JPH10133021A - Light attenuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the quantity of attenuation from being changed due to the wavelength of transmitted light by arranging a convergent optical fiber piece having specific length between two single mode optical fibers and fusing and connecting both the ends of the fiber piece to the end faces of respective single mode optical fibers. SOLUTION: A piece of convergent optical fiber 4 having prescribed length is arranged between two single mode optical fibers 6 and both the end faces of the piece are fused and connected to the end faces of respective fibers 6. In this case, the end faces of the fibers 4, 6 are previously smoothly cut off by a known fiber cutter or the like. Since the diameters of the fibers 4, 6 are the same, both the end faces can be easily and accurately connected by a known fusion connection machine. In the light attenuator, the length of the piece of the fiber 4 to be used is 1/4, 3/4 or its neighborhood. Thereby light passed through the attenuator is expanded on the convergent optical fiber piece part and about 3dB attenuation is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical attenuator whose attenuation is substantially constant even when light of different wavelengths is transmitted.

[0002]

2. Description of the Related Art In an optical circuit, an optical attenuator for attenuating transmitted light power itself is used to adjust light power supplied to a certain device. An optical attenuator is a component for reducing an excessively high optical power to an appropriate intensity, and partially reflects or scatters or absorbs incident power. There are two types of optical attenuators: fixed optical attenuators that provide a constant attenuation, and optical variable attenuators that can continuously vary the amount of attenuation. The former is an attenuation for adjusting section loss of optical system equipment. The latter is used as a component for adjusting optical system equipment and measuring characteristics of optical cables.

An optical attenuator is required to have an attenuation amount that does not depend on the intensity of incident light and to have no wavelength characteristic. In order to satisfy these conditions, a structure for obtaining a predetermined attenuation using a metal deposited film of chromium or the like is generally used. In this structure, the metal film and the attenuation plate are arranged obliquely to prevent the reflected light from returning to the input side.

[0004]

As described above, in a general optical fixed attenuator, a metal film is deposited on an end face of an obliquely cut optical fiber, and a part of the incident optical power is a metal film. Although it is absorbed by the film and the other part is reflected obliquely, the amount of attenuation due to reflection is relatively large. Since this optical fixed attenuator generally has an error rate of the attenuation amount of several percent, it is expected that a smaller error rate will appear.

Further, as a fixed optical attenuator that absorbs incident power, one using a metal-doped optical fiber is manufactured and sold. This optical fixed attenuator has a slightly different absorption depending on the wavelength of the incident light.
There is a defect that the attenuation is slightly different between μm and 1.5 μm.

The present invention has been proposed in order to improve the above-mentioned problems relating to the conventional optical attenuator, and is configured by using only the same material as the optical fiber, so that the transmitted light in the used wavelength band can be reduced. It is an object of the present invention to provide an optical attenuator whose attenuation amount hardly changes depending on the wavelength. It is another object of the present invention to provide an optical variable attenuator or an optical connector manufactured using the configuration as an optical fixed attenuator.

[0007]

In order to achieve the above object, in an optical attenuator according to the present invention, two single-mode optical fibers are coaxially opposed to each other by using a converging optical fiber piece having a predetermined length. After disposing the small piece between two single-mode optical fibers, both end faces are fusion-spliced to end faces of the single-mode optical fibers. The length of the converging optical fiber piece used is preferably 1/4 or 3/4 pitch or near it.

The optical attenuator of the present invention may use a collimating optical fiber in which a small piece of a converging optical fiber is fusion-spliced to an end surface of a single mode optical fiber. The two collimating optical fibers are coaxially opposed to each other, and a short quartz fiber having the same diameter is arranged between the two collimating optical fibers. To the end faces of If the intermediate silica fiber is fusion-spliced with the end face of the converging optical fiber piece, a fixed optical attenuator having a fixed length of the silica fiber is obtained. Is an optical variable attenuator whose variable is variable.

In the present invention, the attenuation is mainly 5 d
In the fixed optical attenuator of B or less, two collimating optical fibers in which a small piece of a converging optical fiber having a predetermined length is fusion-spliced to an end face of a single mode optical fiber are used. In an optical fixed attenuator having an attenuation of more than 5 dB, it is preferable that a short quartz fiber having the same diameter is arranged and fused between two coaxially arranged single-mode optical fibers.

The intermediate quartz fiber used in the present invention has a single composition without a core, and transmitted light travels straight and parallel in the quartz fiber. The optical fixed attenuator of the present invention may be installed inside an optical connector, and the position of the fiber connection in the optical connector may be a suitable position of a single mode optical fiber, a converging optical fiber or an intermediate fiber. At any of the connection points with the quartz fiber.

The quartz fiber may be hollow, and the hollow quartz fiber is preferably used for an optical fixed attenuator having an attenuation of more than 10 dB. With a hollow quartz fiber, the angle of light emitted from the optical fiber is the same as that of air.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Optical fixed attenuators 1 to 3 according to the present invention
2 shows only the main part of the optical fiber in FIGS. 2 to 4 except for a metal or a resin cover. In the optical attenuator 3 according to the present invention, as shown in FIG. 2, a small piece of the converging optical fiber 4 having a predetermined length is disposed between the two single-mode optical fibers 6 and 6, and both end faces of the small piece are connected. It is fusion-spliced with the end face of each single mode optical fiber 6. At this time,
The end faces of the optical fibers 4 and 6 are cut smoothly by a known fiber cutter in advance. Optical fiber 4,6
Have the same diameter, so that smooth end faces can be easily and accurately connected using a known fusion splicer.

The converging optical fiber 4 is usually a multimode optical fiber such as a graded index optical fiber. Since the converging optical fiber 4 has the function of a rod lens, the divergence angle of the light emitted from the end face thereof changes according to the length of the fiber, and the divergence angle of the light is about 0.6 mm in the period of the length. At a minimum of about 2.5 ° to a maximum of about 9.5 °. In the optical attenuator 3, when the length of the small piece of the converging optical fiber 4 to be used is 1/4 or 3/4 pitch or in the vicinity thereof, the light passing through the light attenuator is a part of the converging optical fiber piece. Spread, resulting in about 3 dB of attenuation.

In the fixed optical attenuator 1, as shown in FIG. 1, a collimating optical fiber 8 in which a converging optical fiber 4 is fusion-spliced to an end face of a single mode optical fiber 6 is used. Since the collimated optical fiber is an optical fiber in which the outgoing light is substantially parallel to the incident light having a predetermined wavelength, the opening angle of the outgoing light needs to be as small as possible. Therefore, in the present invention, the opening angle of the emitted light is 3 °.
When the length of the converging optical fiber piece 10 is determined to be 1/4 or 3/4 pitch or in the vicinity thereof by cutting at a position 5 indicated by a chain line in FIG. Preferably, if the pitch is equal to this, the small piece 10 can be made longer.

In the collimating optical fiber 8 used in the present invention, the opening angle of the outgoing light is about 3 °, whereas the opening angle of the outgoing light in a normal collimating optical fiber is about 0.1 °.
Since the angle is 1 to 0.2 °, the optical fiber 8 substantially corresponds to a semicollimator. In the two collimated optical fibers 8 and 8, the connection loss increases as the spatial distance between the end faces increases. However, if the opening angle of the emitted light is about several degrees, the increase in the spatial distance between the end faces will not increase. Since the response of the connection loss is improved, this structure can be used for an optical attenuator (see FIG. 6). On the other hand, in the ordinary single mode optical fiber 6, the opening angle of the emitted light is about 1
0 °

As shown in FIG. 3, in the fixed optical attenuator 1, the collimating optical fibers 8, 8 are coaxially opposed to each other, and a short quartz fiber 12 having the same diameter is placed between the collimating optical fibers 8, 8. After the arrangement, the both end faces of the quartz fiber are fusion-spliced to the end faces of the respective converging optical fiber pieces. The length of the quartz fiber 12 corresponds to the spatial distance between the end faces of the collimating optical fibers 8 (that is, the collimator interval L in FIGS. 3 and 6). When the quartz fiber is hollow as shown in FIG. 5, the hollow silica fiber 13 has an outer diameter of 125 μm and a hollow inner diameter of 10 to 50 μm.
It is preferably μm.

Table 1 below shows the results of measuring the connection loss depending on the spatial distance L between the end faces of the collimated optical fibers 8 and 8. In this experiment, a graded index optical fiber having a relative refractive index difference of 1% was used as the converging optical fiber 4 in the collimating optical fiber 8, and the small piece 1 was used.
The length of 0 is 0.27 mm. For comparison, the connection loss due to the spatial distance L ′ between the end faces of the single mode optical fibers 6 and 6 is also measured (see FIG. 4).

[0018]

[Table 1]

The graph of FIG. 6 is created based on the measured values in Table 1 above. As is clear from the experimental results, in the fixed optical attenuator 1 (FIG. 3) using the collimated optical fibers 8, 8, the connection loss changes remarkably according to the predetermined length of the spatial distance L. Is set to 1 to 10 dB. Since the fixed optical attenuator 1 uses the opening angle of the emitted light, it is difficult to obtain a remarkable change in the amount of attenuation when the amount of attenuation exceeds 10 dB.

Further, when a quartz fiber having a single structure exists at the position of the spatial distance L or L ′, the angle of light emitted from the optical fiber 6 or 8 becomes smaller than that in the case of air, so that the attenuation is reduced by 5 dB. If it exceeds, the fixed optical attenuator 2 (FIG. 4) using the single mode optical fibers 6 and 6 can be used. If the attenuation exceeds 10 dB,
As shown in FIG. 5, a fixed optical attenuator 5 using a hollow quartz fiber 13 and single mode optical fibers 6 and 6 is suitable.

The obtained optical fixed attenuators 1 to 3 are cut at appropriate locations, the cut portions are inserted into a ferrule 30 (FIG. 9) or a silicon chip, and fixed with an adhesive or the like, and then the end faces are cut. Is polished, an optical connector 34 (FIG. 9) of FC type or SC type can be obtained. The cut portion may be a portion of the single mode optical fiber 6 as illustrated in FIG. 9 or may be used without fusing the above-described portion to be fusion spliced. In the fixed optical attenuator 1 or 2, one or both of the single mode optical fibers 6 and 6 may be extended in a pigtail shape.

In the collimated optical fiber tape 14 shown in FIG. 7, the end face of the multi-core converging optical fiber tape 16 is integrally fused to the end face of the multi-core single mode optical fiber tape 18, and the tape 16 is connected. Predetermined length position 22
To form a multi-core tape piece 20. In order to obtain a multi-core fixed optical attenuator, two sets of collimated optical fiber tapes 14 and 14 are coaxially opposed to each other, and short, multi-core quartz fibers (not shown) having the same diameter are used as the tapes 14 and 1.
4, and the both end faces of the quartz fiber are connected to a large number of single mode optical fibers 2 through small converging optical fiber pieces.
4 and fusion-spliced.

When the collimated optical fiber is a multi-core optical fiber tape 14, as shown in FIG.
After fusion splicing to 4, the end of each collimated optical fiber is inserted into the multi-core ferrule 26 or the V-shaped groove of the grooved silicon chip, fixed with an adhesive such as epoxy resin, and polished at the end face. By attaching to the plug 27, an optical connector 28 of FC type, SC type or the like can be obtained.

In the optical connector 28, the end face of the collimated optical fiber fixed by one ferrule 26 is connected via a quartz fiber 25 to the end face of the collimated optical fiber fixed by the other ferrule 26. Although not shown, in the optical connector, the ends of the single mode optical fibers to which the converging optical fiber pieces are fusion-spliced are respectively fixed to ferrules, each ferrule is housed in a plug, and an intermediate adapter incorporating a sleeve (FIG. 9). No. 29) may be attached with a quartz fiber. In this case, both end faces of the quartz fiber and end faces of the respective converging optical fibers are in contact with each other.

In the optical connector 34 shown in FIG. 9, the fiber structure of the fixed optical attenuator is housed in one cylindrical ferrule 30. The fiber structure is inserted into the cylindrical ferrule 30 and then fixed with an adhesive, and the end face of the single mode optical fiber is polished in a conventional manner. Plug ferrules 30 and 30 into plugs 3
2, the FC connector 34 is obtained. The entire optical connectors 28 and 34 may be fixed with metal clips (not shown) or the like.

[0026]

Next, the present invention will be described based on examples, but the present invention is not limited to the examples. Example 1 A converging optical fiber 4 having a length of 0.273 mm corresponding to a quarter pitch (core diameter 50 μm, cladding diameter 125 μm)
And two single mode optical fibers 6 (cladding diameter 125 μm) having a length of 1 m and a wavelength of 1.3 μm are prepared. As shown in FIG. 2, the single mode optical fibers 6 and 6 are coaxially
Is placed between the two single-mode optical fibers 6 and 6, and both end faces of the small piece are fusion-spliced with the end faces of the single-mode optical fibers 6, respectively.

With respect to the obtained optical fixed attenuator 3, semiconductor laser beams having wavelengths of 1.3 mm and 1.55 mm are incident, and the connection loss is measured. As a result, the connection loss is 3 dB at any of the wavelengths, and the connection loss at both wavelengths matches very well.

Embodiment 2 A single-core collimated optical fiber 8 having a wavelength of 1.3 μm was used.
Mode optical fiber 6 (cladding diameter 125μ)
m). A converging optical fiber 4 having a length of 0.273 mm (core diameter: 50 μm, cladding diameter: 125 μm) is fusion-spliced to an end face of a single-mode optical fiber 6 having a length of 1 m, and two of them are prepared.

As shown in FIG. 3, the collimating optical fibers 8, 8 are coaxially opposed with the converging optical fiber pieces 6 facing inward, and the quartz fiber 12 having a length of 1.0 mm and a diameter of 125 μm is collimated. After being disposed between the fibers 8, both end faces of the quartz fiber are fusion-spliced to end faces of the respective converging optical fiber pieces 20.

With respect to the obtained optical fixed attenuator 1, semiconductor laser beams having wavelengths of 1.3 mm and 1.55 mm are incident, and the connection loss is measured. As a result, the connection loss is 1.5 dB at any wavelength, and the connection loss is very well matched at both wavelengths.

Example 3 Using a quartz fiber 12 having a length of 1.0 mm, a fiber manufactured in the same manner as in Example 1 was cut at a position shifted by about 5 mm from the intermediate portion, and a single-mode optical fiber
Leave. Each cut part is made of cylindrical ferrule 30
(FIG. 9), and fixed with an adhesive, and then the end face is polished by an ordinary method. The ferrules 30 are respectively fixed to the plugs 32 to obtain the FC connector 34.

With respect to the obtained optical connector 34, semiconductor laser beams having wavelengths of 1.3 mm and 1.55 mm are incident, and connection loss is measured. As a result, the connection loss was 7.5 dB at any wavelength.

Embodiment 4 For a fixed optical attenuator having an attenuation of 10 dB or more, a length of 1
A hollow silica fiber 13 (having a hollow diameter of 30 μm) having a length of 1.2 mm and a diameter of 125 μm
m) is fusion spliced. Further, a single-mode optical fiber having a length of 1 m and a wavelength of 1.3 μm (cladding diameter 125 μm) is fusion-spliced to the end face of the quartz fiber.

The obtained optical fixed attenuator has a wavelength of 1.
The connection loss is measured by injecting semiconductor laser beams of 3 mm and 1.55 mm. As a result, the connection loss is 19.9 dB when the wavelength is 1.3 mm, and the connection loss is 20.0 dB when the wavelength is 1.55 mm, and the connection loss matches well for both wavelengths.

[0035]

Since the optical attenuator according to the present invention is made of the same glass material as the optical fiber, the optical attenuator absorbs less incident power and is less reflected, and is attenuated by the wavelength of the transmitted light in the used wavelength band. The amount of attenuation does not change and the amount of attenuation is always substantially constant even when light of different wavelengths is transmitted. In the optical attenuator of the present invention, the absorption does not differ depending on the wavelength of the incident light as compared with the fixed optical attenuator using the metal fiber-doped optical fiber, and the amount of attenuation is reduced even at the wavelengths of 1.3 μm and 1.5 μm. Almost agree.

The optical attenuator of the present invention has a continuous optical fiber structure and can be applied to a pigtail type or a receptacle type, and can be easily incorporated into various optical connectors. Therefore, the optical attenuator of the present invention can be used for adjusting section loss of various optical system devices in an optical circuit, adjusting optical system devices as a measuring component, and measuring the characteristics of an optical cable.

In the optical fixed attenuator of the present invention, the amount of attenuation is adjusted to 3 dB, 6 dB, 10 dB, 20 dB or the like in order to adjust the connection loss depending on the spatial distance between the end faces of the collimated optical fiber or the end faces of the single mode optical fiber. It is easy to make and fine adjustment. As a result, the optical fixed attenuator of the present invention is easier to manufacture than a metal-doped optical fiber or a metal film deposited on the end face of an obliquely cut optical fiber, and is a special and expensive material. Since it is not used, it can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is an enlarged cross-sectional view showing a collimated optical fiber in which an end face of a converging optical fiber is fusion-spliced to an end face of a single-mode optical fiber, and schematically shows light propagation in a core portion of the converging optical fiber. I have.

FIG. 2 is an enlarged sectional view showing a main part of the optical fixed attenuator of the present invention.

FIG. 3 is an enlarged sectional view showing a main part of a modification of the present invention.

FIG. 4 is an enlarged sectional view showing another modified example of the present invention used when the amount of attenuation exceeds 5 dB.

FIG. 5 is an enlarged cross-sectional view showing still another modified example of the present invention used when the amount of attenuation exceeds 10 dB.

FIG. 6 is a graph showing a connection loss with respect to a space distance between end faces of a collimated optical fiber and between end faces of a single mode optical fiber.

FIG. 7 is a schematic perspective view showing a multi-core collimated optical fiber tape according to a modification of the present invention.

FIG. 8 is a schematic sectional view showing an example of the optical connector of the present invention.

FIG. 9 is a schematic sectional view showing a modification of the optical connector.

[Explanation of symbols]

 1,2,3 Fixed optical attenuator 4 Focusing optical fiber 6 Single mode optical fiber 8 Collimating optical fiber 10 Focusing optical fiber piece 12 Quartz fiber

Claims (6)

[Claims] 1. A converging optical fiber piece having a predetermined length is disposed between two single-mode optical fibers coaxially opposed to each other, and the piece is fusion-spliced to an end face of each single-mode optical fiber. An optical attenuator wherein the length of the converging optical fiber strip is at or near 1/4 or 3/4 pitch. 2. A collimating optical fiber in which a predetermined length of a converging optical fiber piece is fusion-spliced to an end face of a single mode optical fiber, and a short dimension is provided between two collimating optical fibers which are coaxially opposed to each other. An optical attenuator in which quartz fibers having the same diameter and of a single composition are arranged, and both end faces of the quartz fiber are fusion-spliced to end faces of each of the small pieces of the converging optical fiber. 3. The optical attenuator according to claim 2, wherein the length of the focusing optical fiber piece is at or near 1/4 or 3/4 pitch, and the opening angle of the collimating optical fiber is about 3 °. 4. An optical fixed attenuator used when the attenuation exceeds 5 dB, wherein a single-piece quartz having a short diameter and the same diameter is provided between two single-mode optical fibers arranged coaxially. An optical fixed attenuator in which fibers are arranged and both end faces of the quartz fiber are fusion-spliced to end faces of each single mode optical fiber. 5. The optical attenuator according to claim 2, wherein the intermediately disposed quartz fiber is hollow. 6. An optical connector in which the optical attenuator according to claim 1, 2, or 4 is installed.