JPH04292434A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To provide a method for producing a homogeneous, dense and high- quality optical fiber preform. CONSTITUTION:Core/clad ratios in several points along the longitudinal direction of a target member 1 are previously measured to obtain the measured values and weight increase rate of the target member is continually measured during process. The weight increase rate of the target member is controlled within the range of prescribed preferable value by controlling traverse rate of burners 8A, etc., and glass material gas feed amount, based on these measured values and simultaneously preferable glass material gas feed amount previously calculated is fed when the burners comes to a position corresponding to these each point by calculating from core/clad ratio at each point in the longitudinal direction of the target member and core/clad ratio being uniform in the longitudinal direction of the completed preform is realized to provide the objective optical fiber preform having good quality.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of manufacturing an optical fiber preform.

0002

[Prior Art] While rotating a target member, which is a type of glass rod, a burner that burns a glass material gas such as silicon tetrachloride or germanium tetrachloride together with oxygen and hydrogen is traversed in the longitudinal direction of the target member. The method of manufacturing an optical fiber preform by depositing the glass soot produced by the method on the outer periphery of a target member is well known as a so-called external manufacturing method of an optical fiber preform.

To be precise, the target member does not consist entirely of the core portion 1A, but as shown in FIG. is approximately 1/3 thicker than the finished base material (as is well known, the core/cladding ratio in the finished base material is 1/12.5 in terms of diameter). The thickness of this cladding layer 1B varies in the longitudinal direction of the target member 1, and the diameter of the core portion 1A is also not constant along the longitudinal direction. In other words, as shown in FIG. 2, the outer diameter D of the target member 1 and the diameter d of the core portion are functions of its longitudinal direction x.

0004

[Problems to be Solved by the Invention] Since the core/cladding ratio of the target member 1 itself is not constant in the longitudinal direction at the start of manufacturing the optical fiber preform, the amount of material gas supplied to the burner that generates glass soot is It is naturally impossible to obtain an optical fiber base material with a constant core/cladding ratio along the longitudinal direction by traversing the burner at a constant speed while keeping the traverse speed constant. This problem cannot be solved simply by changing each position along the longitudinal direction of the target member 1. This is because changing the traverse speed is reasonable when the core/cladding ratio fluctuates by a certain amount along the longitudinal direction of the target member 1, but This is because it is difficult to follow and respond to small changes that occur continuously.

In general, in the production of optical fiber preforms, when the same amount of soot is deposited over a long period of time and when it is obtained in a short period of time, in the former case the glass soot deposited layer is more homogeneous and of higher quality. It is obvious that a better product can be obtained, but from the standpoint of manufacturing efficiency, the longer the time, the better. In this way, in the production of optical fiber preforms, there is naturally an optimum value for the weight increase per unit time of the target member, that is, the weight increase rate of the deposited glass soot. Therefore, the optimum traverse speed of the burner and the optimum feed rate of glass material gas to this burner should be determined in order to obtain such an ideal weight increase rate.

[0006]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes a burner that burns glass material gas together with oxygen and hydrogen in the longitudinal direction of the target member while rotating the target member. In a method for manufacturing an optical fiber preform by generating and depositing glass soot around a target member by traversing the target member, in response to a pre-measured change in the core/cladding ratio in the longitudinal direction of the target member, The method for manufacturing an optical fiber preform is characterized in that the traverse speed of the burner and the supply amount of the glass material gas are controlled.

[0007] Furthermore, the present invention traverses a burner that burns glass material gas together with oxygen and hydrogen in the longitudinal direction of the target member while rotating the target member, thereby generating and depositing glass soot around the target member to form an optical fiber. In the method for manufacturing a base material, the traverse speed of the burner and the supply of the glass material gas are adjusted in response to a weight increase rate of the target member and a pre-measured change in the core/cladding ratio in the longitudinal direction of the target member. This is a method for manufacturing an optical fiber preform, characterized by controlling the amount.

[0008]

[Operation] Since the core/clad ratio of the target member is measured in advance at each position in the longitudinal direction, by knowing the position along the longitudinal direction of the target member of the burner, the appropriate core/clad ratio corresponding to the core/clad ratio at that position can be determined. The amount of glass material gas supplied and the traverse speed of the burner are determined, so that a high quality optical fiber preform can be produced.

Furthermore, the traverse speed of the burner is determined so that the weight increase speed of the target member settles at an optimum value,
At the determined traverse speed, the glass material gas supply rate is controlled to correct for variations in the longitudinal core/cladding ratio of the target member, thereby achieving a uniform light longitudinal core/cladding ratio in the finished state. A fiber matrix can be produced.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an apparatus for carrying out the present invention will be described with reference to FIG. What is generally indicated by the reference numeral 3 is a target member support device, and rotation support shafts 31, 31 for rotatably supporting the frame are attached to the middle of a substantially U-shaped frame. A pair of chuck parts 33 that grip both ends of the target member 1 are provided at both ends of the target member 1.
, 33 are provided, and a rotary drive motor 4 for rotating this chuck portion 33 is provided on the outside thereof. Also, the rotation support shaft 3
1, a balance weight 3 having a weight approximately equal to the weight of the target member 1 is provided on the opposite side of the chuck portion 33.
2 is provided. A load measuring arm 34 is attached to a part of the frame relatively distant from the rotational axis of the rotational support shaft 31, and this load measuring arm 34 engages with a load cell 5 for weight detection to measure the weight of the target member 1. This is to measure the weight increase beyond the balance state with the balance weight 32.

Although a plurality of burners for burning glass material gas are normally provided, two burners 8A and 8B are shown in this figure. These burners 8A, 8B
are attached to cam followers 7A and 7B that respectively engage traverse shafts 6A and 6B, which are a type of feed screw cam, and reciprocate in the longitudinal direction of target member 1 in accordance with the rotation of traverse shafts 6A and 6B. Furthermore, position sensors 9A and 9B, which are a type of rotary encoder, are attached to the ends of the traverse shafts 6A and 6B, respectively. In other words, the positions of the target members 1 in the longitudinal direction are detected. Here, reference numeral 11 is a rotational drive motor for the traverse shaft.

[0012] Reference numerals 10A and 10B each indicate a burner 8A.
, 8B, and the amount of gas supplied to the burner can be increased or decreased easily by adjusting the opening/closing degree of a solenoid valve, for example, using an electrical signal from the central controller 12. This central control unit 12 also sends control signals to the rotary drive motor 11 of the traverse shaft. In contrast, the input signals to this central control device 12 are signals from the load cell 5, which can detect the weight increase of the target member 1, and signals from the position sensors 9A, 9B, which indicate the positions of the burners 8A, 8B.

The initial core/cladding ratio at some point along the length of the target member 1, for example d1 /D1 at a distance x1 from the end of the target member 1, as shown in FIG. d at position x2
2 /D2 can be determined by measuring and analyzing the refractive index at each point using a device called a preform analyzer, so the appropriate amount of glass material gas to be supplied at each point can be determined in advance by the central controller 12. Let me remember it. Therefore, position sensor 9A
, 9B detect these positions, the amount of material gas supplied to the corresponding burners 8A, 8B is immediately adjusted to the initial set value by a command from the central controller 12. Note that it goes without saying that the more precisely the core/cladding ratio is known in advance at as many points as possible along the longitudinal direction of the target member 1, the more precisely it becomes possible to manage it.

On the other hand, with this apparatus shown in FIG. 1, it is also possible to control the weight increase rate of the optical fiber preform within an appropriate range. When the glass soot 2 is deposited on the outer peripheral surface of the target member 1 due to the combustion of the glass material gas,
Naturally, the weight increases and the balance around the rotation support shaft 31 of the target member support device 3 is broken, and the target member support device 3 rotates around the rotation support shaft 31 so that the balance weight 32 side faces the top surface of the page. It moves like this. In this way, the load measuring arm 34 pushes the load cell 5 and transmits the weight increase of the target member 1 to the central control unit 12, so this is compared with the appropriate weight increase rate stored in the central control unit 12 in advance. For example, when the speed is high, the rotary drive motor 11 may be rotated quickly to speed up the feeding of the burner 8A, etc. (the adhesion speed will be slow). Since the adjustment of the feed rate of the burner 8A etc. and the adjustment of the glass material gas supply amount are separate, the weight increase rate of the base material must be managed to stay within the desired range, and then the The amount of glass material gas supplied can be adjusted to increase or decrease in accordance with changes in the core/cladding ratio in the longitudinal direction of the target member 1.

[0015]

According to the present invention, since the core/cladding ratio of the target member is measured in advance at each position in the longitudinal direction and stored in the central control unit, the position of the burner along the longitudinal direction of the target member can be known. This gives the appropriate glass material gas supply amount and burner traverse speed corresponding to the core/cladding ratio at that location,
This has the effect of producing a high quality optical fiber preform with a constant core/cladding ratio in the longitudinal direction.

Further, according to the present invention, the traverse speed of the burner is determined so that the weight increase rate of the target member becomes an optimum value, and at the determined traverse speed, the variation of the core/cladding ratio in the longitudinal direction of the target member is By increasing or decreasing the amount of glass material gas supplied to correct the above, it is possible to manufacture an optical fiber preform that is homogeneous, dense, and has a uniform core/cladding ratio in the longitudinal direction.

[Brief explanation of drawings]

FIG. 1 is a side sectional view showing an example of an apparatus used to carry out the method of the present invention.

FIG. 2 is an enlarged partial side sectional view of a target member used in the present invention.

[Explanation of symbols]

1 Target member 2 Glass soot 3 Target member support device 31 Rotation support shaft 32 Balance weight 5 Load cell 6A, 6B Traverse shaft 8A, 8B Burner 9A, 9B Position sensor 10A, 10B Glass material gas supply device 11 Rotation drive motor 12 Central control device

Claims (2)

[Claims] Claim 1: By traversing a burner that burns glass material gas together with oxygen and hydrogen in the longitudinal direction of the target member while rotating the target member, glass soot is generated and deposited around the target member to form an optical fiber preform. A method for manufacturing an optical device, characterized in that the traverse speed of the burner and the supply amount of the glass material gas are controlled in response to a change in the core/cladding ratio in the longitudinal direction of the target member measured in advance. Method for manufacturing fiber base material. 2. By traversing a burner that burns glass material gas together with oxygen and hydrogen in the longitudinal direction of the target member while rotating the target member, glass soot is generated and deposited around the target member to form an optical fiber preform. In the method of manufacturing, the traverse speed of the burner and the supply amount of the glass material gas are adjusted in response to a weight increase rate of the target member and a pre-measured change in the core/cladding ratio in the longitudinal direction of the target member. 1. A method for manufacturing an optical fiber preform, characterized by controlling.