JP3663871B2 - Optical fiber preform manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an optical fiber preform that can accurately manufacture a homogeneous optical fiber preform.
[0002]
[Prior art]
Conventionally, a starting member produced by welding a dummy rod to both ends of a core base material consisting of a core and a clad is reciprocated relative to the glass particle synthesis burner in the axial direction while rotating around the axis, and glass There is a method of manufacturing an optical fiber preform by spraying and depositing glass fine particles synthesized by a fine particle synthesizing burner on the outer periphery of a starting member.
An example of an apparatus configuration for carrying out this method is schematically shown in FIG. In the example of FIG. 1, the burner 2 is fixed to the container 1, and the starting member 3 is reciprocated up and down while being rotated by the lifting device 4. A glass raw material such as SiCl ₄ and a combustion gas are supplied from the raw material supply device 5 to the burner 2, and the synthesized glass fine particles are deposited on the outer periphery of the starting member 3 to form a soot body (glass fine particle deposit) 6. The
[0003]
In this method, when the burner 2 relatively moved from the center side of the starting member 3 reaches the joint between the core member and the dummy rod, the supply of the glass raw material to the burner 2 is stopped. The end of the soot body formed outside the glass raw material supply stop point (the portion where the outer diameter decreases) is heated, or the glass raw material is supplied as the burner 2 to make glass When a burner equipped with an auxiliary burner that only heats before and after the relative movement direction of the burner that synthesizes fine particles (glass synthesis burner) reaches the joint between the core member and the dummy rod. The end of the soot body is heated with an auxiliary burner.
[0004]
When forming a soot body (manufacture of an optical fiber preform) by such a method, the shape of the soot body is as shown in FIG. That is, when the joint 8 between the core member 9 of the starting member 3 and the dummy rod 10 is the raw material supply stop points (when the auxiliary burner is used, the folding point of the glass synthesis burner) 11 and 12, the outer periphery of the soot body ▲ When the outer diameter of the soot body is small as in 1 ▼ (13 in the figure), the length of the outer diameter steady portion of the soot body (the length of the effective portion that provides a stable sintered body when transparent) ) Can be obtained near the length of the core base material 9 as shown in a1 in the figure, but as shown in a2 in the figure as the outer diameter increases as shown in the outer periphery of the soot body (2) (14 in the figure). The length of the outer diameter stationary part of the soot body becomes shorter. This is because the soot particle flow at the position where the raw material is stopped is not parallel to the central axis of the starting member but is inclined because the position where the raw material is stopped is an unsteady outer diameter portion. In this case, the end portion of the core base material is not effectively used, which causes an increase in cost.
[0005]
As described above, the case of using one glass synthesis burner has been described, but there is a similar problem when using a plurality of glass synthesis burners arranged in parallel to the central axis of the starting member. As an example of using such a plurality of glass synthesis burners, there is a technique disclosed in Japanese Patent Laid-Open No. 63-310745. This technology uses multiple burners and eliminates the non-uniformity of density at the end of the glass particulate deposit that occurs when the end of the glass particulate deposit is folded back without stopping the supply of glass material. The purpose is to mass-produce high-quality products that are not damaged by glass. Two or more targets deposited in advance when using multiple glass sources are marked and traversed. Among the plurality of glass generation sources, the one that passes the gauge point is one in which the detection means is immediately activated to stop the supply of the glass raw material. According to this method, there is an effect of solving problems such as non-homogeneous soot density due to interference of a plurality of glass synthesis burners (glass generation sources) at the end, but the outer diameter of the soot body as described above. There remains a problem that the length of the outer diameter steady portion (effective portion) of the soot body becomes shorter with an increase in the soot body.
[0006]
As the outer diameter of the soot body increases, the length of the outer diameter steady portion decreases, and in order to prevent the core base material from being wasted, the glass raw material supply stop point to the glass synthesis burner or the burner The turning point may be set at a position sufficiently away from the joint portion between the core base material and the dummy rod toward the dummy rod, but in this case, the loss of the glass raw material increases, which is not economical.
[0007]
[Problems to be solved by the invention]
In the present invention, in view of such a state of the prior art, a soot body (glass fine particle deposit) having a uniform quality outer diameter portion formed over the entire length of the core base material is obtained, and the loss of the glass raw material is small. An object of the present invention is to provide a method for manufacturing an optical fiber preform.
[0008]
[Means for Solving the Problems]
The present invention has the following aspects (1) to (4) as means for solving the above problems.
(1) A starting member produced by welding a dummy rod to both ends of a core base material composed of a core and a clad is reciprocated relative to the glass synthesis burner in the axial direction while rotating around the axis, and glass A method of spraying and depositing glass fine particles synthesized by a synthesis burner on the outer periphery of a starting member, using a single burner equipped with an auxiliary burner that only performs heating before and after the relative movement direction of the glass synthesis burner. The glass synthesis burner that moves relatively from the core base material side to the dummy rod side is folded at the joint between the core base material and the dummy rod, and the end of the soot body is heated by the auxiliary burner for sooting. In the method of manufacturing the optical fiber preform, the folding position of the glass synthesis burner is changed from the joint between the core preform and the dummy rod to the dummy position as the outer diameter of the soot body increases. Method for manufacturing an optical fiber preform, characterized in that moving the head side.
[0009]
(2) A starting member prepared by welding dummy rods to both ends of a core base material composed of a core and a clad is reciprocated relative to the glass synthesis burner in the axial direction while rotating around the axis, and glass A method of spraying and depositing glass fine particles synthesized by a synthesis burner on the outer periphery of a starting member, using a single glass synthesis burner, and relatively moving from a core base material side to a dummy rod side. Stops the supply of the raw material to the glass synthesis burner when it reaches the joint between the core base material and the dummy rod, and further moves the glass synthesis burner that has stopped the supply of raw material to the dummy rod side soot body In the method of manufacturing an optical fiber preform, sooting is performed so that the raw material supply is started when the end of the glass is heated and the folded glass synthesis burner reaches the joint. An optical fiber characterized in that the raw material supply stop and start position to the glass synthesis burner are moved from the joint between the core base material and the dummy rod to the dummy rod side as the outer diameter of the soot body increases A manufacturing method of a base material.
[0010]
(3) A starting member prepared by welding dummy rods to both ends of a core base material composed of a core and a clad is reciprocated relative to the glass synthesis burner in the axial direction while rotating around the axis, and glass A method of spraying and depositing glass fine particles synthesized by a synthesis burner on the outer periphery of a starting member, using a plurality of glass synthesis burners arranged in parallel to the central axis of the starting member, from the core base material side When the plurality of glass synthesis burners that move relative to the dummy rod side sequentially reach the joint between the core base material and the dummy rod, the supply of the raw material to the glass synthesis burner is stopped, and the supply of the glass is stopped. The end of the soot body is heated with a synthesis burner, and the optical fiber preform is soaked so that the raw material supply is started when each folded glass synthesis burner reaches the joint. In the manufacturing method, the raw material supply stop and start position to the glass synthesis burner is moved from the joint between the core base material and the dummy rod to the dummy rod side in accordance with the increase in the outer diameter of the soot body. An optical fiber preform manufacturing method.
[0011]
(4) The glass synthesis burner is folded when the burner located at the center side of the starting member among the plurality of glass synthesis burners reaches the starting and stopping position of the raw material supply to the glass synthesis burner, The method for producing an optical fiber preform according to (3), wherein the raw material supply to the burner located closest to the center of the starting member is not stopped at that time.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
According to the method of the present invention, as the outer diameter of the soot body increases, the supply range of the glass raw material is gradually increased from the joint between the core base material and the dummy rod (hereinafter simply referred to as a joint) to the dummy rod side. It is characterized by spreading.
That is, the turning point of the glass synthesis burner in the invention of (1), the supply stop or start position of the glass raw material to the glass synthesis burner in the inventions of (2) and (3), ) Is the turning point of the most central glass synthesis burner (the innermost glass synthesis burner at both ends of the reciprocating movement) and the supply of the glass raw material to the other glass synthesis burners The stop or start position is gradually moved from the joint to the dummy rod side as the outer diameter of the soot body increases.
[0013]
The length of the outer part of the soot body (this part becomes an effective part from which a homogeneous and good fiber can be obtained) is almost constant if the outer diameter of the soot body is constant. As the diameter increases, the outer diameter non-stationary part spreads in the front-rear direction of the position of the glass raw material stop and the like, and the length of the outer diameter steady part becomes shorter. That is, when the position of the glass raw material stop or the like is a joint, the end of the outer diameter steady portion gradually shifts from the joint to the center side of the core base material as the outer diameter increases. Therefore, in the present invention, sooting is performed while monitoring the outer diameter of the soot body, and by computer control or the like from the relationship between the soot outer diameter determined in advance and the length variation of the outer diameter steady portion, The position of stopping the glass raw material is moved from the joint to the dummy rod side by a length corresponding to the size of the deviation. Thereby, regardless of the dimension of the outer diameter, the outer diameter steady portion can be formed substantially over the entire length of the core base material.
[0014]
The number of glass synthesis burners to be used may be determined appropriately depending on the size of the target product, etc., but when using a plurality of glass burners, the number should be 3 to 4 in view of the shape and efficiency of the apparatus. preferable. Moreover, in order to maintain a stable flame state, it is preferable to stop and restart the supply of the raw material to the glass synthesis burner over several seconds to 10 seconds instead of instantaneously.
[0015]
【Example】
Hereinafter, the method of the present invention will be described more specifically by way of examples.
(Example 1)
Sooting was performed using the apparatus having the configuration shown in FIG. 1, and the relationship between the soot outer diameter and the length of the outer diameter steady portion was examined. Using a glass rod (core base material) with a diameter of 30 mm having a core / cladding part, a quartz glass dummy rod is welded on both sides to prepare a starting member, and the rod is gripped in a vertical direction while rotating at 40 rpm. Then, glass fine particles generated from a glass fine particle synthesis burner were sequentially laminated while reciprocating up and down to produce a glass fine particle deposit (soot). The burner used was a concentric eight-tube structure and was arranged perpendicular to the rotation axis of the starting member. The burner was supplied with silicon tetrachloride as a raw material: 3 slm (standard liter / min), hydrogen: 60 slm and oxygen: 45 slm for forming a flame, and Ar: 4 slm as a sealing gas.
In addition to the burner of this configuration, concentric double tube auxiliary burners are attached to both sides of the burner in the moving direction at intervals of 200 mm, and oxygen: 10 slm and hydrogen: 30 slm are supplied so that the end of the soot body is It was made to heat.
[0016]
When the burner reaches the position of the joint between the core base material of the starting member and the dummy rod, the direction of the traverse of the starting member is changed, and the soot outer diameter is 100, 150 respectively while continuing the reciprocating traverse in this way. Sooting was continued until 220, 250 mm. Each of the soot bodies thus obtained was made transparent in a furnace heated to a high temperature and then made into fibers, and fiber characteristics such as cutoff wavelength and MFD (mode field diameter) were examined. As it becomes larger, the boundary point between the part where the characteristics at both ends are not stable (corresponding to the outer diameter unsteady part) and the part where the characteristic is stable (corresponding to the outer diameter steady part), that is, the end of the effective part is the core base material. It has shifted | deviated from the junction part with a dummy rod to the core base material center side, and the correlation diagram shown in FIG. 3 was obtained.
[0017]
Sooting was performed under the same conditions as described above using 500 mm of the core base material. During sooting, the soot outer diameter was monitored, and based on the data in FIG. 3, the traverse folding position was gradually moved from the joint to the dummy rod side according to the soot outer diameter at that time. Thus, sooting was performed until the outer diameter reached a target value of 150 mm calculated from the core / cladding ratio of the core base material to obtain a glass particulate deposit (soot body). Finally, the turning point of the traverse was shifted by 50 mm from the joint to the dummy rod side. The obtained soot body was made transparent by a high-temperature furnace to obtain a sintered body having a good transparency with an outer diameter of 80 mm and having no surface, internal cracks, protrusions, foreign matter, etc. This sintered body was converted into a fiber, and fiber characteristics such as cutoff wavelength and MFD were examined.
[0018]
(Example 2)
Using the same core base material as in Example 1, 500 mm, sooting was performed under the same burner conditions as described above. In this example, the auxiliary burner is not used, and when the glass synthesis burner comes to the position of the joint between the core base material of the starting member and the dummy rod, the supply of the raw material to the burner is stopped and further moved in the same direction. Subsequently, the end of the soot body was heated only by the flame. When the burner reached a position 200 mm from the raw material supply stop position, the burner was turned back, and when the burner returned to the raw material supply stop position, the supply of the raw material to the burner was resumed.
Thereafter, while monitoring the outer diameter of the soot, based on the data of FIG. 3, the raw material supply stop and restart position to the burner is gradually moved from the joint to the dummy rod side according to the outer diameter of the soot, and the outer diameter is Sooting was performed until the thickness became 150 mm. Finally, the raw material supply stop and restart positions were shifted by 50 mm from the joint to the dummy rod side. The quality of the sintered body obtained by transparentizing the obtained soot body in a high-temperature furnace was good, and the fiber characteristics were also good over the entire length.
[0019]
(Example 3)
A quartz glass dummy rod is welded to both sides using the same core base material 500 mm used in Example 1, and a starting member is produced. While rotating the rod at 40 rpm with the apparatus having the configuration shown in FIG. A glass fine particle deposit (soot body) was produced by sequentially laminating glass fine particles generated from a glass fine particle synthesis burner while vertically reciprocating and holding in a vertical direction. In this example, three burners having a concentric octuple structure were used, and the three burners were arranged so as to be perpendicular to the rotation axis of the starting member and parallel to each other at equal intervals (200 mm intervals). Each burner was supplied with silicon tetrachloride: 3 slm as a raw material, hydrogen: 60 slm and oxygen: 45 slm for forming a flame, and Ar: 4 slm as a sealing gas.
[0020]
When reciprocating traverse is performed and the burner group approaches one end of the starting member, when the burner reaches the predetermined position for the first and second burners, the glass raw material supply to the burner is stopped by computer control. Further, the end of the soot body was heated only by the flame by continuing the movement in the same direction. When the third burner reaches a predetermined position, the supply of the raw material is turned back without stopping and traversed in the reverse direction, and when the second and first burners sequentially return to the predetermined position, the glass to each burner Raw material supply resumed. This pattern is performed at both ends of the core base material (the order of the burners is reversed at the opposite end), and soot is applied until the outer diameter reaches 150 mm, which is the target value calculated from the core / cladding ratio of the core base material. To obtain a glass fine particle deposit (soot).
[0021]
The predetermined position (stopping and starting point of raw material supply to the first and second burners, and the turning point of the third burner) is a joint at the start of sooting, and thereafter, while monitoring the outer diameter of the soot. Based on the data of No. 3, the predetermined position was gradually moved from the joint to the dummy rod side according to the outer diameter of the soot. Finally, the predetermined position was shifted by 50 mm from the joint to the dummy rod side.
The soot body thus obtained was made transparent by a high-temperature furnace, and a good sintered body having an outer diameter of 82 mm was obtained. The sintered body was converted into a fiber, and fiber characteristics such as cutoff wavelength and MFD were examined. As a result, good characteristics were obtained over the entire length.
[0022]
(Comparative Example 1)
The operation was performed in the same manner as in Example 2 except that the raw material supply stop and start point to the first and second burners, and the predetermined position serving as the turning point of the third burner were fixed to the joint, and the outer diameter was 150 mm. A soot body was produced. The obtained soot body was made transparent in a furnace heated to a high temperature to obtain a good sintered body having an outer diameter of 81 mm. However, when this sintered body was made into a fiber in a drawing furnace and the fiber characteristics such as cutoff wavelength and MFD were examined, the characteristics such as cutoff wavelength and MFD from the joints at both ends to the range of 49 mm and 48 mm respectively were targeted. It was found that there was a gradual deviation from the value.
[0023]
【The invention's effect】
The raw material supply stop and restart position to the glass synthesis burner near the end of the core base material in accordance with the outer diameter of the soot body being synthesized, or the return position of the burner that does not stop the raw material supply, is determined between the core base material and the dummy rod. By moving gradually from the joint to the dummy rod side (outside of the core base material), even when the outer diameter of the soot is large, an outer diameter steady-state part (effective part) that can obtain an optical fiber with stable characteristics over the entire length of the core base material ) Can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration example of an optical fiber preform manufacturing apparatus using a glass fine particle synthesis burner.
FIG. 2 is a diagram for explaining a state of change in the length of a constant outer diameter portion according to a soot outer diameter when forming a soot body;
FIG. 3 is a correlation diagram showing the relationship between the magnitude of deviation from the joint and the soot outer diameter at the end position of the effective portion in the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Container 2 Burner 3 Starting member 4 Lifting device 5 Raw material supply apparatus 6 Soot body 8 Joint part 9 Core base material 10 Dummy rod 11,12 Raw material supply stop point 13 Soot body outer periphery (1) 14 Soot body outer periphery (2)

Claims (4)

A starting member prepared by welding dummy rods to both ends of a core base material composed of a core and a clad is reciprocated relative to the glass composition burner in the axial direction while rotating around the axis, thereby producing a glass composition burner. The glass fine particles synthesized in step 1 are sprayed and deposited on the outer periphery of the starting member, using a single burner with an auxiliary burner that only performs heating before and after the relative movement direction of the glass synthesis burner. An optical fiber preform for sooting in which the glass composition burner that moves relative to the dummy rod side from the material side is folded at the joint between the core preform and the dummy rod, and the end of the soot body is heated by the auxiliary burner. In the material manufacturing method, the folding position of the glass synthesis burner is changed from the joint between the core base material and the dummy rod to the dummy rod as the outer diameter of the soot body increases. Method for manufacturing an optical fiber preform, characterized in that moving the. A starting member prepared by welding dummy rods to both ends of a core base material composed of a core and a clad is reciprocated relative to the glass composition burner in the axial direction while rotating around the axis, thereby producing a glass composition burner. The glass fine particles synthesized in (1) are sprayed and deposited on the outer periphery of the starting member, using a single glass synthesis burner, and the glass synthesis burner moving relatively from the core base material side to the dummy rod side is the core. When the joint between the base material and the dummy rod is reached, the raw material supply to the glass synthesis burner is stopped, and the glass synthesis burner that stopped the raw material supply is further moved to the dummy rod side to end the soot body. In the method of manufacturing an optical fiber preform in which sooting is performed such that the raw material supply is started when the folded glass synthesis burner reaches the joint portion. An optical fiber preform characterized in that the raw material supply stop and start position to the soot synthesis burner are moved from the joint between the core preform and the dummy rod to the dummy rod side as the outer diameter of the soot body increases. A method of manufacturing the material. A starting member prepared by welding dummy rods to both ends of a core base material composed of a core and a clad is reciprocated relative to the glass composition burner in the axial direction while rotating around the axis, thereby producing a glass composition burner. The glass fine particles synthesized in (1) are sprayed and deposited on the outer periphery of the starting member, using a plurality of glass synthesis burners arranged in parallel to the central axis of the starting member, from the core base material side to the dummy rod side When the plurality of glass synthesis burners that move relative to each other reach the joint between the core base material and the dummy rod in sequence, the supply of the raw material to the glass synthesis burner is stopped, and the supply of the raw materials is stopped. A method of manufacturing an optical fiber preform that heats the end of the soot body and starts soot supply when each folded glass synthesis burner reaches the joint. In the above, the light is characterized in that the raw material supply stop and start position to the glass synthesis burner are moved from the joint portion of the core base material and the dummy rod to the dummy rod side as the outer diameter of the soot body increases. Manufacturing method of fiber preform. When the burner located at the center side of the starting member of the plurality of glass synthesis burners reaches the starting and stopping position of the raw material supply to the glass synthesis burner, the glass synthesis burner is folded back at that time. 4. The method of manufacturing an optical fiber preform according to claim 3, wherein raw material supply to the burner located closest to the center of the starting member is not stopped.

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