JPH08213956A - Optical signal transmission method - Google Patents

Abstract

PURPOSE: To improve the noise characteristic at reception of an optical signal by applying optoelectric conversion to an optical signal from upstream sent through an optical transmission path at a light receiving section provided at one terminal of each optical multiplexer of two transmission stations or more and controlling a level of an optical signal sent from each transmission station to each optical multiplexer in response to the electric signal so as to regulate a level of an output signal automatically thereby allowing a reception station to receive optical signals from the transmission stations as the same intensity. CONSTITUTION: A light receiving section 8 is provided to one terminal of an optical multiplexer 4 of each transmission station 2. Then an optical signal sent from an upperstream of an optical transmission path is received by a light receiving section 8 of a downstream transmission station 2 of a downstream to conduct photoelectric conversion and a level of an optical signal sent from the transmission station 2 to the optical multiplexer 4 according to the electric signal is controlled. Thus, noise characteristic at reception by a light receiving device 7 is improved by controlling levels of optical signals sent from the two transmission stations 2 or over and received by the light receiving device 7 of the reception station 6 to be identical to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal transmission method in an optical CATV system, an optical ITV system or the like.

[0002]

2. Description of the Related Art Conventionally, there are various methods for transmitting an optical signal in an optical CATV system, an optical ITV system, etc., and one of them is a method using an optical transmission device shown in FIG. The optical transmission device shown in FIG. 7 transmits images from a plurality (n places) of transmission stations 31 arranged at a distance of several hundreds of meters to several kilometers to the reception station 23 through the optical transmission path 26, and one of the reception stations 23 is transmitted. The light receiver 24 receives the light so that it can be collectively monitored. Each transmitting station 31 in FIG. 7 has a signal source 21, such as a video camera, a modulator 27, a light source (E / O).
A converter) 22 and an optical multiplexer (optical coupler) 25 are installed,
The optical signal from each transmitting station 31 is an optical fiber (optical transmission line) 2
6 to the receiving station 23.

In FIG. 7, a signal (for example, a video signal) from the signal source 21 of each transmitting station 31 is put on a carrier (subcarrier) of a specific frequency by a modulator 27 of each transmitting station 31,
The optical signal modulated by this carrier wave is generated from the semiconductor laser (for example, LD) of the light source 22. The frequency band of the carrier wave varies depending on the optical transmission method, but is in the range of 0.4 to 2 GHz in the optical transmission device of FIG. The optical signal from each transmitting station 31 in FIG.
To be multiplexed and received at a light receiving device (eg, photodiode: PD) 24 of the receiving station 23 for detection, distributed by a distributor 28, and demodulated by a demodulator 29 for each frequency of the carrier wave. The image is received by the monitoring device (for example, monitor TV) 40 for each transmitting station 31 and the image is monitored.

In the case of multiplexing a plurality of optical signals for multiplex transmission as shown in FIG. 7, the carrier waves sent from the respective transmission poles 31 and received by the receiving station 23 have the same size, which is a noise characteristic. desirable. Therefore, conventionally, as shown in FIG. 6, a light source (E / O
The optical attenuator (attenuator) 30 is inserted between the converter 22 and the optical multiplexer (optical coupler) 25, and the level of the optical signal sent to the optical transmission line 26 by each optical attenuator 30 is adjusted, The sizes of the carrier waves in the receiving station 23 are set to be the same.

[0005]

The conventional optical signal transmission method shown in FIG. 6 has the following problems. ． The intensity of the optical signal must be adjusted by the optical attenuator 30 of the transmitting station 31 while measuring the intensity of the carrier wave from each transmitting station 31 at the receiving station 23, which is troublesome. ． When the number of transmitting stations is increased, it is necessary to readjust not only the optical attenuator 30 of the transmitting station to be added but also the attenuation amount of the optical attenuator 30 of the existing transmitting station 23, which makes the adjustment work even more troublesome.

An object of the present invention is to automatically adjust the intensity and modulation degree of optical signals emitted from the light sources of two or more transmitting stations so that the optical signals from each transmitting station are received by the receiving station with the same intensity. Thus, it is an object of the present invention to provide a highly reliable optical signal transmission method that facilitates new installation or extension of a transmission station.

[0007]

The optical signal transmission method according to claim 1 of the present invention is, as shown in FIGS. 1 to 4, from the light sources 3 of two or more transmitting stations 2 to the modulator 1 of each transmitting station 2. Optical signals of different wavelengths modulated by carrier waves of different frequencies are sent out, these optical signals are multiplexed by the optical multiplexer 4 into the optical transmission line 5, and the multiplexed optical signals are received by the receiving station 6. In the optical signal transmission method in which one light receiving device 7 simultaneously receives and demodulates, a light receiving portion 8 is provided at one end of the optical multiplexer 4 of each transmitting station 2, and an optical signal sent from the upstream of the optical transmission path 5 is provided. Is received by the light receiving section 8 of the downstream transmitting station 2 and converted into light / electricity, and the optical signal level sent from the transmitting station 1 to the optical multiplexer 4 is controlled according to the electric signal.

According to a second aspect of the present invention, in the optical signal transmission method according to the first aspect, the optical signal transmitted from the upstream side of the optical transmission line 5 as shown in FIGS. This is a reference optical signal generated from a reference optical signal generator 9 provided upstream of the path 5.

In the optical signal transmission method according to claim 3 of the present invention, in the optical signal transmission method according to claim 1, the optical signal sent from the upstream of the optical transmission line 5 as shown in FIG.
Optical signal from the upstream transmission station 2 of the
In the light receiving section 8 of the optical signal, the optical signal is converted into an electric signal, an electric signal of a desired frequency is extracted from the electric signal, and the optical signal level sent from the transmitting station 2 to the optical multiplexer 4 is controlled according to the electric signal. It was done like this.

An optical signal transmission method according to a fourth aspect of the present invention is the optical signal transmission method according to any one of the first to third aspects, in which the optical signal is output from the light receiving section 8 of the transmitting station 2 as shown in FIG. The optical attenuator 10 provided on the output side of the transmission station 2 is controlled according to the electric signal to control the optical signal level sent from the transmission station 2 to the optical multiplexer 4.

The optical signal transmission method according to a fifth aspect of the present invention is the optical signal transmission method according to any one of the first to third aspects, wherein the optical signal is output from the light receiving section 8 of the transmitting station 2 as shown in FIG. The drive current of the light source 3 of the transmitting station 2 is controlled according to the electric signal to control the optical signal level sent from the transmitting station 2 to the optical multiplexer 4.

The optical signal transmission method according to a sixth aspect of the present invention is the optical signal transmission method according to any one of the first to third aspects, wherein the optical signal is output from the light receiving section 8 of the transmission station 2 as shown in FIG. The modulation degree of the modulator 1 of the transmitting station 2 is controlled according to the electric signal to control the optical signal level sent from the transmitting station 2 to the optical multiplexer 4.

The optical signal transmitting method according to claim 7 of the present invention is the optical signal transmitting method according to any one of claims 1 to 6, in which the light receiving portion 8 of the transmitting station 2 is provided as shown in FIGS. The optical receiver is composed of a photodetector 11 and a filter 12 for extracting a predetermined signal, and an electric signal output from the filter 12 controls the optical signal level sent from the transmitting station 2 to the optical multiplexer 4.

The optical signal transmitting method according to claim 8 of the present invention is the optical signal transmitting method according to claim 7, wherein the filter 12 of the light receiving portion 8 of the transmitting station 2 is electrically converted by the light receiving portion 8. The signal strength is taken out.

The optical signal transmitting method according to claim 9 of the present invention is the optical signal transmitting method according to claim 7, wherein the filter 12 of the light receiving portion 8 of the transmitting station 2 is electrically converted by the light receiving portion 8. A signal of a desired frequency is extracted from the optical signal from the upstream transmitting station 2.

[0016]

In the optical signal transmission method according to claim 1 of the present invention,
An optical signal from the upstream transmitted through the optical transmission line 5 is optically / electrically converted by the light receiving unit 8 provided at one end of each optical multiplexer 4 of the two or more transmitting stations 2, and is transmitted according to the electrical signal. Since the optical signal level sent from the station 1 to the optical multiplexer 4 is controlled,
If the above control is performed so that the optical signal levels sent from two or more transmitting stations 2 and received by one photoreceiver 7 of the receiving station 6 are the same, the noise characteristic at the time of reception by the photoreceiver 7 is deteriorated. It gets harder.

In the optical signal transmission method according to the second aspect of the present invention, the optical signal transmitted from the upstream of the optical transmission line 5 is transmitted.
Since the reference optical signal is generated from the reference optical signal generator 9 provided upstream of the optical receiver, the reference optical signal is received by the light receiving unit 8 of the transmitting station 2 and the electric signal output from each light receiving unit 8 is received. Since the optical signal level sent from each transmitting station 1 to the optical multiplexer 4 is controlled, the optical signal levels sent from two or more transmitting stations 2 and received by one photoreceiver 7 of the receiving station 6 are the same. If the above control is performed so that the noise characteristic at the time of reception by the light receiver 7 is less likely to deteriorate.

In the optical signal transmission method according to the third aspect of the present invention, the optical signal sent from the upstream of the optical transmission line 5 is the optical transmission line 5.
Optical signal from the upstream transmission station 2 of the
In the light receiving section 8 of the optical signal, the optical signal is converted into an electric signal, an electric signal of a desired frequency is extracted from the electric signal, and the optical signal level sent from the transmitting station 2 to the optical multiplexer 4 is controlled according to the electric signal. Therefore, if the above-mentioned control is performed so that the optical signal levels sent from two or more transmitting stations 2 and received by one light receiver 7 of the receiving station 6 are the same, the light receiving device 7 receives Noise characteristics are less likely to deteriorate.

In the optical signal transmitting method according to the fourth aspect of the present invention, the attenuation amount of the optical attenuator 10 provided on the output side of the transmitting station 2 is controlled according to the electric signal output from the light receiving section 8 of the transmitting station 2. Then, since the optical signal level sent from the transmitting station 2 to the optical multiplexer 4 is controlled, the optical signal level sent from two or more transmitting stations 2 and received by one light receiver 7 of the receiving station 6 is the same. If the attenuation amount of the optical attenuator 10 is controlled so that the noise characteristic at the time of reception by the light receiver 7 is less likely to deteriorate.

In the optical signal transmitting method according to the fifth aspect of the present invention, the driving current of the light source 3 of the transmitting station 2 is controlled in accordance with the electric signal output from the light receiving portion 8 of the transmitting station 2 to transmit the transmitting station 2. The optical signal level sent from the optical multiplexer 4 to the optical multiplexer 4 is controlled so that the optical signal levels sent from two or more transmitting stations 2 and received by one light receiver 7 of the receiving station 6 become the same. By controlling the amount of attenuation of the current, the noise characteristic at the time of reception by the light receiver 7 is less likely to deteriorate.

In the optical signal transmitting method according to claim 6 of the present invention, the modulation degree of the modulator 1 of the transmitting station 2 is controlled in accordance with the electric signal output from the light receiving section 8 of the transmitting station 2 and the transmitting station is controlled. Since the optical signal level sent from 2 to the optical multiplexer 4 is controlled, the optical signal level sent from two or more transmitting stations 2 and received by one light receiving device 7 of the receiving station 6 becomes the same. If the modulation degree is controlled, the noise characteristic at the time of reception at the light receiver 7 is less likely to deteriorate.

In the optical signal transmitting method according to claim 7 of the present invention, the light receiving portion 8 of the transmitting station 2 comprises a light receiving device 11 and a filter 12 for taking out a predetermined signal, and an electric signal output from the filter 12 is used. Since the optical signal level sent from the transmitting station 2 to the optical multiplexer 4 is controlled, the filter 12
Of the desired frequency from the optical signal sent from the upstream side by selecting the passing frequency of, the attenuation amount of the attenuator 10 of the transmitting station 2 and the driving of the light source 3 of the transmitting station 2 in accordance with the extracted signal. Current, modulator 1 of transmitter station 2
By controlling the modulation degree of, the optical signal level received by one optical receiver 7 of the receiving station 6 can be made the same,
Noise characteristics at the time of reception at the light receiver 7 are less likely to deteriorate.

In the optical signal transmission method according to claim 8 of the present invention, the filter 12 of the light receiving portion 8 of the transmitting station 2 is the same as the light receiving portion 8 of the same.
Since the intensity of the reference optical signal electrically converted by is extracted, the attenuation amount of the attenuator 10 of the transmitting station 2, the drive current of the light source 3 of the transmitting station 2, the transmitting station, and the transmitting station according to the intensity of the reference optical signal. It is possible to control the modulation degree of the second modulator 1 so that the optical signal level received by one light receiver 7 of the receiving station 6 is equalized, and noise at the time of reception by the light receiver 7 is generated. The characteristics are less likely to deteriorate.

In the optical signal transmitting method according to claim 9 of the present invention, the filter 12 of the light receiving portion 8 of the transmitting station 2 transmits a signal of a desired frequency among the optical signals transmitted from the transmitting station 2 upstream from the own station. Since the signal is taken out, the attenuation amount of the attenuator 10 of the transmitting station 2 is adjusted according to the strength of the signal,
To control the drive current of the light source 3 of the transmitting station 2 and the modulation degree of the modulator 1 of the transmitting station 2 so that the optical signal level received by one of the light receivers 7 of the receiving station 6 is equalized. Can
Noise characteristics at the time of reception at the light receiver 7 are less likely to deteriorate.

[0025]

First Embodiment A first embodiment of the optical signal transmission method of the present invention will be described in detail with reference to FIG. The optical transmission device shown in FIG. 1 includes a signal source 13 such as a video camera, a modulator (MOD) 1 and a light source (E / E) in a plurality (n locations) of transmission stations 1 arranged at a distance of several 100 m to several km. O converter) 3 and optical multiplexer 4 are installed, the optical signal from each transmitting station 2 is modulated by the carrier wave (subcarrier) from modulator 1, and optical multiplexer 4
Is transmitted to the optical fiber (optical transmission line) 5 via the optical fiber, multiplexed, multiplexed, and transmitted to the receiving station 6, where one optical receiver (O / E converter: eg photodiode: PD) ) 7 to receive light at the same time.

In FIG. 1, in addition to the conventional configuration, a reference optical signal generator 9 comprising an oscillator 14 and an E / O converter 15 is installed upstream of the optical transmission line 5 on the transmitter station 1 side, and each of them is provided with a reference optical signal generator 9. At the transmitting station 2, a light receiver (O / E converter) 1 is provided at one end of the optical multiplexer 4.
1 and a filter 12 for extracting only the intensity of the reference optical signal from the reference optical signal generator 9 is provided, and the electric signal output from the filter 12 is input to the optical attenuator 10 to generate an optical signal. The attenuation amount of the attenuator 10 is controlled. In this case, when the level of the received reference optical signal is low, the reduction of the attenuation amount of the optical attenuator 10 is reduced to increase the attenuation amount of the optical attenuator 10 so that the level of the optical signal transmitted from the transmitting station is weakened. To On the contrary, when the level of the received reference signal is high, the attenuation of the optical attenuator 10 is greatly reduced to reduce the attenuation of the optical attenuator 10 to reduce the weakening of the level of the optical signal sent from the transmitting station. To do. As a result, the optical signal intensity transmitted from each transmitting station 2 and received by the receiving station 6 becomes the same.

The branch loss of the optical multiplexer 4 in FIG. 1 is shown in FIG.
As shown in FIG. 3, assuming that the transmission line loss between the adjacent optical multiplexers 4 is 5 dB and 1 dB and 10 dB, in order to adjust the output signals from the respective transmitting stations 2 to be substantially the same at the receiving station 6, Of the two transmitting stations 2 adjacent in 1,
The optical attenuator 10 of the transmitting station 2 on the downstream side needs to be 6 dB larger than the optical attenuator 10 of the transmitting station 2 on the upstream side. On the other hand, the level of the reference signal received by the transmitting station 2 on the downstream side is 6 dB lower than the level of the signal received by the transmitting station 2 on the upstream side, and this value matches the loss difference of the optical attenuator 10. Therefore, both transmitting stations 2
When the optical attenuator 10 of each transmitting station 2 is automatically adjusted in accordance with the level of the reference signal received by the optical transmitting device 2, the amount of attenuation of the optical attenuator 10 of the transmitting station 2 on the downstream side is small, and the transmitting station 2 on the upstream side is reduced. The reduction of the attenuation amount of the optical attenuator 10 is increased. Therefore, the attenuation amount of the optical signal transmitted from the transmission station 2 on the downstream side increases, but the attenuation amount of the optical signal transmitted from the transmission station 2 on the upstream side decreases, and the optical signal is received by the reception station 6. The optical signal intensity from each transmitting station 2 becomes substantially the same.

Although not shown in the receiving station 6 of FIG.
Similar to the receiving station 3 of FIG. 7, the receiving station 6 is provided with a terminal device such as a distributor, a demodulator, and a monitor TV, and the optical signal transmitted through the optical transmission line after being multiplexed is received by the optical receiver. At the same time, the light is received and detected at the same time, and then distributed to the demodulator by the distributor, demodulated for each carrier frequency in the demodulator, and the image is monitored by the receiving device such as a monitor television for each transmitting station.

[0029]

Second Embodiment A second embodiment of the optical signal transmission method of the present invention will be described in detail with reference to FIG. The structure shown in FIG. 2 is the same as that shown in FIG.
The optical attenuator 10 is removed and the output from the filter 12 is input to the light source 3. In FIG. 2, the filter 12 of the light receiving unit 8 extracts only the intensity of the reference optical signal from the reference optical signal generating unit 9, and the light source 3 is extracted based on the reference optical signal extracted by the filter 12.
The drive current of is controlled.

Also in FIG. 2, assuming that the branch loss of the optical multiplexer 4 is 1 dB and 10 dB as shown in FIG. 5 and the transmission line loss between the adjacent optical multiplexers 4 is 5 dB, the light receiving portion of the transmitting station 2 on the downstream side. The level of the reference optical signal received by 6 is low, and the level of the reference optical signal received by the light receiving unit 6 of the upstream transmission station 2 is high. In this case, when the level of the received reference optical signal is low, the drive current of the light source 3 of the transmitting station 2 is reduced to reduce the amount of light emitted from the light source 3, and when the level of the received reference optical signal is high. Increases the drive current of the light source 3 to increase the amount of light emitted from the light source 3,
The optical signal intensities from the respective transmitting stations 2 received by the receiving station 6 become substantially the same.

[0031]

Third Embodiment A third embodiment of the optical signal transmission method of the present invention will be described in detail with reference to FIG. The configuration shown in FIG. 3 is basically the same as that shown in FIG. 2, except that the electrical signal of the reference optical signal output from the filter 12 is input to the modulator 1 and based on the electrical signal. That is, the modulation degree of the modulator 7 is controlled.

Also in FIG. 3, assuming that the branch loss of the optical multiplexer 4 is 1 dB and 10 dB as shown in FIG. 5 and the transmission line loss between the adjacent optical multiplexers 4 is 5 dB, the light receiving portion of the transmitting station 2 on the downstream side. The level of the reference optical signal received by 6 is low, and the level of the reference optical signal received by the light receiving unit 6 of the upstream transmission station 2 is high. When the level of the received reference optical signal is low, the degree of modulation is weakened, and when the level of the reference optical signal is high, the degree of modulation is increased.
The transmission intensities of the optical signals from are almost the same.

[0033]

Fourth Embodiment A fourth embodiment of the optical signal transmission method of the present invention will be described in detail with reference to FIG. The configuration shown in FIG. 4 is basically the same as that shown in FIG. 1, except that the reference optical signal generator 9 in FIG. 4 is removed and the light from the transmitting station 2 upstream of the optical transmission line 5 is removed. The signal is received by the light receiving unit 8 of the downstream transmitting station 2, and the transmitting station 2
The attenuation amount of the optical attenuator 10 is controlled. In this case, the filter 12 of the light receiving unit 8 of each transmitting station 2 can extract a desired optical signal from the transmitting station 2 among the optical signals transmitted from many upstream transmitting stations 2 to the optical transmission path 5. The passing frequency band is decided like this.

Also in FIG. 4, assuming that the branch loss of the optical multiplexer 4 is 1 dB and 10 dB as shown in FIG. 5 and the transmission line loss between the adjacent optical multiplexers 4 is 5 dB, the light receiving section of the transmitting station 2 on the downstream side. The level of the optical signal from the upstream transmitting station 2 received at 8 is low, and the level of the optical signal from the upstream transmitting station 2 received at the light receiving unit 8 of the upstream transmitting station 2 is high. When the level of the received optical signal is low, the attenuation of the optical attenuator 10 is small, and when the level of the received optical signal is high, the attenuation of the optical attenuator 10 is large. That is, the reduction of the attenuation amount of the optical attenuator 10 of the downstream transmitting station 2 is small, and the reduction of the attenuation amount of the optical attenuator 10 of the upstream transmitting station 2 is large. Therefore, the optical signal transmitted from the transmitting station 2 that receives the optical signal from the upstream becomes an optical signal having a level matching the level of the received optical signal, is sent to the optical transmission line 5, and is received by the receiving station 6. The optical signal intensities from the respective transmitting stations 2 are substantially uniform.

[0035]

Other Embodiments In the optical signal transmission method of the present invention, the optical signal transmission device may take any form as long as it is an optical signal system in which optical signals are multiplexed and simultaneously received by one light receiver. Although the one shown in FIGS. 1 to 4 is a bus type system,
Other than these, a star-type, loop-type, tree-type device, or any other type device not shown may be used.

[0036]

The optical signal transmission methods according to claims 1 to 9 of the present invention have the following effects. ． There is no need to manually adjust the output signal level of each transmitter when installing or adding an optical signal transmission device, and the output signal level is automatically adjusted when installing or adding an optical transmission device. Since the optical signal from the transmitting station has the same intensity at the receiving station, the noise characteristic at the time of receiving light is improved. ． Even if the loss changes in the optical transmission line due to changes over time or other causes, the level of the optical signal output from the transmitting station 2 is automatically corrected, and the reliability of optical transmission is improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of an optical signal communication method of the present invention.

FIG. 2 is an explanatory diagram showing a second embodiment of the optical signal communication method of the present invention.

FIG. 3 is an explanatory diagram showing a third embodiment of the optical signal communication method of the present invention.

FIG. 4 is an explanatory diagram showing a fourth embodiment of the optical signal communication method of the present invention.

FIG. 5 is an explanatory diagram of branch loss of the optical multiplexer and transmission line loss between the optical multiplexers.

FIG. 6 is an explanatory diagram of a case where an optical signal from a transmitting station is adjusted by an optical attenuator in a conventional optical communication method.

FIG. 7 is an explanatory diagram of a conventional optical communication method.

[Explanation of symbols]

 1 is a modulator 2 is a transmitting station 3 is a light source 4 is an optical multiplexer 5 is an optical transmission line 6 is a receiving station 7 is a light receiving device 8 is a light receiving part 9 is a reference optical signal generating part 10 is an optical attenuator 11 is a light receiving device 12 filter

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Claims (9)

[Claims] 1. From the light sources (3) of two or more transmitting stations (2),
Optical signals of different wavelengths, which are modulated by carrier waves of different frequencies of the modulator (1) of each transmitting station (2), are sent out, and these optical signals are multiplexed by the optical multiplexer (4) into the optical transmission line (5). Then, in the optical signal transmission method in which the combined optical signal is simultaneously received by one light receiver (7) of the receiving station (6) and demodulated, the optical multiplexer (4) of each transmitting station (2) ) Is provided at one end thereof, and an optical signal sent from the upstream side of the optical transmission line (5) is received by the light receiving section (8) of the downstream transmitting station (2) to be converted into an electrical signal. Transmitting station according to the signal (1)
An optical signal transmission method characterized in that the optical signal level sent from the optical multiplexer to the optical multiplexer (4) is controlled. 2. The optical signal transmission method according to claim 1,
An optical signal transmission method, wherein the optical signal sent from the upstream of the optical transmission line (5) is a reference optical signal from a reference optical signal generation unit (9) provided upstream of the optical transmission line (5). 3. The optical signal transmission method according to claim 1,
The optical signal sent from the upstream of the optical transmission line (5) is the optical signal from the transmission station (2) upstream of the optical transmission line (5), and the optical signal is received by the light receiving unit (8) of the downstream transmission station (2). An optical signal is converted into an electric signal, an electric signal of a desired frequency is extracted from the electric signal, and the optical signal level sent from the transmitting station (2) to the optical multiplexer (4) is controlled according to the electric signal. An optical signal transmission method characterized by the above. 4. The optical signal transmission method according to any one of claims 1 to 3, wherein the output of the transmitting station (2) is output according to the electric signal output from the light receiving section (8) of the transmitting station (2). An optical signal transmission method, characterized in that the amount of attenuation of the optical attenuator (10) provided on the side is controlled to control the optical signal level sent from the transmitting station (2) to the optical multiplexer (4). . 5. The optical signal transmission method according to any one of claims 1 to 3, wherein the light source of the transmitting station (2) is responsive to the electric signal output from the light receiving section (8) of the transmitting station (2). An optical signal transmission method characterized in that the drive current of (3) is controlled to control the optical signal level sent from the transmitting station (2) to the optical multiplexer (4). 6. The optical signal transmission method according to claim 1, wherein the modulation of the transmitting station (2) is performed according to an electric signal output from a light receiving section (8) of the transmitting station (2). An optical signal transmission method characterized in that the modulation level of the optical device (1) is controlled to control the optical signal level sent from the transmitting station (2) to the optical multiplexer (4). 7. The optical signal transmission method according to any one of claims 1 to 6, wherein the light receiving section (8) of the transmitting station (2) and a filter (11) for extracting an electric signal of a desired frequency (11). 12), and an optical signal output from the transmitting station (2) to the optical multiplexer (4) is controlled by an electric signal output from the filter (12). Transmission method. 8. The optical signal transmission method according to claim 7,
The optical signal transmission method, wherein the filter (12) of the light receiving section (8) of the transmitting station (2) extracts the intensity of the reference optical signal electrically converted by the light receiving section (8). 9. The optical signal transmission method according to claim 7,
The filter (12) of the light receiving unit (8) of the transmitting station (2) outputs a signal of a desired frequency among the optical signals from the transmitting station (2) upstream of the own station which are electrically converted by the light receiving unit (8). An optical signal transmission method, characterized in that the optical signal is taken out.