Patent ID: 7151897

Claim:
An optical clock phase-locked loop circuit comprising: a first oscillator that outputs an alternating current signal, a first optical coupler that couples an input optical signal and a modulated optical clock signal, an optical cross-correlation detection device that incorporates said optical signal and said modulated optical clock signal coupled by the first optical coupler, and outputs light that contains the cross-correlation components between both signals, an optical band pass filter that extracts light of a wavelength that contains cross-correlating components from the output from the optical cross-correlation detection device, an optical receiver that converts the light extracted with the optical band pass filter containing cross-correlating components to an electric cross-correlation signal, a phase comparator that outputs a comparison of the phases of the output signal of the first oscillator and the cross-correlation signal output from the optical receiver, a second oscillator that changes its oscillation frequency and phase corresponding to the output of the phase comparator, an optical pulse generator driven by the second oscillator that generates an optical clock output having a narrow enough pulse width for containing an nth harmonic component (where n is an integer of 2 or more), a second optical coupler that divides into two portions the optical clock output from the optical pulse generator, an optical modulator driven by the first oscillator that modulates one portion of the optical clock divided by the second optical coupler, and outputs that portion in the form of the modulated optical clock to the first optical coupler, and an output device that outputs the other portion of the optical clock divided by the second optical coupler.