JPH1164638A - Optical attenuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to prevent an attenuation characteristic from being changed by a change in ambient temp. by butting the ends of optical fibers varying in a mode field diameter against each other and fusion splicing these ends. SOLUTION: The optical attenuator is constituted by connecting the optical fiber 1 having an ordinary core 2 and clad layer 3 of a diameter uniform in a longitudinal direction and the optical fiber 4 having a core 5 flared with the core end by thermal diffusion and a clad 6 formed with the end as a small contact surface in correspondence to thereto to each other by thermal fusion 7 of the contact surfaces. The mode field diameters thereof are varied and the light transmission direction is in an arrow direction. The mode field diameters are varied even with the optical attenuator constituted by forming the connecting ends of both optical fibers 1, 4 in such a manner that the cores flared with the core ends by thermal diffusion are formed to the respectively different sizes, by which the optical attenuator is similarly constituted. The optical attenuator may also be embodied by mechanical connection like end face joining of the optical connectors, etc., as another connecting method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical transmission line,
The present invention relates to an optical attenuator used to reduce the power of light by a certain amount.

[0002]

2. Description of the Related Art Conventionally, various types of optical attenuators of this type have been proposed.
As shown in FIG. 2, the ends of a pair of optical fibers 14 and 14 having a core 12 and a clad 13 on a base 11 are opposed to each other, and a metal deposition film 15 such as glass or polyimide is provided between both ends. With the inclusion 17 attached to the base material 16, a part of the light is reflected by the metal deposition film 15,
A structure that absorbs most of the light and attenuates it,
The principle of attenuation utilizes the absorption and diffusion of light in a metal-deposited film and the reflection and diffusion generated in the gap between the end face of an optical fiber and the metal-deposited film.

[0003]

By the way, in the optical attenuator having such a structure, when the temperature rises due to the temperature change with the end face of the optical fiber, the inclusion provided with the metal deposition of the inclusion expands, and the end face of the optical fiber is expanded. In particular, the amount of light diffusion changes. For example, when the distance is large, light is attenuated.

[0004]

SUMMARY OF THE INVENTION According to the present invention, there is provided an optical fiber which is spliced without using such attenuator in order to improve the problem of the attenuator using a metal-deposited surface from the above viewpoint. This is a simple configuration in which the structure of the end portion is changed, and solves the problems that have occurred in the prior art. That is, in an optical attenuator formed by, for example, fusion splicing of an optical fiber, an optical attenuator characterized by having an optical attenuation effect by abutting and fusing optical fiber ends having different mode field diameters. An optical attenuator characterized in that, of the two optical fibers to be connected, one end of the optical fiber has a core whose diameter is enlarged by thermal diffusion, and a mode in which the ends of both optical fibers are different from each other. An optical attenuator having a core expanded by thermal diffusion so as to have a field diameter.

[0005]

FIG. 1 is a structural example of an optical attenuator according to the present invention. An optical fiber 1 having a normal core 2 and a cladding layer 3 having a uniform diameter in a longitudinal direction, and a core at a connection end. An optical attenuator is formed by connecting the core 5 whose end is expanded by heat diffusion and the optical fiber 4 having the clad 6 whose corresponding end has a small contact surface by heat-fusing the contact surface. It has a different mode field diameter. Reference numeral 11 denotes a base on which both optical fibers are placed. In the case of FIG. 1, the light transmission direction is the direction of the arrow. Although not shown, even if the connection ends of the two optical fibers are configured to be cores in which the core ends are spread to different sizes by thermal diffusion, the mode field diameters are different. As a matter of course, the optical attenuator of the present invention is configured as described above.

When light in the direction of the arrow is transmitted through an optical attenuator having a structure as shown in FIG. 1, the amount of light attenuation is expressed by the following equation. Attenuation (dB) = - 20log (2W 1 W 2 / (W 1 2 + W
₂ ² )) In the above, W ₁ and W ₂ are the mode field diameter (MFD) at the boundary surface of each optical fiber.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An attenuator according to the present invention can be obtained, for example, as follows. A GeO ₂ -doped core fiber is prepared as an optical fiber, and this is split into two. Note that, specifically, 10 μ
m MFD optical fibers were divided into two and prepared. Heat treatment is performed on the tip of the above one optical fiber,
O ₂ is diffused to increase the mode field. This time, the MFD was expanded to about 20 μm. The end faces of both optical fibers to be connected were abutted, fused and connected by heating, and housed in a reinforcing case to obtain a fiber type attenuator module. In this example, an attenuation value of 2 dB was obtained. As a temperature characteristic of the attenuation value, a favorable result of 0.0005 dB / ° C. was obtained.

[0008] Regarding the expansion of the MFD due to thermal diffusion, the core can be expanded in a tapered shape as described below. The coating on the portion where the core of the optical fiber is desired to be enlarged is removed to obtain a bare optical fiber. The portion is fixed straight, and then heated with a burner from the side surface at a temperature of several hundred degrees for several minutes. While monitoring the temperature with a platinum electrode while preventing the outer diameter of the optical fiber from changing, germanium, which is a dopant added to the core, was thermally diffused into the cladding to increase the mode field diameter.

Next, in the middle of the burner heating section, the optical fiber is cut, the core diameter increases in the longitudinal direction of the optical fiber toward the connection end, and the core expands in a tapered shape.
An optical fiber having an enlarged cross-sectional shape was obtained. Next, this is connected to a single mode optical fiber having a normal small diameter core without expanding the core, and the connection is performed by fusion splicing. In other words, the end faces of the optical fibers on both sides are fused and connected to form an optical attenuator (attenuator).
Is completed. In this optical attenuator, only a part of the light in the direction of the arrow enters the left optical fiber core because the mode field diameters of the left and right optical fibers are different. That is, optical loss occurs. Conversely, the light coupling rate from the small-diameter optical fiber on the left to the core-enlarged optical fiber on the right is large.

Next, another embodiment will be described. As a method of substantially enlarging the core by enlarging the mode field diameter of the optical fiber, there is a method of changing the core diameter by heating and stretching the optical fiber. An optical attenuator is completed by fusion-splicing the optical fiber having an enlarged core and an optical fiber having a uniform diameter.
Also in this case, since the left and right core diameters are different, an optical attenuator can be configured, and a higher degree of freedom can be provided for adjusting the attenuation.

[0011] In expanding the mode field diameter by heating and stretching the optical fiber, two optical fibers having different degrees of expansion of the core are produced by the difference in the degree of stretching, and the end face of the section is cut. An optical attenuator can be manufactured by fusion splicing. In this case, an optical fiber having a uniform diameter is not used, but since the core diameters of the connection ends of the optical fibers to be connected are different, the ends of the optical fibers having different mode field diameters are butt-fused and spliced, which is a preferable attenuator. Can be obtained. In the above embodiment, the left and right optical fibers are connected by fusion. However, as another connection method, the present invention can be realized by mechanical connection such as end face bonding of an optical connector or the like. Can be.

[0012]

According to the present invention, since the mode field diameter can be designed to an arbitrary value by adjusting the amount of heating applied to the optical fiber, various optical attenuators having different attenuations can be manufactured. . In the case of using the fusion splicing, since the optical fiber is fused and integrated at the fusion splicing portion,
A change in the ambient temperature prevents the attenuation characteristic from changing.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of one example of a comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical fiber 2 core 3 clad 4 optical fiber 5 core spread by thermal diffusion 6 clad 7 fusion 11 base 12 core 13 clad 14 optical fiber 15 metal deposited film 16 base material 17 inclusion

Claims (3)

[Claims] 1. An optical attenuator comprising an optical fiber, wherein ends of optical fibers having different mode field diameters are butt-connected. 2. The two optical fibers to be connected, one of which is a normal optical fiber having a core having the same diameter, and the other of which is expanded by heat diffusion at a connection end to which the optical fiber is connected. The optical attenuator according to claim 1, wherein the optical attenuator is an optical fiber having a bent core. 3. The optical attenuator according to claim 1, wherein the connection ends of the two optical fibers to be connected have cores expanded to different diameters by thermal diffusion.