JP4400026B2 - Optical fiber manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber manufacturing method for transmitting light with low transmission loss, and an optical fiber.
[0002]
[Prior art]
In the 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 manufacturing method thereof has been proposed.
[0003]
For example, in the document “Sakaguchi, IEICE Transactions 2000/1 Vol.J83-C No.1, pp.30-36”, the Rayleigh scattering loss in the optical fiber is caused by the slow cooling of the 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 (fictive temperature) which is a virtual temperature indicating disorder of the arrangement state of atoms in the glass. Specifically, when the fictive temperature Tf in the glass is high (randomness is large), the Rayleigh scattering intensity increases.
[0004]
In contrast, when the optical fiber preform is drawn by heating, a heat treatment furnace is installed after the drawing furnace, and the optical fiber after drawing passes within the predetermined temperature range when passing through the heat treatment furnace. Then, the optical fiber is annealed by heating. 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, due to the structural relaxation of the glass due to the rearrangement of atoms, the virtual temperature Tf in the optical fiber is lowered, and the Rayleigh scattering intensity in the optical fiber is suppressed.
[0005]
The document “K. Tajima, NTT REVIEW Vol. 10 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 of annealing an optical fiber after drawing using a heat treatment furnace can achieve both reduction in transmission loss of the optical fiber and improvement in productivity of the optical fiber. difficult.
[0007]
For example, when the transmission loss of an optical fiber is reduced by annealing in a heat treatment furnace provided at a subsequent stage of the drawing furnace, a considerable part of the drawing line needs to be used as a heat treatment line. For this reason, when a heat treatment line is added, the length of the line used for cooling the optical fiber is shortened accordingly, and the optical fiber speed during drawing cannot be increased.
[0008]
In addition, when reducing 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, drawing must be performed at a low drawing speed. As in the case of annealing in a heat treatment furnace, there is a problem that the productivity of optical fibers does not increase.
[0009]
The present invention has been made to solve the above-described problems, and provides an optical fiber manufacturing method and an optical fiber in which the transmission loss in the optical fiber is reduced and the productivity is improved. For the purpose.
[0010]
[Means for Solving the Problems]
  In order to achieve such an object, an optical fiber manufacturing method according to the present invention includes: (1) an optical fiber mother made by dehydration and 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. to 1150 ° C. for a predetermined time of 30 hours or more, and (2) a structure relaxation state obtained in the heat treatment step of the heat-treated optical fiber preform by a drawing furnace A drawing step of creating an optical fiber by drawing with heating under a drawing condition whereIn the drawing step, an optical fiber is produced while maintaining the structural relaxation state as a drawing condition in which the optical fiber preform is drawn by heating at a temperature of 2100 ° C. or less in a drawing furnace.It is characterized by that.
[0011]
In the above-described optical fiber manufacturing method, attention is paid not only to the drawing conditions when the optical fiber preform is heated and drawn, but also to the optical fiber preform manufacturing process. Then, before heating and drawing the optical fiber preform made by dehydration and sintering, the optical fiber preform is annealed at a furnace temperature of a predetermined temperature within a range of 950 ° C. to 1150 ° C. At this stage, the optical fiber is drawn by drawing the optical fiber preform so that the structural relaxation state is maintained and the obtained structural relaxation state is maintained.
[0012]
Thereby, an optical fiber with reduced transmission loss can be reliably manufactured. In addition, since the glass structure is relaxed before drawing, the optical fiber productivity can be improved, for example, the drawing speed of the optical fiber during drawing can be increased.
[0013]
Regarding specific drawing conditions for maintaining the structural relaxation state, in the drawing step, the structural relaxation state is set as a drawing condition for drawing the optical fiber preform at a temperature of 2100 ° C. or less by a drawing furnace. There is a method of making an optical fiber while holding it.
[0014]
Alternatively, in the drawing step, the optical fiber drawn in the drawing furnace is subjected to a structure relaxation state as a drawing condition in which heat treatment is performed at a temperature of 1100 ° C. or more and 1600 ° C. or less in a heat treatment furnace provided at a subsequent stage of the drawing furnace. There is a method of making an optical fiber while holding the optical fiber.
[0015]
Thus, by applying the drawing conditions for performing low temperature drawing of the optical fiber at a temperature of 2100 ° C. or lower, slow cooling of the optical fiber by annealing in a heat treatment furnace, or both, it is obtained at the base material stage. The optical fiber can be drawn while suitably maintaining the structured relaxation state. Moreover, you may use drawing conditions other than these.
[0016]
An optical fiber according to the present invention includes a core region and a cladding region provided on the outer periphery of the core region, and is manufactured by the above-described optical fiber manufacturing method. As a result, 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 pure SiO₂Ge is added in an addition amount in which the relative refractive index difference expressed in% with respect to [Ge] is added, and the Rayleigh scattering coefficient A (dB / km · μm).^Four), And transmission loss α at a wavelength of 1.00 μm_1.00(DB / km) is a reference value A represented by the following equation₀, And α₀
A₀= 0.85 + 0.29 [Ge]
α₀= 0.86 + 0.29 [Ge]
It is characterized by being 97% or less.
[0018]
In the optical fiber described above, the optical fiber Rayleigh scattering coefficient A and the transmission loss α including the Rayleigh scattering loss._1.00Is a reference value A indicating a value in a normal optical fiber₀, Α₀The value is reduced by 3% or more to 97% or less. As a result, an optical fiber with a sufficiently reduced transmission loss can be obtained.
[0019]
The core region is pure SiO₂And the Rayleigh scattering coefficient A (dB / km · μm^Four), And transmission loss α at a wavelength of 1.00 μm_1.00(DB / km) is the reference value A₀= 0.85, and α₀= 96% or less with respect to 0.86.
[0020]
In the above-described pure silica core optical fiber, the optical fiber Rayleigh scattering coefficient A 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 a sufficiently reduced transmission loss can be obtained.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical fiber manufacturing method according to the present invention and a preferred embodiment of an optical fiber will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.
[0022]
First, an outline of an optical fiber manufacturing method will be described.
[0023]
In the method of manufacturing an optical fiber according to the present invention, first, an optical fiber preform configured to have a core region and a cladding region provided on the outer periphery of the core region is formed through a dehydration sintering process. Then, for the optical fiber preform obtained by dehydration and sintering, the virtual temperature Tf in the optical fiber preform is lowered by glass structural relaxation, so that the optical fiber preform is subjected to predetermined annealing conditions at the preform stage. The material is heat treated.
[0024]
Specifically, N₂The prepared optical fiber preform is placed in a heat treatment furnace having 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 in the 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). The annealing process for the optical fiber preform is not performed 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 that has been in a structurally relaxed state by heat treatment, the optical fiber preform is heated and drawn by a drawing furnace under a drawing condition in which the obtained structurally relaxed state is maintained. Create a fiber (drawing step). Thereby, an optical fiber with reduced transmission loss due to the relaxation of the glass structure can be obtained.
[0026]
As specific drawing conditions for maintaining the structural relaxation state, for example, drawing conditions for performing low temperature drawing of an optical fiber can be applied. In this case, the optical fiber preform is heated while maintaining the structural relaxation state as a drawing condition for setting the heater temperature, which is the furnace temperature of the drawing furnace, to a relatively low predetermined temperature within a range of 2100 ° C. or less. Draw.
[0027]
Alternatively, a drawing condition in which the optical fiber is gradually cooled 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 after the drawing furnace. Then, with this heat treatment furnace, the optical fiber preform is maintained while maintaining the structural relaxation state as a drawing condition for annealing the optical fiber drawn in the drawing furnace at a temperature of 1100 ° C. or higher and 1600 ° C. or lower. Draw a heating line.
[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]
A drawing apparatus 1 shown in FIG. 1 is a drawing apparatus used for drawing a quartz glass-based optical fiber, and includes a drawing furnace 11, a annealing furnace 21 for slow cooling, and a cooling means 31. Configured. The drawing furnace 11, the heat treatment furnace 21, and the cooling means 31 are installed in this order in the direction in which the optical fiber preform 2 is drawn (the vertical direction in FIG. 1). Further, a resin coating portion 40 for coating the drawn glass fiber 3 with a resin is provided at the subsequent stage 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, the optical fiber preform 2 that has been subjected to the structural relaxation state by the heat treatment at the preform stage as described above is prepared, and the preform supply apparatus (shown) The optical fiber preform 2 held by the optical fiber preform 2 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 obtain the glass fiber 3.
[0031]
Here, when applying a drawing condition for performing low temperature drawing of the optical fiber, the temperature of the heater 12 serving as 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 mother is set. The material 2 is drawn. At this time, the temperature of the optical fiber preform 2 is about 2000 ° C. or lower. Further, a gas supply passage 15 from an inert gas supply unit 14 is connected to the core tube 13 of the drawing furnace 11 so that the inside of the core tube 13 is in an inert gas atmosphere.
[0032]
The heated glass fiber 3 is rapidly cooled in the furnace core 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 core tube 13 and is air-cooled between the drawing furnace 11 and the heat treatment furnace 21. As an inert gas, for example, N₂Gas can be used. N₂The thermal conductivity coefficient λ (T = 300K) of the gas is 26 mW / (m · K). The thermal conductivity coefficient λ (T = 300K) of air 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 annealing is annealed by annealing the glass fiber 3 at a predetermined temperature with the heater 22 in the heat treatment furnace 21. Here, annealing of the glass fiber 3 is performed with the temperature of the heater 22 serving as the furnace temperature of the heat treatment furnace 21 being set to a predetermined temperature in the range of 1100 ° C. to 1600 ° C.
[0034]
The heat treatment furnace 21 has a furnace core 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 the gas supply unit 24 is connected, and the inside of the core tube 23 is N.₂It is comprised so that it may become a gas atmosphere. N₂Instead of using a gas, a gas having a relatively large molecular weight such as air or Ar may be used. However, when the core tube is made of carbon, it is necessary to use a gas that does not contain oxygen. In addition, when the drawing condition which anneals an optical fiber by annealing after drawing is not applied, the heat treatment furnace 21 may be omitted.
[0035]
Subsequently, the annealed glass fiber 3 is cooled between the drawing furnace 11 and the resin coating portion 40 and the cooling means 31 for forced cooling of the glass fiber 3 provided 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 the cooling gas supply unit 34 are provided on the side wall of the cylindrical tube 32. Thereby, the cooling gas from the cooling gas supply part 34 is supplied with respect to the glass fiber 3 which passes the inside of the cylindrical tube 32, and the glass fiber 3 is forcedly cooled. As the cooling gas, He gas is preferably used. In addition, when the glass fiber 3 can be sufficiently cooled by normal air cooling, such a cooling unit 31 may not be used.
[0037]
The outer diameter of the glass fiber 3 exiting 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 rotationally drives the drum 52, and the rotation of the drum 52 is driven and 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 obtains 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 rotation speeds 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 is measured by the outer diameter measuring device 51 is inserted into the resin coating portion 40 configured in two stages (tandem). First, the UV resin 42 is applied by the coating die 41 to the glass fiber 3 that has passed through the outer diameter measuring device 51 in the first-stage resin coating portion. The applied UV resin 42 is cured by ultraviolet light from the UV lamp 44 of the resin curing unit 43.
[0040]
Further, the UV resin 47 is applied to the glass fiber 3 from the resin curing portion 43 by the coating die 46 in the second-stage resin coating portion. The applied UV resin 47 is cured by ultraviolet light from the UV lamp 49 of the resin curing unit 48. Thereby, the optical fiber 4 in which the glass fiber 3 is coated with the resin is formed. Then, the optical fiber 4 is taken up by the drum 52 through the guide roller 56. The drum 52 is supported by a rotation drive shaft 55, and an end portion of the rotation drive shaft 55 is connected to a drive motor 53.
[0041]
As described above, the gas supply passage 15 from the inert gas supply unit 14 is connected to the core tube 13 of the drawing furnace 11 so that the inside of the core tube 13 has an inert gas atmosphere. ing. In contrast, N as the inert gas supply unit 14₂A gas supply unit is provided, and N in the core tube 13₂Supply gas N₂You may comprise so that it may become a gas atmosphere. He gas supply unit and N₂A gas supply unit is also provided, and He gas or N is provided in the core tube 13 according to the linear velocity.₂It is good also as composition which supplies gas.
[0042]
The effect by the manufacturing method of the optical fiber of embodiment mentioned above is demonstrated.
[0043]
In the optical fiber manufacturing method according to the present embodiment, when the glass fiber 3 is manufactured by heating the optical fiber preform 2, not only the drawing conditions for the heating drawing but also the manufacturing of the optical fiber preform 2 is performed. Focus on the process. Then, before heating and drawing the optical fiber preform 2 produced by dehydration and sintering with the drawing apparatus 1, the optical fiber preform at a furnace temperature of a predetermined temperature within a range of 950 ° C. to 1150 ° C. The glass fiber 3 is produced by drawing the optical fiber preform 2 under the drawing conditions that maintain the obtained structure relaxed state.
[0044]
According to such a manufacturing method, by annealing the optical fiber preform, the fictive temperature Tf in the optical fiber preform is lowered due to the structural relaxation of the glass. Further, in the process of heating and drawing the optical fiber preform in the structure relaxed state to form an optical fiber, the glass of the optical fiber preform is not completely melted, and the optical fiber is drawn with the glass softened. Is done.
[0045]
For this reason, if the drawing condition is appropriately set when drawing the optical fiber preform, the optical fiber preform is drawn while maintaining the structural relaxation state of the glass obtained in the preform stage to some extent. It is possible to create an optical fiber. Thereby, the fictive temperature Tf in the obtained optical fiber can be lowered, and an optical fiber with reduced Rayleigh scattering loss and transmission loss including Rayleigh scattering loss can be manufactured.
[0046]
Further, according to this manufacturing method, since the glass structure is relaxed at the base material stage before drawing, the length of the heat treatment line in the drawing line is shortened, or the light at the time of drawing is reduced. The fiber speed of the fiber can be increased. Thereby, drawing of an optical fiber can be performed efficiently and it becomes possible to improve the productivity of an optical fiber. As described above, a method of manufacturing an optical fiber that can suitably achieve both reduction in transmission loss of the optical fiber and improvement in productivity of the optical fiber is realized.
[0047]
As for the specific drawing conditions for maintaining the structure 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. It is possible to apply a drawing condition for performing slow cooling. In this way, 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 base material stage. can do. Moreover, you may use drawing conditions other than these.
[0048]
Next, the optical fiber according to the present invention manufactured by the manufacturing method described above will be described. The optical fiber according to the present invention can be manufactured with high productivity as described above with respect to its manufacturing method, and has good characteristics with reduced transmission loss.
[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 viewed from the central axis of each part in the optical fiber. The vertical axis represents pure SiO at each site in the optical fiber.₂Relative refractive index difference (%).
[0050]
The optical fiber of this 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.₀It is formed as a layer. Further, the core region 100 is made of SiO to which Ge is added in a predetermined addition amount.₂Consists of.
[0051]
Specifically, the core region 100 includes pure SiO.₂When the addition amount of Ge is expressed by the relative refractive index difference [Ge] expressed in% with respect to the addition amount, the addition amount that satisfies the predetermined refractive index difference [Ge] satisfies a predetermined condition (for example, an addition amount that becomes 0.3% or more). Ge is added. Accordingly, the relative refractive index difference Δn of the core region 100 is obtained.₀Is Δn₀= [Ge]> 0.
[0052]
In addition, the clad region 110 is composed of a single clad layer 111 in the present embodiment. The cladding layer 111 has a radius r provided on the outer periphery of the core region 100.₁It is formed as a layer. The cladding layer 111 is made of pure SiO.₂Consists 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 as, for example, a Ge-doped single mode fiber (Ge-SM).
[0053]
A suitable characteristic condition in the present optical fiber will be described. That is, in the optical fiber shown in FIG. 2, the Rayleigh scattering coefficient A (dB / km · μm) indicating the magnitude of the Rayleigh scattering loss in the optical fiber.^Four), And transmission loss α at a wavelength of 1.00 μm_1.00(DB / km) is a reference value A represented by the following equation₀, 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.₂Relative refractive index difference in% relative to A₀For example, if [Ge] = 0.35%, A₀= 0.85 + 0.29 x 0.35 = 0.95.
[0054]
In this preferable characteristic condition, the transmission loss α including the Rayleigh scattering coefficient A of the optical fiber and the Rayleigh scattering loss is used._1.00Is a reference value A indicating a value in a normal optical fiber₀, Α₀The value is reduced by 3% or more to 97% or less. As a result, an optical fiber with a sufficiently reduced transmission loss can be 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. 2, but various configurations, as shown in the second to fourth embodiments described later. May be used. For example, for the core region, pure SiO with no Ge added₂It is good also as composition which consists of. The reference value A described above₀, Α₀The characteristic condition regarding can be similarly applied to the configuration of a pure silica core in which [Ge] = 0.
[0056]
Core is pure SiO₂In the optical fiber made of, the Rayleigh scattering coefficient A (dB / km · μm^Four), And transmission loss α at a wavelength of 1.00 μm_1.00(DB / km) is the reference value A₀= 0.85, and α₀= 96% or less with respect to 0.86 is preferable.
[0057]
In this preferable characteristic condition, the transmission loss α including the Rayleigh scattering coefficient A of the optical fiber and the Rayleigh scattering loss is used._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 a sufficiently reduced transmission loss can be obtained.
[0058]
For the cladding region, pure SiO in the configuration shown in FIG.₂In general, each of the clad layers is made of pure SiO.₂SiO with Ge added₂Or SiO with F added₂It is preferable to have a configuration having one or more clad layers made of any of the above.
[0059]
According to such a configuration, various types of optical fibers such as a single mode fiber (SMF), a dispersion shift fiber (DSF), and a dispersion compensation fiber (DCF) can be used. Therefore, it can be produced with good productivity due to good characteristics.
[0060]
Each characteristic condition of the optical fiber described above will be further described. In the above-described 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._1.00These Rayleigh scattering coefficients A and transmission loss α_1.00Is a reference value A indicating a normal value.₀, Α₀The value is reduced by 3% or more to 97% or less.
[0061]
The transmission loss αλ (dB / km) at the wavelength λ in an optical fiber is generally expressed by the following equation, due to transmission loss components such as Rayleigh scattering loss and other structural irregularities.
αλ = A / λ^Four+ B + C (λ)
It is represented by Of these, the first term A / λ^Four(DB / km) indicates the Rayleigh scattering loss, and the coefficient A is the Rayleigh scattering coefficient (dB / km · μm).^Four). 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, When the addition amount of Ge is represented by [Ge] described above, the Rayleigh scattering coefficient A (dB / km · μm^Four) Value is
A₀= 0.85 + 0.29 [Ge]
It becomes. Therefore, this normal value A₀Can be used as the 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 A₀It is sufficient that the amount is reduced by 3% or more.
[0063]
Further, in order to evaluate the overall 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
α₀= A₀+0.01
= 0.86 + 0.29 [Ge]
It becomes. Therefore, this normal value α₀Transmission loss α_1.00Can be used as a reference value. At this time, transmission loss α in the obtained optical fiber_1.00Is the reference value α₀Is preferably reduced by 3% or more.
[0064]
Thus, Rayleigh scattering coefficient A or 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 reference value A described above₀, Α₀According to the respective expressions, the variable [Ge] relating to the amount of Ge added to the core is included in the expressions. Therefore, it is possible to evaluate the transmission loss according to the added amount of Ge.
[0065]
For the Rayleigh scattering coefficient A, the data on the wavelength dependence of transmission loss (for example, 1 / λ)^Four(Slope in the plot). Further, as an index for evaluating the overall transmission loss, the transmission loss α at a wavelength of 1.00 μm_1.00This is a comparatively short optical fiber sample of about 1 to 10 km in which the value of transmission loss at 1.00 μm is larger than the wavelength band of 1.55 μm used for optical transmission, etc. 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_1.55With a certain relationship, and transmission loss α_1.00Transmission loss α by evaluating the reduction effect at_1.55Similarly, the reduction can be confirmed. As a specific correspondence, transmission loss α at a wavelength of 1.00 μm_1.00As mentioned above
α_1.00= A + 0.01
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 a refractive index profile of the second embodiment of the optical fiber. In this graph, the horizontal axis indicates the position viewed from the central axis of each part in the optical fiber. The vertical axis represents pure SiO at each site in the optical fiber.₂Relative refractive index difference (%).
[0069]
The optical fiber of this 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.₀It is formed as a layer. Further, the core region 200 is made of SiO to which Ge is added with a predetermined addition amount that is [Ge] in terms of relative refractive index difference.₂Consists of. Accordingly, the relative refractive index difference Δn of the core region 200₀Is Δn₀= [Ge]> 0.
[0070]
In the present embodiment, the cladding region 210 includes 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 200.₁It is formed as a layer. The clad layer 211 is made of SiO with Ge added in a predetermined addition amount.₂Consists of. Thereby, 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 211.₂It is formed as a layer. The 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 as a dispersion shifted fiber (DSF), for example. The Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm_1.00Suitable characteristic conditions for the above 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 the refractive index profile of the third embodiment of the optical fiber.
[0073]
The optical fiber of this 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.₀It is formed as a layer. The core region 300 is made of pure SiO to which no Ge is added.₂Consists of. Accordingly, the relative refractive index difference Δn of the core region 300₀Is Δn₀= 0.
[0074]
In addition, the clad region 310 is composed of a single clad layer 311 in this embodiment. The cladding layer 311 has a radius r provided on the outer periphery of the core region 300.₁It is formed as a layer. In addition, this cladding layer 311 is made of SiO with F added in a predetermined addition 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 as a pure silica core optical fiber, for example. The Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm_1.00Suitable characteristic conditions for the above are as described above for the pure silica core optical fiber.
[0075]
FIG. 5 is a graph showing a 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.₀It is formed as a layer. In addition, the core region 400 is made of SiO doped with Ge at a predetermined addition amount of [Ge] as a relative refractive index difference.₂Consists of. Accordingly, 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 400.₁It is formed as a layer. The clad layer 411 is made of SiO with F added in a predetermined addition amount.₂Consists of. Thereby, the relative refractive index difference Δn of the cladding layer 411₁Is Δn₁<0.
[0078]
The outer second cladding layer 412 has a radius r provided on the outer periphery of the first cladding layer 411.₂It is 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 as a dispersion compensating fiber (DCF), for example. The Rayleigh scattering coefficient A and the transmission loss α at a wavelength of 1.00 μm_1.00Suitable characteristic conditions for the above are the same as those described above for the optical fiber of the first embodiment shown in FIG.
[0079]
The optical fiber manufacturing method according to the present invention and the transmission loss reduction effect of the optical fiber manufactured thereby will be described together with specific examples and comparative examples.
[0080]
  FIG. 6 shows an optical fiber embodiment A1.,A3,Reference Example A2,And it is a table | surface shown about the manufacturing conditions in Comparative Examples B1-B3, and its loss characteristic. Here, a Ge-doped single mode fiber (Ge-SM) having the configuration shown in FIG. 2 is assumed as the optical fiber. Specifically, SiO doped with Ge₂The outer diameter of the core region 100 made of 2r is 2r₀= 8 μm, the relative refractive index difference is Δn₀= [Ge] = 0.35%, pure SiO₂The outer diameter of the cladding layer 111 made of₁= 125 μm, the relative refractive index difference is Δn₁= 0%.
[0081]
  As for the manufacturing conditions, the drawing speed for drawing 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 conditions for slow cooling by annealing the optical fiber 3 in the heat treatment furnace 21 subsequent to the drawing furnace 11 are as follows: Example, Reference examples,The comparative example is as shown in the table of FIG.
[0082]
  Also, the table of FIG., Reference examples,As a loss characteristic of the optical fiber in the comparative example, the Rayleigh scattering coefficient A (dB / km · μm⁴), And transmission loss α at a wavelength of 1.55 μm_1.55(DB / km) is shown.
[0083]
  Example A1 of the optical fiber according to the invention shown in the table of FIG.,A3And Reference Example A2Among these, in Example A1, 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 optical fiber was not annealed in the heat treatment furnace. Is set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.90 dB / km · μm.⁴, Transmission loss is α_1.55= 0.182 dB / km.
[0084]
  Also,Reference exampleIn A2, the annealing conditions for the optical fiber preform are 1050 ° C. for 60 hours, the drawing temperature in the drawing furnace is 2200 ° C., and the annealing conditions for the optical fiber in the heat treatment furnace are 1300 ° C. for 1 second. It is set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.89 dB / km · μm.⁴, Transmission loss is α_1.55= 0.182 dB / km.
[0085]
In Example A3, the annealing condition of the optical fiber preform was 1050 ° C. for 60 hours, the drawing temperature in the drawing furnace was 2100 ° 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 has a Rayleigh scattering coefficient of A = 0.89 dB / km · μm.^Four, Transmission loss is α_1.55= 0.180 dB / km.
[0086]
  Example A1 described above,A3And Reference Example A2In either case, the optical fiber preform is annealed under the annealing condition of 1050 ° C. × 60 hours that satisfies the condition that the preform is annealed at a temperature of 950 ° C. to 1150 ° C. for 30 hours or more. Yes. In Example A1, in addition to annealing of the optical fiber preform, an example is shown in which low temperature drawing at 2100 ° C. is performed at the time of drawing. Also,Reference exampleIn A2, in addition to the annealing of the optical fiber preform, an example in which the optical fiber after drawing is gradually cooled is shown. In Example A3, in addition to annealing of the optical fiber preform, an example is shown in which low temperature drawing at the time of drawing and slow cooling after drawing are combined.
[0087]
  That is, these Examples A1,A3And Reference Example A2Then, the optical fiber preform is annealed before drawing to bring it into a structure relaxed state at the preform stage, and the structure relaxed state is maintained under the drawing conditions for performing low temperature drawing, slow cooling, or both. The optical fiber is drawn. This allows any embodimentAnd reference examples, Transmission loss α including Rayleigh scattering coefficient A and Rayleigh scattering loss_1.55Is sufficiently reduced.
[0088]
On the other hand, among the optical fiber comparative examples B1 to B3 shown in the table of FIG. 6, in the comparative example B1, the optical fiber preform is not annealed, and the drawing temperature in the drawing furnace is 2100 ° C. The manufacturing conditions are set such that the optical fiber is not annealed. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.94 dB / km · μm.^Four, Transmission loss is α_1.55= 0.188 dB / km.
[0089]
In Comparative Example B2, the optical fiber preform is not annealed, the drawing temperature in the drawing furnace is 2200 ° C., and the annealing condition of the optical fiber in the heat treatment furnace is 1300 ° C. for 0.5 seconds. Conditions are set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.94 dB / km · μm.^Four, 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 has a Rayleigh scattering coefficient of A = 0.95 dB / km · μm.^Four, Transmission loss is α_1.55= 0.190 dB / km.
[0091]
  In these comparative examples B1 to B3, none of the preforms are annealed to bring the optical fiber preform into a structurally relaxed state before drawing. For this reason, the embodiment A1 regardless of whether or not low temperature drawing or slow cooling is performed in the drawing of the optical fiber.,A3And Reference Example A2Compared to the Rayleigh scattering coefficient A, and transmission loss α including Rayleigh scattering loss._1.55The loss characteristic is deteriorated.
[0092]
As described above, an optical fiber with sufficiently reduced transmission loss can be obtained by annealing the optical fiber preform before drawing under a predetermined annealing condition and drawing under a drawing condition in which the structural relaxation state is maintained. I understand that Further, in such a manufacturing method, as described above, the productivity of the optical fiber can be improved, for example, by increasing the drawing speed of the optical fiber at the time of drawing.
[0093]
FIG. 7 is a table showing manufacturing conditions and loss characteristics of optical fibers in 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 doped with Ge₂The outer diameter of the core region 200 made of₀= 6 μm, relative refractive index difference is Δn₀= [Ge] = 0.6%, SiO doped with Ge₂The outer diameter of the first cladding layer 211 made of₁= 40 μm, relative refractive index difference is Δn₁= 0.1%, pure SiO₂The outer diameter of the second cladding layer 212 made of₂= 125 μm, the relative refractive index difference is Δn₂= 0%.
[0094]
Further, in Examples C1 to C3 and Comparative Examples D1 to D4, the effect is examined mainly by changing the annealing temperature in the annealing of the optical fiber preform before drawing. Further, slow cooling by annealing of the optical fiber in the heat treatment furnace is not performed in any case.
[0095]
Among Examples C1 to C3 of the optical fiber according to the present invention shown in the table of FIG. 7, in Example C1, the annealing condition of the optical fiber preform is 950 ° C. for 60 hours, and the drawing temperature in the drawing furnace is 2100. The manufacturing conditions are set to ℃. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.96 dB / km · μm.^Four, Transmission loss is α_1.55= 0.190 dB / km.
[0096]
In Example C2, the 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 has a Rayleigh scattering coefficient of A = 0.94 dB / km · μm.^Four, Transmission loss is α_1.55= 0.186 dB / km.
[0097]
In Example C3, manufacturing conditions are set such that the annealing condition of the optical fiber preform is 1150 ° C. for 60 hours, and the drawing temperature in the drawing furnace is 2100 ° C. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.96 dB / km · μm.^Four, 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 during drawing. Each of the optical fiber preforms is drawn before drawing under the annealing conditions of 950 ° C., 1050 ° C., and 1150 ° C. × 60 hours that satisfy the condition that the base material is annealed at a temperature of 950 ° C. to 1150 ° C. for 30 hours or more. Annealing is performed on the material. Thereby, in any embodiment, the transmission loss α including the Rayleigh scattering coefficient A and the Rayleigh scattering loss_1.55Is sufficiently reduced.
[0099]
On the other hand, among the optical fiber comparative examples D1 to D4 shown in the table of FIG. 7, in the comparative example D1, the optical fiber preform is not annealed, and the drawing temperature in the drawing furnace is 2200 ° C. Conditions are set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.02 dB / km · μm.^Four, Transmission loss is α_1.55= 0.200 dB / km.
[0100]
In Comparative Example D2, the manufacturing conditions are set such that the drawing temperature in the drawing furnace is 2100 ° C. without annealing the optical fiber preform. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.99 dB / km · μm.^Four, Transmission loss is α_1.55= 0.195 dB / km.
[0101]
In these comparative examples D1 and D2, none of the preforms are annealed to bring the optical fiber preform into a structurally relaxed state before drawing. Therefore, regardless of whether or not the low temperature drawing at 2100 ° C. is performed in the drawing of the optical fiber, the transmission loss α including the Rayleigh scattering coefficient A and the Rayleigh scattering loss as compared with the examples C1 to C3._1.55The loss characteristic is deteriorated.
[0102]
In Comparative Example D3, 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 has a Rayleigh scattering coefficient of A = 0.99 dB / km · μm.^Four, Transmission loss is α_1.55= 0.195 dB / km. In Comparative Example D3, although the optical fiber preform is annealed, the annealing temperature is as low as 850 ° C. It can be seen that under such conditions, the transmission loss reduction effect cannot be obtained as compared with Comparative Example D2 in which the base material is not annealed.
[0103]
In Comparative Example D4, the manufacturing condition is set such that the annealing condition of the optical fiber preform is 1250 ° C. for 60 hours. Under such conditions, the preform is in the middle of annealing the optical fiber preform. The material softens and hangs down. Therefore, this annealing temperature is not suitable for annealing the base material.
[0104]
As described above, by performing annealing of the optical fiber preform at a predetermined temperature in the range of 950 ° C. to 1150 ° C., the effect of reducing the transmission loss of the optical fiber due to the relaxation of the glass structure at the base material stage can be suitably obtained. I understand that
[0105]
FIG. 8 is a table showing manufacturing conditions and loss characteristics of optical fibers in 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, the relative refractive index difference is Δn₀= 0% SiO with F added₂The outer diameter of the cladding layer 311 made of₁= 125 μm, the relative refractive index difference is Δn₁= -0.35%.
[0106]
In Examples E1 to E3 and Comparative Example F1, the effect is examined mainly by changing the annealing time for annealing the optical fiber preform before drawing. Moreover, about the drawing temperature in a drawing furnace, all have set to 2100 degreeC which satisfy | fills the conditions of low temperature drawing. In addition, for annealing by annealing of the optical fiber in the heat treatment furnace, annealing conditions of 0.5 seconds at 1300 ° C. are all set.
[0107]
Among the optical fiber examples E1 to E3 of the optical fiber according to the present invention shown in the table of FIG. 8, in Example E1, a manufacturing condition of 30 hours at 1050 ° C. is set for the annealing condition of the optical fiber preform. The obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.80 dB / km · μm.^Four, Transmission loss is α_1.55= 0.163 dB / km.
[0108]
In Example E2, annealing conditions for the optical fiber preform at 1050 ° C. for 60 hours are set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.79 dB / km · μm.^Four, Transmission loss is α_1.55= 0.161 dB / km.
[0109]
In Example E3, the annealing condition of the optical fiber preform is set at 1050 ° C. for 100 hours. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.78 dB / km · μm.^Four, Transmission loss is α_1.55= 0.159 dB / km.
[0110]
On the other hand, in the optical fiber comparative example F1 shown in the table of FIG. 8, the manufacturing conditions are set such that the optical fiber preform is not annealed. The obtained loss characteristic has a Rayleigh scattering coefficient of A = 0.82 dB / km · μm.^Four, 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, by increasing the annealing time, the effect of reducing the transmission loss of the optical fiber due to the glass structure relaxation at the base material stage It can be seen that is increasing. Therefore, the annealing conditions for the optical fiber preform are preferably set at 950 ° C. to 1150 ° C. for 30 hours or more as described above, but 60 hours or more, or even 100 hours. More preferably, the above annealing time is used.
[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 compensating fiber (DCF) having the configuration shown in FIG. 5 is assumed as the optical fiber. Specifically, SiO doped with Ge₂The outer diameter of the core region 400 made of₀= 4 μm, relative refractive index difference is Δn₀= [Ge] = 1.5%, SiO with F added₂The outer diameter of the first cladding layer 411 made of₁= 8 μm, the relative refractive index difference is Δn₁= -0.4%, pure SiO₂The outer diameter of the second cladding layer 412 made of₂= 125 μm, the relative refractive index difference is Δn₂= 0%.
[0113]
In Examples G1 to G6 and Comparative Example H1, the effect is examined mainly by changing the annealing temperature in annealing by annealing with respect to the optical fiber after drawing. For the annealing of the optical fiber preform, the annealing conditions for 60 hours at 1050 ° C. are set except for Comparative Example H1. Moreover, about the drawing temperature in a drawing furnace, all have set to 2100 degreeC which satisfy | fills the conditions of low temperature drawing.
[0114]
Among the optical fiber examples G1 to G6 of the optical fiber according to the present invention shown in the table of FIG. 9, in the example G1, a manufacturing condition is set such that the annealing condition of the optical fiber in the heat treatment furnace is 0.5 seconds at 1100 ° C. is doing. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.20 dB / km · μm.^Four, Transmission loss is α_1.55= 0.231 dB / km.
[0115]
In Example G2, annealing conditions for the optical fiber at 0.5 seconds at 1300 ° C. are set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.18 dB / km · μm.^Four, Transmission loss is α_1.55= 0.228 dB / km.
[0116]
In Example G3, the annealing conditions for the optical fiber at 0.550 seconds at 1550 ° C. are set. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.20 dB / km · μm.^Four, Transmission loss is α_1.55= 0.231 dB / km.
[0117]
In these Examples G1 to G3, annealing of the base material is performed to bring the optical fiber base material into a structural relaxation state before drawing. Also, after the drawing under the annealing conditions of 1100 ° C., 1300 ° C., and 1550 ° C. × 0.5 seconds satisfying the conditions that the drawn optical fiber is annealed at a temperature of 1100 ° C. or more and 1600 ° C. or less, respectively. Annealing is performed on the optical fiber. Thereby, in any embodiment, the transmission loss α including the Rayleigh scattering coefficient A and the Rayleigh scattering loss_1.55Is sufficiently reduced.
[0118]
In Example G4, annealing conditions for the optical fiber at 900 ° C. for 0.5 seconds are set. The obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.24 dB / km · μm.^Four, Transmission loss is α_1.55= 0.237 dB / km.
[0119]
Further, in Example G5, annealing conditions for the optical fiber are set to 0.5 seconds at 1650 ° C. Further, the obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.25 dB / km · μm.^Four, 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 has a Rayleigh scattering coefficient of A = 1.25 dB / km · μm.^Four, Transmission loss is α_1.55= 0.240 dB / km.
[0121]
On the other hand, in Comparative Example H1, a manufacturing condition is set such that the optical fiber is not annealed in the heat treatment furnace. Furthermore, in this comparative example, the optical fiber preform is not annealed. The obtained loss characteristic has a Rayleigh scattering coefficient of A = 1.28 dB / km · μm.^Four, Transmission loss is α_1.55= 0.245 dB / km.
[0122]
In this comparative example H1, the transmission loss α including the Rayleigh scattering coefficient A and the Rayleigh scattering loss compared to the examples G1 to G6._1.55The loss characteristic is deteriorated. Moreover, compared with Examples G1-G3, Example G4-G6 is somewhat Rayleigh scattering coefficient A and transmission loss (alpha)._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 the annealing of the optical fiber preform before drawing, the optical fiber is annealed 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 optical fiber manufacturing method 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 the 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】
As described in detail above, the optical fiber manufacturing method and the optical fiber according to the present invention have the following effects. That is, the optical fiber preform before drawing is annealed at a temperature of 950 ° C. or higher and 1150 ° C. or lower for 30 hours or more, and the optical fiber is drawn according to a drawing condition in 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 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 optical fiber manufacturing.
FIG. 2 is a graph showing a refractive index profile in the first embodiment of the optical fiber.
FIG. 3 is a graph showing a refractive index profile in the second embodiment of the optical fiber.
FIG. 4 is a graph showing a refractive index profile in the third embodiment of the optical fiber.
FIG. 5 is a graph showing a refractive index profile in the fourth embodiment of the optical fiber.
FIG. 6: Example A1 of an optical fiber,A3,Reference Example A2,It is a table | surface shown about the manufacturing conditions and loss characteristic in Comparative Examples B1-B3.
FIG. 7 is a table showing manufacturing conditions and loss characteristics in Examples C1 to C3 and Comparative Examples D1 to D4 of optical fibers.
FIG. 8 is a table showing manufacturing conditions and loss characteristics in Examples E1 to E3 of the optical fiber and Comparative Example F1.
FIG. 9 is a table showing manufacturing conditions and loss characteristics in Examples G1 to G6 of the optical fiber 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 ... core tube, 24 ... N₂Gas supply section, 25 ... Gas supply passage, 31 ... Cooling means, 32 ... Cylindrical tube, 33 ... Nozzle, 34 ... Cooling gas supply section, 40 ... Resin coating section, 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 device, 52 ... drum, 53 ... drive motor, 54 ... control unit, 55 ... Rotation drive shaft, 56 ... Guide roller.

Claims (2)

A heat treatment in which an optical fiber preform having a core region and a cladding region provided on the outer periphery of the core region is heat-treated at a temperature of 950 ° C. to 1150 ° C. for a predetermined time of 30 hours or more. Steps,
A drawing step of creating an optical fiber by drawing the heat-treated optical fiber preform with a drawing furnace under a drawing condition in which the structural relaxation state obtained in the heat treatment step is maintained ;
Wherein in the wire drawing step, the optical fiber preform as drawing conditions of heating wire drawing at 2100 ° C. or less of the temperature by the wire drawing furnace, that you create the optical fiber while maintaining the structural relaxation state An optical fiber manufacturing method. In the drawing step, as the drawing condition for heat-treating the optical fiber drawn in the drawing furnace 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, the process according to claim 1 Symbol placement of the optical fiber, characterized in that to create the optical fiber while maintaining the structural relaxation state.