Optical transmission system and optical transmission device used therefor

An optical transmission system for multiplexing a plurality of optical modulation signals and for transmitting a multiplexed optical modulation signal through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a signal source for generating a transmission signal including information to be transmitted, said transmission signal having an envelope, wherein the envelope has a shape,
• a carrier generation circuit for generating a carrier signal,
• signal processing means for processing said carrier signal based on said transmission signal and for producing an electric modulation signal, said electric modulation signal being amplitude modulated by said transmission signal and having a high level envelope and a low level envelope, wherein one of said high level envelope and said low level envelope has a shape analogous to the shape of the envelope of said transmission signal and the other of said high level envelope and said low level envelope has an approximately constant level, and
• a light source element for converting said electric modulation signal into an optical modulation signal,
• wherein said signal processing means comprises amplitude modulation means for producing an output signal by amplitude modulating said carrier signal by said transmission signal, and clipping means for producing said electric modulation signal by clipping said output signal from said amplitude modulation means at a predetermined level.

An optical transmission system for multiplexing a plurality of optical modulation signals and for transmitting a multiplexed optical modulation signal through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a signal source for generating a transmission signal including information to be transmitted, said transmission signal having an envelope, wherein the envelope has a shape,
• a carrier generation circuit for generating a carrier signal,
• signal processing means for processing said carrier signal based on said transmission signal and for producing an electric modulation signal, said electric modulation signal having a high level envelope and a low level envelope, wherein one of said high level envelope and said low level envelope has a shape analogous to the shape of the envelope of said transmission signal and the other of said high level envelope and said low level envelope has an approximately constant level, and
• a light source element for converting said electric modulation signal into an optical modulation signal,
• wherein said signal processing means comprises a multiplier for producing said electric modulation signal by multiplying said transmission signal, which is offset by a first predetermined voltage, and said carrier signal, which is offset by a second predetermined voltage, together.

An optical transmission system for multiplexing a plurality of optical modulation signals and for transmitting a multiplexed optical modulation signal through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a signal source for generating a transmission signal including information to be transmitted, said transmission signal having an envelope, wherein the envelope has a shape,
• a carrier generation circuit for generating a carrier signal,
• signal processing means for processing said carrier signal based on said transmission signal and for producing an electric modulation signal, said electric modulation signal having a high level envelope and a low level envelope, wherein one of said high level envelope and said low level envelope has a shape analogous to the shape of the envelope of said transmission signal and the other of said high level envelope and said low level envelope has an approximately constant level, and
• a light source element for converting said electric modulation signal into an optical modulation signal,
• wherein said signal processing means comprises an adder for producing an output signal by adding said transmission signal and said carrier signal together, and clipping means for producing said electric modulation signal by clipping said output signal from said adder at a predetermined level.

An optical transmission system for multiplexing a plurality of optical modulation signals and for transmitting a multiplexed optical modulation signal through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a signal source for generating a transmission signal including information to be transmitted, said transmission signal having an envelope, wherein the envelope has a shape,
• a carrier generation circuit for generating a carrier signal,
• signal processing means for processing said carrier signal based on said transmission signal and for producing an electric modulation signal, said electric modulation signal being amplitude modulated by said transmission signal and having a high level envelope and a low level envelope, wherein one of said high level envelope and said low level envelope has a shape analogous to the shape of the envelope of said transmission signal and the other of said high level envelope and said low level envelope has an approximately constant level, and
• a light source element for converting said electric modulation signal into an optical modulation signal,
• wherein said signal processor comprises an amplitude modulator for producing an output signal by amplitude modulating said carrier signal by said transmission signal, and an adder for producing said electric modulation signal by adding said output signal of said amplitude modulator and said transmission signal together.

An optical transmission system for multiplexing a plurality of optical modulation signals and for transmitting a multiplexed optical modulation signal through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a signal source for generating a transmission signal including information to be transmitted, said transmission signal having an envelope, wherein the envelope has a shape,
• a carrier generation circuit for generating a carrier signal,
• signal processing means for processing said carrier signal based on said transmission signal and for producing an electric modulation signal, said electric modulation signal having a high level envelope and a low level envelope, wherein one of said high level envelope and said low level envelope has a shape analogous to the shape of the envelope of said transmission signal and the other of said high level envelope and said low level envelope has an approximately constant level, and
• a light source element for converting said electric modulation signal into an optical modulation signal,
• wherein said signal processing means comprises angle modulation means for producing an output signal by angle modulating said carrier signal by said transmission signal, an adder for producing an adder output signal by adding said output signal of said angle modulation means and said transmission signal together, and clipping means for producing said electric modulation signal by clipping said adder output signal at a predetermined level.

An optical transmission system for transmitting a plurality of transmission signals, occupying respectively different frequency bands, through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a first conversion circuit for converting one of the plurality of transmission signals, including information to be transmitted, into a first light intensity modulation signal, wherein the one of the plurality of transmission signals has a maximum possible frequency, and
• a second conversion circuit for converting said first light intensity modulation signal into a second light intensity modulation signal by intensity-modulating said first light intensity modulation signal by a pulse train having a basic frequency which is greater than or equal to twice the maximum possible frequency of the one of the plurality of transmission signals;
• and
• a multiplexer for multiplexing said second light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line.

An optical transmission system for transmitting a plurality of transmission signals, occupying respectively different frequency bands, through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a light emitting element for outputting light having a predetermined wavelength,
• means for generating a superimposed signal by superimposing a pulse train on one of the plurality of transmission signals, wherein the one of the plurality of transmission signals has a maximum possible frequency and includes information to be transmitted and said pulse train has a basic frequency which is greater than or equal to twice the maximum possible frequency of the one of the plurality of transmission signals, and
• an optical modulator for externally modulating, by said superimposed signal, the light outputted by said light emitting element;
• and
• a multiplexer for multiplexing said second light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line.

An optical transmission system for transmitting a plurality of transmission signals through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a modulation circuit for generating an electric modulation signal by modulating a sub-carrier by one of the plurality of transmission signals, wherein the one of the plurality of transmission signals has a maximum possible frequency and includes information to be transmitted,
• a first conversion circuit for converting said electric modulation signal into a first light intensity modulation signal,
• a second conversion circuit for converting said first light intensity modulation signal into a second light intensity modulation signal by intensity-modulating said first light intensity modulation signal by a pulse train having a basic frequency, wherein said basic frequency of said pulse train is greater than or equal to twice the maximum possible frequency of the one of the plurality of transmission signals;
• and
• a multiplexer for multiplexing said second light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line;
• wherein each of the sub-carriers occupies a different frequency.

An optical transmission system for transmitting a plurality of transmission signals, occupying respectively different frequency bands, through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a first conversion circuit for converting one of the plurality of transmission signals into a first light intensity modulation signal, wherein the one of the plurality of transmission signals has a maximum possible frequency and includes information to be transmitted,
• a pulsed FM circuit for generating a pulse-shaped electric signal by pulsed frequency modulating a sub-carrier by a predetermined electric signal, wherein said sub-carrier has a frequency which is greater than or equal to twice the maximum possible frequency of the one of the plurality of transmission signals,
• a second conversion circuit for converting said first light intensity modulation signal into a second light intensity modulation signal by intensity-modulating said first light intensity modulation signal by said pulse-shaped electric signal;
• and
• a multiplexer for multiplexing said second light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line.

An optical transmission system for transmitting a plurality of transmission signals through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a first conversion circuit for converting one of the plurality of transmission signals into a first light intensity modulation signal, wherein the one of the plurality of transmission signals has a maximum possible frequency and includes information to be transmitted,
• a second conversion circuit for converting said first light intensity modulation signal into a second light intensity modulation signal by intensity-modulating said first light intensity modulation signal by a pulse train having a basic frequency, wherein said basic frequency of said pulse train is greater than or equal to twice the maximum possible frequency of the one of the plurality of transmission signals;
• and
• a multiplexer for multiplexing said second light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line;
• wherein said basic frequencies of said pulse trains of any two of said plurality of optical transmission devices are spaced from each other at a value larger than a sum of said maximum possible frequencies of respective transmission signals of said any two optical transmission devices.

An optical transmission system for transmitting a plurality of transmission signals, occupying respectively different frequency bands, through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a pulse light generation circuit for outputting a pulse-shaped light signal having a basic frequency, and
• a conversion circuit for generating a light intensity modulation signal by intensity modulating said pulse-shaped light signal by one of the plurality of transmission signals, wherein the one of the plurality of transmission signals has a maximum possible frequency and includes information to be transmitted and said basic frequency of said pulse-shaped light signal is greater than or equal to twice the maximum possible frequency of the one of the plurality of transmission signals;
• and
• a multiplexer for multiplexing said light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line.

An optical transmission system for transmitting a plurality of transmission signals, occupying respectively different frequency bands, through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a light emitting element for outputting light having a predetermined wavelength,
• a pulse signal generation circuit for generating a pulse-shaped electric signal,
• means for generating a superimposed signal by superimposing said pulse-shaped electric signal on one of the plurality of transmission signals, wherein the one of the plurality of transmission signals includes information to be transmitted, and
• an optical modulator for externally modulating, by said superimposed signal, the light outputted by said light emitting element;
• and
• a multiplexer for multiplexing said light intensity modulation signals from each of said plurality of optical transmission devices so as to obtain a multiplexed light intensity signal and for transmitting said multiplexed light intensity signal through the common optical transmission line.

An optical transmission device for converting an electric signal into a light signal and for transmitting the light signal, said optical transmission device comprising:

• a plurality of element signal generation means, each for generating a respective direct current signal having a magnitude and a respective RF signal having an occupied frequency and for generating an element signal by adding said respective direct current signal to said respective RF signal, wherein said respective RF signal has a maximum amplitude value which is less than or equal to the magnitude of said direct current signal;
• multiplication means for generating a cumulative signal by multiplying said element signals together;
• and
• optical modulation means for converting said cumulative signal into a light intensity modulation signal;
• wherein said element signal generation means are operable such that the respective RF signals are generated such that the occupied frequencies of said respective RF signals do not overlap with each other and such that the occupied frequencies of said respective RF signals do not overlap with a frequency of higher harmonics produced by multiplying said RF signals together.

An optical transmission system for transmitting a plurality of transmission signals through a common optical transmission line, said system comprising:

• a plurality of optical transmission devices, each including
• a plurality of element signal generation means, each for generating a respective direct current signal having a magnitude and a respective RF signal having an occupied frequency and for generating an element signal by adding said respective direct current signal to said respective RF signal, wherein said respective RF signal has a maximum amplitude value which is less than or equal to the magnitude of said direct current signal;
• multiplication means for generating a cumulative signal by multiplying said element signals together;
• and
• optical modulation means for converting said cumulative signal into a light intensity modulation signal;
• wherein said element signal generation means are operable such that the respective RF signals are generated such that the occupied frequencies of said respective RF signals do not overlap with each other and such that the occupied frequencies of said respective RF signals do not overlap with a frequency of higher harmonics produced by multiplying said RF signals together.