JP2013028508A - Method for manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber capable of manufacturing a high-quality optical fiber by suppressing excellently fluctuation of a cut-off wavelength.SOLUTION: This method includes: a cut-off wavelength prediction processing of predicting longitudinal direction fluctuation of the cut-off wavelength based on a refractive index distribution in the longitudinal direction of an optical fiber preform 2 which is measured beforehand; a target post-coating tension determination processing of determining a target post-coating tension so that the cut-off wavelength of a drawn glass fiber 3 becomes constant in the longitudinal direction based on a relation between drawing tension and the cut-off wavelength and on a relation between the drawing tension and tension after coating; and a furnace temperature control processing of controlling a furnace temperature of a drawing furnace 12 so that the post-coating tension agrees with the target post-coating tension, wherein, when performing the target post-coating tension determination processing, a target post-coating tension correction processing of correcting the target post-coating tension is performed based on fluctuation of take-up resistance of the optical fiber 4.

Description

  The present invention relates to an optical fiber manufacturing method for manufacturing an optical fiber by drawing an optical fiber preform.

When manufacturing an optical fiber, it is required that the cutoff wavelength, which is one of the characteristics of the optical fiber, be substantially uniform in the longitudinal direction of the optical fiber.
As an optical fiber manufacturing method, the longitudinal variation of the refractive index distribution in the radial direction of the optical fiber preform is measured in advance, and the drawing tension is measured while measuring the drawing tension generated in the glass fiber during drawing. Based on the measurement result of the force and the measurement result of the longitudinal variation of the refractive index distribution of the optical fiber preform, the cutoff wavelength of the glass fiber is predetermined while suppressing the longitudinal variation of the refractive index distribution in the radial direction of the glass fiber. It is known to control the drawing tension of the glass fiber so that the value becomes (for example, see Patent Document 1).

  In addition, an estimated cutoff wavelength value of the optical fiber after drawing is obtained in advance at a plurality of locations in the longitudinal direction of the optical fiber preform so that the cutoff wavelength of the optical fiber after drawing becomes a predetermined value in the longitudinal direction. In addition, it is also known that the drawing is performed by sequentially controlling the drawing tension in the longitudinal direction in accordance with the fluctuation of the estimated cutoff wavelength at the time of drawing (for example, see Patent Document 2).

JP-A-2005-314118 Japanese Patent Laid-Open No. 8-217481

  Conventionally, the refractive index distribution in the longitudinal direction of the optical fiber preform is measured, the longitudinal variation of the cutoff wavelength is estimated from the refractive index distribution, and the correlation between the pre-measured drawing tension and the cutoff wavelength, In addition, an appropriate drawing tension and post-coating tension are determined from the correlation between the drawing tension and the post-coating tension, and the cut-off wavelength of the glass fiber is controlled to be a predetermined constant value.

  When an optical fiber is manufactured by coating a drawn glass fiber with a resin, the coating diameter may vary due to disturbance or the like. Then, since the area of the outer peripheral surface of the optical fiber also varies, the drawing tension of the glass fiber varies even if the post-coating tension is the same. Also, if the cut-off wavelength is measured from the actually drawn glass fiber and fed back to the post-coating tension, various rollers such as the guide roller and the tension measuring roller will deteriorate before the cut-off wavelength data is obtained. As a result, the roller resistance may vary. Then, a deviation may occur in the relationship between the post-coating tension and the linear tensile force, but it was difficult to immediately correct the post-coating tension based on this deviation.

  And, since the tension after coating changes due to fluctuations in take-up resistance such as fluctuations in the coating diameter as described above and fluctuations in roller resistance in various rollers, if this is controlled to be constant, the wire tension will change. As a result, the cut-off wavelength also fluctuates, and there is a possibility that the quality is deteriorated.

  The objective of this invention is providing the manufacturing method of the optical fiber which can suppress the fluctuation | variation of a cutoff wavelength favorably and can manufacture a high quality optical fiber.

The method for producing an optical fiber of the present invention that can solve the above-mentioned problems is that a glass fiber is drawn from an optical fiber preform heated and melted in a drawing furnace, and a resin is coated around the glass fiber to produce an optical fiber. An optical fiber manufacturing method for manufacturing a fiber, comprising:
A cutoff wavelength prediction process for predicting a longitudinal variation in the cutoff wavelength based on a variation in the refractive index distribution in the longitudinal direction of the optical fiber preform measured in advance;
Based on the relationship between the drawing tension, which is the tension of the glass fiber, and the cutoff wavelength, and the relationship between the drawing tension, and the post-coating tension, which is the tension of the optical fiber, the cutoff of the glass fiber after drawing. A target post-coating tension determination process for determining a target post-coating tension such that the wavelength is constant in the longitudinal direction;
Furnace temperature control processing for controlling the furnace temperature of the drawing furnace such that the post-coating tension becomes the target post-coating tension,
In the target post-coating tension determination process, a target post-coating tension correction process for correcting the target post-coating tension based on a change in the take-up resistance of the optical fiber is performed.

In the method for producing an optical fiber of the present invention,
A corrected target post-coating tension P (g) obtained by correcting the target post-coating tension is:
P = P0 + A × (D−D0)
(However, P0: tension after target coating before correction (g), A: constant (g / μm), D: coating diameter of optical fiber (μm), D0: reference coating diameter (μm))
It is preferable to derive from a correction formula consisting of

In the method for producing an optical fiber of the present invention,
An upstream tension F1 on the upstream side of the immediately below roller that guides the optical fiber first, and a downstream tension F2 on the downstream side of the tension measuring roller that measures the post-coating tension on the downstream side of the immediately below roller,
A corrected target post-coating tension T (g) obtained by correcting the target post-coating tension,
T = T0 + Δ (F2-F1)
(However, T0: target post-correction tension (g), Δ (F2-F1): variation (g) of difference value between F2 and F1 from the previous measurement)
It is preferable to derive from a correction formula consisting of

  According to the present invention, the target post-coating tension is finely corrected on the basis of fluctuations in the take-up resistance of the optical fiber that fluctuate due to fluctuations in the coating diameter of the optical fiber and fluctuations in the roller resistance of various rollers that guide the optical fiber downstream. can do. Thereby, the fluctuation | variation of a cutoff wavelength can be suppressed favorably and a high quality optical fiber can be manufactured.

It is a schematic block diagram which shows one Embodiment of the apparatus which implements the manufacturing method of the optical fiber which concerns on this invention. It is a graph which shows the correlation with the post-coating tension | tensile_strength of an optical fiber, and the cutoff wavelength of a glass fiber. It is a graph which shows the correlation with the coating diameter of an optical fiber, and the tension | tensile_strength after a coating.

Hereinafter, an example of an embodiment of an optical fiber manufacturing method according to the present invention will be described with reference to the drawings.
First, the example of the manufacturing apparatus which manufactures an optical fiber with the manufacturing method of the optical fiber of this invention is demonstrated.
As shown in FIG. 1, the manufacturing apparatus 1 is an apparatus for manufacturing an optical fiber 4 by drawing an optical fiber preform 2 to form a glass fiber 3 and coating the outer periphery of the glass fiber 3 with a resin. .

The manufacturing apparatus 1 includes a base material feeding device 11, a drawing furnace 12, a resin coating device 13, ultraviolet irradiation devices 15 and 16, a direct roller 17, a capstan 18, guide rollers 26 and 27, a dancer roller 19 and a winding drum 20. Have.
The preform feeding device 11 holds the optical fiber preform 2 and places the optical fiber preform 2 in the drawing furnace 12. The drawing furnace 12 is an apparatus for heating and melting one end of the optical fiber preform 2. The glass fiber 3 is formed by drawing the melted one end side of the optical fiber preform 2 downward.

  The resin coating device 13 and the ultraviolet irradiation devices 15 and 16 are disposed downstream of the drawing furnace 12 in the drawing direction of the glass fiber 3. The resin coating device 13 applies an ultraviolet curable resin to the outer periphery of the glass fiber 3. The ultraviolet irradiation devices 15, 16 form the first and second coating layers by irradiating the resin applied by the resin coating device 13 with ultraviolet rays, and form the optical fiber 4. In addition, although the dual system which apply | coats the resin used as a 2 layer coating layer with one resin application apparatus was demonstrated to the example here, even if it is a tandem system applied and cured one by one with each resin application apparatus Good.

  The capstan 18 includes a belt 18a and a roller 18b. The capstan 18 presses the belt 18a against the roller 18b, rotates the roller 18b, and sandwiches the optical fiber 4 between the belt 18a and the roller 18b. The optical fiber 4 is taken out and sent to the dancer roller 19 and the winding drum 20. The traveling direction of the optical fiber 4 taken by the capstan 18 is changed by a roller 17 that guides the optical fiber 4 first. The slack of the optical fiber 4 sent out from the capstan 18 is removed by the dancer roller 19, and is taken up by the take-up drum 20.

  The manufacturing apparatus 1 further includes a glass fiber outer diameter measuring device 21, a wire tension measuring device 22, a post-coating outer diameter measuring device 23, and a post-coating tension measuring device 24. The glass fiber outer diameter measuring device 21 is disposed between the drawing furnace 12 and the resin coating device 13 and measures the outer diameter of the glass fiber 3. The coated outer diameter measuring device 23 is disposed between the ultraviolet irradiation device 16 and the roller 17 directly below, and measures the outer diameter of the coated optical fiber 4. The glass fiber outer diameter measuring device 21 and the coated outer diameter measuring device 23 are, for example, non-contact type measuring devices using laser light.

  The drawing tension measuring device 22 is disposed between the glass fiber outer diameter measuring device 21 and the resin coating device 13. The drawing tension measuring device 22 measures the drawing tension generated in the glass fiber 3 during drawing.

  In general, a contact tension meter is often used for the wire tension measuring device 22. While the contact-type tensiometer has the advantages of being inexpensive and having high measurement accuracy, it will damage the glass fiber 3, so that the tension should generally be measured while a good part is being manufactured. I can't. In addition to the contact tension meter, there is a method of irradiating circularly polarized light from the side of the glass fiber 3 and measuring the magnitude of the drawing tension generated in the glass fiber 3 from the change in the polarization state. It is more expensive than a contact tension meter, and the measurement accuracy is also reduced. For this reason, instead of directly measuring the drawing tension, the post-coating tension described below is often measured, and the drawing tension is often obtained from the post-coating tension. In the present embodiment, either a contact tension meter or an optical tension meter may be used as the line tension force measuring device 22.

The post-coating tension measuring device 24 is disposed between the direct roller 17 and the capstan 18. The post-coating tension measuring device 24 measures post-coating tension generated in the optical fiber 4 after coating.
The post-coating tension measuring device 24 includes a tension measuring roller 24 a that is in contact with the optical fiber 4. The post-coating tension measuring device 24 is attached to the central axis of the tension measuring roller 24 a and measures the force applied to the tension measuring roller 24 a by the tension generated in the optical fiber 4. Then, the post-coating tension generated in the optical fiber 4 is obtained from this force. This post-coating tension changes according to the drawing tension, and a proportional relationship is established between the drawing tension and the post-coating tension.

  The manufacturing apparatus 1 further includes a control device 25. The control device 25 is electrically connected to the drawing furnace 12, the glass fiber outer diameter measuring device 21, the drawing tension measuring device 22, the coated outer diameter measuring device 23, the coated tension measuring device 24, the capstan 18, and the like. ing. Measurement results of the glass fiber outer diameter measuring device 21, the wire tension measuring device 22, the coated outer diameter measuring device 23, the coated tension measuring device 24, and the like are input to the control device 25.

Next, the case where the optical fiber 4 is manufactured will be described.
First, before starting drawing, the refractive index distribution in the radial direction is measured in advance with a preform analyzer at a plurality of locations in the longitudinal direction of the optical fiber preform 2. For example, the refractive index distribution of the optical fiber preform 2 is slightly different depending on the measurement location, so that the longitudinal variation of the refractive index distribution of the optical fiber preform 2 can be seen. The result of this measurement is input to the control device 25.

  Next, the optical fiber preform 2 is installed in the preform feeder 11 and placed in the drawing furnace 12. One end of the optical fiber preform 2 is heated and melted by the drawing furnace 12 to be drawn and the glass fiber 3 is drawn.

  When the drawing is started, the outer diameter of the glass fiber 3 is measured by the glass fiber outer diameter measuring device 21. When the wire tension measuring device 22 is a contact-type tension meter, as described above, it is not normally used during the production of a good part. Thereafter, the wire tension measuring device 22 measures the wire tension force as necessary, and is necessary. Is input to the control device 25 accordingly.

  The glass fiber 3 that has passed through the drawing tension measuring device 22 passes through the resin coating device 13 and the ultraviolet irradiation devices 15 and 16 in this order. Thereby, a coating layer is formed on the glass fiber 3, and the optical fiber 4 having two coating layers on the glass fiber 3 is obtained. The outer diameter of the optical fiber 4 is measured by the outer diameter measuring device 23 after coating. The optical fiber 4 that has passed through the outer diameter measuring device 23 after coating is wound around the winding drum 20 via the roller 17 directly below, the tension measuring device 24 after coating, the capstan 18, the guide rollers 26 and 27, and the dancer roller 19.

  As described above, when the optical fiber 4 is manufactured by drawing the glass fiber 3 from the optical fiber preform 2, the control device 25 calculates the refractive index distribution in the longitudinal direction of the optical fiber preform 2 that has been measured in advance. A cutoff wavelength prediction process for predicting the longitudinal variation of the cutoff wavelength is performed based on the fluctuations of.

  The control device 25 also determines the tension of the optical fiber 4 determined from the relationship between the drawing tension of the glass fiber 3 to be drawn and the cutoff wavelength, and the drawing tension and the load of the tension measuring roller 24 a pressed against the optical fiber 4. Based on the relationship with the post-coating tension, the target post-coating tension determining process is performed to determine the target post-coating tension so that the cut-off wavelength after drawing is constant in the longitudinal direction.

  And the control apparatus 25 performs the furnace temperature control process which controls the furnace temperature of the drawing furnace 12 so that the post-coating tension becomes the target post-coating tension.

  Further, the control device 25 changes the take-up resistance of the optical fiber 4 due to the fluctuations of the respective roller resistances of the tension measuring roller 24a and the direct roller 17 and the coating diameter of the optical fiber 4 during the target post-coating tension determination process. Based on the above, a target post-covering tension correction process for correcting the target post-covering tension is performed.

  In this target post-coating tension correction process, first, in order to correct the change in the take-up resistance of the optical fiber 4 due to the change in the coating diameter, the control device 25 corrects the target post-coating tension based on the following equation (1). The post-coating tension P is calculated.

P = P0 + A × (D−D0) (1)
However,
P0: Tension after target covering before correction (g)
A: Constant (g / μm) derived from the correlation between coating diameter variation and post-coating tension
D: coating diameter of optical fiber (μm)
D0: Reference coating diameter (μm)

  The control device 25 controls the furnace temperature of the drawing furnace 12 so that the post-coating tension becomes the calculated corrected target post-coating tension P. For example, when the coating diameter of the optical fiber 4 simply increases, the target post-coating tension increases, and as a result, the furnace temperature of the drawing furnace 12 is not changed (when correction by the coating diameter is not performed). Since the post-coating tension increases, the furnace temperature is controlled to be lowered.) When the coating diameter of the optical fiber 4 is simply reduced, the target post-coating tension is lowered, and the furnace temperature is similarly set. Will not be changed. Thereby, the fluctuation | variation of the drawing tension by the fluctuation | variation of the coating diameter of the optical fiber 4 can be suppressed, and the influence on a cutoff wavelength can be suppressed as much as possible.

  Next, the control device 25 uses the upstream tension F1 on the upstream side of the direct roller 17 and the downstream tension F2 on the downstream side of the tension measuring roller 24a measured by a handy type tension meter or the like based on the following equation (2). Then, a corrected target post-covering tension T obtained by correcting the target post-covering tension is calculated from the upstream tension F1 and the downstream tension F2.

T = T0 + Δ (F2-F1) (2)
However,
T0: Tension after target covering before correction (g)
Δ (F2−F1): Fluctuation of difference value between F2 and F1 from the previous measurement (g)

  The control device 25 controls the furnace temperature of the drawing furnace 12 so that the post-coating tension becomes the calculated corrected target post-coating tension T. For example, when the roller resistance increases, the target post-covering tension is set high in advance, and when the roller resistance decreases, the target post-covering tension is set low in advance. Thereby, the fluctuation | variation of the line tension force by the fluctuation | variation of roller resistance of various rollers, such as the direct roller 17 and the tension | tensile_strength measurement roller 24a, can be suppressed, and the influence on a cutoff wavelength can be suppressed as much as possible.

  As described above, according to the method of manufacturing an optical fiber according to the above-described embodiment, the light that fluctuates due to a change in the coating diameter of the optical fiber 4 or a change in roller resistance of various rollers such as the direct roller 17 and the tension measurement roller 24a. The target post-coating tension can be finely corrected based on the take-up resistance of the fiber 4. Thereby, the fluctuation | variation of a cutoff wavelength can be suppressed favorably and the high quality optical fiber 4 can be manufactured.

Next, a specific example when the correction process is performed to manufacture the optical fiber 4 will be described.
(Manufacture of optical fiber)
Using the optical fiber preform 2 with a base material diameter of 100 mm, the target diameter of the glass fiber 3 is 125 μm, the reference coating diameter (target diameter) of the optical fiber 4 is 245 μm, and the glass fiber 3 is drawn at a linear speed of 1000 m / min. The optical fiber 4 is manufactured.

When the optical fiber 4 is manufactured as described above, the relationship between the post-coating tension and the drawing tension is generally approximately proportional.
Further, the relationship between the cutoff wavelength λc and the post-coating tension is generally approximately proportional as shown in FIG.

  FIG. 3 shows the relationship between the coating diameter of the optical fiber 4 and the post-coating tension. As shown in FIG. 3, even if the drawing tension is the same, if the coating diameter becomes smaller with respect to the target diameter of 245 μm, the post-coating tension becomes small, and if the coating diameter becomes large, the post-coating tension becomes large. Become.

(How to correct)
The correlation between the coating diameter and the post-coating tension is generally approximately proportional as shown in FIG. In the case of FIG. 3, when the coating diameter varies by 1 μm, the post-coating tension also varies by 1 g, and the constant A derived from the correlation between the coating diameter variation and the post-coating tension is approximately A = 1 (g / μm).

Thus, for example, when the optical fiber 4 having a reference coating diameter D0 of 245 μm is manufactured with a target post-correction tension P0 of 200 g, if the actual post-coating tension is 210 g and the coating diameter D is 244 μm, the correction target The post-coating tension P is based on the above equation (1).
P = P0 + A (D-D0)
= 200 + 1 × (244-245)
= 199g
It becomes.

  Then, the control device 25 corrects the target post-coating tension from 200 g to a corrected target post-coating tension P of 199 g, and draws the tension so that the post-coating tension is reduced by 11 g to the actual post-coating tension 210 g. The furnace temperature of the furnace 12 is changed.

  Further, the control device 25 corrects the fluctuations of the roller 17 and the tension measuring roller 24a as they are in the target post-covering tension.

  Here, the measured values of the upstream tension F1 on the upstream side of the roller 17 directly below and the downstream tension F2 on the downstream side of the tension measuring roller 24a are compared with the previous measured values, and the difference value Δ (F2−F1) is obtained. Ask.

  For example, when the upstream tension F1 varies from 215 g to 214 g and the downstream tension F2 varies from 230 g to 232 g, the difference value is Δ (F2−F1) = (232−230) − (214−215) = 2-(-1) = 3 g.

Therefore, in this case, when the pre-correction target post-covering tension T0 is 200 g, the corrected target post-covering tension T is based on the above equation (2).
T = T0 + Δ (F2-F1)
= 200 + 3
= 203g
It becomes.

  Then, the control device 25 corrects the target post-coating tension to a corrected target post-coating tension T of 200 g to 203 g, and changes the furnace temperature of the drawing furnace 12.

(Variation after correction)
As a result of manufacturing the optical fiber 4 by performing the above correction processing, the cut-off wavelength of the glass fiber 3 was the standard deviation σ = 0.151 μm at the time of non-correction, but was corrected according to this embodiment. As a result, the standard deviation σ was 0.0078 μm, and the variation in the cutoff wavelength could be halved.

2: optical fiber preform, 3: glass fiber, 4: optical fiber, 12: drawing furnace, 17: roller directly under, 24a: tension measuring roller, A: constant, D: coating diameter, D0: reference coating diameter, F1 : Upstream tension, F2: downstream tension, P, T: target post-cover tension, P0: target post-correction tension before correction, T0: target post-correction tension before correction, Δ (F2-F1): difference between F2 and F1 Change in value since last measurement

Claims (3)

An optical fiber manufacturing method for manufacturing an optical fiber by drawing a glass fiber from an optical fiber preform heated and melted in a drawing furnace, and coating the resin around the glass fiber,
A cutoff wavelength prediction process for predicting a longitudinal variation in the cutoff wavelength based on a variation in the refractive index distribution in the longitudinal direction of the optical fiber preform measured in advance;
Based on the relationship between the drawing tension, which is the tension of the glass fiber, and the cutoff wavelength, and the relationship between the drawing tension, and the post-coating tension, which is the tension of the optical fiber, the cutoff of the glass fiber after drawing. A target post-coating tension determination process for determining a target post-coating tension such that the wavelength is constant in the longitudinal direction;
Furnace temperature control processing for controlling the furnace temperature of the drawing furnace such that the post-coating tension becomes the target post-coating tension,
A method of manufacturing an optical fiber, comprising performing a target post-coating tension correction process for correcting the target post-coating tension based on a change in take-up resistance of the optical fiber during the target post-coating tension determination process. An optical fiber manufacturing method according to claim 1,
A corrected target post-coating tension P (g) obtained by correcting the target post-coating tension is:
P = P0 + A × (D−D0)
(However, P0: tension after target coating before correction (g), A: constant (g / μm), D: coating diameter of optical fiber (μm), D0: reference coating diameter (μm))
An optical fiber manufacturing method, wherein the optical fiber is derived from a correction formula consisting of: An optical fiber manufacturing method according to claim 1 or 2,
An upstream tension F1 on the upstream side of the immediately below roller that guides the optical fiber first, and a downstream tension F2 on the downstream side of the tension measuring roller that measures the post-coating tension on the downstream side of the immediately below roller,
A corrected target post-coating tension T (g) obtained by correcting the target post-coating tension,
T = T0 + Δ (F2-F1)
(However, T0: target post-correction tension (g), Δ (F2-F1): variation (g) of difference value between F2 and F1 from the previous measurement)
An optical fiber manufacturing method, wherein the optical fiber is derived from a correction formula consisting of:

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