JP2004339004A - Optical fiber manufacturing method - Google Patents

Abstract

A method of manufacturing an optical fiber having a plurality of holes distributed in a cross section orthogonal to a fiber axis and extending in the fiber axis direction, and the holes have substantially the same diameter. .
A method for manufacturing a optical fiber according to the present invention, to produce an optical fiber 10 having a plurality of holes 13 _1, 13 ₂ extending in the axial direction of the fiber are distributed to the cross section perpendicular to the fiber axis a method to prepare the optical fiber preform 20 having a plurality of holes 23 _1, 23 ₂ to be a plurality of holes, the hollow needle 32 1 to each of the plurality of holes each of the optical fiber _preform, 32 ₂ The optical fiber preform is drawn while inserting and pressurizing the inside of each of the plurality of holes through the hollow needles. In this case, the pressure to be applied to the plurality of holes can be controlled for each of the plurality of holes.
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing an optical fiber having a hole extending in a fiber axial direction.
[0002]
[Prior art]
Optical fibers having holes extending in the fiber axis direction include those called holey fibers and photonic crystal fibers. Hereinafter, an optical fiber having such a hole extending in the fiber axis direction is referred to as a microstructured optical fiber.
[0003]
In such a microstructured optical fiber, the average refractive index difference between the core region and the cladding region can be adjusted by adjusting the size and distribution of holes in a cross section orthogonal to the fiber axis. Therefore, it is possible to obtain characteristics superior to those of an optical fiber having no holes.
[0004]
The microstructured optical fiber is manufactured by drawing an optical fiber preform having holes to be holes in a drawing furnace. When an optical fiber preform having holes is heated and melted for drawing, surface tension acts on the interface of the holes in the tangential direction. When the surface tension acts on the interface of the hole, the component of the surface tension in the radial direction of the hole increases in proportion to the curvature of the hole, and acts to crush the hole. As a result, the smaller the diameter of the hole, the more likely it is to be crushed by the influence of surface tension. As a result, in some cases, holes as designed were not formed in the drawn optical fiber.
[0005]
Therefore, there has been proposed a method of drawing an optical fiber preform while applying pressure to the inside of a hole when drawing the optical fiber preform (for example, see Patent Document 1). In this case, pressure is applied to the inside of the hole, and the inside of the hole is drawn in a state higher than the atmospheric pressure, so that collapse of the hole is suppressed.
[0006]
[Patent Document 1]
JP-A-2002-145634
[Problems to be solved by the invention]
However, when the optical fiber preform in which a plurality of holes form a layer structure in a cross section orthogonal to the longitudinal direction is drawn while applying pressure to the inside of the holes, the inner holes in the layer structure expand and the outer holes expand. In some cases, an optical fiber whose pores are crushed is manufactured.
[0008]
The present invention has been made in order to solve the above problems, and has a plurality of holes distributed in a cross section orthogonal to the fiber axis and extending in the fiber axis direction. It is an object of the present invention to provide a method by which an optical fiber having substantially the same can be manufactured.
[0009]
[Means for Solving the Problems]
The present inventors have repeated studies on the mechanism of collapse and deformation of holes when drawing an optical fiber preform having holes extending in the longitudinal direction. And the following knowledge was obtained.
[0010]
In the region where the optical fiber preform starts to be heated by the heater of the drawing furnace (the area above the heat zone), since the outer diameter of the optical fiber preform is large, the diameter of the hole to be a hole is also large, so that the surface tension The effect is small. Therefore, when the inside of the hole is higher than the atmospheric pressure by pressurizing the hole, the hole expands. Then, when the optical fiber preform is drawn and the outer diameter becomes smaller and the hole diameter becomes smaller, the effect of the expansion of the hole due to the pressure applied to the inside of the hole and the effect of the contraction due to the surface tension are balanced in a certain region. When the hole diameter is further reduced from that region, the effect of the surface tension becomes larger than the expansion of the hole due to the pressure applied in the hole, and the hole contracts.
[0011]
By the way, shrinkage of holes due to the effect of surface tension is more likely to progress as the viscosity of the glass constituting the optical fiber preform decreases. When the holes formed in the optical fiber preform are distributed so as to surround the central axis of the optical fiber preform in a cross section orthogonal to the longitudinal direction, the holes in the outermost layer are formed. Functions as a heat insulating layer. This inhibits heat conduction to the holes in the inner layer, so that the glass viscosity around the inner holes becomes higher than the glass viscosity outside the outermost layer. Accordingly, since the influence of the surface tension is larger in the holes in the outermost layer, the holes in the outermost layer are preferentially crushed.
[0012]
Here, when pressure is applied to all of the plurality of holes to such an extent that the holes in the outermost layer are not crushed, the holes constituting the inner layer are excessively expanded and deformed. Conversely, if pressure is applied to all of the plurality of holes to such an extent that the inner holes are not crushed or deformed, the holes in the outermost layer are crushed. The above is the reason why an optical fiber having holes of almost the same diameter cannot be manufactured even when an optical fiber preform having a plurality of holes is drawn while applying pressure to the inside of the holes. The present inventors have conducted further intensive studies based on the above-mentioned findings, and have reached the present invention.
[0013]
That is, the method for manufacturing an optical fiber according to the present invention is a method for manufacturing an optical fiber having a plurality of holes distributed in a cross section orthogonal to the fiber axis and extending in the fiber axis direction, Prepare an optical fiber preform having a plurality of holes to be vacated, insert a hollow needle into each of the plurality of holes of the optical fiber preform, and pressurize the inside of each of the plurality of holes through the hollow needles. While drawing, the optical fiber preform is drawn. In this case, the pressure to be applied to each of the plurality of holes can be controlled through the needle inserted for each hole.
[0014]
Further, in the optical fiber manufacturing method according to the present invention, the outer diameter of each hollow needle inserted into each of the plurality of holes may be gradually reduced toward the end on the side inserted into the plurality of holes. It is suitable. In this case, it is easy to insert the hollow needle into a plurality of holes. Further, the needle can be inserted even if the hole diameter slightly changes.
[0015]
Furthermore, in the optical fiber manufacturing method according to the present invention, it is desirable to control the pressure applied to the inside of the plurality of holes for each of the plurality of holes. Thereby, for each hole, the effect of contracting the hole due to the effect of surface tension and the effect of expanding the hole due to the application of pressure to the hole can be balanced.
[0016]
Furthermore, in the method for manufacturing an optical fiber according to the present invention, in a cross section orthogonal to the fiber axis, a plurality of holes are distributed so as to surround the fiber axis to form a layered structure. It is preferable to apply the same pressure to the inside of the hole that is to be the hole constituting the same layer.
[0017]
In this case, even if the holes constituting the outermost layer function as a heat insulating layer at the time of drawing, since the pressure applied to the holes constituting the layers is controlled for each layer, the diameter of the holes is substantially reduced. Can be the same. Further, since the pressure may be controlled for each layer, the production of the optical fiber is facilitated.
[0018]
Further, in the method of manufacturing an optical fiber according to the present invention, it is preferable that a dry gas is supplied into each of the plurality of holes to pressurize the inside of each of the plurality of holes. By supplying a dry gas that does not affect the transmission characteristics, it is possible to prevent moisture from adsorbing into each of the plurality of holes and causing transmission loss.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to the drawings. In the following description, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.
[0020]
FIG. 1 is a perspective view schematically showing a configuration of a microstructured optical fiber 10 in the present embodiment. The microstructured optical fiber 10 includes a core region 11 extending along the fiber axis, and a cladding region 12 surrounding the outer periphery of the core region 11. The core region 11 and the cladding region 12 have the same composition.
[0021]
As shown in FIG. 1, in the cladding region 12, a plurality of holes 13 ₁ (for example, six holes) are formed in a hexagonal shape in a cross section orthogonal to the fiber axis around a core region 11 extending in the fiber axis direction. Are distributed. Further, a plurality of holes 13 2 _(e.g., 12 holes) are distributed in a hexagonal shape in a cross section perpendicular to the fiber axis so as to surround the layer composed of a plurality of holes 13 _1. In other words, the plurality of holes 13 ₁ and 13 ₂ are distributed so as to surround the fiber axis, forming a two-layer structure.
[0022]
In the microstructured optical fiber 10 having the above-described configuration, the cladding region 12 has the holes 13 ₁ and 13 ₂ , so that the average refractive index of the cladding region 12 is smaller than that of the core region 11.
[0023]
Next, a method of manufacturing the microstructured optical fiber 10 will be described. First, an optical fiber preform 20 to be the microstructured optical fiber 10 is prepared. FIG. 2 is a cross-sectional view when the optical fiber preform 20 is cut along a plane perpendicular to the longitudinal direction. As shown in FIG. 2, the optical fiber preform 20 includes a first region 21 to be the core region 11 and a second region 22 to be the clad region 12. The first region 21 and the second region 22 have the same composition. Further, each of the holes ₁₃ 1, 13 ₂ and the through hole ₂₃ should be 1, 23 ₂ are formed in the second region 22. Through-holes 23 _1, 23 ₂ are arranged in a hexagonal shape in a cross section perpendicular to the longitudinal direction of the optical fiber preform 20 to form a two-layer structure.
[0024]
First, the optical fiber preform 20 is obtained by forming a first region 21 and a second region 22 using a VAD method, an MCVD method, an OVD method, or the like, and then dehydrating and sintering the resulting material into a transparent glass preform. is manufactured by forming a through-hole ₂₃ 1, 23 ₂ in the second region 22. Through-holes ₂₃ 1, 23 ₂ may be formed by, for example, drilling instruments. The optical fiber preform 20 is drawn by a drawing machine and then moved to a drawing step.
[0025]
The higher the line drawing process, drawing an optical fiber preform 20 while the through holes 23 _1, 23 ₂ of the optical fiber preform 20 pressed. Figure 3 is a perspective view schematically showing the configuration of the pressure pipe 30 for pressurizing the through holes 23 _1, 23 ₂ of the optical fiber preform 20. Incidentally, in FIG. 3, the optical fiber preform 20 to indicate the positional relationship between the through holes 23 _1, 23 ₂ and the pressure pipe 30 of the optical fiber preform 20 is also drawn.
[0026]
At the end of the optical fiber preform 20 side opposite to the pressure pipe 30, the gas supply ports 31 1 for filling a nitrogen gas (inert gas) to the pressure pipe _30, 31 ₂ are provided . Inside the pressing pipe 30 has a double structure, and the nitrogen gas flowing from the gas supply port 31 ₁ to the pressure pipe 30, the nitrogen gas flowing from the gas supply port 31 ₂ to the pressure pipe 30, Different internal spaces in the pressure pipe 30 are filled. As the pressurized pipe 30 having a double structure, for example, a second hollow cylinder is disposed inside the first hollow cylinder so that the center axis thereof coincides with the center axis of the first hollow cylinder. It is good. In this case, for example, nitrogen gas flowing from the gas supply port 31 ₁ is filled in the internal space of the second hollow cylinder, the nitrogen gas flowing from the gas supply port 31 _2, and a second hollow cylinder first The inner space between the first hollow cylinder and the first hollow cylinder is filled.
[0027]
In addition, a plurality of hollow needles 32 ₁ (for example, six hollow needles) and a plurality of hollow needles 32 ₂ (for example, 12 hollow needles) are provided at the end of the pressure pipe 30 on the optical fiber preform 20 side. (A hollow needle). Each needle 32 ₁ and each needle 32 ₂ is disposed so as to correspond to the position of each through hole 23 ₁ and the through holes 23 ₂ of the optical fiber preform 20 in a cross section perpendicular to the longitudinal direction of the pressure pipe 30 I have. Needle 32 ₁ supplies the nitrogen gas flowing from the gas supply port 31 ₁ to the pressure pipe 30 into the through-hole 23 ₁ in the optical fiber preform 20. Further, the needle 32 ₂ supplies nitrogen gas flowing from the gas supply port 31 ₂ to the pressure pipe 30 into the through-hole 23 ₂ of the optical fiber preform 20. Figure 4 is a schematic diagram showing a plurality of needles ₃₂ 1, 32 ₂ of the arrangement. The needles 32 ₁ and 32 ₂ are each distributed in a hexagonal shape like the through holes 23 ₁ and 23 ₂ to form a two-layer structure. ₃₂ 1, 32 ₂ of the tip needle is tapered, the outer diameter of the needle ₃₂ 1, 32 ₂ are gradually decreased toward the tip.
[0028]
FIG. 5 is a schematic diagram showing a configuration of a drawing device 40 suitably used for drawing the optical fiber preform 20. FIG. 5 shows a process in which the optical fiber preform 20 is drawn by the drawing device 40.
[0029]
The optical fiber preform 20 is disposed in a drawing furnace 50 with a pressure pipe 30 attached to one end thereof. Although various methods for arranging the optical fiber preform 20 in the drawing furnace 50 are conceivable, for example, the following method may be used. A hollow dummy pipe 60 having substantially the same outer diameter as the optical fiber preform 20 is connected to an upper portion of the optical fiber preform 20, and the dummy pipe 60 is held by a chuck 70 so that the optical fiber preform 20 is drawn. 50 inside. The chuck 70 has a function of moving vertically and sending the optical fiber preform 20 into the drawing furnace 50 in accordance with the drawing.
[0030]
The pressure pipe 30 is attached to the inside of the dummy pipe 60 via a lid 80 for keeping the internal space of the dummy pipe 60 airtight. The lid 80 has a structure in which the insertion amount of the pressure pipe 30 can be changed while keeping the airtightness of the internal space of the dummy pipe 60. When mounting the pressure pipe 30 to the dummy pipe 60, first, the pressure pipe 30, each needle 32 1 of the front end of the pressure pipe _30, 32 ₂ are fixed at a position not in contact with the optical fiber preform 20 . Needle ₃₂ 1 In this state, 32 ₂ and the through hole ₂₃ of the optical fiber preform 20 1, 23 there is a gap between the _two, by evacuating the dummy pipe 60 from the vacuum leading line 90 of the lid 80 inside the through-hole 23 _1, 23 ₂ is also evacuated, it can be removed water adsorbed on the inner surface thereof. Thereby, it is possible to suppress the OH group from remaining near the core of the microstructured optical fiber 10 after drawing, and it is possible to reduce the transmission loss of the microstructured optical fiber 10. Incidentally, at the time of drawing the start to allow evacuation, the lower end of the optical fiber preform 20 is in a state in which the through-holes 23 _1, 23 ₂ is sealed.
[0031]
Subsequently, the needle ₃₂ 1 of the pressure pipe 30, 32 ₂ is inserted into the through holes ₂₃ 1, 23 ₂ of the optical fiber preform 20. As described above, the needle ₃₂ 1, 32 ₂ of the tip since the tapered, can be easily inserted into the through holes ₂₃ 1, 23 ₂ corresponding to each needle ₃₂ 1, 32 _2. The through-holes ₂₃ 1, 23 ₂ of the diameter can be inserted somewhat also be varied each needle ₃₂ 1, 32 ₂ from the design value in the corresponding through-holes ₂₃ 1, 23 _2. Furthermore, it is possible to maintain the airtightness between the through-holes ₂₃ 1, 23 ₂ by pushing the respective needle ₃₂ 1, 32 _2.
[0032]
Then, supplies dry nitrogen from people gas supply port 31 _1, 31 ₂ respectively provided in the pressure pipe 30. Nitrogen gas flowing from the gas supply port 32 ₁ to the pressure pipe 30, through the needle 31 ₁ is supplied to the through-hole 23 ₁ of the optical fiber preform 20. Further, the nitrogen gas flowing from the gas supply port 32 ₂ to the pressure pipe 30, through the needle 31 ₂ is supplied to the through-hole 23 ₂ of the optical fiber preform 20. As described above, the pressure pipe 30 has a double structure, a nitrogen gas inlet gas supply ports 31 _1, 31 ₂ respectively from the pressure pipe 30 satisfy the different internal space in the pressure pipe 30 I have. Therefore, by adjusting the pressure of the nitrogen gas supplied from the s gas supply port 31 _1, 31 ₂ respectively, it is possible to control the pressure to be applied people in the through holes 23 ₁ and the through-hole 23 ₂ respectively. Incidentally, when introducing dry nitrogen gas to the gas supply port 31 _1, 31 _2, it is preferred that by way of the water trap device is introduced into the gas supply port 31 _1, 31 _2. Accordingly, the nitrogen gas supply source water that is slightly remaining on the dried nitrogen gas supplied from a (not shown) can be removed before the gas supply ports 31 _1, 31 _2. Therefore, the OH groups remaining in the microstructured optical fiber 10 can be further reduced.
[0033]
While the through holes 23 1 as described _above, 23 ₂ into the through hole 23 1 applies _pressure, 23 _second internal to a state higher than the atmospheric pressure, heating and drawing the end of the optical fiber preform 20 by the heater 51 Thus, the microstructured optical fiber 10 is obtained. The pressure applied to the through-hole ₂₃ 1, 23 _2, holes ₁₃ 1 of the microstructured optical fiber 10 should be drawing tension and manufacturing, 13 ₂ depends on the desired diameter, 0.1KPa～5.0KPa It is preferred that FIG. 6 is a chart showing an example of a relationship between a desired diameter of the hole of the microstructured optical fiber 10 and a suitable pressure applied to the through hole of the optical fiber preform 20. The pressure to be applied to the through-holes ₂₃ 1, 23 ₂ are optimized pressure to the holes ₁₃ 1, 13 ₂ becomes a desired diameter. Further, on the outside of the through hole 23 _2, applying a large pressure slightly than the pressure applied to the inside of the through-hole 23 _1.
[0034]
FIG. 7 is an electron micrograph of a cross section perpendicular to the fiber axis of a microstructured optical fiber when the same pressure is applied to all of the plurality of holes and drawn, as in the related art. When the same pressure is applied to all the through holes formed in the optical fiber preform, the pores of the outermost layer are deformed, and the pores constituting the inner layer from the outermost layer are expanded. I have.
[0035]
On the other hand, FIG. 8 is an electron micrograph of a cross section orthogonal to the fiber axis of the microstructured optical fiber 10 when the optical fiber preform 20 is drawn by the drawing device 40. In the production of micro-structured optical fiber 10 in FIG. 8, the through hole 23 ₁ of the optical fiber preform 20, a pressure of about 0.8kPa added through needle 32 ₁ of the pressure pipe 30, the through hole 23 ₂ It was added a pressure of about 0.85kPa through the needle 32 _{and second} pressure pipe 30. From Figure 8, it can be seen that the size of the holes 23 and _second diameter holes 23 ₁ of the diameter and the inner outer layers are substantially aligned. This is for the following reason.
[0036]
Referring to FIG. 5, the heater 51 in the glass melting region alpha where the optical fiber preform 20 is heated and melted, drawing start portion whose area alpha ₁ in the through-hole 23 1 of the optical fiber preform _20, 23 ₂ Since the diameter is large, the influence of surface tension is small. Therefore, If left higher than the atmospheric pressure by applying pressure to the through holes ₂₃ 1, 23 _2, through holes ₂₃ 1, 23 ₂ expands. Then, in the area alpha ₂ diameter of the drawn in through-holes 23 _1, 23 ₂ is reduced, the influence of surface tension increases. Therefore, the effect of expanding the through hole ₂₃ 1, 23 ₂ are under the influence of the pressure of the through holes ₂₃ 1, 23 _2, the effect of the through-hole ₂₃ 1 in the influence of surface tension, 23 ₂ contracts are balanced. Further delineated, the region alpha ₃ further outer diameter than the outer diameter in the region alpha ₂ decreases, it increases the effect of surface tension, the through holes 23 _1, 23 ₂ is contracted. The through-holes ₂₃ 1, 23 through-hole ₂₃ 1 by balancing the expansion and contraction occurring in _2, 23 ₂ of the deformation is suppressed.
[0037]
Meanwhile, as shown in FIG. 2, when the through-holes 23 _1, 23 ₂ form a distributed layer structure so as to surround the center axis of the optical fiber preform 20, the through holes constituting the outer layer 23 ₂ becomes the heat insulating layer, inhibiting the heat conduction to the inside. Therefore, towards the outside of the glass viscosity than constructed layer in the through-hole 23 ₂ is lower than the glass viscosity of the inner side than the layer. Thus, the effect of surface tension, towards the through-hole 23 ₂ is larger than the through-hole 23 _1. Microstructured optical fiber 10 shown in FIG. 8, the through-holes ₂₃ 1, 23 ₂ respectively in the hollow needle ₃₂ 1, 32 ₂ respectively under a pressure higher than the through hole 23 ₁ inserted to the through hole 23 ₂ drawing are doing. Thus, in people through hole ₂₃ 1, 23 ₂ respectively, they are able to balance the shrinkage of the through holes ₂₃ 1, 23 ₂ due to the influence of expansion and surface tension of the through-holes ₂₃ 1, 23 ₂ by pressure. Therefore, as shown in FIG. 8, which can be substantially the same diameter of the holes 13 ₂ and the holes 13 ₁ of the inside of the outer.
[0038]
In the method of manufacturing a microstructured optical fiber 10 described above, since the inserts' s hollow needle 32 _1, 32 ₂ respectively in the through holes 23 _1, 23 ₂ respectively, configure them for each inner layer and outer layer pressure applied to it is through-hole ₂₃ 1, 23 ₂ and can be adjusted. Therefore, in people through hole 23 _1, 23 ₂ respectively, it is possible to balance the expansion due to shrinkage and the pressure due to the influence of surface tension. Thus, a micro-structured optical fiber 10 having a plurality of holes 13 _1, 13 ₂ form a distributed layer structure so as to surround the fiber axis, a plurality of holes 13 _1, 13 ₂ of diameter about the same Can be manufactured. The transmission characteristics of the microstructured optical fiber 10 depend on the geometric shapes and distribution of the holes 13 ₁ and 13 ₂ in a cross section orthogonal to the fiber axis. For this reason, by making the diameters of the holes 13 ₁ and 13 ₂ of the microstructured optical fiber 10 substantially the same, the transmission characteristics of the microstructured optical fiber 10 can be more designed than in the case where the diameters of the plurality of holes are different from each other. Can be close.
[0039]
As described above, the preferred embodiments of the present invention have been described in detail, but it goes without saying that the present invention is not limited to the above embodiments. For example, in the above embodiment, in the cross section orthogonal to the fiber axis, each of the holes 13 ₁ and 13 ₂ is arranged in a hexagonal shape to form a two-layer structure, but it is not particularly limited to such an arrangement. For example, the holes are not limited to the two-layer structure, and a plurality of holes may be formed in a cross section orthogonal to the fiber axis.
[0040]
In addition, the arrangement of the holes 13 ₁ and 13 _{2 in} a cross section orthogonal to the fiber axis is a characteristic to be realized by the microstructured optical fiber, for example, a wavelength dispersion having a large absolute value, and an optical fiber having no hole. What is necessary is just to set it as the arrangement | positioning required to implement | achieve a large or small effective core area. Then, the pressure to be applied may be controlled for each through hole to be a hole according to the distribution shape.
[0041]
Further, the diameter of the holes 13 ₁ and holes 13 ₂ are also valid for different structures. If the hole diameter is different, the optimum pressure to be applied to the through hole that becomes a hole changes, but as described above, different pressurization can be performed for each through hole that becomes a hole, so that a hole with the designed diameter is realized. it can.
[0042]
Further, an additive (for example, Ge) that increases the refractive index may be added to the core region 11, and an additive that lowers the refractive index may be added. Furthermore, it is not necessary to add an additive. Further, the core region 11 may be hollow. Further, although nitrogen gas and dried as a gas to be supplied to the through-hole 23 _1, 23 ₂ is not limited to the nitrogen gas. Any dry gas that does not affect the transmission characteristics may be used, and oxygen gas, He gas, Ne gas, Ar gas, and the like can also be used. Furthermore, although the hole to be a hole is a through hole, the hole does not necessarily have to penetrate the optical fiber preform.
[0043]
【The invention's effect】
According to the present invention, it is possible to manufacture an optical fiber having a plurality of holes distributed in a cross section orthogonal to the fiber axis and extending in the fiber axis direction, and the diameters of the holes are substantially the same. it can.
[Brief description of the drawings]
FIG. 1 is a perspective view of an optical fiber manufactured by a method for manufacturing a microstructured optical fiber according to an embodiment.
FIG. 2 is a cross-sectional view when the optical fiber preform is cut along a plane orthogonal to the longitudinal direction.
FIG. 3 is a schematic configuration diagram of a pressure pipe.
FIG. 4 is a schematic diagram showing an arrangement of needles.
FIG. 5 is a schematic configuration diagram of a drawing apparatus.
FIG. 6 is a chart showing an example of a relationship between a desired diameter of a hole and a suitable pressure applied to a through hole.
FIG. 7 is an electron micrograph of a microstructured optical fiber manufactured by drawing an optical fiber preform by applying the same pressure to a plurality of holes.
FIG. 8 is an electron micrograph of a cross section orthogonal to the fiber axis of the microstructured optical fiber.
[Explanation of symbols]
10 ... micro-structured optical fiber, 11 ... core region, 12 ... cladding region, ₁₃ 1, 13 2 _... pore, 20 ... optical fiber preform, 21 ... first region, 22 ... second _region, 23 1, 23 ₂ ... Through holes, 30 ... Pressurized pipes, 31 ₁ , 31 ₂ ... Gas supply ports, 32 ₁ , 32 ₂ ... Hollow needles, 40 ... Drawing apparatus, 50 ... Drawing furnace, 51 ... Heater, α: Glass melting Area: 60: dummy pipe, 70: chuck, 80: lid, 90: vacuum evacuation line, α ₁ : area where the hole expands, α ₂ : area where expansion and contraction of the hole balance, α ₃ : hole shrinks region

Claims (5)

A method for manufacturing an optical fiber having a plurality of holes distributed in a cross section orthogonal to a fiber axis and extending in the fiber axis direction,
Prepare an optical fiber preform having a plurality of holes to be the plurality of holes,
Inserting a hollow needle into each of the plurality of holes of the optical fiber preform and drawing the optical fiber preform while pressurizing the inside of each of the plurality of holes through the hollow needles. Optical fiber manufacturing method. 2. The optical fiber according to claim 1, wherein an outer diameter of each of the hollow needles inserted into each of the plurality of holes gradually decreases toward an end on a side to be inserted into each of the plurality of holes. Method. 3. The method according to claim 1, wherein the pressure applied to the inside of the plurality of holes is controlled for each of the plurality of holes. In a cross section orthogonal to the fiber axis, the plurality of holes are distributed so as to surround the fiber axis to form a layer structure,
4. The method of manufacturing an optical fiber according to claim 3, wherein the same pressure is applied to the inside of the plurality of holes that are to be holes forming the same layer. 5. The optical fiber according to claim 1, wherein a dry gas is supplied into each of the plurality of holes to pressurize the inside of each of the plurality of holes. 6. Method.

Images