JP2002333539A - Polarized wave storage fiber and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarized wave storage fiber which can be easily manufactured and has desired optical propagation characteristics, and a method for manufacturing the same. SOLUTION: A preform of the polarized wave storage fiber is constituted by arranging a core member 1 being a rod in its center, and by forming and arranging 1st cladding members 23 being capillaries on both sides of the member 1, up to an inner wall of a support pipe 19 in a sectorial shape. The 2nd cladding members 25 being the rods are filled between two sectors formed with the 1st cladding members 23, and two sectors are formed with the 2nd cladding members. The cladding is divided into four by the boundaries extended in the radial direction from the core after drawing processing of the preform. Since the effective refractive index of the cladding part originated in the 1st cladding members 23 becomes lower than that originated in the 2nd cladding members 25, the birefringence is produced, and the polarized wave storage fiber is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization maintaining fiber that generates birefringence by appropriately arranging pores in a clad and a method of manufacturing the same.

[0002]

2. Description of the Related Art A polarization preserving fiber having high polarization stability is used for optical fiber sensors and coherent optical fiber communication utilizing polarization and interference. A polarization maintaining fiber is an optical fiber utilizing birefringence. Methods for generating birefringence in an optical fiber include (1) materials in a vertical direction and a horizontal direction in a cross section perpendicular to the axial direction of the optical fiber. And (2) a method of imparting birefringence equivalently by applying different stresses to the core from the longitudinal direction and the lateral direction in the cross section. That is, when the refractive index distribution (including the equivalent refractive index distribution) is rotated by 90 degrees around the center axis of the optical fiber, it does not overlap with the refractive index distribution before rotation (hereinafter, this is referred to as non-axial symmetry). (When rotated 90 degrees).

The conventional polarization preserving fiber will be described with reference to the above two methods. According to the method (1), portions of a material having a lower refractive index than the cladding 3 are provided on both sides of the core 2 called side pit fibers. An optical fiber having 5 (hereinafter, referred to as pits) and an optical fiber called a side tunnel fiber in which the above-mentioned pits are hollow tunnels 5 (the refractive index of quartz is 1.46 and the air is 1) are known. (FIGS. 1, 2). Further, there is also known a side tunnel fiber in which a core shape in a cross section is circular and a tunnel such as a circle is provided in cladding portions on both sides of the core.

In the case of the method (2), FIG.
4, an optical fiber in which a glass (stress applying material 7) having a thermal expansion coefficient larger than quartz (stress imparting material 7) is arranged in a portion of the clad 3 around the core 2. These are optical fibers that generate a large stress in the core during the process of cooling the optical fiber after drawing, and panda fibers (FIG. 3), bow tie fibers (FIG. 4), and the like are known. As the stress applying material, quartz doped with boronia (B ₂ O ₃ ) as a stress applying material is used.

[0005]

The above-mentioned conventional polarization maintaining fiber is manufactured by grinding a preform and inserting a member having a different refractive index and a different coefficient of thermal expansion into the preform as required. Therefore, the number of processes is increased and the cost is increased. Further, it is difficult to produce a complicated shape by grinding, or it becomes impossible to produce the same depending on the shape, and it is not possible to arbitrarily produce a polarization maintaining fiber having desired light propagation characteristics.

[0006] Further, when trying to increase the polarization maintaining capability of a side pit fiber or a side tunnel fiber,
It is necessary to increase the refractive index difference between the core and the clad,
With the conventional technology, the refractive index of the clad can be the same or slightly lower than that of quartz, and it is difficult to increase the refractive index difference between the core and the clad. Fabrication of the fiber was difficult.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a polarization maintaining fiber which can be easily manufactured and has desired light propagation characteristics, and a method of manufacturing the same. It is.

[0008]

In order to achieve the above object, a polarization maintaining fiber having a birefringence caused by appropriately disposing an axially extending pore of an optical fiber in a cladding of the optical fiber. did.

More specifically, the invention according to claim 1 is a polarization maintaining fiber having a cladding provided with a pore extending in the axial direction of the optical fiber, wherein the cladding is formed by four boundaries extending radially from the core. Is divided into four parts, two of the four parts of the cladding are provided with a large number of the pores, and the other two are filled with quartz, and are provided between the two parts having the pores. A polarization-maintaining fiber, characterized in that the portion filled with quartz exists.

According to the structure of the present invention, the effective refractive index of the portion where the pores are present is lower than the refractive index of the portion filled with quartz. Is arranged, as a result, the distribution of the refractive index of the cladding becomes off-axis symmetric (when rotated by 90 degrees), and a polarization maintaining fiber can be easily obtained. Here, the effective refractive index refers to the area fraction occupied by the pores multiplied by the refractive index of air and the area fraction occupied by quartz in the region where the plurality of pores in the optical fiber cross section are arranged. This is the sum of the value obtained by multiplying the value obtained by multiplying the refractive index of quartz and the refractive index shown as the entire region when the region is observed from the outside.

Here, the four boundaries extending in the radial direction from the core may be straight lines in the cross section of the fiber,
It may be a curve or a combination of both. Further, at least one of a straight line and a curve may be bent. Further, the portion filled with quartz may be filled with pure quartz, or another substance such as Ge or F may be doped into quartz.

The method of forming the pores is not particularly limited. It is also possible to form pores at the time of preform, or to fill pores with a substance other than quartz and remove the substance at the time of drawing or after drawing to form pores. I do not care.

Next, a second aspect of the present invention is a polarization maintaining fiber having a cladding having a pore extending in an axial direction of an optical fiber, wherein birefringence is caused in a cross section of the fiber. A polarization maintaining fiber in which the pores are arranged in a cladding portion adjacent to a core.

Here, birefringence is considered when the refractive index distribution differs depending on the directions of the two axes, or when stress is applied when considering two axes orthogonal to each other in the cross section of the optical fiber.
This occurs when the refractive index distribution can be regarded as equivalently different in the two axial directions due to the photoelastic effect.

The fact that the pores are arranged in the clad portion adjacent to the core so as to cause birefringence in the cross section of the optical fiber specifically means that the clad adjacent to the core in the cross section of the optical fiber is In this part, the distribution of the pores themselves, or the distribution of the diameters and shapes of the pores is different depending on the directions of the two orthogonal axes, and as a result, the distribution of the refractive index is non-axially symmetric ( (When rotated 90 degrees).

The region where a plurality of pores are arranged has a lower refractive index than that of the region where only quartz is used, so that the region becomes a pit. Therefore, according to the configuration of the present invention, a polarization maintaining fiber of a side pit type or a stress imparting type can be easily obtained.

Next, a third aspect of the present invention is the polarization maintaining fiber according to the second aspect, wherein the pores are provided in all portions of the cladding in the cross section of the fiber.

According to the structure of the present invention, since the entire cladding has pores, the effective refractive index of the entire cladding can be made much lower than that of quartz, and the polarization maintaining ability can be enhanced. Here, the clad is a portion existing around the core that contributes to the trapping of light propagating through the core into the core and maintaining the polarization of the propagating light. Therefore, the outermost portion of the optical fiber,
A portion that hardly affects the light propagating through the core into the core and maintains the polarization of the propagating light may not be treated as a clad. That is, the optical fiber far away from such a core may not be provided with pores near the outermost periphery.

Next, a fourth aspect of the present invention is a polarization maintaining fiber having a cladding having a pore extending in an axial direction of an optical fiber, wherein the diameter of the fiber is different in two orthogonal directions in a cross section of the fiber. A polarization maintaining fiber comprising a core having a pore extending in the axial direction of the optical fiber having the following.

According to the structure of the present invention, birefringence occurs in the core portion in the cross section of the fiber, and the polarization maintaining fiber is obtained. Here, it is preferable that the major axis directions of the pores of the core are all in the same direction, because the polarization maintaining ability becomes high. In addition, since the cladding is provided with pores, the effective refractive index of the cladding can be made much lower than that of quartz, and the polarization maintaining ability can be enhanced.

Next, the invention according to claim 5 relates to claims 1 to
4. The polarization-maintaining fiber according to any one of 4), further comprising a portion doped with a stress imparting substance on both sides of the core in the cross section of the fiber.

According to the structure of the present invention, the polarization maintaining ability can be enhanced by the presence of the portion doped with the stress imparting substance.

Next, the invention according to claim 6 is directed to claims 1 to 5
Any one of the above, wherein the pores are filled with a substance having a lower refractive index than a substance surrounding the pores.

According to the structure of the present invention, a polarization maintaining fiber can be obtained by selecting various substances having a lower refractive index than quartz surrounding the pores instead of air in the pores. Examples of the substance having a lower refractive index than quartz include a substance in which quartz is doped with fluorine or the like.

Next, a seventh aspect of the present invention is a method for manufacturing a polarization maintaining fiber, comprising forming a preform by bundling a capillary and a rod, and drawing the preform into an optical fiber. Wherein the capillary and the rod are arranged in the preform so as to cause birefringence in a cross section of the polarization maintaining fiber.

According to the structure of the present invention, it is not necessary to form the preform by grinding, and the preform can be formed simply by arranging the capillary and the rod so that the capillary is at an appropriate position. The polarization maintaining fiber having the structure can be easily manufactured, and the process can be simplified, so that the cost can be reduced.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 6 shows a cross-sectional view of a preform of a polarization maintaining fiber according to Embodiment 1. In this embodiment, the cladding is divided into four parts by four boundaries extending in the radial direction from the core, two parts of the cladding are provided with a large number of pores, and the remaining two parts are filled with quartz. Wave preserving fiber.

Specifically, a core member 1 composed of one rod is provided at the center of a circular region surrounded by the support tube 19, and two types of clad members 23 and 25 surround the core member 1.

The first cladding members 23 are arranged in a fan shape having a vertex angle of 60 degrees with the core member 1 at the apex. The two fan shapes formed by the first cladding member 23 with the core member 1 at the apex face each other. I have. The second clad member 25 is arranged in a fan shape having a vertex angle of 120 degrees with the core member 1 at the apex between the two fan shapes formed by the first clad member 23,
Two fan shapes formed by the second clad member 25 with the core member 1 at the apex face each other. Here, the first clad member 23 is a capillary, the second clad member 25 is a rod, and the portion derived from the first clad member 23 after drawing has a smaller effective refractive index than the portion derived from the second clad member 25. . Although not shown in the drawing, the clad portion 17 also has two types of clad members 23, 2 and
5 are closely packed to the support tube 19 so as to form a sector shape.

Next, a method for manufacturing the polarization maintaining fiber of the present embodiment will be described.

First, a support tube 19 which is a circular tube made of SiO ₂ , a plurality of cylindrical (rod) SiO ₂ second clad members 25 having the same diameter as each other, and the same as the second clad member 25. A plurality of first clad members 23 which are capillaries made of SiO ₂ having a diameter and one core member 1 which is a rod made of Ge-doped SiO ₂ having the same diameter as the second clad member 25 are prepared.

The capillary may be formed by drawing a capillary base material, which is a relatively large-diameter cylindrical member, by heating and drawing to reduce the diameter. Further, Ge to be doped into the core member 1 may be added in a known amount so as to obtain a desired refractive index.

The clad members 23, 2 thus prepared
5 and the core member 1 are arranged as shown in FIG.
Fill into 9. Specifically, the core member 1 is disposed at the center of the support tube 19, and the first clad member 23 is disposed on both sides thereof so as to form two sectors having a vertical angle of 60 degrees. The apex angle of the clad member 25 is 120
The closest packing is performed so as to form two fan-shaped sections.

The preform thus manufactured is drawn in a drawing furnace and then drawn to a smaller diameter (a fiber) by drawing. In this drawing process, the adjacent support pipe 19 and the second clad member 25, the support pipe 19 and the first clad member 23, the second clad members 25, the first clad members 23, the first clad member 23
And the second clad member 25, and the clad members 23 and 25 and the core member 1 are fused and integrated with each other.

When the optical fiber is drawn, the support tube and the second clad member are made of the same material, and thus are integrated without boundaries. Four boundaries extend radially from the core in the radial direction, and are divided into four parts: two clad parts having a large number of pores and two parts filled with quartz without any pores. This optical fiber is a polarization maintaining fiber having a shape in which the sector of the core of the bow-tie fiber in FIG. The two sectors each have a number of pores. Note that the region having the pores has a different thermal expansion coefficient from the region having no pores, and thus also serves as a stress applying portion.

Modification 1-1 FIG. 7 shows a cross section of a preform of a polarization maintaining fiber according to a modification 1-1 of the first embodiment. In this modification, the core member 1 composed of one rod is arranged at the center of the preform,
The first clad member 23 is disposed on both sides of the core member 1 so as to extend linearly in the radial direction from the core member 1 to the support tube 19, and the core member 1 and the first clad member 23 define a cross section of the fiber. One straight line having a diameter is formed, and the remaining portion is filled with the second clad member 25. Although not shown in FIG. 7, the first cladding member 23 is also arranged at the portion of the cladding portion 17 up to the support tube 19, and the remaining portion is filled with the second cladding member 25. The materials and shapes of the core member 1, the clad members 23 and 25, and the support tube 19 are the same as those in the first embodiment. The manufacturing method is the same as that of the first embodiment.

In the first embodiment and the modified example 1-1, the clad is divided into four parts by four boundaries extending in the radial direction from the core. The two parts are examples of polarization-maintaining fibers filled with quartz, and the invention is not limited to these examples. By changing the material and type of the core member and the clad member to those described above, the core member may be a rod made of SiO ₂ not doped with Ge, and the second clad member may be a rod made of SiO ₂ doped with F. If the first clad member is a capillary and the effective refractive index after drawing is different from each other and birefringence can be caused in the optical fiber, the type of the substance to be doped into the core member and the clad member, the presence or absence of doping, the capillary Is not particularly limited. Further, the area ratio and the shape of the first clad member and the second clad member in the cross section of the fiber are not limited to the present embodiment, and the required angle of the sector is not limited, and the boundary line is bent in the middle. You may. It is preferable in terms of manufacturing and polarization preserving characteristics that the two portions of the first cladding member and the two portions of the second cladding face each other with the core interposed therebetween. Also, since the contraction rate after drawing is different between the capillary and the rod,
In the present embodiment, a stress is also applied to the core, and the stress contributes to the development of birefringence.

In the first embodiment and the modified example 1-1, the core member may be a plurality of rods. Also,
The core may have a pore distribution. Further, there may be a plurality of types of rods and capillaries. Also,
The diameter of the pores is not limited to one type, and may be any number. The refractive index distribution may be changed by appropriately changing the size distribution. Further, the shape of the pores is circular in cross section in the above-described embodiment and modified examples, but may be polygonal or elliptical, and is not particularly limited. Further, the refractive indices of the support tube and the clad member may be different.

Embodiment 2 FIG. 8 shows a cross section of a preform of a polarization maintaining fiber according to Embodiment 2. In the present embodiment, the core has a non-axially symmetrical shape (when rotated by 90 degrees), and pores are arranged in a clad portion adjacent to the core to generate birefringence.

Specifically, the center 1 in the support tube 19
Ge-doped SiO ₂ in a linear arrangement including three
The core member 11 is made of a rod made of steel. On the other hand, the first clad member 1 made of a capillary made of SiO ₂ , two of which are arranged in parallel on both sides in parallel with the three core members 11.
3. Around these, a second cladding member 15 which is a rod made of SiO ₂ is arranged. The clad part 17 is also filled with the second clad member 15.

When the optical fiber is manufactured by drawing this preform, the first clad member 13 is converted into a portion having a pore at the center thereof, and the effective refractive index of this portion is
Due to the presence of the pores, it becomes lower than in the case of only SiO ₂ , and this portion becomes a pit. Therefore, the optical fiber of the present embodiment is a polarization maintaining fiber having a structure similar to the side pit fiber of FIG. The two side pit portions are each a region having two pores.

The method for manufacturing the polarization maintaining fiber of this embodiment is basically the same as that of the first embodiment. Only the number and arrangement of the core members and the clad members are different, and the preform forming method and the drawing method are not changed.

Modification 2-1 FIG. 9 shows a cross section of a preform of a polarization maintaining fiber according to a modification 2-1 of the second embodiment. In this modification, the core and the pit portion are formed in a hexagonal shape with 19 members, and the surrounding second clad member 15, the clad portion 17, and the support tube 19 are the same as in the second embodiment. The method for manufacturing the polarization maintaining fiber of this modification is basically the same as that of the first embodiment.

In this modification, in the cross section of the fiber, 1
One Ge-doped SiO_TwoMade of rod made of
A member 11 is arranged like a drum at the center of the preform.
iO _TwoClad member 13 made of capillary made of
Are arranged in four recesses on both sides of the drum
It has a shape.

The optical fiber produced by drawing this preform is a polarization maintaining fiber having a structure similar to the side pit fiber having the shape shown in FIG.

Modification 2-2 FIG. 10 shows a cross section of a preform of a polarization maintaining fiber according to Modification 2-2. In this modification, the core and the pit portion are formed in a rhombus with nine members in the cross section of the fiber, and the surrounding second clad member 15 and clad portion 17 are formed.
The support tube 19 is the same as in the second embodiment. In addition, the method of manufacturing the polarization maintaining fiber of the present modified example,
Basically, it is the same as the first embodiment.

The pit portion of this modification is the same as the pit portion of the second embodiment shown in FIG.
The second clad member 15 adjacent to the first clad member is replaced with the first clad member 13 one by one on the left and right sides. That is, three first cladding members 13 are arranged in a triangular shape on both sides of three core members 11 arranged linearly including one fiber center.

The core of the optical fiber produced by drawing this preform is a polarization maintaining fiber having a structure similar to the side pit fiber having the shape shown in FIG.

Modification 2-3 FIG. 11 is a cross-sectional view of a preform of the polarization maintaining fiber according to Modification 2-3. In this modification, the core member 11
Are two Ge-doped rods, the first cladding member 13 is two capillaries, and birefringence is caused by these four arrangements. The surrounding second clad member 15, the clad portion 17, and the support tube 19 are the same as in the second embodiment.

There are two types of arrangement of the core member 11 and the first clad member 13 (FIGS. 12A and 12B).
FIG. 12B shows only one of them. The two types of arrangement will be described. The capillaries 22 as the two first clad members 13 are vertically arranged adjacent to each other, and the core member 1 is formed.
FIG. 12A shows one rod 21 which is arranged next to two capillaries vertically arranged adjacent to both capillaries 22, and FIG. 12B shows the capillary of FIG. This is an arrangement in which the rod 22 and the rod 21 are replaced.

When the optical fiber is drawn, the adjacent rods and capillaries are fused and integrated at the boundary, leaving only the pores of the capillary. When drawn in this manner, the preform having the structure of FIG.
12B is an optical fiber having a pore distribution similar to that of the side tunnel fiber, and the preform having the structure of FIG. 12B is an optical fiber having a pore distribution similar to that of the side tunnel fiber of FIG.

The manufacturing method of the polarization maintaining fiber of this modification is the same as the manufacturing method of Embodiment 1 in which a rod and a capillary are bundled to form a preform.

-Modification 2-4- FIG. 13 shows a cross section of a preform of the polarization maintaining fiber according to Modification 2-4. In this modification, five core members, one at the center of the preform and two at both sides of the preform, are made of Ge-doped SiO ₂ rods, and are arranged in a drum shape. SiO _{2 in} two places where the drum is hollow
A first clad member 13 made of a capillary made of a material is arranged. Surrounding clad member 15 and clad portion 17
The support tube 19 is the same as in the second embodiment.

The core of the optical fiber produced by drawing this preform is a polarization maintaining fiber having a structure similar to the side tunnel fiber of FIG. The method of manufacturing the polarization maintaining fiber of this modification is the same as the manufacturing method of Embodiment 1 in which a rod and a capillary are bundled to form a preform.

The second embodiment and the modified examples 2-1 to 4
This is an example of a polarization-maintaining fiber in which the core is non-axially symmetric (when rotated by 90 degrees) and pores are arranged in a clad portion adjacent to the core, and the present invention is not limited to these. As long as birefringence occurs in the optical fiber, the arrangement of the pores in the cladding may be any. Embodiment 1 and Modification 1-
It may be combined with one pore arrangement. Further, the rods and capillaries may have different diameters as well as the same diameter, and may have a plurality of diameters. Also, the diameter of the pores is not limited to one type, and may be any number. The refractive index distribution may be changed by appropriately changing the size distribution. Also, the shape of the pores,
Although the cross section is circular in the above embodiments and modifications, it may be polygonal, elliptical, or the like, and is not particularly limited. Further, in the above embodiment and the modified example, the core member is doped with Ge,
The cladding member and the second cladding member are not doped with anything, but may be doped with nothing, or may be doped with various substances such as Ge and F to change the refractive index, the coefficient of thermal expansion, and the like. good. Further, the effective refractive index of the support tube and the second clad member may be different.

Embodiment 3 FIG. 15 shows a cross section of a preform of the polarization maintaining fiber according to Embodiment 3. In the present embodiment, the core is non-axisymmetric (90
(When rotated by degrees), birefringence is caused by arranging pores throughout the clad in the cross section of the fiber.

Specifically, the center 1 in the support tube 19
Three of the linear arrangements including _TwoFrom a rod made of
Core member 11. On the other hand, parallel to the three core members 11
4 lines each, 2 lines on each side_TwoInner diameter
The first cladding member 13 made of a capillary having a large
is there. SiO around these_TwoCapillaries with small inner diameter
A second clad member 18 which is a rally is arranged. K
The second clad member 18 is also filled in the lad portion 17.
Have been.

When an optical fiber is manufactured by drawing this preform, the first clad member 13 and the second clad member 18 are converted into a portion having a pore at the center, and the effective refractive index of this portion is reduced. Due to the presence of holes, it is lower than in the case of only SiO ₂ . Since the inner diameter of the capillary of the first clad member 13 is larger than the inner diameter of the capillary of the second clad member 18, the first clad member 13
The origin portion has the lowest effective refractive index in the optical fiber and becomes a pit portion. Therefore, the optical fiber of the present embodiment is a polarization maintaining fiber having a structure similar to the side pit fiber of FIG. Two side pit parts,
Each is a region having two pores.

Since the second clad member 18 is a capillary, the core member 11 has a core function as an optical transmission line even if the core member 11 is a pure quartz rod not doped with Ge. In addition, since the second clad member is a capillary, the effective refractive index difference between the core and the clad can be increased, and the polarization maintaining ability can be improved.

The method for manufacturing the polarization maintaining fiber of this embodiment is basically the same as that of the first embodiment. The method of forming the preform and the method of drawing are not different, only the material, the number, the arrangement, and the like of the core member and the clad member are different.

Modification 3-1 FIG. 16 shows a cross section of a preform of a polarization maintaining fiber according to a modification 3-1 of the third embodiment. In this modification, the core and the pit portion are formed in a hexagon with 19 members.
The surrounding second clad member 18, clad portion 17, and support tube 19 are the same as in the third embodiment. Also,
The method for manufacturing the polarization maintaining fiber of this modification is basically the same as that of the first embodiment.

In this modification, the cross section of the fiber is 1
A core member 11 made of one rod made of SiO ₂ is arranged in the shape of a drum at the center of the preform, and a first clad member 13 made of a capillary made of SiO _{2 having} a large inner diameter is provided on each of the concave portions on both sides of the drum. It has a shape arranged four by four. The second cladding member 18 is a capillary having a small inner diameter.

The optical fiber produced by drawing this preform is a polarization maintaining fiber having a structure similar to the side pit fiber having the shape shown in FIG.

Modification 3-2- FIG. 17 shows a cross section of a preform of a polarization maintaining fiber according to Modification 3-2. In this modification, the core and the pit portion are formed in a rhombus with nine members in the cross section of the fiber, and the surrounding second clad member 18 and clad portion 17 are formed.
The support tube 19 is the same as that of the third embodiment. In addition, the method of manufacturing the polarization maintaining fiber of the present modified example,
Basically, it is the same as the first embodiment.

The pit portion of this modification is the same as the pit portion of the third embodiment shown in FIG.
The second cladding member 18 adjacent to the first 3
The shape is replaced by the clad member 13. That is,
Three first clad members 13 are provided on both sides of three core members 11 in a linear arrangement including one at the center of the fiber.
Have a triangular arrangement.

The core of the optical fiber produced by drawing this preform is a polarization maintaining fiber having a structure similar to the side pit fiber having the shape shown in FIG.

-Modification 3-3- FIG. 18 is a cross-sectional view of a preform of the polarization maintaining fiber according to Modification 3-3. In this modification, the core member 11
Are two rods, the first clad member 13 is two capillaries having a large inner diameter, and birefringence is caused by these four arrangements. The surrounding second clad member 18, clad portion 17, and support tube 19 are the same as in the third embodiment.

Although there are two types of arrangement of the core member 11 and the first clad member 13 (FIGS. 12A and 12B), FIG.
FIG. 12B shows only one of them. The two types of arrangement are as described in the modification 2-3.

When the optical fiber is drawn, the adjacent rods and capillaries are fused and integrated at the boundary, leaving only the pores of the capillary. When drawn in this manner, the preform having the structure of FIG.
12B is an optical fiber having a pore distribution similar to that of the side tunnel fiber, and the preform having the structure of FIG. 12B is an optical fiber having a pore distribution similar to that of the side tunnel fiber of FIG.

The manufacturing method of the polarization-maintaining fiber of this modification is the same as the manufacturing method of Embodiment 1 in which a rod and a capillary are bundled to form a preform.

-Modification 3-4- FIG. 19 shows a preform cross section of a polarization maintaining fiber according to Modification 3-4. In this modification, five core members 11 each composed of SiO ₂ rods, one in the center of the preform and two on both sides of the preform, are arranged like a drum. The first clad members 13 each formed of a capillary made of SiO ₂ and having a large inner diameter are arranged at two places where the drum is depressed. The surrounding second clad member 18, clad portion 17, and support tube 19 are the same as in the third embodiment.

The core of the optical fiber produced by drawing this preform is a polarization maintaining fiber having a structure similar to the side tunnel fiber of FIG. The method of manufacturing the polarization maintaining fiber of this modification is the same as the manufacturing method of Embodiment 1 in which a rod and a capillary are bundled to form a preform.

The above-described Embodiment 3 and Modifications 3-1 to 4 are
This is an example of a polarization-maintaining fiber in which the core is non-axially symmetric (when rotated by 90 degrees) and pores are arranged throughout the clad in the cross section of the fiber, and the present invention is not limited thereto.
As long as birefringence occurs in the optical fiber, the arrangement of the pores in the cladding may be any. The relationship between the inner diameters of the capillaries of the first clad member and the second clad member is such that the effective refractive index of the clad portion derived from the first clad member is smaller than the effective refractive index of the clad portion derived from the second clad member. However, any relationship between the sizes of the inner diameters may be used. The rods and capillaries may not only have the same diameter but also have different diameters, and may have a plurality of diameters. Also, the diameter of the pores is not limited to one type, and may be any number. The refractive index distribution may be changed by appropriately changing the size distribution.
Further, the shape of the pores is circular in cross section in the above-described embodiment and modified examples, but may be polygonal or elliptical, and is not particularly limited. Further, in the above-described embodiments and modified examples, the core member, the first clad member, and the second clad member are not doped with anything, but Ge, F, etc. May be doped.

Embodiment 4 FIG. 14 shows a cross section of a central portion of a preform of a polarization maintaining fiber according to Embodiment 4. In the present embodiment, seven S
The core member 1 is a capillary having pores iO ₂ made of oval are arranged in a hexagonal in the center of the preform. A clad member 30, which is a capillary made of SiO ₂ , is arranged around the core member 1. Although not shown in the figure, the outer periphery of the preform is a support tube,
The support tube is filled with a clad member 30. It should be noted that the pore area ratio in the cross section of the clad member 30 is larger than the pore area ratio in the cross section of the core member 1, and the effective refractive index is set smaller in the clad.

The major axis direction of the elliptical pores of each core member 1 is the same direction, and the same elliptical pores will be distributed in the core even if it becomes an optical fiber after drawing. In a core in which elliptical pores with uniform orientations are distributed, birefringence occurs because the refractive index differs between the major axis direction and the minor axis direction of the ellipse.

The pores arranged in the core need not be elliptical. The pores of the core may have different diameters in two directions orthogonal to each other in cross section, and examples thereof include a rectangle and a rhombus. The shape of the pores of the cladding is not limited. Further, Ge or F may be doped in the quartz of the cladding or the core.

The manufacturing method of the polarization maintaining fiber of the present embodiment is basically the same as the manufacturing method of the first embodiment.

Embodiment 5 FIG. 5 is a cross-sectional view of a preform of a polarization maintaining fiber according to Embodiment 5 of the present invention. The present embodiment is an optical fiber having a pore in a cladding and a portion doped with a stress imparting substance on both sides of a core in a cross section of the fiber.

Center of circular area surrounded by support tube 19
One Ge-doped SiO in part _TwoIs a rod made of
The core member 1 is placed. SiO_TwoCapillary made of No.
One clad member 23 forms one hexagonal cross section with seven
The hexagons are arranged one on each side of the core member 1.
ing. In this manner, the first clad members are provided on both sides of the core member 1.
23, and the same as the core member 1 above and below the core member 1.
Diameter of SiO_TwoThe second clad member 25 which is a rod made of
One by one, and two above and below B_TwoO_ThreeThe
SiO_TwoRod 50, which is a rod made of
Has been arranged. In the rest of the support tube 19,
The second clad member 25 is filled. This pre-
The method for manufacturing the optical fiber and the optical fiber is the same as in the first embodiment.
It is.

In addition to having a low effective refractive index portion having pores derived from the first clad member on both sides of the core, a stress applying portion is also provided above and below the core. In the embodiment, the polarization maintaining ability is enhanced.

The number of capillaries of the first cladding member, the number of stress applying rods, the arrangement position, and the like are not limited to the present embodiment. Also, the second clad member may be a capillary, and the presence / absence and type of the doping material in the core member, the first clad member, and the second clad member are not particularly limited.

Embodiment 6 FIG. 20 is a cross sectional view of a preform of a polarization maintaining fiber according to Embodiment 6. The present embodiment is a polarization maintaining fiber in which a cladding portion adjacent to a core has pores filled with a substance having a lower refractive index than pure quartz.

This embodiment is a modification 2-2 shown in FIG.
The rod of the low refractive index cladding member 12 in which the pores of the first cladding member 13 which is the capillary of the modified example 2-2 are filled with F-doped SiO ₂ is used instead of the first cladding member 13. Three pieces are arranged on both sides of the core member 11 in a triangular shape. The second clad member 15, the clad portion 17, and the support tube 19 are the same as in the second embodiment. The method for manufacturing the polarization maintaining fiber of the present embodiment is basically the same as that of the first embodiment. The rod of the low refractive index clad member 12 may be manufactured by a known method.

This embodiment is merely an example, and the material to be doped into the center of the low refractive index cladding member 12, such as the shape of the core, the number and arrangement of the low refractive index cladding members, etc. There is no particular limitation. Further, the second clad member 15 may be a capillary.

[0086]

The present invention is embodied in the form described above, and has the following effects.

Since the birefringence is caused by arranging the pores in the cladding, polarization maintaining fibers having various structures can be obtained.

Since the polarization maintaining fiber is manufactured by bundling the capillary and the rod, a polarization maintaining fiber having a complicated structure can be easily manufactured. In addition, manufacturing costs can be reduced.

By using a capillary as the cladding member, the refractive index difference between the core and the cladding can be increased, and a polarization maintaining fiber having a high polarization maintaining ability can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic view of a cross section of a first example of a conventional polarization maintaining fiber (side pit fiber, side tunnel fiber).

FIG. 2 is a schematic view of a cross section of a second example of a conventional polarization maintaining fiber (side pit fiber, side tunnel fiber).

FIG. 3 is a schematic diagram of a cross section of a third example (panda fiber) of a conventional polarization maintaining fiber.

FIG. 4 is a schematic view of a cross section of a fourth example (bow-tie fiber) of a conventional polarization maintaining fiber.

FIG. 5 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to a fifth embodiment.

FIG. 6 is a schematic diagram of a cross section of a preform of the polarization maintaining fiber according to the first embodiment.

FIG. 7 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 1-1.

FIG. 8 is a schematic view of a cross section of a preform of the polarization maintaining fiber according to the second embodiment.

FIG. 9 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 2-1.

FIG. 10 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 2-2.

FIG. 11 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 2-3.

FIG. 12A is a diagram illustrating a first arrangement of core members according to Modification Example 2-3. (B) It is a figure showing the 2nd arrangement of the core member of modification 2-3.

FIG. 13 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 2-4.

FIG. 14 is a schematic diagram of a cross section of a central portion of a preform of a polarization maintaining fiber according to a fourth embodiment.

FIG. 15 is a schematic diagram of a cross section of a preform of the polarization maintaining fiber according to the third embodiment.

FIG. 16 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 3-1.

FIG. 17 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification 3-2.

FIG. 18 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification Example 3-3.

FIG. 19 is a schematic diagram of a cross section of a preform of a polarization maintaining fiber according to Modification 3-4.

FIG. 20 is a schematic diagram of a cross section of a preform of the polarization maintaining fiber according to the sixth embodiment.

[Explanation of symbols]

 Reference Signs List 1 core member 2 core 3 clad 11 core member 12 low-refractive index clad member 13 first clad member 15 second clad member 17 clad portion 18 second clad member 19 support tube 21 rod 22 capillary 23 first clad member 25 second Clad member 30 Clad member 50 Stress applying rod

Continued on the front page (72) Inventor Masatoshi Tanaka 4-3 Ikejiri, Itami City, Hyogo Prefecture Inside Mitsubishi Cable Industries, Ltd. Itami Works (72) Inventor Shigeki Koyanagi 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries, Ltd. Itami Inside the factory (72) Inventor, Moriyuki Fujita 4-3-1, Ikejiri, Itami-shi, Hyogo Mitsubishi Cable Industries, Ltd.Itami Works (72) Inventor, Masataka Nakazawa 2-3-1, Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation Inside the company (72) Inventor Hirokazu Kubota 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Satoru Kawanishi 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Telephone Co., Ltd. F term (reference) 2H050 AA05 AB05X AC48 AC62 4G021 BA21

Claims (7)

[Claims] 1. A polarization-maintaining fiber comprising a cladding having a pore extending in an axial direction of an optical fiber, wherein the cladding is divided into four by four boundaries extending in a radial direction from a core, and the cladding is divided into four parts. Of the two parts, two are provided with a large number of the above pores, the other two are filled with quartz, and the part filled with quartz exists between the two parts with the pores A polarization maintaining fiber. 2. A polarization-maintaining fiber comprising a cladding having pores extending in an axial direction of an optical fiber, wherein the cladding portion adjacent to the core has birefringence in a cross section of the fiber. A polarization maintaining fiber having pores arranged therein. 3. The polarization-maintaining fiber according to claim 2, wherein the pores are provided in all portions of the cladding in the cross section of the fiber. 4. A polarization-maintaining fiber comprising a cladding provided with a pore extending in the axial direction of the optical fiber, wherein the narrow fiber extends in the axial direction of the optical fiber having different diameters in two orthogonal directions in the fiber cross section. A polarization maintaining fiber having a hole in a core. 5. The polarization-maintaining fiber according to claim 1, further comprising a portion doped with a stress imparting substance on both sides of the core in the cross section of the fiber. 6. The polarization maintaining fiber according to claim 1, wherein the pores are filled with a substance having a lower refractive index than a substance surrounding the pores. 7. A method for manufacturing a polarization-maintaining fiber, comprising forming a preform by bundling a capillary and a rod, and drawing the preform into an optical fiber, wherein birefringence is caused in a cross section of the optical fiber. A method for manufacturing a polarization maintaining fiber, comprising disposing the capillary and the rod in the preform as described above.