JP2003075680A - Welding type optical fiber coupler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fusion spliced optical fiber coupler having the ability of controlling a branching ratio after fusion splicing and drawing, particularly, a variable broadband branching ratio coupler that has the same ability while holding nondependency on a wavelength, and also to provide the manufacturing method. SOLUTION: In manufacturing a fusion spliced optical coupler by the melting and drawing method, a curved deflection part 4 is formed in an optical fiber fusion spliced part 3, after the fusion splicing/drawing of a plurality of optical fibers 1a, 1b, by reducing by a prescribed distance inversely to the drawing direction. Accordingly, a fusion spliced optical fiber coupler is provided which is formed with a curved deflection in the fusion spliced part of more than one optical fibers. This fusion spliced optical fiber coupler is fixed in a protective storing unit 10, in a fashion that the fixed point on both sides or one side is freely movable, or that the deflection part is electrically or mechanically extendible/contractible, so that the branching ratio can be arbitrarily controlled even after the disposition of the coupler in the protective storing unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion splicing type optical fiber coupler, a method for manufacturing the same, and a method for fixing the splicing member in a protective container. Open to fiber optic coupler technology.

[0002]

2. Description of the Related Art An optical fiber cab is a device that realizes functions such as branching, merging, demultiplexing, and combining of light by using evanescent coupling by bringing two optical fiber cores close to each other. The method includes a polishing method in which the side surface of the optical fiber is polished to the vicinity of the core and overlapped with each other, and a melt drawing method in which a plurality of optical fibers are brought into contact with each other in parallel or twisted to be melted by heating and stretched in the axial direction. However, except for special applications such as a polarization-maintaining coupler using a polarization-maintaining fiber, an optical fiber coupler (fusion-type optical fiber coupler) based on the melt drawing method is widely used.

In a fusion splicing type optical fiber coupler, the confinement of light to the core is weakened at the portion where the core is thinned by stretching. At this time, when the spread light distribution overlaps with the other optical fiber fused in parallel, a part of the light energy is transferred to the other optical fiber, and functions of branching and merging are created. Also,
If the area that is stretched and evanescent bond occurs is long,
A phenomenon occurs in which the power of propagating light moves between both fibers. Since the spread and propagation speed of the light propagating through the optical fiber differ depending on the wavelength, the branching state differs depending on the wavelength of the light, and the demultiplexing / multiplexing function can be obtained. In addition, by fusion-splicing a 3 dB coupler that branches the optical power at a ratio of 1: 1 in a tree shape, m × n (m is 1 or 2, n
4, 8, 16 ...) Star couplers can be formed.

The branching optical fiber coupler is used for branching, monitoring, optical amplifiers, etc. of optical signals. WDM, 3 dB, etc. wavelength-dependent couplers whose branching characteristics change depending on the wavelength of light, and about 1.3 μm. There is a wavelength-independent coupler whose branching characteristic does not change in a wide band of up to 1.5 μm. Performances required for optical fiber couplers include low loss, low PDL, low temperature dependency, long-term reliability, etc., but in applications such as monitoring, the strength of the actual signal is measured from the branched signal. Therefore, the accuracy of the branch ratio is an important performance.

[0005]

However, in the optical fiber coupler, the branching ratio is fixed when the shape is fixed during manufacturing, and the branching ratio cannot be changed during use. For example, the optical characteristics of wavelength-dependent couplers are strongly shape-dependent, so that, for example, Japanese Patent Laid-Open No. 64-38721 discloses that
When a metal coating is applied to the fusion-bonded part, and when the fusion-bonded part is used after being stretched, a voltage is applied to this metal-coated part to cause the part to generate heat and expand, and the taper part of the optical fiber is expanded with this expansion. A method has been proposed in which thermal elongation is applied to control the branching ratio. However, when the branching ratio is adjusted by these wavelength-dependent couplers, there is a problem that even if the characteristics are matched at one wavelength, the branching ratios at other wavelengths are different. Further, there is a limit to the elongation of the glass portion (tapered portion of the optical fiber) in the axial direction, and sufficient elongation cannot be expected. On the other hand, in the wavelength-independent coupler (WIC), the change in the characteristics depending on the wavelength is small, but the change in the optical characteristics due to expansion and contraction is also small, and it has been considered difficult to control the branching characteristics after fusion and stretching.

Accordingly, an object of the present invention is to provide a fusion splicing type optical fiber coupler capable of controlling a branching ratio after fusion splicing / stretching, particularly a wavelength independent coupler (WIC) while maintaining wavelength independence. Another object of the present invention is to provide a wideband branching ratio variable coupler capable of controlling the branching ratio after fusion and drawing. A further object of the present invention is to provide a method capable of easily manufacturing such a fusion ratio type optical fiber coupler of variable branching ratio. Another object of the present invention is a method of fixing an optical fiber coupler capable of controlling the branching ratio even after being arranged in a protective container.
Another object of the present invention is to provide an optical fiber coupler thus arranged in the protective container.

[0007]

In order to achieve the above object, according to the first aspect of the present invention, a fusion splicing formed by forming a curved flexure portion on a fusion splicing portion of a plurality of optical fibers. A fiber optic coupler is provided. According to the second aspect of the present invention, in the production of the fusion-type optical fiber coupler by the fusion drawing method, after fusing / drawing a plurality of optical fibers, the optical fibers are contracted by a predetermined distance in the direction opposite to the drawing direction. There is provided a method for manufacturing a fusion-type optical fiber coupler, which is characterized in that a curved flexible portion is formed in the fusion-bonded portion.

According to the third aspect of the present invention, there is provided a fusion-type optical fiber coupler in which curved flexures are formed in the fusion-bonded portions of a plurality of optical fibers, and the fixing points on both sides or one side are fixed. An optical fiber coupler is provided that is movably disposed within a protective container. Further, according to a fourth aspect of the present invention, a fusion-type optical fiber coupler formed by forming a curved flexure in the fusion-bonded part of a plurality of optical fibers, the flexure is electrically or mechanically A method for fixing an optical fiber coupler is provided, which is fixed in a protective container so that it can expand and contract.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of intensive research to solve the above-mentioned problems, the present inventors have surprisingly found that in a fusion splicing type optical fiber coupler, if a curved flexure portion is formed in the fusion splicing portion. It has been found that, even after being fused and stretched, it can be expanded and contracted due to the elasticity of this flexible portion even in the solidified state, and the branching ratio can be controlled by the expansion and contraction at this portion,
The present invention has been completed. The flexible portion is formed in the smallest diameter portion (central portion) between the taper portions of the optical fiber fusion portion, and the degree of curvature (radius of curvature) of the flexible portion is adjusted even in the manufacturing stage of the fusion optical fiber coupler. By doing so, it is possible to adjust to a predetermined branching ratio,
Further, even during use, the branching ratio can be arbitrarily adjusted by expanding and contracting the flexible portion. Since this flexible portion has a fairly small diameter, it is highly elastic and can be expanded and contracted, and will not break due to expansion and contraction within the adjustment range of the branching ratio.

In order to be able to adjust the branching ratio at the time of use as described above, a fusion splicing type optical fiber coupler in which curved flexures are formed in the fusion splicing portion of a plurality of optical fibers is used. Alternatively, it is fixed in the protective container so that the fixing point on one side is movable or the flexible portion can be expanded or contracted electrically or mechanically. As a result, the branching ratio can be arbitrarily controlled even after it is arranged in the protective container.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS While explaining the embodiments shown in the accompanying drawings,
The present invention will be described in more detail. First, a method of manufacturing a fusion splicing type optical fiber coupler according to the present invention will be described with reference to FIG. First, as shown in FIG. 1 (A), the optical fiber 1b from which the coating 2 has been partially removed is heated while reciprocally moving the micro torch (micro burner) 6 in the lateral direction, and stretched by applying tension. Next, FIG.
As shown in (B), the previously stretched optical fiber 1b and the optical fiber 1a with the coating 2 partially removed (that is, the optical fibers 1a and 1b having different propagation constants) are used.
) Is held by an appropriate gripping means such as a clamp, and the side surfaces of the coating removal portion are in parallel contact with each other, and the micro torch (micro burner) 6 is reciprocally moved in the lateral direction to heat and fuse, As shown in FIG. 1 (C), stretching is performed by applying tension. The swing width of the micro torch 6 is generally about 5 mm. Note that FIGS. 1B to 1D are 2
The figure seen from above is shown in order to show the state of the optical fibers 1a and 1b of the book, and the arrangement state of the micro torch 6 is not accurate, and the side view is shown to show the arrangement state of the micro torch 6 accurately. The drawing has a form similar to that of FIG. In order to obtain predetermined characteristics with good reproducibility, a light source and a light receiving element (not shown) are connected to the optical fiber, and stretching is performed while monitoring the branched state. The cross-sectional shape of the fusion-bonded portion 3 can be changed from a cross-sectional shape in which two circles are connected to each other, depending on the strength of fusion-bonding, to a gourd shape, and further to an oval shape. Then, as shown in FIG. 1 (D), it is slightly contracted in the axial direction. As a result, the optical fiber fusion section 3
A curved flexible portion 4 is formed in the minimum diameter portion (central portion) between the taper portions 5 (see FIG. 2), and a predetermined branching ratio can be obtained by adjusting the degree of curvature (curvature radius) of the flexible portion 4. Can be adjusted.

In the fusion splicing type optical fiber coupler manufactured as described above, the thinnest portion of the coupling portion has an extremely thin wire diameter, for example, a diameter of about 10 μm. Therefore, in order to ensure sufficient mechanical strength and temperature stability of the coupler, the fusion splicing type optical fiber coupler has, as shown in FIGS. 2 and 3, a glass case or the like having a small linear expansion coefficient at both ends thereof. It is fixed in the protective container 10 with an adhesive or glass solder.

FIG. 2 is a schematic sectional view showing the internal structure of the assembled optical fiber coupler, and FIG. 3 is a plan view of the optical fiber coupler with its upper part removed. Optical fiber 1a, 1b
Is a support plate 1 made of a quartz plate or the like in the optical fiber fixing portion 11 and the coupler fixing portion 12 on both sides of the fusion bonding portion 3.
It is fixed at 3. An adhesive such as a UV curable resin is generally used as the fixing agent. The support plate 13 to which the optical fibers 1a and 1b are fixed in this way is arranged in the invar (protective tube) 14, and both ends of the invar 14 are sealed by the sealant 15.

FIGS. 4 and 5 mechanically perform fusion / stretching at the time of manufacturing the optical fiber coupler, or expansion / contraction of the curved flexure portion of the fusion portion of the optical fiber coupler assembled in the protective container. The schematic structure of one aspect is shown. First, in the case of the mechanism shown in FIG. 4, a pair of support plates 13a, 13 having a step portion 16 formed on the lower surface of the end portion which is divided into two.
The sliding member 17 is arranged on the step portion 16 of FIG.
Of the female screw members 18a, 18b and 19 respectively on the lower surface of both end portions of the base plate and the lower surface of the stepped portions of the support plates 13a and 13b facing each other.
a and 19b are projectingly provided, and a pair of female screw members 18a and 19b are provided.
It has a structure in which male screw members 20a and 20b are screwed into a, 18b and 19b, respectively. In the case of this structure, one or both supporting plates 13a, 13b can be moved in the opposite direction by rotating one or both male screw members 20a, 20b.

On the other hand, in the case of the mechanism shown in FIG. 5, female screw members 19a and 19b are respectively provided at predetermined positions on the lower surfaces of the pair of support plates 13a and 13b, which are divided into two and have stepped portions 16 formed on the upper surfaces or the lower surfaces of the opposing ends. Has a structure in which the threaded portions of the male threaded member 21 having oppositely threaded portions formed on both sides are screwed into the female threaded members 19a and 19b, respectively. In the case of this structure, by rotating the male screw member 21, both the support plates 13a and 13b move toward or away from each other. In the case of any of the mechanisms shown in FIG. 4 and FIG. 5, it can be used not only for stretching and shrinking of the fused portion at the time of manufacturing the optical fiber coupler, but also for the fused portion of the optical fiber coupler assembled in the protective container. It can be used as it is for the expansion and contraction of the curved flexure portion.

FIG. 6 shows a schematic construction of one mode for electrically expanding and contracting the curved flexure of the fusion-bonded portion of the optical fiber coupler assembled in the protective container. The apparatus shown in FIG. 6 serves as a support plate for fixing the optical fiber coupler, and includes a metal plate 23 such as a stainless plate and a PZT (piezoelectric composite material Pb (Zr, Ti) O ₃ ) 24 bonded to the back surface thereof.
The embodiment using the EO conversion element (bimorph) 22 composed of is shown. When the EO conversion element (bimorph) 22 is energized, bending occurs due to the piezoelectric effect of the PZT 24. Therefore, it is possible to add desired expansion and contraction to the optical fiber coupler by calibrating the degree of bending when energized in advance.

Next, specific characteristics when light is branched by using the broadband optical fiber coupler in which the curved flexible portion is formed in the fusion portion according to the present invention will be described.
FIG. 7 shows a schematic configuration of a WIC coupler, in which light of wavelength λ _{1 having} a light intensity I (λ ₁ ) and light of wavelength λ _{2 having} a light intensity I (λ ₂ ) is incident from one optical fiber, and Let P ₁ (λ ₁ ) and P ₁ (λ ₂ ) be the powers of the light output from the port ₁ and P ₂ (λ ₁ ) and P ₂ (λ ₂ ) be the powers of the light output from the other port 2. , The branching ratio (expressed in%) is given by the following formula. R (λ ₁ ) = P ₁ (λ ₁ ) / {P ₁ (λ ₁ ) + P ₂ (λ ₁ )}
× 100 R (λ ₂ ) = P ₁ (λ ₂ ) / {P ₁ (λ ₂ ) + P ₂ (λ ₂ )}
× 100

Power of light P ₁ = 1310 (dBm), P ₂
FIG. 8 shows the results of measurement of how the branching ratio at one port 1 when = 1550 (dBm) changes when the curved flexible portion of the fusion-bonded portion is expanded and contracted in the axial direction. . The branching ratio at the other port 2, which is represented symmetrically, is omitted for clarity. The expansion / contraction amount on the horizontal axis indicates the expansion / contraction amount of the optical fiber on one side, and the actual expansion / contraction width is twice this (hereinafter, the expansion / contraction amount, the contraction amount, and the expansion amount are similar expression methods. , Plus indicates growth, and minus indicates contraction. The portion where the amount of expansion and contraction is zero is the state when the optical fiber coupler was manufactured. In this case, it is understood that the branching ratio can be changed by shrinking the curved flexure.

Next, FIG. 9 shows the relationship between the amount of shrinkage and the power of light. It can be seen from FIG. 9 that the loss of light power increases as the amount of contraction increases. Further, it can be seen that there is almost no loss of light power up to the contraction amount of 1.0 mm. In addition, FIG. 10 shows the results of measuring the power loss of light up to the expansion / contraction width of 0.2 mm. From FIG. 10, it can be seen that there is no change in the power loss of light with expansion and contraction within a certain range.

Next, 80:20 produced according to the present invention.
11 to 16 show the results of measuring the wavelength characteristics of the WIC coupler depending on the expansion / contraction change. FIG. 11 is a wavelength characteristic at the time of production, FIG. 12 is a stretching amount of 0.1 mm, and FIG. 13 is a contraction amount of 0.0.
5 mm, FIG. 14 shows the contraction amount of 0.1 mm, FIG. 15 shows the contraction amount of 0.15 mm, and FIG. 16 shows the contraction amount of 0.2 mm. From these figures, it is understood that the coupling ratio can be freely changed by expanding and contracting the curved flexure portion of the fusion-bonded portion in the axial direction while maintaining the wavelength independence.

[0021]

As described above, since the fusion-type optical fiber coupler of the present invention has a curved flexible portion formed in the fusion-bonded portion, even after being fused and stretched, it may be solidified. It is possible to expand and contract due to the elasticity of the flexible portion, and it is possible to control the branching ratio by expanding and contracting at this portion. Also, the fixed points on both sides or one side can be moved freely,
Alternatively, the branching ratio can be arbitrarily controlled even after the flexible portion is arranged in the protective container so that it can be expanded or contracted electrically or mechanically. Especially wavelength independent coupler (WI
In C), the branching ratio can be controlled while maintaining the wavelength independence, and not only a single wavelength but also the same branching characteristic in a wide wavelength band of 1.3 μm to 1.55 μm, and The branching characteristics can be controlled.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a manufacturing process of a fusion splicing type optical fiber coupler of the present invention.

FIG. 2 is a schematic cross-sectional view showing the internal structure of the optical fiber coupler of the present invention.

FIG. 3 is a schematic plan view showing a state where the upper portion of the optical fiber coupler shown in FIG. 2 is removed.

FIG. 4 is a schematic configuration diagram of one mode in which fusion / stretching during manufacturing of the optical fiber coupler or expansion / contraction of a curved flexure portion of the fusion-bonded portion of the optical fiber coupler assembled in the protective container is mechanically performed. is there.

FIG. 5 is a schematic configuration diagram of another mode in which fusion / stretching during manufacturing of the optical fiber coupler or mechanical expansion / contraction of the curved flexure portion of the fusion bonding portion of the optical fiber coupler assembled in the protective container. Is.

FIG. 6 is a schematic configuration diagram of one aspect for electrically expanding and contracting a curved flexible portion of a fusion-bonded portion of an optical fiber coupler assembled in a protective container.

FIG. 7 is a schematic explanatory diagram of a WIC coupler.

FIG. 8 is a graph showing the relationship between the expansion / contraction amount and the branching ratio of a WIC coupler manufactured according to the present invention.

FIG. 9 is a graph showing the relationship between the amount of shrinkage of a WIC coupler manufactured according to the present invention and the magnitude of optical power.

FIG. 10 is a graph showing the relationship between the amount of expansion and contraction of a WIC coupler manufactured according to the present invention and the loss of optical power.

FIG. 11 is a graph showing wavelength characteristics when an 80:20 WIC coupler manufactured according to the present invention was manufactured.

FIG. 12 is a graph showing wavelength characteristics of an 80:20 WIC coupler manufactured according to the present invention at a stretch amount of 0.1 mm.

FIG. 13 is a graph showing wavelength characteristics of an 80:20 WIC coupler manufactured according to the present invention when the contraction amount is 0.05 mm.

FIG. 14 is a graph showing wavelength characteristics of an 80:20 WIC coupler manufactured according to the present invention when the shrinkage amount is 0.1 mm.

FIG. 15 is a graph showing wavelength characteristics of an 80:20 WIC coupler manufactured according to the present invention when the shrinkage amount is 0.15 mm.

FIG. 16 is a graph showing wavelength characteristics of an 80:20 WIC coupler manufactured according to the present invention when the contraction amount is 0.2 mm.

[Simple explanation of symbols]

1a, 1b optical fiber 2 coating 3 Fusion part 4 Deflection part 5 Tapered part 6 micro torch 10 Protective container 11 Optical fiber fixing part 12 Coupler fixing part 12 13, 13a, 13b Support plate 14 Invar (protection tube) 22 EO conversion element (bimorph) 23 Metal plate 24 PZT

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hidenobu Nagahama             4016, Mikkaichi, Kurobe, Toyama

Claims (6)

[Claims] 1. A fusion splicing type optical fiber coupler comprising a plurality of optical fibers (1a, 1b) having a curved flexure (4) formed on the fusion splicing part (3). 2. The fusion splicing type optical fiber coupler according to claim 1, which is an optical fiber coupler produced by fusing and stretching a plurality of optical fibers (1a, 1b) having different propagation constants. 3. A plurality of optical fibers (1a, 1b) in the production of a fusion splicing type optical fiber coupler by a fusion drawing method.
After fusion / stretching, the optical fiber fusion portion (3) is shrunk by a predetermined distance in the direction opposite to the stretching direction, and the curved flexible portion (4) is formed.
A method for manufacturing a fusion splicing type optical fiber coupler, which comprises: 4. The method for producing a fusion-type optical fiber coupler according to claim 3, wherein a plurality of optical fibers (1a, 1b) are arranged in parallel and fused and stretched in a state where the coating removal portions are in contact with each other. 5. A fusion splicing type optical fiber coupler comprising a plurality of optical fibers (1a, 1b) formed with a curved flexure (4) on a fusion splicing part (3), and fixing the both sides or one side thereof. An optical fiber coupler in which points are movably arranged in a protective container (10). 6. A fusion splicing type optical fiber coupler comprising a plurality of optical fibers (1a, 1b) having a fused portion (3) formed with a curved flexure portion (4). Protective container (10) that can expand and contract electrically or mechanically
A method for fixing an optical fiber coupler, characterized in that the optical fiber coupler is fixed inside.