JPH0457005A - Fiber welding type optical branching coupler - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a fiber fusion type optical branching coupler used in the field of optical transmission lines and optical measurement, etc. The present invention relates to a type optical branching coupler.

[Conventional technology]

Conventionally, one of the methods of branching and combining optical signals within an optical fiber
One example is the fire < fusion type optical branching coupler.

This type of fiber fusion type optical branching coupler is made by stripping the coating of two single mode fibers to leave only the core and cladding, bringing them together in parallel for a predetermined distance, and heating the part that was brought into contact. It is formed by fusing both optical fibers and stretching the fused portion.

By the way, in order to reduce the wavelength dependence of the branching ratio in this type of fiber fusion type optical branching coupler, the following manufacturing method has been proposed.

■A manufacturing method in which fusion-stretching sections are provided at two or more locations, and the difference in length of the two optical fibers between the respective fusion-stretching sections is greater than or equal to the coherent length of the signal light (Japanese Unexamined Patent Publication No. 1-182809)
issue).

0 One of the two optical fibers is stretched in advance,
A manufacturing method in which the stretched portion and another optical fiber are crossed, fused and stretched (Japanese Patent Laid-Open No. 1-263605).

■Manufacturing method that involves twisting, fusing and stretching.

■Connect two couplers with different wavelength dependence of branching ratio,
Manufacturing method that selects combinations with less wavelength dependence (JP-A-63-
No. 316007).

■A manufacturing method in which the refractive index of the core of at least one optical fiber is different from the refractive index of the core of other optical fibers (Japanese Patent Application Laid-Open No.
No. 73205). In the examples, the refractive index of the cladding is also made different.

[Problem to be solved by the invention]

However, the conventionally proposed techniques described above have the following drawbacks.

) According to the manufacturing method (■) above, it is necessary to fuse and stretch at two locations, and according to the manufacturing method (■) above, one of the two optical fibers must be pre-stretched in advance. Also ■
The manufacturing method also requires fusing and stretching the optical fiber at two locations, and in both cases there are many steps.

i) According to the manufacturing method (2) above, the length becomes long because the film is fused and stretched at two locations.

Even with the production method (i) (2), not only is the length increased because the welding and stretching are performed at two locations, but it is also complicated because combinations of connections of turnips with different branching ratios must be considered.

iv) Depending on the manufacturing method (2) above, the bending transmission loss of the optical fiber increases due to twisting, and excessive loss of the fiber coupler occurs due to variations in the positional accuracy of the optical fiber.

ν) Depending on the manufacturing method described in (■) above, the propagation constant is made different by changing the refractive index of the core (and cladding), but if these refractive indexes differ, attenuation due to reflection occurs at the connection part of both optical fibers. These adverse effects occur, resulting in poor coupling efficiency and increased loss. In addition, when connecting this fused and stretched optical fiber to other transmission system optical fibers,
Since the refractive indexes of the two are different, end face reflection of light is likely to occur at the connecting portion between the two.

The present invention has been made in view of the above-mentioned points, and has a branching ratio that has little wavelength dependence, a simple structure, and is easy to manufacture.
It is an object of the present invention to provide a fiber fusion type optical branching coupler with low optical loss.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a fiber fusion type optical branching coupler in which the claddings 3 and 7 of two optical fibers 1 and 5 are brought into contact with each other and the contact portion is fused and stretched. The combination of material compositions constituting the core 2 and cladding 3 of one optical fiber 1 and the core 6 of the other optical fiber 5
The combinations of material compositions constituting the and cladding 7 are made different, and the refractive indexes of both the cores 2 and 6 are made the same, and the refractive indices of both the claddings 3 and 7 are made the same.

In addition, the two optical fibers 1.5 have the same mode field diameter, the same fiber diameter, and the same core and clad refractive index as other transmission optical fibers that connect this fiber fusion type optical branching coupler. It was configured so that

[Effect]

According to the fiber fusion type optical branching coupler according to the present invention,
Since the combinations of material compositions of the cores 2, 6 and claddings 3, 7 of the optical fibers 1, 5 to be fused and drawn are different, the physical properties such as linear expansion coefficients of the optical fibers 1, 5 are different. Therefore, the residual stress generated at the joint portion after the two optical fibers 1.5 are fused and stretched is not uniformly generated in the two waveguide core portions.

This causes a difference in the propagation constant of each optical fiber 1.5, and therefore even if the cladding diameter and mode field diameter of both optical fibers 1 and 5 are made the same, the wavelength dependence of the branching ratio can be reduced. Become. Therefore, a fiber fusion type optical branching coupler with a branching ratio that is less dependent on wavelength can be easily manufactured in exactly the same process as a normal coupler manufacturing process without increasing the number of special processes as in the conventional method.

Further, the core diameter and cladding diameter of the two optical fibers may be the same, and the fusion/stretching portion may be provided at only one location, so that the shape of the fiber fusion type optical branching/coupling device does not become particularly large.

Furthermore, since the refractive indexes of both claddings 3 and 7 are the same, no reflection occurs at the fused/stretched portion, resulting in a high degree of coupling and low loss.

In addition, the two optical fibers to be coupled should have the same mode field diameter, the same fiber diameter, and the same core and clad refractive index as the other transmission optical fibers to which this fiber fusion type optical branching coupler is connected. For example, when these two fibers are connected to an optical fiber of another transmission system, the connections are consistent and the refractive indexes are the same, making it difficult for end face reflection to occur at the connection.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on the drawings.

Here, FIG. 1 is a diagram showing a process of manufacturing a fiber fusion type optical branching coupler according to the present invention.

As shown in FIG. 2(a), first, a first optical fiber 1 and a second optical fiber 5 made of single mode fibers are prepared.

Here, the core 2 of the first optical fiber 1 is pure quartz (Sif
t), and the cladding 3 is made of quartz doped with boron B (Siow + B).

On the other hand, the core 6 of the second optical fiber 5 is made of pure quartz (Sin
), and the cladding 7 is made of fluorine F-doped quartz (SiOz+F).

Here, FIG. 2 is a diagram showing a comparison of the refractive indexes of the core and clad of these optical fibers 1 and 5.

As shown in the figure, the refractive indexes of core 2 and core 6 are the same, and the refractive indexes of cladding 3 and cladding 7 are also made to be the same by adjusting the amounts of boron B and fluorine F to be doped. ing.

In other words, the relationship between the two optical fibers is such that the combination of material compositions that make up the core and cladding of one optical fiber is different from the combination of material compositions that make up the core and cladding of the other optical fiber. Both claddings are configured to have the same refractive index.

Moreover, as shown in FIG. 1(a), these two optical fibers 1
, 5, the diameters of the claddings 3, 7, the diameters of the cores 2.6, and the mode field diameters of the cores 2.6 and 5 are configured to be equal.

Next, the claddings 3, 7 and cores 2, 6 of both optical fibers 1, 5
The refractive index of the optical fibers 1 and 5 is configured to be equivalent to the refractive index of the core and cladding of the optical fibers of other transmission systems connecting this fiber fusion type optical branching coupler. The diameter, cladding diameter, and mode field diameter are
It is constructed so that the core diameter, cladding diameter, and mode field diameter are respectively equivalent to those of the optical fibers of other transmission systems.

In other words, the refractive index of the cladding of the optical fiber 1, the optical fiber 5, and other optical fibers of the transmission system,
Both optical fibers 1 and 5 are constructed so that the core refractive index, cladding diameter, core diameter, and mode field diameter are the same.

Then, the cladding 3 of the first optical fiber 1 and the cladding 7 of the second optical fiber 5 shown in FIG. By stretching, a fiber fusion type optical branching/coupling device A according to the present invention as shown in FIG. 2(b) is completed.

According to this fiber fusion type optical branching coupler A, since the material compositions of the core and cladding of the optical fibers 1 and 5 to be fused and stretched are different, the linear expansion coefficients of both the optical fibers 1 and 5 are different. Their physical properties are different. Therefore, both optical fibers 1,
The residual stress generated at the joint after fusing and stretching 5 is 2
This does not occur uniformly in the waveguide core of the book.

This causes a difference in the propagation constant of each optical fiber 1, 5, and therefore, even if the cladding diameter and mode field diameter of both optical fibers 1, 5 are the same, the wavelength dependence of the branching ratio is reduced. be.

Furthermore, since the refractive indexes of both claddings 3 and 7 are the same, no reflection occurs at the fused/stretched portion, resulting in a high degree of coupling and low loss.

On the other hand, since both optical fibers 1 and 5 were formed with the same mode field diameter, the same fiber diameter, and the same core and clad refractive index as other transmission optical fibers, this fiber 1
, 5 is connected to an optical fiber of another transmission system, the connection is consistent and the refractive index is the same, so that end face reflection is less likely to occur at the connection.

FIG. 3 is a diagram showing the material combinations of the cores 2, 6 and the cladding 3.7 of the VAIPA fusion type optical branching coupler A according to another embodiment of the present invention and their refractive indexes.

First, in the case of the embodiment shown in FIG. Germanium Ge-doped quartz (SiOt +
Quartz doped with germanium Ge and fluorine F through the cladding 7 (S10a +Ge+F)
was used.

In this embodiment as well, the amount of the doped material is adjusted so that the refractive indexes of the core 2 and the core 6 are the same, and the refractive indexes of the cladding 3 and the cladding 7 are also the same.

Next, in the case of the embodiment shown in FIG. 2(b), quartz doped with germanium Ge (Siow + Ge) is used as the core 2 of the first optical fiber 1, and pure quartz (Sin, ) is used as the cladding 3. , the core 6 of the second optical fiber 5
As the cladding 7, pure quartz (SiOa) was used.

In this embodiment as well, the amount of the doped material is adjusted so that the refractive indexes of the core 2 and the core 6 are the same, and the refractive indexes of the cladding 3 and the cladding 7 are also the same.

A combination of these materials shown in FIG. 3 also exhibits the above-described effects of the present invention.

Although the embodiments of the fiber fusion type optical branching coupler according to the present invention have been described in detail above, the present invention is not limited thereto and can be modified in various ways.
The combination of material compositions constituting the core and cladding of one of the optical fibers is different from the combination of material compositions constituting the core and cladding of the other optical fiber, and both cores are different from each other. Any combination of materials may be used as long as the refractive indexes of both claddings are made the same and the refractive indices of both claddings are made the same.

〔Effect of the invention〕

As described above in detail, the fiber fusion type optical branching coupler according to the present invention has the following excellent effects.

0 By simply changing the combination of the core and cladding materials of the two optical fibers, a fiber fusion type optical branching coupler with less wavelength dependence of the branching ratio can be constructed, so there is no need to increase the number of special processes required in the past. Even if it is not necessary, it can be easily manufactured using the same process as the normal coupler manufacturing process.

The diameters of the two optical fibers may be the same, and only one fusion/stretching portion is required, so the shape of the fiber fusion type optical branching/coupling device does not become particularly large.

(2) Also, since the refractive index of both claddings is the same, no reflection occurs at the fused/stretched portion, resulting in a high degree of coupling and low loss.

■Also, set the two optical fibers to have the same mode field diameter, same fiber diameter, and same core and clad refractive index as other transmission optical fibers that connect this fiber/<WIHI type optical splitter/coupler. For example, when these two fibers are connected to an optical fiber of another transmission system, the connection is consistent and end face reflections are less likely to occur at the connection.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the process of manufacturing a fiber fusion type optical branching coupler according to the present invention, FIG. 2 is a diagram showing a comparison of the refractive index of the core and cladding of both optical fibers 1 and 5, and FIG. The figure is a diagram showing the material combinations of the cores 2, 6 and cladding 3.7 of a fiber fusion type optical branching coupler according to another embodiment of the present invention and their refractive indexes. In the figure, 1... first optical fiber, 2... core, 3...
... cladding, 5... second optical fiber, 6... core, 7... cladding. tQ) (b) Figure 2 method folding year)

Claims (2)

[Claims] (1) In a fiber fusion type optical branching coupler in which the claddings of at least two optical fibers are brought into contact with each other and the contact portion is fused and stretched, the material composition that constitutes the core and cladding of one optical fiber. and the combination of material compositions constituting the core and cladding of the other optical fiber are different, and the refractive index of both cores is made the same, and the refractive index of both claddings is made the same. Fiber fusion type optical branching coupler. (2) The two optical fibers have the same mode field diameter, the same fiber diameter, and the same core and clad refractive index as the other transmission optical fibers that connect this fiber fusion type optical branching coupler. The fiber fusion type optical branching coupler according to claim 1, wherein the fiber fusion type optical branching coupler is formed.