JPH08234045A - Optical fiber coupler and its use method - Google Patents

Abstract

PURPOSE: To make it possible to produce an optical fiber coupler at a good yield and to adjust a branching ratio by varying the length or/and spacing of a coupling part where two pieces of eccentric core optical fibers face each other in proximity. CONSTITUTION: The eccentric core optical fibers 1 are respectively fixed to an optical fiber holding part 3 and are tightly coupled in the state that cores 2, 2 are held in the extreme proximity. The coupling surfaces 3A of the coupling part 3 are formed as plane surfaces. Regulating members 5 are held by the eccentric core optical fibers 1, 1 in the branching and coupling part at respective both ends of the coupling part 3. The regulating members 5 are arranged variably in their positions in such a manner that the length of the coupling part 3 can be regulated. The method for adjusting the branching ratio is executed by changing the position of the regulating members 5 in such a manner that the length L1 of the coupling part 3 disposed with the cores 2, 2 of two pieces of the eccentric core optical fibers 1, 1 opposite and proximate to each other is varied to the length L2 of the coupling part 3, thereby changing the length of the coupling part 3.

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 in the fields of communication and optics and a method of using the same.

[0002]

2. Description of the Related Art Optical couplers started as products using optical components using lenses, and now optical fiber-using products are the mainstream. Among these optical fiber type optical couplers, there is one called a fusion taper type optical fiber coupler due to its manufacturing method. In the fusion taper type optical fiber coupler, two optical fibers are brought close to each other in parallel, both ends are fixed and set on a jig, and a part of the two optical fibers is heated by a micro torch or the like to be fused and integrated. At the same time, it is stretched and stretched in the longitudinal direction. By melting and drawing, the diameters of the two optical fibers are reduced, the cores come close to each other, and the light propagating in the cores is branched and coupled.

Further, as one of the optical fiber type optical couplers, there is an optical fiber type optical variable coupler 40 as shown in FIG. This optical fiber type variable optical coupler 40 polishes a part of the clad 42 of the optical fiber 41 to reduce the thickness of the clad 42 and brings this part close to each other, and shifts the approached part substantially at right angles to the axial direction. Is generated, the light branching ratio is made variable.

[0004]

Since the fused taper type optical fiber coupler can be produced by closely adhering two optical fibers in parallel and melting and stretching, it is a relatively easy production method. By the way, the branching ratio is a very important factor in not only the fused taper type optical fiber coupler but also the optical coupler in general. In order to obtain a predetermined branching ratio in manufacturing the above fused taper type optical fiber coupler,
Strict control of heating temperature, tensile tension, stretching amount, etc. is required.

Therefore, actually, it is very difficult to manufacture the above-mentioned fused taper type optical fiber coupler. If the optical fiber is stretched beyond the desired branching ratio, it is difficult to rework the optical fiber coupler to adjust the branching ratio, which reduces the manufacturing yield of the optical fiber coupler. . Further, in the melt taper type optical fiber coupler, it is impossible to adjust the branching ratio at the time of use because the branching ratio is uniquely determined at the time of its production.

Further, a part of the clad is polished as shown in FIG.
In the optical fiber type variable optical coupler shown in (a), in order to obtain a desired cladding thickness, the optical fiber 41 is installed on the polishing table 43 as shown in FIG. However, much time and labor were required for polishing and observing the thickness. Further, in the conventional method, only the clad 42 is ground by polishing, and the optical fiber 4
In order to bring the core 2 of No. 1 closer to each other, it was necessary to bend the optical fiber with a certain curvature as shown in FIG. The length of this portion to be brought close (called an effective bond length) had a limit value determined by the curvature of the bent portion shown in Expression 1.

[0007]

## EQU1 ## Limit value ≈√ (πRa / U) ... Equation 1 R: Bending radius a: Core radius, U: Lateral normalized propagation constant peculiar to the optical fiber This effective coupling length L is, for example, usually In the case of the single-mode optical fiber of, the bending radius is about 1.6 mm when the bending radius of the bending portion is 25 cm, and the bending radius is 2 mm.
Even if it is as large as 00 cm, it stays at a little less than 4.8 mm,
Long light bond length cannot be obtained. For this reason, it was necessary to bring the cores sufficiently close to each other in order to obtain the required light coupling for branching. As a result, when one of the optical fibers is shifted to change the branching ratio, the change of the branching ratio with respect to the deviation amount becomes large, and the branching ratio changes with a slight deviation. It was an optical coupler that was difficult to adjust. That is, the operation is unstable, which hinders highly accurate adjustment of the branching ratio.

It is an object of the present invention to solve the above problems, to provide an optical fiber coupler with a high yield, and to provide an optical fiber coupler having an adjustable branching ratio and a method of using the same. More specifically, we realized a variable optical coupler that reduces the labor involved in making an optical fiber coupler and that makes the change in the branch ratio moderate with respect to the amount of movement of the optical fiber, and keeps the set branch ratio constant. It is an object of the present invention to provide an optical fiber coupler that enables highly accurate branching ratio adjustment and a method of using the same.

[0009]

The present invention has the following means in order to solve the above problems.

The optical fiber coupler according to claim 1 of the present invention is an optical fiber coupler in which two eccentric core optical fibers have a coupling portion in which the eccentric cores face each other for a predetermined length and are adjacent to each other. The eccentric core optical fiber is characterized in that the adjacent and adjacent coupling portions have variable lengths and / or distances so that the branching ratio can be adjusted.

The optical fiber coupler according to a second aspect of the present invention is an optical fiber coupler in which two eccentric core optical fibers have a coupling portion in which the eccentric cores face each other for a predetermined length and are adjacent to each other. An optical fiber coupler, wherein lengths of facing coupling portions of an eccentric core optical fiber are regulated by regulating members sandwiched at both ends of the coupling portion.

According to a third aspect of the present invention, the optical fiber coupler is characterized in that the surfaces of the coupling portions of the two eccentric core optical fibers facing each other are flat.

The optical fiber coupler according to a fourth aspect of the present invention is characterized in that one or more kinds of other substances having optical transparency are interposed in the coupling portions of two eccentric core optical fibers facing each other. To do.

In the optical fiber coupler according to a fifth aspect of the present invention, the surface shape of the two eccentric core optical fibers has at least two flat surfaces, and the flat surfaces intersect each other at a predetermined angle. Is characterized by.

In the method of using the optical fiber coupler according to claim 6 of the present invention, the surface shape of the optical fiber has at least one flat surface, and a plurality of eccentric cores each having an eccentric core so as to approach the flat surface. An optical fiber is a method of using an optical fiber coupler in which eccentric cores are opposed to a flat surface by a predetermined length and are in close proximity, and the lengths or intervals of the facing parts of the plurality of eccentric core optical fibers are It is variable, and this change makes it possible to adjust the branching ratio of the light branched from one optical fiber to the other optical fiber.

In the method of using the optical fiber coupler according to claim 7 of the present invention, the core spacing is set by moving the two eccentric core optical fibers vertically or horizontally or both relative to the facing surfaces. It is characterized by changing.

In the method of using the optical fiber coupler according to claim 8 of the present invention, the eccentric core optical fibers are arranged so that the axial directions of the eccentric core optical fibers are substantially parallel to each other at positions where the cores are close to each other. It is characterized in that the ratio of the split light is adjusted by moving one or more of them in the axial direction.

According to the optical fiber coupler of the present invention and the method of using the same, the variable optical coupler can be manufactured more easily than the conventional method. In addition, the bond length can be dramatically increased. The change in the optical branching ratio with respect to the movement amount when the shift movement in the direction perpendicular to the axial direction of the core of the optical fiber is generated can be made gradual as compared with the conventional method.
As a result, it becomes possible to improve the accuracy of the optical branching adjustment and to improve the stability when the set branching ratio is kept constant, as compared with the related art.

More specifically, when the eccentric core optical fiber has a round cross section, it is difficult to determine the core position and twisting occurs in the longitudinal direction, so that the two eccentric core optical fibers are twisted. The relative position of the eccentric core is not stable in the longitudinal direction. Therefore, the characteristics of the optical fiber type coupler using the round eccentric core are not stable. On the other hand,
In an eccentric core optical fiber in which the surface of the coupling portion is a flat surface, it is much easier to determine the position of the eccentric core than the round type. Moreover, the flat surface prevents the optical fiber from being twisted. Further, by using that surface as a reference, it is possible to uniformly determine the positions of the eccentric cores of the two eccentric core optical fibers in the longitudinal direction. Furthermore, if the surface facing the surface of the eccentric core is parallel to the surface of the eccentric core, when the eccentric core optical fiber is mounted on a substrate or a fixing jig, the surface opposite to the eccentric core is used as a reference. It is more desirable because it can be fixed stably.

According to the optical fiber coupler of claim 1 of the present invention, the two eccentric core optical fibers are optical fiber couplers having coupling portions in which the eccentric cores face each other for a predetermined length and are adjacent to each other. Since the eccentric core optical fibers of the opposing and adjacent coupling portions have variable lengths and / or distances, and thereby the branching ratio can be adjusted, two eccentric core optical fiber gripping materials can be used. The branching ratio can be adjusted by changing the lengths of the coupling portions of the core optical fiber facing each other and the distances of the coupling portions, and an optical fiber coupler can be manufactured with a high yield. Moreover, since the branching ratio can be adjusted, the branching ratio can be readjusted at the time of use.

According to the optical fiber coupler of claim 2 of the present invention, the two eccentric core optical fibers are optical fiber couplers having coupling portions in which the eccentric cores face each other for a predetermined length and are adjacent to each other. Since the lengths of the coupling portions of the eccentric core optical fibers facing each other in close proximity are regulated by the regulation members sandwiched at both ends of the coupling portion, the length of the coupling portions of the two eccentric core optical fibers facing each other in proximity is regulated by the regulation member. Since the branching ratio can be adjusted by changing the height, it is possible to manufacture an optical fiber coupler with high yield. Moreover, since the branching ratio can be adjusted, the branching ratio can be readjusted at the time of use.

According to the optical fiber coupler of the third aspect of the present invention, since the surfaces of the coupling portions of the two eccentric core optical fibers facing each other are flat, the branch coupling characteristics are stable. Become.

According to the optical fiber coupler of the fourth aspect of the present invention, since one or more kinds of other substances having optical transparency are interposed in the coupling portions of the two eccentric core optical fibers facing each other, the propagation of the optical fibers is prevented. It is possible to control the light leakage distribution, and as a result, it is possible to adjust the average value of the branching ratio and the like. In addition, the mechanical reliability is improved and the loss is effectively reduced.

According to the optical fiber coupler of claim 5 of the present invention, the surface shape of the two eccentric core optical fibers has at least two flat surfaces, and the flat surfaces intersect each other at a predetermined angle. Therefore, when the optical fiber in the variable optical coupler is moved in the axial direction, the adjustment can be performed more easily.

According to the method of using the optical fiber coupler of the sixth aspect of the present invention, the surface shape of the optical fiber has at least one flat surface, and a plurality of cores having an eccentric core so as to approach the flat surface. A method of using an optical fiber coupler in which an eccentric optical fiber is used, and eccentric cores are opposed to each other by a predetermined length and are adjacent to a flat surface thereof, and the lengths or intervals of the opposed portions of the plurality of eccentric core optical fibers are set. Is variable, and this change made it possible to adjust the branching ratio of the light that splits from one optical fiber to the other optical fiber, so more precise optical branching adjustment and the set branching ratio are kept constant. It has become possible to improve stability when doing.

According to the method of using the optical fiber coupler of claim 7 of the present invention, the two cores of the eccentric core are moved relative to each other in the vertical direction, the horizontal direction, or both relative to each other. By changing, the branch ratio adjusting mechanism can be easily constructed.

According to the method of using the optical fiber coupler of the eighth aspect of the present invention, the eccentric core optical fibers are arranged so that the axial directions thereof are substantially parallel to each other at the positions where the cores are close to each other,
By moving one or more of the eccentric core optical fibers in the axial direction, the ratio of the split light is adjusted, so the split ratio with respect to the amount of movement shows a more gradual change, further improving stability and accuracy. Is obtained.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to embodiments. The optical fiber coupler of the present invention will be described with reference to FIGS. In the figure, 1 is an eccentric core optical fiber, 2 is a core of the eccentric core optical fiber 1, and 3 is a coupling part in which the cores 2 of the two eccentric core optical fibers 1 and 1 face each other. The eccentric core optical fibers 1 are fixed to the optical fiber gripping material 3, respectively, and are tightly coupled to each other with the cores 2 and 2 closest to each other as shown in FIG. Joining part 3
Each of the coupling surfaces 3A is a flat surface.

The eccentric core optical fiber 1 shown in FIG. 2 has a rectangular cross section. The rectangular eccentric core optical fiber 1 shown in FIG. 2 can be obtained by spinning a glass preform produced by vapor phase synthesis. A restriction member 5 is sandwiched between the eccentric core optical fibers 1 and 1 at each of the two ends of the coupling portion 3B. The restriction member 5 is arranged so that its position is variable so that the length of the coupling portion 3 can be restricted.

The branching ratio of the above optical fiber coupler is adjusted as follows. The adjustment method of the branching ratio in FIGS. 3A and 3B is performed by the two eccentric core optical fibers 1, the core 2 of the optical fiber 1,
2 is a method of changing the lengths of the connecting portions 3 that are opposed to and close to each other. By changing the position of the regulating member 5 so that the length L1 of the connecting portion 3 as shown in FIG. 3A becomes the length L2 of the connecting portion 3 as shown in FIG. The branching ratio is adjusted by changing the length. Figure 4 (a),
The method of adjusting the branching ratio of (b) is to move the core 2 in a direction perpendicular to the longitudinal direction of the core 2 of the coupling part 3 in which the two cores 2 of the eccentric core optical fibers 1 and 1 face each other and face each other. This adjusts the distance between the cores 2 and 2 to change the branching ratio.

In the above embodiment, the eccentric core optical fiber has a rectangular cross-sectional shape, but the cross-sectional shape is not limited to a rectangular shape, and an eccentric shape having an octagonal cross-sectional shape as shown in FIG. The core optical fiber 1A or the eccentric core optical fiber 1B in which the eccentric core side of the perfect circle shown in FIG. 6 is a flat surface
It may have a cross-sectional shape such as. In short, core 2,
If the coupling surface 3A of the coupling portion 3 in which 2 is opposed to and adjacent to each other is a flat surface, the branch coupling characteristic becomes more stable. This is because it is easy to make the two eccentric core optical fibers 1 face each other along the core 2 by using the surface close to the core 2. Further, by utilizing the connecting surface 3A, the connecting surface 3A can be moved in the longitudinal or vertical direction of the core 2.
By changing the position of the coupling portion 3 of the eccentric core optical fiber 1 along the distance, the distance between the cores 2 and 2 can be changed and the branching ratio can be adjusted.

In the above embodiment, the eccentric core optical fiber is formed by cutting a glass preform and spinning the glass preform. However, the method is not limited to the above method, and other methods for forming the eccentric core optical fiber. For example, even if a powder molding method is used, the core 2 and the connecting portion 3 in which the cores 2 and 2 face each other face each other.
It is possible to obtain an eccentric core optical fiber having a flat coupling surface 3A. For example, as a powder molding method, JP-A-4-240
By the method disclosed in Japanese Patent Publication No. 42, an eccentric core optical fiber having a rectangular coupling surface 3A of the coupling portion 3 can be obtained. As another method for forming an eccentric core optical fiber, it can be obtained by a pressure molding method disclosed in Japanese Patent Laid-Open No. 4-124043, a cast molding method disclosed in Japanese Patent Laid-Open No. 64-56331, or the like. it can.

Other specific examples of the optical fiber coupler of the present invention and a method of using the same will be described in more detail below. Normally, the cross-sectional structure of an optical fiber is circular,
As shown in FIG. 7, at least one surface is a flat surface 11 in the longitudinal direction, and the core 2 in the optical fiber, which mainly propagates light, is decentered so as to approach the flat surface 11. The eccentric core optical fiber 10 is prepared in advance. A plurality of the eccentric core optical fibers 10 are prepared, and the eccentric flat surfaces 11 of the cores 2 are brought close to each other so as to be substantially parallel to each other. The eccentric core optical fiber 10 has an optical fiber structure having at least one flat surface 11, and since the flat surfaces 11 are brought close to each other, when the eccentric core optical fibers 10 are brought close to each other, as shown in FIG. There is no need to bend the adjacent parts. Therefore, there is no limitation on the bond length due to the radius of curvature. Therefore, a sufficiently long bond length L on the order of cm can be easily obtained, and as a result, it is possible to separate the cores from each other.

If the vertical axis shift amount is x and the interval when the core 2 is closest is y, the proximity interval s is given by equation 2 in the relationship shown in FIG.

S = √ (x ² + y ² ) Equation 2 (FIG. 9 shows a conventional polishing type optical fiber coupler, but the relationship of Equation 2 is the same). In the present invention, the coupling length L Since y is long, y can be set large. When the axis shift (x) perpendicular to the axis of the optical fiber is performed, x with respect to y becomes smaller, so that the change of the coupling interval s with respect to the movement amount x becomes more gradual and the change of the branching ratio with respect to x also becomes gradual.

This was confirmed by calculation and experiment. FIG. 10 shows the relationship between the branching ratio and the axial shift amount. A single mode optical fiber with a core diameter of 8 μm and a relative refractive index difference of 0.3% is used, the signal light wavelength is 1.064 μm, and the minimum core spacing is Is the optimum binding condition (100% in both the conventional example and the present invention example).
Is calculated under the condition that the branching ratio changes monotonically from 0 to 0% and neither over-coupling nor under-coupling is performed. The solid line represents the conventional example, and the dotted line represents the characteristics of the optical coupler having the structure of the present invention.

The calculation result shows that the characteristic of the branching ratio is about 40% gentler at the 50% coupling point with respect to the shift amount (x) than in the conventional example. In the experiment, an eccentric core optical fiber 20 having a flat surface structure on the periphery as shown in FIG. 11 and having the core 2 eccentric to the flat surface 21 was manufactured.
Two eccentric core optical fibers 20 are prepared and are arranged close to each other to form an optical coupler as shown in FIG.
One of 0 was moved in the lateral direction (direction perpendicular to the axis). The characteristics of branching with respect to this shift amount were measured. The measured results are in good agreement with the calculated values shown by the dotted line.

As described above, it was confirmed that the optical coupler using the eccentric core optical fiber 20 having a flat surface structure has a gradual branching ratio characteristic with respect to the lateral shift amount. Therefore, the adjustment accuracy of the branch ratio could be improved. FIG.
The method of adjusting the branching ratio in the optical fiber coupler of the present invention is specifically shown in FIG. In FIG. 13, (a) and (b) and (d) and (e) are adjustment methods of the branching ratio in which two eccentric core optical fibers 20 having a flat surface structure are vertically translated,
(B) and (c) and (e) and (f) are horizontal translational adjustment methods of the branching ratio.

It is also possible to rotate two eccentric core optical fibers 20 having a flat surface structure on a horizontal plane as shown in FIGS. 14 (a) and 14 (b). In this way, two eccentric core optical fibers 20 having a flat surface structure are parallel to a flat surface 21 that is close to each other, or a flat surface 2 that is close to each other.
The branching ratio is adjusted by performing movements such as translation and rotation on the plane perpendicular to 1 and both planes.

FIG. 15 shows a substance 23 having optical transparency interposed between the adjacent portions of two eccentric core optical fibers 20 having a flat surface structure, which is branched according to the value of the refractive index of the intervention. At the same time that the average value of the ratio can be moved, the interposition of the material 23 having optical transparency acts as a protection of the optical fiber and improves the mechanical reliability. Further, when the substance 23 having light transparency is a liquid, light scattering due to minute irregularities on the flat surface is reduced and the loss characteristic is improved.

The optical fiber coupler shown in FIG. 15 has at least one flat surface 21, and two eccentric core optical fibers 20 with the core 2 eccentric to the flat surface 21 face each other, and Is UV curable resin 24
Is coated and the space between them is filled with a liquid 23 having light transparency. The UV curable resin 24 serves to protect the eccentric core optical fiber 20 and adjust the seepage distribution state of the propagating light. When there is no coating, the difference in refractive index between glass and air is large, and the amount of oozing out of propagating light is small. Resin 2 with a refractive index almost in the middle between glass and air
By applying No. 3, the leaching amount could be increased by about 10%. Moreover, scratches are likely to occur on the bare glass surface, and the coating of the UV curable resin 24 is effective from the viewpoint of reliability. Furthermore, a liquid 2 with light transparency
When 3 is satisfied, scattering on the surface is prevented, and 5 dB when larger than when the transparent liquid 23 is not satisfied.
The degree of loss was improved.

Further, as a special case of FIG. 13, when two eccentric core optical fibers 20 in which the core 2 is eccentric to the flat surface 21 are opposed to each other and are moved on a plane which is close to the flat surface 21 and which are adjacent to each other. , Eccentric core optical fiber 2
It was carried out in the direction of 0 axis. When a deviation is caused in the axial direction of the eccentric core optical fiber 20 by utilizing the feature of the present invention having a long coupling length, the change of the branching ratio with respect to the deviation amount is from 0% to 100% as shown in the calculation result of FIG. The amount of movement required to change the branching ratio is several tens of times larger than in the past. In the conventional example, the diameter of about 10 μm is 0.8 mm,
Expanded to sub-mm order, with more gradual characteristics,
The stability and adjustment accuracy for keeping the branching ratio constant has been further improved.

In this case, the calculation condition is a core diameter of 8.0.
μm, wavelength 1.064 μm. The minimum inter-core distance is 8.0 μm. In order to cause a deviation in the axial direction of the eccentric core optical fiber 20, the eccentric core optical fiber 20
Must be moved parallel to the axial direction. In the unlikely event that a movement having an angle with respect to the axial direction is performed, the change with respect to the deviation becomes steep, and the effect of the present invention is difficult to obtain.

Therefore, in the structure of the eccentric core optical fiber 30 as shown in FIG. 17, at least two flat surfaces 3 are formed.
1 and 32 may be provided so that the flat surfaces 31 and 32 intersect each other at an angle θ. Other surface 33
Is an arbitrary aspect. In this way, if a plurality of eccentric core optical fibers 30 are arranged with one flat surface 31 as a reference and the optical fibers are misaligned along the reference surface, it becomes easy to prevent the angular misalignment, which is simple and easy. With this simple configuration, the branching ratio can be adjusted. The prismatic optical fiber shown in FIG. 11 has the above requirement, "It has at least two flat faces, which are at a constant angle to each other (in this case 90 °).
Degrees). Is met.

This eccentric core optical fiber 30 is shown in FIG.
As shown in (a) to (c), for example, they are arranged in parallel with one flat surface 31 as a reference. The eccentric core optical fiber 30 is moved along the surface in the axial direction (direction of → in the figure). At this time, the other flat surfaces 32 are kept at a certain distance from each other. For this purpose, for example, a method of bringing the flat surfaces 32 into close contact with each other or a method of arranging a spacer (not shown) having a uniform thickness between the flat surfaces 32 can be considered.

As described above, in the optical fiber coupler of the present invention, the branching ratio can be adjusted by changing the coupling state of the two adjacent eccentric core optical fibers facing each other, so that the optical fiber coupler can be manufactured with high yield. it can. Moreover, since the branching ratio can be adjusted, the branching ratio can be readjusted at the time of use.

[0046]

As described above, according to the optical fiber coupler of claim 1 of the present invention, the two eccentric core optical fibers are optical fibers each having a coupling portion in which the eccentric cores face each other for a predetermined length and are adjacent to each other. In the fiber coupler, the two eccentric core optical fibers have variable lengths and / or distances between the facing and adjacent coupling portions, and the branching ratio can be adjusted by the variable length. 2 with optical fiber gripping material
The branching ratio can be adjusted by changing the lengths of the coupling portions and the distances between the coupling portions of the eccentric core optical fiber facing each other, so that the optical fiber coupler can be manufactured with high yield. Moreover, since the branching ratio can be adjusted, the branching ratio can be readjusted at the time of use.

According to the optical fiber coupler of claim 2 of the present invention, the two eccentric core optical fibers are optical fiber couplers having coupling portions in which the eccentric cores face each other for a predetermined length and are adjacent to each other. Since the lengths of the coupling portions of the eccentric core optical fibers facing each other in close proximity are regulated by the regulation members sandwiched at both ends of the coupling portion, the length of the coupling portions of the two eccentric core optical fibers facing each other in proximity is regulated by the regulation member. Since the branching ratio can be adjusted by changing the height, it is possible to manufacture an optical fiber coupler with high yield. Moreover, since the branching ratio can be adjusted, the branching ratio can be readjusted at the time of use.

According to the optical fiber coupler of claim 3 of the present invention, since the surfaces of the coupling portions of the two eccentric core optical fibers facing each other are flat, the branch coupling characteristics are stable. Become. Further, the presence of the flat surface makes it difficult for the optical fiber to be twisted, and by using the surface as a reference, it becomes possible to uniformly position the eccentric cores of the two eccentric core optical fibers in the longitudinal direction. Furthermore, if the surface facing the surface of the eccentric core is parallel to the surface of the eccentric core, when the eccentric core optical fiber is mounted on a substrate or a fixing jig, the surface opposite to the eccentric core is used as a reference. It is more desirable because it can be fixed stably.

According to the optical fiber coupler of claim 4 of the present invention, since one or more kinds of other substances having optical transparency are interposed in the coupling portions of the two eccentric core optical fibers facing each other, the propagation is prevented. It is possible to control the light leakage distribution, and as a result, it is possible to adjust the average value of the branching ratio and the like. In addition, the mechanical reliability is improved and the loss is effectively reduced.

According to the optical fiber coupler of claim 5 of the present invention, the surface shape of the two eccentric core optical fibers has at least two flat surfaces, and the flat surfaces intersect each other at a predetermined angle. Therefore, when the optical fiber in the variable optical coupler is moved in the axial direction, the adjustment can be performed more easily.

According to the method of using the optical fiber coupler of the sixth aspect of the present invention, the surface shape of the optical fiber has at least one flat surface, and a plurality of cores eccentric to approach the flat surface are provided. A method of using an optical fiber coupler in which an eccentric optical fiber is used, and eccentric cores are opposed to each other by a predetermined length and are adjacent to a flat surface thereof, and the lengths or intervals of the opposed portions of the plurality of eccentric core optical fibers are set. Is variable, and this change makes it possible to adjust the branching ratio of the light that splits from one optical fiber to the other optical fiber, so more precise optical branching adjustment and the set branching ratio are kept constant. It has become possible to improve stability when doing.

According to the method of using the optical fiber coupler of claim 7 of the present invention, the two cores of the eccentric core are moved vertically or horizontally or both of them relative to the facing surfaces thereof, so that the core spacing is increased. By changing, the branch ratio adjusting mechanism can be easily constructed.

According to the method of using the optical fiber coupler of the eighth aspect of the present invention, the eccentric core optical fibers are arranged so that the axial directions thereof are substantially parallel to each other at the portions where the cores are close to each other,
By moving one or more of the eccentric core optical fibers in the axial direction, the ratio of the split light is adjusted, so the split ratio with respect to the amount of movement shows a more gradual change, further improving stability and accuracy. Is obtained.

[Brief description of drawings]

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

FIG. 2 is a sectional view of a coupling portion of the optical fiber coupler of FIG.

FIG. 3 is an explanatory diagram showing an example of adjusting the branching ratio of the optical fiber coupler of the present invention.

FIG. 4 is an explanatory diagram showing another example of adjusting the branching ratio of the optical fiber coupler of the present invention.

FIG. 5 is a sectional view showing an example of an eccentric core optical fiber used in the optical fiber coupler of the present invention.

FIG. 6 is a cross-sectional view showing another example of the eccentric core optical fiber used in the optical fiber coupler of the present invention.

FIG. 7 is a cross-sectional view showing another example of the eccentric core optical fiber used in the optical fiber coupler of the present invention.

FIG. 8 is a perspective view showing another embodiment of the optical fiber coupler of the present invention.

FIG. 9 is an explanatory diagram showing a relationship between an axial shift amount of an optical fiber coupler and a distance when a core approaches.

FIG. 10 is a characteristic diagram of a branching ratio of the conventional optical fiber coupler and the optical fiber coupler of the present invention.

11 is a cross-sectional view of the eccentric core optical fiber used in the characteristic diagram of the branching ratio of FIG.

12 is a cross-sectional view of the optical fiber coupler used in the characteristic diagram of the branching ratio of FIG.

FIG. 13 is an explanatory diagram showing an embodiment of a usage example of the optical fiber coupler of the present invention.

FIG. 14 is an explanatory diagram showing another embodiment of a usage example of the optical fiber coupler of the present invention.

FIG. 15 is an explanatory diagram showing another embodiment of a usage example of the optical fiber coupler of the present invention.

FIG. 16 is an explanatory diagram showing a change in branching ratio when the optical fiber of the optical fiber coupler is shifted in the axial direction.

FIG. 17 is a cross-sectional view showing another example of the eccentric core optical fiber of the optical fiber coupler of the present invention.

FIG. 18 is a cross-sectional view showing another embodiment of the optical fiber coupler of the present invention.

FIG. 19A is a sectional view of a conventional optical fiber coupler,
(B) is a perspective view showing a part of manufacturing process of the optical fiber coupler of (A).

[Explanation of symbols]

 1 eccentric core optical fiber 2 core 3 coupling part 3A coupling surface 3B branch coupling part 4 optical fiber gripping material 5 regulating member 10 eccentric core optical fiber 11 flat surface 20 eccentric core optical fiber 21 flat surface 22 vertical surface 23 optical transparency Materials 30 eccentric core optical fiber 31 flat surface 32 flat surface

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kazuaki Yoshida 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Ken Yagi 2-6-1, Marunouchi, Chiyoda-ku, Tokyo No. Furukawa Electric Co., Ltd. (72) Inventor Takayuki Morikawa 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Within Furukawa Electric Co., Ltd.

Claims (8)

[Claims] 1. An optical fiber coupler in which two eccentric core optical fibers have a coupling portion in which the eccentric cores face each other for a predetermined length and are adjacent to each other, and the coupling portions of the two eccentric core optical fibers facing to each other are adjacent to each other. An optical fiber coupler characterized in that its length and / or its interval are variable, whereby the branching ratio can be adjusted. 2. An optical fiber coupler in which two eccentric core optical fibers have a coupling portion in which the eccentric cores face each other for a predetermined length and are adjacent to each other, and the two eccentric core optical fibers are coupled to each other in the facing proximity to each other. An optical fiber coupler having a length regulated by regulation members sandwiched between both ends of a coupling portion. 3. The optical fiber coupler according to claim 1 or 2, wherein the surfaces of the coupling portions of the two eccentric core optical fibers facing each other are flat. 4. The light according to claim 1, wherein one or more kinds of other substances having optical transparency are interposed in the coupling portions of the two eccentric core optical fibers facing and close to each other. Fiber coupler. 5. The surface shape of the two eccentric core optical fibers has at least two flat surfaces, and the flat surfaces intersect each other at a predetermined angle. The described optical fiber coupler. 6. A plurality of eccentric optical fibers having a surface shape of an optical fiber having at least one flat surface and having an eccentric core so as to approach the flat surface, wherein the core eccentric to the flat surface is predetermined. A method of using optical fiber couplers that are closely opposed to each other for a long time, wherein the lengths of the opposed portions of the plurality of eccentric core optical fibers or the intervals thereof are variable, and by this change, one optical fiber is A method of using an optical fiber coupler, which is capable of adjusting a branching ratio of light branched to another optical fiber. 7. The optical fiber coupler according to claim 6, wherein the core spacing is changed by moving the two eccentric core optical fibers vertically or horizontally or both relative to the facing surfaces. How to use. 8. The branching is carried out by arranging the eccentric core optical fibers so that the axial directions thereof are substantially parallel to each other at positions where the cores are close to each other, and by moving one or more of the eccentric core optical fibers in the axial direction. The method of using the optical fiber coupler according to claim 6 or 7, wherein the ratio of light to be adjusted is adjusted.