JPS635732B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing an optical connector for connecting optical fibers used in an optical communication system. As the next generation of electrical information transmission systems, optical information transmission systems, i.e.
Optical communication systems are being developed. In this optical communication system, an optical signal oscillated on the transmitting side is sent to the receiving side through an optical fiber formed with a thickness of 100 to several 100 μm, and the receiving side converts the optical signal into an electrical signal. It is something to take out. In such optical communication systems, an important issue is how to efficiently and stably transmit signals from the transmitting side to the receiving side. In an optical communication system, optical loss occurs at the connection (butt) between an optical fiber that transmits a signal and an optical connector that connects the optical fiber. And the loss inside the optical fiber is 0.several dB/Km
Progress is being made to reduce the loss to around 1 dB/Km. On the other hand, in an optical connector, the amount of loss greatly depends on the amount of eccentricity of the axes of a pair of optical fibers that are butted together by the optical connector.
For example, in the case of an optical fiber with a cladding diameter of 125 μm and a core diameter of 50 μm, if the axes of the optical fibers to be butted are eccentric by about 4 μm, it is 0.5 dB, and if the axes of the optical fibers are eccentric by about 7 μm, it is 1 dB.
connection loss occurs. Therefore, in order to carry out long-distance communication, repeaters are installed at required intervals, and attenuated signals are amplified and transmitted each time. At this time, if the connection loss in the optical connector increases, the number of repeaters must be increased. Increasing the number of repeaters is not only economically undesirable, but also requires complicated maintenance and inspection.
Moreover, many problems occur, such as lowering the reliability of the entire communication system. In addition, the length required for each optical fiber differs depending on its installation location and route.
It is required that the work of attaching connectors to optical fiber terminals be easily performed on-site. Therefore, optical connectors are required to have low connection loss and be easy to assemble. Optical connectors usually have a flange formed in the middle of the outer peripheral surface, a plug with a hole in the shaft center to accommodate the optical fiber, and a through hole in the shaft center that fits into the outer peripheral surface of the plug. , a sleeve having a thread formed on its outer peripheral surface, a cap nut that is screwed into the thread of the sleeve, and a spring that is inserted between the plug pin and the cap nut to maintain a constant abutting force of the plug. The positional accuracy of the optical fiber is determined mainly by the accuracy of the plug and the sleeve, and a particularly important issue is to reduce the deviation between the axes of the plug and the optical fiber. For this reason, conventionally, the outer shape of the plug was made of hard metal, and a double eccentric tube was built into the shaft center, and a guide made of gemstone or ceramic was embedded in the shaft center, and the guide was slightly smaller than the optical fiber. Those with large diameter holes are generally used. However, in a plug that uses double eccentric tubes, the optical fiber is fixed to the eccentric tube in the center, and then the two eccentric tubes are moved while observing with a microscope to position the optical fiber at the axis of the plug. This method has the disadvantage of extremely poor workability. Furthermore, in a plug with an embedded guide, the tip of the optical fiber is positioned by the guide, which has the advantage of greatly improving on-site workability. However, machining the plug, that is, drilling a hole of a few millimeters in the guide, requires a high level of skill and a long machining time, which has the disadvantage of extremely poor productivity. An object of the present invention is to provide a method for manufacturing an optical connector that eliminates the drawbacks of the above-mentioned prior art and allows easy and highly accurate assembly at the site where optical fiber connections are required. be. In order to achieve the above object, in the present invention,
When forming the plug, the optical fiber insertion hole of the plug is formed by a core pin protruding from the end surface of the core forming the abutting side end surface of the plug. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a state in which optical fibers are connected using an optical connector according to the present invention. The optical fiber 1 has a structure in which a strand 2 for transmitting light and a primary coat 3 and a secondary coat 4 that reinforce the strand 2 are coated. The plug 6 of the optical connector 5 is formed into a cylindrical shape so that a hole 7 into which the optical fiber 1 from which the secondary coat 4 has been removed is communicated with a hole 8 into which the strand 2 is inserted communicates with each other. A flange 9 is formed at the center of the outer peripheral surface. A through hole 11 into which the plug pin 6 is inserted is formed in the sleeve 10, and tapered guide portions 12 are formed at both ends of the through hole 11 to expand toward the opening. Further, a central flange 13 is formed on the outer peripheral surface of the sleeve 10, and screws 14 are formed at both ends. The plug pin 6 is slidably fitted into the cap nut 15, and the flange 9
The sleeve 10 is formed into a cylindrical shape with a through hole 17 having a protruding flange 16 facing the sleeve 10, and a screw 18 that engages with the screw 14 of the sleeve 10 is formed at one end of the through hole. The spring 19 is inserted into the outer periphery of the plug 6 so as to be located between the flanges 9 and 16. The plug 6 and the secondary coat 4 of the optical fiber 1 are integrally connected by a clamp ring 20 and a cable cap 21, and when the plug 6 is inserted into or removed from the sleeve 10, no insertion or removal force is applied to the strands 2. It seems like there is no such thing. In the above configuration, the optical connector is assembled as follows. the optical fiber 1, the plug 6, the sleeve 10,
The cap nut 15, the spring 19, the clamp ring 20, and the cable cap 21 are each formed into a required shape at a factory, and then transported individually to the site. At the site, first attach the cable cap 21 to the terminal of the optical fiber 1 to be connected.
Insert the clamp ring 20, cap nut 15, and spring 19 in this order, and move them to a position where they will not interfere with the work. Next, the secondary coat 4 is removed to a predetermined length from the end of the optical fiber 1, and the primary coat 3 is removed to a predetermined length from the end.
After removing the coating, the area from which the coating was removed is washed with an organic solvent. Meanwhile, the holes 7 and 8 of the plug pin 6 are filled with an appropriate amount of adhesive. Then, the end of the optical fiber 1 is inserted from the hole 7 side of the plug pin until the strand 2 protrudes from the hole 8 by a predetermined amount. After the adhesive has hardened, the tip of the plug 6 is fixed, and the cap nut 15 is attached to the spring 19.
After moving the plug 6 toward the distal end side within the compressible range and locking it, position the clamp ring 20 so that one end is on the plug 6 and the other end is on the secondary coat 4 of the optical fiber 1, and apply the adhesive. The clamp ring 20, plug 6 and secondary coat 4 are bonded together. Similarly, the cable cap 21 is glued to the clamp ring 20 and the secondary coat 4. Then, the cap nut 15 is released and the spring 19 returns it to the center of the optical fiber 1. Then,
The wire 2 protruding from the tip of the plug 6 is connected to the plug 6.
Cut to fit the tip of the Next, the plug 6 is inserted into a wrapping jig and the tip of the plug 6 is polished. After polishing to the required surface roughness, the surfaces of the plug 6 and the wire are cleaned. Next, plug 6
When the optical fiber 1 is inserted into the sleeve 10 and the cap nut 15 is tightened, the connection of the optical fiber 1 by the optical connector 5 is completed. Note that the space between the hole 7 of the plug 6, the wire 2, and the secondary coat 3, and the space between the hole 8 and the wire 2 are filled with adhesive. The sleeve 10 and cap nut 15 of the optical connector 5 are molded by a conventional molding method. The plug 6 is molded using a mold, only the main part of which is shown in FIG. Note that the parts not shown are the same as those of a known three-layer mold. In FIG. 2, a lock pin 31 is provided protruding from the fixed side mounting plate 30. As shown in FIG. Fixed side template 32
A first core 33 forming the outer periphery of the tip of the plug 6 is embedded therein. At one end of this core 33, there is a second core 3 that forms the tip end surface of the plug 6.
4 are buried. This core 34 has a hole 35 for removing air from the cavity forming the flag 6, and a hole 36 that communicates with the hole 35 and accommodates the air inside the cavity together with the resin. A second cavity is formed by the fixed side mounting plate 30 and the hole 36. The core 34
A core pin 37 that is slightly thicker than the strands 2 of the optical fiber 1 is erected at the center of the end face of the optical fiber 1 . A core 39 that forms the outer periphery of the flange 9 and the rear end of the plug 6 is embedded in the movable template 38 . A disc-shaped groove 40 is formed in the movable template 38 and the core 39, and forms a disc-shaped runner with the template 32, and an annular protrusion 41 formed in the core 39 and the template 32 constitute a circular gate. The core 39 has an ejector pin 4.
2 is slidably inserted and forms the rear end surface of the plug 6. Furthermore, at the axis of the ejector pin 42,
A core pin 43 on the movable side that is thicker than the outer diameter of the secondary coat 4 of the optical fiber 1 is slidably inserted, and when the mold is clamped, the tip of the core pin 43 comes into contact with the core pin 37. . With such a configuration, when the mold is clamped and the synthetic resin 44 is supplied from a molding machine (not shown) to the runner, the synthetic resin 44 fills the runner and passes through the gate to the cores 33, 34 and the core pin 3.
7, it flows into the cavity formed by the core 39, the ejector pin 42 and the core pin 43, and the plug pin 6 is formed. At this time, the air in the cavity that has not been exhausted from the mating surfaces of the mold and other gaps is forced into the second cavity through the hole 35. When opening the mold after the synthetic resin has hardened, the movable mold plate 38 is first moved backward. Then, the molded plug 6 moves together with the movable template 38. At this time, the synthetic resin stuck in the hole 35 is broken, and the plug 6 and the synthetic resin in the second cavity are separated. When the movable mold plate 38 is sufficiently retracted, the ejector pin 42 is activated.
The plug 6 protrudes from the core 39 and further protrudes from the core pin. At the same time, the fixed template 32 moves together with the movable template 38 and separates from the fixed mounting plate 30. Then, the hardened synthetic resin flowing into the second cavity is caught on the ejector pin 31 and remains on the fixed side mounting plate 30, so that the hardened synthetic resin inside the holes 35 and 36 of the core 34 is removed.
In this state, the hardened synthetic resin is removed from the ejector pin 31. In this way, the hole 8 for inserting the strand 2 of the optical fiber 1 into the core that forms the tip end surface of the plug 6.
By forming the plug 6 with the core pin standing upright, the position of the hole 8 relative to the plug 6 can be formed with extremely high precision. Further, by providing the second cavity, the shape accuracy of the tip of the plug 6 can be improved. The plug 6 is molded using a thermosetting resin or a thermoplastic resin, but when using a synthetic resin alone,
Since the hardness of the optical fiber 1 is extremely lower than that of the strand 2, when the end face of the plug 6 is polished after the optical fiber is assembled, the amount of protrusion of the strand 2 from the end face of the plug 6 becomes large. For this reason, an inorganic filler is mixed with the synthetic resin to improve the hardness of the plug 6. As the filler, for example, glass beads, hollow glass spheres, volcanic glasses, metals such as aluminum and iron and their oxides, graphite, calcium carbonate, etc. can be used. Example 1 A plug 6 was formed using a mold shown in FIG. 2 using polycarbonate, which is generally easily available, as a synthetic resin, glass fiber, carbon fiber, and glass beads with an average particle size of 10 μm as a filler.
The dimensions and connection characteristics shown in FIG. 4 and FIG. 4 were measured, and their acceptance or failure was determined. The measurement items are as follows. (1) Roundness of the tip of the plug 6, (2) Concentricity (deviation amount) of the axis of the hole 8 with respect to the axis of the tip of the plug 6, (3) Distance from the flange 9 of the plug 6 to the tip. length l
(4) Surface roughness of the outer circumferential surface of the plug 6, (5) The tip surface of the plug 6 after assembly and polishing and the strand 2
(6) Connection loss as optical connector 5. In addition, the criteria were that the connection loss was 1 dB or less, and the maximum level difference on the end face of the plug was 4 μm or less. The results are shown in Table 1. (In addition,
The connection loss in the table is between plug pin 6 and sleeve 10.
The measurement was made with the fitting clearance between the two parts set to zero. (Same for Tables 2 to 4)

【table】

[Table] As is clear from Table 1 above, glass beads are used as fillers in polycarbonate.
The one containing 30.2wt% is suitable for optical connectors. In addition, as a filler, in addition to glass beads,
A hollow glass bulb or quartz glass may also be used. In addition, when adding more than 30% of glass beads,
The mechanical properties of the plug pin 6 deteriorate or become unmoldable. Furthermore, it is necessary to uniformly disperse glass beads in polycarbonate, and the amount of glass beads added in actual production is preferably 10 to 30%. On the other hand, when used as the optical connector 5, the plug 6 is repeatedly inserted into and removed from the sleeve 10. Therefore, it is desirable to reduce the wear between the plug 6 and the sleeve 10 in locations where the plug is inserted and removed many times. Therefore, among various lubricants, tetrafluoroethylene (PTFE) and molybdenum disulfide (MoS ₂ ) were added and the lubricating effect was measured. The measurement items were the same as those in Table 1 above, with the addition of connection loss after 200 insertions and removals. In addition, the criterion was that the connection loss after 200 insertions and removals should not be greater than 0.2 dB compared to the initial connection loss. Note that polycarbonate with 30 wt% glass beads added was used. The results are shown in Table 2.

[Table] As is clear from Table 2 above, when using PTFE as a lubricant, the expected lubricating effect cannot be obtained unless it is added in an amount of 5 wt% or more. Also, the amount added is
If it exceeds 30 wt%, fluidity during molding will decrease, which is not preferable. Therefore, if PTFE is added, the amount should be 5 to 30 wt%. Moreover, in the case of _MoS2 , 1 to 5% is optimal. Example 2 The same study as in Example 1 was conducted using an epoxy resin as the synthetic resin and glass beads made of quartz glass with an average particle size of 10 μm as the filler. The results are shown in Table 3.

[Table] Note D in the table indicates the case of epoxy resin only.
As is clear from Table 3 above, when the plug 6 is molded from epoxy resin, it is desirable to add 30 to 80 wt % of glass beads as a filler to the epoxy resin. When the amount of glass beads exceeds 81%, the fluidity of the resin during molding decreases and moldability decreases. Here, in the case of epoxy resin, the reason why the amount of filler added is large is considered to be due to the difference in inherent properties between polycarbonate and epoxy resin and the difference in fluidity (viscosity) during molding. In addition, as in Example 1, the amount of lubricant added for insertion and removal of the plug 6 into and out of the sleeve 10 was also confirmed. The sample used was an epoxy resin with 69wt% of silica glass added, and the lubricant was:
Using PTFE, MoS ₂ and graphite. The results are shown in Table 4.

【table】

[Table] As is clear from Table 4 above, adding lubricant can reduce the connection loss after 200 insertions and removals. Note that the amount of lubricant added is preferably 1 to 5 wt% from the viewpoint of lubricating effect, moldability, etc. Next, in order to make it smaller than the connection loss, the third
The outer diameter D 1 of the strand 2 of the optical fiber _{1, the inner diameter d 1 of the hole 8 of the plug 6, the outer diameter D 2 of the} tip of the plug 6, and the inner diameter of the through hole 11 of the sleeve 10 shown in FIGS. must be regulated. First, in order to align the axis of the wire 2 with the axis of the hole 8 of the plug 6, the inner diameter _d1 of the hole 8 only needs to be the same as the outer diameter _D1 of the wire 2. However, if the inner diameter d ₁ of the hole 8 and the outer diameter D ₁ of the strand 2 are the same,
Not only is it difficult to pass the wire 2 through the hole 8,
There is no gap between the hole 8 and the wire 2 for the adhesive to enter. On the other hand, if the diameter d ₁ of the hole 8 is sufficiently larger than the outer diameter D ₁ of the wire 2, the amount of eccentricity between the axis of the hole 8 and the axis of the wire 2 becomes large. For this reason, the inner diameter d ₁ of the hole 8 is made larger than the outer diameter D ₁ of the strand 2 by 1 to 2 μm. Then,
The strand 2 can be easily inserted into the hole 8, and the hole 8 and the strand 2 can be easily inserted.
The amount of eccentricity can also be suppressed to 0.5 to 1 μm. Further, an adhesive flows between the hole 8 and the wire 2 and is bonded thereto. In addition, the outer diameter D ₂ of the plug 6 and the sleeve 1
The inner diameter d ₂ of 0 is determined by the insertion/extraction force of the plug 6 and the connection loss. For example, the outer diameter of plug 6
Using the difference between D ₂ and the inner diameter d ₂ of the sleeve 10 (D ₂ - _{d 2} ) as the fitting clearance, the sleeve 10 of the plug 6
The insertion/extraction force and connection loss are as shown in FIG. FIG. 6 shows a combination of a plug 6 made of epoxy resin with 69% filler added and a sleeve 10. In FIG. 6, A represents insertion/extraction force, and B represents connection loss. In a region where the fitting clearance is (-), the plug 6 is press-fitted into the sleeve 10, and although the insertion/extraction force is large, the connection loss is small. On the other hand, it can be seen that in the region where the fitting clearance is (+), the insertion/extraction force is small, but the connection loss is large. Further, FIG. 7 shows the relationship between the number of insertions and removals and the amount of change in connection loss with respect to initial connection loss. In Figure 7,
a is when the initial fitting clearance is -3μm,
b shows the case where the initial fitting clearance is -2 μm. As is clear from Fig. 7, when the mating clearance increases in the (-) region, the frictional force between the plug 6 and the sleeve during insertion and removal also increases, and wear increases accordingly, resulting in a change in connection loss. growing. Therefore, by setting the fitting clearance between the plug 6 and the sleeve 10 in the range of -3 to +2 μm, it is possible to suppress the connection loss including insertion and removal of the plug 6 to 1 dB or less. FIG. 8 shows the effects of the combination of materials of the plug 6 and sleeve 10 and temperature changes on connection loss. In FIG. 8, A1 indicates that when the sleeve 10 is made of epoxy resin and the plug 6 is made of polycarbonate,
B1 shows that the plug 6 and sleeve 10 are both made of epoxy resin (the fitting clearance is set to 0 at 22°C).As is clear from Fig. 8, if they are made of the same material, they will It will not be affected. Therefore, the plug 6 and the sleeve 10
It is desirable that the two be made of the same kind of material. As an adhesive, use epoxy-based low viscosity (viscosity
(20 poise or less) adhesive. Furthermore, when a filler is added to the adhesive, the amount of eccentricity between the axis of the hole 8 of the plug 6 and the axis of the strand 2 of the optical fiber 1 can be further reduced. For example, as a filler to be added to the adhesive, when d ₁ = D ₁ + 1 μm, add alumina powder with an average particle size of 0.3 μm to the adhesive at a rate of 40 μm.
Add ~60wt%. Then, the hole 8 and the wire 2
Since the filler is uniformly distributed between the holes 8 and the strands 2, the eccentricity between the axes of the holes 8 and the strands 2 can be kept at most 0.2 μm or less. Note that the average particle size of the filler is approximately 50 to 70% of the clearance between the hole 8 and the wire 2. The material of the filler is also selected appropriately. FIG. 9 shows another embodiment of the present invention, in which the same parts as in FIG. 1 are designated by the same reference numerals. The glass pipe 25 is inserted into the wire 2 of the optical fiber 1, and the plug 6 is inserted together with the wire 2.
is inserted into the hole 7 of the plug 6 and connected to the plug 6 and the wire 2 with adhesive. With this configuration, areas that experience large temperature changes, such as pipes in chemical plants, internal monitoring of processing equipment, or data transmission installed in the rolling process of steel plants, can be repeatedly heated and cooled. Suitable for use in places. In other words, if the optical connector 5 is repeatedly heated and cooled to around 100°C or more,
Due to the difference in thermal expansion between the strand 2 of the optical fiber 1, the plug 6, and the adhesive, the adhesive peels off and when the adhesive protrudes from the tip of the plug 6 due to thermal expansion, the strand 2 They will be extruded at the same time. This reduces the reliability of transmission. However, by providing the glass pipe 25, the wire 2 is restrained by the glass pipe 25, so that the wire 2 can be prevented from protruding from the plug 6 even when heated or cooled. According to the present invention, an optical connector that can be assembled easily and with high precision at a site where optical fiber connection is required can be produced inexpensively and efficiently.

[Brief explanation of the drawing]

Figure 1 is a front sectional view showing the optical connector;
The figure is a front sectional view showing the main parts of the mold for molding the plug, Fig. 3 is a front sectional view of the plug, Fig. 4 is an enlarged view of the main part of Fig. 3, and Fig. 5 is a front sectional view of the sleeve. , Fig. 6 is a characteristic diagram showing the relationship between the mating clearance between the sleeve and the plug, plug insertion/extraction force, and connection loss, Fig. 7 is a characteristic diagram showing the relationship between the number of times of plug insertion/extraction and connection loss, and Fig. 8 is a characteristic diagram showing the relationship between the mating clearance of the sleeve and the plug, plug insertion/extraction force, and connection loss. A characteristic diagram showing the relationship between temperature and connection loss depending on the selection of the material of the sleeve, and FIG. 9 is an enlarged view of the main part showing another embodiment of the optical connector. 1... Optical fiber, 2... Bare wire, 3... Primary coat, 4... Secondary coat, 5... Optical connector, 6
...Plug, 7 ... Hole, 8 ... Hole, 9 ... Flange, 10 ... Sleeve, 11 ... Through hole, 12 ...
...Guide part, 13...Flange, 14...Screw,
15... Bag nut, 16... Flange, 17...
Through hole, 18...screw, 19...spring, 2
0... Clamp ring, 21... Cable cap, 25... Glass pipe, 30... Fixed side mounting plate, 31... Lock pin, 32... Template, 33...
...core, 34...core, 35...hole, 36...
Hole, 37...Core pin, 38...Movable side template, 3
9...Core, 40...Groove, 41...Protrusion, 42...
...Ejecta pin, 43...Core pin, 44...
Synthetic resin.

Claims (1)

[Claims] 1. A plug that is attached to the end of the optical fiber with adhesive, a sleeve that has screws formed on both ends of the outer peripheral surface and into which the plug is inserted into the shaft center from both ends, and one end of the inner peripheral surface that has the screws. In a method of manufacturing an optical connector, the method includes: a cap nut having a screw thread formed thereon and fixing the plug to the sleeve; and a spring inserted into the outer periphery of the plug so as to be positioned between the plug and the cap nut. , the plug is arranged at a distance of 1 to several μm from the outer diameter of the optical fiber strand at the center of the first core forming the outer periphery of the plug.
A large first core pin and a second core forming the tip of the plug having an air vent hole around it are fitted together, and the tip of the first core pin is extended from the rear end of the plug. 1. A method of manufacturing an optical connector, the method comprising molding the optical connector using a mold in which the second core pins are brought into contact with each other.