JPS6218892B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a method for attaching an optical fiber core to a core for an optical fiber connector. (Prior art) Generally, in optical fiber connectors, an optical fiber is inserted and fixed into a microhole provided in the center of a core with good outer diameter precision, and two of these cores are connected to a cylindrical sleeve with good inner diameter precision. A method is used in which the two optical fibers inserted into the two cores are inserted from both sides so that the core centers of the two fibers coincide with each other and the fibers are butted and connected. Since optical fiber connectors are used not only indoors but also outdoors, they must have a structure that can prevent the optical fibers from breaking even under severe temperature conditions. The method of attaching the optical fiber core to the core as a pre-step of the above-mentioned connection method will be described below with reference to FIGS. 1a and 1b. FIG. 1a is a sectional view of a core for an optical fiber connector, and FIG. 1b is a diagram showing an optical fiber core wire attached to the core. In the figure, reference numeral 1 denotes a core, which has a shaft shape of a predetermined length, and has an optical fiber 6 with a standard diameter of 125 μm formed of low-loss quartz glass between the rear end surface 1a in the axial direction and the vicinity of the front end surface 1b. A hollow hole 2 into which an optical fiber core 5 whose outer periphery is covered with a nylon jacket having a standard cross-sectional area of at least 0.5 mm ² can be inserted, and the optical fiber core extends from the terminal end 2a side of the hollow hole 2 to the tip surface 1b. The optical fiber positioning microhole 3 into which the optical fiber 6 is inserted after removing the jacket from the wire 5 is penetrated so that the axes thereof coincide with each other. Note that 4 is the adhesive in the hollow hole 2.
The air vent hole 7 is a glass pipe for more firmly fixing the optical fiber 6 inside the hollow hole 2. In order to attach the optical fiber core 5 to the core 1 having such a structure, first, the outer sheath on the tip side of the optical fiber core 5 is removed to expose the optical fiber 6, and a glass pipe 7 is attached to the optical fiber 6. After inserting the core 1, adhesive is applied to the hollow hole 2 of the core 1, the tip of the optical fiber core 5, the optical fiber 6, and the glass pipe 7. Next, the optical fiber core 5, the optical fiber 6, and the glass pipe 7 are inserted into the hollow hole 2 provided at the axis of the core 1, and the tip 6a of the optical fiber 6 is inserted into the microhole 3. Fix with adhesive. In such a mounting method, the micro hole 3
Since the diameter of the hollow hole 2 is approximately 126 μm, it is difficult to spread the adhesive throughout the hollow hole 2, and since the adhesive itself contains air bubbles, it is difficult for the adhesive to harden. In this case, there have been cases where a cavity is created in the adhesive, and the strain force of the optical fiber 6 due to temperature change acts on the cavity, causing the optical fiber 6 to break. In order to reduce the occurrence of such cavities and to more securely fix the optical fiber 6 and the adhesive, the glass pipe 7 is used as described above, but even this cannot completely prevent the occurrence of cavities. When passing the glass pipe 7 through the optical fiber 6, since both are made of glass, the optical fiber 6 is scratched, and this may cause the optical fiber 6 to break over time. (Object of the invention) The object of the present invention is to solve the above-mentioned conventional problems.
It is made of low-loss quartz glass that can reduce the occurrence of optical fiber breakage due to temperature changes, without using a glass pipe that may damage the optical fiber, which is made of low-loss quartz glass. The present invention aims to provide a method for attaching an optical fiber core wire in which the outer periphery of an optical fiber having a standard diameter of 125 μm is covered with a jacket made of nylon having a standard cross-sectional area of at least ^0.5 mm 2 or a resin material having an equivalent modulus of elasticity. It is something. (Structure of the Invention) In order to achieve the above-mentioned object, the first invention provides an optical fiber having a standard diameter of 125 μm made of low-loss quartz glass, and the outer periphery of the optical fiber made of nylon having a standard cross-sectional area of 0.5 mm ² or an elastic modulus equivalent to that of at least 0.5 mm 2. An optical fiber core wire covered with a jacket formed of a resin member having a shaft shape of a predetermined length, and a hollow hole inserted between the rear end surface in the axial direction and the vicinity of the tip, Further, from the innermost end of the hollow hole to the tip surface, the optical fiber positioning microhole into which the optical fiber is inserted after removing the outer sheath from the optical fiber core wire is penetrated so that the axes of the optical fiber are aligned with each other. Using a core for an optical fiber connector made of In an optical fiber attachment method in which the tips of the fibers are fixed to each of the microholes with an adhesive, the length in the axial direction of the microhole is determined from the total length of the optical fiber portion after removing the jacket from the optical fiber core. The second invention is characterized in that the length of the optical fiber portion is set to be 1.5 mm or less after subtracting the length of the optical fiber. A cored optical fiber is formed into a shaft shape of a predetermined length and covered with an outer sheath made of nylon with a standard cross-sectional area of 0.5 mm ² or a resin material with an equivalent modulus of elasticity.
and a hollow hole to be inserted between the rear end surface in the axial direction and the vicinity of the tip, and an optical fiber after removing the outer sheath from the optical fiber core wire from the innermost end of the hollow hole to the tip surface. Using an optical fiber connector core formed by penetrating a microhole for positioning the optical fiber into which the fiber is inserted so that their axes coincide with each other, the core of the optical fiber is inserted into the hollow hole, and the optical fiber is inserted into the microhole. In the method for attaching an optical fiber, the optical fiber is inserted into the core and fixed at a position approximately 30 mm from the end surface of the optical fiber by a crimp/holding member for the optical fiber provided on the rear end side of the core. The present invention is characterized in that the length of the optical fiber portion obtained by subtracting the axial length of the microhole from the total length of the optical fiber portion from which the jacket is removed from the fiber core wire is set to be 3.5 mm or less. (Embodiment) FIG. 2 shows an embodiment of the present invention, in which the same components as those of the conventional example are denoted by the same reference numerals. That is, 1 is a core, which has the same configuration as that described in the conventional example, so its explanation will be omitted. 5
is an optical fiber core wire, and 6 is an optical fiber. l is the axial length of the optical fiber positioning microhole 3, L
is the total length of the optical fiber 6. The method of attaching the optical fiber core 5 to the core 1 requires not using the glass pipe 7, and setting the value of L-l (the length of the inner portion of the hollow hole 3 of the optical fiber 6) as described below. The conditions are the same as in the conventional example except that the adhesive is applied to the inner peripheral surface of the core 1 and the optical fiber core 5.
and the optical fiber 6. Below is L
- Explain the relationship between the value of l and the force acting on the optical fiber 6. A cross-sectional structure of the optical fiber core wire 5 is shown in FIG.
Optical fiber 6 with a standard outer diameter of 125 μm made of low-loss quartz glass in the center 6 with silicone rubber in the middle.
Buffer layer 5 made of material with low Young's modulus such as UV cure
a. It has a structure in which a nylon coating 5b etc. is provided on the outside, and the nylon coating 5b and the optical fiber 6 are not in complete contact with each other. Therefore, shrinkage stress in the longitudinal direction is generated in the nylon coating 5b due to the release of strain in the nylon coating 5b that occurs during the production of the optical fiber core, contraction of the nylon coating 5b due to temperature changes, etc.
An attempt is made to generate a displacement between the optical fiber 6 and the nylon coating 5b. Here, the buffer layer 5a can be excluded because its Young's modulus is small. However, the nylon coating 5b is fixed to the core 1 with adhesive, and the tip 6a of the optical fiber 6 is attached to another connector 1.
Since the stress is fixed at 0, the shrinkage stress generated in the nylon coating 5b acts in a direction that compresses the optical fiber 6 shown in FIG. 2 in the longitudinal direction. It should be noted that since the adhesion of silicon is not good, it has been observed that the optical fiber 6 and the adhesive peel off over time. For this reason, the optical fiber core 5 is connected to the core 1.
If the adhesive is not injected sufficiently deep into the hollow hole 2 of the core 1, a certain amount of void will be generated inside the hollow hole 2 as shown in Fig. 2, and due to the compressive force mentioned above. The optical fiber 6 will easily break near the cavity. Figure 4 shows the low temperature state (-20
3 is a graph showing the results of measuring the amount of optical fiber protrusion after leaving optical fiber cores of various lengths at a temperature of 10.degree. C. for two weeks. Based on the data shown in FIG. 4, the stress acting on the optical fiber 6 is determined. Now, in an optical fiber core wire of length δ (cm),
A strain of ε ₀ occurs in the nylon coating, and the elastic modulus and cross-sectional area of nylon at low temperature are expressed as E _L and A, respectively.
Then, per unit length of nylon, ε ₀ E _L A
The contraction force due to temperature change and the contraction force due to temperature change εtE _L A
occurs. However, εt is the strain due to temperature change. In addition, the frictional force between the buffer layer and the optical fiber is λ
(Kg/mm) and the distance from the end of the optical fiber to x, the frictional force at x is λx.
The relationship between them is shown in FIG. When the optical fiber is long, the frictional force becomes larger than the contraction force as x becomes larger. In this case _, if _the amount of nylon shrinkage at _the terminal is △δ ₁ , ^then _△ δ ₁ = ^∫ /2λ, where λx ₁ =(εo−εt)E _L A (1). Furthermore, when the optical fiber core wire is short, the nylon coating moves over the entire region, so the amount of nylon shrinkage Δδ ₂ at the end face of the optical fiber is expressed by equation (2). By the way, from Fig. 4, when δ=50mm, △δ ₂
= 0.13 mm and δ = 500 mm, △δ ₁ = 0.28 mm, so substitute each value into equations (2) and (1), and get εo−εt=6.01×10 ^-3 (3) λ _{/ELA=6.48×10} ^-5 (4) is obtained. The stress F acting on the optical fiber at the end face portion (x=0) of the optical fiber core wire is expressed as F=(εo−εt)E _L A (5). From E _L = 120Kg/mm ² and A = 0.51mm ² , F = 368g. It is generally known that when a compressive force exceeding a certain value is applied to a long and thin rod such as an optical fiber, the rod will buckle. The load at which buckling occurs (Euler's buckling load) P is expressed by equation (6). P=π ² EI/(L-l) ² (6) where E is the elastic modulus of the optical fiber and I is the cross section 2
This is the next moment. If the radius of the optical fiber is r, E=7200Kg/mm ² , I=π/4r ⁴ , r=0.0625mm, so the buckling load P is P=852×1/(L-l) ² (g) (7) It is expressed as A graph of equation (7) is shown in Figure 6. Assuming that the buckling load P and the stress F acting on the optical fiber are equal, 368=852×1/(L−l) ² (8) gives L−l=1.52 mm. Therefore, if the value obtained by subtracting the length l of the microhole for positioning the optical fiber provided in the core from the length L of the optical fiber part obtained by removing the outer sheath from the optical fiber core wire is set to 1.5 mm or less, the optical fiber As long as the fiber is not damaged, the optical fiber will not break due to the fiber extrusion phenomenon caused by temperature changes, regardless of the presence or absence of adhesive. Figures 7 and 8 show an example of a method for attaching the optical fiber to the core by using the optical fiber core crimping/holding member provided on the rear end side of the core without using adhesive. . The core 21 used in this embodiment has a shaft shape with a predetermined length, and has a hollow hole 22 into which the optical fiber core 5 can be inserted between the rear end surface 21a in the axial direction and the vicinity of the front end surface 21b. The optical fiber positioning microhole 23 into which the optical fiber 6 is inserted after removing the jacket from the optical fiber core wire 5 from the terminal end 22a side of the hollow hole 22 to the tip surface 21b is made so that their axes coincide with each other. The core 21 has a hollow hole 22 at its rear end.
A crimping/holding member 25 is provided for crimping and holding the outer periphery of the optical fiber core 5 inserted therein. This crimping/holding member 25 has a threaded portion 26 of an outer cylinder (described later) having a male thread 26a carved on its outer periphery, and a cylindrical shape extending from the outer periphery of the rear end surface 21a so as to gradually become smaller in diameter toward the rear end. The caulking part 27 and a female thread 28a that engages with the male screw 26a are carved on the inner side of the tip, and the rear end of the caulking part 27 comes into contact with the outer peripheral surface of the caulking part 27 on the inside of the rear end and moves toward the tip side. It consists of an outer cylinder 28 provided with a stepped part 28b for pushing the parts inward. A plurality of cracks 29 are provided at intervals in the circumferential direction over the entire axial length of the caulked portion 27 and a portion of the core 21 adjacent thereto. To attach the optical fiber core 5 to the core 21 having such a structure, first remove the outer tube 28, insert the optical fiber core 5 into the hollow hole 22 in the same way as in the conventional case, and insert the tip 6a of the optical fiber 6 into the hollow hole 22. After inserting into the microhole 23, the outer cylinder 28 may be screwed into the threaded portion 26 again. As a result, the stepped portion 28b of the outer tube 28 pushes the rear end portion of the caulking portion 27 inward, so that the rear end portion is crimped onto the outer periphery of the optical fiber core wire 5 and held therein. FIG. 9 shows the force acting on the optical fiber core of the core 21 in this embodiment. Compared to FIG. 5, a frictional force f is generated due to caulking, and the direction in which f acts is a direction that reduces the stress generated in the optical fiber. If the distance from the end face of the optical fiber core wire to the caulking position is taken as the distance, the stress F in the nylon jacket acting at is expressed by equation (9). F=(εo−εt)E _L A−λ−f (9) εo, εt, H _L , A, and λ are the same as in equation (5). Since the nylon jacket is fixed by the caulking portion 27 and the tip end is also fixed by another connector 10, the force expressed by equation (9) acts on the optical fiber 6 as a compressive force. By the way, from equations (3) and (4), εo−εt=6.01×10 ^-3 (Kg/mm ² ) β=3.97 (g/mm), so equation (9) can be expressed as follows. . F=368−3.97−f(g) (10) Also, the value of the prototype optical connector is 30mm
Therefore, equation (10) can be expressed as the following equation. F=248.9−f (11) In this way, the compressive force acting on the optical fiber 6 can be reduced by the crimping force. The relationship between the value (L-l) obtained by subtracting the length l of the optical fiber positioning microhole 23 provided in the core 21 from the total length L of the optical fiber 6 portion and the buckling load of the optical fiber is as follows.
This is the same as equation (7). Next, the core 2 having the configuration shown in FIGS. 7 and 8
Experiments were also conducted on the case where an optical fiber connector using 1 was fabricated and the value of L-l was changed, and the results will be explained below. Table 1 shows the value of L-l, the state of optical fiber breakage due to temperature cycles, and the buckling load calculated using equation (7). FIG. 10 shows the temperature change in one cycle of the temperature cycle. 1 cycle in 6 hours
The temperature is changed from 60℃ to -20℃.

[Table] When the value of L-l was 13 mm, an experiment was conducted using three samples, and the first sample broke in the second cycle, the second sample in the first cycle, and the third sample in the third cycle. In the table, the average is taken and it is shown that the breakage occurred in the second cycle. In this way, L
- If the value of l is large, long-term reliability as an optical connector cannot be ensured. However, when the buckling load is 70 g or more and the L-l value is 3.5 mm or less, no fracture occurs even after 28 cycles of temperature change. Furthermore, when we monitored the connection loss fluctuations of this connector during 28 cycles of temperature change, the fluctuation range was less than 0.1 dB in all cases.
Thus, it can be concluded that sufficient long-term reliability can be ensured by setting the value of L-l to 3.5 mm or less. Compared to the type of core shown in Figure 2, the L-l value required for the type of core shown in Figures 7 and 8 to have long-term reliability is longer because: Depends on the reason. ○...Ni

Claims (1)

[Claims] 1. Standard diameter 125 made of low-loss quartz glass.
The outer circumference of an optical fiber is at least standard cross-sectional area of μm.
An optical fiber core wire covered with an outer sheath made of 0.5 mm ² nylon or a resin material having an equivalent elastic modulus is formed into a shaft shape of a specified length, and from the rear end surface in the axial direction to the vicinity of the tip. The hollow hole into which the optical fiber is inserted between the ends of the hollow hole and the optical fiber positioning microhole into which the optical fiber is inserted after removing the outer sheath from the optical fiber core from the innermost end of the hollow hole to the tip surface are mutually connected. The optical fiber core is inserted into the hollow hole and the optical fiber is inserted into the micro hole using a core for an optical fiber connector which is penetrated so that the axes of the optical fiber core coincide with each other. In the method for attaching an optical fiber, the outer periphery of the optical fiber is fixed to the inner surface of the hollow hole and the tip of the optical fiber is fixed to the microhole with an adhesive, and the optical fiber is removed from the outer sheath from the optical fiber. 1. A method for attaching an optical fiber core, characterized in that the length of the optical fiber portion, which is calculated by subtracting the axial length of the microhole from the total length of the portion, is set to be 1.5 mm or less. 2 Standard diameter 125 made of low loss quartz glass
The outer circumference of an optical fiber is at least standard cross-sectional area of μm.
An optical fiber core wire covered with an outer sheath made of 0.5 mm ² nylon or a resin material having an equivalent elastic modulus is formed into a shaft shape of a specified length, and from the rear end surface in the axial direction to the vicinity of the tip. The hollow hole into which the optical fiber is inserted between the ends of the hollow hole and the optical fiber positioning microhole into which the optical fiber is inserted after removing the outer sheath from the optical fiber core from the innermost end of the hollow hole to the tip surface are mutually connected. Using an optical fiber connector core formed by penetrating the core so that their axes coincide with each other, insert the optical fiber core into the hollow hole and the optical fiber into the microhole, and In an optical fiber attachment method in which a position approximately 30 mm from the end face of the optical fiber is fixed by a crimp/holding member for the optical fiber, the jacket is removed from the optical fiber. 1. A method for attaching an optical fiber core, characterized in that the length of the optical fiber portion, which is calculated by subtracting the axial length of the microhole from the total length of the optical fiber portion, is set to be 3.5 mm or less.