JP2012171814A - Method and apparatus for producing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce an optical fiber having a constant core diameter and uniform characteristics when an optical fiber preform in which a core part and a clad part are integrated is drawn.SOLUTION: When an optical fiber preform 21 in which a core part and a clad part are integrated is melted and the melted optical fiber preform 21 is drawn to produce an optical fiber, a core diameter measuring unit 13 and a clad diameter measuring unit 14 measure the core diameter and clad diameter of the drawn optical fiber preform 21, respectively, and a control unit 20 calculates the target value of the clad diameter by which the core diameter becomes a predetermined value, based on the measured core diameter and clad diameter, and controls the drawing speed and/or the optical fiber preform feeding speed so that the calculated target value and the measured clad diameter can equate with each other.

Description

  The present invention relates to an optical fiber manufacturing method and an optical fiber manufacturing apparatus for manufacturing an optical fiber by melting an optical fiber preform and drawing the melted optical fiber preform.

In manufacturing an optical fiber, a method is generally used in which an optical fiber preform is heated to a molten state, and the molten optical fiber preform is drawn. In this method, the cladding diameter (outer diameter) of the optical fiber can be adjusted by changing the drawing speed, the optical fiber preform feeding speed, and the like.
In order to keep the characteristics of the optical fiber constant in the longitudinal direction, it is necessary to adjust the cladding diameter of the optical fiber to an appropriate diameter. Therefore, the cladding diameter of the optical fiber is selected so that the required characteristics can be obtained, and is generally controlled so as to be constant.

  However, even if the cladding diameter is appropriately selected and controlled to be constant, if the core diameter changes, the characteristics of the optical fiber such as the mode field diameter will vary. For example, when the ratio between the core diameter and the cladding diameter changes along the longitudinal direction of the optical fiber preform, the core diameter changes even if the cladding diameter of the optical fiber is made constant.

  As a technique for making the core diameter constant, for example, in Patent Document 1, heat softening is performed with a core rod inserted into a cladding quartz tube, and a space between the core rod and the cladding quartz tube is filled. However, there is disclosed a manufacturing apparatus for an optical fiber that draws integrally while adjusting not only the cladding diameter but also the core diameter.

  This manufacturing apparatus includes a core diameter measuring unit that measures the core diameter of an optical fiber immediately after drawing and a fiber clad diameter measuring unit that measures the outer diameter of the fiber. Based on the values measured by the core diameter measuring unit, the core rod The core diameter and the clad diameter are adjusted by adjusting the feed speed and adjusting the feed speed of the clad quartz tube based on the value measured by the fiber clad diameter measuring section.

JP 60-260441 A

  The above-described prior art of Patent Document 1 is a technique called rod-in drawing in which a core rod and a cladding quartz tube are integrated while being integrated. It adjusts independently. Therefore, when the optical fiber preform in which the core portion and the cladding portion are integrated in advance is drawn, the technique of Patent Document 1 described above cannot be applied.

  The prior art of Patent Document 1 adjusts the core diameter by changing the feed speed of the core rod when the core diameter deviates from a desired value. In particular, the time interval for measuring the core diameter Is long, the time interval for resetting the feed speed of the core rod becomes long. As a result, it takes time to return the core diameter to a desired value, and the characteristics of the optical fiber cannot be made uniform.

  The present invention has been made in view of the above-described situation, and when drawing an optical fiber preform in which a core portion and a cladding portion are integrated, an optical fiber having a uniform core diameter and uniform characteristics can be easily obtained. It is an object of the present invention to provide an optical fiber manufacturing method and an optical fiber manufacturing apparatus that can be manufactured easily.

  An optical fiber manufacturing method according to the present invention includes an optical fiber manufacturing method in which an optical fiber preform in which a core portion and a cladding portion are integrated is melted, and the melted optical fiber preform is drawn. Then, the core diameter and the cladding diameter of the drawn optical fiber preform are measured, and based on the measured core diameter and the cladding diameter, the target value of the cladding diameter at which the core diameter becomes a predetermined value is calculated and calculated. The core diameter is controlled by controlling the drawing speed and / or the optical fiber preform feed speed so that the target value matches the measured cladding diameter.

  In the optical fiber manufacturing method according to the present invention, when the optical fiber preform is drawn, the core diameter is measured at a drawing interval of 1000 m or less, and each time the core diameter is measured, the target value of the cladding diameter is set. It can be recalculated. Further, in this manufacturing method, the drawing speed and / or the optical fiber preform feeding speed can be controlled so that the measured variation in the core diameter is within ± 2% of the predetermined value.

  An optical fiber manufacturing apparatus according to the present invention melts an optical fiber preform in which a core portion and a cladding portion are integrated, and produces an optical fiber by drawing the melted optical fiber preform. The core diameter measuring unit for measuring the core diameter of the drawn optical fiber preform, the cladding diameter measuring unit for measuring the cladding diameter of the drawn optical fiber preform, and the core diameter measured by the core diameter measuring unit Then, based on the cladding diameter measured by the cladding diameter measuring unit, a target value of the optical fiber preform whose core diameter is a predetermined value is calculated, and the calculated target value and the cladding diameter measurement are calculated. A control unit that controls the core diameter by controlling the drawing speed and / or the optical fiber preform feeding speed so that the clad diameter measured by the unit matches.

  According to the present invention, based on the measured values of the core diameter and the clad diameter, the target value of the clad diameter at which the core diameter becomes a predetermined value is calculated, and the calculated target value matches the measured value of the clad diameter. Since the drawing speed and / or the optical fiber preform feeding speed are controlled, in the drawing of the optical fiber preform in which the core portion and the cladding portion are integrated, the core diameter is constant and the characteristics are uniform. Is easy to manufacture. In addition, even if the time interval for measuring the core diameter is increased, the cladding diameter is controlled so that the core diameter becomes a predetermined value based on the measured value of the cladding diameter that changes every moment. An optical fiber with uniform characteristics can be easily obtained.

It is a figure which shows an example of the optical fiber manufacturing apparatus which concerns on embodiment of this invention. It is a figure explaining an example of the calculation method of the clad diameter used as control object.

Hereinafter, an optical fiber manufacturing method and an optical fiber manufacturing apparatus according to the present invention will be described. FIG. 1 is a diagram illustrating an example of an optical fiber manufacturing apparatus 10 according to an embodiment of the present invention.
As shown in FIG. 1, the optical fiber manufacturing apparatus 10 includes a drawing furnace 11, a heater 12, a core diameter measuring unit 13, a cladding diameter measuring unit 14, a resin coating die 15, a curing furnace 16, a guide roller 17, and a capstan 18. A winding drum 19 and a control unit 20.

  An optical fiber preform 21 is set in the drawing furnace 11. The optical fiber preform 21 has a core part at the center and a clad part around the core part. Here, for example, the outer diameter of the optical fiber preform 21 is 100 ± 2 mm, and the core diameter of the optical fiber preform 21 is 6.5 ± 0.3 mm. When the optical fiber preform 21 is heated by the heater 12, the tip of the optical fiber preform 21 melts and falls, and the optical fiber 22 is drawn.

  In this drawing process, a resin (protective coating) is applied to the optical fiber 22 using the resin application die 15, and then the optical fiber 22 is sent to the curing furnace 16 to solidify the applied resin. The drawn optical fiber 22 is taken up by the capstan 18 via the guide roller 17 and the like, and further taken up by the take-up drum 19. For example, a 1000 km optical fiber 22 is manufactured from the optical fiber preform 21 in a single drawing process.

  A core diameter measuring unit 13 and a clad diameter measuring unit 14 are installed upstream of the resin coating die 15. The core diameter measuring unit 13 measures the core diameter of the drawn optical fiber 22. The clad diameter measuring unit 14 measures the clad diameter of the drawn optical fiber 22.

Here, the core diameter measuring unit 13 captures a translucent image of the side surface of the optical fiber 22 with a microscope and a high-speed imaging camera, and generates a luminance profile of the optical fiber image from the captured translucent image. Then, the core diameter measuring unit 13 performs image processing on the generated luminance profile to detect the core part of the optical fiber 22 and measures the core diameter. Since detection of the core part and image processing take time, measurement of the core diameter requires a longer time than measurement of the cladding diameter.
In addition, a general outer diameter measuring device is used for the cladding diameter measuring unit 14, and the cladding diameter measuring unit 14 measures the cladding outer diameter at intervals of about several ms.

  The control unit 20 calculates a cladding diameter such that the core diameter becomes a desired value from the core diameter and the cladding diameter measured by the core diameter measuring unit 13 and the cladding diameter measuring unit 14, respectively, The take-up speed (drawing speed) of the optical fiber 22 of the capstan 18 and / or the optical fiber preform feed speed are controlled so that the clad diameter measured by the clad diameter measuring unit 14 matches. That is, when controlling the take-up speed, the control unit 20 sets the take-up speed to a large value to reduce the cladding diameter, and to increase the clad diameter, the control unit 20 sets the take-up speed to a small value. The calculated cladding diameter and the measured cladding diameter are made to coincide. When controlling the optical fiber preform feed rate, the control unit 20 sets the optical fiber preform feed rate to a small value to reduce the cladding diameter, and the control unit 20 increases the optical fiber preform to increase the cladding diameter. The base material feed speed is set to a large value so that the calculated clad diameter and the measured clad diameter coincide. Note that the control of the take-up speed and the control of the optical fiber preform feeding speed may be controlled in combination.

FIG. 2 is a diagram for explaining an example of a method for calculating a clad diameter to be controlled. FIG. 2 shows a core portion 30 and a clad portion 31 of the optical fiber 22. Here, the core diameter measured by the core diameter measuring unit 13 is A, the cladding diameter measured by the cladding diameter measuring unit 14 is B, the target core diameter is Ax, and the core diameter is Ax. The target value of the cladding diameter is Bx. In this case, the control unit 20 sets the clad diameter target value Bx to B / A × Ax.
For example, when the optical fiber 22 having the measured core diameter A and cladding diameter B of 8 μm and 125 μm and the core diameter Ax of 8.1 μm is manufactured, the target value Bx of the cladding diameter is 126.5 μm ( ≈125 / 8 × 8.1).

  The ratio B / A between the cladding diameter B and the core diameter A is such that the optical fiber 22 is drawn at a speed different from the normal drawing speed (for example, 25 m / s) when the optical fiber 22 is manufactured. It is good also as calculating from the clad diameter and core diameter which were measured. For example, the ratio B / A may be calculated from the cladding diameter and the core diameter measured when the drawing speed is small immediately after the start of drawing. When the drawing speed is low, the measurement of the cladding diameter and the core diameter by image processing can be performed with higher accuracy, and the ratio B / A can be calculated more accurately.

  In addition, the measurement of the core diameter A, which takes time to measure, is performed, for example, for each drawing of 1000 m. However, it is better if it is 1000 m or less, and the shorter, the more accurate control can be performed. However, since the measurement of the core diameter A depends on the processing capacity of the core diameter measurement system as described above, there is a limit naturally. On the other hand, the measurement of the cladding diameter B is performed almost continuously.

  The control unit 20 recalculates the target value Bx (= B / A × Ax) of the cladding diameter from the measured values of the core diameter A and the cladding diameter B each time information on the measurement result of the core diameter A is obtained. Then, the take-up speed of the optical fiber 22 in the capstan 18 and / or the optical fiber preform feed speed is controlled so that the clad diameter becomes the target value Bx. As a result, the fluctuation of the core diameter A is controlled to be within ± 2% of the regulation (that is, the target core diameter Ax). In the case of controlling only by the clad diameter, the core diameter fluctuation of the optical fiber preform is almost the same as the core diameter fluctuation of the optical fiber, so that the core diameter fluctuation of about ± 4 to 5% occurs.

  In addition, the control unit 20 does not directly control the core diameter but controls the clad diameter because, for the reason described above, it is more difficult to measure the core diameter at short intervals than in the case of the clad diameter. Therefore, while the measurement interval of the core diameter of the core diameter measurement unit 13 is longer than the measurement interval of the clad diameter of the clad diameter measurement unit 14, while the core diameter is not measured, the control unit 20 determines the core measured immediately before. Using the target value Bx of the cladding diameter calculated by the diameter, the take-up speed of the optical fiber 22 and / or the optical fiber so that the cladding diameter measured at an interval shorter than the core diameter becomes the target value Bx. The base material feed speed is continuously controlled.

  Thereby, compared with the case where only the cladding diameter is controlled, the core diameter can be made constant over the entire length of the optical fiber 22, and the characteristics can be made uniform. That is, by using the above-described method, for example, variation in mode field diameter can be suppressed to about half, and an optical fiber having uniform quality can be manufactured. In addition, when the long optical fiber 22 is divided and wound around a bobbin, it is possible to suppress variations in the characteristics of the optical fiber 22 for each bobbin. Moreover, the optical fiber 22 is sampled and the characteristics are analyzed, and the operation of adjusting the core diameter by trial and error based on the analysis result becomes unnecessary, and the manufacturing efficiency of the optical fiber 22 is improved.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber manufacturing apparatus, 11 ... Drawing furnace, 12 ... Heater, 13 ... Core diameter measurement part, 14 ... Cladding diameter measurement part, 15 ... Resin coating die, 16 ... Curing furnace, 17 ... Guide roller, 18 ... Capstan , 19 ... winding drum, 20 ... control part, 30 ... core part, 31 ... clad part.

Claims (4)

An optical fiber manufacturing method for manufacturing an optical fiber by melting an optical fiber preform in which a core portion and a cladding portion are integrated, and drawing the melted optical fiber preform,
Measure the core diameter and cladding diameter of the drawn optical fiber preform, and calculate the target value of the cladding diameter at which the core diameter becomes a predetermined value based on the measured core diameter and cladding diameter. The core diameter is controlled by controlling the drawing speed and / or the optical fiber preform feed speed so that the measured target value matches the measured cladding diameter.   When the optical fiber preform is drawn, the core diameter is measured at a drawing interval of 1000 m or less, and the target value of the cladding diameter is recalculated every time the core diameter is measured. Item 2. A method for manufacturing an optical fiber according to Item 1.   3. The drawing speed and / or the optical fiber preform feed speed are controlled so that the measured fluctuation of the core diameter is within ± 2% of the predetermined value. Optical fiber manufacturing method. An optical fiber manufacturing apparatus for manufacturing an optical fiber by melting an optical fiber preform in which a core portion and a cladding portion are integrated, and drawing the melted optical fiber preform,
A core diameter measuring unit for measuring the core diameter of the optical fiber preform drawn;
A clad diameter measuring unit for measuring the clad diameter of the optical fiber preform drawn;
Based on the core diameter measured by the core diameter measuring unit and the cladding diameter measured by the cladding diameter measuring unit, the core diameter of the optical fiber preform is a predetermined value of the core diameter of the optical fiber preform. The core diameter is controlled by calculating a target value and controlling the drawing speed and / or the optical fiber preform feed speed so that the calculated target value and the clad diameter measured by the clad diameter measuring unit coincide with each other. A control unit,
An optical fiber manufacturing apparatus comprising:

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