JP2003337251A - Polarization maintaining optical fiber coupler and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization maintaining optical fiber coupler that prevents a polarization extinction ratio from lowering even if an adhesive is used having a comparatively large Young's modulus in fixing to a mounting member, and also to provide a manufacturing method thereof. <P>SOLUTION: This coupler is a polarization maintaining optical fiber coupler in which a pair of polarization maintaining optical fibers 11 is melted, drawn and fixedly stuck to a mounting member 5 with an adhesive 7. For the adhesive 7, an ultraviolet ray setting resin is used which has a cold Young's modulus of 1,800-5,000 MPa after hardening. While heated above 30°C but below the glass-transition temperature, the adhesive 7 is hardened by being irradiated with ultraviolet rays. <P>COPYRIGHT: (C)2004,JPO

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 demultiplexing / combining optical signals in the field of optical communication, and more particularly to a polarization maintaining optical fiber using a polarization maintaining optical fiber. The present invention relates to a coupler and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, in an optical signal device, an optical fiber coupler has been frequently used for pumping and combining an optical amplifier and extracting a monitor light of an optical signal. This fiber optic coupler
It is used to split an optical signal having a single wavelength into a plurality of signals or combine them into one, or to demultiplex a plurality of signals having different wavelengths into wavelengths or combine them into one.

FIG. 4 is a diagram showing an example of a method for manufacturing a general optical fiber coupler. FIG. 4 (A) is a diagram showing a heat fusion process, and FIG. 4 (B) is a diagram showing a drawing process. 4C is a diagram showing a mounting process, and FIG. 4D is a diagram showing an annealing process. In the figure, 1 is an optical fiber, 2 is a glass fiber part,
Reference numeral 3 is a fusion-bonded stretched portion, 4 is a non-stretched portion, 5 is a mounting member, 6 is a lid member, 7 is an adhesive, and 8 is a constant temperature bath.

In manufacturing an optical fiber coupler, first,
As shown in FIG. 4A, for example, two optical fibers 1
Is prepared, the protective coating in the middle of the optical fiber is removed by a predetermined length, and the glass fiber portion 2 is exposed. After that, the exposed central portions of the glass fiber portions 2 are closely contacted in parallel with each other and fused by heating. A burner, a micro torch, or the like (not shown) is used for this heating.

FIG. 4B shows a state in which the fused portion is stretched, and is stretched while the glass is in a softened state at the time of heat fusion, or the optical fiber is heat-softened again and stretched. Let The fused and stretched portion 3 after stretching has, for example, a length of about 15 mm and a glass diameter of 0.15 m in average diameter.
It is about m (not circular). Since the degree of coupling between optical fibers changes depending on the amount of stretching, stretching may be performed while monitoring the degree of coupling using an optical power meter or the like.

The fusion-stretched optical fiber is shown in FIG.
As shown in FIG. 5, the mechanical component is housed in the mounting member 5 and is fixed by adhesion with an adhesive 7. The mounting member 5 is formed in a U-shape in cross section, and a lid member 6 is adhered to the center of the opening to close it. The mounting member 5 and the lid member 6 are generally formed of quartz glass or ceramics having a thermal expansion coefficient close to that of an optical fiber.

The adhesive 7 is applied to the non-stretched portions 4 on both sides of the fusion-bonded stretched portion 3 functioning as an optical coupler, and is adhesively fixed to the mounting member 5. For example, the coating length 2 on both sides of the mounting member 5
6 mm, that is, from the end portion of the mounting member 5 to the crotch portion of the fusion extending portion 3. The application amount of the adhesive 7 is about 0.013 cm ³ on one side. As the adhesive 7, an ultraviolet curable epoxy resin or the like is used. Next, in order to increase the degree of hardening of the adhesive, as shown in FIG.
Heat with. The heating temperature is about 120 ° C. for about 1 hour in consideration of the heat resistance of the protective coating of the optical fiber.

It is also known that the above-mentioned optical fiber coupler is constituted by a polarization maintaining optical fiber to form a polarization maintaining optical fiber coupler. The polarization-maintaining optical fiber is equivalently birefringent by applying different stresses from two directions orthogonal to the core. A typical example of this polarization-maintaining optical fiber is a structure in which stress-applying parts containing boron and the like having different thermal expansion coefficients from the clad part are arranged on both sides of the core part. It has been known. These polarization-maintaining optical fibers can suppress polarization fluctuations due to disturbances such as lateral pressure and bending.

In the polarization-maintaining optical fiber coupler, for example, when only the X polarization of the linearly polarized wave is input to the incident side of the coupler, only the X polarization is output to the exit side, and even if it passes through the coupler, the optical polarization is maintained. The polarization state of can be prevented from changing.
This polarization-maintaining optical fiber coupler is required to construct an optical fiber system using highly accurate single polarization.

FIG. 5 is a schematic view of a coupler element using a polarization maintaining optical fiber. 11 is a polarization maintaining optical fiber, 1
2 is a non-stretched portion, 13 is a fusion stretched portion, 14 is a core portion, 15
Indicates a clad portion, 16 indicates a stress applying portion, and 17 indicates a polarization principal axis plane. As in the case of FIG. 4, the polarization-maintaining optical fiber coupler is formed by closely contacting the central portions of the glass fiber portions, from which the coating has been removed, in parallel with each other, fusing by heating, and stretching. The polarization-maintaining optical fiber 11 has stress applying parts 16 on both sides of the core part 14 surrounded by the cladding part 15, and has a polarization main axis surface 17 passing through the centers of the core part and the stress applying part.

[0011]

In the production of a coupler element using a polarization-maintaining optical fiber, fusion and drawing are carried out with the planes of polarization main axes parallel to each other. The deviation of the polarization principal axis plane 17 causes an increase in loss, a decrease in coupling rate, and a decrease in polarization extinction ratio. Incidentally, the mounting on the mounting member with the adhesive uses the ultraviolet curable resin as in the case of FIG.
Annealing is performed to remove strain or increase the degree of hardening of the adhesive.

Various adhesive materials have been conventionally proposed for the adhesive 7 for bonding and fixing the coupler element to the mounting member from the viewpoint of stress relaxation to the optical fiber coupler. In order to hold and fix the optical fiber coupler on the mounting member, the adhesive must have a certain degree of hardness. Therefore, it is desirable to use an adhesive having a large Young's modulus.

However, in the production of the polarization-maintaining optical fiber coupler, when a UV curable adhesive having a large Young's modulus is used for fixing to the mounting member, the polarization extinction ratio is lowered after the adhesive is cured. There is. The reason for this is that uneven stress is applied to the fiber when the adhesive cures and shrinks,
Particularly, in the case of an adhesive having a large Young's modulus, it is considered that the stress is large and the polarization extinction ratio is lowered.

The present invention has been made in view of the above-mentioned circumstances, and a polarization optical fiber coupler which does not reduce the polarization extinction ratio even when an adhesive having a relatively large Young's modulus is used for fixing to a mounting member, and its manufacture. The challenge is to provide a method.

[0015]

A polarization-maintaining optical fiber coupler of the present invention is a polarization-maintaining optical fiber in which a pair of polarization-maintaining optical fibers are fusion-stretched and stretched and fixed to a mounting member with an adhesive. A fiber coupler, wherein the room temperature Young's modulus of the cured adhesive is 1800 MPa to 5000 MPa, an ultraviolet curable resin is used, and the adhesive is irradiated with ultraviolet rays while being heated at 30 ° C. or higher and below the glass transition temperature. It is characterized by being cured.

A method of manufacturing a polarization maintaining optical fiber coupler according to the present invention is characterized in that a pair of polarization maintaining optical fibers are fused and drawn,
A method of manufacturing a polarization-maintaining optical fiber coupler, which comprises bonding and fixing to a mounting member with an adhesive, wherein the adhesive has a normal temperature Young's modulus after curing of 1800 MPa to 5000 MPa, and an ultraviolet curable resin is used. It is characterized in that it is cured by being irradiated with ultraviolet rays while being heated at 30 ° C. or higher and below the glass transition temperature.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a perspective view of a polarization-maintaining optical fiber coupler, and FIG. 2 is a diagram for explaining a cured state of an adhesive. The reference numerals in the figure are the same as those used in FIG. 4, and the description thereof will be omitted. The polarization-maintaining optical fiber coupler according to the present invention is the same as that described with reference to FIG.
A stretched coupler element is used.

The polarization-maintaining optical fiber coupler according to the present invention is housed in a mounting member 5 made of quartz glass or the like for mechanical protection as shown in FIG. The non-stretched portion is bonded and fixed by the adhesive 7 from the portion. The mounting member 5 is formed to have, for example, a U-shaped cross section, and the lid member 6 is bonded to the center of the opening. An ultraviolet curable resin is used for the adhesive 7, and preferably an epoxy resin is used. The external appearance of the polarization maintaining optical fiber coupler is the same as that described with reference to FIG.

In the present invention, in particular, when the adhesive 7 is irradiated with ultraviolet rays to be cured as shown in FIG. 2, the adhesive 7 is cured while being heated to room temperature or higher. By heating the adhesive 7, it is possible to accelerate the curing by ultraviolet irradiation and reduce the uncured portion at the end of ultraviolet irradiation. The uncured part is
Although it can be hardened by subsequent high temperature annealing, the amount hardened by this annealing causes contraction when the temperature is returned to normal temperature after the end of annealing, which causes an increase in stress.

When UV irradiation is performed while heating, the rate of curing by UV irradiation increases and the rate of curing by annealing decreases, so that the increase in stress after annealing can be reduced and the polarization extinction ratio can be reduced. Can be suppressed.

The Young's modulus of the adhesive 7 at room temperature after curing is preferably in the range of 1800 MPa to 5000 MPa. If the Young's modulus is less than 1800 MPa, the adhesive fixation of the optical fiber is insufficient, and the effect of curing the adhesive due to the above-mentioned heating is small, so that it is meaningless. The heating at the time of irradiation with ultraviolet rays can be easily performed by using a heater or the like, and the heating temperature may be room temperature or higher.
It is desirable to carry out at 0 ° C or higher. Also, if heated above the glass transition temperature of the adhesive, the adhesive becomes softened and the position of the coupler element cannot be fixed, so it is not stable.
It is desirable to work below the glass transition temperature of the adhesive.

Next, examples of the present invention and comparative examples will be described. The mounting member 5 and the lid member 6 can be formed of various materials, but it is preferable that the mounting member 5 and the lid member 6 are formed of quartz glass or ceramics having a thermal expansion coefficient close to that of the optical fiber. The mounting member 5 was made of quartz glass in an elongated rectangular case having a groove cross section of the optical fiber accommodating recess of 0.7 × 0.7 mm and a length of 67 mm. The lid member 6 is also made of quartz glass and has a thickness of 0.8 mm, a width of 2 mm, and a length of 17 mm.
It was formed into a plate shape.

The adhesive 7 was applied to the non-stretched portions 4 on both sides of the fused stretched portion 3 functioning as an optical coupler in the mounting member 5. Specifically, the coating length is 26 mm on both sides of the mounting member 5, that is, from the end portion of the mounting member 5 to the crotch portion of the fusion extending portion 13, and the coating amount of the adhesive 7 is 0.01 on one side.
It was 3 cm ³ . An ultraviolet curable epoxy resin is used for the adhesive 7, and the room temperature Young's modulus after curing is A (100
MPa), B (1020 MPa), C (1910MP)
a), D (3040 MPa), E (4810 MPa),
Six types of samples of F (5910 MPa) were used.

The amount of ultraviolet rays is 200 m to cure the adhesive.
Irradiation was performed at W / cm ² for 10 minutes. When the adhesive 7 is irradiated with ultraviolet rays, the temperature of the mounting member 5 is set to 25 ° C., 45 ° C., 70 ° C.
The adhesive was heated to ℃, 150 ℃. After that, annealing was performed in a constant temperature bath within 1 hour after the irradiation of ultraviolet rays.
In this annealing, heating was performed at about 120 ° C. for about 1 hour in consideration of the heat resistance of the protective coating of the optical fiber.

The polarization-maintaining optical fiber coupler manufactured by the above manufacturing method was evaluated by measuring the polarization extinction ratio as shown in Tables 1 and 2. Note that the polarization extinction ratio is such that the polarized light is incident from one port on the incident side and the difference between the maximum value and the minimum value of the optical power is measured by the optical power meter at the port on the exit side (either of the two). It was measured.

[0026]

[Table 1]

[0027]

[Table 2]

The above measurement results are shown in a graph in FIG. From this result, the polarization extinction ratio tends to be improved by irradiating and curing the adhesive while heating the adhesive, and the polarization extinction ratio tends to improve as the heating temperature increases. This is because the curing component in the adhesive was activated by heating and the degree of curing increased when it was irradiated with ultraviolet rays.
It is considered that the amount of hardening due to the subsequent annealing was reduced and the stress applied to the fiber was reduced. However, the samples A and B, which have a relatively small Young's modulus, have a considerably high polarization extinction ratio even when they are irradiated with ultraviolet light at room temperature (25 ° C.), and therefore the effect of heating is small. Further, when the Young's modulus is small, the fixing force of the fiber is weak and the fixing is loosened due to the temperature change, so that the displacement is likely to occur and the characteristic variation is likely to occur.

On the other hand, in sample F having a large Young's modulus,
Although the polarization extinction ratio was improved by heating at 70 ° C., the value did not reach the pass level (18 dB or more). Therefore, from the evaluation results of Tables 1 and 2, samples C, D,
E is appropriate, and the polarization extinction ratio is significantly improved by heating. That is, the Young's modulus at room temperature after curing the adhesive is 18
It is preferably about 00 MPa to 5000 MPa.

Further, the polarization extinction ratio becomes better as the heating temperature becomes higher, but when it reaches about 150 ° C., which is higher than the transition temperature Tg of the adhesive, it is in a very soft state even though it is cured by ultraviolet irradiation. Therefore, the original purpose of adhesively fixing the fiber to the mounting member cannot be achieved. Therefore, it is desirable that the above heating temperature is higher than room temperature (25 ° C.), preferably 30 ° C. or higher and lower than the glass transition temperature of the adhesive.

[0031]

As is apparent from the above description, according to the present invention, even if an adhesive having a relatively large Young's modulus is used for fixing to a mounting member, the adhesive is cured by being irradiated with ultraviolet rays while being heated. By doing so, it is possible to manufacture a polarization maintaining optical fiber coupler that suppresses a decrease in polarization extinction ratio.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a polarization maintaining optical fiber coupler according to the present invention.

FIG. 2 is a diagram illustrating a cured state of the adhesive according to the present invention.

FIG. 3 is a graph showing evaluation results of the present invention.

FIG. 4 is a diagram illustrating a conventional method for manufacturing an optical fiber coupler.

FIG. 5 is a diagram illustrating an outline of a general polarization maintaining optical fiber coupler.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 2 ... Glass fiber part, 3 ... Fusion extension part, 4 ... Non-expansion part, 5 ... Mounting member, 6 ... Lid member, 7 ... Adhesive agent, 8 ... Constant temperature bath, 11 ... Polarization maintaining light Fiber, 12 ...
Non-stretched portion, 13 ... Fusion stretched portion, 14 ... Core portion, 15 ... Clad portion, 16 ... Stress imparting portion, 17 ... Polarization principal axis plane.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shigeru Hirai             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Maki Ike             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Masayuki Kitani             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Minoru Nakayama             4125 Toyokuni Electric Wire Co., Ltd.             Company Saitama factory (72) Inventor Yoshiaki Shimazaki             4125 Toyokuni Electric Wire Co., Ltd.             Company Saitama factory

Claims (3)

[Claims] 1. A polarization-maintaining optical fiber coupler comprising a pair of polarization-maintaining optical fibers fused and drawn and fixed to a mounting member with an adhesive, wherein the adhesive has a room temperature Young after curing. A polarization-maintaining optical fiber coupler, characterized in that an ultraviolet curable resin having a rate of 1800 MPa to 5000 MPa is used, and the adhesive is cured by being irradiated with ultraviolet rays while being heated at 30 ° C. or higher and lower than the glass transition temperature. . 2. The polarization maintaining optical fiber coupler according to claim 1, wherein the adhesive is an ultraviolet curable epoxy resin. 3. A method of manufacturing a polarization-maintaining optical fiber coupler comprising a pair of polarization-maintaining optical fibers fused together and stretched, and adhered and fixed to a mounting member with an adhesive, after curing with the adhesive. A polarization-maintaining optical fiber coupler, characterized in that an ultraviolet curable resin having a normal temperature Young's modulus of 1800 MPa to 5000 MPa is used, and the adhesive is cured by being irradiated with ultraviolet rays while being heated at a temperature of 30 ° C. or higher and lower than the glass transition temperature. Manufacturing method.