited by doping Si02 with Ge02 to increase the reflection index, and subsequently a preformed optical fiber is manufactured by means of a collapse and closure process.

Ref. 125824 In a process for the manufacture of a fiber optic preform using modified chemical vapor deposition (MCVD), the autocollapse of a tube occurs during deposition when the deposition layer becomes thicker, resulting in an increase in the thickness of the tube. A high temperature calciner is also required to sinter and consolidate a thick deposition layer, and the time for the collapse and closure process becomes longer, such that a substrate tube is exposed to a higher temperature for a period of time higher.

In this process, while a very small amount of water (H20) (usually a few ppm) contained in the substrate tube diffuses into the deposition layer, the diffused water is combined with P205 or Si02 deposited in the coating region, forming thus a combination of Ge-OH link. The OH diffused to the central region is combined with Si02 or Ge02 deposited in the central layer, thus forming a combination of bond Si-O-H or Ge-O-H by dissolving the combination of bond Si-0 or Ge-0.

The combination of O-H or P-O-H bond formed in combination with water in each deposition region as described above results in an additional optical loss due to an absorption band in a specific wavelength region. In the case of a simple mode optical fiber, the wavelength bands in which serious optical losses take place are a band of 1.24 μm - 1.385 μm due to the combination of 0-H bond, and a band of 1.2 - 1.8 μm due to the combination of P-0-H bond. When OH is diffused within the central region, it forms an unbounded oxygen (NBO). And then the structural homogeneity of the glass material of the core layer deteriorates locally, which causes a density fluctuation of the core layer. Consequently, the dispersion loss increases.

The internal and external diameters of a tube contract with an increase in the thickness of the deposition layer during the dispersion effected simultaneously with the deposition, in such a way that it is difficult to obtain an appropriate diameter ratio (ie coating diameter / central diameter = D / d). Therefore, a sufficient distance can not be ensured to avoid the diffusion of OH, thus greatly increasing the losses due to OH.

In the prior art, a thickening method of the coating layer is used to prevent OH diffusion of the substrate tube to the core layer. However, when a large-aperture preform is manufactured by this method, shrinkage of a tube makes it difficult to ensure an appropriate diameter ratio, a high-temperature calciner is required during the deposition of the core layer since the transmission efficiency of Heat to a core layer is degraded due to an increase in the thickness of the tube layer. Consequently, the tube is exposed to a high temperature for a long period, thus increasing the losses due to OH.

BRIEF DESCRIPTION OF THE INVENTION To solve the above problems, it is an object of the present invention to provide an optical fiber preform capable of effectively reducing the losses due to OH by decreasing the ratio of diameters by forming a barrier layer to block or alleviate markedly the diffusion of OH between a substrate tube and a central layer in order to prevent OH from diffusing from the substrate tube within the core layer.

Another object of the present invention is to provide a method of manufacturing an optical fiber preform having a barrier against OH.

Accordingly, to achieve the first objective, a glass fiber preform having a substrate tube, a coating layer and a core layer is provided, the fiber optic preform additionally comprises a first barrier layer deposited by a material having a low level. OH diffusion between the substrate tube and the coating layer, wherein the first barrier layer is to substantially prevent the OH contained in the substrate tube from diffusing into the coating layer.

It is preferred that the optical fiber preform comprises a second barrier layer formed by the deposition of a material with a low OH diffusion coefficient between the coating layer and the core layer, to substantially prevent the OH that has diffused into the coating layer from the substrate tube also diffuses into the core layer.

To achieve this first objective, another optical fiber preform having a substrate tube, a coating layer and a central layer is provided, additionally, the optical fiber preform comprising a first barrier layer deposited by a material having a low coefficient of OH diffusion between the substrate tube and the coating layer, wherein the first barrier layer is to substantially prevent the OH contained in the substrate tube from diffusing into the coating layer, wherein the refractive index of the core layer is greater than the refractive index of the coating layer and increases gradually in the direction from the outside of the core layer to the center of the core layer.

It is preferred that this optical fiber preform additionally comprises a second barrier layer deposited by a material having a low OH diffusion coefficient between the coating layer and the core layer, wherein the second barrier layer is to substantially avoid OH diffused within the coating layer diffuses into the central layer.

To achieve the second objective, a method for manufacturing an optical fiber having a substrate tube, a coating layer and a central layer is provided, the method comprising the steps of: forming a first barrier layer by deposition of a material with a low OH diffusion coefficient; forming a coating layer by means of doping an appropriate material to decrease a process temperature and increasing the deposition efficiency; and forming a central layer being a region through which an optical signal is transmitted.

It is preferred that additionally a second barrier is formed by deposition of a material having a low OH diffusion coefficient, before the core layer is formed after the coating layer is formed. It is also preferred that the core layer be formed such that the refractive index gradually increases in the direction from the outside to the center of the core layer.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view illustrating an optical fiber of general simple mode; Figure 2 is a view illustrating a simple mode optical fiber in accordance with the present invention; Figure 3 is a view illustrating another single mode optical fiber in accordance with the present invention; and Figures 4A, 4B, and 4C are views illustrating a method of manufacturing a single mode optical fiber in accordance with the present invention using a modified method of chemical vapor deposition (MCVD).

DETAILED DESCRIPTION OF THE INVENTION Next, preferred embodiments of the present invention will be described in greater detail with reference to the accompanying drawings. With reference to Figure 1 showing a simple optical fiber of cladding press (DC-SM), the reference number 11 denotes a substrate tube, the number 12 denotes a cladding layer, and the reference number 13 denotes a central layer. Also? + Represents the refractive index of the central layer and? "Represents the refractive index of the coating layer, relative to the refractive index of the substrate tube, respectively, also Fd represents the diameter of the central layer and FD represents the diameter of the coating layer.

The P2O5 is deposited to form the coating layer 12. P205 has a relatively low melting point of about 570 ° C, so that when it is used together with a different source material, the process temperature can be lowered and the temperature increased. Deposition efficiency. On the other hand, since the doped P20s in the coating layer 12 possess a high hygroscopicity, it acts as an OH bridge for the transmission of OH contained in the substrate tube 11 of the central layer 13. Therefore, the losses increase due to the OH in the central layer.

Figure 2 is a view illustrating a simple mode optical fiber in accordance with the present invention. In Figure 2, the reference number 21 denotes a substrate tube, the reference number 22 denotes a first barrier layer (outer coating layer), the reference number 23 denotes an intermediate coating layer, the reference number 24 denotes a second barrier layer (inner lining layer), and the reference number 25 denotes a central layer. Also,? + Represents the refractive index of the central layer 25, and? "Represents the refractive index of the intermediate coating layer 23, which are indexes relative to that of the substrate tube 21.?" Or represents the refractive index of the first barrier layer 22, and? +? represents the refractive index of the second barrier layer 24, which are indexes relative to that of the central barrier layer. FDi represents the diameter of the second barrier layer 24, FD represents the diameter of the intermediate coating layer 23, and FD0 represents the diameter of the first barrier layer 22.

As described above, the coating layer of the optical fiber preform according to the present invention is composed of three layers each having a different chemical composition ratio. In other words, the coating layer is composed of the first barrier layer (outer coating layer) 22, the intermediate coating layer 23, and the second barrier layer (inner coating layer) 24.

The first barrier layer (outer coating layer) 22 is located within the substrate tube 21 having a high concentration of OH and the intermediate coating layer 23 containing the carrier P20s of OH, and prevents the OH contained in the substrate tube 21 from diffuses into the liner layer 23. The second barrier layer (inner liner layer) 24 is located between the intermediate liner layer 23 and the central layer 25, and prevents the OH diffused from the substrate tube 21 within the liner layer. intermediate coating 23 penetrates into the central layer 25 despite the first intermediate barrier layer 22.

The first and second barrier layers 22 and 24 do not have P205 which acts as an OH bridge, their refractive indexes are controlled using Si02 / Ge02, and F, and their thicknesses are appropriately controlled according to the overall thickness of the layer Coating. In particular, only the first barrier layer 22 can be interposed between the substrate tube 21 having a high concentration of OH and the intermediate coating layer 23, or only the second barrier layer 24 can be interposed between the intermediate coating layer 23 and the layer central 25.

With reference to the characteristics of the refractive index of the optical fiber preform, the refractive index of the central layer 25 is greater than that of the coating layers 22, 23 and 24. Therefore, the refractive index of each of the outer and inner layers 22 and 24 are controlled to be equal to or similar to the refractive index of the intermediate coating layer 23. Also, the refractive indices of these three layers can be controlled to be the same.

In general, the concentration of OH in the deposition layer is 1/1000 or less of the OH concentration in the substrate tube. However, the coating layer is deposited by doping P205 in order to lower the process temperature in the coating deposition process. Here, P20s possesses a great hygroscopicity. Consequently, the P2O5 deposited in the coating layer acts as a bridge for the OH transmission of the substrate tube in the central layer, thus increasing the losses due to the OH in the central layer. Therefore, in the present invention, a doped barrier against OH is formed with materials having low OH diffusion coefficients between the substrate tube having a high OH concentration and the coating layer containing the OH PO5 carrier. , or / and between the coating layer and the central layer. The barrier against the OH thus formed can prevent OH diffusion from the substrate tube 21 to the central layer 25.

Figure 3 is a view illustrating another single mode optical fiber in accordance with the present invention. In Figure 3, the reference number 31 denotes a substrate tube, the reference number 34 denotes a first barrier layer (outer coating layer), the reference number 32 denotes an intermediate coating layer, the reference number 35 denotes a second barrier layer (inner lining layer), and the reference number 33 denotes a central layer. Also "N +" represents the refractive index of the core layer 33, and "N" represents the refractive index of the intermediate coating layer 32, which are refractive indices relative to that of the substrate tube 31.

As described above, the coating layer of the optical fiber preform according to the present invention is composed of three layers each having a different chemical composition ratio. In other words, the coating layer is composed of the first barrier layer (outer coating layer) 34, the intermediate coating layer 32, and the second barrier layer (internal coating layer) 35.

The first barrier layer (outer coating layer) 34 is located between the substrate tube 31 having a high OH concentration and the intermediate coating layer 32 containing the OH carrier P205, and prevents the OH contained in the substrate tube. 31 is diffused within the * intermediate coating layer 32. The second barrier layer (intermediate coating layer) 35 is located between the intermediate coating layer 32 and the central layer 33, and prevents the OH from diffusing from the substrate tube 31 within coating layer 32 or that OH resulting from water contained in a chemical material during the deposition of intermediate coating layer 32 penetrates into central layer 33 which is an optical waveguide region . The refractive index of each of the outer and inner coating layers 34 and 35 is controlled to be the same as or similar to the refractive index of the intermediate coating layer 32, and which is not greater than the refractive index of the substrate tube 31 or central layer 33.

The amount of OH contained in the substrate tube is relatively high compared to that of the silica for deposition. Silica is the chemical deposition material most stable against an OH component in structure and can effectively block the diffusion of OH at high temperature. Therefore, the first and second barriers 34 and 35 do not contain P20s which acts as an OH bridge, the refractive index of the coating is controlled using Si02, Ge, or F, and the thickness of these barrier layers are appropriately controlled in accordance to the overall thickness of the coating layer.

With reference to the characteristics of the refractive index of the optical fiber preform, the refractive index of the central layer 33 is greater than that of the coating layers 32, 34 and 35, and the refractive index of the core layer 34. increases in a constant proportion towards the center of the central layer. The thermal stress due to rapid freezing is generated when an optical fiber is removed from the preform at a high speed. Consequently, the refractive index of the central layer 33 gradually increases from the refractive index? N0 of the boundary to its center, thus finally making the refractive index? N the largest. By doing so optical losses of the optical fiber due to thermal stress, and degradation of the mechanical characteristics of the optical fiber can be avoided, and consequently an optical fiber having low losses and a small diameter ratio can be removed at high speed. For example, it is preferred that the refractive index of the outermost portion of the core layer be 75 to 99% of that of the center of the core layer.

Figures 4A, 4B and 4C are views illustrating a simple mode optical fiber manufacturing method in accordance with the present invention shown in Figure 2 or 3 using a modified method of chemical vapor deposition (MCVD). In the MCVD method, high purity carrier gases such as SiCl4, GeCl4, P0C13, or BC13 are introduced together with oxygen into a substrate tube 41 made of glass, and subsequently heat is applied to the substrate tube 41 via a heating means 43 with which soot forms, an oxidized deposit, inside the substrate tube by thermal oxidation in Figure 4A. Here, the concentration of the gas source is precisely controlled by a computer to adjust the refractive index, thus depositing a coating layer / core layer 42. The heating means 43 applies heat to the substrate tube 41 which rotates in the direction indicated by a spin arrow, while the heating means moves in the direction indicated by the straight arrow. The sources of gas to be deposited are introduced into the substrate tube 41 through an inlet connected to a source material storage unit. A mixing valve and a blocking valve measure the flow of the source materials introduced into the substrate tube and make necessary adjustments for the mixing of the source materials.

In a process for the deposition of a coating layer in the present invention, first, an outer coating layer (a first barrier) is formed by the deposition of a material having a low OH diffusion coefficient excluding a carrier material of OH such as P2O5 which has a high hygroscopicity. Another material suitable for decreasing the process temperature and increasing the deposition efficiency is doped, thereby forming an intermediate coating layer. A material having a low OH diffusion coefficient is deposited excluding a carrier material such as P20s, thus forming an inner lining layer (a second barrier). Subsequently, a central layer is formed, a region where an optical signal is transmitted. Therefore, the mixing of the source gases introduced into the substrate tube 41 becomes different according to each deposition layer, and this mixing can be achieved by properly controlling the mixing valve and the blocking valve.

In a process for the deposition of the central layer, the central layer is deposited in such a way that the refractive index is constant from the outside to its center, or such that the refractive index increases gradually in direction from the outside to its center .

Figure 4B shows a coating layer / core layer 40 deposited on the substrate tube 41. In Figure 4B, the reference number 43 denotes an outer coating layer, the reference number 44 denotes an intermediate coating layer, the number reference 45 denotes an inner lining layer, and the reference number 46 denotes a central layer.

With reference to Figure 4C, the deposited layers such as those shown in Figure B are collapsed and closed by applying heat to the substrate tube 41, on which the coating layer / core layer 40 has been deposited, using a heating medium. 43, thus forming a fiber optic preform 47.

In a deposition process, the barriers are deposited against the external and internal OH 43 and 45, which have the intermediate coating layer 44 and do not contain P2Os that acts as an OH bridge, effectively preventing the OH from diffusing in this way of the substrate tube 41 within the central layer 46 during a central deposition process, a collapsing process or a closing process.

Consequently, losses due to an OH absorption band in the central layer can be minimized while maintaining an adequate diameter (D / d) ratio. Also, the ratio of diameters can be made small, and therefore the deposition frequency can be reduced, thus shortening the process time. Here, it is preferred that a relationship (D / d) of the diameter (D) of the coating layer to the diameter (d) of the core layer is from 1.1 to 3.0.

While, in a sintering process performed simultaneously with the deposition, a self-collapse occurs due to the internal surface tension in a process to sinter and consolidate the soot particles. There is a cushion layer having a viscosity similar to that of the substrate tube between the substrate tube having a high viscosity and the coating layer having a low viscosity, such that the dissuasive power of the tube is improved, and is reduced by both the contraction of the tube.

When a fiber optic preform is manufactured using the MCVD method, the total processing time becomes shorter as the ratio of diameters becomes smaller, and a smaller diameter is very favorable for the manufacture of a preform having a large aperture. In the prior art, when a ratio of diameters becomes small, the loss of OH increases, thus deteriorating the quality of an optical fiber. Therefore, it is commonly known that a diameter ratio is around 3.0. However, according to the present invention, even when the ratio of diameters is reduced to less than 3.0, for example, to about 1.1 to 3.0, the loss of OH absorption can be reduced, and the losses due can also be minimized. to the thermal stress.

Industrial Applicability In the present invention, according to an optical fiber preform having a barrier against the OH and its manufacturing method as described above, external and internal barriers are deposited against the OH containing P2O5 between a substrate tube and a layer. of coating and between the coating layer and a central layer in a deposition process, such that the OH is effectively prevented from diffusing from the substrate tube to the central layer in a deposition process, a collapsing process or a closing process . Therefore, the losses due to the OH in the central layer are avoided. The central layer is also formed to increase its refractive index in the direction from the outside to the center, in such a way that the degradation of the characteristics due to a high removal speed of an optical fiber of the preform can be avoided.

It is noted that in relation to this date, the best method known to the applicant for carrying out the aforementioned invention is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims (15)

1. A fiber optic preform having a substrate tube, a coating layer and a core layer, characterized in that the optical fiber preform additionally comprises a first barrier layer deposited by a material having a low OH diffusion coefficient between the substrate tube and the coating layer, wherein the first barrier layer is to substantially prevent the OH contained in the substrate tube from diffusing into the coating layer.
2. The optical fiber preform according to claim 1, characterized in that it additionally comprises a second barrier layer formed by deposition of a material having a low OH diffusion coefficient between the coating layer and the central layer, to substantially prevent the OH that has diffused into the coating layer of the substrate tube is further diffused into the core layer.
3. The optical fiber preform according to claim 1 or 2, characterized in that the refractive index of the second barrier layer is controlled by doping Si02, Ge02, or F, and does not contain P205.
4. The optical fiber preform according to claim 2, characterized in that the refractive index of the first or second barrier layer is controlled to be the same or greater than the refractive index of the coating layer.
5. The optical fiber preform according to claim 1, characterized in that the ratio of diameters (D / d) of the diameter (D) of the coating layer to the diameter (d) of the core layer is from 1.1 to 3.0.
6. A fiber optic preform having a substrate tube, a coating layer and a core layer, characterized in that the optical fiber preform additionally comprises a first barrier layer deposited by a material having a low OH diffusion coefficient between the substrate tube and the coating layer, wherein the first barrier layer is to substantially prevent the OH contained in the substrate tube from diffusing into the coating layer, wherein the refractive index of the core layer is greater than the refractive index. of the coating layer and gradually increases in the direction from the outside of the core layer to the center of the core layer.
7. The optical fiber preform according to claim 6, characterized in that it additionally comprises a second barrier layer formed by deposition of a material having a low OH diffusion coefficient between the coating layer and the central layer, wherein the second layer The barrier is to substantially prevent the OH diffused into the coating layer from diffusing further into the core layer.
8. The optical fiber preform according to claim 6 or 7, characterized in that the refractive index of the second barrier layer is controlled by doping Si02, Ge02, or F, and does not contain P205.
9. The optical fiber preform according to claim 6 or 7, characterized in that the refractive index of the first or second barrier layer is controlled to be the same or greater than the refractive index of the coating layer.
10. The optical fiber preform according to claim 6, characterized in that the ratio of diameters (D / d) of the diameter (D) of the coating layer to the diameter (d) of the central layer is from 1.1 to 3.0.
11. The optical fiber preform according to claim 6, characterized in that the refractive index of the outermost point of the central layer is from 75 to 99% the refractive index in the center of the central layer.
12. A method for manufacturing an optical fiber preform having a substrate, a coating layer and a core layer, characterized in that the method comprises the steps of: forming a first barrier layer by deposition of a material having a low coefficient of OH diffusion; forming a coating layer by doping an appropriate material for the reduction of the process temperature and increasing the deposition efficiency; and forming a central layer being a region through which an optical signal is transmitted.
13. 13. The method according to claim 12, characterized in that a second barrier layer is additionally formed by deposition of a material having a low OH diffusion coefficient, before the core layer is formed after the coating layer is formed.
14. 14. The method according to claim 12, characterized in that the central layer is formed in such a way that the refractive index increases gradually in the direction from the outside to the center of the central layer.
15. 15. The method according to claim 12 or 13, characterized in that the refractive index of the first or second barrier is controlled by doping Si02, Ge02, or F and does not contain P20s having a relatively large hygroscopicity.