Patent ID: 8768174

Claim:
A modulation device for modulating a plurality of baseband signals to generate an optical signal, comprising: a combiner configured to combine the plurality of baseband signals two by two to generate a plurality of combined baseband signals, each of the combined baseband signals including a first component which is a combination of real part signals of two baseband signals, a second component which is a combination of imaginary part signals of the two baseband signals, a third component which is another combination of the real part signals of the two baseband signals, and a fourth component which is another combination of the imaginary part signals of the two baseband signals a plurality of modulation units configured for modulating a plurality of electrical carriers with different frequencies by using the plurality of combined baseband signals, respectively, to generate a plurality of electrical modulated signals, wherein each modulation unit combines a first component of a corresponding combined baseband signal mixed with a corresponding cosine electrical carrier and a second component of the corresponding combined baseband signal mixed with a corresponding sine electrical carrier to generate a real part signal of a corresponding electrical modulated signal, and combines a third component of the corresponding combined baseband signal mixed with the corresponding sine electrical carrier and a fourth component of the corresponding combined baseband signal mixed with the corresponding cosine electrical carrier to generate an imaginary part signal of the corresponding electrical modulated signal; a synthesizer configured for synthesizing the plurality of electrical modulated signals to generate a complex electrical synthesized signal including a real electrical synthesized signal and an imaginary electrical synthesized signal; and, an optical modulation unit configured for modulating a single optical carrier by using the electrical synthesized signal to generate the optical signal, wherein signal components corresponding to the respective baseband signals in the optical signal are distributed on both sides of a carrier frequency of the optical carrier at a predetermined frequency interval.