JP4554530B2 - Optical fiber connection method - Google Patents

Description

  The present invention includes a core and a clad provided so as to cover the core, and an optical fiber in which a plurality of pores extending along the core surround the core and a connected optical fiber. It relates to the method of connection.

  Various methods have been proposed for connecting an optical fiber having a pore in the cladding with another optical fiber.

  For example, in Patent Document 1, a general optical fiber composed of a core part and a clad part, and a plurality of refractive index change parts extending in the axial direction are formed in the clad part, consisting of a hollow core part and a clad part. When connecting to the optical fiber, first, matching oil is injected into the end portion of the hollow core portion of the latter optical fiber that is connected to the former optical fiber, and then the one end side of the former optical fiber and the latter optical fiber are connected. It is disclosed to insert a matching oil injection side of an optical fiber into a glass pipe and connect them.

  In Patent Document 2, the vicinity of the end face of a photonic crystal optical fiber that is inserted and fixed in a connector ferrule is solid, and during polishing, abrasives or polishing debris may enter the pores from the end face. Further, it is disclosed that scratches and sagging do not occur, and even if dust adheres after polishing, it does not enter the pores from the end face and is easy to clean.

Patent Document 3 discloses an optical fiber connector for connecting a holey optical fiber having a plurality of holes around a core to a ferrule, in which holes are blocked at a position away from the end face of the holey optical fiber. Yes.
JP 2002-236234 A JP 2003-307653 A JP 2005-024849 A

  By the way, when connecting a pair of optical fibers using a mechanical splice, a liquid refractive index matching agent is interposed between the connection end faces to prevent reflection of signal light.

  However, if either one is an optical fiber having pores in the clad, the refractive index matching agent flows into the pores, and the optical confinement effect of the clad is lowered at that portion, resulting in a large loss. Further, when the refractive index matching agent further flows into the pores, there is a possibility that a larger loss may be caused.

  The present invention has been made in view of such points, and an object of the present invention is to provide an optical fiber connection method using a mechanical splice that can prevent the refractive index matching agent from flowing into the pores. There is to do.

The present invention includes a core and a clad provided so as to cover the core, and an optical fiber in which a plurality of pores extending along the core surround the core, and an optical fiber to be connected And a method of connecting
An end face processing step for forming and processing a connection end face in which the pores are sealed with respect to the optical fiber;
A connection step of connecting the optical fiber and the optical fiber to be connected using a mechanical splice so that a liquid refractive index matching agent is interposed between the connection end faces;
It is provided with.

  According to the present invention, when connecting the optical fiber having the pores formed in the clad and the optical fiber to be connected using the mechanical splice, the connection end face sealing the pores before connection is formed and processed. It is possible to prevent the refractive index matching agent from flowing into the pores.

  Hereinafter, the connection using the mechanical splice 30 between the optical fiber core wire 10 and the connected optical fiber core wire 20 according to the embodiment will be described in detail based on the drawings.

(Optical fiber core)
FIG. 1 shows an optical fiber core wire 10. The optical fiber core wire 10 is used, for example, for an application that is drawn from an outdoor closure into each home.

  The optical fiber core 10 includes an optical fiber 11 and a coating layer 15 that covers the optical fiber 11. The optical fiber core wire 10 has, for example, a core wire diameter of 250 to 900 μm (typically 250 μm).

  The optical fiber 11 is made of, for example, quartz or acrylic resin, and includes a core 12 that forms the center of the fiber and a clad 13 that is provided so as to cover the core 12. The clad 13 is provided with a plurality of pores 14 extending along the core 12 so as to surround the core 12. For example, the optical fiber 11 has a fiber diameter of 80 to 125 μm (typically 125 μm) and a core diameter of 8 to 11 μm.

  The plurality of pores 14 provided in the clad 13 may be provided in a single layer so as to surround the core 12 or may be provided in a plurality of layers (for example, 2 to 4 layers). The number of holes is preferably 4 to 12 per layer, and more preferably 6 to 10 per layer. The pore diameter is preferably 1 to 5 μm, and more preferably 2 to 3 μm, for example, from the viewpoint of reducing the reduced diameter when the pores 14 are sealed by heating. Further, from the same viewpoint, the occupied area of the entire pore portion with respect to the cross-sectional area (including the pore portion) of the cross section of the fiber is 0.2 to 3 in the fiber cross section. 0.0% is preferable, and 0.2 to 1.0% is more preferable.

  Since the clad 13 is provided with the pores 14, the core 12 is structurally higher in refractive index than the clad 13 even if the optical fiber 11 is uniformly formed of pure quartz, for example. In addition to this, even if the core 12 is doped with germanium or the like to have a higher refractive index than the cladding 13, the cladding 13 is doped with fluorine or the like to have a lower refractive index than the core 12. It may be a configuration.

  The optical fiber core wire 10 is produced by drawing a base material that has been perforated into a base material for manufacturing a general solid optical fiber, or a base material in which a rod material and a capillary are bundled. It can also be produced by a method of drawing it as a material.

  The covering layer 15 is made of, for example, an ultraviolet curable resin.

(Connected optical fiber core wire)
The optical fiber 20 to be connected has the same optical fiber diameter as that of the optical fiber 10 and has an optical fiber 21 to be connected in which a clad has a pore like the optical fiber 10. Alternatively, it may have a normal solid connected optical fiber 21 (for example, a general single mode fiber) in which no fine pores are provided in the clad.

(Mechanical splice)
FIG. 2 shows a mechanical splice 30.

  The mechanical splice 30 includes an elongated plate-like V-groove substrate 31 having a V-groove 31a formed in the lengthwise direction on the upper surface, and an elongated plate-shaped pressing substrate having a lower surface formed on a flat surface. 32 forms a splice body. The pressing substrate 32 may be a single member or may be composed of a plurality of members. The V-groove 31a has a narrow groove width in accordance with the fiber diameters of the optical fiber 11 and the connected optical fiber 21 at the center, and the optical fiber core 10 and the connected optical fiber cores having coating layers 15 and 25 on both sides thereof. The groove width is formed to be wide in accordance with 20. The splice body is fitted with a clamp spring 33 having a U-shaped cross section from the side, whereby the V-groove substrate 31 and the pressing substrate 32 are pressed against each other. Further, tapered guide holes 34 having a diameter expanded outward are formed on both end surfaces of the splice body. Furthermore, a plurality of slit-like wedge insertion ports 35 are formed on the exposed side surface of the splice body at intervals in the length direction. Then, for example, a silicone-based liquid refractive index matching agent 36 (index matching oil) is injected into the price main body so as to fill the V groove 31 a of the V groove substrate 31. The mechanical splice 30 has, for example, a length of 40 mm, a width of 4 mm, and a height of 4 mm.

(Connection method)
<End face machining process>
The coating layer 15 at a predetermined length of the optical fiber core wire 10 is peeled off, and the connection end face 16 in which the pores 14 are sealed with respect to the optical fiber 11 is formed and processed. In addition, the part which peels the coating layer 15 may be an intermediate part of the optical fiber core wire 10 or may be a fiber end part.

  First, the pore 14 is sealed as shown in FIG. 3A by heating a predetermined length of the portion where the optical fiber 11 is exposed.

  Here, the length of the heated portion is preferably, for example, 1 to 18 mm, and more preferably 5 to 10 mm.

  Examples of the heating method include a method performed by discharging a fusion splicer, a method performed by a burner flame, a method performed by heating with a filament, and the like. Of these, existing equipment used for fusion splicing of optical fibers can be used, and from the viewpoint that it can be easily carried out outdoors, it is preferable to carry out by discharging the fusion splicer.

  A difference in outer diameter occurs between the portion of the optical fiber 11 where the pore 14 is sealed and a portion that does not, and when the optical fiber 11 is connected using the mechanical splice 30, the difference in outer diameter can cause an axial shift. Therefore, from this point of view, the diameter reduction rate of the portion of the optical fiber 11 where the pores 14 are sealed is, for example, preferably 1.6% or less, and more preferably 0.8% or less. Specifically, the difference in outer diameter between the portion of the optical fiber 11 where the pores 14 are sealed and the portion that is not so is, for example, preferably 2 μm or less, and more preferably 1 μm or less. In the optical fiber 11 having a fiber diameter of 125 μm, assuming that the outer diameter difference is 2 μm, the axial misalignment is a maximum of 1 μm, and the connection loss at this time is about 0.2 dB, and there is no practical problem.

  Next, the connection end face 16 is formed by cutting the portion of the optical fiber 11 where the pores are sealed, as shown in FIG.

  Here, as a method for cutting the optical fiber 11, for example, a method using a fiber cutter may be mentioned.

  When connecting the optical fiber 11 using the mechanical splice 30, the optical fiber 11 is supported by a portion where the pore 14 having a large outer diameter is sealed. If the length of this portion is short, the optical fiber 11 is loaded. Pressure increases, which can cause axial misalignment. Therefore, from this point of view, the length of the portion of the optical fiber 11 after cutting that seals the pores 14 is preferably, for example, 9 mm or less from the connection end face 16, and preferably 5 mm or less. Is more preferable.

  On the other hand, if the connecting optical fiber 21 is exposed by peeling off the coating layer 25 of a predetermined length from the end of the connecting optical fiber core 20 and the cladding is provided with pores, the same applies. Then, the connection end face 26 in which the pores are sealed is formed and processed.

  In the above method, the pore 14 is sealed by heating the optical fiber 11, and the connection end face 16 is formed by cutting at the portion where the pore 14 is sealed. However, the present invention is not limited to this. Alternatively, the connecting end face may be formed by filling the pores 14 from the fiber end of the optical fiber 11 and closing the end face by polishing the end face.

<Connection process>
Optical fiber core wire 10 and connected optical fiber core wire 20 are connected using mechanical splice 30.

  First, as shown in FIGS. 4A and 4B, a wedge 40 is inserted into the wedge insertion opening 35 to form a gap between the V-groove substrate 31 and the holding substrate 32, and one guide hole 34 is formed in one guide hole 34. The optical fiber core wire 10 is inserted from the optical fiber 11 as an end portion, and the connected optical fiber core wire 20 is inserted into the other guide hole 34 from the connected optical fiber 21 as an end portion.

  Then, as shown in FIGS. 5A and 5B, the wedge 40 is removed after the optical fiber core wire 10 and the connected optical fiber core wire 20 are inserted to such an extent that the connection end faces 16 and 26 are substantially in contact with each other. At this time, each of the optical fiber 11 and the optical fiber to be connected, which are the end portions, is supported at the center portion of the splice body at the three points of both the wall surfaces of the V groove 31a of the V groove substrate 31 and the lower surface of the holding substrate 32. Fixed. Further, as shown in FIG. 6, the optical fiber 11 and the connected optical fiber 21 are in a state of being connected such that a liquid refractive index matching agent 36 is interposed between the connection end faces 16 and 26. It should be noted that the optical fiber core wire 10 or the optical fiber core wire 20 to be connected is divided into three groove wall surfaces of the V-groove 31 a of the V-groove substrate 31 and the lower surface of the holding substrate 32 on each side of the center portion of the splice body. It is fixed at a point.

  According to the connection method as described above, when connecting the optical fiber core wire 10 in which the pores 14 are formed in the clad 13 and the optical fiber core wire 20 to be connected using the mechanical splice 30, the light is connected before the connection. Since the connection end face 16 in which the pore 14 is sealed is formed with respect to the optical fiber 11 of the fiber core wire 10, it is possible to prevent the refractive index matching agent 36 from flowing into the pore 14.

  The present invention includes a core and a clad provided so as to cover the core, and an optical fiber in which a plurality of pores extending along the core surround the core and a connected optical fiber. Useful for how to connect.

It is a perspective view of an optical fiber core wire. It is a perspective view of a mechanical splice. It is explanatory drawing which shows the end surface processing method of an optical fiber. It is explanatory drawing which shows the connection method of an optical fiber core wire and a to-be-connected optical fiber core wire. It is explanatory drawing which shows the connection method of an optical fiber core wire and a to-be-connected optical fiber core wire. It is a figure which shows the connection state of an optical fiber core wire and a to-be-connected optical fiber core wire.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Optical fiber 12 Core 13 Cladding 14 Pore 16, 26 Connection end surface 21 Connected optical fiber 30 Mechanical splice 36 Refractive index matching agent

Claims (6)

An optical fiber having a core and a clad provided so as to cover the core, and an optical fiber provided with a plurality of pores extending along the core surrounding the core and the optical fiber to be connected are connected to each other A way to
An end face processing step for forming and processing a connection end face in which the pores are sealed with respect to the optical fiber;
A connection step of connecting the optical fiber and the optical fiber to be connected using a mechanical splice so that a liquid refractive index matching agent is interposed between the connection end faces;
An optical fiber connection method comprising: In the connection method of the optical fiber described in Claim 1,
The end face processing step includes a step of sealing a pore by heating a portion of the optical fiber having a predetermined length, a step of cutting the portion of the optical fiber where the pore is sealed, and forming a connection end face; An optical fiber connection method comprising: In the optical fiber connection method according to claim 2,
A method for connecting optical fibers, wherein each of the plurality of pores of the optical fiber has a diameter of 3 μm or less. In the connection method of the optical fiber described in Claim 3,
The method for connecting optical fibers, wherein the optical fiber has a cross-sectional area occupied by the plurality of pores of 3% or less. In the optical fiber connection method according to claim 2,
An optical fiber connecting method, wherein a length of the optical fiber in which the pores are sealed is 9 mm or less from the connecting end face. In the optical fiber connection method according to claim 2,
A method for connecting optical fibers, wherein the connection end of the optical fiber is heated by discharge of a fusion splicer.

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