JPH08234049A - Three-terminal optical coupler and its production - Google Patents

Abstract

PURPOSE: To provide a three-terminal optical coupler which is housed with a non-reflection end in a package and which has a long life and lessens the fluctuation in isolation. CONSTITUTION: Two pieces of optical fibers 7, 7 are fused and stretched and the core of one piece of the optical fiber among four pieces of the optical fibers extending from the fusion stretched part is held by two pieces of bar-shaped jigs near the fused part and microcrack is generated in the part. A diagonal cut surface is formed by pulling the fiber in a longitudinal direction. The non- reflection end 2 is formed by the cut surface which is diagonal and, therefore, thenon-reflection end 2 is formed with a short length from the fused part. The non-reflection end is easily housed in the package 5 and since there is no need for bending the optical fiber 7 or filling a matching oil therein, the three- terminal optical coupler having the long life and the less fluctuation in the isolation is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-terminal optical coupler having a non-reflecting end housed in a package for improved mountability and a method for forming the non-reflecting end thereof.

[0002]

2. Description of the Related Art Conventionally, in a three-terminal optical coupler, several types have been manufactured depending on how the non-reflective end is formed. As one of the non-reflective ends, there is one in which a cut surface of an optical fiber is formed obliquely as shown in FIG. Light propagating from the right side of the drawing in the core 11 while repeating total internal reflection at an angle equal to or less than the critical angle θ _C reaches an end having an oblique cut surface. Where the angle θ between the light and the cut surface
_{Since T} is larger than the critical angle θ _C , light is emitted from the cut surface to the outside, and part of the light is reflected into the core 11.

However, since the angle formed by the boundary surface between the core 11 and the clad 12 by the reflected return light is larger than the critical angle, it escapes toward the clad 12. Therefore, the reflected light traveling backward in the core 11 disappears, and the core 11 has a function as a non-reflection end. Therefore, by forming one end of the four optical fibers extending from the fusion-bonded portion so that the cut surface is inclined, a non-reflection end is formed and a three-terminal coupler is obtained.

FIG. 7 shows a three-terminal optical coupler using a non-reflective end with such an oblique cut surface. FIG. 7A is an external view of the coupler. Reference numeral 5 denotes a package for accommodating the fusion-spreading portion 1 (not shown), 7 denotes an optical fiber, and 13 denotes a non-reflecting end, which is covered with a protective tube.

FIG. 7B is a detailed view of the non-reflective end 13. The tip of the optical fiber from which the coating of the optical fiber 7 has been stripped off is formed as an oblique cross section 14, and a protective tube 15 is covered on this portion, and the tip portion thereof is the sealing material 6
Is sealed by.

Conventionally, the formation of the oblique cross section 14 has been performed by polishing with a polishing machine, but for this polishing work, two optical fibers must be separated from each other. Therefore, FIG. As shown in FIG. 5, a constant length L is required, and as a result, the non-reflective end 13 is formed at a position of the length L required for the polishing operation from the package 5. For this reason, when mounting the coupler, it is necessary to perform extra length treatment of the non-reflective end. For example, it is necessary to invert and bend it as shown in FIG. 8 and fix it to a housing or the like with an adhesive or the like.

As an example in which it is not necessary to perform the extra length treatment of the non-reflection end, as shown in FIG. 9A, one of the four optical fibers extending from the fusion splicing section 1 is reinforced. There is one in which the material is cut at a portion protruding from the material 3, the cutting portion 16 is housed in the package 5 together with the fusion extending portion 1, and the inside of the package 5 is filled with the matching oil 17.

In such a structure, FIG.
As enlarged and shown, the light propagating through the core 11 is diffused when it is emitted from the cutting portion 16 into the matching oil 17, hits the sealing material 6, and is diffusely reflected here. As a result, the light that is reflected and returns to the core 11 again becomes very small, and it practically functions as a non-reflection end. In this way, since the non-reflective end is short and can be accommodated in the package 5, the extra length processing up to the non-reflective end as shown in FIG. 8 is unnecessary.

Another example in which extra length processing is not necessary is shown in FIG.
0 is shown. In this, as shown in FIG. 10A, the cut optical fiber is bent near the reinforcing material 3 to form a non-reflection end. Thus, when the optical fiber is bent, the angle θ formed between the traveling light and the side wall of the core 11 becomes larger than the critical angle θ _C in the bent portion, as shown in FIG. Since the light is emitted toward one side and becomes lost light, the light does not reach the cutting portion 16 and no reflection occurs.

[0010]

However, the above-mentioned conventional techniques have the following problems, respectively. First, the coupler shown in FIG. 7, which uses a non-reflective end having an oblique cross section by polishing, has a long length up to the non-reflective end and is not housed inside the package 5, and the non-reflective end is outside the package 5. Since it is formed at the tip of an optical fiber of a certain length, when mounting this coupler in an optical device, the non-reflection end 13 and the optical fiber 7 up to that are provided as shown in FIG. With an adhesive etc. at an appropriate place on the device side,
There is a problem that it must be fixed by adhesion.

Next, as shown in FIG. 9, the matching oil 17
In the configuration filled with, there is a strict condition that the difference in refractive index between the matching oil 17 used and the optical fiber 7 must be as small as possible, and the refractive index of the matching oil 17 changes due to temperature fluctuation. As a result, there is a problem that the isolation between the non-bonded ends fluctuates, and further, there is a problem that the refractive index of the matching oil 17 changes with the passage of time, and the isolation also changes accordingly. .

Next, in the structure in which the tip end of the cut fiber is bent as shown in FIG. 10, there is no loss for reflection-free unless the fiber is bent within a radius of curvature that can normally be used. However, if the fiber is bent to such an extent, the fiber is likely to be broken, the life is remarkably shortened, and the isolation is deteriorated at the time of breaking.

In view of the above-mentioned problems of the prior art, an object of the present invention is to store the non-reflective end in the package without bending the end of the optical fiber or filling the package with matching oil. SUMMARY OF THE INVENTION It is an object of the present invention to provide a three-terminal optical coupler that does not require extra length processing and a manufacturing method thereof.

[0014]

The present invention has the following means for achieving the above object. That is, the three-terminal optical coupler of the present invention is a coupler in which two optical fibers are fusion-stretched, and one of the four optical fibers extending from the fusion-bonded portion is short and the cut surface is oblique. Is a non-reflecting end, the fusion-bonded extended portion and the non-reflecting end are housed in a package, and the remaining three optical fibers are out of the package. .

In the method of manufacturing a three-terminal optical coupler of the present invention, two optical fibers are fusion-stretched and the coating of one of the four optical fibers extending from the fusion-stretched portion is removed. The optical fiber was sandwiched between two rod-shaped jigs to generate microcracks, and then an oblique cut surface was formed by pulling and cutting in the longitudinal direction of the optical fiber. This is a method of manufacturing a three-terminal optical coupler housed in a package.

[0016]

The function of the present invention will be described below. When the cut surface of the optical fiber is formed obliquely, it functions as a non-reflection end as described in the related art. Therefore, the portion having an oblique cutting surface inside the package functions as a non-reflective end, and 3
Only the optical fiber of the book emerges to form a three-terminal coupler.

Therefore, unlike the conventional one, the cutting portion is not bent, and the matching oil is not filled in the package. Therefore, the problems of the prior art associated with such a structure are eliminated. In addition, since the non-reflective end portion is housed in the package, extra length treatment for the non-reflective end is not required unlike the case of using the conventional non-reflective end of the obliquely polished surface.

Next, a method of manufacturing the three-terminal coupler of the present invention,
Above all, the method of forming an oblique cut surface at a short position from the fused portion of the optical fiber is as follows. It is a method of pulling to. This is because by sandwiching the clad of the fiber with a jig, microcracks are generated on the surface of the clad, and if it is pulled in the lengthwise direction, an oblique fracture surface is generated in most cases from the cracked part. Is used.

In this method, the distance from the fusion-bonded portion is shorter than in the prior art because it is simply sandwiched by two rod jigs and pulled, as compared with the conventional method in which the polishing is performed obliquely by a polishing machine. A diagonal cut surface can be formed at the position, and as a result, the non-reflective end can be housed in the package.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway external view of a three-terminal optical coupler of the present invention. Reference numeral 1 denotes a fusion splicing portion which fulfills the coupling action of the coupler, and is a portion where two optical fibers are fused. Since the optical fiber part alone is very fragile, the reinforcing material 3
The adhesive 4 is adhered and fixed to.

Reference numeral 2 denotes a non-reflective end, which is cut off a little from the reinforcing material, and its cut surface is oblique. The optical fiber next to it extends with the coating attached. Then, the fusion-bonded stretched portion 1 reinforced with the reinforcing material 3,
A part of the other three optical fibers 7 connected to the non-reflective end 2 and the fusion extending portion 1 is housed in a package 5, and both ends thereof are sealed by a sealing material 6. The three optical fibers 7 other than the non-reflective end 2 penetrate the sealing material 6 and are exposed to the outside of the package 5.

FIG. 2 is an enlarged view showing the contents stored in the package 5 and a method for forming the non-reflective end 2. The formation of the non-reflective end 2 shows that the clad 12 of the optical fiber with the coating removed is sandwiched between tweezers 8 and pulled to the left side to be cut.

FIG. 3 is an enlarged view of this cutting. When the clad 12 is sandwiched between tweezers 8 as shown in FIG. 3A, microcracks 9 are generated on the surface of the clad 12. In this state, when the clad 12 is pulled to the left as shown in (b), the cut surface is cut from the microcrack 9 at an angle. That is, the cut surface of the bare optical fiber remaining on the reinforcing material 3 is inclined. In this way, the non-reflection end 2 is obtained.

As described above, since the method is to pull by sandwiching the clad of the fiber whose coating has been removed, the cut portion can be brought close to the end of the reinforcing member 3, so that the length of the optical fiber up to the non-reflection end 2 can be increased. Can be very short. In this embodiment, tweezers were used as a cutting tool, but the tweezers are not limited to tweezers, and may have a round, elliptical, triangular, square, or other polygonal cross section. . In short, any material can be used as long as it can cause microcracks when sandwiched.

The inventor has experimentally confirmed that by such a method, the cut surface of the core is formed obliquely and has a non-reflection end, and a practical three-terminal optical coupler can be obtained. As a method for evaluating the performance of such a three-terminal coupler, generally, the degree of interruption (isolation) between non-bonded ends (between terminals that should not be coupled) is measured and expressed in decibels for evaluation. There is.

FIG. 4 shows an explanatory diagram of the isolation measurement. The central portion of the figure is the fusion splicing portion, from which two optical fibers are extended to the left and right like branching. And
The end portions of the two optical fibers on the same side (left side in FIG. 4) are non-reflective ends, and the strength P starts from one on the opposite side (right side in FIG. 4).
The light of ₁ is input, the intensity P ₂ of the light leaking from the other one is measured, and the isolation (d
B) is calculated.

[0027]

[Number 1] isolation (dB) = - 10log (P 2 / P 1)

If the non-reflecting end is completely non-reflecting, all the input P ₁ is not absorbed and reflected, so P ₂
Becomes zero and the value of Equation 1 becomes infinite, which means that the isolation between the two right optical fibers is perfect.

On the other hand, if one or both of the non-reflecting ends is imperfect and reflects some light, it appears as P ₂ smaller than P _1, and therefore Equation 1 shows a finite value. . Then, this value becomes smaller as P ₂ is larger, that is, as the reflection-free end is not perfect and the reflection intensity is stronger, and when 100% is reflected, that is, P
_{When 2} = P ₁ , it becomes zero dB.

Therefore, by measuring and calculating this isolation, it is possible to know the degree of non-reflection of the non-reflection end. Now, considering the coupler of FIG. 1 in detail, a non-reflective end with little reflection is attached to the end of the optical fiber 7 protruding to the left from the package for a measurement test.

On the other hand, the light P ₁ is input from one of the two right optical fibers 7 and the optical output P ₂ from the other one is measured. Then, the isolation is calculated by Expression 1. Since the non-reflecting end of the left optical fiber 7 is close to an ideal one, the isolation value depends solely on the performance of the non-reflecting end 2 in the package 5. Thus
It is possible to know the antireflection performance of the nonreflection end by the method of the present invention.

FIG. 5 shows the 3 produced by the method of the present invention.
FIG. 3 is a graph showing the frequency of isolation obtained by the above measurement and calculation for 100 terminal optical couplers. According to FIG. 5, the isolation is 50
It can be seen that the number of those obtained with dB or more is 81 out of 100. The isolation of 50 dB is a sufficient value for use in an ordinary optical device, and a yield of 80% or more is considered in view of the problems of the conventional technology (excessive length treatment, isolation fluctuation, short life, etc.). Therefore, it can be said that the method of the present invention is very excellent.

[0033]

As described above, since the three-terminal optical coupler of the present invention accommodates the non-reflective end whose cut surface is slanted in the package, there is no mounting of the conventional non-reflective end. There is an advantage that long treatment is not required, and there is an advantage that the life is long and the filling of matching oil is not required because it is not a non-reflective end due to the bending structure.

Further, the formation of the oblique cross section in the manufacturing method of the present invention is different from the conventional polishing method using a polishing machine.
It is simple that it is simply sandwiched between two rod-shaped jigs and pulled, and therefore the non-reflective end can be formed with a short length, and as a result, the non-reflective end can be housed in the package. .

[Brief description of drawings]

FIG. 1 is a partially cutaway external view of a three-terminal optical coupler of the present invention.

FIG. 2 is a diagram showing an expansion of a stored item in a package 5 and a method of forming a non-reflection end 2 by cutting.

FIG. 3 is an enlarged view of the cut in FIG.

FIG. 4 is an explanatory diagram of isolation measurement.

FIG. 5 is data showing frequency values of isolation measurement data of a three-terminal optical coupler manufactured by the method of the present invention.

FIG. 6 is an explanatory diagram of a non-reflective end function of an optical fiber having an oblique cut surface.

FIG. 7 is a diagram showing a conventional three-terminal optical coupler using a non-reflective end with an oblique cut surface.

8 is a diagram showing an example of extra length processing of a non-reflection end in mounting the three-terminal optical coupler of FIG.

FIG. 9 is a diagram showing a conventional three-terminal optical coupler in which a package is filled with matching oil so that a normal vertical cut end of an optical fiber becomes a non-reflection end.

FIG. 10: By bending the cut optical fiber,
It is a figure which shows the conventional 3 terminal optical coupler which formed the non-reflection end and accommodated in the package.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fusion-extended part 2 Non-reflective end 3 Reinforcing material 4 Adhesive 5 Package 6 Sealing material 7 Optical fiber 8 Tweezers 9 Micro crack 10 Cut surface 11 Core 12 Clad 13 Non-reflective end 14 Diagonal cross section 15 Protective tube 16 Cut part 17 Matching oil

Claims (2)

[Claims] 1. A coupler in which two optical fibers are fused and stretched, and one of the four optical fibers extending from the fused portion is short, and its cut surface is an oblique non-reflection end. A three-terminal optical coupler in which the fusion spliced portion and the non-reflecting end are housed in a package, and the remaining three optical fibers are out of the package. 2. An optical fiber obtained by fusion-stretching two optical fibers and removing the coating of one of the four optical fibers extending from the fusion-stretched portion is sandwiched by two rod-shaped jigs. A three-terminal light characterized by forming an oblique cut surface by causing a crack and then pulling and cutting in the longitudinal direction of the optical fiber, and accommodating the fusion stretched portion and the oblique cut surface in a package. Method for manufacturing coupler.