JP3036521B2 - Optical transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical amplifier, an optical transmission device, and an optical transmission system, and more particularly to an optical transmission device and an optical transmission system with a low noise figure.

[0002]

2. Description of the Related Art Along with a demand for lowering the cost of an optical transmission system, a wavelength division multiplexing optical transmission system for transmitting signal lights having different wavelengths to one optical transmission fiber is being studied. In particular,
When it is necessary to exchange information bidirectionally between opposing stations, a bidirectional optical transmission system that bidirectionally transmits signal lights having different wavelengths to one transmission fiber is suitable. In such a technical background, it is important to provide an optical amplifier applicable to a bidirectional optical transmission system.

As a conventional method related to this, Japanese Patent Laid-Open No.
JP-A-85369 discloses that a single optical amplifying medium and a single pumping light source are shared in the forward and reverse directions by providing means for multiplexing and demultiplexing signal light in both forward and reverse directions at both ends of a doped fiber. An optical amplifier that can be applied to a bidirectional optical transmission system and has a simple configuration is described.

Japanese Patent Application Laid-Open No. 9-98136 discloses that
An optical amplifier capable of controlling individual wavelength outputs using an optical signal (probe light) in an amplification band of an optical amplifier even when a signal wavelength multiplexing degree changes is described.

Further, the conventional one-way transmission apparatus is described in "Optical Amplifier and Its Application" (Ohm, May, 1992) 5-3.
As described in [1], it is indispensable to insert an optical isolator in the preceding stage of the doped fiber for suppressing reflection of stimulated emission light. In the optical transmission device having such a configuration,
The optical components required to be inserted before the doped fiber are not limited to optical isolators. In general, optical components such as a wavelength separator for monitoring light wavelength separation, a coupler for monitoring transmission signal strength, and a wavelength multiplexer for pumping light multiplexing, which are necessary as a transmission device, are required, and have respective losses. 25 to 35
In order to obtain a gain of dB, it is necessary to combine a pumping semiconductor laser of about 100 mW with an erbium-doped fiber (hereinafter abbreviated as EDF) of 20 to 30 m, and the noise figure of this EDF cannot be ignored. In the optical transmission device having the above configuration, the optical signal that has been lost by the transmission path is subjected to a further loss, and then the noise figure is high.
Since amplification is performed using the DF, it is difficult to make the noise figure (noise figure; hereinafter abbreviated as NF) defined by the ratio of the S / N ratio on the input side to the S / N ratio on the output side less than 6 dB. is there.

[0006]

In the optical amplifier according to the above-mentioned prior art, the following problems occur in an actual use state.

Generally, in an optical amplifier using a doped fiber, it is known that a signal light input loss at a stage prior to the doped fiber causes deterioration of the S / N ratio. JP-A-6-853
No. 69, the optical amplifier for bidirectional transmission, compared to the one-way optical amplifier, due to the coupling loss of the optical circulator to a different fiber and the coupling loss of the optical directional coupler to a different fiber, The signal light input loss increases and the S / N ratio deteriorates.

In the case of multi-relay transmission using k optical amplifiers, the S / N ratio deterioration amount increases in proportion to the number k of stages. Therefore, in an actual optical transmission system in which the total S / N ratio deterioration amount has an upper limit, the number of relay stages decreases as the S / N deterioration amount of the optical amplifier increases. As a result, the optical transmission distance becomes shorter.

For example, under the condition that the total S / N ratio deterioration amount is 12 dB or less, an optical amplifier having an S / N ratio deterioration amount of 4 dB and 6 dB
4dB when each optical amplifier is installed at 80km interval
The optical amplifier has a total S / N deterioration amount of 12 dB by three-stage relay,
The 6 dB optical amplifier also has a total S / N ratio deterioration amount of 12 dB due to the two-stage relay. In other words, an optical amplifier with an S / N deterioration amount of 4 dB can repeat three stages, and thus can transmit 240 km, whereas an optical amplifier with 6 dB can perform only two stages, so that the transmission distance remains 160 km.

An optical amplifier having an optical isolator, a wavelength separator, and the like in front of a doped fiber has a disadvantage that NF deteriorates.

[0011] A first object of the present invention is to eliminate the above-mentioned disadvantages, and is applicable to an optical transmission system.
An object of the present invention is to provide an optical amplifier suitable for long-distance optical transmission while suppressing deterioration of the / N ratio.

A second object of the present invention is to provide an optical transmission device having a low NF.

[0013] A third object of the present invention is to provide an optical transmission system suitable for long-distance optical transmission.

[0014]

In order to solve the above-mentioned object, a transmission device comprises a low-pumped buffer optical amplifier in contact with a transmission line and a core optical amplifier in contact with the buffer optical amplifier. With this configuration, the signal light weakened by propagation in the transmission path can be amplified by the buffer optical amplifier before the optical signal such as the optical isolator loses the input signal. NF degradation can be prevented.

Thus, it is possible to achieve an optical amplifier and an optical transmission device which are applicable to one-way and two-way optical transmission systems, suppress deterioration of the S / N ratio, and are suitable for long-distance optical transmission. Further, by using the optical transmission device, a one-way and two-way optical transmission system suitable for long-distance optical transmission can be achieved.

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 shows a basic functional block diagram of an example of the optical transmission system according to the first embodiment of the present invention. The optical transmission system includes an optical transmitter 2 including a plurality of optical transmitters 1, an optical receiver 4 including a plurality of optical receivers 3, and a terminal relay device 5. Further, the terminal relay device 5, the intermediate relay device and
Are connected by at least one transmission line 7, and according to this configuration, the optical transmitter 2-1 to the optical receiver 4-2, or the optical transmitter 2-2 to the optical receiver 4-1. The signal light is transmitted bidirectionally. (In the following drawings, displays a 2-1 for simplicity of illustration 2 _1.) Line status of the transmission line 7, the monitoring light introduced from the monitoring device 8 to the transmission line by monitoring light demultiplexer 9 The monitoring light guided by the monitoring light multiplexer / demultiplexer 9 in the terminal relay device 5 or the intermediate relay device 6 is monitored by introducing the monitoring light into the monitoring device 8. However, the monitoring device is not essential, and removing it does not affect the effects of the present invention.

The transmission line 7-1 is connected to at least one buffer optical amplifier 10-1 installed in the terminal repeater 5-1.
, And the buffer optical amplifying device 10-1 is connected to at least one core optical amplifying device 11-1 provided via a monitoring optical multiplexer / demultiplexer 9-1. Further, the core optical amplifier 11-1 is connected to the optical multiplexer / demultiplexer 12-1, and is connected to at least one optical transmitter 1 and optical receiver 3. The terminal relay device 5-2 has the same configuration.

The transmission lines 7-1 and 7-2 are connected to a buffer optical amplifier 10-
2 or 10-3. The buffer optical amplifier 10-2 or 10-3 is connected to the core optical amplifier 11-2 via the monitoring optical multiplexer / demultiplexer 9-2 or 9-3.
It is connected to the. The intermediate relay device 6-2 has the same configuration.

In this transmission system, any number of intermediate repeaters 6 may be installed in series. In this configuration, a so-called bidirectional transmission system is used, but a similar configuration can be applied to a unidirectional transmission system.

According to this configuration, the signal light weakened by the transmission path loss can amplify the input signal by the buffer optical amplifier before receiving the loss of the optical device, so that the NF of the entire optical transmission apparatus can be amplified. Deterioration can be prevented. As a result, an optical transmission system suitable for long-distance optical transmission can be provided.

An example of the optical transmission device according to the second embodiment of the present invention will be described with reference to FIG. FIG. 2 shows FIG.
Out of the two-way optical transmission system shown in FIG.
1 shows a specific configuration diagram. In FIG. 2, the signal light from the transmission line 7-1 is introduced into a buffer optical amplifier 10-1. The introduced signal light is partially split by the optical splitter 13. The split signal light passes through an optical filter 14 that removes the monitoring signal light, and is detected by a photodetector 15. The detected input monitor signal is transmitted to the optical amplifier 16 in the core optical amplifier 11-1.

The signal light passing through the optical splitter 13 is multiplexed by the optical multiplexer 17 together with the pumping light from the pumping light source 18 and introduced into the rare-earth-doped optical fiber 19. Since the rare earth-doped optical fiber 19 is in an excited state by the pumping light, the signal light is amplified and passed through the monitoring light multiplexer / demultiplexer 9-1 to be introduced into the optical multiplexer / demultiplexer 20 in the core optical amplifier 11-1. Is done. After being introduced into the optical amplifier 16 and amplified by the optical multiplexer / demultiplexer 20, a part of the signal light is split by the optical splitter 22 via the optical multiplexer / demultiplexer 21. The split light is detected by the photodetector 23 and transmitted to the optical amplifier 16 in the core optical amplifier 11-1 as an output monitor signal. The signal light that has passed through the splitter 22 is transmitted to the optical multiplexer / demultiplexer 12-.
Reach 1 In the optical multiplexer / demultiplexer 12-1, the signal light is demultiplexed into a predetermined wavelength and reaches the optical receiver 4-1 (not shown).

Here, the optical splitters 13 and 22, the photodetectors 23 and 15 and the optical filter 14 do not necessarily have to be at this position. For example, after the optical amplifier 16,
A plurality of optical multiplexer / demultiplexers 12-1 may be provided at the subsequent stage for each path.

The signal light in the opposite direction from the optical transmitter 2-1 (not shown) is supplied to the optical multiplexer / demultiplexer 12 in the terminal repeater 5-1.
After being multiplexed by -1, the light is partially branched by the optical branching unit 22 in the core optical amplifying device 11-1, and the branched light is detected by the photodetector 24, and is used as an input monitor signal. It is transmitted to the optical amplifier 25 in 11-1.

The signal light passing through the optical splitter 22 is amplified by the optical amplifier 25 via the optical multiplexer / demultiplexer 21. The amplified signal light reaches the monitoring optical multiplexer / demultiplexer 9-1 by the optical multiplexer 20 and passes through the monitoring optical multiplexer / demultiplexer 9-1. Is introduced in the opposite direction to the signal light and amplified.
The amplified signal light passes through the optical multiplexer 17 and passes through the optical splitter 1.
3 is partially branched. The split light passes through an optical filter 26 for removing the monitor signal light, is detected by a photodetector 27, and is output as an output monitor signal to the core optical amplifier 1
The signal is transmitted to the optical amplifier 25 in 1-1. The signal light that has passed through the optical splitter 13 is configured to be delivered to the transmission path 7-1.

Here, the optical splitter 22 and the photodetector 24
Need not necessarily be in this position. For example, a plurality of paths may be provided for each path before the optical amplifier 25 or before the optical multiplexer 12-1. The optical splitter 13, the optical filter 26, and the photodetector 27 do not necessarily need to be at this position. For example, it may be installed downstream of the optical amplifier 25, upstream of the buffer optical amplifier, or the monitoring optical multiplexer / demultiplexer 9-1.
May be installed in the preceding stage.

On the other hand, monitoring light from a monitoring light source (not shown) is introduced by a monitoring light multiplexer / demultiplexer 9-1, passes through a buffer optical amplifier 10-1, and is introduced into a transmission line.

The optical amplifiers 16 and 25 are configured to be controlled by an input monitor signal and an output monitor signal.

In the conventional terminal repeater, the optical multiplexer 20 and the supervisory optical multiplexer / demultiplexer 9-1 installed in the preceding stage of the optical amplifier 16 are used.
In addition, optical loss caused by an optical device such as an optical isolator installed in the optical amplifier 16 causes deterioration of the NF of the terminal relay device as a whole. As in the present invention, before the weakened signal light from the transmission line 7-1 receives the loss of the optical device, the buffered optical amplifier 10
As a result of the configuration in which the input signal is amplified by -1, it is possible to prevent NF degradation of the entire terminal relay device.

At the same time, the buffer photomultiplier 10-1 of this configuration
Has a fiber length of 3 to 6 m and a gain of 10 to 16 dB, which is low pumping. Therefore, it is not necessary to use an optical isolator which is indispensable in a conventional optical amplifier for suppressing reflection of stimulated emission light. Further, since the buffer optical amplifier 10-1 itself has a short fiber length, its NF deterioration is low. As a result, it is possible to prevent NF deterioration of the entire terminal relay device 5-1.

Next, another embodiment of the optical transmission apparatus according to the second embodiment of the present invention will be described with reference to FIG.

FIG. 3 shows a specific configuration diagram of the intermediate repeater 6-1 in the bidirectional optical transmission system shown in FIG.
The signal light from the transmission line 7-1 is supplied to the buffer optical amplifier 10-
2 is introduced. The introduced signal light is partially split by the optical splitter 28, and the split signal light passes through the optical filter 29 for removing the monitoring signal light and is detected by the photodetector 30. The detected input monitor signal is transmitted to the optical amplifier 36 in the core optical amplifier 11-2.

The signal light passing through the optical splitter 28 is multiplexed by the optical multiplexer 32 together with the pumping light from the pumping light source 33, and is introduced into the rare-earth-doped optical fiber 34. Since the rare earth-doped optical fiber 34 is in an excited state by the pumping light, the signal light is amplified, passed through the monitoring light multiplexer / demultiplexer 9-2, and introduced into the optical multiplexer / demultiplexer 35 in the core optical amplifier 11-2. You. The signal light is converted by the optical multiplexer / demultiplexer 35 into an optical amplifier 36
After being introduced to the amplifier and amplified, the light passes through the monitoring optical multiplexer / demultiplexer 9-3 via the optical multiplexer / demultiplexer 37 and passes through the buffer optical amplifier 10-3.
Into the rare earth-doped optical fiber 38.

The rare earth-doped optical fiber 38 is
Since the pumping light from No. 9 is multiplexed and introduced by the optical multiplexer 40 and is in an excited state, the signal light is amplified and the optical multiplexer 40
, And is partially branched by the optical branching device 41. The split light passes through an optical filter 42 for removing the supervisory signal light, is detected by a photodetector 43, and is transmitted as an output monitor signal to the optical amplifier 36 in the core optical amplifier 11-2. The signal light passing through the optical splitter 41 is transmitted to the transmission path 7-2.
Will be delivered to

However, the optical splitter 41, the optical filter 42, and the photodetector 43 need not always be located at this position. For example, it may be installed after the optical amplifier 36, before the buffer optical amplifier 10-3, or the monitor optical multiplexer / demultiplexer 9.
-3 may be installed at the preceding stage.

The signal light in the opposite direction from the transmission path 7-2 is introduced into the buffer light amplifier 10-3. The introduced signal light is partially split by the optical splitter 41, and the split light passes through the optical filter 44 for removing the monitor signal light and is detected by the photodetector 45. The detected input monitor signal is transmitted to the optical amplifier 31 in the core optical amplifier 11-2.

The signal light passing through the optical splitter 41 is multiplexed by the optical multiplexer 40 together with the pumping light from the pumping light source 39, and is introduced into the rare-earth-doped optical fiber 38. Since the rare-earth-doped optical fiber 38 is in an excited state by the pump light, the signal light is amplified, passed through the monitor light multiplexer / demultiplexer 9-3, and introduced into the optical multiplexer / demultiplexer 37 in the core optical amplifier 11-2. You. The signal light is converted by the optical multiplexer / demultiplexer 37 into an optical amplifier 31
After being introduced into the amplifier and amplified, it passes through the monitoring optical multiplexer / demultiplexer 9-2 via the optical multiplexer / demultiplexer 35 and passes through the buffer optical amplifier 10-.
2 is introduced into the rare earth-doped optical fiber 34. Since the excitation light from the excitation light source 33 is multiplexed and introduced by the optical multiplexer 32 and is in an excited state, the signal light is amplified, passes through the optical multiplexer 32, and partially passes through the optical splitter 28. It is forked. The split light passes through an optical filter 46 that removes the monitor signal light, is detected by a photodetector 47, and is transmitted as an output monitor signal to the optical amplifier 31 in the core optical amplifier 11-2. Optical splitter 28
Is transmitted to the transmission path 7-1.

However, the optical splitter 28, the optical filter 46 and the photodetector 47 need not always be located at this position. For example, it may be installed after the optical amplifier 31 or before the buffer optical amplifier 10-2 or the monitoring optical multiplexer / demultiplexer 9.
-2 may be installed at the preceding stage.

On the other hand, the monitoring light from the monitoring light source (not shown) is introduced by the monitoring light multiplexers / demultiplexers 9-2 and 9-3, passes through the buffer optical amplifiers 10-2 and 10-3, and is transmitted through the transmission line 7.
-1, 7-2. The optical amplifiers 31, 36
Are controlled by an input monitor signal and an output monitor signal.

In the conventional intermediate repeater, the optical amplifier 31,
The optical multiplexers 35 and 37, the monitoring optical multiplexers / demultiplexers 9-2 and 9-3 installed in front of the optical amplifier 36, and the optical devices such as optical isolators installed in the optical amplifiers 31 and 36 cause optical loss. This has been a factor of deteriorating the NF of the entire relay device. As in the present embodiment, the transmission paths 7-1 and 7-2
Before the weakened signal light receives the loss of the optical device, the buffer light amplifying device 10-2 or 10-
As a result, the NF deterioration of the entire intermediate repeater can be prevented.

At the same time, the buffer photomultiplier 10-
According to 2, 10-3, it is not necessary to use an optical isolator, which is indispensable in the conventional optical amplifier, so that it is possible to prevent NF deterioration of the buffer optical amplifiers 10-2 and 10-3 themselves, Consequently, the NF of the entire intermediate repeater 6-1
Deterioration can be prevented.

Next, another embodiment of the optical transmission apparatus according to the second embodiment of the present invention will be described with reference to FIGS.

Here. FIG. 4 is a block diagram specifically showing the functions of the terminal relay device. FIG. 5 is a block diagram showing a buffer optical amplifier. FIG. 6 and FIG.
FIG. 3 is a block diagram specifically showing functions of a control device. FIG. 8 to FIG. 10 are diagrams showing experimental results using the intermediate repeater.

In FIG. 4, the signal light is λ1 = 153.
0.33 nm, λ2 = 1531.90 nm, λ3 = 15
Probe light is transmitted by a probe light source 48 having a wavelength of 33.47 nm and λ4 = 1535.04 nm, and a wavelength of λp1 = 1543.73. Further, λ5 = 1555.75 nm, λ6 = 155
7.36 nm, λ7 = 1558.98 nm, λ8 = 15
Four wavelengths of 60.61 nm are received, and a probe light is received by a probe light receiver (not shown) of λp2 = 1546.92.

The wavelengths λ1 to λ4 are split by the optical splitters 22-1 to 22-4 having a split ratio of 5:95, and detected by the photodetectors 24-1 to 24-4, respectively. The detected input monitor signal of each wavelength is transmitted to a control device 49 in the optical amplifier 25 described later. The signal light and the probe light that have passed through the optical splitters 22-1 to 22-4 are multiplexed by the optical multiplexer 50 in the optical multiplexer / demultiplexer 12-1 and pass through the dispersion compensator 51 in the optical amplifier 25. . The dispersion compensator 51 transmits the signal light to the transmission paths 7-1 to 7-.
4 to compensate for the dispersion characteristics caused by passing.
The multiplexed light that has passed through the dispersion compensator 51 is
2 and is introduced into the rare earth-doped optical fiber 53.

The rare earth-doped optical fiber 53 is
Excitation light is introduced from the semiconductor laser having an oscillation wavelength near 1480 nm, which is 4, through the optical multiplexer 55, and is in an excited state. Therefore, the multiplexed light is amplified, passed through the optical isolator 56, the optical multiplexer 20, and the monitoring optical multiplexer / demultiplexer 9-1, and introduced into the buffer optical amplifier 10-1. The monitoring light and signal light of 1.48 μm are multiplexed by the monitoring light multiplexer / demultiplexer 9-1.

The multiplexed light introduced into the buffer light amplifying device 10-1 is obtained by combining the pumping light from a semiconductor laser (pumping light source 18) having an oscillation wavelength near 980 nm with the optical multiplexer 17.
Is introduced into the erbium-doped optical fiber as the rare-earth-doped optical fiber 19. Although the erbium-doped optical fiber 19 is in an excited state, only the multiplexed light of λ1 to λ4 and the probe light are amplified,
The 1.48 μm surveillance light passes after experiencing some loss. The excitation light source 18 is monitored by a photodetector 57 that detects a part of the light output from the excitation light source 18, and is controlled by a control device 58 so that the excitation light source monitor signal becomes constant.

The amplified multiplexed light and the monitor light of 1.48 μm are partially branched by the optical branching device 13 having a branching ratio of 5:95, pass through the narrow band optical filter 26 that allows the probe light to pass through, and are combined with the probe light. The part is detected by the photodetector 27. The detected probe light monitor signal is transmitted to the control device 49. The control device 49 controls the excitation light source 54 so that the probe light monitor signal is constant.

By controlling the probe light monitor signal to be constant in this way, it is possible to control all the signal lights λ1 to λ4 to a constant output.

That is, even when one of the signal lights λ1 to λ4 is interrupted, or when a signal light having a wavelength other than the signal lights λ1 to λ4 is newly added, the signal light λ1
To λ4 (for example, when λ4 is interrupted, λ1 to λ
The light output of 3) is not affected, and can be controlled constantly and stably.

The multiplexed light and monitor light that have passed through the optical splitter 13 are delivered to a single-mode transmission fiber, which is the transmission path 7-1.

Here, the dispersion compensator 51 may be omitted if the dispersion characteristics of the transmission line do not affect the transmission characteristics of the entire system. The installation location of the dispersion compensator 51 does not necessarily need to be at this position. The portions of the rare earth-doped optical fiber 53, the pumping light source 54, and the optical multiplexer 55 may be replaced with a semiconductor optical amplifier. In this case, the amplification factor may be controlled by the excitation current instead of the excitation light source 54. Similarly, the rare earth-doped optical fiber 19, the excitation light source 1
8 and the optical multiplexer 17 may be replaced with a semiconductor optical amplifier.

On the other hand, the multiplexed light of the opposite signal lights λ5 to λ8 and λp2 sent from the transmission fiber 7-1 and the monitor light of 1.48 μm are partly split by the optical splitter 13 having a split ratio of 5:95. Only a part of the probe light is detected by the photodetector 15 after passing through the narrow band optical filter 14 which is branched and allows the probe light to pass. The detected input monitor signal is transmitted to a control device 59 described later. The multiplexed light and the monitoring light that have passed through the optical splitter 13 are pumped by the optical multiplexer 17 in the buffer optical amplifier 10-1.
And is amplified by an erbium-doped optical fiber 19. In this case, similarly, only the multiplexed light of λ5 to λ8 and λp2 receives amplification.
The 48 μm surveillance light passes after undergoing some loss.
The 1.48 μm surveillance light that passed therethrough is transmitted to the surveillance light multiplexer / demultiplexer 9-
1 and delivered to the monitoring light path. The multiplexed light passes through the optical multiplexer 20, passes through the optical isolator 60 in the optical amplifier 16, and has a wavelength of 980 nm as the pump light source 61.
Excitation light from a semiconductor laser having an oscillation wavelength nearby is multiplexed by an optical multiplexer 62 and amplified by an erbium-doped optical fiber 63. The excitation light source 61 is monitored by a photodetector 64 that detects a part of the light output from the excitation light source 61, and is controlled by a control device 65 so that the excitation light source monitor signal becomes constant.

The amplified signal light is supplied to an optical isolator 66
, Is introduced into the dispersion compensator 67, is amplified by the second erbium-doped optical fiber 68, passes through the optical multiplexer 69, and is output from the optical isolator 70. The second erbium-doped optical fiber 69 is a semiconductor laser having an oscillation wavelength near 980 nm (the second pump light source 7).
It is multiplexed with the pumping light from 1) and is in a pumping state. The multiplexed light from the optical isolator 70 is partially split by the optical splitter 72 having a split ratio of 5:95. The split multiplexed light is passed through a narrow-band optical filter 7 that allows the probe light to pass through.
3 and only a part of the probe light is detected by the photodetector 74. The detected output monitor signal is transmitted to the control device 59 in the optical amplifier 16 and controls the excitation light source 71 so that the output monitor signal becomes constant.

The multiplexed light that has passed through the optical splitter 72 is split by the optical splitter 75 in the optical multiplexer / demultiplexer 12-1 for each of the wavelengths λ5 to λ8 and λp2. The light is split by 5:95 optical splitters 22-5 to 22-8 and detected by the photodetectors 23-1 to 23-4, respectively (the receiver of λp2 is not shown).
The detected output monitor signal of each wavelength is transmitted to the control device 59 in the optical amplifier 16. Optical splitter 22-5
The signal light of each wavelength that has passed through 22-8 is delivered to a terminal device (not shown).

The buffer amplifier 10-1 in this configuration
, The signal input power from the transmission path 7-1 is -5 dBm to -30 dBm per wavelength, and the signal amplification gain of the buffer amplifier 10-1 is about 10 dB. Since no optical isolator is provided in the buffer optical amplifier 10-1, attention must be paid to the light oscillation phenomenon.

Therefore, the signal amplification gain of the buffer amplifier 10-1 is desirably 30 dB or less, and more desirably 16 dB or less. The NF in the terminal repeater for the signal input from the transmission line 7-1 is clearly improved from the conventional system by making the signal amplification gain of the buffer amplifier 10-1 a positive gain, but is more desirable. Is 5 dB or more.

The amplification gain distribution of the core optical amplifier 11-1 and the buffer optical amplifier 10-1 is performed by first setting
It is desirable to calculate from the required output power to 1. For example, the output power to the transmission line is +11 per signal wavelength.
Since the total signal power (λ1 to λ4 and λp1) is +18 dBm when it is set to dBm, it is desirable to set the power of the pump light source 18 to about 1.25 to 3.3 times this power. When the power of the pump light source is insufficient, as shown in FIG. 5, a new pump light source 18-a, a photodetector 57-a for detecting this light output, and a control device 58-a for keeping the detected monitor signal constant. , And an optical multiplexer 17-a for introducing pumping light may be provided to perform bidirectional pumping on the erbium-doped optical fiber. However, the transmission path 7
Pump light source 18 which is forward-pumped with respect to multiplexed light of -1
Is desirably installed in any case.

The input power of the multiplexed light delivered from the optical amplifier 25 to the buffered optical amplifier 10-1 is changed according to the set capability of the pumping light source 18 as follows.
1 (+11 dBm) −X dB]. The range of X is preferably from 0 to 20. By adjusting the value of X, the signal amplification gain with respect to the signal input power in the reverse direction, that is, the signal input power from the transmission line 7-1 is set as described above.
It is possible to set a more desirable value.

Here, the pump light source 54 in the optical amplifier 25
May use a 980 nm semiconductor laser. Also,
The excitation light source 71 in the optical amplifier 16 may use a 1480 nm semiconductor laser.

However, the pump light source 18 in the buffer optical amplifier 10-1 and the pump light source 61-1 in the optical amplifier 16 are provided.
Most preferably, a 980 nm semiconductor laser is used. This is 980n higher than the excitation at 1480nm.
This is because the excitation at m is lower noise.

As the monitoring light, a wavelength other than 1.48 μm, for example, 1.51 μm can be used. This is common to the following embodiments.

Next, a specific configuration example of the control device 49 is shown in FIG.
Shown in The output monitor signal transmitted to the control device 49 has a reference value 7 determined in advance by the comparator 76.
7 to control the excitation light source 54 (not shown) by transmitting an error signal from the reference value 77 to the drive circuit 78.

The input monitor signals corresponding to λ1 to λ4 transmitted to the control device 49 have the reference value 7 respectively.
9 is compared with a comparator 80, and when it is higher than a predetermined value, a normal signal is detected by the wavelength number detection circuit 8
1 and, if low, an abnormal signal. The wavelength number detection circuit 81 counts the number of wavelengths of the transmitted normal signal and determines the number of wavelengths that can be transmitted at present. If there is no wavelength that can be transmitted, an alarm is issued. At this time, the alarm is also transmitted to the drive circuit 78 at the same time, and the drive circuit 78 receiving the alarm controls the excitation light source 54 (not shown) to stop.

Next, a specific configuration example of the control device 59 is shown in FIG.
Shown in The output monitor signal transmitted to the control device 59 is compared with a predetermined reference value 83 by a comparator 82, and an error signal from the reference value 83 is output to the drive circuit 8.
4 to control the excitation light source 71 (not shown).

Λ5 to λ8 transmitted to the control device 59
And an input monitor signal corresponding to λp2 are compared by a reference value 85 and a comparator 86, respectively. When the output monitor signal is higher than a predetermined value, a normal signal is transmitted to the wavelength number detection circuit 87. If it is low, an abnormal signal is transmitted. The wavelength number detection circuit 87 counts the number of wavelengths of the transmitted normal signal and determines the currently transmittable wavelength number. If there is no wavelength that can be transmitted, an alarm is issued. At this time, an alarm is issued simultaneously to the drive circuit 84.
The driving circuit 84 receiving the signal also transmits the excitation light source 7
1 (not shown).

Control may be performed so that an alarm is issued even when the transmittable signal is only λp2.

The buffer optical amplifier 10-1 of the present invention is characterized in that multiplexed light is introduced into the rare-earth-doped optical fiber 19 from both directions, and the multiplexed light is amplified in both directions. Also,
It is characterized in that weak multiplexed light introduced from the transmission path 7-1 is amplified before receiving a large loss.

As described above, the control device 58
By controlling the output of the pump light source 18 to be constant, the NF of the buffer amplifier 10-1 can be maintained stably and low, and can function as an optical amplifier having a substantially constant gain. . It is important to control the output of the pumping light source 18 at a constant level in order to reduce the wavelength dependence of the gain that the rare earth-doped optical fiber generally has and to suppress the wavelength deviation fluctuation of the gain which is a problem in the transmission characteristics.

As described above, by controlling the output of the probe light to be constant by the control device 49, it is possible to automatically control the multiplexed light output to the transmission line 7-1 of the buffer optical amplifier 10-1. Becomes possible.

FIGS. 8 to 10 show the measurement results of the input / output characteristics of signal light and NF in this embodiment. Here, FIGS. 8 and 9 are diagrams illustrating measured values of the entire system of the buffer optical amplifier and the core optical amplifier. FIG. 10 is a diagram showing measured values of only the buffer optical amplifier.

Here, the measurement points of the experiment will be described with reference to FIG. 4. The input power in FIG. 8 is the signal level from the transmission line 17-1, and the output power in FIG. This is the later signal level. ASE LEVEL
Is a value obtained by dividing the spontaneous emission light (ASE) near 1550 nm by the wavelength, and is a value used for calculating the S / N ratio on the output side.

FIG. 8 shows the input signal level, the output level of the optical amplifier in the core amplifier, and the ASE LEV.
From the EL, the gain and NF of the entire system of the buffer optical amplifier and the core optical amplifier are required. In this experiment, the buffered optical amplifier 1 was used as a signal in the reverse direction.
It is assumed that a signal of about +11 dBm amplified by the optical amplifier 25 is introduced to 0-1 and a signal output of +17 dBm is always delivered to the transmission line 17-1. this is,
The purpose of this is to check the margin of the buffer optical amplifier used for two directions, and the signal input in the opposite direction of about +11 dBm
This is the maximum possible value. At this time, the output power of the pumping light source in the buffer optical amplifier supplied a power of about 110 mW corresponding to about 2.2 times the signal output +17 dBm.

According to FIG. 8 and FIG. 9 in which the gain and the NF are plotted with respect to the input power in FIG.
It is apparent that the NF for the input signal from No. 1 is controlled to be constant at 3.9 dB or less. According to the present invention, control can be performed to 4.5 dB or less even in consideration of temperature fluctuations in an actual system and manufacturing variations.
Further, it can be reduced to 4.0 dB or less by maintaining the experimental configuration in the actual system.

In this experiment, the pump power of the semiconductor laser 61-1 as the first-stage pump light source of the optical amplifier 16 was set to 75 m.
Since the output power is set to W, the output power cannot be controlled to be constant, but the output power can be controlled to be constant by setting the pump power to 100 to 120 mW.

According to FIG. 10, while maintaining the signal output in the reverse direction +17 dBm, the buffer optical amplifier 10
-1 from the transmission line 7-1 is about 10d
It can be seen that B is constant.

Next, another embodiment of the optical transmission apparatus according to the second embodiment of the present invention will be described with reference to FIG.

FIG. 11 is a block diagram more specifically showing the configuration and functions of the intermediate repeater.

The signal light is transmitted from the transmission line 7-1 at λ1 = 15
30.33 nm, λ2 = 1531.90 nm, λ3 = 1
Four wavelengths of 533.47 nm and λ4 = 1535.04 nm are transmitted, and λp1 = 1543.73.
Is transmitted. Also, the transmission path 7-2
From λ5 = 1555.75 nm, λ6 = 1557.3
6 nm, λ7 = 1558.98 nm, λ8 = 1560.
Four wavelengths of 61 nm are transmitted, and λp2
= 1546.92 probe light is transmitted.

The present embodiment is different from the terminal repeater shown in FIG. 4 in that buffer optical amplifiers 10-2 and 10-3 are provided.
Are installed at both ends of the core optical amplifier 11-2, and the core optical amplifier 11-2 has optical amplifiers 31 and 36 having the same configuration as the optical amplifier 16 in FIG.
This is the point that is composed of two.

The multiplexed light of the signal lights λ1 to λ4 and λp1 sent from the transmission fiber 7-1 and 1.48 μm
The monitoring light is partially branched by the optical branching device 28 having a branching ratio of 5:95, passes through the narrow band optical filter 29 for passing the probe light, and only a part of the probe light is
Is detected by The detected input monitor signal is transmitted to a control device 59-2 described later. The multiplexed light and monitor light that have passed through the optical splitter 28 are supplied to the buffer optical amplifier 10-
98 as the excitation light source 33 by the optical multiplexer 32 in
The light is multiplexed with excitation light from a semiconductor laser having an oscillation wavelength near 0 nm, and is introduced into an erbium-doped optical fiber as the rare-earth-doped optical fiber 34. At this time, the erbium-doped optical fiber 34 is in an excited state, but only the multiplexed light from λ1 to λ4 and the probe light are amplified, and the 1.48 μm monitoring light is subjected to a slight loss. pass.

The excitation light source 33 is monitored by a photodetector 57-2 for detecting a part of the light output from the excitation light source 33, and is controlled by a control device 58-2 so that the excitation light source monitor signal becomes constant. Configuration.

The 1.48 μm monitoring light that has passed is split by the monitoring light multiplexer / demultiplexer 9-2 and delivered to the monitoring light path. The multiplexed light passes through the optical multiplexer 35, passes through the optical isolator 60-2 in the optical amplifier 36, and generates the pump light source 61-2.
And multiplexed by an optical multiplexer 62-2 with an excitation light from a semiconductor laser having an oscillation wavelength near 980 nm, and amplified by an erbium-doped optical fiber 63-2. The excitation light source 61-2 is monitored by a photodetector 64-2 that detects a part of the light output from the excitation light source 61-2, and is controlled by the control device 65-2 so that the excitation light source monitor signal becomes constant. It is configured to control.

The amplified signal light is supplied to an optical isolator 66-
2, the light is introduced into the dispersion compensator 67-2, amplified by the second erbium-doped optical fiber 68-2, passed through the optical multiplexer 69-2, and then passed through the optical isolator 70-2.
2 is output. Second erbium-doped optical fiber 6
8-2 is 980 nm as the second excitation light source 71-2
It is multiplexed with pump light from a semiconductor laser having an oscillation wavelength nearby and is in an excited state. The multiplexed light from the optical isolator 70-2 is supplied to the optical multiplexer 37 and the monitoring optical multiplexer / demultiplexer 9-.
3 and is introduced into the buffer optical amplifier 10-3. The monitor light and the signal light of 1.48 μm are multiplexed by the monitor light multiplexer / demultiplexer 9-3.

The multiplexed light introduced into the buffer light amplifying device 10-3 is obtained by converting an excitation light from a semiconductor laser having an oscillation wavelength in the vicinity of 980 nm as an excitation light source 39 into a rare earth-doped optical fiber 38 by an optical multiplexer 40. An erbium-doped optical fiber is introduced. Although the erbium-doped optical fiber 38 is in an excited state, only the multiplexed light of λ1 to λ4 and the probe light are amplified, and the monitor light of 1.48 μm receives a slight loss after receiving a slight loss.
pass.

The excitation light source 39 is monitored by a photodetector 57-3 for detecting a part of the light output from the excitation light source 39, and is controlled by a control device 58-3 so that the excitation light source monitor signal becomes constant. It has a configuration. The amplified multiplexed light and the monitor light of 1.48 μm are partially branched by an optical branching device 41 having a branching ratio of 5:95, pass through a narrow band optical filter 42 that allows the probe light to pass, and a part of the probe light is light. It is detected by the detector 43. The detected probe light monitor signal is transmitted to the control device 59-2. The control device 59-2 controls the excitation light source 71-2 so that the probe light monitor signal becomes constant. By controlling the probe light monitor signal to be constant in this way, it is possible to control all the signal lights λ1 to λ4 to a constant output.

When any one of the signal lights λ1 to λ4 is interrupted, or when a signal light having a wavelength other than the signal lights λ1 to λ4 is newly added, the signal lights λ1 to λ4
The light output of (for example, from λ1 to λ3 when λ4 is interrupted) is not affected, and can be controlled constantly and stably.

The multiplexed light and monitor light that have passed through the optical splitter 41 are delivered to a single-mode transmission fiber, which is the transmission path 7-2.

Rare earth doped optical fibers 34, 63-2, 6
8-2, 38, excitation light sources 33, 61-2, 71-2, 3
9 and the optical multiplexers 32, 62-2, 69-2, and 40 may be replaced with semiconductor optical amplifiers. In this case, the amplification factor may be controlled by the excitation current instead of the excitation light sources 33, 61-2, 71-2, and 39.

On the other hand, the multiplexed light of λ5 to λ8 and λp2 sent from the transmission fiber 7-2 and the monitor light of 1.48 μm are partially transmitted by the optical splitter 41 having a split ratio of 5:95. Only a part of the probe light is detected by the photodetector 45 after passing through the narrow-band optical filter 44 that allows the probe light to pass. The detected input monitor signal is transmitted to a control device 59-3 described later.

The multiplexed light and monitor light that have passed through the optical splitter 41 are combined with the pump light from a semiconductor laser having an oscillation wavelength near 980 nm as the pump light source 39 by the optical multiplexer 40 in the buffer light amplifier 10-3. The wave is introduced into the erbium-doped optical fiber as the rare-earth-doped optical fiber 38, and the erbium-doped optical fiber 38 is in an excited state. However, only the multiplexed light and the probe light from λ5 to λ8 are amplified, The 1.48 μm surveillance light passes after experiencing some loss.

The excitation light source 39 is monitored by a photodetector 57-3 for detecting a part of the light output from the excitation light source 39, and is controlled by a control device 58-3 so that the excitation light source monitor signal becomes constant. It has a configuration. The 1.48 μm monitoring light that has passed is split by the monitoring light multiplexer / demultiplexer 9-3 and delivered to the monitoring light path. The multiplexed light passes through the optical multiplexer 37, passes through the optical isolator 60-3 in the optical amplifier 31, and 980n as the pump light source 61-3.
Excitation light from a semiconductor laser having an oscillation wavelength near m is multiplexed by an optical multiplexer 62-3 and amplified by an erbium-doped optical fiber 63-3. Also, the excitation light source 61
-3 is monitored by a photodetector 64-3 which detects a part of the light output from the excitation light source 61-3, and is controlled by the control device 65-3 so that the excitation light source monitor signal becomes constant. ing.

The amplified signal light is supplied to an optical isolator 66-
3, the light is introduced into the dispersion compensator 67-3, amplified by the second erbium-doped optical fiber 68-3, and then passed through the optical multiplexer 69-3 to form an optical isolator 70-3.
3 is output. Second erbium-doped optical fiber 6
8-3 is 980 nm as the second excitation light source 71-3.
It is multiplexed with pump light from a semiconductor laser having an oscillation wavelength nearby and is in an excited state. The multiplexed light from the optical isolator 70-3 is supplied to the optical multiplexer 35 and the monitoring optical multiplexer / demultiplexer 9-.
2 and is introduced into the buffer optical amplifier 10-2. The monitor light and signal light of 1.48 μm are multiplexed by the monitor light multiplexer / demultiplexer 9-2.

The multiplexed light introduced into the buffer light amplifier 10-2 is introduced into the erbium-doped optical fiber 34 in an excited state by the excitation light from a semiconductor laser having an oscillation wavelength near 980 nm as the excitation light source 33. , .Lambda.5 to .lambda.8, and only the probe light are amplified, and the 1.48 .mu.m monitoring light passes after undergoing some loss.

The excitation light source 33 is monitored by a photodetector 57-2 for detecting a part of the light output from the excitation light source 33, and is controlled by a control device 58-2 so that the excitation light source monitor signal becomes constant. It has a configuration. The amplified multiplexed light and the 1.48 μm monitoring light are partially branched by the optical splitter 28 having a branching ratio of 5:95, pass through a narrow band optical filter 46 that allows the probe light to pass, and a part of the probe light is converted to light. It is detected by the detector 47.

The detected probe light monitor signal is transmitted to the control device 59-3. The control device 59-3 controls the excitation light source 71-3 so that the probe light monitor signal becomes constant. By controlling the probe light monitor signal to be constant in this manner, it is possible to control all the signal lights λ5 to λ8 to a constant output. When any one of the signal lights λ5 to λ8 is interrupted, or when signal light having a wavelength other than the signal light λ5 to λ8 is newly added, the signal light λ5 to λ8 (for example, when λ8 is interrupted) Does not affect the light output of λ5 to λ7), and it is possible to constantly control the output stably and stably.

The multiplexed light and monitor light that have passed through the optical splitter 28 are delivered to a single-mode transmission fiber which is the transmission path 7-1.

Rare earth doped optical fibers 34, 63-3, 6
8-3, 38, excitation light sources 33, 61-3, 71-3, 3
9 and the optical multiplexers 32, 62-3, 69-3, and 40 may be replaced with semiconductor optical amplifiers. In this case, the amplification factor may be controlled by the excitation current instead of the excitation light sources 33, 61-3, 71-3, and 39.

The buffer amplifying device 10- in this configuration
2, the signal input power from the transmission lines 7-1 and 7-2 to the 10-3 is -5 dBm from -30 dBm per wavelength, and the signal amplification gain of the buffer amplifiers 10-2 and 10-3 is about 10 dB. It is about. Buffer optical amplifier 10-
Since no optical isolator is installed in 2, 10-3,
Attention must be paid to the light oscillation phenomenon. Therefore, the signal amplification gain of the buffer amplifiers 10-2 and 10-3 is 30
dB or less, more preferably 16 dB or less.
dB or less. Further, the NF in the intermediate repeater for the signal input from the transmission lines 7-1 and 7-2 is made clearer than the conventional method by making the signal amplification gain of the buffer amplifiers 10-2 and 10-3 positive. Although improved, it is more preferably 5 dB or more.

The amplification gain distribution of the core optical amplifier 11-2 and the buffer optical amplifiers 10-2 and 10-3 can be calculated first from the required output power to the transmission lines 7-1 and 7-2. desirable. For example, when the output power to the transmission lines 7-1 and 7-2 is +11 dBm per signal wavelength,
Total signal power (λ1 to λ4 and λp1 or λ5
Since λ8 and λp2) are +18 dBm, the power of the pump light sources 33 and 39 is about 1.25 of this power.
Is preferably set to 3.3 times. When the power of the pump light source is insufficient, as shown in FIG. 5, a new pump light source 18-a, a photodetector 57-a for detecting this light output,
A control device 58-a for keeping the detected monitor signal constant and an optical multiplexer 17-a for introducing pumping light may be provided to perform bidirectional pumping on the erbium-doped optical fiber. However, it is desirable to install the pump light sources 33 and 39 which are used for forward pumping the multiplexed light from the transmission paths 7-1 and 7-2.

The input power of the multiplexed light distributed from the optical amplifiers 31 and 36 to the buffer optical amplifiers 10-2 and 10-3 is changed according to the set capabilities of the pump light sources 33 and 39. , Light output from 10-3 (+
11 dBm) -X dB]. The range of X is preferably from 0 to 20. By adjusting the value of X, the signal amplification gain for the signal input power in the opposite direction, that is, the buffer optical amplifier 10-2 is transmitted from the transmission line 7-1 and the buffer optical amplifier 10-3 is transmitted from the transmission line 7-1. It is possible to set a more desirable value.

Here, the pumping light sources 71-2 and 71-3 in the optical amplifiers 31 and 36 are 1480, which is advantageous for high-power pumping.
nm semiconductor laser may be used.

However, the buffer optical amplifiers 10-2, 1
Pump light sources 33 and 39 and optical amplifiers 31 and 3 in 0-3
As the excitation light sources 61-2 and 61-3 in 6, a 980 nm semiconductor laser is preferably used.

As described above, the terminal relay device 5-1 is the terminal relay device 5-2, and the intermediate relay device 6-1 is the intermediate relay device 6-
Needless to say, it can be similarly applied to 2, 6-3 and the like.

Further, the terminal relay device and the intermediate relay device of the present invention may have a configuration in which constituent blocks included therein are provided outside the buffer optical amplifier. For example, FIG. 12 shows an embodiment in which the monitoring light multiplexers / demultiplexers 9-2 and 9-3 are provided outside the buffer amplifier. FIG. 12 is a block diagram specifically showing the configuration and functions of the intermediate relay device.

As is apparent from a comparison of this embodiment with the embodiment shown in FIG. 11, the multiplexed light of the signal lights λ1 to λ4 and λp1 sent from the transmission fiber 7-1,
The monitor light of 1.48 μm means that the monitor light multiplexer / demultiplexer 9-
Separated by two. The monitoring light is converted into an electric signal by a monitoring light receiver (not shown). On the other hand, in the multiplexed signal light, only a part of the probe light is detected by the photodetector 30 as in the embodiment of FIG. Buffer optical amplifier 1
The multiplexed signal light amplified in 0-2 is further amplified in the optical amplifier 36. Next, the subsequent-stage buffer amplifier 10-3
, And are multiplexed with the monitoring light from a monitoring light source (not shown) by the monitoring light
-2.

The multiplexed light of the signal lights λ5 to λ8 and λp2 sent from the transmission fiber 7-2 is also amplified exactly as described above. Also, the monitoring light of 1.51 μm is reproduced and relayed in the same manner as described above.

As described above, the monitoring optical multiplexer / demultiplexers 9-2 and 9-
3 is provided on the transmission fiber side of the buffer optical amplifier,
The insertion loss for the signal light cannot be ignored and is 1.0 dB.
Hereinafter, it is more preferably set to 0.4 dB or less. However, the isolator 60 having a large insertion loss for the signal light.
Since the signal is once amplified at the stage prior to -2 and the optical demultiplexers 35 and 37, NF in the entire transmission device can be greatly improved.

Next, an embodiment of a one-way transmission device serving as a base of the two-way transmission device shown in FIG. 12 will be described with reference to FIGS.

FIG. 13 is a block diagram for explaining an embodiment of the one-way transmission apparatus according to the present invention. First, the multiplexed light of the signal lights λ1 to λ4 and λp1 sent from the transmission fiber 7-1 and the monitor light of 1.48 μm are separated by the monitor light multiplexer / demultiplexer 9-2. The monitoring light is converted into an electric signal by a monitoring light receiver (not shown). On the other hand, as for the multiplexed signal light, only a part of the probe light is detected by the photodetector 47 as in the embodiment of FIG. The multiplexed signal light amplified by the buffer optical amplifier 10-2 is
Is further amplified. Next, the light is multiplexed with the monitoring light from a monitoring light source (not shown) by the monitoring light multiplexer / demultiplexer 9-3 and transmitted to the transmission fiber 7-2.

The insertion loss of the monitoring light multiplexer / demultiplexer 9-2 with respect to the signal light cannot be ignored, and is set to 1.0 dB or less, more preferably 0.4 dB or less. However, since the signal is once amplified before the isolator 60-3 having a large insertion loss with respect to the signal light, NF in the entire transmission device can be significantly improved. As an example, NF, which was about 7.0 dB in the designed transmission device without providing a buffer amplifier, has been greatly improved to 4.0 dB or less by providing a buffer amplifier. Further, as described in FIG. 11, the monitoring optical multiplexer / demultiplexer 9-2 is connected to the buffer amplifier 10-2 and the optical amplifier 31.
NF can be improved by providing between them.

Here, the effectiveness of the present embodiment will be obtained by calculation. First, in the configuration without the conventional buffer amplifier, the insertion loss of the monitoring optical multiplexer / demultiplexer 9-2 is reduced by 0.4 d.
B, the insertion loss of the input signal monitoring coupler 88 is 0.25 dB, and the loss of the isolator 60-3 is 1.25.
Assuming that the dB and the NF of the impurity-doped fiber are 3.5 dB and there is a signal input of -27 dBm, the NF of the entire transmission device is 7 dB or more.

On the other hand, in the embodiment shown in FIG. 13, the insertion loss of the monitoring optical multiplexer / demultiplexer 9-2 is 0.4 dB, and the insertion loss of the input signal monitoring coupler 88 is 0.25.
dB, the gain of the buffer amplifier 10-2 is 15.5 dB,
Eleven pre-stage impurity doped fibers 63-3 of the core amplifier
Is 15.5 dB, and the loss of the dispersion compensator 67-3 is 1
If the gain of the post-impurity doped fiber 68-3 of 0 dB and 11 of the core amplifier is 18 dB, an NF of 3.9 dB can be achieved as a whole transmission apparatus.

The improvement of the NF of 3 dB depends on the S / N of the signal.
This means that the transmittable distance can be extended by about 100 km, and a significant improvement has been obtained.

Next, another embodiment of the one-way transmission apparatus according to the present invention will be described with reference to FIGS. here,
FIGS. 14 and 15 are block diagrams each illustrating an embodiment of the one-way transmission device of the present invention. The difference between the two is the difference in the position of the pump light source that pumps the impurity-doped fiber of the buffer amplifier. That is, in the transmission apparatus of FIG. 14, backward pumping is performed in the opposite direction to the signal light transmission direction. On the other hand, in the transmission device of FIG. 15, the forward pumping is the same as the transmission direction of the signal light. Generally, the forward excitation has lower noise, so only FIG. 15 will be described here. However, all the contents are common to FIG.

The embodiment shown in FIG. 15 is the one-way transmission apparatus shown in FIG. 13, and three pump light sources 33, 61, and 7 are used.
This is an embodiment of a transmission device in which 1 is reduced to 2 units and economy is achieved. The process of amplifying the signal is exactly the same as in the embodiment of FIG. 13 and will not be described. In the configuration of the present embodiment, the excitation light from the excitation light source 33 of 120 mW output that excites the impurity-doped fiber 34 is guided to the coupler 120 having a branching ratio of 2: 8. The pump light from the port having a branching ratio of 2 of the coupler 120 pumps the impurity-doped fiber of the buffer amplifier. The pumping light from the port having a branching ratio of 8 of the coupler 120 pumps the impurity-doped fiber 63-3 of the core amplifier. In this embodiment, the wavelength of the excitation light is 0.9
8 μm was used. This is because the noise is lower than other pump light wavelengths, for example, 1.48 μm.

With this configuration, the NF can be improved only if the gain of the buffer amplifier is about 10 to 16 dB and the fiber length of the impurity-doped fiber 34 is 3 to 6 m.
This is because the degree is good. Conversely, if the buffer amplifier is highly excited, an optical isolator is required at the input stage, which is contrary to the object of the present invention. The gain of the core amplifier due to the impurity-doped fiber 63-3 is 10 to 20 d.
B, The fiber length is 10 to 20 m.

In this embodiment, the transmission fibers 7-1 and 7-
Since a fiber having a large dispersion in the 1.5 μm band is assumed as 2, the dispersion compensator 67-3 is used. For this reason, in order to compensate for the signal loss caused by the dispersion compensator 67-3, the core amplifier includes another one-stage impurity doped fiber 68-3.
Is provided. However, it is apparent that a dispersion compensator 67-3, an impurity-doped fiber 68-3, and a pump light source 71-3 are not required as a transmission device for a transmission line using DSF having a small dispersion in the 1.5 μm band. .

According to the present embodiment, since the signal is once amplified at the stage before the isolator 60-3 having a large insertion loss with respect to the signal light, the NF of the entire transmission device can be greatly improved. As an example, NF, which was about 7.0 dB in the designed transmission device without providing a buffer amplifier, has been greatly improved to 4.0 dB or less by providing a buffer amplifier. Furthermore, since the pump light source of the buffer amplifier and the core amplifier can be shared, an economical transmission device can be obtained.

In all the embodiments described above, the relationship between the doped fiber and the excitation light source is not limited to the configuration shown in the drawing. The pumping may be forward pumping in the same direction as the signal direction, backward pumping in the direction opposite to the signal direction, or bidirectional pumping.

[0121]

According to the present invention, in an optical transmission system constituted by a terminal repeater and an intermediate repeater,
A highly reliable optical amplifier and optical transmission device capable of long-distance transmission can be provided. Also, a highly reliable long-distance optical transmission system could be provided.

[Brief description of the drawings]

FIG. 1 is a basic functional block diagram of a bidirectional optical transmission system according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating functions of a terminal relay device according to an embodiment of the present invention.

FIG. 3 is a block diagram illustrating functions of an intermediate relay device according to an embodiment of the present invention.

FIG. 4 is a block diagram specifically showing the configuration and functions of a terminal relay device according to an embodiment of the present invention.

FIG. 5 is a block diagram illustrating a buffer light amplifying device according to an embodiment of the present invention.

FIG. 6 is a block diagram specifically showing the configuration and functions of a control device according to an embodiment of the present invention.

FIG. 7 is a block diagram specifically showing a configuration and a function of a control device according to the embodiment of the present invention.

FIG. 8 is a diagram showing a measurement result by the whole system of the buffer amplifier and the core amplifier according to the embodiment of the present invention.

FIG. 9 is a diagram showing a measurement result by the whole system of the buffer amplifier and the core amplifier according to the embodiment of the present invention.

FIG. 10 is a diagram showing an experimental result by the buffer amplifier according to the embodiment of the present invention.

FIG. 11 is a block diagram specifically showing a configuration and a function of an intermediate relay device according to an embodiment of the present invention.

FIG. 12 is a block diagram illustrating a configuration of a bidirectional transmission device according to an embodiment of the present invention.

FIG. 13 is a block diagram illustrating a configuration of a one-way transmission device according to an embodiment of the present invention.

FIG. 14 is a block diagram illustrating a configuration of a one-way transmission device according to an embodiment of the present invention.

FIG. 15 is a block diagram illustrating a configuration of a one-way transmission device according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical transmitter, 2 ... Optical transmitter, 3 ... Optical receiver, 4 ... Optical receiver, 5 ... Terminal relay device, 6 ... Intermediate relay device, 7 ...
Transmission line, 8 monitoring device, 9 monitoring light multiplexer / demultiplexer, 10 buffer optical amplifier, 11 core optical amplifier, 12, 2
0, 21, 35, 37 ... optical multiplexer / demultiplexer, 13, 22, 2
8, 41, 72 ... optical branching device, 14, 26, 29, 42,
44, 46, 73 ... bandpass optical filters, 15, 23,
24, 27, 30, 43, 45, 47, 57, 64, 7
4: photodetector, 16, 25, 31, 36: optical amplifier, 1
7, 32, 40, 50, 55, 62, 69 ... optical multiplexer,
18, 33, 39, 54, 61, 71 ... excitation light source, 1
9, 34, 38, 53, 63, 68 ... rare earth-doped optical fiber, 48 ... probe light source, 49, 58, 59, 65 ...
Control device, 51, 67 ... dispersion compensator, 52, 56, 6
0, 66, 70: Optical isolator, 75: Optical demultiplexer, 7
6, 80, 82, 86 ... comparators, 77, 79, 83, 8
5 Reference value, 78, 84 Drive circuit, 81, 87 Wavelength number detection circuit, 100 First terminal station, 101 Optical circulator, 102 Optical directional coupler, 103 Doped fiber, 104 Laser Diode, 105 optical circulator, 106 optical directional coupler, 107 second terminal station, 108 optical transmission path, 109 optical transmission path, 120 coupler.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H04B 10/17 H04B 9/00 G 10/24 -297469 (JP, A) JP-A-9-138432 (JP, A) JP-A-9-98136 (JP, A) JP-A-5-292036 (JP, A) JP-A-8-204267 (JP, A JP-A-10-271094 (JP, A) JP-A-10-107352 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/10 H01S 3/06 H01S 3 / 07 H01S 3/23 H04B 10/16 H04B 10/17 H04B 10/24

Claims (5)

(57) [Claims] An optical transmission device for transmitting an optical signal in two directions, comprising: a first optical signal transmitted from a first transmission line; and a second optical signal transmitted in a direction opposite to the first optical signal. A first optical amplifier for amplifying the first optical signal, a second optical amplifier for amplifying the second optical signal transmitted from the second transmission line, and the first optical signal; A third optical amplifier that amplifies the first signal; a fourth optical amplifier that amplifies the second signal; and a third optical amplifier that amplifies the first optical signal from the first optical amplifier.
A first optical multiplexer / demultiplexer for transmitting the second optical signal from the fourth optical amplifier to the first optical amplifier, and transmitting the second optical signal from the fourth optical amplifier to the first optical amplifier. A second optical multiplexer / demultiplexer for transmitting the second optical signal to the fourth optical amplifier and transmitting the first optical signal from the third optical amplifier to the second optical amplifier. apparatus. 2. The optical transmission device according to claim 1 , wherein the gain of the first optical amplifier and the gain of the second optical amplifier are 16 dB or less. 3. An optical transmission device for transmitting an optical signal in two directions, comprising: an optical transmitter, an optical receiver, a first optical signal transmitted from a transmission line, and a first optical signal. A first optical amplifier that amplifies a second optical signal transmitted in the opposite direction, a second optical amplifier that amplifies the first optical signal, and a third optical amplifier that amplifies the second optical signal An optical amplifier, and the first optical signal from the first optical amplifier to the second
A first optical multiplexer / demultiplexer for transmitting the second optical signal from the third optical amplifier to the first optical amplifier, and transmitting the second optical signal from the third optical amplifier to the first optical amplifier. A second optical multiplexer / demultiplexer for transmitting the first optical signal to a third optical multiplexer / demultiplexer, and transmitting the second optical signal from the third optical multiplexer / demultiplexer to the third optical amplifier; And the third optical multiplexer / demultiplexer transmits the first optical signal from the second optical multiplexer / demultiplexer to the optical receiver, and the second optical multiplexer / demultiplexer from the optical transmitter. An optical transmission device for transmitting a signal to the second optical multiplexer / demultiplexer. 4. An optical transmission device for transmitting an optical signal in two directions, wherein a first optical signal transmitted from a first transmission line and a second optical signal transmitted in a direction opposite to the first optical signal. A first optical amplifier for amplifying the second optical signal; a second optical amplifier for amplifying the first optical signal; a third optical amplifier for amplifying the second optical signal; The first optical signal from the optical amplifier of
A first optical multiplexer / demultiplexer for transmitting the second optical signal from the third optical amplifier to the first optical amplifier, and transmitting the second optical signal from the third optical amplifier to the first optical amplifier. A second optical multiplexer / demultiplexer that transmits the first optical signal to a second transmission path and transmits the second optical signal from the second transmission path to the third optical amplifier. Transmission equipment. A 5. The optical transmission device according to claim 3 or claim 4, the optical transmission and wherein the gain of said first optical amplifier is less than 16 dB.