JPH08211248A - Terminal structure of optical fiber - Google Patents

Abstract

PURPOSE: To lessen an increase in insertion loss and to obtain light input and output stable over a long period of time by relatively fixing a part exposed with a primary coating in a ferrule and a part having a secondary coating through the metallic member of the ferrule, thereby preventing the peeling at the boundary between the primary coating and the secondary coating and making it possible to maintain the stable strength of adhesion. CONSTITUTION: The part 8 which is the secondary coating part 4 at the end of a coated optical fiber 1 and exists in the ferrule 2, the primary coating exposed part 3 which comes into contact with the front end of the secondary coating part 4 and from which the secondary coating is removed and the optical fiber exposed part 1a which comes into contact with the front end of the primary coating exposed part 3 and from which both of the primary coating and the secondary coating are removed are fixed in the ferrule 2 by an adhesive 10. The end of the primary coating exposed part 3 of this terminal structure of the optical fibers on the side being in contact with the optical fiber exposed part 1a exists near the through-hole part 12 and the length A(mm) of the primary coating exposed part 3 satisfies the following equation: 0.5t<=A<t, where t(mm) denotes the length of a coated fiber holding part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber terminal structure in which the coating of an optical fiber core wire is removed and the optical fiber core wire is attached to a ferrule.

[0002]

2. Description of the Related Art FIG. 3 is a sectional view showing the structure of an optical fiber core wire. The optical fiber core wire 1 has an outer diameter of an optical fiber element wire 15 made of silica glass or the like having an outer diameter of 125 μm.
A primary coating 13 made of silicone resin or UV curable acrylic resin is coated, and the outer periphery of this coating is further coated with nylon or polyester elastomer 1
4 is coated. The primary coating 13 and the secondary coating 14 of the tip portion of the optical fiber core wire 1 are removed, and the optical fiber element wire 15 is exposed for use.

FIG. 4 is a sectional view showing the structure of a ferrule. The ferrule 2 has a substantially cylindrical shape with a length of ten and a dozen millimeters, and has a capillary 5 made of a sintered ceramic material and a metal member 6 concentrically covering the outer peripheral portion of the capillary. The hole 7 is formed. The fine holes 7 are precision processed to have a diameter slightly larger than the outer diameter of the optical fiber strand. Further, the core wire holding portion 8 processed to have an inner diameter slightly larger than the outer diameter of the optical fiber core wire having the secondary coating, and the minute hole 7 penetrate through the penetrating portion. An optical fiber core wire and an optical fiber element wire each having a secondary coating are usually located in the core wire holding portion 8 and the minute hole 7, respectively, and further, in the voids generated in the core wire holding portion 8 and the minute hole 7, An adhesive is injected, and the ferrule 2 and the optical fiber core wire and the optical fiber element wire are designed to be adhesively fixed.

5 to 7 show conventionally known methods for removing the coating of the optical fiber core wire and the mounting structure of the ferrule and the optical fiber core wire.

FIG. 5 shows an example disclosed in Japanese Patent Publication No. 5-10643. The optical fiber bare portion 1a from which the coating of the optical fiber core wire 1 has been removed is inserted into the minute hole 7 of the capillary 5 and fixed to the ferrule 2 with an adhesive 10. In this optical fiber core wire coating removing method, the primary coating and the secondary coating of the tip end portion of the optical fiber core wire 1 are collectively removed to expose the optical fiber bare portion 1a. In this example the primary coating is not exposed. In addition, in the mounting structure with the ferrule, the exposed portion 1a of the optical fiber bare wire is provided between the portion where the coating is removed and the capillary 5.
Is not stretched and is in a close contact state.

FIG. 6 shows an example disclosed in JP-A-62-192708. In this method of removing the coating of the optical fiber core wire, only the secondary coating on the tip portion of the optical fiber core wire 1 is removed, and the primary coating is exposed. Further, the primary coating of the tip portion is removed to expose the optical fiber element wire. The optical fiber wire from which the coating has been removed is inserted into the micro hole 7 of the capillary 5 and the ferrule 2 is applied with the adhesive 10.
Has been fixed. Here, in the core wire holding portion 8 of the ferrule 2, there is shown an adhesive fixing structure in which the primary coating is partially left and the secondary coating is removed, that is, a structure having the primary coating exposed portion 3.

FIG. 7 shows an example disclosed in Japanese Utility Model Publication No. 60-27361. The optical fiber element wire from which the coating of the optical fiber core wire 1 has been removed is inserted into the minute hole 7 of the capillary 5 and fixed to the ferrule 2 with an adhesive 10. The method of removing the coating of the optical fiber core wire is the same as the method described with reference to FIG. This structure is characterized by a mounting method, in which the exposed portion 1a of the optical fiber bare wire is extended to the inside of the core wire holding portion 8, and the glass capillary tube 9 is attached to the optical fiber bare wire in the core wire holding portion 8. It has been inserted. Although illustration is omitted, an example without this glass capillary tube 9 is also proposed.

[0008]

Problems to be Solved by the Invention The following problems are present in the method of removing the coating of the optical fiber core wire and the mounting structure of the optical fiber core wire whose coating is removed by the method and the ferrule. was there.

First, as shown in FIG. 5, the component in which the ferrule 2 and the optical fiber core wire 1 are bonded and fixed to each other is bonded by exposing the component to a temperature change under a natural environment and a reliability test environment. A phenomenon was observed in which the fixing strength decreased. The decrease in the fixing strength will induce a change in the fixed state of the ferrule and the optical fiber core wire or optical fiber element wire when a load such as tensile force is applied to the fixed part, and the optical transmission function such as disconnection can be maintained. There was a risk of causing defects to disappear.

Therefore, in order to ensure the reliability of the parts, the present inventor investigated the cause of the decrease in the adhesive fixing strength and the mechanism of the breakage by using the optical fiber terminal structure shown in FIG.

As a means for this, the ferrule obtained after the tensile test for measuring the breaking strength and the optical fiber core wire were observed in detail. As a result, the following was found. Only the secondary coating portion remained in the core wire holding portion of the ferrule, and a part of the optical fiber element wire remained in the minute hole portion. On one side of the optical fiber core, the primary coating was exposed by the amount of the part of the optical fiber and the part of the secondary coating remaining on the ferrule side.

From the above observation results, it was possible to roughly infer the mechanism leading to the destruction. First, due to the application of tensile force, peeling occurs at the boundary between the primary coating and the secondary coating that are adhesively fixed to the core holding portion in the ferrule.
Then, the tensile force was further applied, and the load exceeding the allowable strength of the optical fiber strand was concentrated, and the fracture mechanism could be considered to break. It can be inferred that what is important here is that high strength can be maintained if peeling between the primary coating and the secondary coating does not occur easily. Therefore, regarding the method of attaching the optical fiber core wire to the ferrule, it is necessary to first improve the conventional coating removing method that induces a decrease in the adhesion between the primary coating and the secondary coating.

By the way, in the component shown in FIG. 6 in which the ferrule 2 and the optical fiber core wire 1 are adhesively fixed, a structure in which the primary coating exposed portion 3 is exposed is shown. In this structure, in the core wire holding portion 8 in the ferrule 2,
Both the primary coating exposed portion 3 and the secondary coating portion 4 are fixed to the metal member 6 of the ferrule 2 with the adhesive 10.

However, in the range disclosed in Japanese Patent Laid-Open No. 192708/1987, the length of the exposed portion 3 of the primary coating was short. Therefore, as far as the present inventor has investigated, even if the adhesiveness between the primary coating and the adhesive is good, the adhesive force between the primary coating exposed portion 3 and the metal member 6 is insufficient due to the small adhesive area. there were. For this reason, the adhesive strength between the secondary coating portion 4 and the metal member was sufficient, but the primary coating and the secondary coating were made to face each other via the metal member 6 so that the interface between the primary coating and the secondary coating did not peel off. It could not be fixed with sufficient strength, and the above problems could not be solved.

Further, in the disclosure of the above publication, silicon rubber is used for the primary coating. Silicon rubber has extremely poor adhesiveness with an adhesive, and even if there is a disclosure of a sufficiently long primary coating exposed portion, it cannot be said that the primary coating exposed portion is bonded to the ferrule, and it is not possible to solve the above problems. There wasn't.

In the component in which the ferrule 2 and the optical fiber core wire 1 shown in FIG. 7 are bonded and fixed, the optical fiber core wire 1
The secondary coating portion 4 is adhered by the core wire holding portion 8, but the optical fiber element wire 1a is fixed by the adhesive 10 in both the micro holes 7 and the core wire holding portion 8. Since the layer of the adhesive 10 is thick in the core wire holding portion, stress is applied to the optical fiber strand due to uneven contraction during curing. Due to this stress, the optical fiber element wire 1a is slightly curved or displaced. These phenomena lead to an increase in the connection loss of the amount of light when the ferrules are connected to each other and light guiding is attempted.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to maintain a stable mounting state and adhesive strength with respect to environmental temperature changes, and to prevent light shrinkage and loss increase during curing. It is an object of the present invention to provide a method for removing a coating of a fiber core wire and a mounting structure for an optical fiber core wire and a ferrule obtained by this method.

[0018]

The above object can be achieved by any of the following constitutions (1) to (3).

(1) An end portion of an optical fiber core wire having a primary coating and a secondary coating in this order on the optical fiber wire, at least a micro hole for inserting the optical fiber wire and a core for inserting the optical fiber wire. In an optical fiber terminal structure fixed to a ferrule having a wire holding portion and a penetrating portion penetrating the micro hole and the core wire holding portion, a secondary coating portion of the end portion of the optical fiber core wire, And the part in the ferrule, the primary coating exposed portion in contact with the tip of the secondary coating portion, the secondary coating is removed, and the tip of the primary coating exposed portion, the primary coating and the secondary coating The both ends of the optical fiber bare portion are fixed in the ferrule with an adhesive, and the end of the primary coating exposed portion that is in contact with the optical fiber bare portion is near the through portion. Located in
Further, the optical fiber terminal structure in which the length A (mm) of the exposed portion of the primary coating satisfies the following relational expression.

0.5t ≦ A <t Here, t (mm) represents the length of the core wire holding portion.

(2) The optical fiber terminal structure according to the above (1), in which the exposed portion of the primary coating and the exposed portion of the secondary coating have adhesiveness with respect to the adhesive and are independently adhered and fixed to the ferrule.

(3) The optical fiber terminal structure according to the above (1) or (2), wherein the primary coating is a UV curable acrylic resin.

[0023]

In the optical fiber terminal structure according to the present invention, a part of the tip of the optical fiber core fixed in the ferrule is formed by removing only the secondary coating and exposing the primary coating of a predetermined length. That is, it has a primary coating exposed portion. Since the primary coating has adhesiveness to the adhesive, the exposed primary coating is fixed to the metal member of the ferrule with the adhesive as in the secondary coating.
As a result, the primary coating exposed portion and the secondary coating portion are relatively fixed in the ferrule via the metal member, and even when stress acts between the ferrule and the optical fiber core wire, It is possible to prevent separation of the interface between the primary coating dew and the secondary coating of the optical fiber core wire.

Therefore, in such an optical fiber terminal structure,
Even when exposed to a change in environmental temperature and subjected to thermal stress, it is possible to prevent a decrease in the degree of adhesion between the primary coating and the secondary coating, and to maintain stable strength.

Furthermore, since the length of the exposed primary coating is strictly determined so that the exposed primary coating is fixed to the ferrule metal member with sufficient strength, it is possible to reduce variations in strength between components. Further, as described above, when the exposed portion of the primary coating inserted and fixed in the ferrule is within the range of the specific length, it is possible to sufficiently withstand the strength expected during normal use.

Further, the optical fiber wire is adhered and fixed only to the minute hole portion of the ferrule. Therefore, even if the adhesive hardens, at least the primary coating remains in the core wire holding portion, so that direct stress is prevented from being applied to the wires. Therefore, it is possible to prevent minute bending and displacement of the strands.

[0027]

【Example】

(Example) The present invention will be described in detail below with reference to the drawings. The configurations of the optical fiber core wire and the ferrule used in this embodiment are the same as those shown in FIGS. 3 and 4, and the same components are designated by the same reference numerals.

The optical fiber core wire 1 is formed on the outer peripheral portion of the optical fiber element wire 15 made of silica glass having an outer diameter of 125 μm.
A primary coating 13 made of a UV curable acrylic resin is coated until the size reaches about 50 to 400 μm, and a polyester elastomer is coated as a secondary coating 14 on the outer peripheral portion of the coating so that the outer diameter is φ900 μm. It will be.

In the present invention, as a condition required for the primary coating, it is important to have adhesiveness to the adhesive used. For this reason, it is not appropriate to use an optical fiber element wire having a primary coating made of a general silicone resin having almost no adhesiveness to a general adhesive.

The dimension of the microhole 7 of the ferrule 2 in the longitudinal direction is about 3 mm. It is available as a standard product. In addition, the inner diameter of the micropore is 1 to 2 μm smaller than the outer diameter of the wire.
Use the one with a large size of about m.

FIG. 2 shows an optical fiber core wire 1 used in the present invention.
3 shows the structure of the tip of the. Further, FIG. 1 is a view showing a cross section of the structure of the optical fiber terminal of the present invention, and shows the mounting structure of the optical fiber core wire 1 and the ferrule 2. In FIG. 2, the secondary coating is removed from the tip portion of the optical fiber core wire 1 and the primary coating exposed portion 3 is exposed. Furthermore, the tip of the primary coating exposed portion 3 is removed after the primary coating is left for a certain length, and the optical fiber element wire 1a is exposed.

The tip portion of the optical fiber core wire 1 having the primary coating exposed portion 3 of a predetermined length was manufactured by the following method.

(1) The total length of the ferrule used is B (m
m), only the secondary coating on the tip of the optical fiber core wire 1 is removed over about B + 5 (mm). That is, by this step, the primary coating is exposed for about B + 5 (mm).

(2) The length dimension of the core wire holding part 8 where the optical fiber core part (the part where the primary coating and the secondary coating are exposed) can be inserted and bonded in the ferrule is determined. . This dimension is indicated by t in FIG.

(3) Determine the length A (mm) of the exposed portion of the primary coating. According to the present invention, A is in the range of 0.5 t (mm) or more and less than t (mm), preferably 0.5 t (mm) or more and less than 0.83 t (mm).

The reason for this limitation is based on the following experimental results.

Using a ferrule having a total length of 15 mm and t = 12 mm, the value of A was changed and the adhesive strength of the optical fiber terminal structure shown in FIG. 1 was measured.

The results are shown in FIG. When t is 12 mm,
In the dimensional range of A from 0 to less than 0.5 t (mm), that is, from 0 to 6 mm, the effect of increasing the effective fixing strength was not confirmed with the same strength as when A = 0 mm. Therefore, the lower limit of A is set to 0.5 t (mm).

The upper limit of A was determined by the following items other than strength.

That is, as A approaches t, the length of the secondary coating portion 4 adhered and fixed to the core wire holding portion 8 of the ferrule 2 becomes smaller. It is necessary to consider that the boundary portion 11 between the ferrule 2 and the optical fiber core wire 1 is momentarily bent and twisted during normal use.

For this, t = 12 mm and A = 12 mm
Then, the coating of the optical fiber core wire was removed, and then an optical fiber terminal structure was produced by integrating the ferrule with an adhesive. In this case, the size of the portion of the secondary coating portion 4 to be bonded inside the ferrule is 0 mm. When a bending and twisting test was performed on this component, a break in the optical fiber element wire 1a was detected at the boundary portion 11. Further, t is the same and A is 10
The same experiment was conducted on the structure with mm. This time,
No disconnection of the optical fiber strand 1a was detected at the boundary portion 11. Bending conditions are tensile force 0.5kgf, bending angle ± 9
Repeated 0 degree, 200 cycles, twisting condition: tensile force 0.5
kgf, twist angle ± 360 degrees, 200 cycles repeated.

This is because when the secondary coating portion 4 is extremely small or missing at the boundary portion 11, as compared with the case where the secondary coating portion 4 fixed to the ferrule is sufficiently present, This means that the optical fiber strand 1a is greatly damaged. That is, in the boundary portion 11,
If the secondary coating portion 4 fixed to the ferrule is present to some extent, it is presumed that there is a buffering effect against external force. Therefore, considering the manufacturing accuracy, the upper limit of A is t
It was less than 0.83t, preferably 0.83t or less.

(4) The primary coating is left by A (mm) from the portion where the secondary coating is removed, leaving the primary coating, and the primary coatings other than the A dimension are removed toward the tip of the core wire, Expose. As a result, the B + 5-A (mm) optical fiber element wire is exposed. By such a procedure, the dimension for removing the coating of the optical fiber core wire is determined.

Next, an example of actually removing the coating of the optical fiber core wire will be described.

When removing the coating of the optical fiber,
A commercially available stripper for stripping the coating is used. On this occasion,
A stripper adapted to the outer diameter of the optical fiber, the outer diameter of the primary coating, and the outer diameter of the optical fiber is used. If this is mistaken, each part may be damaged by the blade of the stripper, and in the worst case, the core wire may be broken, so be careful. As a method other than the stripper, a method of dissolving the coating using an organic solvent or a strong acid can be applied.

First, the secondary coating portion of the tip portion of the optical fiber core was removed from the tip portion by a predetermined length to expose the primary coating. The ferrule used here has a total length of 1
Since it is 5 mm and the length of the micropores in the longitudinal direction is 3 mm, t
Is 12 mm. Therefore, the secondary coating portion of the optical fiber core wire was removed from the tip portion by 12 + 5, that is, 17 mm to expose the primary coating.

Subsequently, the primary coating of a predetermined length was left from the boundary portion of the primary coating / secondary coating, and the other primary coatings up to the tip were removed to expose the optical fiber strands. The exposed length of the exposed primary coating is 6 mm or more, 12 mm
Although it is within the range of less than, this is 6 mm in this embodiment. Therefore, the exposed portion of the primary coating remains 6 mm, and 6
mm fiber optic bare.

The optical fiber core wire with the coating thus removed is inserted and fixed in the ferrule 2. The mounting state of the ferrule and the end of the optical fiber core at this time is shown in FIG. The core-holding portion 8 of the ferrule 2 accommodates the exposed portion 3 of the primary coating of the optical fiber, that is, the A-sized portion and the secondary coating portion 4 in the ferrule. Further, the optical fiber strand 1 a is housed in the minute hole 7 in the ferrule 2.

When the tip of the optical fiber core wire 1 is inserted through the opening of the core wire holding portion 8 of the ferrule 2, the optical fiber core wire is gently inserted until it cannot be inserted. It is possible to position the end on the side of contacting the optical fiber element wire 1a in the vicinity of the penetrating portion 12. It is preferable that the penetrating portion is provided with a taper so that the optical fiber element wire can smoothly enter the minute hole when the optical fiber core wire is inserted. Then, the optical fiber strand 1a,
Both the primary coating exposed portion 3 and the secondary coating portion 4 in the ferrule are fixed with an adhesive.

This step was performed as follows.

An adhesive is preliminarily injected into the core wire holding portion and the minute holes of the ferrule. In this embodiment, an epoxy resin adhesive is used. The ferrule was inserted through the opening of the core holding portion from the tip of the optical fiber whose coating was removed by the above method, until the optical fiber could not be inserted. Then, the optical fiber bare wire was slightly projected from the tip of the minute hole.

While maintaining this state, the entire ferrule was heated to thermoset the adhesive.

The adhesive used here is generally the one which has a small shrinkage upon curing and a short curing time, such as the epoxy resin adhesive used in this embodiment. Further, it is necessary to select a material having adhesiveness to both the primary coating and the secondary coating, such as a combination of a UV curable acrylic resin and an epoxy resin and a polyester elastomer and an epoxy resin. Curing was carried out at 80 (° C) for about 1 hour.

After the curing was completed, the protruding portion of the wire at the tip was cut and the surface was precision ground to finish the end surface into a mirror surface.

In this way, the optical fiber terminal structure shown in FIG. 1 was manufactured. When the optical fiber attached to the ferrule of this optical fiber terminal structure is continuously pulled in the longitudinal direction of the ferrule with a force of 2 kgf for 1 minute, the optical fiber is fixed in the ferrule, and No position shift was observed.

A tensile test was conducted to measure the actual fixing strength. The test was performed with the number of samples of n = 20, and the strength up to breaking was 5.3 kgf on average and σ (n-1) = 0.4.

Further, the sample prepared in the same manner was subjected to a thermal shock test environment (temperature range of −40 ° C. to + 85 ° C., exposure time of 30 minutes at each temperature, 1 cycle for 1 hour in total) for 200 hours.
Tensile strength was measured after standing for 0 cycles. The number of samples was n = 20, and the average strength before breaking was 6.15 kgf.
σ (n-1) = 0.78.

Further, the insertion loss of the optical fiber was measured before being left in the thermal shock test environment. When n = 20, the average value was 0.04 dB. After standing, n was 20 and the average value was 0.06 dB. There was no significant change in the measured values, and even the sample left in the thermal shock test environment had practically sufficient characteristics.

Comparative Example 1 The same optical fiber terminal structure as in Example 1 (resultantly the same structure as in FIG. 5) was prepared except that the length of the exposed primary coating 3 was 0 mm in FIG. , N
The tensile test was performed with the number of samples of 20. The strength before breaking was 3.6 kgf on average and σ (n-1) = 0.6.

After being left in the same thermal shock test environment as in Example 1, the number of samples was n = 20, the average strength before breaking was 2.8 kgf, and σ (n-1) = 1. It was .8.

It was 8.

From the above results, in the present invention with A = 6 mm,
It can be seen that a remarkable increase in the adhesive fixing strength of about 50% is obtained as compared with the comparative example of A = 0 mm.

Comparative Example 2 The same optical fiber terminal structure as in Example 1 was prepared by using the same optical fiber as in Example 1 except that the primary coating was a silicone resin. A tensile test was performed in the same manner as in Example 1 with n = 10. As a result, the strength until fracture was 2.6 kgf on average and σ (n-1) = 0.1.

The exposed portion of the primary coating made of silicone resin is
It has no adhesiveness to epoxy resin adhesives. Therefore, since the exposed portion of the primary coating is not fixed to the metal member of the ferrule with an adhesive, a small stress due to the tensile test causes peeling at the interface between the primary coating and the secondary coating, leaving the secondary coating in the ferrule. It was confirmed that it broke as it was.

In the examples, the optical fiber whose primary coating is made of UV curable acrylic resin and whose secondary coating is made of polyester elastomer has been described. However, the condition required for the primary coating and the secondary coating of the optical fiber used in the present invention is that both coatings have adhesiveness to the adhesive used.

However, the optical fiber core wire using a UV-curing acrylic resin having a buffering effect on the primary coating is easily available, and the primary coating has good adhesiveness to general adhesives. Therefore, it is preferable for carrying out the present invention.

In the combination of the primary coating, the secondary coating and the adhesive described in Example 1, both the primary coating and the secondary coating have good adhesiveness to the adhesive, and the ferrule and the optical fiber. It is more preferable since the stress applied to the optical fiber element wire can be reduced and the optical transmission characteristics can be favorably maintained after the adhesion of the core wire.

[0068]

As described above, in the optical fiber terminal structure of the present invention, an optical fiber terminal in which the primary coating portion of a predetermined length is exposed is fixed to the ferrule with an adhesive. In this structure, the exposed portion of the primary coating and the portion having the secondary coating are relatively fixed in the ferrule via the metal member of the ferrule. As a result, when stress acts between the ferrule and the optical fiber core wire,
It is possible to prevent the separation of the interface between the primary coating dew and the secondary coating in the optical fiber in the ferrule.

Therefore, in such an optical fiber terminal structure,
Even if thermal stress is exerted by being exposed to a change in environmental temperature, it is possible to prevent a decrease in adhesion between the primary coating and the secondary coating, and maintain stable strength.

Further, even after being left for a long period of time under a change in environmental temperature, stable adhesive fixing strength can be maintained, and variation in strength between samples can be suppressed to a small level.

Furthermore, since the strands of wire are adhered and fixed only in the fine hole portions of the ferrule, and the uneven stress due to the curing shrinkage of the adhesive is less likely to be applied to the strands of wire, the increase in insertion loss is small. It is possible to obtain stable light input / output over a long period of time.

[Brief description of drawings]

FIG. 1 is a sectional view of an example of the structure of an optical fiber terminal of the present invention.

FIG. 2 is a view showing a structure of a tip end portion of an optical fiber core wire used in the present invention.

FIG. 3 is a cross-sectional view showing a structure of an optical fiber core wire.

FIG. 4 is a cross-sectional view showing the structure of a ferrule.

FIG. 5 is a cross-sectional view of a conventional optical fiber terminal structure.

FIG. 6 is a cross-sectional view of a conventional optical fiber terminal structure.

FIG. 7 is a cross-sectional view of a conventional optical fiber terminal structure.

FIG. 8 is a diagram showing the relationship between the length (A) of the primary exposed portion of the optical fiber core wire and the average fixed strength.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber core wire 1a Optical fiber bare wire exposed portion 2 Ferrule 3 Primary coating exposed portion 4 Secondary coating portion 5 Capillary 6 Metal member 7 Micropores 8 Core wire holding portion 9 Glass tube 10 Adhesive 11 Boundary portion 12 Penetrating portion 13 Primary coating 14 Secondary coating 15 Optical fiber strand

Claims (3)

[Claims] 1. An optical fiber core wire end portion having a primary coating and a secondary coating in this order on an optical fiber element wire, at least a minute hole into which the optical fiber element wire is inserted, and an optical fiber core wire inserting end. A holding part, an optical fiber terminal structure fixed to a ferrule having a penetrating part penetrating the micro hole and the core wire holding part, which is a secondary coating part of the end part of the optical fiber core wire, and A portion in the ferrule, in contact with the tip of the secondary coating portion, the primary coating exposed portion from which the secondary coating is removed, and in contact with the tip of the primary coating exposed portion, the primary coating and the secondary coating The exposed portion of the optical fiber wire from which both are removed is fixed in the ferrule with an adhesive, and the end of the exposed portion of the primary coating contacting the exposed portion of the optical fiber wire is near the through portion. In addition, the primary coating dew Optical fiber terminal structure part of the length A (mm) satisfies the following relation. 0.5t ≦ A <t Here, t (mm) represents the length of the core wire holding portion. 2. The optical fiber terminal structure according to claim 1, wherein the exposed primary coating portion and the secondary coating portion have adhesiveness with respect to the adhesive and are independently fixed to a ferrule by adhesive bonding. 3. The optical fiber terminal structure according to claim 1, wherein the primary coating is a UV curable acrylic resin.