JP2946437B2 - Optical fixed attenuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

[0003] Here, there are the following conventional optical fixed attenuators. This is a fiber type optical attenuator using radiation loss caused by uniform bending. For example, an optical attenuator in which an optical fiber is wound around a bobbin so as to obtain a predetermined attenuation effect (for example, an optical attenuator described in JP-A-2-129603) ).

An optical attenuator that generates a predetermined amount of attenuation by forming a compression bend by compressing an optical fiber while heating it.

[0005]

However, the above-mentioned prior art has the following problems. In the case of the above-described optical attenuator, the size of the bobbin around which the optical fiber is wound is restricted, so that the optical attenuator cannot be incorporated into a small component such as a connector, and thus can be easily adopted in an optical communication system. Did not.

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 heated deformed portion.

As an optical fixed attenuator other than the above-mentioned conventional example, there is an optical fixed attenuator having a structure in which optical parts are combined. There is a problem that the amount of attenuation changes greatly due to this.

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

[0009]

According to the present invention, an optical fixed attenuator 10 connected between two optical fibers 60 and 70 of a transmission system is provided with a core 11 and a cladding 1.
Of 3 constituted by a predetermined length of the optical fiber, a dopant of a part of the core 11 of the optical fiber to Rukoto are thermally diffused
Therefore, the diameter is gradually changed at a predetermined spread angle.
An enlarged core portion is formed, and the mode field diameter of the enlarged core portion is made different from the mode field diameter of the optical fibers 60 and 70 of the transmission system.

[0010]

The diameter of the core 11 of the fixed optical attenuator 10 is enlarged by thermal 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. The mismatch of the mode shape occurs in the portion where the diameter of is increased. Therefore, the optical fibers 60, 70
The light propagating through the inside causes a loss in the enlarged portion, and the light is attenuated by a predetermined amount.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic sectional side view showing an optical fixed attenuator 10 according to a first embodiment of the present invention. As shown in FIG. 1, this optical fixed attenuator 10 cuts an optical fiber consisting of a core 11 and a clad 13 at 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 near both ends of the core 11 and gradually changing the diameter at a predetermined spread angle.
Core enlarged portions a and b are formed . As the optical fiber constituting the fixed optical attenuator 10, a single mode fiber having the same structure as the following transmission optical fibers 60 and 70 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 a transmission system as shown in FIG. 1 (at this time, the optical axes of the cores 61, 11 and 71 coincide with each other). To do that). At this time, the area where the diameter of the core 11 of the optical fixed attenuator 10 is enlarged (core enlarged portion) a,
In b, since the mode field diameter of light is enlarged,
A mode shape mismatch occurs at the connection surface between the two optical fibers 60 and 70. Therefore, the optical fibers 60, 70
The light propagating through the inside causes a loss at the two connection parts,
It is attenuated by a predetermined amount.

Since the core diameter of the fixed optical attenuator 10 is increased by thermal 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 single-mode fibers having the same structure as in this embodiment, no mode conversion occurs at the connection surface. , Only the power of the light is attenuated.

The magnitude of the loss, that is, the magnitude of the attenuation, is
It can be adjusted by adjusting the size of the enlarged core diameter and the spread angle of the core diameter.

In this embodiment, the optical fiber 6
Optical fixed attenuator 10 connected to cores 0, 70 61, 71
Since the diameter of the end face of the core 11 is enlarged, even if a slight optical axis shift occurs at the connection portion, the power distribution of the light is hardly affected, so that the connection between the two becomes easy.

FIG. 2 is a schematic side sectional view showing an optical fixed attenuator 20 according to a comparative example of the present invention. In this comparative example , the core 21 of the optical fiber constituting the optical fixed attenuator 20
Are enlarged by heat diffusion, and the mode field diameter is made different from the mode field diameters of the optical fibers 60 and 70.

FIG. 3 is a schematic side sectional view showing an optical fixed attenuator 30 according to a second embodiment of the present invention. In this embodiment, a region at one end of the core 31 of the optical fixed attenuator 30 (core
(Enlarged part) Only the diameter of c is a predetermined divergence angle by thermal diffusion
And the mode field diameter of the portion is made different from the mode field diameter of the optical fibers 60 and 70 connected thereto. Even with such a configuration, since the mode shape mismatch occurs at the connection surface between one optical fiber 70 of the transmission system and the fixed optical attenuator 10, the optical fibers 60,
Light propagating in 70 causes a loss at the connection and is attenuated by a predetermined amount.

FIG. 4 is a schematic sectional side view showing an optical fixed attenuator 40 according to a third embodiment of the present invention. The core 41 of the fixed optical attenuator 40 in this embodiment has the same core diameter at both ends as the cores 61 and 71 of the optical fibers 60 and 70 of the transmission system. The expanded core portion is formed by making the mode field diameter of the expanded core portion different from the mode field diameter of the optical fibers 60 and 70.

When the core enlarged portion is provided as described above, light is attenuated in the portion. The amount of attenuation varies depending on the size of the expansion angle of the core expansion portion and the size of the diameter of the core expansion portion. For example, how the core expands in the optical axis direction (spread angle). Is sharp, the loss, that is, the amount of attenuation increases.

[0020]

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

The optical fiber constituting the fixed optical attenuator is:
Since no physical force such as deformation of the shape is applied, no residual stress or the like is generated, and the strength is not reduced. Adjust the divergence angle and diameter of the core enlargement
Thus, the magnitude of the attenuation can be adjusted.

[Brief description of the drawings]

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

FIG. 2 is a schematic side sectional view showing an optical fixed attenuator 20 according to a comparative example of the present invention.

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

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

[Explanation of symbols]

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

Claims (1)

(57) [Claims] 1. An optical fixed attenuator connected between two optical fibers of a transmission system, wherein the optical fixed attenuator is constituted by an optical fiber having a predetermined length including a core and a clad, and the dopant partial core by Rukoto is thermally diffused in a predetermined spread
Form a core expansion part whose diameter is gradually changed at the corner,
An optical fixed attenuator characterized in that a mode field diameter of the core enlargement section is different from a mode field diameter of the optical fiber of the transmission system.