Single-mode optical fiber and method for manufacturing single-mode optical fiber

Abstract

Provided are a single-mode optical fiber having good dispersion characteristics, transmission loss and hydrogen resistance, and a method for manufacturing the same. In the refractive index distribution (10), the ratio of the area T of the tail elongated portion (31) further outward than the boundary (11) to the area C of the core region (2), i.e., T / C, is 4% or more and 30% or less; in the region from the center (O) of the core region (2) to the outer periphery (12) of the first cladding region (3), the boundary (11) is defined by the position where the absolute value of the refractive index change is the largest; in the range from the center (O) of the core region (2) to the boundary (11), the refractive index straight line L passing through the first cladding region (3) and the plane of the core region (2) is the largest. The area C is defined by the area between the straight lines with an average refractive index nm; the area T is defined by the area between the refractive index straight line L and the curve (10a) of the refractive index distribution (10) in the range from the boundary (11) to the peripheral part (12) within the range where the refractive index is greater than the refractive index straight line L; the range from the boundary (11) to the peripheral part (12) is divided into three parts, and the refractive index within the range of only a part or all of the middle part (3M) of the three parts is averaged, and the refractive index straight line L is defined by the averaged value or the linear approximation line.

Description

Technical Field

[0001] The present disclosure relates to a single-mode optical fiber and a method for manufacturing the same. Background Art

[0002] Patent Documents 1 and 2 describe methods and apparatuses for manufacturing single-mode optical fiber preforms, and Patent Document 3 describes a single-mode optical fiber and a method for manufacturing the same.

[0003] [Prior art literature]

[0004] [Patent Document]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 7-61830

[0006] [Patent Document 2] Japanese Patent Application Laid-Open No. 9-263418

[0007] [Patent Document 3] International Publication No. 2000 / 26709 DETAILED DESCRIPTION

[0008] [Problems to be solved by the invention]

[0009] The boundary between the core and cladding regions of a single-mode optical fiber has a refractive index profile in which the refractive index changes continuously from the core to the cladding. Within this boundary, there is a portion where the refractive index profile appears to flare out, and this region is called a "south-end extension" (or "tail extension").

[0010] If the area of ​​the tail extension portion is large, there is a problem that the optical power transmitted through the optical fiber is affected by the tail extension portion, the zero dispersion wavelength becomes longer than the transmission wavelength, and the dispersion characteristics deteriorate.

[0011] On the other hand, if the area of ​​the above-mentioned tail elongated portion is too small, due to the difference in viscosity of the materials in the core region and the cladding region, the strain inside the optical fiber will still exist after drawing, which may sometimes lead to an increase in transmission loss, or increase glass defects and cause the hydrogen resistance to deteriorate.

[0012] It is believed that when the area of ​​the tail extension portion is set to T and the area of ​​the core region is set to C, if the ratio of the two areas, that is, the value of T / C, is within an appropriate range, the above-mentioned problem can be solved. The area T of the tail extension portion can be determined by (for example) the contents described in the above-mentioned patent documents 1 and 2. Specifically, in patent documents 1 and 2, in the refractive index distribution, the refractive index of the horizontal portion of the cladding portion is set as the refractive index of the cladding, and the area of ​​the range surrounded by the horizontal line of this value, the interface between the core and the cladding, and the refractive index curve is set as the area T of the tail extension portion. However, even if the area T of the tail extension portion is determined and the value of T / C is within an appropriate range as in the above-mentioned patent documents 1 and 2, there is a case where the dispersion characteristics deteriorate. The reason for this is that there are the following problems in the method for determining the area T of the tail extension portion.

[0013] The methods for determining the area T of the extended tail portion disclosed in Patent Documents 1 and 2 above make it difficult to determine the refractive index of the cladding when there is no horizontal portion in the cladding portion of the refractive index profile. Furthermore, the area T of the extended tail portion calculated using these methods tends to be larger when the horizontal portion of the cladding portion of the refractive index profile is close to the outer periphery of the cladding. However, even when the area T of the extended tail portion calculated using these methods is larger, there are cases where the dispersion characteristics may not necessarily deteriorate.

[0014] An object of the present disclosure is to provide a single-mode optical fiber having excellent dispersion characteristics, as well as excellent transmission loss and hydrogen resistance characteristics, and a method for manufacturing the single-mode optical fiber.

[0015] [Technical solution to the problem]

[0016] A single-mode optical fiber according to one aspect of the present disclosure comprises:

[0017] The core region with the maximum refractive index n1,

[0018] a first cladding region provided on the outer peripheral side of the core region and having a refractive index smaller than the n1, and

[0019] a second cladding region provided on the outer peripheral side of the first cladding region and having a refractive index greater than the refractive index of the outer peripheral portion of the first cladding region,

[0020] The refractive index at the boundary between the core region and the first cladding region becomes a continuously changing refractive index distribution.

[0021] In the refractive index distribution, the ratio of the area T of the tail elongated portion outside the boundary to the area C of the core region, that is, T / C, is 4% or more and 30% or less,

[0022] The boundary is defined by a position where the absolute value of the change in refractive index in the radial direction is maximum within a region extending from the center of the core region to the outer periphery of the first cladding region in the refractive index distribution.

[0023] The area C of the core region is defined by the area between the refractive index straight line of the first cladding region and the average refractive index straight line of the core region within the range from the center of the core region to the boundary in the radial direction in the refractive index distribution.

[0024] The area T of the tail elongated portion is defined by the area between the refractive index straight line of the first cladding region and the curve of the refractive index profile within a range from the boundary to the outer periphery of the first cladding region in the radial direction of the refractive index profile, within a range where the refractive index is greater than the refractive index straight line of the first cladding region.

[0025] The range of the refractive index distribution radially from the boundary to the outer periphery of the first cladding region is divided into three parts, and only the refractive index of part or all of the range within the middle part of the three parts is averaged, and the refractive index straight line of the first cladding region is defined by the averaged value or linear approximation line.

[0026] A method for manufacturing a single-mode optical fiber according to one aspect of the present disclosure is a method for manufacturing a single-mode optical fiber comprising a core region having a maximum refractive index n1, a first cladding region disposed on the outer periphery of the core region and having a refractive index smaller than n1, and a second cladding region disposed on the outer periphery of the first cladding region and having a refractive index larger than the refractive index of the outer periphery of the first cladding region, the single-mode optical fiber having a refractive index profile in which the refractive index continuously changes at a boundary between the core region and the first cladding region.

[0027] The manufacturing method has the following features:

[0028] a step of manufacturing a core base material including the core region and the first cladding region,

[0029] The process of measuring the refractive index distribution of the core matrix to determine whether it is good or not,

[0030] a step of forming the second cladding region on the outer circumference of the core preform determined to be good by the determination of quality to produce an optical fiber preform; and

[0031] The process of drawing the optical fiber mother material to produce a single-mode optical fiber,

[0032] The step of judging whether the refractive index distribution is good or not includes the step of judging by the ratio T / C of the area C of the core region to the area T of the tail elongated portion outside the boundary in the refractive index distribution.

[0033] The boundary is defined by a position where the absolute value of the change in refractive index in the radial direction is maximum within a region extending from the center of the core region to the outer periphery of the first cladding region in the refractive index distribution.

[0034] The area C of the core region is defined by the area between the refractive index straight line of the first cladding region and the straight line of the average refractive index of the core region within a range radially from the center of the core region to the boundary in the refractive index distribution. The area T of the tail elongated portion is defined by the area between the refractive index straight line of the first cladding region and the curve of the refractive index distribution within a range radially from the boundary to the outer periphery of the first cladding region in the refractive index distribution, in which the refractive index is greater than that of the refractive index straight line of the first cladding region.

[0035] The range of the refractive index distribution radially from the boundary to the outer periphery of the first cladding region is divided into three parts, and only the refractive index of part or all of the range within the middle part of the three parts is averaged, and the refractive index straight line of the first cladding region is defined by the averaged value or linear approximation line.

[0036] Effects of the Invention

[0037] According to the present disclosure, a single-mode optical fiber having good dispersion characteristics, good transmission loss and good hydrogen resistance characteristics and a method for manufacturing a single-mode optical fiber can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] [ Figure 1 ] is a schematic diagram showing the cross-sectional structure and refractive index distribution of a single-mode optical fiber according to this embodiment.

[0039] [ Figure 2 ] is used to illustrate Figure 1 Graph showing the definition of the area T of the elongated tail portion and the area C of the core region in the refractive index distribution.

[0040] Explanation of symbols

[0041] 1 single-mode fiber

[0042] 2-core area

[0043] 3 First cladding region

[0044] 3M Middle part of the first cladding area

[0045] 4 Second cladding region

[0046] 10 Refractive index distribution

[0047] 10a Refractive index distribution curve

[0048] 11 Boundary

[0049] 12 The outer periphery of the first cladding region

[0050] 31 Tail extension

[0051] n1 Maximum refractive index of the core region

[0052] n2 Refractive index at the center of the core region

[0053] Average refractive index of the core region nm

[0054] C The area of ​​the core region

[0055] L Refractive index line of the first cladding region

[0056] The area of ​​the extended part of the tail of T DETAILED DESCRIPTION

[0058] [Description of Embodiments of the Present Disclosure]

[0059] First, embodiments of the present disclosure will be listed for description.

[0060] A single-mode optical fiber according to one aspect of the present disclosure,

[0061] (1) It has:

[0062] The core region with the maximum refractive index n1,

[0063] a first cladding region provided on the outer peripheral side of the core region and having a refractive index smaller than the n1, and

[0064] a second cladding region provided on the outer peripheral side of the first cladding region and having a refractive index greater than the refractive index of the outer peripheral portion of the first cladding region,

[0065] The refractive index at the boundary between the core region and the first cladding region becomes a continuously changing refractive index distribution.

[0066] In the refractive index distribution, a ratio of an area T of the tail elongated portion located outside the boundary to an area C of the core region, that is, T / C, is not less than 4% and not more than 30%, and the boundary is defined by a position where an absolute value of a radial change in the refractive index is maximum within a region from the center of the core region to the outer periphery of the first cladding region in the refractive index distribution,

[0067] The area C of the core region is defined by the area between the refractive index straight line of the first cladding region and the average refractive index straight line of the core region within the range from the center of the core region to the boundary in the radial direction in the refractive index distribution.

[0068] The area T of the tail elongated portion is defined by the area between the refractive index straight line of the first cladding region and the curve of the refractive index profile within a range from the boundary to the outer periphery of the first cladding region in the radial direction of the refractive index profile, within a range where the refractive index is greater than the refractive index straight line of the first cladding region.

[0069] The range of the refractive index distribution radially from the boundary to the outer periphery of the first cladding region is divided into three parts, and only the refractive index of part or all of the range within the middle part of the three parts is averaged, and the refractive index straight line of the first cladding region is defined by the averaged value or linear approximation line.

[0070] According to the single-mode optical fiber having the cladding formed of the first cladding region and the second cladding region, by defining the core region area C and the tail extension area T as described above, the relationship between the tail extension amount and the dispersion characteristics is less likely to deviate, making it easier to set the dispersion characteristics to appropriate values. Specifically, by defining the core region area C and the tail extension area T as described above, the refractive index of the cladding is easily determined even when the first cladding region has no horizontal portion in the refractive index profile. Furthermore, even when the horizontal portion of the first cladding region in the refractive index profile is close to the outer periphery of the first cladding region, the calculated value is not significantly increased.

[0071] In addition, since the T / C range is above 4%, the area of ​​the tail elongated portion will not be too small, and the internal strain of the single-mode optical fiber caused by the viscosity difference between the core and cladding materials is suppressed, which can prevent the increase in transmission loss and the deterioration of hydrogen resistance.

[0072] In addition, since the range of T / C is below 30%, the area of ​​the tail extension portion will not be too large, the impact of the tail extension portion on the optical power transmitted by the optical fiber is small, and the value of the zero dispersion wavelength is close to the transmission wavelength, which can make the dispersion characteristics good.

[0073] (2) The T / C may be 6% or more and 20% or less.

[0074] By setting T / C within the range of 6% to 20%, it is possible to more reliably prevent an increase in transmission loss and a deterioration in hydrogen resistance while further improving the dispersion characteristics.

[0075] (3) The refractive index n2 of the center of the core region may be smaller than n1.

[0076] Compared with a refractive index distribution in which the center of the core region has the maximum refractive index, when the refractive index at the center of the core region is low, the dispersion characteristics are improved, and thus the dispersion characteristics can be further improved.

[0077] According to a method for manufacturing a single-mode optical fiber in one aspect of the present disclosure,

[0078] (4) A method for manufacturing a single-mode optical fiber comprising a core region having a maximum refractive index n1, a first cladding region disposed on the outer periphery of the core region and having a refractive index smaller than n1, and a second cladding region disposed on the outer periphery of the first cladding region and having a refractive index larger than the refractive index of the outer periphery of the first cladding region, wherein the single-mode optical fiber has a refractive index profile in which the refractive index continuously changes at a boundary between the core region and the first cladding region.

[0079] The manufacturing method has the following features:

[0080] a step of manufacturing a core base material including the core region and the first cladding region,

[0081] The process of measuring the refractive index distribution of the core matrix to determine whether it is good or not,

[0082] a step of forming the second cladding region on the outer circumference of the core preform determined to be good by the determination of quality to produce an optical fiber preform; and

[0083] The process of drawing the optical fiber mother material to produce a single-mode optical fiber,

[0084] The step of judging whether the refractive index distribution is good or not includes the step of judging by the ratio T / C of the area C of the core region to the area T of the tail elongated portion outside the boundary in the refractive index distribution.

[0085] The boundary is defined by a position where the absolute value of the change in refractive index in the radial direction is maximum within a region extending from the center of the core region to the outer periphery of the first cladding region in the refractive index distribution.

[0086] The area C of the core region is defined by the area between the refractive index straight line of the first cladding region and the average refractive index straight line of the core region within the range from the center of the core region to the boundary in the radial direction in the refractive index distribution.

[0087] The area T of the tail elongated portion is defined by the area between the refractive index straight line of the first cladding region and the curve of the refractive index profile within a range from the boundary to the outer periphery of the first cladding region in the radial direction of the refractive index profile, within a range where the refractive index is greater than the refractive index straight line of the first cladding region.

[0088] The range of the refractive index distribution radially from the boundary to the outer periphery of the first cladding region is divided into three parts, and only the refractive index of part or all of the range within the middle part of the three parts is averaged, and the refractive index straight line of the first cladding region is defined by the averaged value or linear approximation line.

[0089] According to the above-described single-mode optical fiber manufacturing method, the quality of the core base material is determined by the ratio of the area T of the tail extension portion to the area C of the core region, namely, T / C, in the refractive index profile of the core base material. In this quality determination, since the core region area C and the area T of the tail extension portion are defined as described above, the relationship between the tail extension amount and the dispersion characteristics is less likely to deviate, and manufacturing can be managed with an appropriate tail extension amount. The quality of the core base material can be accurately determined based on the T / C value.

[0090] Then, by using the core base material judged to be good in the quality determination, a single-mode optical fiber having excellent dispersion characteristics, transmission loss, and hydrogen resistance characteristics can be manufactured.

[0091] [Details of the embodiment of the present disclosure]

[0092] Hereinafter, specific examples of a single-mode optical fiber and a method for manufacturing the single-mode optical fiber according to an embodiment of the present disclosure will be described with reference to the accompanying drawings.

[0093] It should be noted that the present invention is not limited to these examples but is represented by the scope of the claims, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.

[0094] Figure 1 Schematic diagram showing the cross-sectional structure and refractive index profile 10 of a single-mode optical fiber 1 according to the present embodiment. Figure 2 Yes Figure 1 10 and is a diagram for explaining the definition of the area T of the tail elongated portion 31 and the area C of the core region.

[0095] like Figure 1 As shown, the single-mode optical fiber 1 includes a core region 2, a first cladding region 3, and a second cladding region 4. The refractive index profile 10 of the single-mode optical fiber 1 is a refractive index profile in which the refractive index continuously changes at a boundary 11 between the core region 2 and the first cladding region 3.

[0096] like Figure 2 As shown, the maximum refractive index of the core region 2 is n1. In addition, the refractive index n2 at the center O of the core region 2 is smaller than n1. In addition, the refractive index of the first cladding region 3 is smaller than n1, and the boundary 11 between the core region 2 and the first cladding region 3 is defined as the position where the absolute value of the change in the refractive index in the radial direction is the largest in the region from the center O of the core region 2 to the outer periphery 12 of the first cladding region 3.

[0097] Incidentally, in the prior art such as Patent Documents 1 and 2, in the refractive index distribution, the refractive index of the horizontal portion of the cladding portion is set as the refractive index of the cladding, and the area of ​​the range surrounded by the horizontal line of this value, the interface between the core and the cladding, and the refractive index curve is set as the area of ​​the tail elongated portion.

[0098] However, when the cladding portion of the refractive index profile lacks a horizontal portion, as in the refractive index profile 10 of the single-mode optical fiber 1 of this embodiment, determining the refractive index of the cladding using the aforementioned conventional techniques is difficult. Furthermore, when the horizontal portion of the cladding portion of the refractive index profile is close to the outer periphery of the cladding, the area of ​​the tail extension becomes excessively large in the aforementioned conventional techniques. Consequently, even when the ratio of the tail extension area to the core area is large, the dispersion characteristics do not deteriorate.

[0099] Therefore, when the area of ​​the tail elongated portion determined by the above-mentioned conventional technology is used, it is not possible to appropriately evaluate the characteristics of the single-mode optical fiber.

[0100] In the present invention, the present inventors have found a method for determining the area of ​​the elongated tail portion that can solve the above-mentioned problems in the prior art.

[0101] Therefore, in the single-mode optical fiber 1 according to the present embodiment, within the range of the refractive index profile 10 from the boundary 11 in the radial direction to the outer periphery 12 of the first cladding region 3, the area T of the tail extension portion 31 is defined by the area between the refractive index straight line L and the curve 10a of the refractive index profile 10 within a range where the refractive index is greater than that of the refractive index straight line L of the first cladding region 3.

[0102] Here, the refractive index straight line L can be determined even without a horizontal portion in the first cladding region 3 portion of the refractive index profile 10, and is defined so that the area of ​​the tail elongated portion does not become excessively large as described below.

[0103] That is, the range of the refractive index profile 10 from the boundary 11 to the outer periphery of the first cladding region 3 in the radial direction is divided into three parts, and a linear approximation line corresponding to a portion or all of the refractive index within the range of the middle portion 3M of the three parts is set as the refractive index line L. It should be noted that it is also possible to average only the refractive index within the range of the middle portion 3M, and use a horizontal line passing through the average value instead of the refractive index line L.

[0104] In addition, the portion of the core region 2 in the refractive index distribution 10 may not be constant, for example, it may have a peak at a portion close to the boundary 11 between the core region 2 and the first cladding region 3, and the average refractive index nm of the core region 2 is set as the upper limit of the core region 2.

[0105] Thus, within the refractive index distribution 10 , in the radial direction from the center O of the core region 2 to the boundary 11 , the area C of the core region is defined by the area between the refractive index line L of the first cladding region 3 and the line of the average refractive index nm of the core region 2 .

[0106] In this embodiment, the area C of the core region 2 and the area T of the tail extension portion 31 are defined as described above, and the quality of the single-mode optical fiber 1 is determined by using their area ratio T / C. Furthermore, the T / C ratio of the single-mode optical fiber 1 according to this embodiment is set to be 4% or higher and 30% or lower. Furthermore, the T / C ratio of the single-mode optical fiber 1 is more preferably set to be 6% or higher and 20% or lower.

[0107] According to the single-mode optical fiber 1 of this embodiment, in a single-mode optical fiber 1 configured so that the cladding is divided into the first cladding region 3 and the second cladding region 4, by defining the area C of the core region 2 and the area T of the tail extension portion 31 as described above, the relationship between the tail extension amount and the dispersion characteristics is less likely to deviate, making it easier to set the dispersion characteristics to appropriate values. Specifically, by defining the area C of the core region 2 and the area T of the tail extension portion 31 as described above, the refractive index of the cladding is easily determined even when there is no horizontal portion in the first cladding region 3 of the refractive index profile 10. Furthermore, even when the horizontal portion of the first cladding region 3 of the refractive index profile 10 is close to the outer periphery 12 of the first cladding region 3, the calculated value is not excessive.

[0108] In addition, since the range of T / C is above 4%, the area T of the tail elongated portion 31 will not be too small, and the internal strain of the single-mode optical fiber 1 caused by the viscosity difference between the core and cladding materials is suppressed, which can prevent the increase in transmission loss and the deterioration of hydrogen resistance.

[0109] In addition, since the T / C range is below 30%, the area T of the tail extension portion 31 will not be too large, the tail extension portion 31 has little impact on the optical power transmitted by the optical fiber, and the value of the zero dispersion wavelength is close to the transmission wavelength, which can make the dispersion characteristics good.

[0110] Furthermore, by setting T / C within the range of 6% to 20%, it is possible to more reliably prevent an increase in transmission loss and a deterioration in hydrogen resistance while further improving the dispersion characteristics.

[0111] Furthermore, in the single-mode optical fiber 1, the refractive index n2 at the center O of the core region 2 is lower than the maximum refractive index n1. Compared to a refractive index profile in which the center O of the core region 2 has the maximum refractive index of the core, a lower refractive index at the center O of the core region 2 improves the dispersion characteristics, thereby further improving the dispersion characteristics.

[0112] Next, a method for manufacturing the single-mode optical fiber 1 according to the present embodiment will be described.

[0113] (Process of making core base material)

[0114] First, a porous base material including the core region 2 and the first cladding region 3 provided on the outer periphery of the core region 2 is formed by VAD or OVD, and the porous base material is sintered to produce a transparent core base material.

[0115] (Process for judging whether it is good or not)

[0116] Next, the refractive index distribution of the produced core base material is measured using, for example, a preform analyzer. A preform analyzer is a device that measures the refractive index distribution by passing laser light through the optical fiber base material from the side and measuring the refraction angle of the laser light.

[0117] It should be noted that the definitions of the area C of the core region 2, the refractive index line L of the first cladding region 3, the area T of the tail elongated portion 31, and the boundary 11 in the refractive index distribution of the core matrix can be the same as those in Figure 2 The definition of the refractive index profile 10 of the single-mode optical fiber 1 is the same as that described above, so the description thereof is omitted.

[0118] (Steps for determining whether a process is good or not)

[0119] In the quality determination step, the quality of the core base material is determined based on the ratio T / C, which is the area C of the core region 2 and the area T of the tail elongated portion 31 outside the boundary 11 in the refractive index distribution 10 .

[0120] In the above-mentioned determination of whether the quality is good or not, the core base material having a T / C of 4% or more and 30% or less is determined to be good.

[0121] In addition, a core base material having a T / C of 6% or more and 20% or less may be judged as good.

[0122] Next, a second cladding region 4 is formed on the outer circumference of the core preform determined to be good in the quality determination step to produce an optical fiber preform.

[0123] Then, the optical fiber preform produced as described above is drawn to produce the single-mode optical fiber 1 .

[0124] According to the manufacturing method of the single-mode optical fiber 1 of this embodiment, the quality of the core base material is determined by the ratio of the area T of the tail extension portion 31 to the area C of the core region 2, namely, T / C, in the refractive index profile 10 of the core base material. In this quality determination, since the area C of the core region 2 and the area T of the tail extension portion 31 are defined as described above, the relationship between the tail extension amount and the dispersion characteristics is unlikely to deviate, and manufacturing can be managed with an appropriate tail extension amount. The quality of the core base material can be accurately determined based on the T / C value.

[0125] Then, when determining whether the core material is good or not, a core material having a T / C ratio of 4% to 30% is determined to be good and this good core material is used, thereby manufacturing a single-mode optical fiber 1 having good dispersion characteristics, transmission loss, and hydrogen resistance characteristics. Furthermore, by determining a core material having a T / C ratio of 6% to 20% as good and using this good core material, a single-mode optical fiber 1 having even better dispersion characteristics, transmission loss, and hydrogen resistance characteristics can be manufactured.

[0126] It should be noted that the T / C value described above varies depending on the manufacturing conditions when forming a porous base material having a core region 2 and a first cladding region 3 provided on the outer peripheral side of the core region 2 by a VAD method or an OVD method, etc. For example, if the gas flow rate supplied to the burner forming the portion corresponding to the core region 2 of the porous base material is adjusted so as to reduce the bulk density of the portion corresponding to the core region 2 of the porous base material, the T / C value increases, whereas if the bulk density is increased, the T / C value decreases.

[0127] Furthermore, when the porous base material is sintered to produce a transparent core base material, the T / C value also varies depending on the manufacturing conditions. For example, when the porous base material is dehydrated and then transparentized, the T / C value increases if the dehydration time is extended, while the T / C value decreases if the dehydration time is shortened.

[0128] (Example)

[0129] Single-mode optical fibers with different T / C values, as defined in this embodiment, were manufactured. The cutoff wavelength λc, mode field diameter (MFD), and zero-dispersion wavelength were measured, and transmission loss and hydrogen resistance were evaluated. The results are shown in Table 1. Examples 2 to 6 are examples of the present disclosure, while Examples 1 and 7 are comparative examples.

[0130] It should be noted that in each example, there is no horizontal portion in the first cladding region 3 in the refractive index distribution 10, and the refractive index straight line L of the first cladding region 3 when calculating T / C is set to a value obtained by averaging all the refractive indices within the range of the middle portion 3M, where the middle portion 3M is obtained by dividing the first cladding region 3 in the refractive index distribution 10 into three parts.

[0131] [Table 1]

[0132] T / C (%) n1(％) n2(％) λc(nm) MFD(μm) Zero dispersion wavelength (nm) Transmission loss and hydrogen resistance Example 1 3.0 0.370 0.350 1265 9.15 1308 B Example 2 4.0 0.375 0.345 1265 9.15 1310 A Example 3 6.0 0.380 0.340 1270 9.20 1312 S Example 4 12.0 0.385 0.345 1270 9.20 1314 S Example 5 20.0 0.390 0.350 1275 9.20 1316 S Example 6 30.0 0.395 0.345 1280 9.25 1320 S Example 7 40.0 0.400 0.350 1280 9.25 1326 S

[0133] In the evaluation results of transmission loss and hydrogen resistance in Table 1, A represents a good result, S represents a further good result, and B represents a poor result.

[0134] As shown in the results in Table 1, single-mode optical fibers were evaluated based on the T / C values ​​defined in this embodiment. The zero-dispersion wavelength of a single-mode optical fiber with a T / C of 40% (Comparative Example 7) was 1326 nm. This indicates that the zero-dispersion wavelength of a single-mode optical fiber with a T / C of 40% is shifted toward longer wavelengths relative to the transmission wavelength in the 1.3 μm band, resulting in poor dispersion characteristics and undesirable performance. On the other hand, the zero-dispersion wavelength of the single-mode optical fiber of the embodiment is closer to the transmission wavelength in the 1.3 μm band, resulting in improved dispersion characteristics.

[0135] In addition, regarding the results of transmission loss and hydrogen resistance, Example 1 was B, Example 2 was A, and Examples 3 to 7 were S.

[0136] From the above results, it is understood that by setting T / C defined in this embodiment to 4% or more and 30% or less, it is possible to improve the dispersion characteristics while preventing an increase in transmission loss and a deterioration in hydrogen resistance.

[0137] Furthermore, it is found that by setting T / C to 6% or more and 20% or less, it is possible to more reliably prevent an increase in transmission loss and a deterioration in hydrogen resistance while further improving the dispersion characteristics.

Claims

1. A single-mode optical fiber having: The core region with the maximum refractive index n1, a first cladding region provided on the outer peripheral side of the core region and having a refractive index smaller than the n1, and a second cladding region provided on the outer peripheral side of the first cladding region and having a refractive index greater than the refractive index of the outer peripheral portion of the first cladding region, The refractive index at the boundary between the core region and the first cladding region becomes a continuously changing refractive index distribution. In the refractive index distribution, a ratio of an area T of the tail elongated portion outside the boundary to an area C of the core region, that is, T / C, is 4% or more and 30% or less, The boundary is defined by a position where the absolute value of the change in refractive index in the radial direction is maximum within a region extending from the center of the core region to the outer periphery of the first cladding region in the refractive index distribution. The area C of the core region is defined by the area between the refractive index straight line of the first cladding region and the average refractive index straight line of the core region within the range from the center of the core region to the boundary in the radial direction in the refractive index distribution. The area T of the tail elongated portion is defined by the area between the refractive index straight line of the first cladding region and the curve of the refractive index profile within a range from the boundary to the outer periphery of the first cladding region in the radial direction of the refractive index profile, within a range where the refractive index is greater than the refractive index straight line of the first cladding region. The refractive index distribution is divided into three parts in the radial direction from the boundary to the outer periphery of the first cladding region, and the refractive index of only a part or all of the middle part of the three parts is averaged, and the refractive index straight line of the first cladding region is defined by the averaged value or a linear approximation line. There is no horizontal portion in the first cladding region of the refractive index profile.

2. The single-mode optical fiber according to claim 1, wherein: The T / C is 6% to 20%.

3. The single-mode optical fiber according to claim 1 or 2, wherein: The refractive index n2 of the center of the core region is smaller than n1.

4. A method for manufacturing a single-mode optical fiber, the single-mode optical fiber comprising: a core region having a maximum refractive index n1; a first cladding region disposed on the periphery of the core region and having a refractive index smaller than n1; and a second cladding region disposed on the periphery of the first cladding region and having a refractive index larger than the refractive index of the periphery of the first cladding region; the single-mode optical fiber having a refractive index profile in which the refractive index continuously changes at a boundary between the core region and the first cladding region. The manufacturing method has the following features: a step of manufacturing a core base material including the core region and the first cladding region, The process of measuring the refractive index distribution of the core matrix to determine whether it is good or not, a step of forming the second cladding region on the outer circumference of the core preform determined to be good by the determination of quality to produce an optical fiber preform; and The process of drawing the optical fiber mother material to produce a single-mode optical fiber, The process of determining whether the product is good or not includes: The step of determining the refractive index distribution by using a ratio T / C of an area C of the core region to an area T of the tail elongated portion located outside the boundary. The boundary is defined by a position where the absolute value of the change in refractive index in the radial direction is maximum within a region extending from the center of the core region to the outer periphery of the first cladding region in the refractive index distribution. The area C of the core region is defined by the area between the refractive index straight line of the first cladding region and the average refractive index straight line of the core region within the range from the center of the core region to the boundary in the radial direction in the refractive index distribution. The area T of the tail elongated portion is defined by the area between the refractive index straight line of the first cladding region and the curve of the refractive index profile within a range from the boundary to the outer periphery of the first cladding region in the radial direction of the refractive index profile, within a range where the refractive index is greater than the refractive index straight line of the first cladding region. The refractive index distribution is divided into three parts in the radial direction from the boundary to the outer periphery of the first cladding region, and the refractive index of only a part or all of the middle part of the three parts is averaged, and the refractive index straight line of the first cladding region is defined by the averaged value or a linear approximation line. There is no horizontal portion in the first cladding region of the refractive index profile.

Images