JPH02228609A - Optical fixed attenuator - Google Patents

Abstract

PURPOSE:To obtain an optical fixed attenuator capable of obtaining a desired extent of attenuation with a good reproducibility by heating and drawing an optical fiber having a light absorbing layer in the clad part to obtain the desired extent of attenuation. CONSTITUTION:The optical fiber having a light absorbing layer 2 in a clad part 1 is heated and drawn to obtain a desired extent of attenuation. Since most of energy of signal light is generally propagated in a core part 3 of the optical fiber in optical fiber transmission, the light absorbing layer scarecely has an influence upon the extent of attenuation though the optical fiber has the light absorbing layer in the clad part 1. However, when the optical fiber has the diameter reduced similarly by heating and drawing, a part of energy of signal light is absorbed to realize the optical fixed attenuator because energy of signal light is propagated in not only the core part 3 but also the clad part 1. Since the extent of light absorption is changed in accordance with the shape and the length of a heated and drawn part 4, the extent of attenuation is easily adjusted in accordance with the degree of heating and drawing. Thus, the optical fixed attenuator is realized which can obtain a desired extent of attenuation with a good reproducibility.

Description

[Detailed Description of the Invention] Summary Regarding an optical fixed attenuator, an optical fiber having a light absorption layer in the cladding part is heated and stretched for the purpose of providing an optical fixed attenuator that can obtain a desired amount of attenuation with good reproducibility. The configuration is such that a desired amount of attenuation is obtained.

Industrial applications The present invention relates to an optical fixed attenuator.

In the field of optical communication or optical transmission, it may be necessary to attenuate transmitted signal light to an optimal level depending on the characteristics of an optical receiver or the like. In such cases, usually
A fixed optical attenuator with an appropriate amount of attenuation is connected between an optical transmission line and an optical receiver, etc., and there is a need for a fixed optical attenuator that can obtain the desired amount of attenuation with a simple configuration. There is.

BACKGROUND OF THE INVENTION FIG. 7 is a diagram showing an example of a conventional optical fixed attenuator. The end faces of optical fibers 31 and 32 are obliquely polished, and a light attenuation film 33 is interposed between the polished end faces. Light attenuation film 33
A desired amount of attenuation can be obtained by changing the material and thickness of the material.

The reason why the light attenuation film 33 is provided diagonally with respect to the optical fibers 31 and 32 is to prevent reflected light generated by the difference in refractive index from returning in the opposite direction in the optical fiber.

FIG. 8 is a diagram for explaining a method of manufacturing the conventional optical fixed attenuator shown in FIG. 7. First, as shown in FIG. 3A, the end face of the optical fiber 31 is polished obliquely. 31
a is the core portion of the tip fiber 31; Next, the same figure (b)
As shown in FIG. 3, a light attenuation film 33 made of Ti or the like is formed on the polished end face by vapor deposition or the like. Then, as shown in FIG. 3(C), the optical fiber 32, whose end face is similarly obliquely polished, is aligned on the same axis as the optical fiber 31.
The obliquely polished surface is attached to the light attenuation film 33 using, for example, an optical adhesive.

Problems to be Solved by the Invention In a fixed optical attenuator as shown in FIG. 7, the amount of attenuation is mainly determined by the material and thickness of the optical attenuation film 33, and in addition to the material and thickness of the optical fibers 31 and 32. There is also an axis misalignment. Here, it is not necessarily easy to make the thickness of the light attenuation film 33 constant and the amount of axis deviation of the optical fibers 31, 32 constant (eg, no axis deviation). Therefore, there was a problem in that it was difficult to obtain a desired amount of attenuation with good reproducibility.

The present invention was created in view of these technical problems, and an object of the present invention is to provide a fixed optical attenuator that can obtain a desired amount of attenuation with good reproducibility.

Means to solve problems FIG. 1 is a principle diagram for explaining the present invention in detail.

The fixed optical attenuator of the present invention is constructed by heating and stretching an optical fiber having a light absorbing layer 2 in a cladding portion 1 to obtain a desired amount of attenuation.

In the figure, 3 is the core portion of the optical fiber, and 4 is the heating and stretching portion of the optical fiber.

Function Generally, in optical fiber transmission, most of the energy of signal light propagates within the core of the optical fiber.

Therefore, even if the optical fiber has a light absorption layer in the cladding portion, this light absorption layer has little effect on the amount of light attenuation. However, when an optical fiber is heated and stretched to reduce its diameter in a similar manner, the energy of the signal light propagates not only within the core but also within the cladding, so part of the energy of the signal light is absorbed by the light absorption layer. , an optical fixed attenuator is realized. Furthermore, since the amount of light absorption changes depending on the shape and length of the heat-stretched portion, the amount of attenuation can be easily adjusted by adjusting the degree of heat-stretching.

Example Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows a preform that can be used to manufacture the optical fixed attenuator of FIG. Figure (a)
The outer preform 11 shown in FIG. 1 is one in which a layer 2a serving as a light absorption layer is formed inside a quartz tube 1a by, for example, an internal CVD method. The layer 2a serving as a light absorption layer is a quartz layer containing metal impurities such as Fe5Cu. On the other hand, the same figure (c)
The inner preform 12 shown in FIG.
A layer 3a serving as a core portion is formed inside a quartz tube 1b having a human body smaller in diameter than the inner diameter of layer 2a serving as a light absorption layer by the internal CVD method.

The refractive index of the layer 3a serving as the core portion is adjusted to be larger than the refractive index of the quartz tubes 1a and 1b, thereby realizing an optical fiber waveguide structure.

FIG. 3 shows the inner preform 12 and the outer preform 1.
1 is a diagram showing an optical fiber 13 constructed by inserting the optical fiber into the inside of the optical fiber 1 and spinning the fibers together by a conventional method.

The quartz tubes 1a and lb serve as a cladding part 1, and a layer 2a formed by CVD.

3a are the light absorption layer 2 and the core portion 3, respectively.

In this example, in order to shorten manufacturing time, the preform is manufactured separately into an outer preform and an inner preform. You can also.

That is, by forming a layer to become a light absorption layer, a layer to become a cladding part, and a layer to become a core part in this order on the inside of a quartz tube, and spinning these by a normal method, it is possible to form a layer as shown in Fig. 3. It is possible to obtain an optical fiber with a suitable configuration.

Then, by partially heating and stretching the optical fiber 13, a heated stretching section 4 as shown in FIG. 1 can be formed.

FIG. 4 is a diagram for explaining the light intensity distribution in a portion along the TV-IV line in FIG. 1 that is not heated and stretched. The outer diameter of an optical fiber that has not been heated and stretched is, for example, 100 to 200 μm. In the part that is not heated and stretched, most of the light intensity is distributed within the core part 3,
Therefore, the propagating light is not absorbed by the light absorption layer 2.

FIG. 5 is a diagram for explaining the light intensity distribution in the heated stretching section along the line -V in FIG. 1. Since the outer diameter of the heat-stretched portion is reduced to, for example, 20 to 30 μm, the light intensity is no longer distributed only within the core portion. Therefore, a portion of the propagating light is effectively absorbed by the light absorption layer, and an appropriate amount of attenuation can be obtained.

In this embodiment, the light absorption layer is provided inside the cladding part, but according to the above operating principle, the light absorption layer may be provided in the outermost layer part of the craft part.

FIG. 6 is a diagram for explaining a method of heating and stretching to obtain a desired amount of attenuation. Optical fiber 13 is moved to fine movement table 21
．． 22, and one end of the optical fiber 13 is connected to the light source 23.
and connect the other end of the optical fiber 13 to an optical power meter 24.
The optical fiber 13 is stretched between fine movement tables 21 and 22 while being heated by a heating means 25 such as a 02 Hz burner. A desired amount of attenuation can be obtained by stopping the stretching when the light intensity measurement value by the optical power meter 24 decreases by a predetermined amount from the measurement value before stretching. As described above, according to this embodiment, since heating and stretching are performed while monitoring the amount of attenuation, a desired amount of attenuation can be obtained with good reproducibility. When a plurality of optical fixed attenuators were manufactured using the method of this example, when the design value of the attenuation amount was 20 dB, the variation was ±0.5.
We were able to suppress the noise within dB (with conventional technology, it was ±3 dB).
).

As described in detail, the present invention provides an optical fixed attenuator that can obtain a desired amount of attenuation with good reproducibility.

Further, according to the present invention, it is also possible to readjust the attenuation amount to a different amount by heating and stretching the optical fixed attenuator once the attenuation amount has been set.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing the configuration of the present invention, Fig. 2 is a diagram showing a preform in an embodiment of the present invention, Fig. 3 is a diagram showing an optical fiber in an embodiment of the present invention, and Fig. 4 is a diagram showing IV-IV. A diagram to explain the light intensity distribution along the line (Figure 1), Figure 5 is a diagram to explain the light intensity distribution along the V-V line (Figure 1), and Figure 6 is a diagram to explain the light intensity distribution along the line V-V (Figure 1). FIG. 7 is a diagram illustrating a conventional optical fixed attenuator, and FIG. 8 is a diagram illustrating a conventional optical fixed attenuator manufacturing method. DESCRIPTION OF SYMBOLS 1... Clad part, 2... Light absorption layer, 3... Core part, 4... Heat stretching part, 11... Outer preform, 12... Inner preform, 13... optical fiber.

Claims (1)

[Claims] An optical fixed attenuator characterized in that an optical fiber having a light absorption layer (2) in a cladding portion (1) is heated and stretched to obtain a desired amount of attenuation.