JP2001333016A - Optical wavelength multiplex transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a nonlinear optical effect in an optical fiber transmission line and deterioration of a transmission characteristic in optical wavelength multiplex transmission in which two or more types of transmission speeds coexist. SOLUTION: An optical signal of a high transmission speed is subjected to wavelength multiplexing with strong intensity, and an optical signal of a low transmission speed is subjected to wavelength multiplexing with low intensity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for optical communication in which light having a plurality of different wavelengths is multiplexed and a multiplexed optical signal is transmitted and received using an optical fiber transmission line. In particular, it is used when transmission speeds of multiplexed optical signals are different.

[0002]

2. Description of the Related Art An optical wavelength division multiplexing transmission system is a communication system in which a plurality of optical signals having different wavelengths are wavelength multiplexed and transmitted through an optical fiber transmission line. A plurality of signals are simultaneously transmitted through one optical fiber transmission line. Since communication is possible, communication capacity can be increased.

FIG. 6 shows a conventional optical wavelength division multiplexing transmission system. FIG. 6 shows a configuration example in the case of 8-wavelength multiplexing. Output signals from the optical transmitters 11 to 18 that emit optical signals having different wavelengths are multiplexed (multiplexed) by the optical multiplexer 2. Here, the output signals of the optical transmitters 11 to 18 are hybrid transmissions in which two or more types of transmission rates (bit rates) are mixed, and the signal light intensity for each wavelength (channel) is substantially constant. This multiplexed signal is amplified by an optical amplifier 31 and
Sent from 0.

Since the gain of the optical amplifier 31 does not depend on the transmission speed, the input signal to the optical fiber transmission line 41 is almost constant. The optical signal transmitted through the optical fiber transmission line 41 is sent out to the optical fiber transmission line 42 after being amplified by the optical amplifier 32. After repeating this process, the light arrives at the optical receiving station 50. In the optical receiving station 50, the transmitted wavelength-division multiplexed optical signal is demultiplexed for each wavelength by the optical demultiplexer 5, and received by the optical receivers 61 to 68 different for each wavelength.

[0005]

An optical signal transmitted from an optical transmitter is an optical receiver in digital transmission in which the state of high light intensity is "1" and the state of low light intensity is "0". Need to accurately identify the intensity of light. However, when the transmission rate increases, the number of photons per bit representing the state of “1” decreases, so that the SN ratio, which is the ratio between signal light and noise light, deteriorates in the transmission process, and the optical receiver receives “1”. It becomes difficult to accurately distinguish between "0" and "1".

For this reason, it is necessary to increase the intensity of an optical signal input to an optical fiber transmission line by an optical amplifier for transmission. In such an optical wavelength division multiplexing transmission system, nonlinear optical effects generated in the optical fiber transmission line are required. Is a big problem. Known non-linear optical effects include a self-phase modulation effect, a cross-phase modulation effect, and four-wave mixing (see "Nonlinear Fiber Optics", Agrawar, Yoshioka Shoten).

[0007] The self-phase modulation effect is a phenomenon in which the refractive index of an optical fiber transmission line changes depending on the intensity of light, and light undergoes a phase change by itself. The cross-phase modulation effect is a phenomenon in which when lights having different wavelengths simultaneously propagate in the same direction in an optical fiber transmission line, one light causes a phase change depending on the intensity of the other light. Four-wave mixing is a phenomenon in which light components having different wavelengths are generated when light beams having different wavelengths simultaneously propagate in the same direction in a fiber. When the nonlinear optical effect occurs, waveform deterioration occurs due to the influence of dispersion of the optical fiber transmission line, and the propagation characteristics deteriorate.

For example, in the case of an optical signal having a transmission speed of 2.5 Gbit / s, an input per wavelength to an optical fiber transmission line necessary for an optical receiver to accurately distinguish between "0" and "1". The intensity (ie, the output intensity of the optical amplifier) is 0 dBm
(= 1 mW). If the transmission rate is 10 Gbit / s, about four times the intensity is required to make the number of photons per bit the same as in the case of 2.5 Gbit / s. That is, it must be about 6 dBm (= 4 mW) per wavelength.

In FIG. 6, 2.5 Gbit / s and 10 Gbi
When optical signals having a transmission speed of t / s are mixed (for example, the transmission speed of the optical transmitters 12, 14, 16, 18 is 2.5 Gbit / s, and the optical transmitters 11, 13, 15, 17, 17).
When the transmission speed is 10 Gbit / s), 2.5 G
With an input intensity matched to a bit / s optical signal, 10 Gb
The S / N ratio of the it / s optical signal is degraded, and the transmission characteristics are degraded. On the other hand, with the input intensity adjusted to 10 Gbit / s,
Since the light intensity increases, the nonlinear optical effect becomes remarkable, and the transmission characteristics deteriorate.

As a method for suppressing the nonlinear optical effect, a method using an optical fiber transmission line having a large core diameter (light intensity per unit area of a propagation light is reduced to reduce the nonlinear optical effect), and Raman amplification is used. A method of partially compensating for the loss of the transmission line and reducing the intensity of light amplified by the optical amplifier (the nonlinear optical effect decreases as the intensity of light decreases) has been proposed. In the former method,
It is necessary to install a new optical fiber transmission line, and in the latter method, it is necessary to install a device for Raman amplification in the transmission line. However, in a transmission system in which a plurality of transmission rates are mixed, a simple and effective method for suppressing a nonlinear optical effect such as a cross-phase modulation effect has not been proposed.

SUMMARY OF THE INVENTION The present invention has been made in view of such a background, and is intended to suppress nonlinear optical effects occurring in an optical fiber transmission line in optical wavelength multiplex transmission in which two or more types of transmission speeds coexist. It is an object of the present invention to provide an optical wavelength multiplex transmission system in which characteristic deterioration is suppressed.

[0012]

SUMMARY OF THE INVENTION In an optical wavelength division multiplexing transmission system according to the present invention, an optical signal having a high transmission speed has a high intensity and an optical signal having a low transmission speed has a low intensity. Input to the road.

When the amplifying means operates to keep the gain (a value obtained by dividing the intensity of the output signal light by the intensity of the input signal light) constant, a certain wavelength (channel) incident on the amplifying means at a weak intensity P1. And an optical signal of another wavelength (channel) incident on the amplifying means at a high intensity P2 are GP1 and GP2, respectively, assuming that the gain is G, and the intensity ratio of the input signal light is kept constant at the output. .

That is, since an optical signal having a high transmission rate has a high intensity and an optical signal having a low transmission rate has a low intensity, it is input to the optical fiber transmission line. Therefore, the nonlinear optical effect is reduced by the decrease in the intensity of the optical signal. Is done. In the amplifying means for compensating for the loss that occurs when propagating through the optical fiber transmission line, if the operation is performed so as to keep the gain constant, the intensity difference depending on the transmission speed always occurs in the entire optical fiber transmission line. The wavelength multiplexed signal is transmitted while being maintained, and the nonlinear optical effect is reduced.

In actual transmission, the type of transmission line, transmission line distance,
Although the control mode of the signal strength changes depending on various conditions such as the transmission form depending on how many wavelengths are transmitted at what wavelength interval, roughly, the signal strength is reduced by half when the transmission speed is reduced by half. Is controlled so that That is, if two types of transmission speeds b1 and b2 (b1 = nb2) are mixed, the signal light intensity of b2 is set to 1 / n of the signal light intensity of b1.

Thus, in optical wavelength multiplex transmission in which two or more types of transmission speeds coexist, nonlinear optical effects generated in an optical fiber transmission line can be suppressed, and deterioration of transmission characteristics can be suppressed.

That is, the present invention provides a plurality of optical transmitters which generate optical signals having different wavelengths and at least some of which have different transmission speeds, and multiplexing means for multiplexing output optical signals of the plurality of optical transmitters. Optical transmission means including amplification means for amplifying the multiplexed optical signal; an optical fiber transmission line to which an output optical signal of the optical transmission means is inputted; and an amplification interposed in the optical fiber transmission line. Means for transmitting light comprising:
An optical receiving unit including a separating unit that separates the optical signal transmitted by the optical transmitting unit for each wavelength, and a plurality of optical receivers that receive an optical signal for each wavelength that is separated by the separating unit. Optical wavelength division multiplexing transmission system.

Here, a feature of the present invention is that a plurality of light intensity varying means for variably setting the intensity of the optical signal output from the plurality of optical transmitters to an intensity corresponding to the transmission speed. It is in the prepared place.

When the transmission speeds of the plurality of optical transmitters are fixedly set, the set intensity of the light intensity variable means may be fixedly set to a predetermined value in advance. When the transmission speeds of the plurality of optical transmitters change frequently, a unit that collects transmission speed information of the plurality of optical transmitters, and the plurality of units according to the transmission speed information collected by the collecting unit. It is preferable to include means for setting the light intensity varying means.
This makes it possible to automatically respond to the frequently changing transmission speeds of the plurality of optical transmitters.

Generally, it is desirable that the level of the transmission speed of the optical transmitter and the level of the set intensity of the light intensity variable means are set in a proportional relationship.

It is preferable that the amplifying means is an optical amplifier whose gain is controlled to be constant. Thereby, the relationship between the transmission speed and the intensity of the optical signal can be maintained in the entire system.

Further, the optical transmission means includes an error correction encoding means for an optical signal to be transmitted, and the optical reception means includes an error correction decoding means for an optical signal to be received. Transmission characteristic degradation can be compensated for using error correction coding and decoding techniques.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of an optical wavelength division multiplexing transmission system according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an overall configuration diagram of a wavelength division multiplexing transmission system according to a first embodiment of the present invention. FIG. 4 is an overall configuration diagram of a wavelength division multiplexing transmission system according to a second embodiment of the present invention.

According to the present invention, a plurality of optical transmitters 11 to 18 which generate optical signals having different wavelengths from each other and at least partially differ in transmission speed, and multiplex output optical signals of the plurality of optical transmitters 11 to 18 are provided. The optical transmission station 10 includes an optical multiplexer 2 that performs optical transmission, an optical amplifier 131 that amplifies a multiplexed optical signal, and an optical fiber transmission line 4 to which an output optical signal of the optical transmission station 10 is input.
1 and 42, and an optical transmission line including optical amplifiers 132 and 133 interposed in the optical fiber transmission lines 41 and 42, and a demultiplexer for demultiplexing an optical signal transmitted through the optical transmission line for each wavelength. An optical wavelength division multiplexing transmission system including an optical receiver and a plurality of optical receivers for receiving optical signals for each wavelength demultiplexed by the demultiplexer.

Here, a feature of the present invention is that a plurality of light intensity variable units each variably set the intensity of an optical signal output from a plurality of optical transmitters 11 to 18 to an intensity corresponding to the transmission speed. It is provided with optical attenuators 71 to 78 as means.

In the second embodiment shown in FIG. 4, there is provided a network manager 6 for collecting transmission speed information of a plurality of optical transmitters 11 to 18, respectively. , The settings of the plurality of light intensity changers 81 to 88 are respectively performed.

Whether the transmission speed of the optical transmitters 11 to 18 is high or low,
The magnitude of the set intensity of the light attenuators 71 to 78 or the light intensity changers 81 to 88 is set in a substantially proportional relationship. The gains of the optical amplifiers 131, 132, and 133 are controlled to be constant.

In the third embodiment shown in FIG.
Include optical transmitters 91 to 98 for performing error correction coding on an optical signal to be transmitted, and the optical receiving station 50 includes optical receivers 101 to 98 for performing error correction decoding on an optical signal to be received.
108. Hereinafter, embodiments of the present invention will be described in more detail.

(First Embodiment) An optical wavelength division multiplexing transmission system according to a first embodiment of the present invention shows a configuration example in the case of 8-wavelength multiplexing. The present invention relates to optical transmitters 11 to 18 that emit optical signals having different wavelengths (the wavelengths are λ1 to λ8, respectively), and the intensity of the optical signals from the optical transmitters 11 to 18 to the optical transmitters 11 to 18.
Optical attenuator 71 for making variable according to the transmission speed of 18.
To 78, an optical multiplexer 2 for multiplexing an optical signal, an optical amplifier 131 for amplifying the multiplexed optical signal, and an optical fiber transmission line 4.
1, 42; optical amplifiers 132 and 133 for compensating for a loss occurring when propagating through an optical fiber transmission line; an optical separator 5 for demultiplexing a transmitted wavelength-division multiplexed optical signal; an optical receiver 61 different for each wavelength ~ 68.

The optical transmitting station 10 comprises optical transmitters 11 to 18, optical attenuators 71 to 78, an optical multiplexer 2, and an optical amplifier 131. The optical receiving station 50 includes the optical separator 5, the optical receivers 61 to 61.
68. The optical amplifiers 131, 132,
133 are each controlled to have a constant gain, and are suitable for controlling the signal strength according to the transmission speed.

In FIG. 1, the optical transmitters 11, 13, 1
The transmission speed of the optical signals 5 and 17 is f1, and the optical transmitters 12 and 1
The transmission speed of the optical signals of 4, 16, and 18 is set to f2 (f1> f
2). Since f2 has a lower transmission speed than f1, the attenuation of the optical attenuators 72, 74, 76, 78 is reduced by the optical attenuators 71,
It is set to be larger than 73, 75 and 77, and the intensity of the optical signal at the transmission speed f2 is made smaller than the intensity of the optical signal at the transmission speed f1. The eight optical signals having the difference in intensity are multiplexed by the optical multiplexer 2 and input to the optical amplifier 31. The optical amplifier 131 is operated with a constant gain, and the output light is input to the optical fiber transmission line 41.

The wavelength-division multiplexed signal input to the optical fiber transmission line 41 propagates through the optical fiber transmission line while keeping the intensity difference depending on the transmission speed constant. The wavelength-division multiplexed optical signal attenuated by the propagation loss of the optical fiber transmission line is amplified by the optical amplifier 132 whose gain is controlled to be constant, propagates through the optical fiber transmission line 42, and arrives at the optical receiving station 50 after this process is repeated. . The interval between the optical amplifiers is called a relay interval, and the sum of the optical fiber transmission lines is the transmission distance. In the optical receiving station 50, the wavelength division multiplexed signal is demultiplexed into respective wavelengths by the optical demultiplexer 5 and received by the optical receivers 61 to 68.

Although the optical signal of the transmission speed f2 is weaker than the optical signal of the transmission speed f1, the number of photons per bit is large, so that the SN ratio does not deteriorate in the transmission process and there is no problem in the reception characteristics. Does not occur. On the other hand, since the light intensity transmitted through the optical fiber transmission line is weak, the non-linear optical effects such as the self-phase modulation effect and the cross-phase modulation effect on the light of the transmission speed f1 are reduced, and the non-linear optical effect which has been a problem in the past has Waveform deterioration due to the effect can be avoided.

For example, λ1 = 1550.12 nm, λ2
= 155.52 nm, λ3 = 155.92 nm, λ
4 = 1551.32 nm, λ5 = 1551.72 nm,
λ6 = 1552.12 nm, λ7 = 1552.52n
m, λ8 = 1552.93 nm (wavelength interval is 50 GH
z), f1 = 10 Gbit / s, f2 = 2.5 Gbit
/ S, the relay interval between optical amplifiers is 80 km, and the transmission distance is 3
When compared with the conventional example, the bit error rate in the optical receiver (the ratio of the number of error bits to the number of transmitted bits, that is, “0” is transmitted, but it is identified as “1” or “1” Was transmitted, the ratio of which was identified as “0”) was determined by computer simulation. The optical fiber transmission line used a single mode fiber with dispersion compensation.

In the conventional example, optical signals of respective wavelengths (channels) are input to the optical amplifier 31 operating with constant gain control at substantially the same intensity, and after amplification, are input to the optical fiber transmission line at substantially the same intensity. In this state, the input intensity to the optical fiber transmission line is set to -3, -2, -1, per wavelength (channel).
The code error rate was calculated by changing to 0, +1, +2, and +3 dBm / ch (without providing an optical signal intensity difference depending on the transmission speed).

FIG. 2 is a diagram showing the bit error rate when the optical signals of all the channels are input to the optical transmission line with the same intensity. The input intensity (dBm) is plotted on the horizontal axis, and the bit error rate is plotted on the vertical axis. Take. Out of 8 wavelengths (channels), reception intensity -23dB
The channel with the worst bit error rate at m is plotted against the input strength. All the channels having a bad bit error rate are 10 Gbit / s channels. If the input intensity is weak, the number of photons per bit decreases,
The transmission signal becomes difficult to distinguish from noise (that is, the SN ratio becomes worse), and the code error rate increases. As the input intensity increases, the S / N ratio improves, but the nonlinear optical effect that occurs in the optical fiber transmission line becomes significant, the waveform deteriorates, and the code error rate increases. In FIG. 2, the input intensity is 0 dBm /
The channel has the best transmission characteristics, but has a value larger than 10 ⁻¹⁰ .

In this embodiment, wavelengths λ1, λ3, and λ3, λ3 having a transmission speed of 10 Gbit / s using the optical attenuators 71 to 78.
The signal light intensity of the four channels λ5 and λ7 is +1 dBm / c
h, wavelengths λ2, λ having a transmission rate of 2.5 Gbit / s
The signal light intensity of the four channels of 4, λ6 and λ8 is -3 dBm
/ Ch. This is an example in which the signal light intensity of four channels having a transmission speed of 10 Gbit / s is set to 2.5 times the signal light intensity of four channels having a transmission speed of 2.5 Gbit / s. Further, the signal light intensity of four channels having a transmission speed of 10 Gbit / s is set to +2 dBm / ch,
The signal light intensity of four channels having a transmission speed of 2.5 Gbit / s is set to -4 dBm / ch, and the signal light intensity of four channels having a transmission speed of 10 Gbit / s is set to 2.5 Gbit.
/ S can be set to four times the signal light intensity of four channels having a transmission rate of / s.

FIG. 3 shows the bit error rate at the reception intensity of -23 dBm for all channels. The horizontal axis represents the channel, and the vertical axis represents the bit error rate. Four channels having a transmission rate of 2.5 Gbit / s have a low light intensity but a low transmission rate, and are received without deterioration of the SN ratio.

On the other hand, the four channels having a transmission rate of 10 Gbit / s have a high light intensity but a low intensity of the adjacent channel, so that the cross-phase modulation effect is reduced and the waveform is greatly deteriorated by the nonlinear optical effect. Received.
For this reason, all the channels having both transmission rates have good transmission characteristics, and even the worst channel has 10
^−11, and the transmission characteristic can be improved by a factor of 30 or more compared to the conventional case shown in FIG.

(Second Embodiment) An optical wavelength division multiplexing transmission system according to a second embodiment of the present invention will be described with reference to FIG. FIG.
FIG. 5 is an overall configuration diagram of an optical wavelength multiplex transmission system according to a second embodiment of the present invention. The difference from the first embodiment shown in FIG. 1 is that the light intensity variable devices 81 to 8 are used instead of the optical attenuators 71 to 78 shown in FIG.
8 and the network manager 6 operates the optical transmitter 1
The transmission speed information from 1 to 18 is collected, and the light intensity of the light intensity variable devices 81 to 88 is set accordingly. As a result, even if the transmission speed of the optical transmitters 11 to 18 changes, the change can be automatically followed.

That is, the transmission speed information from the optical transmitters 11 to 18 is transmitted to the network manager 6 by an electric signal, and the network manager 6 recognizes the transmission speed information. The light intensity is automatically adjusted according to the command sent from 6. For example, in the case of a signal of 10 Gbit / s, the attenuation in the light intensity variable devices 81 to 88 is 3 dB,
If the signal is 2.5 Gbit / s, the light intensity changers 81 to 81
If the attenuation at 88 is programmed to be 7 dB, a 4 dB intensity difference is automatically provided.

For example, f1 = 10 described in the first embodiment
Gbit / s, f2 = 2.5 Gbit / s and f1 = 2.
Even when it changes to 5 Gbit / s and f2 = 10 Gbit / s, it can automatically cope with the change. Further, the transmission speed of the optical signals of the optical transmitters 11, 13, 15, 17 is f1, and the transmission speed of the optical signals of the optical transmitters 12, 14, 16, 18 is f.
2, the transmission speed of the optical signal of the optical transmitters 12, 15, 18 is f1, and the optical transmitters 11, 13, 14, 16,
Even when the transmission speed of the optical signal 17 changes to f2, the change can be automatically handled.

(Third Embodiment) A third embodiment of the present invention will be described with reference to FIG. FIG. 5 is an overall configuration diagram of an optical wavelength division multiplexing transmission system according to a third embodiment of the present invention. In the third embodiment,
This is an example in which an error correction coding technique is applied to the present invention. The error correction coding technology is a technology in which a redundant code is added to signal light in optical transmitters 91 to 98, and a code error generated in an optical transmission line is corrected in optical receivers 101 to 108. Etc. are frequently used in digital communication systems. Error correction code technology can improve the transmission characteristics to some extent due to the degradation of the SN ratio that occurs during the transmission process.
If this technology is used in the present invention, a more effective optical wavelength division multiplexing transmission system can be constructed.

That is, using the above example, 10 Gb
wavelengths λ1, λ3, λ5, λ7 having a transmission rate of it / s
From the signal light intensity of +1 dBm / ch to-
When the gain is reduced to 1 dBm / ch and at the same time the coding gain (the ability to correctly correct an error code in the error correction coding technique) is about 3 dB (the wavelengths λ2, λ4, λ6, and λ8 having a transmission rate of 2.5 Gbit / s). The signal light intensities of the four channels are unchanged at -3 dBm / ch, and no coding gain is provided.) Waveform deterioration due to the nonlinear optical effect can be reduced, and transmission characteristics can be effectively improved.

In the above embodiment, signal light intensities of four channels λ1, λ3, λ5 and λ7 having a transmission rate of 10 Gbit / s and wavelengths λ2, λ4 and λ6 having a transmission rate of 2.5 Gbit / s are provided. , Λ8 and the signal light intensities of four channels have been described, but the present invention can also be applied to a case where three or more types of signals having different transmission rates are mixed. For example, three transmission speeds (b
1, b2, b3, and b1 = nb2 = nmb3), the signal light intensity of b2 is 1 / n of the signal light intensity of b1.
And the signal light intensity of b3 is 1 / nm of the signal light intensity of b1.
(The signal light intensity of b3 is 1 / m of the signal light intensity of b2.
To). The present invention also improves transmission characteristics when the number of wavelengths (the number of channels) increases.

[0046]

As described above, according to the present invention,
In an optical wavelength division multiplexing transmission system in which two or more transmission speeds coexist, by changing the input intensity of the optical fiber transmission line according to the transmission speed, the nonlinear optical effect is suppressed,
Transmission characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an optical wavelength multiplex transmission system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a bit error rate when optical signals of all channels are input to an optical transmission line at the same intensity.

FIG. 3 is a diagram showing a bit error rate at a reception intensity of -23 dBm for all channels.

FIG. 4 is an overall configuration diagram of an optical wavelength multiplex transmission system according to a second embodiment of the present invention.

FIG. 5 is an overall configuration diagram of an optical wavelength division multiplexing transmission system according to a third embodiment of the present invention.

FIG. 6 is an overall configuration diagram of a conventional optical wavelength multiplex transmission system.

[Explanation of symbols]

 2 optical multiplexer 5 optical separator 6 network manager 10 optical transmitting station 11-18, 91-98 optical transmitter 31-33, 131-133 optical amplifier 41, 42 optical fiber transmission line 50 optical receiving station 61-68, 101-108 Optical receiver 71-78 Optical attenuator 81-88 Light intensity variable device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04L 29/08 F-term (Reference) 5K002 AA01 AA03 BA05 CA01 CA09 CA13 DA02 FA01 5K014 AA01 BA05 FA11 HA05 HA10 5K034 AA05 DD01 EE01 EE05 FF13 HH09 MM01 MM08 MM31

Claims (5)

[Claims] 1. A plurality of optical transmitters that generate optical signals having different wavelengths and at least some of which have different transmission speeds, multiplexing means for multiplexing output optical signals of the plurality of optical transmitters, and multiplexing. Optical transmitting means including an amplifying means for amplifying the obtained optical signal; an optical fiber transmission line to which an output optical signal of the optical transmitting means is input; and an amplifying means interposed in the optical fiber transmission line. An optical transmission device comprising: an optical transmission unit; a separation unit that splits an optical signal transmitted by the optical transmission unit for each wavelength; and a plurality of optical receivers that receive an optical signal for each wavelength split by the separation unit. An optical wavelength division multiplexing transmission system comprising: a plurality of light intensity variable means for variably setting the intensities of the optical signals output from the plurality of optical transmitters to intensities corresponding to their transmission speeds. Wavelength division multiplexing characterized by: Transmission system. Means for collecting transmission rate information of the plurality of optical transmitters, and means for setting the plurality of light intensity variable means in accordance with the transmission rate information collected by the collecting means, respectively. The optical wavelength division multiplexing transmission system according to claim 1, further comprising: 3. The optical wavelength division multiplexing transmission system according to claim 1, wherein the level of the transmission speed of the optical transmitter and the level of the set intensity of the optical intensity variable means are set in a proportional relationship. 4. The optical wavelength multiplex transmission system according to claim 1, wherein said amplifying means is an optical amplifier whose gain is controlled to be constant. 5. The optical transmission means according to claim 1, wherein said optical transmission means includes an error correction encoding means for an optical signal to be transmitted, and said optical reception means includes an error correction decoding means for an optical signal to be received. The optical wavelength multiplex transmission system according to any one of the above.