JPH07104130A - Stationary attenuator - Google Patents

Abstract

PURPOSE:To lessen the influence of reflection at the butt end faces of a pair of optical fibers, to obtain excellent optical stability and to assure a large light attenuation quantity by interpoosing a glass rod of the same diameter as the diameter of the optical fibers between these end faces and fusing the glass rod to the end faces, thereby constituting the attenuator. CONSTITUTION:The glass rod 22 of the same diameter as the diameter of the optical fibers 201, 202 is interposed between the butt end faces of a pair of the optical fibers 201, 202 of an attenuator element 19 and both ends of the glass rod 22 are respectively fused to the butt end faces of the respective optical fibers 201, 202. Further, light absorbers 24 consisting of vapor deposited films of C (carbon), etc., are respectively clad on the outer peripheries of the clads 2012, 2022 of each optical fibers 201, 202 and the outer periphery of the glass rod 22. For example, the light emitted from the end face of the core 2011 of the optical fiber 201 on the left side diffuses at the time of passing the glass rod 22 and only the part of the diffused light is made incident into the core 2021 of the optical fiber 202 on the opposite right side, by which the light is attenuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixed attenuator used for giving a certain amount of attenuation to light intensity.

[0002]

2. Description of the Related Art Generally, an avalanche photodiode (A) used as a light receiving element in a system such as an optical communication system.
In a light receiving element such as PD), when there is an optical input having a predetermined light intensity or more, the response characteristic cannot maintain linearity and is distorted, and an electric signal corresponding to the light intensity cannot be extracted. Therefore, in order to prevent such a problem, an attenuator is provided to attenuate the light intensity to some extent.

There are two types of attenuators for attenuating the light intensity, a variable type in which the amount of attenuation is variable and a fixed type in which the amount of attenuation is fixed to a constant value.

The former variable type has an advantage that the amount of attenuation can be adjusted over a wide range, but has a complicated structure and is expensive. On the other hand, the latter fixed type does not have the degree of freedom of the attenuation amount, but the structure is relatively simple and small,
Since it is lightweight and inexpensive, it is often incorporated in an optical system and used as a means for adjusting the light level of each part.

By the way, conventionally, as such a fixed attenuator, the one shown in FIG. 4 is known.

The one shown in FIG. 4A is a so-called air-gap type in which the abutting end faces of a pair of ferrules b ₁ and b ₂ into which optical fibers a ₁ and a ₂ are inserted are obliquely polished. At the same time, a predetermined space c is provided between the abutting end faces to form an attenuator element.

In this air gap type, for example, the light incident through the left optical fiber a ₁ diverges when it exits from the end face of the optical fiber a _{1, and} only a part of the diverged light is emitted. Since the light is incident on the opposing right-side optical fiber a ₂ , the light is attenuated by the loss at that time. The abutting end faces are obliquely polished in order to remove the influence of the returning light into the optical fiber a ₁ due to the reflection at the abutting end faces.

The one shown in FIG. 4 (b) is a so-called absorption type, in which the abutting end faces of a pair of ferrules b ₁ and b ₂ into which the optical fibers a ₁ and a ₂ are inserted are polished obliquely. At the same time, a light absorbing plate d such as colored glass is provided between the both end faces to form an attenuator element.

In this absorption type, for example, a part of the light incident through the optical fiber a ₁ on the left side is absorbed by the light absorbing plate d, and a part of the light passing through the light absorbing plate d is absorbed. Since only the incident light is incident on the opposing right-side optical fiber a ₂ , the light is attenuated by the loss due to the absorption.

Further, what is shown in FIG. 4 (c) is a so-called reflection type, and the abutting end faces of a pair of ferrules b ₁ and b ₂ into which optical fibers a ₁ and a ₂ are inserted are obliquely polished. In addition, a thin film e of metal such as Ag (for example, about 0.1 μm) is vapor-deposited between the abutting end faces to form an attenuator element.

That is, in this reflection type, for example, the light incident through the optical fiber a ₁ on the left side is a thin film e.
Since a part of the light is reflected by and the light passing through the thin film e is incident on the opposing right-side optical fiber a ₂ , the light is attenuated by the loss due to the reflection.

[0012]

By the way, in the air gap type (FIG. 4 (a)), the amount of attenuation can be freely adjusted by changing the distance between the abutting end faces of the optical fibers a ₁ and a _2. Although it can be set to, but since the space c is interposed between the butt end faces, it is easily affected by vibration, etc.
Lack of stability.

Absorption type (FIG. 4 (b)) and reflection type (FIG. 4 (c))
When the incident light intensity is high, the absorption plate d and the thin film e of the above may burn out.

The air gap type (FIG. 4 (a)),
Each of the absorption type (FIG. 4 (b)) and reflection type (FIG. 4 (c)) attenuator elements has optical fibers a ₁ and a ₂ between the abutting end faces.
Since a substance different from the above-mentioned material is present, the end face reflection occurs as it is, and the reflected light returns to the optical fiber a ₁ on the emission side again, and the light intensity becomes unstable. Therefore, although the abutting end faces have been conventionally polished obliquely, it is unavoidable that the light reflected from the end faces re-enters the optical fiber a _1, and the influence of the returning light cannot be sufficiently eliminated. In addition, it takes a lot of time to grind each of the butted end faces obliquely. To eliminate the above disadvantages, as shown in FIG. 5, a pair of the butted end faces of the optical fibers a _1, a _2, the optical axis o _1, o ₂ a predetermined amount of each of these core f ₁ of, f ₂ It is conceivable that the optical attenuator is constructed by directly fusing with the deviations δ and δ ′.

[0015] Thus, if directly fusion splicing optical fibers a _1, a ₂ each other, because foreign substances are never interposed between both a _1, a _2, except the influence of the edge reflection, Moreover, there is no risk of burning. Furthermore, since there is no space between the two a ₁ and a ₂ , the stability against vibration and the like is also excellent.

However, as shown in FIG. 5 (a), when the abutting end faces of the optical fibers a ₁ and a ₂ are completely melted and joined together, due to the influence of the maximum surface tension of fusion, Both cores
Since f _1, the optical axis of the f ₂ o _1, f ₂ deviation amount between δ decreases,
The maximum amount of light attenuation is about 3 to 5 dB, and it is not possible to sufficiently cope with equipment that requires a larger amount of light attenuation.

On the other hand, if the abutting end faces of the optical fibers a ₁ and a ₂ are incompletely melted so that a large amount of optical attenuation can be obtained, as shown in FIG. 5B, both cores f ₁ and f _{2 are} Optical axis
The displacement amount δ ′ between o ₁ and o ₂ can be increased (thus, the optical attenuation amount can also be set to a large amount), but the step h remains at the fused portion between the optical fibers a ₁ and a _2. In addition, for example, it becomes impossible to assemble the optical connector by inserting the attenuator element into the ferrule.

The present invention has been made in order to solve the above-mentioned problems, and the influence of the end face reflection is extremely small, the optical stability is excellent, and a large light attenuation amount is secured if necessary. The object is to obtain a fixed type attenuator that can be used.

[0019]

In order to solve the above-mentioned problems, the present invention adopts the following structure in a fixed attenuator in which a pair of optical fibers are provided with optical attenuating portions at their abutting end faces.

That is, according to the present invention, the light attenuating portion interposes a glass rod having the same diameter as the optical fiber between the abutting end faces of the pair of optical fibers, and both end portions of the glass rod are fused to the abutting end faces. It is configured to wear.

[0021]

In the above structure, the light emitted from the end face of one optical fiber into the glass rod is diverged when passing through the glass rod, and only a part of the diverged light is incident on the other optical fiber facing the other optical fiber. Therefore, the light is attenuated by the loss at that time. This light attenuation amount can be freely set by the length of the glass rod.

Further, since a glass rod of the same quality as the optical fiber is interposed between both abutting end faces and both ends thereof are fused, there is almost no influence of return light due to reflection at the abutting end faces of the optical fiber. Moreover, it is also excellent in stability against vibration and the like.

[0023]

1 is a front view showing a portion connecting an optical connector and a photodetector via a fixed attenuator according to an embodiment of the present invention, and FIG. 2 is a sectional view of the fixed attenuator of FIG. .

In these figures, 1 is a fixed attenuator, 2 is a photodetector, and 4 is an optical connector.

The fixed attenuator 1 of this embodiment has a hollow cylindrical shell 6, the diameter of the left side of the shell 6 in the figure is enlarged, and the cap nut 8 of the optical connector 4 is screwed onto the outer periphery thereof. While the threaded portion 10 is formed, the cap nut 14 screwed to the threaded portion 12 of the photodetector 2 is slidably fitted on the outer periphery of the right side of the shell 6 in the figure. In addition, a split sleeve 16 is inserted inside the shell 6,
A ferrule 18 is fitted to the split sleeve 16 in a state where the right end portion in the drawing is exposed.
An attenuator element 19 is inserted into the inside of the device 8.

FIG. 3 is an enlarged sectional view showing the attenuator element 19 inserted into the ferrule 18.

The attenuator element 19 of this embodiment is provided with a pair of optical fibers 20 ₁ and 20 _2, and the optical fiber ₂ is placed between the abutting end faces of the optical fibers 20 ₁ and 20 2.
A glass rod 22 having the same diameter as that of 0 ₁ , 20 ₂ is interposed, and both ends of the glass rod 22 are connected to the respective optical fibers 20.
They are fused to the abutting end faces of ₁ and 20 ₂ .
Furthermore, the clads 20 _{12 of} the optical fibers 20 ₁ and 20 ₂ ,
The outer circumference of the 20 _22, and each of the outer peripheral light absorber 24 made of vapor-deposited film such as C (carbon) of the glass rod 22 is coated.

As a procedure for manufacturing the fixed attenuator 1, a pair of optical fibers 20 ₁ and 20 ₂ having a light absorber 24 formed on the surfaces of the clads 20 ₁₂ and 20 ₂₂ are prepared in advance. 20 ₁ , 20 ₂ are cores 20 of each other
The optical axes of ₁₁ , 20 ₂₁ are abutted with each other, and the glass rod 22 is interposed between the abutted end faces. In this case, the length L of the glass rod 22 determines the light attenuation amount. Then, both ends of the glass rod 22 are heated and fused by spark discharge or the like. At that time, since the light absorbers 24 covered by the optical fibers 20 ₁ and 20 ₂ are partly scattered, the light absorbers 24 are covered over the respective surfaces of the optical fibers 20 ₁ and 20 ₂ and the glass rod 22. The attenuator element 19 is used. Next, after inserting the attenuator element 19 into the ferrule 18, end face polishing is performed and the split sleeve 16 is fitted and assembled.

In the fixed attenuator 1 having the above structure, for example, the light emitted from the end face of the core 20 _{11 of} the left optical fiber 20 ₁ into the glass rod 22 diverges when passing through the glass rod 22 and diverges. Since only part of the light is incident on the core 20 _{21 of} the right optical fiber 20 ₂ facing the light, the light is attenuated by the loss at that time.
Therefore, if the length L of the glass rod 22 is increased,
A large amount of attenuation can be obtained.

Further, the optical fiber 20 _1, 20 between each butted end faces of the _two optical fibers 20 _1, 20 ₂ of the same quality of the glass rod 22 is interposed, and, since both ends are fused, light There is almost no influence of return light due to reflection at the abutting end faces of the fibers 20 ₁ and 20 ₂ , and there is no fear of burning. Further, it has excellent stability against vibration and the like.

Moreover, even when the light emitted from the left optical fiber 20 ₁ and diverging enters the clad 20 ₂₂ of the right optical fiber 20 ₂ , the incident light is the incident light.
_The light absorber 24 formed on the outer periphery of ₂₂ quickly absorbs and attenuates the light, and the cladding propagation mode is suppressed.

In the above embodiment, each optical fiber 2
0 ₁ , 20 ₂ and the light absorber 2 on the surface of the glass rod 22.
4 but is suppressed clad propagation mode by forming, instead, the cladding 20 _12, 20 Ag in _22,
Or doped as a light absorber material such as Pt, also the refractive index of the cladding 20 _12, 20 _22, as directed in the radial direction outer peripheral, also by setting such gradually higher, as in the cladding The propagation mode can be suppressed.

[0033]

According to the present invention, since the glass rod is fused between the abutting end faces of the respective optical fibers constituting the attenuator element, there is almost no influence of the returning light due to the end face reflection and there is no fear of burning. Further, it is also excellent in stability against vibration and the like.

Moreover, by setting the length of the glass rod appropriately, a large amount of light attenuation can be secured.

[Brief description of drawings]

FIG. 1 is a front view showing a portion for connecting an optical connector and a photodetector using a fixed attenuator according to an embodiment of the present invention.

2 is a cross-sectional view of the fixed attenuator of FIG.

FIG. 3 is an enlarged cross-sectional view showing an attenuator element inserted into a ferrule.

FIG. 4 is a configuration diagram of an attenuator element that constitutes a conventional fixed attenuator.

FIG. 5 is a cross-sectional view in the case where the abutting end faces of the optical fibers are directly fusion-spliced together to form an attenuator element.

[Explanation of symbols]

1 ... fixed attenuator 18 ... ferrule, 19 ... attenuator element 20 _1, 20 ₂ ... optical fiber, 20 _11,
20 ₂₁ ... Core, 20 ₁₂ , 20 ₂₂ ... Clad, 22 ... Glass rod, 24 ... Light absorber.

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[Procedure amendment]

[Submission date] October 7, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016] However, as shown in FIG. 5 (a), when the end faces with the match of the optical fiber a _1, a ₂ joined completely melted, the effect of surface tension during fusion , The deviation amount δ between the optical axes o ₁ and f _{2 of} both cores f ₁ and f ₂ is small, so that the maximum optical attenuation amount is about 3 to 5 dB, and a device requiring a larger optical attenuation amount is required. I can't handle enough.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tohru Funabashi 4-3 Ikejiri, Itami City, Hyogo Prefecture Mitsubishi Cable Industries Itami Works Co., Ltd.

Claims (1)

[Claims] 1. A fixed attenuator comprising a pair of optical fibers, the attenuating portion being formed between the abutting end surfaces of the pair of optical fibers, wherein the optical attenuating portion has a glass having the same diameter as the optical fiber between the abutting end surfaces of the pair of optical fibers. A fixed attenuator, characterized in that a rod is interposed and both ends of this glass rod are fused to each abutting end face.