JP2001264579A - Optical fiber assembling member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an optical fiber 2 from breaking without causing separation between an adhesive 3 and a bonding interface even under a severe temperature change. SOLUTION: Relating to an optical fiber assembling member 10, an optical fiber 2 with a coating removed at its end is inserted into a ferrule 1 having a through-hole and is fixed with an adhesive 3 filled in the through-hole. Then, a layer of a coupling agent 4 is formed on the outer circumferential surface of the optical fiber and/or on the inner circumferential surface of the through- hole in the ferrule 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber assembly used for optical communication and the like.

[0002]

2. Description of the Related Art Conventionally, optical fiber connectors have been used in places where detachable optical connections such as switching of devices, removal of transmission / reception ports, adjustment of devices, measurement, and the like are required in optical communication systems. A fiber assembly is used. In addition, an optical fiber assembly member for coupling light emitted from the laser diode to an optical fiber is used inside the optical package having the laser diode mounted thereon.

As shown in FIG. 4A, an optical fiber 2 is joined to a ferrule 1 having a through hole consisting of a shaft hole 1a and a coating fixing hole 1b continuous with the shaft hole 1a. It has an integral structure. The shaft hole 1a is a hole slightly larger than the outer diameter of the coating removal portion 2b of the optical fiber 2, and the coating fixing hole 1b is a hole slightly larger than the outer diameter of the coating portion 2a. The ferrule 1 is made of a material such as ceramics or metal, and the ferrule 1 and the optical fiber 2 are fixed with an adhesive 3 such as an epoxy resin filled in a through hole.

[0004] As shown in FIGS. 4 (b) to 4 (d), a core 1c to which a coating removal portion 2b of the optical fiber 2 is fixed is provided.
In some cases, the flange 1d to which the covering portion 2a is fixed is made of a separate member. The core 1c is made of ceramic, metal, or the like, the flange 1d is made of metal, and the core 1c and the flange 1d are fixed by press-fitting, bonding, or the like. Further, the ferrule 1 and the optical fiber 2 are fixed with an epoxy adhesive or the like as described above.

[0005]

However, the bonding strength between the ferrule 1 and the optical fiber 2 of the conventional optical fiber assembly member 10 depends on the adhesive strength between the shaft hole 1a and the coating removing portion 2b, and the coating fixing hole 1b and the coating portion. It is secured by the adhesive force with 2a. Since the epoxy adhesive used for this bonding expands slightly during curing, sufficient strength could be obtained at room temperature.

However, the optical fiber assembly 10 includes an epoxy adhesive and a coating 2a having a large thermal expansion coefficient, a coating removing section 2b made of quartz glass having a low thermal expansion coefficient, and a ferrule 1 having an intermediate thermal expansion coefficient. Due to the mixed configuration, a severe temperature change of −40 ° C. to + 85 ° C. causes peeling between the adhesive 3 and the bonding interface, losing the bonding strength and applying a slight tensile force to the optical fiber 2. There has been a problem that the optical fiber is broken just by the application.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention is directed to an optical fiber having a coating removed portion at an end inserted into a ferrule having a through hole, and an adhesive filled in the through hole. In the optical fiber assembly fixed with the agent,
A coupling agent is applied to one or both of the outer peripheral surface of the optical fiber and the inner peripheral surface of the through hole of the ferrule.

Further, the present invention is characterized in that in the optical fiber assembly member, at least a surface of a portion of the optical fiber coating portion in the ferrule fixed to the adhesive is oxidized.

Further, the optical fiber coating portion is oxidized by a surface treatment using plasma discharge.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an optical fiber assembly according to a first embodiment of the present invention. In the optical fiber assembly member 10 according to the present invention, an optical fiber 2 is inserted into a ferrule 1 having a through hole composed of a shaft hole 1a and a coating fixing hole 1b smoothly connected to the shaft hole 1a, and bonded with an adhesive 3. It has an integral structure. The shaft hole 1a is a hole slightly larger than the outer diameter of the coating removal portion 2b of the optical fiber 2, and the coating fixing hole 1b
Are holes slightly larger than the outer diameter of the covering portion 2a.

The shaft hole 1a and the cover fixing hole 1 of the ferrule 1
Coupling agent 4 is applied to the inner surface of b. or,
The coupling agent 4 is also applied to the coating removal portion 2b made of quartz glass of the optical fiber 2, and at least the portion where the adhesive is fixed is surface-treated. Further, the surface of the coating portion 2a made of a resin such as nylon, Hytrel, etc.
c. Then, by filling an adhesive 3 made of an epoxy resin into an interface where each component is surface-treated, it can be firmly fixed.

Here, the coupling agent is a surface treating agent having a functional group having a good binding property to the surface of an inorganic substance and another functional group showing a strong binding property to an organic polymer. The coupling agent may be a chromium coupling agent, an organic titanium coupling agent, an organic phosphoric acid coupling agent, a coupling agent such as silyl peroxide, etc. By doing so, a strong adhesive effect is obtained, which is preferable.

Next, the reason why the surface treatment of ceramics, metal, and quartz glass with a coupling agent improves the adhesive strength will be described.

A typical silane coupling agent among the coupling agents is generally represented by the following chemical structural formula.

[0016]

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In Chemical Formula 1, the molecule has two or more kinds of functional groups having different reactivities. X is a hydrolyzable group bonded to a silicon atom, and includes a chloro group, an alkoxy group, an acetoxy group, an isopropenoxy group, an acyloxy group, an amino group and the like. The hydrolyzable group X is hydrolyzed by an aqueous solution, moisture in the air, or moisture adsorbed on the surface of the inorganic material to form a highly reactive silanol group (Si—OH) as shown in Chemical formula 2. I do.

[0018]

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The silanol group is a reactive group capable of adsorbing or chemically bonding to the surface of the inorganic material.

On the other hand, Y is an organic functional group that reacts with an organic matrix, and is typically a vinyl group, an epoxy group,
Examples include a methacryl group, an amino group, and a mercapto group. The organic functional group Y is bonded to the silicon atom via a short-chain alkylene group R via a Si—C bond, and is chemically and thermally stable.

Regarding this bonding mechanism, a chemical bonding theory model in which SiOM (M is a silicon atom or a metal atom such as glass) is formed with the surface of the inorganic substance and chemically bonded thereto, At the interface, the theories of a physical adsorption model that physically adsorbs and a reversible equilibrium model in which a reversible equilibrium reaction occurs in which a reversible equilibrium reaction occurs between the hydroxyl group on the inorganic material surface and the silanol group of the silane coupling agent The adhesion is strengthened.

As the silane coupling agent, vinyl triethoxy silane, gamma methacryloxypropyl trimethoxy silane, gamma amino propyl triethoxy silane, or the like can be used.

Therefore, by applying the coupling agent 4 to the ferrule 1 made of an inorganic substance and the coating removal portion 2b of the optical fiber 2, the adhesive strength with the adhesive 3 made of an organic substance can be improved.

Next, the reason why the adhesive strength is improved by forming an oxidized portion 2c by oxidizing the surface of a resin such as a thermoplastic resin forming the coating portion 2a will be described.

The plasma discharge causes the molecular chains on the resin surface to be cut or gradually collapsed to form an oxidized portion 2c.
In addition, cross-bonding, hydrogen bonding, ozonation, and the like are complexly entangled to improve the activation of the resin surface and improve the adhesiveness.

Plasma discharge is a type of gas discharge. When a voltage is applied between two electrodes and the electric field loses uniformity, the gas in a portion having a large potential gradient causes local ionization, A phenomenon that emits faint sound and faint light to discharge.

Electrons activated by this discharge have energy of 2 to 2 to break molecular bonds on the surface of the material to be treated.
The free radicals that collide with the surface of the material with three times the force and consequently react with the oxides generated by the discharge or with the free radicals in the adjacent molecular chains rapidly cross-link. I do. The solid surface is then oxidized, which increases the surface energy and increases the wettability and adhesion of the material.

Therefore, by oxidizing the surface of the covering portion 2a, the adhesive strength with the adhesive 3 can be increased.

As the surface oxidation treatment method, glow discharge,
Plasma discharge such as corona discharge, arc discharge, high-frequency discharge, and microwave discharge is effective. Among them, corona discharge, which can be processed at a low temperature and is inexpensive, is particularly desirable.

Although the description has been made with reference to the above-described plasma discharge, the method is not particularly limited as long as the method is capable of forming the oxidized portion 2c by cutting off the chain of molecules on the resin surface or gradually reducing the surface.

Next, generally, the evaluation of the "wetting property" between a solid surface and a liquid can be expressed by Young's equation as shown below.

Tsv = ts1 + t1v × cos θ tsv: gas-solid interfacial tension ts1: solid-liquid interfacial tension t1v: liquid surface tension θ: the contact angle θ shown in FIG. 2 (b) )
As shown in the figure, it is difficult to wet when 90 ° ≦ θ <180 °,
It is sufficient that the contact angle θ is less than 90 °.
As shown in FIG.
Thereby, the adhesive strength can be significantly improved.

Both the optical fiber coating removal portion 2b and the ferrule shaft hole 1a, which are surface-treated with the coupling agent 4, have a contact angle .theta.
Has been significantly improved, thereby making it possible to increase the adhesive strength.

The optical fiber coating 2a of the present invention, which has been subjected to a surface oxidation treatment by corona discharge, has a contact angle θ of 70 ° or less similarly to the above, and the "wettability" is remarkably improved. This makes it possible to increase the adhesive strength.

The presence or absence of the surface treatment with the coupling agent 4 can be analyzed and measured by ESCA which measures the momentum distribution of electrons generated by irradiating the sample with X-rays. More preferably, TOF- is a method that gives small energy to a sample and ionizes the sample in a certain amount without breaking the sample surface.
Analytical measurement is preferably performed using SIMS.

The presence or absence of the oxidized surface treatment by corona discharge can be analyzed and measured by ESCA which measures the momentum distribution of electrons generated by irradiating the sample with X-rays in the same manner as described above.

Next, FIG. 3 is a sectional view of an optical fiber assembly member 10 showing a second embodiment of the present invention. The ferrule 1 is divided into a core 1c and a flange 1d as compared with the first embodiment, and is fixed by a method such as press-fitting, bonding, low-melting glass, soldering, or the like.

In the above embodiment, the material of the ferrule 1 of FIG. 1 or the core 1c of FIG. 3 is alumina, zirconia, silicon nitride, silicon carbide, alumina-zirconia, borosilicate glass, crystallized glass, or A metal, a resin, or the like can be used. The flange 1d in FIG. 3 can also be made of a metal such as stainless steel, brass, nickel plating, or a resin such as a liquid crystal polymer, polybutylene terephtalate, polyetherimide, or polyether sulfide. .

Further, the present invention is not limited to the structure shown in FIGS. 1 and 3, but the same effect can be obtained with the structure of the ferrule 1 as shown in FIGS. 4 (c) and 4 (d). Furthermore, in the figure, the tip surface of the ferrule 1 is drawn all at right angles to the longitudinal direction of the optical fiber, but any shape such as oblique, spherical, or oblique spherical can be used.

Further, it is effective to apply the coupling agent 4 to only one of the ferrule 1 and the optical fiber 2, not both. The effect can also be obtained by performing only one of the application of the coupling agent 4 and the oxidation treatment without performing both.

Next, each processing method will be described.

First, the surface treatment with the coupling agent 4
After being sufficiently dried after the degreasing cleaning, the ferrule 1 is immersed in the coupling agent bath for several minutes while applying ultrasonic waves, and then air blow is performed so that the shaft hole 1a is opened.
Skip the solution. Thereafter, the outer peripheral surface, the front end surface, and the rear end surface are wiped with clean cotton soaked with ethyl alcohol to remove an excess coupling agent, and dried sufficiently with a dryer.

After the optical fiber coating removing section 2b is immersed in the coupling agent bath, the whole is blown off with air to blow off excess liquid agent, and is dried sufficiently by a dryer.

Next, in a corona discharge treatment, which is a kind of plasma discharge treatment, a surface oxidation treatment is performed by applying a corona discharge to the optical fiber coating portion 2a for several tens of seconds. In this case, it is desirable to carry out the bonding work immediately after the surface treatment, and if left for several days after the treatment, the oxidized surface returns to the original state, and the effect of enhancing the adhesive strength is lost.

[0045]

EXAMPLE Here, a first experiment was conducted by the following method.

A disk having a diameter of 20 mm and a thickness of 5 mm was made of zirconia ceramics, quartz glass and nylon 12, and the surface thereof was finished to a surface roughness Ra of 0.2 μm and subjected to degreasing cleaning. Furthermore, the surface treatment of the silane coupling agent is performed, the other 10 are subjected to the surface oxidation treatment by corona discharge, and the remaining 10 are dropped as they are, the epoxy adhesive is dropped, the curing treatment is performed, and the contact after curing is performed. The angle θ was measured.

Table 1 shows the average of the measured values.

The sample obtained by subjecting zirconia ceramics and quartz glass to a surface treatment with a silane coupling agent has a small contact angle θ. Also, the sample obtained by subjecting nylon 12 to a surface oxidation treatment by corona discharge has a contact angle θ of 70 ° or less, and has good wettability.

[0049]

[Table 1]

Next, a second experiment was performed by the following method.

Outer diameter D = φ2.5 mm, length L = 1 of single mode ferrule 1 made of zirconia ceramics
The conventional optical fiber assembly member 10 shown in FIG. 4A as a comparative example, with 0.5 mm, shaft hole 1a = φ0.126 mm, coating fixing hole 1b = φ1.0 mm, and shaft hole 1a length = 4 mm, As a first embodiment of the present invention, the optical fiber assembly member 10 shown in FIG.
A thermal shock test was performed under the following conditions, and the insertion loss before and after the test was measured.

Thermal shock test conditions Temperature conditions High temperature; + 85 ° C, 30 minutes normal temperature; 5 minutes Low temperature; -40 ° C, 30 minutes High temperature-normal temperature-low temperature-normal temperature 1 cycle 70 minutes 2. Table 2 shows the results.

Conventional optical fiber assembly 1 as a comparative example
In the sample No. 0, the connection loss was large and the variation was large, and some samples were completely broken. This is because the optical fiber 2 is not fixed in the through-hole because the interface of the adhesive 3 has peeled off during the severe temperature change. On the other hand, the optical fiber assembly 10 of the present invention resulted in a small average value of the connection loss and a small variation.

[0054]

[Table 2]

[0055]

As described above, according to the present invention, an optical fiber having a coating removed portion at an end is inserted into a ferrule having a through hole, and the adhesive filled in the through hole is inserted into the ferrule. In the optical fiber assembly member fixed by fixing, a coupling agent layer is formed on one or both of the outer peripheral surface of the optical fiber and the inner peripheral surface of the through hole of the ferrule, and at least the adhesive of the optical fiber coating portion in the ferrule is fixed. By oxidizing the surface of the part to be removed, it prevents the adhesive and the adhesive interface from peeling even under severe temperature changes,
A highly reliable optical fiber assembly member without breaking the optical fiber can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical fiber assembly member showing a first embodiment of the present invention.

FIG. 2 is a view showing a typical shape of a contact angle θ;
(A) is a diagram showing a contact angle where θ is less than 70 °,
(B) is a diagram showing a contact angle where θ exceeds 90 °.

FIG. 3 is a sectional view of an optical fiber assembly according to a second embodiment of the present invention.

4 (a) to 4 (d) are cross-sectional views of a conventional optical fiber assembly member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ferrule 1a Shaft hole 1b Coating fixing hole 1c Core 1d Flange 2 Optical fiber 2a Coating part 2b Coating removal part 2c Oxidation part 3 Adhesive 4 Coupling agent 10 Optical fiber assembly member

Claims (3)

[Claims] 1. An optical fiber assembly member comprising: a ferrule having a through hole; an optical fiber having a coating removed portion at an end inserted therein; and an optical fiber assembly fixed with an adhesive filled in the through hole. An optical fiber assembly member, wherein a coupling agent is applied to one or both of an outer peripheral surface of a fiber and an inner peripheral surface of a through hole of the ferrule. 2. An optical fiber assembly member wherein an optical fiber having a coating removed portion at an end is inserted into a ferrule having a through hole and fixed with an adhesive filled in the through hole. An optical fiber assembly member characterized in that at least a surface of a portion of the optical fiber covering portion fixed to the adhesive is oxidized. 3. An optical fiber assembly according to claim 2, wherein said optical fiber coating portion is oxidized by surface treatment by plasma discharge.