JP2005314118A - Drawing method and drawing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drawing method and a drawing apparatus by which the variation of a glass fiber in the longitudinal direction is suppressed while keeping the cut-off wavelength of the glass fiber to a prescribed value. <P>SOLUTION: In the method of drawing method for forming the glass fiber 3 by drawing an optical fiber preform 2 heated and melted in a drawing furnace 12, the variation in longitudinal direction of the refractive index distribution in the diameter direction of the optical fiber preform is measured in advance, the drawing tension produced in the glass fiber in drawing is measured, and the drawing tension of the glass fiber is controlled so that the cut-off wavelength of the glass fiber becomes a prescribed value, while suppressing the variation in the longitudinal direction of the refractive index distribution in the diameter direction of the glass fiber on the basis of the measured result of the drawing tension and the variation in the longitudinal direction of the refractive index distribution of the optical fiber preform. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a drawing method and a drawing apparatus for forming a glass fiber by drawing an optical fiber preform.

  One of the characteristics of an optical fiber is a cutoff wavelength. As a method of manufacturing an optical fiber so that the cut-off wavelength is substantially uniform in the longitudinal direction of the optical fiber, for example, there is an optical fiber drawing method described in Patent Document 1.

  In the method described in Patent Document 1, the cutoff wavelength of the optical fiber depends on the drawing tension at the time of drawing, and the cutoff wavelength can be estimated from the refractive index distribution of the optical fiber preform. We are using. This will be described more specifically.

  First, the estimated cutoff wavelength of the optical fiber is obtained in advance at a plurality of locations in the longitudinal direction of the optical fiber preform. From the estimated value and the desired cut-off wavelength, a target line tension force that achieves the desired cut-off wavelength is calculated. Then, when drawing the optical fiber preform, the drawing tension generated in the optical fiber in which the glass fiber is coated with the resin is measured, and the drawing tension is controlled so that the measurement result becomes the target drawing tension. .

  In the method described in Patent Document 1, the tensile force of the optical fiber is measured with a load meter attached to the shaft of the turn pulley on which the optical fiber is applied. On the other hand, a method using light has been proposed as a method of measuring the tension generated in the glass fiber.

For example, in the method described in Patent Document 2, light is irradiated from the side of the glass fiber, and the light that has passed through the glass fiber is detected. When tension is generated in the glass fiber, birefringence corresponding to the tension is generated in the light passing through the glass fiber. Thereby, the polarization state of the light that has passed through changes from the polarization state of the light irradiated on the glass fiber. In the method described in Patent Document 2, the tension generated in the glass fiber is measured from the change in the polarization state generated in the light by passing through the glass fiber.
Japanese Patent Laid-Open No. 8-217481 International Publication No. 03/056288 Pamphlet

  By the way, even if the optical fiber preform is drawn while controlling the drawing tension according to the estimated cutoff wavelength as in the method described in Patent Document 1, the cutoff wavelength of the optical fiber varies in the longitudinal direction. There is a case.

  Then, the objective of this invention is providing the drawing method and drawing apparatus which can suppress the longitudinal direction fluctuation | variation, setting the cutoff wavelength of a glass fiber to a predetermined value.

  The present inventors diligently studied to suppress the cut-off wavelength variation in the longitudinal direction of the glass fiber. In the technique described in Patent Document 1, since the drawing tension (hereinafter referred to as post-coating tension) generated in the optical fiber in which the glass fiber is coated with the resin is measured, the variation in the cutoff wavelength remains. I found out.

  That is, it is the drawing tension generated in the glass fiber drawn from the optical fiber preform that affects the cutoff wavelength of the glass fiber. The post-coating tension is the sum of the drawing tension generated on the glass fiber itself (hereinafter referred to as glass tension) and the drawing tension acting on the coating layer itself. As a result of studies by the present inventors, it has been found that there is no one-to-one correspondence between glass tension and post-coating tension. Therefore, even if the post-coating tension is controlled based on the measurement result, the glass tension is not kept constant, and the variation in the cutoff wavelength remains.

  Therefore, a drawing method according to the present invention is a drawing method in which a glass fiber is formed by drawing an optical fiber preform heated and melted in a drawing furnace, wherein the refractive index in the radial direction of the optical fiber preform is Measure the longitudinal variation of the distribution in advance, measure the tensile force generated in the glass fiber during drawing, measure the tensile force, and measure the longitudinal variation of the refractive index distribution of the optical fiber preform. Based on the above, the drawing tension of the glass fiber is controlled so that the cutoff wavelength of the glass fiber becomes a predetermined value while suppressing the longitudinal fluctuation of the refractive index distribution in the radial direction of the glass fiber. .

  In this method, based on the measurement result of the longitudinal variation of the refractive index distribution in the optical fiber preform and the measurement result of the drawing tension generated in the glass fiber at the time of drawing, the glass fiber as described above is used. The drawing tension is controlled. Therefore, the longitudinal variation of the refractive index distribution of the glass fiber can be suppressed more accurately than in the case of controlling based on the drawing tension generated in the optical fiber having the coating layer made of resin. And since the cutoff wavelength is dependent on the refractive index distribution of the radial direction of a glass fiber, it can suppress that a cutoff wavelength fluctuates in the longitudinal direction of a glass fiber, making a cutoff wavelength into a predetermined value.

  Moreover, in the drawing method according to the present invention, it is preferable that the method for measuring the drawing tension of the glass fiber is a non-contact type. In this case, the glass fiber is not easily broken and the glass fiber is hardly damaged.

  Furthermore, in the drawing method according to the present invention, it is preferable to measure the drawing tension of the glass fiber using light. By irradiating light from the side of the glass fiber and detecting a change in the light due to the drawing tension generated in the glass fiber, the drawing tension of the glass fiber can be measured.

  Furthermore, in the drawing method according to the present invention, it is preferable to adjust the drawing tension of the glass fiber by controlling the furnace temperature of the drawing furnace or the drawing speed of the glass fiber. By controlling the furnace temperature, the viscosity of the optical fiber preform changes and the drawing tension changes. Further, by controlling the drawing speed, the pulling force of the glass fiber changes, and the drawing tension changes.

  The drawing apparatus according to the present invention is a drawing apparatus that forms a glass fiber by drawing an optical fiber preform heated and melted in a drawing furnace, and that draws a drawing tension generated in the glass fiber. The refractive index distribution in the radial direction of the glass fiber based on the tension measuring device to be measured, the measurement result of the longitudinal variation of the refractive index distribution in the radial direction of the optical fiber preform, and the drawing tension measured by the tension measuring device And a control device for controlling the furnace temperature of the drawing furnace or the drawing speed of the glass fiber so that the cut-off wavelength of the glass fiber becomes a predetermined value.

  In this drawing device, the drawing tension generated in the glass fiber during drawing of the optical fiber preform is measured by a tension measuring device. And based on the measurement result and the longitudinal direction fluctuation | variation of the said refractive index distribution of an optical fiber preform | base_material, a control apparatus controls the furnace temperature of a drawing furnace, or the linear velocity of a glass fiber as mentioned above. Since the furnace temperature or the linear velocity of the glass fiber is controlled so that the cutoff wavelength becomes a predetermined value while suppressing the longitudinal fluctuation of the refractive index distribution of the glass fiber, the cutoff wavelength of the glass fiber is set to a predetermined value. It can be set to a value, and its longitudinal variation can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the drawing method and drawing apparatus which can suppress the longitudinal direction fluctuation | variation can be provided, setting the cutoff wavelength of glass fiber to a predetermined value.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same reference numerals are used for the same elements, and duplicate descriptions are omitted.

  FIG. 1 is a schematic diagram illustrating a configuration of a drawing apparatus 1 according to the present embodiment. The drawing apparatus 1 is an apparatus for producing 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 drawing apparatus 1 includes a base material feeding device 11, a drawing furnace 12, applicators 13 and 14, ultraviolet irradiation devices 15 and 16, a guide roller 17, a capstan 18, and a winding drum 19.

  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 forming the glass fiber 3 by heating and melting one end of the optical fiber preform 2 and drawing.

  The applicator 13 and the ultraviolet irradiation device 15 are disposed downstream of the drawing furnace 12 in the drawing direction of the glass fiber 3. The applicator 13 applies an ultraviolet curable resin to the outer periphery of the glass fiber 3. The ultraviolet irradiation device 15 irradiates the resin applied by the applicator 13 with ultraviolet rays and cures it to form a first coating layer.

  Further, the applicator 14 and the ultraviolet irradiation device 16 are arranged downstream of the ultraviolet irradiation device 15. The applicator 14 applies an ultraviolet curable resin to the outer periphery of the first coating layer. The ultraviolet irradiation device 16 irradiates the resin applied by the applicator 14 with ultraviolet rays and cures it to form a second coating layer, and forms the optical fiber 4 having the first and second coating layers.

  The capstan 18 includes a belt 18a and a roller 18b. The capstan 18 takes out the optical fiber 4 by the rotation of the belt 18a and the rotation of the roller 18b and sends the optical fiber 4 to the winding drum 19. The traveling direction of the optical fiber 4 taken up by the capstan 18 is changed by the guide roller 17. The winding drum 19 winds the optical fiber 4.

  The drawing device 1 further includes an outer diameter measuring device 21, a tension measuring device 22, an outer diameter measuring device 23, and a load meter 24. The outer diameter measuring device 21 is disposed between the drawing furnace 12 and the applicator 13 and measures the outer diameter of the glass fiber 3. The outer diameter measuring device 23 is disposed between the ultraviolet irradiation device 16 and the guide roller 17 and measures the outer diameter of the coated optical fiber 4. The outer diameter measuring devices 21 and 23 are non-contact type measuring devices using a laser, for example.

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

  The tension measuring device 22 measures the drawing tension using light. More specifically, the tension measuring device 22 irradiates circularly polarized light from the side of the glass fiber 3 and detects the light that has passed through the glass fiber 3. Since birefringence acting on the glass fiber 3 due to the drawing tension is generated, the light that has passed changes to elliptically polarized light. This change in polarization state depends on the magnitude of the drawing tension generated in the glass fiber 3.

  The tension measuring device 22 calculates the drawing tension based on the change in the polarization state generated in the light that has passed through the glass fiber 3. The drawing tension generated in the glass fiber 3 measured by the tension measuring device 22 is also referred to as glass tension.

  The load meter 24 is attached to the central axis of the guide roller 17 and measures the force applied to the guide roller 17 by the tension generated in the optical fiber 4. Since this force changes according to the drawing tension generated in the optical fiber 4, the force measured by the load meter 24 can be regarded as the drawing tension generated in the optical fiber 4. The wire tensile force measured by the load meter 24 is also referred to as post-coating tension.

  The drawing device 1 further includes a control device 25. The control device 25 is a computer and is electrically connected to the drawing furnace 12, the tension measuring device 22, the load meter 24, and the capstan 18. The control device 25 receives the measurement result of the tension measuring device 22 and the measurement result of the load cell 24.

  Based on the measurement result of the longitudinal variation of the refractive index distribution in the radial direction of the optical fiber preform 2 and the measurement result of the tension measurement device 22, the control device 25 varies the longitudinal direction of the refractive index distribution in the radial direction of the glass fiber 3. The drawing tension of the glass fiber 3 is controlled so that the cutoff wavelength of the glass fiber 3 becomes a predetermined value while suppressing the above. The predetermined value is a cutoff wavelength that the glass fiber 3 to be formed should have.

  The control of the drawing tension by the control device 25 will be described more specifically. An estimated value of the cutoff wavelength of the glass fiber 3 is calculated from the refractive index distribution of the optical fiber preform 2. Furthermore, based on the estimated value of the cut-off wavelength, a target drawing tension for obtaining the predetermined cut-off wavelength is calculated. Then, the furnace temperature of the drawing furnace 12 or the capstan 18 is controlled so that the glass tension measured by the tension measuring device 22 becomes the target drawing tension. If the furnace temperature of the drawing furnace 12 is adjusted, the viscosity of the optical fiber preform 2 changes, so that the glass tension can be controlled. Further, if the take-up speed of the optical fiber 4 is changed by the capstan 18, the linear speed of the glass fiber 3 is changed. In this case, since the force with which the glass fiber 3 is pulled changes, the glass tension can be controlled.

  Next, a drawing method of the glass fiber 3 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. The refractive index distribution of the optical fiber preform 2 slightly changes in the longitudinal direction. Therefore, the measurement corresponds to the measurement of the fluctuation in the longitudinal direction of the refractive index distribution of the optical fiber preform 2. The result of this measurement is input to the control device 25.

  Next, the optical fiber preform 2 is installed in the preform delivery apparatus 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 and pulled to form the glass fiber 3. The outer diameter of the glass fiber 3 is measured by the outer diameter measuring device 21. Subsequently, the tensile force (glass tension) generated in the glass fiber 3 is measured by the tension measuring device 22. The glass tension measured by the tension measuring device 22 is input to the control device 25.

  The glass fiber 3 that has passed through the tension measuring device 22 sequentially passes through the applicator 13 and the ultraviolet irradiation device 15. As a result, a first coating layer is formed on the glass fiber 3.

  The glass fiber 3 that has passed through the ultraviolet irradiation device 15 passes through the applicator 14 and the ultraviolet irradiation device 16, and a second coating layer is formed on the outer periphery of the first coating layer. As a result, an 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. The optical fiber 4 that has passed through the outer diameter measuring device 23 is wound around the winding drum 19 through the guide roller 17 and the capstan 18.

  In this drawing method, the drawing tension when drawing the optical fiber preform 2 is determined by measuring the longitudinal variation of the refractive index distribution in the radial direction of the optical fiber preform 2 and the tension during drawing. Based on the glass tension measured by the measuring device 22, the control device 25 performs the following control.

  That is, the drawing tension is controlled so as to cancel the longitudinal fluctuation of the refractive index distribution in the radial direction of the optical fiber preform 2 and to suppress the longitudinal fluctuation of the refractive index distribution in the radial direction of the glass fiber 3. The drawing tension is controlled so that the cutoff wavelength of 3 is a predetermined value. The drawing tension is adjusted by adjusting the furnace temperature of the drawing furnace 12 or the take-up speed of the capstan 18.

  Next, referring to FIG. 2 to FIG. 5, it is possible to suppress the longitudinal fluctuation of the cutoff wavelength in the glass fiber 3 while setting the cutoff wavelength of the glass fiber 3 to a predetermined value by the above drawing method. explain.

  FIG. 2 is a graph showing the relationship between glass tension and cutoff wavelength. The cut-off wavelength shown in FIG. 2 is the cut-off wavelength of the glass fiber 3 formed as follows. That is, when drawing one optical fiber preform 2, the drawing speed of the glass fiber 3 was changed in three stages. Then, the optical fiber preform 2 was drawn while changing the glass tension at each drawing speed. And in the glass fiber 3, the cutoff wavelength in the area | region drawn in each glass tension was calculated | required. In FIG. 2, the diamond, square, and triangle marks correspond to the measurement results at each linear velocity changed in three stages.

  As shown in FIG. 2, there is a correlation between the glass tension and the cutoff wavelength. Although the cut-off wavelength cannot be measured during drawing, there is a correlation between glass tension and cut-off wavelength as described above. The off wavelength can be controlled.

FIG. 3 is a graph showing the relationship between glass tension and cut-off wavelength error Δλ _c . The cutoff wavelength error Δλ _c is a difference between a predicted cutoff wavelength obtained from the radial refractive index distribution of the optical fiber preform 2 and an actual measured cutoff wavelength of the glass fiber 3. The measured value is obtained by changing the glass tension (drawing force of the glass fiber 3) stepwise when drawing the optical fiber preform 2, and the glass fiber 3 obtained when the drawing conditions are stabilized at each glass tension. Is the cutoff wavelength.

As shown in FIG. 3, Δλ _C can be reduced by controlling the glass tension, that is, the cutoff wavelength of the actually formed glass fiber 3 and the refraction in the radial direction of the optical fiber preform 2. The cutoff wavelength predicted from the rate distribution can be made substantially coincident.

Figure 4 is a graph showing the relationship between the coating after tension and [Delta] [lambda] _c. Here, when forming the glass fiber 3 from the three optical fiber preforms 2, each optical fiber obtained by drawing the optical fiber preform 2 so that the post-coating tension becomes 1.86 N (190 g). A cut-off wavelength of 4 was measured. Then, the difference between the actually measured value and the predicted value was calculated.

  As shown in FIG. 4, even if the glass fiber 3 is formed while controlling the linear velocity or the furnace temperature so that the post-coating tension becomes constant (so that the post-coating tension does not vary), the optical fiber preform 2 The predicted cut-off wavelength cannot be obtained.

  FIG. 5 is a graph showing the relationship between glass tension and post-coating tension. Here, in the drawing of the four optical fiber preforms 2, the results measured by the load meter 24 when the glass tension is changed stepwise are plotted. As shown in FIG. 5, when the optical fiber preform 2 is drawn so that the glass tension is about 1.17 N (120 g) and about 1.19 N (122 g), the post-coating tension varies. ing. For example, when the two optical fiber preforms 2 are drawn with a glass tension of about 1.17 N (120 g), the results of the load meter 24 are different even though the measured glass tensions are the same. ing. This is the same when the glass tension is about 1.19 N (122 g). Therefore, it is considered that the variation in the measurement result of the load meter 24 with respect to the measurement result of the tension measuring device 22 is caused by the coating layer made of resin.

  By the way, since there is a correlation between the glass tension and the cutoff wavelength as shown in FIG. 2, even if the optical fiber preform 2 is drawn based on the post-coating tension that causes variations in the glass tension as in the prior art. The cutoff wavelength of the glass fiber 3 cannot be set to a predetermined value.

  On the other hand, if the glass fiber 3 is formed based on the glass tension as in the drawing method shown in the present embodiment, the cutoff wavelength of the glass fiber 3 can be set to a predetermined value. This is also clear from the fact that the glass tension and the cutoff wavelength have a good correlation (see FIG. 2).

  Further, since the cutoff wavelength is determined by the refractive index distribution in the radial direction of the glass fiber 3, the fluctuation of the refractive index distribution of the glass fiber 3 may be suppressed in order to suppress the fluctuation in the longitudinal direction of the cutoff wavelength. Further, the longitudinal variation of the refractive index distribution of the glass fiber 3 depends on the longitudinal variation of the refractive index distribution of the optical fiber preform 2 and the glass tension. Therefore, it is possible to form the glass fiber 3 having a predetermined cutoff wavelength while suppressing fluctuation in the longitudinal direction of the cutoff wavelength of the glass fiber 3 by the above drawing method.

  As a method for measuring the glass tension, for example, a contact type is also conceivable. However, in the contact type, it is difficult to make contact without breaking during high-speed drawing. In this case, it is necessary to estimate the drawing tension at high speed by multiplying the result measured when the linear speed is low. Further, even if the contact is made without disconnection, the glass is scratched, so that the glass tension cannot be measured during the production of a good optical fiber in drawing.

  On the other hand, in the present embodiment, since the measuring method of the tension measuring device 22 is a non-contact type, when a good optical fiber 4 is produced (that is, when the linear velocity is high), In addition, the tension measuring device 22 can measure the drawing tension generated in the glass fiber 3. And the drawing tension can be controlled based on the measurement result. Moreover, since the measuring method of the drawing tension in the tension measuring device 22 is a non-contact type, even if the drawing tension generated in the glass fiber 3 is measured, the glass fiber 3 is hardly damaged.

  As a non-contact type, for example, a method using a sound wave is conceivable, but if a sound wave is used, the glass fiber 3 needs to be forcedly vibrated. As described above, when the glass fiber 3 is forcibly vibrated, it may be difficult to control the outer diameter of the glass fiber 3.

  On the other hand, since the tension measuring device 22 measures the tension using light, there is no influence on the outer diameter control of the glass fiber 3.

  As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment. For example, the tension measuring device 22 may be disposed between the outer diameter measuring device 21 and the drawing furnace 12. Moreover, in the drawing apparatus 1, the load meter 24 is provided, but the position of the load meter 24 may be a position where the tension acting on the coated optical fiber 4 can be measured. The drawing apparatus 1 shown in FIG. In this case, it suffices to be between the ultraviolet irradiation device 16 and the capstan 18. Alternatively, it is not always necessary to measure the drawing tension generated in the optical fiber 4 with the load meter 24.

It is a schematic diagram which shows the structure of the drawing apparatus of this embodiment. It is a graph which shows the relationship between glass tension and a cutoff wavelength. It is a graph which shows the relationship between glass tension and cutoff wavelength error (DELTA) ₍ lambda) _c . It is a graph which shows the relationship between tension | tensile_strength after coating | cover and (DELTA) ₍ lambda) _c . It is a graph which shows the relationship between glass tension and tension after covering.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Drawing apparatus, 2 ... Optical fiber preform | base_material, 3 ... Glass fiber, 4 ... Optical fiber, 12 ... Drawing furnace, 22 ... Tension measuring apparatus, 25 ... Control apparatus.

Claims (5)

A drawing method for forming a glass fiber by drawing an optical fiber preform heated and melted in a drawing furnace,
Preliminarily measured longitudinal variation of the refractive index distribution in the radial direction of the optical fiber preform,
When drawing, measure the tensile force generated in the glass fiber,
Based on the measurement result of the drawing tension and the measurement result of the longitudinal variation of the refractive index distribution of the optical fiber preform, while suppressing the longitudinal variation of the radial refractive index distribution of the glass fiber, A drawing method, wherein the drawing force of the glass fiber is controlled so that a cutoff wavelength of the glass fiber becomes a predetermined value.   The drawing method according to claim 1, wherein the method of measuring the drawing tension of the glass fiber is a non-contact type.   The drawing method according to claim 2, wherein the drawing tension of the glass fiber is measured using light.   4. The wire pulling force of the glass fiber is adjusted by controlling a furnace temperature of the drawing furnace or a drawing speed of the glass fiber. 5. Drawing method. A drawing apparatus for forming a glass fiber by drawing an optical fiber preform heated and melted in a drawing furnace,
A tension measuring device for measuring a drawing tension generated in the glass fiber;
Based on the measurement result of the longitudinal fluctuation of the refractive index distribution in the radial direction of the optical fiber preform and the drawing tension measured by the tension measuring device, the longitudinal direction of the refractive index distribution in the radial direction of the glass fiber And a controller for controlling a furnace temperature of the drawing furnace or a drawing speed of the glass fiber so that a cut-off wavelength of the glass fiber becomes a predetermined value while suppressing fluctuations. .

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