JPH08116112A - Optical fiber amplifier and optical fiber transmission system - Google Patents

Abstract

PURPOSE: To provide an optical fiber amplifier by which a plurality of beams of signal light whose quantity of input light and wavelength band are different can be amplified at an equal gain. CONSTITUTION: A beam of 1.56-μm signal light 51 and a beam of 1.53-μm signal light 53 are multiplexed, and they are incident on an erbium-doped optical fiber 32 form an optical fiber 34. A beam of exciting light 56 from a semiconductor laser 12 for excitation at a wavelength of 1.48μm is multiplexed with the beams of signal light by a multiplexer-branching filter 22 so as to be input to the doped optical fiber 32. The beam of exciting light 56 which has been transmitted through the doped optical fiber 32 is input to a doped optical fiber 33 via a multiplexer-branching filter 24. The beam of 1.56-μm signal light 52 out of both beams of amplified signal light is branched by the multiplexer- branching filter 24, and it is output via an optical fiber 35. On the other hand, a beam of 1.53-μm signal light 54 is branched by the multiplexer-branching filter 24, and it is input to the doped optical fiber 33. At this time, the beam of 1.53-μm signal light 54 is amplified additionally by a beam of transmitted exciting light, and it is then output by an optical fiber 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier capable of amplifying a plurality of signal light gains in an optical transmission system using an optical fiber as a transmission line so that a plurality of signal light gains are equalized.

[0002]

2. Description of the Related Art Conventional multi-wavelength optical fiber amplifiers and bidirectional optical fiber amplifiers include at least a rare earth-doped optical fiber, a pumping semiconductor laser light source for pumping rare earth ions, and a pumping light coupled to the rare earth-doped optical fiber. And an optical coupler that does. When the signal light is input to this optical fiber amplifier, the signal light is amplified by stimulated emission of rare earth ions in a population inversion state due to the excitation light. When a plurality of signal lights are amplified at the same time by the same rare earth-doped optical fiber, the gain exhibits a wavelength characteristic because it reflects the absorption / emission cross section of rare earth ions.

As a method of suppressing such a gain difference due to wavelength, there are the following reports. The wavelength dependence of the absorption and emission cross sections of rare-earth-doped optical fibers, which is the reason for the gain difference, decreases with the co-addition of aluminum.Journal of Lightwave Technology Vol.9, No.9, ( (1991) pp. 1105 to 1112
Page (Journal of Lightwave Technology, Vol.9, No.9,
pp.1105-1112, 1991.).

Further, a method of using an acousto-optic device is disclosed in the document OFC / I OOC'93, ThD2, 1993, (OFC / IOOC'93, paper ThD2,199).
In 3), the method using the fiber grating is described in the document OFC '91 Proceedings PD20-1, 1991, (OFC '
91, paper PD20-1), a method of connecting optical fiber amplifiers in multiple stages so that the gain-wavelength characteristics cancel each other is described in the literature OAA '93 Proceedings SuE3-1, 19
1993, (OAA'93, paper SuE3-1, pp.70-73, 1993).

In either case, the gain characteristics are made uniform only when the input light quantity is uniform, and no method for making the gain uniform when the input light quantity is different has been studied.

[0006]

In an optical fiber amplifier, a large input light is input when an analog signal is amplified and a small signal light is input when a digital signal is amplified. Therefore, in the case of amplifying them simultaneously, such as in a bidirectional optical amplifier, since the input light amount levels of the respective signals greatly differ, the gain is basically non-uniform. On the other hand, even when used in a distribution system by connecting multiple cascades, since the distribution loss received by each signal is equal, the nonuniform gain causes a shortage of the light amount in the light receiving part, which deteriorates the transmission characteristics. Occurs.

The present invention is an optical fiber amplifier capable of obtaining a uniform gain for a plurality of signal light wavelengths having different input light amounts,
And a bidirectional optical fiber amplifier.

[0008]

An optical fiber amplifier according to the present invention comprises a plurality of rare earth-doped optical fibers connected in series, and pumping light for pumping the plurality of rare earth-doped optical fibers connected in series. An optical fiber amplifier for optically amplifying a plurality of input signal lights having different wavelengths, the first signal light of the plurality of signal lights being provided. , Propagating through some rare earth-doped optical fibers of the plurality of rare earth-doped optical fibers connected in series, and a second signal light of the plurality of signal lights is connected to the plurality of rare earth-doped optical fibers connected in series. The rare earth doped optical fiber propagates through all of the rare earth doped optical fibers, thereby achieving the above objective.

A branch optical fiber connected in the middle of the plurality of rare earth-doped optical fibers connected in series may be provided, and the first signal light may be output via the branch optical fiber.

It is also possible to provide a branch optical fiber connected in the middle of the plurality of rare earth-doped optical fibers connected in series, and to input the first signal light via the branch optical fiber.

In a preferred embodiment, each of the plurality of rare earth-doped optical fibers is excited into a state in which a gain higher than that for the second signal light is given to the first signal light.

In a preferred embodiment, the at least one pump light source comprises a semiconductor laser.

In a preferred embodiment, a multiplexer / demultiplexer that multiplexes the pumping light generated by the pumping light source and the plurality of signal lights is provided with the plurality of rare earth-doped optical fibers connected in series. Connected to any of the input sections of the.

In a preferred embodiment, a multiplexer / demultiplexer for multiplexing the pumping light generated by the pumping light source and the plurality of signal lights is provided with the plurality of rare earth-doped optical fibers connected in series. Connected to any of the output sections of the.

In a preferred embodiment, both the light belonging to the first wavelength band and the light belonging to the second wavelength band are selectively transmitted, and the light not belonging to the first and second wavelength bands is branched. A means for separating the optical fibers is provided in the middle of the plurality of rare earth-doped optical fibers connected in series.

In a preferred embodiment, the wavelength of the first signal light is not included in the first wavelength band and the second wavelength band, and the wavelength of the second signal light is the first wavelength. Band or included in the second wavelength band.

In a preferred embodiment, the wavelength of the excitation light is included in the first wavelength band or the second wavelength band.

In a preferred embodiment, the wavelength of the first signal light is longer than the wavelength of the second signal light, the first signal light is analog-modulated, and the wavelength of the second signal light is Is digitally modulated.

A bidirectional optical amplifier according to the present invention comprises a first input / output section for outputting at least a first signal light and inputting a second signal light, and at least an input for the first signal light and the second signal light. A bidirectional optical amplifier comprising: a second input / output part for outputting the signal light; and an optical fiber amplifying part connected to the first input / output part and the second input / output part. The amplification section includes a plurality of rare earth-doped optical fibers connected in series, and at least one pumping light source that generates pumping light for pumping the plurality of rare earth-doped optical fibers connected in series, and an input An optical fiber amplifier for optically amplifying a plurality of signal lights having different wavelengths,
Moreover, the first signal light of the plurality of signal lights propagates through some rare earth-doped optical fibers of the plurality of rare earth-doped optical fibers connected in series, and the first signal light of the plurality of signal lights Second optical signal is an optical fiber amplifying section that propagates through all the rare earth-doped optical fibers of the plurality of rare earth-doped optical fibers connected in series, and the first signal received from the optical fiber amplifying section The above-mentioned object is achieved by further comprising demultiplexing means for selectively propagating light to the first input / output portion.

In a preferred embodiment, the second signal light input from the first input / output section and the first signal light input to the second input / output section are combined to generate the second signal light. It is provided with a multiplexing means for inputting both the first signal light and the second signal light to the input sections of the plurality of rare earth-doped optical fibers connected in series.

In a preferred embodiment, there is provided a multiplexing means for inputting the first signal light input from the second input / output portion in the middle of the plurality of rare earth-doped optical fibers connected in series. ing.

The first input / output portion may be provided with a first optical circulator, and the second input / output portion may be provided with a second optical circulator.

The first input / output portion may be provided with a first multiplexing / demultiplexing means, and the second input / output portion may be provided with a second multiplexing / demultiplexing means.

The optical fiber transmission system of the present invention is the first
A first signal light source that emits the signal light, and a first light receiver that detects the second signal light; a second light receiver that detects the first signal light; A receiving station including a second signal light source for emitting two signal lights, an optical fiber transmission line connecting the transmitting station and the receiving station, and an optical fiber amplifier provided in the middle of the optical fiber transmission line. An optical fiber transmission system comprising:
A plurality of rare earth-doped optical fibers connected in series and at least one pumping light source that generates pumping light for pumping the plurality of rare earth-doped optical fibers connected in series, and different input wavelengths Of the plurality of signal lights, wherein the first signal light of the plurality of signal lights is one of the plurality of rare earth-doped optical fibers connected in series. Part of the rare-earth-doped optical fiber, and the second signal light of the plurality of signal-lights propagates through all of the plurality of rare-earth-doped optical fibers connected in series, The above object is achieved by the above.

In a preferred embodiment, at least one analog-modulated signal light is used as the first signal light, and a plurality of digitally-modulated signal lights are used as the second signal light.

The bidirectional optical fiber transmission system of the present invention comprises a first signal light source for emitting a first signal light, and a second signal light source.
A receiver including a first light receiver for detecting the signal light, a second light receiver for detecting the first signal light, and a receiver including a second signal light source for emitting the second signal light A station, an optical fiber transmission line connecting the transmitting station and the bidirectional optical amplifier,
A bidirectional optical fiber transmission system comprising: a bidirectional optical amplifier provided in the middle of the optical fiber transmission line, wherein the bidirectional optical amplifier outputs the first signal light and the second signal. A second input / output portion for inputting light, a second input / output portion for inputting the first signal light and an output of the second signal light, the first input / output portion and the second input / output And a plurality of rare earth-doped optical fibers connected in series and a plurality of rare earth-doped optical fibers connected in series. An optical fiber amplifying unit that includes at least one pumping light source that generates pumping light for optically amplifying a plurality of input signal lights having different wavelengths. The first signal light of the plurality is connected to the plurality of serially connected signal lights. The second signal light of the plurality of signal lights propagates through a part of the rare earth-doped optical fibers, and the second signal light of the plurality of signal lights is the rare earth-doped optical fibers of the plurality of rare earth-doped optical fibers connected in series. An optical fiber amplifying section for propagating through an optical fiber, further comprising demultiplexing means for selectively propagating the first signal light received from the optical fiber amplifying section to the first input / output section, whereby the above The purpose is achieved.

In a preferred embodiment, at least one analog-modulated signal light is used as the first signal light, and a plurality of digitally-modulated signal lights are used as the second signal light.

As described above, in the present invention, gain compensation is performed by additionally amplifying the signal light having a small gain, and an equal gain is obtained for a plurality of signal lights having different signal light wavelengths and different input light amounts. Can be given.

When pumping light is input from one of the rare earth-doped optical fibers, the transmitted light is effectively used to pump the rare earth-doped optical fiber for additional amplification. When pumping light is input from both ends of the rare earth-doped optical fiber, gain compensation can be performed over a wider input light amount range.

By exciting the rare earth-doped optical fiber used for the incident portion of the signal light with 0.98 μm light, the noise characteristic can be improved even when the total input light amount of the plurality of signal light is large.

Further, by using the optical fiber amplifier for performing such gain compensation in the amplification section, a bidirectional optical amplifier for amplifying each signal light without causing a gain difference depending on the transmission direction is provided.

[0032]

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

First, the gain wavelength characteristic of the erbium-doped optical fiber is shown in FIG. As shown in the figure, the gain characteristic of the optical fiber has wavelength dependence. In the case of performing simultaneous amplification of two signals of analog signal and digital signal, considering the wavelength separation characteristics of commercially available optical filters, each signal is
It is appropriate to set each gain peak wavelength of μm and 1.56 μm.

Since an analog signal is required to have a higher signal-to-noise ratio than a digital signal, it operates in a high input state. In such a case, 1.56 μm
By assigning a high input analog signal to the band and a low input digital signal to the 1.53 μm band, it is possible to minimize the characteristic variation of the analog signal with respect to the variation of the digital signal. However, in such a case, the long wavelength side has a high gain, but the short wavelength side loses the gain, resulting in a low gain.

In the following description of the embodiments, the 1.56 μm light modulated by the analog signal is referred to as “first signal light”, and the 1.53 μm light modulated by the digital signal is referred to as “second signal light”. Light. In addition, the input light amount of the first signal light is 0
The input light amount of the second signal light is set to -30 dBm.

(Example 1) Hereinafter, referring to FIG.
An embodiment of the optical fiber amplifier according to the present invention will be described in detail.

The optical fiber amplifier shown in FIG. 1 has a single input end to which a plurality of signal lights having different wavelengths are input, and an amplifier for optically amplifying the plurality of signal lights input to the input end. It has a plurality of output ends which respectively output a plurality of amplified signal lights. In this example, the signal light having a wavelength of 1.56 μm (first signal light 5
1) and a wavelength of 1.53 μm modulated by a digital signal
Signal light (second signal light 53) is input to the input end,
Amplified.

The amplification section includes a first erbium-doped optical fiber 32 that amplifies both the first and second signal lights 51 and 53, and a second erbium-doped optical fiber 33 that amplifies only the second signal light 53. have. The two erbium-doped optical fibers 32 and 33 are connected via a multiplexer / demultiplexer 24. This multiplexer / demultiplexer 24
Of the plurality of signal lights propagating through the first erbium-doped optical fiber 32, the second signal light 53 is transmitted to the second erbium-doped optical fiber 33, while the first signal light 51 is selectively separated. Input to the optical fiber 35.

The first signal light 51 is the optical isolator 26.
Is output to another output end through the inserted optical fiber 35. The output first signal light is as shown in FIG.
It is shown by "52". The second signal light 53 amplified by the second erbium-doped optical fiber 33 is output to the output end via the optical fiber 36 in which the optical isolator 27 is inserted. The output second signal light is as shown in FIG.
It is shown by "54".

The amplification section pumps the pumping light (wavelength: 1.4) that pumps the first and second erbium-doped optical fibers 32 and 33.
8 μm) 56 for emitting a semiconductor laser 12 for excitation. The pumping light in the 1.48 μm band is combined / demultiplexed by the multiplexer / demultiplexer 22.
Then, it is multiplexed with the signal light in the 1.55 μm band and input to the first erbium-doped optical fiber 32. The first and second signal lights 51 and 53 are input to the multiplexer / demultiplexer 22 via the optical fiber 34 in which the optical isolator 25 is inserted. The pumping light in the 1.48 μm band is combined / demultiplexed 2
4 and is input to the second erbium-doped optical fiber 33 and also excites the second erbium-doped optical fiber 33. The operation when signal light enters the optical fiber amplifier will be described in more detail.

The 1.56 μm signal light as the first signal light 51 and the 1.53 μm signal light as the second signal light 53 are
It is incident on the input end of the optical fiber 34. The 1.48 μm pump light is combined with the signal lights 51 and 53 by the multiplexer / demultiplexer 22 and input to the erbium-doped optical fiber 32.
Here, after the pumping light 56 amplifies the signal lights 51 and 53, the attenuated transmission component is input to the erbium-doped optical fiber 33 via the multiplexer / demultiplexer 24. 1.56 μm
The signal light 51 is demultiplexed by the multiplexer / demultiplexer 24, transmitted through the optical isolator 26, and output. On the other hand, 1.53μ
The m signal light 53, after passing through the multiplexer / demultiplexer 24, is input to the erbium-doped optical fiber 33. In this erbium-doped optical fiber 33, a 1.53 μm signal light 53
Is amplified by the transmitted excitation light and output through the optical isolator 27.

FIG. 3 shows the transmitted pumping light quantity (vertical axis) with respect to the input light quantity (horizontal axis) of the first and second signal lights. From FIG. 3, when only the first signal light of 1.56 μm is incident,
The excitation light transmitted through the erbium-doped optical fiber 32 is 1
It can be seen that there is also 0 to 30 mW. In addition, the input light amount of the first signal light is several dBm (for example, +5 dBm in FIG. 3),
Even when the second signal light is changed from −20 to −3 dBm, about 10 mW of pumping light passes through the erbium-doped optical fiber 32, and this pumping light is a loss in the conventional configuration. I understand. In the present embodiment, the transmitted excitation light, which has been a loss in the past, is incident on the second erbium-doped optical fiber 33, and at the same time, the first excitation light is transmitted.
Only the second signal light excluding the signal light is incident on the second erbium-doped optical fiber 33. By doing this,
The second signal light will be additionally amplified. That is, in this embodiment, the transmitted pumping light that causes a loss is positively used, and as a result, it is possible to give the second signal light a gain equivalent to the gain for the first signal light. .

It will be described with reference to FIG. 4 that the gains of the first and second signal lights can be made equal by the configuration of this embodiment. The horizontal axis of FIG. 4 indicates 1.
The input light quantity of the signal of 53 μm is shown, and the vertical axis shows the gain of the signal light of 1.53 μm. In this figure, □ is the gain of the signal light of 1.53 μm without the doped optical fiber 33, and ◯ is the gain with the fiber 33.
Also, the gain of the signal light of 1.56 μm is shown as a black circle in FIG. 4 so that it can be compared with the signal light of 1.56 μm. Here, the input light amount of the 1.56 μm signal light is +5 dB
It is assumed that m is constant.

From this figure, a gain of 1.53 μm,
A gain of 1.56 μm means that the input light quantity of 1.53 μm is −
It can be seen that the values are almost the same in the range of 40 to -20 dBm. This is 1.53 as described in the embodiment.
This is because the signal light of μm was amplified by the erbium-doped optical fiber 32 and then by the optical fiber 33. From this result, the effect of the present embodiment that the gains of the signal lights of 1.53 μm and 1.56 μm having different input wavelengths and amounts of input light can be made substantially the same was confirmed.

Example 2 Hereinafter, referring to FIG. 5,
Another embodiment of the optical fiber amplifier according to the present invention will be described in detail. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The difference between the optical fiber amplifier of FIG. 5 and the optical fiber amplifier of FIG. 1 is that the optical fiber amplifier of FIG. 5 further includes a 1.48 μm pumping semiconductor laser 13 as the second pumping light source, The point is that a multiplexer / demultiplexer 23 for inputting the excitation light emitted from the semiconductor laser 13 for use in the erbium-doped optical fiber 33 is provided between the erbium-doped optical fiber 33 and the optical isolator 27. This multiplexer / demultiplexer 23 uses 1.48 μm light and 1.
Combines and demultiplexes 55 μm light.

The case where two signal lights are made incident on this optical fiber amplifier will be described.

The 1.56 μm signal light that is the first signal light 51 and the 1.53 μm signal light that is the second signal light 53 are
It is incident from the optical fiber 34. The pumping light 56 is multiplexed with the signal lights 51 and 53 by the multiplexer / demultiplexer 22 and input to the erbium-doped fiber 32. Here excitation light 56
After amplifying the signal lights 51 and 53, the attenuated transmission component is input to the erbium-doped optical fiber 33 via the multiplexer / demultiplexer 24. 1.56 μm signal light 51 is combined
It is demultiplexed by the demultiplexer 24, transmitted through the optical isolator 26, and output. The 1.53 μm signal light 53 is input to the erbium-doped optical fiber 33 after passing through the multiplexer / demultiplexer 24. On the other hand, the pumping light 57 is multiplexed with the signal light 53 by the multiplexer / demultiplexer 23 and input to the erbium-doped fiber 33. In the erbium-doped optical fiber 33, the 1.53 μm signal light 53 is amplified by the transmitted pumping light 56 and pumping light 57 and output through the optical isolator 27.

From FIG. 3, the input light quantity of the first signal light is several d.
It can be seen that when it is as large as Bm or more, the amount of transmitted excitation light becomes very small, which is insufficient for additional excitation of the second signal light. Even in such a case, in order to compensate the gain of each signal light wavelength, the configuration in which the pumping light is obtained from the rear of the erbium-doped optical fiber 33 is effective as in the present embodiment.

(Embodiment 3) Hereinafter, referring to FIG.
Still another embodiment of the optical fiber amplifier according to the present invention will be described in detail. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The optical fiber amplifier of FIG. 6 differs from the optical fiber amplifier of FIG. 5 in that the optical fiber amplifier of FIG. 6 further includes an erbium-doped optical fiber 31, a pumping semiconductor laser 11, and a demultiplexing / combining device. It has the wave instrument 21 and. Here, the pumping semiconductor laser 11 has a wavelength of 0.98.
Emits excitation light of μm. The multiplexer / splitter 21 is 0.98
Combines and demultiplexes μm light and 1.55 μm light. In FIG. 6, 55 indicates 0.98 μm excitation light.

A case where two signal lights are incident on this optical fiber amplifier will be described.

The 1.56 μm signal light as the first signal light 51 and the 1.53 μm signal light as the second signal light 53 are
It is incident from the optical fiber 34. 0.98 μm excitation light 5
5 is multiplexed with the signal lights 51 and 53 by the multiplexer / demultiplexer 21 and input to the erbium-doped fiber 31. Here, the signal lights 51 and 53 amplified by the pump light 55
Is input to the erbium-doped optical fiber 32 via the multiplexer / demultiplexer 22. The pumping light 56 is multiplexed with the signal lights 51 and 53 by the multiplexer / demultiplexer 22 and input to the erbium-doped fiber 32. Here, the pump light 56 is the signal light 5
After amplifying 1 and 53, the attenuated transmission component
It is input to the erbium-doped optical fiber 33 via the demultiplexer 24. The 1.56 μm signal light 51 is combined / demultiplexed by the multiplexer / demultiplexer 24.
Is demultiplexed by the optical isolator 26 and output through the optical isolator 26. On the other hand, the 1.53 μm signal light 53 is combined / demultiplexed by the multiplexer / demultiplexer 24.
After being transmitted, the light is input to the erbium-doped optical fiber 33. In this erbium-doped optical fiber 33,
The 1.53 μm signal light 53 is amplified by the transmitted excitation light,
The signal light 54 is output through the optical isolator 27.

When signal lights having a plurality of wavelengths are input, the noise characteristic is deteriorated due to an increase in the total input light amount. Even in that case, according to this configuration, noise can be reduced by exciting the signal light input unit by 0.98 μm. In addition, when simultaneously amplifying with 0.98 μm pumping light and 1.48 μm pumping light, deterioration of noise characteristics occurs,
In this structure, such a problem does not occur because 1.48 μm light does not enter the 0.98 μm excitation region.

Example 4 Hereinafter, referring to FIG. 7,
Still another embodiment of the optical fiber amplifier according to the present invention will be described in detail. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The optical fiber amplifier shown in FIG. 7 has two input ends to which a plurality of signal lights having different wavelengths are input, and an amplifying section which optically amplifies the plurality of signal lights input to the input ends. And a single output end for outputting each of the plurality of amplified signal lights. In this example, the signal light having a wavelength of 1.56 μm (first signal light 5
1) and a wavelength of 1.53 μm modulated by a digital signal
Signal light (second signal light 53) is input to separate input ends and amplified.

The amplification section includes a first erbium-doped optical fiber 132 that amplifies only the second signal light 53 and a second erbium-doped optical fiber 133 that amplifies both the first and second signal lights 51 and 53. Have The two erbium-doped optical fibers 1132 and 133 are connected via a multiplexer / demultiplexer 148. The multiplexer / demultiplexer 148 multiplexes the first signal light 51 and the second signal light 53 propagating in the first erbium-doped optical fiber 132, and inputs them to the second erbium-doped optical fiber 133. . The first signal light 51 is multiplexed / demultiplexed 148 via the optical fiber 135 in which the optical isolator 126 is inserted.
Is input to

The first and second signal lights 51 and 53 amplified by the second erbium-doped optical fiber 133 are output to the common output end via the optical fiber 36 in which the optical isolator 27 is inserted.

The amplifying section has a pumping semiconductor laser 12 which emits pumping light (wavelength 1.48 μm) for pumping the first and second erbium-doped optical fibers 132 and 133. The second signal light 53 is input to the multiplexer 22 via the optical fiber 34 in which the optical isolator 25 is inserted. The pumping light in the 1.48 μm band is combined / demultiplexed by the multiplexer / demultiplexer 22.
Is combined with the second signal light of 1.53 μm by the
It is input to the erbium-doped optical fiber 132. First
1.48 transmitted through erbium-doped optical fiber 132
The excitation light in the μm band further passes through the multiplexer / demultiplexer 148, is input to the second erbium-doped optical fiber 133, and also excites the second erbium-doped optical fiber 133.

(Embodiment 5) Hereinafter, referring to FIG.
Still another embodiment of the optical fiber amplifier according to the present invention will be described in detail. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The difference between the optical fiber amplifier shown in FIG. 8 and the optical fiber amplifier shown in FIG. 7 is that the optical fiber amplifier shown in FIG. 8 further includes a 1.48 μm pumping semiconductor laser 13 as a second pumping light source. The multiplexer / demultiplexer 23 for inputting the excitation light emitted from the semiconductor laser 13 for use in the erbium-doped optical fiber 133 is provided between the erbium-doped optical fiber 133 and the optical isolator 27. The multiplexer / demultiplexer 23 multiplexes / demultiplexes the 1.48 μm light and the 1.55 μm light.

Example 6 Hereinafter, referring to FIG. 9,
Still another embodiment of the optical fiber amplifier according to the present invention will be described in detail. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The difference between the optical fiber amplifier of FIG. 9 and the optical fiber amplifier of FIG. 8 is that the optical fiber amplifier of FIG. 9 further includes an erbium-doped optical fiber 131, a pumping semiconductor laser 11, and demultiplexing / combining. It has the wave instrument 21 and. Here, the pumping semiconductor laser 11 has a wavelength of 0.9.
Emit excitation light of 8 μm. The multiplexer / demultiplexer 21 is 0.9
The 8 μm light and 1.55 μm light are combined and demultiplexed.

(Embodiment 7) An embodiment of the bidirectional optical amplifier according to the present invention will be described in detail below with reference to FIG. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The optical amplifying section of this embodiment is similar to the embodiment of FIG. 1 except that the pumping semiconductor laser 12 having a wavelength of 1.48 μm
1.48 μm light and 1.55 μm light multiplexer / demultiplexer 22, wavelength band 1.55 μm or less and 1.55 μm light multiplexer / demultiplexer 24, optical isolators 25, 26 and 27, erbium-doped optical fiber 32 and 33 are provided. Further, by using the optical circulators 46 and 47, the multiplexer / demultiplexer 48, and the optical fibers 37 and 38, a multiplexer / demultiplexer for the signal light from both directions is configured.

51 is the first signal light input to the optical fiber 37, 52 is the amplified first signal light output from the optical fiber 38, and 53 is the second signal light input to the optical fiber 38. , 54 are amplified second signal lights outputted from the optical fiber 37.

Next, the case where two signal lights are incident on this bidirectional optical amplifier will be described.

Now, the first signal light 51 is input from the right side of the optical fiber 37. When this signal light 51 is input to the optical circulator 46, only the signal light from the optical fiber 37 is multiplexed / demultiplexed by the function of the optical circulator 48.
Incident on the second signal light 53, and after being multiplexed with the second signal light 53, it is input to the erbium-doped optical fiber 32 via the optical isolator 25.

The amplified first signal light 51 is demultiplexed by the multiplexer / demultiplexer 24 in the optical amplification section, and is emitted only in the direction of the optical circulator 47 and not in the direction of the optical circulator 46. When the amplified first signal light 51 is input to the optical circulator 47, it is transmitted to the optical fiber 38 and output by the function of the optical circulator. The second signal light 53 having a wavelength of 1.53 μm input from the left side of the optical fiber 38 enters the optical circulator 47, and is then multiplexed with the signal light 51 of 1.56 μm by the multiplexer / demultiplexer 48. It is amplified by the erbium-doped optical fibers 32 and 33. When the amplified signal light 53 is input to the optical circulator 46, it is transmitted to the right side of the optical fiber 37 by the function of the optical circulator and is output as the amplified signal light 54.

According to this configuration, since the optical fiber amplifier of FIG. 1 is used for optical amplification, it is possible to provide a bidirectional optical amplifier in which the gain of signal light amplified bidirectionally is uniform.

(Embodiment 8) Hereinafter, another embodiment of the bidirectional optical amplifier according to the present invention will be described in detail with reference to FIG. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The optical amplifying section of this embodiment is similar to the embodiment of FIG. 5 in that the pumping semiconductor lasers 12 and 1 having a wavelength of 1.48 μm are used.
3, 1.48 μm light and 1.55 μm light multiplexer / demultiplexer 22
And 23, wavelength band 1.55 μm or less and 1.55 μm light multiplexer / demultiplexer 24, optical isolators 25, 26 and 27, and erbium-doped optical fibers 32 and 33. Furthermore, optical circulators 46 and 47, multiplexer / demultiplexer 48,
The optical fibers 37 and 38 are used to perform bidirectional signal light multiplexing / demultiplexing.

Reference numeral 51 is the first signal light input to the optical fiber 37, 52 is the amplified first signal light output from the optical fiber 38, and 53 is the second signal light input to the optical fiber 38. , 54 are amplified second signal lights outputted from the optical fiber 37.

Next, the case where two signal lights are incident on this optical fiber amplifier will be described.

Now, the first signal light 51 is input from the right side of the optical fiber 37. When this signal light 51 is input to the optical circulator 46, only the signal light from the optical fiber 37 is multiplexed / demultiplexed by the function of the optical circulator 48.
And is input to the erbium-doped optical fiber 32 after being multiplexed with the second signal light 53.

The amplified first signal light 51 is demultiplexed by the multiplexer / demultiplexer 24 in the optical amplification section, and is emitted only in the direction of the optical circulator 47, not in the direction of the optical circulator 46. When the amplified first signal light 52 is input to the optical circulator 47, it is transmitted to the optical fiber 38 and output by the action of the optical circulator. The second signal light 53 having a wavelength of 1.53 μm input from the left side of the optical fiber 38 enters the optical circulator 47, and is then multiplexed with the signal light 51 of 1.56 μm by the multiplexer / demultiplexer 48. It is amplified by the erbium-doped optical fibers 32 and 33. When the amplified signal light 53 is input to the optical circulator 46, it is transmitted to the right side of the optical fiber 37 by the function of the optical circulator and is output as the amplified signal light 54.

According to this structure, since the optical fiber amplifier of FIG. 5 is used for the optical amplifier, the bidirectional optical amplifier in which the gain of the signal light amplified bidirectionally is uniform even when the input light amount is large. Can be provided.

(Embodiment 9) Still another embodiment of the bidirectional optical amplifier according to the present invention will be described in detail below with reference to FIG. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

As in the optical fiber amplifier shown in FIG. 6, the optical amplifying section of this embodiment has a pumping semiconductor laser 11 having a wavelength of 0.98 μm, pumping semiconductor lasers 12 and 13 having a wavelength of 1.48 μm, and 0.98 μm light. And 1.55 μm light multiplexer / demultiplexer 2
1, 1.48 μm light and 1.55 μm light multiplexer / demultiplexer 22
And 23, wavelength band 1.55 μm or less and 1.55 μ light multiplexer / demultiplexer 24, optical isolators 25, 26 and 27, and erbium-doped optical fibers 31 and 32 and 33. Further, by using the optical circulators 46 and 47, the multiplexer / demultiplexer 48, and the optical fibers 37 and 38, a multiplexer / demultiplexer for the signal light from both directions is configured.

Reference numeral 51 is the first signal light input to the optical fiber 37, 52 is the amplified first signal light output from the optical fiber 38, and 53 is the second signal light input to the optical fiber 38. , 54 are amplified second signal lights outputted from the optical fiber 37.

Next, the case where signal light is incident on this optical fiber amplifier will be described.

Now, the first signal light 51 is inputted from the right side of the optical fiber 37. When this signal light 51 is input to the optical circulator 46, only the signal light from the optical fiber 37 is multiplexed / demultiplexed by the function of the optical circulator 48.
Is input to the erbium-doped optical fiber 31 and then input to the erbium-doped optical fiber 31.

The amplified first signal light 51 is demultiplexed by the multiplexer / demultiplexer in the optical amplifier, and the optical circulator 47
The light is emitted only in the direction of, and is not emitted in the direction of the optical circulator 46. When this signal light 51 is input to the optical circulator 47, it is transmitted to the optical fiber 38 and output by the action of the optical circulator.

Similarly, the second signal light 53 having a wavelength of 1.53 μm input from the left side of the optical fiber 38 is incident on the optical circulator 47, and then is transmitted by the multiplexer / demultiplexer 48 to 1.5
It is multiplexed with the signal light 51 of 6 μm and amplified by the erbium-doped optical fibers 31, 32 and 33. When the amplified signal light 53 is input to the optical circulator 46, it is transmitted to the right side of the optical fiber 37 by the function of the optical circulator and is output as the amplified signal light 54.

According to this configuration, since the optical amplifier shown in FIG. 6 is used for the optical amplification section, even if the total input light amount of all the signal light is large, the gain of the signal light amplified bidirectionally is uniform. ,
In addition, it is possible to provide a bidirectional optical amplifier having excellent noise characteristics.

(Embodiment 10) Still another embodiment of the bidirectional optical amplifier according to the present invention will be described in detail with reference to FIG. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The difference between the bidirectional optical amplifier shown in FIG. 13 and the bidirectional optical amplifier shown in FIG. 10 is that the bidirectional optical amplifier shown in FIG. 13 has a demultiplexer / multiplexer 146 and a multiplexer / demultiplexer 146 instead of the optical circulators 46 and 47. 147 is used. A WDM coupler is preferable as the demultiplexer / multiplexer.

In the bidirectional optical amplifiers of FIGS. 11 and 12, the demultiplexers / multiplexers 146 and 147 may be used instead of the optical circulators 46 and 47.

(Embodiment 11) Another embodiment of the bidirectional optical amplifier according to the present invention will be described in detail below with reference to FIG. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The optical amplifying portion of this embodiment is similar to the embodiment of FIG. 7 in that the pumping semiconductor laser 12 having a wavelength of 1.48 μm
1.48 μm light and 1.53 μm light multiplexer / demultiplexer 22, wavelength band 1.55 μm or less and 1.55 μm light multiplexer / demultiplexer 124 and 148, optical isolators 25, 126, 12
7 and 227, and erbium-doped optical fibers 132 and 133. Further, by using the optical circulators 46 and 47 and the optical fibers 37 and 38, a multiplexing / demultiplexing unit for bidirectional signal light is configured.

Reference numeral 51 is the first signal light input to the optical fiber 37, 52 is the amplified first signal light output from the optical fiber 38, and 53 is the second signal light input to the optical fiber 37. 54 are amplified second signal lights outputted from the optical fiber 38.

Next, the case where two signal lights are incident on this bidirectional optical amplifier will be described.

Now, the first signal light 51 is input from the right side of the optical fiber 37. When this signal light 51 is input to the optical circulator 46, only the signal light from the optical fiber 37 enters the multiplexer / demultiplexer 148 by the function of the optical circulator 46, and is multiplexed with the second signal light 53. Then, it is input to the erbium-doped optical fiber 133.

The first signal light 51 amplified by the erbium-doped optical fiber 133 is the multiplexer / demultiplexer 1 in the optical amplifier section.
It is demultiplexed by 24, propagates through the optical isolator 127 to the side where the optical circulator 47 exists, and does not propagate to the side where the optical circulator 46 exists. When the amplified first signal light 51 is input to the optical circulator 47, it is transmitted to the optical fiber 38 and output by the function of the optical circulator.

Similarly, the second signal light 53 having a wavelength of 1.53 μm input from the left side of the optical fiber 38 is incident on the optical circulator 47, and then is multiplexed by the multiplexer 22.
It is multiplexed with the excitation light from and is input to the erbium-doped optical fiber 132. Erbium-doped optical fiber 13
The second signal light 53 amplified by 2 is added to the multiplexer / demultiplexer 14
At 8, the signal light 51 of 1.56 μm is multiplexed and further amplified by the erbium-doped optical fiber 133. The amplified second signal light 53 is separated to the right side in the figure by the multiplexer 124, passes through the optical isolator 227, and then passes through the optical circulator 4.
6 is input. The amplified second signal light 53 is transmitted to the right side of the optical fiber 37 by the function of the optical circulator 46, and is output as the signal light 54.

(Embodiment 12) Still another embodiment of the bidirectional optical amplifier according to the present invention will be described in detail below with reference to FIG. In the following description, the same reference numerals are given to corresponding parts of the already described embodiments.

The difference between the bidirectional optical amplifier of FIG. 15 and the bidirectional optical amplifier of FIG. 14 is that the bidirectional optical amplifier of FIG. 15 further includes a 1.48 μm pumping semiconductor laser 13 as a second pumping light source. In addition, the multiplexer / demultiplexer 23 for inputting the pumping light emitted from the pumping semiconductor laser 13 to the erbium-doped optical fiber 32 is provided between the erbium-doped optical fiber 32 and the optical isolator 27. is there. This multiplexer / demultiplexer 23 uses 1.48 μm light and 1.
Combines and demultiplexes 55 μm light.

(Embodiment 13) Hereinafter, an embodiment of the optical fiber transmission system according to the present invention will be described in detail with reference to FIG.

The transmitting station 101 has a signal light source 102, and the subscriber 105 has a light receiver 107. The transmitting station 101 and the subscriber 105 are connected by a transmission line 131, and the optical fiber amplifier 111 and the 1 × 8 optical branching device 1 described in the first embodiment are provided on the way.
21 is inserted.

Next, the case of transmitting and receiving an analog optical signal in this optical transmission system will be described.

In the transmitting station 101, the output light from the 1.56 μm semiconductor laser as the signal light source 102 which is intensity-modulated by the analog signal is amplified by the optical fiber amplifier 111, and then is transmitted as a single transmission line 131 with a length of 10 km. Mode optical fiber. This analog signal light is a pin-
Received by PD.

As described above, as the optical fiber amplifier 111, any optical fiber amplifier according to the present invention may be used. According to the present embodiment, since the gains of the respective signal lights are equal, even when the number of optical amplifier connection stages is increased, there is no variation in the amount of received light between the signal lights, and stable characteristics can be obtained. In particular, if the optical fiber amplifier of FIG. 5 is used, the gain of each signal light can be equalized even when the input light amount is large in order to obtain the signal-to-noise ratio of the analog signal light. Therefore, even when the number of optical amplifier connection stages is increased, there is no deviation between channels in the amount of light received by the light receiver, and stable characteristics can be obtained. If the optical fiber amplifier of FIG. 6 is used, the signal light incident part is excited by 0.98 μm,
Good noise characteristics can be obtained even when the input light amount of all signal lights is large.

(Embodiment 14) Hereinafter, an embodiment of the optical fiber transmission system according to the present invention will be described in detail with reference to FIG.

The transmitting station 101 includes a signal light source 102 and a light receiver 1.
03 and a multiplexer / demultiplexer 104, and a subscriber 105
Is a signal light source 106, a light receiver 107, and a multiplexer / demultiplexer 108.
And have. The transmission station 101 and the subscriber 105 are connected by a transmission line 131, and the bidirectional optical amplifier 114 and the 1 × 8 optical branching device 121 are inserted in the middle of the transmission line 131.

Next, in the case of transmitting and receiving an analog optical signal and a digital optical signal in this optical transmission system, the downlink analog signal from the transmitting station to the subscriber side, and then the uplink digital signal will be described.

In the transmitting station 101, the output light from the 1.56 μm semiconductor laser as the signal light source 102, the intensity of which is modulated with an analog signal, is output through the multiplexer / demultiplexer 104. After this is amplified by the analog / digital bidirectional optical amplifier 114, the transmission line 131 has a length of 1
It is transmitted to a 0 km single mode optical fiber. This analog signal light is sent to the multiplexer / demultiplexer 1 at the subscriber 105.
After 08, the light is received by the pin-PD as the light receiver 107.

In the subscriber 105, 1.53 μm as the signal light source 106 intensity-modulated by the digital signal is used.
The output light from the semiconductor laser is combined with the 1.56 μm light in the multiplexer / demultiplexer 108 and sent out to the single-mode optical fiber as the transmission line 131 having a length of 10 km. This digital signal light is a bidirectional optical fiber amplifier 1
After being amplified by 15, the signal reaches the transmitting station 101. At the transmitting station 101, the multiplexer / demultiplexer 104 allows 1.56μ.
After being demultiplexed with m light, it is received by the light receiver 103 made of Ge-APD.

Thus, the present optical fiber transmission system is
Since the bidirectional optical amplifier according to the present invention is used, the gain becomes equal to the signal light propagating in both directions. Therefore, even when the number of optical amplifier connection stages is increased or when the signal light amount from the subscriber side is increased or decreased, the light amount received by the light receiver does not change, and stable characteristics can be obtained.

As described above, since the bidirectional optical amplifier of the present invention is used, the gain of the signal light propagating in both directions can be equalized even when the input light quantity is large in order to obtain the signal-to-noise ratio of the analog signal light. Therefore, even when the number of optical amplifier connection stages is increased or when the signal light amount from the subscriber side is increased or decreased, the light amount received by the light receiver does not change, and stable characteristics can be obtained.

FIG. 18 shows the difference in the 1.53 μm digital signal transmission characteristic in this embodiment depending on the presence or absence of the erbium-doped optical fiber 33 in the bidirectional optical amplifier 115. The transmission rate is 200 Mbps. When the erbium-doped optical fiber 33 is not provided, the minimum amount of received light that gives a code error rate of 10 ⁻⁹ is −26 dBm, but when it is present, it is −35 dBm, which is an improvement of 9 dB. That is, it is clear that the adoption of this configuration in a bidirectional optical transmission system has a great effect on the improvement of transmission characteristics.

As described above, when the bidirectional optical amplifier according to the present invention is used, since the gain is equal to the signal light propagating in both directions, the amount of signal light from the subscriber side is increased even when the number of optical amplifier connection stages is increased. Even when is increased or decreased, the amount of light received by the light receiver does not change, so that stable characteristics can be obtained. Further, since the signal light incident portion is excited by 0.98 μm, good noise characteristics can be obtained even when the input light amount of all the signal light is large.

In this embodiment, the bidirectional optical amplifier is installed at a position close to the transmitting station side and operates as a postamplifier for analog signal light and as a preamplifier for digital signal light. Depending on the installation position of the bidirectional optical amplifier, it can operate as a post-amplifier, an in-line amplifier, or a pre-amplifier.

Further, in the present embodiment, as the signal light of the first wavelength band, only the analog signal light of one wavelength is shown, but at the same time, other wavelengths in the first wavelength band are used and other wavelengths are used. It is possible to transmit a plurality of analog or digital signal lights. In addition, similarly, it goes without saying that the signal light of a plurality of wavelengths can be transmitted as the signal light of the second wavelength band.

Furthermore, the idea of the present invention also includes the case where there are three or more wavelength bands transmitted by the multiplexer / demultiplexer.

In this embodiment, the 1.5 μm band optical amplifier to which the rare earth erbium is added has been described.
The present invention can obtain the same effect with respect to optical amplifiers of different wavelength bands using other rare earths such as neodymium and praseodymium, and does not limit the constituent materials or the like.

[0116]

As described above, according to the present invention,
It is possible to provide an optical fiber amplifier having an equal gain of signal lights of multiple wavelengths. Further, it is possible to provide a bidirectional optical fiber amplifier that amplifies multi-wavelength signal light input from two different directions with equal gain. Further, even when the optical fiber amplifiers are connected in multiple stages, the amount of light received in the light receiving section becomes equal among the channels, so that an optical transmission system with stable characteristics can be provided.

Further, according to the present invention, even when the bidirectional optical amplifiers are connected in multiple stages, the bidirectional gain becomes uniform, so that it is possible to provide an optical transmission system which can obtain stable characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an optical fiber amplifier according to the present invention.

FIG. 2 is a graph showing the wavelength dependence of gain in an erbium-doped optical fiber used in an example of the present invention.

FIG. 3 is a diagram showing an input light amount dependency of an excitation light transmitted light amount in an erbium-doped optical fiber used in an example of the present invention.

FIG. 4 is a diagram comparing the gains of the signal light of 1.53 μm and the signal light of 1.56 μm used in the embodiment of the present invention.

FIG. 5 is a diagram showing the configuration of another embodiment of the optical fiber amplifier according to the present invention.

FIG. 6 is a diagram showing the configuration of still another embodiment of the optical fiber amplifier according to the present invention.

FIG. 7 is a diagram showing the configuration of still another embodiment of the optical fiber amplifier according to the present invention.

FIG. 8 is a diagram showing the configuration of still another embodiment of the optical fiber amplifier according to the present invention.

FIG. 9 is a diagram showing the configuration of still another embodiment of the optical fiber amplifier according to the present invention.

FIG. 10 is a diagram showing a configuration of an embodiment of a bidirectional optical amplifier according to the present invention.

FIG. 11 is a diagram showing the configuration of another embodiment of the bidirectional optical amplifier according to the present invention.

FIG. 12 is a diagram showing the configuration of still another embodiment of the bidirectional optical amplifier according to the present invention.

FIG. 13 is a diagram showing the configuration of still another embodiment of the bidirectional optical amplifier according to the present invention.

FIG. 14 is a diagram showing the configuration of still another embodiment of the bidirectional optical amplifier according to the present invention.

FIG. 15 is a diagram showing the configuration of still another embodiment of the bidirectional optical amplifier according to the present invention.

FIG. 16 is a diagram showing a configuration of an embodiment of an optical fiber transmission system according to the present invention.

FIG. 17 is a diagram showing the configuration of another embodiment of the optical fiber transmission system according to the present invention.

FIG. 18 is a graph showing the difference in the 1.53 μm digital signal transmission characteristic depending on the presence or absence of the second erbium-doped optical fiber in the bidirectional optical amplifier according to the present invention.

[Explanation of symbols]

11 pumping semiconductor laser with a wavelength of 0.98 μm 12 and 13 pumping semiconductor laser with a wavelength of 1.48 μm 21 multiplexer / demultiplexer of 0.98 μm light and 1.55 μm light 22, 23 1.48 μm light and 1.55 μm Optical multiplexer / demultiplexer 24 Wavelength band 1.55 μm or less and 1.5
5 μm optical multiplexer / demultiplexer 25, 26, 27 Optical isolator 31, 32, 33 Erbium-doped optical fiber 34, 35, 36 Optical fiber 46, 47 Optical circulator 48 Multiplexer / demultiplexer 51 Input to optical fiber 34 The first signal light 52 is output from the optical fiber 35 and the amplified first signal light 53 is input to the optical fiber 34. The second signal light 54 is output from the optical fiber 36. Signal light 55 0.98 μm pumping light 56, 57 1.48 μm pumping light 101 Transmitting station 102 Signal light source 103 Light receiver 104 Combiner / demultiplexer 105 Subscriber 106 Signal light source 107 Light receiver 108 Combiner / demultiplexer 111 Light Fiber amplifier 114 Bidirectional optical amplifier 121 1x8 optical branching device 131 Optical fiber

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01S 3/17 H04B 10/17 10/16

Claims (20)

[Claims] 1. A plurality of rare earth-doped optical fibers connected in series, and at least one pumping light source for generating pumping light for pumping the plurality of rare earth-doped optical fibers connected in series, An optical fiber amplifier that optically amplifies a plurality of input signal lights having different wavelengths, wherein a first signal light of the plurality of signal lights is a plurality of rare earth-doped lights connected in series. The rare-earth doped optical fiber propagates through a part of the rare-earth doped optical fibers, and the second signal light of the plurality of signal lights propagates all the rare-earth doped optical fibers of the plurality of rare-earth doped optical fibers connected in series. Propagating fiber optic amplifier. 2. A branch optical fiber connected in the middle of the plurality of rare earth-doped optical fibers connected in series, wherein the first signal light is output via the branch optical fiber. The optical fiber amplifier according to claim 1. 3. A branch optical fiber connected in the middle of the plurality of rare earth-doped optical fibers connected in series, wherein the first signal light is input via the branch optical fiber. The optical fiber amplifier according to claim 1. 4. The light according to claim 1, wherein each of the plurality of rare earth-doped optical fibers is excited into a state in which a gain higher than a gain for the second signal light is given to the first signal light. Fiber amplifier. 5. The optical fiber amplifier according to claim 1, wherein the at least one pumping light source includes a semiconductor laser. 6. A multiplexer / demultiplexer that multiplexes the pumping light generated by the pumping light source and the plurality of signal lights,
The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier is connected to any one of the input sections of the plurality of rare earth-doped optical fibers connected in series. 7. A multiplexer / demultiplexer for multiplexing the pumping light generated by the pumping light source and the plurality of signal lights,
The optical fiber amplifier according to claim 1, wherein the optical fiber amplifier is connected to any one of the output sections of the plurality of rare earth-doped optical fibers connected in series. 8. A light which selectively transmits both the light belonging to the first wavelength band and the light belonging to the second wavelength band and which does not belong to the first and second wavelength bands is introduced into the branch optical fiber. 4. The optical fiber amplifier according to claim 2, wherein the separating means is provided in the middle of the plurality of rare earth-doped optical fibers connected in series. 9. The wavelength of the first signal light is not included in the first wavelength band and the second wavelength band, and the wavelength of the second signal light is the first wavelength band or the first wavelength band. The optical fiber amplifier according to claim 8, which is included in the second wavelength band. 10. The optical fiber amplifier according to claim 8, wherein the wavelength of the pumping light is included in the first wavelength band or the second wavelength band. 11. The wavelength of the first signal light is longer than the wavelength of the second signal light, the first signal light is analog-modulated, and the wavelength of the second signal light is digitally modulated. The optical fiber amplifier according to claim 8, which is provided. 12. A first input / output part for outputting at least a first signal light and inputting a second signal light, and at least for inputting the first signal light and outputting the second signal light A bidirectional optical amplifier comprising: a second input / output portion; and an optical fiber amplifier connected to the first input / output portion and the second input / output portion, wherein the optical fiber amplifier is serial A plurality of rare earth-doped optical fibers connected to each other and at least one pumping light source for generating pumping light for pumping the plurality of rare earth-doped optical fibers connected in series, and having different input wavelengths. An optical fiber amplifier for optically amplifying a plurality of signal lights, wherein a first signal light of the plurality of signal lights is a plurality of rare earth-doped optical fibers connected in series. Propagated through some rare earth-doped optical fibers, The second of the plurality of signal lights
Of the plurality of rare earth-doped optical fibers connected in series is an optical fiber amplifier that propagates through the rare earth-doped optical fibers, and the first signal light received from the optical fiber amplifier is A bidirectional optical amplifier further comprising demultiplexing means for selectively propagating to the first input / output portion. 13. The first signal light input from the first input / output unit and the first signal light input to the second input / output unit are combined to generate the first signal light. A multiplexing means for inputting both the light and the second signal light into the input parts of the plurality of rare earth-doped optical fibers connected in series,
The bidirectional optical amplifier according to claim 12. 14. A multiplexing unit is provided for inputting the first signal light input from the second input / output portion in the middle of the plurality of rare earth-doped optical fibers connected in series. The bidirectional optical amplifier according to claim 12. 15. The bidirectional optical amplifier according to claim 12, wherein the first input / output portion includes a first optical circulator, and the second input / output portion includes a second optical circulator. 16. The method according to claim 12, wherein the first input / output portion is provided with a first multiplexing / demultiplexing means, and the second input / output portion is provided with a second multiplexing / demultiplexing means. Bidirectional optical amplifier. 17. A transmitting station including a first signal light source for emitting a first signal light and a first light receiver for detecting a second signal light, and a second station for detecting the first signal light. Receiver, and a receiving station including a second signal light source for emitting the second signal light, an optical fiber transmission line connecting the transmitting station and the receiving station, and an optical fiber transmission line in the middle of the optical fiber transmission line. An optical fiber transmission system comprising: an optical fiber amplifier provided, wherein the optical fiber amplifier comprises a plurality of rare earth-doped optical fibers connected in series and a plurality of rare earth-doped optical fibers connected in series. An optical fiber amplifier, which comprises at least one pumping light source for generating pumping light for pumping a fiber, and which optically amplifies a plurality of input signal lights having different wavelengths, The first signal light of the Of the plurality of rare earth-doped optical fibers, the second signal light of the plurality of signal lights propagates through the rare earth-doped optical fibers, and the second signal light of the plurality of signal lights of the plurality of rare earth-doped optical fibers connected in series is used. An optical fiber transmission system that propagates all rare-earth-doped optical fibers. 18. At least 1 as the first signal light
The optical fiber transmission system according to claim 17, wherein one analog-modulated signal light is used, and a plurality of digitally-modulated signal lights are used as the second signal light. 19. A transmitting station including a first signal light source for emitting a first signal light and a first light receiver for detecting a second signal light, and a second station for detecting the first signal light. Of the optical receiver, and a receiving station including a second signal light source for emitting the second signal light, an optical fiber transmission line connecting the transmitting station and the bidirectional optical amplifier, and an optical fiber transmission line of the optical fiber transmission line. A bidirectional optical fiber transmission system including a bidirectional optical amplifier provided on the way, wherein the bidirectional optical amplifier outputs the first signal light and inputs the second signal light. A second input / output section, a second input / output section for inputting the first signal light and outputting the second signal light, and a first input / output section and a second input / output section connected to the second input / output section. And an optical fiber amplifying section, wherein the optical fiber amplifying section comprises a plurality of rare earth-doped optical fibers connected in series. And at least one pumping light source that generates pumping light for pumping the plurality of rare earth-doped optical fibers connected in series, and optically amplifies a plurality of input signal lights having different wavelengths. In the optical fiber amplification section, the first signal light of the plurality of signal lights propagates through a part of the plurality of rare earth-doped optical fibers connected in series. , A second of the plurality of signal lights
Of the plurality of rare earth-doped optical fibers connected in series is an optical fiber amplifier that propagates through the rare earth-doped optical fibers, and the first signal light received from the optical fiber amplifier is A bidirectional optical fiber transmission system further comprising a demultiplexing means for selectively propagating to the first input / output portion. 20. At least 1 as the first signal light
The bidirectional optical fiber transmission system according to claim 19, wherein one analog-modulated signal light is used, and a plurality of digitally-modulated signal lights are used as the second signal light.