JPH08198634A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE: To prevent the fluctuation in outside diameter and striae which occur in parts where a deposition density is not uniform and on the surface of the outside diameter by allowing the pulling up speed of a seed rod at the time of depositing core soot to follow up a change in a deposition growth speed with good accuracy. CONSTITUTION: The front end image of a porous optical fiber preform 4 projected by a CCD camera 11 is taken-in by a digital signal at every prescribed time and the growth speed of the porous optical fiber preform 4 is calculated from the reference position of the glass particulate deposition and the front end position of the glass particulate deposition of the taken in porous optical fiber preform 4. The growth acceleration of the porous optical fiber preform 4 per unit time is calculated from this growth speed and the growth speed of the previous time. The previously calculated growth speed is subjected to D/A conversion and the speed of a motor 9 for pulling up is set. The previously calculated acceleration is subjected to D/A conversion and the speed change gradient until the above mentioned set speed of the motor 9 for pulling up is attained is changed by changing the capacity of the capacitor C of an RC circuit. The seed rod 1 is pulled up according to this growth acceleration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an optical fiber preform which produces glass fine particles by a flame hydrolysis reaction and deposits them on a starting material to obtain a porous glass body, and more particularly to a method for producing a core soot density. The present invention relates to a method for manufacturing an optical fiber preform that can be uniformly deposited in the longitudinal direction of the material.

[0002]

2. Description of the Related Art Generally, in an optical fiber, light propagates in the core while being totally reflected by the boundary surface between the core and the clad of the optical fiber. Conventionally, the manufacturing method of such an optical fiber preform has been based on a shafting method (VAD method Vapor Phase).
Axial Deposition) is well known, and the manufacturing method of the optical fiber preform by this axial attachment method is as follows: oxyhydrogen burner to SiCl ₄ , GeCl ₄ , POCl ₃ , BBr.
₃ is sent out, and SiO ₂ and Ge are attached to the tip of the seed quartz rod.
Soot such as O ₂ and B ₂ O ₃ is deposited and the quartz rod is pulled up while rotating to grow a porous preform containing a large amount of air.

A conventional porous optical fiber preform is manufactured by the VAD method as shown in FIG. 10, and is carried out as follows. That is, a seed rod 1 composed of a glass seed rod made of pure quartz or Ge-containing quartz is suspended from a seed rod lifting mechanism 10, and a core soot provided opposite the lower end of the seed rod 1 is provided. A flame 3 is emitted from the burner 2. The core soot burner 2 is arranged below the seed rod 1 and is supported by a supporting rod so that it can be maintained at a constant height. The gas of SiCl ₄ as a glass raw material and GeCl ₄ as a dope raw material are provided. Hydrogen source gas
It is supplied together with a combustion gas such as oxygen, and a flame 3 containing glass particles is emitted from the core soot burner 2.
In the flame 3 containing the glass particles, a hydrolysis reaction occurs, SiO ₂ is produced, and the SiO ₂ soot is generated by the seed rod 1.
Is deposited on the tip (lower end) of the glass to form a glass particle deposition layer. In this way, the core soot burner 2 deposits glass particles on the lower end of the seed rod 1 to form the porous optical fiber preform 4, and the state of this deposition growth proceeds toward the lower end of the porous optical fiber preform 4. And a light receiver 6 which receives light when the light emitted from the light projector 5 is not blocked by the lower end of the porous optical fiber preform 4. The detection by the light receiver 6 is taken in at a constant cycle (interval of t seconds) t _{1 to} t _{n as shown} in FIG.

Then, the glass particles are deposited on the lower end of the seed rod 1 by the core soot burner 2 to form the porous optical fiber preform 4, and the porous optical fiber is sampled at time t ₁ as shown by G in FIG. When the light emitted from the light projector 5 is blocked by the lower end of the base material 4, the light receiver 6
Since no light is detected during detection, no detection signal is output to the controller 7, and the controller 7 sends an operation signal to the motor driver 8. As a result, the motor driver 8 supplies electric power to the pulling motor 9 that pulls up the seed rod pulling mechanism 10, and turns on the pulling motor 9 for a certain period of time as shown in FIG. When the pulling motor 9 is turned on, the seed rod pulling mechanism 10 pulls up, and the porous optical fiber preform 4 is pulled up at a constant rate and at a constant rate. At the time of the next sampling (after t seconds), at t ₂ as shown by G in FIG. 11, the light emitted from the projector 5 by the lower end of the porous optical fiber preform 4 is shown in FIG.
When the light is blocked by the optical receiver 6, no signal is output from the optical receiver 6 to the controller 7 because the light is not detected by the optical receiver 6, and the porous optical fiber preform 4 is operated by the same operation as described above.
Is raised. Even when the porous optical fiber base material 4 is pulled up, glass core particles are deposited on the lower end of the seed rod 1 by the core soot burner 2 to form the porous optical fiber base material 4, which is shown in FIG. As shown in G of FIG. 1G, the light emitted from the light projector 5 is not blocked by the lower end of the porous optical fiber preform 4 at the sampling time t ₄ , and the light receiver 6 is not blocked.
If it is received by the above, the pulling motor 9 is kept OFF as shown in FIG. 11, and the porous optical fiber preform 4
Will not be raised. As described above, according to the conventional method for manufacturing the optical fiber preform, the state of the lower end of the porous optical fiber preform 4 is monitored at a constant cycle, and the seed rod 1 is set every time the lower end of the porous optical fiber preform 4 is detected. When the lower end of the porous optical fiber preform 4 is no longer detected, the porous optical fiber preform 4 is not pulled up, so that the seed rod pulling mechanism 10 is turned on and off at fixed sampling intervals. The operation was repeated by repeating the manufacture of the porous optical fiber preform 4.

In recent years, for example, Japanese Unexamined Patent Publication No. 6-92.
As shown in Japanese Patent Publication No. 666, the seed rod 1 is continuously pulled up by the seed rod pulling mechanism 10 to manufacture the optical fiber preform 4, and at this time, the lower end of the porous optical fiber preform 4 causes the light projector 5 to receive light. There is disclosed a method of controlling the pulling speed of the seed rod 1 by comparing the light passing / shielding state of light with the vessel 6 and the previous light passing / shielded state.

[0006]

However, in all of the conventional methods for producing an optical fiber preform by the on / off method, the lower end of the porous optical fiber preform 4 is irradiated with laser light and the light is transmitted therethrough. Since the growth state of the porous optical fiber preform 4 due to the deposition of glass particles by light shielding is detected, the detection accuracy, that is, the control accuracy is limited by the size of the spot diameter of the laser light to be irradiated, and the accuracy is controlled. However, it is difficult to control the seed rod withdrawal speed accurately to follow the growth rate, and it is difficult to prevent the fluctuation of the outer diameter and the striae which occur on the portion where the deposition density is not uniform or the outer diameter surface.

An object of the present invention is to make the seed rod pull-up speed during core soot deposition accurately follow changes in the deposition growth rate by incorporating the deposition growth rate by an image processing and measuring device and feedback control by a D / A conversion unit. ,
It is intended to prevent an outer diameter variation and striae that occur on a portion where the deposition density is not uniform or the outer diameter surface.

[0008]

According to the present invention, a raw material gas such as SiCl ₄ , GeCl ₄ or the like is mixed with a combustion gas such as hydrogen or oxygen from a core soot burner, radiates in a flame state, and is generated by flame hydrolysis. In a method of manufacturing an optical fiber preform by obtaining a porous optical fiber preform by an axial method in which glass particles are deposited and grown on a seed bar while pulling up a seed bar, a CCD camera is directed toward the tip of the porous optical fiber preform. The front end image of the porous optical fiber preform which is fixed and photographed by the CCD camera is digitally processed and taken in every predetermined time, and the glass fine particle deposition reference position and the glass fine particle deposition front end position of the taken porous optical fiber preform From the digital calculation of the growth rate of the porous optical fiber base material,
The speed of the pulling motor is set on the basis of the calculated growth rate, and the porous optical fiber per unit time is calculated from the calculated growth rate and the growth rate of the porous optical fiber base material previously stored and stored. RC for digitally processing the growth acceleration of the base material, D / A converting the calculated growth acceleration, and smoothing and supplying electric power based on the growth acceleration
By changing the capacitance of the circuit capacitor to change the speed change gradient until reaching the set speed of the pulling motor,
The seed rod is pulled up according to the growth acceleration.

[0009]

According to the present invention, the front end image of the porous optical fiber preform, which is picked up by the CCD camera fixed toward the front end of the porous optical fiber preform, is digitally processed and taken in every predetermined time. . Then, the growth rate of the porous optical fiber preform is calculated from the tip image position of the porous optical fiber preform taken every predetermined time and the preset glass particulate deposition reference position, and this is calculated. The speed of the pulling motor for pulling up the seed rod is set based on the growth rate of the porous optical fiber preform. The calculated growth rate of the porous optical fiber preform is compared with the previously calculated growth rate of the porous optical fiber preform to calculate the growth acceleration of the porous optical fiber preform per unit time. To do. Convert the calculated digital value of growth acceleration into an analog value,
Based on the converted analog value of the growth acceleration, a capacitor corresponding to the analog value of the growth acceleration is selected from a plurality of capacitors of different capacities that are selectably connected and constitute an RC circuit that smoothes and supplies electric power. The capacitor is selected and connected to control the electric power supplied to the take-up control motor so that the pulling speed of the seed rod is raised at the same change gradient speed as the growth acceleration.

When the pulling speed of the seed rod is controlled as described above, if there is a variation in the detected growth rate as shown in FIG. 9, a control method for ON / OFF control as shown in FIG. 10 is used. It is possible to perform control that accurately follows the actual growth rate. By doing so, the growth acceleration of the porous optical fiber preform per unit time obtained by the digital value is converted into an analog value, and the capacitance of the capacitor forming the RC circuit is selected by this analog value. , The seed rod can be pulled up according to the growth acceleration by changing the speed change gradient of the pulling motor until it reaches the set speed, and the seed rod pulling speed during core soot deposition can be accurately adjusted to the change in the deposition growth rate. It is possible to follow well, and it is possible to prevent fluctuations in the outer diameter and striae that occur in the portion where the deposition density is not uniform and the outer diameter surface.

[0011]

Embodiments of the present invention will be described below. FIG. 1 shows an embodiment of a method for manufacturing an optical fiber preform according to the present invention. In the figure, the present embodiment is different from the conventional example shown in FIG. 10 in that the conventional example shown in FIG. 10 detects the deposition growth state of the glass fine particles at the tip (lower end) of the seed rod 1 with the projector 5 and the light receiving device. In the present embodiment, the CCD camera 11 is used to capture an image of the tip of the porous optical fiber preform 4 and the CCD camera 1 is used.
1, the front end image of the porous optical fiber preform 4 imaged by 1 is digitally processed, taken in every predetermined time, and digitally measured. In this embodiment, in which the growth state of the porous optical fiber preform 4 is detected by image input as described above, the CCD camera 11 is used as shown in FIG.
The image processing and measurement device 12, the growth rate / growth acceleration calculation unit 13, and the D / A conversion unit 14 are inserted and connected.

CCD (Charge Coupled Device)
As the camera 11 is commercialized as a home video camera, it creates a large number of light-sensitive elements on a silicon substrate, converts the light image formed here into an electric signal quantity, and transfers it sequentially. It is a camera that uses a MOS structure solid-state imaging device to obtain an image signal. An image processing and measuring device 12 is connected to the CCD camera 11, and the tip of the porous optical fiber preform 4 as shown in FIG. 2 obtained by the CCD camera 11 is sent to the image processing and measuring device 12. The image processing / measuring device 12 digitally processes the tip image of the porous optical fiber preform 4 as shown in FIG. 2 sent from the CCD camera 11 to set the reference position of B shown in FIG. The value at the tip of the optical fiber preform 4 is obtained as a digital value and sent to the growth rate / growth acceleration calculation unit 13. The measurement speed by the image processing measuring device 12 is about μm to several tens of μm using a general image processing measuring device (about 520 * 480 pixels), and a constant interval t seconds (for example, 3 seconds).
The growth rate V is obtained based on the growth displacement ΔL in (sec.

Growth rate / growth acceleration calculation unit 13
Is calculated by calculating the deposition growth displacement ΔL from the value of the reference position B shown in FIG. 2 sent from the image processing and measurement device 12 and the value of the tip position of the detected porous optical fiber preform 4. The growth rate V is calculated from this growth displacement ΔL, and the speed of the pulling motor 9 that drives the seed rod pulling mechanism 10 is set by this growth rate V. In this way, the speed of the pulling motor 9 is set by the detected growth speed V, and the pulling motor 9 is driven at this set speed. Then, if there is no change in the growth rate of the glass particles, that is, if the growth rate and the pulling rate are the same, the tip position of the porous optical fiber preform 4 does not change as shown in FIG. The speed changes with time as shown by the growth rate C of the glass particles shown in FIG. Therefore, at the next sampling (after 3 seconds),
The growth displacement ΔLa from the reference position B as shown by D in FIG. 5 to the previous tip position of the porous optical fiber preform 4 is more than the growth displacement ΔLa as shown by E in FIG. When the growth displacement ΔLb to the tip position of the material 4 is larger than the growth displacement ΔLa from the reference position B as shown by D in FIG. 5 to the tip position of the previous porous optical fiber preform 4. In some cases, however, the growth displacement ΔLc from the reference position B to the tip position of the porous optical fiber preform 4 is smaller as shown by F in FIG.

Therefore, it is necessary to periodically sample the tip position of the porous optical fiber preform 4 to obtain the growth rate V with respect to the reference position B, and set the speed of the pulling motor 9 each time. Growth of the porous optical fiber preform 4 is periodically delayed by sampling the tip position of the porous optical fiber preform 4 to obtain the growth rate V and setting the speed of the pulling motor 9 each time. The seed rod pulling mechanism 10 is driven so that the seed rod 1 is pulled up following the speed, and the tip position of the porous optical fiber preform 4 changes from the reference position B to a fixed position. Although it is possible to obtain the porous optical fiber preform 4 having a uniform core soot density to some extent, it is not possible to obtain the porous optical fiber preform 4 having a desired core soot density. Therefore, in the growth rate / growth acceleration calculation unit 13, first, when the first sampling is performed, digital processing is performed by the image processing measurement device 12 to obtain the value of the reference position B and the value of the tip position of the porous optical fiber preform 4. And the growth displacement / L1 is calculated by the growth rate / growth acceleration calculation unit 13,
The growth rate V1 is obtained based on this growth displacement ΔL1. Then, at the next sampling, the value of the reference position B and the value of the tip position of the porous optical fiber preform 4 are obtained by digital processing by the image processing measuring device 12, and the growth displacement ΔL2 is calculated by the growth rate / growth acceleration calculation unit 13. Is calculated, and the growth rate V2 is obtained based on this growth displacement ΔL2. This 2
The acceleration a is obtained from the two growth rates V1 and V2 as a = (V2-V1) / t, and the value of this acceleration a is calculated by the D / A conversion unit 14
The digital value is converted into an analog value and then sent to the motor driver 8.

As shown in FIG. 6, the motor driver 8 is a power supply device for driving the pulling motor 9, and includes a motor speed setting device 81 and an RC circuit 82. The motor speed setting device 81
The speed of the pulling motor 9 that drives the seed rod pulling mechanism 10 is set by a control signal that converts the growth rate signal output as a digital value from the growth acceleration calculation unit 13 into an analog value by the D / A conversion unit 14 and outputs the analog value. To do. The RC circuit 82 smoothes the power supplied from the power supply connected to the input side and supplies the smoothed power to the pulling motor 9. R is a resistor, C1 to C3 are capacitors, and a plurality of capacitors C1 to C1. C3 (three in the present embodiment) is configured to be appropriately selected according to the value of the acceleration a D / A converted by the D / A conversion unit 14. In the method of selecting the capacitors C1 to C3 based on the value of the acceleration a, when the value of the acceleration a is large (the growth acceleration gradient is large), a capacitor having a small capacity is selected and the value of the acceleration a is small (the growth acceleration gradient is large). Is small), a capacitor with a large capacitance is selected. The values of the resistor R and the capacitors C1 to C3 of the RC circuit 82 are set, for example, to 1 kΩ for the resistor R, 0.3 μF for the capacitor C1, 1 μF for the capacitor C2, and 2.4 μF for the capacitor C3. By thus selecting the capacitors C1 to C3 of the RC circuit 82 with the value of the acceleration a, as shown in FIG. 7, with respect to the pulling speed D of the seed rod 1 matched with the growth speed of the porous optical fiber preform 4, Pulling motor 9 for driving seed rod pulling mechanism 10
7 is controlled by a rising slope or a falling slope based on the acceleration a, as shown by E in FIG. The image processing / measuring device 12, the growth rate / growth acceleration calculation unit 13, and the D / A conversion unit 14 can be configured by a microcomputer. In this case, the motor driver 8 is controlled by the microcomputer. .

Next, a method of manufacturing the optical fiber preform according to this embodiment will be described with reference to the control flowchart of FIG. The tip of the seed rod 1 is aligned with the position of the reference position B on the screen captured by the CCD camera 11, and then the image processing / measuring device 12 and the growth rate / growth acceleration calculation unit 13 are turned on. Then, first, in step 20, the measurement speed is 3 when a predetermined time (the general image processing measurement device (about 520 * 480 pixels) is used for the image processing measurement device 12) from the previous data acquisition (previous sampling). Second)) has elapsed. With respect to the calculation of this predetermined time, the initial time is the time when the core soot burner 2 starts to radiate the flame 3 containing glass particles at the tip of the seed rod 1. In step 20, after waiting for a predetermined time, in step 21, the tip image of the porous optical fiber preform 4 imaged by the CCD camera 11 is digitally processed by the image processing / measuring device 12 and taken in, Then, the size of the tip of the porous optical fiber preform 4 on which the glass particles are deposited and grown is calculated, and in step 22, the value of the tip position of the porous optical fiber preform 4 and the preset reference position B are set. Are compared to determine whether the value of the tip position of the porous optical fiber preform 4 is larger than the value of the preset reference position B.
The fact that the value of the tip position of the porous optical fiber preform 4 is larger than the value of the preset reference position B means that the porous optical fiber is faster than the speed at which the seed rod pulling mechanism 10 is driven to pull up the seed rod 1. This means that the growth rate of the base material 4 (deposition of glass particles on the tip of the seed rod 1) is faster.

In this step 22, the value of the tip position of the porous optical fiber preform 4 and the preset reference position B are set.
When it is determined that the value of the tip position of the porous optical fiber preform 4 is larger than the value of the reference position B set in advance, in step 23, the porous optical fiber preform taken from the CCD camera 11 is compared. The deposition rate (+) ΔL is calculated by the growth rate / growth acceleration calculation unit 13 from the value of the tip position of 4 and the value of the preset reference position B, and the growth rate (+) ΔL is used to calculate the growth rate ( +) V is calculated. When the growth rate (+) V is calculated in this step 23, the calculated growth rate (+) V is stored as a value of V2 in a memory area (RAM when a microcomputer is used) in step 24, and
The D / A conversion unit 14 converts the digital value into an analog value and outputs it to the motor speed setting device 81.
When the growth rate V calculated in step 24 is output to the motor speed setting device 81, it is determined in step 25 whether or not the previous growth rate value V1 is stored. In this step 25, the previous growth rate value V
If it is determined that 1 is not stored, the process returns to step 20 and, after a lapse of a predetermined time, the value of the tip position of the porous optical fiber preform 4 imaged by the CCD camera 11 and the reference position B set in advance. Capture growth rate values from.

If it is determined in step 25 that the previous growth rate value V1 has been stored, then in step 26, from the values of the growth rate V2 calculated this time and the growth rate V1 stored in the memory area, Acceleration a
The value of is calculated by the calculation a = (V2-V1) / t. When the value of the acceleration a is calculated in step 26, the calculated growth acceleration a at the tip of the porous optical fiber preform 4 is calculated as D in step 27.
A / A conversion unit 14 converts into an analog value, and a capacitor C that forms an RC circuit according to the analog value.
Select values 1 to C3 to connect. This capacitor C1
The rising gradient of the pulling motor 9 is determined by selecting the values of C3 to C3, and the speed of the pulling motor 9 is quickly converged to the set speed. Then, in step 28, it is determined whether or not the manufacture of the porous optical fiber preform 4 is completed, and if it is completed, this control flowchart is ended, and if not completed, the process returns to step 20.

Further, the fact that the value of the tip position of the porous optical fiber preform 4 in step 22 is smaller than the value of the preset reference position B means that the seed rod pulling mechanism 10 is driven and the seed rod 1 is moved. Growth of porous optical fiber preform 4 than the pulling speed (deposition of glass particles on the tip of seed rod 1)
It means that the speed is slower. In this step 22, the value of the tip position of the imported porous optical fiber preform 4 is compared with the preset reference position B, and the value of the tip position of the porous optical fiber preform 4 is set in advance. If it is determined that the value is smaller than a certain reference position B, in step 29, the growth rate / growth acceleration is calculated from the value of the tip position of the porous optical fiber preform 4 taken in from the CCD camera 11 and the preset value of the reference position B. The calculation unit 13 calculates and obtains the deposition growth displacement (−) ΔL, and calculates the growth rate (−) V from the growth displacement (−) ΔL. When the growth rate (-) V is calculated in step 29, the calculated growth rate (-) V is calculated in step 30.
Is stored in a memory area (RAM when a microcomputer is used) and the D / A conversion unit 1
The digital value is converted into an analog value by 4 and output to the motor speed setting device 81. When the growth rate V calculated in step 30 is output to the motor speed setting device 81, it is determined in step 31 whether or not the previous growth rate value V1 is stored. If it is determined in step 31 that the previous growth rate value V1 is not stored, the process returns to step 20 and after the elapse of a predetermined time, the value of the tip position of the porous optical fiber preform 4 imaged again by the CCD camera 11 and The growth rate value is fetched from a preset reference position B.

If it is determined in step 31 that the previous growth rate value V1 has been stored, then in step 32, from the values of the growth rate V2 calculated this time and the growth rate V1 stored in the memory area, Acceleration a
The value of is calculated by performing the calculation a = (V2-V1) / t. The acceleration a calculated in step 32 has a negative value, which means a falling slope (deceleration slope). When the value of the acceleration a is calculated in step 32, the calculated growth acceleration a of the tip of the porous optical fiber preform 4 is converted into an analog value by the D / A conversion unit 14 in step 33, and the calculated acceleration a is calculated according to the analog value. The values of the capacitors C1 to C3 forming the RC circuit are selected and connected.
By selecting the values of the capacitors C1 to C3, the falling slope of the pulling motor 9 is determined.
The speed of is converged to the set speed early. Then, in step 28, it is determined whether or not the manufacture of the porous optical fiber preform 4 is completed, and if it is completed, this control flowchart is ended, and if not completed, the process returns to step 20.

[0021]

According to the present invention, since the pulling rate of the seed rod 1 can be controlled so as to accurately follow the growth rate of the core soot (glass fine particles), the porous soot density of the porous optical fiber preform 4 can be controlled. It is possible to prevent an outer diameter variation and striae that occur on the non-uniform portion and the outer diameter surface of the porous optical fiber preform 4, and continuously grow a core soot of uniform density at the tip of the seed rod 1. You can

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a method for manufacturing an optical fiber preform according to the present invention.

FIG. 2 is a view showing an image of a front end portion of a porous optical fiber preform captured by the CCD camera shown in FIG.

FIG. 3 is a diagram showing a converged state of a tip position of a porous optical fiber preform to a reference position when a deposition rate of glass particles is constant.

FIG. 4 is a diagram showing a deposition growth rate of glass particles with respect to time.

FIG. 5 is a diagram comparing the growth displacement of the porous optical fiber preform at the previous sampling with the growth displacement of the porous optical fiber preform at the current sampling.

FIG. 6 is a detailed circuit diagram of the motor driver shown in FIG.

FIG. 7 is a diagram showing rise (fall) speed control of a pulling motor corresponding to a deposition growth rate.

8 is a control flowchart of a method for manufacturing the optical fiber preform shown in FIG.

FIG. 9 is a diagram showing a sampling state of a growth rate of a porous optical fiber preform.

FIG. 10 is a schematic view showing a conventional method for manufacturing an optical fiber preform.

11 is a diagram showing a pulling control method for a porous optical fiber preform in the conventional method for producing an optical fiber preform shown in FIG.

[Explanation of symbols]

1 ……………………………… Seed rod 2 ……………………………… Core soot burner 3 ……………………………… Flame 4 ………… …………………… Porous optical fiber base material 8 ……………………………… Motor driver 9 ……………………………… Pulling motor 10 ………… ………………… Seed rod lifting mechanism 11 ……………………………… CCD camera 12 ……………………………… Image processing and measurement device 13 …………………… ……… Growth speed / growth acceleration calculation unit 14 ……………………………… D / A conversion unit 81 ……………………………… Motor speed setting device 82 ……………… …………… RC circuit

Claims (1)

[Claims] 1. A core soot burner for SiCl ₄ , G
A raw material gas such as eCl ₄ is mixed with a combustion gas such as hydrogen and oxygen, radiated in a flame state, and glass fine particles generated by flame hydrolysis are deposited on the seed rod while being deposited and grown porous by an axial method. In a method of manufacturing an optical fiber preform for obtaining an optical fiber preform, a CCD camera is fixed toward the tip of the porous optical fiber preform, and a tip image of the porous optical fiber preform projected by the CCD camera Is digitally processed and taken in every predetermined time, and the growth rate of the porous optical fiber preform is digitally calculated from the glass fine particle deposition reference position and the glass fine particle deposition tip position of the taken in porous optical fiber preform, and the calculated The speed of the pulling motor is set based on the growth rate, and the calculated growth rate and the composition of the porous optical fiber preform stored previously sampled and stored. RC for digitally processing the growth acceleration of the porous optical fiber preform per unit time based on the speed and D / A converting the calculated growth acceleration to smooth the motor drive voltage supplied based on the growth acceleration. A method of manufacturing an optical fiber preform in which a capacitance of a circuit capacitor is changed to change a speed change gradient of a pulling motor until the set speed is reached, and a seed rod is pulled up according to the growth acceleration.