JPH06204950A - Optical transmission system - Google Patents

Abstract

PURPOSE:To provide an optical transmission system of an N:1 or N:N form which is never deteriorated by the beat noises caused among the signal beams. CONSTITUTION:The optical modulators 110, 111 and 112 are concatenated to an optical fiber transmission path 10 to which carrier waves 120, 121 122 of different in wavelength from each other are impressed and an optical transmitter 20 and an optical receiver 40 are connected at both ends. Then the carrier waves 120, 121 and 122 of different frequencies are applied to those modulators 110-112. Thus the receiver 40 can obtain a high frequency signal 50 multiplexed by the waves 120-122. Under such conditions, only the signal light 30 is received by the receiver 40 and therefore no beat noise is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is of the type N to 1 or N to N.
Type optical communication system for realizing an optical communication network.

[0002]

2. Description of the Related Art Conventionally, as one of methods for realizing an N to 1 type or N to N type optical communication network in which a plurality of transmitting terminals and one or a plurality of receiving terminals are connected by an optical fiber network,
An optical multi-access method using a sub-carrier multiplex transmission method is under study.

According to this method, signal light modulated by carrier waves having different frequencies is output from each of the N transmitting terminals. This signal light is multiplexed by an optical fiber network, input to a receiving terminal, and converted into a high frequency signal by a light receiving element. N carrier waves having different frequencies are frequency-multiplexed on the high-frequency signal. Therefore, the receiving terminal can receive the transmission signal from the arbitrary transmitting terminal by taking out and demodulating the arbitrary carrier from the N carriers by the tuner.

Regarding the optical multi-access method using such a sub-carrier multiplex transmission method, for example, Shibuya et al., "Wide Area Monitoring Information Transmission System-Aiming at Information Transmission at Arbitrary Point in City", IEICE Technical Research It is described in detail in the literature such as the report OCS92-25 (1992).

[0005]

In the optical multi-access system using the above-mentioned sub-carrier multiplex transmission system, a plurality of signal lights are multiplexed on the optical fiber network. When the wavelengths of these signal lights coincide with each other or are very close to each other, noise occurs due to the beat between these signal lights at the receiving terminal, and in some cases, it becomes impossible to receive the transmission signal.

Therefore, it is necessary to control the wavelength of the optical transmitter in order to prevent the occurrence of this beat noise, which causes problems such as complication of the network, increase of cost, and limitation of the number of connectable transmitting terminals. The problem of beat noise in the optical multi-access system using such a subcarrier multiplex transmission system is described, for example, by Shibuya et al. In "Wide Area Monitoring Information Transmission System-Aiming at Information Transmission at Arbitrary Point in City", IEICE Technology. It is described in detail in the literature such as the research report OCS92-25 (1992).

Therefore, an object of the present invention is to realize an optical multi-access network using a subcarrier multiplexing system in which beat noise does not occur.

[0008]

In the optical transmission system of the first invention, one optical transmitter and one or a plurality of optical receivers are connected by an optical fiber transmission line, and the optical fiber transmission lines are connected to each other. A plurality of optical modulators to which carrier waves of different frequencies are applied are connected in cascade, and when the signal light output from the optical transmitter passes through the plurality of optical modulators, it is modulated by the carrier waves. Characterize.

In the optical transmission system of the second invention, a plurality of optical transmitters and one or a plurality of optical receivers are connected by an optical fiber network, and carrier waves having different frequencies are applied to the optical fiber network. A plurality of optical modulators are cascaded, a plurality of signal light output from the plurality of optical transmitters is an optical transmission system that is modulated by the carrier when passing through the plurality of optical modulators, The minimum value of the optical frequency interval between the plurality of signal lights is larger than the maximum frequency of the carrier wave.

In the optical transmission system of the third invention, a plurality of optical transmitters and one or a plurality of optical receivers are connected by an optical fiber network, and carrier waves having different frequencies are applied to the optical fiber network. A plurality of optical modulators are cascaded, a plurality of signal light output from the plurality of optical transmitters is an optical transmission system that is modulated by the carrier when passing through the plurality of optical modulators, The maximum value of the optical frequency interval between the plurality of signal lights is smaller than the minimum frequency of the carrier wave.

In the optical transmission system of the fourth invention, a plurality of optical transmitters and one or a plurality of optical receivers are connected by an optical fiber network, and carrier waves having different frequencies are applied to the optical fiber network. A plurality of optical modulators are cascaded, a plurality of signal light output from the plurality of optical transmitters is an optical transmission system that is modulated by the carrier when passing through the plurality of optical modulators, The minimum value of the line widths of the plurality of signal lights is larger than the maximum frequency of the carrier wave.

In the optical transmission system of the fifth invention, the signal light output from one optical transmitter is divided into a plurality of pieces and input into a plurality of optical fiber transmission paths, and the plurality of optical fiber transmission paths are mutually connected. A plurality of optical modulators to which carrier waves of different frequencies are applied are connected in series, and the plurality of signal lights are modulated by the carrier waves when passing through the plurality of modulators, and then multiplexed again to form an optical receiver. It is received at.

In the optical transmission system of the sixth invention, an optical transmitter and an optical receiver are connected to both ends of one optical fiber transmission line, and the signal light output from the optical transmitter is sent to the optical transmitter. A plurality of terminals having an optical modulator and an optical receiver, which are modulated by an applied transmission signal and are applied with a carrier of a different frequency for each terminal, are cascade-connected to the optical fiber transmission line, and the signal The light is modulated by the carrier when passing through the plurality of terminals, and at the same time, a part of the signal light is branched in the terminal and is received by the optical receiver in the terminal.

In the optical transmission system of the seventh invention, the first and second optical transmitters are connected to both ends of one optical fiber transmission line, and output from the first and second optical transmitters. First and second signal lights are input to the optical fiber transmission line from opposite directions, and an optical modulator and an optical receiver to which carrier waves having different frequencies are applied to each terminal are provided in the optical fiber transmission line. A plurality of terminals, which are connected in cascade, in which each of the first and second signal lights is simultaneously modulated by the carrier wave, and at the same time, a part of the first and second signal lights is branched in each terminal. The signal is received by the optical receiver in the terminal.

[0015]

In the first aspect of the invention, a plurality of optical modulators are cascaded in the optical fiber transmission line, and carrier waves having different frequencies are applied to the optical modulators. The signal light sent from the optical transmitter is intensity-modulated according to the carrier every time it passes through each optical modulator, and then is input to the optical receiver and converted into a high frequency signal. A carrier wave applied to each optical modulator is frequency-multiplexed with this high-frequency signal, and a tuner extracts and demodulates an arbitrary carrier wave. As a result, similar to the optical multi-access method using the conventional subcarrier multiplex transmission method,
Any of the information transmitted from each optical modulator can be received. Moreover, according to the present invention, since only a single signal light is transmitted, beat noise is not likely to occur unlike the prior art.

In the second aspect of the invention, a plurality of signal lights are transmitted through a plurality of optical fiber transmission lines in which optical modulators are connected in cascade, and then multiplexed and received by an optical receiver. However, the minimum value of the optical frequency intervals of the plurality of signal lights is larger than the maximum frequency of the carrier wave. In this case, beat noise occurs on the higher frequency side than the carrier wave. Therefore, the carrier wave is not affected by beat noise.

In the third aspect of the invention, a plurality of signal lights are transmitted through a plurality of optical fiber transmission lines in which optical modulators are connected in cascade, and then multiplexed and received by an optical receiver. However, the maximum value of the optical frequency intervals of the plurality of signal lights is smaller than the lowest frequency of the carrier wave. In this case, beat noise occurs on the low frequency side of the carrier. Therefore, the carrier wave is not affected by beat noise.

According to the fourth aspect of the invention, a plurality of signal lights are transmitted through a plurality of optical fiber transmission lines in which optical modulators are connected in cascade, and then multiplexed and received by an optical receiver. However, signal light having a line width wider than the maximum frequency of the carrier wave is used. In this case, the beat noise is distributed over a wide band, and the spectral density of the beat noise generated in the carrier frequency band becomes low. Therefore, the influence of beat noise on carrier wave transmission is small.

In the fifth invention, one signal light is demultiplexed into a plurality of signals, and each signal light is transmitted after being transmitted through a plurality of optical fiber transmission lines in which optical modulators are connected in cascade, and then combined to generate an optical signal. It is received by the receiver. In this case, the same signal light is combined after passing through different paths, and the beat noise is distributed near DC. Therefore, the carrier wave is not affected by beat noise.

In the sixth invention, a plurality of terminals having an optical modulator and an optical receiver are cascade-connected to the optical fiber transmission line, and the signal light transmitted through the optical fiber transmission line is added to the optical transmitter. Is modulated by the transmitted signal. Further, each terminal modulates the signal light with an optical modulator according to the carrier wave, and at the same time, branches a part of this signal light and receives it by an optical receiver in the terminal. Thereby, each terminal can receive the transmission signal sent from the optical transmitter at the same time as transmitting the carrier wave to the optical receiver.

In the seventh invention, two optical transmitters are connected to both ends of the optical fiber transmission line, and the first and second signal lights outputted from the two optical transmitters are in opposite directions to each other. It is input to the transmission line. A plurality of terminals each having an optical modulator and an optical receiver are cascade-connected to this optical fiber transmission line, and each terminal simultaneously modulates the first and second signal lights by the optical modulator. Further, each terminal splits a part of the first and second signal lights and receives this by the optical receiver in the terminal. This allows each terminal to transmit a carrier wave to another terminal and simultaneously receive a carrier wave from another terminal. That is, according to the seventh aspect, mutual information transmission between terminals can be performed.

[0022]

The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a basic configuration of an optical transmission system according to the present invention. Optical fiber transmission line 1 in FIG.
Three optical modulators 110, 111 and 112 are inserted in series at 0, and carrier waves 120, 121 and 122 having different frequencies are applied to the optical modulators 110, 111 and 112, respectively. From the optical transmitter 20 to the optical fiber transmission line 1
The signal light 30 output to 0 is the optical modulators 110 and 11
Carrier waves 120 and 12 when passing through
1, 122 is subjected to intensity modulation. After passing through the optical fiber transmission line 10, the signal light 30 is received by the optical receiver 40 and converted into a high frequency signal 50. In this way, in the optical receiver 40, the carrier waves 120, 121, 122
It is possible to obtain the high frequency signal 50 in which the frequency is multiplexed. Further, at this time, since the optical receiver 40 receives only the signal light 30, there is no fear that beat noise, which is a problem when a plurality of signal lights are received, is generated.

FIG. 2 is a block diagram of the first embodiment of the present invention. The optical fiber transmission line 10 includes optical modulators 110 and 11
1, 112, high frequency modulators 130, 131, 132, and signal sources 140, 141, 142
00, 101, 102 are connected in cascade. As the optical transmitter 20, a 1.5 μm band DFB-LD was used. Further, the signal light 30 is split into two by the optical demultiplexer 60 after passing through the transmission terminal 102, and the optical receivers 40 and 41 and the tuner 9 are separated.
It is received by the receiving terminals 200 and 201 having 0 and 91, respectively. Further, in this embodiment, the transmitting terminal 101,
An optical amplifier 80 is inserted between 102. In this embodiment, an erbium-doped optical fiber amplifier is used as the optical amplifier 80. Regarding this optical amplifier, for example, “Characteristics when an Er-doped optical amplifier is used for optical CATV” by Izumi et al., IEICE Technical Report OC
S90-24, etc. are described in detail.

In the transmitting terminals 100, 101 and 102, television cameras are used as the signal sources 140, 141 and 142 in this embodiment, and high frequency modulators 130, 131 and 1 are used.
An FM modulator for satellite broadcasting was used as 32. From the high frequency modulators 130, 131 and 132, the frequency is 1
049.48MHz, 1087.84MHz, 111
Carrier waves 120, 121, 122 of 2.62 MHz are output. Each carrier wave is a signal source 140, 141, 142.
Baseband signals 150, 151, 15 output from
2 is frequency-modulated. Optical modulator 110,1
11,112 Mach-Zehnder type Ti: LiN
A bO ₃ light intensity modulator (LN light modulator) was used. Regarding this LN optical modulator, for example, “Preparation of light-stabilized LiNbO ₃ waveguide type analog modulator” by Doi et al., 19
It is described in detail in literatures such as the 1992 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, C-169. This optical modulator 110, 11
A DC bias voltage is applied to 1,112 so that the output level is 3 dB lower than the input level, and the carrier waves 120, 121, 122 are further applied. As a result, the signal light 30 is subjected to intensity modulation with an optical modulation degree of 5% each time it passes through each optical modulator.

Further, PIN type photodiodes are used for the optical receivers 40 and 41 of the receiving terminals 200 and 201, and the high frequency signals 50 and 51 output from the PIN type photodiodes are amplified by the high frequency amplifiers 210 and 211, and thereafter, It is input to tuners 90 and 91 for satellite broadcasting. Tuner 9
At 0 and 91, one wave of the carrier waves 120, 121 and 122 multiplexed with the high frequency signals 50 and 51 is selected and demodulated, and any one wave of the baseband signals 150, 151 and 152 is output. To do.

In this embodiment, the optical transmitter 20 and the transmitting terminal 10
The lengths of the optical fibers connecting 0, 101, 102 and the receiving terminals 200, 201 are all 5 km,
The optical loss in this optical fiber was 2 dB. The optical output of the optical transmitter 10 is 6 dBm, and the optical modulators 110 and 1
The loss of 11 and 112 was 6 dB, the amplification degree of the optical amplifier 80 was 15 dB, and the optical loss of the optical demultiplexer 60 was 4 dB. Therefore, a signal light of -9 dBm was input to the receiving terminal. At this time, a very high quality video signal with a video SN ratio of 48 dB or more was output from the tuners 90 and 91.

In the first embodiment described above, the optical modulator 11
Although LN optical modulators are used as 0, 111, and 112, other optical modulators, such as semiconductor optical modulators, can be used, and optical switches can also be used as optical modulators. is there. Regarding semiconductor type optical modulator,
For example, it is described in detail in documents such as "50-channel FM-FDM long-distance transmission experiment using an MQW external modulator" by Kagami et al. Regarding the use of the optical switch as an optical modulator, for example, “Cross-type optical switch /
Reflection and Transmission Characteristics of Modulators ", 1989 Spring Conference of the Institute of Electronics, Information and Communication Engineers, C-470, and the like. Although an erbium-doped optical fiber amplifier is used as the optical amplifier 80, other optical amplifiers such as a semiconductor optical amplifier can be applied. Regarding the semiconductor optical amplifier, for example, “1.5 μm band traveling waveform semiconductor optical amplifier with window structure on both ends” by Kuruma et al., 1989.
It is described in detail in the literature of the IEICE Spring Conference, C-409, etc.

FIG. 3 is a block diagram of the second embodiment of the present invention. In this embodiment, a plurality of optical transmitters having different wavelengths are used. In FIG. 3, the signal lights 30 and 31 output from the two optical transmitters 20 and 21 are the optical fiber transmission lines 10 and 11, respectively.
And is multiplexed by the optical multiplexer 70, then passes through the optical fiber transmission line 12 and is input to the receiving terminal 200. The optical fiber transmission line 10 has transmission terminals 100, 101.
However, the transmission terminal 102 is inserted in the optical fiber transmission line 11, and the transmission terminal 103 is inserted in the optical fiber transmission line 12. As these transmitting terminals, the same ones as in the first embodiment are used, and the transmitting terminals 100, 101, 102, 1 are used.
Carrier frequency in 03 is 1049.48M respectively
Hz, 1087.84 MHz, 112.62 MHz,
It was 1164.56 MHz. FIG. 4 shows a frequency spectrum of the high frequency signal 50 in the receiving terminal 200 of this embodiment. In this embodiment, DFB-LDs having oscillation wavelengths of 1.510 μm and 1.514 μm are used as the optical transmitters 20 and 21, respectively. In this case, the signal lights 30, 3
Since the oscillation wavelength interval between 1 is 4 nm, beat noise is generated in the vicinity of about 500 GHz as shown in FIG. Therefore, this beat noise does not affect the carrier wave near the frequency of 1 GHz.

The third embodiment has the same structure as the second embodiment shown in FIG. 3, but the wavelengths of the optical transmitters 20 and 21 are the same. FIG. 5 shows a frequency spectrum of the high frequency signal 50 in the receiving terminal 200 of this embodiment. In this embodiment, the wavelengths of the optical transmitters 20 and 21 are controlled so that the signal light 3
The optical frequency difference between 0 and 31 is suppressed to 100 MHz or less. In this case, as shown in FIG. 5, the beat noise occurs at a frequency of about 100 MHz or less, so that the beat noise does not affect the carrier wave near the frequency of 1 GHz. Regarding the specific wavelength control of the optical transmitter,
For example, KAI et al., “Acetylene molecular absorption line (1.531
Absolute wavelength stabilized DFB laser miniature module using 59 μm ”, 1989 Autumn Meeting of the Institute of Electronics, Information and Communication Engineers, B
-464, etc.

The fourth embodiment has the same structure as the second embodiment shown in FIG. 3 and uses an optical transmitter having a very wide line width. FIG. 6 shows a frequency spectrum of the high frequency signal 50 in the receiving terminal 200 of this embodiment. In this embodiment, as the optical transmitters 20 and 21, superluminescent diodes having a line width of 20 nm are used. In this case,
As shown in, the beat noise is substantially evenly distributed over the band of 5 THz or more, so that the beat noise density in the reception band of the carrier becomes very low, and the signal transmission is hardly affected. Regarding the super luminescent diode used as the optical transmitters 20 and 21,
For example, it is described in detail in documents such as "High coupling efficiency super luminescent diode" by Kashima et al., 1989 Spring Conference of The Institute of Electronics, Information and Communication Engineers, C-429.

FIG. 7 is a block diagram of the fifth embodiment of the present invention. In this embodiment, a plurality of signal lights having the same wavelength are obtained by branching the output of one optical transmitter. Figure 7
After the signal light 30 output from the optical transmitter 20 is split into two by the optical demultiplexer 60 and amplified by the optical amplifiers 80 and 81,
It is input to the optical fiber transmission lines 10 and 11. The signal light 30 that has passed through the optical fiber transmission lines 10 and 11 is transmitted to the optical multiplexer 7
The signal is multiplexed again by 0, passes through the optical fiber transmission line 12, and is input to the receiving terminal 200. In order to avoid interference when the signal lights 30 are combined, an optical path length difference of 100 m or more is provided between the optical fiber transmission lines 10 and 11. FIG. 8 shows a frequency spectrum of the high frequency signal 50 in the receiving terminal 200 of the present embodiment.

As shown in FIG. 8, in the present embodiment, the beat noise is generated around DC, so that this beat noise does not affect the carrier wave near the frequency of 1 GHz. It is a block diagram of 6th Example.
In this embodiment, it is possible to mutually transmit information between the network center and the transmission terminal. In Figure 9,
The optical transmitter 20 is installed in the network center 300, and the optical transmitter 20 is modulated by the transmission signal 310. In this embodiment, a baseband digital signal having a bit rate of 2 Mbps is used as the transmission signal 310. The transmission light 310 causes the signal light 30 to undergo intensity modulation with an extinction ratio of 4: 5. This signal light 30 is transmitted to the transmission terminals 100, 101, 10 connected in cascade to the optical fiber transmission line 10.
After passing through 2, the data is input to the network center 300 again.

The transmitting terminals 100, 101 and 102 modulate the signal light 30 with carrier waves 120, 121 and 122, respectively. The frequencies of the carriers 120, 121 and 122 are 1049.48 MHz, 1087.84 MHz and 11 respectively.
It was 12.62 MHz.

At the same time, the transmitting terminals 100, 101, 1
Reference numeral 02 designates a part of the signal light 30 as optical demultiplexers 160, 161,
The signals are demultiplexed at 162 and received by the optical receivers 170, 171, 172. Further, the low-pass components of the outputs of the optical receivers 170, 171, 172 are extracted by using the low-pass filters 180, 181, 182 having a cutoff frequency of 2 MHz. This allows each transmitting terminal to receive the transmission signal 310 transmitted from the network center. On the other hand, in the network center 300, the optical receiver 40 uses the signal light 3
0 is received, and the high-pass component of the output of the optical receiver 40 is extracted using the high-pass filter 320 having a cutoff frequency of 2 MHz. As a result, the transmitting terminals 100, 101, 10
It is possible to receive the carrier waves 120, 121, 122 sent from the No. 2.

In this embodiment, the network center 300
A baseband digital signal having a bit rate of 2 Mbps was used as the transmission signal 310 from the carrier wave 120,
Other types of signals may be used as long as they do not affect the transmission of 121 and 122. For example, bit rate 6
Frequency 1.5M modulated with 4 kbps digital signal
It is also possible to use a carrier wave of Hz as the transmission signal 310.

As described above, in this embodiment, it is possible to mutually transmit information between the network center and the transmission terminal, and using this, for example, the carrier frequency of each transmission terminal is controlled on the network center side. The so-called demand assign method or the like can be realized. This demand assign method is a technique widely used in satellite communication and the like, and is described in detail in the literature such as "New Edition Satellite Communication Engineering", edited by Kenichi Miya, published by Latteris Co.

FIG. 10 is a block diagram of the seventh embodiment of the present invention. In this embodiment, mutual information transmission between terminals is possible. In FIG. 10, optical transmitters 20 and 21 are connected to both ends of the optical fiber transmission line 10 and have wavelengths of 1.
The signal lights 30 and 31 of 510 μm and 1.514 μm are output. A transmission / reception terminal 4 is provided in the middle of the optical fiber transmission line 10.
00, 401 and 402 are inserted in series.

In the transmission / reception terminal 401, the signal light 30 and the signal light 31 are simultaneously transmitted by the optical modulator 111 by the carrier wave 1
21 to be modulated. Further, in the transmission / reception terminal 401, the optical demultiplexer 161 demultiplexes part of the signal lights 30 and 31. In this embodiment, an optical fiber coupler having four input / output ports is used as the optical demultiplexer 161. The optical receiver 162 receives a part of the signal light 31, and the output thereof includes the carrier wave 122 from the transmission / reception terminal 402. The optical receiver 163 receives a part of the signal light 30, and the output thereof includes the carrier wave 120 from the transmitting / receiving terminal 400.
The outputs of the optical receivers 162 and 163 are multiplexed by the high frequency multiplexer 191 and input to the tuner 91. Tuner 9
By selecting an arbitrary carrier wave from the high frequency signal input to 1 and demodulating this, the transmitting / receiving terminal 401 can receive information from the transmitting / receiving terminal 400 or the transmitting / receiving terminal 402.

Similarly, the transmission / reception terminals 400 and 402 transmit the signal lights 30 and 3 by the carrier waves 120 and 122, respectively.
1 is modulated at the same time, and information is transmitted to other transmitting / receiving terminals.
At the same time, the transmission / reception terminals 400, 402 receive the signal lights 30, 31, and receive information from other transmission / reception terminals. In this way, the transmitting / receiving terminals 400, 401, 402 can mutually transmit information.

[0041]

As described above, according to the present invention, it is possible to realize an optical multi-access network using a subcarrier multiplexing system in which beat noise does not occur.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an optical transmission system according to the present invention.

FIG. 2 is a configuration diagram of a first embodiment of the present invention.

FIG. 3 is a configuration diagram of second, third and fourth embodiments of the present invention.

FIG. 4 is a wavenumber spectrum diagram of a received signal in the second embodiment of the present invention.

FIG. 5 is a wavenumber spectrum diagram of a received signal in the third embodiment of the present invention.

FIG. 6 is a wave number spectrum diagram of a received signal in the fourth embodiment of the present invention.

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

FIG. 8 is a wave number spectrum diagram of a received signal in the fifth embodiment of the present invention.

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

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

[Explanation of symbols]

10, 11, 12 Optical fiber transmission line 20, 21 Optical transmitter 30, 31 Signal light 40, 41, 170, 171, 172, 173, 17
4,175 Optical receiver 50,51 High frequency signal 60,160,161,162 Optical demultiplexer 70 Optical demultiplexer 80,81 Optical amplifier 90,91,92 Tuner 100,101,102,103 Transmission terminal 110,111 , 112 Optical modulator 120, 121, 122 Carrier wave 130, 131, 132 High frequency modulator 140, 141, 142 Signal source 150, 151, 152 Baseband signal 180, 181, 182 Low pass filter 190, 191, 192 High frequency combination Wave device 200,201 Receiving terminal 210,211 High frequency amplifier 300 Network center 310 Transmission signal 320 High-pass filter 400,401,402 Transmission / reception terminal

Claims (7)

[Claims] 1. An optical transmitter and one or a plurality of optical receivers are connected by an optical fiber transmission line, and a plurality of optical modulators to which carrier waves of different frequencies are applied are provided to the optical fiber transmission line. An optical transmission system, which is cascade-connected and is modulated by the carrier wave when the signal light output from the optical transmitter passes through the plurality of optical modulators. 2. A plurality of optical transmitters and one or a plurality of optical receivers are connected by an optical fiber network, and a plurality of optical modulators to which carrier waves of different frequencies are applied are cascade-connected to the optical fiber network. It is an optical transmission system in which a plurality of signal lights output from the plurality of optical transmitters are modulated by the carrier when passing through the plurality of optical modulators, and light between the plurality of signal lights is An optical transmission method, wherein a minimum value of frequency intervals is larger than a maximum frequency of the carrier wave. 3. A plurality of optical transmitters and one or a plurality of optical receivers are connected by an optical fiber network, and a plurality of optical modulators to which carrier waves of different frequencies are applied are cascade-connected to the optical fiber network. It is an optical transmission system in which a plurality of signal lights output from the plurality of optical transmitters are modulated by the carrier when passing through the plurality of optical modulators, and light between the plurality of signal lights is An optical transmission method, wherein the maximum value of frequency intervals is smaller than the minimum frequency of the carrier wave. 4. A plurality of optical transmitters and one or a plurality of optical receivers are connected by an optical fiber network, and a plurality of optical modulators to which carrier waves of different frequencies are applied are cascade-connected to the optical fiber network. It is an optical transmission system in which a plurality of signal lights output from the plurality of optical transmitters are modulated by the carrier when passing through the plurality of optical modulators, and the line widths of the plurality of signal lights are The optical transmission method is characterized in that the minimum value of is larger than the maximum frequency of the carrier wave. 5. The signal light output from one optical transmitter is divided into a plurality of pieces and input to a plurality of optical fiber transmission lines,
A plurality of optical modulators to which carrier waves of different frequencies are applied are cascade-connected to the plurality of optical fiber transmission lines, and the plurality of signal lights are modulated by the carrier waves when passing through the plurality of modulators. The optical transmission method is characterized in that after being multiplexed, they are multiplexed again and received by an optical receiver. 6. An optical transmitter and an optical receiver are connected to both ends of one optical fiber transmission line, and a signal light output from the optical transmitter is modulated by a transmission signal applied to the optical transmitter. Further, a plurality of terminals each having an optical modulator to which a carrier of a different frequency is applied to each terminal and an optical receiver are cascade-connected to the optical fiber transmission line, and the signal light passes through the plurality of terminals. Is modulated with the carrier when
At the same time, a part of the signal light is branched in the terminal and is received by the optical receiver in the terminal. 7. A first and a second optical signal output from the first and second optical transmitters, wherein first and second optical transmitters are connected to both ends of one optical fiber transmission line. Are input to the optical fiber transmission line in mutually opposite directions, and a plurality of terminals having an optical modulator and an optical receiver to which carrier waves of different frequencies are applied for each terminal are cascade-connected to the optical fiber transmission line. In each terminal, the first and second signal lights are simultaneously modulated by the carrier wave, and at the same time, a part of the first and second signal lights is branched in each terminal and the optical receiver in the terminal receives them. An optical transmission system characterized by being received.