KR100855800B1 - Optical fiber preform manufacturing method for polarization mode dispersion reduction amd optical fiber preform made by the method and optical fiber using the optical fiber preform - Google Patents

Abstract

A fabrication method of optical fiber basic material, an optical fiber basic material manufactured by the method and an optical fiber drawn from the basic material are provided to reduce polarization mode dispersion, to simplify optical fiber drawing process and to improve the mechanical strength of optical fiber by modifying refractive index on the outer layer of the core. A fabrication method of optical fiber basic material comprises a step of carrying out a vapor deposition process comprising forming, lamination and calcination of soot particles in the thermal oxidation of reactant gas and oxygen gas on the surface of an substrate repeatedly depending on the refractive index profile in order to form core layer and clad layer, wherein fluorine gas is diffused locally into the core layer for forming outer layer of the core while the diffuse point of the fluorine gas varies randomly along the longitudinal direction of the basic material. In modified chemical vapor deposition, the reaction gas(50') from the reaction gas supply part(50) is put into the quartz tube(10) which rotates in a direction, the quartz tube is heated with high temperature furnace(60) which is transported to-and-fro along the outer respect of the quartz tube, and then preparing the optical fiber basic material by depositing a glass film which is a clad layer(20) and a core layer(30) repeatedly inside the quartz tube and making the quartz tube solid. When the reaction gas is provided from the reaction gas supply part, a little fluorine gas(40') is provided irregularly from the fluorine gas supply part(40) at the same time. The fluorine gas which is supplied irregularly is diffused to the core layer, and the refractive index in the part having the fluorine gas is locally lowered.

Description

Optical fiber preform manufacturing method for polarization mode dispersion reduction amd Optical fiber preform made by the method and Optical fiber using the optical fiber preform}

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 graph showing the relationship between the oxide content and the refractive index used in optical fiber production.

2 is a flowchart illustrating a method of manufacturing the optical fiber base material according to the first embodiment of the present invention.

3 is a flowchart illustrating a method of manufacturing the optical fiber base material according to the second embodiment of the present invention.

4 is a view showing a case in which the refractive index of the core layer is changed for each position of the base material when the optical fiber base material is manufactured according to the present invention.

<Description of main reference numerals in the drawings>

10: quartz tube 20: cladding layer

30: core layer 40: fluorine gas supply unit

40 ': fluorine gas 50: reaction gas supply unit

50 ': reaction gas 60: heating furnace

The present invention relates to a method for manufacturing an optical fiber base material, and more particularly, an optical fiber base material manufacturing method capable of reducing a polarization mode dispersion (PMD) by causing a refractive index change in a core outer layer, and an optical fiber manufactured using the same. A base material and an optical fiber drawn from the base material.

In general, the frequency response of transmission and reception in an optical fiber is limited by various dispersion modes such as color dispersion, transmission dispersion, and polarization dispersion. Nowadays, the development of various device technologies such as laser diodes with a very precise beam width has solved some of the color dispersion and transmission dispersion, but the polarization dispersion mode remains a difficult problem to solve.

Theoretically, a circular symmetric single mode optical fiber has two independent and mutually canceling orthogonal polarization modes. In addition, the electric field of light propagating through the optical fiber can be seen as a linear superposition of these two polarization eigenmodes. In practice, a single-mode fiber is offset by both incomplete polarization modes due to symmetrical lateral stresses or eccentricity of the circular core. These two modes propagate at different phase velocities, which causes the two polarization modes to propagate at different propagation constants β ₁ and β ₂ . This difference in propagation constants is called birefringence (Δβ), and the increase in birefringence means an increase in the speed difference between the two polarization modes.

Here, the differential time delay between the two polarization modes is called polarization mode dispersion. The polarization mode dispersion spreads a pulse of light transmitted through an optical fiber to increase a bit error rate. Thus, in data transmission through optical fibers, polarization mode dispersion acts as a major factor in limiting the capacity of data, which is undesirable in signal transmission systems, especially for optical fibers operating over long distances.

In order to ensure the transmission and reception performance of the optical fiber, it is essential to minimize the attenuation of the polarization mode dispersion and thus the signal dispersion. The most preferable countermeasure of the polarization mode dispersion is a uniform circular shape without mechanical stress and ovality. It is to make a fiber having a low specific ratio with a cross section, and it is difficult to completely remove the mechanical stress and ovality of the fiber.

As an example of the prior art for reducing the polarization mode dispersion of an optical fiber, US 5,298,047 includes forward and reverse directions in which the spin roller is rocked at an angle with respect to the optical fiber edge, or linearly reciprocated in a direction perpendicular to the optical axis. By applying a non-constant spin, there is a method of applying twist to an optical fiber such that the spin applied to the optical fiber has a non-constant spatial frequency.

In another example, US 5,992,181 is a method of inducing a polarization mode dispersion reduction by changing a refractive index of an optical fiber by irradiating a laser irregularly to an optical fiber by placing a laser device on an edge path of an optical fiber melted and drawn by a high temperature heating furnace. have.

However, in the case of US 5,298,047, in order to apply spin to the optical fiber in the optical fiber cutting process, physical contact between the optical fiber and the spin application device must be accompanied, and in order to sufficiently reduce the polarization mode dispersion through the twist generated in the optical fiber, the number of twists in a short length is sufficient. Should be. However, in order to increase the twist, sufficient spin has to occur. In this process, the fiber coating property due to the fiber vibration may deteriorate or the fiber breakage may be caused. In addition, the addition of spin force through contact increases the probability of providing mechanical defects on the surface of the optical fiber, which may weaken the optical fiber strength. Especially, when the optical fiber is drawn at high speed, it is difficult to control due to difficulties such as mechanical control and vibration. Losing problems will occur. In addition, in US 5,992,181, there is no physical contact to the optical fiber, but it is difficult to cope with a fast cutting speed in irradiating a laser to the optical fiber.

The present invention has been made to solve the problems of the prior art as described above, in order to improve the polarization mode dispersion, the polarization mode dispersion by controlling the refractive index rather than giving a change in the cross-sectional shape of the optical fiber by physical contact It is an object of the present invention to provide a method for manufacturing an optical fiber base material to be reduced.

Optical fiber base material manufacturing method for reducing the polarization mode dispersion according to the present invention for achieving the above object, the generation, deposition, and sintering of soot particles by the thermal oxidation reaction of the reaction gas and oxygen gas on the surface of a predetermined substrate In the method of manufacturing an optical fiber base material to form a core layer and a cladding layer by repeatedly performing a deposition process of a glass film through a predetermined refractive index profile, the fluorine gas is locally diffused into the core layer when the core outer layer is formed, The diffusion point of the fluorine gas is characterized in that it changes irregularly along the longitudinal direction of the base material.

Preferably, the core outer layer is one to five glass layers.

Preferably, the local diffusion of the fluorine gas, while supplying the fluorine gas with the reaction gas and oxygen gas to the surface of the substrate in a state in which the substrate is rotated in a constant direction, the fluorine gas supply time is changed irregularly.

delete

In the present invention, the fluorine gas is hexafluoroethane (C ₂ F ₆ ).

Preferably, the fluorine gas is introduced within 5 to 10 cc / min.

In the present invention, the method for producing the optical fiber base material is prepared by a crystal chemical vapor deposition method, the substrate is a rotating quartz tube.

In the present invention, the method for manufacturing the optical fiber base material is manufactured by an external vapor deposition method, and the substrate is a rotating woolen rod.

In the present invention, the method for producing the optical fiber base material is manufactured by vapor phase axial deposition, and the base material is a wool rod which is installed in the axial direction and rotates.

According to another aspect of the present invention, in the optical fiber base material manufactured by the optical fiber base material manufacturing method, fluorine is locally diffused in the core outer layer, and the fluorine diffusion point is irregularly changed along the length direction of the optical fiber base material. Provides an optical fiber base material.

According to another aspect of the present invention, in the optical fiber drawn from the optical fiber base material, fluorine is locally diffused in the core outer layer, and the fluorine diffusion point is irregularly changed along the longitudinal direction of the optical fiber. do.

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 specification and claims should not be construed as having a conventional or dictionary meaning, 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.

In the present invention, the optical fiber base material is manufactured to reduce polarization mode dispersion by controlling other factors, such as refractive index, rather than a method of applying spin to an optical fiber in a specific ratio improvement or optical fiber cutting process, which has been used in the prior art to reduce polarization mode dispersion. The method is disclosed.

1 is a graph showing the relationship between the oxide content and the refractive index used in optical fiber production.

As can be seen from FIG. 1, it can be seen that fluorine (F) has a great effect of reducing the refractive index even with a small amount. Therefore, in the method of manufacturing the optical fiber base material according to the present invention, two polarization modes are canceled by a change in the refractive index of the core outer layer by irregularly injecting fluorine having a good refractive index reduction effect even with a small amount in the process of depositing the core outer layer. Reduce polarization mode dispersion.

2 is a flowchart illustrating a method of manufacturing the optical fiber base material according to the first embodiment of the present invention.

Referring to FIG. 2, the first embodiment of the present invention is a case in which an optical fiber base material is manufactured using Modified Chemical Vapor Deposition (MCVD). That is, in the optical fiber base material manufacturing method according to the first embodiment, the reaction gas 50 'supplied from the reaction gas supply unit 50 is introduced into the quartz tube 10 rotating in a predetermined direction, and the quartz tube 10 The glass film corresponding to the cladding layer 20 and the core layer 30 inside the quartz tube 10 is heated in units of layers by heating the quartz tube 10 using a high temperature heating furnace 60 reciprocated along the outside. It is a method of manufacturing an optical fiber base material by repeatedly depositing and then solidifying.

More specifically, in order to form the cladding layer 20 on the inner wall of the quartz tube 10, the reaction gas 50 ′ is introduced from the reaction gas supply unit 50, and at a predetermined speed in the longitudinal direction of the quartz tube 10. The outside of the quartz tube 10 is heated using a moving furnace 60. The reactant gas 50 'is GeCl ₄ for the SiCl ₄ gas and the refractive index control of the silicon source Gas and POCl ₃ gas, oxygen gas is used as a carrier of these reaction gases (50 '). However, the present invention is not limited by the type of reaction gas 50 '. Then, the reaction gas 50 ′ injected into the quartz tube 10 and the oxygen gas undergo a thermal oxidation reaction to generate soot particles, and the generated soot particles are quartz tubes located in front of the heating furnace 60 by thermophoretic phenomenon. It is deposited on the inner surface of 10. The deposited soot particles are sintered and vitrified by the immediately approaching heating furnace 60 to form a transparent clad layer 20. The clad layer 20 of one layer is completed by the above process, and the clad layer 20 formation process is repeatedly performed until the thickness of the clad layer 20 becomes desired thickness.

Subsequently, the reaction gas 50 ′ is introduced from the reaction gas supply unit 50 to form the core layer 30 into the quartz tube 10 in which the clad layer 20 is deposited. At this time, the reaction gas 50 ′ forming the core layer 30 has a different composition of the reaction gas 50 ′ on which the clad layer 20 is formed so that the refractive index of the core layer 30 has a refractive index of the clad layer 20. Control to be greater than

Further, the reaction gas 50 'is introduced from the reaction gas supply unit 50, and at the same time, a small amount of fluorine gas 40' is irregularly introduced from the fluorine gas supply unit 40. Here, the injected fluorine gas 40 'is a hexafluoroethane (C ₂ F ₆ ) gas, and the supply amount of the injected fluorine gas 40' is supplied within 5 to 10 cc / min.

Then, the outside of the quartz tube 10 is heated using the heating furnace 60 moving at a predetermined speed in the longitudinal direction of the quartz tube 10. Then, the reaction gas 50 ′ injected into the quartz tube 10 and the oxygen gas cause a thermal oxidation reaction to generate soot particles. The soot particles thus produced are deposited in front of the heating furnace 60 by a thermophoretic phenomenon, and the deposited soot particles are sintered and vitrified by the heat provided by the heating furnace 60, which is subsequently approached, to form the core layer 30. Form one layer. In this case, the fluorine gas 40 ′ irregularly introduced into the quartz tube 10 diffuses into the core layer 30 to include fluorine atoms as impurities of the core layer 30. As a result, the refractive index of the region of the core layer 30 including fluorine atoms is locally lowered. The step of forming the core layer 30 while injecting the fluorine gas 40 'is preferably performed only until about five layers of the core layer 30 are formed, and thereafter, the fluorine gas 40' is formed. The process of forming the core layer 30 is performed until the thickness of the core layer 30 becomes desired thickness in the state which stopped supplying of. When the thickness of the core layer 30 is formed to a desired thickness, the optical fiber base material manufacturing is completed.

3 is a flowchart illustrating a method of manufacturing the optical fiber base material according to the second embodiment of the present invention.

Referring to FIG. 3, a second embodiment of the present invention is a case of manufacturing an optical fiber base material by using an external vapor deposition method (OVD). In the optical fiber base material manufacturing method according to the second embodiment, the combustion gas 71 and the reaction gas 51 are moved to the mother rod 11 side by using the burner 61 which periodically reciprocates along the longitudinal direction of the rotating mother rod 11. Squirt '). Then, a thermal oxidation reaction of the reaction gas 51 ′ is caused by the high temperature flame generated by the combustion reaction of the combustion gas 71, soot particles are generated, and the soot particles are thus formed by the thermophoretic phenomenon. After depositing on the surface of the c), it is sintered and vitrified by heat provided by the flame to form a glass film corresponding to the clad layer 20 or the core layer 30. This glass film forming process is repeatedly performed until the desired thickness of the cladding layer 20 and the core layer 30 is formed.

More specifically, the combustion gas 71 and the reaction gas using the burner 61 reciprocating at a predetermined speed in the longitudinal direction of the bristle 11 in order to form the core layer 30 on the rotating bristle 11 The reaction gas 51 'supplied from the supply part 51 is injected to the bristle stick 11 side. Then, a flame is generated by the combustion reaction of the combustion gas 71, and soot particles are generated by the thermal oxidation reaction and the hydrolysis reaction of the reaction gas 51 'in the high temperature atmosphere formed by the flame. The resulting soot particles move toward the relatively low temperature woolen rod 11 by thermophoresis and are deposited on the surface of the woolen blade 11. The soot deposition layer is sintered and vitrified by the heat supplied by the burner 61 to form one core layer 30. Since the burner 61 periodically reciprocates along the longitudinal direction of the bristle 11, the core layer 30 is repeatedly stacked on the bristle 11 every time the burner 61 reciprocates.

On the other hand, a small amount of fluorine gas 41 'is additionally supplied through the burner 61 to the latter part of the core layer 30 forming process. At this time, the supply of the fluorine gas 41 'is made irregular. Fluorine gas 41 'is supplied substantially the same as in the first embodiment described above. The process of forming the core outer layer 30 'while supplying the fluorine gas 41' is preferably applied when depositing the last five layers of core layers based on the total thickness of the core layer 30. When the fluorine gas 41 'is irregularly supplied in the process of forming the core outer layer 30', the fluorine atoms in the core outer layer 30 'are sintered and vitrified in the process of sintering and vitrifying the soot particles constituting the core outer layer 30'. As a result, the refractive index of the core outer layer 30 'is reduced locally.

After the deposition of the core outer layer 30 'through the irregular supply of the fluorine gas 41' is completed, the clad layer 20 is formed by the above process. At this time, the reaction gas 51 ′ used to form the cladding layer 20 has a composition different from that of the reaction gas 51 ′ for forming the core layer 30. This is to make the refractive index of the cladding layer 20 smaller than the refractive index of the core layer 30. When the cladding layer forming process is performed and the thickness of the cladding layer 20 is formed to a desired thickness, the preparation of the optical fiber base material is completed.

On the other hand, in the above-described embodiment, the configuration of the present invention was mainly focused on the method of manufacturing the base material by the crystal chemical vapor deposition method and the external vapor deposition method. However, the method of manufacturing the optical fiber base material according to the present invention is not limited thereto, and it is obvious that the method may be applied to the method of manufacturing the optical fiber base material by vapor deposition in addition to the above method.

4 is a view showing a case in which the refractive index of the core layer is changed for each position of the base material when the optical fiber base material is manufactured according to the present invention.

As shown in FIG. 4, when the optical fiber base material is manufactured according to the present invention, the refractive index of the core layer 30 is changed irregularly. The core outer layer 30 ′ in which the refractive index is changed irregularly cancels each other with the polarization mode dispersion caused by the change in specific ratio of the optical fiber, and as a result, the polarization mode dispersion can be reduced.

Although the invention has been described above by means of limited embodiments and drawings, the invention is not limited thereto and will be described below by the person skilled in the art and the technical spirit of the invention. Of course, various modifications and variations are possible within the scope of the claims.

According to the present invention, to reduce the polarization mode dispersion by providing an optical fiber base material manufacturing method that can change the refractive index of the core outer layer without applying a physical deformation to the optical fiber, the polarization mode dispersion due to the change of specific ratio of the optical fiber is the core The polarization mode dispersion can be reduced as a result of being offset by the change in the refractive index of the outer layer. In addition, a complicated spin process is not required in the optical fiber manufacturing process, thereby simplifying and stabilizing the optical fiber cutting process. In addition, it is possible to produce an optical fiber with improved mechanical strength.

Claims (11)

A core layer and a cladding layer are formed by repeatedly performing a process of generating, depositing, and sintering a glass film through a thermal oxidation reaction of a reaction gas and oxygen gas on a predetermined substrate surface according to a predetermined refractive index profile. In the manufacturing method of the optical fiber base material, A method of manufacturing an optical fiber base material for reducing polarization mode dispersion, wherein the fluorine gas is locally diffused into the core layer when the core outer layer is formed, and the diffusion point of the fluorine gas is irregularly changed along the length direction of the base material. The method of claim 1, The core outer layer is an optical fiber base material manufacturing method for polarization mode dispersion reduction, characterized in that the glass film of 1 to 5 layers. The method of claim 1, Local diffusion of the fluorine gas is performed by supplying fluorine gas together with the reaction gas and oxygen gas to the surface of the substrate while rotating the substrate in a constant direction, and irregularly changing the fluorine gas supply timing. Optical fiber base material manufacturing method for reducing the polarization mode dispersion. delete The method of claim 1, The fluorine gas is hexafluoroethane (C ₂ F ₆ ) characterized in that the optical fiber base material manufacturing method for polarization mode dispersion reduction. The method of claim 1, The fluorine gas is the optical fiber base material manufacturing method for reducing the polarization mode dispersion, characterized in that the input within 5 to 10 cc / min. The method of claim 1, The method for manufacturing the optical fiber base material is prepared by a crystal chemical vapor deposition method, the substrate is a method for manufacturing an optical fiber base material for polarization mode dispersion reduction, characterized in that the rotating quartz tube. The method of claim 1, The method of manufacturing the optical fiber base material is manufactured by an external vapor deposition method, the substrate is a fiber base material manufacturing method for polarization mode dispersion reduction, characterized in that the rotating rod. The method of claim 1, The method of manufacturing the optical fiber base material is manufactured by the vapor phase axial deposition method, and the substrate is an optical fiber base material manufacturing method for reducing the polarization mode dispersion, characterized in that the rod is installed and rotated in the axial direction. An optical fiber base material manufactured by the method for manufacturing an optical fiber base material according to claim 1, wherein fluorine is locally dispersed in the core outer layer, and a fluorine diffusion point is irregularly changed along the longitudinal direction of the optical fiber base material. Optical fiber base material for reducing polarization mode dispersion. The optical fiber drawn from the optical fiber base material according to claim 10, wherein fluorine is locally diffused in the core outer layer and the diffusion point of fluorine is irregularly changed along the longitudinal direction of the optical fiber. Fiber optics.

Images