JPH0588022A - Optical fixed attenuator - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical fixed attenuator that is compact, has high strength, and has stable connection characteristics with an optical fiber. [Structure] A fixed optical attenuator 10 connected between two optical fibers 60 and 70 of a transmission system. The optical fixed attenuator 10
Is composed of an optical fiber of a predetermined length consisting of a core 11 and a clad 13, and the dopant of the core 11 in the regions a and b near both ends of the optical fiber is thermally diffused to expand the core diameter, and thereby the core is expanded. The mode field diameter of the enlarged diameter is made different from the mode field diameter of the optical fibers 60 and 70 of the transmission system. As a result, the light propagating in the optical fibers 60 and 70 causes a loss in the regions a and b in which the diameter of the core 11 of the fixed optical attenuator 10 is enlarged, and is attenuated by a predetermined amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed optical attenuator, and more particularly to a fixed optical attenuator suitable for use in a transmission system of a single mode optical fiber.

[0002]

2. Description of the Related Art Conventionally, when an optical fiber is used in the fields of optical communication systems and optical measurement, an optical fixed attenuator is used for the purpose of causing a light receiving device to receive a signal at an optimum level.

The conventional fixed optical attenuator has been as follows. A fiber-type optical attenuator utilizing radiation loss due to uniform bending, for example, an optical attenuator in which an optical fiber is wound around a bobbin to obtain a predetermined attenuation effect (for example, the optical attenuator described in JP-A-2-129603). ).

An optical attenuator that produces a predetermined amount of attenuation by compressing an optical fiber while heating it to form a compression bend (for example, the optical fixed attenuator described in Japanese Patent Laid-Open No. 153055/1993).

[0005]

However, the above-mentioned conventional example has the following problems. In the case of the above optical attenuator, it is not possible to incorporate it into a small component such as a connector because it is restricted by the size of the bobbin diameter around which the optical fiber is wound, and therefore it can be easily adopted in an optical communication system. There wasn't.

Further, in the case of the above-mentioned optical attenuator, since the optical fiber is deformed by heating, there is a risk that residual stress is generated in the heating deformed portion.

Further, as a fixed optical attenuator other than the above-mentioned conventional example, there is a fixed optical attenuator having a structure in which optical components are combined. When this is connected to an optical fiber, the deviation of the optical axis depends on the connection state. There was a problem in that the amount of attenuation would change significantly.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an optical fixed attenuator having a small size, high strength, and stable connection characteristics with an optical fiber.

[0009]

In order to solve the above problems, the present invention provides an optical fixed attenuator 10 connected between two optical fibers 60 and 70 of a transmission system with a core 11 and a clad 1.
3 is composed of an optical fiber having a predetermined length, and the dopant of the core 11 in a predetermined portion of the optical fiber is thermally diffused to increase the core diameter, thereby increasing the mode field diameter of the portion having the increased core diameter. The optical fiber 6 of the transmission system
It was configured to be different from the mode field diameter of 0.70.

[0010]

The diameter of the core 11 of the fixed optical attenuator 10 is enlarged by heat diffusion, and the mode field diameter of the enlarged portion is made different from the mode field diameter of the optical fibers 60 and 70 of the transmission system. Inconsistency of mode shapes occurs in the part where the diameter of is enlarged. Therefore, the optical fibers 60, 70
The light propagating inside has a loss in the enlarged portion, and the light is attenuated by a predetermined amount.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a schematic side sectional view showing an optical fixed attenuator 10 according to a first embodiment of the present invention. As shown in the figure, this optical fixed attenuator 10 cuts an optical fiber composed of a core 11 and a clad 13 into a predetermined length, heats the vicinity of both ends of the optical fiber, and removes the dopant of the core 11 in the optical fiber. Is thermally diffused, thereby expanding the diameter of both ends of the core 11 in the vicinity thereof. As the optical fiber constituting the optical fixed attenuator 10, a single mode fiber having the same structure as the optical fibers 60 and 70 of the transmission system described below is used (the same applies to the following second, third and fourth embodiments. ).

The fixed optical attenuator 10 is connected between two optical fibers 60 and 70 of the transmission system as shown in FIG. 1 (at this time, the optical axes of the respective cores 61, 11, and 71 are coincident with each other. To do). At this time, in the regions a and b in which the diameter of the core 11 of the optical fixed attenuator 10 is enlarged, the mode field diameter of light is enlarged, so that a mode shape is formed on the connection surface with the two optical fibers 60 and 70. Cause inconsistency. Therefore, the light propagating in the optical fibers 60 and 70 causes a loss in both the connection portions and is attenuated by a predetermined amount.

By the way, in this optical fixed attenuator 10, since the core diameter is expanded by heat diffusion, the standardized frequency in the attenuator does not change and the single mode condition does not change.
Therefore, if the optical fiber constituting the optical fixed attenuator 10 and the optical fibers 60 and 70 of the transmission system are constituted by the single mode fiber having the same structure as in this embodiment, the mode is not converted at the connection surface. , Only the power of that light will be attenuated.

The amount of loss, that is, the amount of attenuation is
It can be adjusted by adjusting the size of the expanded core diameter and the divergence angle of the core diameter.

In this embodiment, the optical fiber 6
Optical fixed attenuator 10 connected to cores 61 and 71 of 0 and 70
Since the diameter of the end surface of the core 11 is enlarged, even if the optical axis is slightly deviated in the connection portion, the power distribution of the light is not affected, and thus the connection between the two becomes easy.

FIG. 2 is a schematic side sectional view showing an optical fixed attenuator 20 according to the second embodiment of the present invention. In this embodiment, all of the diameters of the cores 21 of the optical fibers constituting the optical fixed attenuator 20 are expanded by thermal diffusion, and the mode field diameters thereof are made different from the mode field diameters of the optical fibers 60 and 70. Even with such a configuration, since the mode shapes do not match at the connection surface between the optical fibers 60 and 70 of the transmission system and the fixed optical attenuator 10, the optical fiber 6
The light propagating in the 0 and 70 causes a loss in both the connection portions and is attenuated by a predetermined amount.

FIG. 3 is a schematic side sectional view showing an optical fixed attenuator 30 according to the third embodiment of the present invention. In this embodiment, only the diameter of the region c at one end of the core 31 of the optical fixed attenuator 30 is expanded by thermal diffusion, and the mode field diameter of that portion is connected to the mode field diameter of the optical fibers 60 and 70. Is different. Even with this configuration, one optical fiber 70 of the transmission system and the fixed optical attenuator 10
Since a mode shape mismatch occurs at the connection surface of, the light propagating in the optical fibers 60 and 70 causes a loss at the connection portion and is attenuated by a predetermined amount.

FIG. 4 is a schematic side sectional view showing an optical fixed attenuator 40 according to the fourth embodiment of the present invention. In the core 41 of the optical fixed attenuator 40 in this embodiment, both ends thereof have the same core diameter as the cores 61 and 71 of the optical fibers 60 and 70 of the transmission system, and the region d at the center thereof is heated by the dopant of the core 41. The diffused core expansion portion is configured so that the mode field diameter of the core expansion portion is different from the mode field diameter of the optical fibers 60 and 70.

When the expanded core portion is provided in this manner, light is attenuated in this portion. This amount of attenuation changes depending on the size of the expansion spread angle of the core expansion part and the size of the diameter of the core expansion part. For example, how the core expands in the optical axis direction (spread angle). When is steep, the loss, that is, the amount of attenuation increases.

[0020]

As described in detail above, the optical fixed attenuator according to the present invention has the following excellent effects. Since the optical fixed attenuator is configured by using the optical fiber, it is small in size and can be easily incorporated in an optical communication device.

The optical fiber constituting the optical fixed attenuator is
Since no physical force such as the deformation of the shape is applied, residual stress does not occur and its strength does not become weak.

[Brief description of drawings]

FIG. 1 is an optical fixed attenuator 10 according to a first embodiment of the present invention.
FIG.

FIG. 2 is an optical fixed attenuator 20 according to a second embodiment of the present invention.
FIG.

FIG. 3 is an optical fixed attenuator 30 according to a third embodiment of the present invention.
FIG.

FIG. 4 is an optical fixed attenuator 40 according to a fourth embodiment of the present invention.
FIG.

[Explanation of symbols]

 10 optical fixed attenuator 11 core 13 clad 60, 70 optical fiber

Claims (1)

[Claims] 1. A fixed optical attenuator connected between two optical fibers of a transmission system, wherein the fixed optical attenuator is composed of an optical fiber of a predetermined length composed of a core and a clad. Of the core of the optical fiber of the transmission system is made different from the mode field diameter of the optical fiber of the transmission system by thermally diffusing the core dopant of a predetermined portion of the optical fiber to expand the core diameter. Attenuator.