JP4124254B2 - Optical fiber, optical fiber preform manufacturing method, and optical fiber manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber in which tension control during line drawing is facilitated, enabling transmission loss to be reduced; and also to provide a manufacturing method of the optical fiber base material and of the optical fiber. <P>SOLUTION: The optical fiber is formed which is provided with a core region 100 and a clad layer 201 of the clad region 200 to which F is added so that a refractive index becomes lower than that of the core region 100. Then, in the outer edge part 205 including the outer circumference of the clad layer 201 that becomes the outermost clad layer, the addition of the F is designed to be reduced successively from the inside to the outside, wherein a stress imparted inside the optical fiber is suitably dispersed because the viscosity of the outer edge part 205 is increased. Consequently, stress concentration on the core is suppressed, the tension control during the line drawing is facilitated and the transmission loss is reduced. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to an optical fiber that transmits light, an optical fiber preform manufacturing method, and an optical fiber manufacturing method.

  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 due to the glass structure in the optical fiber becomes a problem.

On the other hand, as an optical fiber having a low transmission loss, an optical fiber in which fluorine (F), which is an additive for lowering the refractive index, is added to a quartz (SiO ₂ ) -based core region in Japanese Patent Laid-Open No. 60-255646. Is described. F-added SiO ₂ glass has a smaller Rayleigh scattering coefficient than pure SiO ₂ glass or Ge-added SiO ₂ glass. Thus, the core region of an optical fiber in which light is transmitted by the F addition SiO ₂ glass, it is possible to reduce the transmission loss.

  Also, in the paper “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.

In contrast, when the optical fiber preform is drawn by heating, a heating furnace is installed after the drawing furnace, and the optical fiber after drawing passes within the predetermined temperature range when passing through the heating furnace. Heat until Accordingly, rapid cooling of the optical fiber after drawing is prevented by heating using a heating furnace, and the optical fiber is gradually cooled. At this time, the fictive temperature Tf in the optical fiber is lowered by the structural relaxation of the glass due to the rearrangement of atoms, and the Rayleigh scattering intensity in the optical fiber is suppressed.
JP-A-60-255646 Sakaguchi, IEICE Transactions 2000/1 Vol.J83-C No.1, pp.30-36

  However, even when a manufacturing method capable of reducing the Rayleigh scattering loss is used, the tension control conditions during drawing of the optical fiber preform and the configuration of the core region and the cladding region in the optical fiber preform The inventor of the present application has found that the transmission loss as a whole is not necessarily reduced, such as an increase in the structural irregularity loss due to stress concentration on the core.

  The present invention has been made to solve the above-described problems, and an optical fiber capable of facilitating tension control during drawing and reducing transmission loss, an optical fiber preform manufacturing method, And it aims at providing the manufacturing method of an optical fiber.

In order to achieve such an object, an optical fiber according to the present invention includes a core region to which fluorine is added so that the refractive index is equal to or lower than that of pure SiO ₂ , and an outer periphery of the core region. And an outermost cladding layer located on the outermost side of the one or more clad layers, the clad region having one or more clad layers to which fluorine is added so that the refractive index is lower In the outer edge portion including the outer periphery and having a thickness of 7.5 μm from the outer periphery, the amount of fluorine added is sequentially decreased so that the refractive index sequentially increases from the inner side to the outer side. When the relative refractive index difference is defined as% in terms of the refractive index of pure SiO ₂ , the difference between the maximum and minimum relative refractive index differences at the outer edge is 0.15% or more. And at the outer periphery The relative refractive index difference Δn _a is the condition Δn _a ≧ −0.35%
It is characterized by satisfying.

  In the optical fiber, the cladding region is composed of two cladding layers, an inner cladding layer provided on the outer periphery of the core region and an outer cladding layer provided on the outer periphery of the inner cladding layer and serving as the outermost cladding layer. In addition, it is preferable that the average addition amount of fluorine in the outer cladding layer is smaller than the average addition amount of fluorine in the inner cladding layer.

Further, when the optical fiber defines the relative refractive index difference in each part in terms of% with respect to the refractive index of pure SiO ₂ , the average relative refractive index difference Δn _{0 of} the optical fiber satisfies the condition Δn ₀ > -0.3%
It is preferable to satisfy.

The method for manufacturing an optical fiber preform according to the present invention deposits glass fine particles on the outer periphery of a core preform including at least a core region to which a fluorine is added so that the refractive index is equal to or less than that of pure SiO ₂ . A synthesizing step of synthesizing a glass fine particle layer which is an outermost clad layer located on the outermost side among one or a plurality of clad layers provided in the outer periphery of the core region, and the synthesized glass fine particle layer A dehydration step of heating and dehydrating, an impregnation step of impregnating and adding fluorine to the glass fine particle layer in a gas atmosphere containing fluorine at a predetermined concentration, and an outermost cladding layer by heating and sintering the dehydrated glass fine particle layer A sintering step of forming an optical fiber preform comprising a core region and a cladding region having one or more cladding layers, and in the sintering step, heat sintering When the concentration of fluorine contained in the gas atmosphere is lower than the predetermined concentration at the time of impregnation, it is added from the outer edge that becomes 7.5 μm thick from the outer periphery when the optical fiber including the outer periphery of the glass fine particle layer is used. The amount of fluorine added is sequentially reduced from the inner side to the outer side of the outer edge portion, and the relative refractive index difference in each portion is changed to the refractive index of pure SiO ₂ when an optical fiber is obtained. when defining expressed in percent based on the difference between the maximum value and the minimum value of the relative refractive index difference at the outer edge becomes 0.15% or more, and conditions are the relative refractive index difference [Delta] n _a of the outer periphery Δn _a ≧ −0.35%
An optical fiber preform satisfying the requirements is formed.

Alternatively, in the method for manufacturing an optical fiber preform according to the present invention, glass fine particles are deposited on the outer periphery of a core preform including at least a core region to which fluorine is added so that the refractive index is equal to or less than that of pure SiO _2. A synthesizing step of synthesizing a glass fine particle layer to be an outermost clad layer located on the outermost side out of one or a plurality of clad layers of the clad region provided on the outer periphery of the core region, and the synthesized glass An optical fiber comprising: a dehydration process for heating and dehydrating the fine particle layer; a dehydrated glass fine particle layer by heating and sintering to form an outermost clad layer; and a core region and a clad region having one or more clad layers A sintering process for forming a base material, and in the synthesis process, chlorine is added to the glass particulate layer using a chlorine-containing source gas and the outer periphery of the glass particulate layer is included. A glass fine particle layer is prepared by adjusting the chlorine-containing source gas so that the amount of chlorine added decreases gradually from the inside to the outside in the outer edge portion, which is 7.5 μm thick from the outer periphery when the optical fiber is formed. When the added chlorine is replaced with fluorine to form an optical fiber, the relative refractive index difference in each part is defined in terms of% based on the refractive index of pure SiO ₂ , and the outer edge. the difference between the maximum value and the minimum value of the specific refractive index difference in parts becomes 0.15% or more, and conditions are the relative refractive index difference [Delta] n _a of the outer peripheral Δn _a ≧ -0.35%
An optical fiber preform satisfying the requirements is formed.

  An optical fiber manufacturing method according to the present invention provides an optical fiber drawn by a drawing furnace when the optical fiber preform manufactured by the above-described optical fiber preform manufacturing method is heated and drawn. Heating is performed so that the temperature is within a predetermined temperature range by a heating furnace provided at a subsequent stage.

  In addition, a first optical fiber according to the present invention includes a core region to which fluorine that lowers the refractive index is added, and one or more layers that are provided on the outer periphery of the core region and to which fluorine is added in an amount larger than the core region. A clad region having a clad layer, and the outermost clad layer located on the outermost side of one or a plurality of clad layers has a minimum fluorine content in the outer edge including the outer periphery thereof. It is characterized in that the addition amount of fluorine is gradually decreased to a predetermined addition amount that becomes the addition amount.

In the optical fiber described above, F (fluorine) is added to the core region. As described above, when the core region of the optical fiber is made of F-added SiO ₂ glass, the Rayleigh scattering loss in the optical fiber is reduced, and the transmission loss is reduced. Further, in the core region made of F-added SiO ₂ , the viscosity is smaller than that of pure SiO ₂ , so that the concentration of stress applied in the optical fiber on the core is suppressed. Further, the reduction in viscosity promotes structural relaxation by viscous flow in the core region.

  Further, among the clad layers formed by adding F (fluorine), the F content distribution in the outermost clad layer is within the outer edge portion (outer periphery and the vicinity thereof) of the outermost clad layer. The outermost cladding layer is configured so that the amount of F added gradually decreases from the outside toward the outside. At this time, since the viscosity increases at the outer edge portion of the outermost cladding layer with a small amount of F added, the stress applied in the optical fiber is dispersed in the outer edge portion of the outermost cladding layer, and the stress concentration on the core Is further suppressed. In addition, the stress distribution enables a wide range of numerical values for a suitable tension value range that is permitted when the optical fiber is drawn.

  As a result, the optical fiber according to the present invention is an optical fiber having a configuration in which stress applied in the optical fiber is suitably dispersed in the core region and the cladding region, and tension control during drawing is facilitated. At the same time, an increase in transmission loss and deterioration of transmission characteristics caused by excessive stress concentration on the core are prevented, and structural relaxation by viscous flow is promoted, realizing an optical fiber with stable transmission characteristics over the entire length. The

  Regarding the distribution of the amount of F added in the cladding region described above, since the region where the amount of F added is decreased is the outer edge of the outermost cladding layer, the F region is transmitted through the core region and the nearby cladding region. It does not affect the transmission characteristics of light. Accordingly, it is possible to facilitate the tension control or reduce the transmission loss by maintaining the transmission characteristics of the optical fiber suitably.

  The cladding region is composed of two cladding layers, an inner cladding layer provided on the outer periphery of the core region and an outer cladding layer provided on the outer periphery of the inner cladding layer and serving as the outermost cladding layer. The average addition amount of fluorine in the layer is smaller than the average addition amount of fluorine in the inner cladding layer.

  The optical fiber described above has an effect of adjusting the transmission characteristics and the inner cladding layer having a large F addition amount (small relative refractive index difference) in order to efficiently confine transmitted light in the core region and the vicinity thereof. And a clad region having a two-layer structure with an outer clad layer having an effect of reducing stress concentration on the core and having a small F addition amount (a large relative refractive index difference). Even in an optical fiber having such a configuration, by reducing the amount of F added at the outer edge of the outer cladding layer, which is the outermost cladding layer, the optical fiber is similar to an optical fiber having a one-layer cladding region. It is possible to facilitate fiber tension control.

  Further, the outer cladding layer may be characterized in that the amount of fluorine added in the vicinity of the inner periphery thereof is smaller than the maximum amount of fluorine added in the layer. In the case of the clad region having the two-layer structure described above, when the outer clad layer (outermost clad layer) is formed, the amount of F added may be slightly reduced in the vicinity of the inner circumference. Even in the case of such an addition amount distribution, stress distribution to the outer edge portion can be realized by applying the configuration of the optical fiber described above.

The outermost cladding layer has a maximum difference at a portion in the outer edge portion to which fluorine is added with a minimum addition amount when the relative refractive index difference in each portion is defined as% based on the refractive index of pure SiO _2. The relative refractive index difference Δn _a is smaller than the minimum relative refractive index difference Δn _b at the portion inside the outer edge portion where fluorine is added at the maximum addition amount, and the condition Δn _a ≧ Δn _b + 0.05%
It is characterized by satisfying.

  As described above, the amount of decrease in F addition amount at the outer edge portion of the outermost cladding layer is set to 0.05% or more in terms of the relative refractive index difference, so that the effect of stress distribution to the outer edge portion is sufficiently obtained. Can be improved. Further, the amount of decrease in the addition amount of F is more preferably 0.1% or more in terms of relative refractive index difference.

  In addition, the outermost cladding layer is characterized in that the addition amount of fluorine is substantially constant at the minimum addition amount within a predetermined range on the outer peripheral side in the outer edge portion in the outer edge portion.

  In this way, by providing a region where the addition amount of F is substantially constant at the minimum addition amount in the vicinity of the outer periphery which is the outer portion in the outer edge portion, the viscosity in that region is increased, and the stress on the outer edge portion is increased. Dispersion can be realized more efficiently.

Further, when the relative refractive index difference in each part is defined in terms of% based on the refractive index of pure SiO ₂ , the core region has an average relative refractive index difference Δn ₀ of the condition Δn ₀ > −0.3. %
It is preferable to satisfy. Thus, by setting the amount of F added to the core region within a certain range, the optical fiber having the above-described configuration in which F is added to both the core region and the cladding region can be suitably and easily manufactured.

  Further, the core region may be characterized in that an additive for increasing the refractive index is further added. Thereby, the refractive index of a core area | region can be adjusted to a suitable value.

  The viscosity in the core region may be smaller than the viscosity in the outer edge portion of the outermost cladding layer. Thereby, the stress applied in the optical fiber can be sufficiently dispersed to the outer edge portion of the outermost cladding layer. However, even when the viscosity in the core region is equal to or greater than the viscosity in the outer edge of the outermost cladding layer, the effect of stress distribution to the outer edge of the outermost cladding layer can be obtained as described above. .

  In addition, a second optical fiber according to the present invention includes a core region to which fluorine that lowers the refractive index is added, and a cladding layer that is provided on the outer periphery of the core region and to which fluorine is added in a larger addition amount than the core region. A clad region having one or more clad layers, wherein the clad region includes an inner clad layer provided on the outer periphery of the core region, and an outer clad layer provided on the outer periphery of the inner clad layer. It consists of two cladding layers, the outermost cladding layer being the outermost cladding layer located on the outermost side of the layers, and the average amount of fluorine added in the outer cladding layer is the average amount of fluorine added in the inner cladding layer It is comprised so that it may become smaller than this.

In the optical fiber described above, F (fluorine) is added to the core region. As described above, when the core region of the optical fiber is made of F-added SiO ₂ glass, the Rayleigh scattering loss in the optical fiber is reduced, and the transmission loss is reduced. Further, in the core region made of F-added SiO ₂ , the viscosity is smaller than that of pure SiO ₂ , so that the concentration of stress applied in the optical fiber on the core is suppressed. Further, the reduction in viscosity promotes structural relaxation by viscous flow in the core region.

  Further, of the two clad layers formed by adding F (fluorine), the amount of F added in the outer clad layer serving as the outermost clad layer is larger than the amount of F added in the inner clad layer. The cladding region is configured so that the addition amount is small. At this time, since the viscosity of the outer cladding layer with a small amount of F is increased, the stress applied to the optical fiber is dispersed in the outer cladding layer, and the stress concentration on the core is further suppressed. In addition, the stress distribution enables a wide range of numerical values for a suitable tension value range that is permitted when the optical fiber is drawn.

  As a result, the optical fiber according to the present invention is an optical fiber having a configuration in which stress applied in the optical fiber is suitably dispersed in the core region and the cladding region, and tension control during drawing is facilitated. At the same time, an increase in transmission loss and deterioration of transmission characteristics caused by excessive stress concentration on the core are prevented, and structural relaxation by viscous flow is promoted, realizing an optical fiber with stable transmission characteristics over the entire length. The

When such two clad layers are provided, the outer clad layer is preferably made of pure SiO ₂ . Thereby, the stress applied in the optical fiber can be sufficiently dispersed into the cladding region.

  Further, the method for manufacturing an optical fiber preform according to the present invention includes (1) depositing glass fine particles on the outer periphery of a core preform including at least a core region to which fluorine that lowers the refractive index is added. A synthesizing step of synthesizing a glass fine particle layer to be an outermost clad layer located on the outermost side in one or a plurality of clad layers of the clad region provided; and (2) heating the synthesized glass fine particle layer. An optical fiber mother comprising: a dehydration step of dehydration; and (3) a dehydrated glass fine particle layer is heated and sintered to form an outermost clad layer, and a core region and a clad region having one or more clad layers. (4) Before heating and sintering the glass fine particle layer, fluorine is added to the glass fine particle layer and added from the outer edge including the outer periphery thereof. And removing a portion of Tsu element.

  By drawing an optical fiber preform obtained by using such an optical fiber preform manufacturing method, F is added to the core region, and the outermost outermost layer of the cladding layers in the cladding region is added. In the outer edge portion of the cladding layer, an optical fiber in which F is added and removed so that the addition amount of F is sequentially reduced to a predetermined addition amount that is the minimum addition amount of F in the layer can be obtained. .

  Specifically, the method further comprises an impregnation step of impregnating and adding fluorine to the glass fine particle layer in a gas atmosphere containing fluorine at a predetermined concentration between the dehydration step and the sintering step, There is a method of removing a part of the added fluorine from the outer edge portion of the glass fine particle layer by setting the concentration of fluorine contained in the gas atmosphere at the time of heating and sintering to a concentration lower than the predetermined concentration at the time of impregnation.

  Alternatively, in the method for manufacturing an optical fiber preform according to the present invention, (1) glass fine particles are deposited on the outer periphery of a core preform including at least a core region doped with fluorine that lowers the refractive index, and the outer periphery of the core region is deposited. A synthesizing step of synthesizing a glass fine particle layer to be an outermost clad layer located on the outermost side in one or a plurality of clad layers of the clad region provided; and (2) heating the synthesized glass fine particle layer. An optical fiber mother comprising: a dehydration step of dehydration; and (3) a dehydrated glass fine particle layer is heated and sintered to form an outermost clad layer, and a core region and a clad region having one or more clad layers. (4) In the synthesis step, fluorine is added to the glass fine particle layer using a raw material gas containing fluorine, and in the outer edge portion including the outer periphery thereof. There are as the added amount of fluorine successively decreased, and performs the synthesis of glass fine particle layer by adjusting the source gas containing fluorine.

  Similarly, by drawing an optical fiber preform obtained by using such an optical fiber preform manufacturing method, F is added to the core region, and in the outer edge of the outermost cladding layer, An optical fiber to which F is added can be obtained so that the addition amount of F is sequentially decreased to a predetermined addition amount that is the minimum addition amount of F in the layer.

  In this case, in the synthesis step, after adding chlorine to the glass fine particle layer using a source gas containing chlorine instead of fluorine, the added chlorine may be replaced with fluorine.

  Further, the optical fiber preform manufacturing method according to the present invention is provided on the outer periphery of the core region to which fluorine that lowers the refractive index is added, and with respect to the inner cladding layer to which fluorine is added in a larger addition amount than the core region, On the outer periphery of the inner cladding layer, an outer cladding layer serving as an outermost cladding layer located in the outermost layer among one or a plurality of cladding layers included in the outer periphery of the core region is formed as an inner cladding layer. Forming a core region and a clad region composed of two clad layers of an inner clad layer and an outer clad layer by forming fluorine with an average addition amount smaller than the average addition amount of fluorine at An optical fiber preform is provided.

  F is added to the core region by drawing the optical fiber preform obtained by using such a method of manufacturing an optical fiber preform, and the outer cladding layer of the two cladding layers An optical fiber in which the addition amount of F is smaller than that in the inner cladding layer can be obtained.

  The first optical fiber manufacturing method according to the present invention includes a core region to which fluorine for decreasing the refractive index is added, and an outer periphery of the core region, in which fluorine is added in a larger addition amount than the core region. A clad region having one or more clad layers, and the outermost clad layer located on the outermost side of the one or plural clad layers is within the outer edge including its outer periphery. When producing an optical fiber preform that is configured so that the amount of fluorine added decreases sequentially to a predetermined addition amount that is the minimum amount of fluorine added, and when drawing the optical fiber preform, The optical fiber drawn by the drawing furnace is heated to a temperature within a predetermined temperature range by a heating furnace provided at a subsequent stage of the drawing furnace.

  A second optical fiber manufacturing method according to the present invention includes a core region to which fluorine that lowers the refractive index is added, and a cladding layer that is provided on the outer periphery of the core region and to which fluorine is added in a larger additive amount than the core region. Including a clad region having one or more clad layers, wherein the clad region is provided on the outer periphery of the core region, and the outer periphery of the inner clad layer is provided with one or more layers. The clad layer consists of two clad layers, the outermost clad layer being the outermost clad layer located on the outermost side, and the average addition amount of fluorine in the outer clad layer is the average addition amount of fluorine in the inner clad layer An optical fiber preform that is configured to be smaller than the amount is manufactured, and when the optical fiber preform is heated and drawn, the optical fiber drawn by the drawing furnace is placed in the subsequent stage of the drawing furnace. Establishment Wherein the heating to be a temperature within a predetermined temperature range by the heating furnace was.

  As described above, when the optical fiber preform is drawn by heating, the optical fiber is slowly cooled using a heating furnace provided at the subsequent stage of the drawing furnace, thereby suppressing and transmitting stress concentration due to the above-described structure. In addition to reducing the loss, the fictive temperature Tf in the optical fiber can be lowered by structural relaxation to further reduce the Rayleigh scattering loss.

  In the above-described optical fiber manufacturing method, for the heating furnace provided at the subsequent stage of the drawing furnace, if there is a resin coating portion that covers the drawn optical fiber with resin, the drawing furnace and the resin coating It is preferable to be provided between the parts.

  The heating furnace preferably heats the drawn optical fiber for 0.05 to 5 seconds so that the temperature of the optical fiber is in the range of 800 to 1500 ° C.

  By setting it as such a temperature range and heating time, reduction of fictive temperature Tf by slow cooling of the optical fiber after drawing can be realized suitably. Moreover, about conditions, such as these temperature ranges, it is preferable to set suitably suitable conditions according to drawing speed etc.

  Further, when the optical fiber preform is drawn by heating, the optical fiber preform is drawn with a tension within a range of 0.05 to 0.20 N.

  The structure of the optical fiber base material (optical fiber) in which stress is dispersed at the outer edge of the outermost cladding layer, and the tension during drawing is maintained within a suitable tension value range of 0.05 to 0.20 N. By performing tension control in this way, an optical fiber having suitable transmission characteristics with low transmission loss over the entire length can be obtained.

  As described in detail above, the optical fiber, the optical fiber preform manufacturing method, and the optical fiber manufacturing method according to the present invention have the following effects. That is, in an optical fiber including a core region and a cladding region provided on the outer periphery of the core region, F is added to the core region, and the amount of F added is sequentially increased in the outer edge portion of the outermost cladding layer of the cladding region. According to the decreasing configuration of the optical fiber, the viscosity of the core region decreases and the viscosity of the outer edge increases. Therefore, the stress applied in the optical fiber is suitably distributed to the core region and the cladding region, and the stress concentration on the core is suppressed.

  Further, in an optical fiber including a core region and a cladding region composed of an inner cladding layer and an outer cladding layer provided on the outer periphery of the core region, F is added to the core region, and the amount of F added in the outer cladding layer is Even with an optical fiber configured to be smaller than the amount of F added in the inner cladding layer, the viscosity of the core region is decreased and the viscosity of the outer cladding layer is increased. Therefore, the stress applied in the optical fiber is suitably distributed to the core region and the cladding region, and the stress concentration on the core is suppressed.

  As a result, a preferable tension value range allowed when drawing the optical fiber becomes a wider numerical range, and tension control during drawing is facilitated. In addition, an increase in transmission loss and deterioration of transmission characteristics caused by excessive stress concentration on the core and insufficient tension control are prevented, and structural relaxation by viscous flow is promoted, resulting in stable transmission characteristics over the entire length. Is realized. Thus, according to the optical fiber having excellent transmission characteristics such as low transmission loss, when applied to a long-distance optical transmission system, the number of repeaters in which an optical amplifier or the like is installed can be reduced. An efficient optical transmission system can be constructed.

  Hereinafter, preferred embodiments of an optical fiber, an optical fiber preform manufacturing method, and an optical fiber manufacturing method according to the present invention 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.

Here, in the following, the relative refractive index difference indicating the value of the refractive index in each part, the refractive index of pure SiO 2 _(pure silica) as a reference (relative refractive index difference = 0), the refractive index of pure SiO ₂ The difference is defined as a percentage. In addition, regarding the average addition amount or average relative refractive index difference of F (fluorine) in each region and each layer, the addition amount of F or the relative refractive index difference is weighted by the area in the region (in the layer), respectively. It is defined by the average value.

  First, the configuration of the optical fiber will be described. FIG. 1 is a diagram schematically showing a cross-sectional structure and a refractive index profile in a fiber radial direction (direction indicated by a line L in the drawing) of a first embodiment of an optical fiber according to the present invention. The horizontal axis of the refractive index profile (relative refractive index difference distribution) shown in FIG. 1 is different in scale, but with respect to the central axis of the optical fiber along the line L shown in the sectional structure in the figure. Corresponds to each position on the vertical section.

This optical fiber is an optical fiber based on SiO ₂ glass (quartz glass), and includes a core region 100 including the central axis of the optical fiber and a cladding region 200 provided on the outer periphery of the core region 100. ing. In such a configuration, light transmitted in the optical fiber is transmitted in the core region 100 and in the region near the core region 100 on the inner peripheral side of the cladding region 200.

The core region 100 is formed a radius of the outer periphery as r _0. A predetermined amount of F (fluorine) is added to the core region 100 as an additive for reducing the refractive index of pure SiO ₂ glass. Thereby, the average relative refractive index difference in the core region 100 is Δn ₀ (where Δn ₀ <0).

On the other hand, the clad region 200 has a single clad layer 201 in the present embodiment. The clad layer 201 is formed with an outer periphery radius of r ₁ . In this clad layer 201, a predetermined amount of F (fluorine) is added to pure SiO ₂ glass. Thereby, the average relative refractive index difference in the cladding layer 201 is Δn ₁ (where Δn ₁ <0). The average addition amount of F in the cladding layer 201 is set larger than the average addition amount of F in the core region 100. Therefore, the average relative refractive index differences Δn ₀ and Δn ₁ have a relationship of 0> Δn ₀ > Δn ₁ as shown in FIG.

The clad layer 201 is the outermost clad layer located on the outermost side in the clad region 200 in the configuration of the present embodiment. And it is a region including the outer periphery (part of radius r ₁ ), and a region range from radius r _a (where r ₀ <r _a <r ₁ ) to radius r ₁ is defined as outer edge portion 205, and this outer edge portion In 205, the addition amount of F and the relative refractive index difference are configured to have a predetermined distribution.

That is, of the cladding layer 201 is the outermost cladding layer in a region ranging from the radius r ₀ consisting outer edge 205 and inward to r _a, substantially constant amount of the maximum amount of F in the cladding layer F is added. As a result, the inner portion of the outer edge portion 205 is set to Δn _b where the relative refractive index difference becomes the minimum relative refractive index difference of F within the layer (corresponding to the maximum addition amount of F and the maximum absolute value). ing.

On the other hand, at the outer edge portion 205, the amount of addition is gradually decreased from the inside toward the outside from the maximum addition amount of F described above to a predetermined addition amount that is the minimum addition amount of F in the layer. Is added. Thus, outer portion 205, difference that the relative refractive index is from the minimum relative refractive index difference [Delta] n _b described above, the maximum relative refractive index difference within the layer (equivalent to the minimum amount of F, the minimum absolute value) become until [Delta] n _a, is configured to gradually change from the inside to the outside.

In the optical fiber of the present embodiment, F is added to the core region 100 as described above. As described above, when the core region 100 of the optical fiber is made of F-added SiO ₂ glass, the Rayleigh scattering loss in the optical fiber is reduced, and the transmission loss is reduced.

Further, if the viscosity of the core region is larger than that of the cladding region, stress generated in the optical fiber is concentrated on the core when the optical fiber preform is drawn, causing transmission loss to increase. On the other hand, in the core region 100 made of F-added SiO ₂ , the viscosity is smaller than that of pure SiO ₂ , so that the stress applied to the core in the optical fiber is suppressed. Further, the reduction in viscosity promotes structural relaxation by viscous flow in the core region.

  Further, as shown in FIG. 1, the F addition amount distribution in the cladding layer 201 which is the outermost cladding layer of the cladding region 200 is such that the F addition amount gradually decreases at the outer edge portion 205 as shown in FIG. The cladding layer 201 is configured.

The core region 100 of the present optical fiber is made of F-added SiO ₂ . In the core region 100, although the viscosity is reduced as described above by the addition of F, the core region 100 has a larger viscosity than the cladding region 200 due to the addition amount and the like. Therefore, if the clad layer 201 provided on the outer periphery thereof has a normal configuration in which F is added with a substantially constant addition amount, excessive stress concentration on the core may occur.

  On the other hand, by reducing the addition amount of F in the outer edge portion 205 of the clad layer 201 as described above, the viscosity of the outer edge portion 205 is increased, and the stress is distributed to the outer edge portion 205 to the core. Stress concentration is further suppressed. That is, by combining the effect of addition of F into the core region 100 and the effect of the addition amount of F at the outer edge portion 205 of the cladding layer 201, stress applied in the optical fiber is applied to the core region 100 and the cladding region 200. And the concentration of stress on the core is suppressed.

  As a result, a preferable tension value range allowed when drawing the optical fiber becomes a wider numerical range, and tension control during drawing is facilitated. In addition, an increase in transmission loss and deterioration of transmission characteristics caused by excessive stress concentration on the core and insufficient tension control are prevented, and structural relaxation due to viscous flow of glass in the core region is promoted. . From the above, an optical fiber having suitable and stable transmission characteristics over the entire length is realized.

Here, with respect to the amount of F added to the core region 100, the average relative refractive index difference Δn ₀ of the core region 100 satisfies the condition Δn ₀ > −0.3%.
It is preferable to satisfy. This corresponds to making the amount of F added to the core region 100 smaller than the amount of addition where Δn ₀ = −0.3%.

Thus, by setting the amount of F added to the core region 100 within a certain range, the optical fiber having the above-described configuration in which F is added to both the core region 100 and the cladding region 200 can be suitably and easily manufactured. it can. Further, regarding the addition amount of F to the cladding region 200, the average relative refractive index difference Δn ₁ of the cladding region 200 is such that the condition Δn ₁ > −0.6%.
It is preferable to satisfy.

  Further, an additive for increasing the refractive index may be further added to the core region 100. Thereby, the refractive index of the core region 100 can be adjusted to a suitable value. Examples of the additive for increasing the refractive index include Ge (germanium) and Cl (chlorine). The refractive index distribution in the core region 100 may be a substantially constant refractive index distribution in the core region 100, or may be a graded type refractive index distribution.

Further, when Ge, Cl, and the like are added together with F to the core region 100 as described above, the average relative refractive index difference Δn ₁ of the cladding region 200 with respect to the amount of F added to the cladding region 200 is Condition Δn ₁ > −0.5%
Is preferably further satisfied.

Also, the minimum relative refractive index difference [Delta] n _b at the site than the inner edge portion 205, for a maximum relative refractive index difference [Delta] n _a of the outer circumference near the outer edge portion 205, the relative refractive index difference [Delta] n _a than [Delta] n _b 0 0.05% or more is preferable (Δn _a ≧ Δn _b + 0.05%). Alternatively, it is preferably set to be higher by 0.1% or more (Δn _a ≧ Δn _b + 0.1%).

As described above, the decrease amount of the F addition amount at the outer edge portion 205 of the clad layer 201 is set to 0.05% or more, or further 0.1% or more in terms of the relative refractive index difference, whereby the outer edge portion 205 is reduced. The effect of stress distribution to the outer edge portion 205 can be sufficiently improved, for example, the viscosity in the vicinity of the outer periphery of the core region 100 can be made comparable to the viscosity of the core region 100. In this case, for example, the amount of addition of F in the vicinity of the outer periphery of the outer edge portion 205 may be reduced to almost 0 so that Δn _a ˜0.

  Alternatively, the viscosity in the core region 100 may be smaller than the viscosity in the outer edge portion 205 of the clad layer 201 that is the outermost clad layer. Thereby, the stress applied in the optical fiber can be sufficiently dispersed to the outer edge portion 205 of the cladding layer 201.

Such a configuration corresponds to reducing the addition amount of F at the outer edge of the outermost cladding layer to an addition amount smaller than the addition amount of F to the core region so that Δn _a > Δn _0. . However, the viscosity in the core region may be the same as or higher than the viscosity in the outer edge portion of the outermost cladding. Even in such a case, the effect of stress distribution to the outer edge portion of the outermost cladding layer can be obtained by the above-described configuration in which the addition amount of F is reduced at the outer edge portion of the outermost cladding layer.

For reducing transmission loss by suppressing stress concentration on the core or facilitating tension control during manufacturing (drawing), specifically, the Rayleigh scattering coefficient A is 0.79 dB / km. · [mu] m ⁴ or less, or, it is preferable that the transmission loss alpha _1.00 at a wavelength of 1.00μm is less 0.80dB / km.

The Rayleigh scattering coefficient A and the transmission loss α _1.00 are values (reference values) of about 0.85 dB / km · μm ⁴ and 0.86 dB / km, respectively, in a pure SiO ₂ core optical fiber having a normal configuration. is there. On the other hand, according to the optical fiber of the present embodiment, the Rayleigh scattering coefficient A or the transmission loss α _1.00 can be set to the above numerical range reduced by about 7% from these reference values. is there.

Such a reduction in Rayleigh scattering coefficient A or transmission loss α _1.00 is realized by a combination of the above-described optical fiber configuration or a manufacturing method capable of reducing transmission loss due to Rayleigh scattering loss or the like. . The reduction of transmission loss by the manufacturing method will be described later.

Here, the Rayleigh scattering coefficient A will be described. The Rayleigh scattering coefficient A is an amount that serves as an index of the Rayleigh scattering loss included in the transmission loss of the optical fiber. The transmission loss α _λ (dB / km) at the wavelength λ in an optical fiber is generally expressed by the following equation: α _λ = A / λ ⁴ + B + C (λ) due to transmission loss components such as Rayleigh scattering loss and other structural irregularities.
It is represented by Among them, the first term A / λ ⁴ (dB / km) indicates the Rayleigh scattering loss, and the coefficient A is the Rayleigh scattering coefficient (dB / km · μm ⁴ ). From the above equation, the Rayleigh scattering loss is proportional to the Rayleigh scattering coefficient A. Therefore, the Rayleigh scattering coefficient A can be used as an index for reducing the Rayleigh scattering loss. Note that the Rayleigh scattering coefficient A, the above equation can be obtained from the data of wavelength dependence of transmission loss (e.g. slope at 1 / lambda ⁴ plots).

Further, regarding the transmission loss of the optical fiber of the present invention, a numerical range is given to the transmission loss α1.00 at the wavelength of _1.00 μm under the above-described conditions. This is because the value of transmission loss at 1.00 μm is large compared to the 1.55 μm band used for optical transmission, etc., and can be evaluated with sufficient accuracy using a relatively short optical fiber sample of about 1 to 10 km. is there.

Further, the transmission loss α _1.00 at the wavelength of _1.00 μm and the transmission loss α _1.55 at the wavelength of 1.55 μm correspond to each other with a certain relationship, and the transmission loss α _1.00 is reduced. As a result, the reduction of the transmission loss α _1.55 can be confirmed in the same manner. Specifically, transmission loss α _1.00 and α _1.55 are expressed by α _1.00 = A + B + C (1.00) from the above equation, respectively.
α _1.55 = A × 0.17325 + B + C (1.55)
And the relationship is
α _1.00 = α _1.55 + A × 0.82675
+ C (1.00) -C (1.55)
It becomes.

  FIG. 2 is a diagram schematically showing a cross-sectional structure and a refractive index profile in the fiber radial direction of the second embodiment of the optical fiber according to the present invention.

Similar to the first embodiment, this optical fiber is a SiO ₂ glass (quartz glass) optical fiber, and includes a core region 100 including the central axis of the optical fiber, and a clad provided on the outer periphery of the core region 100. The region 200 is configured. Among these, the configuration of the core region 100 is substantially the same as that of the core region 100 in the optical fiber shown in FIG.

  On the other hand, in this embodiment, the clad region 200 is a two-layer clad layer of an inner clad layer 201 provided on the outer periphery of the core region 100 and an outer clad layer 202 further provided on the outer periphery of the inner clad layer 201. It is comprised.

The inner cladding layer 201 is formed with an outer periphery radius of r ₁ . A predetermined amount of F (fluorine) is added to the inner cladding layer 201 as an additive for reducing the refractive index of pure SiO ₂ glass. Thereby, the average relative refractive index difference in the inner cladding layer 201 is Δn ₁ (where Δn ₁ <0).

The outer cladding layer 202 is formed to a radius of the outer periphery as r _2. The outer cladding layer 202 is added with a predetermined amount of F (fluorine) in pure SiO ₂ glass. Thereby, the average relative refractive index difference in the outer cladding layer 202 is Δn ₂ (where Δn ₂ <0). However, the average addition amount of F in the outer cladding layer 202 is smaller than the average addition amount of F in the inner cladding layer 201. Further, the average addition amount of F in the inner cladding layer 201 and the outer cladding layer 202 is set larger than the average addition amount of F in the core region 100, respectively. Therefore, the average relative refractive index difference [Delta] n ₀ of the core region 100, an inner cladding layer 201 and the outer cladding layer 202,, Δn _1, Δn _2, as shown in FIG. _{2, 0> Δn 0> Δn} 2> Δn 1 Have the relationship.

In addition, the outer cladding layer 202 is the outermost cladding layer located on the outermost side in the cladding region 200 in the configuration of the present embodiment. And it is a region including the outer periphery, and the region range from the radius r _a (where r ₁ <r _a <r ₂ ) to the radius r ₂ is defined as the outer edge portion 205, and the amount of F added in the outer edge portion 205 And the relative refractive index difference has a predetermined distribution.

That is, of the outer cladding layer 202 is the outermost cladding layer in a region ranging from the radius r ₁ made of outer edge 205 and inward to r _a, substantially constant amount of the maximum amount of F in the layer F is added. Thus, the inner portion of the outer edge portion 205, the relative refractive index difference, there is a [Delta] n _b that minimizes relative refractive index difference within the layer.

On the other hand, at the outer edge portion 205, the amount of addition is gradually decreased from the inside toward the outside from the maximum addition amount of F described above to a predetermined addition amount that is the minimum addition amount of F in the layer. Is added. Thus, outer portion 205, difference that the relative refractive index is from the minimum relative refractive index difference [Delta] n _b described above, to [Delta] n _a of maximum relative refractive index difference within the layer, and changes from the inside to the outside It is configured to go.

  Also in the optical fiber of the present embodiment, as in the first embodiment, F is added to the core region 100, and at the outer edge portion 205 in the outer cladding layer 202 that becomes the outermost cladding layer of the cladding region 200, The F addition amount distribution is such that the F addition amount gradually decreases. Accordingly, the viscosity of the core region 100 is reduced and the viscosity of the outer edge portion 205 is increased. Therefore, stress applied in the optical fiber is preferably dispersed in the core region 100 and the cladding region 200, and stress concentration on the core is concentrated. It is suppressed.

  As a result, a preferable tension value range allowed when drawing the optical fiber becomes a wider numerical range, and tension control during drawing is facilitated. In addition, an increase in transmission loss and deterioration of transmission characteristics caused by excessive stress concentration on the core and insufficient tension control are prevented, and structural relaxation due to viscous flow of glass in the core region is promoted. . From the above, an optical fiber having suitable and stable transmission characteristics over the entire length is realized.

  Further, in the optical fiber of the present embodiment, the cladding region 200 in the optical fiber of the first embodiment is composed of a single cladding layer 201, whereas the amount of F added is large (relative refractive index). The clad region 200 is composed of two clad layers, an inner clad layer 201 (with a small difference) and an outer clad layer 202 with a small amount of F added (with a large relative refractive index difference).

  According to the clad region 200 having such a two-layer structure, the transmitted light can be efficiently confined in the core region 100 and the vicinity thereof by the inner clad layer 201 located on the outer periphery of the core region 100. Further, the outer cladding layer 202 has an effect of adjusting transmission characteristics of the optical fiber, an effect of reducing stress concentration on the core, and the like. The concentration of stress on the core region 100 can be reliably suppressed by the configuration of the outer cladding layer 202 and the outer edge portion 205 inside the outer cladding layer 202.

  Next, an optical fiber preform and an optical fiber manufacturing method will be described. FIG. 3 is a flowchart schematically showing an example of an optical fiber preform having the above-described configuration and an optical fiber manufacturing method for obtaining an optical fiber, including an optical fiber preform manufacturing method.

  In the manufacturing method shown in FIG. 3, as shown in the configuration examples of the optical fibers of the first and second embodiments, F is added to the core region, and in the outer edge portion of the outermost cladding layer, An optical fiber preform having a configuration in which the addition amount of F is sequentially decreased (the relative refractive index difference is sequentially increased) up to a predetermined addition amount that is the minimum addition amount of F in the outermost cladding layer (step) S100: including steps S101 to S106). Then, the obtained optical fiber preform is heated and drawn (S107) to obtain an optical fiber having a configuration as shown in FIGS. 1 and 2 (S108).

  First, production of the optical fiber preform (S100) will be described. First, a core base material including at least a core region to which F is added in a predetermined addition amount is manufactured (S101). As the core base material, a normal core base material can be used. For example, a base material in which a core region or a part of a clad region is further extended to a predetermined length can be used. Further, the core region may be configured such that, for example, an additive for increasing the refractive index such as Ge and Cl is added together with F.

  Here, when a part of the clad region is formed in the core base material (core extended body), in the configuration having one clad layer 201 as shown in FIG. 1, a part of the clad region is formed by the core base material. There is a way. However, in this case, it is necessary to prevent the region range including at least the outer edge portion 205 from being included in the core base material. In the configuration having two clad layers 201 and 202 as shown in FIG. 2, there is a method of forming the inner clad layer 201 with a core base material. A part of the clad region formed in the core base material may be formed by synthesis, dehydration, and sintering as in the outermost clad layer described later, or a rod-in collapse method may be used. good.

  A glass fine particle layer is synthesized on the outer periphery of such a core base material using a synthesis method such as the VAD method or the OVD method (S102, synthesis step). Specifically, a glass fine particle layer is formed by generating glass fine particles by a flame from a glass synthesis burner supplied with a raw material gas having a predetermined gas composition, and depositing the glass fine particles on the outer periphery of the core base material. Is synthesized. The glass fine particle layer is a layer that becomes the outermost cladding layer (or a predetermined portion outside the outermost cladding layer including at least the outer edge portion) after the heating and sintering.

  Subsequently, the synthesized glass fine particle layer is heated and dehydrated (S103, dehydration step), and further, the dehydrated glass fine particle layer is heated and sintered (S105, sintering step), and the outermost cladding layer is formed from the glass fine particle layer. An optical fiber preform on which is formed is prepared (S106).

  If necessary, in the step between the dehydration step (S103) and the sintering step (S105), the glass fine particle layer may be impregnated with F and added (S104, impregnation step). In the impregnation step, the atmosphere in the sintering furnace is a gas atmosphere containing F at a predetermined concentration, and the glass fine particle layer is impregnated with F in this gas atmosphere and added.

  In such an optical fiber preform manufacturing method, as shown in FIG. 1 and FIG. 2, the F addition amount distribution is such that the addition amount gradually decreases at the outer edge of the glass fine particle layer (outermost cladding layer). For example, F is added to the glass fine particle layer before heating and sintering the glass fine particle layer, and after the addition, the outer edge portion including the outer periphery of the glass fine particle layer (the outer edge portion of the outermost cladding layer). There is a method of removing a part of the added F.

Specifically, for example, a glass fine particle layer made of SiO ₂ is synthesized as a jacket layer on the outer periphery of the core base material (sooting, synthesizing step). Then, after dehydration (dehydration step) by heating in a SiCl ₄ atmosphere at 1200 ° C., F is impregnated and added to the glass fine particle layer by heating in a SiF ₄ atmosphere at 1200 ° C. (impregnation step).

Subsequently, the glass fine particle layer (glass fine particle body) is sintered by heating at 1500 ° C. (sintering step). Here, F (SiF ₄ ) is removed from the gas atmosphere at the time of heat sintering, or at the time of impregnation. The concentration is lower than the concentration of (for example, a very small concentration). At this time, a part of the added F is removed during the heating and sintering from the outer edge portion of the glass fine particle layer (outermost cladding layer) in contact with the gas atmosphere described above, and the amount of F added at the outer edge portion An additive amount distribution is formed in such a structure that gradually decreases.

  As described above, according to the method of removing a part of F at the outer edge after adding F, a new process can be added such that F can be removed at the time of heating and sintering as in the above example. In addition, an addition amount distribution in which the addition amount of F gradually decreases at the outer edge portion can be obtained. Therefore, the optical fiber having the above-described configuration can be obtained without increasing the manufacturing cost.

  Such a method can be applied in the same manner when F is added at the time of synthesizing the glass fine particle layer without performing the impregnation of F, for example, regardless of the method of adding F. Further, the removal of F is not limited to the method performed in the sintering process, but uses a combination of the set temperature, gas composition, gas flow rate, processing time, etc. in each of the dehydration process, the impregnation process, and the sintering process. The removal of F can be realized by various methods. In addition, the removal amount of F, the slope of the decrease in the added amount distribution, and the like can be adjusted by setting these various conditions.

As described above, when the glass fine particle layer is impregnated with F in the process between the dehydration process and the sintering process, the amount of F added is empirically proportional to the 1/4 power of the flow rate of the SiF ₄ gas. . Therefore, for example, in order to double the addition amount of -0.3% F with a relative refractive index difference Δn to -0.6%, it is necessary to supply SiF ₄ gas at a flow rate of about 16 times. In this case, the manufacturing cost of the optical fiber is increased, and the equipment such as a gas supply system and an exhaust gas treatment system necessary for manufacturing is increased in size. In addition, when the flow rate of the SiF ₄ gas is increased, the amount of F added to the glass fine particle layer may be saturated to some extent.

For this reason, it is preferable that the average addition amount and addition amount distribution of F in each of the core region and the cladding region of the optical fiber are set to suitable addition amounts in consideration of such manufacturing conditions. Specifically, for example, with respect to the amount of F added to the core region, as described above, the condition Δn ₀ > −0.3%
It is preferable to add F in an addition amount that satisfies the above.

  Similarly, as a method of obtaining an F added amount distribution in which the additive amount gradually decreases at the outer edge of the glass fine particle layer (outermost clad layer), F is not removed after the addition of F, but F is added to the glass fine particle layer. It is also possible to gradually decrease the amount of F to be added at the time of addition.

  Specifically, for example, when the glass fine particle layer is synthesized as a jacket layer on the outer periphery of the core base material (synthesis process), the raw material gas containing F is supplied to the glass synthesis burner and deposited. Add F to At this time, if the amount of F contained in the supplied raw material gas is reduced as the glass fine particles are deposited, an addition amount distribution having a configuration in which the addition amount of F gradually decreases at the outer edge portion is formed. be able to.

  It is also possible to replace Cl with F after adding Cl during the synthesis of the glass fine particle layer. In this case, the amount of Cl contained in the source gas may be reduced similarly.

  Next, heating drawing (step S107 in FIG. 3) of the manufactured optical fiber preform will be described. FIG. 4 is a block diagram schematically showing an embodiment of an optical fiber manufacturing method and a drawing apparatus used for manufacturing an optical fiber according to the present invention.

  A drawing apparatus 1 shown in FIG. 4 is a drawing apparatus for drawing a quartz glass-based optical fiber, and includes a drawing furnace 11, a heating furnace 21 for slow cooling, and a resin curing unit 31. Has been. The drawing furnace 11, the heating furnace 21, and the resin curing unit 31 are arranged in the direction in which the optical fiber preform 2 is drawn (the vertical direction in FIG. 4). They are installed in order.

  First, the optical fiber preform 2 held by a preform supply device (not shown) is supplied to the drawing furnace 11, and the lower end of the optical fiber preform 2 is heated by the heater 12 in the drawing furnace 11. Soften and draw the optical fiber 3. An inert 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 of the drawing furnace 11 has an inert gas atmosphere. Has been.

  Here, for the optical fiber preform 2 supplied from the preform supply device, as described above, F is added to the core region, and in the outer edge portion of the outermost cladding layer, A structure manufactured in such a manner that the amount of F added gradually decreases to a predetermined amount of addition that is the minimum amount of F added is used.

The heated optical fiber 3 is rapidly cooled in the furnace core tube 13 to about 1700 ° C. by an inert gas. Thereafter, the optical 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 heating furnace 21. As the inert gas, for example, N ₂ gas can be used, and the thermal conductivity coefficient λ (T = 300K) of this N ₂ gas is 26 mW / (m · K). The thermal conductivity coefficient λ (T = 300K) of air is 26 mW / (m · K).

  Next, the air-cooled optical fiber 3 is sent to a heating furnace 21 for gradual cooling provided in the subsequent stage of the drawing furnace 11 and between the drawing furnace 11 and the resin curing unit 31. Then, the predetermined section of the optical fiber 3 is heated to a temperature within a predetermined temperature range, and is gradually cooled at a predetermined cooling rate. Regarding the heating conditions by the heating furnace 21, the heating furnace 21 heats the drawn optical fiber 3 for 0.05 to 5 seconds so that the temperature of the optical fiber 3 is in the range of 800 to 1500 ° C. It is preferable.

The heating furnace 21 has a furnace core tube 23 through which the optical fiber 3 passes. The core tube 23 has a total length L2 (m) in the drawing direction of the optical fiber preform 2 (vertical direction in FIG. 4).
L2 ≧ V / 8
It is preferable to set so as to satisfy the above. Here, V is a drawing speed (m / s).

In the heating furnace 21, the position of the core tube 23 is set to a position where the temperature of the optical fiber 3 (entrance temperature) immediately before entering the core tube 23 is in the range of 1000 to 1800 ° C. Against
L1 ≦ 0.2 × V
Is preferably provided so as to satisfy the above. Here, L1 is the distance (m) from the lower end of the heater 12 of the drawing furnace 11 to the upper end of the core tube 23, and V is the drawing speed (m / s). The temperature of the heater 22 of the heating furnace 21 is such that the temperature at the furnace center (portion through which the optical fiber 3 passes) is in the range of 800 to 1500 ° C., particularly in the range of 1200 to 1400 ° C. Is set.

  Depending on the setting of the position and length of the heating furnace 21 (core tube 23) described above, the temperature of the optical fiber 3 drawn by heating in the heating furnace 21 for slow cooling is in the range of 800 to 1500 ° C. Heated to be In particular, in a portion where the temperature of the optical fiber 3 is 800 to 1500 ° C., a section where the temperature difference of the optical fiber 3 is 50 ° C. or more, for example, a portion where the temperature of the optical fiber 3 is 1200 to 1400 ° C. The section where the temperature becomes 200 ° C.) is gradually cooled at a cooling rate of 1000 ° C./second or less.

  In addition, by setting the temperature of the furnace center to a temperature within the range of 800 to 1500 ° C., the temperature difference of the optical fiber 3 in the portion where the temperature becomes 800 to 1500 ° C. in the heated optical fiber 3 is increased. The section of 50 ° C. or higher is gradually cooled at a cooling rate of 1000 ° C./second or lower.

An N ₂ gas supply passage 25 from the N ₂ gas supply unit 24 is connected to the core tube 23 of the heating furnace 21, and the inside of the core tube 23 of the heating furnace 21 is configured to have an N ₂ gas atmosphere. Yes. Instead of using N ₂ gas, it is also possible to use a gas having a relatively high molecular weight such as air or Ar. However, when a carbon heater is used, it is necessary to use an inert gas.

  The outer diameter of the optical fiber 3 exiting the heating furnace 21 is measured online by an outer diameter measuring device 41 serving as an outer diameter measuring means, and the measured value is fed back to a drive motor 43 that rotationally drives the drum 42 to obtain the outer diameter. It is controlled to be constant. The output signal from the outer diameter measuring device 41 is sent to a control unit 44 as control means, and the rotational speed of the drum 42 (drive motor 43) is adjusted so that the outer diameter of the optical fiber 3 becomes a predetermined value set in advance. Is obtained by calculation.

  The control unit 44 outputs an output signal indicating the rotation speed of the drum 42 (drive motor 43) obtained by the calculation to a drive motor driver (not shown). The drive motor driver is supplied from the control unit 44. Based on the output signal, the rotational speed of the drive motor 43 is controlled.

  Thereafter, the UV resin 52 is applied to the optical fiber 3 by the coating die 51. The applied UV resin 52 is cured by the UV lamp 32 of the resin curing unit 31 to form the optical fiber 4. Then, the optical fiber 4 is wound around the drum 42 through the guide roller 61. The drum 42 is supported by a rotation drive shaft 45, and an end portion of the rotation drive shaft 45 is connected to a drive motor 43.

  Here, in the present embodiment, the coating die 51 and the resin curing portion 31 constitute a resin coating portion that covers the optical fiber with resin. As this resin coating | coated part, you may comprise not only the above-mentioned structure but apply | coating thermosetting resin and making it harden | cure with a heating furnace.

As described above, the inert gas supply passage 15 from the inert gas supply unit 14 is connected to the core tube 13 of the drawing furnace 11, and the inside of the core tube 13 of the drawing furnace 11 is inert gas. Although an atmosphere is configured, an N ₂ gas supply unit may be provided as the inert gas supply unit 14 and N ₂ gas may be supplied into the core tube 13 to form an N ₂ gas atmosphere. Good.

When the drawing speed is low, for example, 100 m / min, the optical fiber 3 may be cooled to 1000 ° C. or less in the drawing furnace 11 (core tube 13) in a He gas atmosphere. It is preferable that the temperature of the optical fiber 3 at the outlet of the drawing furnace 11 (furnace core tube 13) is 1000 ° C. or higher, with the inside of the core tube 13 being an N ₂ gas atmosphere. Further, a He gas supply unit and an N ₂ gas supply unit may be provided, and He gas or N ₂ gas may be supplied into the core tube 13 in accordance with the drawing speed. Actually, even if the temperature is set to 800 to 1500 ° C. by reheating after cooling, the structure can be relaxed. However, in this case, the heater length is lost for reheating.

  In the optical fiber manufacturing method described above, F was added to the core region as the optical fiber preform 2, and the F addition amount was sequentially reduced at the outer edge of the outermost cladding layer. An optical fiber preform is used. According to the optical fiber preform and the optical fiber having such a configuration, the stress is distributed to the core region and the cladding region due to the decrease in the viscosity in the core region and the increase in the viscosity at the outer edge of the outermost cladding layer. In addition, stress concentration on the core is suppressed.

  At this time, in tension control for heating drawing in the drawing furnace 11, a range of tension values allowed to obtain a suitable optical fiber is widened, and tension control is facilitated. Also, an optical fiber obtained after drawing can be an optical fiber having excellent transmission loss and transmission characteristics (for example, low transmission loss).

  That is, if the tension at the time of drawing deviates from the preferred tension value range, structural loss increases at low tension, and conversely, Rayleigh scattering loss increases at high tension. Become. On the other hand, according to the manufacturing method in which the tension control is facilitated as described above, the tension dependency of the transmission loss is reduced, so that an increase in the transmission loss due to a tension change, transmission characteristics other than the transmission loss, and the like. Deterioration is suppressed. Further, since high accuracy is not required for tension control, the manufacturing process is simplified and the manufacturing yield is also improved. In addition, as a suitable tension value range, it is preferable to perform tension control so that the tension is within a range of 0.05 to 0.20 N (5 to 20 gw).

  Regarding the F addition amount distribution in the outer edge portion of the outermost cladding layer, since the region where the F addition amount is reduced is the outer edge portion of the outermost cladding layer, transmission of light transmitted through the core region and the vicinity thereof. It does not affect the characteristics. Therefore, it is possible to achieve easy tension control while suitably maintaining the transmission characteristics of the optical fiber.

  Further, in the manufacturing method and the drawing apparatus 1 shown in FIG. 4, after drawing the optical fiber preform 2, an optical fiber is used by using a heating furnace 21 for slow cooling provided at the subsequent stage of the drawing furnace 11. 3 is gradually cooled. Thereby, the virtual temperature Tf can be lowered by generating structural relaxation of the glass due to viscous flow in the optical fiber, and Rayleigh scattering loss can be reduced.

  Thus, even when a manufacturing method having the effect of reducing Rayleigh scattering loss is applied, the transmission loss is not necessarily reduced as the overall transmission loss. This is because while Rayleigh scattering loss is reduced, other transmission loss components such as structural irregularity loss increase due to excessive stress concentration on the core, and the overall transmission loss reduction effect cannot be obtained. Conceivable. On the other hand, if it is attempted to suppress the occurrence of structural irregularity loss, the effect of reducing Rayleigh scattering loss cannot be obtained sufficiently.

On the other hand, by applying the optical fiber preform and the optical fiber having the above-described configuration in which F is added to the core region and the addition amount of F is reduced at the outer edge of the outermost cladding layer, the Rayleigh scattering loss is applied. (For example, the Rayleigh scattering coefficient A is 0.79 dB / km · μm ⁴ or less), and at the same time, the occurrence of structural irregularity loss due to stress concentration on the core is suppressed, resulting in low transmission loss (for example, wavelength An optical fiber having a transmission loss α _{1.00 at 1.00} μm of 0.80 dB / km or less) can be realized.

In addition, in the configuration in which the core region is made of F-added SiO ₂ glass, the viscosity of the core region is greatly reduced by the addition of F, so that the glass structure is easily relaxed by viscous flow (see “K. Shiraki et al., Electronics”). Letters, Vol. 29 No. 14, pp. 1263-1264 (1993) ”). Therefore, by applying the optical fiber having the above configuration to the manufacturing method in which the optical fiber is gradually cooled by the heating furnace 21 provided at the subsequent stage of the drawing furnace 11, the effect of lowering the virtual temperature Tf due to structural relaxation is achieved. Is promoted, and the Rayleigh scattering loss in the optical fiber can be efficiently reduced.

  In addition, the viscosity of the glass decreases as the temperature increases. For this reason, in the above-described manufacturing method in which the optical fiber is gradually cooled, the processing temperature is set so that the viscosity in the core region or the like is reduced to a sufficient viscosity to generate the viscous flow, and the light from the heating furnace 21 is set. It is necessary to heat the fiber.

  On the other hand, according to the optical fiber having a configuration in which the viscosity of the core region is reduced by the addition of F, the processing temperature at which viscous flow occurs is lowered. Therefore, since the heating temperature of the optical fiber by the heating furnace 21 can be set to a lower temperature, the optical fiber using the heating furnace 21 can be gradually cooled. In addition, by promoting structural relaxation by viscous flow, the fictive temperature Tf of the glass obtained after slow cooling also decreases with the processing temperature, so the effect of reducing Rayleigh scattering loss is improved.

  Regarding the conditions of such heat treatment for slow cooling, as described above, the heating temperature within the range of 800-1500 ° C. and the heating time within the range of 0.05-5 seconds, It is preferable to heat the fiber. By setting it as such a temperature range and heating time, reduction of fictive temperature Tf by slow cooling of the optical fiber after drawing can be realized suitably. Moreover, about conditions, such as these temperature ranges, it is preferable to set suitably suitable conditions according to drawing speed etc.

As an example of the effect of promoting viscous flow by adding F to the core region, for example, Ge is added at an addition amount of + 0.61% with a relative refractive index difference Δn, and at an addition amount of −0.18%. Ge was added F, against F added SiO ₂ glass, Ge with increased amount of F to -0.7%, considering the F-doped SiO ₂ glass, to compare the viscosity of both. At this time, in the latter glass in which the addition amount of F is increased, the viscosity at the same temperature is lower than that in the former glass. Further, if the viscous flow in the glass becomes a constant viscosity, as described above, when the addition amount of F is increased from −0.18% to −0.7%, the viscous flow is increased. The generated processing temperature is about 130 ° C. lower.

At this time, when it is considered that the fictive temperature Tf of the glass after structure relaxation by slow cooling is similarly reduced by 130 ° C., the Rayleigh scattering loss in the optical fiber is reduced by about 8% as the fictive temperature Tf is lowered. . For example, if an optical fiber having a transmission loss α _{1.55 at} a wavelength of 1.55 μm is 0.17 dB / km, and the loss of 0.145 dB / km is due to Rayleigh scattering loss, it is about 0.012 dB / km. An effect of reducing transmission loss can be obtained. In other words, the transmission loss reduction effect of about 2.3 mdB / km can be obtained when the amount of F added is about -0.1%.

  By adding F to the core region in this way, the transmission loss due to Rayleigh scattering is reduced, but on the other hand, the fluorine concentration fluctuation affects the transmission loss. Therefore, when these effects are combined, when the addition amount of F is -0.2%, the decrease in transmission loss due to the decrease in density fluctuation is about 5 mdB / km and the increase in concentration fluctuation compared with the case where F is not added. The increase in transmission loss due to the transmission is about +2 mdB / km, and a transmission loss reduction effect of about 3 mdB / km is obtained as a whole.

  FIG. 5 is a diagram schematically showing a cross-sectional structure and a refractive index profile in the fiber radial direction of the third embodiment of the optical fiber according to the present invention.

Similar to the first embodiment, this optical fiber is a SiO ₂ glass (quartz glass) optical fiber, and includes a core region 100 including the central axis of the optical fiber, and a clad provided on the outer periphery of the core region 100. The region 200 is configured. Among these, the configuration of the core region 100 is substantially the same as that of the core region 100 in the optical fiber shown in FIG.

  On the other hand, in the present embodiment, the cladding region 200 includes an inner cladding layer 201 provided on the outer periphery of the core region 100, and an outer cladding layer 202 that is an outermost cladding layer further provided on the outer periphery of the inner cladding layer 201. The two clad layers are configured.

The inner cladding layer 201 is formed with an outer periphery radius of r ₁ . A predetermined amount of F (fluorine) is added to the inner cladding layer 201 as an additive for reducing the refractive index of pure SiO ₂ glass. Thereby, the average relative refractive index difference in the inner cladding layer 201 is Δn ₁ (where Δn ₁ <0). In addition, the average addition amount of F in the inner cladding layer 201 is set larger than the average addition amount of F in the core region 100. Therefore, the average relative refractive index differences Δn ₀ and Δn ₁ between the core region 100 and the inner cladding layer 201 have a relationship of 0> Δn ₀ > Δn ₁ as shown in FIG.

The outer cladding layer 202 is formed to a radius of the outer periphery as r _2. The outer cladding layer 202 is added with a predetermined amount of F (fluorine) in pure SiO ₂ glass. Thereby, the average relative refractive index difference in the outer cladding layer 202 is Δn ₂ (where Δn ₂ <0). The average addition amount of F in the outer cladding layer 202 is set smaller than the average addition amount of F in the inner cladding layer 201. Therefore, the average relative refractive index differences Δn ₁ and Δn ₂ between the inner cladding layer 201 and the outer cladding layer 202 have a relationship of 0> Δn ₂ > Δn ₁ as shown in FIG.

In the optical fiber of the present embodiment, F is added to the core region 100 as in the first embodiment. Thereby, Rayleigh scattering loss in the optical fiber is reduced, and transmission loss is reduced. Further, in the core region 100 made of F-added SiO ₂ , the viscosity is smaller than that of pure SiO ₂ , so that stress applied to the optical fiber is suppressed from being concentrated on the core. Further, the reduction in viscosity promotes structural relaxation by viscous flow in the core region.

  Further, regarding the configuration of the clad region 200 including the two clad layers 201 and 202, the amount of F added in the outer clad layer 202 is smaller than the amount of F added in the inner clad layer 201 as shown in FIG. The cladding region 200 is configured so as to have an added amount.

  With such a configuration, the viscosity of the outer cladding layer 202 is increased, the stress is dispersed in the outer cladding layer 202, and the stress concentration on the core is further suppressed. That is, by combining the effect of adding F to the core region 100 with the effect of reducing the amount of F added to the outer cladding layer 202, the stress applied in the optical fiber is applied to the core region 100 and the cladding region 200. And the stress concentration on the core is suppressed.

  As a result, the preferred tension value range allowed when drawing the optical fiber becomes a wider numerical range, and tension control during drawing is facilitated. In addition, an increase in transmission loss and deterioration of transmission characteristics caused by excessive stress concentration on the core and insufficient tension control are prevented, and structural relaxation due to viscous flow of glass in the core region is promoted. . As described above, an optical fiber having suitable and stable transmission characteristics over the entire length is realized.

Here, the average relative refractive index difference [Delta] n ₀ of the core region 100, the relationship between the average relative refractive index difference [Delta] n ₂ of the outer cladding layer 202, any may be larger, but the transmission characteristics of light in the optical fiber In consideration of the effect of suppressing stress concentration on the core and the like, it is preferable to set the appropriate addition amount of F and the average relative refractive index difference, respectively.

Further, among the inner cladding layer 201 and the outer cladding layer 202 constituting the cladding region 200, the outer cladding layer 202 which is the outermost cladding layer may be formed as pure SiO ₂ so that Δn ₂ = 0. Thereby, the stress applied in the optical fiber can be sufficiently dispersed into the cladding region 200.

  In addition, about the optical fiber preform used for manufacture of the optical fiber of this embodiment, and the manufacturing method of an optical fiber, it is possible to apply the manufacturing method similar to what was mentioned above regarding 1st and 2nd embodiment. Yes (see FIGS. 3 and 4). However, the configuration of the optical fiber preform needs to be an optical fiber preform having the refractive index profile shown in FIG.

Further, when the outer cladding layer 202 is a pure SiO ₂ layer, the optical fiber preform is composed of, for example, a pure SiO ₂ layer on the outer periphery of the inner cladding layer 201 to which F is added by the VAD method or the OVD method, It can be manufactured by heating and sintering. Further, a glass rod composed of the core region 100 and the inner cladding layer 201 may be inserted into a pure silica pipe serving as the outer cladding layer 202 for collapse.

  About an above-mentioned optical fiber and its manufacturing method, a concrete Example and a comparative example are shown. In addition, the optical fiber in the following Examples and Comparative Examples is manufactured by a manufacturing method in which the drawn optical fiber is gradually cooled using the heating furnace 21 shown in FIG. As for the heating conditions of the optical fiber in the heating furnace 21 for slow cooling, the heating temperature is about 1300 ° C., the linear velocity is 25 m / min, and the length of the heating furnace is about 1.5 m. At this time, the heating time in the heating furnace 21 is 3.6 seconds.

The optical fiber according to the first embodiment is manufactured by the refractive index profile shown in FIG. The radii r ₀ , r _a and r ₁ are 2r ₀ = 10 μm, 2r _a = 110 μm, and 2r ₁ = 125 μm, respectively.

As for the refractive index in each region, F is added to the core region 100 so that the average relative refractive index difference is Δn ₀ = −0.2%. On the other hand, the cladding layer 201 of the cladding region 200 is doped such that the minimum relative refractive index difference is Δn _b = −0.65% and the maximum relative refractive index difference at the outer edge portion 205 is approximately Δn _a = −0.35%. Add F in quantity distribution. At this time, the average value is approximately Δn ₁ = −0.58%.

The optical fiber according to the second embodiment is manufactured by the refractive index profile shown in FIG. The radii r ₀ , r ₁ , r _a , and r ₂ are 2r ₀ = 10 μm, 2r ₁ = 55 μm, 2r _a = 110 μm, and 2r ₂ = 125 μm, respectively.

As for the refractive index in each region, F is added to the core region 100 so that the average relative refractive index difference is Δn ₀ = −0.2%. On the other hand, F is added to the inner cladding layer 201 in the cladding region 200 so that the average relative refractive index difference is Δn ₁ = −0.58%. Further, the outer cladding layer 202 has an additive amount distribution such that the minimum relative refractive index difference is Δn _b = −0.50% and the maximum relative refractive index difference at the outer edge portion 205 is approximately Δn _a = −0.35%. Add F.

The optical fiber according to the third embodiment is manufactured by the refractive index profile shown in FIG. The radii r ₀ , r ₁ , and r ₂ are 2r ₀ = 10 μm, 2r ₁ = 55 μm, and 2r ₂ = 125 μm, respectively.

As for the refractive index in each region, F is added to the core region 100 so that the average relative refractive index difference is Δn ₀ = −0.2%. On the other hand, F is added to the inner cladding layer 201 in the cladding region 200 so that the average relative refractive index difference is Δn ₁ = −0.58%. Further, F is added to the outer cladding layer 202 so that the average relative refractive index difference becomes Δn ₂ = −0.50%.

FIG. 6 is a diagram showing a refractive index profile of a comparative example of an optical fiber. The configuration of the optical fiber of this comparative example is the same as that of the first embodiment described above except that the outer edge portion where the addition amount of F decreases is not formed, and the core region 300 and the cladding region 400 have the same structure. The radii r ₀ and r ₁ of the cladding layer 401 are 2r ₀ = 10 μm and 2r ₁ = 125 μm, respectively.

As for the refractive index in each region, F is added to the core region 300 so that the average relative refractive index difference is Δn ₀ = −0.2%. On the other hand, F is added to the cladding layer 401 in the cladding region 400 so that the average relative refractive index difference is Δn ₁ = −0.65%.

About the above 1st, 2nd, 3rd Example, and a comparative example, the tension dependence of transmission loss (alpha) _1.55 at the time of drawing by the manufacturing method with slow cooling by a heating furnace is shown. As shown in FIG. From this graph, the transmission loss α in the first example and the comparative example in the configuration having one clad layer, and in the second example and the third example in the configuration having two clad layers. Comparing the tension dependence of _1.55 respectively, in each case, the value of the transmission loss is reduced in the first and second embodiments provided with the outer edge portion where the amount of addition of F decreases. At the same time, it can be seen that the tension dependency is also reduced.

For example, when comparing the value of the transmission loss α _1.55 at a tension of 0.10 N with respect to the example shown in FIG. 7, in the case of a single clad layer, the comparison example is 0.163 dB / km. In one embodiment, it is 0.158 dB / km. Further, in the case of two clad layers, the third embodiment is 0.157 dB / km, whereas the second embodiment is 0.155 dB / km.

  Further, when the first embodiment having one clad layer is compared with the second embodiment having two clad layers, the transmission loss is lower in the second embodiment. Also, when the comparative example having one clad layer and the third example having two clad layers are compared, the third embodiment has a lower transmission loss. This is because, of the two clad layers, the outer outer cladding layer has a smaller amount of F added than the inner cladding layer, and the outer cladding layer itself has a stress dispersion function.

Further, when the values of the Rayleigh scattering coefficient A and the transmission loss α _1.00 at the wavelength of _1.00 μm are obtained for the optical fibers of the first, second, and third examples with the tension set at 0.10 N, In this case, the Rayleigh scattering loss A is 0.79 dB / km · μm ⁴ or less, and the transmission loss α _1.00 is 0.80 dB / km or less.

  As described above, by adding F to the core region and reducing the addition amount of F at the outer edge of the outermost cladding layer, or by reducing the addition amount of F in the outer cladding layer, Stress concentration on the surface is suppressed. Thereby, tension control at the time of drawing is facilitated, and an optical fiber in which transmission loss is stably reduced over the entire length is realized.

Here, regarding the amount of F added to the core region and the cladding region in the above-described embodiment, for example, in the second embodiment having two cladding layers, Δn ₁ = −0 with respect to the inner cladding layer 201. F is added in an addition amount of .58%. Although the amount of addition of F satisfies the condition of Δn ₁ > −0.6%, it is slightly larger. On the other hand, if the core region 100 is configured such that an additive for increasing the refractive index such as Ge and Cl is added together with F, the amount of F added to the cladding region 200 can be reduced.

For example, as a modified example of the second embodiment, an addition amount of Δn = + 0.08% is further added to the core region 100 to which F is added at an addition amount of Δn ₀ = −0.2%. Consider a configuration in which Cl is added. At this time, the average relative refractive index difference of the core region 100 becomes 0.08% higher by Δn ₀ = −0.12% by co-addition of F and Cl. In accordance with this, the amount of F added to the inner cladding layer 201 can be reduced to an amount of Δn ₁ = −0.50%.

As described above, the amount of addition to the inner cladding layer 201 is reduced from −0.58% to −0.50% at Δn ₁ , so that the amount of addition of F becomes 1/4 of the flow rate of the SiF ₄ gas. In consideration of the proportionality, the flow rate of the SiF ₄ gas supplied in the F impregnation step is about half. In addition, with this amount of addition, an increase in Rayleigh scattering loss due to fluctuations in the concentration of Cl added to the core region 100 does not pose a problem.

Further, as another modification of the second embodiment, the core region 100 where F is added at an addition amount of the [Delta] n ₀ = -0.2%, further, [Delta] n = + 0.3% and becomes added Consider a configuration in which Ge is added in an amount. At this time, the average relative refractive index difference of the core region 100 becomes higher by Δn ₀ = + 0.1% and + 0.3% by co-addition of F and Ge. In accordance with this, the amount of F added to the inner cladding layer 201 can be reduced to an amount of Δn ₁ = −0.28%, and the flow rate of SiF ₄ gas supplied in the F impregnation step is reduced. Is done.

Here, when Ge is added to the core region 100 with the above-described addition amount, the increase in Rayleigh scattering loss due to Ge addition almost offsets the loss reduction effect due to the addition of F, which is about the same as that of a pure SiO ₂ core optical fiber. Transmission loss (for example, α _1.55 is about 0.170 dB / km). However, even in such a case, while adding F to the core region 100 and reducing the amount of F added at the outer edge of the outermost cladding layer, the effect of suppressing stress concentration on the core, and tension control during drawing The effect of facilitating the process is similarly obtained. Therefore, according to such a configuration, an optical fiber having a transmission loss equivalent to that of a pure SiO ₂ core optical fiber can be manufactured with higher manufacturing efficiency and at low cost.

  In the clad region having the two clad layers of the inner clad layer and the outer clad layer, the effect of stress dispersion to the outer clad layer can be obtained with the configuration in which the addition amount of F is reduced in the entire outer clad layer. Thus, the configuration of the cladding region may have some influence on the light transmission characteristics in the optical fiber. Therefore, in such a configuration, it is preferable to suitably set the amount of F added to the outer cladding layer in consideration of the effect of stress dispersion to the outer cladding layer and the effect of influence on the transmission characteristics. .

  On the other hand, in the configuration in which the amount of F added is reduced at the outer edge of the outermost cladding layer, it is possible to efficiently suppress stress concentration on the core without degrading the transmission characteristics of the optical fiber. Further, according to such a configuration, an optical fiber preform having a configuration in which stress concentration on the core is suppressed without adding a new process such as forming a new layer for stress dispersion to the manufacturing process. And an optical fiber can be realized.

  The optical fiber, the optical fiber preform manufacturing method, and the optical fiber manufacturing method according to the present invention are not limited to the above-described embodiments and examples, and various modifications and configuration changes are possible. For example, the configuration of the cladding region is not limited to the configuration examples shown in FIGS. 1, 2, and 5, and various configurations can be used.

  Further, the F addition amount distribution at the outer edge portion of the outermost cladding layer may be an addition amount distribution other than the configuration shown in FIGS. 1 and 2 according to the manufacturing method. For example, the F addition amount may be substantially constant at the minimum addition amount within a predetermined range on the outer peripheral side in the outer edge portion, and the F addition amount may change on the inner side (inner peripheral side in the outer edge portion). In this way, by providing a region where the addition amount of F is substantially constant at the minimum addition amount in the vicinity of the outer periphery which is the outer portion in the outer edge portion, the viscosity in that region is increased, and the stress on the outer edge portion is increased. Dispersion can be realized more efficiently.

  Further, in the outermost cladding layer such as the outer cladding layer, the F addition amount in the vicinity of the inner periphery thereof may be smaller than the maximum addition amount of F in the layer. That is, when the outermost cladding layer is formed, the amount of F added may be slightly reduced in the vicinity of the inner periphery thereof. Even in the case of such an addition amount distribution, stress distribution to the outer edge portion can be realized by applying the configuration of the optical fiber described above.

It is a figure which shows typically the cross-sectional structure and refractive index profile of 1st Embodiment of an optical fiber. It is a figure which shows typically the cross-section and refractive index profile of 2nd Embodiment of an optical fiber. It is a flowchart which shows the manufacturing method of an optical fiber roughly. It is a block diagram which shows schematically one Embodiment of the manufacturing method of an optical fiber, and the drawing apparatus used for manufacture of an optical fiber. It is a figure which shows typically the cross-section and refractive index profile of 3rd Embodiment of an optical fiber. It is a figure which shows the refractive index profile in the comparative example of an optical fiber. It is a graph which shows the tension dependence of the transmission loss in an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Drawing apparatus, 11 ... Drawing furnace, 12 ... Heater, 13 ... Core tube, 14 ... Inert gas supply part, 15 ... Inert gas supply passage, 21 ... Heating furnace, 22 ... Heater, 23 ... Core tube , 24... N ₂ gas supply section, 25... N ₂ gas supply passage, 31... Resin curing section, 32... UV lamp, 41. ... rotation drive shaft, 51 ... coating die, 52 ... UV resin, 61 ... guide roller,
DESCRIPTION OF SYMBOLS 2 ... Optical fiber base material, 3 ... Optical fiber, 4 ... Optical fiber strand, 100 ... Core area | region, 200 ... Cladding area | region, 201 ... Inner clad layer, 202 ... Outer clad layer, 205 ... Outer edge part.

Claims (6)

A core region to which fluorine is added so that the refractive index is equal to or lower than that of pure SiO ₂ , and fluorine is added so that the refractive index is lower than that of the core region. A clad region having one or more clad layers,
The outermost clad layer located on the outermost side among the one or more clad layers has a refractive index sequentially from the inner side to the outer side in the outer edge portion including the outer periphery and having a thickness of 7.5 μm from the outer periphery. When the relative refractive index difference in each part is defined in terms of% on the basis of the refractive index in pure SiO ₂ , the outer edge portion is configured so that the amount of fluorine added decreases sequentially. the maximum value of the relative refractive index difference at the difference between the minimum value is not less 0.15% or more, and the relative refractive index difference with the outer peripheral [Delta] n _a condition [Delta] n _a ≧ -0.35%
An optical fiber characterized by satisfying The cladding region is composed of two cladding layers, an inner cladding layer provided on the outer periphery of the core region and an outer cladding layer provided on the outer periphery of the inner cladding layer and serving as the outermost cladding layer,
The optical fiber according to claim 1, wherein an average addition amount of fluorine in the outer cladding layer is smaller than an average addition amount of fluorine in the inner cladding layer. When the relative refractive index difference in each part is defined in terms of% based on the refractive index of pure SiO ₂ , the core region has an average relative refractive index difference Δn ₀ of the condition Δn ₀ > −0.3%.
The optical fiber according to claim 1 or 2, wherein: The clad region provided on the outer periphery of the core region has glass fine particles deposited on the outer periphery of the core base material including at least the core region to which fluorine is added so that the refractive index is equal to or lower than the refractive index of pure SiO _2. A synthesizing step of synthesizing a glass fine particle layer to be an outermost clad layer located on the outermost side in one or a plurality of clad layers;
A dehydration step of heating and dehydrating the synthesized glass fine particle layer;
An impregnation step of impregnating and adding fluorine to the glass fine particle layer in a gas atmosphere containing fluorine at a predetermined concentration;
The dehydrated glass fine particle layer is heated and sintered to form the outermost cladding layer, and a firing is performed to form an optical fiber preform including the core region and a cladding region having the one or more cladding layers. A linking process,
In the sintering step, the concentration of fluorine contained in the gas atmosphere at the time of heating and sintering is set to a concentration lower than the predetermined concentration at the time of impregnation, and when the optical fiber including the outer periphery of the glass fine particle layer is formed, 7 When a part of the added fluorine is removed from the outer edge part having a thickness of 0.5 μm, and the amount of fluorine added is gradually decreased from the inner side to the outer side of the outer edge part to obtain an optical fiber in each part. when defining represent relative refractive index difference% based on the refractive index of pure SiO _2, the difference between the maximum and minimum values of the relative refractive index difference at the outer edge becomes 0.15% or more, and , conditions relative refractive index difference [Delta] n _a of the outer peripheral Δn _a ≧ -0.35%
An optical fiber preform manufacturing method characterized by forming the optical fiber preform satisfying The clad region provided on the outer periphery of the core region has glass fine particles deposited on the outer periphery of the core base material including at least the core region to which fluorine is added so that the refractive index is equal to or lower than the refractive index of pure SiO _2. A synthesizing step of synthesizing a glass fine particle layer to be an outermost clad layer located on the outermost side in one or a plurality of clad layers;
A dehydration step of heating and dehydrating the synthesized glass fine particle layer;
The dehydrated glass fine particle layer is heated and sintered to form the outermost cladding layer, and a firing is performed to form an optical fiber preform including the core region and a cladding region having the one or more cladding layers. A linking process,
In the synthesis step, chlorine is added to the glass fine particle layer using a chlorine-containing source gas, and the outer periphery of the glass fine particle layer is 7.5 μm thick from the outer periphery when the optical fiber is formed including the outer periphery of the glass fine particle layer. After adjusting the raw material gas containing chlorine and synthesizing the glass fine particle layer so that the amount of chlorine added gradually decreases from the inside toward the outside, the added chlorine is replaced with fluorine, When the relative refractive index difference in each part is defined as% based on the refractive index of pure SiO ₂ when an optical fiber is used, the difference between the maximum and minimum relative refractive index differences at the outer edge is It becomes 0.15% or more, and conditions are the relative refractive index difference [Delta] n _a of the outer peripheral Δn _a ≧ -0.35%
An optical fiber preform manufacturing method characterized by forming the optical fiber preform satisfying   An optical fiber drawn by a drawing furnace is provided at a subsequent stage of the drawing furnace when the optical fiber preform manufactured by the method of manufacturing an optical fiber preform according to claim 4 or 5 is drawn by heating. A method for producing an optical fiber, wherein the heating is performed by a heating furnace so that the temperature is within a predetermined temperature range.

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