JP3741832B2 - Dispersion shifted fiber glass preform manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a glass base material by a VAD method, and more particularly to a method for manufacturing a dispersion-shifted fiber glass base material that stabilizes characteristics in a soot deposition process.
[0002]
[Prior art]
In the VAD method, an oxyhydrogen flame is generated from a burner, and a glass raw material gas such as silicon tetrachloride is fed into it to generate glass fine particles by a hydrolysis reaction, which is deposited on the lower end of the target rod. At this time, the dopant material gas is fed into the burner together with the source gas to generate glass fine particles, and the refractive index is controlled by the content of the dopant material. A columnar porous soot preform is formed by pulling up the target according to the growth of the preform formed by the deposition of the soot. The soot preform is dehydrated and sintered to form a transparent preform, which is melt-drawn to produce an optical fiber.
[0003]
In the case of a glass base material for an optical fiber, glass particles generated by hydrolyzing a source gas and a dopant material gas in an oxyhydrogen flame are deposited on the lower end of the target. The target is pulled up at a constant speed in order to stably produce the soot preform. Along with the growth of the soot preform formed by the deposition of the soot, various factors such as axial deviation and atmospheric pressure fluctuation influence the subtle position of the soot preform. The pulling speed is finely adjusted so that the positional relationship between the burner and the soot preform tip does not change due to the change in the tip position, so that the tip position is always constant. After a certain time, the deposition rate is changed by changing the silicon tetrachloride flow rate of the raw material gas, and the average pulling rate has been controlled to be constant.
[0004]
[Problems to be solved by the invention]
However, the core consists of a center core around which a side core having a refractive index lower than the center core, in yet producing the glass preform for dispersion shifted fiber around the side core is made of a cladding layer (hereinafter referred to as DSF) is conventionally Was controlled so that the position of the tip portion of the soot preform was constant by changing the raw material gas for the center core, but the amount of the raw material gas at the side core and at the boundary between the center core and the side core was not examined. For this reason, if the control of the raw material gas for the center core is performed when the raw material gas flow rate is changed, the content ratio of the dopant material from the center core boundary to the side core portion changes due to subtle changes such as flame interference. The refractive index distribution of the optical fiber changes in the longitudinal direction, causing the optical fiber characteristics such as zero dispersion wavelength to change.
[0005]
In view of the above, in the production of the DSF glass base material, the present invention changes the silicon tetrachloride gas flow rate of the raw material gas of the center core in order to keep the tip position of the soot preform constant, and the dopant material gas of the center core portion Providing a method for producing a DSF glass base material that forms a soot preform in which the refractive index distribution from the center core boundary to the side core portion is stable and the optical fiber characteristics are stable in the longitudinal direction when the flow rate is changed correspondingly Is an issue.
[0006]
[Means for Solving the Problems]
The present invention relates to a method for manufacturing an optical fiber preform in which a porous optical fiber preform is formed by depositing glass fine particles synthesized in a flame of a plurality of burners on a lower end of a target in a method for producing a DSF glass preform. In order to correct the deviation from the set speed after a certain period of time, the flow rate of the glass material gas to the center core burner is changed after a certain period of time due to the position control that keeps the positional relationship between the tip of the soot preform and the burner constant. When the content of the dopant material in the center core part is increased or decreased by changing the core material, the change in the refractive index due to the dopant material in the center core and the side core boundary part and the side core part becomes constant corresponding to this change. The supply amount of the glass raw material gas and the dopant material gas of the burner is controlled.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a longitudinal sectional view of a DSF glass base material manufacturing apparatus used in the present invention. Inside a chamber 1, an exhaust pipe 2, a soot generating cladding burner 3, a side core burner 4, a center core burner 5, and a soot The target rod 6 that is pulled up according to the growth of the soot preform 7 due to adhesion, the tip detector 8 that detects the tip position of the soot preform 7 in the chamber, and the pulling speed according to the detected tip position change. A flow rate regulator 9 (not shown) is provided for adjusting the flow rate of the source gas by an average pulling rate after a certain time, and the gas flow rate of the dopant material is adjusted accordingly. The side core burner 4 and the center core burner 5 are provided.
[0008]
As the soot preform 7 is gradually pulled up as it grows, the soot preform tip position changes slightly or the deposition efficiency changes due to various factors such as atmospheric pressure fluctuations, temperature changes, and shaft misalignment of the lifting machine. Will do. In order to always keep the positional relationship between the soot preform tip and the burner constant, it is necessary to slightly change the pulling speed with this change. However, in order to perform the pulling up at a constant speed throughout the pulling process, it is necessary to adjust the raw material gas flow rate for the purpose of correcting the deviation from the set speed after a certain time. When the raw material gas flow rate is changed, the dopant material content changes, so the dopant material content in the center core portion is changed. Here, because the delicate relationship between the flame of the center core burner and the side core burner changes with the flow rate change of the center core burner, the reason is that the refractive index distribution of the center core and side core boundary and side core changes. Become. For this reason, when the flame of the center core burner changes, the gas flow rate of the side core burner and the dopant material content in the side core so that the content of the dopant material in the side core portion in the deposition soot is constant corresponding to this change Adjust the amount. As a result, a soot preform having a constant dopant content in the center core portion and the side core portion in the longitudinal direction can be pulled up.
[0009]
Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG.
A target rod 6 is suspended and rotated in the chamber 1, and a soot preform 7 is deposited on the lower end thereof. The respective parts are deposited by the center core burner 5, the side core burner 4, and the cladding burner 3. The target bar 6 is suspended by a lifting device, and is sequentially lifted as the soot preform 7 grows.
[0010]
The tip position is always measured by the tip detector 8 attached to measure the position of the tip portion of the soot preform 7, and the lifting speed is controlled by the lifting speed controller so that the tip portion is placed at a fixed position. Is done. After a certain time, the gas flow rate of the silicon tetrachloride as the center core raw material gas is controlled in order to keep the average pulling speed constant. With this change, the gas flow rate of germanium tetrachloride as the dopant material is also controlled. Next, the gas flow rates of silicon tetrachloride as the side core raw material gas and germanium tetrachloride as the dopant material are changed in such a direction as to suppress changes in the side core due to changes in the flame of the center core burner. The gas flow rates of the source gas and the dopant material are controlled by flow rate adjusters 9 provided in the center core burner 5 and the side core burner 4, respectively.
In this way, by changing the gas flow rate of the side core portion in accordance with the gas flow rate change of the center core portion, the dopant content of the center core and side core of the glass base material becomes constant, and the refractive index distribution is stabilized. A DSF optical fiber having stable fiber characteristics in the longitudinal direction can be easily manufactured from a glass base material.
[0011]
【Example】
(Example)
Using the apparatus of FIG. 1, the center core burner 5 has a silicon tetrachloride gas of 25 cc / min, a germanium tetrachloride gas of 15 cc / min, a hydrogen gas of 1.0 liter / min, an oxygen gas of 3.0 liter / min, and an argon gas of 1.0 liter / min. The side core burner 4 is supplied with silicon tetrachloride gas 150 cc / min, germanium tetrachloride gas 40 cc / min, hydrogen gas 5.5 liter / min, oxygen gas 7.0 liter / min, and argon gas 1.5 liter / min. In addition, silicon tetrachloride gas 250 cc / min, hydrogen gas 20 liter / min, oxygen gas 20 liter / min, and argon gas 25 liter / min are supplied to the cladding burner 3 and produced by an oxyhydrogen flame hydrolysis reaction. The soot preform 7 was formed by depositing the glass fine particles on the lower end of the rotating target rod. As the soot preform grows, the target bar 6 is lifted upward, the tip detector 8 attached to the chamber measures the position of the tip of the soot preform 7, and control is performed so that the tip is always placed at a fixed position. The pulling speed is controlled by the vessel, and after a certain time, the average flow rate of pulling is made constant, so that the flow rate regulator 9 controls the gas flow rate of the silicon core tetrachloride as the center core raw material gas. The gas flow rate of the dopant material germanium tetrachloride was also controlled. Next, the flow rate regulator 9 is used to change the gas flow rate of silicon tetrachloride as the side core raw material gas and germanium tetrachloride as the dopant material in such a direction as to suppress the change in the side core due to the change in the flame of the center core burner. It was.
In this way, a porous preform having a diameter of 80 mm and a length of 1,000 mm was produced, dehydrated at 1,000 ° C., sintered and formed into a transparent glass at 1,500 ° C., and a DSF glass mother having a diameter of 40 mm and a length of 600 mm. A material was obtained. The zero dispersion wavelength of the optical fiber at each position of 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm and 500 mm in the longitudinal direction of this base material was measured. As a result, it was confirmed that there was almost no variation in the longitudinal direction with respect to the target value of 1,550 nm (dotted line).
[0012]
(Comparative example)
The silicon tetrachloride gas flow rate of the side core burner and the germanium tetrachloride gas flow rate of the dopant material were the same as in the example except that control was not performed to change the gas flow rate of the center core burner. A porous preform having a diameter of 80 mm and a length of 1,000 mm was prepared and similarly dehydrated, sintered, and converted into a transparent glass to obtain a DSF glass base material having a diameter of 40 mm and a length of 600 mm. For this base material, the zero dispersion wavelength of the optical fiber in the longitudinal direction was measured in the same way. As a result, the result indicated by the ● mark in FIG. 2 was obtained, and there was variation with respect to the target value of 1,550 nm (dotted line). I understood.
[0013]
【The invention's effect】
According to the present invention, in the manufacture of the DSF glass base material, the dopant content in the center core and side core of the base material becomes constant even if the raw material gas flow rate for the center core is changed in order to keep the average pulling rate constant. A DSF optical fiber having a stable refractive index distribution and stable characteristics in the longitudinal direction can be easily manufactured from this base material.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a DSF glass base material manufacturing apparatus used in the present invention.
FIG. 2 is a graph showing variations in zero dispersion wavelength of optical fibers in the longitudinal direction of DSF glass preforms obtained in Examples and Comparative Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Chamber 2 ... Exhaust pipe 3 ... Clad burner 4 ... Side core burner 5 ... Center core burner 6 ... Target stick 7 ... Soot preform 8 ... Tip detector 9 ... Flow controller

Claims (1)

In a method of manufacturing an optical fiber preform in which glass particles synthesized in the flame of multiple burners are deposited on the lower end of the target to form a porous optical fiber preform, the positional relationship between the tip portion of the soot preform and the burner is constant. In order to correct the deviation from the set speed after a certain period of time, the pulling speed changed with the position control is changed to change the glass raw material gas flow rate to the center core burner to change the content of the dopant material in the center core portion. When increasing or decreasing, the supply amount of the glass raw material gas and the dopant material gas of the side core burner is adjusted so that the refractive index change due to the dopant material at the center core and the side core boundary portion and the side core portion becomes constant corresponding to this change. A method for producing a dispersion-shifted fiber glass preform characterized by controlling the dispersion-shifted fiber glass preform.

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