Patent ID: 7751722

Claim:
An optical transmission system that includes an optical transmitter and an optical receiver connected to the optical transmitter via an optical fiber, and outputs a radio-frequency electrical signal having a radio frequency from the optical receiver, the optical transmitter comprising: an electrical/optical converter operable to generate an intermediate-frequency optical signal that has been intensity-modulated based on an intermediate-frequency electrical signal having an intermediate frequency different from the radio frequency, and output the generated intermediate-frequency optical signal to the optical receiver via the optical fiber, the optical receiver comprising: a frequency converter operable to generate a first radio-frequency optical signal and a second radio-frequency optical signal by intensity-modulating and thereby frequency-converting the intermediate-frequency optical signal based on a local oscillator electrical signal having a constant frequency, the first and second radio-frequency optical signals each including an intensity-modulated component having the radio frequency and a noise component, the intensity-modulated components being in antiphase, and the noise components being in phase; and a balanced optical/electrical converter operable to generate a radio-frequency electrical signal by converting the first radio-frequency optical signal to a first electrical signal, converting the second radio-frequency optical signal to a second electrical signal, inverting a phase of the first electrical signal, and adding the first electrical signal to the second electrical signal so that noise components of the first and second electrical signals are cancelled out.