JP2009192702A - Optical fiber and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber having holes and improved handleability. <P>SOLUTION: The optical fiber is composed of: a core part 11; a first clad part 12 having a smaller refractive index than the core part 11 and surrounding the core part 11; a second clad part 13 having a refractive index equal to or smaller than that of the first clad part 12, having a plurality of holes 14 in each wall of one or more glass layer, and surrounding the first clad part 12; and a third clad part 15 having a refractive index equal to or smaller than that of the first clad part 12 and surrounding the second clad part 13. The plurality of holes 14 are designed to be formed in a plurality of places along the axial direction and in the circumferential direction, and also formed extendedly in the direction from the first clad part 12 toward the third clad part 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical fiber used for optical signal propagation and a manufacturing method thereof, and more particularly to an optical fiber used as a transmission medium in optical communication and a manufacturing method thereof.

  In general, in optical communication using an optical fiber, an optical signal propagates through the optical fiber in a state of being confined in the core portion due to total reflection due to a difference in refractive index between the core portion and the cladding portion. In recent years, research and development of optical fibers that propagate optical signals by total reflection using the refractive index difference between air and glass by providing a plurality of holes in the cross section of the optical fiber along the axial direction of the optical fiber Is underway. The optical fiber having a plurality of holes can be realized with the conventional optical fiber because the relative refractive index difference between the core part and the clad part made of the holes can be increased as compared with the conventional optical fiber. It is possible to realize an impossible characteristic (for example, see Patent Document 1). For example, the optical fiber can be bent (communication is possible even if the optical fiber is bent).

  For manufacturing such an optical fiber, a method of drawing a bundle of capillaries (see Patent Document 2) and a method of drawing a hole by making a hole in an optical fiber preform are known.

Republished patent WO2004 / 092793 JP 2002-97034 A JP-A-56-84330

  However, the method of bundling capillaries described in Patent Document 2 has a problem that the shape of the hole tends to collapse when drawing. Furthermore, there is a problem that OH groups and impurities adhere to the outer surface of the capillary and it is difficult to reduce the loss. On the other hand, in the method of drawing a hole by making a hole in an optical fiber preform, quartz glass is very hard, so it is necessary to use a special method such as ultrasonic vibration grinding. When the length is increased, there is a problem that the shaft is displaced due to high-speed rotation and grinding becomes impossible. Therefore, the optical fiber having a structure in which a plurality of holes are provided in the cross section of the optical fiber along the optical fiber axial center direction has a problem that it is difficult to reduce the loss and length.

  In addition, in a conventional optical fiber with a hole, in order to prevent impurities such as dust from entering the hole, both ends of the optical fiber are sealed or both ends of the optical fiber are sealed. It was necessary to perform an operation such as attaching a sealing member to be stopped, and the handleability was not good.

Therefore, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an optical fiber having a hole and having improved handleability.
In addition, the present invention has been made to solve the above-described problems, and provides a method for manufacturing an optical fiber having a hole, which can reduce loss and can be manufactured in a long length. Objective.

The optical fiber according to the first invention for solving the above-described problem is:
The core,
A first cladding portion having a refractive index smaller than that of the core portion and surrounding the core portion;
A second clad having a plurality of holes in each wall portion of one or more glass layers having a refractive index equal to or smaller than that of the first clad portion and surrounding the first clad portion And
A third clad part having a refractive index equal to or smaller than that of the first clad part and surrounding the second clad part;
The plurality of holes are formed at a plurality of locations along the axial direction at a plurality of locations in the circumferential direction, and are formed to extend in a direction from the first cladding portion to the third cladding portion. And

An optical fiber according to a second invention for solving the above-described problem is an optical fiber according to the first invention,
The plurality of holes are formed at equal intervals in the circumferential direction.

An optical fiber according to a third invention for solving the above-described problem is the optical fiber according to the first or second invention,
The radius of the first cladding part is set in a region where the intensity of the electric field distribution is 3% or more.

An optical fiber manufacturing method according to a fourth invention for solving the above-described problem is an optical fiber manufacturing method for manufacturing an optical fiber according to any one of the first to third inventions,
A first process for producing an optical fiber preform having a core portion and a first cladding portion having a refractive index smaller than that of the core portion;
A glass tube having a refractive index that is equal to or smaller than that of the first cladding part and that can be attached to the outside of the optical fiber preform produced by the first process. A second process to produce;
A third process of providing a plurality of punched holes in the wall of the glass tube produced in the second process;
Outside the glass tube having a plurality of holes made in the third process and having a refractive index equal to or smaller than that of the first clad part made in the first process. A fourth process for producing a glass tube of a size that can be attached;
A glass tube having a plurality of holes produced by the third process is inserted into the glass tube produced by the fourth process, and the glass tube having the plurality of holes is inserted by the first process. A fifth process of inserting the fabricated optical fiber preform;
And a sixth process of melting and stretching the glass tube into which the optical fiber preform obtained in the fifth process is inserted.

An optical fiber manufacturing method according to a fifth invention for solving the above-described problem is an optical fiber manufacturing method for manufacturing an optical fiber according to any one of the first to third inventions,
An optical fiber preform comprising a core part, a first cladding part having a refractive index smaller than that of the core part, and a second cladding part having a refractive index equal to or smaller than that of the first cladding part. A first process for producing
A second process of providing a plurality of non-penetrating holes in the outer wall of the optical fiber preform produced in the first process;
The optical fiber preform having the refractive index which is equal to or smaller than the first clad part produced by the first process and is attached to the outside of the optical fiber preform produced by the second process. A third process for producing a glass tube of a possible size;
A fourth process of inserting the optical fiber preform produced in the second process inside the glass tube produced in the third process;
And a fifth process of melting and stretching a glass tube into which the optical fiber preform obtained in the fourth process is inserted.

An optical fiber manufacturing method according to a sixth invention for solving the above-described problem is an optical fiber manufacturing method for manufacturing an optical fiber according to any one of the first to third inventions,
A first process for producing an optical fiber preform having a core portion and a first cladding portion having a refractive index smaller than that of the core portion;
The optical fiber preform having a refractive index that is equal to or smaller than that of the first cladding part manufactured in the first process and that is attached to the outside of the optical fiber preform manufactured in the first process. A second process for producing a glass tube of a possible size;
A third process of providing a plurality of holes that do not penetrate through the inner wall of the glass tube produced by the second process;
A fourth process of inserting the optical fiber preform produced in the first process inside the glass tube produced in the third process;
And a fifth process of melting and stretching a glass tube into which the optical fiber preform obtained in the fourth process is inserted.

An optical fiber manufacturing method according to a seventh invention for solving the above-described problem is an optical fiber manufacturing method for manufacturing an optical fiber according to any one of the first to third inventions,
An optical fiber preform comprising a core part, a first cladding part having a refractive index smaller than that of the core part, and a second cladding part having a refractive index equal to or smaller than that of the first cladding part. A first process for producing
A second process of providing a plurality of non-penetrating holes in the outer wall of the optical fiber preform produced in the first process;
The optical fiber preform having a refractive index that is equal to or smaller than that of the first cladding part manufactured in the first process and that is attached to the outside of the optical fiber preform manufactured in the first process. A third process for producing a glass tube of a possible size;
A fourth process of providing a plurality of non-piercing holes in the inner wall of the glass tube produced in the third process;
A fifth process of inserting the optical fiber preform produced in the second process inside the glass tube produced in the fourth process;
And a sixth process of melting and stretching the glass tube into which the optical fiber preform obtained in the fifth process is inserted.

  According to the optical fiber of the present invention, the core portion, the first cladding portion having a smaller refractive index than the core portion, and surrounding the core portion, the same as the first cladding portion or the first cladding A plurality of holes in each wall portion of one or more glass layers having a refractive index smaller than the portion, a second cladding portion surrounding the first cladding portion, and the same as the first cladding portion or the A plurality of holes formed at a plurality of locations along the axial direction at a plurality of locations in the circumferential direction, the third cladding portion having a refractive index smaller than that of the first cladding portion and surrounding the second cladding portion; In addition, by extending in the direction from the first cladding portion toward the third cladding portion, it is possible to make a structure without holes at both ends, and the existing light with holes Optical fiber required for fiber Mounting operation of the sealing member into sealing process or an optical fiber ends in the driver ends is not required. At the time of mechanical splice connection or the like, it is possible to omit the process of removing the sealing portions at both ends of the optical fiber and the process of removing the sealing members attached to both ends of the optical fiber. As a result, handleability is improved as compared with existing optical fibers with holes.

  According to the optical fiber manufacturing method of the present invention, a plurality of through holes or non-through holes are provided in the wall portion of the glass tube or the optical fiber preform. No) the length of the hole is short, so that it is possible to manufacture an optical fiber with a structure having holes in the cross section of the optical fiber without causing axial misalignment due to ultrasonic vibration grinding. It becomes possible. In addition, entry of impurities into the holes can be suppressed, and a reduction in loss can be achieved.

  The best mode of an optical fiber and an optical fiber manufacturing method according to the present invention will be described below in detail with reference to the drawings.

[First embodiment of optical fiber]
A first embodiment of an optical fiber according to the present invention will be described with reference to FIG.
FIG. 1 is a diagram showing a first embodiment of an optical fiber according to the present invention. FIG. 1 (a) schematically shows the first embodiment of the optical fiber, and FIG. 2 shows a cross section of a first embodiment of a fiber.

  As shown in FIGS. 1A and 1B, the optical fiber 10 according to this embodiment includes a core portion 11 having an arbitrary refractive index distribution to which a dopant is added, and a first refractive index having a uniform refractive index. The clad part 12, the second clad part 13 including a plurality of holes 14, and the third clad part 15 having a uniform refractive index, and the core part 11 and the first clad part 12 emit main light. A waveguide structure is formed. The plurality of holes 14 are formed at a plurality of locations along the axial direction and are formed in the circumferential direction. The plurality of holes 14 are formed by communicating the inner wall portion 13 a and the outer wall portion 13 b of the second cladding portion 13. That is, the plurality of holes 14 are formed to extend in the direction from the first cladding portion 12 toward the third cladding portion 15.

  The first clad portion 12 surrounds the core portion 11. The second cladding part 13 surrounds the first cladding part 12. Further, the third cladding part 15 surrounds the second cladding part 13. The first cladding part 12 has a smaller refractive index than the core part 11. The second cladding portion 13 has a plurality of holes 14 in the wall portion of the glass layer having a refractive index equal to or smaller than that of the first cladding portion 12.

  Here, FIG. 1A and FIG. 1B show a diagram in which the glass layer that forms the second cladding portion 13 is a single layer, but the glass layer that forms the second cladding portion has a plurality of layers. It is also possible. Further, the third clad portion 15 has a refractive index that is equal to or smaller than that of the first clad portion 13. In FIG. 1 (a), a plurality of circular cylindrical (cylindrical) holes 14 are provided in the wall portion of the second cladding portion 13, but the shape of the holes is a rectangular column shape in addition to a circular cylindrical shape. It is also possible to use a columnar shape such as a cone shape or a cone shape such as a quadrangular pyramid. In FIG. 1B, eight holes 14 are provided in the optical fiber cut portion, but the number of holes may be 9 or more or 7 or less.

  Further, in FIG. 1, the plurality of holes 14 provided in the wall portion of the second cladding portion 13 are regularly arranged in the longitudinal direction of the optical fiber and the cross section of the optical fiber. For example, as shown in FIG. In addition, the plurality of holes 114 are irregularly arranged in the cross section of the optical fiber 100 so as to be biased to the left and right positions in FIG. 2, or the plurality of holes are irregularly arranged in the longitudinal direction of the optical fiber. It is also possible to do. As shown in FIG. 2, by arranging the plurality of holes 114 so as to be biased, it is possible to control the polarization state and hold only a single polarized wave.

  Therefore, according to the optical fiber 10 according to the present embodiment, it is possible to have a structure having no holes at both ends, and sealing processing at both ends of the optical fiber, which is necessary for an existing optical fiber with holes, It is not necessary to attach the sealing member to both ends of the optical fiber. Furthermore, the process of removing the sealing portions at both ends of the optical fiber and the process of removing the sealing members attached to both ends of the optical fiber can be omitted during mechanical splice connection. As a result, handleability is improved as compared with existing optical fibers with holes.

[First Embodiment of Optical Fiber Manufacturing Method]
A first embodiment of an optical fiber manufacturing method according to the present invention will be described with reference to FIG.
FIG. 3 is a flowchart for explaining an optical fiber manufacturing method.

  In the optical fiber manufacturing method according to the present embodiment, as shown in FIG. 3, first, in a first process, an optical fiber preform having a core portion and a first cladding portion having a refractive index smaller than that of the core portion. It is produced (step S11). Here, a VAD (Vapor Phase Axial Deposition) method, an OVD (Outside Vapor Deposition) method, an MCVD (Modified Chemical Vapor Deposition) method, and a PCVD (Plasma ChemDrop prefabrication method). It is possible.

  Next, in the second (second process) of the flowchart, the optical fiber preform having the refractive index that is equal to or smaller than that of the first cladding part and is manufactured in the first process. A glass tube having a size that can be attached to the outside is prepared (step S12). For example, it is possible to produce a glass tube by using the method for producing a quartz glass tube described in Patent Document 3.

  Subsequently, in the third process, a plurality of penetrated holes are provided in the wall portion of the glass tube produced in the second process (step S13). For example, the holes can be provided by ultrasonic vibration grinding. Further, in the fourth process, a plurality of refractive indexes having a refractive index that is equal to or smaller than that of the first cladding portion manufactured in the first process and that is manufactured in the third process. A glass tube having a size that can be attached to the outside of the glass tube having holes is produced (step S14). For example, it is possible to produce a glass tube by using the method for producing a quartz glass tube described in Patent Document 3.

  Then, in the fifth process, the glass tube having a plurality of holes produced by the third process is inserted inside the glass tube produced by the fourth process, and the glass tube having the plurality of holes is inserted. The optical fiber preform produced by the first process is inserted inside the glass tube (step S15), and the glass tube into which the optical fiber preform obtained by the fifth process is inserted in the sixth process is melt-drawn ( Line drawing) (step S16).

  Therefore, the optical fiber according to the first embodiment can be manufactured by the manufacturing procedure described above.

  Therefore, according to the optical fiber manufacturing method according to the present embodiment, the length of the hole to be ground (through) is short by providing a plurality of through holes in the wall portion of the glass tube. An optical fiber having a structure having holes in the cross section of the optical fiber can be manufactured in a long length without causing an axis deviation due to grinding, and mass production becomes possible. In addition, entry of impurities into the holes can be suppressed, and a reduction in loss can be achieved.

  In the optical fiber manufacturing method according to the present embodiment, the optical fiber according to the first embodiment having the second clad portion of two or more glass layers by repeating the second process and the third process. Can also be manufactured.

[Second Embodiment of Optical Fiber Manufacturing Method]
A second embodiment of the optical fiber manufacturing method according to the present invention will be described with reference to FIG.
FIG. 4 is a flowchart for explaining an optical fiber manufacturing method.

  In the optical fiber manufacturing method according to the present embodiment, as shown in FIG. 4, first, in a first process, a core part, a first cladding part having a refractive index smaller than that of the core part, and the first cladding part An optical fiber preform comprising a second cladding part having a refractive index equal to or smaller than that of the first cladding part is produced (step S21). Here, an optical fiber preform can be manufactured by using the VAD method or the like.

  Next, in the second (second process) of the flowchart, a plurality of holes that do not penetrate through are provided in the outer wall portion of the optical fiber preform manufactured in the first process (step S22). For example, it is possible to provide a hole only in the region of the second cladding part by the ultrasonic vibration grinding in which the length of the drill to be ground is adjusted.

  Subsequently, in a third process, an optical fiber having a refractive index equal to or smaller than that of the first cladding part manufactured in the first process and manufactured in the second process. A glass tube having a size that can be attached to the outside of the preform is prepared (step S23). For example, it is possible to produce a glass tube by using the method for producing a quartz glass tube described in Patent Document 3.

  Further, in the fourth process, the optical fiber preform produced in the second process is inserted inside the glass tube produced in the third process (step S24), and in the fifth process, the fourth process is performed. The glass tube into which the optical fiber preform obtained in the process is inserted is melt-drawn (drawn) (step S25).

  Therefore, the optical fiber according to the first embodiment can be manufactured by the manufacturing procedure described above.

  Therefore, according to the optical fiber manufacturing method according to the present embodiment, since the plurality of holes that do not penetrate are provided in the wall portion of the optical fiber preform, the length of the hole to be ground (not penetrated) is short. An optical fiber having a structure having holes in the cross section of the optical fiber can be produced in a long length without causing an axis deviation due to ultrasonic vibration grinding, and mass production becomes possible. In addition, entry of impurities into the holes can be suppressed, and a reduction in loss can be achieved.

[Third embodiment of optical fiber manufacturing method]
A third embodiment of the optical fiber manufacturing method according to the present invention will be described with reference to FIG.
FIG. 5 is a flowchart for explaining an optical fiber manufacturing method.

  In the optical fiber manufacturing method according to the present embodiment, as shown in FIG. 5, first, in a first process, an optical fiber preform having a core portion and a first cladding portion having a refractive index smaller than that of the core portion. It is produced (step S31). Here, an optical fiber preform can be manufactured by using the VAD method or the like.

  Next, in the second (second process) of the flowchart, the refractive index is equal to or smaller than that of the first cladding part manufactured in the first process, and in the first process, A glass tube having a size that can be attached to the outside of the produced optical fiber preform is produced (step S32). For example, it is possible to produce a glass tube by using the method for producing a quartz glass tube described in Patent Document 3.

  Subsequently, in the third process, a plurality of holes that do not penetrate are provided in the inner wall portion of the glass tube produced in the second process (step S33). For example, it is possible to provide a hole only in the region of the second cladding part by the ultrasonic vibration grinding in which the length of the drill to be ground is adjusted.

  Further, in the fourth process, the optical fiber preform produced in the first process is inserted inside the glass tube produced in the third process (step S34). The glass tube into which the optical fiber preform obtained by the four processes is inserted is melt-drawn (drawn) (step S35).

  Therefore, the optical fiber according to the first embodiment can be manufactured by the manufacturing procedure described above.

  Therefore, according to the optical fiber manufacturing method according to the present embodiment, since the plurality of holes that cannot be penetrated are provided in the wall portion of the glass tube, the length of the hole to be ground (not penetrated) is short. An optical fiber having a structure having holes in the cross section of the optical fiber can be manufactured in a long length without causing an axis deviation due to vibration grinding, and mass production becomes possible. In addition, entry of impurities into the holes can be suppressed, and a reduction in loss can be achieved.

[Fourth Embodiment of Optical Fiber Manufacturing Method]
A fourth embodiment of the optical fiber manufacturing method according to the present invention will be described with reference to FIG.
FIG. 6 is a flowchart for explaining an optical fiber manufacturing method.

  In the optical fiber manufacturing method according to the present embodiment, as shown in FIG. 6, first, in a first process, a core part, a first cladding part having a refractive index smaller than that of the core part, and the first cladding part An optical fiber preform composed of a second cladding part having a refractive index equal to or smaller than that of the first cladding part is produced (step S41). Here, an optical fiber preform can be manufactured by using the VAD method or the like.

  Next, in the second (second process) of the flowchart, a plurality of holes that do not penetrate through are provided in the outer wall portion of the optical fiber preform manufactured in the first process (step S42). For example, it is possible to provide a hole only in the region of the second cladding part by the ultrasonic vibration grinding in which the length of the drill to be ground is adjusted.

  Subsequently, in a third process, an optical fiber having a refractive index that is equal to or smaller than that of the first cladding part manufactured in the first process and manufactured in the first process. A glass tube having a size that can be attached to the outside of the preform is produced (step S43). For example, it is possible to produce a glass tube by using the method for producing a quartz glass tube described in Patent Document 3.

  Further, in the fourth process, a plurality of holes that do not penetrate through are provided in the inner wall portion of the glass tube produced in the third process (step S44). For example, it is possible to provide a hole only in the region of the second cladding part by the ultrasonic vibration grinding in which the length of the drill to be ground is adjusted.

  Thereafter, in the fifth process, the optical fiber preform produced in the second process is inserted inside the glass tube produced in the fourth process (step S45). The glass tube into which the optical fiber preform obtained by the five processes is inserted is melt-drawn (drawn) (step S46).

  Therefore, it is possible to manufacture the optical fiber according to the first embodiment having the second cladding portion made of the two glass layers by the manufacturing procedure described above.

  Therefore, according to the optical fiber manufacturing method according to the present embodiment, a plurality of holes that cannot be penetrated are provided in the wall portions of the glass tube and the optical fiber preform. Since it is short, an optical fiber having a structure having holes in the cross section of the optical fiber can be produced in a long length without causing an axis deviation due to ultrasonic vibration grinding, and mass production becomes possible. In addition, entry of impurities into the holes can be suppressed, and a reduction in loss can be achieved.

A first embodiment of the optical fiber according to the present invention will be described with reference to FIG.
FIG. 7 is a diagram showing structural parameters of the optical fiber. FIG. 7 shows the second cladding including the core portion 11, the first cladding portion 12, and the eight holes 14 in the cross section of the optical fiber according to the present embodiment. An enlargement of part 13 is shown.
In the present embodiment, in the optical fiber, the number of glass layers of the second cladding portion 13 is one, and the holes 14 provided in the wall portion of the second cladding portion 13 are arranged at equal intervals in the circumferential direction. The holes 14 have a circular cylindrical shape (columnar shape).

As shown in FIG. 7, to define the diameter of the core portion 11 2a ₁ and the diameter of the first cladding portion 12 2a ₂ and defines, it defines the diameter of the second cladding part 13 and 2a _3. In addition, the diameter of the hole 14 provided in the second cladding part 13 is defined as 2R.

  In this embodiment, the core portion 11 has a step-type refractive index distribution having a relative refractive index difference of 0.35% with respect to the first cladding portion 12. Moreover, the refractive index of the 1st clad part 12, the 2nd clad part 13, and the 3rd clad part (not shown) surrounding the circumference | surroundings of the 2nd clad part 13 was made into the refractive index of pure quartz glass.

FIG. 8 shows an example of the ratio P of the holes included in the second cladding part per unit length of the optical fiber. In FIG. 8, a solid line indicates a case where there are 10 holes, a one-dot broken line indicates a case where there are eight holes, and a two-dot broken line indicates a case where there are six holes. Here, the radius R of the hole provided in the second cladding portion is 0.5 times the core radius a ₁ , and the difference between the radius a ₃ of the second cladding portion and the radius a ₂ of the first cladding portion is the core radius a. _When equal to ₁ , the ratio P of the holes included in the second cladding portion in the length a ₁ of the optical fiber can be obtained by calculation from the equation (1) using the number N of holes included in the cross section of the optical fiber. Is possible.

  Here, an optical fiber having only a core portion and a clad portion based on the conventional material addition, that is, the normalized electric field strength and the core portion in the case where no hole is present in the second clad portion in the optical fiber according to the present embodiment. The relationship between the normalized radius and the radius will be described with reference to FIG. However, the characteristic of FIG. 9 shows an electric field distribution at a wavelength of 1550 nm.

From FIG. 9, it can be seen that, for example, at the point where the normalized radius is 1.5, the normalized electric field strength attenuates to 20% or less. That is, when the radius a ₂ of the first cladding part is 1.5 times the radius a ₁ of the core part, a normalized electric field strength of about 20% exists.

The relationship of the mode field diameter at a wavelength of 1550 nm with respect to the ratio a ₂ / a ₁ of the radius of the first cladding portion to the radius of the core portion will be described with reference to FIG. However, the characteristic of FIG. 10 shows the case where there are six holes.

FIG. 10 shows that the mode field diameter rapidly decreases in the region where the ratio of the radius of the first cladding part to the radius of the core part a ₂ / a ₁ is 2 or less. This is because the confinement of the electric field distribution in the first cladding portion is improved because the refractive index of air contained in the hole provided in the second cladding portion is smaller than that of pure quartz glass. .

Further, from FIG. 9, the normalized electric field strength in the conventional optical fiber in the region where the ratio a ₂ / a ₁ of the radius of the first cladding portion to the radius of the core portion is 2 is about 8%.

Therefore, in the optical fiber according to the present invention, the mode field diameter characteristic equivalent to that of the conventional optical fiber is maintained by setting the radius a ₂ of the first cladding portion in a region where the electric field distribution intensity is 8% or less. It becomes possible. Conversely, by setting the radius a ₂ of the first cladding part in a region where the intensity of the electric field distribution is 8% or more, confinement of the electric field distribution near the core part can be improved and the mode field diameter can be reduced. It becomes possible.

Here, the relationship of the chromatic dispersion at the wavelength of 1550 nm with respect to the ratio a ₂ / a ₁ of the radius of the first cladding part to the radius of the core part will be described with reference to FIG. However, the characteristic of FIG. 11 shows the case where there are six holes.

From FIG. 11, it can be seen that the chromatic dispersion increases rapidly in the region where the ratio of the radius of the first cladding part to the radius of the core part a ₂ / a ₁ is 2.5 or less. This is because the refractive index of air contained in the hole provided in the second cladding portion is smaller than the refractive index of pure silica glass, confinement of the electric field distribution to the first cladding portion occurs, and the waveguide dispersion characteristic is This is due to being affected.

Further, from FIG. 9, the normalized electric field strength in the conventional optical fiber in the region where the ratio a ₂ / a ₁ of the radius of the first cladding portion to the radius of the core portion is 2.5 is about 3%.

Therefore, in the optical fiber according to the present invention, by setting the radius a ₂ of the first cladding portion in a region where the electric field distribution intensity is 3% or less, the same wavelength dispersion characteristic as that of the conventional optical fiber is maintained. Is possible. Conversely, the wavelength dispersion characteristic can be varied by setting the radius a ₂ of the first cladding portion to a region where the intensity of the electric field distribution is 3% or more. In particular, the chromatic dispersion characteristic of 30 ps / nm · km or more at a wavelength of 1550 nm is a characteristic that cannot be realized with a conventional optical fiber due to restrictions on the amount of change in refractive index. One.

  The relationship of the bending loss at a wavelength of 1550 nm with respect to the ratio P of the holes included in the second cladding part per unit length of the optical fiber will be described with reference to FIG. In FIG. 12, the vertical axis indicates the loss increase amount when bending with a radius of 5 mm is applied 10 turns. Here, the ratio P of the holes contained in the second cladding part per unit length of the optical fiber is 0% indicates a conventional optical fiber having only the core part and the cladding part based on the material addition.

  From FIG. 12, it can be seen that better bending loss characteristics can be obtained as the ratio P of the holes contained in the second cladding portion per unit length of the optical fiber increases. This is because, in the optical fiber according to the present invention, since the refractive index of air contained in the hole provided in the second cladding portion is smaller than the refractive index of pure silica glass, the second cladding per unit length of the optical fiber. This is because the effective refractive index of the second cladding portion is reduced and the confinement of the electric field distribution in the first cladding portion is improved by increasing the ratio P of the holes included in the portion. The effect is independent of the hole shape and the number of holes.

  From FIG. 12, it can be seen that when the ratio P of the holes included in the second cladding portion per unit length of the optical fiber is about 15%, the bending loss becomes 1/10 compared to the conventional optical fiber.

  Therefore, according to the optical fiber according to the present embodiment, it is possible to have a structure having no holes at both ends, and the sealing process or light at both ends of the optical fiber, which is necessary for the existing optical fiber with holes, is possible. The attachment work of the sealing member to both ends of the fiber becomes unnecessary. At the time of mechanical splice connection or the like, it is possible to omit the process of removing the sealing portions at both ends of the optical fiber and the process of removing the sealing members attached to both ends of the optical fiber. As a result, handleability is improved as compared with existing optical fibers with holes. Furthermore, by adjusting the number of holes, the circumferential arrangement of the holes, and the arrangement of the holes in the axial direction, it is possible to control wavelength dispersion and mode field diameter, and when the optical fiber is bent. It is possible to reduce the increase in loss that occurs.

  INDUSTRIAL APPLICABILITY The present invention can be used for an optical fiber that can control wavelength dispersion and a mode field diameter and can be manufactured in a long length, and a manufacturing method thereof.

It is a figure which shows 1st embodiment of the optical fiber which concerns on this invention. It is sectional drawing of other embodiment of the optical fiber which concerns on this invention. It is a flowchart for demonstrating 1st embodiment of the optical fiber manufacturing method which concerns on this invention. It is a flowchart for demonstrating 2nd embodiment of the optical fiber manufacturing method which concerns on this invention. It is a flowchart for demonstrating 3rd embodiment of the optical fiber manufacturing method which concerns on this invention. It is a flowchart for demonstrating 4th embodiment of the optical fiber manufacturing method which concerns on this invention. It is a figure which shows the structural parameter of 1st Example of the optical fiber which concerns on this invention. It is a figure which shows an example of the ratio P of the hole contained in the 2nd clad part per unit length of an optical fiber. It is a figure which shows the relationship of the normalized radius with respect to the normalized electric field strength and the radius of a core part. It is a diagram showing the relationship between mode field diameter at the wavelength 1550nm to the radius of the ratio a ₂ / a ₁ of the first cladding portion to the radius of the core portion. Is a diagram showing the relationship between chromatic dispersion at a wavelength of 1550nm to the radius of the ratio a ₂ / a ₁ of the first cladding portion to the radius of the core portion. It is a figure which shows the relationship of the bending loss in wavelength 1550nm with respect to the ratio P of the hole contained in the 2nd clad part per unit length of an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,100 Optical fiber 11 Core part 12 1st clad part 13 2nd clad part 14,114 Hole 15 3rd clad part

Claims (7)

The core,
A first cladding portion having a refractive index smaller than that of the core portion and surrounding the core portion;
A second clad having a plurality of holes in each wall portion of one or more glass layers having a refractive index equal to or smaller than that of the first clad portion and surrounding the first clad portion And
A third clad part having a refractive index equal to or smaller than that of the first clad part and surrounding the second clad part;
The plurality of holes are formed at a plurality of locations along the axial direction at a plurality of locations in the circumferential direction, and are formed to extend in a direction from the first cladding portion to the third cladding portion. And optical fiber. The optical fiber according to claim 1, wherein the plurality of holes are formed at equal intervals in the circumferential direction. 3. The optical fiber according to claim 1, wherein the radius of the first cladding portion is set in a region where the intensity of the electric field distribution is 3% or more. A first process for producing an optical fiber preform having a core portion and a first cladding portion having a refractive index smaller than that of the core portion;
A glass tube having a refractive index that is equal to or smaller than that of the first cladding part and that can be attached to the outside of the optical fiber preform produced by the first process. A second process to produce;
A third process of providing a plurality of punched holes in the wall of the glass tube produced in the second process;
Outside the glass tube having a plurality of holes made in the third process and having a refractive index equal to or smaller than that of the first clad part made in the first process. A fourth process for producing a glass tube of a size that can be attached;
A glass tube having a plurality of holes produced by the third process is inserted into the glass tube produced by the fourth process, and the glass tube having the plurality of holes is inserted by the first process. A fifth process of inserting the fabricated optical fiber preform;
The optical fiber according to any one of claims 1 to 3, further comprising a sixth process of melt-drawing a glass tube into which the optical fiber preform obtained in the fifth process is inserted. An optical fiber manufacturing method for manufacturing. An optical fiber preform comprising a core part, a first cladding part having a refractive index smaller than that of the core part, and a second cladding part having a refractive index equal to or smaller than that of the first cladding part. A first process for producing
A second process of providing a plurality of non-penetrating holes in the outer wall of the optical fiber preform produced in the first process;
The optical fiber preform having the refractive index which is equal to or smaller than the first clad part produced by the first process and is attached to the outside of the optical fiber preform produced by the second process. A third process for producing a glass tube of a possible size;
A fourth process of inserting the optical fiber preform produced in the second process inside the glass tube produced in the third process;
The optical fiber according to any one of claims 1 to 3, further comprising a fifth process of melt-drawing a glass tube into which the optical fiber preform obtained in the fourth process is inserted. An optical fiber manufacturing method for manufacturing. A first process for producing an optical fiber preform having a core portion and a first cladding portion having a refractive index smaller than that of the core portion;
The optical fiber preform having a refractive index that is equal to or smaller than that of the first cladding part manufactured in the first process and that is attached to the outside of the optical fiber preform manufactured in the first process. A second process for producing a glass tube of a possible size;
A third process of providing a plurality of holes that do not penetrate through the inner wall of the glass tube produced by the second process;
A fourth process of inserting the optical fiber preform produced in the first process inside the glass tube produced in the third process;
The optical fiber according to any one of claims 1 to 3, further comprising a fifth process of melt-drawing a glass tube into which the optical fiber preform obtained in the fourth process is inserted. An optical fiber manufacturing method for manufacturing. An optical fiber preform comprising a core part, a first cladding part having a refractive index smaller than that of the core part, and a second cladding part having a refractive index equal to or smaller than that of the first cladding part. A first process for producing
A second process of providing a plurality of non-penetrating holes in the outer wall of the optical fiber preform produced in the first process;
The optical fiber preform having a refractive index that is equal to or smaller than that of the first cladding part manufactured in the first process and that is attached to the outside of the optical fiber preform manufactured in the first process. A third process for producing a glass tube of a possible size;
A fourth process of providing a plurality of non-piercing holes in the inner wall of the glass tube produced in the third process;
A fifth process of inserting the optical fiber preform produced in the second process inside the glass tube produced in the fourth process;
The optical fiber according to any one of claims 1 to 3, further comprising a sixth process of melt-drawing a glass tube into which the optical fiber preform obtained in the fifth process is inserted. An optical fiber manufacturing method for manufacturing.

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