JP2004134660A - Optical amplification transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplification transmission system capable of preventing a fiber fuse from proceeding by means of providing a fuse stopper in an optical fiber transmission path equipped with an optical wave multiplexer/demultiplexer. <P>SOLUTION: The optical amplification transmission system 10 includes an input side signal transmission path 12 for transmitting signal light, an excitation light transmission path 20 that is branched from the input side signal transmission path 12 via a photo-coupler 18 and transmits the excitation light combining with the signal light to amplify the signal light, an excitation light source 24 that is used for the optical amplification and outputs the excitation light to the excitation light transmission path 20, and a fuse stopper 26 that is inserted into at least one location among locations that sandwich the photo-coupler 18 from both sides thereof in the input side signal transmission path 12. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical amplification transmission system that amplifies and transmits signal light.
[0002]
[Related background art]
This type of optical amplification transmission system includes an input-side signal light transmission line for transmitting signal light, an output-side signal light transmission line connected to the input-side light signal transmission line via an optical coupling unit, and an input-side signal light. An optical amplifier provided in the middle of the optical transmission line, and both the input-side and output-side signal light transmission lines are made of optical fibers.
More specifically, the optical amplification unit includes an excitation light transmission line branched from the input-side signal light transmission line via the optical coupling unit, and an excitation light source connected to the excitation light transmission line via the optical coupling unit. The signal light is amplified by multiplexing the signal light with the pump light from the pump light source on the optical transmission line. Here, the excitation light source is composed of an excitation laser light source and outputs laser light as excitation light, and the excitation light transmission line is also composed of an optical fiber.
[0003]
In order to prevent the fiber fuse from advancing in the optical transmission line, for example, an optical component including a component fiber is provided in the optical transmission system. The component fiber has a larger and constant core diameter than the optical fiber of the signal light transmission path, so that the threshold of the optical power for generating the fiber fuse is larger than the optical fiber of the signal light transmission path and smaller than a predetermined value. (For example, see Patent Document 1).
[0004]
Alternatively, for example, in a component fiber, the core diameter is formed so as to gradually increase, and the threshold of the optical power in the longitudinal direction of the fiber is increased by the expansion of the core diameter (for example, see Patent Document 1). .
Due to such an increase in the core diameter of the component fiber, the occurrence threshold of the fiber fuse in the expanded core is larger than the power of the signal light propagating through the core. Therefore, the progress of the fiber fuse that has propagated through the signal light transmission line is prevented at the component fiber portion.
[0005]
[Patent Document 1]
U.S. Pat. 200221554
[0006]
[Problems to be solved by the invention]
In the case of the optical amplification transmission system described above, it is necessary to greatly amplify the signal light in order to secure a long transmission distance of the signal light, and the pump light or the amplified signal light has a high optical power.
When pumping light or signal light with high optical power propagates through the transmission path, a situation in which the core of the optical fiber in the transmission path is melted, that is, a so-called fiber fuse occurs, particularly at the optical coupling section described above. Once such a fiber fuse has been generated, it may not only stay at the place where the fiber fuse is generated but also travel in the length direction of the optical fiber, possibly causing damage to the optical amplification section, that is, the entire optical amplification transmission system.
[0007]
The phenomenon of the fiber fuse described above will be described in detail. When high-power pumping light or signal light is propagated, the optical energy density at the end face of the optical coupling part is necessarily increased. Therefore, if foreign matter such as dirt or fine scratches is present in the optical coupling portion, heat is locally generated by concentration of light energy, and the heat is used as a trigger to generate a fiber fuse. When the heat generation is large, the core is melted, and the melting of the core proceeds in the longitudinal direction of the optical fiber toward the light source. When the melting of the core reaches the optical amplifying unit, the optical amplifying unit is destroyed, not only the function of the optical amplifying transmission system is impaired, but also the restoration of the system becomes more difficult, resulting in a large loss. Will be.
[0008]
A technique for preventing the progress of such a fiber fuse is disclosed, for example, in the above-mentioned patent document. The disclosure of the patent document is to prevent the propagation of the fiber fuse by increasing the core diameter of the component fiber as compared with the optical fiber of the transmission line and increasing the threshold value of the occurrence of the fiber fuse in the component fiber. .
[0009]
However, when such a component fiber is used, there are the following problems.
(1) Since the component fiber is provided in the middle of the optical fiber of the transmission line so as to be directly connected to the optical fiber without interruption, the fiber fuse generated in the transmission line and propagated to the component fiber is the component fuse. It can propagate directly in the fiber. That is, even if the component fiber has a core diameter exceeding the optical power threshold value for preventing the fiber fuse, even if the fiber fuse propagates along the fiber fuse propagation path inside the component fiber core, for example, a foreign matter trigger If there are scratches or flaws, the fiber fuse may propagate further through the component fiber through the trigger.
[0010]
(2) When the core diameters of the component fiber and the optical fiber of the transmission line are different from each other, their mode field diameters are generally different from each other. When optical fibers having different mode field diameters are connected to each other, a connection loss occurs. I do.
(3) The optical fibers having different core diameters, that is, the component fiber and the optical fiber of the transmission line, need to be fusion-spliced. The usual method or condition for fusing fibers cannot be used as it is. In general, for example, even if it can be applied by improving the ordinary fusion method or conditions, the application increases the number of steps and becomes complicated and costly.
[0011]
(4) When the core diameter increases stepwise in the connection from the optical fiber to the component fiber in the transmission path, the length of the component fiber is not considered. Therefore, in normal transmission, when signal light that has entered the one end face of the component fiber from the optical fiber of the transmission path and propagated through the component fiber exits from the other end face, the efficiency of optical coupling may decrease.
[0012]
The present invention has been made to solve the above problem, and effectively prevents the fiber fuse from advancing even if a fiber fuse occurs in a core of an optical fiber serving as a transmission path of signal light or pump light. It is an object of the present invention to provide an optically amplified transmission system and a method of manufacturing an optically amplified transmission system that can minimize the loss of signal light and pumping light that propagates in signal light and pumping light transmission lines. I do.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, an optical amplification transmission system of the present invention is a signal optical fiber transmission line that propagates signal light, and is branched from the signal optical fiber transmission line via a first optical multiplexer / demultiplexer, A pumping optical fiber transmission line that propagates pumping light that amplifies the signal light by multiplexing the signal light, and a pumping light source for optical amplification that outputs the pumping light to the pumping optical fiber transmission line; A light energy density reduction path inserted in at least one of the portions of the pumping optical fiber transmission line and the signal optical fiber transmission line that sandwich the first optical multiplexer / demultiplexer. A characteristic optical amplification transmission system is provided (claim 1).
[0014]
More specifically, the light energy density reduction path divides the optical fiber transmission path and includes a light propagation space secured between both ends of the optical fiber transmission path (claim 2).
The optical energy density reduction path further includes a lens system disposed in the light propagation space and optically coupling between the two divided ends of the optical fiber transmission path (Claim 3).
[0015]
The lens system includes one of a graded index fiber, a condenser lens, and a pair of collimating lenses.
Alternatively, the optical component constituting the lens system has a portion that secures a propagation distance of 1 mm or more between the divided end of the optical fiber transmission line or between the optical components in the light propagation space ( Claim 5).
[0016]
According to such an optical amplification transmission system, a fiber fuse stopper having good performance determined by detecting light and entering the light for a predetermined time into an optical fiber transmission line having an optical multiplexer / demultiplexer is used. With this arrangement, even if a fiber fuse occurs in an optical fiber serving as a transmission path of the amplified signal light or pump light, it is possible to prevent the fiber fuse from advancing. In addition, the fiber fuse stopper itself has high reliability such that the fiber fuse stopper itself does not cause a fuse due to a problem due to an unexpected situation at the time of manufacturing the fiber fuse stopper.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment according to an optical amplification transmission system 10 of the present invention will be described in detail with reference to FIG.
FIG. 1 is a schematic diagram of an optical amplification transmission system 10. The optical amplification transmission system 10 includes an input-side signal transmission line 12 through which signal light composed of laser light is propagated.
[0018]
The input-side signal transmission line 12 is connected to an output-side signal transmission line 16 via an optical connection section 14, and the optical connection section 14 is formed of an optical connector.
An excitation light transmission line 20 is branched from the input-side signal transmission line 12 via an optical coupler 18 as an optical coupling unit. The excitation light transmission line 20 is divided into a plurality of optical signals via an optical coupler 22 as an optical coupling unit. It is connected to an excitation light source 24 for optical amplification.
[0019]
Each light amplification pumping light source 24 is composed of a semiconductor laser module (LD module) and outputs pumping light composed of laser light. The output pump light is propagated to the input signal transmission path 12 via the optical coupler 22, the pump light transmission path 20, and the optical coupler 18, and excites the signal light propagating in the input signal transmission path 12, that is, amplifies the signal light. I do.
Here, the input-side and output-side signal transmission lines 12 and 14 and the pumping light transmission line 20 are optical fibers including, for example, a single mode fiber (SMF).
[0020]
A fuse stopper 26 is inserted in the pumping light transmission line 20, and a fuse stopper 26 is also inserted in both sides of the input-side signal transmission line 12 across the optical coupler 18.
Although the optical coupler 18 was used as an optical multiplexer for multiplexing the pump light into the signal light transmission line, a fiber fusion type or a dielectric multilayer filter was used as an optical multiplexer having an equivalent function. An optical multiplexer, a fiber grating and an optical circulator may be used in combination. Further, as an optical multiplexer having the same function as the optical coupler 22 for multiplexing a plurality of pump lights, an optical multiplexer using a polarization combiner or a dielectric multilayer filter, a Mach-Zehnder type optical waveguide, or the like is used. The used optical multiplexer or the like can be used.
[0021]
Since each fuse stopper 26 has the same function, the fuse stopper 26 of the first embodiment inserted in the pumping light transmission line 20 will be described with reference to FIG.
The optical fiber of the pumping light transmission line 20 is separated by a fuse stopper 26 into an upstream optical fiber portion 20a on the optical amplification pumping light source 24 side and a downstream optical fiber portion 20b on the optical coupler 18 side. Reference numeral 28 indicates a ferrule adhered to the separated ends of the optical fiber portions 20a and 20b.
[0022]
In the fuse stopper 26, the separated ends of the optical fiber portions 20a and 20b are arranged on the same optical axis at a predetermined interval. A first lens 30 and a second lens 32 are arranged on the optical axis between the ferrules 28, and an interval of 1.0 mm or more is secured between the first and second lenses 30, 32. I have.
[0023]
The fuse stopper 26 having the above-described configuration converts the emitted light (excitation light or signal light) from the upstream optical fiber portion 20a into collimated light by the first lens 30, and then condenses the collimated light by the second lens 32. Then, the light is made to enter the downstream optical fiber portion 20b. Therefore, the fuse stopper 26 has a spatial propagation path of the excitation light between the upstream optical fiber portion 20a and the downstream optical fiber portion 20b.
[0024]
Here, the diameter D of the collimated light converted by the first lens 30 is secured to 120 μm or more, more preferably 360 μm or more, and the condensing diameter d incident on the downstream optical fiber portion 20b is determined by the core diameter. If e, it is preferable that e is in the range of e <d <D. Further, a fiber collimator in which the first lens 30 or the second lens 32 and the ferrule are integrated may be used.
[0025]
In addition, the fuse stopper 26 on the input-side signal light transmission line 12 is used to connect the optical fibers constituting the input-side signal light transmission line 12 to the upstream optical fiber portion 20a and the downstream optical fiber portion 20b in the same manner as described above. It is inserted by separating into.
As described above, the fuse stopper 26 forms the spatial propagation path of the pump light or the signal light in the incident-side signal light transmission path 12 and the pump light transmission path 20, and converts the pump light or the signal light into the divergent light and the collimated light. By doing so, the light energy density of light in the fuse stopper 26 is reduced. Therefore, even if the fiber fuse propagates through the incident-side signal light transmission line 12 or the pumping light transmission line 20, the fiber fuse can be prevented from advancing when the fiber fuse reaches the fuse stopper 26.
[0026]
Further, as described above, since the distance of 1.0 mm or more is secured between the first and second lenses 30 and 32, the propagation of the fiber fuse reaching the fuse stopper 26 is prevented by the first and second lenses 30 and 32. , 32 are completely blocked.
FIG. 3 shows a fuse stopper 34 according to the second embodiment.
The fuse stopper 34 uses one lens 36 instead of the first and second lenses 30 and 32. According to the fuse stopper 34, light emitted from the end face of the upstream optical fiber portion 20a (excitation light or signal light) is condensed by the lens 36 and is incident on the downstream optical fiber portion 20b.
[0027]
That is, the fuse stopper 34 forms a spatial propagation path of light in the incident-side signal light transmission path 12 and the pump light transmission path 20 and converts the pump light or the signal light into a collimated light to generate the pump light in the fuse stopper 34. Alternatively, the energy density of the signal light is reduced. Therefore, even if the fiber fuse propagates through the incident-side signal light transmission line 12 or the pumping light transmission line 20, it can be stopped when the fiber fuse reaches the fuse stopper 26. Further, even when light is condensed on the space propagation path, the fiber fuse can be blocked on the space propagation path.
[0028]
FIG. 4 shows a fuse stopper 38 according to the third embodiment.
The fuse stopper 38 uses first and second fiber elements 40 and 42 instead of the first and second lenses 30 and 32 in the first embodiment. These first and second fiber elements 40, 42 are coaxially welded to the end faces of the upstream and downstream optical fiber portions 20a, 20b. More specifically, the first and second fiber elements 40 and 42 are formed from a part of a graded index fiber (GI fiber) that causes the incident signal light or the pump light to converge at a convergence distance (P / 2). Thus, each of the lengths of the first and second fiber elements 40 and 42 has a length of nxP / 2 + P / 4 (n is 0 or a natural number). The first and second fiber elements 40 and 42, which are part of the GI fiber, have a core diameter about five times the core diameter of the SMF. This GI fiber has an axially symmetric refractive index distribution such that the refractive index gradually decreases from the axis of the core toward the boundary with the cladding, and this refractive index distribution exerts a lens effect.
[0029]
Therefore, according to the above-described fuse stopper 38, the beam diameter of the excitation light or the signal light emitted from the upstream fiber portion 20a is enlarged by the first fiber element 40. Subsequently, the pumping light or the signal light propagates in the space between the first and second fiber elements 40 and 42 as collimated light, and the collimated light is emitted from the upstream fiber portion 20a by the second fiber element 42. And enters the downstream optical fiber portion 20b in the same phase.
[0030]
That is, the fuse stopper 38 forms a spatial propagation path of the laser light in the incident-side signal light transmission path 12 and the excitation light transmission path 20, and enlarges the diameter of the excitation light or the signal light to be the collimated light. The energy density of the excitation light or the signal light is reduced in the fuse stopper 38. Therefore, even if the fiber fuse propagates through the incident-side signal light transmission line 12 or the pumping light transmission line 20, when the fiber fuse reaches the fuse stopper 38, the progress can be prevented.
[0031]
FIG. 5 shows a fuse stopper 44 according to the fifth embodiment.
The fuse stopper 44 has a configuration in which an optical isolator 46 is added to the fuse stopper 26 of the first embodiment, and the optical isolator 46 is inserted between the first lens 30 and the second lens 32. In the fuse stopper 44, a space of 1 mm or more is secured between the optical isolator 46 and the first lens 30.
[0032]
According to the fuse stopper 44 described above, similarly to the case of the first embodiment, after the excitation light or the signal light emitted from the upstream optical fiber portion 20a is converted into the collimated light by the first lens 30, the second lens 32 The collimated light is condensed and incident on the downstream optical fiber portion 20b. Further, according to the fuse stopper 44, the optical isolator 46 deviates the reflection path of the excited signal light and / or the excitation light returning from the downstream optical fiber portion 20b from the axis of the upstream optical fiber 20a.
[0033]
That is, the fuse stopper 44 forms a spatial propagation path of the pump light or the signal light in the incident-side signal light transmission path 12 and the pump light transmission path 20. Then, the light energy density of the excitation light or the signal light is reduced in the fuse stopper 26 by the collimated light. Therefore, even if the fiber fuse propagates through the incident-side signal light transmission line 12 or the pumping light transmission line 20, the fiber fuse can be prevented from advancing when the fiber fuse reaches the fuse stopper 26.
[0034]
Further, as described above, since the distance of 1.0 mm or more is secured between the optical isolator 46 and the first lens 30, the propagation of the fiber fuse reaching the fuse stopper 26 is prevented by the optical isolator 46 and the first lens 30. It is completely blocked between the lens 30.
FIG. 6 shows a fuse stopper 48 of the fourth embodiment.
[0035]
The fuse stopper 48 has a fiber element 50 connecting between the upstream optical fiber portion 20a and the downstream optical fiber portion 20b. This fiber element 50 also consists of a part of GI fiber and has a length of nxP / 2 (n is 0 or a natural number). The fiber element 50 also has a core diameter on the order of five times the core diameter in SMF.
[0036]
According to the above-described fuse stopper 48, since the GI fiber has a lens effect, the pump light or the signal light emitted from the upstream fiber portion 20a propagates in the fiber element 50 with the beam diameter enlarged. Subsequently, the pump light or the signal light whose beam diameter has been expanded converges in the same beam shape as when emitted from the upstream optical fiber portion 20a, and is incident on the downstream optical fiber portion 20b.
[0037]
That is, the fuse stopper 48 reduces the optical energy density of the excitation light in the fuse stopper 48 by enlarging the diameter of the excitation light or the signal light in the incident-side signal light transmission path 12 and the excitation light transmission path 20. Therefore, even if the fiber fuse propagates through the incident-side signal light transmission line 12 or the pumping light transmission line 20, it can be stopped when the fiber fuse reaches the fuse stopper 44. In addition, the beam whose diameter has increased in the fuse stopper 48 converges at the entrance end of the downstream optical fiber portion 20b and then recombines, so that transmission loss can be minimized.
[0038]
Next, a method for manufacturing the optical amplification transmission system 10 will be described.
First, the fuse stopper is irradiated with a laser beam to perform a characteristic test. It is preferable that the laser light at this time is set to have a light power of 500 mW and is continuously incident for a predetermined time or more. In this inspection, a predetermined reference is provided, and if the power of the laser light emitted from the fuse stopper does not decrease, or even if it decreases, the optical power of the laser light emitted from the fuse stopper is 90% relative to the incident light. % Or more, it is determined to be acceptable. In addition, as a cause of the deterioration of the fuse stopper when the laser beam is incident, for example, a foreign substance such as dust interposed in a part of the fuse stopper can be cited. When a foreign substance is present in a part of the fuse stopper, heat is locally generated, which triggers a fiber fuse. This in turn leads to significant damage to the fuse stopper. When the deterioration is remarkable in this way, it goes without saying that even if a fuse stopper is provided in the optical amplification transmission system 10, the performance as the original fuse stopper cannot be exhibited. It can be a source and cause system damage. Therefore, by providing such an inspection step, even if there is a fine foreign matter that cannot be confirmed by ordinary visual inspection, it can be removed in advance, and therefore, a fiber fuse is not erroneously generated. Thus, a highly reliable fiber fuse stopper can be obtained.
[0039]
The fuse stopper that has been determined to pass in such an inspection is installed at a predetermined position of an optical amplification transmission system including a semiconductor laser module, an optical fiber, an optical coupler, and an optical connector.
As described above, the present invention provides a method of manufacturing the optical amplification transmission system 10 including the fuse stopper having good performance, in which the characteristics of the fuse stopper are inspected in advance by irradiating the laser light to the fuse stopper. .
[0040]
As described above, according to the optical amplification transmission system and the method for manufacturing the optical amplification transmission system according to the present embodiment, a fuse stopper having more reliable and good performance is provided, and becomes a transmission path for signal light or pump light. Even if a fiber fuse is generated in the core of the optical fiber, it is possible to provide an optically amplified transmission system and a method of manufacturing the optically amplified transmission system that can effectively prevent the progress of the fiber fuse by the fuse stopper.
[0041]
In the present embodiment, a distance of 1.0 mm or more is provided between the first lens and the second lens or between the optical isolator and the first lens. However, the present invention is not limited to this. For example, between the split end of the pump light transmission line and the fiber element made of GI fiber, between the split end of the pump light transmission line and the lens, between the first and second fiber elements, between the optical isolator and the second A distance of 1.0 mm or more may be provided between the lens and the optical component constituting the optical isolator.
[0042]
In the present embodiment, the fuse stopper is inserted in a part of the pumping light transmission path and the input side optical transmission path, but the insertion place is not limited to this. Further, in this embodiment, three fuse stoppers are inserted, but the number is not limited to three.
In the present embodiment, a GI fiber having a core is used. Alternatively, a so-called coreless GI fiber having no boundary between a core and a clad (synonymous with a core as a whole) may be used.
[0043]
Further, in the present embodiment, the optical isolator is used as the optical component disposed between the collimating lenses in the fuse stopper, but a member other than the optical isolator may be used as long as the optical component functions in the collimated optical path. For example, a filter or the like may be used instead of the optical isolator.
[0044]
【The invention's effect】
According to the optical amplification transmission system of the present invention (claims 1 to 5), by providing a fuse stopper having good performance in an optical fiber transmission line including an optical multiplexer / demultiplexer, amplified signal light or pump light. Even if a fiber fuse is generated in the optical fiber serving as the transmission path, an extremely effective effect of preventing the progress of the fiber fuse can be exerted.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an optical amplification transmission system according to an embodiment of the present invention.
FIG. 2 is a view showing a fuse stopper according to the first embodiment of the present invention.
FIG. 3 is a view showing a fuse stopper according to a second embodiment of the present invention.
FIG. 4 is a view showing a fuse stopper according to a third embodiment of the present invention.
FIG. 5 is a view showing a fuse stopper according to a fourth embodiment of the present invention.
FIG. 6 is a view showing a fuse stopper according to a fifth embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Optical amplification transmission system 12 Input side signal light transmission line 14 Optical connection part 16 Output side signal light transmission line 18 Optical coupler 20 Excitation light transmission line 22 Optical coupler 24 Optical amplification excitation light source 26 Fuse stopper 30 First lens 32 Second Lens 34 Fuse stopper 36 Lens 38 Fuse stopper 40 First fiber element 42 Second fiber element 44 Fuse stopper 46 Optical isolator 48 Fuse stopper 50 Fiber element

Claims (5)

A signal optical fiber transmission line for transmitting signal light;
A pumping optical fiber transmission line that is branched from the signal optical fiber transmission line via a first optical multiplexer / demultiplexer and propagates pumping light that multiplexes with the signal light and amplifies the signal light;
The pumping optical fiber transmission line, a pumping light source for optical amplification that outputs the pumping light,
And a light energy density reduction path interposed at least in one of the portions on the pumping optical fiber transmission line and the signal optical fiber transmission line sandwiching the first optical multiplexer / demultiplexer. Characteristic optical amplification transmission system. 2. The optical amplifying transmission according to claim 1, wherein the optical energy density reduction path divides the optical fiber transmission path and includes a light propagation space secured between both ends of the optical fiber transmission path. system. 3. The light according to claim 2, wherein the light energy density reduction path further includes a lens system disposed in the light propagation space and optically coupling the two divided ends of the optical fiber transmission path. Amplified transmission system. The optical amplification transmission system according to claim 3, wherein the lens system includes one of a graded index fiber, a condenser lens, and a pair of collimating lenses. The optical component constituting the lens system has a portion that secures a propagation distance of 1 mm or more between the split end of the optical fiber transmission line or between the optical components in the light propagation space. The optical amplification transmission system according to claim 3, wherein

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