JP2004137095A - Method for producing optical fiber preform - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the yield in a method for producing an optical fiber preform, wherein a glass pipe 2 and a glass rod 3 inserted thereinto are successively melted and integrated with each other in the axial direction while the pressure inside the glass pipe 2 is kept low. <P>SOLUTION: While the glass pipe 2 is being integrated with the glass rod 3, a defect appearing in the optical fiber preform 7 is detected at the exit side of a heating furnace 5. Then, the optical fiber preform 7 is cut off at the site of the defect. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention, in a glass pipe for cladding, by inserting a glass rod for core, or a glass rod for core and cladding, and heating both while decompressing the inside of the glass pipe, the glass pipe and the glass rod The present invention relates to a method of manufacturing an optical fiber preform for performing integration and stretching.
[0002]
[Prior art]
Conventionally, a glass rod serving as a core in an optical fiber, or a glass rod serving as a core and a cladding, is inserted into a glass pipe serving as a cladding in an optical fiber, and the glass pipe and the glass rod are integrated into an optical fiber motherboard. A so-called rod-in-tube method for manufacturing a material is known (for example, see Patent Document 1). In the rod-in-tube method, for example, both the glass pipe and the glass rod are passed through the heating furnace in the axial direction while reducing the pressure in the glass pipe in which the glass rod is inserted. By doing so, the glass pipe and the glass rod are sequentially heated from one end to the other end, and the diameter of the molten glass pipe is reduced by the pressure difference between the inside and outside of the glass pipe. As a result, the glass pipe and the glass rod are sequentially integrated, and the optical fiber preform is manufactured.
[0003]
The optical fiber preform manufactured in this manner is converted into an optical fiber by a drawing step. A method is also known in which this drawing step is performed simultaneously with the production of the optical fiber preform by the rod-in-tube method (for example, see Patent Reference 2).
[0004]
By the way, in recent years, from the viewpoint of reduction in production cost and the like, it has been required to increase the size of the optical fiber preform. For this reason, the diameter of the optical fiber preform has been increased.
[0005]
However, if such a large-diameter optical fiber preform is drawn as it is, it takes a long time to stabilize the optical fiber of the target diameter, and a large amount of the preform is consumed for initial stabilization. It becomes like this. As a result, the yield from the optical fiber preform to the optical fiber deteriorates, and the enlargement of the optical fiber preform originally performed for the purpose of cost reduction cannot achieve the purpose. There is an inconvenience.
[0006]
Therefore, in order to eliminate such inconveniences, the diameter of the normally manufactured large diameter optical fiber preform is reduced to an optimum diameter that maximizes the yield before the drawing step. A method of improving the productivity by performing the diameter reducing step of the optical fiber preform simultaneously with the production of the optical fiber preform by integrating the glass pipe and the glass rod is known (for example, Patent Reference 3).
[0007]
[Patent Document 1]
JP-B-56-45867
[Patent Document 2]
JP-A-50-85345
[Patent Document 3]
JP-A-7-10580
[0008]
[Problems to be solved by the invention]
In such a method of manufacturing an optical fiber preform by the rod-in-tube method, while the glass pipe and the glass rod are sequentially integrated in the axial direction, the optical fiber preform integrated with the glass pipe and the glass rod is used. The material is cut at a predetermined length. This is because when the optical fiber preform is manufactured, the optical fiber preform that has passed through the heating furnace is sandwiched between a pair of rollers to be drawn, and the optical fiber preform that has passed through the heating furnace is cut. If the production is continued as it is, the length of the optical fiber preform below the roller becomes too long, and the weight of the preform prevents the optical fiber preform from being supported by the rollers.
[0009]
On the other hand, when the optical fiber preform is manufactured by the rod-in-tube method, bubbles, peeling, and the like may occur at the interface between the integrated glass pipe and the glass rod. Bubbles are caused by scratches on the outer surface of the glass rod or the inner surface of the glass pipe, or moisture, gas, foreign matter, or the like attached to the outer surface or the inner surface. In addition, the peeling corresponds to a portion where the glass pipe and the glass rod were not surely integrated. In addition, among the above-mentioned bubbles and peeling, there are minute ones that are difficult to confirm as they are, but such minute air bubbles and the like can be obtained by irradiating light in the axial direction from the end face of the optical fiber preform. Since it shines like a dot, it can be seen with the naked eye. Hereinafter, a minute bubble or a peeled portion generated at the interface between the glass pipe and the glass rod is referred to as a luminescent spot.
[0010]
Such bright spots cause a loss failure or a connection failure in the optical fiber, so that the portion of the optical fiber preform where the bright spot occurs must be discarded. Therefore, whether or not a bright spot is generated in each optical fiber preform cut at a predetermined length during the integration is inspected after manufacturing the optical fiber preform, and a bright spot is generated. In such a case, the optical fiber preform is further cut at the generation position.
[0011]
The optical fiber preform thus cut is drawn in the next drawing step. However, in the drawing step, a predetermined amount of the optical fiber preform is consumed until the optical fiber having the target diameter is stabilized. If the length of the material is too short, the product cannot be obtained as a result. For this reason, the optical fiber preform that has become shorter than a predetermined length by cutting at the position of the bright spot is discarded without being sent to the drawing process, but in such a case, the yield is reduced. It cannot be denied.
[0012]
The present invention has been made in view of such circumstances, and an object of the present invention is to heat and integrate a glass pipe and a glass rod, thereby manufacturing an optical fiber preform. An object of the present invention is to improve the yield in a method of manufacturing a material.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method of melting the glass pipe and the glass rod sequentially in the axial direction while reducing the pressure inside the glass pipe in which the glass rod is inserted, and integrating the glass pipe and the glass pipe. The present invention relates to a method for manufacturing an optical fiber preform for manufacturing an optical fiber preform by stretching an integrated product of a fiber and a glass rod in the axial direction.
[0014]
And the manufacturing method of the optical fiber preform according to the present invention is such that both the glass pipe and the glass rod are caused to enter the heating furnace in the axial direction from the tip thereof, and the glass pipe and the glass rod are moved in the axial direction. In the integrating step of sequentially integrating and extending the glass pipe and the glass pipe and the glass rod in the integrating step, at the outlet side of the heating furnace, the glass pipe and the glass A detecting step of detecting a defect occurring in the optical fiber preform integrated with the rod; a setting step of setting a defect position detected in the detecting step to a cutting position of the optical fiber preform; Cutting the optical fiber preform at the cutting position set in the setting step on the outlet side of the furnace.
[0015]
Thereby, in the integration step, both the glass pipe and the glass rod are made to enter the heating furnace in the axial direction from the ends thereof. As a result, the glass pipe and the glass rod are sequentially heated in the axial direction and melted. At this time, since the inside of the glass pipe is depressurized, the diameter of the glass pipe is sequentially reduced in the axial direction, whereby the glass pipe is sequentially integrated with the glass rod in the axial direction. The glass pipe and the glass rod integrated in the heating furnace in this manner, that is, the optical fiber preform, are sequentially sent out from the outlet.
[0016]
While the glass pipe and the glass rod are sequentially integrated in this manner, in the detection step, a defect (bright spot) occurring in the optical fiber preform at the outlet side of the heating furnace is detected.
[0017]
Here, in the detection step, a defect occurring in the optical fiber preform may be detected using light emitted from the heating furnace.
[0018]
That is, the light radiated from the heating furnace is transmitted through the optical fiber preform sent from the outlet of the heating furnace in the axial direction, and is scattered by defects generated in the optical fiber preform. For this reason, it is possible to detect a defect that has occurred in the optical fiber preform visually or by performing image processing. In this way, by using the light emitted from the heating furnace, it is possible to detect defects in the optical fiber preform while integrating the glass pipe and glass rod without the need to provide a new light source. become.
[0019]
Then, in the setting step, the defect position detected in the detection step is set as a cutting position of the optical fiber preform, and in the cutting step, during the integration step, on the outlet side of the heating furnace, The optical fiber preform is cut at the cutting position set in the setting step.
[0020]
In the case where the optical fiber preform is cut uniformly at a predetermined length during the integration step, the optical fiber preform after the cutting needs to be further cut at the defect position according to the present invention. Now, it is necessary to detect the defects in the optical fiber preform during the integration step and cut the optical fiber preform at the detected defect position. There is no. Therefore, the length of each optical fiber preform (each cut optical fiber preform) is relatively long. This reduces the number of optical fiber preforms that must be discarded without being sent to the drawing step, that is, optical fiber preforms shorter than a predetermined length. Thus, the effective length of the optical fiber preform is increased, and the yield is improved.
[0021]
Here, in the setting step, when the distance from the end of the optical fiber preform to the defect detected in the detection step is shorter than the preset minimum length of the optical fiber preform, the defect position is set to the cutting position. It is preferable not to set.
[0022]
This is because, in the cutting step, the optical fiber preform is cut while the glass pipe and the glass rod are integrated, so that vibrations and the like during the cutting propagate in the axial direction, and the glass pipe and the glass rod are cut. This is because there is a risk of adversely affecting the integration with the device. That is, when the distance from the end of the optical fiber preform to the defect detected in the detection step is shorter than the preset minimum length of the optical fiber preform, the defect position is not set as the cutting position, The number of times the optical fiber preform is cut in the cutting step is reduced. As a result, the glass pipe and the glass rod are appropriately integrated. Note that the optical fiber preform may be cut at a defect position that is not set at the cutting position after its manufacture.
[0023]
Further, in the setting step, when the distance from the end of the optical fiber preform to the defect detected in the detection step is longer than a preset maximum length of the optical fiber preform, the distance from the end of the optical fiber preform is The position of the maximum length is preferably set as a cutting position.
[0024]
By doing so, even if no defect occurs in the optical fiber preform in which the glass pipe and the glass rod are integrated, the optical fiber preform is cut at least to the maximum length. The maximum length is determined according to the optical fiber preform manufacturing equipment or the like (specifically, according to the gripping force of the roller that grips the optical fiber preform at the exit side of the heating furnace, or from the lower end of the manufacturing equipment. (Depending on the length up to the floor).
[0025]
Further, in the setting step, in the detection step, a plurality of defects that are axially separated from each other are detected between a position of the minimum length from the end of the optical fiber preform and a position of the maximum length from the end. In such a case, the defect position closest to the position of the maximum length is preferably set as the cutting position.
[0026]
By doing so, the length of each optical fiber preform becomes as long as possible, and the yield in the drawing step of drawing the optical fiber preform is improved.
[0027]
【The invention's effect】
As described above, according to the method for manufacturing an optical fiber preform of the present invention, while integrating a glass pipe and a glass rod, a defect position generated in the optical fiber preform is detected, Since the optical fiber preform is cut at the defect position, the length of each cut optical fiber preform can be made longer than in a case where the optical fiber preform is uniformly cut at a predetermined length. Thereby, the number of optical fiber preforms to be discarded decreases, and the yield can be improved.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0029]
FIG. 1 shows an optical fiber preform manufacturing apparatus 1 according to an embodiment of the present invention. This manufacturing apparatus 1 manufactures an optical fiber preform 7 by a rod-in-tube method, and specifically, a glass pipe 2 serving as a cladding in an optical fiber, and a core or a core in an optical fiber. The optical fiber preform 7 is manufactured by integrating the glass rod 3 serving as a clad with the glass rod 3.
[0030]
Here, as the glass pipe 2, for example, a glass pipe manufactured by an OVD (Outside Vapor-phase Deposition) method or the like may be used. The glass pipe 2 has an outer diameter of about 180 mm, an inner diameter of about 50 mm, and a length of about 2000 mm.
[0031]
The glass rod 3 is obtained by sintering and stretching a glass fine particle deposit obtained by depositing glass fine particles by a vapor-phase axial deposition (VAD) method, or a cladding pipe formed by a modified chemical vapor deposition (MCVD) method. A core glass formed on the inner surface and solidified may be used. The glass rod 3 has a diameter of about 45 to 50 mm and a length of about 2500 mm.
[0032]
The manufacturing apparatus 1 includes a first holding unit that holds the upper end portion of the glass pipe 2 that is disposed to extend in the Z direction (the vertical direction in the drawing), thereby bringing the glass pipe 2 into a suspended state. 41 and a second grip portion 42 that grips an upper end portion of the glass rod 3 that is also provided to extend in the Z direction, thereby bringing the glass rod 3 into a suspended state. The first and second grippers 41 and 42 are configured to be able to move the positions of the glass pipe 2 and the glass rod 3 in the X direction (lateral direction in the drawing) and the Y direction (direction perpendicular to the drawing). In addition, the inclination of the glass pipe 2 and the glass rod 3 with respect to the Z direction can be adjusted. With this configuration, the glass pipe 2 and the glass rod 3 are positioned vertically and coaxially with each other.
[0033]
Each of the grips 41 and 42 is configured to be movable in the Z direction, and the glass pipe 2 and the glass rod 3 are respectively lowered with the downward movement of the grips 41 and 42. I try to move. The moving speeds of the first and second grips 41 and 42 can be changed, and the first grip 41 and the second grip 42 can be set to different speeds. For this reason, the moving speed of the glass pipe 2 and the glass rod 3 (the feeding speed to the heating furnace 5 to be described later) is adjustable, and the feeding speed of the glass pipe 2 and the feeding speed of the glass rod 3 are further adjusted. Can be different from each other.
[0034]
A heating furnace 5 that heats the glass pipe 2 and the glass rod 3 is disposed below the first holding portion 41. The heating furnace 5 has an inner diameter larger than the outer diameter of the glass pipe 2 and is disposed at a position substantially coaxial with the glass pipe 2 and the glass rod 3. Thus, the glass pipe 2 and the glass rod 3 can pass through the heating furnace 5 in the axial direction.
[0035]
With this configuration, when the glass pipe 2 and the glass rod 3 are moved downward by the first and second grippers 41 and 42, the glass pipe 2 and the glass rod 3 move through the heating furnace 5 at one end (lower end). ). Thereby, the glass pipe 2 and the glass rod 3 are sequentially heated from one end to the other end.
[0036]
The heating furnace 5 is specifically exemplified by a carbon resistance heating furnace and a high-frequency induction heating furnace.
[0037]
Below the heating furnace 5, two rollers 6, 6,... Are respectively disposed on both sides of the center axis of the heating furnace 5. Each of the rollers 6 is configured to be rotatable, and passes through the heater 5 to integrate the glass pipe 2 and the glass rod 3 (the optical fiber preform 7) which are integrated into two pairs of rollers 6, 6. ,.., And the integrated body is configured to be pulled downward. The rotation speed of each of the rollers 6 and 6 is configured to be changeable, and thereby, it is possible to adjust the speed of taking out the integrated material from the heater 5. By adjusting the pulling speed of the integrated member from the heater 5 in this manner, the outer diameter of the integrated member is set to the optical fiber preform 7 having a predetermined diameter.
[0038]
A closing cap 8 for closing the upper end opening is attached to the upper end surface of the glass pipe 2 held by the first holding portion 41. A vacuum pump (not shown) is connected to the closing cap 8, and the inside of the glass pipe 2 can be depressurized by driving the vacuum pump.
[0039]
The manufacturing apparatus 1 is provided with a detecting device 8 for detecting a defect (bright point) generated in the optical fiber preform.
[0040]
The detection device 8 includes a camera 81 disposed below the heating furnace 5. The camera 81 is configured to capture an image of the optical fiber preform 7 passing through the heating furnace 5. I have. Here, the light radiated from the heating furnace 5 is transmitted in the axial direction to the optical fiber preform 7 that has passed through the heating furnace 5, so that when a defect occurs in the optical fiber preform 7, Light becomes scattered. The camera 81 captures an image of a defect that looks shining by light emitted from the heating furnace. From the viewpoint of reliably imaging the defect of the optical fiber preform 7, it is preferable that the camera 81 be disposed immediately below the heating furnace 5 outlet.
[0041]
The camera 81 is connected to an image processing unit 82, and the image processing unit 82 detects a defect in the optical fiber preform 7 by processing image data captured by the camera 81. Then, the size of the detected defect is specified, and it is determined whether or not the defect is larger than a predetermined size (whether or not the defect needs to be removed).
[0042]
Further, the detection device 8 includes a rotation integrator 83 connected to the roller 6, and the rotation integrator 83 is configured to integrate the rotation of the roller 6. Thus, the rotation integrator 83 measures the length of the optical fiber preform 7 that has passed through the heating furnace 5.
[0043]
The image processing unit 82 and the rotation integrator 83 are connected to an arithmetic processing unit 84, and the arithmetic processing unit 84 performs an optical fiber motherboard based on the data from the image processing unit 82 and the rotation integrator 83. The cutting position of the material 7 is set. As will be described later in detail, the arithmetic processing unit 84 determines the distance from the tip of the optical fiber preform 7 to a defect (a defect of a predetermined size or more) based on data from the image processing unit 82 and the rotation integrator 83. , And by comparing this distance with a preset minimum length and maximum length of the optical fiber preform 7, the cutting position of the optical fiber preform 7 is set. .
[0044]
A display unit 85 is connected to the arithmetic processing unit 84. The display unit 85 displays the current length of the optical fiber preform 7 and the optical fiber preform 7 set by the arithmetic processing unit 84. And the cutting position (length from the end of the optical fiber preform 7) is displayed to notify the operator of the cutting position of the optical fiber preform 7.
[0045]
Next, a method of manufacturing the optical fiber preform 7 by the manufacturing apparatus 1 will be described. First, the upper end portion of the glass pipe 2 is gripped by the first gripping part 41, and the X and Y of the glass pipe 2 are coaxial with the heating furnace 5 by the first gripping part 41. The direction position is adjusted, and the inclination of the glass pipe 2 is adjusted so that the glass pipe 2 is disposed vertically.
[0046]
Next, the upper end portion of the glass rod 3 is gripped by the second gripper 42, and the X and X of the glass rod 3 are co-axial with the glass pipe 3 by the second gripper 42. The position in the Y direction is adjusted, and the inclination of the glass rod 3 is adjusted so that the glass rod 3 is disposed vertically. Then, the glass rod 3 is inserted into the glass pipe 2.
[0047]
Although not shown, an auxiliary pipe is attached to the upper end of the glass pipe 2 so as to be coaxial with the glass pipe 2, and the upper end of the auxiliary pipe may be gripped by the first grip 41. Good. Further, an auxiliary rod may be attached to the upper end of the glass rod 3 so as to be coaxial with the glass rod 3, and the upper end portion of the auxiliary rod may be gripped by the second grip 42. Furthermore, an auxiliary pipe may be attached to the lower end of the glass pipe 2 so as to be coaxial with the glass pipe 2, and an auxiliary rod may be attached to the lower end of the glass rod 3 so as to be coaxial with the glass rod 3. Good.
[0048]
Then, the upper end opening of the glass pipe 2 is closed by a closing cap 8, and the inside of the glass pipe 2 is depressurized by driving a vacuum pump. The glass pipe 2 and the glass rod 3 are sent into the heating furnace 5 by moving the first and second gripping portions 41 and 42 downward at a predetermined speed, respectively, while reducing the pressure inside the glass pipe 2. .
[0049]
Thereby, the glass pipe 2 and the glass rod 3 pass through the inside of the heating furnace 5 in the axial direction, and the glass pipe 2 and the glass rod 3 move from the lower end toward the upper end thereof. It is sequentially heated by the heating furnace 5. For this reason, the glass pipe 2 and the glass rod 3 are sequentially melted from the lower end to the upper end. The diameter of the reduced glass pipe 2 is reduced. As a result, the glass pipe 2 and the glass rod 3 are sequentially integrated in the longitudinal direction.
[0050]
The integrated body of the glass pipe 2 and the glass rod 3 is drawn by the rollers 6, 6,... And stretched to a predetermined outer diameter, whereby the optical fiber preform 7 is manufactured.
[0051]
The detection device 8 detects a defect (bright spot) generated in the optical fiber preform 7 while the optical fiber preform 7 is being manufactured in this way, and determines a cutting position of the optical fiber preform 7. Set. Based on the cutting position thus set (the cutting position displayed on the display unit 85), the operator cuts the optical fiber preform 7 below the roller 6 during the production of the optical fiber preform 7. I do.
[0052]
Next, the processing in the detection device 8 will be described with reference to the flowchart shown in FIG.
[0053]
First, in step S1, it is determined whether the length of the optical fiber preform 7 (if the optical fiber preform 7 has already been cut, the length starting from the cutting position) exceeds a preset minimum length. Is determined. If the answer is NO that the minimum length is not exceeded, this step S1 is repeated. On the other hand, if it is determined that the minimum length is exceeded, the process proceeds to step S2. As a result, when the length of the optical fiber preform 7 does not exceed the minimum length, even if a defect occurs, cutting is not performed at the defect position.
[0054]
In the following step S2, it is determined whether or not a defect that needs to be removed (a defect larger than a predetermined size) is detected. If not detected, this step S2 is repeated, and if detected, the process proceeds to step S3.
[0055]
In step S3, it is determined whether or not the length of the optical fiber preform 7 exceeds a preset maximum length when cutting is performed at the detected defect position. If the maximum length is exceeded, that is, YES, in step S4, the position of the maximum length from the tip of the optical fiber preform 7 is set as the cutting position, and the routine returns.
[0056]
On the other hand, if NO is determined not to exceed the maximum length, it is determined in step S5 whether the length of the optical fiber preform 7 exceeds the maximum length when cutting is performed at the next detected defect position. If the maximum length is exceeded, the process proceeds to step S6, whereas if the maximum length is not exceeded, the process proceeds to step S7.
[0057]
In the step S6, the previously detected defect position is set as the cutting position, and the process returns. On the other hand, in step S7, the defect position closest to the position of the maximum length is set as the cutting position, and the routine returns.
[0058]
Thus, in the present embodiment, a defect that has occurred in the optical fiber preform 7 during the manufacture of the optical fiber preform 7 is detected, and the optical fiber preform 7 is cut at the detected defect position.
[0059]
When the distance from the tip of the optical fiber preform 7 to the defect is shorter than the minimum length, the optical fiber preform 7 is not cut at the defect position (see step S1 in FIG. 2). The number of times the optical fiber preform 7 is cut during the manufacture of the optical fiber preform 7 can be reduced, and adversely affecting the integration of the glass pipe 2 and the glass rod 3 can be suppressed.
[0060]
Further, when the distance from the tip of the optical fiber preform 7 to the defect is longer than the maximum length, the position of the maximum length from the tip of the optical fiber preform 7 is set as the cutting position (step S4 in FIG. 2). reference). As a result, the length of the optical fiber preform 7 becomes less than or equal to the maximum length, and the optical fiber preform 7 can be separated according to the manufacturing equipment of the optical fiber preform 7.
[0061]
In addition, when a plurality of defects separated from each other in the axial direction are detected between the position of the minimum length from the end of the optical fiber preform 7 and the position of the maximum length from the end, the maximum length is detected. The defect position closest to the position is set as the cutting position (see step S7 in FIG. 2). Thereby, the length of each optical fiber preform 7 becomes relatively long, and the yield from the optical fiber preform 7 to the optical fiber can be improved. That is, in the drawing step, a predetermined amount of the optical fiber preform 7 is consumed for the initial stabilization. Therefore, the length of each optical fiber preform 7 is made as long as possible, and the number of the cut optical fiber preforms 7 is reduced. Thus, the production amount of the optical fiber increases as compared with the case where a large number of optical fiber preforms 7 having a short length are prepared. Therefore, the yield from the optical fiber preform 7 to the optical fiber is improved by making the length of each optical fiber preform 7 relatively long.
[0062]
Thus, in the method for manufacturing an optical fiber preform according to the present embodiment, the yield can be improved as compared with a case where the optical fiber preform 7 is uniformly cut at a predetermined length.
[0063]
This will be described with reference to FIG. FIG. 3 shows a comparative example in which the optical fiber preform 7 is uniformly cut at a predetermined length during the production of the optical fiber preform 7, and the optical fiber preform 7 is cut at a defect position generated in the optical fiber preform 7. In the example of cutting, the optical fiber preform 7 that is discarded without being sent to the drawing step is shown (a shaded portion shown in the figure).
[0064]
In the figure, the positions indicated by broken lines indicate positions of defects occurring in the optical fiber preform, and the positions indicated by thick solid lines indicate positions cut during the production of the optical fiber preform 7. In the comparative example, since the cutting is performed at a predetermined length, the intervals between the thick solid lines are equal. On the other hand, in the embodiment, since the cutting is performed at the defect position, the interval between the thick solid lines is not equal, and each thick solid line corresponds to the defect position.
[0065]
In each of the comparative example and the example, each optical fiber preform 7 cut during manufacturing is further cut at the position (defect position) indicated by the broken line.
[0066]
In the comparative examples and the examples, the hatched portions indicate portions that are discarded due to their short length. Note that the portion from the base material length 0 to the first defect is discarded because the entire surface has peeled off.
[0067]
According to the figure, it can be seen that the total length of the hatched portion (discarded portion) of the example is shorter than that of the comparative example. Conversely, the total length (effective length) of the portion not shaded (the portion to be drawn) is longer in the example than in the comparative example. Therefore, the yield can be improved by cutting the optical fiber preform 7 at the defect position during the manufacturing of the optical fiber preform 7 as in the embodiment.
[0068]
<Other embodiments>
It should be noted that the present invention is not limited to the above embodiment, but includes various other embodiments. That is, in the above embodiment, the detection device 8 is configured to display the cutting position on the display unit 85, and the operator cuts the optical fiber preform 7 based on the display on the display unit 85. However, for example, a cutting device for cutting the optical fiber preform 7 is provided, and the cutting device is configured to automatically cut the optical fiber preform 7 at the cutting position set by the detection device 8. You may. As the cutting device, for example, a device using laser light is exemplified.
[0069]
In the above-described embodiment, the detection device 8 is configured to detect a defect of the optical fiber preform 7 by processing an image captured by the camera 81. The defect of the material 7 may be detected.
[0070]
In addition, by comparing the defect position visually detected by the operator with the minimum length and the maximum length of the optical fiber preform 7, the cutting position of the optical fiber preform 7 can be determined according to the flowchart shown in FIG. May be set by the operator.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an apparatus for manufacturing an optical fiber preform.
FIG. 2 is a flowchart illustrating a process in the detection device.
FIG. 3 is an explanatory view showing a discarded portion in each of optical fiber preforms of a comparative example and an example.
[Explanation of symbols]
2 Glass pipe
3 Glass rod
5 heating furnace
7 Optical fiber preform

Claims (5)

While decompressing the inside of the glass pipe in which the glass rod is inserted, the glass pipe and the glass rod are sequentially melted and integrated in the axial direction, and the integrated product of the glass pipe and the glass rod is axially integrated. A method for producing an optical fiber preform by producing an optical fiber preform by stretching,
An integrating step of extending both the glass pipe and the glass rod into the heating furnace in the axial direction from the distal end thereof, thereby sequentially integrating the glass pipe and the glass rod in the axial direction and extending the same.
During the integration of the glass pipe and the glass rod in the integration step, at the outlet side of the heating furnace, defects occurring in the optical fiber preform in which the glass pipe and the glass rod are integrated A detecting step of detecting
A setting step of setting the defect position detected in the detection step to a cutting position of the optical fiber preform,
A cutting step of cutting the optical fiber preform at the cutting position set in the setting step on the outlet side of the heating furnace. In claim 1,
In the setting step, when the distance from the end of the optical fiber preform to the defect detected in the detection step is shorter than a preset minimum length of the optical fiber preform, the defect position is not set as the cutting position. A method for producing an optical fiber preform, comprising: In claim 1,
In the setting step, when the distance from the end of the optical fiber preform to the defect detected in the detection step is longer than the preset maximum length of the optical fiber preform, the maximum distance from the end of the optical fiber preform is used. A method of manufacturing an optical fiber preform, wherein a length position is set to a cutting position. In claim 1,
In the setting step, when a plurality of defects separated from each other in the axial direction are detected between the position of the minimum length from the end of the optical fiber preform and the position of the maximum length from the end in the detection step, And setting a defect position closest to the position of the maximum length as a cutting position. In claim 1,
The method for manufacturing an optical fiber preform, wherein in the detecting step, a defect occurring in the optical fiber preform is detected using light emitted from the heating furnace.

Images