JP2012171829A - Method and apparatus for producing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing an optical fiber having a small loss and high strength.SOLUTION: In this method for producing an optical fiber in which an optical fiber preform 2 is heated, melted and drawn, and the drawn optical fiber 4 is introduced into an annealing furnace 5 to be subjected to annealing treatment, the surface of the optical fiber 4 after annealing treatment is continuously heated in the longitudinal direction, to thereby perform flame polishing treatment to the optical fiber 4 after annealing treatment.

Description

  The present invention relates to an optical fiber manufacturing method and apparatus.

  2. Description of the Related Art Conventionally, a method of manufacturing a low-loss optical fiber by reducing the Rayleigh scattering loss, which is a loss factor of the optical fiber, by performing an annealing process on the optical fiber being drawn (for example, Patent Document 1) is known. , 2).

  In this method, an optical fiber manufacturing apparatus 21 as shown in FIG. 2 is used, and the optical fiber preform 2 is heated, melted and drawn in a drawing furnace 3, and the drawn optical fiber 4 is subjected to an annealing furnace ( It is introduced into a heating furnace 5 and annealed, and then the annealed optical fiber 4 is passed through a coating device 6.

  However, the above-described conventional method has a problem that the transmission loss of the optical fiber is not sufficiently reduced, and further, the strength (mechanical strength) of the optical fiber is deteriorated. This is because impurities such as water vapor and Si powder adhere to the optical fiber 4 in the drawing furnace 3, the annealing furnace 5, or the space between the drawing furnace 3 and the annealing furnace 5. This is thought to be due to the fact that crystallization progresses during the annealing process or that fine scratches (called microcracks) on the surface of the optical fiber are enlarged.

  In order to solve this problem, in Patent Document 2, the optical fiber immediately after drawing is guided into a vacuum vessel, and heat treatment (annealing) is performed in the vacuum vessel, thereby suppressing the adhesion of impurities to the optical fiber. A method for suppressing a decrease in fiber strength has been proposed.

JP-A-4-59631 JP 2003-48743 A

  However, in the method of Patent Document 2, microcracks on the surface of the optical fiber cannot be repaired, and impurities adhering in the vacuum container cannot be avoided. Therefore, the impurities attached in the vacuum vessel become nuclei and the crystallization progresses, or the micro cracks on the surface of the optical fiber are enlarged, so that an optical fiber with sufficiently low loss and high strength can be obtained. There was a problem that it could not be manufactured.

  In addition, the method of Patent Document 2 requires a huge vacuum container having a length of 17 m, for example, and there is a problem that the apparatus becomes very large.

  Therefore, an object of the present invention is to provide an optical fiber manufacturing method and apparatus capable of solving the above-described problems and manufacturing a low-loss and high-strength optical fiber.

  The present invention was devised in order to achieve the above-mentioned object. An optical fiber preform is manufactured by drawing an optical fiber preform by heating, melting and introducing the drawn optical fiber into an annealing furnace. In the manufacturing method, the surface of the optical fiber after the annealing treatment is continuously heated in the longitudinal direction, and the optical fiber after the annealing treatment is subjected to a flame polishing treatment.

  The flame polishing treatment may be performed so that the surface temperature of the optical fiber after the annealing treatment is 2000 ° C. or higher.

  On the surface of the optical fiber preform, a low-temperature softened layer in which impurities are added and the softening temperature is controlled low is formed, and the temperature of the surface of the optical fiber after the annealing treatment is equal to or higher than the softening temperature of the low-temperature softening layer. As described above, the flame polishing treatment may be performed.

  The flame polishing treatment may be performed while purging an inert gas into the annealed optical fiber.

  The surface of the optical fiber immediately before being introduced into the annealing furnace may be continuously heated in the longitudinal direction so that the optical fiber before the annealing treatment is subjected to flame polishing treatment.

  In addition, the present invention provides an optical fiber manufacturing apparatus comprising: a drawing furnace that heats, melts, and draws an optical fiber preform; and an annealing furnace that anneals the optical fiber drawn by the drawing furnace The optical fiber manufacturing apparatus includes a first fiber surface heating device that continuously heats the surface of the optical fiber after the annealing process in a longitudinal direction and performs a flame polishing process on the optical fiber after the annealing process. is there.

  You may further provide the 2nd fiber surface heating apparatus which heats the surface of the optical fiber just before introduce | transducing into the said annealing furnace in a longitudinal direction, and performs a flame polishing process to the optical fiber before the said annealing process.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and apparatus of an optical fiber which can manufacture a low-loss and high intensity | strength optical fiber can be provided.

It is a schematic block diagram of the manufacturing apparatus of the optical fiber used for the manufacturing method of the optical fiber which concerns on one embodiment of this invention. It is a schematic block diagram of the conventional optical fiber manufacturing apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an optical fiber manufacturing apparatus used in the optical fiber manufacturing method according to the present embodiment.

  As shown in FIG. 1, an optical fiber manufacturing apparatus 1 performs an annealing process on a drawing furnace 3 that draws an optical fiber preform 2 by heating, melting, and an optical fiber 4 drawn by the drawing furnace 3. An annealing furnace 5 and a coating device 6 for coating the surface of the optical fiber 4 with resin are provided. The core of the optical fiber preform 2 is made of, for example, Ge-added pure silica glass having a concentration of 10% or less, and the clad of the optical fiber preform 2 is made of, for example, pure silica glass.

  The annealing furnace 5 maintains the optical fiber 4 drawn by the drawing furnace 3 at a predetermined annealing temperature, thereby lowering the virtual temperature of the optical fiber 4 and reducing the Rayleigh scattering loss that is a loss factor of the optical fiber 4. It is something to be made. The fictive temperature is a temperature indicating how many times the state of the supercooled liquid in the thermal equilibrium state is the same as that of the supercooled liquid, and is a good index of the structure frozen in the glass ( In other words, solidified glass has a fictive temperature that varies depending on its structure.

  Now, in the optical fiber manufacturing apparatus 1 according to the present embodiment, the surface of the annealed optical fiber 4 is continuously arranged in the longitudinal direction downstream of the annealing furnace 5 (between the annealing furnace 5 and the coating device 6). And a first fiber surface heating device 7 that performs a flame polishing process (FP; Fire Polishing, Flame Polishing) on the annealed optical fiber 4.

  The first fiber surface heating device 7 continuously heats the surface of the optical fiber 4 over its entire length in the longitudinal direction, melts (softens) the surface of the optical fiber 4, and causes defects on the surface of the optical fiber 4 during the annealing process. That is, it repairs a portion where crystallization has progressed using impurities as nuclei, microcracks, and the like. Therefore, in the first fiber surface heating device 7, the temperature of the surface of the optical fiber 4 becomes a temperature at which the surface of the optical fiber 4 melts (softens), that is, a temperature of 2000 ° C. or higher at which pure silica glass melts (softens). Thus, it is configured to perform a flame polishing process.

  The first fiber surface heating device 7 is configured to heat only the surface of the optical fiber 4 and is configured not to heat the core portion of the optical fiber 4 (the core and the cladding around the core). This is because if the core portion of the optical fiber 4 is heated, the effect of the annealing treatment is reduced, the Rayleigh loss is increased, and the transmission loss of the optical fiber 4 is increased.

As the first fiber surface heating device 7, for example, a CO ₂ laser device, a low temperature arc discharge device, or the like can be used. Since the CO ₂ laser is highly absorbed by glass, only the surface of the optical fiber 4 can be heated if the CO ₂ laser is irradiated for a short time. Further, only the surface of the optical fiber 4 can be heated even if the low-temperature arc discharge is performed for a short time. Here, the short time means a heating time for a certain point of the optical fiber 4 being drawn, and the first fiber surface heating device 7 is actually configured to continuously heat. The The surface temperature of the optical fiber 4 is controlled by adjusting the output of the first fiber surface heating device 7 (for example, the output of the CO ₂ laser).

Although not shown, the first fiber surface heating device 7 includes an inert gas purge device for purging an inert gas such as N ₂ or He in the optical fiber 4, and the inert gas is supplied to the optical fiber 4. Flame polishing is performed while purging. This is to prevent impurities from adhering to the surface of the optical fiber 4 that has been activated at a high temperature by the flame polishing process.

Further, although not shown, the first fiber surface heating device 7 has a temperature measuring device for detecting the temperature of the surface of the optical fiber 4 immediately after the flame polishing process, and the surface of the optical fiber 4 detected by the temperature measuring device. And a control device that feedback-controls the output (for example, the output of the CO ₂ laser) of the first fiber surface heating device 7 so that the temperature becomes a desired value (preset temperature set in advance). .

  The first fiber surface heating device 7 may be provided anywhere as long as it is downstream of the annealing furnace 5 and upstream of the coating device 6, but impurities are present between the first fiber surface heating device 7 and the coating device 6. In order to avoid adhesion, it is desirable to provide it just before the coating device 6.

  By the way, if defects (crystallized parts with impurities as nuclei, microcracks, etc.) become too large during the annealing process, it may be possible that the defects cannot be sufficiently repaired only by the flame polishing process by the first fiber surface heating device 7.

  Therefore, in the present embodiment, the surface of the optical fiber 4 immediately before being introduced into the annealing furnace 5 is continuously heated in the longitudinal direction, and the second fiber surface heating is performed to perform the flame polishing process on the optical fiber 4 before the annealing process. An apparatus 8 is further provided, and the second fiber surface heating apparatus 8 is configured to remove impurities adhering to the optical fiber 4 in the drawing furnace 3 or in a space between the drawing furnace 3 and the annealing furnace 5. .

  The second fiber surface heating device 8 is provided immediately before the annealing furnace 5 in order to prevent impurities from adhering between the second fiber surface heating device 8 and the annealing furnace 5.

  Since the second fiber surface heating device 8 is intended to remove impurities, the surface of the optical fiber 4 is melted (softened) as the surface of the optical fiber 4 is melted (softened) like the first fiber surface heating device 7. There is no need to increase the temperature. That is, in the flame polishing process by the second fiber surface heating device 8, the temperature of the surface of the optical fiber 4 may be less than 2000 ° C., and may be appropriately adjusted to an output that can remove impurities.

As the second fiber surface heating device 8, as with the first fiber surface heating device 7, for example, a CO ₂ laser device, a low-temperature arc discharge device, or the like can be used. Similarly to the first fiber surface heating device 7, the second fiber surface heating device 8 includes an inert gas purge device (not shown) for purging the optical fiber 4 with an inert gas, and further, an optical fiber. 4 is provided with a temperature measuring device (not shown) for detecting the surface temperature of 4 and a control device (not shown) for feedback controlling the output of the second fiber surface heating device 8 in accordance with the detected value of the temperature measuring device. Also good.

  Next, a method for manufacturing an optical fiber according to the present embodiment will be described.

  In the optical fiber manufacturing method according to the present embodiment, first, the optical fiber preform 2 is heated, melted and drawn in the drawing furnace 3, and the surface of the drawn optical fiber 4 is heated to the second fiber surface. The apparatus 8 is continuously heated to perform a flame polishing process to remove impurities adhering to the optical fiber 4, and then the optical fiber 4 is introduced into an annealing furnace 5 to perform an annealing process.

  At this time, in the second fiber surface heating device 8, impurities are attached to the surface of the optical fiber 4 activated by the flame polishing process by performing a flame polishing process while purging an inert gas to the optical fiber 4. It suppresses that. By removing impurities with the second fiber surface heating device 8 immediately before introduction into the annealing furnace 5, the optical fiber 4 in a state where the impurities are removed can be introduced into the annealing furnace 5, and defects (impurities due to annealing treatment) The occurrence of crystallized parts or microcracks (or the expansion or progress of defects) can be minimized.

  Thereafter, the surface of the optical fiber 4 after the annealing treatment is continuously heated by the first fiber surface heating device 7 to perform the flame polishing treatment. At this time, a flame polishing process is performed so that the temperature of the surface of the optical fiber 4 is 2000 ° C. or more, the surface of the optical fiber 4 is melted (softened), and a defect ( Repair crystallized parts and microcracks using impurities as nuclei. Further, by performing a flame polishing process while purging the optical fiber 4 with an inert gas, it is possible to prevent impurities from adhering to the surface of the optical fiber 4 that has been heated to a high temperature by the flame polishing process.

  Thereafter, the optical fiber 4 is passed through the coating device 6 and the surface of the optical fiber 4 is coated with a resin to obtain a product.

  As described above, in the optical fiber manufacturing method according to the present embodiment, the surface of the annealed optical fiber 4 is continuously heated in the longitudinal direction to perform the flame polishing process.

  Thereby, the surface of the optical fiber 4 is heated and melted (softened) to repair defects generated on the surface of the optical fiber 4 due to the annealing treatment, that is, a portion where microcrystallization has progressed with the impurities as nuclei or micro cracks. It becomes possible to manufacture the optical fiber 4 with low loss and high strength.

  In the present embodiment, since the flame polishing process is performed while purging the inert gas to the optical fiber 4, it is possible to prevent impurities from adhering to the surface of the optical fiber 4 during the flame polishing process.

  Further, in the present embodiment, the surface of the optical fiber 4 just before being introduced into the annealing furnace 5 is heated so that the optical fiber 4 before the annealing treatment is also subjected to the flame polishing treatment, so that the impurities are removed. In this state, the optical fiber 4 can be introduced into the annealing furnace 5, and the generation of defects (or the expansion and progress of defects) during the annealing process can be minimized. Therefore, the first fiber surface heating device 7 installed on the downstream side of the annealing furnace 5 can surely repair the defect, and the reliability can be improved.

  Further, the optical fiber manufacturing apparatus 1 according to the present embodiment can be realized only by adding the first fiber surface heating apparatus 7 and the second fiber surface heating apparatus 8 to the existing optical fiber manufacturing apparatus. The production of the low-loss and high-strength optical fiber 4 can be realized at low cost without providing a huge vacuum vessel as in FIG.

  The present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the spirit of the present invention.

  For example, in the above embodiment, the surface temperature of the optical fiber 4 is set to 2000 ° C. or higher so that the first fiber surface heating device 7 melts (softens) the surface of the optical fiber 4 made of pure silica glass. However, the present invention is not limited to this, and a low-temperature softened layer in which an impurity such as fluorine is added to the surface of the optical fiber preform 2 and the softening temperature (softening point) is controlled low is formed in advance. The first fiber surface heating device 7 may perform the flame polishing process so that the surface temperature of the optical fiber 4 is equal to or higher than the softening temperature of the low-temperature softening layer.

  By configuring in this way, even if the temperature of the surface of the optical fiber 4 during the flame polishing process by the first fiber surface heating device 7 is lowered, the surface of the optical fiber 4 is melted (softened) and sufficiently defective. It becomes possible to repair, and it becomes possible to suppress the temperature rise of the core part of the optical fiber 4 more. What is necessary is just to adjust the thickness of a low-temperature softening layer suitably, for example so that it may become a thickness of about 10 micrometers after drawing. As an example, when fluorine is used as an impurity to be added, the softening temperature can be lowered by about 100 ° C. compared to pure silica glass by adding about 0.3% fluorine to pure silica glass. The low-temperature softened layer can be formed using a known method such as a gas phase axis method or a rod-in-tube method. Further, the impurity to be added is not limited to fluorine but may be, for example, an OH group.

DESCRIPTION OF SYMBOLS 1 Optical fiber manufacturing apparatus 2 Optical fiber base material 3 Drawing furnace 4 Optical fiber 5 Annealing furnace 6 Coating device 7 1st fiber surface heating apparatus 8 2nd fiber surface heating apparatus

Claims (7)

In an optical fiber manufacturing method in which an optical fiber preform is heated, melted and drawn, and the drawn optical fiber is introduced into an annealing furnace and annealed.
A method of manufacturing an optical fiber, wherein a surface of the optical fiber after the annealing treatment is continuously heated in a longitudinal direction, and the optical fiber after the annealing treatment is subjected to a flame polishing treatment.   The optical fiber manufacturing method according to claim 1, wherein the flame polishing treatment is performed so that the temperature of the surface of the optical fiber after the annealing treatment is 2000 ° C. or higher. On the surface of the optical fiber preform, a low-temperature softened layer in which impurities are added and the softening temperature is controlled low is formed,
The method of manufacturing an optical fiber according to claim 1, wherein the flame polishing treatment is performed so that a temperature of the surface of the optical fiber after the annealing treatment is equal to or higher than a softening temperature of the low-temperature softening layer.   The optical fiber manufacturing method according to claim 1, wherein the flame polishing is performed while purging an inert gas on the annealed optical fiber.   The surface of the optical fiber immediately before introduction into the annealing furnace is continuously heated in the longitudinal direction, and the optical fiber before the annealing treatment is also subjected to flame polishing treatment. An optical fiber manufacturing method. In an optical fiber manufacturing apparatus comprising: a drawing furnace that heats, melts and draws an optical fiber preform; and an annealing furnace that anneals the optical fiber drawn by the drawing furnace;
An optical fiber comprising: a first fiber surface heating device that continuously heats the surface of the optical fiber after the annealing treatment in a longitudinal direction and performs a flame polishing treatment on the optical fiber after the annealing treatment. Manufacturing equipment.   7. The apparatus according to claim 6, further comprising a second fiber surface heating device that continuously heats the surface of the optical fiber immediately before being introduced into the annealing furnace in a longitudinal direction, and performs a flame polishing process on the optical fiber before the annealing process. Optical fiber manufacturing equipment.

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