JP5879842B2 - Optical fiber manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing an optical fiber having a plurality of holes extending in the fiber axial direction.

  An optical fiber having a plurality of holes extending in the fiber axis direction is known. Such an optical fiber is manufactured by drawing an optical fiber preform having a hole extending in the axial direction as described in Patent Documents 1 to 5.

  In the optical fiber manufacturing methods described in Patent Documents 1 to 3, the optical fiber preform is drawn while introducing the Cl gas or the like into the pores of the optical fiber preform and pressurizing the pores. In these documents, by introducing Cl gas or the like into the pores, it is possible to remove the OH groups adhering to the pore wall surface and the water existing in the glass near the pore wall surface, and light with low transmission loss. It is said that the fiber can be manufactured.

  In the optical fiber manufacturing method described in Patent Document 4, the inside of the hole of the optical fiber preform is dried, then both ends of the hole are sealed, and the optical fiber preform is drawn to manufacture the optical fiber. To do. In this document, it is possible to draw an optical fiber with a low transmission loss because it is possible to perform drawing while the inside of a hole sealed with an optical fiber preform is dried.

  In the optical fiber manufacturing method described in Patent Document 5, the pressure in the holes of the optical fiber preform is controlled so that the plurality of holes in the optical fiber preform are reduced to a predetermined hole diameter after drawing. The optical fiber preform is drawn while manufacturing an optical fiber.

JP 2002-145634 A JP 2002-249335 A Japanese Patent Laid-Open No. 2003-313045 JP 2002-211941 A JP 2003-81656 A

  In the optical fiber manufacturing methods described in Patent Documents 1 to 3, since harmful gas is used, the management cost of equipment is high. In the optical fiber manufacturing method described in Patent Document 4, since both ends of the holes of the optical fiber preform are sealed and drawn, the degree of freedom in controlling the hole diameter of the optical fiber is low. Further, in the optical fiber manufacturing method described in Patent Document 5, since the hole diameter is reduced during drawing, the hole diameter of the optical fiber preform is designed to be large, so that the hole wall surface of the optical fiber preform is formed on the hole wall surface. Many OH groups are likely to be bonded, and therefore, transmission loss of an optical fiber obtained by drawing is likely to increase.

  The present invention has been made to solve the above-described problems, and can reduce the amount of harmful gas used in drawing, easily manufacture an optical fiber having a desired hole diameter and low transmission loss. An object is to provide a method that can be used.

  An optical fiber manufacturing method of the present invention is a method for manufacturing an optical fiber having a hole extending in the axial direction by drawing an optical fiber preform having a hole extending in the axial direction. The surface area of the hole of the fiber preform is S, the radius of the optical fiber preform is R, the volume of the optical fiber preform including the hole volume is V, the surface area of the hole of the optical fiber is S ′, When the radius of the fiber is R ′ and the volume of the optical fiber including the hole volume is V ′, the light is such that ((S ′ / V ′) / (S / V)) is larger than R / R ′. An optical fiber is manufactured by drawing a fiber preform. More preferably, the optical fiber preform is drawn so that ((S ′ / V ′) / (S / V)) is larger than 2R / R ′ to manufacture an optical fiber.

  In the optical fiber manufacturing method of the present invention, in the cross section of the optical fiber, a / b is not less than 0.84, where a is a radial hole length and b is an angular hole length. It is preferable to produce an optical fiber by drawing an optical fiber preform so that More preferably, the optical fiber is manufactured by drawing an optical fiber preform so that a / b is 0.90 or more.

  The optical fiber manufacturing method of the present invention can reduce the amount of harmful gas used during drawing, and can easily manufacture an optical fiber having a desired hole diameter and low transmission loss.

It is a figure which shows the cross-section of each of the optical fiber preform | base_material 10 and the optical fiber 20 in the optical fiber manufacturing method of a comparative example. It is a figure which shows the cross-section of each of the optical fiber preform | base_material 10 and the optical fiber 20 in the optical fiber manufacturing method of this embodiment. It is a graph which shows the relationship between transmission loss (DELTA) ( _alpha) 1.38 in the wavelength of 1.38 micrometers by an OH group of an optical fiber, and a hole expansion coefficient. 2 is a schematic view and a photograph of a cross-sectional structure of the optical fiber 20. 2 is a schematic view and a photograph of a cross-sectional structure of the optical fiber 20. 2 is a schematic view and a partially enlarged view of a cross-sectional structure of the optical fiber 20. FIG. It is a graph which shows the relationship between transmission loss (DELTA) ( _alpha) 1.38 in wavelength 1.38micrometer by the OH group of an optical fiber, and the ellipticity a / b of the hole of an optical fiber.

  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 diagram showing cross-sectional structures of an optical fiber preform 10 and an optical fiber 20 in an optical fiber manufacturing method of a comparative example. As shown in FIG. 2A, an optical fiber preform 10 includes a core 11 made of glass, a clad 12 made of glass surrounding the core 11, and formed in the clad 12 and extending in the axial direction. And a plurality of existing holes 13. The plurality of holes 13 are provided at regular intervals on the circumference of a circle centered on the core 11 and have a substantially circular cross section.

  As shown in FIG. 2B, the optical fiber 20 includes a core 21 made of glass, a clad 22 made of glass surrounding the core 21, and formed in the clad 22 and extending in the axial direction. A plurality of holes 33. The plurality of holes 23 are provided at regular intervals on the circumference of a circle centered on the core 21 and have a substantially circular cross section.

The cores 11 and 21 may be quartz glass to which GeO ₂ is added. The clads 12 and 22 may be quartz glass to which a halogen element is added. Although the number of holes 13 in the optical fiber preform 10 and the number of holes 23 in the optical fiber 20 are 10 in the drawing, the number is not limited to this. Such an optical fiber 20 is called HAF (Hole-Assisted Fiber).

  The optical fiber 20 can be manufactured by drawing the optical fiber preform 10. In the optical fiber manufacturing method of the comparative example, the cross section of the optical fiber preform 10 and the cross section of the optical fiber 20 are similar to each other. On the other hand, in the optical fiber manufacturing method of this embodiment, as shown in FIG. 2, the cross section of the optical fiber preform 10 and the cross section of the optical fiber 20 are not similar to each other.

  FIG. 2 is a diagram showing cross-sectional structures of the optical fiber preform 10 and the optical fiber 20 in the optical fiber manufacturing method of the present embodiment. In the optical fiber manufacturing method of the present embodiment, the ratio of the hole diameter to the cladding diameter is increased during drawing. Specifically, it is as follows.

  The surface area of the holes 13 in the optical fiber preform 10 is S, the radius of the optical fiber preform 10 is R, and the volume of the optical fiber preform 10 including the volume of the holes 13 is V. Further, the surface area of the hole 23 of the optical fiber 20 is S ′, the radius of the optical fiber 20 is R ′, and the volume of the optical fiber 20 including the volume of the hole 23 is V ′. At this time, the optical fiber 20 is manufactured by drawing the optical fiber preform 10 so that ((S ′ / V ′) / (S / V)) is larger than R / R ′. More preferably, the optical fiber preform 10 is drawn so that ((S ′ / V ′) / (S / V)) is larger than 2R / R ′ to manufacture the optical fiber 20.

FIG. 3 is a graph showing the relationship between the transmission loss Δα _1.38 and the hole expansion coefficient at a wavelength of 1.38 μm due to the OH group of the optical fiber. The hole expansion coefficient is the rate of change of the ratio of the hole diameter to the cladding diameter due to drawing. As can be seen from the figure, the larger the hole expansion coefficient, the smaller the optical fiber transmission loss Δα _1.38 .

  Compared to the optical fiber manufacturing method of the comparative example, in the optical fiber manufacturing method of the present embodiment, when manufacturing the optical fiber 20 having the same cross-sectional structure, the area of the wall surface of the hole 13 of the optical fiber preform 10 is smaller. It is small and the amount of OH groups taken into the wall surface of the hole 13 can be reduced. The larger the hole expansion coefficient, the smaller the amount of OH groups taken into the wall surface of the hole 23 of the optical fiber 20. Therefore, in the optical fiber manufacturing method of this embodiment, the optical fiber 20 having a desired hole diameter and low transmission loss can be easily manufactured. Moreover, in the optical fiber manufacturing method of this embodiment, when manufacturing the optical fiber 20 having the same transmission loss as the optical fiber manufactured by the optical fiber manufacturing method of the comparative example, the use of harmful gas at the time of drawing is used. The amount can be reduced.

  4 and 5 are a schematic view and a photograph of a cross-sectional structure of the optical fiber 20, respectively. Each figure (a) is a schematic diagram, and each figure (b) is a photograph of a broken-line rectangular region in the schematic diagram. In the cross section of the optical fiber 20 shown in FIG. 4, the hole 23 has a substantially perfect circle shape. On the other hand, in the cross section of the optical fiber 20 shown in FIG. 5, the hole 23 has a substantially elliptical shape.

  FIG. 6 is a schematic view and a partially enlarged view of a cross-sectional structure of the optical fiber 20. The length of the radial hole 23 is a, and the length of the angular hole 23 is b. As the ellipticity a / b of the hole 23 is smaller, the radial spread of the power of the light propagating through the core 21 is more easily blocked by the hole 23, and the power distribution of the light propagating through the core 21 and the Overlap with the surface becomes large and is easily affected by light absorption by OH groups. Further, as the roughness Ra of the wall surface of the hole 13 of the optical fiber preform 10 increases, the substantial surface area of the wall surface of the hole 13 increases, so that the OH group taken into the wall surface of the hole 23 of the optical fiber 20 is increased. Increases and is susceptible to light absorption by OH groups.

Therefore, in this embodiment, it is preferable that the ellipticity a / b of the hole 23 of the optical fiber 20 is 0.84 or more, and it is more preferable that the ellipticity a / b is 0.90 or more. FIG. 7 is a graph showing the relationship between the transmission loss Δα _{1.38 at} a wavelength of 1.38 μm due to the OH group of the optical fiber and the ellipticity a / b of the hole of the optical fiber. The figure shows the relationship between the transmission loss Δα _1.38 and the ellipticity a / b of the hole 23 when the roughness Ra of the wall surface of the hole 13 of the optical fiber preform 10 is 0.6 μm and 15 μm, respectively. Has been.

As can be seen from the figure, when the roughness Ra of the wall surface of the hole 13 of the optical fiber preform 10 is 0.6 μm, the ellipticity a / b of the hole 23 of the optical fiber 20 should be 0.84 or more. For example, the transmission loss Δα _{1.38 at} a wavelength of 1.38 μm due to the OH group of the optical fiber 20 is 0.06 dB / km or less, and the optical fiber 20 can satisfy the international standard defined in ITU-T G652D. Further, when the roughness Ra of the wall surface of the hole 13 of the optical fiber preform 10 is 15 μm, the OH of the optical fiber 20 is sufficient if the ellipticity a / b of the hole 23 of the optical fiber 20 is 0.90 or more. The transmission loss Δα _{1.38 at} a wavelength of 1.38 μm by the base is 0.06 dB / km or less, and the optical fiber 20 can meet the international standard defined in ITU-T G652D.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber preform, 11 ... Core, 12 ... Cladding, 13 ... Hole, 20 ... Optical fiber, 21 ... Core, 22 ... Cladding, 23 ... Hole

Claims (3)

A method for producing an optical fiber having a hole extending in the axial direction by drawing an optical fiber preform having a hole extending in the axial direction,
The surface area of the holes of the optical fiber preform is S, the radius of the optical fiber preform is R, the volume of the optical fiber preform including the void volume is V, and the surface area of the holes of the optical fiber is When S ′, the radius of the optical fiber is R ′, and the volume of the optical fiber including the void volume is V ′, ((S ′ / V ′) / (S / V)) is 2 R / Producing the optical fiber by drawing the optical fiber preform so as to be larger than R ′;
An optical fiber manufacturing method.   In the cross section of the optical fiber, when the length of the hole in the radial direction is a and the length of the hole in the angular direction is b, the light is adjusted so that a / b is 0.84 or more. The optical fiber manufacturing method according to claim 1, wherein the optical fiber is manufactured by drawing a fiber base material. 3. The optical fiber manufacturing method according to claim 2 , wherein the optical fiber is manufactured by drawing the optical fiber preform so that a / b is 0.90 or more.