JP3754844B2 - Manufacturing method and manufacturing apparatus for optical fiber preform - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for manufacturing an optical fiber preform by dehydrating and sintering an optical fiber porous preform deposited by, for example, a gas phase axial method (VAD method).
[0002]
[Prior art]
Conventionally, as a method of manufacturing an optical fiber preform by a gas phase axis method (VAD method), while rotating a starting base material such as a quartz rod, silicon tetrachloride (SiCl ₄ ) as an optical fiber material and a refractive index are rotated from below. A dopant such as germanium tetrachloride (GeCl ₄ ) necessary for control is sprayed together with H ₂ and O ₂ gas from the burner for the core, and a porous base material for the core is deposited in the axial direction of the quartz rod and directed toward the periphery Then, silicon tetrachloride (SiCl ₄ ) or the like as an optical fiber raw material is sprayed together with H ₂ and O ₂ gas from the cladding burner to deposit the porous preform for the cladding, and the deposited optical fiber porous preform is heated. A method is known in which an optical fiber preform is manufactured by dehydration and sintering and forming into a transparent glass.
[0003]
Here, when the optical fiber porous preform is dehydrated and sintered, the optical fiber porous preform is put into a quartz furnace core tube of a heating furnace, and a gas having a dehydrating action such as chlorine is introduced into the furnace core tube. At the same time as the introduction, a method of dehydration and sintering may be employed by heating with a heater arranged around the furnace core tube. In such a technique, impurities are contained in the furnace core tube. In general, a temperature measuring device is attached to the outer wall of the furnace core tube, and the temperature is controlled based on the temperature measured by this temperature measuring device. It is carried out.
[0004]
[Problems to be solved by the invention]
However, when a temperature measuring device is attached to the outer wall of the furnace core tube as described above and temperature management is performed, for example, even if the furnace core tube deteriorates and the internal processing temperature changes slightly, the change is not detected. Even if the temperature is controlled with a temperature measuring instrument on the outer wall, especially when an old furnace core tube is replaced with a new one, the degree of change in the internal processing temperature may increase. There has been a problem in that the optical fiber preform has a dispersion in characteristics such as the refractive index distribution.
[0005]
The present invention has been made in view of the above-mentioned problems. In producing an optical fiber preform by dehydrating and sintering an optical fiber porous base material, it accompanies changes in the actual processing temperature of the dehydration and sintering processes. An object is to prevent variation in characteristics such as a refractive index distribution.
[0006]
[Means for Solving the Problems]
To achieve the above object, according to the present invention, in claim 1, after depositing an optical fiber porous preform in the axial direction of the starting preform, the optical fiber porous preform is heated at a predetermined temperature to be dehydrated and baked. In the manufacturing method in which the optical fiber preform is manufactured by repeating the steps and this process is repeated, the refractive index of the manufactured optical fiber preform is measured, and the difference between the refractive index and the target refractive index is obtained. The difference is converted into a correction value for the heating temperature of the optical fiber porous preform, and the heating temperature of the optical fiber porous preform in the next manufacturing process is corrected with the correction value.
[0007]
By measuring the refractive index of the optical fiber preform manufactured in the previous process for the optical fiber preform manufactured in such a process, the change in the actual processing temperature during dehydration and sintering is read. In the manufacturing process, the actual processing temperature is corrected to be constant so that stable characteristics can be obtained.
Even if the furnace core tube is deteriorated by such a method or the furnace core tube is replaced and the actual processing temperature is changed, the actual temperature cannot be detected by the temperature measuring means. Therefore, it is possible to manufacture a stable optical fiber preform in which the change in characteristics of each lot is suppressed and the change in characteristics is small.
The refractive index measured here is not particularly limited, but is preferably the refractive index difference Δn (%) obtained by measuring the refractive index distribution of the optical fiber preform.
[0008]
According to the second aspect of the present invention, the heating temperature of the optical fiber porous preform is corrected when the difference between the measured refractive index and the target refractive index exceeds a predetermined value.
That is, if correction is made every time for each manufacturing process, it is possible to manufacture an optical fiber preform with more stable characteristics. However, on the other hand, a complicated equipment configuration is likely to occur, and the equipment cost also increases.
Therefore, it is more practical and economical if the heating temperature is corrected when the difference between the measured refractive index and the target refractive index exceeds a predetermined value, and the refractive index is controlled within a desired range. It is.
[0009]
According to a third aspect of the present invention, as an optical fiber preform manufacturing apparatus, a heating furnace for heating, dehydrating and sintering an optical fiber porous base material deposited in the axial direction of the starting base material, and the heating furnace Find the difference between the measured refractive index and the target refractive index, and the temperature controller that adjusts the heating temperature of the fiber, the preform analyzer that measures the refractive index of the dehydrated and sintered optical fiber preform, Is converted into a correction value for the heating temperature of the heating furnace, and then a sequencer is provided for instructing the temperature regulator to the heating temperature corrected by this correction value.
[0010]
Then, the refractive index of the manufactured optical fiber preform is measured by a preform analyzer, the difference from the target refractive index is obtained by a sequencer, converted into a correction value for the heating temperature, and a command is issued to the adjuster. The heating temperature of the next manufacturing process is corrected.
At this time, it is also possible to correct the heating temperature when the difference in refractive index exceeds a predetermined management width.
[0011]
According to a fourth aspect of the present invention, there is provided a heating furnace comprising: a furnace core tube in which an optical fiber porous preform is accommodated; heating means disposed around the furnace core tube; and temperature measurement attached to an outer wall of the furnace core tube It consisted of a vessel.
By adopting such a configuration, it is possible to simply configure using existing equipment.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings.
Here, FIG. 1 is a schematic configuration diagram of the manufacturing apparatus.
[0013]
The optical fiber preform manufacturing apparatus according to the present invention uses silicon tetrachloride (SiCl ₄ ) as an optical fiber raw material from a core burner with respect to a starting base material S such as a quartz rod, and a dopant for controlling the refractive index. A porous base material for the core is deposited in the axial direction by spraying germanium tetrachloride (GeCl ₄ ) or the like together with H ₂ and O ₂ gases, and silicon tetrachloride as an optical fiber raw material is applied from the cladding burner toward the periphery. (SiCl ₄ ) or the like is sprayed together with H ₂ and O ₂ gases to deposit a porous base material for cladding, and then an optical fiber porous base material comprising the core porous base material and the porous base material for cladding. 1 is constructed as an apparatus for producing an optical fiber preform by dehydration and sintering, and as shown in FIG. 1, the optical fiber porous preform Sf formed in the axial direction of the starting preform S is heated. You A heating furnace 1 is provided.
[0014]
The heating furnace 1 includes a furnace core tube 2 that can accommodate the optical fiber porous base material Sf, a heater 3 as a heating means disposed around the furnace core tube 2, and the furnace core tube 2. The thermocouple 4 is provided as a temperature measuring device attached to the outer wall of the gas. The furnace core tube 2 is provided with a gas introduction part 5 for introducing a gas having a dehydrating action such as chlorine, and the introduced gas is discharged. A gas discharge unit 6 is provided.
[0015]
The heating temperature of the heater 3 can be adjusted by a temperature regulator 7, and the temperature regulator 7 is connected to a sequencer 8.
The apparatus is also provided with a preform analyzer 9 for measuring the refractive index or refractive index distribution of the manufactured optical fiber preform so that the measured refractive index data can be sent to the sequencer 8. Yes.
At this time, the refractive index to be measured is not particularly limited, but in the embodiment, the refractive index distribution of the optical fiber preform is measured, and the refractive index difference Δn (%) obtained therefrom is obtained.
Here, the refractive index difference Δn (%) indicates a difference in refractive index between the core base material and the clad base material, which is expressed by multiplying this difference by 100 (%).
[0016]
In the manufacturing apparatus as described above, after the optical fiber preform Sf composed of the core porous preform and the cladding porous preform in the axial direction of the starting preform S is produced in the porous preform producing apparatus (not shown). Then, the optical fiber preform Sf is set in the furnace core tube 2 and heated by the heater 3 while introducing a gas having a dehydrating action into the furnace core tube 2, dehydrated and sintered to form a transparent glass. An optical fiber preform having a base material and a clad base material is manufactured, and a series of manufacturing processes are repeated to manufacture a large number of optical fiber preforms. The refractive index distribution of the core base material measured is measured by the preform analyzer 9 and this measurement data is sent to the sequencer 8 to obtain the refractive index difference Δn (%), and the difference from the target refractive index difference Δn (%) is calculated. Find the difference in refractive index difference, Correction is performed by converting the correction value to the heating temperature of the heater 3 corresponding to the minute.
Therefore, a calibration curve representing the relationship between the difference between the measured refractive index difference Δn (%) and the target refractive index difference Δn (%) and the correction value of the heating temperature is defined.
[0017]
At this time, the correction of the heating temperature may be performed every time for each production, but in the present embodiment, the heating temperature is corrected when the difference in the refractive index difference exceeds a predetermined management width.
[0018]
【Example】
Next, examples and comparative examples of the present invention will be described.
(Example)
An optical fiber preform is manufactured by replacing the furnace core tube 2 with a new one using the apparatus described above, and the refractive index distribution of the core preform is measured by the preform analyzer 9 to obtain the refractive index difference Δn (%). As a result, as shown in FIG. 2B, the refractive index difference Δn (%) was increased by 0.01% compared to the case before the replacement, so that the sintering temperature was changed as shown in FIG. The temperature was changed from 1200 ° C. to 1250 ° C., and the optical fiber preform of the next lot was manufactured.
As a result, the refractive index difference Δn (%) could be adjusted to the target value of 0.36.
[0019]
Moreover, when manufactured 13 times using the same furnace core tube 2, the refractive index difference Δn (%) decreased slightly, and in the 13th time, the refractive index difference Δn (%) exceeded ± 0.002% of the control range. When the sintering temperature was reduced by 5 ° C., the refractive index difference Δn (%) returned to the control range.
[0020]
(Comparative example)
For comparison, when the furnace core tube 2 was replaced as before and sintered at the same temperature until the furnace core tube 2 cracked, the refractive index difference Δn (%) changed with time as shown in FIG. An optical fiber preform with stable characteristics could not be manufactured.
From this result, the effectiveness of the present invention was confirmed.
[0021]
The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
For example, the optical fiber raw material, the kind of dopant, etc. are arbitrary.
[0022]
【The invention's effect】
As described above, the method for manufacturing an optical fiber preform according to the present invention measures the refractive index of the manufactured optical fiber preform and determines the difference between the refractive index and the target refractive index. This difference is converted into a correction value for the heating temperature of the optical fiber porous base material to correct the heating temperature in the next manufacturing process, so that even if the actual processing temperature of the dehydration and sintering processes changes. This can be corrected, and an optical fiber preform with stable characteristics can be manufactured.
At this time, as described in claim 2, the correction of the heating temperature of the optical fiber porous preform is performed when the difference between the measured refractive index and the target refractive index exceeds a predetermined value. It can be managed within a desired range, and is more practical and economical.
[0023]
Further, as an optical fiber preform manufacturing apparatus, as in claim 3, a heating furnace for heating and dehydrating and sintering an optical fiber porous preform, and a temperature for adjusting the heating temperature of the heating furnace After converting the difference between the measured refractive index and the target refractive index into a correction value for the heating temperature after adjusting the conditioner, the preform analyzer that measures the refractive index of the dehydrated and sintered optical fiber preform, If a sequencer for instructing the temperature adjustment to the correction temperature is provided, the optical fiber preform can be manufactured by the above method.
According to a fourth aspect of the present invention, the heating furnace is attached to the furnace core tube in which the optical fiber porous preform is accommodated, the heating means disposed around the furnace core tube, and the outer wall of the furnace core tube. If it comprises a temperature measuring device, it can be simply constructed using existing equipment.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a manufacturing apparatus according to the present invention.
2A and 2B are measurement data when manufactured by the manufacturing method of the present invention, where FIG. 2A is a graph showing the relationship between the sintering temperature (vertical axis) and the number of furnace core tubes used (horizontal axis), and FIG. It is a graph showing the relationship between a rate difference (vertical axis) and the use frequency (horizontal axis) of a furnace core tube.
FIG. 3 is a graph showing a change in refractive index difference when manufactured by a conventional manufacturing method, where the vertical axis indicates the refractive index difference and the horizontal axis indicates the number of times the furnace core tube is used.
[Explanation of symbols]
1 ... heating furnace, 2 ... furnace core tube,
3 ... heater, 4 ... thermocouple,
5 ... Gas introduction part, 6 ... Gas discharge part,
7 ... Temperature controller, 8 ... Sequencer,
9 ... Preform analyzer,
S: Starting base material, Sf: Optical fiber base material.

Claims (4)

After depositing an optical fiber porous preform in the axial direction of the starting preform, this optical fiber porous preform is heated at a predetermined temperature, dehydrated and sintered to produce an optical fiber preform. The manufacturing method is to repeat the measurement, the refractive index of the manufactured optical fiber preform is measured, the difference between this refractive index and the target refractive index is obtained, and this difference is calculated as the heating temperature of the optical fiber porous preform. And a heating temperature of the optical fiber porous preform in the next manufacturing process is corrected with the correction value. 2. The method of manufacturing an optical fiber preform according to claim 1, wherein the correction of the heating temperature of the optical fiber porous preform is performed when the difference between the measured refractive index and the target refractive index exceeds a predetermined value. An optical fiber preform manufacturing method characterized by the above. A heating furnace for heating, dehydrating and sintering the optical fiber porous base material deposited in the axial direction of the starting base material, a temperature controller for adjusting the heating temperature of the heating furnace, and dehydrating and sintering The difference between the measured refractive index and the target refractive index is calculated and the difference is converted into a correction value for the heating temperature of the heating furnace. An apparatus for manufacturing an optical fiber preform, comprising: a sequencer that instructs the temperature regulator to correct a heating temperature corrected with a correction value. The apparatus for manufacturing an optical fiber preform according to claim 3, wherein the heating furnace includes a furnace core tube in which the optical fiber porous preform is accommodated, and a heating unit disposed around the furnace core tube. An apparatus for manufacturing an optical fiber preform, comprising a temperature measuring device attached to the outer wall of the furnace core tube.

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