Frequency separation stabilization method for optical heterodyne or optical homodyne communication

Claim 3

An apparatus for stabilizing a frequency separation according to claim 1, wherein the light sources are semiconductor lasers or multi-electrode lasers.

Claim 4

An apparatus for stabilizing a frequency separation according to claim 1, wherein the adding means includes a frequency discrimination circuit comprising a delay circuit delaying the multiplied signal and a double balance mixer mixing the delayed signal with the multiplied signal.

Claim 13

An apparatus for stabilizing a frequency separation between two light sources according to claim 7, wherein the variable temperature device is a Peltier device.

Claim 16

An optical communication system comprising: a photo-coupler forming a combined optical signal with a first optical signal from a transmission line and a second optical signal from a local oscillation light source; an optical detector forming a first electric signal having a frequency separation between the first and second optical signals; and a control circuit including an oscillator generating a second electric signal having a reference frequency, for adding a control current obtained from a multiplied signal formed with the first and second electric signals to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 17

An optical communication system comprising: a photo-coupler forming a combined optical signal with a first optical signal from a transmission line and a second optical signal from a local oscillation light source; an optical detector forming a first electric signal having a frequency separation between the first and second optical signals; and a control circuit including an oscillator generating a second electric signal having a reference frequency, for adding a control current obtained from a multiplied signal formed with the first and second electric signals to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 18

A balanced type communication system comprising: a photo-coupler forming a combined optical signal with a first optical signal from a transmission line and a second optical signal from a local oscillation light source; two optical detectors detecting the combined optical signal to form a first electric signal having a frequency separation between the first and second optical signals; and a control circuit including an oscillator generating a second electric signal having a reference frequency and a multiplier forming a multiplied signal from the first and second electric signals, for adding a control current obtained from the multiplied signal to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 19

A balanced type communication system comprising: a photo-coupler forming a combined optical signal with a first optical signal from a transmission line and a second optical signal from a local oscillation light source; two optical detectors detecting the combined optical signal to form a first electric signal having a frequency separation between the first and second optical signals; and a control circuit including an oscillator generating a second electric signal having a reference frequency and a multiplier forming a multiplied signal from the first and second electric signals, for adding a control current obtained from the multiplied signal to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 20

A polarization diversity optical communication system comprising: a photo-coupler forming a combined optical signal with a first optical signal from a transmission line and a second optical signal from a local oscillation light source; a polarization beam splitter splitting the combined optical signal into crossing two polarization components; two optical detectors, each detecting the corresponding polarization component to form a first electric signal having a frequency separation between the first and second optical signals; two demodulation circuits, each demodulating the first electric signal; an adder adding the demodulated signals; and a control circuit including an oscillator generating a second electric signal having a reference frequency and a multiplier forming a multiplied signal from the first and second electric signals, for adding a control current obtained from the multiplied signal to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 21

A polarization diversity optical communication system comprising: a photo-coupler forming a combined optical signal with a first optical signal from a transmission line and a second optical signal from a local oscillation light source; a polarization beam splitter splitting the combined optical signal into crossing two polarization components; two optical detectors, each detecting the corresponding polarization component to form a first electric signal having a frequency separation between the first and second optical signals; two demodulation circuits, each demodulating the first electric signal; an adder adding the demodulated signals; and a control circuit including an oscillator generating a second electric signal having a reference frequency and a multiplier forming a multiplied signal from the first and second electric signals, for adding a control current obtained from the multiplied signal to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 22

A balanced type polarization diversity optical communication system comprising: a first polarization separator separating a first optical signal form a transmission line into first x and y polarization components; a second polarization separator separating a second optical signal from a local oscillation light source into second x and y polarization components; a first photo-coupler forming a first combined optical signal with the first x polarization component from the first polarization separator and a second x polarization component from the second polarization separator; two first optical detectors detecting the x polarization optical signal to form a first electric signal having a frequency separation between the first and second optical signals; a second photo-coupler forming a second combined optical signal with the first y polarization component from the first polarization separator and a second y polarization component from the second polarization separator; two second optical detectors detecting the combined y polarization optical signal to form a second electric signal having a frequency separation between the first and second optical signals; first and second receivers receiving the combined x polarization optical signal and the combined y polarization optical signal, respectively; means for adding outputs of the first and second receivers; and a control circuit including an oscillator generating a third electric signal having a reference frequency and a multiplier forming a multiplied signal from the third electric signal and one of the first and second electric signals, for adding a control current obtained from the multiplied signal to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 23

A balanced type polarization diversity optical communication system comprising: a first polarization separator separating a first optical signal form a transmission line into first x and y polarization components; a second polarization separator separating a second optical signal from a local oscillation light source into second x and y polarization components; a first photo-coupler forming a first combined optical signal with the first x polarization component from the first polarization separator and a second x polarization component from the second polarization separator; two first optical detectors detecting the x polarization optical signal to form a first electric signal having a frequency separation between the first and second optical signals; a second photo-coupler forming a second combined optical signal with the first y polarization component from the first polarization separator and a second y polarization component from the second polarization separator; two second optical detectors detecting the combined y polarization optical signal to form a second electric signal having a frequency separation between the first and second optical signals; first and second receivers receiving the combined x polarization optical signal and the combined y polarization optical signal, respectively; means for adding outputs of the first and second receivers; and a control circuit including an oscillator generating a third electric signal having a reference frequency and a multiplier forming a multiplied signal from the third electric signal and one of the first and second electric signals, for adding a control current obtained from the multiplied signal to a driving current of the local oscillation light source so as to stabilize a desired frequency separation between the first and second optical signals.

Claim 24

An optical transmitter comprising: a multiplexer forming a combined beam from output beams of two light sources, each having a driving current superposed with a signal current corresponding to an independent digital information signal; an optical detector converting part of the combined beam to a first electric signal having a frequency separation between the light sources; an oscillator generating a second electric signal having a reference frequency; a multiplier forming a multiplied signal from the first and second electric signals; and means for adding a control current obtained from the multiplied signal to at least one of driving currents of the light sources so as to stabilize a desired frequency separation between the output beams of the light sources.

Claim 25

An optical transmitter comprising: a multiplexer forming a combined beam from output beams of two light sources, each having a driving current superposed with a signal current corresponding to an independent digital information signal; an optical detector converting part of the combined beam to a first electric signal having a frequency separation between the light sources; an oscillator generating a second electric signal having a reference frequency; a multiplier forming a multiplied signal from the first and second electric signals; and means for adding a control current obtained from the multiplied signal to at least one of driving currents of the light sources so as to stabilize a desired frequency separation between the output beams of the light sources.

Claim 26

An optical communication system for wave length multiplexing or frequency multiplexing with stabilized frequency separation, comprising: an optical transmitter comprising, a multiplexer forming a combined beam from output beams of two light sources, each having a driving current superposed with a signal current corresponding to an independent digital information signal, an optical detector converting part of the combined beam to a first electric signal having a frequency separation between the light sources, an oscillator generating a second electric signal having a reference frequency, a multiplier forming a multiplied signal from the first and second electric signals, and means for adding a control current obtained from the multiplied signal to at least one of driving currents of the light sources so as to stabilize a desired frequency separation between the output beams of the light sources; an optical transmission line transmitting the combined beam; an optical demultiplexer separating the combined beam into two beams, a frequency of one of the beams is different from that of the other beam; and an optical receiver having an optical detector and an amplifier, for outputting a received signal obtained from one of the beams to demodulate a signal.

Claim 27

An optical communication system for wave length multiplexing or frequency multiplexing with stabilized frequency separation, comprising: an optical transmitter comprising, a multiplexer forming a combined beam from output beams of two light sources, each having a driving current superposed with a signal current corresponding to an independent digital information signal, an optical detector converting part of the combined beam to a first electric signal having a frequency separation between the light sources, an oscillator generating a second electric signal having a reference frequency, a multiplier forming a multiplied signal from the first and second electric signals, and means for adding a control current obtained from the multiplied signal to at least one of driving currents of the light sources so as to stabilize a desired frequency separation between the output beams of the light sources; an optical transmission line transmitting the combined beam; an optical demultiplexer separating the combined beam into two beams, a frequency of one of the beams is different from that of the other beam; and an optical receiver having an optical detector and an amplifier, for outputting a received signal obtained from one of the beams to demodulate a signal.

Claim 28

An optical communication system for wave length multiplexing or frequency multiplexing with stabilized frequency separation, comprising: an optical transmitter comprising, a multiplexer forming a combined beam from output beams of two light sources, each having a driving current superposed with a signal current corresponding to an independent digital information signal, an optical detector converting part of the combined beam to a first electric signal having a frequency separation between the light sources, an oscillator generating a second electric signal having a reference frequency, a multiplier forming a multiplied signal from the first and second electric signals, and means for adding a control current obtained from the multiplied signal to at least one of driving currents of the light sources so as to stabilize a desired frequency separation between the output beams of the light sources; an optical transmission line transmitting an output beam from the optical transmitter; and an optical heterodyne or homodyne receiver comprising a local oscillator optical source, a photo-coupler combining a transmitted beam from the optical transmission line and a local beam from the local oscillator optical source, an optical detector detecting an output from the photo-coupler as an optical signal having an intermediate frequency signal, and a demodulation circuit converting the electric signal to a baseband signal.

Claim 29

An optical communication system for wave length multiplexing or frequency multiplexing with stabilized frequency separation, comprising: an optical transmitter comprising, a multiplexer forming a combined beam from output beams of two light sources, each having a driving current superposed with a signal current corresponding to an independent digital information signal, an optical detector converting part of the combined beam to a first electric signal having a frequency separation between the light sources, an oscillator generating a second electric signal having a reference frequency, a multiplier forming a multiplied signal from the first and second electric signals, and means for adding a control current obtained from the multiplied signal to at least one of driving currents of the light sources so as to stabilize a desired frequency separation between the output beams of the light sources; an optical transmission line transmitting an output beam from the optical transmitter; and an optical heterodyne or homodyne receiver comprising a local oscillator optical source, a photo-coupler combining a transmitted beam from the optical transmission line and a local beam from the local oscillator optical source, an optical detector detecting an output from the photo-coupler as an optical signal having an intermediate frequency signal, and a demodulation circuit converting the electric signal to a baseband signal.