JP2004043231A - Method for manufacturing optical fiber, and optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber with its transmission loss reduced and with its productivity improved, and to provide an optical fiber. <P>SOLUTION: Glass of an optical fiber preform before drawing is made to be in a structure-relaxed state by annealing the preform for a predetermined time of 30 hours or longer at a predetermined temperature of from 950°C to 1150°C. After heating and drawing the optical fiber preform at 2100°C or lower with a drawing furnace 11 to form an optical fiber 3, the optical fiber 3 after drawing is slowly cooled by annealing at a predetermined temperature of from 1100°C to 1600°C in a heat treatment furnace 21 installed at the later step of the drawing furnace 11. Thus, the optical fiber with a low transmission loss is manufactured in high productivity by suitably maintaining the structure-relaxed state obtained in the preform stage by applying drawing conditions under which at least either the low temperature drawing or the slow cooling is conducted. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an optical fiber that transmits light with low transmission loss, and an optical fiber.
[0002]
[Prior art]
In transmission of light using an optical fiber, transmission loss such as Rayleigh scattering loss caused by Rayleigh scattering in the optical fiber and structural irregularity loss caused by structural disorder in the optical fiber becomes a problem. On the other hand, an optical fiber capable of reducing transmission loss or a method for manufacturing the same has been proposed.
[0003]
For example, in the document “Sakaguchi, IEICE Transactions 2000/1 Vol. J83-C No. 1, pp. 30-36”, Rayleigh scattering loss in an optical fiber by slow cooling of an optical fiber after drawing. Is described. That is, the Rayleigh scattering intensity in the glass is not fixed depending on the material, but depends on a virtual temperature Tf (Five-Temperature) which is a virtual temperature indicating disorder of the arrangement state of atoms in the glass. Specifically, as the virtual temperature Tf in the glass increases (the disorder increases), the Rayleigh scattering intensity increases.
[0004]
On the other hand, when the optical fiber preform is heated and drawn, a heat treatment furnace is installed after the drawing furnace, so that the drawn optical fiber passes through the heat treatment furnace within a predetermined temperature range. And the optical fiber is annealed. By such annealing of the optical fiber, rapid cooling of the optical fiber after drawing is prevented, and the optical fiber is gradually cooled. At this time, the virtual temperature Tf in the optical fiber decreases due to the structural relaxation of the glass due to the rearrangement of atoms, and the Rayleigh scattering intensity in the optical fiber is suppressed.
[0005]
In addition, the document “K. Tajima,“ NTT REVIEW NEW Vol. 10 No. 6, No. 6, pp. 109-113 (1998) ”describes that Rayleigh scattering intensity is similarly suppressed by drawing at low temperature. .
[0006]
[Problems to be solved by the invention]
However, conventional manufacturing methods, such as the above-described manufacturing method in which an optical fiber after drawing is annealed using a heat treatment furnace, can achieve both a reduction in optical fiber transmission loss and an improvement in optical fiber productivity. difficult.
[0007]
For example, when the transmission loss of an optical fiber is reduced by annealing in a heat treatment furnace provided downstream of the drawing furnace, it is necessary to use a considerable part of the drawing line as a heat treatment line. For this reason, if the line for heat treatment is added, the length of the line used for cooling the optical fiber is shortened by that much, and the line speed of the optical fiber at the time of drawing cannot be increased.
[0008]
Further, when reducing the transmission loss of an optical fiber by drawing at a low temperature, in order to maintain the transmission characteristics of the optical fiber such as dispersion while keeping the tension constant, it is necessary to draw at a low drawing speed, As in the case of annealing in a heat treatment furnace, there was a problem that the productivity of optical fibers did not increase.
[0009]
The present invention has been made to solve the above problems, and provides a method for manufacturing an optical fiber, in which the transmission loss in the optical fiber is reduced and the productivity is improved, and an optical fiber. The purpose is to:
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing an optical fiber according to the present invention comprises the steps of (1) an optical fiber mother made by dehydration sintering and having a core region and a cladding region provided on the outer periphery of the core region. A heat treatment step of heat-treating the material at a temperature of 950 ° C. or more and 1150 ° C. or less for a predetermined time of 30 hours or more; and (2) a structural relaxation state obtained in the heat treatment step of the heat-treated optical fiber preform by a drawing furnace. And a drawing step of creating an optical fiber by heating and drawing under the drawing condition in which is maintained.
[0011]
In the optical fiber manufacturing method described above, attention is paid not only to the drawing conditions when the optical fiber preform is heated and drawn, but also to the manufacturing process of the optical fiber preform. Before heating and drawing the optical fiber preform prepared by dehydration sintering, the optical fiber preform is annealed at a furnace temperature of a predetermined temperature within a range of 950 ° C. or more and 1150 ° C. or less, In the step (2), the optical fiber is made by drawing the optical fiber preform so that the obtained structural relaxation state is maintained.
[0012]
Thus, an optical fiber with reduced transmission loss can be reliably manufactured. Further, since the structure of the glass is relaxed before drawing, the productivity of optical fibers can be improved, for example, the linear speed of the optical fibers at the time of drawing can be increased.
[0013]
Regarding specific drawing conditions for maintaining the structural relaxation state, in the drawing step, as the drawing conditions for heating and drawing the optical fiber preform at a temperature of 2100 ° C. or less by a drawing furnace, the structural relaxation state is set. There is a method of creating an optical fiber while holding it.
[0014]
Alternatively, in the drawing step, the structural relaxation state is set as a drawing condition in which the optical fiber drawn by the drawing furnace is heat-treated at a temperature of 1100 ° C. or more and 1600 ° C. or less by a heat treatment furnace provided at a subsequent stage of the drawing furnace. There is a method of creating an optical fiber while holding the optical fiber.
[0015]
As described above, by applying the drawing conditions of drawing the optical fiber at a temperature of 2100 ° C. or lower at a low temperature, gradually cooling the optical fiber by annealing in a heat treatment furnace, or both, the base material can be obtained. The optical fiber can be drawn while suitably maintaining the relaxed state of the structure. Further, other drawing conditions may be used.
[0016]
Further, an optical fiber according to the present invention includes a core region and a cladding region provided on an outer periphery of the core region, and is manufactured by the above-described method for manufacturing an optical fiber. Thus, an optical fiber that can be manufactured with high productivity and has good characteristics with reduced transmission loss can be obtained.
[0017]
The core region is made of pure SiO₂Ge is added at an addition amount where the relative refractive index difference expressed in% with respect to [Ge] is, and the Rayleigh scattering coefficient A (dB / km · μm⁴) And transmission loss α at a wavelength of 1.00 μm._1.00(DB / km) is a reference value A represented by the following equation.₀, And α₀
A₀= 0.85 + 0.29 [Ge]
α₀= 0.86 + 0.29 [Ge]
97% or less.
[0018]
In the optical fiber described above, the Rayleigh scattering coefficient A of the optical fiber and the transmission loss α including the Rayleigh scattering loss_1.00Is a reference value A indicating a value in a normal optical fiber.₀, Α₀The value is reduced by 3% or more, and becomes a value of 97% or less. As a result, an optical fiber with sufficiently reduced transmission loss is obtained.
[0019]
The core region is made of pure SiO₂And the Rayleigh scattering coefficient A (dB / km · μm⁴) And transmission loss α at a wavelength of 1.00 μm._1.00(DB / km) is the reference value A₀= 0.85 and α₀96% or less with respect to 0.86.
[0020]
In the pure silica core optical fiber described above, the Rayleigh scattering coefficient A of the optical fiber and the transmission loss α including the Rayleigh scattering loss_1.00Is a reference value A indicating a value in an ordinary pure silica core optical fiber.₀, Α₀The value is reduced by 4% or more to 96% or less. As a result, an optical fiber with sufficiently reduced transmission loss is obtained.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of an optical fiber manufacturing method and an optical fiber according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.
[0022]
First, an outline of a method for manufacturing an optical fiber will be described.
[0023]
In the method for manufacturing an optical fiber according to the present invention, first, an optical fiber preform having a core region and a clad region provided on the outer periphery of the core region is prepared through a dehydration sintering process. Then, in order to lower the virtual temperature Tf in the optical fiber preform by relaxing the structure of the glass with respect to the optical fiber preform obtained by the dehydration sintering, the optical fiber preform is subjected to predetermined annealing conditions at the preform stage. Heat-treat the material.
[0024]
Specifically, N₂The prepared optical fiber preform is placed in a heat treatment furnace in a predetermined gas atmosphere such as a gas atmosphere. Then, the furnace temperature of the heat treatment furnace (the temperature of the heater provided in the heat treatment furnace) is set to a predetermined temperature within a range of 950 ° C. to 1150 ° C., and the optical fiber preform is annealed for a predetermined time of 30 hours or more. (Heat treatment step). Note that the step of annealing the optical fiber preform is not shown in FIG. 1 because it is performed using, for example, a heat treatment furnace provided separately from the drawing apparatus.
[0025]
Subsequently, using the optical fiber preform in a structurally relaxed state by the heat treatment, the optical fiber preform is heated and drawn by a drawing furnace under drawing conditions in which the obtained structurally relaxed state is maintained. Create a fiber (drawing step). Thus, an optical fiber with reduced transmission loss due to the relaxation of the glass structure can be obtained.
[0026]
As a specific drawing condition for maintaining the structural relaxation state, for example, a drawing condition for performing low-temperature drawing of an optical fiber can be applied. In this case, as a drawing condition for setting the temperature of the heater, which is the furnace temperature of the drawing furnace, to a relatively low predetermined temperature within the range of 2100 ° C. or less, the optical fiber preform is heated while maintaining the structural relaxation state. Draw.
[0027]
Alternatively, a drawing condition for gradually cooling the optical fiber by annealing in a heat treatment furnace can be applied. In this case, a heat treatment furnace for annealing the drawn optical fiber is provided downstream of the drawing furnace. Then, as a drawing condition in which the optical fiber drawn by the drawing furnace is gradually cooled while being annealed at a temperature of 1100 ° C. or more and 1600 ° C. or less by the heat treatment furnace, the optical fiber preform is maintained while maintaining the structurally relaxed state. Draw a heating wire.
[0028]
A drawing apparatus 1 shown in FIG. 1 shows an example of a configuration of a drawing apparatus used in a drawing step in the above-described optical fiber manufacturing method.
[0029]
The drawing apparatus 1 shown in FIG. 1 is a drawing apparatus used for drawing a quartz glass optical fiber, and includes a drawing furnace 11, a heat treatment furnace 21 for slow cooling, and a cooling means 31. It is configured. The drawing furnace 11, the heat treatment furnace 21, and the cooling means 31 are installed in this order in a direction in which the optical fiber preform 2 is drawn (vertical direction in FIG. 1). Further, a resin coating portion 40 for coating the drawn glass fiber 3 with a resin is provided downstream of the heat treatment furnace 21 and the cooling means 31.
[0030]
In the production of an optical fiber using the main drawing apparatus 1, first, an optical fiber preform 2 whose structure has been relaxed by the heat treatment at the preform stage as described above is prepared, and a preform supply device (shown in the drawing). (Not shown) is supplied to the drawing furnace 11. Then, the lower end of the optical fiber preform 2 is heated and softened by the heater 12 in the drawing furnace 11 and drawn at a predetermined drawing speed to form the glass fiber 3.
[0031]
Here, when the drawing conditions for performing the low-temperature drawing of the optical fiber are applied, the temperature of the heater 12, which is the furnace temperature of the drawing furnace 11, is set to a predetermined temperature within a range of 2100 ° C. or less, and the optical fiber base is set. Material 2 is drawn. At this time, the temperature of the optical fiber preform 2 is about 2000 ° C. or less. Further, a gas supply passage 15 from an inert gas supply unit 14 is connected to the furnace tube 13 of the drawing furnace 11, and the inside of the furnace tube 13 is configured to have an inert gas atmosphere.
[0032]
The glass fiber 3 drawn by heating is rapidly cooled in the furnace tube 13 by, for example, an inert gas to about 1700 ° C. Thereafter, the glass fiber 3 is taken out of the drawing furnace 11 from the lower part of the furnace tube 13 and is air-cooled between the drawing furnace 11 and the heat treatment furnace 21. As the inert gas, for example, N₂Gas can be used. N₂The heat conductivity coefficient λ (T = 300K) of the gas is 26 mW / (m · K). The coefficient of heat conduction of air λ (T = 300K) is 26 mW / (m · K).
[0033]
Next, the drawn and air-cooled glass fiber 3 is placed in a heat treatment furnace 21 for annealing provided between the drawing furnace 11 and the resin coating portion 40 and at a predetermined position after the drawing furnace 11. send. Then, the glass fiber 3 after drawing is gradually cooled by annealing the glass fiber 3 at a predetermined temperature by the heater 22 in the heat treatment furnace 21. Here, the glass fiber 3 is annealed by setting the temperature of the heater 22, which is the furnace temperature of the heat treatment furnace 21, to a predetermined temperature in the range of 1100 ° C to 1600 ° C.
[0034]
The heat treatment furnace 21 has a furnace tube 23 through which the glass fiber 3 passes. The core tube 23 of the heat treatment furnace 21 has N₂A gas supply passage 25 from a gas supply unit 24 is connected, and N₂It is configured to have a gas atmosphere. N₂Instead of using a gas, it is also possible to use air or a gas having a relatively large molecular weight such as Ar or the like. However, when the furnace tube is made of carbon, it is necessary to use a gas containing no oxygen. When the drawing conditions for gradually cooling the optical fiber by annealing after drawing are not applied, the heat treatment furnace 21 may not be provided.
[0035]
Subsequently, the annealed glass fiber 3 is cooled by a cooling means 31 for forced cooling of the glass fiber 3 provided between the drawing furnace 11 and the resin coating section 40 and at a predetermined position after the heat treatment furnace 21. Send to Then, the glass fiber 3 is cooled to a predetermined temperature by the cooling means 31.
[0036]
The cooling means 31 has a cylindrical tube 32 through which the glass fiber 3 passes. A plurality of nozzles 33 connected to a cooling gas supply unit 34 are provided on the side wall of the cylindrical tube 32. Thus, the cooling gas is supplied from the cooling gas supply unit 34 to the glass fiber 3 passing through the cylindrical tube 32, and the glass fiber 3 is forcibly cooled. He gas is preferably used as the cooling gas. If the glass fiber 3 can be sufficiently cooled by ordinary air cooling, such a configuration that the cooling means 31 is not used may be adopted.
[0037]
The outer diameter of the glass fiber 3 that has exited the cooling means 31 is measured online by the outer diameter measuring device 51. Then, the measured value is fed back to the drive motor 53 that drives the rotation of the drum 52, and the rotation of the drum 52 is drive-controlled so that the outer diameter becomes constant. An output signal from the outer diameter measuring device 51 is sent to a control unit 54 as control means. The control unit 54 calculates the rotational speeds of the drum 52 and the drive motor 53 by calculation so that the outer diameter of the glass fiber 3 becomes a predetermined value set in advance.
[0038]
From the control unit 54, an output signal indicating the rotational speed of the drum 52 and the drive motor 53 obtained by calculation is output to a drive motor driver (not shown). The drive motor driver controls the rotation speed of the drive motor 53 based on an output signal from the control unit 54.
[0039]
The glass fiber 3 whose outer diameter has been measured by the outer diameter measuring device 51 is input to the resin coating portion 40 configured in two steps (tandem). First, in the first-stage resin coating portion, a UV resin 42 is applied to the glass fiber 3 having passed through the outer diameter measuring device 51 by the coating die 41. The applied UV resin 42 is cured by ultraviolet light from a UV lamp 44 in a resin curing section 43.
[0040]
Further, in the second-stage resin coating portion, a UV resin 47 is applied to the glass fiber 3 from the resin cured portion 43 by the coating die 46. The applied UV resin 47 is cured by ultraviolet light from a UV lamp 49 of a resin curing section 48. Thereby, the optical fiber 4 in which the glass fiber 3 is covered with the resin is formed. Then, the optical fiber 4 is wound by the drum 52 via the guide roller 56. The drum 52 is supported by a rotary drive shaft 55, and an end of the rotary drive shaft 55 is connected to a drive motor 53.
[0041]
In addition, the gas supply passage 15 from the inert gas supply unit 14 is connected to the furnace tube 13 of the drawing furnace 11 as described above, and the inside of the furnace tube 13 is configured to have an inert gas atmosphere. ing. On the other hand, as the inert gas supply unit 14, N₂A gas supply unit is provided, and N₂Supply gas and N₂The gas atmosphere may be configured. Also, the He gas supply unit and N₂A gas supply unit is provided, and He gas or N₂It is good also as a structure which supplies gas.
[0042]
Effects of the optical fiber manufacturing method according to the above-described embodiment will be described.
[0043]
In the method of manufacturing the optical fiber according to the present embodiment, when the optical fiber preform 2 is heated and drawn to manufacture the glass fiber 3, not only the drawing conditions of the heating drawing but also the manufacturing of the optical fiber preform 2 are performed. We focus on the process. Before the optical fiber preform 2 made by dehydration sintering is heated and drawn by the drawing apparatus 1, the optical fiber preform is heated at a predetermined temperature within a range of 950 ° C. or more and 1150 ° C. or less. Is annealed to bring the structure into a relaxed state at the stage of the preform, and the optical fiber preform 2 is drawn under the drawing conditions for maintaining the obtained relaxed state to produce the glass fiber 3.
[0044]
According to such a manufacturing method, by annealing the optical fiber preform, the virtual temperature Tf in the optical fiber preform decreases due to the relaxation of the glass structure. Also, in the process of heating the optical fiber preform in the relaxed state into an optical fiber, the glass of the optical fiber preform is not completely melted, and the optical fiber is drawn while the glass is softened. Is done.
[0045]
For this reason, when the optical fiber preform is heated and drawn, by appropriately setting the drawing conditions, the optical fiber preform is drawn while maintaining a certain degree of the structural relaxation state of the glass obtained in the preform stage. It is possible to make an optical fiber by drawing. Thereby, the virtual temperature Tf in the obtained optical fiber is reduced, and an optical fiber with reduced transmission loss including Rayleigh scattering loss and Rayleigh scattering loss can be manufactured.
[0046]
Further, according to this manufacturing method, since the structure of the glass is relaxed at the stage of the base material before drawing, the length of the heat treatment line in the drawing line can be shortened, or the light at the time of drawing can be reduced. The linear velocity of the fiber can be increased. Thereby, the optical fiber can be efficiently drawn, and the productivity of the optical fiber can be improved. As described above, a method of manufacturing an optical fiber that can suitably achieve both a reduction in the transmission loss of the optical fiber and an improvement in the productivity of the optical fiber is realized.
[0047]
In addition, as to the specific drawing conditions for maintaining the structural relaxation state, as described above, the drawing conditions for drawing the optical fiber at a low temperature or the optical fiber after drawing by annealing in a heat treatment furnace are used. Can be applied. As described above, by setting the drawing conditions for performing low-temperature drawing, slow cooling, or both of the optical fiber, the optical fiber is drawn while suitably maintaining the structural relaxation state obtained at the preform stage. can do. Further, other drawing conditions may be used.
[0048]
Next, an optical fiber according to the present invention manufactured by the above-described manufacturing method will be described. The optical fiber according to the present invention can be manufactured with high productivity, and has good characteristics with reduced transmission loss, as described above for the manufacturing method.
[0049]
FIG. 2 is a graph showing a refractive index profile of the first embodiment of the optical fiber according to the present invention. In this graph, the horizontal axis indicates the position of each part in the optical fiber as viewed from the central axis. The vertical axis represents pure SiO at each site in the optical fiber.₂The relative refractive index difference (%) with respect to is shown.
[0050]
The optical fiber of the present embodiment includes a core region 100 and a cladding region 110 provided on the outer periphery of the core region 100. The core region 100 has a radius r including the central axis of the optical fiber.₀Is formed as a layer. The core region 100 is made of SiO doped with Ge in a predetermined amount.₂Consists of
[0051]
Specifically, the core region 100 includes pure SiO₂When the amount of Ge is represented by the relative refractive index difference [Ge] expressed in% with respect to the addition amount, the relative refractive index difference [Ge] satisfies a predetermined condition (for example, the addition amount becomes 0.3% or more). Ge is added. Thereby, the relative refractive index difference Δn of the core region 100₀Is Δn₀= [Ge]> 0.
[0052]
In the present embodiment, the cladding region 110 is formed of a single cladding layer 111. The cladding layer 111 has a radius r provided on the outer periphery of the core region 100.₁Is formed as a layer. The cladding layer 111 is made of pure SiO₂Consists of Thereby, the relative refractive index difference Δn of the cladding layer 111₁Is Δn₁= 0. The optical fiber having such a configuration can be suitably applied, for example, as a Ge-doped single mode fiber (Ge-SM).
[0053]
Preferred characteristic conditions of the present optical fiber will be described. That is, in the optical fiber shown in FIG. 2, the Rayleigh scattering coefficient A (dB / km · μm⁴) And transmission loss α at a wavelength of 1.00 μm._1.00(DB / km) is a reference value A represented by the following equation.₀, And α₀
A₀= 0.85 + 0.29 [Ge]
α₀= 0.86 + 0.29 [Ge]
Is preferably 97% or less. Here, [Ge] is pure SiO indicating the amount of Ge added to the core region, as described above.₂Is a relative refractive index difference expressed in% with respect to. Also, A₀Is, for example, if [Ge] = 0.35%, A₀= 0.85 + 0.29 x 0.35 = 0.95.
[0054]
In this preferable characteristic condition, the Rayleigh scattering coefficient A of the optical fiber and the transmission loss α including the Rayleigh scattering loss_1.00Is a reference value A indicating a value in a normal optical fiber.₀, Α₀The value is reduced by 3% or more, and becomes a value of 97% or less. As a result, an optical fiber with sufficiently reduced transmission loss is obtained.
[0055]
The specific configuration of the optical fiber according to the present invention is not limited to the configuration of the first embodiment shown in FIG. May be used. For example, for the core region, pure SiO without Ge is added.₂It is good also as composition consisting of. In addition, the above-mentioned reference value A₀, Α₀The characteristic conditions regarding [Ge] = 0 can be similarly applied to the configuration of the pure silica core where [Ge] = 0.
[0056]
The core is pure SiO₂In the optical fiber composed of, the Rayleigh scattering coefficient A (dB / km · μm⁴) And transmission loss α at a wavelength of 1.00 μm._1.00(DB / km) is the reference value A₀= 0.85 and α₀It is preferably 96% or less with respect to 0.86.
[0057]
In this preferable characteristic condition, the Rayleigh scattering coefficient A of the optical fiber and the transmission loss α including the Rayleigh scattering loss_1.00Is a reference value A indicating a value in an ordinary pure silica core optical fiber.₀, Α₀The value is reduced by 4% or more to 96% or less. As a result, an optical fiber with sufficiently reduced transmission loss is obtained.
[0058]
In the cladding region, the structure shown in FIG.₂Although it was configured to have a single cladding layer made of₂, Ge-added SiO₂Or F-added SiO₂It is preferable to have a configuration having one or a plurality of cladding layers composed of any one of the above.
[0059]
According to such a configuration, various types of optical fibers such as a single mode fiber (SMF: Single Mode Fiber), a dispersion shift fiber (DSF: Dispersion Shift Fiber), and a dispersion compensation fiber (DCF: Dispersion Compensation Fiber) are used. It can be manufactured with good productivity due to good characteristics.
[0060]
Each characteristic condition of the optical fiber described above will be further described. Under the above-mentioned preferable characteristic conditions in the optical fiber according to the present invention, the Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm are used as indices for evaluating the effect of reducing the Rayleigh scattering loss and the like._1.00And the Rayleigh scattering coefficient A and the transmission loss α_1.00Is a reference value A indicating a normal value.₀, Α₀The value is 97% or less, which is reduced by 3% or more than that.
[0061]
The transmission loss αλ (dB / km) at a wavelength λ in an optical fiber is generally expressed by the following equation, based on the Rayleigh scattering loss and other transmission loss components such as structural irregularity loss.
αλ = A / λ⁴+ B + C (λ)
Is represented by Among them, the first term A / λ⁴(DB / km) indicates the Rayleigh scattering loss, and its coefficient A is the Rayleigh scattering coefficient (dB / km · μm⁴). From the above equation, the Rayleigh scattering loss is proportional to the Rayleigh scattering coefficient A. Therefore, if the Rayleigh scattering coefficient A is reduced by 3% from the reference value, the Rayleigh scattering loss is reduced by 3%.
[0062]
Here, in an optical fiber obtained by a normal manufacturing method that does not perform annealing of the optical fiber preform before drawing, low-temperature drawing of the optical fiber, or slow cooling of the optical fiber after drawing, the core region has When the amount of Ge added is represented by the above [Ge], the Rayleigh scattering coefficient A (dB / km · μm⁴) Is given by
A₀= 0.85 + 0.29 [Ge]
It becomes. Therefore, this normal value A₀Can be used as a reference value of the Rayleigh scattering coefficient A. At this time, the Rayleigh scattering coefficient A in the obtained optical fiber is a reference value A₀Should be reduced by 3% or more.
[0063]
Further, in order to evaluate the entire transmission loss including the Rayleigh scattering loss, the transmission loss α at a wavelength of 1.00 μm_1.00May be used as an index. At a wavelength of 1.00 μm, B + C (λ) is approximately 0.01 in the above expression of the transmission loss αλ. Therefore, in an optical fiber obtained by a normal manufacturing method, the transmission loss α_1.00The value of (dB / km) is calculated by the following equation.
α₀= A₀+0.01
= 0.86 + 0.29 [Ge]
It becomes. Therefore, this normal value α₀Is the transmission loss α_1.00Can be used as the reference value. At this time, the transmission loss α in the obtained optical fiber_1.00Is the reference value α₀Is preferably reduced by at least 3%.
[0064]
Thus, the Rayleigh scattering coefficient A or the transmission loss α_1.00By using as an index, it is possible to reliably obtain the effect of reducing the Rayleigh scattering loss or the entire transmission loss including the Rayleigh scattering loss. In addition, the above-mentioned reference value A₀, Α₀According to the respective expressions, a variable [Ge] related to the amount of Ge added to the core is included in the expression. Therefore, it is possible to evaluate the transmission loss according to the amount of Ge added.
[0065]
From the above equation, the Rayleigh scattering coefficient A is obtained from the wavelength dependence data of the transmission loss (for example, 1 / λ⁴Slope on the plot). As an index for evaluating the overall transmission loss, a transmission loss α at a wavelength of 1.00 μm is used._1.00This is a relatively short optical fiber sample with a transmission loss value of 1.00 μm, which is larger than a wavelength band of 1.55 μm used for optical transmission and the like, and is about 1 to 10 km. This is because the evaluation can be performed with sufficient accuracy.
[0066]
Also, the transmission loss α at a wavelength of 1.00 μm of the optical fiber_1.00And transmission loss α at a wavelength of 1.55 μm_1.55Has a certain relationship with the transmission loss α_1.00The transmission loss α_1.55, The reduction can be similarly confirmed. As a specific correspondence, the transmission loss α at a wavelength of 1.00 μm_1.00Is as described above
α_1.00= A + 0.01
Where the transmission loss α at a wavelength of 1.55 μm corresponding to this expression_1.55The expression of
α_1.55= A × 0.17325 + 0.025
It is.
[0067]
Another example of the specific configuration of the optical fiber according to the present invention will be described.
[0068]
FIG. 3 is a graph showing the refractive index profile of the second embodiment of the optical fiber. In this graph, the horizontal axis indicates the position of each part in the optical fiber as viewed from the central axis. The vertical axis represents pure SiO at each site in the optical fiber.₂The relative refractive index difference (%) with respect to is shown.
[0069]
The optical fiber of the present embodiment includes a core region 200 and a cladding region 210 provided on the outer periphery of the core region 200. The core region 200 has a radius r including the central axis of the optical fiber.₀Is formed as a layer. The core region 200 is made of SiO to which Ge is added in a predetermined addition amount so that the relative refractive index difference becomes [Ge].₂Consists of Thereby, the relative refractive index difference Δn of the core region 200₀Is Δn₀= [Ge]> 0.
[0070]
In the present embodiment, the cladding region 210 is composed of two cladding layers 211 and 212. The inner first cladding layer 211 has a radius r provided on the outer periphery of the core region 200.₁Is formed as a layer. The cladding layer 211 is made of SiO doped with a predetermined amount of Ge.₂Consists of Thus, the relative refractive index difference Δn of the cladding layer 211₁Is Δn₁> 0.
[0071]
The outer second cladding layer 212 has a radius r provided on the outer periphery of the first cladding layer 211.₂Is formed as a layer. This cladding layer 212 is made of pure SiO.₂Consists of Thereby, the relative refractive index difference Δn of the cladding layer 212₂Is Δn₂= 0. The optical fiber having such a configuration can be suitably applied, for example, as a dispersion-shifted fiber (DSF). Here, the Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm_1.00The preferred characteristic conditions for are the same as those described above for the optical fiber of the first embodiment shown in FIG.
[0072]
FIG. 4 is a graph showing a refractive index profile of the third embodiment of the optical fiber.
[0073]
The optical fiber of the present embodiment includes a core region 300 and a cladding region 310 provided on the outer periphery of the core region 300. The core region 300 has a radius r including the central axis of the optical fiber.₀Is formed as a layer. The core region 300 is made of pure SiO to which Ge is not added.₂Consists of Thereby, the relative refractive index difference Δn of the core region 300₀Is Δn₀= 0.
[0074]
In the present embodiment, the cladding region 310 is composed of a single cladding layer 311. The cladding layer 311 has a radius r provided on the outer periphery of the core region 300.₁Is formed as a layer. The cladding layer 311 is made of SiO to which F is added in a predetermined amount.₂Consists of Thereby, the relative refractive index difference Δn of the cladding layer 311₁Is Δn₁<0. The optical fiber having such a configuration can be suitably applied, for example, as a pure silica core optical fiber. Here, the Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm_1.00The preferred characteristic conditions for are as described above for the pure silica core optical fiber.
[0075]
FIG. 5 is a graph showing the refractive index profile of the fourth embodiment of the optical fiber.
[0076]
The optical fiber of the present embodiment includes a core region 400 and a cladding region 410 provided on the outer periphery of the core region 400. The core region 400 has a radius r including the central axis of the optical fiber.₀Is formed as a layer. Further, the core region 400 is made of SiO to which Ge is added in a predetermined addition amount that becomes [Ge] in relative refractive index difference.₂Consists of Thereby, the relative refractive index difference Δn of the core region 400₀Is Δn₀= [Ge]> 0.
[0077]
In the present embodiment, the cladding region 410 includes two cladding layers 411 and 412. The inner first cladding layer 411 has a radius r provided on the outer periphery of the core region 400.₁Is formed as a layer. The cladding layer 411 is made of SiO to which F is added in a predetermined amount.₂Consists of Thereby, the relative refractive index difference Δn of the cladding layer 411 is obtained.₁Is Δn₁<0.
[0078]
The outer second cladding layer 412 has a radius r provided on the outer periphery of the first cladding layer 411.₂Is formed as a layer. The cladding layer 412 is made of pure SiO.₂Consists of Thereby, the relative refractive index difference Δn of the cladding layer 412₂Is Δn₂= 0. The optical fiber having such a configuration can be suitably applied, for example, as a dispersion compensating fiber (DCF). Here, the Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm_1.00The preferred characteristic conditions for are the same as those described above for the optical fiber of the first embodiment shown in FIG.
[0079]
The method of manufacturing an optical fiber according to the present invention, the effect of reducing transmission loss by the optical fiber manufactured by the method, and the like will be described together with specific examples and comparative examples.
[0080]
FIG. 6 is a table illustrating manufacturing conditions and loss characteristics of optical fiber examples A1 to A3 and comparative examples B1 to B3. Here, a Ge-doped single mode fiber (Ge-SM) having the configuration shown in FIG. 2 is assumed as the optical fiber. Specifically, SiO to which Ge is added₂The outer diameter of the core region 100 made of₀= 8 μm and the relative refractive index difference Δn₀= [Ge] = 0.35%, pure SiO₂The outer diameter of the cladding layer 111 made of₁= 125 μm and the relative refractive index difference Δn₁= 0%.
[0081]
As for the manufacturing conditions, the drawing speed of the optical fiber 3 is 500 m / min, and the drawing tension is about 0.88 N (90 gw). The conditions for annealing the optical fiber preform 2 before drawing, the drawing temperature in the drawing furnace 11, and the annealing conditions for annealing the optical fiber 3 in the heat treatment furnace 21 subsequent to the drawing furnace 11 are as follows. Examples and comparative examples are as shown in the table of FIG.
[0082]
The table in FIG. 6 shows the Rayleigh scattering coefficient A (dB / km · μm) as the loss characteristic of the optical fiber in each example and comparative example.⁴) And transmission loss α at a wavelength of 1.55 μm_1.55(DB / km).
[0083]
Among the examples A1 to A3 of the optical fiber according to the present invention shown in the table of FIG. 6, in the example A1, the annealing condition of the optical fiber preform was set at 1050 ° C. for 60 hours and the drawing temperature in the drawing furnace was set at 2100. The manufacturing conditions are set such that the optical fiber is not annealed in a heat treatment furnace at a temperature of ℃. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.90 dB / km · μm⁴, Transmission loss is α_1.55= 0.182 dB / km.
[0084]
In Example A2, the annealing condition of the optical fiber preform was 1050 ° C. for 60 hours, the drawing temperature in the drawing furnace was 2200 ° C., and the annealing condition of the optical fiber in the heat treatment furnace was 1300 ° C. for 1 second. Manufacturing conditions are set. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.89 dB / km · μm⁴, Transmission loss is α_1.55= 0.182 dB / km.
[0085]
In Example A3, the annealing conditions for the optical fiber preform were 1050 ° C. for 60 hours, the drawing temperature in the drawing furnace was 2100 ° C., and the annealing condition for the optical fiber in the heat treatment furnace was 1300 ° C. for 1 second. Manufacturing conditions are set. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.89 dB / km · μm⁴, Transmission loss is α_1.55= 0.180 dB / km.
[0086]
In each of the above Examples A1 to A3, the optical fiber preform was subjected to annealing at 1050 ° C. for 60 hours, which satisfies the condition that the preform was annealed at a temperature of 950 ° C. to 1150 ° C. for 30 hours or more. Is annealed. Example A1 shows an example in which low-temperature drawing at 2100 ° C. was performed at the time of drawing in addition to annealing of the optical fiber preform. Further, Example A2 shows an example in which, in addition to the annealing of the optical fiber preform, the optical fiber after drawing is gradually cooled. Example A3 shows an example in which low-temperature drawing during drawing and slow cooling after drawing are performed in addition to annealing of the optical fiber preform.
[0087]
That is, in these Examples A1 to A3, the optical fiber preform was annealed before drawing to make the structure relaxed at the stage of the preform, and the drawing conditions were such that low-temperature drawing, slow cooling, or both were performed. In addition, the optical fiber is drawn so that the structural relaxation state is maintained. Accordingly, in any of the embodiments, the Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss_1.55Is sufficiently reduced.
[0088]
On the other hand, among Comparative Examples B1 to B3 of the optical fiber shown in the table of FIG. 6, in Comparative Example B1, the optical fiber preform was not annealed, the drawing temperature in the drawing furnace was 2100 ° C., and the heat treatment furnace was used. The manufacturing conditions are set such that annealing of the optical fiber is not performed. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.94 dB / km · μm⁴, Transmission loss is α_1.55= 0.188 dB / km.
[0089]
In Comparative Example B2, the optical fiber preform was not annealed, and the drawing temperature in the drawing furnace was 2200 ° C., and the annealing condition of the optical fiber in the heat treatment furnace was 1300 ° C. for 0.5 seconds. Conditions have been set. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.94 dB / km · μm⁴, Transmission loss is α_1.55= 0.188 dB / km.
[0090]
In Comparative Example B3, the manufacturing conditions are set such that the optical fiber preform is not annealed, the drawing temperature in the drawing furnace is 2200 ° C., and the optical fiber is not annealed in the heat treatment furnace. . Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.95 dB / km · μm⁴, Transmission loss is α_1.55= 0.190 dB / km.
[0091]
In all of these comparative examples B1 to B3, the preform was not annealed to bring the optical fiber preform into a structurally relaxed state before drawing. Therefore, regardless of whether low-temperature drawing or slow cooling is performed in drawing the optical fiber, the Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss are higher than those in Examples A1 to A3._1.55And the loss characteristics have deteriorated.
[0092]
As described above, the optical fiber preform is annealed under the predetermined annealing conditions before drawing, and the drawing is performed under the drawing conditions in which the structural relaxation state is maintained, whereby an optical fiber with sufficiently reduced transmission loss is obtained. It is understood that it can be done. Further, in such a manufacturing method, as described above, the productivity of optical fibers can be improved, for example, by increasing the linear speed of the optical fibers during drawing.
[0093]
FIG. 7 is a table showing manufacturing conditions and loss characteristics in optical fiber examples C1 to C3 and comparative examples D1 to D4. Here, a dispersion-shifted fiber (DSF) having the configuration shown in FIG. 3 is assumed as the optical fiber. Specifically, SiO to which Ge is added₂The outer diameter of the core region 200 made of₀= 6 μm and the relative refractive index difference Δn₀= [Ge] = 0.6%, Ge-added SiO₂The outer diameter of the first cladding layer 211 made of₁= 40 μm and the relative refractive index difference Δn₁= 0.1%, pure SiO₂The outer diameter of the second cladding layer 212 made of₂= 125 μm and the relative refractive index difference Δn₂= 0%.
[0094]
In Examples C1 to C3 and Comparative Examples D1 to D4, the effects are mainly examined by changing the annealing temperature in annealing the optical fiber preform before drawing. In addition, slow cooling by annealing the optical fiber in the heat treatment furnace was not performed in any case.
[0095]
Among the examples C1 to C3 of the optical fiber according to the present invention shown in the table of FIG. 7, in the example C1, the annealing condition of the optical fiber preform was 950 ° C. for 60 hours, and the drawing temperature in the drawing furnace was 2100. ℃, the manufacturing conditions are set. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.96 dB / km · μm⁴, Transmission loss is α_1.55= 0.190 dB / km.
[0096]
Further, in Example C2, manufacturing conditions are set such that the annealing condition of the optical fiber preform is 1050 ° C. for 60 hours and the drawing temperature in the drawing furnace is 2100 ° C. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.94 dB / km · μm⁴, Transmission loss is α_1.55= 0.186 dB / km.
[0097]
In Example C3, the manufacturing conditions were set such that the annealing condition of the optical fiber preform was 1150 ° C. for 60 hours and the drawing temperature in the drawing furnace was 2100 ° C. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.96 dB / km · μm⁴, Transmission loss is α_1.55= 0.190 dB / km.
[0098]
In these examples C1 to C3, low-temperature drawing at 2100 ° C. is performed at the time of drawing. In addition, under the annealing conditions of 950 ° C., 1050 ° C., and 1150 ° C. × 60 hours, respectively, the preform is annealed at a temperature of 950 ° C. or more and 1150 ° C. or less for 30 hours or more. The material is annealed. Accordingly, in any of the embodiments, the Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss_1.55Is sufficiently reduced.
[0099]
On the other hand, among the comparative examples D1 to D4 of the optical fiber shown in the table of FIG. 7, in Comparative Example D1, the optical fiber preform was not annealed, and the drawing temperature in the drawing furnace was 2200 ° C. Conditions have been set. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.02 dB / km · μm⁴, Transmission loss is α_1.55= 0.200 dB / km.
[0100]
In Comparative Example D2, the production conditions were set such that the optical fiber preform was not annealed and the drawing temperature in the drawing furnace was 2100 ° C. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.99 dB / km · μm⁴, Transmission loss is α_1.55= 0.195 dB / km.
[0101]
In each of Comparative Examples D1 and D2, the preform was not annealed to bring the optical fiber preform into a structurally relaxed state before drawing. For this reason, regardless of whether or not low-temperature drawing is performed at 2100 ° C. in the drawing of the optical fiber, the Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss are higher than those in Examples C1 to C3._1.55And the loss characteristics have deteriorated.
[0102]
In Comparative Example D3, the manufacturing conditions are set such that the annealing condition of the optical fiber preform is 850 ° C. for 60 hours and the drawing temperature in the drawing furnace is 2100 ° C. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.99 dB / km · μm⁴, Transmission loss is α_1.55= 0.195 dB / km. In Comparative Example D3, although the optical fiber preform was annealed, the annealing temperature was as low as 850 ° C. Under such conditions, it can be seen that the effect of reducing transmission loss cannot be obtained as compared with Comparative Example D2 in which the base material has not been annealed.
[0103]
In Comparative Example D4, the manufacturing conditions were set such that the annealing conditions of the optical fiber preform were set at 1250 ° C. for 60 hours. However, under such conditions, the optical fiber preform was annealed during annealing. The material softens and sags. Therefore, this annealing temperature is not suitable for annealing the base material.
[0104]
As described above, by annealing the optical fiber preform at a predetermined temperature within the range of 950 ° C. or more and 1150 ° C. or less, the effect of reducing the transmission loss of the optical fiber due to the relaxation of the glass structure at the stage of the preform is suitably obtained. It is understood that it can be done.
[0105]
FIG. 8 is a table showing manufacturing conditions and loss characteristics in optical fiber examples E1 to E3 and comparative example F1. Here, a pure silica core optical fiber having the configuration shown in FIG. 4 is assumed as the optical fiber. Specifically, pure SiO₂The outer diameter of the core region 300 made of₀= 8 μm and the relative refractive index difference Δn₀= 0%, F-added SiO₂The outer diameter of the cladding layer 311 made of₁= 125 μm and the relative refractive index difference Δn₁= -0.35%.
[0106]
In the examples E1 to E3 and the comparative example F1, the effect is mainly examined by changing the annealing time in annealing the optical fiber preform before drawing. Further, the drawing temperature in the drawing furnace is set to 2100 ° C. which satisfies the condition of low-temperature drawing. In addition, as for the slow cooling of the optical fiber by annealing in the heat treatment furnace, annealing conditions of 1300 ° C. and 0.5 seconds are set in each case.
[0107]
Among the examples E1 to E3 of the optical fiber according to the present invention shown in the table of FIG. 8, in the example E1, the production conditions are set such that the annealing condition of the optical fiber preform is 1050 ° C. for 30 hours. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.80 dB / km · μm⁴, Transmission loss is α_1.55= 0.163 dB / km.
[0108]
In Example E2, the annealing condition of the optical fiber preform was set to 60 hours at 1050 ° C. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.79 dB / km · μm⁴, Transmission loss is α_1.55= 0.161 dB / km.
[0109]
In Example E3, the annealing condition of the optical fiber preform was set to be 100 hours at 1050 ° C. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.78 dB / km · μm⁴, Transmission loss is α_1.55= 0.159 dB / km.
[0110]
On the other hand, in Comparative Example F1 of the optical fiber shown in the table of FIG. 8, the manufacturing conditions are set such that the optical fiber preform is not annealed. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 0.82 dB / km · μm⁴, Transmission loss is α_1.55= 0.165 dB / km.
[0111]
From these Examples E1 to E3 and Comparative Example F1, when the annealing temperature is constant, the effect of reducing the transmission loss of the optical fiber due to the relaxation of the glass structure at the stage of the base material by increasing the annealing time. It can be seen that is larger. Therefore, as for the annealing conditions of the optical fiber preform, it is preferable that the annealing time is 30 hours or more at a temperature of 950 ° C. or more and 1150 ° C. or less as described above, but the annealing time is 60 hours or more, or 100 hours or more. It is more preferable to set the annealing time as described above.
[0112]
FIG. 9 is a table showing manufacturing conditions and loss characteristics of optical fiber examples G1 to G6 and comparative example H1. Here, a dispersion compensation fiber (DCF) having the configuration shown in FIG. 5 is assumed as the optical fiber. Specifically, SiO to which Ge is added₂The outer diameter of the core region 400 made of₀= 4 μm and the relative refractive index difference Δn₀= [Ge] = 1.5%, F-added SiO₂The outer diameter of the first cladding layer 411 made of₁= 8 μm and the relative refractive index difference Δn₁= -0.4%, pure SiO₂The outer diameter of the second cladding layer 412 made of₂= 125 μm and the relative refractive index difference Δn₂= 0%.
[0113]
In the examples G1 to G6 and the comparative example H1, the effect is mainly studied by changing the annealing temperature of the optical fiber after drawing by slow cooling by annealing. Regarding the annealing of the optical fiber preform, annealing conditions at 1050 ° C. for 60 hours are set except for Comparative Example H1. Further, the drawing temperature in the drawing furnace is set to 2100 ° C. which satisfies the condition of low-temperature drawing.
[0114]
Among the examples G1 to G6 of the optical fiber according to the present invention shown in the table of FIG. 9, in the example G1, the manufacturing conditions for annealing the optical fiber in the heat treatment furnace at 1100 ° C. for 0.5 second are set. are doing. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.20 dB / km · μm⁴, Transmission loss is α_1.55= 0.231 dB / km.
[0115]
In Example G2, the annealing condition of the optical fiber was set to 1300 ° C. for 0.5 second. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.18 dB / km · μm⁴, Transmission loss is α_1.55= 0.228 dB / km.
[0116]
In Example G3, the annealing condition of the optical fiber was set to 1550 ° C. for 0.5 second. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.20 dB / km · μm⁴, Transmission loss is α_1.55= 0.231 dB / km.
[0117]
In all of Examples G1 to G3, the preform was annealed to bring the optical fiber preform into a structurally relaxed state before drawing. In addition, annealing after drawing at 1100 ° C., 1300 ° C., and 1550 ° C. × 0.5 seconds, which satisfies the condition of annealing the drawn optical fiber at a temperature of 1100 ° C. or more and 1600 ° C. or less, respectively. The optical fiber is annealed. Accordingly, in any of the embodiments, the Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss_1.55Is sufficiently reduced.
[0118]
In Example G4, the annealing condition of the optical fiber was set at 900 ° C. for 0.5 second. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.24 dB / km · μm⁴, Transmission loss is α_1.55= 0.237 dB / km.
[0119]
In Example G5, the annealing condition of the optical fiber was set to 1650 ° C. for 0.5 second. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.25 dB / km · μm⁴, Transmission loss is α_1.55= 0.240 dB / km.
[0120]
In Example G6, the manufacturing conditions are set such that the optical fiber is not annealed in the heat treatment furnace. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.25 dB / km · μm⁴, Transmission loss is α_1.55= 0.240 dB / km.
[0121]
On the other hand, in Comparative Example H1, the manufacturing conditions are set such that the optical fiber is not annealed in the heat treatment furnace. Further, in this comparative example, annealing of the optical fiber preform is not performed. Further, the obtained loss characteristic is such that the Rayleigh scattering coefficient is A = 1.28 dB / km · μm⁴, Transmission loss is α_1.55= 0.245 dB / km.
[0122]
In the comparative example H1, the Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss are larger than those in Examples G1 to G6._1.55And the loss characteristics have deteriorated. Further, Examples G4 to G6 are slightly more Rayleigh scattering coefficient A and transmission loss α than Examples G1 to G3._1.55Is getting bigger.
[0123]
As described above, in the case where annealing is performed by annealing the optical fiber after drawing in addition to annealing the optical fiber preform before drawing, the annealing of the optical fiber is performed at a predetermined temperature in the range of 1100 ° C. to 1600 ° C. It can be seen that the effect of reducing the transmission loss of the optical fiber can be suitably obtained by performing the above.
[0124]
The method for manufacturing an optical fiber and the optical fiber according to the present invention are not limited to the above-described embodiments and examples, and various modifications are possible. For example, FIG. 1 shows an example of a specific configuration of a drawing apparatus, and a drawing apparatus having another configuration may be used as long as the above-described manufacturing method can be realized.
[0125]
【The invention's effect】
The method for manufacturing an optical fiber and the optical fiber according to the present invention have the following effects as described in detail above. That is, an optical fiber preform before drawing is annealed at a temperature of 950 ° C. or more and 1150 ° C. or less for 30 hours or more, and an optical fiber that draws an optical fiber according to a drawing condition under which the obtained structural relaxation state is maintained. According to the manufacturing method and the optical fiber, it is possible to reduce the transmission loss in the optical fiber and to improve the productivity.
[Brief description of the drawings]
FIG. 1 is a configuration diagram schematically showing an embodiment of an optical fiber manufacturing method and a drawing apparatus used for manufacturing an optical fiber.
FIG. 2 is a graph showing a refractive index profile of the optical fiber according to the first embodiment.
FIG. 3 is a graph showing a refractive index profile of an optical fiber according to a second embodiment.
FIG. 4 is a graph showing a refractive index profile of an optical fiber according to a third embodiment.
FIG. 5 is a graph showing a refractive index profile of an optical fiber according to a fourth embodiment.
FIG. 6 is a table showing manufacturing conditions and loss characteristics in optical fiber examples A1 to A3 and comparative examples B1 to B3.
FIG. 7 is a table showing manufacturing conditions and loss characteristics in optical fiber examples C1 to C3 and comparative examples D1 to D4.
FIG. 8 is a table showing manufacturing conditions and loss characteristics in optical fiber examples E1 to E3 and comparative example F1.
FIG. 9 is a table showing manufacturing conditions and loss characteristics in optical fiber examples G1 to G6 and comparative example H1.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Drawing apparatus, 2 ... Optical fiber preform, 3 ... Glass fiber, 4 ... Optical fiber strand, 11 ... Drawing furnace, 12 ... Heater, 13 ... Core tube, 14 ... Inert gas supply part, 15 ... Gas supply passage, 21: heat treatment furnace, 22: heater, 23: furnace tube, 24: N₂Gas supply unit, 25 gas supply passage, 31 cooling means, 32 cylindrical tube, 33 nozzle, 34 cooling gas supply unit, 40 resin coating unit, 41 coating die, 42 UV resin, 43 resin Curing unit, 44 UV lamp, 46 coating die, 47 UV resin, 48 resin curing unit, 49 UV lamp, 51 outer diameter measuring instrument, 52 drum, 53 driving motor, 54 control unit, 55: rotary drive shaft, 56: guide roller.

Claims (6)

A heat treatment in which an optical fiber preform made by dehydration sintering and having a core region and a cladding region provided on the outer periphery of the core region is subjected to a heat treatment at a temperature of 950 ° C. or more and 1150 ° C. or less for a predetermined time of 30 hours or more. And a drawing step of drawing an optical fiber by drawing the heat-treated optical fiber preform by a drawing furnace under a drawing condition in which the structural relaxation state obtained in the heat treatment step is maintained. A method for manufacturing an optical fiber, comprising: In the drawing step, as the drawing conditions for heating and drawing the optical fiber preform at a temperature of 2100 ° C. or lower by the drawing furnace, the optical fiber is created while maintaining the structural relaxation state. The method for producing an optical fiber according to claim 1. In the drawing step, the optical fiber drawn by the drawing furnace is subjected to a heat treatment at a temperature of 1100 ° C. or more and 1600 ° C. or less by a heat treatment furnace provided at a subsequent stage of the drawing furnace. 3. The method of manufacturing an optical fiber according to claim 1, wherein the optical fiber is produced while maintaining a state of structural relaxation. An optical fiber, comprising: a core region; and a cladding region provided on an outer periphery of the core region, wherein the optical fiber is manufactured by the method for manufacturing an optical fiber according to claim 1. In the core region, Ge is added in an amount such that the relative refractive index difference expressed in% with respect to pure SiO ₂ is [Ge], and
The Rayleigh scattering coefficient A (dB / km · μm ⁴ ) and the transmission loss α _1.00 (dB / km) at a wavelength of _1.00 μm are the reference values A ₀ and α ₀ represented by the following equations, respectively.
A ₀ = 0.85 + 0.29 [Ge]
α ₀ = 0.86 + 0.29 [Ge]
The optical fiber according to claim 4, wherein the optical fiber is 97% or less. The core region is made of pure SiO ₂ ,
The Rayleigh scattering coefficient A (dB / km · μm ⁴ ) and the transmission loss α _1.00 (dB / km) at a wavelength of _1.00 μm are the reference values A ₀ = 0.85 and α ₀ = 0.86, respectively. 5. The optical fiber according to claim 4, wherein said optical fiber is 96% or less.

Images