JPS589113A - Reinforcing member for optical fiber connecting part and reinforcing method - Google Patents

Abstract

PURPOSE:To stabilize a transmission loss and to improve reliability, by covering an optical fiber connecting part with a reinforcing member in which an electric resistance heating element and a heat-shrinkable tube are unified into one body, and electrically conducting and reinforcing the connecting part. CONSTITUTION:A reinforcing member is constituted of a heat-shrinkable tube 1 which is shrunk lengthwise by heating, a thermosetting resin prepolymer tube 2 which is disposed in the inside of the tube 1 and which is made of an epoxy resin to be cured by heating and an electric resistance heating element 4 consisting of a rod-shaped carbon fiber which is coated and attached lengthwise to a epoxy resin prepolymer layer 3 which is extended and inserted almost in an axial direction in the tube 2, and a connecting part 5 of an optical fiber is inserted into a hollow part 10 in the tube 2. When voltage is applied to both ends of the heating element, the tube 2 is heated and softened, and at the same time the tube 1 is shrunk lengthwise and is unified into one body by being adhered with the connecting part.

Description

[Detailed description of the invention] This article provides information on reinforcement and reinforcement methods.

As a method for connecting optical fibers, there is a method in which the plastic coatings of two optical fibers to be connected are removed and the two cored fibers are thermally fused together by arc discharge or the like. In this case, the plastic coating layer of the optical fiber, which has the role of maintaining the mechanical strength of the optical fiber, is removed and heat fusion is performed.
After optical fiber connection, it is necessary to reinforce the removed portion of the coating layer.

Several methods for reinforcing this connection have been proposed in the past.
No. 03 and G. In Pacey and J. F. Bal
By gleyghK” Fusion Splicin
of Optical Fibers”.

Electronics Letter, v'o1.
ts'e&t, p. n<tm>K has been proposed, but the conventional heat shrink tube method requires an electric heater, torch, burner, etc. to heat shrink the heat shrink tube.
An external heating device such as a hot gun is required. Therefore,
It is necessary to bring such an external heating device into the work site, for example, inside a manhole or on a pillar, and there are problems from safety and fire prevention measures, and no matter what kind of external heating device is used, it will not be possible to heat the area. The drawback was that it took several minutes. Additionally, the Young's modulus of heat-shrinkable tubes and hot-melt adhesives used as reinforcing members is several hundred to t,0ookf/■, and the Young's modulus of optical fibers is as low as t,000 ki/wx. When a tensile stress is applied to the reinforced portion, the reinforcing member stretches and a single breaking stress/force is applied to the optical fiber, which may cause the optical fiber to break. Furthermore, the elongation of the heat-shrinkable tube or hot-melt adhesive used as a reinforcing member is 10-
5~IO-'/'e, which is larger than the coefficient of linear expansion of optical fiber IO-7~10''/''C, so the plastic of the above-mentioned reinforcing member expands or contracts due to temperature changes, causing light to be emitted. There are disadvantages in that transmission loss changes due to localized fiber breakage, and furthermore, breakage occurs due to protrusion of the optical fiber.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electrical resistance heating element made of a material that has a Young's modulus as high as that of Optical 7 Eyepa and a coefficient of thermal expansion that is as low as that of an optical fiber. In addition to being used as a tension member, this electric resistance heating element is energized, making it possible to easily and quickly reinforce optical fiber connections at work sites, and to prevent changes in optical fiber transmission loss. It is an object of the present invention to provide a good reinforcing member that has no fear of breakage.

Another object of the present invention is to use the above-mentioned reinforcing member to easily and quickly reinforce the connecting portion of an optical fiber at the site, and to eliminate the risk of the fiber I wire being broken after reinforcement. To propose a method of reinforcing an optical fiber connection part that solves the above-mentioned conventional drawbacks Q by preventing
Toru.

The reinforcing member of the present invention includes a heat-shrinkable tube that can be radially contracted by heating, a hollow member made of a thermosetting resin or a thermosetting resin prepolymer disposed inside and inside the heat-shrinkable tube, and a hollow member made of a thermosetting resin or a thermosetting resin prepolymer, and the heat-shrinkable tube. The heat-shrinkable tube and the hollow portion are disposed in the axial direction of the heat-shrinkable tube so that the material can be heated, and the thermosetting resin is coated or impregnated with a thermosetting resin prepolymer. The device is characterized in that it includes an electric resistance heating element, and an optical fiber can be inserted into the inside of the hollow member.

The method of the present invention includes a heat-shrinkable tube that can be contracted in the radial direction by heating, a hollow member made of a thermosetting resin or a thermosetting resin prepolyi disposed inside the heat-shrinkable tube, and an inner side of the heat-shrinkable tube. The heat-shrinkable tube and the hollow member are arranged extending in the axial direction of the heat-shrinkable tube so as to be heatable, and the thermosetting resin is coated with a thermosetting resin prepolymer and the base is soaked in electricity. The fusion-spliced optical fiber connection portion is inserted into the hollow member using a strong member that is equipped with a resistance heating element and allows the optical fiber to be inserted inside the hollow member, and then the electrical resistance heating element is inserted into the hollow member. Applying electricity to the body to heat the heat-shrinkable tube and shrink it in the radial direction, and heat and harden the thermosetting resin or thermosetting resin prepolymer coated or impregnated on the hollow member and the electric resistance heating element. The optical fiber connecting portion is integrated with the thermosetting layer in a state where the optical fiber connecting portion and the electrical resistance heating element are contained in a shrinkable heat-shrinkable tube. It is something to do.

Here, it is preferable that the hollow member is a tube made of the thermosetting resin or thermosetting resin prepolymer, and that the tube is arranged substantially parallel to the inside of the heat-shrinkable tube. Alternatively, the hollow member may be a layer of thermosetting resin prepolymer applied to the inner surface of the heat shrinkable tube.

In a preferred embodiment of the present invention, the thermosetting resin is a resin having high adhesiveness to optical fibers, plastic coating materials and electrical resistance heating elements, such as epoxy resin, phenolic resin, unsaturated polyester resin, alkyd resin, polyurethane resin. Resin, amino alkyd resin, silicone resin, 7tsun resin.

Melamine resin, diallyl phthalate resin, :s-ria resin, etc. can be used.

As an electric resistance heating element, Young's modulus is 20×10”~$
3 x 10" kll/l 3112, which is as high as that of Hikari 7 Eyepa, and whose coefficient of linear expansion is about /f'/" (and materials as small as optical fiber, such as carbon fiber', silicon carbide fiber, Unichrome alloy wire iron) A chromium-aluminum alloy wire, a tungsten wire, a molybdenum wire, a platinum wire, or a rod-shaped, net-shaped or chain-shaped wire made of these wires can be used.

The material for heat shrink tubing is polyethylene, ethylene copolymer, or a mixture thereof.

It is possible to use polyvinyl chloride, fluorine resin, etc., but the material is not particularly limited to these.

Hereinafter, the present invention will be explained in detail by way of examples with reference to the drawings.

Embodiment FIG. 1 is a cross-sectional view of an embodiment of the reinforcing member of the present invention. The reinforcing member of this example consists of a heat-shrinkable tube 1 that contracts in the radial direction when heated, a thermosetting resin prepolymer tube made of epoxy resin 11 disposed inside the tube 11 that hardens when heated, and this tube λ. The space 1 in the tube 2 is made up of an electric resistance heating element made of longitudinally attached rod-shaped carbon fibers which are inserted and extended in the axial direction and covered with an epoxy resin prepolymer layer 3. Enables insertion of the optical fiber connection part. heat shrink tube l,
Here the length is 4 csa, the inner diameter is 11$1 e
A polyethylene tube with a thickness of O was used. Its shrinkage rate was 17%. The epoxy resin prepolymer tube λ had a length t on , an outer diameter of 2.2 mm, and a thickness of 0.2 mm. As the rod-shaped electric resistance heating element, a high-strength and highly elastic 4000 filament carbon fiber coated with an epoxy resin prepoly I layer 3 and having a diameter of 01EII and a rod-like length of 1 cIa was used.

-Next, using this reinforcing member, the procedure for reinforcing the penis will be explained with reference to the Figures. First of all, supplementary
An optical 7-eyeper is inserted into the hollow space 10 of the tension member in advance, and then the bare optical fiber is fusion-spliced without removing the plastic coating layer. Next, before fusion splicing the optical fibers j, the previously inserted reinforcing member is inserted into the plastic coating layer 7 (usually a primary coating layer) at both ends of the fusion spliced part j of the optical fiber.

(consisting of three layers: a buffer layer and a secondary coating layer). Finally, by applying a voltage of about 10 V from 6cjv to both ends of the electric resistance heating element, the tube made of thermosetting resin prepolymer was heated and softened, and the heat-shrinkable tube l contracted in its radial direction and became soft. The tube is glued to the optical fiber plastic coating 7 and the heat shrink tube 1, and the optical fiber is fused in x-9 seconds! The cured layer 2' was formed by integrating the cured layer 2' with the rubber layer.

It is assumed that the optical fiber connection section reinforced by the method of the present invention has the following excellent characteristics.

(1) The tensile strength of the optical fiber connection was more than 100 yen, and the optical fiber broke in areas other than the reinforced area.

(2) Transmission loss due to reinforcement work li O,0/d
The connection point was below B/l.

(5) To cycle test (-0''℃~+60℃
, 6 hours/l cycles), the change in transmission loss after 100 cycles is less than 0.021 iB/l connection point.

(4) Temperature dependence is only o at 0°C to +to°C.
, less than 0 dB/l connection point.

(5) High temperature storage at +ro℃ (after 30 days) and tO
When left at high temperature and high humidity at ℃tS% (after 30 days), the change in transmission loss was 0. ．． 0 (less than iB/l connection point).

Embodiment 2 FIG. 2 is a cross-sectional view of a second embodiment of the reinforcing member of the present invention. In this example, the core wire 3 of Hikari 7 Aiper, which is fused and spliced almost parallel to the carbon fiber filament da coated with the thermosetting resin layer 3, is housed inside the thermosetting resin prepolymer tube λ. A thermosetting resin prepolymer tube t having a cavity 10 is inserted. Heat shrink tube l is length JIG C
11, inner diameter, jltml.

A polyethylene tube with a thickness of C6-thickness was used. Its shrinkage rate was s0%. The thermosetting resin tube 1 and the resin layer 3 are made of unsaturated polyester, and the tube 20
Dimensions are length 4 elm, outer diameter 1, JI 1 ml, thickness 0.
2 cranes, the dimensions of the tube t are length 11 outer diameter/, ttm
e Thickness O, the connection. Carbon fiber yarn (length/(l cta), pesphi) is used as an electric resistance heating element.
ilM-6000 (Toho Rayon, trade name) was used.

This reinforcing member is used to reinforce the plastic coating layer 7 at both ends of the spliced portion S of the fusion spliced optical fiber core yss<length 30 ta) so as to cover each of the plastic coating layers 7, respectively, as shown in the figure. After installing the members, when a direct current pressure of 7V is applied to both ends of the electric resistance heating element 3, the thermosetting resin prevolume tubes 2 and t soften, and the heat shrinkable tube 1 contracts. The softened portion 2' of B was integrated with the fusion spliced portion sh of the optical fiber in about a second to form a reinforcing portion.

The Hikari 7 Eyeper connection portion reinforced with the reinforcing member shown in FIG. 2 had the following excellent characteristics.

(1) The tensile strength of the optical fiber connection was Jkf or higher. Note that the breakage of the optical fiber occurred in areas other than the reinforced portion.

(2) Transmission loss due to reinforcement work shall be less than 0.01 dB/l at the connection point.

(3) Heat cycle test (-0°C to +40°C,
6 hours/l cycle), the change in transmission loss after 100 cycles is 0. The connection point was O2dB or less/l.

(4) - High temperature storage test (10°C, SO day after day, the change in transmission loss was o, o2dB / / connection point.

(5) The change in transmission loss was 0.02 (less than iB/l) in a high temperature, high humidity test (at tz°C, is% high, after 30 days).
It was a connection point.

(6) Temperature dependence is 0 from 0℃ to +ω'C.
．． 02dB/l or less at the connection point.

By using the reinforcing member of the present invention in this way, it was possible to easily perform excellent reinforcement with high reliability in a short period of time.

Embodiment 5 FIG. 3 is a cross-sectional view of a third embodiment of the reinforcing member of the present invention.
Ru. Carbon fiber yarn (Besphite HM-6000, Toho Rayon Co., Ltd., trade name) (major diameter/IEIIφ) coated with an alkyd resin layer J was placed inside a heat-shrinkable tube l made of cross-linked polyethylene with a length of 4 oa. Alkyd resin prepolymer 1-piece (length 6C snow, inner diameter/, J
III p (thickness 0, thickness 0) 6 is inserted in the axial direction so that the optical fiber connecting portion can be inserted into the cavity 10 of this tube B. After passing the fusion-spliced optical fiber core wire 3 through the prepolymer tube B, a voltage of about tV is applied to the carbon fiber yarn to shrink the heat-shrinkable tube L, as shown in Figure D. , the softened part λ′
was integrated with the optical fiber core wire 5 and cured in about fS seconds, thereby completing the reinforcement.

The joints reinforced by the method of the present invention had the following excellent properties.

(1) The tensile strength of the optical fiber connection was 3.3 hours or more. The breakage of the optical fiber occurred in areas other than the reinforced part.

(2) Transmission loss due to reinforcement work was less than 0.0/dB/l connection point.

(3) Heat cycle test (-z”c to +40°C,
The change in transmission loss after 4w#□/l cycles) is less than o, oxa'v/l at the connection point.9.

(4) In the high temperature storage test (10°C, after 10 days), the change in transmission loss was 0.0λdB / / connection point.

(5) High temperature and high humidity test (rz℃, rs%RH, !OE
After l), the change in transmission loss is 0.0 co(less than IB/
It was a connection point.

(6) Temperature dependence was 0.02 dB or less at -30,"C~+to"c//connection point.

Embodiment 4 FIG. 3 shows a second embodiment of the reinforcing member of the present invention, in which the reinforcing member is a heat-shrinkable tube l made of cross-linked polyethylene with a length of 4 cx, and inside thereof a carbon fiber yarn. (
Besphite HM-6000, Toho Rayon Co., Ltd., trade name) phenolic resin thermosetting resin prepolymer tube (length 4 cm
Im, inner diameter/, JI111. Thickness 0.2wg)λ, and
Among them, the optical fiber 3 is disposed at 11 and is composed of a phenol resin-based thermosetting resin prepolymer chain through which the fusion-spliced optical fiber 3 can be inserted.

The optical fiber connection section, which was formed into a reinforcing tube using this reinforcing member by the gAho method of the present invention, had the following excellent properties.

(1) The tensile strength of the optical fiber connection portion was # hours, and the optical fiber broke at a portion other than the reinforced portion.

(2) Transmission loss due to reinforcement work is 0.0/ (iB
Below was the /l connection point.

(5) Heat cycle test (-J"C to +60℃,
time/l cycle), the change in transmission loss after the cycle was less than 0.01 dB/l connection point.

(4) In the high temperature test <10°C, after 30 days), the change in transmission loss was less than 0.02+iB/l connection point.

(5) High temperature and high humidity test (ts”c, tz% starvation, 30
(days later), the change in transmission loss is o, osdBR below/l
Connection point l Connection point.

(6) Temperature dependence The connection point was less than 11B/l at -30°C to +40°C.

Embodiment No. 411 shows an embodiment of the reinforcing member of the present invention. It consists of an electrical resistance heating element 3 in the shape of a councilor O, which is made of carbon fiber yarn hardened with diallyl phthalate resin, attached vertically to the 6 and 0 sections.

The connecting portion of the optical fiber in which the reinforcing portion was formed by the method of the present invention using this reinforcing member had a tensile strength of #- or more, and no breakage of the optical fiber occurred within the 6L reinforcing member. -20
Even after performing a heat test (1 hour/l cycle) between 100°C and +40°C for 100 cycles, the change in transmission loss was less than 0.02 dB. rz”c
In the high temperature and high humidity test of .

Embodiment 4 FIG. 7 shows a fourth embodiment of the reinforcing member of the present invention, which consists of a heat-shrinkable tube 1, a thermosetting resin prepolymer tube 6 disposed inside the tube 1, and a tube. It consists of a tube made of carbon fiber yarn (Pesphyte HM-4000, Toho Rayon Co., Ltd., trade name) impregnated with a thermosetting resin prepolymer, which is longitudinally attached between L and B. Here, the heat shrink tube l has length/cx, inner diameter co-jail, thickness 0.2
wz polyethylene tube and its shrinkage rate y%
Met. The thermosetting resin prepolymer chain t was made of alkyd resin, had a length of 4 CI+, two holes on the inner diameter, and a thickness of 0.2 cm. The optical fiber connection section reinforced by the method of the present invention using this reinforcing member had the following excellent optical characteristics.

, (1) The tensile strength of the optical fiber connection portion was greater than jk#, and the optical fiber fracture occurred at a portion other than the reinforced portion.

(2) Heat cycle test (-20℃~+60℃,
At 4 hours/l cycle), the change in transmission loss after 100 cycles is less than 0.0/dB/l connection point and light.

(3) Temperature dependence 14-30℃~+to”crtc
bvhteo, ca (iB or less/l at the connection point.

(4) + I! "C, Change in transmission loss after X8 in 11% high temperature high lI storage test d 0.02 d
B and below // @ comma.

Example 1 Figure 2 is a cross-sectional view of a seventh embodiment of the reinforcing member of the present invention, and Figure 1 is a longitudinal cross-sectional view of a reinforcing member obtained by carrying out the method of the present invention using the reinforcing member shown in Figure 1. It is a front view.

Here, the reinforcing member includes a heat shrink tube made of polyethylene that contracts in the radial direction when heated, a thermosetting resin prepolymer layer 12 made of epoxy resin coated on the inner surface of the tube and cured when heated, and an epoxy resin prepolymer layer 12. A rod-shaped electric resistance heating element is inserted into the cavity 10 formed by the heating element 12 and covered with an epoxy resin prepolymer layer 13.

The electrical resistance heating element is arranged to extend in the axial direction of the heat shrink tube 1, and is capable of heating the heat shrink tube 1 and the epoxy resin prepolymer layers 12 and 13. It is assumed that the connecting portion S of the optical fiber core IIj can be inserted into the space IO.

Next, the reinforcing method of the present invention using this reinforcing member will be explained step by step. ) First, before performing the fusion splicing of the optical fiber core S, this optical fiber core! Hollow space 1 of the reinforcing member
0, and this reinforcing member is placed so as to cover the plastic coating layer 7 at both ends of the fusion spliced portion S5 of the optical fiber. When the electric resistance heating element is then energized, the heat-shrinkable cable is heated and shrunk, and the thermosetting resin prepolymer layers 12 and 13 are softened. The softened epoxy resin prepolymer layer/2' is formed with the connecting portion 5 and the electrical resistance heating element contained inside the heat-shrinked tube L.
It is integrated with the optical fiber fusion splice S.

According to this method of the present invention, the same effects as in Example 10 described above were obtained.

Embodiment a FIG. 10 is a cross-sectional view of a first embodiment of the reinforcing member of the present invention. The reinforcing member of this example consists of a cross-linked polyethylene heat-shrink tube 1, a phenolic resin-based thermosetting resin premer layer 12 coated with - An electric resistance heating element made of a plurality of linear carbon fiber yarns extending and arranged in a circumferential manner, and a thermosetting phenol resin-based heating element placed inside the chain 2. Here, the electric resistance heating element can heat the heat-shrinkable tube l and the thermosetting resin prepolymer layer 12.In addition, a fiber optic fiber core is installed in the space IO. The connecting part of the wire S can be inserted.

In carrying out the method of the present invention, the connecting portion of the optical fiber j is inserted into the cavity 10 formed on the inner surface of the resin pre-197 layer 12, as in the case of FIGS. r' and 9. ,Next! Electricity is applied to the air resistance heating element to heat and shrink the heat shrink tube I, and at the same time shrink the poxy resin prepolymer layer I2.
This is the same as in the case of the eighth embodiment described above, in which the fiber core is heated and softened to be integrated with the optical fiber core ajo connection portion for reinforcement. According to this example, the same effects as in Example 4 described above were obtained.

As explained above, according to the present invention, a thermosetting resin or a thermosetting resin prepolymer is applied to the inner surface of a heat shrinkable tube, or a thermosetting resin is applied to the inner surface of the heat shrinkable tube.
A tube made of # or thermosetting resin prepolymer is arranged, and the optical fiber connection part can be inserted into the space inside such a hollow member, and the electric resistance heating element attached vertically inside the heat shrinkable tube is energized. By doing this, it is possible to heat the reinforcing member from the inside of the heat-shrinkable tube and integrate it with the optical fiber connection part, so there is no need for an external heater used in the conventional heat-shrinkable tube reinforcing method, and the process is easy. Moreover, the optical fiber connection portion can be stably reinforced in a short time. In addition, in the present invention, since the optical fiber is integrally coated with the thermosetting resin titanium or thermosetting resin prelimer, it is possible to stabilize transmission loss over a long period of time, and furthermore, the optical fiber protrudes from the coating layer. Therefore, the mechanical strength is strong over a long period of time, and there is no fear of strength deterioration. In addition,
The present invention uses an electrical resistance heating element with a high tensile Young's modulus and a coefficient of thermal expansion as low as that of an optical fiber. This has the advantage that a highly reliable reinforcing portion with no change in loss can be formed.

[Brief explanation of the drawing]

Figure 1, Figure 3, Figure J, Figure 3. Fig. 7, Fig. 10, and Fig. 10 are cross-sectional views showing various embodiments of the reinforcing member of the present invention. FIG. 9 is a vertical cross-sectional view showing the main reinforcing portion formed by the method of the present invention using the reinforcing member shown in FIG. l...Heat shrink tube, j7-thermosetting resin (prepolymer) tube, 2'
, /2'--hardened layer, 3.12... thermosetting resin GL (-prepolymer) layer, 4
', /#, 7, jF, #...electric resistance heating element,! ...Optical fiber, jmu...Optical fiber connection part, 7...Plastic, coating layer 1 10-...Vacancy. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Scope of Claims] 1) An external heat-shrinkable tube that can be contracted in the radial direction by heating, a hollow member made of a thermosetting resin or a thermosetting resin prepolymer disposed inside the heat-shrinkable tube, and the heat-shrinkable tube. The heat-shrinkable tube and the hollow member are arranged so as to extend in the axial direction of the heat-shrinkable tube so that the heat-shrinkable tube and the hollow member can be heated, and are coated with or impregnated with a thermosetting resin prepolymer. 1. A reinforcing member for an optical fiber connection portion, comprising: an electrical resistance heating element, and an optical fiber can be inserted into the inside of the hollow member. 2) Permissible % Range In the reinforcing member described in item 1, the hollow member is a tube made of the thermosetting resin or thermosetting resin prepolymer, and the tube is made of the heat-shrinkable tube. A reinforcing member for an optical fiber connection portion, characterized in that the reinforcing member is arranged substantially parallel to each other on both sides. 2. The reinforcing member according to claim 1, wherein the hollow member is a layer that extends over the thermosetting resin or thermosetting resin prepolymer coated on the inner surface of the heat shrinkable tube. Reinforcing member for fiber connection. 4) In the reinforcing member according to any one of claims 1 to 5, the electrical resistance heating element is
Carbon fiber, fused silicon fiber. Nichrome alloy wire, iron-xemal ξ alloy wire, tungsten wire, molybdenum wire. A reinforcing member for an optical fiber connection part, characterized in that it is made of a platinum wire, a material mainly composed of platinum wires, or a material made by bundling them into a rod shape, a net shape, a chi, or a knee shape. 5) In the reinforcing member according to any one of claims S 1 to 4 Or, as the thermosetting resin,
Epoxy resin, phenolic resin g1. An optical fiber connection part characterized in that the resin is selected from the resin group consisting of unsaturated polyether resin, alkyd resin, polyurethane resin, amino alkyd resin, silicone resin, furan resin, melamine resin, diallyl phthalate resin, and area resin. reinforcing member. 6) a heat-shrinkable tube that can be radially contracted by heating;
a hollow member made of a thermosetting resin or a thermosetting resin prepolymer disposed inside the heat-shrinkable tube; and a heat-shrinkable tube arranged inside the heat-shrinkable tube such that the heat-shrinkable tube and the hollow member can be heated. a reinforcing member, comprising an electrical resistance heating element extending in the axial direction of the hollow member and coated with or impregnated with a thermosetting resin or a thermosetting resin prepolymer, and allowing an optical fiber to be inserted into the inside of the hollow member. is used to insert the fusion spliced optical fiber connecting portion into the hollow member, and then energizes the electrical resistance heating element to heat the heat shrinkable tube and shrink it in the radial direction. The thermosetting resin rI coated or impregnated on the hollow member and the electric resistance heating element! 1 or a thermosetting resin prepolymer is heat-cured to form a thermosetting layer, and the optical fiber connection part is heated to form a thermosetting layer with the optical fiber connection part and the electrical resistance heating element contained in the shrunk heat-shrinkable tube. A method for reinforcing an optical fiber joint, characterized by integrating it with a hardened layer.