JP2003185874A - Optical fiber coupler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the cost of a system by simplifying the structure and reducing the number of components. <P>SOLUTION: The Optical fiber coupler 10 consists of a plurality of optical fibers 3, a coupling part 4 of the optical fibers, and a plurality of ports 6 extending from the coupling part 4, with the coupling part 4 stored in a protective case 1. An optical fiber 7 for attenuation is connected to at least one place of the optical fibers 3 linking from the coupling part 4 to the ports 6 inside the protective case 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler with a built-in attenuating optical fiber used in an optical communication system or the like.

[0002]

2. Description of the Related Art With the development of optical communication, the cost for constructing an optical system has become cheaper, and DWDM has been explosively increasing in recent years. This is to bundle lights of different wavelengths emitted from multiple laser diodes into one and send a wavelength-multiplexed signal to one optical fiber, transmit it over a long distance, and split it at a branch point. The method of letting it take. Here, an optical coupler is used for a device that bundles light and a device that splits light.

Here, after the light is split by the optical coupler, the light is received by the photodiode and electrically converted, but the output of the light differs depending on the distance transmitted at that time.
The output is too large for short distances and small for long distances.

Therefore, a system is adopted in which, after splitting by an optical coupler, a fixed optical attenuator is used to adjust the light output to a small one.

Here, the conventional fusion-spreading type optical fiber coupler is one in which a plurality of optical fibers are fused and stretched to form a fusion-spreading portion, and light propagating in one optical fiber is branched. Or, conversely, it is used as a component that joins the propagating lights that are incident from a plurality of optical fiber terminals.

This optical fiber coupler 30 is shown in FIG.
As shown in (a) and (b), two optical fibers 3 are used, and a coupling part 4 and a plurality of ports 6 are provided in the optical fiber extending from the coupling part 4 to protect the coupling part 4. Case 1
It has a structure in which it is accommodated via an adhesive agent 5. An upper lid 2 that covers the optical fiber coupler main body is joined to the upper portion of the protective case 1 to form a hollow cylindrical shape or a prismatic shape when combined.

The optical fiber 3 is roughly composed of a bare optical fiber consisting of a core 3a and a clad 3b, and a coating 3c made of resin or the like provided on the circumference of the bare optical fiber. In order to fuse and stretch the optical fibers with each other, it is necessary to remove a part of the coating 3c to expose the bare optical fibers.

The main body of the optical fiber coupler and the protective case 1 are fixed in the vicinity of both ends of the protective case 1 so that the adhesive 5 is not applied to the joint portion 4 (Japanese Patent Laid-Open No. 9-29138). -105832).

Next, in the fields of optical communication, optical measurement, CATV system, etc., an optical fixed attenuator is used for attenuating the intensity of an optical signal at a constant rate.

Although several methods of attenuating an optical signal by a certain amount have been proposed, a product having a high attenuation amount requires further stability to withstand a high input power. As attenuating means capable of coping with such high attenuation products, a method of inserting a filter into an optical fiber and a method of adding a light attenuating dopant to the optical fiber are known.

Among them, the method of adding a dopant for light attenuation has advantages such as ease of assembly, high reliability and low cost.

FIG. 7 is a sectional view showing a fixed optical attenuator using a conventional optical attenuating optical fiber.
1 is held and fixed to a ferrule 42 made of zirconia. In this case, the attenuating optical fiber 41 is connected to the ferrule 42.
After being inserted and fixed by adhesion, both end faces of the ferrule 42 are PC-polished, and the length thereof is 22 mm, which is a typical dimension of the SC adapter type attenuator.

The length of the optical attenuation optical fiber 5 to be used is defined by the length of the ferrule 42.
The attenuation amount of the optical signal is determined by 1 and the added concentration of Co that is the dopant.

Here, the sleeve 43 is a member for aligning the central axes of the attenuating optical fibers 41 by applying a uniform force to the cylindrical ferrule 41 in the radial direction,
The housing 44 is a case of an SC adapter type fixed attenuator (see Japanese Patent Laid-Open No. 9-311221).

FIG. 8 shows a state in which the optical fiber coupler 30 and the fixed optical attenuator 40 are connected to each other. An optical connector plug 51 is connected to the optical fiber coupler 30, then an optical fixed attenuator 40, and an optical adapter 53 fixed to the panel 52.
The optical connector plug 54 is connected to an optical device having a photodiode.

[0016]

However, in the configuration shown in FIG. 8, the structure is complicated and the number of parts is increased, so that the system itself becomes expensive. As a result, it was temporarily exposed to an explosive spotlight, but the number of related parts increased and the cost also increased, so that the actual use was interrupted.

Further, since the panel 52 has a heavy load on the panel 52, the rigidity of the panel itself must be increased. Therefore, the load of the entire device called a fiber terminal module for branching a few thousand optical fibers becomes excessive,
In order to install this on the floor, there is a problem that floor work must be performed to increase the load resistance of the floor.

Further, since the number of connection points increases, not only the connection loss increases but also the reflection loss increases, which causes a problem in optical characteristics.

[0019]

SUMMARY OF THE INVENTION In view of the above problems, the present invention comprises a plurality of optical fibers, each optical fiber has a coupling portion and a plurality of ports extending from the coupling portion, and the coupling portion is a protective case. An optical fiber coupler housed inside, wherein an attenuating optical fiber is connected to at least one portion of the optical fiber connected from the coupling portion to the port in the protective case.

The attenuating optical fiber is characterized in that it is fused and fixed between the optical fibers between the coupling portion and the port.

Further, the optical fiber extending from the coupling portion is fixed inside the alignment sleeve, and the attenuation optical fiber is arranged so as to be incorporated inside the alignment sleeve.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 1 is a sectional view of an optical fiber coupler according to the present invention.

The optical fiber coupler 10 of the present invention comprises two optical fibers 3, a coupling portion 4 and a plurality of ports 6 extending from the coupling portion 4, and the coupling portion 4 is housed in the protective case 1. In the protective case 1, the attenuation optical fiber 7 is fused and connected to at least one location of the optical fiber 3 connected from the coupling portion 4 to the port 6.

The protective case 1 used in the present invention may have any shape as long as it has at least a groove-shaped recess 1a for accommodating the optical fiber coupler body. For example, it may be a box body having an upper lid 2 of any shape that closes the opening above the recess 1a. Further, the side surface of the concave portion 1a may have any structure as long as it is configured to project the optical fiber 3 to the outside. The protective case 1 is preferably a trough-shaped one having a concave portion 1a which is opened on the side surface, and for example, a half-split pipe or the like can be used.

The protective case 1 and the upper lid 2 are preferably formed of a material having a linear expansion coefficient which is the same as or larger than that of the silica glass fiber material forming the optical fiber coupler body. Quartz glass, crystallized glass, or the like can be used.

There is a method of fixing the protective case 1 and the upper lid 2 with an adhesive, but a method of joining them by laser welding may be used.

Although not shown, the optical fiber coupler of the present invention may be provided with an outer case made of plastics, metal, glass, or ceramics on the outer peripheral portions of the protective case 1 and the upper lid 2. For this purpose,
This is to prevent dust and moisture from entering the inside of the optical fiber coupler from the external environment, and to reinforce the strength of the protective case 1.

Next, as the adhesive 5 used in the present invention, any adhesive can be used as long as it can bond the optical fiber 3 and the coating 3c to the inner wall of the protective case 1,
For example, an epoxy adhesive or the like is preferably used. The adhesive 5 is preferably one having a small shrinkage upon curing in order to suppress the occurrence of stress on the optical fiber coupler main body due to the contraction of the adhesive 5 at the time of adhesive fixing, and the optical fiber coupler optical In order to stabilize the characteristics and the environment resistance, it is preferable that the glass transition temperature is high and the adhesive strength is strong. When the optical fiber 3 is adhesively fixed to the protective case 1, the adhesive 5 can be accurately applied to a predetermined bonding position, and the adhesive 5 can sufficiently enter the gap between the optical fiber 3 and the inner wall of the protective case 1. Thus, those having an appropriate viscosity (1000 to 500,000 cps) are preferable, and those having a short curing time are preferable in order to improve production efficiency.

As such an adhesive 5, an epoxy adhesive, an acrylate adhesive, or a silicone rubber adhesive can be used.

In the present invention, various kinds of optical fibers 3 can be used as the optical fiber 3 constituting the main body of the optical fiber coupler. For example, a high refractive index core portion made of quartz to which a dopant such as germanium oxide is added. A single-mode fiber or a multi-mode fiber is preferably used, which is provided with a clad portion having a low refractive index made of, for example, quartz and surrounding the same.

Next, the attenuating optical fiber 7 of the present invention will be described with reference to FIG.

FIG. 2 is a diagram showing a cross section of the attenuating optical fiber 7 used in the optical fiber coupler of the present invention and its refractive index distribution. The core 7a for propagating light, the inner cladding 7b, the outer cladding 7c, and the low refractive index are shown. It consists of part 7d. Quartz glass is doped with GeO ₂ as a dopant in order to make a difference in refractive index between the core 7a and the inner cladding 7b.

The core diameter was 8 μm, the relative refractive index difference between the core 7a and the inner cladding 7b was 0.3%, and the cutoff wavelength at this time was about 1.1 μm. The core 7a is further doped with Co (cobalt) so that the intensity of the optical signal is attenuated. Co is an element suitable for optical attenuation in the wavelength band of 1.55 μm.

The inner clad 7b is a supplementary part of the clad mode, is substantially uniformly doped with Co as a dopant, and has an outer diameter of about 40 μm. However, the Co concentration at this time was about half of the concentration of the core 7a, and there was almost no change in the refractive index due to Co doping, so C
It was possible to reduce the Co doping amount of the core 7a by doping o.

The outer cladding 7c is made of pure silica glass, and its outer diameter, that is, the outer diameter of the attenuating optical fiber of the first embodiment is the same as that of a standard optical fiber.
μm. The low refractive index portion 7d has a width of 15 μm on the outside of the inner cladding 7b, that is, the inside of the outer cladding 7c.
It is a layer uniformly doped with (fluorine), and its concentration is such that the relative refractive index is approximately constant at -0.15%.

In the optical attenuating optical fiber of the first embodiment, the relative refractive index difference of the low refractive index portion 7d is such that the low refractive index portion 7d is separated from the core 7a, so that the optical signal propagating through the core 7a is Has little effect. This is a problem in the design of the optical fiber, and by determining the structure of the low refractive index portion 7d in consideration of the influence on the optical signal in advance, as in the dispersion-shifted fiber, the problem of the fiber structure does not occur. .

The relative refractive index difference of the low refractive index portion 7d applied to the outer cladding 7c has almost no effect on the optical signal propagating through the core 7a because the outer cladding 7c is separated from the core 7a.

Since the attenuation amount of the optical signal depends on the concentration of Co added in the attenuation optical fiber 7, several kinds are prepared in advance.
The attenuation optical fiber 7 is selected from several types according to the required attenuation amount, and the attenuation amount is finely adjusted by adjusting the length of the fiber.

Although the attenuation optical fiber 7 used in the optical fiber coupler 10 of the present invention has been described above, the present invention is not limited to this example, and the attenuation optical fiber formed so as to reduce the influence of the clad mode generated at the time of connection. Any structure can be used for the fiber 7.

Next, the connected state of the optical fiber coupler of the present invention is shown in FIG.

The optical fiber coupler 10 of the present invention uses a 1 × 2 coupler having one input port 6a and two output ports 6b and 6c, and the output port 6b inside the protective case 1 of the optical fiber coupler 10 is used. The attenuating optical fiber 7 is fused and fixed to the optical fibers on the side of 6c. An optical connector plug 11 is connected to each of the ports 6b and 6c, and an optical adapter 13 attached to the panel 12 is attached.
It is used internally by connecting to the optical connector plug 14 connected to the optical device.

Here, the optical signal P1 is input from the input port 6a, is demultiplexed into P2 and P3 in the coupling section 4, and then the respective lights are attenuated by the attenuating optical fibers 7 and 7a. It becomes P2 'and P3' and is transmitted. With such a configuration, the structure is simplified and the number of parts is reduced, so that the system itself is inexpensive.

Here, the attenuation optical fiber 7 is spliced and connected, and the splicing point is arbitrary, but in terms of reliability, it is embedded in the adhesive 5 as shown in FIG. Is desirable.

As described above, as the attenuating optical fiber 7, several kinds are prepared in advance, and the attenuating optical fiber 7 is selected from the several kinds according to the required attenuation amount. Fine adjustment of the attenuation amount is performed by adjusting the length of the fiber.

The length is preferably 1 mm to 15 mm, and if it is less than 1 mm, fusion splicing is difficult, and if it exceeds 15 mm, the optical fiber coupler main body itself becomes too large and cannot be used. Is.

The attenuation optical fiber 7 of the present invention may be provided at any of the input port 6a and the output ports 6b, 6c, but it is provided at the output port 6b, 6c side for the purpose of adjusting the power of the branched output. Is desirable.

Next, another embodiment of the optical fiber coupler of the present invention will be described with reference to FIG.

The optical fiber coupler 20 is composed of two optical fibers 3, has a coupling part 4 and a plurality of ports 6 extending from the coupling part 4, and the coupling part 4 is housed in the protective case 1. At least one portion of the optical fiber 3 connected from the coupling portion 4 to the port 6 in the protective case 1 is fixed inside the alignment sleeve 8, and the attenuation optical fiber 7 is detachably arranged inside the alignment sleeve 8.
An optical signal can be sent to the output ports 6b and 6c by connecting to the alignment sleeve 8 a simplified optical fiber connector 9 in which the attenuating optical fiber 7 is sandwiched and removable.

The advantage of this method is that, after the optical fiber coupler is assembled, the attenuation optical fiber 7 is used depending on the required attenuation amount.
Can be selected and incorporated.

Next, a method of manufacturing the optical fiber coupler of the present invention will be described with reference to FIG.

First, as shown in FIG. 5 (a), the coating 3c is removed at an intermediate portion of the optical fiber 3 and cut at a portion apart from the coupling portion 4, and an attenuating optical fiber 7 having a required attenuation amount is provided between them. Fusion splice to.

Next, as shown in FIG. 5B, the two optical fibers are aligned with the coupling portion 4 of the optical fiber 3,
It is heated by the burner 11 and fusion-stretched to obtain an optical fiber coupler body as shown in FIG.

Next, as shown in FIG. 5D, the optical fiber coupler body is fixed to the protective case 1 with the adhesive 5,
Lastly, the optical fiber coupler 10 of the present invention is provided by covering the protective case 1 with an upper lid 2 (not shown) and fixing the same.
Can be obtained.

Although the optical fiber coupler of the present invention has been described above as the one in which the coupling portion 4 is fused and stretched, the present invention is not limited to this and can be applied to a substrate having a waveguide formed therein.

[0056]

EXAMPLES Here, an experiment was conducted by the following method.

The optical fiber coupler 10 shown in FIG. 1 of the present invention.
Were prepared and connected by the method shown in FIG. As a comparative example, the conventional optical fiber coupler 30 shown in FIG. 6 was prepared, connected by the method shown in FIG. 8, and the reflected light returning to the input port was measured to obtain the reflection loss.

The optical fiber coupler is an optical branching device having a branching ratio of 50:50 using a single mode fiber. The adhesive 5 was an epoxy adhesive, and the protective case 2 and the upper lid 1 were made of quartz glass. The optical connector plugs and optical adapters used at the connection points adopted the SC type connector series.

Here, the optical fiber connector 10 of the present invention.
Then, a 20 dB attenuating optical fiber 7 was used on the output port 6b side, and a 10 dB attenuating optical fiber 7 was used on the output port 6c side.

Ten sets of each sample were prototyped, an optical signal was input from the input port 6a, and the light returning to the input port 6a was measured as reflection loss.

The results are shown in Table 1.

[0062]

[Table 1]

From these results, the conventional optical fiber coupler of FIG. 6 has an average value of reflection loss of 51.01 dB and a variation of 1.700 dB, whereas the optical fiber coupler of the present invention shown in FIG. The average value of 41.84d
B, the variation was 2.812 dB.

Therefore, by using the optical fiber coupler of the present invention, the number of connection points of the optical connector is reduced, and the light reflected and returned from the connector is further attenuated by the attenuating optical fiber. The reflection loss could be greatly reduced.

[0065]

As described above, according to the present invention, a plurality of optical fibers are provided, each optical fiber has a coupling portion and a plurality of ports extending from the coupling portion, and the coupling portion is provided in a protective case. An optical fiber coupler housed in the protective case, wherein the attenuating optical fiber is connected to at least one of the optical fibers connected to the port in the protective case, thereby simplifying the structure and reducing the number of parts. Therefore, the price of the system itself is reduced.

[Brief description of drawings]

1A is a vertical sectional view of an optical fiber coupler of the present invention, and FIG. 1B is a sectional view taken along line XX in FIG.

FIG. 2 is a diagram illustrating a refractive index distribution of an attenuation fiber used in the optical fiber coupler of the present invention.

FIG. 3 is a conceptual diagram showing a connection state of the optical fiber coupler of the present invention.

FIG. 4 is a conceptual diagram showing another embodiment of the optical fiber coupler of the present invention.

5A to 5D are diagrams showing a method for manufacturing an optical fiber coupler according to the present invention.

6A and 6B are cross-sectional views showing a conventional optical fiber coupler.

FIG. 7 is a sectional view showing a conventional optical attenuator.

FIG. 8 is a conceptual diagram showing a connection state of a conventional optical fiber coupler.

[Explanation of symbols]

1: Protective case 2: Top lid 3: Optical fiber 3a: Core 3b: clad 3c: coating 4: Connection part 5: Adhesive 6: Port 7: Optical fiber for attenuation 8: Alignment sleeve 9: Simple optical fiber connector 10: Optical fiber coupler 11: Optical connector plug 12: Panel 13: Optical adapter 14: Optical connector plug 20: Optical fiber coupler 30: Optical fiber coupler 40: Optical fixed attenuator 41: Optical fiber for attenuation 42: Ferrule 43: Sleeve 44: housing 51: Optical connector plug 52: Panel 53: Optical adapter 54: Optical connector plug

Claims (3)

[Claims] 1. An optical fiber coupler comprising a plurality of optical fibers, having a coupling part of each optical fiber and a plurality of ports extending from the coupling part, the coupling part being housed in a protective case. An optical fiber coupler, wherein an attenuating optical fiber is connected to at least one portion of an optical fiber connected from a coupling portion to a port in the protective case. 2. The optical coupler according to claim 1, wherein the attenuation optical fiber is fused and fixed between the optical fibers between the coupling portion and the port. 3. The optical fiber coupler according to claim 1, wherein the optical fiber extending from the coupling portion is fixed inside the alignment sleeve, and the attenuation optical fiber is arranged so that it can be incorporated inside the alignment sleeve.