JP2000312046A - Optical transmission apparatus, optical amplifier, and optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of a inter-wavelength gain deviation of an optical amplifier caused by a change in an optical fiber transmission path loss or the like. SOLUTION: The operation of an optical amplifier 100 is controlled, based on a received strength of reference light by a means built in the optical transmission apparatus. For example, an output light (wavelength λr) from a reference light source 106 is transmitted being wavelength-multiplexed with a main signal (wavelength λs). An optical relay 100 controls the optical amplifier 100 on the basis of intensity information of the reference light. Monitor light of the relay 107 can be used also as the reference light. Even when a transmitter of wavelength-multiplex signal becomes faulty or a channel number is changed, the operational state or the input power of the optical relay can be kept constant, and an increase in an inter-wavelength gain difference can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission device. Further, the present invention relates to an optical amplifier. Further, the present invention relates to an optical transmission system of the present invention.

[0002]

2. Description of the Related Art A wavelength division multiplexing (WDM) optical transmission system in which a plurality of optical signals having different wavelengths are multiplexed in one optical fiber to transmit information is an extremely effective method for increasing the capacity of optical fiber communication. . EDFAs are used for relaying / amplifying such optical signals.
(Erbium-doped Fiber Amplifier).

FIG. 2 schematically shows a change in a typical example of the gain of an EDFA due to a change in input light intensity. Also,
FIG. 3 shows a typical configuration example of a wavelength division multiplexing optical repeater amplification transmission system using such optical amplifiers in multiple stages. The configuration of FIG. 3 is as follows. First optical transmission terminal device 110-
1 to the second optical transmission terminal apparatus 110-2, between which a two-stage optical repeater 115 is inserted. The optical repeater 115 has at least the optical amplifier 113 therein. In addition, 114-1, 114-2,
And 114-3 are optical transmission lines, more specifically optical fibers. Note that spectrum A in FIG. 3 illustrates a spectrum when the input power is smaller than the standard value, and spectrum B illustrates a spectrum when the input power is larger than the standard value. A plurality of optical transmitters 11 that output main signal lights of different wavelengths λ1 to λn are provided to the optical transmission terminal apparatus 110-1.
1 is arranged. These optical signals are transmitted to the wavelength multiplexer 11.
After being multiplexed in step 2, the signal is input to the optical fiber transmission line 114-1. Then, they are collectively amplified by the optical amplifier 113.

On the other hand, curve 1 in FIG. 2 is a characteristic of the optical amplifier at a certain input power, curve 2 is a characteristic when the input power is smaller than the standard value of the input power, and curve 3 is an input power larger than the input power. This shows the characteristics in the case of power.
This is an optical amplifier that is controlled so as to be constant with respect to a certain input power. Even if the gain is flat with respect to the wavelength as shown by the curve 1, if the input power changes, the gain at the output terminal becomes Change. This is because the inversion distribution state in the EDFA changes, for example, when the input power is small, the gain on the short wavelength side increases when the input power is large, and the gain on the long wavelength side increases when the input power is large.

Several methods have been proposed for expanding the input dynamic range of such a wavelength division multiplexing optical fiber amplifier. A typical example is disclosed in Japanese Patent Laid-Open Publication No. Hei 9-212507, “Optical Equalization Amplifier and Optical Equalization Amplification Method” (Reference 1), in which the output signal level deviation of the optical amplifier is suppressed. A method of controlling an input level to an optical amplifier has been proposed. FIG. 4 illustrates this example. In the optical repeater 125, the optical amplifier 1
A part of the output light of No. 00 is separated by the optical coupler 121, and the light of two specific wavelength bands (for example, center λ1 and λn) is extracted by the wavelength multiplexing optical coupler 122. Then, the light is converted into an electric signal by the photodetector 123 (123-1, 123-2). A variable optical attenuator 12 is provided at the input of the optical amplifier 100.
0 is inserted, and the control circuit 124 controls the variable optical attenuator 12 so that the intensities of the optical signals of the two wavelengths are the same.
The attenuation amount of 0 is controlled.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical transmission device having a large dynamic range. Another object of the present invention is to provide a transmission device having small wavelength dependence even in optical multiplex communication. An object of the present invention is to provide a transmission device having an extremely small optical output deviation.

[0007] The optical amplifier has an uneven amplification factor depending on the level of the optical power. When amplifying wavelength-division multiplexed light using the optical amplifier, it is general that the optical amplifier is collectively amplified. Further, when signals of a plurality of channels having different wavelengths are collectively amplified, the amplification factor has wavelength dependence.

For example, in a wavelength-division multiplexing transmission system as shown in FIG. 3, the S / N ratio of an optical signal deteriorates and the optical power deviates due to the shortage of the dynamic range of an optical amplifier. When such an optical amplifier is used for wavelength division multiplexing transmission, it is a practical difficulty that the wavelength dependency of the gain changes when the input light intensity changes. In other words, in other words, the dynamic range of the optical amplifier is narrow.

That is, the optical transmission terminal device 110-1 is provided with the optical transmitters 111 for outputting the main signal lights having different wavelengths λ1 to λn. These optical signals are multiplexed by a wavelength multiplexer 112, and then are transmitted through an optical fiber transmission line 114-1.
Is input to At this point, the optical signals of each wavelength are set to almost the same output level as shown in the spectrum A of FIG. However, since the loss of each optical fiber transmission line section 114-1, 2, 3 is not constant, the input light intensity to each optical amplifier 113 disposed in the optical repeater 115 and the optical transmission terminal equipment 110-2. Changes, causing a gain gradient. For this reason, a deviation occurs in the optical signal level after transmission as shown in spectrum B of FIG. As a result, in such a transmission system, the S /
This may cause deterioration of the N ratio or increase in the deviation of the optical power, which may deviate from the input dynamic range of the optical receiver 117, resulting in a large deterioration of the characteristics.

In addition to the above-mentioned method of separating the optical signals of the specific two wavelengths, a variable optical attenuator is arranged at the input part of the optical amplifier so that the total light intensity of the main signal input to the optical amplifier is always constant. Methods have also been proposed. However, this method also has a disadvantage that it cannot cope with a change in the number of wavelength channels of the main signal, or a control error occurs due to the influence of accumulation of noise light of the optical amplifier.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical transmission device having a large dynamic range.

Another object of the present invention is to provide a transmission device having small wavelength dependence even in optical multiplex communication. The present invention can provide a transmission device having an extremely small optical output deviation.

Still another object of the present invention is to provide an optical amplifier having a large input dynamic range.

Still another object of the present invention is to provide an optical amplifying device having a small wavelength dependence even in an input in optical wavelength multiplexing. The present invention provides an optical amplifying device having an extremely small optical output deviation.

Still another object of the present invention is to provide an optical transmission system having a large dynamic range even in optical multiplex communication.

It is a further object of the present invention to solve the above-mentioned problems in the conventional optical amplifier control and to provide a practical optical amplifier or optical transmission device. More specific examples of the optical transmission device include a transmitter, a receiver, an optical repeater / optical transmission terminal device, a wavelength division multiplex transmission device, and an add / drop device.

First, the inventive concept of the present invention will be described, and then, main modes of the present invention will be listed.

According to a first aspect of the present invention, there is provided at least an optical input unit, an optical amplifying unit, means for splitting a plurality of wavelength multiplexed lights into a plurality of wavelength bands, and an optical output unit. Signal light having a wavelength different from that of the signal light is at least branched, and the gain of the optical amplifier is controlled to a desired gain based on the intensity level of the light having a wavelength different from the branched main signal light. Optical transmission device. This embodiment can also be used as an optical amplifier.
Similarly, the embodiments of the present invention described below can also function as an optical amplifier together with the optical transmission device.

Thus, the present invention can provide an optical transmission device having a large dynamic range. Furthermore,
The present invention can provide a transmission device with small wavelength dependence even in optical multiplex communication.

Here, in the present invention, it is particularly important to use light having a wavelength different from that of the main signal light for controlling the gain of the optical amplifier. The present invention is an optical signal having a wavelength different from the main signal light used for information transmission, that is, a so-called reference light is wavelength-division multiplexed with the main signal light, the reception intensity of the reference light is measured, and the operation control of the optical amplifier is performed. It can be achieved by doing. The present invention is applicable to a case where the main signal has a single wavelength, but is most effective in optical wavelength multiplex transmission in which a plurality of main signal lights having different wavelengths are multiplexed.

Although the wavelength of the reference light may be any wavelength in principle, the problem of the present invention can be more effectively solved by setting the wavelength outside the gain band of the optical amplifier used for amplifying the main signal. Furthermore, by sharing the monitoring light used for transmitting the monitoring information of the optical repeater as the reference light of the present invention, for example, the complexity of the configuration of the optical transmission device or the optical amplification device can be eliminated.

For example, in the system of the above-mentioned Document 1, since it is necessary to separate optical signals of two specific wavelengths, extra components such as a wavelength division multiplexing optical coupler and a photodetector are required. Because of this,
The configuration of the device becomes complicated. According to the method of Reference 1, in a wavelength division multiplexing transmission system, a fixed number of optical signals are always present in two wavelength bands separated by a wavelength division multiplexing optical coupler due to a failure of a transmitter or an unused optical channel. Not always. For this reason, there is a possibility that a large error may occur in control depending on the presence or absence of an optical signal at or near a specific wavelength, or operation may be disabled. In addition, errors tend to occur in the light intensity measurement due to the influence of accumulation of noise light of the optical amplifier. On the other hand, in the present invention, in particular, a light having a wavelength different from that of the main signal light, that is, a so-called reference light is used for controlling the gain of the optical amplifying section, and an effective effect can be obtained more simply.

In the above-described loss measurement of the optical transmission line downstream of the main signal, the transmission of the reference light of the present invention in the opposite direction to the main signal light and the reception of the reference light from the reception side to the transmission side are performed. Achieved by signaling strength information. At this time, when the reference light cannot be detected, the effect of the present invention can be further enhanced by cutting off the output of the optical amplifier on the optical signal receiving side.

For example, in a system using the light intensity and the spectrum information of the main signal, generally, only the optical loss and the optical spectrum information on the upstream side of the main signal can be known from the optical repeater. For this reason, the optical output intensity of the optical repeater needs to be set to a high level corresponding to the maximum loss regardless of the loss of the optical transmission line on the downstream side, and the transmission quality is greatly deteriorated due to the influence of the optical fiber nonlinearity. Specific examples of the optical fiber nonlinearity include a self-phase modulation effect, a cross-phase modulation effect, and a four-wave mixing effect.

The operation control of the optical amplifier in the present invention is as follows.
For example, this can be achieved by changing the input level and the output level to the optical amplifier according to the loss of the transmission line. By such control, for example, the input level to the optical amplifier is kept constant, and even if the loss of the optical transmission line changes, the occurrence of the gain difference between wavelengths can be suppressed, and the input dynamic range of the optical amplifier can be improved. Specifically, the above control can be achieved by, for example, changing the current of the optical amplifier or the intensity of the pump light. Alternatively, as described above, this can also be achieved by changing the gain of another optical amplifier placed before, after or inside the optical amplifier. Further, it can be achieved by changing the attenuation of an optical attenuator arranged before, after or inside the optical amplifier. There is no problem if other means, such as a variable gain transmitter using a variable optical filter, is used as the control means.

Further, when significant information is transmitted on the reference light, the control operation is performed only when the apparatus is installed, when a failure is recovered, when a command is sent from the outside, and the like. Can be avoided, and the effectiveness of the present invention increases. Conversely, the same applies when the control operation is stopped only when the reference light source or the transmission line / optical transmission device is abnormal.

Also, by controlling the transmission power of the reference light to a constant value, or transmitting the output intensity information of the reference light from the transmitting side of the reference light to the receiving side, or transmitting the receiving intensity information of the reference light from the receiving side. By notifying the side,
It is possible to further improve the accuracy of the control operation of the present invention.

In the optical transmission system, a fiber amplifier is frequently used for the optical amplifier. In particular,
Rare earth doped fiber amplifiers are practical. Conventional fiber amplifiers are sufficient. In addition, as the optical amplifier, for example, a semiconductor optical amplifier,
An optical amplifier using a nonlinear Raman gain of an optical fiber, a waveguide optical amplifier in which a rare earth is added to an optical waveguide such as a glass substrate, and the like can be given. As means for splitting the wavelength-multiplexed light having a plurality of wavelengths into a plurality of wavelength bands, for example, a common optical coupler or wavelength-multiplexing coupler is sufficient.

Generally, in the art, light having a wavelength different from the main signal light is set as a reference light. Further, a signal for transmitting information from the optical transmission device to the optical receiving device is generally called a main signal light in the technical field. This main signal light is usually modulated by signal information. Generally, other signals are used for various controls for transmitting the main signal, and these signals are also transmitted between each optical transmission device or between the optical transmission device and the optical receiving device. These terms have the same meaning in the following description of the present specification.

Based on the above general description, various embodiments of the present invention will be listed below.

According to a second aspect of the present invention, there is provided at least an optical input unit, an optical amplifier, a unit for splitting a plurality of wavelength multiplexed lights into a plurality of wavelength bands, and an optical output unit. A light having a wavelength different from at least the main signal light is branched from the wavelength multiplexed light having a plurality of wavelengths input from the input unit, and the light is divided based on the intensity level of the light having a wavelength different from the at least main signal light. An optical transmission device or an optical amplification device wherein the gain of the optical amplification unit is controlled to a desired gain.

According to a third aspect of the present invention, there is provided at least an optical input unit, an optical amplifying unit, means for splitting a plurality of wavelength multiplexed lights into a plurality of wavelength bands, and an optical output unit. The light having a wavelength different from at least the main signal light transmitted from the output unit to the optical transmission device is branched, and the optical amplification is performed based on the intensity level of the light having a wavelength different from at least the branched main signal light. An optical transmission device or an optical amplification device characterized in that the gain of the section is controlled to a desired gain.

A fourth aspect of the present invention is the optical transmission apparatus according to any one of the above items 1, 2 or 3, wherein the main signal light is a plurality of main signal lights having different wavelengths.

According to a fifth aspect of the present invention, a light having a wavelength different from at least the main signal light is used to control the gain of the optical amplifier to a desired gain based on the light intensity level of the light. 5. The optical transmission device or the optical amplification device according to any one of Items 1, 2, 3, and 4, wherein the light has a wavelength outside the gain band of the optical amplification unit.

According to a sixth aspect of the present invention, there is provided a light source having a wavelength different from at least the main signal light, wherein the gain of the optical amplifier is controlled to a desired gain based on the light intensity level of the light. The optical transmission device according to any one of claims 1, 2, 3, 4, and 5, wherein the light is used for transferring a signal other than the main main signal in the optical transmission device. An optical amplifier.

The means capable of controlling the intensity level of the optical output includes, for example, the optical amplifier itself, another optical amplifier, an optical attenuator, or a variable gain transmitter. The means capable of controlling the intensity level of the optical output is provided by a method of installing the optical amplifier inside the optical amplifying unit or an optical output unit or an optical input unit of the optical transmitting apparatus. You can also take the method.

According to a seventh aspect of the present invention, the optical amplifying unit is coupled to an optical amplifier and has at least one means capable of controlling the intensity level of the optical output, and the gain of the optical amplifying unit is controlled to a desired gain. Wherein the control is performed by controlling a light output level of a means capable of controlling a light output level of the light amplifying unit.
7. The optical transmission device or the optical amplification circuit device according to any one of items 3, 4, 5, and 6.

According to an eighth aspect of the present invention, the optical amplifying unit has at least one optical amplifier, and the intensity level of the optical output is provided between the optical amplifying unit and the optical output unit or the optical input unit. Having at least one controllable means for controlling the gain of the optical amplifier to a desired gain by controlling the light output level of the means capable of controlling the intensity level of the light output. The above-mentioned 1, 2, characterized in that
7. An optical transmission device or an optical amplification device according to any one of items 3, 4, 5, and 6.

In a ninth aspect of the present invention, the means capable of controlling the intensity level of the optical output is a second optical amplifier different from the optical amplifier. It is a transmission device or an optical amplifier circuit device.

A tenth aspect of the present invention is the optical transmission device or optical amplifier circuit device according to the seventh aspect, wherein the means capable of controlling the intensity level of the optical output is an optical attenuator.

According to an eleventh aspect of the present invention, the optical amplifier has at least one first optical amplifier, and the intensity level of optical output can be controlled between the optical amplifier and the optical output unit. Controlling at least one of the means and controlling the gain of the optical amplifier to a desired gain by controlling the light output level of the means capable of controlling the intensity level of the light output. An optical transmission device or an optical amplifier circuit device according to any one of the first, second, third, fourth, fifth and sixth modes.

According to a twelfth aspect of the present invention, the means for controlling the intensity level of the light output is a second means different from the optical amplifier.
The optical transmission device or the optical amplification circuit device according to the eleventh embodiment, wherein

According to a thirteenth aspect of the present invention, in the optical transmission device or the optical amplifier circuit device according to the eleventh aspect, the means capable of controlling the intensity level of the optical output is an optical attenuator. is there.

A fourteenth aspect of the present invention is the optical transmission device according to the eleventh aspect, wherein the means capable of controlling the intensity level of the optical output is an optical attenuator.

According to a fifteenth aspect of the present invention, in any one of the first to fourteenth aspects, the transmission power of light having a wavelength different from that of the main signal light is controlled to a constant value. An optical transmission device or an optical amplification device. Since the power of light having a wavelength different from that of the main signal light is constant, the light reception and the subsequent operation based on the received light intensity become easier.

According to a sixteenth aspect of the present invention, in the various aspects according to the first to fifteenth aspects, transmission intensity information of light having a wavelength different from that of the main signal light is transmitted from the transmission side of the reference light to the reception side. An optical transmission device for notifying an optical amplifier or an optical transmission device, or notifying reception intensity information of a reference light from a reception side of the reference light to an optical amplifier or an optical transmission device on a transmission side; Alternatively, it is an optical amplifier circuit device.

A seventeenth aspect of the present invention is an optical fiber transmission system using the optical transmission device according to any one of the first to fifteenth aspects.

[0048]

FIG. 1 is a block diagram showing a first embodiment of the present invention. This example shows the configuration of an optical repeater to which the present invention is applied. The input optical fiber 101 and the output optical fiber 102 are connected to the optical repeater 107. In this example, the main signal light (wavelength λs) and the reference light (wavelength λ
r) is an example of wavelength multiplex transmission in the same direction.

The main signal light and the reference light input from the input fiber 101 are wavelength-separated by the wavelength division multiplexing optical coupler 103-1 and the main signal light is amplified by the optical amplifier 100. The main signal light may be an information signal of a single wavelength, or a plurality of information signals may be wavelength-multiplexed. The reference light is a photodetector 104
Received at.

According to the present invention, the intensity of the main signal light is controlled by the detected intensity of the reference light so that a flat gain can be secured over the wavelength range. That is, the control circuit 105 controls the operation of the optical amplifier based on the intensity information of the reference light. If the detected intensity of the reference light deviates from a reference value scheduled based on the ratio of the intensity of the reference light to the intensity of the main signal light, the gain of the optical amplifier 100 is adjusted according to the magnitude thereof, As a result, a rat gain is secured over the desired wavelength range.

At the output of the optical amplifier 100, the reference light source 10
The output light of wavelength λr output from 6 is multiplexed with the main signal light again and sent to the output fiber 102. Here, conventional optical amplifiers, photodetectors and the like are sufficient. As described above, a rare earth-doped fiber optical amplifier is frequently used as the optical amplifier. If the wavelength of the signal light is, for example,
In the case of the 1.55 μm band, for example, erbium-doped
Fibers can be mentioned. In the case of a fiber optical amplifier, pumping light for the fiber optical amplifier is required, but this is omitted in the following description and drawings as a matter of course.

When the present invention is applied to the optical receiving terminal, the output part (103-2, 106) is not necessarily required. When the present invention is applied to an optical transmitting terminal, an output part (103-2, 106) is provided to the terminal optical output unit.
It is sufficient to provide only.

FIG. 5 is a diagram showing a second embodiment of the present invention. This example is an example of an optical repeater in which main signal light and reference light propagate in opposite directions.

The main signal light may be an information signal of a single wavelength, or a plurality of information signals may be wavelength-multiplexed.
The main signal light (wavelength λ) input from the input fiber 101
s) is amplified by the optical amplifier 100 and guided to the output fiber 102.

In this example, the reference light (wavelength λr) used for controlling the amplification factor of the optical amplifier 100 is incident from the output fiber 102 side, contrary to the first embodiment.
Then, this reference light is received by the photodetector 104.
If the detected value deviates from a reference value based on the ratio of the intensity of the reference light and the intensity of the main signal light, the amplification factor of the optical amplifier 100 is adjusted by the control circuit 105 according to the magnitude thereof, and as a result, the gain is adjusted to a desired wavelength range. It is a rat gain across. That is, a wavelength division multiplexing coupler 103-1 is arranged between the optical fiber amplifier 100 and the output fiber 102, and separates the reference light having the wavelength λr transmitted from the downstream direction of the main signal light and guides it to the photodetector 104. ing. As in the previous embodiment, the control circuit 105 controls the operation of the optical amplifier 100 based on the intensity information of the received reference light.

Further, in this example, the optical repeater 107 is provided with a wavelength multiplex coupler 103-2 between the input fiber 101 and the optical amplifier 100. The output light of the reference light source 106 is sent upstream of the main signal. This reference light is for the optical repeater in front of the optical repeater 107.

FIG. 6 shows a third embodiment of the present invention. This example shows a part of an optical multi-relay transmission system. That is,
3 illustrates an example of a connection relationship between a first optical transmission device and a second optical transmission device. This example is an example of connection of an optical repeater. Generally, such an optical transmission system is connected in multiple stages in an optical multi-relay transmission system.

The optical repeater 108 shown in FIG. 6 shows only a main part of an optical output unit of an optical repeater (or, for example, an optical transmission terminal equipment). The output unit of the optical repeater 108 is the optical repeater 1
07 and an optical fiber transmission line 114. Here, an example using an optical repeater is shown, but the same inventive concept can be applied to another device such as an optical transmission terminal device. As described above, the optical transmission device of the present invention includes at least one optical amplifier and includes general devices for transmitting light. In other words, the present invention can be applied to these general optical transmission devices.

At the output of the optical repeater 108, the optical amplifier 1
The reference light (wavelength λr) from the reference light source 106 is wavelength-multiplexed with the main signal light (wavelength λs) which is the output light of 00-1 and transmitted to the downstream optical repeater 107. If the difference between the main signal wavelength (λs) and the reference light wavelength (λr) is small, the two receive substantially the same loss. Therefore, if the optical intensity of the reference light is measured by the optical repeater 107, the loss of the optical fiber transmission line 114 can be accurately determined. It becomes possible to measure. Unlike the case where the main signal light intensity is measured, the present method is not affected by the change in the number of wavelengths of the main signal or the effect of accumulation of noise light.
1 can be applied even when the constant power control is not performed. Note that an example other than the constant power control of the optical amplifier is, for example, the case of the constant gain control.

In the optical repeater 107, the light from the optical fiber 114 is multiplexed by the wavelength multiplexing optical coupler 103-1 into the wavelength λr.
, And is guided to the photodetector 104. The control circuit 105 receives the light intensity information of the reference light. And
Based on this information, the variable optical attenuator 130 is controlled so that the input light intensity to the optical amplifier 100-2 always has a constant value. Thus, no matter how the loss of the optical fiber transmission line 114 changes, it is possible to keep the operation state of the optical amplifier 100-2 constant and suppress the occurrence of the gain deviation between wavelengths.

FIG. 12 shows an example of a specific configuration of the control circuit 105 according to the third embodiment. This figure is an example in which the control circuit is configured by an analog circuit. The intensity signal 150 of the reference light is input to a division circuit 153, and is divided by a voltage preset in an internal reference voltage source 152 to compare the magnitude. The conversion circuit 154 outputs a variable optical attenuator control signal 151 according to the result of the division. For example, when the division result is 1, the attenuation of the variable attenuator becomes zero (ie, when the value of the reference signal is equal to the set level), and when the result is 2, the attenuation of the variable optical attenuator 130 is decreased. Is set to 3 dB, it is possible to always keep the optical signal input to the optical amplifier 130 constant. Note that the configuration of the control signal is not limited to this example. For example, it can be configured by an A / D converter, a digital circuit, and a control program.

In the optical repeater 107 of this embodiment, the variable optical attenuator 130 is disposed immediately after the wavelength multiplexing optical coupler 103-1. However, the arrangement of both may be reversed. In this case, for example, if the control circuit 105 performs control so that the reference light intensity detected by the photodetector 104 becomes a predetermined constant value, the input light intensity to the optical amplifier 100-2 always becomes constant, It is possible to achieve the object of the present invention.

Further, in the optical repeater 107 of this embodiment, a wavelength multiplex coupler 103-2 is disposed between the optical amplifier 100-2 and the output fiber 102.
-2 has a reference light source 106 for inputting reference light to the next stage. Thus, the output light of the reference light source 106 is sent to the upstream side of the main signal.

As a wavelength of the reference light, any wavelength can be used as long as it does not overlap with the main signal wavelength. For example, when the main signal is wavelength-multiplexed in the wavelength band of 1530 to 1560 nm, a wavelength of 1530 nm or less, 1560 nm or more can be used as the wavelength of the reference light. Also, a specific light wavelength within the main signal wavelength band may be allocated for reference light. When the reference light is shared with the monitoring signal of the optical repeater, it is possible to use the monitoring signal wavelength such as the 1510 to 1520 nm band as it is.

In particular, by setting the wavelength of the reference light outside the gain band of the optical amplifier, in measuring the light intensity of the reference light, the accumulation of the spontaneous emission light emitted from the optical amplifier and the spontaneous emission light in the multistage repeater are measured. Less susceptible.
At the same time, since the optical amplifier acts as a loss medium for the reference light, there is an effect of suppressing crosstalk due to leakage of the reference light at the preceding stage.

In the above embodiment, the wavelength division multiplexing coupler is used to separate the reference light and the main signal. However, other optical devices may be used as long as they have the function of separating the two. For example, there is an example in which a part of the optical signal in the input optical fiber 101 is separated by an optical coupler, and only the wavelength component of the reference light is extracted using a band-pass optical filter and guided to the photodetector 104. Conceivable. Further, when the reference signal is transmitted in the opposite direction to the main signal, it is also possible to separate them using an optical circulator or an optical coupler.

FIG. 7 is a diagram showing a fourth embodiment of the present invention. This example shows a part of the optical multi-relay transmission system as in the example of FIG. 6, but the reference signal (λr) and the reference light wavelength (λs) are transmitted in the opposite direction to the main signal light. An example is shown. This example also shows an example of the connection relationship between the first optical transmission device and the second optical transmission device, and is an example of the connection of an optical repeater. The optical repeater 109 only shows the optical input unit. Although an example using an optical repeater is shown here, the same idea can be applied to another device, for example, an optical transmission terminal device, as in the example of FIG.

A reference light source 106 is arranged at an optical input section of an optical repeater (or, for example, an optical transmission terminal equipment) 109.
The reference light (wavelength λr) is transmitted to the optical repeater 107 on the upstream side of the main signal light (wavelength λs).

In the optical repeater 107 of this example, the light of the reference light wavelength (λr) is separated by the wavelength multiplexing optical coupler 103-1 and the light intensity is detected by the photodetector 104. Since the loss of the optical fiber transmission line 114 can be known from this value, the attenuation of the optical variable attenuator 130 is changed in accordance with the loss, and control is performed so that the input light intensity to the optical amplifier 100-2 becomes constant.

Also in the present embodiment, it is possible to reverse the arrangement positions of the variable optical attenuator 130 and the wavelength multiplexing optical coupler 103-1. In this case, for example, the control circuit 105 is detected by the photodetector 104. The object of the present invention can be achieved by performing control so that the light intensity of the reference light becomes a predetermined constant value. In the case of the present embodiment, since it is possible to know the loss of the optical fiber transmission line 114 on the downstream side of the main signal, it is possible to reduce the optical output when the transmission line loss is small, Signal degradation due to non-linear effects can be minimized.

When the reference light cannot be received by the photodetector 104, the connectors 131-1 and 131-2
May have been released. At this time, by cutting off the pump light of the optical amplifier 100 or increasing the attenuation of the variable optical attenuator 130, unnecessary optical output can be prevented from being emitted to the outside from the end face of the optical connector.

FIG. 8 shows a fifth embodiment of the present invention.
This is an example in which the gain of the optical amplifier 133 is controlled instead of the variable optical attenuator. For example, if an optical amplifier such as a fluoride fiber optical amplifier / semiconductor optical amplifier is used as the optical amplifier 133, the gain of which is less dependent on a change in input level with respect to a change in input level, the same effect as that of the variable optical attenuator can be obtained. In addition, it is also possible to cancel the occurrence of the wavelength deviation of the optical repeater due to the change in the input level by using an optical amplifier or an optical filter whose gain and transmission characteristics have variable wavelength dependence for control. As a means for changing the gain of the optical amplifier, a technique of controlling a pump light source or a pump current is widely applicable. In FIG. 8, the same reference numerals as those in the other drawings denote the same members, and a detailed description thereof will be omitted.

FIG. 9 shows a sixth embodiment of the present invention.
This is an example in which constant intensity control is performed on the reference light source 106 in order to keep the transmission light intensity of the reference light constant.

In this example, a part of the reference light (wavelength λr) from the reference light source 106 is separated by the optical coupler 134, and the output intensity is measured by the photodetector 135. Then, the current of the reference light source 106 is feedback-controlled by the constant intensity control circuit 136 so that the value detected by the photodetector 135 becomes a constant value. By performing such constant light intensity control, it is possible to improve the measurement accuracy of the loss amount of the optical transmission line. Note that the photodetector 135, the control circuit 136 for constant intensity, and the like may be conventional ones.

FIG. 10 shows a seventh embodiment of the present invention. This example has a function of monitoring various data and various information in an optical repeater, and notifying various data and various information to another optical transmission device. Although an optical transmission device having a function of notifying such various data and various information to another optical transmission device is known, a feature of the present embodiment is that a monitoring light used for this monitoring is particularly used as a reference light. It is an example.

In this example, in addition to the examples of the above embodiments, the output light intensity of the monitor light / reference light transmitter 138 is further measured by the photodetector 135, and the monitor information processing circuit 139 is provided.
This configuration is written on the monitoring information and is notified as a part of the monitoring information to an optical transmission device such as an optical repeater on the upstream side of the main signal. When the monitoring light is used as the reference light, it is not necessary to adopt a configuration for notifying the light intensity of the monitoring light, and an appropriate method is used only when necessary (for example, controlling the monitoring light intensity to a constant value). Should be applied.

The transmission form of the monitoring information is a so-called SONE
T (Synchronous Optical Network)
or) Any method such as a signal format and subcarrier modulation may be used. For example, in the SONET signal format, the transmission apparatus has a memory unit for storing information on overhead of a transmission frame in digital transmission, and stores various data and various information in the memory unit. The stored various data and various information are transmitted to another optical transmission device as needed. In the optical transmission device connected to the optical fiber 102 on the upstream side of the main signal (wavelength λs), the monitoring information processing circuit 139 uses the received signal of the monitoring light / reference light receiver 137 to monitor the optical repeater and control the state. At the same time as extracting the information, the transmission intensity information of the monitoring light transferred from the downstream optical transmission device is extracted. The control circuit 105 calculates the loss of the optical transmission line from the transmission intensity information and the reception intensity information of the reference light, and sets the attenuation of the variable optical attenuator 130.
This facilitates the application of the present invention even when the intensity of the reference light cannot be controlled to a constant value on the transmission side. Further, the monitoring information processing circuit 139 can determine whether valid monitoring information is always transferred from the SONET header information of the monitoring signal or the like.

The monitoring information processing circuit 130 is a circuit usually used in a multi-relay transmission device when an optical amplifier is used. The monitoring information is information used for maintenance / management of the optical repeater / transmitter, for example, whether there is a failure in the optical amplifier or the optical repeater / transmitter, an operation state such as optical output intensity / presence / absence of the main signal, etc. And the like.
Generally, such information is transmitted by monitoring light different from the main signal. The monitoring information processing device functions to terminate the monitoring information sent by the upstream monitoring light, read / write necessary information, and then send the information downstream.

Therefore, by operating the control circuit 105 only when the monitoring signal is valid, it is possible to minimize the influence on the main signal even when a problem such as failure of the monitoring / reference light source occurs. . Also, when the temporal variation of the loss amount of the optical fiber transmission line is small,
The control circuit 105 does not need to always operate, and it is sufficient that the control circuit 105 operates only immediately after installation of the apparatus or immediately after recovery from a failure such as a fiber break.

The monitoring light / reference light receiver 137 is not necessarily required to be a single optical receiver even when the monitoring light and the reference light are shared, and an optical receiver having a monitoring signal receiving function and an optical receiver Separate the photodetector with the function to detect the intensity,
There is no problem even if they are coupled by an optical coupler or the like. Further, contrary to the present embodiment, it is also possible to notify the transmitting side of the reception intensity of the reference light.

FIG. 11 shows an eighth embodiment of the present invention, and shows an example of the configuration of a wavelength division multiplexing optical transmission system to which the present invention is applied.

Each optical transmission terminal device 140-1, 140-2
The optical transmitters and receivers within are connected to the optical transmission terminal stations 140-3, 140-1, 1-2 at different points via the wavelength division multiplex transmission device 141-1, the optical fiber transmission line 114, the optical repeater 142, and the wavelength division transmission device 141-2
The main signal is transmitted in opposition to 40-4. WDM optical transmission devices 14 disposed at both ends of each optical fiber transmission line
1. The reference light source 106,
A photodetector 104 is arranged, measures the loss of each optical fiber transmission line based on the reference light intensity, controls the output light intensity of the optical amplifier 103 and the like according to the value, and controls the main signal light to be wavelength-division multiplexed. Suppress the generation of the gain difference between wavelengths. Although this figure shows a configuration in which optical transmission terminal stations are arranged to face each other, it can be used in any configuration such as an insertion / separation type optical network using an optical ADM. Further, although the present example shows a configuration of one-way transmission using different optical fibers for upstream / downstream main signals, the present invention can also be applied to a bidirectional transmission system that uses both of them. In this case, since the loss of the upstream / downstream optical fiber transmission line is the same, the reference light source / reference light detection unit of the present invention can also be used for the upstream / downlink.

The embodiments of the present invention have been described above, and the various effects will be summarized and listed below.

According to the present invention, an optical transmission device having a large dynamic range can be provided. Further, according to the present invention, it is possible to provide a transmission device which has good transmission characteristics even in optical multiplex communication, and in particular, has a very small optical output deviation.

The present invention has the effect that the input dynamic range of the optical amplifier having a small input dynamic range can be expanded to reduce the gain difference between wavelengths. That is, by changing the input level and the output level to the optical amplifier according to the loss of the transmission line, for example, control can be performed so that the input level to the optical amplifier becomes constant. Therefore, even if the loss of the optical transmission line changes, the generation of the gain difference between wavelengths can be suppressed, and the input dynamic range of the optical amplifier can be improved.

Therefore, in the optical repeater transmission system using the optical amplifying device or the optical transmission device of the present invention, there is an effect that the number of relay stages or the transmission distance / the number of wavelength channels can be increased.

In the present invention, the reception intensity of the reference light having a wavelength different from that of the main signal is measured, and the operation of the optical amplifier is controlled based on this information. Therefore, even if the number of signal wavelengths changes, the effect on the control operation can be suppressed.

It is almost standardized that an optical repeater using an optical amplifier has a monitor light having a wavelength different from that of the signal light. Therefore, the structure of the apparatus is simplified by sharing the monitor light and the reference light. This has the effect of reducing costs.

If the wavelength of the reference light is set outside the amplification band of the optical amplifier, there is an effect that the influence of noise light of the optical amplifier and increase / decrease of the number of wavelengths of the main signal is reduced, and the accuracy is improved.

In the case where the reference light is transmitted in the reverse direction, or in the configuration in which the light intensity of the received reference light is notified to the transmitting side as monitoring information, the downstream side of the main signal as viewed from the optical transmission device / optical repeater. Since the loss of the optical transmission line is known, the output light intensity of the optical amplifier can be reduced in accordance with the loss. As a result, there is an effect that deterioration of transmission quality can be suppressed due to the influence of optical fiber nonlinearity (self-phase modulation effect, cross-phase modulation effect, four-wave mixing effect, etc.).

Further, by using the reference light for the connector release detection, the apparatus configuration can be simplified, the cost can be reduced, and the accuracy of the connector release detection can be increased. As a result, the possibility that unnecessary optical output is emitted from the end face of the connector is reduced, and safety for the user of the apparatus can be improved.

The control operation of the present invention is restricted only when significant information is transmitted on the reference light, or when the apparatus is installed, when a failure is recovered, when an external command is sent, or the like. When the light source itself breaks down, malfunction can be prevented and reliability can be improved. The same effect can be obtained by stopping the control operation when an abnormality is detected in the reference light source or the like.

Further, the transmission power of the reference light is controlled to a constant value, the output intensity information of the reference light is notified from the transmission side of the reference light to the reception side, or the reception intensity information of the reference light is received. By notifying the transmitting side from the side, the measurement accuracy of the loss in the optical transmission line can be improved, and the occurrence of the wavelength deviation of the optical amplifier can be suppressed more effectively.

[0094]

According to the present invention, an optical transmission device having a large dynamic range can be provided. Furthermore,
According to the present invention, it is possible to provide an optical transmission device having good transmission characteristics even in optical multiplex communication, particularly, having a very small optical output deviation.

According to another aspect of the present invention, an optical amplifier having a large input dynamic range can be provided.

Further, according to another aspect of the present invention, it is possible to provide an optical amplifier having good characteristics even in the input in the optical wavelength division multiplexing, in particular, having a very small optical output deviation.

According to still another aspect of the present invention, it is possible to provide an optical transmission system having a large dynamic range even in optical multiplex communication.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a gain spectrum of the optical amplifier.

FIG. 3 is a diagram illustrating a change in signal level in a wavelength division multiplexing optical repeater amplification transmission system.

FIG. 4 is a configuration diagram showing a configuration of a conventional optical amplifier.

FIG. 5 is a configuration diagram showing a second embodiment of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of the present invention.

FIG. 7 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 8 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 9 is a configuration diagram showing a sixth embodiment of the present invention.

FIG. 10 is a configuration diagram showing a seventh embodiment of the present invention.

FIG. 11 is a configuration diagram showing an eighth embodiment of the present invention.

FIG. 12 is a diagram illustrating an example of a control circuit used in the embodiment.

[Explanation of symbols]

100: optical amplifier, 101: input optical fiber, 102: output optical fiber, 103: wavelength multiplexing optical coupler, 104: photodetector,
105: control circuit, 106: reference light source, 107: optical repeater,
108: optical output unit of optical repeater, 109: optical input unit of optical repeater, 110: optical transmission terminal equipment, 111: optical transmitter, 112: optical multiplexer, 113: Optical amplifier, 114: Optical fiber transmission line, 11
5 ・ ・ ・ Optical repeater, 116 ・ ・ ・ Optical demultiplexer, 117 ・ ・ ・ Optical receiver, 120 ・
..Variable optical attenuator, 121 ... optical coupler, 122 ... wavelength multiplexing optical coupler, 123 ... photodetector, 124 ... control circuit, 125 ... optical repeater, 130 ... Variable optical attenuator, 131 ・ ・ ・ Optical connector, 132 ・ ・ ・ First stage optical amplifier, 133 ・ ・ ・ Post stage optical amplifier, 134 ・ ・ ・ Wavelength multiplexing optical coupler, 135 ・ ・ ・ Photodetector, 136 ・ ・ ・ Constant Intensity control circuit, 137
..Monitoring light / reference light receiver, 138 monitoring light / reference light transmitter, 139 monitoring information processing circuit, 140 optical transmission terminal equipment,
Reference numeral 141 denotes a wavelength division multiplexing optical transmission device, 142 denotes an optical repeater, 143 denotes an optical transmitter, 144 denotes an optical receiver, and 145 denotes a wavelength multiplexer / demultiplexer.

Claims (20)

[Claims] An optical input unit, an optical amplifying unit, means for splitting a wavelength multiplexed light of a plurality of wavelengths into a plurality of wavelength bands, and an optical output unit, wherein a wavelength different from the main signal light is used. An optical transmission device, comprising: branching at least light having the same; and controlling the gain of the optical amplifier to a desired gain based on the intensity of light having a wavelength different from that of the branched main signal light. 2. An optical input unit, an optical amplifying unit, means for splitting wavelength multiplexed light of a plurality of wavelengths into a plurality of wavelength bands, and an optical output unit, wherein the plurality of optical input units are provided. At least a light having a wavelength different from the main signal light is split from the wavelength multiplexed light of the wavelength, and the gain of the optical amplifier is set to a desired gain based on the intensity of the light having a wavelength different from the split main signal light. An optical transmission device characterized in that: 3. An optical transmission unit comprising: an optical input unit; an optical amplifying unit; means for splitting a plurality of wavelength multiplexed lights into a plurality of wavelength bands; and an optical output unit. The light having a wavelength different from at least the main signal light transmitted to the main signal light is branched, and the gain of the optical amplification unit is controlled to a desired gain based on the intensity of the light having a wavelength different from the at least main signal light thus branched. An optical transmission device, comprising: 4. The optical transmission device according to claim 1, wherein the main signal light is a plurality of main signal lights having different wavelengths. 5. The light having a wavelength different from at least the main signal light, the light being used to control the gain of the optical amplifier to a desired gain based on the light intensity of the light. 5. The optical transmission device according to claim 1, wherein the wavelength is outside the gain band. 6. The optical transmission device, wherein the light has a wavelength different from at least the main signal light and is used to control the gain of the optical amplifier to a desired gain based on the light intensity of the light. 6. The optical transmission device according to claim 1, wherein the light is used for transferring signals other than the main signal in the optical transmission device. 7. The optical amplifying unit is coupled to an optical amplifier and has at least one unit capable of controlling the intensity of the optical output, and controlling the gain of the optical amplifying unit to a desired gain.
7. The method according to claim 1, wherein the light output is controlled by controlling the light output intensity of a unit capable of controlling the light output intensity of the light amplification unit. Optical transmission equipment. 8. The optical amplifying unit has at least one optical amplifier, and has at least one unit between the optical amplifying unit and the optical output unit for controlling the intensity of the optical output. 3. The method according to claim 1, wherein controlling the gain of the amplifying unit to a desired gain is performed by controlling an optical output level of a unit capable of controlling an intensity of an optical output of the optical amplifying unit. 7. The optical transmission device according to any one of items 3, 4, 5, and 6. 9. The optical transmission device according to claim 7, wherein the means capable of controlling the intensity of the optical output is a second optical amplifier different from the optical amplifier. 10. The optical transmission device according to claim 7, wherein the means capable of controlling the intensity of the optical output is an optical attenuator. 11. The optical amplifying unit has at least one first optical amplifier, and has at least one unit capable of controlling the intensity of optical output between the optical amplifying unit and the optical output unit. 6. The optical amplifier according to claim 1, wherein the gain of the optical amplifier is controlled to a desired gain by controlling an optical output of a unit capable of controlling the intensity of the optical output. Or 6
The optical transmission device according to any one of the above items. 12. The optical transmission apparatus according to claim 11, wherein the means capable of controlling the intensity of the optical output is a second optical amplifier different from the optical amplifier. 13. The optical transmission device according to claim 11, wherein the means capable of controlling the intensity of the optical output is an optical attenuator. 14. The optical transmission apparatus according to claim 1, wherein a transmission power of light having a wavelength different from that of the main signal light is controlled to a constant value. 15. A transmission intensity information of light having a wavelength different from the main signal light is notified from a transmission side of the light having a wavelength different from the main signal light to an optical amplifier or an optical transmission device on a reception side, or 15. The method according to claim 1, wherein the reception intensity information of the light having a wavelength different from that of the main signal light can be notified from the reception side of the light to an optical amplifier or an optical transmission device on the transmission side. The optical transmission device according to any one of the above. 16. An optical fiber transmission system using the optical transmission device according to claim 1. 17. An optical input unit, an optical amplifying unit, means for splitting a wavelength multiplexed light having a plurality of wavelengths into a plurality of wavelength bands, and an optical output unit, wherein at least a wavelength different from the main signal light is used. An optical amplifying device, comprising: branching at least the light having the same; and controlling the gain of the optical amplifier to a desired gain based on the intensity of the light having a wavelength different from that of the branched main signal light. 18. An optical input unit, an optical amplifying unit, means for splitting wavelength-multiplexed light having a plurality of wavelengths into a plurality of wavelength bands, and an optical output unit, wherein a wavelength different from the main signal light is used. A transmitter comprising: an optical amplifying device that at least splits the light having the same and controls the gain of the optical amplifier to a desired gain based on the intensity of the light having a wavelength different from that of the split main signal light. . 19. An optical input unit, an optical amplifying unit, means for splitting wavelength-division multiplexed light of a plurality of wavelengths into a plurality of wavelength bands, and an optical output unit, wherein a wavelength different from the main signal light is used. A repeater comprising: an optical amplifier that splits at least the light having the same and controls the gain of the optical amplifier to a desired gain based on the intensity of light having a wavelength different from that of the split main signal light. . 20. An optical input unit, an optical amplifying unit, means for splitting wavelength-multiplexed light having a plurality of wavelengths into a plurality of wavelength bands, and an optical output unit, wherein a wavelength different from the main signal light is used. A receiver having at least a light amplifier for controlling the gain of the optical amplifier to a desired gain based on the intensity of light having a wavelength different from that of the branched main signal light. .