JP2002250837A - Optical fiber coupler and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber coupler having little wavelength shift in insertion loss even if used under high humidity and high temperature. SOLUTION: The optical fiber coupler is structured by fusing/drawing plural optical fibers 1 and by sticking/fixing them to a mounting member 6 with an adhesive 8. The adhesive 8 has a Young's modulus of 100 MPa or above at 85 deg.C, fixing the fused/drawn part 3 on the mounting member 6 with a tensile force of not less than 40 mN and not more than 200 mN at room temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler used for branching / coupling or splitting / combining optical signals in the field of optical communication.

[0002]

2. Description of the Related Art Optical fiber couplers are used to split or combine optical signals of a single wavelength into a plurality of optical signals, or to split or combine optical signals having different wavelengths into one for each wavelength. ing. Generally, as this optical fiber coupler,
2. Description of the Related Art A configuration in which a plurality of optical fibers are bundled, fused by heating, and stretched is known.

FIGS. 1 and 2 show the shape of a general optical fiber coupler. FIG. 1 shows the shape of an optical fiber coupler when a pair of optical fibers are used.
FIG. 2A is a perspective view housed in a mounting member, and FIG. 2B is a view showing an applied state of an adhesive. In the figure, 1 is an optical fiber,
Reference numeral 2 denotes a glass fiber portion, 3 denotes a fusion-stretched portion, 4 denotes a non-stretched portion, 5 denotes a protective coating, 6 denotes a mounting member, 7 denotes a lid member, and 8 denotes an adhesive.

In the optical fiber coupler, the protective coating of the plurality of optical fibers 1 is removed, the central portions of the glass fiber portions 2 are brought into contact with each other, and they are heated and fused, and the fused portions are stretched in the optical axis direction. It is formed. The fusion extending portion 3 functions as an optical coupler, and the branching ratio and the like can be changed depending on the degree of fusion bonding. As a method of fusion-stretching the optical fiber 1,
Normally, the fused portion is heated and stretched by a micro torch or the like while tension is applied to the fused optical fiber 1.

After that, the optical fiber coupler is fixed to a mounting member 6 such as a fixing stand or a sleeve by an adhesive 8.
The adhesive 8 is applied to the non-stretched portions 4 on both sides of the fusion-stretched portion 3 functioning as an optical coupler. The adhesive 8 may be an epoxy or acrylic thermosetting or ultraviolet curable organic adhesive having good adhesive properties, an adhesive having heat resistance and a low coefficient of thermal expansion, and an inorganic adhesive may be added to the organic adhesive. It is known to use an adhesive filled with a material to increase the softening temperature.

Conventionally, as an adhesive for fixing an optical fiber coupler, a plurality of types of a soft adhesive and a hard adhesive are used in combination by changing the Young's modulus in order to prevent stress fluctuation due to a temperature change. Is known (for example, see Japanese Patent Application Laid-Open No. 9-138322). It is also known that a glass transition temperature lower than the operating temperature of an optical fiber coupler is used and fixed with a single adhesive (for example, see Japanese Patent Application Laid-Open No. 10-10360).

Further, it is known that the degree of coupling and the wavelength characteristics are made uniform by controlling the tension applied to the optical fiber coupler when the optical fiber coupler is fixed with an adhesive (for example, see Japanese Unexamined Patent Publication No. -250040). In addition, by setting the length of the fusion-stretched portion of the optical fiber coupler and the adhesive fixing position, it is possible to increase the minimum resonance frequency without applying excessive tensile tension and to improve mechanical properties such as vibration and impact. Known (see, for example,
-262261).

As described above, conventionally, selection of an adhesive for fixing an optical fiber coupler, application of tension during fixing,
Various improvements have been made from the viewpoint of the bonding structure. However, when the optical fiber coupler is used in a high-temperature or high-humidity environment, the transmission characteristics deteriorate.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has clarified that the relationship between the insertion loss and the wavelength used gradually shifts from the initial state and does not satisfy the target level. Another object of the present invention is to provide an optical fiber coupler in which the mounting tension of the optical fiber coupler is not loosened even when used at high temperature and high humidity, the wavelength does not shift, and the insertion loss does not increase.

[0010]

An optical fiber coupler according to the present invention is an optical fiber coupler obtained by fusing and stretching a plurality of optical fibers and bonding and fixing to a mounting member with an adhesive.
The adhesive has a Young's modulus at 85 ° C of 100 MPa or more, and the fusion-stretched portion has a tensile tension at room temperature of 40 mN or more and 200 mN.
In the following, it is characterized in that it is mounted on a mounting member.

The method of manufacturing an optical fiber coupler according to the present invention is a method of manufacturing an optical fiber coupler which is fixed to a mounting member with an adhesive, wherein the adhesive has a Young's modulus at 85 ° C. of 100 MPa or more. And the tensile strength of the fusion-stretched portion at room temperature is 40 mN or more and 200 mN or less.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. Since the drawing is the same as that used in the description of the conventional technique, the detailed description is omitted. In the optical fiber coupler of the present invention, the protective coating 5 of the plurality of optical fibers 1 is removed, the central portions of the glass fiber portions 2 having a nominal outer diameter of 125 μm are brought into contact with each other, and heated and fused. It is formed by extending in the axial direction. The fusion-stretched portion 3 functions as an optical coupler, and the branching ratio and the like can be changed depending on the degree of fusion bonding. The fusion-stretching of the optical fiber 1 can be performed by a method in which the fusion-spliced portion is heated with a micro torch or the like and stretched while tension is applied to an ordinary fused optical fiber.

The optical fiber coupler formed as described above is fixed with an adhesive 8 to a mounting member 6 such as a fixing stand or a sleeve. A single adhesive is used as the adhesive 8, and the non-stretched portions 4 on both sides of the fused stretched portion 3 functioning as an optical coupler are applied including a part of the protective coating 5. Although the adhesive 8 is applied to the crotch portion of the non-stretched portion 4 in the drawing, the adhesive 8 may not be applied to the crotch portion. As the adhesive 8, an epoxy-based or acrylic-based thermosetting or ultraviolet curable resin having good adhesiveness is used. In addition, an adhesive having heat resistance and a low coefficient of thermal expansion, or an adhesive in which an organic adhesive is filled with an inorganic filler to increase the softening temperature may be used.

In the present invention, the adhesive 8 for fixing the optical fiber coupler to the mounting member 6 is provided with a Young's modulus at 85 ° C. of 100.
A material having a pressure of not less than MPa is used. By increasing the Young's modulus at a high temperature, it is possible to prevent the tensile strength from being loosened due to the deformation of the adhesive, and to suppress the wavelength shift. If the Young's modulus is too large, there is no problem regarding the wavelength shift, but a problem such as breakage of the mounting member occurs due to the influence of the curing shrinkage or thermal expansion of the adhesive. Therefore, it is desirable to use one of 5880 MPa or less. Note that the Young's modulus of the adhesive can be increased by increasing the ratio of the polyfunctional oligomer.

In addition, when the optical fiber coupler is bonded and fixed to the mounting member 6 for mounting, a tensile tension is applied to the fusion-bonded and stretched portion 3, and the tensile tension at room temperature (20 ° C.) is 200 mN or less. By applying a low tensile tension in mounting to the mounting member 6 during manufacturing, in subsequent use,
Fluctuation in tensile tension due to loosening of the adhesive fixing portion can be reduced. Note that a tensile tension of at least 40 mN is applied so that the optical fiber does not break when the stretched and fused portion 3 comes into contact with the mounting member 6 due to vibration or impact.

In order to adjust the characteristics of the lower frequency band, the optical fiber coupler may be mounted by twisting the fused extension 3 by several turns. Since this twist twists the glass fiber, loosening of the torsional force at the bonded and fixed portion occurs as in the case of tensile tension. In order to suppress the wavelength shift, the number of twisting turns is preferably four or less.

Next, specific examples of the present invention will be described together with comparative examples. Sample for evaluation of the present invention (148
(For wavelength division multiplexing of 0/1550 nm), the fusion extending portion 3 of the optical fiber coupler was formed to have an outer diameter of about 15 μm and a fusion length of about 15 mm. The optical fiber stretched by fusion is housed in the mounting member 6 for mechanical protection, and the adhesive 8
To fix the adhesive. The mounting member 6 is formed in a U-shaped cross section, and is closed by bonding a lid member 7 to the center of the opening. Although the mounting member 6 and the lid member 7 can be formed of various materials, quartz glass having a thermal expansion coefficient close to that of an optical fiber is used.

The mounting member 6 is made of quartz glass and has a groove cross section of 0.7 mm × 0.7 mm in the concave portion for storing the optical fiber.
, And was formed in an elongated rectangular case having a length of 67 mm. The lid member 7 is also made of quartz glass and has a thickness of 0.8 mm.
It was formed into a plate having a width of 2 mm and a length of 17 mm. Adhesive 8
Is applied, including the non-stretched portions 4 on both sides of the fused stretched portion 3 functioning as an optical fiber coupler and a part of the protective coating 5, and is adhered and fixed to the mounting member 6. The adhesive 8 is applied on both sides of the mounting member 6 to a coating length of 26 mm, that is, from the end of the mounting member 6 to the crotch portion of the fusion-stretched portion 3. The applied amount of the adhesive 8 was 0.013 × 10 ⁻⁶ m ³ on one side.

The adhesive 8 used is different in the Young's modulus of the three types of UV-curable epoxy adhesive, UV-curable acrylic adhesive, and thermosetting epoxy adhesive. Several kinds were prepared. Specifically, A (206) with an ultraviolet-curable epoxy adhesive is used.
0 MPa), B (100 MPa) and C (20 MPa), and D (930 M) with an ultraviolet curable acrylic adhesive.
Evaluation was performed using two types of adhesives, Pa) and E (70 MPa), a thermosetting epoxy adhesive, one type of F (40 MPa), and a total of six types A to F. In addition, A ~
The Young's modulus of F is at 85 ° C. For some optical fiber couplers, after the optical fiber was fusion-stretched, the fusion-stretched portion 3 was twisted several turns, and then the adhesive was applied and cured.

Samples 1 to 12 were prepared for 2000 hours in a degraded atmosphere at a temperature of 85 ° C. and a relative humidity of 85%.
And then left at room temperature for 24 h. The measurement of the wavelength shift for evaluation was carried out before placing in a degraded atmosphere and after standing at room temperature.

The prepared sample was measured with an α-λ measuring device.
The wavelength dependence of the insertion loss of the optical fiber coupler was measured.
Focusing on the fact that the wavelength near 1480 nm shows the minimum insertion loss, the measurement content is how much the wavelength showing the minimum insertion loss shifts before and after exposure to a degraded environment. The evaluation was made based on whether or not this wavelength shift was equal to or less than a predetermined value. Table 1 below shows the measurement results.

[0022]

[Table 1]

In Table 1, Samples 1 to 6 show the embodiment of the present invention, and Samples 7 to 12 are shown as comparative examples. In the measurement results, all wavelength shifts shifted to the longer wavelength side. Here, those having a wavelength shift amount of 2 nm or less were regarded as acceptable products, and those exceeding 2 nm were regarded as rejected products.

As a result, the Young's modulus at 85 ° C. of the adhesive for bonding and fixing the optical fiber coupler to the mounting member is 100 M
Samples 7 to 9 of less than Pa have a wavelength shift of 7.4 to 20 nm, which is larger than a predetermined value. This is related to humidity, but it is considered that the bonding state of the fiber was loosened by softening at a high temperature because the adhesive was soft.

The wavelength shift of the samples 10 and 11 in which the tensile tension at room temperature exceeds 200 mN when the optical fiber coupler is bonded and fixed to the mounting member is 15
It is larger than a predetermined value in nm. It is considered that if the tensile tension is too large, loosening will gradually occur in a high-temperature, high-humidity environment even when fixed with a hard adhesive.

Samples 5, 6, and 12 are examples in which the number of torsion turns is changed with the same Young's modulus and the same tensile tension during mounting.
Has a wavelength shift of 5.5 nm, which is larger than a predetermined value.
This is thought to be due to the fact that, if twisted too much, the torsional force will gradually loosen in a high-temperature, high-humidity environment even when fixed with a hard adhesive, as in the case of increasing the tensile tension. Can be

From the above results, in order to suppress the wavelength shift amount to 2 nm or less, the adhesive for fixing the optical fiber coupler to the mounting member has a Young's modulus at 85 ° C. of 100M.
It is preferable to use a material having a pressure of Pa or more and to apply a tensile tension at room temperature of 40 mN to 200 mN when fixing to a mounting member. Also, when twisting the optical fiber coupler,
It is best to do this with no more than four turns.

[0028]

As is apparent from the above description, according to the optical fiber coupler of the present invention, the wavelength shift of transmission loss can be suppressed to 2 nm or less even in a high temperature and high humidity use environment. In addition, it is possible to perform stable optical signal transmission without deterioration of insertion loss while maintaining the characteristics of the initial stage of manufacturing. Further, the production yield can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a shape of an optical fiber coupler using a pair of optical fibers for explaining the present invention.

FIG. 2 is a diagram showing a mounted state of an optical fiber coupler for explaining the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Glass fiber part, 3 ... Fused fusion part, 4 ... Non-stretched part, 5 ... Protective coating, 6 ... Mounting member, 7 ...
Lid member, 8 ... adhesive.

Claims (4)

[Claims] 1. An optical fiber coupler comprising: a plurality of optical fibers fused and drawn; and an adhesive fixed to a mounting member with an adhesive, wherein the adhesive has a Young's modulus at 85 ° C. of 100 MPa.
a, wherein the fusion-stretched portion has a tensile tension at room temperature of 40 mN to 200 mN, and is mounted on the mounting member. 2. The optical fiber coupler according to claim 1, wherein the fusion-spread portion is twisted with four or less turns. 3. A method for manufacturing an optical fiber coupler, comprising: fusing and stretching a plurality of optical fibers, and bonding the optical fibers to a mounting member with an adhesive, wherein the adhesive has a Young's modulus at 85 ° C. of 100 MPa. A method for manufacturing an optical fiber coupler, wherein the adhesive is mounted on the mounting member with a tensile tension of the fusion-stretched portion at room temperature of 40 mN or more and 200 mN or less. 4. The method of manufacturing an optical fiber coupler according to claim 3, wherein the optical fiber coupler is mounted after being twisted into the fusion-stretched portion with four or less turns.