JP4568003B2 - Optical fiber manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for manufacturing an optical fiber with low transmission loss.

  As shown in FIGS. 5 and 6, the optical fiber manufacturing apparatus includes a drawing furnace 53 that melts the fiber preform 54 and an annealing process that heats the drawn optical fibers in the order in which the optical fibers 52 are drawn. A furnace 55 and a fiber take-up machine 56 for taking up the optical fiber 52 are provided.

  The fiber take-up machine 56 includes a take-up capstan 58 that controls a drawing speed, a pulley 59 that forms a drawing path, and a bobbin 57 that winds up an optical fiber.

  The optical fiber 52 is heated and melted by the heater 61 of the drawing furnace 53 and drawn, and the fiber temperature is controlled by passing the optical fiber 52 through the annealing furnace 55 provided with the heater 62, and the drawing speed is drawn by the fiber taker 56. The optical fiber 52 is taken out while controlling the above.

  Light scattering that accounts for most of the loss factors of the optical fiber 52 is performed by controlling the fiber temperature to be maintained at a certain temperature for a certain period of time in the annealing furnace 55 immediately after drawing, thereby promoting relaxation of the glass structure of the optical fiber 52. Loss can be reduced (see, for example, Patent Documents 1 and 2).

  Also, there is an optical fiber manufacturing method in which an optical fiber preform is heated and drawn to produce an intermediate optical fiber, and the intermediate optical fiber is reheated to lower the fictive temperature and reduce light scattering loss ( For example, see Patent Document 3).

JP 2000-335933 A JP 2000-335934 A Japanese Patent Laid-Open No. 10-25127

  FIG. 7 shows the temperature distribution in the longitudinal direction of the optical fiber 52 in the annealing furnace 55 when the position 65 where the optical fiber 52 enters the annealing furnace 55 is 0 mm. As shown in FIG. 7, when the optical fiber 52 enters the annealing furnace 55 at a temperature higher or lower than the temperature of the inner wall 64 of the annealing furnace 55, the fiber temperature changes until it becomes the same as the inner wall temperature of the annealing furnace 55. When the temperature of the inner wall of the furnace 55 becomes the same, the temperature is kept constant until the optical fiber 52 exits the annealing furnace 55.

  However, at the position 65 where the optical fiber 52 enters the annealing furnace 55, if the fiber temperature is too high or too low than the inner wall temperature of the furnace, the fiber temperature is 150 m / min (curve 73). There is not enough time to be kept constant in the furnace, and the glass structure relaxation of the optical fiber 52 is not sufficiently promoted. Therefore, there is a problem that the fictive temperature cannot be lowered, and as a result, the light scattering loss of the manufactured optical fiber becomes large.

  When the fiber speed is 20 m / min (curve 71) or 60 m / min (curve 72), the glass structure relaxation is sufficiently promoted in the annealing furnace 55, but the drawing speed of the optical fiber 52 is slow. So productivity is bad and not practical.

  Accordingly, an object of the present invention is to provide an optical fiber manufacturing method and manufacturing apparatus that solves the above-described problems, sufficiently promotes structural relaxation of glass, and reduces the light scattering loss of the optical fiber.

In order to achieve the above object, the invention of claim 1 is characterized in that an optical fiber preform is heated and drawn in a drawing furnace, and the drawn optical fiber is annealed in the annealing furnace provided under the drawing furnace. In an optical fiber manufacturing method for maintaining an annealing temperature at which glass structure relaxation is promoted, a passage through which the optical fiber passes, and a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage Is controlled so that the temperature of the optical fiber at the inlet of the annealing furnace becomes equal to the annealing temperature of the annealing furnace, and the annealing temperature is expressed by the following equation: T = −40. 089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing method characterized by satisfying the above.

According to a second aspect of the present invention, an optical fiber preform is heated and drawn in a drawing furnace, and an annealing furnace in which the drawn optical fiber is provided under the drawing furnace is used to accelerate the glass structure relaxation of the optical fiber. In a method of manufacturing an optical fiber that maintains temperature, a cooling device that includes a passage through which the optical fiber passes and a cooling gas supply unit that blows the cooling gas directly onto the optical fiber by flowing a cooling gas in the passage. The optical fiber at the inlet of the annealing furnace is cooled so that the fiber temperature is equal to the annealing temperature of the annealing furnace, and the annealing temperature is expressed by the following equation: T = −40.089 × ln (t) +1307 .8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing method characterized by satisfying the above.

According to a third aspect of the present invention, an optical fiber preform is heated and drawn in a drawing furnace, and annealing in which the relaxation of the glass structure of the optical fiber is promoted in an annealing furnace provided with the drawn optical fiber under the drawing furnace. In the method of manufacturing an optical fiber kept at a temperature, the temperature of the optical fiber at the inlet of the annealing furnace is measured, and the passage through which the optical fiber passes in the preceding stage of the annealing furnace so that the measured value becomes equal to the annealing temperature. The temperature of the optical fiber is controlled using a cooling device having a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas into the optical fiber, and the annealing temperature is expressed by the following equation T = -40.089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing method characterized by satisfying the above.

A fourth aspect of the present invention, an optical fiber comprising: a drawing furnace for heating and melting an optical fiber preform, and a annealing furnace for holding the drawn optical fiber to an annealing temperature of the glass structural relaxation is promoted of the optical fiber A passage through which the optical fiber passes between the drawing furnace and the annealing furnace, and a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage. And a cooling device that cools the optical fiber to a temperature equal to the annealing temperature of the annealing furnace, and the annealing temperature of the annealing furnace is expressed by the following formula: T = −40.089 × ln (t) +1307. 8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing apparatus characterized by satisfying the above.

The invention of claim 5 is an optical fiber comprising a drawing furnace for heating and melting an optical fiber preform, and an annealing furnace for holding the drawn optical fiber at an annealing temperature at which relaxation of the glass structure of the optical fiber is promoted. A passage through which the optical fiber passes between the drawing furnace and the annealing furnace, and a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage. A cooling device that cools the optical fiber to a temperature equal to the annealing temperature of the annealing furnace, a temperature measuring device that measures the temperature of the optical fiber is provided on the outlet side of the cooling device, and the annealing furnace The annealing temperature is as follows: T = −40.089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing apparatus characterized by satisfying the above.

The invention of claim 6 is an optical fiber manufacturing apparatus in which the cooling gas supply means includes a gas flow rate controller, and the flow rate of the cooling gas is adjusted according to the temperature measured by the temperature measuring device.

According to a seventh aspect of the present invention, the cooling device includes a cooling main body in which a passage through which an optical fiber passes, a cooling gas pipe connected to the cooling main body, a cooling gas formed in the cooling main body, and the cooling gas from the cooling gas pipe. Is an optical fiber manufacturing apparatus comprising a gas flow path that flows through the passage.

  According to the present invention, excellent effects such as sufficiently promoting the structural relaxation of glass and reducing the light scattering loss of the optical fiber are exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic view showing a preferred embodiment of an optical fiber manufacturing apparatus according to the present invention.

  The optical fiber manufacturing apparatus according to the present embodiment includes a drawing furnace 12, a cooling device 13, a temperature measuring device 14, and an annealing furnace 15. The drawing furnace 12 and the annealing furnace 15 are arranged in this order in the direction of drawing the optical fiber preform 16 (from the top to the bottom in FIG. 1), and the cooling device 13 is disposed between the drawing furnace 12 and the annealing furnace 15. The temperature measuring device 14 is installed at the entrance of the annealing furnace 15, respectively.

  The drawing furnace 12 includes a heater 17 for heating and melting the optical fiber preform 16.

  The annealing furnace 15 includes a heater 21 for keeping the optical fiber 11 constant at a predetermined temperature (annealing process).

  As shown in FIG. 2, the cooling device 13 includes a cooling main body 23, a cooling gas pipe 19 connected to the cooling main body 23, and a cooling gas supply unit connected to the cooling gas pipe 19. The cooling body 23 is a solid body made of aluminum or copper and has a length in the longitudinal direction of 250 mm. The cooling body 23 is formed with a circular passage 24 having a diameter of 30 mm through which the optical fiber 11 passes and a gas passage 25 through which the cooling gas flows through the passage 24. The cooling gas supply means connected to the cooling gas pipe 19 is a gas flow rate controller 18 that supplies a cooling gas and controls the gas flow rate.

  Since the cooling gas pipe 19 is connected to a plurality of gas flow paths 25 formed in the cooling main body 23, the cooling gas pipe 19 is branched into a plurality of branch pipes 27 and connected to the gas flow paths 25 via the branch pipes 27. The gas flow path 25 communicates the passage 24 and the outside of the cooling body 23. The gas flow paths 25 are preferably formed symmetrically in the fiber cross-sectional direction in order to uniformly cool the optical fiber 11. In the present embodiment, He gas is used as the cooling gas.

  An infrared radiation thermometer is provided as the temperature measuring instrument 14 above the annealing furnace 15 (on the optical fiber inlet side), and a monitoring device 20 connected thereto is disposed outside the optical fiber manufacturing apparatus.

  Although not shown, a fiber take-up machine as described in the background art is provided under the annealing furnace 15, and a device for coating a coating resin for protecting the optical fiber may be further provided. .

  Next, the operation of the present embodiment will be described.

  In the optical fiber manufacturing method, the optical fiber preform 16 is heated and melted in the drawing furnace 12 to become a small-diameter optical fiber 11 by free fall, and the optical fiber 11 solidified as the fiber temperature decreases is a fiber take-up machine. It is drawn.

  The annealing furnace 15 has a structure in which the optical fiber is kept constant at a predetermined temperature, thereby promoting relaxation of the glass structure and reducing light scattering loss.

  In the cooling device 13 arranged in the front stage of the annealing furnace 15, the optical fiber 11 introduced into the passage 25 is cooled by the cooling gas supplied from the gas flow rate controller 18 through the gas passage 25 to the passage 25. .

  Since the cooling body 23 is made of a material having high thermal conductivity such as aluminum, the cooling body 23 radiates the heat of the cooling gas whose temperature has been increased by cooling the optical fiber 11 immediately after drawing, and the cooling body 23. Is formed thick so that the optical fiber 11 is prevented from being rapidly cooled by outside air.

  Since He gas is used as the cooling gas, it does not react with the quartz material forming the optical fiber. Further, since the gas is lighter than the outside air (air or nitrogen), the He gas rises in the passage 24 and can cool the optical fiber 11 without affecting the temperature of the annealing furnace 15 below the cooling device 13. .

  Further, if a guard member (not shown) that prevents the cooling gas from flowing into the annealing furnace 15 is provided between the cooling device 13 and the annealing furnace 15, a gas heavier than the outside air may be used as the cooling gas.

  The temperature of the optical fiber immediately after drawing is made substantially equal to the temperature in the annealing furnace 15 by the cooling device 13, and then the optical fiber is introduced into the annealing furnace 15. Thereby, the optical fiber 11 can be sufficiently maintained at a predetermined temperature in the annealing furnace 15, and the structural relaxation of the glass can be sufficiently promoted.

  Here, in FIG. 3, the temperature change amount at one point on the fiber from when the optical fiber 11 is introduced to the cooling device 13 to when it is exited, and from when the optical fiber 11 is introduced to the cooling device 13 until it exits. The relationship with the flow volume of the cooling gas which flows into the channel | path 24 between is shown. The cooling gas was He gas, and the drawing speed of the optical fiber 11 was 20 m / min.

  The position where the optical fiber 11 enters the annealing furnace 15 by adjusting the gas flow rate controller 18 according to the change in the fiber temperature measured by the temperature measuring device 14 and adjusting the flow rate of the cooling gas flowing through the passage 24. The fiber temperature at the (annealing furnace inlet) 22 can be controlled.

  The gas flow controller 18 is adjusted while the fiber temperature is monitored by the monitoring device 20. The gas flow controller 18 and the temperature measuring device 14 may be linked to adjust the gas flow controller 18 so that the fiber temperature is controlled.

  Specifically, as shown in FIG. 3, the change amount of the fiber temperature per unit time and the He gas flow rate are in a substantially proportional relationship. When the fiber temperature at the position 22 that enters the annealing furnace 15 is higher than the temperature in the annealing furnace 15, the fiber temperature is lowered by increasing the flow rate of the cooling gas flowing through the passage 24 to increase the cooling effect of the optical fiber 11. Can do. Conversely, when the fiber temperature at the position 22 entering the annealing furnace 15 is lower than the temperature in the annealing furnace 15, the cooling effect of the optical fiber 11 is reduced by reducing the flow rate of the cooling gas flowing through the passage 24, thereby reducing the fiber temperature. Can be suppressed. Therefore, the temperature of the optical fiber 11 entering the annealing furnace 15 can be made substantially equal to the temperature in the annealing furnace 15.

  Further, a thermocouple (not shown) is provided on the inner wall of the annealing furnace 15, the inner wall temperature of the annealing furnace 15 is constantly measured, and the output of the heater 21 is adjusted in accordance with the change in the inner wall temperature. The inner wall temperature can be controlled.

  Next, the relationship between the fiber temperature kept constant in the annealing furnace 15 and the time during which one point of the optical fiber 11 is annealed when the glass structure relaxation of the optical fiber 11 is most promoted will be shown.

As shown in FIG. 4, the calibration curve 40 shows the relationship between the annealing temperature (fiber temperature) T [° C.] and the annealing treatment time t [second] , and T = −40.089 × ln (t) +1307.8. This calibration curve 40 is based on the experiments of the present inventors. As shown in Appl. Phys. 83, 8175 (2003), the light kept at a constant annealing temperature T [° C.] using a fiber sample. The fictive temperature of the fiber was evaluated by the Raman scattering method, and the relationship with the annealing time t [second] was investigated.

  The time (annealing time) t for which the optical fiber 11 passes through the annealing furnace 15 is determined from the drawing speed of the optical fiber 11 and the length of the annealing furnace 15. Ask from. The fiber temperature at the position 22 where the optical fiber 11 enters the annealing furnace 15 is made substantially equal to the annealing temperature T in order to maintain the fiber temperature sufficiently at the annealing temperature T until the optical fiber 11 enters the annealing furnace 15 and exits. After that, the flow rate of the cooling gas is adjusted so as to be introduced into the annealing furnace 15.

  At that time, the output of the heater 21 of the annealing furnace 15 is adjusted so that the inner wall temperature of the annealing furnace 15 becomes the annealing temperature T. Thus, the optical fiber in which the relaxation of the glass structure of the optical fiber 11 is most promoted, that is, the light scattering loss is minimized, can be manufactured without reducing the drawing speed.

  Next, embodiments of the present invention will be described based on examples, but the embodiments of the present invention are not limited to these examples.

  An optical fiber in which Ge was added to the core was manufactured using an optical fiber manufacturing apparatus (for example, the drawing furnace 12 in FIG. 1). As shown in FIG. 4, the annealing temperature T is 1270 ° C. and the annealing time t is 1.8 seconds. An annealing furnace having a length of 3 m was used, and the drawing speed was 100 m / min. While monitoring the temperature of the optical fiber with an infrared radiation thermometer, the flow rate of He gas input to the cooling device is adjusted so that the temperature when the drawn optical fiber enters the annealing furnace becomes 1270 ° C. Controlled.

  The transmission loss of the optical fiber obtained in this example was 0.168 dB / km at a wavelength of 1.55 μm, which was sufficiently lower than the conventional optical fiber. Moreover, when the fictive temperature of the obtained optical fiber was evaluated by the Raman scattering method, the fictive temperature was lowered to 1280 ° C., and it was confirmed that the structural relaxation of the glass was sufficiently advanced.

It is the schematic which shows the manufacturing apparatus of the optical fiber of this Embodiment. It is an expansion perspective view of the cooling device of FIG. It is a figure which shows the relationship between a cooling gas flow volume and a temperature variation. It is a figure which shows the relationship between annealing treatment time and annealing temperature. It is the schematic which shows the manufacturing apparatus of the conventional optical fiber. It is a principal part enlarged view of the drawing furnace and annealing furnace of FIG. It is a figure which shows the temperature distribution of the optical fiber longitudinal direction in an annealing furnace.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical fiber 12 Drawing furnace 13 Cooling device 14 Temperature measuring device 15 Annealing furnace 16 Optical fiber preform 18 Gas flow controller 19 Cooling gas piping 23 Cooling main body 25 Gas flow path

Claims (7)

The optical fiber preform is heated and drawn in a drawing furnace, and the drawn optical fiber is held in an annealing temperature provided under the drawing furnace at an annealing temperature that promotes relaxation of the glass structure of the optical fiber. In the manufacturing method,
Using a cooling device having a passage through which the optical fiber passes and a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage, the temperature of the optical fiber at the annealing furnace inlet is The temperature is controlled to be equal to the annealing temperature of the annealing furnace, and the annealing temperature is expressed by the following equation: T = −40.089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
The manufacturing method of the optical fiber characterized by satisfy | filling. The optical fiber preform is heated and drawn in a drawing furnace, and the drawn optical fiber is held in an annealing temperature provided under the drawing furnace at an annealing temperature that promotes relaxation of the glass structure of the optical fiber. In the manufacturing method,
The optical fiber at the inlet of the annealing furnace is cooled using a cooling device having a passage through which the optical fiber passes and cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage. The fiber temperature is made equal to the annealing temperature of the annealing furnace, and the annealing temperature is expressed by the following equation: T = −40.089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
The manufacturing method of the optical fiber characterized by satisfy | filling. The optical fiber preform is heated and drawn in a drawing furnace, and the drawn optical fiber is held in an annealing temperature provided under the drawing furnace at an annealing temperature that promotes relaxation of the glass structure of the optical fiber. In the manufacturing method,
The temperature of the optical fiber at the inlet of the annealing furnace is measured, and a path through which the optical fiber passes in the front stage of the annealing furnace so that the measured value becomes equal to the annealing temperature, and a cooling gas is allowed to flow in the path to the optical fiber. The temperature of the optical fiber is controlled using a cooling device having cooling gas supply means for directly blowing the cooling gas, and the annealing temperature is expressed by the following equation: T = −40.089 × ln (t) +1307. 8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
The manufacturing method of the optical fiber characterized by satisfy | filling. In an optical fiber manufacturing apparatus comprising: a drawing furnace that heats and melts an optical fiber preform; and an annealing furnace that holds the drawn optical fiber at an annealing temperature that promotes relaxation of the glass structure of the optical fiber.
An annealing furnace having a passage through which an optical fiber passes between the drawing furnace and the annealing furnace, and a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage A cooling device for cooling the optical fiber to a temperature equal to the annealing temperature of the annealing furnace is provided, and the annealing temperature of the annealing furnace is expressed by the following equation: T = −40.089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing apparatus, characterized in that: In an optical fiber manufacturing apparatus comprising: a drawing furnace that heats and melts an optical fiber preform; and an annealing furnace that holds the drawn optical fiber at an annealing temperature that promotes relaxation of the glass structure of the optical fiber.
An annealing furnace having a passage through which an optical fiber passes between the drawing furnace and the annealing furnace, and a cooling gas supply means for directly blowing the cooling gas onto the optical fiber by flowing a cooling gas in the passage A cooling device that cools the optical fiber to a temperature equal to the annealing temperature is provided, a temperature measuring device that measures the temperature of the optical fiber is provided on the outlet side of the cooling device, and the annealing temperature of the annealing furnace is: The following formula T = −40.089 × ln (t) +1307.8
(Here, T is the annealing temperature [° C.] and t is the annealing time [seconds] .)
An optical fiber manufacturing apparatus, characterized in that:   6. The optical fiber manufacturing apparatus according to claim 5, wherein the cooling gas supply means includes a gas flow rate controller, and the flow rate of the cooling gas is adjusted according to the temperature measured by the temperature measuring device.   The cooling device includes a cooling main body in which a passage through which an optical fiber passes, a cooling gas pipe connected to the cooling main body, a gas flow formed in the cooling main body and flowing the cooling gas from the cooling gas pipe to the passage. The optical fiber manufacturing apparatus according to claim 4, comprising a path.

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