JP3653724B2 - Optical fiber and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber and a method for manufacturing the optical fiber.
[0002]
[Prior art]
Dispersion compensating fibers are used to compensate for chromatic dispersion such as single mode fibers and dispersion shifted fibers. In order to effectively compensate the chromatic dispersion, it is preferable that the chromatic dispersion of the dispersion compensating fiber has a negative value and a large absolute value. This is because the larger the absolute value of the chromatic dispersion, the shorter the length of the dispersion compensating fiber to be used, and the miniaturization of the system becomes possible. Furthermore, it is preferable that the dispersion slope compensation rate by the dispersion compensating fiber is close to 100%. This is because the transmission band can be expanded particularly when a dispersion compensating fiber is used in the wavelength division multiplexing transmission system.
[0003]
[Problems to be solved by the invention]
However, according to the results of the research conducted by the present inventors, the bending loss tends to increase in a dispersion compensating fiber having a large absolute value of chromatic dispersion or a slope compensation factor close to 100%. For this reason, when a dispersion compensating fiber having such characteristics is applied to an optical communication system, there is a problem that loss in a long wavelength region increases and a transmission band is limited.
[0004]
In order to prevent the transmission band from being limited as the bending loss increases while realizing the desired chromatic dispersion characteristics, the maximum value of the relative refractive index difference Δn in the core region may be increased. However, in this case, transmission loss tends to increase. Therefore, when such a dispersion compensating fiber is used, there is a problem that the performance of the optical communication system is deteriorated.
[0005]
The present invention has been made in view of the above circumstances, and provides an optical fiber that achieves desired chromatic dispersion characteristics, suppresses an increase in transmission loss, and reduces bending loss, and a method for manufacturing the same. The purpose is to provide.
[0006]
[Means for Solving the Problems]
In the method of manufacturing an optical fiber according to the present invention, the distribution of the relative refractive index difference Δn (r) based on the refractive index of pure silica glass indicates that the maximum value of the relative refractive index difference is n.₀(%), When the distance from the central axis is r (r ≦ a) and the radius is a,
n₀× [1- (r / a)^1.5] ≦ Δn (r) ≦ n₀× [1- (r / a)^3.5] ... Formula (1)
A first glass rod that satisfies the relationship expressed by the following formula is prepared, and the outer peripheral portion of the first glass rod is ground so that the relative refractive index difference at the outer peripheral surface is 0.2 based on the refractive index of pure quartz glass. The second glass rod is made to be not less than 0.3% and not more than 0.35%, and the optical fiber is manufactured so that the core region of the optical fiber is formed from the second glass rod.
[0007]
According to the above manufacturing method, first, a glass rod is prepared in which the relative refractive index difference based on the refractive index of pure quartz glass satisfies the relationship of the above formula (1). Next, this glass rod is ground so that the relative refractive index difference on the outer peripheral surface is 0.2% or more and 0.35% or less based on the refractive index of pure quartz glass. And an optical fiber is manufactured so that a core area | region may be formed from this glass rod. Therefore, the relative refractive index difference in the core region of the manufactured optical fiber is maximized in the central axis of the core region, decreases along the direction from the central axis toward the cladding region, and is 0 at the interface between the core region and the cladding region. .2% or more and 0.35% or less. As a result, chromatic dispersion characteristics suitable for chromatic dispersion compensation are ensured, bending loss is reduced, and increase in transmission loss is suppressed.
[0008]
An optical fiber according to the present invention is manufactured by the above-described optical fiber manufacturing method. The optical fiber according to the present invention is manufactured by the above-described optical fiber manufacturing method, and the maximum value of the relative refractive index difference of the core region based on the refractive index of pure silica glass is 1.35% or more and 1.55. %, The chromatic dispersion at a wavelength of 1.55 μm is −30 ps / nm / km or less, and the dispersion slope at a wavelength of 1.55 μm is −0.03 ps / nm.²The bending loss at a wavelength of 1.55 μm is 10 dB / m or less and the transmission loss at a wavelength of 1.55 μm is 0.30 dB / km or less when bent to a diameter of 20 mm. can do. The chromatic dispersion is −55 ps / nm / km or more and −30 ps / nm / km or less, and the dispersion slope is −0.15 ps / nm.²/ Km or more -0.03ps / nm²/ Km or less is preferable.
[0009]
The optical fiber of the present invention is manufactured by the above optical fiber manufacturing method, and the maximum value of the relative refractive index difference in the core region based on the refractive index of pure silica glass is 1.50% or more and 1.65%. The chromatic dispersion at a wavelength of 1.55 μm is −45 ps / nm / km or less, and the dispersion slope at a wavelength of 1.55 μm is −0.078 ps / nm.²/ Km or less, bending loss at a wavelength of 1.55 μm when bent to a diameter of 20 mm is 30 dB / m or less, and transmission loss at a wavelength of 1.55 μm is 0.35 dB / km or less. Also good. The chromatic dispersion is -70 ps / nm / km or more and -45 ps / nm / km or less, and the dispersion slope is -0.30 ps / nm.²/ Km or more -0.078ps / nm²/ Km or less is preferable.
[0010]
Furthermore, the optical fiber of the present invention is manufactured by the above-described optical fiber manufacturing method, and the maximum value of the relative refractive index difference in the core region based on the refractive index of pure silica glass is 1.70% or more and 2.0%. The chromatic dispersion at a wavelength of 1.55 μm is −80 ps / nm / km or less, and the dispersion slope at a wavelength of 1.55 μm is −0.14 ps / nm.²It is preferable that the bending loss at a wavelength of 1.55 μm is 50 dB / m or less and the transmission loss at a wavelength of 1.55 μm is 0.40 dB / km or less when bent to a diameter of 20 mm. . The chromatic dispersion is -120 ps / nm / km or more and -80 ps / nm / km or less, and the dispersion slope is -0.50 ps / nm.²/ Km or more -0.14ps / nm²/ Km or less is preferable.
[0011]
Furthermore, the optical fiber of the present invention is manufactured by the above optical fiber manufacturing method, and the maximum value of the relative refractive index difference in the core region based on the refractive index of pure silica glass is 2.4% or more and 2.6. % Or less, the chromatic dispersion at a wavelength of 1.55 μm is −95 ps / nm / km or less, and the dispersion slope at a wavelength of 1.55 μm is −0.16 ps / nm.²The bending loss at a wavelength of 1.55 μm when bent to a diameter of 20 mm is 50 dB / m or less, and the transmission loss at a wavelength of 1.55 μm is preferably 0.70 dB / km or less. The chromatic dispersion is -180 ps / nm / km or more and -95 ps / nm / km or less, and the dispersion slope is -0.75 ps / nm.²/ Km or more -0.16ps / nm²/ Km or less is preferable.
[0012]
The above optical fibers have various dispersion characteristics, and in these optical fibers, bending loss is reduced and increase in transmission loss is suppressed. If such an optical fiber is used, chromatic dispersion can be effectively compensated in various optical communication systems.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of an optical fiber manufacturing method and an optical fiber manufactured by the manufacturing method according to the present invention will be described. In the following description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted. In the following description, the relative refractive index difference is a value based on the refractive index of pure quartz glass unless otherwise specified.
[0014]
FIG. 1 is a diagram for explaining a method of manufacturing an optical fiber according to the present embodiment. First, a glass rod 1 having a predetermined relative refractive index difference distribution is prepared (step S1). Here, the predetermined relative refractive index difference distribution means that the relative refractive index difference is Δn (r), and the maximum relative refractive index difference is n.₀(%) When the radius of the glass rod 1 is a and the distance from the central axis is r (r ≦ a),
n₀× [1- (r / a)^1.5] ≦ Δn (r) ≦ n₀× [1- (r / a)^3.5] ... Formula (1)
This distribution satisfies the relationship represented by the equation (1). A glass rod 1 having such a relative refractive index difference distribution is, for example, GeO.₂It is made of quartz glass to which a refractive index increasing agent such as is added and is manufactured by the VAD method or the like.
[0015]
FIG. 2A is a graph showing an example of the distribution of the relative refractive index difference Δn in the radial direction of the glass rod 1 having the relative refractive index difference distribution represented by the expression (1). Specifically, the distribution shown in the figure is
Δn = 1.5 × [1− (r / a)^2.0] (%) …… Formula (2)
Is a relative refractive index difference distribution. As shown in the figure, the relative refractive index difference of the glass rod 1 is maximum (1.5%) in the central axis of the glass rod 1 and decreases as it approaches the outer peripheral surface from the central axis, and the outer peripheral surface (r / a = ± 1), the distribution is 0%.
[0016]
Next, the outer peripheral portion of the glass rod 1 is ground with an etching solution such as a hydrofluoric acid (HF) solution, and the glass rod 2 having a relative refractive index difference on the outer peripheral surface of 0.2% or more and 0.35% or less is obtained. Make it. At this time, the grinding amount is determined based on the target value (0.2% or more and 0.35% or less) of the relative refractive index difference on the outer peripheral surface after grinding and the above equation (1). Then, the etching time is determined from the amount of grinding and the etching rate obtained from a preliminary experiment or the like. Etching is stopped when this etching time has elapsed after the start of etching. Thereby, the glass rod 2 in which the relative refractive index difference on the outer peripheral surface becomes a target value is obtained (step S2).
[0017]
FIG. 2B is a graph showing an example of the radial relative refractive index difference distribution of the glass rod 2 obtained by grinding the glass rod 1 having the relative refractive index difference distribution shown in FIG. Comparing FIG. 2 (a) and FIG. 2 (b), the outer diameter of the glass rod 2 is reduced by the amount of grinding of the outer peripheral portion, and the relative refraction at the outer peripheral surface of the glass rod 2 after grinding. It can be seen that the rate difference is specifically about 0.35%.
[0018]
Next, an optical fiber preform is produced by a rod in collapse method using the glass rod 2 thus ground. That is, the ground glass rod 2 is inserted into the first glass pipe 3 having a predetermined refractive index (step S3). Thereafter, the glass pipe 3 and the glass rod 2 are heated from the outer peripheral surface of the glass pipe 3 with an oxyhydrogen flame burner. Thereby, the glass pipe 3 and the glass rod 2 are integrated, and the base material intermediate body 4 is obtained (step S4). Next, the base material intermediate 4 is stretched by an oxyhydrogen flame burner to reduce the diameter (step S5). Then, the outer peripheral surface of the reduced base material intermediate 5 is chemically ground with hydrofluoric acid (HF) to become a core region formed by the glass rod 2 and a clad formed by the glass pipe 3. The diameter ratio with the region is adjusted (step S6). The base material intermediate body 6 whose diameter ratio has been adjusted is inserted into the second clad glass pipe 7 (step S7).
[0019]
After the base material intermediate 6 is inserted into the glass pipe 7, the glass pipe 7 and the base material intermediate 6 are heated from the outer peripheral surface of the glass pipe 7 with an oxyhydrogen flame burner. Thereby, the glass pipe 7 and the base material intermediate body 6 are integrated, and the optical fiber base material 8 is obtained (step S8). If the optical fiber preform 8 is a glass pipe made of quartz glass to which fluorine (F) is added as the first glass pipe 3 and a glass pipe made of pure quartz glass is used as the second glass pipe 7, for example. 3 has a refractive index distribution as shown in FIG. Next, by drawing this optical fiber preform 8 under predetermined conditions, the optical fiber 9 of the present embodiment having a predetermined chromatic dispersion value and dispersion slope is obtained (step S9).
[0020]
As described above, in the optical fiber manufacturing method of the present embodiment, first, the glass rod 1 whose relative refractive index difference distribution is represented by the formula (1) is prepared. Then, the glass rod 2 whose relative refractive index difference in an outer peripheral surface is 0.2% or more and 0.35% or less is manufactured by grinding the outer peripheral part. The ground glass rod 2 is inserted into a first glass pipe 3 having a predetermined relative refractive index difference, and then heated and integrated to obtain a base material intermediate 4. After obtaining the base material intermediate body 5 by stretching the base material intermediate body 4, the outer peripheral surface of the base material intermediate body 5 is ground so that the diameter ratio between the region to be the core and the region to be the cladding is increased. Adjusted. Subsequently, the base material intermediate body 6 with the adjusted diameter ratio is inserted into the glass pipe 7 for the second cladding. Thereafter, the glass pipe 7 and the base material intermediate 6 are heated and integrated to obtain an optical fiber base material 8. An optical fiber 9 is obtained by drawing the optical fiber preform 8.
[0021]
In the optical fiber 9 obtained in this way, the relative refractive index difference of the core region becomes maximum at the central axis of the core region, and decreases with approaching the cladding region along the radial direction. It becomes a predetermined value (0.2% or more and 0.35% or less) at the interface. Since the relative refractive index difference is thus distributed, in this optical fiber, desired wavelength dispersion characteristics can be obtained, bending loss is reduced, and transmission loss is prevented from increasing. In particular, even when the absolute value of chromatic dispersion is increased, bending loss can be suppressed low, and increase in transmission loss can be suppressed.
[0022]
Hereinafter, the optical fiber of the present embodiment will be described in more detail using examples. For the measurement of bending loss and transmission loss described below, a laser light source that emits laser light having a wavelength of 1.55 μm was used. The bending loss was measured by winding the manufactured optical fiber into a coil having a diameter of 20 mm.
[0023]
  (Example 1)
First, two glass rods were prepared. These glass rods were manufactured by stretching a quartz sintered body manufactured by the VAD method to a diameter of 8 mm with an electric furnace. These glass rods have GeO₂Is added, and the relative refractive index difference is distributed as represented by the formula (2). By immersing one of the two glass rods in the HF solution for 19 hours and the other one in the HF solution for 29 hours, the outer periphery of the two glass rods was chemically uniformly ground. . By this grinding, the relative refractive index difference on the outer peripheral surface of the glass rod after grinding was 0.2% for one glass rod and 0.3% for the other.
[0024]
Subsequently, an optical fiber preform was produced by a rod-in collapse method. That is, first, one of the ground glass rods was inserted into an F-added quartz glass pipe to be the first cladding. This F-added quartz glass pipe has a uniform relative refractive index difference of about −0.45%. The inner diameter is 5 mm and the outer diameter is 25 mm. After the insertion, the F-added quartz glass pipe and the glass rod were heated from the outer peripheral surface of the F-added quartz glass pipe with an oxyhydrogen flame burner. As a result, the F-added quartz glass pipe and the glass rod were integrated to obtain an intermediate. Next, this intermediate was stretched by an oxyhydrogen flame burner and reduced in diameter so that its outer diameter was 8 mm. And the diameter ratio with the area | region which should become a core and the area | region which should become a clad in an intermediate body was adjusted by chemically grinding the outer peripheral surface of the diameter-reduced intermediate body with HF. Specifically, by this adjustment, the diameter of the region to be the core is changed to R._aAnd the outer diameter of the region to be the cladding is R_bThen R_a/ R_b= 0.5.
Subsequently, the intermediate body having the above diameter ratio was inserted into a pure quartz glass pipe to be the second cladding. The pure quartz glass pipe has an inner diameter of 5 mm and an outer diameter of 25 mm. Thereafter, the pure quartz glass pipe was heated from the outside by an oxyhydrogen flame burner, and the pure quartz glass pipe and the intermediate were integrated. For the other one glass rod, the same process using two glass pipes having the same refractive index as described above was performed to obtain a total of two optical fiber preforms.
[0025]
Thereafter, by drawing each of the two optical fiber preforms, the chromatic dispersion value at a wavelength of 1.55 μm becomes −55 ps / nm / km, and the dispersion slope becomes −0.15 ps / nm.²Two types of optical fibers of / km were obtained.
[0026]
Next, in order to compare with the optical fiber of Example 1, three types of optical fibers were produced. Two of these optical fibers were produced by the same procedure as that of the optical fiber of Example 1 except that the relative refractive index difference on the outer peripheral surface of the glass rod after grinding was different. The relative refractive index difference was 0.5% for one glass rod and 1.0% for the other glass rod. Another type of optical fiber was produced by the same procedure as the optical fiber of Example 1 without grinding the glass rod. In any optical fiber, the chromatic dispersion value at a wavelength of 1.55 μm is about −55 ps / nm / km, and the dispersion slope is −0.15 ps / nm.²/ Km or so.
[0027]
Bending loss and transmission loss were measured for the two types of optical fibers of Example 1 and the three types of optical fibers for comparison. The result will be described. FIG. 4 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm. In the figure, the horizontal axis represents the relative refractive index difference on the outer peripheral surface of the glass rod after grinding. Also, point A in the figure₁, B₁Shows the result of bending loss of the optical fiber of Example 1, point C₁, D₁These show the result of the transmission loss of the optical fiber of Example 1.
[0028]
As can be seen from FIG. 4, the bending loss tends to decrease as the relative refractive index difference increases. On the other hand, the transmission loss tends to increase as the relative refractive index difference increases. When the relative refractive index difference is smaller than 0.2%, the transmission loss is almost constant and kept at a low value, but the bending loss increases rapidly. Further, when the relative refractive index difference is larger than 0.35%, the bending loss is reduced, but the transmission loss is increased. Therefore, the present inventors consider that 0.2% or more and 0.35% or less are preferable as the range of the relative refractive index difference in which the bending loss is sufficiently low for practical use and the increase in transmission loss is suppressed. Yes. The optical fiber of Example 1 having a relative refractive index difference in this range (point A₁, B₁, C₁, D₁) Satisfies the condition that the bending loss is sufficiently low and the condition that the increase in the transmission loss can be suppressed as compared with the comparative optical fiber. Specifically, the optical fiber of Example 1 has a bending loss of 10 dB / m or less and a transmission loss of 0.30 dB / km or less.
[0029]
As can be seen from FIG. 4, the transmission loss is the minimum value when grinding is not performed, that is, when the relative refractive index difference on the outer peripheral surface of the glass rod is 0%. The transmission loss becomes almost the same as this minimum value when the relative refractive index difference is 0.3% when grinding is performed. At this time, the bending loss is also sufficiently reduced. From these facts, the present inventors consider that the case where the relative refractive index difference is 0.3% is particularly suitable.
[0030]
In Example 1, the chromatic dispersion is −55 ps / nm / km, and the chromatic dispersion is −0.15 ps / nm.²The optical fiber manufactured to be / km has been described, but the wavelength dispersion is in the range of −55 ps / nm / km to −30 ps / nm / km and the dispersion slope is −0.15 ps / nm.²/ Km or more -0.03ps / nm²Similar results were obtained in the range of / km or less.
[0031]
  (Example 2)
In Example 2, two types of optical fibers were manufactured by the same procedure as the optical fiber of Example 1 except for the following differences. The difference is that (a) the distribution of the relative refractive index difference along the radial direction of the two prepared glass rods is
Δn = 1.6 × [1− (r / a)^2.0] (%) …… Formula (3)
And (b) the obtained optical fiber has a chromatic dispersion value of −70 ps / nm / km at a wavelength of 1.55 μm and a dispersion slope of −0.30 ps / nm.²/ Km.
[0032]
For comparison with the optical fiber of Example 2, three types of comparative optical fibers were manufactured. Of these, two types of optical fibers were prepared by the same procedure as that of the optical fiber of Example 2 except that the relative refractive index difference on the outer peripheral surface after glass rod grinding was different. Specifically, the relative refractive index difference on the outer peripheral surface after glass rod grinding was 0.5% for one glass rod and 1.0% for the other glass rod. Another type of optical fiber was prepared by the same procedure as the optical fiber of Example 2 without grinding the glass rod. In any optical fiber, the chromatic dispersion value at a wavelength of 1.55 μm is about −70 ps / nm / km, and the dispersion slope is −0.30 ps / nm.²/ Km or so.
[0033]
Bending loss and transmission loss were measured for the two types of optical fibers of Example 2 and the three types of optical fibers for comparison. FIG. 5 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm. In the figure, the horizontal axis represents the relative refractive index difference on the outer peripheral surface of the glass rod after grinding. Also, point A in the figure₂, B₂Is the result of the bending loss of the optical fiber of Example 2, point C₂, D₂These are the results of the transmission loss of the optical fiber of Example 2.
[0034]
As shown in FIG. 5, the bending loss decreases as the relative refractive index difference increases, and the transmission loss tends to increase as the relative refractive index difference increases. Compared with the optical fiber for comparison with Example 1 and Example 1 shown in FIG. 4, in the case of the optical fiber for comparison with Example 2 and Example 2, bending loss is also transmitted. It turns out that the loss is also increasing as a whole. This is because the maximum relative refractive index difference of the glass rod prepared for the production of the optical fiber is large. As a result, the chromatic dispersion value and the absolute value of the dispersion slope are increased.
[0035]
Even in such a case, the bending loss is sufficiently small and the increase in transmission loss is suppressed when the relative refractive index difference is in the range of 0.2% to 0.35%. Specifically, the optical fiber of Example 2 has a bending loss of 30 dB / m or less and a transmission loss of 0.35 dB / km or less.
[0036]
Further, as can be seen from FIG. 5, the transmission loss is the minimum value when grinding is not performed, that is, when the relative refractive index difference on the outer peripheral surface of the glass rod is 0%. In the case of grinding, when the relative refractive index difference on the outer peripheral surface of the glass rod after grinding is 0.3%, the transmission loss is approximately the same as this minimum value. At this time, the bending loss is also sufficiently reduced. For this reason, the present inventors consider that the case where the relative refractive index difference is 0.3% is particularly suitable.
[0037]
In Example 1, the chromatic dispersion is −70 ps / nm / km, and the chromatic dispersion is −0.30 ps / nm.²The optical fiber manufactured to be / km has been described, but the chromatic dispersion is in the range of −70 ps / nm / km to −45 ps / nm / km and the dispersion slope is −0.30 ps / nm.²/ Km or more -0.078ps / nm²Similar results were obtained in the range of / km or less.
[0038]
  Example 3
In Example 3, two types of optical fibers were manufactured by the same procedure as that of the optical fiber of Example 1 except for the following points. The difference is that (a) the distribution of the relative refractive index difference along the radial direction of the two prepared glass rods is
Δn = 1.9 × [1- (r / a)^2.0] (%) …… Formula (4)
And (b) the obtained optical fiber has a chromatic dispersion value of −120 ps / nm / km at a wavelength of 1.55 μm and a dispersion slope of −0.50 ps / nm.²/ Km.
[0039]
For comparison with the optical fiber of Example 3, three types of optical fibers for comparison were produced. Of these, two types of optical fibers were prepared by the same procedure as that of the optical fiber of Example 3 except that the relative refractive index difference on the outer peripheral surface after glass rod grinding was different. Specifically, the relative refractive index difference on the outer peripheral surface after glass rod grinding was 0.5% for one glass rod and 1.0% for the other glass rod. The other one type of optical fiber was produced by the same procedure as that of the optical fiber of Example 3 without grinding the glass rod. In any optical fiber, the chromatic dispersion value at a wavelength of 1.55 μm is about −120 ps / nm / km, and the dispersion slope is −0.50 ps / nm.²/ Km or so.
[0040]
With respect to the two types of optical fibers of Example 3 and the three types of optical fibers for comparison, measurement of bending loss and transmission loss was performed using laser light having a wavelength of 1.55 μm. The result is shown in FIG. FIG. 6 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm. In the figure, the horizontal axis represents the relative refractive index difference on the outer peripheral surface of the glass rod after grinding. Moreover, the point which attached | subjected the code | symbol in the figure has shown the result of the optical fiber of Example 3. FIG. Specifically, point A_Three, B_ThreeIs the result of bending loss, point C_Three, D_ThreeIs the result of transmission loss. The point without a code | symbol shows the result of the optical fiber for a comparison.
[0041]
From FIG. 6, the optical fiber of Example 3 (point A_Three, B_Three, C_Three, D_Three) Satisfies the condition that the bending loss is sufficiently lower than that of the comparative optical fiber and the condition that the increase in transmission loss can be suppressed. From this result, it is understood that the relative refractive index difference on the outer peripheral surface of the glass rod after grinding is in the range of 0.2% to 0.35%. Specifically, the optical fiber of Example 3 has a bending loss of 50 dB / m or less and a transmission loss of 0.40 dB / km or less.
[0042]
Further, when the relative refractive index difference is 0.3%, it is almost the same as the case where the relative refractive index difference is 0% at which the transmission loss is minimized, and the bending loss is sufficiently reduced. Therefore, the present inventors consider that the case where the relative refractive index difference is 0.3% is particularly suitable.
[0043]
In Example 1, the chromatic dispersion is −120 ps / nm / km, and the chromatic dispersion is −0.50 ps / nm.²The optical fiber manufactured to be / km has been described, but the chromatic dispersion is in the range of −120 ps / nm / km or more and −80 ps / nm / km or less, and the dispersion slope is −0.50 ps / nm.²/ Km or more -0.14ps / nm²Similar results were obtained in the range of / km or less.
[0044]
  Example 4
In Example 4, two types of optical fibers were manufactured by the same procedure as Example 1 except for the following three points. The difference is that (a) the distribution of the relative refractive index difference along the radial direction of the two prepared glass rods is
Δn = 2.5 × [1− (r / a)^2.0] (%) …… Formula (5)
(B) The manufactured optical fiber has a chromatic dispersion value of about −180 ps / nm / km at a wavelength of 1.55 μm and a dispersion slope of −0.75 ps / nm.²And (c) the F-added quartz glass pipe to be the first cladding has a uniform relative refractive index difference of about −0.36%.
[0045]
For comparison with the optical fiber of Example 4, three types of comparative optical fibers were manufactured. Two of these optical fibers have the relative refractive index difference on the outer peripheral surface after glass rod grinding of 0.5% for one and 1.0% for the other, so that the optical fiber of Example 4 can be used. It was produced by the same procedure as the production procedure. Another type of optical fiber was prepared by the same procedure as the optical fiber of Example 2 without grinding the glass rod. In any optical fiber, the chromatic dispersion value at a wavelength of 1.55 μm is about −180 ps / nm / km, and the dispersion slope is −0.75 ps / nm.²/ Km or so.
[0046]
FIG. 7 shows the results of measurement of bending loss and transmission loss for the two types of optical fibers of Example 4 and the three types of comparative optical fibers. FIG. 7 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm. In the figure, the horizontal axis represents the relative refractive index difference on the outer peripheral surface of the glass rod after grinding. Further, in the figure, reference numerals are assigned to points indicating the results of the optical fiber of Example 4. Point A_Four, B_FourIs the result of bending loss and point C_Four, D_FourIs the result of transmission loss. The other unsigned points indicate the results of comparative optical fibers.
[0047]
As shown in FIG. 7, the bending loss decreases as the relative refractive index difference increases, and the transmission loss increases as the relative refractive index difference increases. The optical fiber of Example 4 (point A) having a relative refractive index difference in the range of 0.2% to 0.35%._Four, B_Four, C_Four, D_Four), Both bending loss and transmission loss are kept low. Specifically, the optical fiber of Example 1 has a bending loss of 50 dB / m or less and a transmission loss of 0.70 dB / km or less.
[0048]
Further, when the relative refractive index difference is 0.3%, it is almost the same as the case where the relative refractive index difference is 0% at which the transmission loss is minimized, and the bending loss is sufficiently reduced. Therefore, the present inventors consider that the case where the relative refractive index difference is 0.3% is particularly suitable.
[0049]
In Example 1, the chromatic dispersion is −180 ps / nm / km, and the chromatic dispersion is −0.75 ps / nm.²The optical fiber manufactured to be / km has been described, but the wavelength dispersion is in the range of −180 ps / nm / km or more and −95 ps / nm / km or less, and the dispersion slope is −0.75 ps / nm.²/ Km or more -0.16ps / nm²Similar results were obtained in the range of / km or less.
[0050]
As described above, the optical fiber and the manufacturing method thereof according to the present invention have been described using the embodiment and some examples. However, the present invention is not limited thereto, and various modifications are possible.
[0051]
In the above embodiments and examples, the glass pipe to be the cladding region is used in a double manner, but the number of glass pipes may be one, or three or more. It goes without saying that the number of glass pipes to be used, the inner and outer diameters, and the refractive index should be determined so as to realize various characteristics that the optical fiber to be manufactured should have.
[0052]
Further, in the above-described embodiment and examples, an optical fiber preform was produced using a rod in collapse method, and an optical fiber was produced by drawing this preform. An optical fiber preform may be produced by depositing glass to be a cladding region by an external CVD method, and the preform is drawn to produce an optical fiber.
[0053]
Furthermore, as a method for grinding the glass rod, a method using a machine tool such as a lathe may be employed in addition to a method using an etching solution such as a hydrofluoric acid (HF) solution.
[0054]
Furthermore, when determining the grinding amount, in addition to the method based on the above formula (1), the grinding amount may be determined based on a result measured in advance by a nondestructive refractive index measuring device such as a preform analyzer. . Further, grinding may be performed while measuring with a refractive index measuring device.
[0055]
In the above-described embodiment and examples, the optical fiber preform is once produced, and then the preform is drawn to produce an optical fiber. An optical fiber may be manufactured.
[0056]
【The invention's effect】
As described above, according to the method for manufacturing an optical fiber according to the present invention, first, the distribution of the relative refractive index difference Δn (r) based on the refractive index of pure silica glass is the maximum value of the relative refractive index difference. N₀When the distance from the central axis is r (r ≦ a) and the radius is a,
n₀× [1- (r / a)^1.5] ≦ Δn (r) ≦ n₀× [1- (r / a)^3.5] ... Formula (1)
A glass rod that satisfies this relationship is prepared. Next, this glass rod is ground so that the relative refractive index difference on the outer peripheral surface is 0.2% or more and 0.35% or less based on the refractive index of pure quartz glass. And an optical fiber is manufactured so that a core area | region may be formed from this glass rod. Therefore, even in the manufactured optical fiber, the relative refractive index difference of the core region is maximized in the central axis of the core region and decreases along the direction from the central axis toward the cladding region. The value of 0.2% or more and 0.35% or less can be obtained at the interface. As a result, chromatic dispersion characteristics suitable for chromatic dispersion compensation are ensured, bending loss is reduced, and increase in transmission loss is suppressed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an optical fiber manufacturing method according to an embodiment.
FIG. 2 (a) is a graph showing an example of a relative refractive index difference distribution in the radial direction of a glass rod. FIG. 2B is a graph showing an example of the relative refractive index difference distribution in the radial direction after grinding the glass rod having the relative refractive index difference distribution shown in FIG.
FIG. 3 is a graph showing an example of a refractive index distribution of an optical fiber preform.
FIG. 4 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm.
FIG. 5 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm.
FIG. 6 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm.
FIG. 7 is a graph showing the relative refractive index difference dependence of bending loss and transmission loss at a wavelength of 1.55 μm.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Glass rod, 2 ... Glass rod after grinding, 3 ... 1st glass pipe, 4, 5, 6 ... Base material intermediate body, 7 ... Glass pipe, 8 ... Optical fiber base material, 9 ... Optical fiber.

Claims (6)

The distribution of the relative refractive index difference Δn (r) based on the refractive index of pure silica glass is
n ₀ × {1- (r / a) ^1.5 } ≦ Δn (r) ≦ n ₀ × {1- (r / a) ^3.5 }
However,
n ₀ : Maximum value of relative refractive index difference (%),
r: distance from the central axis (r ≦ a),
a: radius,
Prepare a first glass rod that satisfies the relationship represented by
By grinding the outer peripheral portion of the first glass rod, a second glass rod having a relative refractive index difference on the outer peripheral surface of 0.2% or more and 0.35% or less based on the refractive index of pure quartz glass is provided. Made,
An optical fiber manufacturing method, wherein an optical fiber is manufactured so that a core region is formed from the second glass rod. An optical fiber manufactured by the optical fiber manufacturing method according to claim 1. The maximum value of the relative refractive index difference in the core region based on the refractive index of pure silica glass is 1.35% or more and 1.55% or less, and the chromatic dispersion at a wavelength of 1.55 μm is −30 ps / nm / km or less. The dispersion slope at a wavelength of 1.55 μm is −0.03 ps / nm ² / km or less, the bending loss at a wavelength of 1.55 μm is 10 dB / m or less when bent to a diameter of 20 mm, The optical fiber according to claim 2, wherein a transmission loss at 55 µm is 0.30 dB / km or less. The maximum value of the relative refractive index difference of the core region based on the refractive index of pure silica glass is 1.50% or more and 1.65% or less, and the chromatic dispersion at a wavelength of 1.55 μm is −45 ps / nm / km or less. The dispersion slope at a wavelength of 1.55 μm is −0.078 ps / nm ² / km or less, the bending loss at a wavelength of 1.55 μm is 30 dB / m or less when bent to a diameter of 20 mm, The optical fiber according to claim 2, wherein a transmission loss at 55 μm is 0.35 dB / km or less. The maximum value of the relative refractive index difference in the core region based on the refractive index of pure silica glass is 1.70% or more and 2.0% or less, and the chromatic dispersion at a wavelength of 1.55 μm is −80 ps / nm / km or less. The dispersion slope at a wavelength of 1.55 μm is −0.14 ps / nm ² / km or less, the bending loss at a wavelength of 1.55 μm is 50 dB / m or less when bent to a diameter of 20 mm, The optical fiber according to claim 2, wherein a transmission loss at 55 µm is 0.40 dB / km or less. The maximum value of the relative refractive index difference of the core region based on the refractive index of pure silica glass is 2.4% to 2.6%, and the chromatic dispersion at a wavelength of 1.55 μm is −95 ps / nm / km or less. The dispersion slope at a wavelength of 1.55 μm is −0.16 ps / nm ² / km or less, the bending loss at a wavelength of 1.55 μm when bent to a diameter of 20 mm is 50 dB / m or less; The optical fiber according to claim 2, wherein a transmission loss at 55 µm is 0.70 dB / km or less.

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