JP2011219339A - Method for producing optical fiber and optical fiber preform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an optical fiber in which the improvement of yield is achieved, and an optical fiber preform for producing the optical fiber.SOLUTION: A plurality of grooves 140A whose bottom faces have U-shape are formed to the side faces of a core material rod 100A by a rotary blade whose cross-section has U-shape. Then, a jacket tube (second member) is integrated so as to cover the side faces of the core material rod 100A formed with the grooves 140A whose bottom faces have U-shape to form an optical fiber preform, and thereafter, this is drawn to produce an optical fiber in which the plurality of grooves 140A are made into a plurality of vacancies arranged along the outer circumference of a clad region 120A. Thus, the breakage of the core material rod 100A on the formation of the U-shaped grooves 140A can be prevented. Further, the accumulation of dust such as abrasive grain material or the like on the bottom faces of the grooves 140A can be prevented, and the generation of spike and disconnection on the drawing of the optical fiber preform can be reduced.

Description

  The present invention relates to an optical fiber manufacturing method and an optical fiber preform.

  Generally, an optical fiber is manufactured by drawing an optical fiber preform. The optical fiber preform is manufactured by an OVD (Outside Vapor Deposition) method, an MCVD (Modified Chemical Vapor Deposition) method, a VAD (Vapor phase Axial Deposition) method, a rod in collapse method, or the like.

  By the way, a single mode optical fiber has a very large transmission capacity compared to a multimode optical fiber because it has no mode dispersion. However, the single mode optical fiber has a large allowable bending radius, and is difficult to use particularly in a place where there are many bends such as indoors. In addition, it is possible to reduce the allowable bending radius by devising the refractive index distribution, but there are problems that the mode field diameter becomes small and the multimode becomes easy. On the other hand, the hole-assisted optical fiber has a structure in which holes are provided in a conventional single mode optical fiber, and the hole confinement effect can be enhanced by the holes and the bending loss can be reduced. Are known. This hole-assisted optical fiber is a method of drawing after a through-hole serving as a hole in an optical fiber preform, or a rod provided with a groove serving as a hole is integrated with a cylindrical jacket. It is manufactured by a method of drawing (see, for example, Patent Documents 1 and 2).

JP 2002-321935 A International Publication No. 2004/092793

  However, an optical fiber provided with holes, such as the above-described hole assist optical fiber, has a problem that it is difficult to process and the yield tends to decrease.

  The present invention has been made in view of the above, and an object of the present invention is to provide an optical fiber manufacturing method in which the yield is improved and an optical fiber preform for manufacturing the optical fiber.

  In order to achieve the above object, a method of manufacturing an optical fiber according to the present invention includes a core region extending along the optical axis, a cladding region covering the core region, and a jacket region surrounding the optical cladding region, A method of manufacturing an optical fiber by drawing an optical fiber preform provided with a plurality of holes along an outer periphery of a cladding region, wherein a cross section is formed on a side surface of a first member constituting the core region and the cladding region. A U-shaped blade is used to form a plurality of U-shaped grooves on the bottom surface along the optical axis, and the first member is inserted into the cylindrical second member forming the jacket region. And an optical fiber preform is manufactured by integrating them.

  According to the optical fiber manufacturing method, a plurality of U-shaped grooves are formed on the side surface of the first member by the blade having a U-shaped cross section. Then, after forming the optical fiber preform by integrating the second member so that the bottom surface covers the side surface of the first member in which the U-shaped groove is formed, the plural members are drawn. An optical fiber having a plurality of holes arranged along the outer periphery of the cladding region is manufactured. According to this manufacturing method, when the U-shaped groove is formed, the first member can be prevented from being damaged such as being cracked or chipped. Also, compared to the case where corners are provided on the bottom surface of the groove, dust can be prevented from accumulating on the bottom surface of the groove, and the occurrence of spikes and disconnections when drawing the optical fiber preform is reduced. can do.

  Here, as a configuration that effectively exhibits the above-described action, specifically, an aspect in which the depth of the groove is larger than the width of the groove is exemplified.

  Further, it is preferable that the ratio of the groove depth to the groove width is 1.5 or more.

  As described above, when the groove depth is increased with respect to the groove width and the ratio is particularly 1.5 or more, the groove is deformed when the first member and the second member are integrated. This can be prevented, and further improvement in yield can be achieved.

  An optical fiber preform according to the present invention includes a core region extending along the optical axis, a cladding region covering the core region, and a jacket region surrounding the cladding region, and along the outer periphery of the cladding region. An optical fiber preform provided with a plurality of holes, wherein the cross-sectional shape of the holes is noncircular in the cross section perpendicular to the optical axis, and the inner surface on the cladding region side is U-shaped And

  According to the above optical fiber preform, since the cross-sectional shape of the hole is non-circular and the inner surface on the cladding region side is U-shaped, the occurrence of cracks and chips when forming the hole is avoided. Can be suppressed.

  Here, as a configuration that effectively exhibits the above-described operation, specifically, an aspect in which the inner surface of the hole on the jacket region side is rectangular in a cross section perpendicular to the optical axis.

  In addition, the air holes may have an aspect in which the major axis extends along the radial direction of the optical fiber preform and the minor axis extends along the circumferential direction of the optical fiber preform.

  Here, it is preferable that the ratio of the length of the long axis to the length of the short axis is 1.5 or more.

  As described above, the depth of the groove is increased with respect to the width of the groove, and the optical fiber is manufactured using the optical fiber preform whose ratio is particularly 1.5 or more, thereby further improving the yield. be able to.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the optical fiber by which the improvement of the yield was achieved, and the optical fiber preform | base_material for manufacturing this optical fiber are provided.

1 is a schematic configuration diagram of an optical fiber according to an embodiment of the present invention. It is sectional drawing of the optical fiber which concerns on embodiment of this invention. It is sectional drawing of the 1st member which comprises the optical fiber preform for manufacturing the optical fiber of FIG. It is sectional drawing of the optical fiber preform for manufacturing the optical fiber of FIG. It is sectional drawing of the 1st member which comprises the optical fiber preform for manufacturing the optical fiber which concerns on a comparative example. It is sectional drawing of the optical fiber preform for manufacturing the optical fiber which concerns on a comparative example.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a schematic configuration diagram of an optical fiber according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of the optical fiber according to the present embodiment. Optical fiber 100 shown in FIG. 1 includes a core 110 extending along the optical axis _{A X,} the cladding 120 which covers the periphery of the core 110, a jacket 130 covering the cladding 120, provided along the outer periphery of the clad 120 And a plurality of holes 140. That is, the optical fiber 100 according to the present embodiment is a single mode optical fiber, and is called a hole-assisted optical fiber (HAF). In the optical fiber 100, the incident laser light propagates mainly in the core 110 due to the refractive index difference between the core 110 and the clad 120. Further, the bending loss characteristics are improved by the holes 140 formed around the core 110.

  The core 110, the clad 120, and the jacket 130 that constitute the optical fiber 100 are each made of quartz glass, but have different refractive indexes, and the relative refractive index of the central core region 110 with respect to the clad 120 is 0.35%. The relative refractive index of the clad 120 with respect to the jacket 130 is adjusted to be substantially the same. Further, as shown in FIG. 2, the air hole 140 provided between the clad 120 and the jacket 130 has a substantially circular cross-sectional shape perpendicular to the optical axis, and 10 holes along the outer periphery of the clad 120. One is provided.

  A method for manufacturing the optical fiber 100 will be described below. First, a core material rod (first member) 100A for forming the core 110 and the clad 120 shown in FIGS. 1 and 2 is prepared. This core material rod is made of quartz glass and has a core region 110A as the core 110 as the center, and its periphery is covered with a cladding region 120A that is made of quartz glass and becomes the cladding 120, and is manufactured by, for example, the VAD method. Things are used. Specifically, in this core material rod, the relative refractive index of the central core region 110A with respect to the cladding material is 0.35%, and the outer diameter of the cladding region 120A is 4.3 with respect to the outer diameter of the core region 110A. It has been doubled.

  Next, a plurality of grooves are formed on the side surface of the core rod 100A along the optical axis. Specifically, the core material rod 100A is cut by traversing a rotating blade from the side surface, and 10 grooves are formed on the surface at equal intervals with respect to the side surface of the core material rod 100A. At this time, the tip shape of the rotary blade is preferably a U-shaped cross section. FIG. 3 shows a cross section perpendicular to the optical axis in the core material rod 100A in which a groove is formed by this rotating blade. As shown in FIG. 3, in the core material rod 100A, in the clad region 120A that becomes the clad 120, ten grooves 140A by the rotating blade are formed.

  The shape of the groove 140A reflects the shape of the rotating blade, and its cross-sectional shape is U-shaped. Further, in the groove 140A formed by the rotating blade, the relationship between the width W and the depth D is D> W. More specifically, the groove 140A is formed so that W: D = 1: 1.5. The ratio of the depth D to the width W is preferably 1.5 or more.

  Next, the core material rod 100A after the processing of the groove 140A by the rotating blade is immersed in an HF aqueous solution and the surface layer is etched in order to remove impurities attached by grinding before the next process.

  Next, a jacket tube (second member, jacket region) 130A serving as a jacket 130 in the optical fiber 100 is prepared, and jacket collapse is performed using the core rod 100A provided with ten grooves 140A as a central rod. In this collapsing process, the core material rod 100A and the jacket tube 130A are heated and integrated. In addition, in order to remove impurities which may remain on the surface of the core material rod 100A before this heat integration, a chlorine heat treatment may be performed.

  A cross-sectional view of the optical fiber preform obtained after the jacket collapse is shown in FIG. As shown in FIG. 4, in the optical fiber preform 100B, the groove 140A provided on the surface of the cladding region 120A is covered with a jacket region 130A in which the region that has been opened becomes a jacket 130, thereby providing a hole 140B. Remain as. As a result, the hole 140B has a non-circular shape, and the inner surface on the cladding region 120A side forming the cladding 120 is U-shaped, while the inner surface on the jacket region 130A side is rectangular. Since the shape of the hole 140B of the optical fiber preform 100B is based on the shape of the groove 140A, the major axis is the radial direction of the optical fiber preform 100B (that is, the groove in the core rod 100A in FIG. 3). The minor axis is the circumferential direction of the optical fiber preform 100B (that is, the direction corresponding to the groove width W in the core rod 100A in FIG. 3), and the major axis is shorter. The length is longer than that of the shaft.

  And the optical fiber 100 shown in FIG.1 and FIG.2 is obtained by drawing this optical fiber preform | base_material 100B. In this drawing process, due to the influence of the surface tension acting on the surface of the hole 140B, the region provided with the corners of the inner surface of the hole 140B disappears completely, and the shape of the hole 140 in the optical fiber 100 is almost true. Yen. An elliptical hole may be obtained by slightly reflecting the shape of the optical fiber preform, but it does not affect the characteristics of the optical fiber.

  Next, as a comparative example, a case will be described in which an optical fiber preform in which the holes provided in the optical fiber preform are square is manufactured and the optical fiber is manufactured by drawing this.

  As a method of manufacturing an optical fiber preform having a square hole, when forming ten grooves on the surface of the core rod as in the above embodiment, the cross-sectional shape is replaced with a U-shaped blade. There is a method using a square blade. Thereby, as shown in FIG. 5, the rectangular groove | channel 141A is formed in the side surface of the core material rod 200A. Then, by inserting the core material rod 200A into the jacket tube and performing jacket collapse, an optical fiber preform 200B shown in FIG. 6 is obtained. In this optical fiber preform 200B, the holes 141B are square on both the inner surface of the cladding region 120A side (inside the optical fiber preform 100B) and the inner surface of the jacket region 130A side (outside of the optical fiber preform 100B). It becomes.

  In the case of manufacturing the optical fiber preform 200B as described above, when the groove is formed on the core material rod 200A, the core material rod 200A is formed from the corner formed on the bottom surface of the groove. It was confirmed that the core material rod 200A was cracked and cracked, or the core material rod 200A was broken, and the core material rod 200A was often damaged. In addition, ceramic-based abrasives used during grinding are likely to accumulate on the bottom surface of the groove, and are accumulated in the groove during etching by immersion in an HF aqueous solution after the groove is processed and before chlorination is performed before jacket collapse. It is difficult to completely remove the abrasive material. And it was confirmed that foreign materials, such as the abrasives which remained in this groove | channel, lead the spike and disconnection in a drawing process.

  Further, in order to realize an optical fiber having the same structure, the distance between the bottom surface of the groove of the core material rod after processing the groove and the core region is equal to each other, and the cross-sectional areas of the core region 110A and the cladding region 120A are equal to each other. When the core material rod 100A and the core material rod 200A are processed as described above (in this case, the diameter of the core material rod 100A is larger than that of the core material rod 200A) and the jacket collapse process is performed, the shape of the groove 141A is The core material rod 200A which is a square shape has a larger deformation of the shape of the groove 141A (hole 141B) in the jacket collapse process than the core material rod 100A. Compared with the core material rod 100A, in the core material rod 200A, the width of the clad region 120A between the holes and in contact with the jacket region 130A is smaller than the width of the groove 141A. This is because when the rod 200A is heated, it is relatively difficult to maintain its shape.

  As described above, according to the manufacturing method of the optical fiber 100 according to the present embodiment, the bottom surface is U-shaped with respect to the side surface of the core material rod (first member) 100A by the rotating blade having a U-shaped cross section. A plurality of grooves 140A are formed. Then, after forming the optical fiber preform 100B by integrating the jacket tube (second member) 130A so as to cover the side surface of the core material rod 100A in which the bottom surface of the U-shaped groove 140A is formed, this is drawn. By drawing the optical fiber 100, the plurality of grooves 140A become a plurality of holes 140B arranged along the outer periphery of the cladding region 120A. According to this manufacturing method, when the U-shaped groove 140A is formed, the core material rod 100A is damaged because the core material rod 100A is cracked from the groove or the core material rod 100A is chipped. Can be prevented. Further, since the bottom surface of the groove 140A is U-shaped, it is possible to prevent accumulation of dust such as an abrasive material on the bottom surface of the groove 140A, compared to the case where corners are provided on the bottom surface, The occurrence of spikes and disconnections when drawing the optical fiber preform 100B can be reduced.

  Further, when the depth D is increased with respect to the width W of the groove 140A and the ratio is particularly 1.5 or more, the groove is deformed when the core material rod 100A and the jacket tube 130A are integrated. Can be prevented, and further improvement in yield can be achieved.

  Further, according to the optical fiber preform 100B according to the present embodiment, the hole 140B has a non-circular cross-sectional shape, and the inner surface on the cladding region 120A side is U-shaped. The occurrence of cracks and chips at the time can be suppressed.

  As mentioned above, although embodiment of this invention was described, the manufacturing method of an optical fiber and optical fiber preform which concern on this invention are not limited to said aspect, A various change is possible.

  For example, in the above embodiment, the application to the hole-assisted optical fiber has been described. However, application to other optical fibers is also possible. As an application to other optical fibers, for example, a holey fiber can be cited.

DESCRIPTION OF SYMBOLS 100 ... Optical fiber, 100A ... Core material rod (1st member), 100B ... Optical fiber preform | base_material, 110A ... Core area | region, 120A ... Cladding area | region, 130A ... Jacket area | region (2nd member), 140 ... Hole 140A ... groove.

Claims (7)

An optical fiber mother having a core region extending along the optical axis, a cladding region covering the core region, and a jacket region surrounding the optical cladding region, and having a plurality of holes along the outer periphery of the cladding region A method for producing an optical fiber by drawing a material,
Using a blade having a U-shaped cross section on the side surface of the first member constituting the core region and the clad region, a plurality of U-shaped grooves having a bottom surface are formed along the optical axis,
An optical fiber manufacturing method, wherein an optical fiber preform is manufactured by inserting and integrating the first member into a cylindrical second member forming the jacket region.   The optical fiber manufacturing method according to claim 1, wherein a depth of the groove is larger than a width of the groove.   The method of manufacturing an optical fiber according to claim 2, wherein a ratio of the depth of the groove to the width of the groove is 1.5 or more. An optical fiber mother having a core region extending along the optical axis, a cladding region covering the core region, and a jacket region surrounding the optical cladding region, and having a plurality of holes along the outer periphery of the cladding region Material,
In the cross section perpendicular to the optical axis, the hole has a noncircular cross section, and the inner surface of the clad region side is U-shaped.   The optical fiber preform according to claim 4, wherein an inner surface of the hole on the jacket region side is rectangular in a cross section perpendicular to the optical axis.   5. The optical fiber according to claim 4, wherein the hole has a major axis extending along a radial direction of the optical fiber preform and a minor axis extending along a circumferential direction of the optical fiber preform. Base material. The optical fiber preform according to claim 6, wherein a ratio of the length of the major axis to the length of the minor axis is 1.5 or more.

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