Optical communication system

An optical communication method comprising the steps of:

• a) mixing signal light and local light with a polarization of the signal light coinciding with a polarization of the local light, to thereby produce a mixed light;
• b) optically transmitting the mixed lights;
• c) detecting the transmitted, mixed light and converting the detected light into a converted electric signal;
• and
• d) extracting an electric signal from the converted electric signal by a band-pass filter, the extracted electric signal being in an intermediate frequency band including a frequency component of a channel.

An optical communication method for transmitting a plurality of optical signals which each have a different carrier frequency corresponding to different channels, each optical signal having a corresponding local light signal, the method comprising the steps of:

• a) mixing each of the plurality of optical signals with the corresponding local light signal after polarization states of each respective optical signal and the corresponding local light signal are made coincident with each other, to thereby produce a plurality of multiplexed optical signals;
• b) combining the multiplexed optical signals, to thereby produce a combined signal;
• c) optically transmitting the combined signal;
• d) detecting the transmitted, combined signal and converting the detected signal into an electric signal;
• and
• e) extracting an electric signal from the converted electric signal with a band-pass filter, the extracted electric signal being in an intermediate frequency band including a frequency component of each channel.

An optical communication method comprising the steps of:

• a) allocating transmission signals on more than one channel having different microwave frequencies;
• b) modulating carriers of the microwave frequencies with the transmission signals, to thereby produce modulated signals;
• c) combining the modulated signals, to thereby produce a multiplexed signal;
• d) modulating an optical frequency modulator with the multiplexed signal, to thereby produce a modulated optical signal;
• e) mixing the modulated optical signal with local light with polarization states of the modulated optical signal and the local light made to be coincident with each other, to thereby produce a mixed light signal, and optically transmitting the mixed light signal;
• f) detecting the transmitted, mixed light signal and converting the detected signal into a converted electric signal;
• g) extracting an electric signal from the converted electric signal with a band-pass filter, the extracted electric signal being in an intermediate frequency band including a frequency component of each channel;
• h) extracting channel signals from the extracted electrical signal by filters;
• and
• i) demodulating each of the extracted channel signals.

An optical communication system comprising:

• a plurality of optical modulated signal generating units, each including
• a plurality of modulators modulating carriers having different microwave frequencies with transmission signals and outputting frequency modulated signals,
• adding means for generating a microwave frequency multiplexed signal by adding the frequency modulated signals, and
• an optical frequency modulator generating an optical frequency modulated signal by frequency modulation with said microwave frequency multiplexed signal;
• optical mixing means for mixing the optical frequency modulated signals of the optical frequency modulated signal generating units, to thereby generate an optical frequency multiplexed signal, the optical frequency multiplexed signal including a signal component, in an intermediate frequency band;
• and
• an optical frequency discriminator, connected to said optical mixing means, receiving and dividing the optical frequency multiplexed signal into first and second signals, the first signal having a time delay with respect to the second signal, and mixing the first and second signals to generate an optical frequency multiplexed signal to be transmitted to a receiver.

An optical communication system comprising:

• a plurality of optical frequency modulated signal generating units for modulating a plurality of carriers with a plurality respectively corresponding transmission signals, each carrier having a different microwave frequency and each optical frequency modulated signal generating unit including
• a plurality of modulators corresponding, respectively, to the plurality of carriers, each modulator modulating the corresponding carrier with the transmission signal corresponding to the respective carrier, and
• adding means for generating a microwave frequency multiplexed signal by adding the modulated carriers, and
• an optical frequency modulator generating an optical frequency modulated signal by frequency modulation with said. microwave frequency multiplexed signal;
• optical mixing means for mixing the optical frequency modulated signals generated by said plurality of optical frequency modulated signal generating units, to produce a mixed signal including a signal component in an intermediate band;
• and
• an optical frequency discriminator
• dividing the mixed signal into a first signal and a second signal, the first signal being delayed by a delay time with respect to the second signal, and
• mixing the first signal and the second signal.

A sending device for transmitting a signal light to a receiving device in an optical communication system, comprising:

• a plurality of optical frequency modulated signal generating units for modulating a plurality of carriers with a plurality of respectively corresponding transmission signals, each carrier having a different microwave frequency and each optical frequency modulated signal generating unit including
• a plurality of modulators corresponding, respectively, to the plurality of carriers, each modulator modulating the corresponding carrier with the transmission signal corresponding to the respective carrier to thereby produce a modulated carrier, and
• a plurality of band limiting filters corresponding, respectively, to the plurality of modulators, each band limiting filter band limiting the modulated carrier produced by the corresponding modulator to thereby Produce a band limited signal,
• adding means for generating a microwave frequency multiplexed signal by adding the band limited signals produced by the plurality of band limiting filters, and
• an optical frequency modulator generating an optical frequency modulated signal by frequency modulation with said microwave frequency multiplexed signal;
• and
• optical mixing means for mixing the optical frequency modulated signals generated by said optical frequency modulators of said plurality of optical frequency modulated signal generating units, to thereby produce an optical frequency multiplexed signal to be transmitted to a receiver and including a signal component in an intermediate frequency band.

An optical communication system comprising:

• a plurality of signal generating units, each signal generating unit
• modulating a plurality of carriers with a plurality of data signals, respectively, to thereby produce a plurality of modulated carrier signals, each carrier being at a different frequency,
• combining the plurality of modulated carrier signals to thereby produce a multiplexed signal, and
• modulating the multiplexed signal;
• and
• a mixer mixing together the modulated, multiplexed signals of the signal generating units, to produce a resulting signal for transmission to a receiver and which includes a signal component in an intermediate frequency band.