JP2866502B2 - Manufacturing method of optical fiber coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber coupler used for an optical fiber communication system, an optical fiber sensor, an optical measurement, and the like. The present invention relates to a manufacturing method for producing a semiconductor device with significantly higher reproducibility.

[0002]

2. Description of the Related Art A conventional low-loss optical fiber coupler is shown in FIG.
Shown in This holds multiple optical fibers 101 in parallel,
It is produced by heat-sealing a part thereof and further stretching it until a desired branching ratio is obtained. FIG. 6 shows the wavelength characteristics of the branching ratio of this optical fiber coupler. The wavelength is shown on the horizontal axis and the branching ratio is shown on the vertical axis, and it can be seen that there is a difference in the branching ratio when the wavelength is different. When the wavelength is 1.3 μm, the branching ratio is 50%. When the wavelength is larger than 1.3 μm, the branching ratio is also larger than 50%, and when the wavelength is smaller than 1.3 μm, the branching ratio is smaller than 50%. Since this conventional example has a large wavelength dependence of the branching ratio, it is not suitable for a wavelength division multiplexing communication system using a plurality of wavelengths, and its use is limited.

[0003] In the production of a multi-branched optical star coupler, a method of twisting an optical fiber at the time of fusing and stretching is often used in order to improve adhesion and distribution characteristics. FIG. 7 shows a second example of a conventional optical fiber coupler. This is Electronics by DBMortimore
Letters Vol.21, No.17, pp742, Wavelength-Fla in 1985
Published as ttenedFused Couplers. In this method, one of the two optical fibers 102 is heated and stretched in advance, and optical fibers having slightly different outer diameters are twisted and brought into close contact with each other, heated and fused and drawn. Thereby, the wavelength dependence of the branching ratio can be reduced. FIG. 8 shows an example of the wavelength dependence of this type of branching ratio. Wavelength 1.3μm and 1.55μm, branching ratio 50%, wavelength 1.3μ
between m and 1.55 μm, the branching ratio is slightly greater than 50%,
And gradually changes, the wavelength is less than 1.3μm and 1.55μ
Above m, the branching ratio is smaller than 50% and gradually decreases. Thus, it can be clearly understood that the change in the branching ratio is small with respect to the change in the wavelength. Since such an optical fiber coupler can be used in a wide wavelength band, it is also called a broadband optical fiber coupler.

As disclosed in US Pat. No. 4,798,438, one of two optical fibers is previously drawn to a small diameter having a diameter substantially equal to that of the other optical fiber. In some cases, a method is used in which the other optical fiber is closely contacted and aligned and fusion-stretched to provide a difference in the propagation constant between the two optical fibers.

[0005]

However, in the above-mentioned fusion-stretched optical fiber coupler, optical characteristics such as loss and branching ratio of the produced optical fiber coupler vary depending on the fusion range and fusion state. Cheap. In the case where the optical fiber is melt-stretched while being twisted in order to improve the adhesion and distribution characteristics, the reproducibility is further impaired. Furthermore, when manufacturing an optical fiber coupler in which the wavelength dependence of the branching ratio is reduced, there is a problem that reproducibility is very poor because one optical fiber is previously drawn and then fused and drawn. .

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention removes the coating of the middle part of the plurality of optical fibers and makes the coating removed parts parallel with an alignment jig. Aligning, stretching a predetermined length using a low-temperature heat source to soften the plurality of optical fibers, at least one alignment jig, by rotating the plurality of optical fibers at an angle at which the plurality of optical fibers are in contact at the narrowest diameter portion, the stretching portion. Closely adhered, after that, the stretched portion that has been brought into close contact with the high-temperature heat source with the temperature of the low-temperature heat source raised is fused, and the temperature of the high-temperature heat source is lowered and again as a low-temperature heat source, whereby the desired bonding of the bonded portion is obtained. This is a manufacturing method of stretching to

[0007]

By using the manufacturing method of the present invention, not only the fusion condition of the optical fiber at the time of fusion is stabilized, but also
Since the joint portion is produced without applying a twist during the fusion-stretching, the reproducibility of the optical characteristics of the produced fusion-stretched optical fiber coupler is extremely improved. In particular, it is very effective in producing a broadband optical fiber coupler or the like in which the wavelength dependence of the branching ratio having poor reproducibility is reduced.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows, for example, Corning SMF-
Shows a method of manufacturing an optical fiber coupler of the single-mode optical fiber 1 and 2 two such 28 ^TM and fused and extended. In FIG. 1 (a), the coating at the intermediate portion between the two optical fibers 1 and 2 is partially removed, and the coating removing portions 21 and 22 are aligned in parallel by an alignment jig 3 arranged at a predetermined distance. .

In FIG. 1B, a low-temperature heat source 4 such as an oxyhydrogen burner for softening the optical fibers 1 and 2 is stretched for a predetermined length while oscillating in the axial direction of the optical fibers 1 and 2. The narrowest diameter portions of the drawn optical fibers 1 and 2 are separated without contact. The low-temperature heat source 4 of the oxyhydrogen burner is a high-temperature heat source 14 for increasing the temperature and fusing the optical fibers 1 and 2. The temperature is controlled by the flow rate of the gas, and the flow rate of the hydrogen gas is increased to make the high-temperature heat source 14.

In FIG. 1C, the alignment jig 3 is rotated by an angle such that the narrowest diameter portions of the two optical fibers 1 and 2 which are separated from each other come into contact with each other. The rotation of the alignment jig 3 may be such that only one of the alignment jigs 3 is rotated. However, in this case, the alignment jigs 3 on both sides are rotated in the opposite direction by the same angle. As shown in FIG. 3, the positional relationship between the optical fibers 1 and 2 in the narrowest diameter portion is such that the contact points P of the optical fibers 1 and 2 are located on the central axis LL of the low-temperature heat source 4 such as an oxyhydrogen burner.
Is located approximately, the distance from the low-temperature heat source 4 is constant, and the heating condition is stable. 3B is a cross-sectional view taken along the line BB of the center of FIG. 1C, FIG. 3A is a cross-sectional view taken along the line AA of the left end of FIG. 1C, and FIG. FIG. 1C shows a cross section taken along the line CC of the right end portion, in which the left end portion and the right end portion of the optical fibers 1 and 2 are rotated in directions opposite to each other. In contrast,
When only one of the alignment jigs 3 is rotated, the optical fibers 1 and 2 are rotated.
Becomes difficult to be located on the central axis LL of the low-temperature heat source 4, the distance from the low-temperature heat source 4 is not constant, and the heating condition becomes unstable.

The stretching length in FIG. 1 (b) is 125 μm in outer diameter.
When the optical fibers 1.2 are used and the thinnest portion of the optical fibers 1.2 is stretched to about 89 μm, the alignment jig 3 is rotated in the opposite direction by 45 degrees, and the optical fibers 1.2 are rotated. By applying uniform tension from both ends of the optical fiber, the optical fibers 1 and 2 are brought into close contact with each other at the narrowest diameter portion. Here, the radius R is 2
When the single mode optical fibers 1 and 2 are pre-drawn and brought into close contact with each other, the sum of the two radii of the portions whose diameters have been reduced by the pre-drawing is calculated.

[0012]

When the rotation angle of the alignment jig 3 is set to 90 degrees at 45 degrees in the reverse direction, it has been confirmed that the best contact condition is obtained in which the narrowest diameter portion contacts at one point. FIG. 2 shows an example of a rotation mechanism of the alignment jig 3. This rotation mechanism is provided in a precision V-groove 6 of the turntable 5 having a precision V-groove 6 whose upper surface is precisely finished.
An alignment jig 3 in which a cylindrical body is divided in half in the axial direction is placed with its circular outer periphery S in contact therewith. The optical fibers 1 and 2 are aligned on the support plane 7 of the alignment jig 3. The support plane 7 is set so as to include the central axis of the cylindrical body of the alignment jig 3, and the circular outer periphery S of the alignment jig 3 is set. By positioning the center axis of the rotation on the support plane 7, the alignment jig 3 can be rotated on the precision V-groove 6 in the forward direction or the reverse direction.

Further, in FIG. 1 (d), as the high-temperature heat source 14 in which the flow rate of the hydrogen gas of the low-temperature heat source 4 is increased and the temperature is increased, a drawn portion in which the optical fibers 1 and 2 are brought into close contact with the high-temperature heat source 14 is used. Fusion is performed to form a fusion portion F. Finally Figure 1
In (e), the temperature of the high-temperature heat source 14 is lowered, and the low-temperature heat source 4 is used again as in the case shown in FIG.
While the low-temperature heat source 4 is oscillated in the axial direction, the fused portion F is stretched until a desired bond is obtained.

Although not shown, in each step,
Light is incident from one end of one optical fiber 1 using a stabilized light source, and light emitted from the other ends of the two optical fibers 1 and 2 is constantly monitored using an optical power meter. The above example is an example of an optical fiber coupler whose branching ratio has a normal wavelength dependence. However, when a broadband optical fiber coupler is manufactured, the pre-stretching step shown in FIG. 2-223,873, "Apparatus for manufacturing optical fiber coupler", disclosed in the present applicant, at least one optical fiber can be drawn at a different speed than another optical fiber, using two optical fibers. By drawing at different speeds, the diameters of the narrowest diameter portions of the optical fibers 1 and 2 are made different from each other.
(c) The following steps may be performed.

FIG. 9 shows an embodiment of this apparatus, in which an alignment jig 3 for the optical fibers 1 and 2 is arranged at a predetermined distance, and a pair of opposed opposing movable members, at least one of which is movable outside the alignment jig 3. Drive tables 11 and 12 are provided, and holding tools 41 and 42 are provided on the drive tables 11 and 12, respectively, and the heat source 4 is arranged between the alignment jigs 3. Here, the coating removing portions 21 of the optical fibers 1 and 2
22 is closely aligned by the alignment jig 3, and the optical fiber 1
2 Both ends of 2 are gripped on the driving bases 11 and 12 by the grippers 41 and 42, and the driving bases 11 and 12 can draw and drive the optical fibers 1 and 2 at different speeds. The diameters of the narrowest diameter portions of the optical fibers 1 and 2 are made different, and the alignment jig 3 is rotated to bring the small diameter portions into close contact. Thereafter, as described above, the temperature of the heat source 4 is raised to fuse the small diameter portion, and the temperature of the heat source 4 is lowered again to stretch the fused portion by the driving stands 11 and 12 until a desired connection is obtained.

The driving bases 11 and 12 are separately provided. However, as shown in FIG. 10, the driving base 32 is mounted on the driving base 31 so that the driving base 32 can be driven on the driving base 31. It may be. FIG. 4 shows an example of measuring the wavelength dependence of the branching ratio of an optical fiber coupler manufactured using the apparatus of FIGS. 9 and 10 so that the branching ratio becomes 50% at a wavelength of 1.3 μm. 1.3μ wavelength
The branching ratio is about 50% from 1.5 m to 1.55 μm, and the wavelength is 1.
At 3 μm, the branching ratio is less than 50%, and at 1.55 μm, the branching ratio is greater than 50%. It was confirmed that this kind of broadband optical fiber coupler manufactured using the manufacturing method of the present invention had better reproducibility and exhibited almost the same wavelength characteristics as those manufactured using the conventional method.

Incidentally, in the example using FIGS. 9 and 10,
As described above, the sum of the radii of the narrowest diameter portions of the two optical fibers having the radius R is given by:

[0019]

If the rotation angle of the alignment jig 3 is set to 90 ° in 45 ° increments in the opposite direction, the best contact condition is obtained. In the above example, two optical fibers were used, but an optical star coupler using a large number of optical fibers could be reproduced without twisting during fusion stretching by using the same configuration. Needless to say, it can be manufactured with good properties.

In the above example, a single mode fiber is used. However, it is needless to say that even when a multimode fiber is used, the thinnest portion can be in close contact and the fusion conditions are stable.

[0022]

By using the production method of the present invention,
Not only ordinary optical fiber couplers (including optical star couplers) but also broadband optical fiber couplers with reduced wavelength dependence of the branching ratio can be manufactured with good reproducibility.
Further, according to the present invention, the yield can be greatly improved by slightly changing the apparatus itself from the conventional manufacturing apparatus, so that an inexpensive optical fiber coupler can be provided.

[Brief description of the drawings]

FIGS. 1A to 1E are conceptual views showing an example of a method for manufacturing an optical fiber coupler of the present invention.

FIG. 2 is a cross-sectional view illustrating an example of a rotation mechanism of an alignment jig used in the present invention.

FIGS. 3 (a) to 3 (c) are cross-sectional views showing the alignment state of the optical fiber of FIG. 1 (c) at various points in the axial direction.

FIG. 4 is a characteristic diagram of a wavelength and a branching ratio according to the present invention.

FIG. 5 is a perspective view of a conventional optical fiber coupler.

FIG. 6 is a characteristic diagram showing a relationship between a wavelength and a branching ratio of a conventional optical fiber coupler.

FIG. 7 is a perspective view of another conventional optical fiber coupler.

FIG. 8 is a characteristic diagram showing a relationship between a wavelength and a branching ratio of another conventional optical fiber coupler.

FIG. 9 is a schematic configuration diagram of a manufacturing apparatus showing one embodiment according to the present invention.

FIG. 10 is a schematic configuration diagram of another manufacturing apparatus showing one embodiment according to the present invention.

[Explanation of symbols]

 1.2 Optical fiber 21/22 Coating removal part 3 Alignment jig 4 Low temperature heat source 14 High temperature heat source F Fused part

Claims (4)

(57) [Claims] A step of aligning the coating removal portions of the plurality of optical fibers from which the coating of the intermediate portion has been removed in parallel with an alignment jig arranged oppositely; and an alignment jig for softening the optical fiber of the coating removal portion. Elongating a predetermined length using a low-temperature heat source disposed between the components, and rotating at least one of the alignment jigs by an angle such that the thinnest portions of the coating removal portions formed by the elongation come into contact with each other. A step of bringing the stretched portion into close contact with each other, a step of fusing the contacted stretched portion with a high-temperature heat source having a high temperature of the low-temperature heat source, and a step of lowering the temperature of the high-temperature heat source to make it a low-temperature heat source again; Stretching the portion until a desired connection is obtained. 2. The method according to claim 1, wherein, in the step of stretching the coating removing section by a predetermined length using a low-temperature heat source, at least one optical fiber is stretched at a different speed from other optical fibers. Of manufacturing an optical fiber coupler. 3. In the step of rotating the alignment jig by an angle such that the narrowest diameter portions of the coating removing portions come into contact with each other and bringing the extension portion into close contact, the opposing alignment jigs are rotated in the opposite directions by a desired rotation angle. 3. The method of manufacturing an optical fiber coupler according to claim 1, wherein the optical fiber coupler is rotated by a half. 4. A method according to claim 1, wherein the plurality of optical fibers are two optical fibers having a radius R, and the sum of the radii of the two thinnest portions is 4. The method according to claim 3, wherein the desired rotation angle of the alignment jig is set to 90 degrees.