JP2001228353A - Optical fiber connection structure and optical fiber communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connection structure of an optical fiber and an optical fiber communication system which can prevent a connection portion from being damaged by high propagating optical power. SOLUTION: In a connection structure of an optical fiber for connecting a connection optical fiber 110 and a transmission optical fiber 120 by physical contact, a core diameter enlarged region 114 having a core diameter enlarged at a connection end portion of each optical fiber 110 and 120; In addition to providing the linearity holding portion, the linearity holding portion for holding the linearity of the optical fibers 110 and 120 in a range including the core diameter enlarged regions 114 and is provided. Thereby, the intensity of the propagated light on the physical contact surface 101 can be reduced, so that the end face damage of the optical fiber can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber communication system for performing communication using an optical fiber as a transmission line, and more particularly to a connection structure between optical fibers.

[0002]

2. Description of the Related Art FIG. 11 shows a configuration diagram of a conventional optical fiber communication system. The present invention relates to a connector connection (connector connector) between a transmission fiber and an optical transmitter, an optical receiver, or an optical repeater. FIG.
1A shows a configuration near an optical transmitter or an optical repeater, FIG. 11B shows a configuration near an optical receiver or an optical repeater,
FIG. 11C shows the case where distributed Raman amplification is used (Reference: H. Suzuki et al., Proc. ECOC, PD, pp. 30-
31, 1999) is shown near the optical receiver or optical repeater.

In FIG. 11A, a signal light output from an optical transmitter or an optical repeater 1 through a connection fiber 2 connected to the optical transmitter or the optical repeater 1 passes through a connector connecting section 3. , Into the transmission fiber 4. However, it is obviously also possible to regard the connecting fiber 2 as part of the optical transmitter or optical repeater 1. FIG.
In (b), the signal output from the transmission fiber 4 passes through the connector connection section 3 and is introduced into the optical receiver or the optical repeater 1 via the connection fiber 2.

Further, in FIG. 11 (c), the propagation of signal light is the same as in FIG. 11 (b).
Excitation light emitted from the Raman excitation light source 5 installed on the optical receiver or the optical repeater propagates through the multiplexer 6 in a direction opposite to the signal light. The pump light is used for Raman amplification in the transmission fiber 4, passes through the connection fiber 2 and the connector connection part 3, and is introduced into the transmission fiber 4.
Instead of or simultaneously with distributed Raman amplification, remote pumping of rare-earth-doped fibers (Ref.
-P. Blondel et al., Proc. ECOC, PD, pp.34-35, 199
It is also possible to do 9). In that case, a remote excitation excitation light source is used instead of the Raman excitation light source or also as the Raman light source. In any case, the excitation light passes through the connector connection part 3 in addition to the signal light. FIG.
1 (c) shows, for simplicity, only the case of so-called backward pumping in which the pumping light propagates in the opposite direction to the signal light, but the so-called forward direction in which the pumping light propagates in the same direction as the signal light. Excitation is also possible.

FIG. 12 is a cross-sectional view of a configuration of a connector connecting portion according to the prior art. This is the case of forward pumping in FIG. 11C in which signal light and pumping light propagate in the same direction.
FIG. 12A shows a case of a normal physical contact (physical contact), FIG. 12B shows a case of a physical contact having an enlarged core region (reference: Japanese Patent Application Laid-Open No. 9-269433), and FIG. c) is the case of fusion splicing. In the figure, 10a, 10b, 10c are connecting fibers, 20a,
20b and 20c are transmission fibers, 11a, 21a and 11
b, 21b, 11c, 21c are cores, 12a, 22a,
12b, 22b, 12c, 22c are claddings, 13a,
23a, 13b, 23b, 13c, 23c are beam waists, 30a, 30b are ferrules, 40a, 40b,
40c is a connection surface.

FIGS. 12A and 12B show connecting fibers 10a and 10b and transmission fibers 20a and 20b.
Are physically contacted and connected by a connection method called physical contact. In physical contact, the end face of the fiber is slightly polished to a spherical surface so that the core of the fiber is stably contacted and connected. In the figure, the end face is represented by a plane for simplicity. Further, although there appears to be a gap in the connection surface in the figure, it is merely for convenience of showing the boundary between the two fibers, and actually, at least the core is connected without any gap.

The propagating light (signal light and pumping light) has a shape approximated by a Gaussian shape or the like as the light intensity distribution in the radial direction of the fiber, and a beam waist, which is a typical index of the spread, is used. Is shown in the figure. The beam waist is, for example, a position in the radial direction where the light intensity is equal to 1 / e (e is a natural logarithm) of the peak value.

In FIG. 12B, an enlarged core region 50a is provided near the physical contact surface for the purpose of reducing the intensity of the propagated light on the physical contact surface and preventing burn-in and damage of the fiber end surface. In FIG. 12 (c), the connection fiber and the transmission fiber are fusion-spliced for the purpose of preventing seizure and damage of the fiber end face on the physical contact surface.

[0009]

The physical contact surfaces shown in FIGS. 12 (a) and 12 (b) are located at the end surfaces of the optical connectors provided on the connecting fibers 10a and 10b and the transmission fibers 20a and 20b, and the system It is detached at the time of startup and repair. At the time of attachment / detachment, the end face of the optical connector is cleaned, but dust in the air and dust coming out of the adapter holding the connector may adhere to the end faces of the connection fiber and the transmission fiber and remain after cleaning. . Although depending on the degree of contamination of the connector, in general, when the power of the propagating light increases, the end faces of the connecting fiber and the transmission fiber are damaged, and excessive loss or reflection of the signal light occurs to cause system deterioration. For example, 17 dBm (50 mW) can be cited as an example of the propagation light power that causes damage to the dirty connector end face. This value is about the same as or less than the power of the signal light propagating in a large-capacity, long-distance wavelength multiplexing system or the power of pumping light used for distributed Raman amplification or remote pumping of a rare-earth-doped fiber. Therefore, if the connector is not sufficiently cleaned, there is a high probability that the connector end face will be damaged.

In FIG. 12B, the intensity of the propagated light on the physical contact surface is reduced by providing a core enlargement region 50a. However, conventionally, the core enlargement ratio is limited to about 2.5 times. The reason for the limitation is that the core enlarged area 50a is set in the ferrule 30b in a normal connector. In the core enlarged region 50a, the degree of confinement of the propagating light in the core is weak, so that if there is a bend in the fiber, a bend loss is likely to occur. On the other hand, in order to increase the core enlargement ratio, it is necessary to increase the length of the core enlargement region 50a in the fiber axial direction.

On the other hand, the propagation signal light power tends to increase with the recent progress in broadening the wavelength division multiplexing system.
Therefore, there is a need for a connector connection that allows a propagation signal light power that exceeds the propagation signal light power in the prior art system. In addition, the power of the pumping light used for the distributed Raman amplification and the remote pumping of the rare-earth-doped fiber is generally larger than the propagating signal light power by several hundreds.
It is necessary to have a connector connection part having a power of at least mW and a high allowable propagation light power. That is, the conventional techniques shown in FIGS. 12A and 12B have a drawback that the allowable propagation light power is limited or the connector connection is damaged by the high propagation light power.

On the other hand, the prior art shown in FIG. 12C in which a connecting fiber and a transmission fiber are fusion-spliced is employed in a submarine system, but in a land system, an optical repeater, an optical transmitter, and an optical receiver are used. From the viewpoint of securing maintenance operation, a connector connection of physical contact is used. That is, when a system is configured by fusion splicing in a terrestrial system, it is not possible to monitor propagation output light from a repeater or the like.
There has been a problem that maintenance operation operability such as maintenance operation such as a search for a fault point is restricted in the transmission fiber.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical fiber connection structure and an optical fiber communication system capable of preventing a connection portion from being damaged by high propagating optical power. To provide.

[0014]

In order to achieve the above object, according to the first aspect of the present invention, there is provided an optical fiber connection structure for connecting end faces of a pair of optical fibers by physical contact. In addition to providing a core diameter expansion region where the core diameter at the connection end face is larger than the core diameter in the transmission line, at least the core diameter expansion region so that the connection portion of the optical fiber keeps linearity in the fiber axis direction. The present invention proposes an optical fiber having an optical fiber linearity holding section for holding the range including the optical fiber.

According to the present invention, since the core diameter enlarged region is formed near the physical contact surface, the beam waist at the physical contact surface is significantly widened. Thus, the intensity of the propagated light on the physical contact surface can be reduced, so that it is possible to prevent the connection portion from being damaged even when the high-power propagated light is passed through the optical fiber. Also, since the optical fiber linearity holding portion holds at least a range including the core diameter enlarged region so that the connection portion of the optical fiber maintains the linearity in the fiber axis direction, the core diameter enlarged region is bent. Will not occur. Therefore, it is possible to reliably connect the optical fiber without increasing the bending loss.

According to a second aspect of the present invention, in the optical fiber connection structure according to the first aspect, the length of the optical fiber linearity holding portion in the fiber axis direction is 10 mm or more. Suggest features. According to a third aspect of the present invention, in the optical fiber connection structure according to any one of the first to second aspects, the diameter of the core diameter enlarged region at the end face of each of the optical fibers exceeds 25 μm. suggest.

According to a fourth aspect of the present invention, in the optical fiber connection structure according to any one of the first to third aspects, the core diameter enlarged region is formed on the transmission line side and the core diameter gradually increases toward the end face. The present invention proposes a structure having a gradually increasing region and a constant diameter region formed from the gradually increasing region to the end face and having a constant core diameter.

According to the present invention, the transmission path of the optical fiber and the fixed area of the enlarged core diameter area are optically and smoothly connected between the transmission path of the optical fiber and the fixed area of the enlarged core diameter area. Can be reliably reduced.

According to a fifth aspect of the present invention, in the optical fiber connection structure according to any one of the first to third aspects,
It is proposed that the core diameter expansion region is formed by fusion-splicing another optical fiber having a core diameter larger than the core diameter in the transmission path of the optical fiber.

According to the present invention, the core diameter changes sharply at the connection point between the transmission line of the optical fiber and another optical fiber. Light intensity can be reliably reduced.
Further, since the core diameter does not need to be gradually increased, the optical fiber can be connected at low cost.

According to a sixth aspect of the present invention, in the optical fiber connection structure according to any one of the first to third aspects,
It is proposed that the core diameter enlarged region has a clad diameter larger than a clad diameter in a transmission line of an optical fiber.

According to the present invention, since the clad diameter in the core diameter enlarged region is enlarged, it is possible to prevent loss due to scattering of propagating light and the like. In other words, as the core diameter increases and approaches the cladding diameter, the electric field of the propagating light has a magnitude that cannot be ignored near the outer boundary of the cladding, and scattering of the propagating light at the outer boundary of the cladding occurs. Although this is easy, this can be prevented in the present invention.

Further, according to the invention of claim 7, in the optical fiber connection structure in which the end faces of the pair of optical fibers are opposed to each other, the light refracting means is provided between the end faces of the pair of optical fibers corresponding to each optical fiber. We propose the one that is characterized by the arrangement.

According to the present invention, the propagating light emitted from the end face of one optical fiber has its beam waist and the light intensity distribution diameter expanded and collimated by the light refracting means arranged on the optical fiber side, and the propagating light is The light is condensed by the other light refracting means and coupled to the other optical fiber. As a result, the diameter of the light intensity distribution is remarkably enlarged on the surface between the light refracting means, which is the connection surface, and the intensity of the propagated light on the surface is reduced. This can prevent the connection portion from being damaged even when high-power propagation light is passed through the optical fiber.

As a preferred embodiment of the present invention, in the invention of claim 8, in the optical fiber connection structure according to claim 7, at least one of the end face of the optical fiber and the end face of the light refracting means on the optical fiber side. It is proposed to provide an outside air blocking region for blocking one or both surfaces from outside air. According to a ninth aspect of the present invention, in the optical fiber connection structure according to any one of the seventh and eighth aspects,
The present invention proposes an optical fiber in which a non-reflective dielectric film is deposited on an end face of the optical fiber. According to a tenth aspect of the present invention, there is provided the optical fiber connection structure according to any one of the seventh to ninth aspects, wherein an end face of the optical fiber is subjected to non-reflective oblique polishing. Further, in the invention of claim 11, any one of claims 7 to 10
In the optical fiber connection structure described in the above item, it is proposed that the input / output surface of the light refraction means is formed so as to be non-perpendicular to the traveling direction of light.

Further, according to the twelfth aspect of the present invention, an optical communication device such as an optical transmitter, an optical receiver, and an optical repeater, an optical fiber for transmission, and an optical fiber between the optical communication device and the optical fiber for transmission are installed. An optical branching coupler having three or more ports, wherein a first port of the optical branching coupler is fusion-spliced to a connection optical fiber connected to an optical transmitting device, and a second port of the optical branching coupler is provided. Wherein a transmission optical fiber is fusion-spliced, and a third port of the optical branch coupler is provided with monitoring means for monitoring an optical signal from an optical communication device or a transmission optical fiber. Suggest a system.

According to the present invention, since the optical branching coupler is fusion-spliced to the transmission optical fiber and the connection optical fiber, it is possible to prevent the occurrence of damage at the connection portion even through high-power propagated light. At the same time, the monitoring unit can monitor the propagated light.

As a preferred embodiment of the present invention, according to the invention of claim 13, in the optical fiber communication system according to claim 12, the monitoring means is connected to a third port of the optical branch coupler for monitoring optical communication. A light source having light introducing means for introducing light is proposed.

Further, according to the invention of claim 14, optical communication equipment such as an optical transmitter, an optical receiver and an optical repeater, a transmission optical fiber, an excitation light source for Raman amplification and remote excitation, etc.
12. A multiplexer for multiplexing the pump light from the pump light source and the signal light from an optical communication device or a transmission optical fiber, wherein the multiplexer and the pump light source are combined with each other. Or 1
An optical fiber communication system characterized in that the optical fiber communication system is connected by the optical fiber connection structure described in the section.

According to the present invention, since the connection structure of the optical fiber according to any one of claims 1 to 10 is used for the connection between the excitation light source and the multiplexer, the fusion splicing is not performed.
It is possible to prevent damage to the connection part even through high-power propagated light. Further, since the optical fibers are connected by physical contact instead of fusion splicing, maintenance work such as inspection, repair, and replacement of the excitation light source can be easily performed.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A connection structure of an optical fiber according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of an optical fiber connection structure according to the first embodiment, and FIG. 2 is a graph illustrating a relationship between a light intensity distribution diameter and a propagation light intensity.

This optical fiber connection structure is used for a connector for connecting optical fibers to each other, and is used for connection to optical communication equipment (not shown) such as an optical transmitter, an optical receiver, and an optical repeater. The optical fiber 110 for transmission and the optical fiber 120 for transmission are optically connected by physical contact (physical contact) at the end face. The end faces of the connection optical fiber 110 and the transmission optical fiber 120 are slightly polished to spherical surfaces. In FIG. 1, reference numerals 111 and 121 denote cores of optical fibers, 112 and 122 denote claddings, 11
Numeral 3, 123 indicates a propagating light beam waist. In FIG. 1, the end face of each optical fiber is represented by a plane for simplicity. Although FIG. 1 shows that there is a gap between the end faces of the optical fibers, the boundary between the two optical fibers is simply shown for the sake of convenience. Actually, at least the core is connected without any gap.

At the ends of the connection optical fiber 110 and the transmission optical fiber 120, there are formed core diameter enlarged regions 114 and 124 in which the core diameter gradually increases toward the end face. The light intensity at the physical contact surface 101 of each optical fiber depends on the radial position of the optical fiber,
In general, the same radial direction intensity distribution is inversely proportional to the square of the light intensity distribution diameter (interval between beam waist radial direction positions). The graph of FIG. 2 shows the dependence of the propagation light intensity and the light intensity distribution diameter. As shown in FIG. 2, when the light intensity distribution diameter is doubled, for example, the propagation light intensity is reduced to one fourth. In the present embodiment, the core diameter enlarged region 114,
By forming 124, the diameter of the light intensity distribution on the physical contact surface 101 is significantly enlarged, thereby reducing the intensity of the propagated light. Each of the optical fibers 110 and 1 is reduced by reducing the intensity of the propagated light on the physical contact surface 101.
20 avoids damage to the end face.

The method of forming the core diameter enlarged regions 114 and 124 is described in a reference (S. Sudo ed., "Optical Fiber Ampl."
ifiers ", Artech House Inc., Chapter 5, 1997. That is, the cores 111 and 121 of the connecting optical fiber 110 and the transmitting optical fiber 120 are silica doped with germanium (Ge), 11
It is assumed that 2 and 122 are silica containing no Ge. The core diameter enlarged regions 114 and 124 are heated so that Ge diffuses into the clad and the diffusion increases toward the physical contact surface 101 position. The beam waist position changes corresponding to the Ge-containing region. Such processing technology is called TEC (Thermally Expanded Cored).
e) Technology.

The connection between the connection optical fiber 110 and the transmission optical fiber 120 is kept linear by a linearity holding section 130 such as a ferrule. Here, the characteristic point is that the linearity holding portion 130 is provided at least in the core diameter enlarged regions 114 and 12 of both optical fibers 110 and 120.
In order to prevent the fiber from being bent at the portion where 4 is formed, the length is extended in the fiber axis direction as compared with the conventional one.

Examples of the transmission optical fiber 120 include a dispersion-shifted fiber (DSF) and a 1.3 μm zero-dispersion fiber (CF). The connection optical fiber is usually the same type of fiber as the transmission optical fiber 120. Used. Mode field diameter (MFD) of DSF and CF
Are about 8 μm and about 10 μm, respectively. The light intensity distribution diameter (MID) is 1.41 times smaller than that of the MFD, and is about 5.7 μm and about 7.0 for DSF and CF, respectively.
1 μm. Incidentally, the MID shows a value close to the diameter of the core. The light intensity distribution diameter at the physical contact surface 101 of the core diameter enlarged regions 114 and 124 of the connection optical fiber 110 and the transmission optical fiber 120 is preferably 25 μm or more. For example, for DSF and CF, their 1
It is about 57 μm and about 71 μm which are 0 times. This allows
The propagation light intensity at the physical contact surface 101 is 10
It becomes 1/0, and a remarkable improvement effect can be obtained.

In the present embodiment, the total length of the core diameter enlarged regions 114 and 124 in the fiber axial direction is about 100 mm. Further, the linearity holding unit 13
In the case of 0, a connector in which the length of the ferrule in the fiber axial direction was extended was created by changing the size of the current connector. Here, the length of the linearity holding portion such as a ferrule in the related art is about 5 mm. In the present embodiment, the size of the linearity holding portion 130 is about 60 mm per one connector, and the total size of the connectors on both sides is about 1 mm.
20 mm. That is, the lengths of the core diameter enlarged regions 114 and 124 in the fiber axis direction are equal to or smaller than the size of the linearity holding unit 130 such as a ferrule. In addition, deterioration such as excess loss due to the enlargement of the core region can be ignored.

As described above, in the optical fiber connection structure according to the present embodiment, since the core diameter enlarged regions 114 and 124 are formed near the physical contact surface 101, the beam waist at the physical contact surface 101 is remarkable. Spread. Thus, the intensity of the propagation light on the physical contact surface 101 can be reduced, so that it is possible to prevent the connection portion from being damaged even when the high-power propagation light is passed through the optical fiber.

Further, the linearity maintaining section 130 is provided so that the connecting portion of each of the optical fibers 110 and 120 maintains linearity in the axial direction of the fiber.
Since the range including 4 and 124 is maintained, the core diameter enlarged regions 114 and 124 are not bent. Thus, the connection of the optical fiber can be reliably performed without increasing the bending loss.

(Second Embodiment) An optical fiber connection structure according to a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a configuration diagram of an optical fiber connection structure according to the second embodiment.

This optical fiber connection structure is used in a connector for connecting optical fibers to each other, and is used for connection to optical communication equipment (not shown) such as an optical transmitter, an optical receiver, and an optical repeater. The optical fiber 210 for transmission and the optical fiber 220 for transmission are optically connected to each other by making the end faces physically contact (physical contact). The end faces of the connection optical fiber 210 and the transmission optical fiber 220 are slightly polished to spherical surfaces. In FIG. 3, reference numerals 211 and 221 denote cores of optical fibers, 212 and 222 denote claddings,
3, 223 indicates a propagating light beam waist. In FIG. 3, for the sake of simplicity, the end face of each optical fiber is represented by a plane. Although FIG. 3 shows that there is a gap between the end faces of the optical fibers, the boundary between the two optical fibers is simply shown for the sake of convenience. Actually, at least the core is connected without any gap.

At the ends of the connection optical fiber 210 and the transmission optical fiber 220, the core diameter of the end face is
Core diameter enlargement regions 214 and 224 formed larger than the core diameter in the transmission lines 10 and 220 are formed. The core diameter enlarged areas 214 and 224 are formed on the transmission line side of the optical fibers 210 and 220, and the core diameters are gradually increased in the end face direction.
a and constant diameter regions 214b and 224 formed from the gradually increasing regions 214a and 224a to the end face and having a constant core diameter.
b. The constant diameter regions 214b and 224b are made of another optical fiber having a larger core diameter than the transmission path of each of the optical fibers 210 and 220. As a result, the core diameters at the end faces of the core diameter expansion regions 214 and 224, which are the physical contact surfaces 201, are significantly larger than the core diameters in the transmission paths of the optical fibers 210 and 220. Therefore, similarly to the first embodiment, the light intensity distribution diameter on the physical contact surface 201 is significantly enlarged, so that the propagation light intensity is reduced.
, And 220 are avoided.

Here, as an example of the optical fiber constituting the transmission path portion (portion excluding the core diameter enlarged region) of each of the optical fibers 210 and 220 and the same diameter regions 214b and 224b, a dispersion shift fiber (DSF) and an optical fiber Fibers having an intensity distribution diameter of about 57 μm can be mentioned. At this time, in the present embodiment, the light intensity distribution diameter on the physical contact surface 201 is ten times as large as that of the conventional connector connection portion without the core diameter enlarged regions 214 and 224. Therefore, the intensity of the propagating light on the physical contact surface 201 is reduced to 1/100.
0 and 220 have a remarkable improvement effect on the end face damage prevention.

The connection between the connection optical fiber 210 and the transmission optical fiber 220 is kept linear by a linearity holding section 230 such as a ferrule. The length of the linearity maintaining portion 230 in the fiber axis direction is the core diameter enlarged region 21.
4 and 224 are set to be larger than the fiber axial lengths. In the present embodiment, the fiber axis length of the linearity holding section 230 is set to 120 mm. In addition, deterioration such as excess loss due to the enlargement of the core region can be ignored.

As described above, the connection structure of the optical fiber according to the present embodiment can reduce the intensity of the propagation light on the physical contact surface 201 similarly to the effect of the first embodiment. It is possible to prevent the connection portion from being damaged even through high-power propagated light. Other effects are similar to those of the first embodiment.

In this embodiment, the same diameter regions 214b and 224b made of optical fibers are formed one by one in each of the core diameter enlarged regions 214 and 224. However, two or more may be formed. .

(Third Embodiment) An optical fiber connection structure according to a third embodiment of the present invention will be described with reference to FIG. FIG. 4 is a configuration diagram of an optical fiber connection structure according to the third embodiment.

This optical fiber connection structure is used in a connector for connecting optical fibers to each other, and is used for connection to optical communication equipment (not shown) such as an optical transmitter, an optical receiver, and an optical repeater. The optical fiber 310 for transmission and the optical fiber 320 for transmission are optically connected by making the end faces physically contact (physical contact). The end surfaces of the connection optical fiber 310 and the transmission optical fiber 320 are slightly polished to spherical surfaces. In FIG. 4, 311 and 321 are the cores of the optical fibers, 312 and 322 are the claddings,
Reference numeral 3,323 denotes a propagating light beam waist. In FIG. 4, the end face of each optical fiber is represented by a plane for simplicity. Also, in FIG. 4, although there is a gap between the end faces of the optical fibers, the boundary between the two optical fibers is merely shown for convenience, and the cores are actually connected without any gap at least in the core.

At the ends of the connection optical fiber 310 and the transmission optical fiber 320, the core diameter of the end face is
Core diameter enlarged regions 314 and 324 are formed which are larger than the core diameters in the transmission paths 10 and 320. Each of the expanded core diameter regions 314 and 324 has another optical fiber 314 a and 324 a having a larger core diameter than the core diameter in the transmission path of each of the optical fibers 310 and 320.
Are fusion-spliced. Therefore, each of the optical fibers 310 and 320 is provided with the core diameter enlarged regions 314 and 3.
24, the beam waist and the light intensity distribution diameter are sharply expanded.

Here, the core diameter enlarged regions 314 and 324
Examples of the optical fibers 314a and 324a that constitute the optical fiber include a dispersion-shifted fiber (DSF) and a fiber having a light intensity distribution diameter of about 11.4 μm. At this time, in the present embodiment, the light intensity distribution diameter on the physical contact surface 301 is twice as large as that of the conventional connector connection portion in which the core diameter enlarged regions 314 and 324 are not provided. Therefore, the intensity of the propagating light on the physical contact surface 301 is reduced to 、, which has a remarkable effect of preventing the end faces of the optical fibers 310 and 320 from being damaged. The excess loss of the signal light at the fusion point between the core diameter enlarged regions 314 and 324 is about 1 dB, and there is some deterioration.

The connection between the connection optical fiber 310 and the transmission optical fiber 320 is kept linear by a linearity holding section 330 such as a ferrule. The length of the linearity holding section 330 in the fiber axis direction is not particularly limited, unlike the second embodiment. For example, core diameter enlarged area 3
With the length of 14 and 324 being 10 mm, a connector of normal size can be used.

As described above, the optical fiber connection structure according to the present embodiment can reduce the intensity of propagating light on the physical contact surface 301 as in the effects of the first and second embodiments. Further, even when high-power propagating light passes through the optical fiber, it is possible to prevent occurrence of damage at the connection portion. Further, as compared with the second embodiment, there is no need to provide a gradual increase region in which the core diameter gradually increases, so that there is an advantage that the configuration is simple and can be realized at low cost. Other effects are similar to those of the first embodiment.

In this embodiment, each of the core diameter enlarged regions 314 and 324 is connected to one optical fiber 314.
a and 324a, but may be formed by two or more optical fibers.

(Fourth Embodiment) An optical fiber connection structure according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a configuration diagram of an optical fiber connection structure according to the fourth embodiment.

This optical fiber connection structure is used in a connector for connecting optical fibers to each other, and is used for connection to optical communication equipment (not shown) such as an optical transmitter, an optical receiver, and an optical repeater. The optical fiber 410 for transmission and the optical fiber 420 for transmission are optically connected by physical contact (physical contact) at the end face. The end surfaces of the connection optical fiber 410 and the transmission optical fiber 420 are slightly polished to spherical surfaces. In FIG. 5, reference numerals 411 and 421 denote cores of optical fibers, 412 and 422 denote claddings,
Reference numeral 3,423 denotes a propagating light beam waist. In FIG. 5, for the sake of simplicity, the end face of each optical fiber is represented by a plane. Further, in FIG. 5, although there is a gap between the end faces of the optical fibers, the boundary between the two optical fibers is simply shown for convenience. Actually, at least the core is connected without any gap.

At the ends of the connection optical fiber 410 and the transmission optical fiber 420, similarly to the first embodiment, core diameter enlarged regions 414 and 424 where the core diameter gradually increases gradually toward the end face are formed. Have been. This embodiment differs from the first embodiment in that the clad diameters of the core diameter enlarged regions 414 and 424 are enlarged. This is because, when the enlarged core diameter approaches the clad diameter, the electric field of the propagating light comes to have a magnitude that cannot be ignored near the outer boundary of the cladding, and is caused by scattering of the propagating light at the outer boundary of the cladding. This is because the loss cannot be ignored. In the present embodiment, the core diameter enlarged regions 414 and 4
By increasing the cladding diameter of 24, loss due to scattering of propagating light or the like is eliminated.

In the present embodiment, each connection optical fiber 4
The light intensity distribution diameter (MID) of the transmission path portion (excluding the core diameter enlarged region) of the transmission optical fiber 10 and the transmission optical fiber 420 is the same as that of the first embodiment in the DSF MID (about 5.7 μm).
m). The enlarged MID on the physical contact surface 401 was about 80 μm. Normal cladding diameter is 12
In the present embodiment, the core diameter enlarged region 4 is 5 μm.
MID of about 80 mm with cladding diameters of 12 and 424
Of which the loss due to scattering or the like is negligible.
μm. Therefore, M at the physical contact surface 401
The ID is 14 times that of the prior art, and the propagation light intensity is 196
It's a fraction.

Note that the configuration of the linearity holding section 430 is the same as in the first embodiment, and a description thereof will not be repeated.

As described above, the connection structure of the optical fiber according to the present embodiment can reduce the intensity of the propagated light on the physical contact surface 401 similarly to the effect of the first embodiment. It is possible to prevent damage to the connection part even through high-power propagated light. Other effects are similar to those of the first embodiment.

(Fifth Embodiment) An optical fiber connection structure according to a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a basic configuration diagram of an optical fiber connection structure according to the fifth embodiment, FIG. 7 is a detailed configuration diagram of an optical fiber connection structure according to the fifth embodiment, and FIG. 8 is a fifth embodiment. FIG. 10 is a detailed configuration diagram of an optical fiber connection structure according to another example of the embodiment.

As shown in FIG. 6, this optical fiber connection structure is used in a connector for connecting optical fibers to each other, and is connected to a connection optical fiber 510 for connection to an optical communication device (not shown). The optical fibers 520 are arranged with their end faces facing each other at a predetermined distance, and lenses 514 and 524 as light refracting means are arranged on the connection surface side of the optical fibers 510 and 520. The propagation light emitted from the connection optical fiber 510 is
The beam waist and the light intensity distribution diameter are expanded by the lens 514 disposed on the side 10, and the expanded propagation light is condensed by the lens 524 disposed on the transmission optical fiber 520 side, and is coupled to the transmission optical fiber 520. are doing. Thus, also in the present embodiment, the light intensity distribution diameter at the connection surface is enlarged to reduce the intensity of the propagated light, thereby avoiding damage to the end faces of the optical fibers 510 and 520. Here, a spherical lens (or a ball lens) or the like is used as the lenses 514 and 524. Lenses 514 and 5
Numeral 24 denotes supporting parts 515 and 525 such as ferrules, respectively.
And a guide portion 53 such as an external split sleeve.
It is kept parallel at 0. That is, a connection portion similar to a normal connector connection using a connector having a ferrule and an adapter having a split sleeve can be formed.

In FIG. 6, 511 and 521 indicate cores, 512 and 522 indicate claddings, and 513 and 523 indicate propagating light beam waists.

The connection structure of the optical fiber will be described in detail with reference to FIG. 7, the same components as those of FIG. 6 are denoted by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 7, in this optical fiber connection structure, since the connection optical fiber 510 and the transmission optical fiber 520 have a boundary surface in the air instead of a connection such as physical contact. The end faces 510a and 520a are obliquely polished to prevent Fresnel reflection at the glass-air interface. Further, in order to reduce transmission loss due to reflection at the boundary surface, the end faces 510a and 520a of the optical fibers 510 and 520 and the lens 51
The 4 and 524 spherical surfaces 514a and 524a are non-reflection coated. Further, the end face 510a having a large propagation light intensity
In order to prevent dust and the like in the air from adhering to the spherical surfaces of the lenses 514 and 524 facing the end faces, the end faces 5a and 5
Sealing regions 515a and 525a are provided in which regions in the directions of 10a and 520a are hermetically sealed.

The details of the optical fiber connection structure according to another example will be described with reference to FIG. In FIG. 8, FIG.
The same components as those described above are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 8, the connection structure of this optical fiber is similar to that shown in FIG. 7, except that cylindrical lenses 516 and 526 are used as lenses as light refraction means. End face 5 of this cylindrical lens 516
16a and 516b and the end face 52 of the cylindrical lens 526
6a and 526b are obliquely polished and non-reflective coated similarly to the connection optical fiber 510 and the transmission optical fiber 520. Thus, cylindrical lenses 516 and 52
Since the end face of No. 6 is obliquely polished, it is possible to remove the residual reflection from the lens to the optical fibers 510 and 520, which has occurred in the configuration shown in FIG. Typical values of the residual reflection in the configuration shown in FIG.
Although about 30 dB is not necessarily sufficient, FIG.
The typical value of the residual reflection in the configuration shown in FIG. 7 is -40 dB or less, which is a sufficiently low value.

Examples of the connection optical fiber 510 and the transmission optical fiber 520 according to the present embodiment shown in FIGS. 6 to 8 include a dispersion shift fiber (DSF), and the light intensity distribution diameter thereof. (MID) is about 5.7μ
m. The MID of the propagating light beam collimated by the lens is about 570 μm. Therefore, connection surface 5
01, the MID is 100 times, and the light intensity of the propagating light is 10
One thousandth, a significant improvement is obtained. In addition, the light intensity of the lens surface that comes into contact with the outside air on the connection surface 501 side is sufficiently small, and there is no possibility that the lens is damaged. The lens is small (1 mm or less in diameter) and can be stored in a normal connector. Further, the connection surface portion can be configured by, for example, abutting portions of the outer frame like a normal connector. Further, the insertion loss of the connector connection portion using this lens with respect to signal light and pump light can be about 1 dB or less, which is about the same as the insertion loss of the prior art.

(Sixth Embodiment) An optical fiber communication system according to a sixth embodiment of the present invention will be described with reference to FIG. FIG. 9 is a configuration diagram of the optical fiber communication system according to the sixth embodiment.

In this optical fiber communication system, an optical communication device 601 is provided between a connection optical fiber 602 and a transmission optical fiber 603 connected to an optical communication device 601 such as an optical transmitter, an optical receiver, or an optical repeater. A branch coupler 604 having a fiber pigtail for monitoring output light from the optical fiber 603 and monitoring a failure of the transmission optical fiber 603 is installed. The fiber pigtail of the branch coupler 604 is connected to each connection optical fiber 602 and the transmission optical fiber 602. Optical fiber 603
And fusion bonding. That is, the branch coupler 604 branches a part of the propagating light, and makes it possible to multiplex external monitoring light for transmission to the transmission optical fiber 603 for searching for a fault.

More specifically, the branch coupler 604 is, for example, a four-port fiber coupler having a branching ratio of 1 to 10, and has a non-reflection terminal installed in order to remove induced noise due to end face reflection of signal light. Since the non-reflection terminal can be realized by a connector with an oblique polishing, the propagation light can be extracted from the non-reflection terminal monitor port or external light can be introduced into the transmission optical fiber. 9A, the monitor port 604a is used to monitor the wavelength and power of the signal light from the optical communication device 601 which is a transmitter or a repeater.
Using b, external light for searching for a fault point is multiplexed to the transmission optical fiber 603. In FIG. 9B, the wavelength and power of the pump light from the Raman pump light source 605 are monitored using the monitor port 604a.
4b, the external light is used to search for a fault point or the like.
06, it is possible to multiplex with the transmission optical fiber 603 and to monitor the wavelength and power of the signal light emitted from the transmission optical fiber 603. Note that the branch coupler 604 is not limited to a four-port coupler, but may use a three-port coupler or the like according to the content of the monitor.

As described above, in the optical fiber communication system according to the present embodiment, since the branch coupler 604 is fusion-spliced between the connection optical fiber 602 and the transmission optical fiber 603, a high-power propagating light And the easiness of monitoring the communication system and the like can be realized.

(Seventh Embodiment) An optical fiber communication system according to a seventh embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 10 is a configuration diagram of the optical fiber communication system according to the seventh embodiment.

This optical fiber communication system is suitable to be applied to Raman amplification using a high-power pump light or a system using a remote pump light source. In this optical fiber communication system, as shown in FIG. 10, a multiplexer 705 for multiplexing pump light and signal light and a transmission optical fiber 703 are fusion-spliced. An optical fiber 702 for connection from an optical communication device 701 which is a receiver or a repeater and a multiplexer 70
The fiber pigtails 5 are connected by a normal connector 707. Conventionally, fusion splicing is used for the connection between the multiplexer 705 and the Raman excitation light source 704, but in this embodiment, an optical fiber using the connector described in the first to fifth embodiments is used. A connection structure is used. Thereby, the light intensity is reduced at the connection surface between the multiplexer 705 and the Raman excitation light source 704, so that damage to the connector due to the high-power excitation light can be avoided. Further, when the pumping light source 704 is out of order, the pumping light source can be easily replaced with an expensive pumping light source. That is, the maintainability is improved. The connection fiber 7 from the optical communication device 701
02 and the fiber pigtail of the multiplexer 705 may be connected using the optical fiber connection structure using the connector described in the first to fifth embodiments.

In the first to fifth embodiments, the case where the optical fiber connection structure is employed in the connector for connecting the transmission optical fiber and the connection optical fiber has been described. However, the present invention is not limited to this. That is, the optical fiber connection structure according to the present invention can be applied to a place where a high-power signal light and pump light pass and a connector connection is performed without performing fusion splicing. For example, the present invention can be applied to a connection portion between components that require a connector to be attached and detached in an optical amplifier.

[0075]

As described above in detail, according to the optical fiber connection structure according to the present invention, the allowable connection power is limited or the connector connection portion due to the high transmission power, which is a problem in the prior art. This can eliminate the problem of causing damage to the device. That is, since the intensity of the propagated light at the connection portion of the optical fiber can be reduced, it is possible to prevent the connection portion from being damaged even when high-power propagated light is passed through the optical fiber.

Further, according to the optical fiber communication system of the present invention, it is possible to transmit a high-power propagated light while maintaining high maintainability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical fiber connection structure according to a first embodiment;

FIG. 2 is a graph illustrating a relationship between a light intensity distribution diameter and a propagating light intensity.

FIG. 3 is a configuration diagram of an optical fiber connection structure according to a second embodiment;

FIG. 4 is a configuration diagram of an optical fiber connection structure according to a third embodiment.

FIG. 5 is a configuration diagram of an optical fiber connection structure according to a fourth embodiment.

FIG. 6 is a basic configuration diagram of an optical fiber connection structure according to a fifth embodiment.

FIG. 7 is a detailed configuration diagram of an optical fiber connection structure according to a fifth embodiment.

FIG. 8 is a detailed configuration diagram of an optical fiber connection structure according to another example of the fifth embodiment.

FIG. 9 is a configuration diagram of an optical fiber communication system according to a sixth embodiment.

FIG. 10 is a configuration diagram of an optical fiber communication system according to a seventh embodiment.

FIG. 11 is a configuration diagram of a conventional optical fiber communication system.

FIG. 12 is a cross-sectional view of a configuration of a conventional connector connecting portion.

[Explanation of symbols]

110, 210, 310, 410, 510, 602, 7
02 ... optical fiber for connection, 120, 220, 320, 4
20,520,603,703 ... transmission optical fiber, 1
14, 124, 214, 224, 314, 324, 41
4,424: core diameter enlarged region, 130, 230, 33
0, 430: linearity holding unit, 601, 701: optical communication device, 604: branch coupler, 605, 704: Raman excitation light source, 606, 705: multiplexer

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H04B 10/135 10/13 10/12 (72) Inventor Katsumi Iwazuki 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 2H036 MA01 NA01 2H037 AA01 BA31 CA05 DA04 DA06 2H050 AC83 AC86 AD16 5K002 AA06 BA33 CA13 EA03 EA06 FA02

Claims (14)

[Claims] In an optical fiber connection structure for connecting end faces of a pair of optical fibers by physical contact, a core diameter at a connection end face of each optical fiber is larger than a core diameter at a transmission path. A light having a core diameter enlarged region, and an optical fiber linearity holding portion that holds at least a region including the core diameter enlarged region so that the connection portion of the optical fiber keeps linearity in the fiber axis direction. Fiber connection structure. 2. The optical fiber connection structure according to claim 1, wherein a length of the optical fiber linearity holding portion in a fiber axis direction is 10 mm or more. 3. The optical fiber connection structure according to claim 1, wherein a diameter of the core diameter enlarged region at an end face of each of the optical fibers exceeds 25 μm. 4. The core diameter expanding region has a gradually increasing region formed on the transmission line side and having a core diameter gradually increasing toward the end face, and a constant diameter region formed from the gradually increasing region to the end face and having a constant core diameter. 4. The method according to claim 1, wherein:
The connection structure of the optical fiber according to the item. 5. The optical fiber according to claim 1, wherein the core diameter enlarged region is formed by fusion splicing another optical fiber having a core diameter larger than the core diameter in the transmission line of the optical fiber.
4. An optical fiber connection structure according to claim 1. 6. The optical fiber connection structure according to claim 1, wherein the core diameter enlarged region has a clad diameter larger than a clad diameter in a transmission line of the optical fiber. 7. An optical fiber connection structure in which end faces of a pair of optical fibers are opposed to each other, wherein a light refracting means is arranged between the end faces of the pair of optical fibers so as to correspond to each optical fiber. Optical fiber connection structure. 8. An outside air blocking area for blocking at least one or both of the end face of the optical fiber and the end face of the light refracting means on the optical fiber side from outside air. Optical fiber connection structure. 9. The optical fiber connection structure according to claim 7, wherein a non-reflective dielectric film is deposited on an end face of the optical fiber. 10. The optical fiber connection structure according to claim 7, wherein an end face of said optical fiber is subjected to non-reflective oblique polishing. 11. The light according to claim 7, wherein an incident / exit surface of the light refracting means is formed to be a surface that is non-perpendicular to a traveling direction of the light. Fiber connection structure. 12. An optical communication device such as an optical transmitter, an optical receiver, or an optical repeater, a transmission optical fiber, and three or more ports provided between the optical communication device and the transmission optical fiber. A connection optical fiber for connecting to an optical transmitting device is fusion-spliced to a first port of the optical branch coupler, and a transmission optical fiber is connected to a second port of the optical branch coupler. An optical fiber communication system, comprising: a fusion splicing unit; and a third port of the optical branching coupler provided with monitoring means for monitoring an optical signal from an optical communication device or a transmission optical fiber. 13. The optical fiber communication system according to claim 12, wherein said monitoring means has an optical introduction means for introducing light for optical communication monitoring to a third port of said optical branch coupler. 14. An optical communication device such as an optical transmitter, an optical receiver, or an optical repeater, a transmission optical fiber, an excitation light source for Raman amplification or remote excitation, and excitation light and light from the excitation light source. The optical fiber according to any one of claims 1 to 11, further comprising: a multiplexer configured to multiplex signal light from a communication device or a transmission optical fiber, wherein the multiplexer and the pump light source are connected to each other. An optical fiber communication system characterized by being connected by a structure.