JP2001057537A - Optical transmitter and optical amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmitter that is used for a wavelength multiplex optical transmission system, multiplexes a plurality of optical signals with different wavelengths and transmits the multiplexed signal in spite of a simple and small-scale configuration and by which the strength of each transmitted optical signal can respectively be kept constant even if number of multiplexed optical signals (that is, number of multiplexed waves) is changed. SOLUTION: Optical signal sources 121-124 output an optical signal. Pilot light sources 111, 112 output a pilot light, preferably a pilot light with stronger strength than that of the optical signal. A synthesis section 13 synthesizes each optical signal and each pilot light and outputs the result as a wavelength multiplex optical signal where each optical signal and each pilot light are multiplexed. An optical amplifier section 14 has a characteristic where its own gain can be kept constant when all input light strength is constant even when number of optical signals given to itself is changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitting apparatus and an optical amplifying apparatus, and more particularly to an optical transmitting apparatus and an optical amplifying apparatus which are used in a wavelength division multiplexing optical transmission system and multiplex and amplify a plurality of optical signals having different wavelengths. The present invention relates to an optical transmitting apparatus for transmitting and transmitting, and an optical amplifying apparatus used in a wavelength multiplexing optical transmission system and amplifying a wavelength multiplexing optical signal obtained by multiplexing a plurality of optical signals having different wavelengths from each other.

[0002]

2. Description of the Related Art In recent years, wavelength multiplexing optical transmission systems have been actively developed for the purpose of increasing transmission capacity. A general conventional wavelength division multiplexing optical transmission system has a configuration in which one transmitting station and one receiving station are connected via one optical transmission line. This is because wavelength division multiplexing optical transmission is mainly performed only on the trunk line between Tokyo and Osaka. Recently, however, there has been a demand not only between Tokyo and Osaka, but also between Tokyo and Kobe, Kyoto, Wakayama, and the like around Osaka to perform wavelength division multiplexed optical transmission. Therefore, one transmitting station and one relay station are connected via one optical transmission line, and one relay station and a plurality of receiving stations are connected via one optical transmission line. A new wavelength division multiplexing optical transmission system has been developed. In this case, for example, the transmitting station is located in Tokyo, the relay station is located somewhere in Osaka or Kinki district, and the receiving station is located in each city in the Kinki district such as Osaka or Kobe. Hereinafter, a new conventional wavelength multiplexing optical transmission system as described above will be described with reference to the drawings.

FIG. 16 is a block diagram showing a configuration of a new conventional wavelength division multiplexing optical transmission system. In FIG. 16, a new conventional wavelength multiplexing optical transmission system includes a transmitting station 5
0, a relay station 54, and a plurality of receiving stations (here, two receiving stations 581 and 582). The transmitting station 50 and the relay station 54 are connected via an optical transmission line 53.
The relay station 54 and each of the receiving stations 581 and 582 are 1
They are connected via the optical transmission lines (here, the optical transmission lines 571 and 572).

The transmitting station 50 includes a plurality of optical signal sources (here, three optical signal sources 511 to 513) and a multiplexing unit 52. The optical signal sources 511 to 513 output optical signals having different wavelengths from each other. The reason for making the wavelengths different from each other is to allow the receiving side to separate each optical signal from each other or to select a specific optical signal. The multiplexing unit 52 multiplexes the optical signals output from the signal sources 511 to 513 with each other. In this way, all the optical signals are collectively transmitted from the transmitting station 50 to the relay station 54 via the optical transmission line 53 in the form of a wavelength multiplexed optical signal obtained by wavelength multiplexing the optical signals.

[0005] The relay station 54 includes an optical amplifier 55 and a signal branch.
Section 56. The optical amplifier 55 is connected to each optical transmission line 5
Loss at 3,571,572 and signal splitter
Provided to compensate for the branch loss at 56. Signal
The branch unit 56 includes an optical signal for the receiving station 581 and the receiving station 58.
The optical signal for the second is separated by the wavelength. For example,
The multiplexed wave number of the optical signal transmitted from the transmitting station 50 is N,
Long λ₁~ Λ_kIs the k-wave optical signal for the receiving station 581.
The wavelength λ _{k + 1}~ Λ_N(Nk) wave optical signal is received by the receiving station
582, the signal splitter 56 has a wavelength λ₁~
λ_kIs output to the optical transmission line 571, and the wavelength λ_{k + 1}~
λ_NIs output to the optical transmission path 572. In this way
The optical signal split at the relay station 54 is
1 and 572 to each receiving station 581 and 582
Can be

[0006] Each of the receiving stations 581 and 582 separates the received optical signal for each wavelength or selects a desired wavelength, and then converts it into an electric signal. In other words, after demultiplexing the wavelength multiplexed signal into optical signals, each optical signal is converted into an electrical signal, or after selecting an optical signal addressed to the own station from the wavelength multiplexed signal, the optical signal is converted into an electrical signal. Convert to

[0007] In the new conventional wavelength multiplexing optical transmission system configured as described above, the receiving side (ie, each receiving station 5).
81, 582), it is necessary that the intensity of each optical signal received is kept constant (that is, does not fluctuate over time). Therefore, the optical amplifier 55 is required to amplify each input optical signal so that the output intensity of each optical signal does not fluctuate with time.

Here, the most common and practical optical amplifier used in the wavelength division multiplexing optical transmission system is an erbium-doped optical fiber amplifier (hereinafter referred to as EDFA).
Notation). The EDFA has a characteristic that when the input light intensity is constant, the sum of the light intensity output from the EDFA is uniquely determined with respect to the excitation light intensity injected into the EDFA.
Therefore, when an EDFA is used as an optical amplifier,
By adjusting the intensity of the pumping light to A, the total sum of the intensity of the output light from the optical amplifier can be kept constant.

Therefore, in the new conventional wavelength division multiplexing optical transmission system, an EDFA is used as the optical amplifier 55, and the total output intensity of the optical amplifier 55 (ie, the sum of the output intensity of all optical signals) is kept constant. It is considered that if such control is performed, as a result, the intensity of each optical signal output from the optical amplifier 55 can be prevented from fluctuating with time.

However, if control is performed to keep the total output intensity of the optical amplifier 55 constant, when the number of wavelength-multiplexed optical signals (ie, the number of multiplexed waves) changes due to failure of the optical signal sources 511 to 513, etc. Then, there arises a problem that the output intensity of each optical signal fluctuates. That is, since the total output intensity is kept constant by the control, if the number of signals changes, the output intensity of each optical signal fluctuates with time. For example, in the above-described conventional wavelength multiplexing optical transmission system, when the number of multiplexed waves is 2, 1
Assuming that the output light intensity per wave is +5 dBm,
When the multiplex wave number is reduced to 1, the output light intensity per wave increases to +8 dBm.

In order to solve the above problem, it is conceivable to use, as the optical amplifier 55, an optical amplifier that controls the output light intensity according to the number of multiplexed waves in the new conventional wavelength multiplexing optical transmission system. . Such an optical amplifier is described in JP-A-8-95097.

FIG. 17 is a block diagram showing the configuration of a conventional optical amplifier that controls the output light intensity according to the number of multiplexed waves. In FIG. 17, the conventional optical amplifier includes an optical amplifier 61, an optical output monitor 62, and a controller 63. The optical amplifier 61 amplifies an input optical signal.
The optical output monitor 62 monitors the intensity of the optical signal output from the optical amplifier 61. The control unit 63 includes:
The gain of the optical amplifier 61 is controlled based on the monitoring result of the optical output monitor 62.

In the conventional optical amplifier configured as described above, in addition to the output from the optical output monitoring unit 62, wave number information indicating the number of multiplexed waves is input to the control unit 63. The wave number information is supplied from outside the optical amplifier, or
It is obtained by detecting the wave number inside the optical amplifier.
The control unit 63 controls the optical amplification unit 6 according to the wave number indicated by the wave number information.
The gain of the optical amplifier 61 is controlled such that the output light intensity of each wavelength from 1 is kept constant.

Therefore, in the new conventional wavelength-division multiplexing optical transmission system (see FIG. 16), if the conventional optical amplifier (see FIG. 17) is used as the optical amplifier 55, the number of multiplexed optical signals (ie, multiplexing) is reduced. When the (wave number) changes, the intensity of each optical signal output from the optical amplifier 55 can be kept constant. As a result, each of the receiving stations 581, 58
It is expected that the intensity of each optical signal received by each of the optical signals 2 can be kept constant.

[0015]

However, in the new conventional wavelength division multiplexing optical transmission system, even if the above conventional optical amplifier is used as the optical amplifier 55, the expected result is not always obtained. Absent. Because
This is because the conventional optical amplifier is premised on being used in the general conventional wavelength multiplexing optical transmission system. The general conventional wavelength division multiplexing optical transmission system has the following features.
Since one transmitting station and one receiving station are connected via one optical transmission line, if the output intensities of the optical signal sources on the transmitting side are made equal to each other, the receiving station receives each optical signal. The intensity is also equal.

On the other hand, in the new conventional wavelength division multiplexing optical transmission system, since the lengths of the optical transmission lines 571 and 572 are not always the same, each optical signal output from each of the optical signal sources 511 to 513 is received by each reception signal. The transmission distance until the light is received by the stations 581 and 582 may vary depending on the optical signal. In this case, in order to make the intensity of each optical signal received by each of the receiving stations 581 and 582 equal, the optical signal sources 511 to 513 are required.
Must be set to different values according to the lengths of the optical transmission paths 571 and 572.

Assuming that the above-mentioned conventional optical amplifier is used in the new conventional wavelength-division multiplexing optical transmission system, if the optical signal intensities are equal to each other at all wavelengths as shown in FIG. If the output intensities of the sources 511 to 513 are equal to each other, even if the multiplex wave number changes, the control unit 6
3 controls the gain of the optical amplifier 61 based on the wave number information, so that the output light intensity of each signal from the optical amplifier 61 can be kept constant. However, as shown in FIG. 19, when the optical signal intensity differs depending on the wavelength, that is, when at least one of the optical signal sources 511 to 513 has a different output intensity from the other, the control unit 63 sets the Even if the gain of the optical amplifier 61 is controlled based on the information, the output light intensity of each signal from the optical amplifier 61 cannot be kept constant.

In the latter case, in addition to the wave number information, intensity information indicating the input optical signal intensity of each wavelength is further provided to the control unit 63, and the control unit 63 performs optical amplification based on the wave number information and the intensity information. If the gain control of the unit 61 is performed,
It is considered that the output light intensity of each wavelength from the optical amplifier 61 can be kept constant. But,
For this purpose, an input light monitoring unit (not shown) for monitoring the intensity of each optical signal input to the optical amplification unit 61 is further required, and the control unit 63 performs more complicated control processing. Therefore, it is inevitable that the scale of the optical amplifier becomes large and the control processing becomes complicated.

Alternatively, a dedicated spare light source (not shown) is prepared for each of the optical signal sources 511 to 513, so that even if the optical signal sources 511 to 513 are damaged, It is also conceivable to keep the signal strength almost constant. But in that case,
Since the same number of spare light sources as the number of optical signal sources is required, it is inevitable to increase the size of the wavelength division multiplexing optical transmission system. In particular, when the number of multiplexed waves is large, the increase in the size becomes remarkable.

As described above, the new conventional wavelength-division multiplexing optical transmission system has the advantage that when the number of multiplexed optical signals (ie, the number of multiplexed waves) changes, each of the optical signals received by each of the receiving stations 581 and 582 is changed. There is a problem that the strength cannot be kept constant. There has not been an optical amplifier or an optical transmission device used in the new conventional wavelength division multiplexing optical transmission system and capable of solving the above problems. An optical amplifier used in the above-mentioned general conventional wavelength-division multiplexed optical transmission system and capable of keeping the intensity of each optical signal received on the receiving side constant when the number of multiplexed waves is changed, conventionally exists. (Figure 1
7), it is conceivable to improve it to realize a new optical amplifier that can solve the above problem. However, in that case, the configuration of the optical amplifier is inevitably complicated and large-scale.

Therefore, an object of the present invention is to use a wavelength division multiplexing optical transmission system to multiplex a plurality of optical signals having different wavelengths from each other and transmit them with a simple and small configuration. It is an object of the present invention to provide an optical transmission device capable of keeping the intensity of each optical signal to be transmitted constant even when the number of optical signals to be multiplexed (that is, the number of multiplexed waves) changes.

Another object of the present invention is to provide a wavelength-division multiplexed optical transmission system for use in a wavelength-division multiplexed optical transmission system, which is obtained by multiplexing a plurality of optical signals having different wavelengths from each other with a simple and small-scale configuration. An object of the present invention is to provide an optical amplifier capable of amplifying a signal and maintaining the intensity of each of the amplified and output optical signals even if the number of multiplexed waves changes.

[0023]

Means for Solving the Problems and Effects of the Invention A first invention is provided in a wavelength division multiplexing optical transmission system and transmits a wavelength division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed. An optical signal output unit that outputs a plurality of optical signals that are intensity-modulated by an electric signal and have different wavelengths, a pilot light output unit that outputs one or more pilot lights having different wavelengths from each optical signal, Each optical signal output from the signal output unit and each pilot light output from the pilot light output unit are multiplexed with each other, in the form of a wavelength multiplexed optical signal in which each optical signal and each pilot light are multiplexed with each other. The multiplexing unit includes an output multiplexing unit and an optical amplifying unit that amplifies the wavelength multiplexed optical signal output from the multiplexing unit.

In the first aspect, the total input light intensity to the optical amplifier is increased in advance by adding pilot light to the optical signal. As a result, the ratio of the change in the total input light intensity caused by the change in the number of multiplexed waves to the total input light intensity to the optical amplification unit, that is, the change in the total input light intensity with respect to a constant change in the number of multiplexed waves can be reduced. At this time, the fluctuation of the total input light intensity is smaller as the intensity of the pilot light is larger than that of the optical signal. Therefore, if the intensity of the pilot light is made sufficiently high, the gain of the optical amplifier can be kept constant even if the number of multiplexed waves changes, and as a result, the intensity of each optical signal to be transmitted can be kept constant. Becomes possible.

According to a second aspect, in the first aspect, the optical amplifying unit is configured to transmit the signal to the optical amplifying unit even if the number of optical signals input to the optical amplifying unit (ie, the number of multiplexed waves) changes. It is characterized in that if the total input light intensity is constant, the gain of the optical amplifier is also kept constant.

According to a third aspect of the present invention, in the first aspect, each pilot light output from the pilot light output section has a higher intensity than each optical signal output from the optical signal output section.

In the third aspect, the intensity of the pilot light is made larger than that of the optical signal. As a result, the gain of the optical amplifier can be kept almost constant, and as a result, the intensity of each optical signal to be transmitted can be kept almost constant.

According to a fourth aspect based on the third aspect, each pilot light output from the pilot light output section is intensity-modulated by an electric signal, and the pilot light output from the pilot light output section is intensity-modulated. The modulation method used for the electric signal is different from the modulation method used for the electric signal that intensity-modulates each optical signal output from the optical signal output unit and requires a higher CNR or SNR. It is characterized by.

In the fourth aspect, the pilot light for keeping the transmission intensity of each optical signal constant is intensity-modulated by the electric signal. That is, since the electric signal is transmitted using the pilot light, the limited transmission capacity can be effectively used. Moreover, since the intensity of the pilot light is larger than that of the optical signal, the electric signal for intensity-modulating the pilot light has a relatively high CNR or SNR as compared with the modulation method used for the electric signal for intensity-modulating the optical signal. The required modulation scheme can be used. Typically, baseband digital modulation is used for an electric signal for intensity-modulating an optical signal, and AM modulation is used for an electric signal for intensity-modulating a pilot light, as in the fifth invention described below.

In a fifth aspect based on the fourth aspect, each pilot light output from the pilot light output section is intensity-modulated by an analog electric signal, and each optical signal output from the optical signal output section is a digital signal. It is characterized in that the intensity is modulated by an electric signal.

In a sixth aspect based on the first aspect, each pilot light output from the pilot light output section is intensity-modulated by an electric signal, and the pilot light output from the pilot light output section is intensity-modulated. The modulation method used for the electric signal is different from the modulation method used for the electric signal for intensity-modulating each optical signal output from the optical signal output unit.

According to the sixth aspect, the pilot light is also intensity-modulated by the electric signal. Then, different modulation schemes are used for the pilot light and the optical signal. It should be noted that if the modulation method is different, the required CNR is generally used.
Or the SNR is also different.

According to a seventh aspect based on the sixth aspect, the intensity of each pilot light output from the pilot light output section and the intensity of each optical signal output from the optical signal output section are obtained by controlling the intensity of each of the electric signals. It is characterized in that it is determined individually according to the CNR or SNR required for the signal modulation method.

According to the seventh aspect, the intensity of the pilot light and the intensity of the optical signal are determined by the CN required for each modulation method.
Since it is determined individually according to R or SNR, good transmission characteristics can be obtained for both pilot light and optical signal.

According to an eighth aspect based on the first aspect, the sum of the intensities of all the pilot lights output from the pilot light output section is larger than the sum of the intensities of all the optical signals output from the optical signal output section. It is characterized by:

In the eighth aspect, the sum of the intensities of all the pilot lights is made larger than the sum of the intensities of all the optical signals. Thereby, the gain of the optical amplifier can be kept almost constant, and as a result, the intensity of each optical signal to be transmitted is
It can be kept substantially constant.

According to a ninth aspect, in the first aspect, the optical signals output from the optical signal output section have different intensities.

In the ninth aspect, the optical signals have different intensities. Even in such a case, if the intensity of the pilot light is made sufficiently high, the optical amplifying unit can change even if the number of multiplexed waves changes. Can be kept constant, so that
The intensity of each optical signal to be transmitted can be kept constant.

According to a tenth aspect, in the first aspect, at least one of the plurality of optical signals output from the optical signal output section is provided.
First, the wavelength is variable.

In the tenth aspect, at least one optical signal is variable in wavelength. In such an optical signal, the intensity may temporarily become zero at the moment of switching the wavelength. The period in which the intensity is 0 is equivalent to a decrease in the number of signals (the number of multiplexed waves), but even in such a case, if the intensity of the pilot light is sufficiently increased, the gain of the optical amplification unit is kept constant. , And as a result, the intensity of each optical signal to be transmitted can be kept constant.

According to an eleventh aspect, in the first aspect, at least one optical signal output from the optical signal output section is intensity-modulated by an intermittent electric signal.

In the eleventh aspect, the optical signal is intensity-modulated by an intermittent electric signal (for example, a digital electric signal). In such an optical signal, there is a period in which the intensity is temporarily zero, and the period in which the intensity is zero is equivalent to a decrease in the number of signals (the number of multiplexed waves). If the intensity of the pilot light is set sufficiently high, the gain of the optical amplifier can be kept constant, and as a result, the intensity of each optical signal to be transmitted can be kept constant.

In a twelfth aspect based on the first aspect, the optical signal output section includes a plurality of optical signal sources each generating one optical signal, and a plurality of optical signal sources generated by the respective optical signal sources. An optical signal is output as a plurality of optical signals, and the pilot light output unit includes one or more pilot light sources each of which generates one pilot light, and outputs one or more pilot lights generated by each of the pilot light sources. The above pilot light is output, and when each pilot light source cannot generate the pilot light, one or more light sources that generate the same pilot light as that generated by each of the pilot light sources in place of each of the pilot light sources are provided. A backup light source is further provided.

According to the twelfth aspect, even when the pilot light source cannot be generated due to damage of the pilot light source, the intensity of each optical signal to be transmitted can be kept constant. In addition, by preparing a spare light source for each optical signal source (that is, preparing the same number of spare light sources as the number of optical signal sources), compared with a case where the intensity of each optical signal to be transmitted is kept almost constant. Since it is only necessary to provide the same number of spare light sources as the pilot light sources, the intensity of each optical signal to be transmitted can be kept substantially constant with a simpler configuration. This is particularly effective when the number of multiplexed waves is large.

According to a thirteenth aspect, in the first aspect, the intensity of each pilot light included in the amplified wavelength-division multiplexed optical signal output from the optical amplifier is monitored, and the intensity becomes constant. As described above, it further includes a monitoring unit that controls the optical amplification unit.

In the thirteenth invention (and the fourteenth invention described below), since the fluctuation of the pilot light intensity is prevented,
More reliably, the intensity of each optical signal to be transmitted can be kept constant.

According to a fourteenth aspect, in the first aspect, the pilot light included in the amplified wavelength multiplexed optical signal output from the optical amplifier is converted into an electric signal, and the power of each electric signal is reduced. There is further provided a monitoring unit that controls the optical amplification unit so as to monitor the power and make each power constant.

A fifteenth invention is an optical amplifying apparatus provided in a wavelength division multiplexing optical transmission system for amplifying a wavelength division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed. A pilot light output unit that outputs one or more pilot lights different from each other, a wavelength multiplexed optical signal and each pilot light output from the pilot light output unit are multiplexed with each other, and each optical signal and each pilot light are multiplexed with each other. And a light amplifying unit for amplifying the wavelength multiplexed optical signal output from the multiplexing unit.

In the fifteenth aspect, the total input light intensity to the optical amplifier is increased in advance by adding pilot light to the optical signal. As a result, the ratio of the change in the total input light intensity caused by the change in the number of multiplexed waves to the total input light intensity to the optical amplification unit, that is, the change in the total input light intensity with respect to a constant change in the number of multiplexed waves can be reduced. At this time, the fluctuation of the total input light intensity is smaller as the intensity of the pilot light is larger than that of the optical signal. Therefore, if the intensity of the pilot light is sufficiently increased, the gain of the optical amplifier can be kept constant even if the number of multiplexed waves changes, and as a result,
The intensity of each optical signal to be amplified and output can be kept constant.

A sixteenth invention is a wavelength division multiplexing optical transmission system provided with an optical transmission device for transmitting a wavelength division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed. An optical signal output unit that outputs a plurality of optical signals that are intensity-modulated by signals and have different wavelengths, a pilot light output unit that outputs one or more pilot lights having different wavelengths from each optical signal, and an output from the optical signal output unit Multiplexing unit that multiplexes each optical signal to be output and each pilot light output from the pilot optical output unit with each other, and outputs each optical signal and each pilot light in the form of a wavelength multiplexed optical signal multiplexed with each other. And an optical amplifying unit for amplifying the wavelength multiplexed optical signal output from the multiplexing unit.

In the sixteenth invention (and the seventeenth invention described below), by adding pilot light to an optical signal,
The total input light intensity to the optical amplifier is increased in advance. As a result, the ratio of the change in the total input light intensity caused by the change in the number of multiplexed waves to the total input light intensity to the optical amplification unit, that is, the change in the total input light intensity with respect to a constant change in the number of multiplexed waves can be reduced. At this time, the fluctuation of the total input light intensity is smaller as the intensity of the pilot light is larger than that of the optical signal. Therefore, if the intensity of the pilot light is made sufficiently high, the gain of the optical amplifier can be kept constant even if the number of multiplexed waves changes. As a result, the intensity of each optical signal to be transmitted can be kept constant. Becomes possible.

A seventeenth invention is a wavelength division multiplexing optical transmission system provided with an optical amplification device for amplifying a wavelength division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed. A pilot light output unit that outputs one or more pilot lights having different wavelengths from the optical signal, a wavelength multiplexed optical signal, and each pilot light output from the pilot light output unit are multiplexed with each other to form each optical signal and each pilot signal. It has a multiplexing unit that outputs in the form of a wavelength multiplexed optical signal in which light is multiplexed with each other, and an optical amplifier that amplifies the wavelength multiplexed optical signal output from the multiplexing unit.

[0053]

Embodiments of the present invention will be described below in detail with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing a configuration of an optical transmission apparatus according to a first embodiment of the present invention. The optical transmission apparatus shown in FIG. 1 is used in a wavelength division multiplexing optical transmission system (not shown) for multiplexing and transmitting a plurality of optical signals having different wavelengths. That is, the optical transmission device is provided on the transmission side of the wavelength division multiplexing optical transmission system, and is connected to the optical reception device provided on the reception side via the optical transmission path.

A wavelength division multiplexing optical transmission system using the optical transmission device according to the first embodiment of the present invention is, for example, a single transmission station like the above-mentioned general conventional wavelength division multiplexing optical transmission system. One receiving station may be connected via one optical transmission line, or one transmitting station and one relay station may be connected as in the new conventional wavelength multiplexing optical transmission system. Connected via one optical transmission line,
Further, the configuration may be such that the one relay station and the plurality of receiving stations are connected via one optical transmission line.

In FIG. 1, the optical transmitter according to the first embodiment includes a pilot light output unit 11 including one or more pilot light sources (here, two pilot light sources 111 and 112), and a plurality of optical signal sources ( Here, four optical signal sources 12
1 to 124), and a multiplexing unit 13
And an optical amplifier 14. Note that the numbers of the pilot light sources and the optical signal sources are not limited to those shown in FIG. 1, and any number of pilot light sources and one or more optical signal sources may be used as long as the number is one.

Each of the pilot light sources 111 and 112 outputs a pilot light. Each of the optical signal sources 121 to 124 outputs an optical signal having a different wavelength. The multiplexing unit 13 multiplexes the pilot light output from each of the pilot light sources 111 and 112 and the optical signal output from each of the optical signal sources 121 to 124 with each other. The optical amplifying unit 14
The output light from the amplifier is amplified.

The optical amplifier 14 is realized by using the same EDFA (ie, erbium-doped optical fiber amplifier) as that described in the section of the prior art. ED
Any type of optical amplifier may be used as long as it has an input light intensity-gain characteristic (described later) similar to that of the FA.

The operation of the optical transmission device configured as described above will be described below. First, each pilot light source 111,
112 outputs a pilot light, while each optical signal source 1
21 to 124 output optical signals of different wavelengths. At this time, the pilot light output from each of the pilot light sources 111 and 112 has a different wavelength from the optical signal output from each of the optical signal sources 121 to 124. The different wavelengths are used so that the optical signal and the pilot light can be distinguished on the receiving side.

Preferably, each pilot light source 111, 1
Reference numeral 12 denotes each of the optical signal sources 121 to 121 as shown in FIG.
The pilot light (211, 211) having a greater intensity than the optical signals (221-224) output from
12) is output (the reason will be described later). When the intensity of each optical signal is different from each other, each pilot light source 111, 1
Reference numeral 12 outputs a pilot light having a greater intensity than that of the optical signal output from each of the optical signal sources 121-124. Alternatively, each optical signal source 12
A pilot light having an intensity such that the total sum of the optical signals output from 1 to 124 is larger than that of the optical signals is output.

Next, the multiplexing unit 13 is provided for each pilot light source 1
The pilot light output from each of the optical signal sources 11 and 112 and the optical signal output from each of the optical signal sources 121 to 124 are multiplexed with each other. Next, the optical amplifier 14 amplifies the output light (wavelength multiplexed light) of the multiplexer 13. That is, the pilot light output from each of the pilot light sources 111 and 112 and the optical signal output from each of the optical signal sources 121 to 124 are obtained by wavelength-multiplexing the pilot light and the optical signal. In this manner, the signals are collectively amplified in the optical amplifier 14.

The output light (wavelength multiplexed light after amplification) of the optical amplifier 14 is sent out of the optical transmitter shown in FIG.
The transmitted wavelength-division multiplexed light is transmitted through an optical transmission line (not shown) and received by an optical receiver (not shown). Thereafter, the operation performed by the optical receiver is the same as the operation performed by the receiving stations 581 and 582 in FIG. 16 (see the section of the prior art). The above is the operation of the optical transmission device according to the first embodiment.

Here, the EDF used for the optical amplifier 14
The characteristics of A (particularly, input light intensity-gain characteristics) will be described in more detail (partially described in the section of the prior art). First, a general input light intensity-gain characteristic of an EDFA will be described. FIG. 3 is a diagram showing the input light intensity-gain characteristics of the EDFA used in the optical amplifier 14 of FIG. ED
An FA generally has an input light intensity-gain characteristic as shown in FIG. That is, if the input light intensity is smaller than the predetermined value α, the gain is kept substantially constant even if the input light intensity changes, but if the input light intensity is larger than the above value α, the gain becomes It decreases with increasing light intensity.

However, when used in the optical amplifier 14, the operating point β of the EDFA is
Usually, it is set to a position larger than the above value. Therefore, it can be seen that, generally, when the input light intensity to the optical amplifier 14 changes, the gain also changes accordingly. When the gain changes, the output light intensity from the optical amplifier 14 also changes.

From the above, in the optical transmitter of FIG. 1, in order to keep the intensity of each optical signal to be transmitted constant even when the number of multiplexed waves changes, it is essential that the optical amplifier 14
It can be seen that it is sufficient to keep the gain of.

Next, the relationship between the input light intensity-gain characteristics of the EDFA and the number of multiplexed waves will be described. 4 and 5 are diagrams (1 wave and 8 waves) showing the input light intensity-gain characteristics of the EDFA used in the optical amplifying unit 14 of FIG. 1 while changing the number of multiplexed waves. However, in FIG. 4, the input light intensity on the horizontal axis of the graph is the input light intensity per one wave, and in FIG. 5, the input light intensity on the horizontal axis of the graph is the total input light intensity.
In each case, control for keeping the output light intensity constant as described in the section of the related art is not performed.

As shown in FIG. 4, in the EDFA, the input light intensity-gain characteristics vary depending on the number of multiplexed waves. That is, even if the input light intensity per wave is determined, the gain is not uniquely determined, and the value changes depending on the number of multiplexed waves. On the other hand, as shown in FIG.
In the case of the EDFA, the input light intensity-gain characteristics do not change even if the number of multiplexed waves changes, when viewed as a whole wave. That is, if the total input light intensity is determined, the gain is uniquely determined regardless of the number of multiplexed waves.

Based on the input light intensity-gain characteristics of the EDFA described above, in the optical transmitter of FIG.
By adding pilot light to the optical signal upstream of
The total input light intensity to the optical amplification unit 14 is set to be higher. This is because if the total input light intensity increases, the influence of the change in the multiplex wave number decreases relatively. When the input light intensity changes by the same amount between the case where the total input light intensity is high and the case where the total input light intensity is low, the ratio of the change amount to the total input light intensity is smaller in the former case than in the latter case.

As described above, in the optical transmitting apparatus according to the first embodiment, by adding the pilot light to the optical signal,
The total input light intensity to the optical amplifier 14 is increased in advance.
This makes it possible to reduce the ratio of the change in the total input light intensity caused by the change in the number of multiplexed waves to the total input light intensity to the optical amplifying unit 14 (that is, the change in the total input light intensity with respect to a certain change in the number of multiplexed waves). Can be smaller).

At this time, the fluctuation of the total input light intensity becomes smaller as the intensity of the pilot light is larger than that of the optical signal. Therefore, if the intensity of the pilot light is made sufficiently large, the gain of the optical amplifier 14 can be kept constant, and as a result, the intensity of each optical signal to be transmitted can be kept constant.

However, since the optical amplifying unit 14 has an input allowable value, if the intensity of the pilot light is increased, the number of multiplexable waves decreases accordingly. Therefore, in general, the intensity of the pilot light is set to a value such that a certain number of multiplexable waves can be ensured and the fluctuation of the total input light intensity falls within a predetermined amount or less.

Here, the condition regarding the intensity of the pilot light is determined in particular as follows. That is, the intensity of the pilot light is made larger than that of the optical signal. As a result, the gain of the optical amplifier 14 can be kept almost constant, and as a result, the intensity of each optical signal to be transmitted can be kept almost constant.

The conditions for the intensity of the pilot light are as follows:
Hereinafter, specific verification will be made. It is assumed that the output light intensity is not controlled. FIG. 6 is a diagram illustrating the intensity of an optical signal input to the optical amplifier 14 in FIG. First, FIG.
As shown in FIG. 5, consider a case where four optical signals having an intensity per wave of −20 dBm are input to the optical amplifying unit 14.
At this time, the total input light intensity to the optical amplifier 14 is -14d
Bm. Thereafter, when the number of multiplexed waves is reduced by one wave to three waves, the total input light intensity becomes −15.2 dBm. That is, it is reduced by 1.2 dBm as compared with the case where the number of multiplexed waves is four.

FIG. 7 is a diagram showing the intensity of an optical signal and pilot light input to the optical amplifier 14 of FIG. Next, as shown in FIG. 7, the intensity per wave is -20 dB.
In addition to the four optical signals of m, the intensity per wave is -10 dB
Consider a case where two m pilot lights are input. At this time, the total input light intensity to the optical amplifier 14 is -6.2 dBm
It is. Thereafter, when the number of multiplexed waves is reduced by one wave to three waves, the total input light intensity becomes -6.4 dBm. That is,
The number is reduced by 0.2 dBm as compared with the case where the number of multiplexed waves is four.

This reduction amount of 0.2 dBm is sufficiently smaller than the reduction amount of 1.2 dBm when the pilot light is not input, and is almost close to 0, so that the total input light intensity to the optical amplifier 14 is changed by the multiplex wave number. However, it can be considered that it is almost constant. Therefore, the intensity of each output light from the optical amplifying unit 14 is kept constant, and therefore, the optical transmitter of FIG. 1 can keep the intensity of each optical signal to be transmitted constant.

In the above description, the optical signals have the same intensity. However, even if the optical signals 225 to 228 have different intensities as shown in FIG. , These optical signals 225-2
28 (more specifically, if the intensity of each pilot light 211, 212 is greater than the maximum intensity among the respective intensities of the plurality of wavelength-multiplexed optical signals (225 to 228); Even if the intensities of the pilot lights 211 and 212 do not need to be equal to each other), and even if the number of multiplexed waves (the number of wavelength-multiplexed optical signals) decreases, the total input light intensity to the optical amplifier 14 is kept substantially constant. It is.

The optical signal sources 121 to 124 shown in FIG.
The oscillation wavelength need not always be fixed, but may be variable. Optical signal source 1 whose oscillation wavelength is variable
In the case where the wavelengths 21 to 124 are used, as shown in FIG.
2, there is a possibility that there is a time when the optical signal is not output because there is no instantaneous switching. Since this is equivalent to a temporary decrease in the number of optical signals from the viewpoint of the entire system, the input light intensity to the optical amplifier 14 may fluctuate temporarily. Also in such a case, in the optical transmission device of FIG. 1, it is possible to avoid the fluctuation of each output light intensity from the optical amplifier 14.

As described above, according to the present embodiment, the number of multiplexed optical signals used in a wavelength division multiplexed optical transmission system without performing any complicated control (accordingly, with a simple and small configuration) Even if the multiplex wave number changes, the intensity of each optical signal to be transmitted can be kept constant.

(Second Embodiment) FIG. 10 is a block diagram showing a configuration of an optical transmission device according to a second embodiment of the present invention. The optical transmitter shown in FIG. 10 is provided on the transmitting side of a wavelength division multiplexing optical transmission system (not shown) for multiplexing and transmitting a plurality of optical signals having different wavelengths to each other, similarly to the optical transmitter shown in FIG. And is connected to an optical receiving device provided on the receiving side via an optical transmission line.

The wavelength division multiplexing optical transmission system using the optical transmission apparatus according to the second embodiment of the present invention is, for example, similar to the above-mentioned general conventional wavelength division multiplexing optical transmission system, in which one transmission station is used. One receiving station may be connected via one optical transmission line, or one transmitting station and one relay station may be connected as in the new conventional wavelength multiplexing optical transmission system. Connected via one optical transmission line,
Further, the configuration may be such that the one relay station and the plurality of receiving stations are connected via one optical transmission line.

In FIG. 10, an optical transmitter according to the second embodiment includes a pilot light output unit 11 including one or more pilot light sources (here, two pilot light sources 111 and 112), and a plurality of optical signal sources ( Here, four optical signal sources 1
21 to 124) and a multiplexing unit 13
And an optical amplifier 14. Note that the numbers of pilot light sources and optical signal sources are not limited to those shown in FIG.

Each of the pilot light sources 111 and 112 outputs a pilot light intensity-modulated by an externally input electric signal. Optical signal sources 121 to 124, multiplexing unit 1
3 and the optical amplifying unit 14 perform the same operation as that shown in FIG. 1 (see the first embodiment). Optical amplifier 14
Is realized using an EDFA as in the case of FIG.
In addition, regarding the input light intensity-gain characteristics of the EDFA,
This has already been described in the first embodiment.

The operation of the optical transmission apparatus configured as described above is similar to that of the first embodiment except that the pilot light output from each of the pilot light sources 111 and 112 is intensity-modulated by an externally input electric signal. This is similar to the first embodiment.

As described above, in the optical transmitter according to the second embodiment, as in the first embodiment, by adding pilot light to an optical signal, the total input light intensity to the optical amplifier 14 is increased in advance. are doing. Thereby, the ratio of the fluctuation of the total input light intensity caused by the change of the multiplex wave number to the total input light intensity to the optical amplification unit 14 is reduced, and the gain of the light amplification unit 14 is kept constant. The intensity of each optical signal to be transmitted is kept constant.

Also, the conditions relating to the intensity of the pilot light are set in the same manner as in the first embodiment.
Similar effects can be obtained. At that time, the pilot light source 11
If the intensity of each pilot light from the optical signal sources 1 and 112 is greater than the intensity of each optical signal from each optical signal source 121 to 124,
The first embodiment differs from the first embodiment in that the intensity of each optical signal from these optical signal sources may be different (see FIG. 8) and that the oscillation wavelength of the optical signal sources 121 to 124 may be variable. Is the same as

Then, in addition to the same effects as in the first embodiment, the following other effects are obtained. That is, in the optical transmission device according to the second embodiment, the pilot light for keeping the transmission intensity of each optical signal constant is intensity-modulated by the electric signal. That is, since the electric signal is transmitted using the pilot light, the limited transmission capacity can be effectively used.

Further, since the intensity of the pilot light is larger than that of the optical signal, the electric signal obtained by photoelectrically converting the pilot light in the optical receiver has a higher CNR than the electric signal obtained by photoelectrically converting the optical signal. Alternatively, SNR can be secured. Therefore, the pilot light sources 111,
The electrical signals input to 112 include optical signal sources 121-1.
A modulation scheme that requires a relatively high CNR or SNR as compared to the modulation scheme used for the electric signal input to the input terminal 24 can be used. Here, in general, an SNR (signal-to-noise ratio) required to achieve high transmission quality (low error rate when transmitting a digital electric signal)
Alternatively, the CNR (carrier-to-noise ratio) differs depending on the modulation scheme. For example, in AM modulation and baseband digital modulation, the required SNR or CNR is higher in the former than in the latter.

Therefore, the baseband digital modulation can be used for the electric signals input to the optical signal sources 121 to 124, and the AM modulation can be used for the electric signals input to the pilot light sources 111 and 112. Thereby, the second
In the wavelength division multiplexing optical transmission system provided with the optical transmission device according to the embodiment, not only the optical signal is intensity-modulated by a digital electric signal (for example, a signal subjected to baseband digital modulation) and transmitted with high quality, but also a pilot signal is transmitted. Light can be intensity-modulated by an analog electric signal (for example, an AM-modulated signal) and transmitted with high quality.

In this embodiment, the condition that the intensity of the pilot light is higher than that of the optical signal is determined first.
Under these conditions, the electric signals input to the pilot light sources 111 and 112 require a relatively high CNR or SNR as compared with the modulation method used for the electric signals input to the optical signal sources 121 to 124. It was stated that such a modulation scheme could be used, but instead, the optical signal source 1
The modulation method to be used for each of the electric signals input to 21 to 124 and the electric signals input to pilot light sources 111 and 112 is determined in advance, and according to the CNR or SNR required for each modulation method. , The intensity of the pilot light and the intensity of the optical signal may be determined. That is, FIG.
0, the intensity of each pilot light from the pilot light sources 111 and 112 and the intensity of each optical signal from the optical signal sources 121 to 124 are converted into the SNR required for each modulation method.
Alternatively, it is set according to the CNR. Accordingly, in the wavelength division multiplexing optical transmission system provided with the optical transmission device according to the second embodiment, high quality transmission can be performed using two different modulation schemes. In other words, not only can the optical signal be intensity-modulated with an electric signal modulated by a predetermined method and transmitted with high quality, but also the pilot light can be intensity-modulated with an electric signal modulated with another method and transmitted with high quality. become able to.

(Third Embodiment) The configuration of the optical transmission apparatus according to the third embodiment of the present invention is the same as that of the optical transmission apparatus according to the second embodiment. FIG. 10 is referred to. The optical transmitter shown in FIG. 10 is provided on the transmitting side of a wavelength division multiplexing optical transmission system (not shown) for multiplexing and transmitting a plurality of optical signals having different wavelengths to each other, similarly to the optical transmitter shown in FIG. And is connected to an optical receiving device provided on the receiving side via an optical transmission line. Each component included in the optical transmission device illustrated in FIG. 10 performs the same operation as in the second embodiment except for the optical signal sources 121 to 124.

The wavelength division multiplexing optical transmission system using the optical transmission apparatus according to the third embodiment of the present invention is, for example, a single transmission station like the general conventional wavelength division multiplexing optical transmission system. One receiving station may be connected via one optical transmission line, or one transmitting station and one relay station may be connected as in the new conventional wavelength multiplexing optical transmission system. Connected via one optical transmission line,
Further, the configuration may be such that the one relay station and the plurality of receiving stations are connected via one optical transmission line.

At least one of the optical signal sources 121 to 124 converts an electric signal composed of intermittent data input from the outside (ie, an intermittent electric signal) into an intermittent optical signal. The remaining optical signal sources convert a continuous electric signal into a continuous optical signal. Each of the pilot light sources 111 and 112 outputs a pilot light modulated by an electric signal composed of continuous data input from the outside.

The operation of the optical transmission apparatus configured as described above is the same as that of the second embodiment except for the following points. That is, at least one of the optical signal sources 121 to 124 converts an intermittent electric signal into an intermittent optical signal.

The optical transmitter according to the third embodiment has the following advantages in addition to the advantages of the second embodiment. FIG. 11 is a diagram illustrating an intermittent optical signal transmitted by the optical transmitter illustrated in FIG. In the case of transmitting an intermittent optical signal as shown in FIG. 11, for example, the output light intensity of the optical signal source 121 changes during the signal transmission period, but the optical signal source 121 does not transmit the signal during the signal transmission period. Output light intensity is always 0
This is equivalent to a decrease in the number of optical signals to be transmitted (that is, a decrease in the number of multiplexed waves). Moreover, the latter period may last longer than the former period.

Therefore, when the optical signal source 121 transmits an intermittent optical signal, the total input light intensity to the optical amplifying unit 14 changes at the moment when the period changes from the signal transmission period to the non-transmission period. The intensity of each optical signal output from the optical amplifier 14 fluctuates with time. On the other hand, in the optical transmitting apparatus according to the third embodiment, the pilot light, preferably, the pilot light having a higher intensity than the intermittent optical signal is input to the optical amplifier 14, so that the optical amplifier The ratio of the change of the total input light intensity caused by the intermittent optical signal to the total input light intensity to the unit 14 is suppressed to a small value, and the gain of the optical amplification unit 14 is kept substantially constant. As a result, the optical transmitter according to the third embodiment can keep the intensity of each optical signal to be transmitted substantially constant.

(Fourth Embodiment) FIG. 12 is a block diagram showing a configuration of an optical transmission device according to a fourth embodiment of the present invention. The optical transmitter shown in FIG. 12 is provided on the transmitting side of a wavelength division multiplexing optical transmission system (not shown) for multiplexing and transmitting a plurality of optical signals having different wavelengths from each other, similarly to the optical transmitter shown in FIG. And is connected to an optical receiving device provided on the receiving side via an optical transmission line.

The wavelength division multiplexing optical transmission system using the optical transmission apparatus according to the fourth embodiment of the present invention is, for example, a single transmission station like the above-mentioned general conventional wavelength division multiplexing optical transmission system. One receiving station may be connected via one optical transmission line, or one transmitting station and one relay station may be connected as in the new conventional wavelength multiplexing optical transmission system. Connected via one optical transmission line,
Further, the configuration may be such that the one relay station and the plurality of receiving stations are connected via one optical transmission line.

The optical transmitter shown in FIG. 12 is different from the optical transmitter shown in FIG. 10 (see the third embodiment) in that one or more auxiliary light sources (here, two auxiliary light sources 161 and 162) are used.
And a standby light output unit 16 including The number of backup light sources is not limited to that shown in FIG. 12, but may be any number. However, it is preferable to use the same number as the pilot light sources.

Each of the spare light sources 161 and 162 is provided in case the pilot light sources 111 and 112 lose their output due to damage or the like. That is, each spare light source 161,
162, when each pilot light source 111, 112 loses its output,
, And outputs pilot light equivalent to that output from each of the pilot light sources 111 and 112. Thus, even if each pilot light source is damaged, the decrease in the total input light intensity to the optical amplifying unit 14 can be compensated for.

As described above, in the optical transmission device according to the fourth embodiment, the following other effects can be obtained in addition to the same effects as those of the third embodiment. That is, in the optical transmission device according to the fourth embodiment, each pilot light source 11
Even if 1,112 is damaged, the intensity of each optical signal to be transmitted is
Each can be kept almost constant.

On the other hand, by preparing a spare light source for each of the optical signal sources 121 to 124 (that is, preparing the same number of spare light sources as the number of optical signal sources), the intensity of each optical signal to be transmitted is substantially constant. As compared with the case where the number of auxiliary light sources is equal to that of the pilot light source (see the column of the problem to be solved), the optical transmitter according to the fourth embodiment only needs to have the same number of spare light sources as the pilot light sources. It can be said that the intensity of each optical signal to be transmitted can be kept substantially constant. This is particularly effective when the number of multiplexed waves is large.

(Fifth Embodiment) FIG. 13 is a block diagram showing a configuration of an optical transmission device according to a fifth embodiment of the present invention. The optical transmission device shown in FIG. 13 is provided on the transmission side of a wavelength division multiplexing optical transmission system (not shown) for multiplexing and transmitting a plurality of optical signals having different wavelengths to each other, similarly to the optical transmission device shown in FIG. And is connected to an optical receiving device provided on the receiving side via an optical transmission line.

The wavelength division multiplexing optical transmission system using the optical transmission device according to the fifth embodiment of the present invention is, for example, a single transmission station like the above-mentioned general conventional wavelength division multiplexing optical transmission system. One receiving station may be connected via one optical transmission line, or one transmitting station and one relay station may be connected as in the new conventional wavelength multiplexing optical transmission system. Connected via one optical transmission line,
Further, the configuration may be such that the one relay station and the plurality of receiving stations are connected via one optical transmission line.

In FIG. 13, an optical transmitter according to the fifth embodiment includes a pilot light output unit 11 including one or more pilot light sources (here, one pilot light source 111).
And a plurality of optical signal sources (here, four optical signal sources 121 to 1)
24), an optical signal output unit 12 including the optical signal output unit 24, a multiplexing unit 13, an optical amplifying unit 14, and a monitoring unit 17. Note that the numbers of pilot light sources and optical signal sources are not limited to those shown in FIG.

The monitoring unit 17 monitors the intensity of the pilot light included in the output light of the optical amplifier 14, and controls the optical amplifier 14 so that the intensity of the pilot light becomes constant. The function of the monitoring unit 17 as described above can be realized using a filter for extracting the pilot light, a CPU for controlling the optical amplifying unit 14, a memory, and the like (neither is shown). In that case, a program describing the control processing is stored in the memory, and the CPU operates according to the program in the memory. The configuration of the monitoring unit 17 is not limited to the configuration described above, and any configuration may be used as long as the above function can be realized.

The other components, that is, the pilot light source 111, the optical signal sources 121 to 124, the multiplexing unit 13 and the optical amplifying unit 14 operate in the same manner as those shown in FIG. See). The optical amplifying unit 14 is realized using an EDFA as in the case of FIG. ED
The input light intensity-gain characteristics and the like of the FA have already been described in the first embodiment.

The operation of the optical transmitter configured as described above is characterized in that the monitoring unit 17 controls the optical amplifying unit 14 so that the intensity of the pilot light included in the output light is kept constant. Except for this, the third embodiment is the same as the first embodiment.

The operation in which the monitoring unit 17 controls the optical amplification unit 14 will be described below. A part of the output light from the optical amplifier 14 is provided to the monitoring unit 17, and the monitoring unit 17 first extracts the pilot light therefrom. Next, the monitoring unit 17 measures the intensity of the extracted pilot light and stores the measurement result. Next, after a predetermined time has elapsed since the pilot light intensity measurement / storage processing,
The same pilot light intensity measurement and storage processing as above is performed again, and the new and old measured values are compared with each other. Then, as a result of the comparison, if there is a change in the measured value, the gain of the optical amplifier 14 is changed so as to cancel the change. The intensity of the pilot light output from the optical amplifier 14 is kept constant by the monitoring unit 17 controlling the optical amplifier 14 as described above.

As described above, in the optical transmitter according to the fifth embodiment, as in the first embodiment, by adding pilot light to an optical signal, the total input light intensity to the optical amplifier 14 is increased in advance. are doing. Thereby, the ratio of the fluctuation of the total input light intensity caused by the change of the multiplex wave number to the total input light intensity to the optical amplification unit 14 is reduced, and the gain of the light amplification unit 14 is kept constant. The intensity of each optical signal to be transmitted is kept constant.

Also, the conditions and the like relating to the intensity of the pilot light are set in the same manner as in the first embodiment.
Similar effects can be obtained. At that time, the pilot light source 11
The intensity of the pilot light from the optical signal sources 121 to 1
If the intensity of each optical signal from the optical signal source 24 is greater than the intensity of each optical signal from the optical signal source (see FIG. 8), the oscillation wavelength of the optical signal sources 121 to 124 is variable. This may be the same as in the first embodiment.

In the present embodiment, since the fluctuation of the pilot light intensity is prevented, the same effects as those of the first embodiment can be more surely obtained.

(Sixth Embodiment) FIG. 14 is a block diagram showing a configuration of an optical transmitting apparatus according to a sixth embodiment of the present invention. The optical transmission device shown in FIG. 14 is provided on the transmission side of a wavelength division multiplexing optical transmission system (not shown) for multiplexing and transmitting a plurality of optical signals having different wavelengths, as in the optical transmission device shown in FIG. And is connected to an optical receiving device provided on the receiving side via an optical transmission line.

The wavelength division multiplexing optical transmission system using the optical transmission apparatus according to the sixth embodiment of the present invention is, for example, a single transmission station like the general conventional wavelength division multiplexing optical transmission system. One receiving station may be connected via one optical transmission line, or one transmitting station and one relay station may be connected as in the new conventional wavelength multiplexing optical transmission system. Connected via one optical transmission line,
Further, the configuration may be such that the one relay station and the plurality of receiving stations are connected via one optical transmission line.

In FIG. 14, an optical transmitter according to the sixth embodiment includes a pilot light output unit 11 including one or more pilot light sources (here, one pilot light source 111).
And a plurality of optical signal sources (here, four optical signal sources 121 to 1)
24), an optical signal output unit 12 including a multiplexing unit 13, an optical amplifying unit 14, and a monitoring unit 18. Note that the numbers of pilot light sources and optical signal sources are not limited to those shown in FIG.

The pilot light source 111 outputs a pilot light intensity-modulated by an externally input electric signal. The monitoring unit 18 converts the pilot light included in the output light of the optical amplifying unit 14 into an electric signal, monitors the power of the electric signal, and controls the optical amplifying unit 14 so that the signal power becomes constant. I do. The functions of the monitoring unit 18 as described above include:
This can be realized using a filter for extracting the pilot light, a photoelectric conversion element for converting the pilot light into an electric signal, a CPU for controlling the optical amplifying unit 14, a memory, and the like (all not shown). In this case, a program that describes the control processing is stored in the memory, and the CPU
Operate according to a program in the memory. The configuration of the monitoring unit 18 is not limited to the configuration described above, and any configuration may be used as long as the above function can be realized.

The other components, ie, each optical signal source 12
1 to 124, the multiplexing unit 13 and the optical amplifying unit 14 perform the same operation as that shown in FIG. 1 (see the first embodiment). The optical amplifying unit 14 is realized using an EDFA as in the case of FIG. The input light intensity-gain characteristics and the like of the EDFA have already been described in the first embodiment.

The operation of the optical transmission apparatus configured as described above is based on the point that the pilot light output from the pilot light source 111 is intensity-modulated by an externally supplied electric signal, and that the monitoring unit 18 has an optical amplifying unit. 14 is controlled in the same manner as the first embodiment except that the power of an electric signal obtained by photoelectrically converting the pilot light included in the output light is kept constant. In addition, the difference from the fifth embodiment is that, when controlling the optical amplifying unit 14, the intensity of the pilot light is kept constant or the power of the electric signal obtained by converting the pilot light is kept constant. It is only the point.

The operation in which the monitoring unit 18 controls the optical amplification unit 14 will be described below. The monitoring unit 18 is provided with a part of the output light from the optical amplifying unit 14. First, the monitoring unit 18 extracts pilot light therefrom and converts the pilot light into an electric signal. Next, the monitoring unit 18 measures the power of the electric signal obtained by converting the pilot light,
Store the measurement result. Next, after a predetermined time has elapsed from the above-described signal power measurement and storage processing, the monitoring unit 18 performs the same signal power measurement and storage processing again as described above, and compares the new and old measured values with each other. Then, as a result of the comparison, if there is a change in the measured value, the gain of the optical amplifier 14 is changed so as to cancel the change. When the monitoring unit 18 controls the optical amplifying unit 14 as described above, the power of the electric signal obtained by converting the pilot light output from the optical amplifying unit 14 is kept constant. Is also kept constant.

As described above, in the optical transmitter according to the sixth embodiment, similarly to the first embodiment, by adding pilot light to an optical signal, the total input light intensity to the optical amplifier 14 is increased in advance. are doing. Thereby, the ratio of the fluctuation of the total input light intensity caused by the change of the multiplex wave number to the total input light intensity to the optical amplification unit 14 is reduced, and the gain of the light amplification unit 14 is kept constant. The intensity of each optical signal to be transmitted is kept constant.

Further, the conditions regarding the intensity of the pilot light and the like are set in the same manner as in the first embodiment.
Similar effects can be obtained. At that time, the pilot light source 11
The intensity of the pilot light from the optical signal sources 121 to 1
If the intensity of each optical signal from the optical signal source 24 is greater than the intensity of each optical signal from the optical signal source (see FIG. 8), the oscillation wavelength of the optical signal sources 121 to 124 is variable. This may be the same as in the first embodiment.

In the present embodiment, as in the fifth embodiment, the fluctuation of the pilot light intensity is prevented, so that the same effects as those of the first embodiment can be further ensured. be able to.

(Seventh Embodiment) FIG. 15 is a block diagram showing a configuration of an optical amplifier according to a seventh embodiment of the present invention. The optical amplifying device shown in FIG. 15 multiplexes a plurality of optical signals having different wavelengths from each other and transmits them on a transmission path (for example, in a wavelength division multiplexed optical transmission system (not shown)).
(The output stage of the optical transmitting device installed on the transmitting side, the input stage of the optical receiving device installed on the receiving side, or a relay device installed between them).

The wavelength division multiplexing optical transmission system using the optical amplifying device according to the seventh embodiment of the present invention comprises, for example, one transmitting station and one The receiving station may be connected to the receiving station via one optical transmission line, or one transmitting station and one relay station may be connected to each other as in the above-mentioned conventional wavelength division multiplexing optical transmission system. Connected via an optical transmission path of
The one relay station and the plurality of receiving stations may be connected to each other via one optical transmission line.

In FIG. 15, the optical amplifying device according to the seventh embodiment includes an optical amplifying unit 41, a pilot optical output unit 42 including one or more pilot light sources (here, one pilot light source 421), and a multiplexing unit. And a portion 43. Note that the number of pilot light sources is not limited to that shown in FIG.

[0124] The pilot light source 241 outputs pilot light. The multiplexing unit 43 includes an external input optical signal (that is, a wavelength multiplexed optical signal transmitted through the wavelength multiplexing optical transmission system and obtained by wavelength multiplexing a plurality of optical signals) and a pilot light from the pilot light source 421. Light and light are combined with each other. The optical amplifier 41 amplifies the output light from the multiplexing unit 43.

The operation of the optical amplifying device configured as described above will be described below. Initially, the pilot light source 421
Outputs pilot light. The output pilot light is
The signal is input to the multiplexing unit 43 together with an externally input optical signal. Next, the multiplexing unit 43 multiplexes the pilot light and the input optical signal with each other, and converts the multiplexed optical signal into
Output to the outside again.

In the above operation, preferably, the pilot light source 421 outputs a pilot light having an intensity higher than that of the externally input optical signal, as in the first embodiment. Further, the optical amplifying unit 41 is similar to the first embodiment.
This is realized using EDFA.

As described above, in the optical amplifying device according to the seventh embodiment, as in the first embodiment, by adding pilot light to an optical signal, the total input light intensity to the optical amplifying unit 41 is increased in advance. are doing. Thereby, the ratio of the fluctuation of the total input light intensity caused by the change of the multiplex wave number to the total input light intensity to the optical amplification unit 41 is reduced, and the gain of the light amplification unit 41 is kept constant. The intensity of each optical signal to be amplified and output is kept constant.

Also, the conditions regarding the intensity of the pilot light and the like are set in the same manner as in the first embodiment.
Similar effects can be obtained.

(Other Embodiments) In another embodiment of the present invention, there is provided a wavelength division multiplexing apparatus including any one of the optical transmitter according to the first to sixth embodiments and the optical amplifier according to the seventh embodiment. An optical transmission system.

A wavelength division multiplexing optical transmission system according to another embodiment of the present invention comprises, as in the above-mentioned general conventional wavelength division multiplexing optical transmission system, one transmitting station and one receiving station, one for one. It may be configured to be connected via an optical transmission line, or, as in the above-mentioned new conventional wavelength division multiplexing optical transmission system, one transmitting station and one relay station are connected via one optical transmission line. The configuration may be such that one relay station and a plurality of receiving stations are connected via one optical transmission line.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an optical transmission device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between pilot light output from pilot light sources 111 and 112 in FIG. 1 and the intensity of optical signals output from optical signal sources 121 to 124;

FIG. 3 is a diagram illustrating an input light intensity-gain characteristic of an EDFA used in the optical amplifier 14 of FIG. 1;

FIG. 4 is a diagram showing input light intensity-gain characteristics of an EDFA used in the optical amplifying unit 14 of FIG.
And 8 waves) (however, the input light intensity is the intensity per wave).

FIG. 5 is a diagram showing input light intensity-gain characteristics of an EDFA used in the optical amplifying unit 14 of FIG.
And 8 waves) (where the input light intensity is the total input light intensity).

FIG. 6 is a diagram illustrating the intensity of an optical signal input to the optical amplifier 14 of FIG. 1;

FIG. 7 is a diagram showing the intensities of an optical signal and a pilot light input to the optical amplifying unit 14 in FIG. 1 (when the optical signal intensities are equal to each other).

FIG. 8 is a diagram showing the intensities of an optical signal and pilot light input to the optical amplifying unit 14 in FIG. 1 (when the optical signal intensities are different from each other).

FIG. 9 shows a case where light sources having variable oscillation wavelengths are used as the optical signal sources 121 to 124 of FIG.
It is a figure showing signs that intensity of the optical signal which 1-124 changes with time.

FIG. 10 is a block diagram illustrating a configuration of an optical transmission device according to a second embodiment of the present invention (also used in the third embodiment).

11 is a diagram illustrating an intermittent optical signal transmitted by the optical transmission device illustrated in FIG.

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

FIG. 13 is a block diagram illustrating a configuration of an optical transmission device according to a fifth embodiment of the present invention.

FIG. 14 is a block diagram illustrating a configuration of an optical transmission device according to a sixth embodiment of the present invention.

FIG. 15 is a block diagram illustrating a configuration of an optical amplifying device according to a seventh embodiment of the present invention.

FIG. 16 is a block diagram showing a configuration of a new conventional wavelength multiplexing optical transmission system.

FIG. 17 is a block diagram illustrating an example of a configuration of a conventional optical amplifier.

18 is a diagram illustrating a relationship between a wavelength and an output intensity of an optical signal output from the optical signal sources 511 to 513 in FIG. 16 (when all the optical signals have the same output intensity).

19 is a diagram illustrating a relationship between a wavelength and an output intensity of an optical signal output from the optical signal sources 511 to 513 in FIG. 16 (when there is a difference in output intensity of each optical signal).

[Explanation of symbols]

 11, 42 pilot light output unit 111, 112, 421 pilot light source 12 optical signal output unit 121 to 124 optical signal source 13, 43 multiplexing unit 14, 41 optical amplification unit 16 spare light output unit 161, 162 spare light source 17, 18 Monitoring units 211 and 212 Pilot light 221 to 228 Optical signal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04J 14/02

Claims (17)

[Claims] 1. An optical transmitter provided in a wavelength division multiplexing optical transmission system for transmitting a wavelength division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed, wherein the intensity is modulated by an electric signal and the wavelength An optical signal output unit that outputs a plurality of optical signals different from each other; a pilot optical output unit that outputs one or more pilot lights having different wavelengths from the optical signals; an optical signal output from the optical signal output unit; A multiplexing unit that multiplexes the respective pilot lights output from the pilot light output unit with each other, and outputs the respective optical signals and the respective pilot lights in the form of a wavelength multiplexed optical signal multiplexed with each other; and the multiplexing unit. An optical transmission device, comprising: an optical amplification unit that amplifies a wavelength-division multiplexed optical signal output from the optical transmission device. 2. The optical amplifier according to claim 1, wherein the number of optical signals input to the optical amplifier (ie, the number of multiplexed waves) changes.
2. The optical transmission device according to claim 1, wherein if the total input light intensity to the optical amplifying unit is constant, the gain of the optical amplifying unit is also kept constant. 3. The optical transmission apparatus according to claim 1, wherein each pilot light output from the pilot light output unit has a greater intensity than each optical signal output from the optical signal output unit. . 4. The pilot light output from the pilot light output section is intensity-modulated by an electric signal, and the modulation method used for the electric signal for intensity-modulating each pilot light output from the pilot light output section is as follows. The modulation method is different from a modulation method used for an electric signal for intensity-modulating each optical signal output from the optical signal output unit and requires a higher CNR or SNR. 4. The optical transmission device according to 3. 5. The pilot light output from the pilot light output unit is intensity-modulated by an analog electric signal, and the optical signal output from the optical signal output unit is intensity-modulated by a digital electric signal. The optical transmission device according to claim 4, wherein: 6. The pilot light output from the pilot light output unit is intensity-modulated by an electric signal, and the modulation method used for the electric signal for intensity-modulating each pilot light output from the pilot light output unit is: 2. The optical transmission apparatus according to claim 1, wherein the modulation method is different from a modulation method used for an electric signal for intensity-modulating each optical signal output from the optical signal output unit. 7. The intensity of each pilot light output from the pilot light output unit and the intensity of each optical signal output from the optical signal output unit are required for a modulation method of an electric signal for intensity-modulating each of them. The optical transmission device according to claim 6, wherein the optical transmission device is individually determined according to CNR or SNR. 8. The apparatus according to claim 1, wherein the sum of the intensities of all the pilot lights output from the pilot light output unit is larger than the sum of the intensities of all the optical signals output from the optical signal output unit. 2. The optical transmission device according to 1. 9. The optical transmission apparatus according to claim 1, wherein the optical signals output from the optical signal output unit have different intensities. 10. The optical transmitter according to claim 1, wherein at least one of the plurality of optical signals output from the optical signal output unit has a variable wavelength. 11. The optical transmission device according to claim 1, wherein at least one optical signal output from the optical signal output unit is intensity-modulated by an intermittent electric signal. 12. The optical signal output section includes a plurality of optical signal sources each of which generates one optical signal, and outputs the plurality of optical signals generated by each of the optical signal sources to the plurality of optical signal sources. The pilot light output unit includes one or more pilot light sources each generating one pilot light, and outputs one or more pilot lights generated by each of the pilot light sources.
The above-mentioned pilot light is output, and when each of the pilot light sources cannot generate the pilot light, one or more of the pilot light sources generate the same pilot light as that generated by each of the pilot light sources instead of the respective pilot light sources. The optical transmission device according to claim 1, further comprising: a standby light source. 13. An optical amplification unit that monitors the intensity of each pilot light included in the amplified wavelength-division multiplexed optical signal output from the optical amplification unit and controls the optical amplification unit so that each intensity is constant. The optical transmission device according to claim 1, further comprising a monitoring unit that performs the monitoring. 14. After converting each pilot light included in the amplified wavelength multiplexed optical signal output from the optical amplifying unit to an electric signal, the power of each electric signal is monitored, and the electric power is The optical transmission device according to claim 1, further comprising a monitoring unit that controls the optical amplification unit so as to be constant. 15. A device provided in a wavelength division multiplexing optical transmission system,
An optical amplifying device for amplifying a wavelength-division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed, wherein each of the optical signals outputs one or more pilot lights having a different wavelength from each other. A multiplexing unit that multiplexes the multiplexed optical signal and each pilot light output from the pilot light output unit with each other and outputs the optical signal and the pilot light in the form of a wavelength multiplexed optical signal multiplexed with each other; And an optical amplifying unit for amplifying the wavelength multiplexed optical signal output from the multiplexing unit. 16. A wavelength-division multiplexing optical transmission system provided with an optical transmission device for transmitting a wavelength-division multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed, wherein the optical transmission device has an intensity based on an electric signal. An optical signal output unit that outputs a plurality of optical signals that are modulated and have different wavelengths; a pilot light output unit that outputs one or more pilot lights having different wavelengths from each of the optical signals; output from the optical signal output unit A multiplexing unit that multiplexes each optical signal and each pilot light output from the pilot light output unit with each other and outputs each optical signal and each pilot light in the form of a wavelength multiplexed optical signal multiplexed with each other. And a light amplifying unit that amplifies the wavelength multiplexed optical signal output from the multiplexing unit. 17. A wavelength multiplexing optical transmission system provided with an optical amplifying device for amplifying a wavelength multiplexed optical signal in which a plurality of optical signals having different wavelengths are multiplexed, wherein the optical amplifying device comprises: And a pilot light output unit that outputs one or more pilot lights having different wavelengths, the wavelength multiplexed optical signal and each pilot light output from the pilot light output unit are multiplexed with each other, and each optical signal and each A wavelength division multiplexing optical transmission system, comprising: a multiplexing unit that outputs pilot light in the form of a wavelength multiplexed optical signal multiplexed with each other; and an optical amplification unit that amplifies the wavelength multiplexing optical signal output from the multiplexing unit.