JPH1093509A - Optical amplifier relay system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow the system to withstand a path change by reducing the system cost. SOLUTION: An optical amplifier 10 and an optical receiver 12 are connected by an optical transmission line relaying optical fiber transmission lines 14-1-14-5 with optical amplifiers 16-1-16-4. Specifications of the optical amplifiers 16-1-16-4, especially the gain of them is completely the same and the system is designed to compensate the loss of the longest optical transmission line 14-3. Optical attenuators 18-1, 18-2, 18-4 are connected properly to output stages of the optical amplifiers 16-1-16-4 so that an input optical level to optical fiber transmission lines 14-2-14-5 of the next stage does not exceed a limit power. That is, the gain of the optical amplifiers 16-1-16-4 is made constant and the attenuation of the optical attenuators 18-1, 18-2, 18-4 connecting to the output stage is individually adjusted to as to adjust the signal level to be a limit power or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical amplification repeater system.

[0002]

2. Description of the Related Art FIG. 3 shows a schematic configuration of a conventional optical amplification repeater system. FIG. 3A shows a schematic configuration block diagram of an optical amplification repeater system, and FIG. 3B shows an optical amplifier 116-1.
And (3) show changes in the signal light level when the gains of the optical amplifiers 116-1 to 116-4 are individually set. .

A plurality of optical fiber transmission lines 114-1, 114-2, 114 are provided between an optical transmitter 110 and an optical receiver 112.
, 114-5 are replaced by optical amplifiers 116-1, 116-
, 116-4 are connected. The signal light transmitted from the optical transmitter 110 is attenuated while propagating through the optical fiber transmission line 114-1, but is amplified by the optical amplifier 116-1. Thereafter, the attenuation by the optical fiber transmission lines 114-2 to 114-4 and the amplification by the optical amplifiers 116-2 to 116-4 are repeated, attenuated by the optical fiber transmission line 114-5, and input to the optical receiver 112. .

When an optical amplification repeater system as shown in FIG. 3A is laid on land, optical amplifiers 116-1 to 116-1
-4, the optical fiber transmission line 114
It is difficult to make all the lengths of -1 to 114-5 the same. Therefore, the optical fiber transmission lines 114-1 to 114-
In general, the amount of loss of the optical signal due to No. 4 differs. Further, when such an optical amplification repeater system is configured, in order to avoid deterioration of transmission characteristics due to nonlinear optical effects (such as stimulated Brillouin scattering and self-phase modulation effect) in the optical fiber, the optical amplifiers 116-1 to 116- It is necessary to limit the output light power of No. 4 to a certain value Pt or less.

On the other hand, it is desirable that the optical amplifiers 116-1 to 116-4 be designed with the same specifications from the viewpoint of manufacturing cost and the like. However, when the transmission line lengths of the optical fiber transmission lines 114-1 to 114-5 are not the same, when the optical amplifiers 116-1 to 116-4 are designed with the same specifications and have the same gain, FIG. As shown in 2), the output optical power values of the optical amplifiers 116-1 to 116-4 do not become constant. For example, it may exceed the limit power value Pt, and it is difficult to satisfy desired transmission characteristics.

On the other hand, each of the optical amplifiers 116-1 to 116-1
The gain may be adjusted individually so that the output power value of 116-4 does not exceed Pt. In this case, the power level of the signal light changes as shown in FIG. 3 (3), and the signal light level does not exceed the limit power value Pt at any position.

[0007] As a means for individually adjusting the relay gain of the relay amplifier, a configuration in which a variable attenuator is connected to the output stage of the relay amplifier is described in Japanese Patent Application Publication No. 154338/1995. That is, in this publication, the variable optical attenuator 70 is connected to the output stage of the relay amplifier, and even when the signal wavelength is changed after the optical transmission line is laid, the amplification peak wavelength of the relay amplifier 30 is changed to the changed signal wavelength. A configuration adapted to match is disclosed.

FIG. 4 shows a gain wavelength characteristic (pump wavelength: 1,480 nm, pump power: 30 mW) of a typical erbium-doped optical fiber amplifier used as a relay amplifier in a long-distance optical fiber transmission line. As can be seen from FIG. 4, the gain peak wavelength of the erbium-doped optical fiber amplifier changes with the input power. Therefore, in the configuration described in this publication, the relay loss is adjusted by the variable attenuator 70, and the input power is adjusted so that the gain peak wavelength of the next relay amplifier 30 matches the signal wavelength.

[0009]

As shown in FIG. 3 (3), each of the optical amplifiers 116-1 is used as described above.
Their gains must be individually adjusted so that the output power values of ~ 116-4 do not exceed Pt. In this case, when realizing the optical amplification repeater system, not only must different specifications be made for each of the optical amplifiers 116-1 to 116-4, but also their evaluations must be performed under different conditions. This leads to an increase in the cost of the system.

Also, as described above, the optical amplifiers 116-1 to 116-1
In the optical amplification repeater system in which the specifications of 16-4 are individually set, any one of the optical fiber transmission lines 114-1 to 114-4 is used.
Is difficult to change. For example, if installed on land,
It may be necessary to change the routes of the optical fiber transmission lines 114-1 to 114-4. If the path is changed, the loss of the optical fiber transmission line may be different from the initial loss. In this case, the optical amplifier needs to be readjusted by reviewing the signal level, which consumes a great deal of labor and time.

In the configuration described in Japanese Patent Application Publication No. 154338/1995, the problem of the power limit value is not considered. In addition, since the vicinity of the gain peak wavelength at which noise increases is used, it is not suitable for multistage connection. As shown in FIG. 4, the gain of an optical fiber amplifier generally depends on the input optical power and the wavelength, and the gain peak wavelength strongly depends on the input optical power. Therefore, the gain near the gain peak wavelength strongly depends on both the input optical power and the wavelength. In this regard, the configuration of the above publication using the vicinity of the gain peak wavelength is very difficult to cope with a change in the relay distance.

For example, consider a case where a certain relay section must be lengthened. In this case, the gain peak wavelength must remain the same as the signal wavelength in the repeater amplifier after the repeater section, and the variable attenuator in the preceding stage must be adjusted so as to offset the increase in loss due to the new optical fiber. The amount of attenuation will be reduced. As described above, the gain near the gain peak wavelength strongly depends on the input optical power and the wavelength, so that the input optical power is adjusted so that the attenuation of the variable attenuator is almost the same as the value before the change of the relay distance. Must be finely adjusted, which is very troublesome.

In an optical transmission system, particularly a long-distance optical fiber transmission system, it is common to use a portion having a flat gain wavelength characteristic in a gain band of an optical amplifier, and a gain peak having a large gain difference depending on wavelength. Do not use near the wavelength. After the optical transmission line is laid and the optical communication system is operated, the signal wavelength is not usually changed.

An object of the present invention is to provide an optical amplification repeater system which can solve such inconveniences and can share the specifications of an optical amplifier to be used.

Another object of the present invention is to provide an optical amplifying repeater system capable of flexibly responding to changes in individual optical fiber transmission lines.

[0016]

According to the present invention, in an optical amplification repeater system for repeating and amplifying a signal light transmitted through an optical fiber transmission line by an optical amplifier repeater, each optical amplifier repeater includes:
Optical amplification means having substantially the same specifications (for example, saturated output power, gain and noise characteristics) are provided. The at least one optical amplifying repeater further includes a level adjusting unit connected to at least one of the input stage and the output stage of the optical amplifying unit to adjust the signal light level to a desired value. Then, the input level of each optical fiber transmission line (that is, the output level of the optical amplification repeater)
Is not more than a predetermined limit value.

With such a configuration, the difference in loss between the optical fiber transmission lines can be absorbed by the level adjusting means, so that the signal light level does not exceed the limit power value which causes deterioration of the transmission characteristics due to the nonlinear effect on the transmission line. Easy to adjust. Since the specifications of each optical amplifying means may be substantially the same, the cost and labor of manufacturing and maintenance can be reduced.

The level adjusting means is connected to the input stage and / or the output stage of the optical amplifying means. When the level adjustment means is connected to the input stage and when it is connected to the output stage, in the former case, the signal-to-noise ratio (SN ratio) is inferior to that in the latter case. Means may be sufficient.
Conversely, in the latter case, the SN ratio is good, but high-power optical amplification means is required. The high-power optical amplifying means requires a high pumping light level, and has the disadvantage of lowering reliability and increasing costs due to heat generation as compared with the low-power optical amplifying means. When the level adjusting means is divided into two and distributed to both the input stage and the output stage of the optical amplifying means, both have the advantages and disadvantages depending on the distribution ratio.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention. FIG. 1A is a schematic block diagram of the first embodiment, and FIG. 5 illustrates a change in power level.

A plurality of optical fiber transmission lines 14-1, 14-2,..., 1 are provided between the optical transmitter 10 and the optical receiver 12.
4-5 to optical amplifiers 16-1, 16-2, ..., 16-
The optical transmission line relayed at 4 is connected. In the present embodiment, the specifications of the optical amplifiers 16-1 to 16-4 (for example, the saturation output power, the gain and the noise characteristics) are substantially the same,
It is designed to have a gain that can compensate for the loss amount of the longest optical fiber transmission line (optical fiber transmission line 14-3 in FIG. 1).

In this state, the level of the signal light is
In this embodiment, the output power of each of the optical amplifiers 16-1 to 16-4 is appropriately set to an optical attenuator, since the output power of the optical amplifiers 16-1 to 16-4 may change as shown in (2) and exceed the limit power value Pt. 18
-1, 18-2, and 18-4 are connected, and the attenuation is adjusted so that the input light level to the next-stage optical fiber transmission lines 14-2 to 14-5 is equal to or less than the limited power value Pt or the limited power. Value Pt
The following predetermined value is set. In other words, in the present embodiment, instead of individually adjusting the gains of the optical amplifiers 16-1 to 16-4, the optical attenuators 18-1 and 18-1 connected to the output stage are not adjusted.
By individually adjusting the attenuation amounts of 18-2 and 18-4,
The signal light level is equal to or less than the limit power value Pt or
The following predetermined value is set.

The optical amplifiers 16-1 to 16-16 of the present embodiment
The gain wavelength characteristic of -4 basically shows substantially the same characteristic as the characteristic shown in FIG. 4, but in this embodiment, a flat portion (generally, around 1,540 to 1560 nm) independent of the wavelength is obtained. use. When such a flat portion of the gain wavelength characteristic is used, even if optical amplifiers are connected in multiple stages, the flatness of the characteristic is maintained, and it is suitable for a wavelength division multiplexing transmission system. Suppose that the gain is near the gain peak wavelength (1,530 in FIG. 4).
(1,535 nm), the noise characteristics are poor in this wavelength range, and in the case of multi-stage connection, the signal band providing the maximum gain is extremely narrow. Of course, in the wavelength division multiplexing transmission method, the light intensity level of each wavelength changes with transmission, so that the vicinity of the gain peak wavelength cannot be used.

The signal light output from the optical transmitter 10 is attenuated by the optical fiber transmission line 14-1, and is attenuated by the optical amplifier 16-.
By 1 the signal is amplified to a value equal to or higher than the limit power value Pt. However, the optical attenuator 18-1 attenuates the output light of the optical amplifier 16-1 to the level of the limit power value Pt, and the optical fiber transmission line 14
Input to -2. The signal light propagated through the optical fiber transmission line 14-2 and attenuated is subjected to the limited power value P by the optical amplifier 16-2.
t, but is attenuated to the level of the limit power value Pt by the optical attenuator 18-2, and the optical fiber transmission line 14
Enter -3.

The signal light that has propagated and attenuated in the optical fiber transmission line 14-3 is amplified to the limit power value Pt by the optical amplifier 16-3 and is input to the optical fiber transmission line 14-4. The signal light propagated through the optical fiber transmission line 14-4 and attenuated is temporarily amplified by the optical amplifier 16-4 to the limit power value Pt or more, but is reduced to the level of the limit power value Pt by the optical attenuator 18-4. The signal is attenuated and input to the optical fiber transmission line 14-5. The signal light that has propagated through the optical fiber transmission line 14-5 is input to the optical receiver 12, and is subjected to reception processing.

Thus, in this embodiment, the signal light level does not exceed the limit power value Pt in any part of the optical fiber transmission lines 14-1 to 14-5. In addition, the specifications (for example, saturation output power, gain, and noise characteristics) of the optical amplifiers 16-1 to 16-4 are exactly the same and improved.
Optical attenuators 18-1, 18-2, 18 with variable attenuation
Since -4 can be realized easily and at low cost, the optical amplification repeater system can be realized at a much lower cost than before.

In this embodiment, the optical amplifiers 16-1 to 16-
Although the signal light level temporarily exceeds the limit power value Pt inside and at the output portion of the optical fiber transmission line 1,
In 4-1 to 14-5, the signal light level has the limited power value P
It does not exceed t. Optical amplifiers 16-1 to 16-
For No. 4, an erbium-doped optical fiber is usually used. Even if the signal light level temporarily exceeds the limit power value Pt, the effect on the transmission characteristics of the entire optical transmission line can be almost ignored.

When it is necessary to change the routes of the optical fiber transmission lines 14-1 to 14-4, the loss of the new optical fiber transmission line may be different from that of the previous optical fiber transmission line. Is canceled out by adjusting the attenuation of the optical attenuator connected to the output stage of the subsequent optical amplifier. If the length of the optical fiber transmission line 14-3 is shortened, a new optical attenuator may be inserted in the output stage of the optical amplifier 16-3. Therefore, in the present embodiment, it is possible to easily cope with a change in the optical fiber transmission line, particularly, a change in the length.

It is needless to say that the specifications of the optical amplifiers 16-1 to 16-4 are preferably determined so as to compensate for the largest amount of attenuation due to an expected path change.

In the configuration described in Japanese Patent Application Laid-Open No. 154338/1995, the variable attenuator in the preceding stage of the repeater section is set so that the input optical power of the latter repeater amplifier becomes the same as before the change of the repeater distance. The amount of attenuation must be finely adjusted. That is, while monitoring the optical power on the rear side of the relay section, the attenuation of the variable attenuator on the front side of the relay section is finely adjusted.

However, in this embodiment, the optical attenuator 18-
It is sufficient that the optical power at the output units 1, 18-2, 18-4 is equal to or less than the limit power value Pt.
The adjustment of the attenuation amounts of -1, 18-2, and 18-4 may be roughly. This is also because a part having weak or no wavelength dependency is used as an amplification band of the optical amplifiers 16-1 to 16-4. Optical amplifiers 16-1 to 16-16 due to differences in input optical power
It is not necessary to worry about the fluctuation of the gain of -4, and the operation is extremely simple.

In the embodiment shown in FIG. 1, an optical attenuator connected to the output stage of the optical amplifier reduces the signal light level to the limited power value P.
Although restricted to t or less, a similar optical attenuator may be connected to the input stage of the optical amplifier.

FIG. 2 shows a schematic configuration of the embodiment. FIG. 2A shows a schematic block diagram of the second embodiment.
(2) shows a change in the power level of the signal light.

A plurality of optical fiber transmission lines 24-1, 24-2,..., 2 are provided between the optical transmitter 20 and the optical receiver 22.
4-5 to optical amplifiers 26-1, 26-2, ..., 26-
The optical transmission line relayed at 4 is connected. Also in this embodiment, the specifications (for example, saturation output power, gain and noise characteristics) of the optical amplifiers 26-1 to 26-4 are completely the same, and the longest optical fiber transmission line (the optical fiber transmission line 2 in FIG.
It is designed to have a gain that can compensate for the loss amount of 4-3). As in the case of FIG. 1, the optical amplifiers 26-1 to 26-2
6-4 uses a flat part whose gain does not depend on the wavelength.

In the embodiment shown in FIG. 2, the optical amplifier 26-1
To the input stages of the optical attenuators 28-1 and 28-
2, 28-4 are connected so that the input light levels of the optical amplifiers 26-1 to 26-4 become a constant value Pi. In this embodiment, the optical amplifiers 26-1 to 26-4 have input optical power P
At the time of i, the gain is set so that the output optical power becomes the limited power Pt. Each optical amplifier 26-1 to 26-
4, optical attenuators 28-1, 28-2, and 2 connected to the input stage
By individually adjusting the attenuation of 8-4, the optical amplifier 26
The output light levels of -1 to 26-4 become the limited power value Pt.

Of course, if the output light levels of the optical amplifiers 26-1 to 26-4 are equal to or less than the limit power value Pt, the limit power value P
Deterioration of transmission characteristics due to transmission of light exceeding t can be avoided.

The signal light output from the optical transmitter 20 is attenuated by the optical fiber transmission line 24-1 and is attenuated by the optical attenuator 28-.
It is further attenuated by 1 to reach the level Pi. The optical amplifier 26-1 converts the output light of the optical attenuator 28-1 to the limited power value Pt.
, And input to the optical fiber transmission line 24-2. The signal light propagated and attenuated in the optical fiber transmission line 24-2 is attenuated to the level Pi by the optical attenuator 28-2, and then amplified to the limit power value Pt by the optical amplifier 26-2.
Input to the optical fiber transmission line 24-3. The signal light that has propagated through the optical fiber transmission line 24-3 has been attenuated to the level Pi, is amplified to the limit power value Pt by the optical amplifier 26-3, and is input to the optical fiber transmission line 24-4.

The signal light that has propagated and attenuated in the optical fiber transmission line 24-4 is attenuated to the level Pi by the optical attenuator 28-4, and then amplified to the limit power value Pt by the optical amplifier 26-4. Input to the fiber transmission line 24-5.
The signal light that has propagated through the optical fiber transmission line 24-5 is input to the optical receiver 22, and is subjected to reception processing.

Thus, in the embodiment shown in FIG.
Optical fiber transmission lines 24-1 to 24-5, optical amplifier 26-
1-26-4 and optical attenuators 28-1, 28-2, 28-
In any part of the optical transmission line consisting of
When the level is equal to or higher than the level Pi, the power level becomes equal to or lower than the limit power value Pt. FIG.
The specifications of the optical amplifiers 26-1 to 26-4 are exactly the same as in the embodiment shown in FIG. Since the optical attenuators 28-1, 28-2, and 28-4, whose attenuation can be freely changed, can be realized easily and at low cost, the optical amplification repeater system can be realized at much lower cost than before.

By changing the route, the optical fiber transmission line 24-1 is changed.
If the amount of attenuation changes for ２４24-4, the optical attenuator 2
What can be dealt with by changing the attenuation amounts of 8-1, 28-2, and 28-4 is the same as the case of FIG. When the length of the optical fiber transmission line 24-3 is shortened, a new optical attenuator may be inserted into the input stage of the optical amplifier 26-3.

In the embodiment shown in FIG. 1, the optical amplifier 16-1
To the output stage of 16-4, attenuators 18-1 for level adjustment,
18-2 and 18-4, and in the embodiment shown in FIG.
Although the attenuators 28-1, 28-2, and 28-4 for level adjustment are connected to the input stages of the optical amplifiers 26-1 to 26-4, logically, the input stages and the output stages of the optical amplifiers are connected. An attenuator for level adjustment may be connected to both, and the attenuators on both sides may perform the level adjustment function integrally.

The level adjusting attenuators 18-1, 18-2, and 18-4 are connected to the output stages of the optical amplifiers 16-1 to 16-4. The embodiment shown in FIG. 26-
4, the level adjustment attenuators 28-1 and 28-
2, 28-4, compared with the embodiment shown in FIG.
Although the ratio is good, high-power optical amplifiers 16-1 to 16-4 are required. In other words, in the embodiment shown in FIG. 2, although the SN ratio is inferior, the optical amplifiers 26-1 to 26-2
6-4 may be of low power. The high-power optical amplifier has a disadvantage that the pumping light level must be increased, and the heat generation lowers the reliability and increases the cost as compared with the low-power optical amplifier. Optical attenuator to optical amplifier 16
In the case of distributing to both the input stage and the output stage of -1 to 16-4; 26-1 to 26-4, both of the advantages and disadvantages are obtained depending on the distribution ratio.

Optical attenuators 18-1, 18-2, 18-4;
As the optical elements 28-1, 28-2, and 28-4, any optical element capable of providing a desired optical attenuation can be used, in addition to an optical attenuator in a narrow sense generally used for the purpose of attenuation. For example, using optical components such as optical isolators, optical filters, optical splitters, optical couplers and optical circulators alone or in combination,
If necessary, the optical attenuator may be used in combination with an optical attenuator in a narrow sense.

[0044]

As can be easily understood from the above description, according to the present invention, the specifications of the optical amplifier can be unified in the optical amplification repeater systems having different repeater intervals, and as a result, the system construction cost can be reduced. Can be reduced. In addition, it is possible to flexibly cope with a change in the optical fiber transmission line, particularly, a change in the relay loss, thereby facilitating the path change.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of the present invention and a change in signal light level.

FIG. 2 is a diagram showing a schematic configuration of a second embodiment of the present invention and a change in signal light level.

FIG. 3 is a diagram showing a schematic configuration of a conventional example and a change in signal light level.

FIG. 4 is an example of a gain wavelength characteristic of an optical fiber amplifier.

[Explanation of symbols]

 10: Optical transmitter 12: Optical receiver 14-1 to 14-5: Optical fiber transmission line 16-1 to 16-4: Optical amplifier 18-1, 18-2, 18-4: Optical attenuator 20: Light Transmitter 22: Optical receiver 24-1 to 24-5: Optical fiber transmission line 26-1 to 26-4: Optical amplifier 28-1, 28-2, 28-4: Optical attenuator 110: Optical transmitter 112 : Optical receiver 114-1 to 114-5: optical fiber transmission line 116-1 to 116-4: optical amplifier

Claims (5)

[Claims] 1. An optical amplification repeater system comprising: a plurality of optical fiber transmission lines; and at least one optical amplification repeater for repeating and amplifying signal light transmitted through each optical fiber transmission line. The means comprises optical amplifying means having substantially the same specification, and the at least one optical amplifying and repeating means is further connected to at least one of the input stage and the output stage of the optical amplifying means to bring the signal light level to a desired value. An optical amplifying repeater system comprising level adjusting means for adjusting, wherein an input level of the optical fiber transmission line is equal to or less than a predetermined limit value. 2. The optical amplifying repeater system according to claim 1, wherein said level adjusting means is connected to an input stage of said optical amplifying means. 3. The optical amplifying repeater system according to claim 1, wherein said level adjusting means is connected to an output stage of said optical amplifying means. 4. The optical amplifying repeater system according to claim 1, wherein said level adjusting means is an optical attenuating means. 5. The optical amplification repeater system according to claim 1, wherein each of said optical amplification means has substantially the same amplification characteristics.