JPH0483727A - Method for preparing optical fiber preform - Google Patents

Abstract

PURPOSE:To control the weight of deposited glass fine powder constant by continuously measuring the weight of a porous glass base material and the transfer speed of a core glass to determine the increase in the weight of the porous glass base material subsequently controlling the transfer speed of the core glass so that the weight of the deposited glass fine powder is constant. CONSTITUTION:A core glass rod 9 held with a scroll chuck attached to the upper end of a target bar 7 through the target bar 7 is rotated with a rotation motor 5 loaded on a supporting fitting 4 and transferred in the longitudinal direction with a motor 1 for transferring a target. A raw material such as SiCl4 is simultaneously blown on the surface of the glass rod by AVD method from burners 10, 11 to deposit glass fine powder on the surface of the glass rod 9. While the glass fine powder is deposited on the surface of the glass rod, the weight of the deposited glass fine powder is continuously measured with a load cell 3 and the transfer speed of the core glass rod 9 is controlled so that the weight of the deposited porous glass fine powder is constant, whereby a prescribed amount of the glass fine powder is deposited to provide an optical fiber preform with high precision without requiring any retreatment.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention involves depositing fine glass powder on the surface of a core glass rod having a core and a part of cladding, and then sintering it to obtain an optical fiber preform. , relates to a method for manufacturing an optical fiber preform by an external total synthesis method.

``Prior Art'' Conventionally, as one of the methods for manufacturing an optical fiber preform (so-called preform), the core is placed on the surface of a core glass opening/yield that includes a core made by the VAD method and a part of the cladding. While rotating the glass rod and moving it in the longitudinal direction,
There is a method for manufacturing an optical fiber base material by the so-called external total synthesis method, in which a porous base material is created by depositing glass fine powder using the VAD method, and this is sintered to form a cladding. Improved characteristics.

This method has been adopted as a method to improve scientific stability and reduce eccentricity.

In the method for manufacturing an optical fiber preform using the external total synthesis method, the transmission characteristics, core diameter, etc. are controlled by depositing a predetermined amount of glass on the surface of the core glass rod. Therefore,
In order to deposit a predetermined amount of glass, the flow rate of raw materials such as 5iCJ< or H2,0□ flowing into the oxyhydrogen burner is kept constant and adjusted by changing the moving speed of the core glass lot.

Alternatively, the moving speed of the core glass rod may be kept constant and adjusted by changing the gas flow rate, for example, the flow rate of 5iCJ 4 or H2.

[Problems to be Solved by the Invention] Although the above manufacturing method is performed by changing the moving speed or gas flow rate, the basis of the idea is that the same product can be manufactured if manufactured under the same conditions as the results of setting the conditions. It is based on the premise that.

However, in reality, the amount of glass deposited on the surface of the core glass rod differs from one core glass rod to another, and the positional relationship with the burner changes due to rotation of the core glass rod, and changes in the positional relationship with the burner due to bending of the glass rod. As a result, the amount of deposition exceeds the predetermined value.

Figure 3 shows the case where the magnification of the external part (outer diameter D) relative to the core glass rod (outer diameter d) is adjusted to a predetermined value by changing the moving speed of the glass rod. When making dashi, the white circles indicate the variation in magnification of continuously manufactured products obtained using the results of the dashi under those conditions.

As described above, in the conventional manufacturing method, since the amount of deposition exceeds a predetermined value, it is necessary to perform reprocessing by applying fine glass powder to the surface again or polishing the surface. Further, even if the flow rate of gas such as 5iCJ 4 or H2O2 gas changes, it is difficult to know what the product will look like until it is completed, and it takes time to see the results of setting the conditions.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing an optical fiber preform, which eliminates the drawbacks of the prior art described above and can control the deposition amount of fine glass powder on the surface of a core glass rod to a predetermined amount. It is in.

[Means for Solving the Problems] The present invention involves depositing fine glass powder on the surface of a core glass having a core and a portion of cladding by a VAD method while rotating and moving the core glass in the longitudinal direction. In a method for manufacturing an optical fiber preform by an external total synthesis method in which a porous preform is left behind and is sintered to form a cladding, the porous preform is continuously removed when depositing the fine glass powder. Measure the weight of the core glass, calculate the increased weight per unit length of the porous base material based on the measured weight and the moving speed, and control the moving speed of the core glass according to the result of comparing this with the indicated value. By doing so, the deposited weight per unit length of the porous base material is made constant.

[Function] The present invention continuously measures the weight while depositing fine glass powder, and adjusts the moving speed of the core glass so that the amount of increase in the amount of deposited fine glass powder becomes a predetermined value. This makes it possible to deposit a predetermined amount of fine glass powder at all times even with slight changes in conditions, and to manufacture an optical fiber preform with high precision and without the need for reprocessing.

[Example] A specific example of the present invention will be described in detail with reference to FIGS. 1 and 2.

FIG. 1 is a schematic diagram of an optical fiber preform manufacturing apparatus, in which 1 is a motor for moving the target, 2 is a ball screw for moving the target, 3 is a load cell, 4 is a support metal fitting for the target rotation part,
5 is a motor for rotating the target, 6 is a scroll chuck, 7 is a target rod, 8 is an external porous base material, 9 is a VA
Core glass rod made by D method, 10 is burner I, 1
1 indicates a burner (2), and 12 indicates a control device.

A core glass rod 9 is attached to a target rod 7 via a target, and the upper end of the target rod 7 is gripped by a scroll chuck 6 hanging from the support metal fitting 4, and a target rotation motor placed on the support metal fitting 4 is held at the upper end of the target rod 7. 5
The upper part of the support metal fitting 4 is placed on the load cell 3 located inside the support metal fitting 4, and therefore the support metal fitting 4 is supported from below by the load cell 3. 3 itself is attached to a moving frame (not shown) that engages with a ball screw 2 for moving the target, and the ball screw 2 for moving the target is rotated by the motor 1 for moving the target. There is.

In short, the support fitting 4 is suspended from the moving frame via the load cell 3, and thereby the external porous base material 8. Core glass rod9. Target, target stick7. The total weight of the scroll chuck 6 and rotation motor 5 is measured by the load cell 3.

Further, as the target moving ball screw 2 is rotated, the moving frame and the load cell 3 move upward together, and accordingly, the supporting metal fittings 4. Target stick7. Core glass rod9. The external porous base material 8 and the like also move together. The pulling speed of the core glass rod 9 is determined by the moving speed 13 given to the moving motor 1 from the control device 12.

The weight measurement accuracy of the load cell 3 is 1g, and 0
The hanging weight is output and displayed using an electrical signal of ~IOV magnitude. The suspended weight 14 output as an electrical signal from the load cell 3 is continuously input to the control device 12,
It is processed as follows.

That is, the control device 12 moves the suspended weight 14 at a moving speed 13.
This is calculated and converted into a weight change of 15 per unit length of the external porous base material 8. Then, this weight change 15 per unit length is compared with an externally inputtable instruction value 16, and the moving speed 13 is changed according to the difference as a result of the comparison.
The corrected movement signal is sent to the target movement motor 1.

The method for manufacturing the optical fiber preform includes the above-mentioned core glass rod 9.
This is an external total synthesis method in which fine glass powder is deposited by the flames of burners 10 and 11 on the surface of the rod using the AVD method while the rod is rotated by the rotation motor 5 and moved in the longitudinal direction by the movement motor 1. At this time, the weight is continuously measured while depositing the glass fine powder, so that the amount of glass fine powder deposited on the external porous base material 8 becomes a predetermined value.
Adjust the moving speed of the core glass rod 9. Thereby, even if there is a slight change in conditions, a predetermined amount of fine glass powder can always be deposited, and an optical fiber preform can be manufactured with high precision and without the need for reprocessing.

Specifically, referring to FIG. 2, the above-mentioned apparatus is used to obtain a length L = 1000 mm, including a portion of the core and cladding, and an outer diameter d = φ16. Omm core glass rod 9, Part 2
．． 3 times (ratio of the outer diameter of the external part and the outer diameter of the core glass rod d;
The case of externally attaching the D/d) will be explained.

Burner 10 (Burner I) contains 5iCJ, 2.5 g/
1 lin, 5 tcn was flowed at 13.5 g/l 1 in into the burner 11 (burner ■), and while the core glass rod 9 was rotated, a porous base material made of fine glass powder was deposited on the surface thereof. Regarding the movement speed, first, the deposition at point a in Fig. 2 is carried out at a constant speed of seeding.
Thereafter, up to point b in FIG. 2, the deposition was carried out at a constant moving speed expected from the relationship between moving speed and magnification in the manufacturing results up to now. Up to this point, the outer diameter of the porous base material 8 becomes constant.

After 60 minutes from the start of external attachment, the outer diameter became uniform at 83 mm, the moving speed was 85 mm/hr, and the amount of weight increase due to the deposition of fine glass powder was also constant. At this time, the weight increase per 1 mm length was 2.000 g.

When the time at point b in FIG. 2 is reached, control based on weight measurement is started. The amount of external attachment to the rod core is 1.897g
/mm, and this is given to the control device 212 as the instruction value 16. The control device 12 receives this instruction value 1.
A comparison control 17 is performed between 897 g/mm and the weight change of 2.000 g/mm, and a moving speed 13 corresponding to the difference is fed back to the target moving motor 1. Due to this feedback control, the moving speed is adjusted to 85 mm above so that the deposit amount is 1.897 g/mm after about 1 hour.
/hr to 85.7mm/hr, and the second
After the 0 point in the figure, deposition was performed at a nearly constant speed.

As a result, when the signal was evaluated using a preform analyzer after sintering, the outer diameter R of the external part was 2.3 times the outer diameter r of the core glass rod, as desired.

[Effects of the Invention] As described above, according to the present invention, while depositing Gaaras fine powder, the deposition status is monitored by weight change, and the target value is set so that the value becomes a predetermined value. Optical fiber preforms can be produced that do not require on-site reprocessing.

Furthermore, it is possible to grasp slight changes in manufacturing conditions, and if there are any changes, the optical fiber preform can be manufactured under the changed conditions.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing a control situation showing an embodiment of the present invention, and is a diagram showing the relationship between longitudinal movement speed and weight change. The figure shows the relationship between the moving speed of a glass rod and the variation in magnification when an optical fiber preform is manufactured by a conventional method. In the figure, 1 is a motor for moving the target, 2 is a ball screw for moving the target, 3 is a load cell, 4 is a support bracket for the target rotating part, 5 is a motor for rotating the target, 6 is a scroll chuck, 7 is a target rod, and 8 is an outer Reference numeral 9 indicates a porous base material, 9 indicates a core glass rod, 10 indicates a burner I, 11 indicates a burner ①, and 12 indicates a control device. Patent Applicant Hitachi Cable Co., Ltd. Representative Patent Attorney Shin Kinuya Shin Figure 2 9 Core Sword Busuro 7 Toka Ranuro Tonharmtsu'hr) Figure 3

Claims (1)

[Claims] 1. While rotating and moving the core glass in the longitudinal direction, fine glass powder is deposited on the surface of the core glass having a core and a part of the cladding using a VAD method to create a porous base material. In a method for manufacturing an optical fiber base material using an external total synthesis method in which it is sintered to form a cladding, the weight of the porous base material is continuously measured when depositing the above-mentioned glass fine powder, and the measured weight and moving speed are measured. By calculating the increased weight per unit length of the porous base material based on the above, and controlling the above-mentioned moving speed of the core glass according to the result of comparing this with the indicated value, the unit length of the porous base material is determined. 1. A method for manufacturing an optical fiber preform, characterized in that the weight of each deposited material is made constant.