JP2005250023A - Method and apparatus for manufacturing photonic crystal fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for manufacturing a PCF (photonic crystal fiber) to prevent intrusion of water or a foreign matter into a hollow part. <P>SOLUTION: A photonic crystal fiber preform 13 is heated and fused to a stretching temperature and stretched to manufacture a photonic crystal fiber 15 having a hollow part 12 in the longitudinal direction in at least either a core part or a clad part. In this manufacture, the inside of the hollow part of the photonic crystal fiber preform 13 is replaced by inert gas, and the stretched photonic crystal fiber 15 is provided with a sealing part to control the inner pressure of the hollow part 12 and to block up the hollow part so as to seal the inert gas in the hollow part 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for producing a photonic crystal fiber having a hollow portion.

  A photonic crystal fiber (PCF) is an optical fiber having a photonic crystal structure, that is, a periodic structure of refractive index, in a core or a clad, and a large number of cylindrical holes in the circumferential direction around the core. Is formed.

  The PCF has characteristics such as a large relative dispersion and a large single mode region in addition to a large relative refractive index difference and a small influence on bending as compared with a normal optical fiber.

  FIG. 3 shows a structural diagram of a conventional PCF 45 manufacturing apparatus.

  As shown in FIG. 3, in the PCF manufacturing apparatus 41, an internal pressure controller 44 is provided in a drawing furnace 43 into which a PCF base material 42 in which a hollow portion 54 is formed is inserted, and the drawn PCF 45 is in the following order. A fiber cutter 46, an outer diameter measuring device 47, a cooling pipe 48, a coating device 49, a resin curing furnace 50, a take-up capstan 51, and a winder 52 are provided, and a hollow portion pressurizing device 53 is provided in the PCF base material 42. It has been.

  The PCF 45 manufacturing method using the PCF manufacturing apparatus 41 starts with a PCF in which a hollow portion 54 is formed in a drawing furnace 43 provided with an internal pressure controller 44 that keeps the internal pressure of the core 55 of the drawing furnace 43 constant. The base material 42 is inserted, and the PCF base material 42 is heated and melted. At that time, the core 55 is maintained at about 25 Pa by the internal pressure controller 44. Further, the PCF base material 42 is pressurized to about 1000 Pa by the hollow portion pressurizing device 53.

  The PCF 45 drawn from the PCF base material 42 has an outer diameter measured by an outer diameter measuring device 47 and cooled by a cooling pipe 48. Next, the UV resin is coated on the PCF 45 by the coating device 49 and irradiated with ultraviolet rays in the resin curing furnace 50, so that the UV resin is cured.

  Finally, the PCF 45 passes through the take-up capstan 51 and is wound around the winder 52. The take-up speed of the PCF 45 is adjusted by the take-up capstan 51 so that the outer diameter of the PCF 45 measured by the outer diameter measuring device 47 is controlled to be constant. At the end of drawing, the PCF 45 is automatically disconnected by the fiber cutter 46, and the PCF 45 is obtained.

  Further, the PCF 45 obtained by the manufacturing apparatus 41 is used by sealing the connection end face in order to prevent entry of foreign matter into the hollow portion and to reduce connection loss. As the method, for example, as shown in Patent Document 1, there are a method of melting and closing the hollow portion of the end face of the PCF 45 and a method of filling the resin near the end face of the PCF 45 and sealing the hollow portion.

JP 2002-323625 A

  However, since the manufacturing method of the prior art is not considered at all for the protection of the glass surface in the PCF hollow portion, during the PCF manufacturing process, foreign matter and water vapor (OH group) are exposed to the end surface of the PCF hollow portion after drawing. There is a problem of entering from the upper end of the hollow portion of the PCF base material during drawing.

  When OH groups are contained in the fiber, they give a very large loss. Technology for removing OH groups has been realized with ordinary silica-based optical fibers, but photonic crystal fibers with a hollow portion in the cladding have not been improved, and moisture in the air can easily enter the hollow portion. . As a result, degradation of optical characteristics such as an increase in transmission loss occurs, and degradation of fiber strength is promoted.

  In addition, when the end face sealing process is performed after the PCF 45 is manufactured, there is a problem that the process of filling the resin or the like from the end face of the PCF into the hollow part requires damage to the end face from the hollow part or increases the manufacturing cost. is there.

  Then, the objective of this invention is providing the manufacturing method and apparatus of PCF which can solve the said subject and prevent that a water | moisture content and a foreign material enter into a hollow part.

  In order to achieve the above object, according to the first aspect of the present invention, a photonic crystal fiber preform is heated to a stretching temperature, melted and stretched to have a hollow portion in a longitudinal direction in at least one of a core portion and a cladding portion. In the production of the photonic crystal fiber, the photonic crystal fiber is produced by replacing the inside of the hollow portion of the photonic crystal fiber preform with an inert gas.

  According to the second aspect of the present invention, a photonic crystal fiber having a hollow portion in the longitudinal direction in at least one of a core portion and a clad portion is produced by heating and melting a photonic crystal fiber base material at a drawing temperature and melting it. The inside of the hollow portion of the photonic crystal fiber base material is replaced with an inert gas, and in the photonic crystal fiber to be stretched, a sealing portion for closing the hollow portion by controlling the internal pressure of the hollow portion is formed, The method for producing a photonic crystal fiber according to claim 1, wherein the inert gas is sealed in a hollow portion.

  According to a third aspect of the present invention, an internal pressure of the hollow portion is determined by a pressurizing device, a vacuum pump, and a hollow portion internal pressure control device that are attached to the photonic crystal fiber preform through a supply / exhaust line at the end of the production of the photonic crystal fiber. The method for producing a photonic crystal fiber according to claim 1, wherein the sealing portion is formed by reducing the pressure.

  According to a fourth aspect of the present invention, the hollow part is sealed or expanded at an arbitrary position of the photonic crystal fiber by reducing or increasing the internal pressure of the hollow part during the production of the photonic crystal fiber. 3. A method for producing a photonic crystal fiber according to any one of 3 above.

  In the invention of claim 5, the upper end of the photonic crystal fiber base material is connected to a supply / exhaust line for supplying / discharging an inert gas into the hollow portion, and the inert gas is introduced into the supply / exhaust line so as to be hollow. It is a manufacturing method of the photonic crystal fiber in any one of Claims 1-4 which connected the pressurization apparatus for controlling internal pressure, a vacuum pump, and an internal pressure control apparatus.

  Invention of Claim 6 manufactures the photonic crystal fiber which has a hollow part in the longitudinal direction in at least one of a core part or a clad part by heating a photonic crystal fiber preform to a stretching temperature, melting it and stretching it In the apparatus, an air supply / exhaust line for supplying and discharging an inert gas in the hollow portion is connected to the upper end of the photonic crystal fiber preform, and a pressurizing device for controlling the internal pressure of the hollow portion, a vacuum pump, and This is a photonic crystal fiber manufacturing apparatus to which an internal pressure control device is connected.

  According to the present invention, an excellent effect of preventing deterioration of optical characteristics and strength of the photonic crystal fiber is exhibited.

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

  FIG. 1 shows a structural diagram of the photonic crystal fiber manufacturing apparatus of the present embodiment.

  As shown in FIG. 1, the PCF manufacturing apparatus 11 according to the present embodiment includes a fiber cutter 16 in the order in which a drawing furnace 14 into which the PCF base material 13 is inserted and a PCF 15 drawn from the PCF base material 13 follow. An outer diameter measuring device 17, a cooling pipe 18, a coating device 19, a resin curing furnace 20, a take-up capstan 21, and a winder 22 are provided. The drawing furnace 14 is provided with a core 23 and a heating device 24 for heating the core 23, and an internal pressure controller 25 for controlling the pressure in the core 23 is connected. An air supply / exhaust line 27 is connected to the upper end portion 26 of the PCF base material 13, and a hollow portion internal pressure control device 28 is provided in the air supply / exhaust line 27. The air supply / exhaust line 27 branches into an air supply line 34 and an exhaust line 35. The air supply line 34 is connected to the pressurizing device 29 connected to the gas supply device 33, and the exhaust line 35 is connected to the vacuum pump 30. The hollow portion internal pressure control device 28 is a device that raises or lowers the internal pressure of the hollow portion 12 by switching between supply and exhaust, or keeps the internal pressure constant. The vacuum pump 30 is a device that evacuates the hollow portion 12, and the gas supply device 33 is a device that supplies the inert gas to the hollow portion 12.

  The PCF base material 13 has a plurality of hollow portions 12 periodically formed in the circumferential direction of the cross section around the core portion, and the cross-sectional structure of the PCF base material 13 is substantially similar to the cross-sectional structure of the PCF 15 to be manufactured. It has become.

  Next, the manufacturing method of PCF15 is demonstrated.

First, the hollow portion 12 of the PCF base material 13 is evacuated by the vacuum pump 30. Next, the air in the hollow portion 12 is replaced with an inert gas by the pressurizing device 28. Inert gas used is _{Cl 2, N 2, Ar,} He or the like. At that time, the internal pressure of the hollow portion 12 can be maintained at a constant value P by the hollow portion internal pressure control device 28.

  Next, the PCF base material 13 is inserted into a drawing furnace 14 in which the internal pressure of the core 23 is maintained at 25 Pa or more, and is heated to about 2100 ° C. by the heating device 24, and the lower end portion 31 of the PCF base material 13 is melted. The PCF 15 is reduced in diameter by drawing.

  At this time, as will be described in detail later by the hollow part internal pressure control device 28, the PCF 15 is adjusted by adjusting the hollow part diameter in the vicinity of the lower end part 31 of the PCF base material 13 by adjusting the internal pressure of the hollow part 12. A sealing portion that closes the hollow portion is formed.

  The PCF 15 to be drawn is measured by an outer diameter measuring device 17 and cooled by a cooling pipe 18. Next, the UV resin is coated on the PCF 15 by the coating device 20, and the coated UV resin is cured by being irradiated with ultraviolet rays in the resin curing furnace 20, so that the PCF 15 becomes the resin-coated PCF core wire 32.

  Finally, the PCF core wire 32 passes through the take-up capstan 21 and is wound around the winder 22. The take-up speed of the PCF core wire 32 is adjusted by the take-up capstan 21 so that the outer diameter of the PCF 15 measured by the outer diameter measuring device 18 is controlled to be constant. At the end of drawing, the PCF 15 is automatically cut by the fiber cutter 16.

In the manufacturing method according to the present embodiment, using the hollow part pressurizing device 29, the vacuum pump 30, and the hollow part internal pressure control device 28 attached to the upper end part 26 of the PCF base material 13 via the air supply / exhaust line 27, The air in the hollow portion 12 of the PCF base material 13 is replaced with an inert gas such as N ₂ and the internal pressure is adjusted to seal both ends of the hollow portion of the PCF 15 so that the hollow portion is blocked from the outside air.

  The diameter of the hollow part of the PCF 15 to be produced depends on the internal pressure P of the hollow part 12 when the PCF base material 13 is melted. Here, FIG. 2 shows the relationship between the internal pressure and the diameter of the hollow portion 12. In this graph, the horizontal axis represents the internal pressure P [Pa] of the hollow portion 12, and the vertical axis represents the diameter [μm] of the hollow portion 12.

  As shown in FIG. 2, when the pressure P of the hollow portion 12 is 700 Pa or less, the pressure P is smaller than the surface tension of quartz, which is the medium of the PCF base material 13, so that the hollow portion 12 is always crushed. The PCF base material 13 is melted. That is, the hollow portion 12 is not formed under this pressure. The PCF hollow part can be sealed by lowering the internal pressure of the hollow part during melting to 700 Pa or less.

  When the 12 internal pressure P in the hollow portion is maintained at a pressure of 700 <P <1200 Pa, the internal pressure P of the hollow portion 12 becomes larger than the surface tension of quartz, so that the hollow portion is formed.

  When the internal pressure P is 1200 Pa or more, since the internal pressure P of the hollow portion 12 is too larger than the surface tension of quartz, the expansion of the hollow portion becomes intense and the outer diameter of the cladding becomes unstable.

  Utilizing the above characteristics, 700 to 1200 Pa is maintained during PCF drawing. Furthermore, from the characteristics shown in FIG. 2, when the internal pressure P of the hollow portion 12 is 1000 Pa, the hollow portion diameter can be stably manufactured at 10 μm. At the end of drawing, the pressure is reduced to 700 Pa or less, the hollow portion at the end of the PCF 15 is sealed, and drawing is finished.

  Further, not only at the time of drawing, but also during drawing, the sealing part is formed by setting the internal pressure P of the hollow part 12 to 700 Pa or less, and the hollow part 12 is expanded by setting 700 <P <1200 Pa again, The sealing part can be formed again by setting the internal pressure P to 700 Pa or less at an arbitrary position of the PCF 15, and the PCF 15 in which the hollow parts at both ends (tip and end) are sealed can be manufactured. Further, by continuously repeating the formation of the hollow portion and the sealing portion, both ends of one PCF base material 13 are sealed, and the PCF 15 filled with an inert gas and sealed is continuously manufactured in a desired length. can do.

The PCF 15 manufactured by the PCF manufacturing method according to the present embodiment replaces the air in the hollow portion of the PCF 15 with an inert gas such as N ₂ during the manufacturing process, and forms sealing portions at both ends of the PCF. The hollow part between the sealing parts is filled and sealed with an inert gas.

  The hollow portion of the PCF 15 is always stored without being exposed to air from the time of manufacture, and moisture (OH group) contained in the air and foreign matters can be prevented from entering the hollow portion of the PCF 15. Of the transmission loss of the optical fiber, a portion due to the OH group is very large. However, since the OH group in the PCF 15 is reduced, deterioration of optical characteristics such as an increase in the transmission loss of the PCF 15 can be suppressed.

  In addition, since moisture and foreign matter are blocked from the outside air in the hollow portion, it is possible to prevent deterioration of fiber strength such as PCF end face breakage from the hollow portion.

It is the schematic which shows suitable embodiment of this invention. It is a figure which shows the relationship between the internal pressure and diameter of a PCF hollow part. It is the schematic which shows the conventional PCF manufacturing apparatus.

Explanation of symbols

11 PCF manufacturing equipment 12 Hollow part 13 PCF base material 15 PCF
27 Supply / Exhaust Line 28 Internal Pressure Control Device 29 Pressurization Device 30 Vacuum Pump

Claims (6)

  When manufacturing a photonic crystal fiber having a hollow portion in the longitudinal direction in at least one of a core portion and a cladding portion by heating and melting the photonic crystal fiber preform at a drawing temperature and then drawing the photonic crystal fiber preform, A method for producing a photonic crystal fiber, comprising substituting a hollow portion of a material with an inert gas.   When manufacturing a photonic crystal fiber having a hollow portion in the longitudinal direction in at least one of a core portion and a cladding portion by heating and melting the photonic crystal fiber preform at a drawing temperature and then drawing the photonic crystal fiber preform, The inside of the hollow portion of the material is replaced with an inert gas, and the drawn photonic crystal fiber is formed with a sealing portion for closing the hollow portion by controlling the internal pressure of the hollow portion, and the inert gas is formed in the hollow portion. The method for producing a photonic crystal fiber according to claim 1, wherein:   At the end of the production of the photonic crystal fiber, the internal pressure of the hollow portion is reduced by a pressurizing device, a vacuum pump, and a hollow internal pressure control device attached to the photonic crystal fiber base material through an air supply / exhaust line. The method for producing a photonic crystal fiber according to claim 1 or 2, wherein a stop is formed.   4. The photo according to claim 1, wherein during the production of the photonic crystal fiber, the hollow portion is sealed or expanded at an arbitrary position of the photonic crystal fiber by reducing or increasing the internal pressure of the hollow portion. Nick crystal fiber manufacturing method.   The upper end of the photonic crystal fiber preform is connected to an air supply / exhaust line for supplying / discharging inert gas into the hollow portion, and the inert gas flows into the air supply / exhaust line to control the internal pressure of the hollow portion. The manufacturing method of the photonic crystal fiber in any one of Claims 1-4 which connected the pressurization apparatus, the vacuum pump, and the internal pressure control apparatus. In a manufacturing apparatus for manufacturing a photonic crystal fiber having a hollow part in a longitudinal direction in at least one of a core part or a clad part by heating a photonic crystal fiber base material to a drawing temperature, melting and drawing the photonic crystal fiber, A photo in which a supply / exhaust line for supplying and discharging an inert gas in the hollow portion is connected to the upper end of the base material, and a pressurizing device, a vacuum pump, and an internal pressure control device for controlling the internal pressure of the hollow portion are connected to the line Nick crystal fiber manufacturing equipment.

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