JP4056778B2 - Manufacturing method of optical fiber preform - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an optical fiber preform composed of a core portion and a cladding portion, and suppresses fluctuations in characteristics of an optical fiber obtained by drawing the optical fiber preform, thereby improving the yield of the manufacturing process. is there.
[0002]
[Prior art]
One conventional optical fiber manufacturing method is as follows.
First, a soot deposit made of quartz glass fine particles is made by the VAD method, the CVD method, or the like, and this is sintered and transparentized to produce a glass base material. This glass base material consists of only the core part, or a part of the clad part is formed around the core part. And after extending this glass base material to a predetermined outer diameter to form a glass rod, the remaining clad portion is formed on the outer periphery of the glass rod by an external method (OVD method), a rod-in-tube method, or the like. Thus, an optical fiber preform is obtained. Next, the optical fiber preform is drawn and spun to obtain an optical fiber.
[0003]
[Problems to be solved by the invention]
In the above-described conventional method, a longitudinal variation may occur in the refractive index distribution of the glass base material. For this reason, the characteristic variation in the longitudinal direction may occur in the optical fiber preform and the optical fiber obtained from the glass preform.
The characteristic variation in the longitudinal direction of the optical fiber is not a problem in practical use because a normal single mode optical fiber has a large allowable range of characteristic variation. However, in a type of optical fiber that has a narrow allowable range of characteristic fluctuation in the longitudinal direction, such as a dispersion-shifted optical fiber, if the characteristic fluctuation is large, a part of the optical fiber in the longitudinal direction becomes defective and the yield is reduced. There is.
[0004]
Accordingly, an object of the present invention is to provide an optical fiber preform manufacturing method that can improve the yield of the optical fiber preform manufacturing process and that can manufacture an optical fiber preform with small fluctuations in the longitudinal characteristics.
[0005]
[Means for Solving the Problems]
The problem is that a glass base material having a core part or a core part and a part of a clad part is prepared, and the glass base material is stretched to form a glass rod, and then the remaining clad part on the outer periphery of the glass rod In the manufacturing method of the optical fiber preform that produces the optical fiber preform by applying
When stretching the glass base material, the refractive index distribution of the glass base material is measured at a plurality of different positions in the longitudinal direction, and from these measured values, the required amount of the remaining cladding portion is calculated, and this calculated value is On the basis, the glass base material is stretched so that the required amount of the remaining cladding portion is constant in the longitudinal direction.
As a result, the required amount of the remaining cladding portion to be applied becomes constant in the longitudinal direction of the glass rod, so that it is easy to apply the remaining cladding portion without excess and deficiency, and the characteristic fluctuation in the longitudinal direction is extremely small. An optical fiber preform can be manufactured with a high yield.
[0006]
The deviation of the outer diameter at each position in the longitudinal direction of the glass rod after stretching is preferably -10 to + 10% of the average diameter of the glass rod. Within this range, it is easier to apply the remaining clad portion with a uniform thickness on the glass rod.
The required amount of the remaining cladding portion is preferably calculated so as to minimize the longitudinal variation of the predetermined optical characteristics of the target optical fiber preform. Thereby, an optical fiber preform with small variations in optical characteristics can be manufactured with high productivity.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments.
In the method for manufacturing the optical fiber preform of the present embodiment, the method for producing the glass preform having the core portion or the core portion and a part of the clad portion is not particularly limited, and VAD method, MCVD. This method can be applied to any of the conventionally known methods such as the method and the PCVD method. Further, the type of the target optical fiber is not particularly limited, but is particularly suitable for manufacturing an optical fiber having a narrow allowable width of characteristic fluctuation in the longitudinal direction. Examples of such an optical fiber include a dispersion shifted optical fiber and a dispersion compensating optical fiber.
[0008]
In the conventional method for manufacturing an optical fiber preform, the glass preform is drawn to a predetermined outer diameter to form a glass rod, and the remaining clad portion is formed on the outer periphery of the glass rod. It is said. At this time, the glass base material is generally stretched so that fluctuations in the outer diameter in the longitudinal direction of the glass rod after stretching are reduced. The remaining clad portion is provided on the glass rod with a thickness as uniform as possible.
[0009]
However, as a result of diligent investigations by the present inventors, the longitudinal direction of the refractive index distribution of the glass rod can be reduced simply by reducing the fluctuation of the outer diameter of the glass rod and uniformly providing the remaining cladding on the glass rod. Therefore, it was found that an optical fiber preform with a small characteristic variation cannot always be obtained. In this case, in order to obtain an optical fiber preform having a small characteristic variation, for example, a method of changing the thickness of the remaining cladding portion in the longitudinal direction in accordance with the variation of the refractive index distribution can be considered. However, it is generally difficult to change the thickness for providing the remaining cladding portion, which may increase the manufacturing cost.
[0010]
In the present embodiment, when the glass base material is stretched, first, the refractive index distribution of the glass base material is measured at a plurality of positions different in the longitudinal direction. Then, from these measured values, when the optical fiber preform is finally used, the required amount of the remaining cladding portion is calculated so that the fluctuation of predetermined optical characteristics such as chromatic dispersion and cut-off wavelength is reduced. Furthermore, based on this calculated value, the target drawing diameter is calculated so that the required amount of the remaining cladding portion is constant in the longitudinal direction, and the glass base material is drawn according to this target. Specifically, for example, when there is a change in the longitudinal direction of the refractive index distribution of the glass base material, the outer diameter of the stretched glass rod is changed in the longitudinal direction in accordance with this change.
[0011]
Thus, in the glass base material, even if there is a fluctuation in the longitudinal direction of the required amount of the remaining clad portion, the required amount of the remaining clad portion in the stretched glass rod by stretching as described above. Becomes substantially constant in the longitudinal direction. Therefore, it becomes easy to provide the remaining clad part, and the yield and productivity for manufacturing the optical fiber preform are improved.
[0012]
The measurement of the refractive index distribution of the glass base material is performed at a plurality of positions different in the longitudinal direction in order to know in detail the longitudinal fluctuation of the refractive index distribution of the glass base material.
The refractive index distribution of the glass base material is measured using a known appropriate method such as an optical method using a preform analyzer or a method using X-ray analysis.
Examples of the optical method include a method in which a parallel light beam or a thin laser beam is irradiated from the side of a glass base material, and a refractive index distribution is measured from an incident angle of light refracted and transmitted to a measuring instrument. As a method using X-ray analysis, for example, a glass base material is irradiated with X-rays, the amount of germanium doped is measured from the intensity of the characteristic X-rays emitted from the glass base material, and the refractive index distribution is obtained therefrom. A method is mentioned.
[0013]
Next, the required amount of the remaining cladding portion is calculated from the measured value of the refractive index distribution of the glass base material.
The required amount of the remaining clad portion may be determined so that the outer diameter ratio of the core portion / cladding portion in the target optical fiber preform is constant in the longitudinal direction. It is determined by applying Maxwell's equations to the optical fiber preform and analyzing the optical fiber obtained from the optical fiber preform so that longitudinal fluctuations regarding characteristics such as chromatic dispersion and cutoff wavelength are minimized. Also good.
[0014]
Furthermore, based on the calculated value of the required amount of the remaining cladding portion obtained in this way, the outer diameter of the target glass rod is calculated at each position in the longitudinal direction of the glass rod after stretching. Specifically, for example, a desired core part / clad part outer diameter ratio is calculated from the required amount of the remaining cladding part calculated for the glass base material, and the position where the required amount of the remaining cladding part is large is the stretched diameter. The stretched diameter can be calculated at each position in the longitudinal direction by making the stretched diameter thicker at a portion where the required amount of the remaining cladding portion is small.
[0015]
Further, the glass base material is stretched based on the target value so that the required amount of the remaining cladding portion is constant in the longitudinal direction.
The method for stretching the glass base material is not particularly limited, but for example, the following method can be used.
[0016]
As a first method, as shown in FIG. 1, one end of a glass base material 1 is attached to a glass lathe 3 via a fixed chuck 2, and the other end is held by a moving chuck 4. Examples include a method in which the moving chuck 4 is moved and stretched while being heated by a flame burner 5 such as an oxyhydrogen flame or a plasma flame.
In this case, the outer diameter of the glass rod can be controlled by appropriately controlling the moving speed of the moving chuck 4 and the flame burner 5.
[0017]
As a second method, as shown in FIG. 2, a heating furnace 10 such as a carbon heater or an induction heating furnace is used, and the glass base material 1 is inserted into the heating furnace 10 from one end at a predetermined speed. There is a method in which the tip of the glass base material 1 is drawn by the moving chuck 11 and stretched while being heated. Furthermore, the extending portion 12 of the glass base material 1 may be sandwiched by a roller, a caterpillar 13 or the like, and the extending portion 12 may be pushed downward by rotating the caterpillar 13 or the like.
In this case, the outer diameter of the glass rod can be controlled by changing conditions such as the speed at which the glass base material 1 enters the heating furnace, the moving speed of the moving chuck 11, and the heating temperature of the heating furnace 10.
[0018]
The glass rod obtained by stretching does not necessarily have a constant outer diameter in the longitudinal direction. As long as the variation in optical properties of the optical fiber preform finally obtained is extremely small, for example, even if the outer diameter variation within a certain limit occurs due to the variation in the dopant concentration and refractive index distribution in the glass rod Good.
However, if there is a position where the deviation of the outer diameter at each position in the longitudinal direction of the glass rod (difference between the outer diameter of the position and the average outer diameter) exceeds ± 10% of the average outer diameter of the glass rod, In the OVD method, there is a possibility that the deposition of the glass fine particles may be non-uniform in the formation of the cladding portion. In the rod-in-tube method, the gap between the glass rod and the quartz tube serving as the remaining cladding portion is crushed. When collapsing, bubbles may be generated. For this reason, it is preferable that the deviation of the outer diameter of the glass rod is in the range of −10 to + 10%.
[0019]
Subsequently, the remaining clad part is formed on the outer periphery of the glass rod. For this, a known method such as a conventionally used external method (OVD method) or rod-in-tube method (RIT method) can be used.
As is well known, the OVD method is a method of forming the remaining clad portion by synthesizing glass fine particles with a burner and depositing the glass fine particles on a glass rod. In the RIT method, a quartz glass tube serving as the remaining clad portion is covered with a glass rod and heated, and the gap between the inner wall of the quartz glass tube and the side surface of the glass rod is crushed and integrated (collapsed). This is a method for obtaining an optical fiber preform.
[0020]
In any method, according to the present embodiment, since the required amount of the remaining cladding portion is substantially constant in the longitudinal direction of the glass rod, it is easy to apply the remaining cladding portion without excess or deficiency. It is. Therefore, it becomes easy to manufacture an optical fiber preform as designed, and an optical fiber with extremely small longitudinal characteristic variation can be manufactured.
[0021]
Next, a specific example of the embodiment of the present invention will be described.
In this embodiment, the present invention is applied to the production of an optical fiber preform for a dispersion shifted optical fiber.
First, a glass base material having a length of 1 m and a diameter of 101 mm having a core part and a part of the clad part was produced, and the refractive index distribution of the glass base material was measured by a preform analyzer. Then, the required amount of the remaining clad portion was calculated so that the fluctuation in the longitudinal direction of chromatic dispersion was minimized.
FIG. 3 is a graph showing the variation in the longitudinal direction of the required amount of the remaining cladding as a deviation from the average value of the required amount. From this figure, it can be seen that the required amount of the remaining cladding portion varies greatly in the longitudinal direction of the glass base material.
[0022]
Next, the target outer diameter of the stretched glass rod was estimated so that the required amount of the remaining cladding portion was uniformly 80 mm in the longitudinal direction. The result is shown in FIG.
The glass base material was actually stretched based on the target outer diameter of the glass rod of FIG. The fluctuation in the longitudinal direction of the measured value of the outer diameter of the obtained glass rod is shown in FIG.
[0023]
Furthermore, an optical fiber preform was obtained by providing the remaining cladding on the outer periphery of the glass rod. Further, a dispersion-shifted optical fiber was manufactured by drawing the optical fiber preform.
FIG. 6 shows fluctuations in the longitudinal direction of chromatic dispersion of the obtained dispersion-shifted optical fiber. As is apparent from FIG. 6, by applying the present invention, a dispersion-shifted optical fiber with very little variation in chromatic dispersion could be obtained.
[0024]
FIG. 7 is a graph showing an example of fluctuation in the longitudinal direction of chromatic dispersion of a dispersion-shifted optical fiber manufactured using a conventional manufacturing method as a comparative example. A dispersion-shifted optical fiber obtained by a conventional manufacturing method has a large fluctuation in the longitudinal direction of chromatic dispersion, and has a section that deviates from a range that conforms to the standard.
[0025]
【The invention's effect】
As described above, according to the method for producing an optical fiber preform of the present invention, it is possible to easily produce an optical fiber having excellent characteristics while suppressing fluctuations in the longitudinal characteristics of the optical fiber. become.
[Brief description of the drawings]
FIG. 1 is a schematic view illustrating an example of a method for stretching a glass base material.
FIG. 2 is a schematic view for explaining another example of a method for stretching a glass base material.
FIG. 3 is a graph showing an example of fluctuations in the longitudinal direction of the required amount of the remaining cladding portion estimated from the refractive index distribution of the glass base material.
FIG. 4 is a graph showing an example of a target outer diameter of a glass rod.
FIG. 5 is a graph showing an example of measured values of the outer diameter of a glass rod after stretching.
FIG. 6 is a graph showing an example of fluctuation in the longitudinal direction of chromatic dispersion of a dispersion-shifted optical fiber manufactured using the method for manufacturing an optical fiber preform of the present invention.
FIG. 7 is a graph showing an example of fluctuation in the longitudinal direction of chromatic dispersion of a dispersion-shifted optical fiber manufactured using a conventional manufacturing method.
[Explanation of symbols]
1 ... Glass base material.

Claims (3)

A glass base material having a core part or a core part and a part of a clad part is prepared, and after the glass base material is drawn into a glass rod, the remaining clad part is provided on the outer periphery of the glass rod. In the manufacturing method of the optical fiber preform that produces the optical fiber preform by
When stretching the glass base material, the refractive index distribution of the glass base material is measured at a plurality of different positions in the longitudinal direction, and the required amount of the remaining cladding portion is calculated from these measured values. Based on the above, the glass preform is stretched so that the required amount of the remaining cladding is constant in the longitudinal direction. 2. The optical fiber preform according to claim 1, wherein a deviation of an outer diameter at each position in the longitudinal direction of the glass rod after stretching is within a range of −10 to + 10% of an average diameter of the glass rod. Manufacturing method. The required amount of the remaining clad portion is calculated so as to minimize the longitudinal variation of a predetermined optical characteristic of a target optical fiber preform. Manufacturing method of optical fiber preform.

Images