Two-Wavelength Square-Waveform Generation Based on Fiber Optical Parametric Oscillator

A square-waveform generator based on a fiber optical parametric oscillator (FOPO) is proposed and demonstrated experimentally. The FOPO works fundamentally by extracting the longitudinal modes beating signal to drive the intracavity amplitude modulator. In order to broaden the longitudinal mode spacing, two sub-ring cavities with a short cavity length are used. The longitudinal modes are phase locked, which ensures the generated microwave signal with very low phase noise. By biasing the amplitude modulator, the even-order beating signals are suppressed, while the odd-order beating signals are enhanced. Thus, the FOPO is self-starting and can provide stable square-waveform output with the repetition rate of 1.133 GHz at the signal and idler simultaneously. It is tunable over 10 nm, which is only limited by the gain bandwidth of the fiber optical parametric amplifier of the current configuration.