JP2006160550A - Photonic crystal fiber, its production method, preform for producing photonic crystal fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method capable of producing stably and in a high yield a photonic crystal fiber having high quality using capillaries that have the shape of a circular tube and are available at a low cost and a support tube. <P>SOLUTION: The production method for a photonic crystal fiber is characterized in that a preform is prepared by arranging a plurality of capillaries together with a solid core rod or a hollow core tube in a cylindrical support tube, and in that the preform is wire-drawn after the gap between capillaries has been closed by fusion splicing capillaries to each other in the preform to obtain a photonic crystal fiber having a structure that has a core surrounded with a plurality of voids. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a photonic crystal fiber having holes in a clad, and in particular, when forming holes using a capillary, the gap between the capillaries is closed in a step separate from spinning (drawing), and then The present invention relates to a manufacturing method capable of spinning photonic crystal fibers while maintaining holes with a simple configuration.

  Since the photonic crystal fiber has holes in the optical fiber, it is possible to realize characteristics that cannot be obtained with a conventional optical fiber having a core / clad structure. For this reason, photonic crystal fibers are expected to be used as various types of functional fibers and future transmission fibers, and are being studied. This photonic crystal fiber can be roughly classified into a refractive index guided fiber and a photonic bandgap fiber based on its guiding principle.

Refractive index guided fiber uses the low refractive index of holes to form an equivalent cladding with holes, and has a wideband single mode characteristic, ultra-low nonlinearity (large effective area) characteristic, super High nonlinear characteristics, polarization maintaining characteristics, ultra-high NA multimode characteristics, and the like can be obtained.
A photonic bandgap fiber is a fiber that confines light inside the fiber by forming a periodic structure in the cladding.

  As an example of the former, there is a hole assist type holey fiber that realizes a low bending loss. In this fiber, holes are placed around the conventional high-refractive-index core to form an equivalently large refractive index difference and realize low bending loss without extremely reducing the mode field diameter (MFD). is doing. As such a fiber, for example, as shown in FIG. 1, a hole assist type holey comprising a core 2 and a clad 3 on the outer periphery thereof, and a plurality of holes 4A, 4B having different diameters are provided around the core 2. A fiber 1 has been reported (for example, see Non-Patent Document 1).

As another example of the refractive index guided fiber, there is a double clad fiber 5 as shown in FIG. 2 (see, for example, Non-Patent Document 2). The double clad fiber 5 includes a first clad 6 having a D-shaped cross-section in which a core (not shown) is disposed in the center, an air hole layer 7 provided surrounding the first clad 6, and the air hole layer. 7 and a second clad 8 provided on the outer periphery of 7.
The double clad fiber 5 needs to have a high NA (Numerical Aperture) in order to reduce the area of the first clad 6 to increase the pumping light density and increase the incident efficiency of the pumping light. A structure having a large NA is provided by arranging holes around the first clad 6, and development for the purpose of increasing the output of optical amplifiers and fiber lasers is being promoted.

Further, the photonic band gap fiber may have a structure in which the core is an air hole and the light is confined depending on the size and period of the air hole in the clad portion.
Furthermore, there are many photonic crystal fibers having structures and characteristics not exemplified here, and the hole position, hole size, and hole position are determined according to the characteristics. In the case of hole-assisted holey fibers with relatively few holes, in addition to the method of bundling capillaries and drawing, it is possible to make holes by making holes in the base material, but when the structure has a large number of holes, A method of manufacturing a fiber by bundling capillaries and spinning is common.
Patent Documents 1 to 4 disclose a method for manufacturing a photonic crystal fiber by bundling capillaries in this way.
Kanning, et al. “Hall Assisted Holey Fiber for Low Bending Loss”, IEICE Technical Report, OFT 2004-7 (2004) Kazunori Fuchiguchi, et al. “Air-hole type Yb-doped double clad fiber”, 2003 IEICE General Conference, C-3-88 JP 2002-55242 A JP 2002-97034 A JP 2002-211941 A JP 2004-238246 A

  However, the conventional photonic crystal fiber manufacturing methods described in Patent Documents 1 to 4 have the following problems.

In Patent Document 1, a cylindrical support tube is filled with a large number of capillaries in parallel with the center axis of the support tube, and a core member serving as a solid core is disposed on the center axis of the support tube. In the photonic crystal fiber manufacturing method in which a preform is manufactured and the preform is thinned by drawing, the cross-sectional shape of the outer periphery of the capillary 9 is a hexagonal shape as shown in FIG. A method is disclosed which forms the capillary layer 10 without gaps by fusing.
However, producing such a capillary 9 having a hexagonal cross-sectional shape on the outer periphery requires a further work as compared with a normal circular tube (circular cross-sectional shape on the outer periphery). Finally, there is a problem that the preform manufacturing cost increases.

Patent Document 2 includes a core that extends in the longitudinal direction in the center of the fiber and is formed solid or hollow, and a porous portion that is provided so as to surround the core and has a large number of pores extending along the core. In the photonic crystal fiber manufacturing method provided, a cylindrical support tube is filled with a number of capillaries parallel to the central axis of the support tube, and a core rod that is a solid core is disposed on the central axis of the support tube. A method of manufacturing a preform and reducing the diameter of the preform by drawing is disclosed. Specifically, as shown in FIG. 4, a support tube 12 having a hexagonal cross section on the inner wall is used, and the support tube 12 is filled with a core rod 13 and a number of capillaries 14. A preform 11 is illustrated. By combining this method with the method described in Patent Document 1, a preform without a gap between capillaries can be produced.
However, in the conventional technique described in Patent Document 2, as in the method of Patent Document 1, it is possible to produce a support tube having a hexagonal cross section on the inner wall by using a normal circular tube ( Compared with the production of a support tube having a circular inner wall cross-sectional shape), there is a problem that the manufacturing cost is finally increased because further processing work is required.

In Patent Document 3, in order to suppress the formation of hydroxyl groups (OH groups) at the time of drawing, a preform 17 in which both ends of each capillary 15 are sealed as shown in FIG. A method of manufacturing a photonic crystal fiber is disclosed. In FIG. 5, reference numeral 15 is a capillary, 15a is a capillary sealing part, 16 is a support pipe, 16a is a support pipe sealing part, 17 is a preform, 17a is an auxiliary pipe, and 18 is a drawing furnace.
The presence of the hydroxyl group absorbs light having a wavelength of 1.38 μm, and is therefore undesirable because it causes deterioration in transmission loss as an optical fiber. Although the method described in Patent Document 3 seems to be effective in suppressing the formation of hydroxyl groups during the drawing process, the present inventors have examined that the pore diameter changes in the longitudinal direction in the drawing process, and is stable. There is a possibility that the photonic crystal fiber having the structure described above cannot be manufactured. This is probably because the pressure inside the capillary 15 sealed at both ends gradually changes as the drawing progresses. Moreover, in the drawing process after sealing both ends, since the pressure at the time of sealing is maintained, there is a problem that the hole diameter cannot be adjusted during the drawing process and the yield is deteriorated.
Furthermore, a phenomenon that a part of the capillary 15 is deformed in the drawing process also occurred. This is presumably because when the both ends of the capillaries 15 are sealed, there is a slight difference in internal pressure between the capillaries 15 and, as a result, the hole size varies in the drawing process. To prevent this, it is necessary to accurately control the internal pressure at the time of sealing, and there is a problem in stably producing photonic crystal fibers.

In Patent Document 4, a support tube is filled with a core rod as a solid core and a plurality of capillaries as a clad part, or a plurality of capillaries that form a core formation space as a hollow core and serve as a clad part. A method of manufacturing a photonic crystal fiber is disclosed that includes a preform manufacturing process for manufacturing a preform and a drawing process for heating and stretching the preform to draw it into a fiber shape. In Patent Document 4, as a drawing process, as shown in FIG. 6, a preform in which a capillary 19 is arranged on a support tube 20 with its rear end protruding is provided as a capillary external pressure control chamber 21 and a capillary internal pressure control. The target photonic crystal fiber is attached to a drawing apparatus provided with a chamber 22 for controlling the external pressure of the plurality of capillaries 19 and / or the internal pressure of the plurality of capillaries in the support tube 20 during the drawing process. It has gained.
However, such pressure adjustment has a problem in that the preform processing of the portion connected to the pressure control unit is complicated, and the pressure control system is also complicated, so that the production cost of the fiber is increased.

There is also a structural problem with photonic crystal fibers. FIG. 7 is a cross-sectional view showing a preform 23 for producing a double clad fiber having a first clad 25 having a circular cross section as another example of the double clad fiber mentioned in Non-Patent Document 2. In this preform 23, a core rod having a core / cladding structure including a core 24 and a first cladding 25 surrounding the core 24 is accommodated in a quartz tube 27 serving as a second cladding, and a capillary 26 is interposed between the core rod and the quartz tube 27. It is constituted by filling.
When manufacturing such a preform 23, in order to keep the NA of the first cladding 25 high, it is necessary to expand the hole diameter in the capillary 26 and to crush the gap between the capillaries 26. Therefore, in the spinning process, it is necessary to adjust the pressure in the capillary 26 to be high and the pressure in the gap between the capillaries 26 to be low. When such a preform 23 is manufactured, it is difficult to process the conventional capillary outer peripheral shape and the support tube inner wall shape, and even if manufactured, the photonic crystal fiber becomes very expensive.
Moreover, if each pressure is controlled at once in the spinning process, a very complicated control system is obtained.

  Similarly, the same applies to the case where a preform 28 having a core tube 29 and a large number of capillaries 30 filled in a support tube 31 having a hexagonal hole in the cross section of the inner wall as shown in FIG. As described in Patent Document 4, the capillary 30 can be improved by making it longer. However, the capillary 30 is very thin, so that it is easy to break when an excessive force is applied, and it is difficult to process stably. there were.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of stably producing a high-quality photonic crystal fiber with a high yield by using a circular capillary and a support tube that are available at low cost. .

  In order to achieve the above object, the present invention prepares a preform by arranging a solid core rod or a hollow core tube together with a plurality of capillaries in a cylindrical support tube, and connects the capillaries in the preform together. A photonic crystal having a structure in which a core is surrounded by a plurality of pores by fusing and sealing gaps between capillaries and drawing the preform. A method of manufacturing a fiber is provided.

  In the method for producing a photonic crystal fiber of the present invention, the solid core rod preferably has a core / cladding structure.

  In the method for producing a photonic crystal fiber of the present invention, it is preferable that the cross-sectional shape of the outer periphery of the capillary is substantially a perfect circle.

  In the method for producing a photonic crystal fiber of the present invention, it is preferable that the cross-sectional shape of the inner wall of the support tube is substantially a perfect circle.

  In the method for producing a photonic crystal fiber according to the present invention, a solid core rod is disposed together with a plurality of capillaries in a cylindrical support tube, and a preform is sealed using a capillary sealed at one end. It is preferable to make a reform and then seal both ends of the capillary under an appropriate pressure, and then fuse the capillaries together to close the gap between the capillaries.

  In the photonic crystal fiber manufacturing method of the present invention, when a preform is produced by arranging a solid core rod together with a plurality of capillaries in a cylindrical support tube and integrated, the gap between the capillaries is closed. Thereafter, it is preferable to perform drawing while applying a uniform pressure to the preform in the drawing step.

  The present invention also provides a photonic crystal fiber manufactured by the above-described manufacturing method according to the present invention.

  The present invention also provides a preform for producing a photonic crystal fiber in which a solid core rod or a hollow core tube and a plurality of capillaries surrounding it are filled in a cylindrical support tube, and adjacent capillaries are formed. Provided is a preform for producing a photonic crystal fiber characterized by being welded.

  In the photonic crystal fiber manufacturing preform of the present invention, the solid core rod preferably has a core / cladding structure.

  In the preform for manufacturing a photonic crystal fiber of the present invention, it is preferable that the cross-sectional shape of the outer periphery of the capillary before welding is a substantially perfect circle.

  In the preform for producing the photonic crystal fiber of the present invention, it is preferable that the cross-sectional shape of the inner wall of the support tube is substantially a perfect circle.

  In the preform for producing a photonic crystal fiber of the present invention, it is preferable that one end of the capillary is sealed.

In the production method of the present invention, a preform is prepared by arranging a solid core rod or a hollow core tube together with a plurality of capillaries in a cylindrical support tube, and the capillaries in the preform are fused together. After closing the gap between capillaries, the fiber is formed by drawing, so the gap between capillaries can be easily and stably closed. During drawing, one pressure is applied to holes of uniform diameter. Since it is sufficient to control, a photonic crystal fiber having the hole size and hole position as designed easily can be obtained.
Also, by using a solid core rod having a core / cladding structure, a rare earth element such as Er or Yb is added to the core to obtain a fiber for an optical amplifier or a fiber laser capable of high-power laser oscillation. be able to. Furthermore, conversion efficiency can be improved by co-adding Al, P, etc. with a rare earth element to this core. Furthermore, a fiber grating or the like can be manufactured by adding Ge to the core.
In addition, since a capillary having a substantially circular cross-sectional shape can be used, no special processing is required and it is easy to manufacture and obtain. Therefore, a photonic crystal fiber can be manufactured at low cost.
In addition, since a support tube having a substantially circular cross-sectional shape on the inner wall can be used, no special processing is required and it is easy to manufacture and obtain. Therefore, a photonic crystal fiber can be manufactured at low cost.
Further, when the preform is manufactured and integrated, the gap between the capillaries is closed, and then, in the drawing process, drawing can be performed while applying uniform pressure to the preform cross section. The photonic crystal fiber can be manufactured easily without leaving holes in unnecessary portions.
In addition, the gap between the capillaries can be closed during integration, and then drawing can be performed while applying uniform pressure to the preform cross section in the drawing process, so the hole size and position as designed are maintained. However, it is possible to manufacture a long photonic crystal fiber with a high yield.

  The method for producing a photonic crystal fiber (hereinafter, referred to as a fiber) of the present invention comprises forming a preform by arranging a solid core rod or a hollow core tube together with a plurality of capillaries in a cylindrical support tube. The capillaries in the preform are fused together to close the gap between the capillaries, and then the preform is drawn to obtain a fiber having a structure in which the core is surrounded by a plurality of holes. It is a feature.

  In the production method of the present invention, the structure and material of the fiber to be produced, the core diameter, the relative refractive index difference of the core, the clad diameter, the number and diameter of the holes, and the arrangement structure of the holes are not limited. It can be applied to the manufacture of

  In the production method of the present invention, the support tube, capillary and core rod (or core tube) used for producing the preform are preferably made of quartz glass. The solid core rod can be a silica glass small-diameter core rod that consists of only the portion that will become the fiber core after drawing, or a quartz core with a high refractive index and a quartz with a lower refractive index than the core surrounding it. A core rod having a core / cladding structure made of a first clad made of glass can be mentioned.

  In the production method of the present invention, a rare earth element such as Er or Yb can be added to the solid core rod. In particular, by adding the rare earth element to the core of a core rod having a core / cladding structure, a double clad fiber having high output amplification characteristics can be obtained. Furthermore, Al, P, etc. can be co-added to the core together with the rare earth element, and conversion efficiency can be improved by co-adding Al, P, etc. It is also possible to produce a fiber grating by adding Ge to the core.

  In the production method of the present invention, the capillary used for producing the preform is preferably a capillary having a substantially circular outer cross section, that is, a circular capillary. Capillaries with a substantially circular outer cross-sectional shape can be easily manufactured by drawing a cylindrical base material made of quartz glass, and extra post-processing such as forming the outer cross-sectional shape into a polygon is required. It is not necessary and can be obtained at low cost.

  In the manufacturing method of the present invention, the support tube used for producing the preform is preferably a support tube having an inner wall having a substantially circular cross section, that is, a circular support tube. This type of support tube can be easily manufactured and can be obtained at low cost without the need for extra post-processing such as grinding the cross-sectional shape of the inner wall into a polygon.

  In the manufacturing method of the present invention, first, the above-described support tube, capillary, and core rod are prepared, and the core rod and a plurality of capillaries are filled in the support tube so that the core rod is at the center, thereby producing a preform. In a preferred embodiment of the present invention, a preform is produced using a capillary with one end sealed at the time of producing the preform.

  FIG. 9 is a configuration diagram illustrating a preform manufacturing process in the manufacturing method of the present invention. In this figure, reference numeral 32 denotes a quartz tube serving as a second cladding, and 33 denotes a high refractive index core and a first surrounding it. A core rod having a core / cladding structure composed of a clad, 34 is a capillary sealed at one end, 35 is a connector attached to one end of a quartz tube 32, 36 is a quartz dummy rod, and 37 is a burner. In this example, the quartz tube 32 has a circular tube shape, the core rod 33 has a cylindrical shape, and the capillary 34 has a circular tube shape. In this preform, a large number of capillaries 34 are arranged around the core rod 33 with the sealing side facing the connector 35, inserted into the quartz tube 32, and a quartz dummy rod is inserted from the open end of the quartz tube 32. 36 is inserted. Next, the quartz dummy rod 36 is fused to one end of the quartz tube 32 by heating with a burner 37. Next, while controlling the internal pressure of the capillary 34 to an appropriate pressure, the capillary 34 is heated by a burner 37 to seal the open end of the capillary 34, and both ends of the capillary 34 are sealed.

Next, the capillaries 34 in the preform are fused together to close the gap between the capillaries 34 and integrate.
FIG. 10 is a configuration diagram illustrating the preform integration step. In this figure, reference numerals 32 to 35 are the same constituent elements as reference numerals 32 to 35 in FIG. 9, and reference numeral 38 is a pressure adjusting system, 39. Is a heater. In this integration process, a pressure adjustment system 38 is connected to the quartz tube 32 via a connector 35 so that the pressure in the tube can be adjusted, the local part of the preform is heated by the heater 39, and an arrow in the figure is shown if necessary. The preform is stretched in the direction, and the capillaries 34 in the preform are fused together under a predetermined pressure. Further, while moving the relative position of the heater 39 and the preform along the longitudinal direction of the preform, it is heated and stretched over the entire length of the preform, and the capillaries 34 in the preform are fused together under a predetermined pressure so that the space between the capillaries 34 is increased. The gap is closed and the core rod 33, capillary 34 and quartz tube 32 are fused and integrated.

  Next, the integrated preform is drawn to produce a fiber. In this drawing process, it is preferable to perform drawing while applying a uniform pressure to the preform.

In this manufacturing method, a solid core rod 33 and a plurality of capillaries 34 are arranged in a quartz tube 32 serving as a support tube to produce a preform, and the capillaries 34 in the preform are fused together to form a capillary. Since the fiber is formed by drawing after closing the gap between the gaps, the gap between the capillaries 34 can be closed easily and stably. At the time of drawing, one pressure is applied to the holes having a uniform diameter. Since it only has to be controlled, it is possible to obtain a fiber having the hole size and hole position as designed easily.
Further, by using a solid core rod 33 having a core / cladding structure, a rare earth element such as Er or Yb is added to the core, so that a fiber for an optical amplifier or a fiber laser capable of high-power laser oscillation can be obtained. Obtainable. Furthermore, conversion efficiency can be improved by co-adding Al, P, etc. with a rare earth element to this core. Furthermore, a fiber grating or the like can be manufactured by adding Ge to the core.
Further, since the capillary 34 having a substantially circular cross-sectional shape and the quartz tube 32 which is a support tube having a substantially circular cross-sectional shape on the inner wall can be used, no special processing is required, and it can be manufactured and obtained. Easy. Therefore, the fiber can be manufactured at a low cost.
Further, when the preform is manufactured and integrated, the gap between the capillaries 34 is closed, and then, in the drawing process, drawing can be performed while applying uniform pressure to the preform cross section. Can be easily closed, and finally a fiber can be produced without leaving holes in unnecessary portions.
Further, when integrating, the gap between the capillaries 34 is closed, and thereafter, in the drawing process, drawing can be performed while applying a uniform pressure to the preform cross section, so the hole size and position as designed can be set. It is possible to manufacture a long fiber with a high yield while maintaining it.

[Example 1]
A quartz tube 32 having an outer diameter of 42 mm and an inner diameter of 33 mm and a core having a relative refractive index difference of 0.35%, in which Er is added at 1300 mass ppm and Al is added at 25000 mass ppm, and an outer cladding having a first cladding surrounding the core. A cylindrical core rod 33 made of quartz glass having a diameter of 31 mm was inserted, and as shown in FIG. 9, a capillary 34 having an outer diameter of 1 mm with one end sealed between them was packed. Thereafter, the quartz dummy rod 36 was inserted from the side opposite to the connector 35, and the quartz tube 32 and the quartz dummy rod 36 were welded by the burner 37 while rotating. At this time, contamination was performed inside the quartz tube 32 by performing the operation while flowing an inert gas inside the quartz tube 32. Moreover, by heating, the inside of the capillary 34 could be dried, and bursting during the spinning process could be prevented.

Thereafter, the internal pressure (differential pressure from the atmospheric pressure) inside the quartz tube 32 was set to −2200 mmH ₂ O, and the capillary 34 was sealed while being welded to the outer periphery of the first clad of the core rod 33. The reason why the pressure is reduced at this time is that the temperature at the time of integration is different from the temperature at the time of integration, and the temperature at the time of integration is high.

Furthermore, the internal pressure (differential pressure with respect to the atmospheric pressure) inside the preform was set to −8000 mmH ₂ O, and integration was performed while crushing the gaps of the capillaries 34 with the integrated apparatus shown in FIG. The state of integration at this time is shown in FIG. A cross section of the preform obtained by this integration is shown in FIG. A preform 40 for producing a double clad fiber shown in FIG. 11 includes a core rod composed of a central core 41 and a first clad 42 surrounding the core 41, and a large number of capillaries 43 fused to the outer periphery of the first clad 42 without any gaps. And a second cladding 44 in which a quartz tube 32 surrounding them is fused and integrated.

The preform 40 was applied to a drawing device, and spinning was performed with the internal pressure (differential pressure from the atmospheric pressure) of the pores set to +450 mmH ₂ O. A cross section of the obtained double clad fiber 45 is shown in FIG. The obtained double clad fiber 45 includes a central core 46, a first clad 47 provided on the outer periphery of the core 46, a number of holes 48 provided around the first clad 47, and an outer periphery of the holes 48. And a second cladding 49 provided on the surface. It can be seen that the double clad fiber 45 has no gaps between the capillaries 34 and the portions of the capillaries 34 are evenly provided with holes 48. The diameter of the first clad 47 of the double clad fiber 45 was 40 μm, and the NA of the first clad 47 was a high value of 0.5. The outer diameter of the second cladding 49 at this time was 125 μm.

[Example 2]
A preform was prepared in the same manner as in Example 1 until the preparation of the preform before spinning.
The preform was applied to a drawing apparatus, and spinning was performed with the internal pressure (differential pressure from the atmospheric pressure) of the pores set to +470 mmH ₂ O. A cross section of the obtained double clad fiber 50 is shown in FIG. The obtained double clad fiber 50 includes a central core 51, a first clad 52 provided on the outer periphery of the core 51, a large number of holes 53 provided around the first clad 52, and an outer periphery of the holes 53. And a second clad 54 provided on the surface. The double clad fiber 50 has no gaps between the capillaries 34, the portions of the capillaries 34 are evenly formed with the holes 53, and the glass portion between the first clad 52 and the second clad 54 is very thin. I understand. The NA of the first cladding of this fiber was as high as 0.7. At this time, the outer diameter of the clad was 125 μm.

[Example 3]
A preform was prepared in the same manner as in Example 1 until the preform was produced before spinning, except that the core rod 33 having a core / cladding structure in which Yb was added at 10,000 ppm by mass and Al was added at 25000 ppm by mass.
The preform was applied to a drawing apparatus, and spinning was performed with the internal pressure (differential pressure from the atmospheric pressure) of the pores set to +470 mmH ₂ O. A cross section of the obtained double clad fiber 50 is shown in FIG. The obtained double-clad fiber 50 has no gap between the capillaries 34, the portions of the capillaries 34 are evenly formed with holes 53, and the glass portion between the first clad 52 and the second clad 54 is also very thin. I understand that. The diameter of the first clad 52 of the double clad fiber 50 was 200 μm, and the NA of the first clad 52 was a high value of 0.7. At this time, the outer diameter of the second cladding 54 was 250 μm.

[Example 4]
A large number of capillaries 34 having an outer diameter of 1.5 mm and an inner diameter of 0.8 mm and a core rod arranged so as to come to the center of the bundle of capillaries 34 are inserted into a circular quartz tube 32 having an outer diameter of 40 mm and an inner diameter of 20 mm. did. The preform was assembled in the same arrangement as in FIG. Thereafter, the quartz dummy rod 36 was inserted from the side opposite to the connector 35, and the quartz tube 32 and the quartz dummy rod 36 were welded by the burner 37 while rotating. At this time, contamination was performed inside the quartz tube 32 by performing the operation while flowing an inert gas inside the quartz tube 32. Moreover, by heating, the inside of the capillary 34 could be dried, and bursting during the spinning process could be prevented. Thereafter, the internal pressure (differential pressure from the atmospheric pressure) inside the quartz tube 32 was set to −8000 mmH ₂ O, and integration was performed while crushing the gaps of the capillaries 34 with a stretching machine.

This preform was applied to a drawing apparatus, and spinning was performed with the internal pressure (differential pressure from the atmospheric pressure) of the pores set to +290 mmH ₂ O. A cross section of the obtained fiber 55 is shown in FIG. The obtained fiber 55 includes a central core 56, a large number of holes 57 surrounding the core 56, and a cladding 58 on the outer periphery thereof. It can be seen that the fiber 55 has no gaps between the capillaries 34 and the portions of the capillaries 34 are evenly holes 57.

It is sectional drawing which illustrates a hole assist type | mold holey fiber. It is sectional drawing which illustrates a double clad fiber. It is sectional drawing of the capillary which shows the 1st example of the conventional fiber manufacturing method. It is sectional drawing of the preform which shows the 2nd example of the conventional fiber manufacturing method. It is a side view of the preform which shows the 3rd example of the conventional fiber manufacturing method. It is a block diagram of the drawing apparatus which shows the 4th example of the conventional fiber manufacturing method. It is sectional drawing which illustrates the preform for double clad fiber manufacture. It is sectional drawing which illustrates another preform for fiber manufacture. It is a block diagram which shows the preform preparation process in the Example of this invention. It is a block diagram which shows the preform integration process in the Example of this invention. It is sectional drawing of the preform for double clad fiber manufacture produced in the Example of this invention. It is sectional drawing which shows an example of the double clad fiber produced in the Example of this invention. It is sectional drawing which shows another example of the double clad fiber produced in the Example of this invention. It is sectional drawing which shows another fiber produced in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hole assist type holey fiber, 2 ... Core, 3 ... Cladding, 4A, 4B ... Hole, 5 ... Double clad fiber, 6 ... First cladding, 7 ... Air hole layer, 8 ... Second cladding, 9, 10 ... Capillary, 11 ... Preform, 12 ... Support tube, 13 ... Core rod, 14 ... Capillary, 15 ... Capillary, 15a ... Capillary sealing part, 16 ... Support pipe, 16a ... Support pipe sealing part, 17 ... Preform, 17a ... auxiliary pipe, 18 ... drawing furnace, 19 ... capillary, 20 ... support pipe, 21 ... chamber for external pressure control of capillary, 22 ... chamber for internal pressure control of capillary, 23 ... preform, 24 ... core, 25 ... first Cladding 26 ... capillary 27 ... second cladding 28 ... preform 29 ... core rod 30 ... capillary 3 ... support tube, 32 ... quartz tube, 33 ... core rod, 34 ... capillary, 35 ... connector, 36 ... quartz dummy rod, 37 ... burner, 38 ... pressure adjusting system, 39 ... heater, 40 ... preform, 41 ... core, 42 ... first clad, 43 ... hole, 44 ... second clad, 45 ... double clad fiber, 46 ... core, 47 ... first clad, 48 ... hole, 49 ... second clad, 50 ... double clad fiber, DESCRIPTION OF SYMBOLS 51 ... Core, 52 ... 1st clad, 53 ... Hole, 54 ... Second clad, 55 ... Fiber, 56 ... Core, 57 ... Hole, 58 ... Cladding

Claims (12)

  After a solid core rod or a hollow core tube is placed in a cylindrical support tube together with a plurality of capillaries to produce a preform, and the capillaries in the preform are welded together to close the gap between the capillaries A method for producing a photonic crystal fiber, wherein the preform is drawn to obtain a photonic crystal fiber having a structure in which a core is surrounded by a plurality of holes.   The method for producing a photonic crystal fiber according to claim 1, wherein the solid core rod has a core / cladding structure.   3. The method for producing a photonic crystal fiber according to claim 1, wherein a cross-sectional shape of the outer periphery of the capillary is substantially a perfect circle.   The method for manufacturing a photonic crystal fiber according to any one of claims 1 to 3, wherein the inner wall of the support tube has a substantially circular cross-sectional shape.   Place a solid core rod with multiple capillaries in a cylindrical support tube and make a preform using a capillary with one end sealed, and then under appropriate pressure The method for producing a photonic crystal fiber according to any one of claims 1 to 4, wherein the capillaries are sealed at both ends, and then the capillaries are welded together to close the gap between the capillaries.   In a cylindrical support tube, a solid core rod is placed together with a plurality of capillaries to make a preform, and when integrating, the gap between the capillaries is closed, and then in the drawing process, the preform is made uniform. 6. The method for producing a photonic crystal fiber according to claim 1, wherein drawing is performed while applying pressure.   The photonic crystal fiber manufactured by the manufacturing method in any one of Claims 1-6.   A preform for manufacturing a photonic crystal fiber in which a solid core rod or hollow core tube and a plurality of capillaries surrounding it are filled in a cylindrical support tube, and adjacent capillaries are welded. A preform for manufacturing photonic crystal fibers.   The preform for producing a photonic crystal fiber according to claim 8, wherein the solid core rod has a core / cladding structure.   The preform for manufacturing a photonic crystal fiber according to claim 8 or 9, wherein a cross-sectional shape of the outer periphery of the capillary before welding is substantially a perfect circle.   The preform for producing a photonic crystal fiber according to any one of claims 8 to 10, wherein the inner wall of the support tube has a substantially circular cross-sectional shape. The preform for producing a photonic crystal fiber according to any one of claims 8 to 11, wherein one end of the capillary is sealed.

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